Nickel is widely used in mechanical engineering and instrument making, as well as in various industries. In the food industry, nickel replaces tin coatings, and in the field of optics, it has spread thanks to the black nickel metal plating procedure. Nickel is applied to parts made of non-ferrous metals and steel to increase the resistance of products to mechanical wear and protection against corrosion. The presence of phosphorus in nickel makes the film close in hardness to a chromium film!

Nickel plating procedure

Nickel plating is the application to the surface of a part of a nickel coating, which usually has a thickness of 1 to 50 microns. Nickel coatings are shiny or matte black, but regardless of this, they provide reliable protection for the metal in aggressive environments (acids, alkalis) and at elevated temperatures.

Before the nickel plating process, the product must be prepared. It is treated with sandpaper to remove the oxide film, wiped with a brush, washed with water, degreased in a hot soda solution and washed again. Nickel coatings tend to lose their original luster over time, so they often cover the nickel layer with a more stable chromium layer.

Nickel applied directly to steel is cathodic and protects the material purely mechanically. The discontinuity of the protective coating contributes to the formation of corrosion pairs, in which steel acts as a soluble electrode. As a result, corrosion forms under the coating, destroying the steel substrate and provoking peeling of the nickel coating. To prevent this, the metal should always be coated with a thick layer of nickel.

Nickel coatings can be applied to iron, copper, their alloys, as well as tungsten, titanium and other metals. Metals such as lead, cadmium, tin, lead, antimony and bismuth cannot be plated with chemical nickel plating. When nickel plating steel products, it is customary to apply a copper sublayer.

Nickel coatings are used in various industries for special, protective and decorative purposes, and also as a sublayer. Nickel plating technology is used to restore worn-out auto parts and machine parts, coating chemical equipment, medical instruments, measuring instruments, household items, parts that are operated with light loads under dry friction or exposure to strong alkalis.

Types of nickel plating

In practice, two types of nickel plating are known - electrolytic and chemical. The latter method is somewhat more expensive than the electrolytic method, however, it is able to provide the possibility of creating a coating of uniform quality and thickness on any surface areas, if the condition of solution access to them is met.

electrolytic nickel plating

Electrolytic coatings are characterized by some porosity, depending on the thoroughness of the preparation of the substrate and the thickness of the protective coating. To organize high-quality corrosion protection, a complete absence of pores is required; for this, it is customary to pre-copper plating a metal part or apply a multilayer coating, which is more reliable than a single layer even with equal thickness.

To do this, you need to prepare an electrolyte. Take 30 grams of nickel sulfate, 3.5 grams of nickel chloride and 3 grams of boric acid per 100 milliliters of water, pour this electrolyte into a container. Nickel plating of steel or copper requires nickel anodes, which should be lowered into the electrolyte.

A part should be hung on a wire between nickel electrodes. The wires coming from the nickel plates must be connected together. The parts are connected to the negative pole of the current source, and the wires to the positive. Then you need to include a rheostat in the circuit to adjust the current and a milliammeter. Choose a DC source that has a voltage of 6V or less.

The current must be turned on for approximately twenty minutes. Then the part must be removed, washed and dried. The product is covered with a matte layer of grayish nickel. In order for the protective coating to become shiny, it must be polished. However, when working, remember the significant disadvantages of electrolytic nickel plating at home - the uneven deposition on the relief surface of nickel and the impossibility of coating deep and narrow holes, as well as cavities.

Chemical nickel plating

In addition to the electrolytic method, another very simple method can be used to coat iron or polished steel with a thin but strong layer of nickel. It is customary to take a 10% solution of zinc chloride and gradually add to a solution of nickel sulfate until the liquid turns bright green. After that, the liquid must be heated to a boil, it is better to use a porcelain vessel for this.

In this case, a characteristic turbidity appears, however, it has no effect on the process of nickel plating of parts. When you bring the liquid to a boil, you should lower the object to be nickel-plated into it. Pre-clean the part and degrease. The product should boil in the solution for about an hour, add distilled water from time to time as it evaporates.

If you notice during the boil that the liquid has changed color from bright green to faint green, then you need to add a little nickel sulfate to get the original color. After the specified time, remove the product from the solution, rinse in water in which a little chalk is dissolved, and dry thoroughly. Steel or polished iron plated in a similar nickel plating process, this protective coating holds very well.

The procedure for chemical nickel plating is based on the reaction of nickel reduction from an aqueous solution of its salts using sodium hypophosphite and other chemical reagents. Solutions that are used for chemical nickel plating are acidic with a pH level of 4-6.5 and alkaline with a pH value above 6.5.

It is advisable to use acidic solutions for coating ferrous metals, brass and copper. Alkaline are intended for stainless steels. An acidic solution, compared to an alkaline solution, gives a smoother surface to the polished part. Another important feature of acidic solutions is the lower probability of self-discharge when the operating temperature threshold is exceeded. Alkaline solutions guarantee a more reliable adhesion of the nickel film to the base metal.

All do-it-yourself aqueous solutions for nickel plating are universal, that is, suitable for all metals. Distilled water is used for chemical nickel plating, but you can also use condensate from a household refrigerator. Chemical reagents are suitable pure - with the designation "H" on the label.

The sequence for making the solution is as follows. All chemical reagents, with the exception of sodium hypophosphite, must be dissolved in water using enamelware. Then heat the solution to operating temperature, dissolve the sodium hypophosphite and place the parts in the solution. With one liter of the solution, it is possible to nickel-plated parts that have a surface area of ​​up to 2 dm2.

Black coatings

Black nickel coatings are used for special and decorative purposes. Their protective properties are very low, so it is customary to apply them on a sublayer of ordinary nickel, zinc or cadmium. Steel products must first be galvanized, and copper and brass must be nickel plated.

Black nickel plating is hard but brittle, especially when thick. In practice, they stop at a thickness value of 2 microns. Nickel bath for such coatings, as a rule, contains a large amount of thiocyanate and zinc. Nearly half of nickel is present in the coating, while the remaining 50% are sulfur, nitrogen, zinc and carbon.

Baths of black nickel plating of aluminum or steel are usually prepared by dissolving all the components in warm water and filtering with filter paper. If difficulties arise during the dissolution of boric acid, then it is separately dissolved in water, which is heated to 70 degrees Celsius. Achieving deep blacks depends on choosing the correct current density value.

Nickel plating baths

In the workshops, a bath is widely used, which consists of 3 main components: boric acid, sulfate and chloride. Nickel sulfate is a source of nickel ions. Chloride significantly affects the operation of nickel anodes, its concentration in the bath is not precisely standardized. In chloride-free baths, a strong passivation of nickel occurs, after which the nickel content in the bath decreases, and the result is a decrease in current efficiency and a drop in the quality of the coatings.

Anodes in the presence of chlorides dissolve in sufficient quantities for the normal course of the copper or aluminum nickel plating process. Chlorides increase the conductivity of the bath and its functioning when contaminated with zinc. Boric acid helps maintain the pH at a certain level. The effectiveness of this action depends to a large extent on the concentration of boric acid.

As chloride, sodium, zinc or magnesium chloride can be used. Watts sulfate baths are widely used, which contain as an additive electrically conductive salts, which increase the electrical conductivity of the baths and improve the appearance of protective coatings. The most used among these salts is magnesium sulfate (about 30 grams per liter).

Nickel sulfate is most often introduced at a concentration of about 250-350 grams per liter. Recently, there has been a trend towards limiting nickel sulfate - less than 200 g / l, which helps to significantly reduce solution losses.

The concentration of boric acid is 25-40 grams per liter. Below 25 g/l, there is an increased tendency for the bath to rapidly alkalize. And exceeding the permissible level is considered unfavorable due to the possible crystallization of boric acid and the settling of crystals on the walls of the nickel bath and anodes.

Nickel bath works in different temperature ranges. However, nickel plating at home is rarely used at room temperature. Nickel often flakes off coatings applied in cold baths, so the bath must be heated to at least 30 degrees Celsius. The current density is chosen experimentally so that the coating does not burn.

The sodium bath works reliably over a wide pH range. Previously, the pH was maintained at a level of 5.4-5.8, motivated by less aggressiveness and higher covering abilities of the bath. However, high pH values ​​provoke a significant increase in stresses in the nickel coating. Therefore, in most baths, the pH is 3.5-4.5.

The subtleties of nickel plating

The adhesion of the nickel film to the metal is comparatively low. This problem can be solved by heat treatment of nickel films. The low-temperature diffusion procedure consists in heating nickel-plated products to a temperature of 400 degrees Celsius and holding the parts for one hour at this temperature.

But remember that if parts that are nickel-plated were hardened (fish hooks, knives and springs), then at a temperature of 400 degrees they can be released, losing hardness - their main quality. Therefore, low-temperature diffusion in such a situation is carried out at a temperature of about 270-300 degrees with an exposure of up to 3 hours. Such heat treatment can also increase the hardness of the nickel coating.

Modern nickel baths require special equipment for nickel plating and agitation of the aqueous solution to intensify the nickel plating process and reduce the risk of pitting - the formation of small depressions in the coating. Agitation of the bath after it entails the need for continuous filtration to eliminate contaminants.

Stirring with a movable cathode rod is not as effective as using compressed air for this purpose, and, among other things, requires a special ingredient that eliminates foaming.

Removal of nickel plating

Nickel coatings on steel are usually removed in dilute sulfuric acid baths. Add to 20 liters of cold water in portions 30 liters of concentrated sulfuric acid with constant stirring. Control that the temperature does not exceed 60 degrees Celsius. After cooling to room temperature of the bath, its density should reach 1.63.

In order to reduce the risk of seeding the material from which the substrate is made, glycerin is added to the bath in an amount of 50 grams per liter. Bathtubs are usually made of vinyl plastic. Products are hung on the middle rod, which is connected to the plus of the current source. The rods on which the lead sheets are fixed are connected to the minus of the current source.

Make sure that the temperature of the bath does not exceed 30 degrees, as the hot solution acts aggressively on the substrate. The current density should be 4 A / dm2, but a voltage change of 5-6 Volts is allowed.

Add concentrated sulfuric acid after a certain time to keep the density at 1.63. To prevent dilution of the bath, immerse items in the bath after pre-drying. Control of the process is not difficult, because the current density drops sharply at the moment of nickel removal.

Thus, nickel plating is the most popular electroplating process. Nickel plating is distinguished by its hardness, high corrosion resistance, reasonable price of nickel plating, good reflectivity and electrical resistivity.

Nickel plating, which is a fairly common technological operation, is performed in order to deposit a thin layer of nickel on the surface of a metal product. The thickness of such a layer, the value of which can be adjusted using various techniques, can vary from 0.8 to 55 microns.

Nickel plating is used as a protective and decorative coating, as well as to obtain a sublayer during chromium plating.

With the help of metal nickel plating, it is possible to form a film that provides reliable protection against such negative phenomena as oxidation, the development of corrosion processes, reactions caused by interaction with hydrochloric, alkaline and acidic environments. In particular, nickel-plated pipes, which are actively used for the production of sanitary ware, are very widespread.

Most often, nickel plating is subjected to:

• metal products that will be used outdoors;
• body parts of motorcycles and vehicles, including those for the manufacture of which aluminum alloy was used;
• equipment and instruments used in general medicine and dentistry;
• metal products that are used in water for a long time;
• enclosing structures made of steel or aluminum alloys;
• metal products exposed to strong chemicals.

There are several methods used both in production and at home for nickel plating of metal products. Of greatest interest in practical terms are methods of nickel plating of metal parts that do not require the use of complex technological equipment and are implemented at home. These methods include electrolytic and chemical nickel plating.

electrolytic nickel plating

The essence of the technology of electrolytic nickel plating of metal parts, which has another name - "galvanic nickel plating", can be considered on the example of how copper plating of the surface of a metal product is performed. This procedure can be carried out both with the use of an electrolytic solution and without it.

The part, which will be further processed in an electrolytic solution, is carefully processed, for which an oxide film is removed from its surface with sandpaper. Then the workpiece is washed in warm water and treated with a soda solution, after which it is washed again with water.

The nickel plating process itself is carried out in a glass container, into which an aqueous solution (electrolyte) is poured. This solution contains 20% copper sulphate and 2% sulfuric acid. The workpiece, on the surface of which it is necessary to apply a thin layer of copper, is placed in an electrolyte solution between two copper anodes. To start the copper plating process, it is necessary to apply an electric current to the copper anodes and the workpiece, the value of which is calculated based on an indicator of 10–15 mA per square centimeter of the workpiece area. A thin layer of copper on the surface of the product appears after half an hour of its stay in the electrolyte solution, and such a layer will be the thicker, the longer the process will take place.

It is possible to apply a copper layer on the surface of the product using another technology. To do this, you need to make a brush from copper (you can use a stranded wire, after removing the insulating layer from it). Such a handmade brush must be fixed on a wooden stick, which will serve as a handle.

The product, the surface of which is preliminarily cleaned and degreased, is placed in a container made of dielectric material and filled with electrolyte, which can be used as a saturated aqueous solution of copper sulphate. A homemade brush is connected to the positive contact of the electric current source, and the workpiece is connected to its minus. After that, proceed to the procedure of coppering. It consists in the fact that a brush, which is previously dipped in electrolyte, is carried over the surface of the product without touching it. It is possible to apply a coating using this technique in several layers, which will make it possible to form a copper layer on the surface of the product, on which there are practically no pores.

Electrolytic nickel plating is carried out according to a similar technology: it also uses an electrolyte solution. As in the case of copper plating, the workpiece is placed between two anodes, only in this case they are made of nickel. The anodes placed in the nickel plating solution are connected to the positive contact of the current source, and the product suspended between them on a metal wire is connected to the negative one.

For the implementation of nickel plating, including do-it-yourself, electrolytic solutions of two main types are used:

• an aqueous solution containing nickel sulphate, sodium and magnesium (14:5:3), 2% boric acid, 0.5% common salt;
• neutral water-based solution containing 30% nickel sulfate, 4% nickel chloride, 3% boric acid.

Electrolyte for bright nickel plating with the addition of organic brighteners (sodium salts)

Leveling electrolyte bright nickel plated. Suitable for low cleaning grade surfaces

To prepare an electrolytic solution, a dry mixture of the above elements is poured with one liter of neutral water and mixed thoroughly. If a precipitate forms in the resulting solution, it is discarded. Only then can the solution be used for nickel plating.

This process typically takes half an hour and uses a 5.8-6V power source. The result is a surface with an uneven, matte gray color. To make it beautiful and shiny, you need to clean it and polish it. It should be borne in mind that this technology cannot be used for parts that have a high surface roughness or have narrow and deep holes. In such cases, the coating of the surface of a metal product with a layer of nickel should be carried out according to a chemical technology, which is also called blackening.

The essence of the blackening process is that an intermediate coating is first applied to the surface of the product, the basis of which can be zinc or nickel, and a layer of black nickel with a thickness of no more than 2 microns is formed on the upper part of such a coating. Nickel plating, made using the blackening technology, looks very beautiful and provides reliable protection of the metal from the negative effects of various environmental factors.

In some cases, a metal product is simultaneously subjected to two technological operations at once, such as nickel plating and chromium plating.

Chemical nickel plating

The procedure for chemical nickel plating of metal products is carried out according to the following scheme: the workpiece is immersed in a boiling solution for a while, as a result of which nickel particles settle on its surface. When using this technology, there is no electrochemical effect on the metal from which the part is made.

The result of using this nickel plating technology is the formation of a nickel layer on the surface of the workpiece, which is firmly bonded to the base metal. This nickel plating method is most effective when it is used to process objects made of steel alloys.

It is not difficult to perform such nickel plating at home or even in a garage. In this case, the nickel plating procedure takes place in several stages.

• Dry reagents, from which the electrolytic solution will be prepared, are mixed with water in an enamel bowl.
• The resulting solution is brought to a boil, and then sodium hypophosphite is added to it.
• The product to be processed is placed in an electrolytic solution, and this is done so that it does not touch the side walls and the bottom of the container. In fact, it is necessary to manufacture a household apparatus for nickel plating, the design of which will consist of an enameled container of the appropriate volume, as well as a dielectric bracket on which the workpiece will be fixed.
• The boiling time of the electrolytic solution, depending on its chemical composition, can be from one to three hours.
• After the completion of the technological operation, the already nickel-plated part is removed from the solution. Then it is washed in water, which contains slaked lime. After thorough washing, the surface of the product is polished.

Electrolytic solutions for nickel plating, which can be subjected not only to steel, but also to brass, aluminum and other metals, necessarily contain the following elements in their chemical composition - nickel chloride or sulfate, sodium hypophosphite of various acidity, any of the acids.

To increase the rate of nickel plating of metal products, lead is added to the composition for this technological operation. As a rule, in one liter of the electrolytic solution, nickel coating of the surface is carried out, the area of ​​which is 20 cm 2 . In electrolytic solutions with a higher acidity, nickel plating of ferrous metal products is carried out, and brass is processed in alkaline solutions, nickel plating of aluminum or stainless steel parts is carried out.

Some nuances of technology

When performing nickel plating of brass, steel products of various grades and other metals, some nuances of this technological operation should be taken into account.

• Nickel film will be more stable if it is applied to a pre-coppered surface. The nickel-plated surface will be even more stable if the finished product is subjected to heat treatment, which consists in holding it at a temperature exceeding 450 °.
• If parts made of hardened steels are subjected to nickel plating, then they can be heated and maintained at a temperature not exceeding 250-300 °, otherwise they may lose their hardness.
• Nickel plating of large parts requires constant stirring and regular filtration of the electrolytic solution. This complexity is especially typical for nickel plating processes that are carried out not in industrial, but at home.

Using a technology similar to nickel plating, brass, steel and other metals can be coated with a layer of silver. A coating of this metal is applied, in particular, to fishing tackle and other products to prevent tarnishing.

The procedure for applying a layer of silver to steel, brass and other metals differs from traditional nickel plating not only by the temperature and holding time, but also by the fact that an electrolytic solution of a certain composition is used for it. In this case, this operation is performed in a solution whose temperature is 90 °.

Properties and applications of the coating. The basis of the chemical nickel plating process is the reduction reaction of nickel from aqueous solutions of its salts with sodium hypophosphite. Industrial applications have received methods for the deposition of Nickel from alkaline and acidic solutions. The deposited coating has a semi-brilliant metallic appearance, a fine crystalline structure, and is an alloy of nickel and phosphorus. The content of phosphorus in the sediment depends on the composition of the solution and ranges from 4-6% for alkaline to 8-10% for acidic solutions.

In accordance with the content of phosphorus, the physical constants of the nickel-phosphorus precipitate also change. Its specific gravity is 7.82-7.88 g/cm 3 , melting point 890-1200°, electrical resistivity is 0.60 ohm mm 2 /m. After heat treatment at 300-400°, the nickel-phosphorus coating hardness increases to 900-1000 kg/mm ​​2 . At the same time, the adhesion strength also increases many times over.

These properties of the nickel-phosphorus coating also determine its areas of application.

It is advisable to use it for coating parts with a complex profile, the inner surface of tubes and coils, for uniform coating of parts with very precise dimensions, to increase the wear resistance of rubbing surfaces and parts subjected to temperature effects, for example, for coating molds.

Parts made of ferrous metals, copper, aluminum and nickel are subjected to nickel-phosphorus coating.

This method is not suitable for nickel deposition on metals or coatings such as lead, zinc, cadmium and tin.

Nickel precipitation from alkaline solutions. Alkaline solutions are characterized by high stability, ease of adjustment, lack of tendency to violent and instantaneous precipitation of nickel powder (self-discharge phenomenon) and the possibility of their long-term operation without replacement.

The nickel deposition rate is 8-10 microns/hour. The process goes with intensive release of hydrogen on the surface of the Parts.

The preparation of the solution consists in dissolving each of the components separately, after which they are poured together into a working bath, with the exception of sodium hypophosphite. It is poured only when the solution is heated to operating temperature and the parts are prepared for coating.

Preparation of the surface of steel parts for coating has no specific features.

After heating the solution to the operating temperature, it is corrected with a 25% ammonia solution to a stable blue color, sodium hypophosphite solution is added, the parts are hung and the coating is started without preliminary study. The solution is adjusted mainly with ammonia and sodium hypophosphite. With a large volume of the nickel plating bath and a high specific loading of parts, the solution is adjusted with ammonia directly from a cylinder with gaseous ammonia, with a continuous supply of gas to the bottom of the bath through a rubber tube.

A solution of sodium hypophosphite for the convenience of adjustment is prepared with a concentration of 400-500 g / l.

Nickel chloride solution is usually prepared for correction together with ammonium chloride and sodium citrate. For this purpose, it is most advisable to use a solution containing 150 g/l nickel chloride, 150 g/l ammonium chloride and 50 g/l sodium citrate.

The specific consumption of sodium hypophosphite per 1 dm 2 of the coating surface, with a layer thickness of 10 microns, is about 4.5 g, and nickel, in terms of metal, is about 0.9 g.

The main problems in the chemical deposition of Nickel from alkaline solutions are given in Table. eight.

Deposition of Nickel from Acid Solutions. Unlike alkaline solutions, acidic solutions are characterized by a wide variety of additives to solutions of nickel and hypophosphite salts. So, for this purpose, sodium acetate, succinic, tartaric and lactic acids, Trilon B and other organic compounds can be used. Among the many compositions, below is a solution with the following composition and precipitation regime:

The pH value should be adjusted with a 2% sodium hydroxide solution. The nickel deposition rate is 8-10 microns/hour.

Overheating the solution above 95° can lead to self-discharge of nickel with an instant dark spongy precipitate and the solution splashing out of the bath.

The solution is adjusted according to the concentration of its constituent components only until 55 g/l of sodium phosphite NaH 2 PO 3 is accumulated in it, after which nickel phosphite can precipitate out of the solution. Upon reaching the specified concentration of phosphite, the nickel solution is drained and replaced with a new one.

heat treatment. In cases where nickel is applied to increase surface hardness and wear resistance, the parts are heat treated. At high temperatures, the nickel-phosphorus precipitate forms a chemical compound, which causes a sharp increase in its hardness.

The change in microhardness depending on the heating temperature is shown in Fig. 13. As can be seen from the diagram, the greatest increase in hardness occurs in the temperature range of 400-500 °. When choosing a temperature regime, it should be borne in mind that for a number of steels that have been hardened or normalized, high temperatures are not always acceptable. In addition, heat treatment carried out in air causes tempering colors on the surface of parts, ranging from golden yellow to purple. For these reasons, the heating temperature is often limited within 350-380°. It is also necessary that the nickel-plated surfaces be clean before laying in the furnace, since any impurities are detected after heat treatment very intensively and their removal is possible only by polishing. The heating time is 40-60 min. is sufficient.

Equipment and accessories. The main task in the manufacture of equipment for chemical nickel plating is the choice of bath linings that are resistant to acids and alkalis and heat conductive. For experimental work and for coating small parts, porcelain and steel enameled baths are used.

When coating large items in baths with a capacity of 50-100 liters or more, enameled tanks with enamels resistant to strong nitric acid are used. Some factories use steel cylindrical baths lined with a coating consisting of glue No. 88 and powdered chromium oxide, taken in equal weight quantities. Chromium oxide can be replaced with emery micropowders. The coating is produced in 5-6 layers with intermediate air drying.

At the Kirov Plant, for this purpose, the lining of cylindrical baths with removable plastic covers is successfully used. If it is necessary to clean the baths, the solutions are pumped out with a pump, and the covers are removed and treated in nitric acid. Carbon steel should be used as the material for hangers and baskets. Separate sections of parts and suspensions are insulated with perchlorovinyl enamels or plastic compounds.

To heat the solution, electric heaters should be used with heat transfer through a water jacket. Heat treatment of small parts is carried out in thermostats. For large products, shaft furnaces with automatic temperature control are used.

Nickel plating of stainless and acid-resistant steels. Nickel plating is carried out to increase surface hardness and wear resistance, as well as to protect against corrosion in those aggressive environments in which these steels are unstable.

For the adhesion of the nickel-phosphorus layer to the surface of high-alloy steels, the method of preparation for coating is of decisive importance. So, for stainless steel grade 1×13 and the like, surface preparation consists in its anodic treatment in alkaline solutions. The parts are mounted on carbon steel suspensions, using, if necessary, internal cathodes, hung in a bath with a 10-15% caustic soda solution and anode treated at an electrolyte temperature of 60-70 ° and an anode current density of 5-10 A / dm 2 for 5-10 minutes. until a uniform brown coating without metal gaps is formed. Then the parts are washed in cold running water, decapitated in hydrochloric acid (sp. weight 1.19), diluted twice, at a temperature of 15-25 ° for 5-10 seconds. After washing in cold running water, the parts are hung in a chemical nickel plating bath in an alkaline solution and plated in the usual way to a given layer thickness.

For parts made of acid-resistant steel type IX18H9T, anodic treatment should be carried out in a chromic acid electrolyte with the following composition and process mode:

After anodic treatment, the parts are washed in cold running water, decapitated in hydrochloric acid, as indicated for stainless steel, and hung in a nickel plating bath.

Nickel plating of non-ferrous metals. To deposit nickel on the previously deposited nickel layer, the parts are degreased and then decapitated in a 20-30% hydrochloric acid solution for 1 minute, after which they are hung in a bath for chemical nickel plating. Parts made of copper and its alloys are nickel-plated in contact with a more electronegative metal, such as iron or aluminum, using wire or pendants made of these metals for this purpose. In some cases, for a deposition reaction to occur, it is sufficient to create a short-term contact of an iron rod with the surface of a copper part.

For nickel plating of aluminum and its alloys, parts are etched in alkali, brightened in nitric acid, as is done before, with all types of coatings, and subjected to a double zincate treatment in a solution containing 500 g/l of sodium hydroxide and 100 g/l of zinc oxide, at a temperature 15-25°. The first immersion lasts 30 seconds, after which the contact zinc precipitate is etched off in dilute nitric acid, and the second immersion is 10 seconds, after which the parts are washed in cold running water and nickel plated in a bath with an alkaline nickel phosphorus solution. The resulting coating is very loosely bound to aluminum, and to increase the adhesion strength, the parts are heated by immersing them in lubricating oil at a temperature of 220-250 ° for 1-2 hours.

After heat treatment, the parts are degreased with solvents and, as necessary, wiped, polished or subjected to other types of machining.

Nickel plating of cermets and ceramics. The technological process of nickel plating of ferrites consists in the following operations: parts are degreased in a 20% solution of soda ash, washed with hot distilled water and pickled for 10-15 minutes. in an alcoholic solution of hydrochloric acid with a ratio of components 1:1. Then the parts are again washed with hot distilled water while cleaning the sludge with hair brushes. A solution of palladium chloride with a concentration of 0.5-1.0 g/l and a pH of 3.54:0.1 is applied to the coated surfaces of the parts with a brush. After air drying, the application of palladium chloride is repeated once more, dried and immersed for preliminary nickel plating in a bath with an acidic solution containing 30 g/l of nickel chloride, 25 g/l of sodium hypophosphite and 15 g/l of sodium succinic acid. For this operation, it is necessary to maintain the temperature of the solution within 96-98° and pH 4.5-4.8. Then the parts are washed in distilled hot water and nickel-plated in the same solution, but at a temperature of 90 °, until a layer 20-25 microns thick is obtained. After that, the parts are boiled in distilled water, copper-plated in a pyrophosphate electrolyte until a layer of 1-2 microns is obtained, after which they are subjected to acid-free soldering. The adhesion strength of the nickel-phosphorus coating with the ferrite base is 60-70 kg/cm 2 .

In addition, various types of ceramics are subjected to chemical nickel plating, for example, ultra-porcelain, quartz, steatite, piezoceramics, tikond, thermocond, etc.

Nickel plating technology consists of the following operations: parts are degreased with alcohol, washed in hot water and dried.

After that, for parts made of ticond, thermocond and quartz, their surface is sensitized with a solution containing 10 g/l of tin chloride SnCl 2 and 40 ml/l of hydrochloric acid. This operation is performed with a brush or by rubbing with a wooden washer moistened with a solution, or by immersing the parts in a solution for 1-2 minutes. Then the surface of the parts is activated in a solution of palladium chloride PdCl 2 2H 2 O.

For ultra-porcelain, a heated solution is used with a concentration of PdCl 2 ·2H 2 O 3-6 g / l and with an immersion time of 1 sec. For tikond, thermocond and quartz, the concentration decreases to 2-3 g / l with an increase in exposure from 1 to 3 minutes, after which the parts are immersed in a solution containing calcium hypophosphite Ca (H 2 PO 2) 2 in an amount of 30 g / l, without heating, for 2-3 minutes.

Parts made of ultra-porcelain with an activated surface are hung for 10-30 seconds. into a pre-nickel plating bath with an alkaline solution, after which the parts are washed and hung again in the same bath to build up a layer of a given thickness.

Parts made of tikond, thermocond and quartz after treatment in calcium hypophosphite are nickel-plated in acidic solutions.

Chemical deposition of nickel from carbonyl compounds. When heating vapors of nickel tetracarbonyl Ni(CO) 4 at a temperature of 280°±5, the reaction of thermal decomposition of carbonyl compounds occurs with the deposition of metallic nickel. The precipitation process takes place in a hermetically sealed container at atmospheric pressure. The atmosphere consists of 20-25% (by volume) nickel tetracarbonyl and 80-75% carbon monoxide CO. The admixture of oxygen in the gas is admissible not more than 0.4%. For uniform deposition, gas circulation should be created at a feed rate of 0.01-0.02 m/s and reversal of the feed direction every 30-40 seconds. . Preparation of parts for coating is to remove oxides and grease. The nickel deposition rate is 5-10 microns/min. The deposited nickel has a matte surface, a dark gray tint, a fine crystalline structure, a hardness of 240-270 Vickers, and a relatively low porosity.

The adhesion strength of the coating to the metal of the products is very low, and to increase it to satisfactory values, heat treatment at 600-700°C for 30-40 minutes is necessary.

Information for action
(technology tips)
Erlykin L.A. DIY 3-92

Before any of the home craftsmen did not get up the need to nickel or chrome this or that part. What do-it-yourselfer did not dream of installing a “non-working” bushing with a hard, wear-resistant surface obtained by saturating it with boron in a critical node. But how to do at home what, as a rule, is carried out at specialized enterprises by methods of chemical-thermal and electrochemical processing of metals. You will not build gas and vacuum furnaces at home, or build electrolysis baths. But it turns out that it is not necessary to build all this at all. It is enough to have on hand some reagents, an enameled pan and, perhaps, a blowtorch, as well as to know the recipes of "chemical technology", with which metals can also be copper-plated, cadmium, tinned, oxidized, etc.

So, let's start getting acquainted with the secrets of chemical technology. Please note that the content of the components in the solutions given, as a rule, are given in g / l. If other units are used, a special clause follows.

Preparatory operations

Before applying paints, protective and decorative films to metal surfaces, as well as before coating them with other metals, it is necessary to carry out preparatory operations, that is, to remove pollution of various nature from these surfaces. Please note that the final result of all work depends to a large extent on the quality of the preparatory operations.

Preparatory operations include degreasing, cleaning and pickling.

Degreasing

The process of degreasing the surface of metal parts is carried out, as a rule, when these parts have just been processed (ground or polished) and there are no rust, scale and other foreign products on their surface.

With the help of degreasing, oil and grease films are removed from the surface of the parts. For this, aqueous solutions of some chemicals are used, although organic solvents can also be used for this. The latter have the advantage that they do not have a subsequent corrosive effect on the surface of the parts, but they are toxic and flammable.

aqueous solutions. Degreasing of metal parts in aqueous solutions is carried out in enameled dishes. Pour water, dissolve chemicals in it and put on a small fire. When the desired temperature is reached, the parts are loaded into the solution. During processing, the solution is stirred. Below are the compositions of the degreasing solutions (g/l), as well as the operating temperatures of the solutions and the processing time of the parts.

Compositions of degreasing solutions (g/l)

For ferrous metals (iron and iron alloys)

Liquid glass (stationery silicate glue) - 3 ... 10, caustic soda (potassium) - 20 ... 30, trisodium phosphate - 25 ... 30. Solution temperature - 70...90°C, processing time - 10...30 min.

Liquid glass - 5 ... 10, caustic soda - 100 ... 150, soda ash - 30 ... 60. Solution temperature - 70...80°C, processing time - 5...10 min.

Liquid glass - 35, trisodium phosphate - 3 ... 10. Solution temperature - 70...90°С, processing time - 10...20 min.

Liquid glass - 35, trisodium phosphate - 15, preparation - emulsifier OP-7 (or OP-10) -2. Solution temperature - 60-70°С, processing time - 5...10 min.

Liquid glass - 15, preparation OP-7 (or OP-10) -1. Solution temperature - 70...80°С, processing time - 10...15 min.

Soda ash - 20, potassium chromium peak - 1. Solution temperature - 80 ... 90 ° C, processing time - 10 ... 20 minutes.

Soda ash - 5 ... 10, trisodium phosphate - 5 ... 10, preparation OP-7 (or OP-10) - 3. Solution temperature - 60 ... 80 ° C, processing time - 5 ... 10 min .

For copper and copper alloys

Caustic soda - 35, soda ash - 60, trisodium phosphate - 15, preparation OP-7 (or OP-10) - 5. Solution temperature - 60 ... 70, processing time - 10 ... 20 minutes.

Caustic soda (potassium) - 75, liquid glass - 20 Solution temperature - 80 ... 90 ° C, processing time - 40 ... 60 minutes.

Liquid glass - 10 ... 20, trisodium phosphate - 100. Solution temperature - 65 ... 80 C, processing time - 10 ... 60 minutes.

Liquid glass - 5 ... 10, soda ash - 20 ... 25, preparation OP-7 (or OP-10) - 5 ... 10. Solution temperature - 60...70°С, processing time - 5...10 min.

Trisodium phosphate - 80...100. Solution temperature - 80...90°С, processing time - 30...40 min.

For aluminum and its alloys

Liquid glass - 25...50, soda ash - 5...10, trisodium phosphate-5...10, preparation OP-7 (or OP-10) - 15...20 min.

Liquid glass - 20 ... 30, soda ash - 50 ... 60, trisodium phosphate - 50 ... 60. Solution temperature - 50…60°С, processing time - 3...5 min.

Soda ash - 20 ... 25, trisodium phosphate - 20 ... 25, preparation OP-7 (or OP-10) - 5 ... 7. Temperature - 70...80°С, processing time - 10...20 min.

For silver, nickel and their alloys

Liquid glass - 50, soda ash - 20, trisodium phosphate - 20, preparation OP-7 (or OP-10) - 2. Solution temperature - 70 ... 80 ° C, processing time - 5 ... 10 minutes.

Liquid glass - 25, soda ash - 5, trisodium phosphate - 10. Solution temperature - 75 ... 85 ° C, processing time - 15 ... 20 minutes.

For zinc

Liquid glass - 20 ... 25, caustic soda - 20 ... 25, soda ash - 20 ... 25. Solution temperature - 65...75°С, processing time - 5 min.

Liquid glass - 30...50, soda ash - 30..,50, kerosene - 30...50, preparation OP-7 (or OP-10) - 2...3. Solution temperature - 60-70°С, processing time - 1...2 min.

organic solvents

The most commonly used organic solvents are B-70 gasoline (or "lighter gasoline") and acetone. However, they have a significant drawback - they are easily flammable. Therefore, they have recently been replaced by non-flammable solvents such as trichlorethylene and perchlorethylene. Their dissolving power is much higher than that of gasoline and acetone. Moreover, these solvents can be fearlessly heated, which greatly accelerates the degreasing of metal parts.

Degreasing the surface of metal parts with organic solvents is carried out in the following sequence. The parts are loaded into a container with a solvent and incubated for 15 ... 20 minutes. Then the surface of the parts is wiped directly in the solvent with a brush. After such treatment, the surface of each part is carefully treated with a swab moistened with 25% ammonia (it is necessary to work with rubber gloves!).

All work on degreasing with organic solvents is carried out in a well-ventilated area.

cleaning

In this section, as an example, the decarbonization process of internal combustion engines will be considered. As you know, carbon deposits are asphalt-resinous substances that form hard-to-remove films on the working surfaces of engines. Removing carbon deposits is a rather difficult task, since the carbon film is inert and firmly adhered to the surface of the part.

Compositions of cleaning solutions (g/l)

For ferrous metals

Liquid glass - 1.5, soda ash - 33, caustic soda - 25, laundry soap - 8.5. Solution temperature - 80...90°C, processing time - Zh.

Caustic soda - 100, potassium dichromate - 5. Solution temperature - 80 ... 95 ° C, processing time - up to 3 hours.

Caustic soda - 25, liquid glass - 10, sodium bichromate - 5, laundry soap - 8, soda ash - 30. Solution temperature - 80 ... 95 ° C, processing time - up to 3 hours.

Caustic soda - 25, liquid glass - 10, laundry soap - 10, potash - 30. Solution temperature - 100 ° C, processing time - up to 6 hours.

For aluminum (duralumin) alloys

Liquid glass 8.5, laundry soap - 10, soda ash - 18.5. Solution temperature - 85...95 C, processing time - up to 3 hours.

Liquid glass - 8, potassium dichromate - 5, laundry soap - 10, soda ash - 20. Solution temperature - 85 ... 95 ° C, processing time - up to 3 hours.

Soda ash - 10, potassium dichromate - 5, laundry soap - 10. Solution temperature - 80 ... 95 ° C, processing time - up to 3 hours.

Etching

Etching (as a preparatory operation) allows you to remove contaminants (rust, scale and other corrosion products) firmly adhered to their surface from metal parts.

The main purpose of etching is the removal of corrosion products; while the base metal should not be etched. To prevent metal etching, special additives are introduced into the solutions. Good results are obtained by the use of small amounts of hexamethylenetetramine (urotropine). In all solutions for etching ferrous metals, add 1 tablet (0.5 g) of urotropine per 1 liter of solution. In the absence of urotropin, it is replaced with the same amount of dry alcohol (sold in sports stores as fuel for tourists).

Due to the fact that inorganic acids are used in recipes for etching, it is necessary to know their initial density (g / cm 3): nitric acid - 1.4, sulfuric acid - 1.84; hydrochloric acid - 1.19; phosphoric acid - 1.7; acetic acid - 1.05.

Compositions of solutions for etching

For ferrous metals

Sulfuric acid - 90...130, hydrochloric acid - 80...100. Solution temperature - 30...40°С, processing time - 0.5...1.0 h.

Sulfuric acid - 150...200. Solution temperature - 25...60°С, processing time - 0.5...1.0 h.

Hydrochloric acid - 200. Solution temperature - 30...35°С, processing time - 15...20 min.

Hydrochloric acid - 150 ... 200, formalin - 40 ... 50. Solution temperature 30...50°C, treatment time 15...25 min.

Nitric acid - 70...80, hydrochloric acid - 500...550. Solution temperature - 50°С, processing time - 3...5 min.

Nitric acid - 100, sulfuric acid - 50, hydrochloric acid - 150. Solution temperature - 85°C, processing time - 3...10 min.

Hydrochloric acid - 150, phosphoric acid - 100. Solution temperature - 50°C, processing time - 10...20 min.

The last solution (when processing steel parts), in addition to cleaning the surface, also phosphates it. And phosphate films on the surface of steel parts make it possible to paint them with any paint without a primer, since these films themselves serve as an excellent primer.

Here are a few more recipes for etching solutions, the compositions of which this time are given in% (by weight).

Orthophosphoric acid - 10, butyl alcohol - 83, water - 7. Solution temperature - 50...70°C, processing time - 20...30 min.

Orthophosphoric acid - 35, butyl alcohol - 5, water - 60. Solution temperature - 40...60°C, processing time - 30...35 min.

After etching of ferrous metals, they are washed in a 15% solution of soda ash (or drinking) soda. Then rinse thoroughly with water.

Note that below the compositions of the solutions are again given in g/L.

For copper and its alloys

Sulfuric acid - 25...40, chromic anhydride - 150...200. Solution temperature - 25°С, processing time - 5...10 min.

Sulfuric acid - 150, potassium bichromate - 50. Solution temperature - 25.35°C, processing time - 5...15 min.

Trilon B-100. Solution temperature - 18...25°C, processing time - 5...10 min.

Chromic anhydride - 350, sodium chloride - 50. Solution temperature - 18...25°С, processing time - 5...15 min.

For aluminum and its alloys

Caustic soda -50...100. Solution temperature - 40...60°С, treatment time - 5...10 s.

Nitric acid - 35...40. Solution temperature - 18...25°С, treatment time - 3...5 s.

Caustic soda - 25 ... 35, soda ash - 20 ... 30. Solution temperature - 40...60°С, processing time - 0.5...2.0 min.

Caustic soda - 150, sodium chloride - 30. Solution temperature - 60°C, processing time - 15 ... 20 s.

Chemical polishing

Chemical polishing allows you to quickly and efficiently process the surface of metal parts. The great advantage of this technology is that with the help of it (and only it!) It is possible to polish parts with a complex profile at home.

Compositions of solutions for chemical polishing

For carbon steels (the content of components is indicated in each case in various units (g / l, percent, parts)

Nitric acid - 2.-.4, hydrochloric acid 2 ... 5, Orthophosphoric acid - 15 ... 25, the rest is water. Solution temperature - 70...80°С, processing time - 1...10 min. The content of the components - in% (by volume).

Sulfuric acid - 0.1, acetic acid - 25, hydrogen peroxide (30%) - 13. Solution temperature - 18 ... 25 ° C, processing time - 30 ... 60 minutes. Content of components - in g/l.

Nitric acid - 100...200, sulfuric acid - 200..,600, hydrochloric acid - 25, Orthophosphoric acid - 400. Mixture temperature - 80...120°С, treatment time - 10...60 s. Content of components in parts (by volume).

For stainless steel

Sulfuric acid - 230, hydrochloric acid - 660, acid orange dye - 25. Solution temperature - 70...75°С, processing time - 2...3 min. Content of components - in g/l.

Nitric acid - 4 ... 5, hydrochloric acid - 3 ... 4, Orthophosphoric acid - 20..30, methyl orange - 1..1.5, the rest is water. Solution temperature - 18...25°С, treatment time - 5..10 min. The content of the components - in% (by weight).

Nitric acid - 30...90, potassium ferricyanide (yellow blood salt) - 2...15 g/l, preparation OP-7 - 3...25, hydrochloric acid - 45..110, phosphoric acid - 45. ..280.

Solution temperature - 30...40°С, processing time - 15...30 min. The content of components (except for yellow blood salt) - in pl / l.

The latter composition is applicable for polishing cast iron and any steels.

For copper

Nitric acid - 900, sodium chloride - 5, soot - 5. Solution temperature - 18 ... 25 ° C, processing time - 15 ... 20 s. Content of components - g/l.

Attention! Sodium chloride is added to solutions last, and the solution must be pre-cooled!

Nitric acid - 20, sulfuric acid - 80, hydrochloric acid - 1, chromic anhydride - 50. Solution temperature - 13..18°C, processing time - 1...2 min. Content of components - in ml.

Nitric acid 500, sulfuric acid - 250, sodium chloride - 10. Solution temperature - 18 ... 25 ° C, processing time - 10 ... 20 s. Content of components - in g/l.

For brass

Nitric acid - 20, hydrochloric acid - 0.01, acetic acid - 40, phosphoric acid - 40. Mixture temperature - 25...30°C, processing time - 20...60 s. Content of components - in ml.

Copper sulphate (copper sulfate) - 8, sodium chloride - 16, acetic acid - 3, water - the rest. Solution temperature - 20°С, processing time - 20...60 min. The content of components - in% (by weight).

For bronze

Orthophosphoric acid - 77 ... 79, potassium nitrate - 21 ... 23. Mixture temperature - 18°C, processing time - 0.5-3 min. The content of components - in% (by weight).

Nitric acid - 65, sodium chloride - 1 g, acetic acid - 5, orthophosphoric acid - 30, water - 5. Solution temperature - 18 ... 25 ° C, processing time - 1 ... 5 s. The content of components (except sodium chloride) - in ml.

For nickel and its alloys (cupronickel and nickel silver)

Nitric acid - 20, acetic acid - 40, phosphoric acid - 40. Mixture temperature - 20°C, processing time - up to 2 minutes. The content of components - in% (by weight).

Nitric acid - 30, acetic acid (glacial) - 70. Mixture temperature - 70...80°С, treatment time - 2...3 s. The content of components - in% (by volume).

For aluminum and its alloys

Orthophosphoric acid - 75, sulfuric acid - 25. Mixture temperature - 100°C, processing time - 5...10 min. The content of components - in parts (by volume).

Orthophosphoric acid - 60, sulfuric acid - 200, nitric acid - 150, urea - 5g. The temperature of the mixture is 100°C, the processing time is 20 s. The content of components (except urea) - in ml.

Orthophosphoric acid - 70, sulfuric acid - 22, boric acid - 8. Mixture temperature - 95°C, processing time - 5...7 min. The content of components - in parts (by volume).

Passivation

Passivation is the process of chemically creating an inert layer on the surface of a metal, which prevents the metal itself from oxidizing. The process of passivating the surface of metal products is used by chasers when creating their works; craftsmen - in the manufacture of various crafts (chandeliers, sconces and other household items); sports anglers passivate their homemade metal lures.

Compositions of solutions for passivation (g/l)

For ferrous metals

Sodium nitrite - 40...100. Solution temperature - 30...40°С, processing time - 15...20 min.

Sodium nitrite - 10...15, soda ash - 3...7. Solution temperature - 70...80°С, processing time - 2...3 min.

Sodium nitrite - 2...3, soda ash - 10, preparation OP-7 - 1...2. Solution temperature - 40...60°С, processing time - 10...15 min.

Chromic anhydride - 50. Solution temperature - 65 ... 75 "C, processing time - 10 ... 20 minutes.

For copper and its alloys

Sulfuric acid - 15, potassium dichromate - 100. Solution temperature - 45°C, processing time - 5...10 min.

Potassium dichromate - 150. Solution temperature - 60°C, processing time - 2...5 min.

For aluminum and its alloys

Orthophosphoric acid - 300, chromic anhydride - 15. Solution temperature - 18...25°C, processing time - 2...5 min.

Potassium dichromate - 200. Solution temperature - 20°C, "treatment time -5...10 min.

For silver

Potassium dichromate - 50. Solution temperature - 25 ... 40 ° C, processing time - 20 minutes.

For zinc

Sulfuric acid - 2...3, chromic anhydride - 150...200. Solution temperature - 20°С, processing time - 5...10 s.

Phosphating

As already mentioned, the phosphate film on the surface of steel parts is a fairly reliable anti-corrosion coating. It is also an excellent primer for paintwork.

Some low-temperature phosphating methods are applicable to the treatment of car bodies before coating them with anti-corrosion and anti-wear compounds.

Compositions of solutions for phosphating (g/l)

For steel

Mazhef (phosphate salts of manganese and iron) - 30, zinc nitrate - 40, sodium fluoride - 10. Solution temperature - 20 ° C, processing time - 40 minutes.

Monozinc phosphate - 75, zinc nitrate - 400 ... 600. Solution temperature - 20°С, processing time - 20...30 s.

Majef - 25, zinc nitrate - 35, sodium nitrite - 3. Solution temperature - 20°C, processing time - 40 min.

Monoammonium phosphate - 300. Solution temperature - 60 ... 80 ° C, processing time - 20 ... 30 s.

Phosphoric acid - 60...80, chromic anhydride - 100...150. Solution temperature - 50...60°С, processing time - 20...30 min.

Orthophosphoric acid - 400 ... 550, butyl alcohol - 30. Solution temperature - 50 ° C, processing time - 20 minutes.

Application of metal coatings

The chemical coating of some metals with others impresses with the simplicity of the technological process. Indeed, if, for example, it is necessary to chemically nickel-plating any steel part, it is enough to have suitable enameled dishes, a heating source (gas stove, stove, etc.) and relatively non-deficient chemicals. An hour or two - and the part is covered with a shiny layer of nickel.

Note that only with the help of chemical nickel plating it is possible to reliably nickel-plating parts of a complex profile, internal cavities (pipes, etc.). True, chemical nickel plating (and some other similar processes) is not without its drawbacks. The main one is not too strong adhesion of the nickel film to the base metal. However, this drawback can be eliminated; for this, the so-called low-temperature diffusion method is used. It allows you to significantly increase the adhesion of the nickel film to the base metal. This method is applicable to all chemical coatings of some metals by others.

nickel plating

The process of chemical nickel plating is based on the reaction of nickel reduction from aqueous solutions of its salts using sodium hypophosphite and some other chemicals.

Nickel coatings obtained by chemical means have an amorphous structure. The presence of phosphorus in nickel makes the film close in hardness to a chromium film. Unfortunately, the adhesion of the nickel film to the base metal is relatively low. Heat treatment of nickel films (low-temperature diffusion) consists in heating nickel-plated parts to a temperature of 400°C and holding them at this temperature for 1 hour.

If nickel-plated parts are hardened (springs, knives, fish hooks, etc.), then at a temperature of 40 ° C they can be released, that is, they can lose their main quality - hardness. In this case, low-temperature diffusion is carried out at a temperature of 270...300 C with an exposure of up to 3 hours. In this case, the heat treatment also increases the hardness of the nickel coating.

All the listed advantages of chemical nickel plating did not escape the attention of technologists. They have found practical application for them (except for the use of decorative and anti-corrosion properties). So, with the help of chemical nickel plating, the axes of various mechanisms, worms of thread-cutting machines, etc. are repaired.

At home, with the help of nickel plating (of course, chemical!) You can repair parts of various household devices. The technology here is extremely simple. For example, the axis of a device was demolished. Then they build up (with excess) a layer of nickel on the damaged area. Then the working section of the axis is polished, bringing it to the desired size.

It should be noted that chemical nickel plating cannot cover metals such as tin, lead, cadmium, zinc, bismuth and antimony.
Solutions used for chemical nickel plating are divided into acidic (pH - 4 ... 6.5) and alkaline (pH - above 6.5). Acidic solutions are preferably used for coating ferrous metals, copper and brass. Alkaline - for stainless steels.

Acidic solutions (compared to alkaline ones) on a polished part give a smoother (mirror-like) surface, they have less porosity, and the speed of the process is higher. Another important feature of acidic solutions is that they are less likely to self-discharge when the operating temperature is exceeded. (Self-discharge - instantaneous precipitation of nickel into a solution with splashing of the latter.)

In alkaline solutions, the main advantage is a more reliable adhesion of the nickel film to the base metal.

And the last. Water for nickel plating (and when applying other coatings) is taken distilled (you can use condensate from household refrigerators). Chemical reagents are suitable at least pure (designation on the label - H).

Before coating parts with any metal film, it is necessary to conduct a special preparation of their surface.

Preparation of all metals and alloys is as follows. The treated part is degreased in one of the aqueous solutions, and then the part is decapitated in one of the solutions listed below.

Compositions of solutions for decapitation (g/l)

For steel

Sulfuric acid - 30...50. Solution temperature - 20°С, processing time - 20...60 s.

Hydrochloric acid - 20...45. Solution temperature - 20°С, treatment time - 15...40 s.

Sulfuric acid - 50...80, hydrochloric acid - 20...30. Solution temperature - 20°С, processing time - 8...10 s.

For copper and its alloys

Sulfuric acid - 5% solution. Temperature - 20°C, processing time - 20s.

For aluminum and its alloys

Nitric acid. (Attention, 10 ... 15% solution.) Solution temperature - 20 ° C, processing time - 5 ... 15 s.

Please note that for aluminum and its alloys, before chemical nickel plating, one more treatment is carried out - the so-called zincate. Below are solutions for zincate treatment.

For aluminum

Caustic soda - 250, zinc oxide - 55. Solution temperature - 20 C, treatment time - 3 ... 5s.

Caustic soda - 120, zinc sulfate - 40. Solution temperature - 20 ° C, processing time - 1.5 ... 2 minutes.

When preparing both solutions, first, caustic soda is dissolved separately in half of the water, and the zinc component in the other half. Then both solutions are poured together.

For cast aluminum alloys

Caustic soda - 10, zinc oxide - 5, Rochelle salt (crystal hydrate) - 10. Solution temperature - 20 C, processing time - 2 minutes.

For wrought aluminum alloys

Ferric chloride (crystal hydrate) - 1, sodium hydroxide - 525, zinc oxide 100, Rochelle salt - 10. Solution temperature - 25 ° C, processing time - 30 ... 60 s.

After zincate treatment, the parts are washed in water and hung in a nickel plating solution.

All solutions for nickel plating are universal, that is, they are suitable for all metals (although there are some specifics). Prepare them in a certain sequence. So, all chemicals (except sodium hypophosphite) are dissolved in water (enamelled dishes!). Then the solution is heated to the operating temperature and only after that sodium hypophosphite is dissolved and the parts are hung into the solution.

In 1 liter of solution, a surface up to 2 dm2 in area can be nickel plated.

Compositions of solutions for nickel plating (g/l)

Nickel sulphate - 25, sodium succinic acid - 15, sodium hypophosphite - 30. Solution temperature - 90°C, pH - 4.5, film growth rate - 15...20 µm/h.

Nickel chloride - 25, sodium succinic acid - 15, sodium hypophosphite - 30. Solution temperature - 90 ... 92 ° C, pH - 5.5, growth rate - 18 ... 25 μm / h.

Nickel chloride - 30, glycolic acid - 39, sodium hypophosphite - 10. Solution temperature 85..89°С, pH - 4.2, growth rate - 15...20 µm/h.

Nickel chloride - 21, sodium acetate - 10, sodium hypophosphite - 24, Solution temperature - 97 ° C, pH - 5.2, growth rate - up to 60 μm / h.

Nickel sulfate - 21, sodium acetate - 10, lead sulfide - 20, sodium hypophosphite - 24. Solution temperature - 90 ° C, pH - 5, growth rate - up to 90 μm / h.

Nickel chloride - 30, acetic acid - 15, lead sulfide - 10 ... 15, sodium hypophosphite - 15. Solution temperature - 85 ... 87 ° C, pH - 4.5, growth rate - 12 ... 15 microns /h

Nickel chloride - 45, ammonium chloride - 45, sodium citrate - 45, sodium hypophosphite - 20. Solution temperature - 90 ° C, pH - 8.5, growth rate - 18 ... 20 microns / h.

Nickel chloride - 30, ammonium chloride - 30, sodium succinic acid - 100, ammonia (25% solution - 35, sodium hypophosphite - 25).
Temperature - 90°C, pH - 8...8.5, growth rate - 8...12 µm/h.

Nickel chloride - 45, ammonium chloride - 45, sodium acetate - 45, sodium hypophosphite - 20. Solution temperature - 88 .... 90 ° C, pH - 8 ... 9, growth rate - 18 ... 20 microns / h.

Nickel sulphate - 30, ammonium sulphate - 30, sodium hypophosphite - 10. Solution temperature - 85°C, pH - 8.2...8.5, growth rate - 15...18 µm/h.

Attention! According to existing state standards, a single-layer nickel coating per 1 cm2 has several tens of through (to the base metal) pores. Naturally, in the open air, a nickel-plated steel part will quickly become covered with a “rash” of rust.

In a modern car, for example, the bumper is covered with a double layer (a sublayer of copper, and chrome on top) and even a triple layer (copper - nickel - chrome). But even this does not save the part from rust, since according to GOST and the triple coating has several pores per 1 cm2. What to do? The way out is in the surface treatment of the coating with special compounds that close the pores.

Wipe the part with a nickel (or other) coating with a slurry of magnesium oxide and water and immediately lower it for 1 ... 2 minutes in a 50% hydrochloric acid solution.

After heat treatment, lower the part that has not yet cooled down into non-vitaminized fish oil (preferably old, unsuitable for its intended purpose).

Wipe the nickel-plated surface of the part 2...3 times with the composition of LPS (easy penetrating lubricant).

In the last two cases, excess fat (grease) is removed from the surface with gasoline in a day.

The treatment of large surfaces (bumpers, car moldings) with fish oil is carried out as follows. In hot weather, wipe them with fish oil twice with a break of 12-14 hours. Then, after 2 days, excess fat is removed with gasoline.

The effectiveness of such processing is characterized by the following example. Nickel-plated fishing hooks begin to rust immediately after the first sea fishing. The same hooks treated with fish oil do not corrode for almost the entire summer sea fishing season.

Chrome plating

Chemical chromium plating allows you to get a gray coating on the surface of metal parts, which after polishing acquires the desired shine. Chrome adheres well to nickel plating. The presence of phosphorus in chemically produced chromium greatly increases its hardness. Heat treatment for chrome plating is essential.

Below are proven recipes for chemical chromium plating.

Compositions of solutions for chemical chromium plating (g/l)

Chromium fluoride - 14, sodium citrate - 7, acetic acid - 10 ml, sodium hypophosphite - 7. Solution temperature - 85 ... 90 ° C, pH - 8 ... 11, growth rate - 1.0 ... 2 .5 µm/h.

Chromium fluoride - 16, chromium chloride - 1, sodium acetate - 10, sodium oxalate - 4.5, sodium hypophosphite - 10. Solution temperature - 75 ... 90 ° C, pH - 4 ... 6, growth rate - 2 ...2.5 µm/h.

Chromium fluoride - 17, chromium chloride - 1.2, sodium citrate - 8.5, sodium hypophosphite - 8.5. Solution temperature - 85...90°C, pH - 8...11, growth rate - 1...2.5 µm/h.

Chromium acetate - 30, nickel acetate - 1, sodium glycolate - 40, sodium acetate - 20, sodium citrate - 40, acetic acid - 14 ml, sodium hydroxide - 14, sodium hypophosphite - 15. Solution temperature - 99 ° C, pH - 4...6, growth rate - up to 2.5 µm/h.

Chromium fluoride - 5 ... 10, chromium chloride - 5 ... 10, sodium citrate - 20 ... 30, sodium pyrophosphate (replacing sodium hypophosphite) - 50 ... 75.
Solution temperature - 100°C, pH - 7.5...9, growth rate - 2...2.5 µm/h.

Boronickel plating

The film of this dual alloy has increased hardness (especially after heat treatment), high melting point, high wear resistance and significant corrosion resistance. All this allows the use of such a coating in various responsible home-made structures. Below are the recipes for solutions in which boronickeling is carried out.

Compositions of solutions for chemical boron nickel plating (g/l)

Nickel chloride - 20, sodium hydroxide - 40, ammonia (25% solution): - 11, sodium borohydride - 0.7, ethylenediamine (98% solution) - 4.5. Solution temperature - 97°C, growth rate - 10 µm/h.

Nickel sulfate - 30, triethylsyntetramine - 0.9, sodium hydroxide - 40, ammonia (25% solution) - 13, sodium borohydride - 1. Solution temperature - 97 C, growth rate - 2.5 μm / h.

Nickel chloride - 20, sodium hydroxide - 40, Rochelle salt - 65, ammonia (25% solution) - 13, sodium borohydride - 0.7. Solution temperature - 97°C, growth rate - 1.5 µm/h.

Caustic soda - 4 ... 40, potassium metabisulphite - 1 ... 1.5, potassium tartrate - 30 ... 35, nickel chloride - 10 ... 30, ethylenediamine (50% solution) - 10 ... 30 , sodium borohydride - 0.6 ... 1.2. Solution temperature - 40...60°C, growth rate - up to 30 µm/h.

Solutions are prepared in the same way as for nickel plating: first, everything except sodium borohydride is dissolved, the solution is heated and sodium borohydride is dissolved.

Borocobalting

The use of this chemical process makes it possible to obtain a film of particularly high hardness. It is used to repair friction pairs, where increased wear resistance of the coating is required.

Compositions of solutions for boron cobalt treatment (g/l)

Cobalt chloride - 20, sodium hydroxide - 40, sodium citrate - 100, ethylenediamine - 60, ammonium chloride - 10, sodium borohydride - 1. Solution temperature - 60 ° C, pH - 14, growth rate - 1.5 .. .2.5 µm/h.

Cobalt acetate - 19, ammonia (25% solution) - 250, potassium tartrate - 56, sodium borohydride - 8.3. Solution temperature - 50°С, pH - 12.5, growth rate - 3 µm/h.

Cobalt sulphate - 180, boric acid - 25, dimethylborazan - 37. Solution temperature - 18°C, pH - 4, growth rate - 6 µm/h.

Cobalt chloride - 24, ethylenediamine - 24, dimethylborazan - 3.5. Solution temperature - 70 C, pH - 11, growth rate - 1 µm/h.

The solution is prepared in the same way as boronickel.

Cadmium plating

On the farm, it is often necessary to use fasteners coated with cadmium. This is especially true for parts that are operated outdoors.

It is noted that chemically obtained cadmium coatings adhere well to the base metal even without heat treatment.

Cadmium chloride - 50, ethylenediamine - 100. Cadmium should be in contact with parts (suspension on cadmium wire, small parts are sprinkled with cadmium powder). Solution temperature - 65°C, pH - 6...9, growth rate - 4 µm/h.

Attention! Ethylenediamine is dissolved last in the solution (after heating).

copper plating

Chemical copper plating is most often used in the manufacture of printed circuit boards for radio electronics, in electroforming, for metallizing plastics, for double coating some metals with others.

Compositions of solutions for copper plating (g/l)

Copper sulphate - 10, sulfuric acid - 10. Solution temperature - 15...25°C, growth rate - 10 µm/h.

Potassium-sodium tartrate - 150, copper sulphate - 30, caustic soda - 80. Solution temperature - 15 ... 25 ° C, growth rate - 12 μm / h.

Copper sulphate - 10 ... 50, caustic soda - 10 ... 30, Rochelle salt 40 ... 70, formalin (40% solution) - 15 ... 25. Solution temperature - 20°C, growth rate - 10 µm/h.

Sulfuric copper - 8...50, sulfuric acid - 8...50. Solution temperature - 20°C, growth rate - 8 µm/h.

Copper sulphate - 63, potassium tartrate - 115, sodium carbonate - 143. Solution temperature - 20 C, growth rate - 15 µm/h.

Copper sulphate - 80 ... 100, caustic soda - 80 ..., 100, sodium carbonate - 25 ... 30, nickel chloride - 2 ... 4, Rochelle salt - 150 ... 180, formalin (40% - solution) - 30...35. Solution temperature - 20°C, growth rate - 10 µm/h. This solution makes it possible to obtain films with a low nickel content.

Copper sulfate - 25 ... 35, sodium hydroxide - 30 ... 40, sodium carbonate - 20-30, trilon B - 80 ... 90, formalin (40% solution) - 20 ... 25, rhodanine - 0.003 ... 0.005, potassium ferricyanide (red blood salt) - 0.1..0.15. Solution temperature - 18...25°C, growth rate - 8 µm/h.

This solution is highly stable over time and makes it possible to obtain thick copper films.

To improve the adhesion of the film to the base metal, heat treatment is the same as for nickel.

Silvering

Silver plating of metal surfaces is perhaps the most popular process among craftsmen, which they use in their work. Dozens of examples could be given. For example, restoration of the silver layer on cupronickel cutlery, silvering of samovars and other household items.

For chasers, silvering, together with chemical coloring of metal surfaces (it will be discussed below), is a way to increase the artistic value of chased paintings. Imagine a minted ancient warrior with silver plated chain mail and a helmet.

The process of chemical silvering can be carried out using solutions and pastes. The latter is preferable when processing large surfaces (for example, when silvering samovars or parts of large chased paintings).

Composition of solutions for silvering (g/l)

Silver chloride - 7.5, potassium ferricyanide - 120, potassium carbonate - 80. The temperature of the working solution is about 100 ° C. Processing time - until the desired thickness of the silver layer is obtained.

Silver chloride - 10, sodium chloride - 20, acid potassium tartrate - 20. Processing - in a boiling solution.

Silver chloride - 20, potassium ferricyanide - 100, potassium carbonate - 100, ammonia (30% solution) - 100, sodium chloride - 40. Processing - in a boiling solution.

First, a paste is prepared from silver chloride - 30 g, tartaric acid - 250 g, sodium chloride - 1250, and everything is diluted with water to the density of sour cream. 10 ... 15 g of paste is dissolved in 1 liter of boiling water. Processing - in a boiling solution.

Details are hung in solutions for silvering on zinc wires (strips).

The processing time is determined visually. It should be noted here that brass is better silvered than copper. On the latter, it is necessary to apply a rather thick layer of silver so that dark copper does not shine through the coating layer.

One more note. Solutions with silver salts cannot be stored for a long time, as explosive components can be formed in this case. The same applies to all liquid pastes.

Compositions of pastes for silvering.

2 g of lapis pencil is dissolved in 300 ml of warm water (sold in pharmacies, it is a mixture of silver nitrate and amino acid potassium, taken in a ratio of 1: 2 (by weight). A 10% sodium chloride solution is gradually added to the resulting solution until it stops The curdled precipitate of silver chloride is filtered off and thoroughly washed in 5-6 waters.

Dissolve 20 g of sodium thiosulfite in 100 ml of water. Silver chloride is added to the resulting solution until it no longer dissolves. The solution is filtered and tooth powder is added to it to the consistency of liquid sour cream. This paste is rubbed (silvered) with a cotton swab.

Lapis pencil - 15, citric acid (food) - 55, ammonium chloride - 30. Each component is ground into powder before mixing. The content of components - in% (by weight).

Silver chloride - 3, sodium chloride - 3, sodium carbonate - 6, chalk - 2. The content of components - in parts (by weight).

Silver chloride - 3, sodium chloride - 8, potassium tartrate - 8, chalk - 4. Content of components - in parts (by weight).

Silver nitrate - 1, sodium chloride - 2. Content of components - in parts (by weight).

The last four pastes are used as follows. Finely divided components are mixed. With a wet swab, powdering it with a dry mixture of chemicals, they rub (silver) the desired part. The mixture is added all the time, constantly moistening the swab.

When silvering aluminum and its alloys, the parts are first galvanized and then coated with silver.

Zincate treatment is carried out in one of the following solutions.

Compositions of solutions for zincate treatment (g/l)

For aluminum

Caustic soda - 250, zinc oxide - 55. Solution temperature - 20°C, treatment time - 3...5 s.

Caustic soda - 120, zinc sulfate - 40. Solution temperature - 20°C, processing time - 1.5...2.0 min. To obtain a solution, first caustic soda is dissolved in one half of the water, and zinc sulfate is dissolved in the other. Then both solutions are poured together.

For duralumin

Caustic soda - 10, zinc oxide - 5, Rochelle salt - 10. Solution temperature - 20°C, processing time - 1...2 min.

After zincate treatment, the parts are silvered in any of the above solutions. However, the following solutions (g / l) are considered the best.

Silver nitrate - 100, ammonium fluoride - 100. Solution temperature - 20°C.

Silver fluoride - 100, ammonium nitrate - 100. Solution temperature - 20°C.

Tinning

Chemical tinning of surfaces of parts is used as an anti-corrosion coating and as a preliminary process (for aluminum and its alloys) before soft soldering. Below are compositions for tinning some metals.

Compositions for tinning (g/l)

For steel

Stannous chloride (fused) - 1, ammonia alum - 15. Tinning is carried out in a boiling solution, the growth rate is 5 ... 8 microns / h.

Tin chloride - 10, aluminum-ammonium sulphate - 300. Tinning is carried out in a boiling solution, the growth rate is 5 microns / h.

Stannous chloride - 20, Rochelle salt - 10. Solution temperature - 80°C, growth rate - 3...5 µm/h.

Stannous chloride - 3 ... 4, Rochelle salt - until saturation. Solution temperature - 90...100°С, growth rate - 4...7 µm/h.

For copper and its alloys

Stannous chloride - 1, potassium tartrate - 10. Tinning is carried out in a boiling solution, the growth rate is 10 μm / h.

Stannous chloride - 20, sodium lactate - 200. Solution temperature - 20°C, growth rate - 10 µm/h.

Stannous chloride - 8, thiourea - 40...45, sulfuric acid - 30...40. Solution temperature - 20°C, growth rate - 15 µm/h.

Stannous chloride - 8...20, thiourea - 80...90, hydrochloric acid - 6.5...7.5, sodium chloride - 70...80. Solution temperature - 50...100°C, growth rate - 8 µm/h.

Stannous chloride - 5.5, thiourea - 50, tartaric acid - 35. Solution temperature - 60 ... 70 ° C, growth rate - 5 ... 7 μm / h.

When tinning parts made of copper and its alloys, they are hung on zinc pendants. Small parts are “powdered” with zinc filings.

For aluminum and its alloys

The tinning of aluminum and its alloys is preceded by some additional processes. First, the parts degreased with acetone or gasoline B-70 are treated for 5 minutes at a temperature of 70 ° C of the following composition (g / l): sodium carbonate - 56, sodium phosphate - 56. Then the parts are lowered for 30 s into a 50% solution of nitric acid, rinse thoroughly under running water and immediately place in one of the solutions (for tinning) below.

Sodium stannate - 30, sodium hydroxide - 20. Solution temperature - 50...60°C, growth rate - 4 µm/h.

Sodium stannate - 20 ... 80, potassium pyrophosphate - 30 ... 120, sodium hydroxide - 1.5..L, 7, ammonium oxalate - 10 ... 20. Solution temperature - 20...40°C, growth rate - 5 µm/h.

Removal of metal coatings

Usually this process is necessary to remove low-quality metal films or to clean any metal product being restored.

All of the following solutions work faster at elevated temperatures.

Compositions of solutions for removing metal coatings in parts (by volume)

For steel removing nickel from steel

Nitric acid - 2, sulfuric acid - 1, iron sulphate (oxide) - 5 ... 10. The temperature of the mixture is 20°C.

Nitric acid - 8, water - 2. Solution temperature - 20 C.

Nitric acid - 7, acetic acid (glacial) - 3. Mixture temperature - 30°C.

For removing nickel from copper and its alloys (g/l)

Nitrobenzoic acid - 40 ... 75, sulfuric acid - 180. Solution temperature - 80 ... 90 C.

Nitrobenzoic acid - 35, ethylenediamine - 65, thiourea - 5...7. Solution temperature - 20...80°С.

Technical nitric acid is used to remove nickel from aluminum and its alloys. The temperature of the acid is 50°C.

For removing copper from steel

Nitrobenzoic acid - 90, diethylenetriamine - 150, ammonium chloride - 50. Solution temperature - 80°C.

Sodium pyrosulfate - 70, ammonia (25% solution) - 330. Solution temperature - 60 °.

Sulfuric acid - 50, chromic anhydride - 500. Solution temperature - 20°C.

For removing copper from aluminum and its alloys (zinc finish)

Chromic anhydride - 480, sulfuric acid - 40. Solution temperature - 20...70°C.

Technical nitric acid. The temperature of the solution is 50°C.

For removing silver from steel

Nitric acid - 50, sulfuric acid - 850. Temperature - 80°C.

Nitric acid technical. Temperature - 20°C.

Silver is removed from copper and its alloys with technical nitric acid. Temperature - 20°C.

Chrome is removed from steel with a solution of caustic soda (200 g/l). Solution temperature - 20 C.

Chromium is removed from copper and its alloys with 10% hydrochloric acid. The temperature of the solution is 20°C.

Zinc is removed from steel with 10% hydrochloric acid - 200 g / l. The temperature of the solution is 20°C.

Zinc is removed from copper and its alloys with concentrated sulfuric acid. Temperature - 20 C.

Cadmium and zinc are removed from any metals with a solution of aluminum nitrate (120 g/l). The temperature of the solution is 20°C.

Tin from steel is removed with a solution containing sodium hydroxide - 120, nitrobenzoic acid - 30. The temperature of the solution is 20°C.

Tin is removed from copper and its alloys in a solution of ferric chloride - 75 ... 100, copper sulfate - 135 ... 160, acetic acid (glacial) - 175. The temperature of the solution is 20 ° C.

Chemical oxidation and coloring of metals

Chemical oxidation and coloring of the surface of metal parts are intended to create an anti-corrosion coating on the surface of the parts and enhance the decorative effect of the coating.

In ancient times, people already knew how to oxidize their crafts, changing their color (silver blackening, gold coloring, etc.), burn steel objects (heating a steel part to 220 ... 325 ° C, they lubricated it with hemp oil).

Compositions of solutions for oxidation and coloring of steel (g/l)

Note that before oxidation, the part is ground or polished, degreased and decapitated.

Black color

Caustic soda - 750, sodium nitrate - 175. Solution temperature - 135°C, processing time - 90 minutes. The film is dense, shiny.

Caustic soda - 500, sodium nitrate - 500. Solution temperature - 140°C, processing time - 9 minutes. The film is intense.

Caustic soda - 1500, sodium nitrate - 30. Solution temperature - 150°C, processing time - 10 min. The film is matte.

Caustic soda - 750, sodium nitrate - 225, sodium nitrite - 60. Solution temperature - 140 ° C, processing time - 90 minutes. The film is shiny.

Calcium nitrate - 30, phosphoric acid - 1, manganese peroxide - 1. Solution temperature - 100°C, processing time - 45 min. The film is matte.

All of the above methods are characterized by a high working temperature of the solutions, which, of course, does not allow processing large parts. However, there is one "low-temperature solution" suitable for this business (g / l): sodium thiosulfate - 80, ammonium chloride - 60, phosphoric acid - 7, nitric acid - 3. Solution temperature - 20 ° C, processing time - 60 minutes . The film is black, matte.

After oxidation (blackening) of steel parts, they are treated for 15 minutes in a solution of potassium chromium peak (120 g/l) at a temperature of 60°C.

Then the parts are washed, dried and coated with any neutral machine oil.

Blue

Hydrochloric acid - 30, ferric chloride - 30, mercury nitrate - 30, ethyl alcohol - 120. Solution temperature - 20 ... 25 ° C, processing time - up to 12 hours.

Sodium hydrosulphide - 120, lead acetate - 30. Solution temperature - 90...100°C, processing time - 20...30 min.

Blue color

Lead acetate - 15 ... 20, sodium thiosulfate - 60, acetic acid (glacial) - 15 ... 30. The temperature of the solution is 80°C. The processing time depends on the intensity of the color.

Compositions of solutions for oxidation and coloring of copper (g/l)

bluish black colors

Caustic soda - 600 ... 650, sodium nitrate - 100 ... 200. Solution temperature - 140°C, processing time - 2 hours.

Caustic soda - 550, sodium nitrite - 150 ... 200. Solution temperature - 135...140°С, processing time - 15...40 min.

Caustic soda - 700...800, sodium nitrate - 200...250, sodium nitrite -50...70. Solution temperature - 140...150°С, processing time - 15...60 min.

Caustic soda - 50 ... 60, potassium persulfate - 14 ... 16. Solution temperature - 60...65 C, processing time - 5...8 min.

Potassium sulfide - 150. Solution temperature - 30°C, processing time - 5...7 min.

In addition to the above, a solution of the so-called sulfuric liver is used. Sulfur liver is obtained by fusing in an iron can for 10 ... 15 minutes (with stirring) 1 part (by weight) of sulfur with 2 parts of potassium carbonate (potash). The latter can be replaced by the same amount of sodium carbonate or caustic soda.

The glassy mass of sulfuric liver is poured onto an iron sheet, cooled and crushed to a powder. Store sulfur liver in an airtight container.

A solution of sulfuric liver is prepared in an enamel bowl at the rate of 30...150 g/l, the temperature of the solution is 25...100°C, the processing time is determined visually.

With a solution of sulfuric liver, in addition to copper, silver can be well blackened and steel satisfactorily.

Green color

Copper nitrate - 200, ammonia (25% solution) - 300, ammonium chloride - 400, sodium acetate - 400. Solution temperature - 15...25°C. The color intensity is determined visually.

Brown color

Potassium chloride - 45, nickel sulphate - 20, copper sulphate - 100. Solution temperature - 90...100°C, color intensity is determined visually.

Brownish yellow color

Caustic soda - 50, potassium persulfate - 8. Solution temperature - 100°C, processing time - 5...20 min.

Blue

Sodium thiosulfate - 160, lead acetate - 40. Solution temperature - 40 ... 100 ° C, processing time - up to 10 minutes.

Compositions for oxidation and coloring of brass (g/l)

Black color

Copper carbonate - 200, ammonia (25% solution) - 100. Solution temperature - 30 ... 40 ° C, processing time - 2 ... 5 minutes.

Copper bicarbonate - 60, ammonia (25% solution) - 500, brass (sawdust) - 0.5. Solution temperature - 60...80°С, processing time - up to 30 min.

Brown color

Potassium chloride - 45, nickel sulfate - 20, copper sulfate - 105. Solution temperature - 90 ... 100 ° C, processing time - up to 10 minutes.

Copper sulphate - 50, sodium thiosulfate - 50. Solution temperature - 60 ... 80 ° C, processing time - up to 20 minutes.

Sodium sulfate - 100. Solution temperature - 70°C, processing time - up to 20 minutes.

Copper sulphate - 50, potassium permanganate - 5. Solution temperature - 18 ... 25 ° C, processing time - up to 60 minutes.

Blue

Lead acetate - 20, sodium thiosulfate - 60, acetic acid (essence) - 30. Solution temperature - 80 ° C, processing time - 7 minutes.

3 green color

Nickel ammonium sulphate - 60, sodium thiosulfate - 60. Solution temperature - 70 ... 75 ° C, processing time - up to 20 minutes.

Copper nitrate - 200, ammonia (25% solution) - 300, ammonium chloride - 400, sodium acetate - 400. Solution temperature - 20 ° C, processing time - up to 60 minutes.

Compositions for oxidation and coloring of bronze (g/l)

Green color

Ammonium chloride - 30, 5% acetic acid - 15, medium acetic copper salt - 5. Solution temperature - 25...40°C. Hereinafter, the color intensity of bronze is determined visually.

Ammonium chloride - 16, acidic potassium oxalate - 4, 5% acetic acid - 1. Solution temperature - 25...60°C.

Copper nitrate - 10, ammonium chloride - 10, zinc chloride - 10. Solution temperature - 18...25°C.

yellow green color

Nitrate copper - 200, sodium chloride - 20. Solution temperature - 25°C.

Blue to yellow-green

Depending on the processing time, it is possible to obtain colors from blue to yellow-green in a solution containing ammonium carbonate - 250, ammonium chloride - 250. The temperature of the solution is 18 ... 25 ° C.

Patination (giving the appearance of old bronze) is carried out in the following solution: sulfuric liver - 25, ammonia (25% solution) - 10. Solution temperature - 18 ... 25 ° C.

Compositions for oxidation and coloring of silver (g/l)

Black color

Sulfuric liver - 20...80. Solution temperature - 60..70°С. Hereinafter, the color intensity is determined visually.

Ammonium carbonate - 10, potassium sulfide - 25. Solution temperature - 40...60°C.

Potassium sulphate - 10. Solution temperature - 60°C.

Copper sulphate - 2, ammonium nitrate - 1, ammonia (5% solution) - 2, acetic acid (essence) - 10. Solution temperature - 25...40°C. The content of the components in this solution is given in parts (by weight).

Brown color

A solution of ammonium sulphate - 20 g / l. Solution temperature - 60...80°С.

Copper sulphate - 10, ammonia (5% solution) - 5, acetic acid - 100. Solution temperature - 30...60°C. The content of the components in the solution - in parts (by weight).

Copper sulphate - 100, 5% acetic acid - 100, ammonium chloride - 5. Solution temperature - 40...60°C. The content of the components in the solution - in parts (by weight).

Copper sulphate - 20, potassium nitrate - 10, ammonium chloride - 20, 5% acetic acid - 100. Solution temperature - 25...40°C. The content of the components in the solution - in parts (by weight).

Blue

Sulfuric liver - 1.5, ammonium carbonate - 10. Solution temperature - 60°C.

Sulfuric liver - 15, ammonium chloride - 40. Solution temperature - 40...60°C.

Green color

Iodine - 100, hydrochloric acid - 300. Solution temperature - 20°C.

Iodine - 11.5, potassium iodide - 11.5. The temperature of the solution is 20°C.

Attention! When dyeing silver green, you must work in the dark!

Composition for oxidation and coloring of nickel (g/l)

Nickel can only be painted black. The solution (g/l) contains: ammonium persulfate - 200, sodium sulfate - 100, iron sulfate - 9, ammonium thiocyanate - 6. Solution temperature - 20...25°C, processing time - 1-2 minutes.

Compositions for the oxidation of aluminum and its alloys (g/l)

Black color

Ammonium molybdate - 10...20, ammonium chloride - 5...15. Solution temperature - 90...100°С, treatment time - 2...10 min.

Grey colour

Arsenic trioxide - 70...75, sodium carbonate - 70...75. Solution temperature - boiling, processing time - 1...2 min.

Green color

Orthophosphoric acid - 40 ... 50, acidic potassium fluoride - 3 ... 5, chromic anhydride - 5 ... 7. Solution temperature - 20...40 C, processing time - 5...7 min.

Orange color

Chromic anhydride - 3...5, sodium fluorine silicate - 3...5. Solution temperature - 20...40°С, processing time - 8...10 min.

tan color

Sodium carbonate - 40 ... 50, sodium chlorate - 10 ... 15, caustic soda - 2 ... 2.5. Solution temperature - 80...100°С, processing time - 3...20 min.

Protective compounds

Often, the craftsman needs to process (paint, cover with another metal, etc.) only part of the craft, and leave the rest of the surface unchanged.
To do this, the surface that does not need to be covered is painted over with a protective compound that prevents the formation of a particular film.

The most accessible, but non-heat-resistant protective coatings are waxy substances (wax, stearin, paraffin, ceresin) dissolved in turpentine. To prepare such a coating, wax and turpentine are usually mixed in a ratio of 2: 9 (by weight). Prepare this composition as follows. Wax is melted in a water bath and warm turpentine is introduced into it. In order for the protective composition to be contrasting (its presence could be clearly seen, controlled), a small amount of dark-colored paint soluble in alcohol is introduced into the composition. If this is not available, it is easy to introduce a small amount of dark shoe cream into the composition.

You can give a recipe that is more complex in composition,% (by weight): paraffin - 70, beeswax - 10, rosin - 10, pitch varnish (Kuzbasslak) - 10. All components are mixed, melted over low heat and mixed thoroughly.

Wax-like protective compounds are applied hot with a brush or swab. All of them are designed for operating temperatures up to 70°C.
Somewhat better heat resistance (operating temperature up to 85°С) is possessed by protective compositions based on asphalt, bituminous and pitch varnishes. Usually they are thinned with turpentine in a ratio of 1:1 (by weight). The cold composition is applied to the surface of the part with a brush or swab. Drying time - 12...16 hours.

Perchlorovinyl paints, varnishes and enamels withstand temperatures up to 95°C, oil-bitumen varnishes and enamels, asphalt-oil and bakelite varnishes - up to 120°C.

The most acid-resistant protective composition is a mixture of 88N glue (or Moment) and filler (porcelain flour, talc, kaolin, chromium oxide), taken in the ratio: 1:1 (by weight). The required viscosity is obtained by adding to the mixture a solvent consisting of 2 parts (by volume) of B-70 gasoline and 1 part of ethyl acetate (or butyl acetate). The working temperature of such a protective composition is up to 150 C.

A good protective composition is epoxy varnish (or putty). Operating temperature - up to 160°С.

During operation, materials are subject to physical wear. Numerous methods of protection are used to restore the properties of the metal. One of the most effective protection methods is nickel plating of materials.

For applying nickel at home, methods of chemical and electrolytic nickel plating are used.

What is nickel plating

Nickel plating is the process of applying a thin nickel coating to the surface of a material. The nickel layer is taken equal to 1–50 µm.

The nickel layer is used to improve the anti-corrosion and wear-resistant properties of materials. Quite often, such a coating has a protective and decorative value.

Nickel plating is used for processing steel and non-ferrous alloys. A thin layer of nickel is used to protect products made from manganese, titanium, tungsten, molybdenum and alloys based on them.

Methods for applying a nickel protective coating to ceramics, plastic, porcelain, glass and other non-metallic surfaces have been developed and successfully implemented.

Types of nickel plating

Nickel plating in simple home conditions is carried out in two ways:

• electrolytic;
• chemical.

The choice of method depends on the structure and shape of the material.

In the electrolytic method, substances are used that are partially or completely composed of ions and have ionic conductivity. Nickel coating is applied due to the electrochemical properties of these substances. The most widely used electrolytes are sodium sulfate and chromium.

Depending on the degree of reflection of the coating, nickel plating is distinguished:

Functions of electrolytic nickel plating

• matte;
• brilliant.

Electrolytes without additives are used for matt coating. Products with a matte finish do not have a metallic sheen.

Brilliant nickel plating is obtained by adding special brighteners based on chloramine, propargyl alcohol, bepzosulfamide and other oxidizing agents to the electrolyte.

The best protection of the nickel coating is achieved with a minimum porosity of the protective layer. For this purpose, it is copper-plated or a multilayer structure of the material is used.

For your information. With the same thickness, multilayer coatings are several times more reliable than single-layer materials.

The most common examples of multilayer materials are copper-nickel-chromium coatings.

The main disadvantages of electrolytic nickel plating are:

• high degree of porosity;
• uneven nickel deposition;
• the complexity of processing surfaces with complex shapes.

The method is based on the property of nickel ions to be reduced in a liquid medium. For this purpose, sodium hypophosphite or other chemical reagents are used. The chemical method allows processing products with a complex surface shape.

The disadvantage of this method is the relative high cost of dry reagents used for the preparation of aqueous chemical solutions.

Carrying out electrolytic nickel plating at home

Electrolytic (galvanic) nickel plating of parts is carried out in two ways:

• immersion of parts in electrolyte;
• without immersing the parts in the electrolyte.

The first method is used when processing small parts. The second method is used when processing large and heavy objects.

Before nickel plating, the metal is copper-plated.

Electrolyte immersion method

According to the first method, the surface of the product is ground with sandpaper to remove the oxide film. The sample is then washed in warm water. After that, it is treated with a soda solution and washed again in warm clean water.

Then two thin copper plates are placed in a glass or porcelain dish. The plates play the role of anodes. They are placed in a vertical position, parallel to each other.

The product is placed between these two plates. To do this, the sample is suspended with a wire. The wire is attached to the plates with both ends.

An aqueous electrolyte solution with the following composition is added to the dishes:

• distilled water;
• 20% copper sulfate;
• 2% sulfuric acid.

Copper plates are connected to the power supply. The voltage value is determined at the rate of 15–20 mA per 1 cm2 of the material surface.

For your information. Nickel electrolyte is sensitive to changes in acidity. To maintain the acidity level, buffer compounds based on boric acid are used.

In the electrolyte solution, copper chloride dissociates (decomposes) into its constituent components. The ions move towards the cathode and become neutral atoms. Chlorine ions are oxidized at the anode.

When current is passed through the electrolyte, copper ions go into solution. From the solution, copper settles on the cathode in the form of neutral atoms. Impurities remain at the bottom of the dish. The purity of the resulting copper is almost 100%.

After 30 minutes, a thin layer of copper forms on the part. The impact of electric current causes an increase in the thickness of the copper layer. The greater the layer thickness, the fewer pores remain on the treated surface.

Method without immersing parts in electrolyte

Galvanic nickel plating of large parts is carried out without immersing them in an electrolyte. To do this, use a brush of loose copper wires. As a brush, a stranded copper cable, stripped of insulation, is often used.

By increasing the deposited copper layer, the porosity of the sample surface is eliminated.

The nickel deposition process is carried out similarly to the surface copper plating process. To do this, an electrolyte is added to the container. The composition of the electrolyte includes the following chemical reagents, g/l:

• sodium sulfate solution - 310;
• nickel chloride solution - 65;
• orthoboric acid - 45;
• 1,4-butanediol - 0.15;
• ortho-sulfobenzimid (saccharin) - 2.0;
• kaolin (lime) - 1.0.

Thin nickel plates are lowered into the electrolyte. They play the role of anodes. The product is placed between them. The ends of the plates are connected to the power supply terminal with a positive charge. The body of the part is connected to the negative pole.

A rheostat is used to control the current. The control of the magnitude of the supplied electric current is carried out using a milliammeter. The applied current should not exceed 6 V. Nickel deposition is carried out at a temperature of about 50°C and an electric current density of 4–5 A/dm2. The duration of the process is 3 minutes.

For your information. Nickel plating without a backing has a rather weak adhesion to the surface. In order to increase adhesion, heat treatment of the product is used at a temperature of 450 degrees.

The final stage of processing the part

The treated part is washed under a stream of clean warm water and dried.

The nickel-plated finish has a matte finish. To give shine, the part is polished.

Defective nickel coatings are removed by anodic dissolution in an electrolyte. For this, sulfuric acid is included in the composition of the electrolyte. The chemical density of the acid is assumed to be 1.2-2.8 kg/m3. The process of removing the nickel layer is carried out at a temperature of 20-25° C and an anode electric current density of 5 A/dm2.

Carrying out chemical nickel plating at home

The chemical method of nickel plating at home is carried out using working solutions. Depending on the amount of dry reagents, the nickel layer growth rate is 80 µm/h or more.

The composition of the working solution includes the following reagents, g/l:

• nickel vitriol (nickel sulfate powder) - 20;
• galena (lead sulfide powder) - 20;
• sodium acetate - 15;
• sodium hypophosphite solution - 25.

The working temperature of the chemical solution is 90°C. When the lead reagent is removed, the reaction rate decreases to 50 μm/h or less.

When the operating temperature is reached, the workpiece is lowered into the container with the solution. Before nickel plating, the coating is cleaned and degreased.

The product is kept in the working solution for 1 hour. As it evaporates, distilled water is added.

At the end of the process, the part is removed and washed in warm water. After rinsing, the product is subjected to thorough drying. Polish carefully if necessary.

Extended nickel plating life

Nickel plating can be subject to continuous surface corrosion. The corrosion process appears only in the initial period. As the temperature of the working solution increases, surface corrosion penetrates deep into the material. Then this process slows down and stops completely.

To increase the service life of the nickel coating, copper plating technology is used. Copper plating also eliminates minor surface defects. The application of copper as a substrate ensures the reliability and durability of nickel protection.

The porosity of the copper coating causes the destruction of the protective layer and reduces the service life of the finished product. The substrate metal undergoes corrosion, followed by peeling of the protective layer.

Most often, products with a single-layer protective coating are exposed to corrosion processes. Multilayer parts are exposed to harmful factors to a lesser extent.

To protect products from damage, a number of additional measures are taken. Special additives are used to close the pores.

For your information. To prevent loss of hardness, nickel plating of steel is carried out at a temperature of 250-300ºС.

Additional processing of parts to extend the service life

Nickel plating at home is carried out using the following methods:

• Dry magnesium oxide reagent is mixed with water to a mushy state. With the resulting mass, the part is carefully processed and immersed for several minutes in 50% hydrochloric or sulfuric acid.
• The working surface is wiped with a penetrating lubricant. Then the product is immersed in purified fish oil. Excess fat is removed after a day with gasoline or other solvents.
• Large parts are treated with fish oil in two passes. The interval between treatments should be at least 12 hours. After two days, excess slave fat is removed.

The use of nickel alloys with other metals can improve the physicochemical properties of nickel.

Aluminum improves the electrical resistance and corrosion resistance of nickel.

Tungsten, molybdenum and titanium increase its heat resistance.

The addition of chromium leads to an increase in the resistance of the nickel coating in oxidizing and reducing solutions.

Copper increases the resistance of nickel to the action of various acids.