RU2088700C1 - Electrolyte for preliminary iron plating - Google Patents

Abstract

FIELD: galvanic coatings. SUBSTANCE: invention relates to using galvanic procedure for applying iron coatings onto objects of casting zinc alloys and may find use in radio electronic and automotive industries. Electrolyte contains, g/l: ferrous sulfate, 4-7; ammonium oxalate, 40-60; boric acid, 10- 30; and acetylsalicylic acid, 0.1-0.2. Deposition is effected at cathode current density 1-10 A/sq.dm, temperature 50-70 C, and pH 6- 7.8. When using such electrolyte, application of coatings leads to increased bonding strength of iron coating with zinc or zinc alloy substrate, formation of plastic iron deposits, and, in addition, to possibility of using a wide range of cathode current density. EFFECT: improved strength of coatings. 2 tbl

Description

 The invention relates to the field of deposition of metal coatings, in particular iron, in a galvanic manner on products from foundry zinc alloys of the TsAM type and can be used in the radio-electronic industry, automotive industry, etc.

Known sulfate electrolyte iron [1] containing, g / l:
Iron (II) sulfate 400 450
Aluminum sulfate 100 120
Hydrochloric acid 1 1.5
pH 1.4 1.6
Temperature, ^o C 18 40
Cathode current density, A / dm ² 5 20
The disadvantage of the analogue is the low adhesion strength of the iron precipitate with alloys of the TsAM type, which does not comply with GOST 9.302-88.

Closest to the proposed is a sulfate electrolyte for pre-ironing [2] containing, g / l:
Iron (II) sulfate 150
Chloride Iron 75
Ammonium sulfate 120
Ammonium oxalate 8
Water up to 1 liter
Temperature, ^o C 18 25
Cathode current density, A / dm ² 1
The disadvantages of the prototype are: low adhesion strength of the iron precipitate with zinc alloys of the TsAM type, which does not comply with GOST 9.302-88; narrow range of cathodic current density; the impossibility of ironing at high temperatures, since brittle deposits with high internal stresses are obtained from a burning sulfate electrolyte; In addition, the electrolyte is expensive.

 The purpose of the invention is to increase the adhesion strength of iron coatings with zinc alloys of the CAM type, the possibility of using a wide range of cathodic current density, conducting electrolysis from hot electrolytes, allowing plastic iron deposits to be obtained, reducing the concentration of electrolyte components and, therefore, its cost.

The goal is achieved by creating an electrolyte for preliminary ironing of zinc alloys, including iron (II) sulfate, ammonium oxalate and water, which additionally contains boric and acetylsalicylic acid in the following ratio of components, g / l:
Iron (II) sulfate 4 7
Ammonium oxalate 40 60
Boric acid 10 30
Acetylsalicylic acid 0.1 0.2
Water up to 1 liter
pH 6 7.8
Temperature, ^o C 50 70
Cathode current density, A / dm ² 1 10
Comparative analysis with the prototype allows us to conclude that the claimed electrolyte differs from it by the introduction of new components, namely boric and acetylsalicylic acids.

Iron (II) sulfate, 7-water, GOST 4148-78, h, chemical formula FeSO ₄ • 7H ₂ O, density 1.898 g / cm ³ , melting point 64 ^o C, solubility 33 g in 100 g of cold and 149 g in 100 g of hot water.

Ammonium oxalate, 1-aqueous, ammonium oxalate, GOST 5712-78, analytical grade, chemical formula (NH ₄ ) ₂ C ₂ O ₄ • H ₂ O, density 1.50 g / cm ³ , melting point decomposes, solubility 2.6 g in 100 g of cold water and 11.8 g in 100 g of hot water.

Boric acid (ortho), GOST 9656-75, h, chemical formula H ₃ BO ₃ , density 1.435 g / cm ³ , melting point 185 ^o C decomposes, solubility 2.7 g in 100 g of cold water and 39 g in 100 g hot water.

Acetylsalicylic acid, aspirin, o-acetooxybenzoic acid, chemical formula CH ₃ COOC ₆ H ₄ COOH, melting point 133 135 ^o C, solubility in water 0.25 g per 100 ml.

Example 1. To prepare 1 l of an electrolyte, 50 g of oxalic ammonium ammonium was dissolved in water at a temperature of 60 ^o C. 6 g of iron (II) sulfate was added to the solution with thorough stirring. Boric acid in an amount of 20 g was dissolved in 200 g of water at 60 ^° C. and introduced into the solution with stirring. Acetylsalicylic acid in an amount of 0.15 g was dissolved in 100 g of water at 60 ^o C, then introduced with stirring into a solution of iron (II) sulfate and ammonium oxalate. Then, the volume of the resulting solution was adjusted to 1 L with water and cooled to room temperature. The desired pH value of 7 was set using sulfuric acid or 25% ammonia solution. The prepared electrolyte has the following composition, g / l:
Iron (II) sulfate 6
Ammonium oxalate 50
Boric acid 20
Acetylsalicylic acid 0.15
pH 7
Temperature, ^o C 60
Cathode current density, A / dm ² 1-10
Examples with other values of the inventive electrolyte are given in table 1.

After the preparation of electrolytes, the surface of the samples of the ZAM zinc alloy was electrochemically degreased in a solution [2] containing, g / l:
Sodium hydroxide 10
Sodium carbonate 10
Sodium phosphate 5
Sodium silicate 27
Sulfonol NP-3 0.2
Temperature, ^o C 65
Cathode current density, A / dm ² 1.5
Duration, min 0.5
Then, the samples were chemically activated in technical sulfuric acid at 50 g / l at room temperature for 10 s and iron coatings were deposited in the prepared electrolyte. The resulting iron coatings were tested for adhesion to zinc alloy. When determining the range of the working current density, the upper and lower boundaries of the cathodic current density were established. For their determination, ZAM alloy samples were coated with an iron coating up to 6 μm thick, and then chromium up to 12 μm. The resulting coatings in appearance correspond to the requirements of GOST 9.301-86, and for adhesion to the base metal, GOST 9.302-88.

Quantitative tests of the adhesion strength of coatings to a base made of a ZAM zinc alloy were carried out by the separation method using a tensile testing machine 2063 P-0.05. The amount of adhesion was expressed in kJ / m ² . In all tests of the characteristics of the obtained iron coating, at least 4–5 parallel experiments were carried out and the arithmetic mean of the values was taken. The test results are presented in table. 2.

 From the table. 2 shows that the proposed electrolyte (examples 1 to 3) allows to obtain iron coatings having an adhesion strength on average 50 times greater than that of the prototype, and in addition has a wider range of working current density, operates at elevated temperatures, which allows to obtain plastic iron deposits, as well as in the electrolyte, the concentrations of the main components are reduced, so it has a lower cost.

 Another advantage of the inventive electrolyte is that the electrolyte has a higher buffer capacity, which requires less frequent pH adjustment during operation.

Claims (1)

The electrolyte for pre-ironing, containing iron (II) sulfate and ammonium oxalate, characterized in that it additionally contains boric and acetylsalicylic acid in the following ratio of components, g / l:
Iron (II) sulfate 4 7
Ammonium oxalate 40 60
Boric acid 10 30
Acetylsalicylic acid 0.1 0.20

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