Nickel plating at home - obtaining beautiful and reliable coatings. H - nickel plating How to determine nickel at home

Chemical coatings with nickel, copper, silver, palladium, cobalt and less often with tin, chromium and other metals have found the greatest distribution.

Chemical nickel plating. The recovery of nickel ions from solutions occurs due to the oxidation of hypophosphite according to the overall reaction

H 2 PO - 2 + H 2 O + Ni 2+ \u003d H 2 PO - 3 + 2H + + Ni.

In this case, the recovery can proceed as follows:

NiCl 2 + NaH 2 PO 2 + H 2 O \u003d Ni + 2HCl + NaH 2 PO 3

NaH 2 PO 3 + H 2 O \u003d NaH 2 PO 3 + H 2

or H 2 RO - 2 \u003d RO - 2 + 2H +

(decomposition of hypophosphite)

Ni 2+ + 2H \u003d Ni + 2H +

(nickel recovery).

The liberated hydrogen also reduces phosphite to phosphorus, so the nickel coating contains 6–8% phosphorus, which largely determines its specific properties (Table 24).

24. Properties of chemical and electroplating nickel

Although chemically deposited nickel has significant corrosion resistance, it cannot be used for corrosion protection in nitric and sulfuric acid environments. After heat treatment, such nickel has a hardness of HV 1000-1025.

Mostly technological process nickel plating is as follows. Parts made of steel, copper and its alloys are prepared in the same way as for galvanized coatings.

Nickel plating is carried out in a solution of the following composition (g/l):

Nickel sulfate 20

Sodium hypophosphite 25

Sodium acetate 10

Thiourea (or maleic anhydride) 0.003 (1.5 - 2)

Temperature 93 ± 5°С, sedimentation rate 18 µm/h (at 90°С and loading density 1 dm 2 /l), pH = 4.1 ÷ 4.3.

Parts in the nickel plating process must be shaken. It is allowed to replace thiourea with maleic anhydride in the amount of 1.5 - 2 g / l.

To initiate nickel deposition on parts made of copper and its alloys, it is necessary to ensure their contact with steel or aluminum. The process is carried out in porcelain or steel containers lined with polyethylene film, as well as in containers made of silicate glass.

With high-speed deposition and with a high loading density of parts of a simple profile, it is recommended to use a solution of the following composition (in g/l):

Nickel sulfate 60

Sodium hypophosphite 25

Sodium acetate 12

Boric acid 8

Ammonium chloride 6

Thiourea 0.003

Solution temperature 93 ± 5°С, sedimentation rate 18 µm/h (at 90°С and loading density 3 dm 2 /l), pH = 5.6 ÷ 5.7.

After chemical nickel plating, the parts are washed in a trap, then in running cold and hot water, dried at 90 ± 10°С for 5–10 min and thermally treated at 210 ± 10°С for 2 h (in order to relieve internal stresses and increase the strength of adhesion to the base). Further, depending on the operating conditions, the parts are varnished, treated with a hydrophobic liquid (GCL, etc.), or fed to the assembly without treatment.

The main reasons for poor-quality coating in chemical nickel plating are:

1) spontaneous precipitation of nickel in the form of black dots due to poor cleaning of the baths, the presence of traces of nickel or other crystallization centers on the bottom and walls of the bath, as well as due to overheating of the solution;

2) the presence of uncoated places on parts of a complex configuration due to the formation of gas bubbles and uneven washing of parts with a solution;

3) partial deposition of nickel on the inner surface of the bath due to parts touching the walls or bottom of the bath during nickel plating;

4) decrease in the acidity of the solution (cracking, brittle coating);

5) an increase in the acidity of the solution (coating is rough and rough).

The pH value is adjusted by adding a 10% solution of acetic acid or sodium hydroxide.

Silicon parts are nickel-plated in alkaline solutions of the following composition (in g/l):

Nickel chloride 30

Sodium hypophosphite 10

Sodium citrate 100

Ammonium chloride 50

The sedimentation rate is 8 µm/h, pH = 8÷10 (due to the introduction of NH 4 OH).

The order of chemical nickel plating of ceramics: degreasing in alkaline solutions and chemical etching of the surface (a mixture of sulfuric and hydrofluoric acids), sensitization in a solution (150 g/l) of sodium hypophosphite at 90°C, nickel plating in an alkaline bath. The thickness of the coatings of parts, depending on the conditions of their operation, is indicated in Table. 25.

25. Coating thickness values ​​depending on operating conditions

So, at pH = 5.5, sediments contain 7.5% phosphorus, and at pH = 3.5, 14.6%. An increase in the hardness of the coating to 1100–1200 kgf/mm 2 at 200–300°C is caused by the precipitation of the Ni 3 P phase, which crystallizes in a tetragonal system with a crystal lattice constant a = b = 8.954. 10 -10 m and c=4.384.10 -10 m. The maximum hardness of nickel corresponds to 750°C. The modulus of elasticity in this case is 19000 kgf/mm 2 . The ultimate tensile strength is 45 kgf/mm 2 (at 20°C) and 55 kgf/mm 2 after heat treatment at 200°C for 1 hour. and shiny chrome. The specific wear of the nickel coating at 100°C is 2.10 -3 mm 3 /m.

When the acidic solution is stirred, the brilliance of the precipitates and the rate of deposition increase. If the deposition process is interrupted for a few minutes, the parts can be loaded into the bath without additional activation. In case of a long break (24 hours), the parts should be stored in a cold nickel plating solution, and then transferred to a working bath.

The rate of metal deposition is the lower, the lower the pH of the solution. In addition, the rate is a function of the Ni 2+ : H 2 PO - 2 ratio. For a normal acidic bath, it should fluctuate between 0.25 and 0.60 (for an acetate-buffered bath, 0.3-0.4).

In the presence of ammonium salts, the deposition rate decreases. In newly prepared solutions, the precipitation rate is initially high and then decreases with aging. Thus, in acetate and citrate solutions, it decreases from 25 to 2–5 µm/h. The most optimal deposition rate is ~10 µm/h.

The gloss of the coating is determined by the quality of the preparation base surface to be polished. In alkaline baths, the coatings are more brilliant than in acid ones. Coatings containing<= 2% фосфора — матовые, 5% фосфора — полублестящие и =>10% phosphorus - very shiny, but with a yellowish tint. The scatter in the coating thickness of 30 µm is, for example, no more than 1–2 µm even on parts of complex configuration. When the bath is operated at a constant pH, the amount of phosphorus in the coating is proportional to the concentration of hypophosphite in the bath.

The normal content of phosphorus in the coating is 5-6%. The phosphorus content is the higher, the greater the ratio of H 2 PO 2:Ni 2+ . On low-carbon steels, the adhesion of nickel coatings is very high (2200 - 4400 kgf / cm 2), but worsens if the temperature of the solution drops to 75 ° C. Adhesion on steels alloyed with Al, Be, Ti, and copper-based alloys depends on the surface treatment method and is improved by subsequent heat treatment at 150-210°C.

The first sign of a violation of the stability of the composition of the solution is the formation of a white foam due to excessive hydrogen evolution throughout the entire volume of the bath. Then a very fine black Ni-P suspension appears, which accelerates the decomposition reaction of the solution.

The reasons for premature decomposition of the solution can be: too rapid introduction of alkali and hypophosphite (add a dilute aqueous solution with vigorous stirring); local overheating; too much high content hypophosphite (you need to lower the pH and temperature); the introduction of palladium into the solution with parts activated in PdCl 2 , the wrong ratio of the total area of ​​the parts to the volume of the solution.

The level of the solution in the bath must be kept constant, since lowering it due to evaporation leads to concentration of the solution. In the process of coating parts should not be allowed to turn off heaters (steam, thermal electric heating, etc.).

Unlike hydrozine, sodium hypophosphite has an important advantage, since the precipitate contains 8-10 times less gases. The addition of sodium thiosulfate helps to reduce the porosity of nickel. Thus, at a thickness of 20 μm, it decreases from 10 to 2 pores/cm2. When choosing a bath material, it should be taken into account that the solutions evaporate at a temperature approximately equal to the boiling point and are highly sensitive to various contaminants. In addition, the material must be resistant to HNO 3 , since nickel deposits must be periodically removed from the walls of the bath. Bathtubs with a volume of 20 liters are made of pyrex, and larger ones are made of polished ceramics. inner surface steel tanks are covered with vitreous enamel. Stainless steel baths must be passivated with concentrated nitric acid for several hours. To prevent the occurrence of galvanic couples between the steel bath and the coated parts, its walls must be lined with glass or rubber. As a lining in small-capacity baths, polyethylene liners are used.

After each unloading of parts, electric rod-type heaters must be etched in HNO 3 .

Defective coatings from parts made of steel, aluminum and titanium should be removed in concentrated nitric acid at a temperature not exceeding 35 ° C, from parts made of corrosion-resistant steels in a 25% HNO 3 solution, and from brass and copper - by anodic dissolution in H 2 SO 4 .

In order to improve the stability of the composition of the solution, foreign companies recommend adding chromium salts. The porosity of coatings obtained in a solution containing 10 g/l K 3 Fe(CN) 6 and 20 g/l NaCl is determined within 10 minutes. Pores are completely absent at a coating thickness of => 100 µm.

NICKEL PLATE, the technical process of applying to the surface of metals b. or m. thin film of nickel metal or nickel alloys; the purpose of this application is to reduce metal corrosion, increase the hardness of the outer layer, increase or change the reflectivity of the surface, give it a more beautiful appearance. First obtained by Bettger in 1842 and commercially carried out in the USA since 1860, nickel plating has now become one of the most widely adopted metal plating methods by industry.

The existing numerous methods of nickel plating can be divided into two main groups: contact methods and methods electroplating; at present, the latter are especially often resorted to. The deposition of a nickel film is applied to surfaces of various metals, and in accordance with the nature of nickel plating, they can be divided into groups: 1) copper, brass, bronze, zinc, 2) iron, 3) tin, lead and from alloys such as Britain-metal, 4 ) aluminum and aluminum alloys. Nickel films provide quite satisfactory protection of iron against rust in interior spaces.

However, they are insufficient in the open air; in addition, hot fats, vinegar, tea, mustard act on polished nickel-plated surfaces, as a result of which nickel-plated tableware and kitchen utensils become stained. In cases where it is necessary to reliable protection from the effects of bad weather and at the same time an elegant appearance of the nickel-plated surface, on iron d. b. a double film is applied - zinc, and then nickel. This method of double coating (zinc and then nickel) is also applied to the so-called. corset steel. If it is necessary to obtain particularly resistant films, such as on wires, nickel and platinum are deposited simultaneously, the content of the latter being gradually increased from 25% to 100% and, finally, the object is calcined in a hydrogen jet at 900-1000°C. Large products, for example, boiling kettles, centrifuge drums or fans, if due to economic conditions cannot be made of pure nickel, but are not resistant enough with a nickel film on iron or copper, are lined with a lead layer of several mm, and over it with a layer of nickel 1-2 mm. The rusting of nickel-plated iron and steel products is due to the presence of electrolyte remaining in the thin pores of the nickel film. This phenomenon is eliminated if the products are kept in oil at 200°C before nickel plating, degreased after cooling, slightly copper-plated, then nickel-plated in a low-current nickel citrate bath, and finally dried in a cabinet at 200°C; then moisture is removed from the pores, which are clogged by the oil in them.

There are a number of proposals to apply double protective films on cast iron, iron or steel sheets, wires and strips in the reverse order of the above, i.e. first cover the products with a thin film of nickel by contact or electrolytic method, and then immerse in a bath of molten zinc or tin (Vivien and Lefebvre, 1860). It is also proposed to add a certain amount of nickel to an alloy of 25-28 kg of zinc, 47-49 kg of lead and 15 kg of tin, which is used for hot coating of iron sheets. The resistance of surfaces of aluminum and its alloys against salt and sea water can be. achieved by electroplating on them, after cleaning them with a sand jet, successive layers of nickel 6 µm thick, copper 20 µm and then again nickel 50 µm, after which the surface is polished. The resistance of aluminum against 15% sodium hydroxide is achieved by a nickel film 40 microns thick. In some cases, a coating is applied not with pure nickel, but with an alloy, for example, nickel-copper; for this, electrolysis is carried out in a bath containing cations in the ratio of the required alloy; the deposited film is then transferred to the alloy by heating the product to red-hot heat.

Contact nickel plating. Steel objects, according to the instructions of F. Stolba (1876), after polishing and proper degreasing, are boiled in a bath of 10-15% aqueous solution of pure zinc chloride, to which nickel sulfate is added until a green turbidity is formed from the basic nickel salt. Nickel plating takes about 1 hour. After that, the object is rinsed in water with chalk, and the bath, after filtering and adding nickel salt, can be used again. The resulting nickel film is thin but holds firmly. To increase the temperature of the bath, it was proposed either to carry out the process under pressure (F. Stolba, 1880) or to use a bath with a concentrated solution of zinc chloride. In order to avoid rusting of objects, they are kept for 12 hours in milk of lime. A more complex bath for iron objects, previously copper-plated in a bath of 250 g of copper sulfate in 23 liters of water with a few drops of sulfuric acid, contains 20 g of cream of tartar, 10 g of ammonia, 5 g of sodium chloride, 20 g of tin chloride, 30 g of nickel sulfate and 50 g double sulfate nickel-ammonium salt.

electroplated nickel plating. Depletion of the nickel bath m. b. prevented by rather easy dissolution of nickel anodes. Rolled, and especially from pure nickel, anodes are difficult to dissolve and therefore, in technical nickel plating, nickel bars containing up to 10% iron are used as anodes. However, such anodes lead to the deposition of iron on the object, and the presence of iron in the nickel film entails whole line nickel plating defects. As pointed out by Kalgane and Gammage (1908), it is impossible to obtain, with anodes containing iron, a deposit completely free of the latter. But the nickel deposit will already contain only 0.10-0.14% iron, if the iron content in the anodes is reduced to 7.5%; the iron content of the precipitate can be further reduced by enclosing the anodes in fabric bags, while the rotation of the electrodes leads to an increased content of iron in the precipitate and to a decrease in its yield. The presence of iron in the nickel film leads to the deposition of deposits with a gradually decreasing iron content and, therefore, inhomogeneous in relation to mechanical properties at different depths; K. Engemann (1911) considers this inhomogeneity to be the only reason for the easy detachment of nickel films. The presence of iron m. the cause of a number of other defects in nickel plating (see table), for example, the ease of rusting of films.

The electrolytic bath for nickel plating is compiled by Ch. from double nickel-ammonium salt, and weak acids are added to eliminate basic salts. Higher acidity of the bath leads to harder films. It must be borne in mind that technical nickel vitriol is not suitable for baths, since it often contains copper; it should be removed by passing hydrogen sulfide through an aqueous solution of vitriol. Chlorine salts are also used, but with sulfate baths the precipitates are harder, whiter and more resistant than with chloride ones. It is beneficial to reduce the high resistance of a nickel bath by adding various conductive salts - especially ammonia and sodium chloride - and by heating. Neutralization of excess sulfuric acid in old solutions is successfully carried out with nickel carbonate, which is obtained from a warm aqueous solution of nickel sulfate precipitated with soda. For the whiteness and smoothness of the films, a large number of proposals have been made to add various organic acids (tartaric, citric, etc.) and their salts to the nickel bath, for example, acetic, citric and tartaric salts of alkali and alkaline earth metals (Keith, 1878 ), propionic nickel, borate-tartrate salts of alkali metals. If it is necessary to obtain thick nickel deposits, it is proposed to add boric, benzoic, salicylic, gallic or pyrogallic acids, and in addition 10 drops of sulfuric, formic, lactic acid per 1 liter of bath to prevent polarization on the product. As Powell (1881) pointed out, the addition of benzoic acid (31 g per bath of 124 g of nickel sulfate and 93 g of nickel citrate in 4.5 liters of water) eliminates the need to use chemically pure salts and acids. The nickel precipitate has good properties also with a simple bath of nickel-ammonium sulfate, but under the condition of alkalinity of the solution, which is achieved by adding ammonia. Very good precipitation is obtained from a neutral solution of nickel fluoride-borate at room temperature(at temperatures above 35 ° C, the solution decomposes to form an insoluble basic salt) and a current density of 1.1-1.65 A / dm 2 . Here are some bath recipes. 1) 50 hours of sodium bisulfite, 4 hours of nickel oxide nitrate and 4 hours of concentrated ammonia are dissolved in 150 hours of water. 2) 10-12 hours nickel sulfate, 4 hours double nickel-ammonium sulfate, 1-3 hours. boric acid, 2 hours of magnesium chloride, 0.2-0.3 hours of ammonium citrate, topped up to 100 hours (total) of water. Current density 1.6 A/dm 2 deposits a film at a rate of 2 µm/h; By raising the temperature to 70°C, the resistance of the bath can be reduced by a factor of two or three, and thereby accelerate nickel plating. 3) An electrolyte of 72 g of double nickel-ammonium sulfate, 8 g of nickel sulfate, 48 g of boric acid and 1 liter of water is especially favorable for the softness and non-porosity of the precipitate, because it reduces the release of hydrogen.

Obtaining Nickel Films of a Special Kind. 1) A white film on zinc, tin, lead and britanium metal is obtained in a bath of 20 g double nickel ammonium sulphate and 20 g nickel carbonate dissolved in 1 liter of boiling water and neutralized at 40°C acetic acid; the bath must be kept neutral. 2) A dull white film is obtained in a bath of 60 g of double nickel-ammonium sulfate, 15 g of recrystallized nickel sulfate, 7.4 g of ammonia, 23 g of sodium chloride and 15 g of boric acid per 1 liter of water; bath e. b concentrated to 10 ° Vẻ; voltage from 2 to 2.5 V. 3) A black film is obtained on surfaces carefully degreased or coated with a thin layer of white nickel by electrolysis in a bath of 60 g of double nickel-ammonium sulfate, 1.5 g of ammonium thiocyanate and about 1 g of sulphate zinc per 1 liter of water 4) A black film is also obtained in an electrolyte from 9 g of double nickel-ammonium sulfate salt in 1 liter of water, followed by the addition of 22 g of potassium thiocyanate, 15 g of copper carbonate and 15 g of white arsenic, previously dissolved in ammonium carbonate; the depth of the black tone increases with the content of arsenic in the solution. 5) A deep blue film is obtained in a bath of equal parts of double and simple nickel sulphates, brought to 12 ° Bẻ, and 2 hours of ammonia decoction of licorice root are added per liter; electrolysis lasts 1 hour at 3.5 V, and then another 1/2 hour at 1.4 V. salt and 60 g of nickel sulfate, dissolved in the smallest possible amount of boiling water, added to 50 cm 3 and then mixed with solutions of 30 g of nickel sulfate and 60 g of sodium thiocyanate, each in 0.5 l of water, after which the solution is added to 4, 5 l. The resulting black film is given a brown tint by immersing the product for several seconds in a bath of 100.6 g of iron perchlorate and 7.4 g of hydrochloric acid in 1 liter of water: after washing and drying, the surface of the product is varnished to fix the tone.

Nickel plating of aluminum and its alloys. Several processes have been proposed. 1) Surface preparation of aluminum products consists of degreasing, then cleaning with pumice and finally immersing in a 3% aqueous solution of potassium cyanide; after electrolysis in a nickel bath, the products are washed cold water. 2) After washing with a 2% solution of potassium cyanide, the products are immersed in a solution of 1 g of ferric chloride (ferrochloride) per 0.5 l of water and technical hydrochloric acid until the surface becomes silver-white, and then nickel-plated for 5 minutes. at a voltage of 3 V. 3) Polishing products, removing the polishing composition with gasoline, exposure for several minutes in a warm aqueous solution of sodium phosphate, soda and resin, washing, immersing for a short time in a mixture of equal parts of 66% sulfuric acid (containing some ferric chloride) and 38% nitric acid, new washing and electrolysis in a bath containing nickel salt, bitter salt and boric acid; voltage 3-3.25 V. 4) According to J. Kanak and E. Tassilly: etching the product with boiling potassium alkali, brushing in milk of lime, 0.2% cyano-potassium bath, bath of 1 g of iron in 500 g of hydrochloric acid and 500 g of water, washing, nickel plating in a bath of 1 liter of water, 500 g of nickel chloride and 20 g of boric acid at a voltage of 2.5 V and a current density of 1 A/dm 2 , finally polishing the dull gray precipitate. The iron bath serves to roughen the aluminum surface and thus contributes to the strength with which the film is held on the metal. 5) According to Fischer, the nickel plating bath is made up of 50 g of nickel sulfate and 30 g of ammonia in 1 liter of water at a current density of 0.1-0.15 A / dm 2, in 2-3 hours a thick precipitate is obtained, which has a high gloss after polishing with stearin oil and Vienna lime. 6) Hot bath (60°C) is made up of 3400 g double nickel-ammonium sulphate, 1100 g ammonium sulphate and 135 g milk sugar in 27 liters of water. 7) The cold bath contains nickel nitrate, potassium cyanide and ammonium phosphate.

Nickel film control. Recognition of the composition of a metal film on an object, according to L. Loviton (1886), can be carried out by heating the object in the external flame of a Bunsen burner: the nickel film turns blue, receives a black reflection and remains intact; silver does not change in the flame, but blackens when treated with a dilute solution of ammonium sulfide; finally, the tin coating quickly turns gray-yellow to gray and disappears when treated with the indicated reagent. Checking the quality of the nickel film on iron and copper in relation to pores and flaws can be done using the so-called. ferroxyl test and with particular convenience using ferroxyl paper coated with agar-agar gel with potassium ferric bluesulfide and sodium chloride. Apply wetted to the surface to be tested and after 3-5 minutes. fixed in water, this paper gives a documentary image of the smallest pores, which can be. saved.

Nickel recovery from old products. Removal of nickel coating from products made of iron and other non-amalgamated metals is carried out in the following ways: a) with mercury vapor under vacuum or under ordinary pressure; b) heating scraps with sulfur, after which the metal layer is easily removed with hammers; c) heating scraps with substances that release sulfur when high temperature) upon sudden cooling, the nickel film jumps off; d) treatment with sulfuric or nitric acid heated to 50-60°C; iron goes into solution, and nickel remains almost undissolved; however, despite its simplicity, this method is of little use, since the obtained nickel still retains a significant iron content, which is not removed even during repeated treatment with acid (T. Fleitman); e) prolonged heating with access to air or water vapor, after which the trimmings are subjected to mechanical shocks and the nickel rebounds; e) electrolytic dissolution: an iron plated with nickel is made an anode in a bath containing ammonium carbonate; if the coating consists of a nickel alloy, then it is necessary to regulate the voltage, and at 0.5 V copper is deposited, and at a voltage greater than 2 V - nickel; in this process, iron is not corroded; g) iron or steel scraps are made an anode in a bath of an aqueous solution of sodium nitrate, while the cathode consists of a carbon stick; voltage should not exceed 20 V; h) Nickel is removed from zinc mugs by electrolysis of objects made with an anode in 50° sulfuric acid; an acid of this concentration has the property of dissolving only nickel, silver and gold, but not other metals, if there is a current; voltage applied 2-5V; iron sheets serve as cathodes, on which nickel is deposited in the form of dust; zinc does not dissolve, even though the circles remain in the electrolyte for a long time.

Covering parts made of non-ferrous metals and steel with nickel increases their resistance to corrosion processes and mechanical wear. Nickel plating at home is available to everyone and is characterized by simple technology.

1 Nickel plating of metal surfaces - the basics of technology

Nickel plating consists in applying a thin nickel coating to the surface of the workpiece, the thickness of which, as a rule, is 1–50 microns. Parts are subjected to this operation in order to protect them or to obtain a characteristic (matte black or shiny) appearance nickel plated surface. The coating, regardless of shade, reliably protects metal objects from corrosion on outdoors, in solutions of salts, alkalis, weak organic acids.

As a rule, parts made of steel or such metals and alloys from them as copper, aluminum, zinc, less often - titanium, manganese, molybdenum, tungsten are nickel-plated. It is impossible to process the surface of products made of lead, tin, cadmium, bismuth, antimony by chemical nickel plating. Nickel coatings are used in various industries for protective, decorative and special purposes or as a sublayer.

This technology is used to restore the surface of worn parts of various mechanisms and vehicles, coatings of measuring and medical instruments, household items and products, chemical equipment, parts operated under light loads under the influence of strong alkali solutions or dry friction. There are 2 methods of applying nickel plating - electrolytic and chemical.

The second one is somewhat more expensive than the first one, however, it allows to obtain a coating of uniform thickness and quality on the entire surface of the part, provided that the solution is provided with access to all its sections. Nickel plating at home is quite a feasible task. Before starting work, the product is thoroughly cleaned of dirt and rust (if any), treated with fine sandpaper to remove the oxide film, washed with water, then degreased and washed again.

2 Secrets to increasing the durability and service life of nickel plating

Before nickel plating steel, it is desirable to perform copper plating of the product (cover with a copper sublayer). This technology is used in industry as a separate process, as well as a preparatory process before silvering, chromium plating, nickel plating. Copper plating, prior to the application of other layers, allows you to even out surface defects and ensures the reliability and durability of the outer protective coating. Copper adheres to steel very strongly, and other metals are deposited on it much better than on pure steel. In addition, nickel coatings are not continuous and have through (to the substrate metal) pores per 1 cm2:

• several tens - for single-layer nickel coatings;
• several - for three-layer.

As a result, the metal of the substrate under the nickel undergoes corrosion processes, and conditions arise that provoke peeling of the protective coating. Therefore, even with preliminary copper plating, multi-layer nickel plating, and especially with single-layer nickel plating, it is necessary to treat the surface of the nickel protective coating with special compounds that close the pores. With self-processing at home, the following methods are possible:

• wipe the coated part with a mushy mixture of water and magnesium oxide and immediately immerse it for 1–2 minutes in a 50% hydrochloric acid composition;
• wipe the surface of the part 2–3 times with an easily penetrating lubricant;
• immediately after processing, immerse the product that has not yet cooled down in fish oil (not fortified, preferably old, which is no longer suitable for its intended purpose).

In the last two cases, excess lubricant (fat) is removed from the surface in a day with gasoline. In the case of processing large surfaces (moldings, car bumpers), fish oil is used as follows. In hot weather, they wipe the item 2 times with an interval of 12-14 hours, and after 2 days remove the excess with gasoline.

3 Electrolytic nickel plating at home

This method requires the preparation of an electrolyte, the composition of which is as follows:

• 140 g of nickel sulfate;
• 50 g of sodium sulfate;
• 30 g of magnesium sulfate;
• 5 g of table salt (sodium chloride);
• 20 g of boric acid;
• 1000 g of water.

The chemicals are dissolved separately in water, the resulting solutions are filtered and then mixed. Ready electrolyte is poured into a container. Nickel plating requires nickel electrodes (anodes), which are immersed in an electrolyte bath (one electrode is not enough, since the resulting coating will be uneven). A workpiece is suspended on a wire between the anodes. The copper conductors coming from the nickel plates are connected into one circuit and connected to the positive terminal of the DC source, the wire from the part to the negative.

To control the current strength, a resistance (rheostat) and a milliammeter (device) are included in the circuit. The voltage of the current source must be no more than 6 V, the current density must be maintained at the level of 0.8–1.2 A/dm2 (the surface area of ​​the product), the electrolyte temperature is room temperature 18–25 °C. Current is applied for 20–30 minutes. During this time, a nickel layer with a thickness of approximately 1 µm is formed. Then the part is taken out, properly washed with water and dried. The resulting coating will be grayish-matte in color. In order for the nickel layer to become shiny, the surface of the part is polished.

If there is no sodium and magnesium sulfate, then take more nickel sulfate, bringing its amount in the electrolyte to 250 g, as well as boric acid - 30 g, sodium chloride - 25 g. Nickel plating in this case is carried out at current density values ​​​​in the range of 3–5 A/dm2, the solution is heated to 50–60 °C.

Disadvantages of the electrolytic method:

• on embossed, uneven surfaces nickel is deposited unevenly;
• the impossibility of coating in deep and narrow cavities, holes and the like.

4 Chemical nickel plating of products at home

All compositions for chemical nickel plating are universal - suitable for processing any metal. Solutions are prepared following a certain sequence. All chemicals are dissolved in water (excluding sodium hypophosphite). Dishes must be enamelled. Then the solution is heated, bringing its temperature to the working temperature, after which sodium hypophosphite is dissolved. The part is hung in a liquid composition, the temperature of which is maintained at the required level. In 1 liter of the prepared solution, it is possible to carry out nickel plating of the product, the surface area of ​​which is up to 2 dm2.

Use the following compositions of solutions, g/l:

• Sodium succinic acid - 15, nickel chloride - 25, sodium hypophosphite - 30 (acidity of the pH solution - 5.5). The working temperature of the mixture is 90–92 °C, the coating growth rate is 18–25 µm/h.
• Nickel sulfate - 25, sodium succinic acid - 15, sodium hypophosphite - 30 (pH - 4.5). Temperature - 90 °С, speed - 15–20 µm/h.
• Nickel chloride - 30, glycolic acid - 39, sodium hypophosphite - 10 (pH - 4.2). 85–89 °С, 15–20 µm/h.
• Nickel sulfate - 21, sodium acetate - 10, lead sulfide - 20, sodium hypophosphite - 24 (pH - 5). 90 °С, up to 90 µm/h.
• Nickel chloride - 21, sodium acetate - 10, sodium hypophosphite - 24 (pH - 5.2). 97 °С, up to 60 µm/h.
• Nickel chloride - 30, acetic acid - 15, lead sulfide - 10-15, sodium hypophosphite - 15 (pH - 4.5). 85–87 °С, 12–15 µm/h.
• Nickel chloride - 30, ammonium chloride - 30, sodium succinic acid - 100, ammonia (25% solution) - 35, sodium hypophosphite - 25 (pH - 8–8.5). 90 °С, 8–12 µm/h.
• Nickel chloride - 45, ammonium chloride - 45, sodium citrate - 45, sodium hypophosphite - 20 (pH - 8.5). 90°С, 18–20 µm/h.
• Nickel sulfate - 30, ammonium sulfate - 30, sodium hypophosphite - 10 (pH - 8.2–8.5). 85 °С, 15–18 µm/h.
• Nickel chloride - 45, ammonium chloride - 45, sodium acetate - 45, sodium hypophosphite - 20 (pH - 8–9). 88–90 °С, 18–20 µm/h.

After the required time has elapsed, the product is washed in water containing a small amount of dissolved chalk, then dried and polished. The steel and iron coating obtained in this way hold quite firmly.

The chemical process of nickel plating is based on a reaction in which nickel is reduced from a solution of salts based on it in the presence of sodium hypophosphite and with the help of other chemical reagents. The compositions used are divided into alkaline (pH level exceeds 6.5) and acidic (pH value is 4–6.5). The latter are best used for processing ferrous metals, copper, brass, and alkaline ones are designed for nickel plating.

The use of acid compositions makes it possible to obtain a smoother, more uniform surface on a polished product than with alkaline ones. Acidic solutions have another important feature - the probability of their self-discharge when the values ​​are exceeded. operating temperature less than alkaline. Do-it-yourself nickel plating using alkaline compounds guarantees a stronger and more reliable adhesion of the nickel layer to the metal on which it was applied.

The property of nickel to create a thin oxide film on its surface, which is resistant to acids and alkalis, makes it possible to use it for anticorrosion protection of metals.

The main method used in industry is nickel plating, but it requires fairly sophisticated equipment and involves working with acids and alkalis, the vapors of which are released during operation and can greatly harm human health. Can be applied to steel, aluminium, brass, bronze and other metals chemical method, as it is easy to use and the process can be carried out at home.

To date, there are two main methods of coating metal parts with nickel: galvanic and chemical. The first method requires a constant current source - an electrolytic bath with electrodes and a large number chemical reagents. The second way is much easier. For its implementation, the presence of measuring utensils and an enameled container for heating reagents is required. Despite all the seeming simplicity, this is a rather complicated process that requires a lot of attention and compliance with safety rules. If possible, carry out reactions in a well-ventilated area. The ideal option there will be an equipment of the workplace with an exhaust hood, in no case connected to the general house ventilation. When working, use safety glasses, do not leave the container with reagents unattended.

Nickel plating of metal parts

The main steps for chemical nickel plating are as follows:

1. In order for the nickel to cover the surface with a thin and uniform layer, the product is preliminarily ground and polished.
2. Degreasing. Since even the thinnest film of fat on the surface of the workpiece can cause an uneven distribution of nickel over the area of ​​the part, the latter is degreased in a special solution consisting of 25-35 g / l NaOH or KOH, 30-60 g of soda ash and 5-10 g of liquid glass.
3. The part or product to be coated with nickel is washed in water, after which it is immersed in a 5% HCl solution for 0.5-1 minute. This step is taken in order to remove a thin layer of oxides from the metal surface, which will significantly reduce adhesion between materials. After pickling, the part is rinsed again in water, then immediately transferred to a container with nickel plating solution.

Actually nickel plating is carried out by boiling a metal product in a special solution, which is prepared as follows:

• take water (preferably distilled) at the rate of 300 ml / dm 2 of the surface area of ​​\u200b\u200bthe part, including both internal and external;
• water is heated to 60 ° C, after which 30 g of nickel chloride (NiCl 2) and 10 g of sodium acetate (CH 3 COONa) are dissolved in it per 1 liter of water;
• the temperature is raised to 80 ° C and 15 g of sodium hyposulfite are added, then the workpiece is immersed in a container with a solution.

Boiling a metal product

After the part is immersed, the solution is heated to 90-95°C and the temperature is maintained at this level during the entire nickel plating process. If you see that the amount of solution has greatly decreased, you can add pre-heated distilled water to it. Boiling should take at least 1-2 hours. Sometimes, to obtain a multilayer coating, metal products are subjected to a series of short (20-30 minutes) boilings, after each of which the part is removed from the solution, washed and dried. This makes it possible to obtain a nickel layer from 3-4 interlayers, which in total have a higher density and quality than a single layer of the same thickness.

A feature of the coating of steel products is that nickel is deposited spontaneously due to the catalytic effect of iron. A different composition is used to deposit a protective layer on non-ferrous metals.

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Chemical nickel plating of non-ferrous metals allows you to create protective film on the surface of brass, copper and bronze. To do this, the part is first degreased with a solution whose composition is indicated in the first method, and it is not necessary to remove the oxide film from the metal. The solution for nickel plating is prepared as follows: a 10% solution of zinc chloride (ZnCl 2), which is better known as "soldering acid", is poured into an enameled container. Nickel sulphate (NiSO 4) is gradually added to it to a concentration at which the solution turns into green color. The composition is brought to a boil, after which the part is immersed in it for 1.5-2 hours. After the reaction is over, the product is removed from the solution and placed in a container with chalk water (prepared by adding 50-70 g of powdered chalk per 1 liter of water), and then washed.

Nickel sulfate solution

Aluminum nickel plating follows a similar technology, but the composition of the solution is slightly different:

• 20 g of nickel sulfate;
• 10 g sodium acetate;
• 25 g sodium hypophosphite;
• 3 ml of thiourea with a concentration of 1 g/l;
• 0.4 g sodium fluoride;
• 9 ml of acetic acid.

Machining of aluminum parts

Before processing, aluminum products are immersed in a solution caustic soda, concentration of 10-15%, and heated to a temperature of 60-70°C. In this case, a violent reaction occurs with the release of hydrogen, the bubbles of which clean the surface of oxides and pollution. Depending on the degree of contamination, the parts are kept in a cleaning solution from 15-20 seconds to 1-2 minutes, after which they are washed in running water and immersed in a nickel-plating solution.

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Due to nickel plating, the physical, mechanical and decorative properties metal products. Nickel has a silvery-white color, in air it is quickly covered with a film of oxides that is invisible to the human eye, which practically do not change its appearance, but at the same time reliably protect it from further oxidation and reactions with an aggressive environment. Nickel plating is used to protect steel, bronze, brass, aluminium, copper and other materials.

Protection of metal products from oxidation

It is cathodic protection. This means that if the integrity of the coating is damaged, the metal begins to react with the external environment. To improve the mechanical properties of the protective layer, it is necessary to apply it, strictly adhering to the technology and sequence of actions. Nickel deposited on a surface with traces of contamination and rust, with a large number of irregularities, may begin to swell and peel off during operation.

Products coated with nickel are almost in no way inferior to chrome ones - they have a similar luster and hardness. At large sizes containers for chemical reaction Nickel can be plated quite big details such as car rims.

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Nickel plating gives the metal a beautiful shiny appearance, high corrosion resistance and increases the surface hardness. Nickel-plated parts can be used to decorate fence posts, if the design of the site provides for this. They look good and have long term operation of various hardware - fixing bolts, brackets, elements furniture fittings. They can be used in conditions of high humidity, temperature and stress - in places where steel quickly rusts and loses its properties.

Chemical nickel plating can be done by hand in a well-ventilated garage or workshop.

Nice shiny surface

It is undesirable to do the described technological operations in the kitchen, since the evaporation of any chemical substances may be hazardous to health.

Nickel plating with the help of chemical reagents does not require high energy consumption, unlike galvanic, but allows you to get a fairly high-quality, shiny and hard coating.

Nickel is a metal of the iron subgroup, which has received the most widespread use in electroplating.

Compared with copper plating, brass plating, silver plating, etc., nickel plating has received industrial application much later, but since the end of the 19th century, this process has become the most common method of “ennobling” the surface of metal products. Only in the twenties of the current century was another process widely used - chromium plating, which seemed to replace nickel plating. However, both of these processes - nickel plating and chromium plating for protective and decorative purposes are used in combination, that is, the products are first nickel-plated and then coated with a thin layer of chromium (tenths of a micron). In this case, the role of nickel coating is not diminished; on the contrary, increased requirements are imposed on it.

The widespread use of nickel plating in electroplating is explained by the valuable physical and chemical properties of electrolytically deposited nickel. Although in a number of voltages nickel is higher than hydrogen, due to a strongly pronounced tendency to passivation, however, it turns out to be quite resistant to atmospheric air, alkalis and some acids. In relation to iron, nickel has a less electronegative potential, therefore, the base metal - iron - is protected from corrosion by nickel only if there are no pores in the coating.

Nickel coatings obtained from solutions of simple salts have a very fine structure, and since at the same time electrolytic nickel perfectly accepts polishing, the coatings can be brought to a mirror finish. This circumstance makes it possible to widely use nickel coatings for decorative purposes. When brightening agents are introduced into the electrolyte, it is possible to obtain shiny nickel coatings in layers of sufficient thickness without polishing. The structure of normal nickel deposits is extremely fine and difficult to detect even at high magnification.

Most often, nickel plating has two goals: protection of the base metal from corrosion and decorative trim surfaces. Such coatings are widely used for the exterior parts of cars, bicycles, various apparatus, instruments, surgical instruments, household items, etc.

From an electrochemical point of view, nickel can be characterized as a representative of the metals of the iron group. In a strongly acidic environment, the deposition of these metals is generally impossible - almost one hydrogen is released at the cathode. Moreover, even in solutions close to neutral, a change in pH affects the current efficiency and properties of metal deposits.

The phenomenon of sediment peeling, which is most characteristic of nickel, is also strongly associated with the acidity of the medium. From this follows the first care to maintain and regulate the proper acidity in nickel plating, as well as the selection of the proper temperature for the correct conduct of the process.

The first electrolytes for nickel plating were prepared based on the double salt NiSO 4 (NH 4) 2 SO 4 6H 2 O. These electrolytes were first researched and developed by Harvard University professor Isaac Adams in 1866. Compared to modern high-performance electrolytes with a high concentration of nickel salt double salt electrolytes allow a current density not exceeding 0.3-0.4 A/dm 2 . The solubility of double nickel salt at room temperature does not exceed 60-90 g/l, while nickel sulfate heptahydrate dissolves at room temperature in an amount of 270-300 g/l. The content of nickel metal in the double salt is 14.87%, and in the simple (sulfate) salt 20.9%.

The nickel plating process is very sensitive to impurities in the electrolyte and anodes. It is quite obvious that a salt that is slightly soluble in water is easier to free during crystallization and washing from harmful impurities, such as sulfates of copper, iron, zinc, etc., than a more soluble simple salt. It is largely for this reason that double salt electrolytes dominated the second half of the 19th and early 20th centuries.

Boric acid, which is now regarded as a very essential component for nickel plating electrolyte buffering and nickel electrolytic refining, was first proposed in the late 19th and early 20th centuries.

Chlorides were proposed to activate nickel anodes at the beginning of the 20th century. To date, a wide variety of electrolytes and modes for nickel plating has been proposed in the patent and journal literature, apparently more than any other metal electrodeposition process. However, it can be said without exaggeration that most of the modern electrolytes for nickel plating is a variation of the one proposed in 1913 by University of Wisconsin professor Watts based on a detailed study of the influence of individual components and the electrolyte regime. Somewhat later, as a result of improvement, he found that in nickel-concentrated electrolytes, at elevated temperature and intensive stirring (1000 rpm), it is possible to obtain nickel coatings satisfactory in thick layers at a current density exceeding 100 A / dm 2 (for products of simple forms). These electrolytes are made up of three main components: nickel sulfate, nickel chloride, and boric acid. It is fundamentally possible to replace nickel chloride with sodium chloride, but, according to some reports, such a replacement somewhat reduces the allowable cathode current density (possibly due to a decrease in the total concentration of nickel in the electrolyte). Watts electrolyte has the following composition, g/l:
240 - 340 NiSO 4 7H 2 O, 30-60 NiCl 2 6H 2 O, 30 - 40 H 3 BO 3.

From other electrolytes, which in Lately are increasingly attracting the attention of researchers and finding industrial application, should be called fluoroborate, allowing the use of increased current density and sulfamate, providing the possibility of obtaining nickel coatings with lower internal stresses.

At the beginning of the thirties of the current century, and especially after the Second World War, the attention of researchers was riveted to the development of such brighteners that make it possible to obtain shiny nickel coatings in layers of sufficient thickness not only on the base metal surface polished to a shine, but also on a matte surface.

The discharge of nickel ions, as well as other metals of the iron subgroup, is accompanied by significant chemical polarization, and the release of these metals at the cathode begins at potential values ​​that are much more negative than the corresponding standard potentials.

Much research has been devoted to elucidating the causes of this increased polarization, and several widely divergent explanations have been proposed. According to some data, the cathodic polarization during the electrodeposition of metals of the iron group is sharply expressed only at the moment of the beginning of their precipitation, with a further increase in the current density, the potentials change insignificantly. With an increase in temperature, the cathodic polarization (at the moment of the onset of precipitation) sharply decreases. So, at the moment of the beginning of nickel precipitation at a temperature of 15 ° C, the cathodic polarization is 0.33 V, and at 95 ° C 0.05 V; for iron, the cathodic polarization decreases from 0.22 V at 15° C to zero at 70° C, and for cobalt from 0.25 V at 15° C to 0.05 V at 95° C.

The high cathodic polarization at the start of the precipitation of iron group metals was explained by the precipitation of these metals in a metastable form and the need to expend additional energy for their transition to a stable state. Such an explanation is not generally accepted, and there are other views on the reasons for the large cathodic polarization, in which the iron-group metals precipitate, and the fine-grained structure associated with polarization.

Other followers attributed special role hydrogen film formed as a result of the combined discharge of hydrogen ions, which hinders the aggregation of small crystals and leads to the formation of finely dispersed deposits of iron group metals, as well as alkalization of the cathode layer and the associated precipitation of colloidal hydroxides and basic salts, which can co-precipitate with metals and hinder growth crystals.

Some proceeded from the fact that the large polarization of the iron group metals is associated with a high activation energy during the discharge of highly hydrated ions, the calculations of others showed that the dehydration energy of the iron group metals is approximately the same as the dehydration energy of such divalent metal ions as copper, zinc, cadmium, the discharge of ions of which proceeds with an insignificant cathodic polarization, approximately 10 times less than during the electrodeposition of iron, cobalt, nickel. The increased polarization of the metals of the iron group was explained and is now explained by the adsorption of foreign particles; the polarization noticeably decreased with continuous stripping of the cathode surface.

This does not exhaust the review of various views on the causes of increased polarization during the electrodeposition of metals of the iron group. However, it can be assumed that, except for the region of low concentrations and high current densities, the kinetics of these processes can be described by the equation of the theory of delayed discharge.

Due to the large cathodic polarization at a relatively low hydrogen overvoltage, the processes of electrodeposition of iron-group metals are extremely sensitive to the concentration of hydrogen ions in the electrolyte and to temperature. The allowable cathode current density is the higher, the higher the temperature and the concentration of hydrogen ions (the lower the pH).