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1. NICKEL PLATING

2. CHROME PLATING

LIST OF SOURCES USED

1. NICKEL PLATING

Nickel-plated coatings have a number of valuable properties: they are well polished, acquiring a beautiful long-lasting mirror shine, they are durable and protect the metal well from corrosion.

The color of nickel coatings is silver-white with a yellowish tint; They are easily polished, but become dull over time. The coatings are characterized by a fine-crystalline structure, good adhesion to steel and copper substrates, and the ability to passivate in air.

Nickel plating is widely used as a decorative coating for parts of lamps intended for lighting public and residential premises.

To coat steel products, nickel plating is often carried out over an intermediate sublayer of copper. Sometimes a three-layer nickel-copper-nickel coating is used. In some cases, the nickel layer is coated with thin layer chromium, thereby forming a nickel-chrome coating. Nickel is applied to parts made of copper and copper-based alloys without an intermediate sublayer. The total thickness of two and three-layer coatings is regulated by mechanical engineering standards; it is usually 25–30 microns.

On parts intended to operate in humid tropical climates, the coating thickness must be at least 45 microns. In this case, the regulated thickness of the nickel layer is no less than 12–25 microns.

To obtain a shiny finish, nickel-plated parts are polished. Recently, bright nickel plating has been widely used, which eliminates the labor-intensive operation of mechanical polishing. Bright nickel plating is achieved by introducing brightening agents into the electrolyte. However, the decorative qualities of mechanically polished surfaces are higher than those obtained by bright nickel plating.

Nickel deposition occurs with significant cathodic polarization, which depends on the temperature of the electrolyte, its concentration, composition and some other factors.

Electrolytes for nickel plating are relatively simple in composition. Currently, sulfate, hydrofluoride and sulfamite electrolytes are used. Lighting factories use exclusively sulfate electrolytes, which make it possible to work with high current densities and thus obtain coatings High Quality. The composition of these electrolytes includes salts containing nickel, buffer compounds, stabilizers and salts that promote the dissolution of the anodes.

The advantages of these electrolytes are the non-scarcity of components, high stability and low aggressiveness. Electrolytes are allowed in their composition high concentration nickel salts, which makes it possible to increase the cathode current density and, consequently, increase the productivity of the process.

Sulfate electrolytes have high electrical conductivity and good dissipation ability.

The following electrolyte composition, g/l, is widely used:

NiSO4 7H2O 240–250

*Or NiCl2·6H2O – 45 g/l.

Nickel plating is carried out at a temperature of 60°C, pH = 5.6 h6.2 and a cathodic current density of 3–4 A/dm2.

Depending on the composition of the bath and its operating mode, coatings with varying degrees of gloss can be obtained. For these purposes, several electrolytes have been developed, the compositions of which are given below, g/l:

for matte finish:

NiSO4 7H2O 180–200

Na2SO4 10H2O 80–100

Nickel plating at a temperature of 25–30°C, at a cathodic current density of 0.5–1.0 A/dm2 and pH=5.0h5.5;

for a semi-gloss finish:

Nickel sulfate NiSO4 7H2O 200–300

Boric acid H3BO3 30

2,6–2,7-Disulfonaphthalic acid 5

Sodium fluoride NaF 5

Sodium chloride NaCl 7–10

Nickel plating is carried out at a temperature of 20–35°C, cathodic current density of 1–2 A/dm2 and pH = 5.5 h 5.8;

for a shiny finish:

Nickel sulfate (hydrate) 260–300

Nickel chloride (hydrate) 40–60

Boric acid 30–35

Saccharin 0.8–1.5

1,4-butynediol (100% equivalent) 0.12–0.15

Phthalimid 0.08–0.1

Operating temperature of nickel plating is 50–60°C, electrolyte pH 3.5–5, cathode current density with intensive stirring and continuous filtration 2–12 A/dm2, anodic current density 1–2 A/dm2.

A special feature of nickel plating is a narrow range of electrolyte acidity, current density and temperature.

To maintain the composition of the electrolyte within the required limits, buffer compounds are introduced into it, which most often use boric acid or a mixture of boric acid and sodium fluoride. In some electrolytes, citric, tartaric, acetic acid or their alkaline salts are used as buffer compounds.

A special feature of nickel coatings is their porosity. In some cases, pinpoint spots, so-called “pitting,” may appear on the surface.

To prevent pitting, intensive air mixing of the baths and shaking of the pendants with parts attached to them are used. The reduction of pitting is facilitated by the introduction of surface tension reducers or wetting agents into the electrolyte, which are sodium lauryl sulfate, sodium alkyl sulfate and other sulfates.

The domestic industry produces good anti-pitting detergent"Progress", which is added to the bath in an amount of 0.5 mg/l.

Nickel plating is very sensitive to foreign impurities that enter the solution from the surface of parts or due to anodic dissolution. When nickel plating steel parts

When coating copper-based alloys, the solution becomes clogged with iron impurities, and when coating copper-based alloys, it becomes clogged with its impurities. Removal of impurities is carried out by alkalizing the solution with nickel carbonate or hydroxide.

Organic contaminants that contribute to pitting are removed by boiling the solution. Sometimes tinting of nickel-plated parts is used. This produces colored surfaces with a metallic sheen.

Toning is carried out chemically or electrochemically. Its essence lies in the formation of a thin film on the surface of the nickel coating, in which light interference occurs. Such films are produced by applying organic coatings several micrometers thick to nickel-plated surfaces, for which the parts are treated in special solutions.

Black nickel coatings have good decorative qualities. These coatings are obtained in electrolytes, to which zinc sulfates are added in addition to nickel sulfates.

The composition of the electrolyte for black nickel plating is as follows, g/l:

Nickel sulfate 40–50

Zinc sulfate 20–30

Rhodane potassium 25–32

Ammonium sulfate 12–15

Nickel plating is carried out at a temperature of 18–35°C, cathodic current density of 0.1 A/dm2 and pH = 5.0 h5.5.

2. CHROME PLATING

Chrome coatings have high hardness and wear resistance, a low coefficient of friction, are resistant to mercury, firmly adhere to the base metal, and are also chemical and heat resistant.

In the manufacture of lamps, chrome plating is used to obtain protective and decorative coatings, and also as reflective coatings in the manufacture of mirror reflectors.

Chrome plating is carried out over a previously applied copper-nickel or nickel-copper-nickel sublayer. The thickness of the chromium layer with such a coating usually does not exceed 1 micron. In the manufacture of reflectors, chrome plating is currently being replaced by other coating methods, but in some factories it is still used for the manufacture of reflectors for mirror lamps.

Chrome has good adhesion to nickel, copper, brass and other deposited materials, but poor adhesion is always observed when depositing other metals onto a chrome coating.

A positive property of chromium coatings is that parts become shiny directly in galvanic baths; this does not require mechanical polishing. Along with this, chrome plating differs from other galvanic processes in that it has more stringent requirements for the operating conditions of the baths. Minor deviations from the required current density, electrolyte temperature and other parameters inevitably lead to deterioration of coatings and massive defects.

The dissipative ability of chromium electrolytes is low, which leads to poor coverage of internal surfaces and recesses of parts. To increase the uniformity of coatings, special suspensions and additional screens are used.

For chrome plating, solutions of chromic anhydride with the addition of sulfuric acid are used.

Three types of electrolytes have found industrial application: diluted, universal and concentrated (Table 1). To obtain decorative coatings and to obtain reflectors, concentrated electrolyte is used. When chrome plating, insoluble lead anodes are used.

Table 1 - Compositions of electrolytes for chrome plating

During operation, the concentration of chromic anhydride in the baths decreases, therefore, to restore the baths, daily adjustments are made by adding fresh chromic anhydride to them.

Several formulations of self-regulating electrolytes have been developed in which the concentration ratio is automatically maintained.

The composition of this electrolyte is as follows, g/l:

Chromium plating is carried out at a cathodic current density of 50–80 A/dm2 and a temperature of 60–70°C.

Depending on the relationship between temperature and current density, different types of chrome coating can be obtained: milky shiny and matte.

The milky coating is obtained at a temperature of 65–80°C and

low current density. A shiny coating is obtained at temperatures of 45–60°C and medium current density. Matte coating is obtained at temperatures of 25–45°C and high current density. In the production of lamps, shiny chrome coating is most often used.

To obtain mirror reflectors, chrome plating is carried out at a temperature of 50–55°C and a current density of 60 A/dm2. in the manufacture of mirror reflectors, copper and nickel are pre-deposited. The reflective surface is polished after applying each layer. The technological process includes the following operations:

surface grinding and polishing;

copper plating;

nickel plating;

polishing, degreasing, pickling;

chrome plating;

clean polishing.

After each technological operation, 100% quality control of the coating is carried out, since failure to comply with technology requirements leads to peeling of the sublayer along with the chrome coating.

Products made of copper and copper alloys are chrome plated without an intermediate layer. The parts are immersed in the electrolyte after voltage is applied to the bath. When applying multilayer coatings to steel products, the layer thickness is regulated by GOST 3002-70. Thickness values ​​are given in Table 2.

Table 2 - Minimum thickness of multilayer galvanic coatings

Chrome plating baths are equipped with powerful exhaust ventilation to remove toxic chromic acid vapors.

During chrome plating, part of the hexavalent chromium Cr6+ enters wastewater Therefore, to prevent Cr6+ emissions into open water bodies, protective measures are used - neutralizers and treatment facilities are installed.

LIST OF SOURCES USED

Afanasyeva E.I., Skobelev V.M. "Light sources and control equipment: Textbook for technical schools", 2nd ed., revised, M: Energoatomizdat, 1986, 270 p.

Bolenok V.E. "Production of electric lighting devices: Textbook for technical schools", M: Energoizdat, 1981, 303p.

Denisov V.P. "Production of electric light sources", M: Energia, 1975, 488p.

Characteristics of solid waste from the chrome plating process. Titration with ferrous sulfate and permanganate. Theory of determination of chromium experimentally. Qualitative analysis of solid waste components from the chrome plating process. Colorimetric methods for the determination of chromium.

Those around us metal objects rarely consist of pure metals. Only aluminum pans or copper wire have a purity of about 99.9%. In most other cases, people deal with alloys. So, different kinds iron and steel, contain, along with metal additives, insignificant...

Ministry of Education Russian Federation State educational institution higher and vocational education IRKUTSK STATE UNIVERSITY

Physicochemical and thermodynamic properties of concentrated aqueous solutions containing components of iron-nickel alloy deposition electrolytes. Kinetic patterns of anodic dissolution of the iron-nickel alloy under non-stationary conditions.

PLAN

1. NICKEL PLATING

2. CHROME PLATING

LIST OF SOURCES USED

1. NICKEL PLATING

Nickel-plated coatings have a number of valuable properties: they are well polished, acquiring a beautiful long-lasting mirror shine, they are durable and protect the metal well from corrosion.

The color of nickel coatings is silver-white with a yellowish tint; They are easily polished, but become dull over time. The coatings are characterized by a fine-crystalline structure, good adhesion to steel and copper substrates, and the ability to passivate in air.

Nickel plating is widely used as a decorative coating for parts of lamps intended for lighting public and residential premises.

To coat steel products, nickel plating is often carried out over an intermediate sublayer of copper. Sometimes a three-layer nickel-copper-nickel coating is used. In some cases, a thin layer of chromium is applied to the nickel layer to form a nickel-chrome coating. Nickel is applied to parts made of copper and copper-based alloys without an intermediate sublayer. The total thickness of two and three-layer coatings is regulated by mechanical engineering standards; it is usually 25–30 microns.

On parts intended to operate in humid tropical climates, the coating thickness must be at least 45 microns. In this case, the regulated thickness of the nickel layer is no less than 12–25 microns.

To obtain a shiny finish, nickel-plated parts are polished. Recently, bright nickel plating has been widely used, which eliminates the labor-intensive operation of mechanical polishing. Bright nickel plating is achieved by introducing brightening agents into the electrolyte. However, the decorative qualities of mechanically polished surfaces are higher than those obtained by bright nickel plating.

Nickel deposition occurs with significant cathodic polarization, which depends on the temperature of the electrolyte, its concentration, composition and some other factors.

Electrolytes for nickel plating are relatively simple in composition. Currently, sulfate, hydrofluoride and sulfamite electrolytes are used. Lighting factories use exclusively sulfate electrolytes, which make it possible to work with high current densities and obtain high-quality coatings. The composition of these electrolytes includes salts containing nickel, buffer compounds, stabilizers and salts that promote the dissolution of the anodes.

The advantages of these electrolytes are the non-scarcity of components, high stability and low aggressiveness. Electrolytes allow a high concentration of nickel salt in their composition, which makes it possible to increase the cathode current density and, consequently, increase the productivity of the process.

Sulfate electrolytes have high electrical conductivity and good dissipation ability.

Wide Application received an electrolyte of the following composition, g/l:

NiSO4 7H2O 240–250

*Or NiCl2·6H2O – 45 g/l.

Nickel plating is carried out at a temperature of 60°C, pH=5.6÷6.2 and a cathodic current density of 3–4 A/dm2.

Depending on the composition of the bath and its operating mode, coatings with varying degrees of gloss can be obtained. For these purposes, several electrolytes have been developed, the compositions of which are given below, g/l:

for matte finish:

NiSO4 7H2O 180–200

Na2SO4 10H2O 80–100

Nickel plating at a temperature of 25–30°C, at a cathodic current density of 0.5–1.0 A/dm2 and pH=5.0÷5.5;

for a semi-gloss finish:

Nickel sulfate NiSO4 7H2O 200–300

Boric acid H3BO3 30

2,6–2,7-Disulfonaphthalic acid 5

Sodium fluoride NaF 5

Sodium chloride NaCl 7–10

Nickel plating is carried out at a temperature of 20–35°C, cathodic current density of 1–2 A/dm2 and pH=5.5÷5.8;

for a shiny finish:

Nickel sulfate (hydrate) 260–300

Nickel chloride (hydrate) 40–60

Boric acid 30–35

Saccharin 0.8–1.5

1,4-butynediol (100% equivalent) 0.12–0.15

Phthalimid 0.08–0.1

Operating temperature of nickel plating is 50–60°C, electrolyte pH 3.5–5, cathode current density with intensive stirring and continuous filtration 2–12 A/dm2, anodic current density 1–2 A/dm2.

A special feature of nickel plating is a narrow range of electrolyte acidity, current density and temperature.

To maintain the composition of the electrolyte within the required limits, buffer compounds are introduced into it, which most often use boric acid or a mixture boric acid with sodium fluoride. In some electrolytes, citric, tartaric, acetic acid or their alkaline salts are used as buffer compounds.

A special feature of nickel coatings is their porosity. In some cases, pinpoint spots, so-called “pitting,” may appear on the surface.

To prevent pitting, intensive air mixing of the baths and shaking of the pendants with parts attached to them are used. The reduction of pitting is facilitated by the introduction of surface tension reducers or wetting agents into the electrolyte, which are sodium lauryl sulfate, sodium alkyl sulfate and other sulfates.

The domestic industry produces a good anti-pitting detergent "Progress", which is added to the bath in an amount of 0.5 mg/l.

Nickel plating is very sensitive to foreign impurities that enter the solution from the surface of parts or due to anodic dissolution. When nickel plating steel parts

When coating copper-based alloys, the solution becomes clogged with iron impurities, and when coating copper-based alloys, it becomes clogged with its impurities. Removal of impurities is carried out by alkalizing the solution with nickel carbonate or hydroxide.

Organic contaminants that contribute to pitting are removed by boiling the solution. Sometimes tinting of nickel-plated parts is used. This produces colored surfaces with a metallic sheen.

Toning is carried out chemically or electrochemically. Its essence lies in the formation of a thin film on the surface of the nickel coating, in which light interference occurs. Such films are produced by applying organic coatings several micrometers thick to nickel-plated surfaces, for which the parts are treated in special solutions.

Black nickel coatings have good decorative qualities. These coatings are obtained in electrolytes, to which zinc sulfates are added in addition to nickel sulfates.

The composition of the electrolyte for black nickel plating is as follows, g/l:

Nickel sulfate 40–50

Zinc sulfate 20–30

Rhodane potassium 25–32

Ammonium sulfate 12–15

Nickel plating is carried out at a temperature of 18–35°C, cathodic current density of 0.1 A/dm2 and pH=5.0÷5.5.

2. CHROME PLATING

Chrome coatings have high hardness and wear resistance, a low coefficient of friction, are resistant to mercury, firmly adhere to the base metal, and are also chemical and heat resistant.

None of the home craftsmen has ever faced the need to nickel-plate or chrome-plate this or that part. What do-it-yourselfer hasn’t dreamed of installing a “non-working” bushing with a hard, wear-resistant surface obtained by saturating it with boron in a critical component. But how to do at home what is usually done at specialized enterprises using chemical-thermal and electrochemical processing of metals. You won’t build gas and vacuum furnaces at home, or construct electrolysis baths. But it turns out that there is no need to build all this at all. It is enough to have on hand some reagents, an enamel pan and, perhaps, a blowtorch, and also to know the recipes of “chemical technology”, with the help of which metals can also be copper-plated, cadmium-plated, tin-plated, oxidized, etc.

So, let's begin to get acquainted with the secrets of chemical technology. Please note that the content of components in the solutions given is usually given in g/l. If other units are used, a special disclaimer follows.

Preparatory operations

Before applying paints, protective and decorative films to metal surfaces, as well as before covering them with other metals, it is necessary to carry out preparatory operations, that is, remove contaminants of various natures from these surfaces. Please note that the quality of preparatory operations in strong degree The final result of all work depends.

Preparatory operations include degreasing, cleaning and pickling.

Degreasing

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

Using degreasing, oil and grease films are removed from the surface of parts. For this purpose, aqueous solutions of certain chemical reagents 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 at the same time they are toxic and flammable.

Aqueous solutions. Degreasing of metal parts in aqueous solutions is carried out in enamel containers. Pour in water, dissolve chemicals in it and place on low heat. When the desired temperature is reached, the parts are loaded into the solution. During processing, the solution is stirred. Below are the compositions of 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 minutes.

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

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

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

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

Soda ash - 20, potassium chromium - 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, treatment 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°C, processing time - 5...10 minutes.

Trisodium phosphate - 80...100. Solution temperature - 80...90°C, processing time - 30...40 minutes.

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°C, processing time - 3...5 minutes.

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

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°C, processing time - 5 minutes.

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

Organic solvents

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

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

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

Cleaning

In this section, the process of cleaning carbon deposits from internal combustion engines will be considered as an example. As is known, carbon deposits are asphalt-resinous substances that form difficult-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 - 3 hours.

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 bichromate - 5, laundry soap - 10, soda ash - 20. Solution temperature - 85...95 ° C, processing time - up to 3 hours.

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

Etching

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

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

Due to the fact that in recipes for pickling they use inorganic acids, you need to know their initial density (g/cm 3): Nitric acid - 1,4, sulfuric acid - 1,84; hydrochloric acid- 1.19; orthophosphoric acid - 1.7; acetic acid - 1.05.

Compositions of etching solutions

For ferrous metals

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

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

Hydrochloric acid - 200. Solution temperature - 30...35°C, processing time - 15...20 minutes.

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

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

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

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

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 allow them to be painted with any paint without 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 minutes.

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

After etching 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°C, processing time - 5...10 minutes.

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

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

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

For aluminum and its alloys

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

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

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

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 surfaces 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 specific case in certain units (g/l, percentage, parts)

Nitric acid - 2.-.4, hydrochloric acid 2...5, Phosphoric acid - 15...25, the rest is water. Solution temperature - 70...80°C, processing time - 1...10 minutes. Contents of components - in% (by volume).

Sulfuric acid - 0.1, acetic acid - 25, hydrogen peroxide (30%) - 13. Solution temperature - 18...25°C, treatment 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°C, processing 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°C, processing time - 2...3 minutes. Content of components - in g/l.

Nitric acid - 4...5, hydrochloric acid - 3...4, Phosphoric acid - 20..30, methyl orange - 1..1.5, the rest is water. Solution temperature - 18...25°C, processing time - 5...10 minutes. Contents of components - in% (by weight).

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

Solution temperature - 30...40°C, processing time - 15...30 minutes. Content of components (except for yellow blood salt) - in pl/l.

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

For copper

Nitric acid - 900, sodium chloride - 5, soot - 5. Solution temperature - 18...25°C, treatment time - 15...20 s. Component content - g/l.

Attention! Sodium chloride is introduced into 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, treatment time - 1...2 min. Component content - in ml.

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

For brass

Nitric acid - 20, hydrochloric acid - 0.01, acetic acid - 40, orthophosphoric acid - 40. Mixture temperature - 25...30 ° C, processing time - 20...60 s. Component content - in ml.

Copper sulfate ( copper sulfate) - 8, sodium chloride - 16, acetic acid - 3, water - the rest. Solution temperature - 20°C, processing time - 20...60 minutes. Component content - in% (by weight).

For bronze

Phosphoric acid - 77...79, potassium nitrate - 21...23. Mixture temperature - 18°C, processing time - 0.5-3 minutes. Component content - 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. Contents of components (except sodium chloride) - in ml.

For nickel and its alloys (nickel silver and nickel silver)

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

Nitric acid - 30, acetic acid (glacial) - 70. Mixture temperature - 70...80°C, processing time - 2...3 s. 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 minutes. Contents of components - in parts (by volume).

Phosphoric acid - 60, sulfuric acid - 200, nitric acid - 150, urea - 5g. Mixture temperature - 100°C, processing time - 20 s. Content of components (except urea) - in ml.

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

Passivation

Passivation is the process of chemically creating an inert layer on the surface of a metal that prevents the metal itself from oxidizing. Surface passivation process metal products used by minters when creating their works; craftsmen - in production various crafts(chandeliers, sconces and other household items); sports fishermen passivate their homemade metal baits.

Compositions of solutions for passivation (g/l)

For ferrous metals

Sodium nitrite - 40...100. Solution temperature - 30...40°C, processing time - 15...20 minutes.

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

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

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

For copper and its alloys

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

Potassium bichromate - 150. Solution temperature - 60°C, processing time - 2...5 minutes.

For aluminum and its alloys

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

Potassium dichromate - 200. Solution temperature - 20°C, “processing 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°C, 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 for car body treatments passenger cars before coating them with anti-corrosion and anti-wear compounds.

Compositions of solutions for phosphating (g/l)

For steel

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

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

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

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

Orthophosphoric acid - 60...80, chromic anhydride - 100...150. Solution temperature - 50...60°C, processing time - 20...30 minutes.

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

Metal coating

Chemical coating of some metals with others is captivating with its simplicity technological process. Indeed, if, for example, it is necessary to chemically nickel-plate any steel part, it is enough to have suitable enamel cookware, a heating source (gas stove, primus stove, etc.) and relatively scarce 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 can parts with complex profiles and internal cavities (pipes, etc.) be reliably nickel-plated. True, chemical nickel plating (and some other similar processes) is not without its drawbacks. The main one is that the adhesion of the nickel film to the base metal is not too strong. 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 with others.

Nickel plating

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

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

If the parts coated with nickel are hardened (springs, knives, fishhooks, etc.), then at a temperature of 40°C they can be tempered, 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 a holding time of up to 3 hours. In this case, heat treatment also increases the hardness of the nickel coating.

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

At home, using nickel plating (chemical, of course!) you can repair parts of various household devices. The technology here is extremely simple. For example, the axis of some device was demolished. Then a layer of nickel is built up (in excess) on the damaged area. Then the working area of ​​the axle is polished, bringing it to the desired size.

It should be noted that chemical nickel plating cannot be used to coat 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 process speed is higher. Another important feature of acidic solutions: they are less likely to self-discharge when the operating temperature is exceeded. (Self-discharge is the instantaneous precipitation of nickel into the solution with the latter splashing.)

Alkaline solutions have the main advantage of more reliable adhesion of the nickel film to the base metal.

And one last thing. 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 clean (designation on the label - C).

Before covering parts with any metal film, it is necessary to carry out special preparation of their surface.

The 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 pickled in one of the solutions listed below.

Compositions of solutions for pickling (g/l)

For steel

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

Hydrochloric acid - 20...45. Solution temperature - 20°C, processing time - 15...40 s.

Sulfuric acid - 50...80, hydrochloric acid - 20...30. Solution temperature - 20°C, 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, another treatment is carried out - the so-called zincate treatment. Below are solutions for zincate treatment.

For aluminum

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

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

When preparing both solutions, first dissolve caustic soda 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 (crystalline hydrate) - 10. Solution temperature - 20 C, processing time - 2 minutes.

For wrought aluminum alloys

Ferric chloride (crystalline hydrate) - 1, caustic soda - 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, suitable for all metals (although there are some specifics). They are prepared in a certain sequence. So, all chemical reagents (except for sodium hypophosphite) are dissolved in water (enamel dishes!). Then the solution is heated to operating temperature and only after that sodium hypophosphite is dissolved and the parts are hung in the solution.

In 1 liter of solution you can nickel-plate a surface with an area of ​​up to 2 dm2.

Compositions of solutions for nickel plating (g/l)

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

Nickel chloride - 25, sodium succinate - 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°C, 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 µm /h.

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

Nickel chloride - 30, ammonium chloride - 30, sodium succinate - 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 µm/ h.

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

Attention! According to existing GOSTs, a single-layer nickel coating per 1 cm2 has several dozen through pores (to the base metal). Naturally, on outdoors A steel part coated with nickel will quickly become covered with a “rash” of rust.

In a modern car, for example, the bumper is covered with a double layer (an underlayer of copper, and on top - chrome) and even a triple layer (copper - nickel - chrome). But this does not save the part from rust, since according to GOST and triple coating there are several pores per 1 cm2. What to do? The solution is to treat the surface of the coating special compounds, closing the pores.

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

After heat treatment, dip 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 LPS (easily penetrating lubricant).

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

Large surfaces (bumpers, car moldings) are treated with fish oil 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 fishing in the sea. The same hooks treated with fish oil do not corrode almost all summer season sea ​​fishing.

Chrome plating

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

Below are practice-tested recipes for chemical chrome 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 glycolic acid - 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 (replacement of sodium hypophosphite) - 50...75.
Solution temperature - 100°C, pH - 7.5...9, growth rate - 2...2.5 µm/h.

Boronickel plating

The film made from this dual alloy has increased hardness (especially after heat treatment), high temperature melting, high wear resistance and significant corrosion resistance. All this allows the use of such coating in various responsible homemade structures. Below are recipes for solutions in which boronickel plating 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. The solution temperature is 97°C, the growth rate is 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. The solution temperature is 97°C, the growth rate is 1.5 µm/h.

Caustic soda - 4...40, potassium metabisulfite - 1...1.5, sodium 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.

Borocobaltation

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 required increased wear resistance coverings.

Compositions of solutions for borocobaltation (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°C, pH - 12.5, growth rate - 3 µm/h.

Cobalt sulfate - 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 used outdoors.

It has been noted that chemically produced cadmium coatings adhere well to the base metal even without heat treatment.

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

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

Copper plating

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

Compositions of solutions for copper plating (g/l)

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

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

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

Copper sulfate - 8...50, sulfuric acid - 8...50. The solution temperature is 20°C, the growth rate is 8 µm/h.

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

Copper sulfate - 80...100, caustic soda - 80...,100, sodium carbonate - 25...30, nickel chloride - 2...4, Rochelle salt - 150...180, formalin (40% - nal solution) - 30...35. The solution temperature is 20°C, the growth rate is 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 iron sulfide (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 films of copper.

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

Silvering

Silvering metal surfaces, perhaps the most popular process among craftsmen, which they use in their activities. Dozens of examples can be given. For example, restoring the silver layer on cupronickel silver cutlery, silvering samovars and other household items.

For coiners, silvering, together with chemical coloring of metal surfaces (which will be discussed below), is a way to increase the artistic value of embossed paintings. Imagine a minted ancient warrior, whose chain mail and helmet are silvered.

The chemical silvering process itself 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 embossed paintings).

Composition of solutions for silver plating (g/l)

Silver chloride - 7.5, potassium iron sulfide - 120, potassium carbonate - 80. Working solution temperature - about 100°C. Processing time - until received required thickness layer of silver.

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

Silver chloride - 20, potassium ferric sulfide - 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 until the thickness of sour cream. 10...15 g of paste is dissolved in 1 liter of boiling water. Processing - in a boiling solution.

The parts are hung in silvering solutions on zinc wires (strips).

Processing time is determined visually. It should be noted here that brass is better silvered than copper. A fairly thick layer of silver must be applied to the latter so that the dark copper does not show through the coating layer.

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

Compositions of pastes for silvering.

In 300 ml warm water dissolve 2 g of lapis pencil (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% solution of sodium chloride is gradually added to the resulting solution until the precipitation stops. Curdled sediment silver chloride is filtered and washed thoroughly in 5...6 waters.

20 g of sodium thiosulfite are dissolved in 100 ml of water. Silver chloride is added to the resulting solution until it stops dissolving. The solution is filtered and tooth powder is added to it until it reaches the consistency of liquid sour cream. Rub (silver) the part with this paste using a cotton swab.

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

Silver chloride - 3, sodium chloride - 3, sodium carbonate - 6, chalk - 2. 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 ground components are mixed. Using a wet swab, powdering it with a dry mixture of chemicals, rub (silver) the desired part. The mixture is added all the time, constantly moistening the tampon.

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, processing time - 3...5 s.

Caustic soda - 120, zinc sulfate - 40. Solution temperature - 20°C, processing time - 1.5...2.0 minutes. To obtain a solution, first dissolve sodium hydroxide in one half of the water and zinc sulfate 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 minutes.

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

Tinning compounds (g/l)

For steel

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

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

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

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

For copper and its alloys

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

Tin chloride - 20, sodium lactic acid - 200. Solution temperature - 20°C, growth rate - 10 µm/h.

Tin chloride - 8, thiourea - 40...45, sulfuric acid - 30...40. The solution temperature is 20°C, the growth rate is 15 µm/h.

Tin 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.

Tin 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 hangers. Small parts are “powdered” with zinc filings.

For aluminum and its alloys

Tinning of aluminum and its alloys is preceded by some additional processes. First, parts degreased with acetone or gasoline B-70 are treated for 5 minutes at a temperature of 70 ° C with the following composition (g/l): sodium carbonate - 56, sodium phosphate - 56. Then the parts are immersed for 30 s in a 50% solution of nitric acid. acid, rinse thoroughly under running water and immediately place in one of the solutions (for tinning) given 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, caustic soda - 1.5..L.7, ammonium oxalate - 10...20. Solution temperature - 20...40°C, growth rate - 5 µm/h.

Removing metal coatings

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

All of the solutions below 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 sulfate (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.

To remove 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. The solution temperature is 20...80°C.

To remove nickel from aluminum and its alloys, commercial nitric acid is used. Acid temperature - 50°C.

To remove 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 (with zincate treatment)

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

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

To remove silver from steel

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

Technical nitric acid. Temperature - 20°C.

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

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

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

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

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

Chemical oxidation and coloring of metals

Chemical oxidation and painting 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 (blackening silver, painting gold, etc.), burnishing steel objects (heating a steel part to 220...325°C, they lubricated it with hemp oil).

Compositions of solutions for oxidizing and painting steel (g/l)

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

Black color

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

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

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

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

After oxidizing (blackening) the steel parts, they are treated for 15 minutes in a solution of potassium chromium (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 hydrosulfide - 120, lead acetate - 30. Solution temperature - 90...100°C, processing time - 20...30 minutes.

Blue color

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

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, treatment time - 2 hours.

Caustic soda - 550, sodium nitrate - 150...200. Solution temperature - 135...140°C, processing time - 15...40 minutes.

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

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

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

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

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

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

In addition to copper, a solution of sulfur liver can blacken silver well and satisfactorily blacken steel.

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 sulfate - 20, copper sulfate - 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 minutes.

Blue

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

Compositions for oxidizing and painting 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°C, processing time - up to 30 minutes.

Brown color

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

Copper sulfate - 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 sulfate - 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, treatment time - 7 minutes.

3green color

Nickel ammonium sulfate - 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, treatment time - up to 60 minutes.

Compositions for oxidizing and painting bronze (g/l)

Green color

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

Copper nitrate - 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. Solution temperature - 18...25°C.

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

Compositions for oxidizing and coloring silver (g/l)

Black color

Sulfur liver - 20...80. Solution temperature - 60..70°C. Here and below, the color intensity is determined visually.

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

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

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

Brown color

Ammonium sulfate solution - 20 g/l. The solution temperature is 60...80°C.

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

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

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

Blue

Liver sulfur - 1.5, ammonium carbonate - 10. Solution temperature - 60°C.

Liver sulfur - 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 solution temperature is 20°C.

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

Composition for oxidizing and painting 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°C, processing time - 2...10 minutes.

Grey colour

Arsenic trioxide - 70...75, sodium carbonate - 70...75. The solution temperature is boiling, the processing time is 1...2 minutes.

Green color

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

Orange color

Chromic anhydride - 3...5, sodium fluorosilicate - 3...5. Solution temperature - 20...40°C, processing time - 8...10 minutes.

Yellow-brown color

Sodium carbonate - 40...50, sodium chloride - 10...15, caustic soda - 2...2.5. Solution temperature - 80...100°C, processing time - 3...20 minutes.

Protective compounds

Often a craftsman needs to process (paint, coat 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 coated is painted over with a protective composition that prevents the formation of one or another film.

The most affordable, but not heat-resistant protective coatings- 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). This composition is prepared as follows. The wax is melted in a water bath and warm turpentine is added to it. To protective composition would be contrasting (its presence could be clearly seen and controlled), a small amount of dark-colored paint soluble in alcohol is introduced into the composition. If this is not available, it is not difficult to add a small amount of dark shoe cream to the composition.

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

Waxy protective compounds are applied hot with a brush or swab. All of them are designed for operating temperatures no higher than 70°C.
Protective compounds based on asphalt, bitumen and pitch varnishes have somewhat better heat resistance (operating temperature up to 85°C). They are usually liquefied 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 can 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 glue 88N (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) B-70 gasoline and 1 part ethyl acetate (or butyl acetate). The operating 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°C.

Nickel-plated coatings have a number of valuable properties: they are well polished, acquiring a beautiful long-lasting mirror shine, they are durable and protect the metal well from corrosion.

The color of nickel coatings is silver-white with a yellowish tint; They are easily polished, but become dull over time. The coatings are characterized by a fine-crystalline structure, good adhesion to steel and copper substrates, and the ability to passivate in air.

Nickel plating is widely used as a decorative coating for parts of lamps intended for lighting public and residential premises.

To coat steel products, nickel plating is often carried out over an intermediate sublayer of copper. Sometimes a three-layer nickel-copper-nickel coating is used. In some cases, a thin layer of chromium is applied to the nickel layer to form a nickel-chrome coating. Nickel is applied to parts made of copper and copper-based alloys without an intermediate sublayer. The total thickness of two and three-layer coatings is regulated by mechanical engineering standards; it is usually 25–30 microns.

On parts intended to operate in humid tropical climates, the coating thickness must be at least 45 microns. In this case, the regulated thickness of the nickel layer is no less than 12–25 microns.

To obtain a shiny finish, nickel-plated parts are polished. Recently, bright nickel plating has been widely used, which eliminates the labor-intensive operation of mechanical polishing. Bright nickel plating is achieved by introducing brightening agents into the electrolyte. However, the decorative qualities of mechanically polished surfaces are higher than those obtained by bright nickel plating.

Nickel deposition occurs with significant cathodic polarization, which depends on the temperature of the electrolyte, its concentration, composition and some other factors.

Electrolytes for nickel plating are relatively simple in composition. Currently, sulfate, hydrofluoride and sulfamite electrolytes are used. Lighting factories use exclusively sulfate electrolytes, which make it possible to work with high current densities and obtain high-quality coatings. The composition of these electrolytes includes salts containing nickel, buffer compounds, stabilizers and salts that promote the dissolution of the anodes.

The advantages of these electrolytes are the non-scarcity of components, high stability and low aggressiveness. Electrolytes allow a high concentration of nickel salt in their composition, which makes it possible to increase the cathode current density and, consequently, increase the productivity of the process.

Sulfate electrolytes have high electrical conductivity and good dissipation ability.

The following electrolyte composition, g/l, is widely used:

NiSO4 7H2O240–250

*Or NiCl2·6H2O – 45 g/l.

Nickel plating is carried out at a temperature of 60°C, pH=5.6÷6.2 and a cathodic current density of 3–4 A/dm2.

Depending on the composition of the bath and its operating mode, coatings with varying degrees of gloss can be obtained. For these purposes, several electrolytes have been developed, the compositions of which are given below, g/l:

for matte finish:

NiSO4 7H2O180–200

Na2SO4 10H2O80–100

Nickel plating at a temperature of 25–30°C, at a cathodic current density of 0.5–1.0 A/dm2 and pH=5.0÷5.5;

for a semi-gloss finish:

Nickel sulfate NiSO4 7H2O200–300

Boric acid H3BO330

2,6–2,7-Disulfonaphthalic acid5

Sodium fluoride NaF5

Sodium chloride NaCl7–10

Nickel plating is carried out at a temperature of 20–35°C, cathodic current density of 1–2 A/dm2 and pH=5.5÷5.8;

for a shiny finish:

Nickel sulfate (hydrate) 260–300

Nickel chloride (hydrate) 40–60

Boric acid30–35

Saccharin0.8–1.5

1,4-butynediol (100% equivalent) 0.12–0.15

Phthalimide0.08–0.1

Operating temperature of nickel plating is 50–60°C, electrolyte pH 3.5–5, cathode current density with intensive stirring and continuous filtration 2–12 A/dm2, anodic current density 1–2 A/dm2.

A special feature of nickel plating is a narrow range of electrolyte acidity, current density and temperature.

To maintain the composition of the electrolyte within the required limits, buffer compounds are introduced into it, which most often use boric acid or a mixture of boric acid and sodium fluoride. Some electrolytes use citric, tartaric, acetic acid or their alkaline salts as buffer compounds.

A special feature of nickel coatings is their porosity. In some cases, pinpoint spots, so-called “pitting,” may appear on the surface.

To prevent pitting, intensive air mixing of the baths and shaking of the pendants with parts attached to them are used. The reduction of pitting is facilitated by the introduction of surface tension reducers or wetting agents into the electrolyte, which are sodium lauryl sulfate, sodium alkyl sulfate and other sulfates.

The domestic industry produces a good anti-pitting detergent "Progress", which is added to the bath in an amount of 0.5 mg/l.

Nickel plating is very sensitive to foreign impurities that enter the solution from the surface of parts or due to anodic dissolution. When nickel plating steel parts

When coating copper-based alloys, the solution becomes clogged with iron impurities, and when coating copper-based alloys, it becomes clogged with its impurities. Removal of impurities is carried out by alkalizing the solution with nickel carbonate or hydroxide.

Organic contaminants that contribute to pitting are removed by boiling the solution. Sometimes tinting of nickel-plated parts is used. This produces colored surfaces with a metallic sheen.

Toning is carried out chemically or electrochemically. Its essence lies in the formation of a thin film on the surface of the nickel coating, in which light interference occurs. Such films are produced by applying organic coatings several micrometers thick to nickel-plated surfaces, for which the parts are treated in special solutions.

Black nickel coatings have good decorative qualities. These coatings are obtained in electrolytes, to which zinc sulfates are added in addition to nickel sulfates.

The composition of the electrolyte for black nickel plating is as follows, g/l:

Nickel sulfate40–50

Zinc sulfate20–30

Rhodane potassium25–32

Ammonium sulfate12–15

Nickel plating is carried out at a temperature of 18–35°C, cathodic current density of 0.1 A/dm2 and pH=5.0÷5.5.

2. CHROME PLATING

Chrome coatings have high hardness and wear resistance, a low coefficient of friction, are resistant to mercury, firmly adhere to the base metal, and are also chemical and heat resistant.

In the manufacture of lamps, chrome plating is used to obtain a protective decorative coatings, and also as reflective coatings in the manufacture of mirror reflectors.

Chrome plating is carried out over a previously applied copper-nickel or nickel-copper-nickel sublayer. The thickness of the chromium layer with such a coating usually does not exceed 1 micron. In the manufacture of reflectors, chrome plating is currently being replaced by other coating methods, but in some factories it is still used for the manufacture of reflectors for mirror lamps.

Chrome has good adhesion to nickel, copper, brass and other deposited materials, but poor adhesion is always observed when depositing other metals onto a chrome coating.

Positive attribute The advantage of chromium coatings is that the parts become shiny directly in galvanic baths; this does not require mechanical polishing. Along with this, chrome plating differs from other galvanic processes in that it has more stringent requirements for the operating conditions of the baths. Minor deviations from the required current density, electrolyte temperature and other parameters inevitably lead to deterioration of coatings and massive defects.

The dissipation ability of chromium electrolytes is low, which leads to poor coverage internal surfaces and recesses of parts. To increase the uniformity of coatings, special suspensions and additional screens are used.

For chrome plating, solutions of chromic anhydride with the addition of sulfuric acid are used.

Three types of electrolytes have found industrial application: diluted, universal and concentrated (Table 1). To obtain decorative coatings and to obtain reflectors, concentrated electrolyte is used. When chrome plating, insoluble lead anodes are used.

Table 1 - Compositions of electrolytes for chrome plating

During operation, the concentration of chromic anhydride in the baths decreases, therefore, to restore the baths, daily adjustments are made by adding fresh chromic anhydride to them.

Several formulations of self-regulating electrolytes have been developed, in which the concentration ratio is automatically maintained

The composition of this electrolyte is as follows, g/l:

Chromium plating is carried out at a cathodic current density of 50–80 A/dm2 and a temperature of 60–70°C.

Depending on the relationship between temperature and current density, different types of chrome coating can be obtained: milky shiny and matte.

PLAN 1. NICKEL PLATING 2. CHROME PLATING 6 LIST OF SOURCES USED 1. NICKEL PLATING Nickel plating has a number of valuable properties: they are well polished, acquiring a beautiful long-lasting mirror shine, are durable and protect the metal well from corrosion. The color of nickel coatings is silver-white with a yellowish tint; they are easily polished, but become dull over time. The coatings are characterized by a fine-crystalline structure, good adhesion to steel and copper bases, and the ability to passivate in air.

Nickel plating is widely used as a decorative coating for parts of lamps intended for lighting public and residential premises. To coat steel products, nickel plating is often carried out over an intermediate sublayer of copper. Sometimes a three-layer nickel-copper-nickel coating is used. In some cases, a thin layer of chromium is applied to the nickel layer to form a nickel-chrome coating. Nickel is applied to parts made of copper and copper-based alloys without an intermediate sublayer.

The total thickness of two and three-layer coatings is regulated by mechanical engineering standards; it is usually 25–30 microns. On parts intended to operate in humid tropical climates, the coating thickness must be at least 45 microns. In this case, the regulated thickness of the nickel layer is no less than 12–25 microns. To obtain a shiny finish, nickel-plated parts are polished.

Recently, bright nickel plating has been widely used, which eliminates the labor-intensive operation of mechanical polishing. Bright nickel plating is achieved by introducing brightening agents into the electrolyte. However, the decorative qualities of mechanically polished surfaces are higher than those obtained by bright nickel plating. Nickel deposition occurs with significant cathodic polarization, which depends on the temperature of the electrolyte, its concentration, composition and some other factors.

Electrolytes for nickel plating are relatively simple in composition. Currently, sulfate, hydrofluoride and sulfamite electrolytes are used. Lighting factories use exclusively sulfate electrolytes, which make it possible to work with high current densities and obtain high-quality coatings. The composition of these electrolytes includes salts containing nickel, buffer compounds, stabilizers and salts that promote the dissolution of the anodes.

The advantages of these electrolytes are the non-scarcity of components, high stability and low aggressiveness. Electrolytes allow a high concentration of nickel salt in their composition, which makes it possible to increase the cathode current density and, consequently, increase the productivity of the process. Sulfate electrolytes have high electrical conductivity and good dissipation ability. The following electrolyte composition, g/l, is widely used: NiSO4 7H2O 240–250 NaCl* 22.5 H3BO3 30 *Or NiCl2 6H2O – 45 g/l. Nickel plating is carried out at a temperature of 60°C, pH=5.6÷6.2 and a cathodic current density of 3–4 A/dm2. Depending on the composition of the bath and its operating mode, coatings with varying degrees of gloss can be obtained.

For these purposes, several electrolytes have been developed, the compositions of which are given below, g/l: for a matte coating: NiSO4 7H2O 180–200 Na2SO4 10H2O 80–100 H3BO3 30–35 NaCl 5–7 Nickel plating at a temperature of 25–30°C, at cathode density current 0.5–1.0 A/dm2 and pH=5.0÷5.5; for a semi-shiny coating: Nickel sulfate NiSO4 7H2O 200–300 Boric acid H3BO3 30 2,6–2,7-Disulfonaphthalic acid 5 Sodium fluoride NaF 5 Sodium chloride NaCl 7–10 Nickel plating is carried out at a temperature of 20–35°C, cathodic current density 1 –2 A/dm2 and pH=5.5÷5.8; for a shiny coating: Nickel sulfate (hydrate) 260–300 Nickel chloride (hydrate) 40–60 Boric acid 30–35 Saccharin 0.8–1.5 1,4-butynediol (100% equivalent) 0.12–0 .15 Phthalimide 0.08–0.1 Operating temperature of nickel plating 50–60°C, electrolyte pH 3.5–5, cathode current density with intensive stirring and continuous filtration 2–12 A/dm2, anodic current density 1–2 A /dm2. A special feature of nickel plating is a narrow range of electrolyte acidity, current density and temperature. To maintain the composition of the electrolyte within the required limits, buffer compounds are introduced into it, which most often use boric acid or a mixture of boric acid and sodium fluoride.

Some electrolytes use citric, tartaric, acetic acid or their alkaline salts as buffer compounds. A special feature of nickel coatings is their porosity.

In some cases, pinpoint spots, so-called “pitting,” may appear on the surface. To prevent pitting, intensive air mixing of the baths and shaking of the pendants with parts attached to them are used.

The reduction of pitting is facilitated by the introduction of surface tension reducers or wetting agents into the electrolyte, which are sodium lauryl sulfate, sodium alkyl sulfate and other sulfates.

The domestic industry produces a good anti-pitting detergent "Progress", which is added to the bath in an amount of 0.5 mg/l. Nickel plating is very sensitive to foreign impurities that enter the solution from the surface of parts or due to anodic dissolution.

When nickel-plating steel parts, the solution becomes clogged with iron impurities, and when coating copper-based alloys, it becomes clogged with its impurities. Removal of impurities is carried out by alkalizing the solution with nickel carbonate or hydroxide. Organic contaminants that contribute to pitting are removed by boiling the solution.

Sometimes tinting of nickel-plated parts is used. This produces colored surfaces with a metallic sheen. Toning is carried out chemically or electrochemically. Its essence lies in the formation of a thin film on the surface of the nickel coating, in which light interference occurs. Such films are produced by applying organic coatings several micrometers thick to nickel-plated surfaces, for which the parts are treated in special solutions.

Black nickel coatings have good decorative qualities. These coatings are obtained in electrolytes, to which zinc sulfates are added in addition to nickel sulfates. The composition of the electrolyte for black nickel plating is as follows, g/l: Nickel sulfate 40–50 Zinc sulfate 20–30 Potassium rhodium oxide 25–32 Ammonium sulfate 12–15 Nickel plating is carried out at a temperature of 18–35°C, cathode current density 0.1 A/dm2 and pH=5.0÷5.5. 2. CHROME PLATING Chrome coatings have high hardness and wear resistance, a low coefficient of friction, are resistant to mercury, firmly adhere to the base metal, and are also chemical and heat resistant.

In the manufacture of lamps, chrome plating is used to obtain protective and decorative coatings, and also as reflective coatings in the manufacture of mirror reflectors. Chrome plating is carried out over a previously applied copper-nickel or nickel-copper-nickel sublayer. The thickness of the chromium layer with such a coating usually does not exceed 1 micron. In the manufacture of reflectors, chrome plating is currently being replaced by other coating methods, but in some factories it is still used for the manufacture of reflectors for mirror lamps.

Chrome has good adhesion to nickel, copper, brass and other deposited materials, but poor adhesion is always observed when depositing other metals onto a chrome coating. A positive property of chromium coatings is that parts become shiny directly in galvanic baths; this does not require mechanical polishing.

Along with this, chrome plating differs from other galvanic processes in that it has more stringent requirements for the operating conditions of the baths. Minor deviations from the required current density, electrolyte temperature and other parameters inevitably lead to deterioration of coatings and massive defects. The dissipative ability of chromium electrolytes is low, which leads to poor coverage of internal surfaces and recesses of parts.

To increase the uniformity of coatings, special suspensions and additional screens are used. For chrome plating, solutions of chromic anhydride with the addition of sulfuric acid are used. Three types of electrolytes have found industrial application: diluted, universal and concentrated (Table 1). To obtain decorative coatings and to obtain reflectors, concentrated electrolyte is used. When chrome plating, insoluble lead anodes are used. Table 1 – Compositions of electrolytes for chrome plating components electrolyte compositions, g/l diluted universal concentrated chromic anhydride sulfuric acid cathodic current density, A/dm2 solution temperature, °C 150 1.5 45–100 55–60 250 2.5 15–60 45–55 350 3.5 10–30 35–45 During operation, the concentration of chromic anhydride in the baths decreases, therefore, to restore the baths, daily adjustments are made by adding fresh chromic anhydride to them. Several formulations of self-regulating electrolytes have been developed in which the concentration ratio is automatically maintained. The composition of such an electrolyte is as follows, g/l: Cr2O3 250 SrSO4 5-6 K2SiF6 20 Chromium plating is carried out at a cathodic current density of 50–80 A/dm2 and a temperature of 60–70°C. Depending on the relationship between temperature and current density, different types of chrome coating can be obtained: milky shiny and matte. Milky coating is obtained at a temperature of 65–80°C and low current density. A shiny coating is obtained at a temperature of 45–60°C and medium current density. A matte finish is obtained at a temperature of 25–45°C and high density current In the production of lamps, shiny chrome coating is most often used.

To obtain mirror reflectors, chrome plating is carried out at a temperature of 50–55°C and a current density of 60 A/dm2. in the manufacture of mirror reflectors, copper and nickel are pre-deposited.

The reflective surface is polished after applying each layer.

The technological process includes the following operations: grinding and polishing the surface; copper plating; polishing, degreasing, pickling; nickel plating; polishing, degreasing, pickling; chrome plating; clean polishing.

After each technological operation carry out 100% quality control of the coating, since failure to comply with technology requirements leads to peeling of the sublayer along with the chrome coating. Products made of copper and copper alloys are chrome plated without an intermediate layer.

The parts are immersed in the electrolyte after voltage is applied to the bath. When applying multilayer coatings to steel products, the layer thickness is regulated by GOST 3002-70. Thickness values ​​are given in Table 2. Table 2 – Minimum thickness multilayer galvanic coatings working conditions symbol coating groups coating thickness, µm minimum average-calculated nickel without sublayer multilayer copper-nickel or nickel-copper-nickel chrome total top layer of nickel light medium hard L SZh 10 30 – 10 30 45 5 10 15 0.5 0.5 0.5 Chrome plating baths are equipped with a powerful exhaust ventilation to remove toxic chromic acid vapors.

When chrome plating, part of the hexavalent chromium Cr6+ ends up in wastewater, therefore, to prevent emissions of Cr6+ into open water bodies, protective measures are used - neutralizers and treatment facilities are installed.

2. 3. "Technology and equipment for the production of electric light sources... etc. 6.

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