RU2792669C1 - Method for chemical nickel plating of the surface of a metal-matrix composite material aluminum-silicon carbide - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: chemical metallization of the surface of metal-matrix composite materials. Method includes etching, washing, nickel chemical precipitation, washing and drying. When etching, the first etching is carried out in an aqueous solution of alkali containing 50 g/l of caustic soda, for 2-60 s at a temperature of 60-70°C and a second etching in a solution containing 800 ml/l nitric acid and 200 ml/l hydrofluoric acid for 5-60 s at a temperature of 18-25°C. In this case, after the first etching, washing is carried out in hot water for 10-15 minutes and in cold water for 15-30 seconds, and after the second etching, washing is carried out only in cold water for 15-30 seconds. Nickel chemical precipitation is carried out in an acidic solution with a pH value of 4.2-4.4.

EFFECT: continuous and uniform nickel coating with adhesion to the combined surface of MMCM AlSiC.

2 cl, 4 dwg, 1 ex

Description

The invention relates to the field of chemical metallization of the surface of metal-matrix composite materials, in particular aluminum-silicon carbide metal-matrix composite material (hereinafter MMCM AlSiC), and can be used to obtain functional coatings in the electronics industry, instrument making, aviation industry. The surface of MMCM AlSiC is a combination of alternating surfaces of aluminum and silicon carbide. When applying metal coatings to combined surfaces, there are difficulties associated with the preparation of the surface of the material before chemical plating.

A method is known for preparing a combined metal-dielectric surface for chemical metallization, which consists in carrying out etching, sensitization and activation operations, in which, after the etching operation, the surface is additionally treated in a solution containing sodium hydroxide, monoethanolamine, triethanolamine, surface activation is carried out in a solution containing PdCl2, HCl and glycine. [RU 2041575, 03/10/1992].

The disadvantages of the method are:

- a large number of technological operations of surface pretreatment, such as sensitization and activation.

- an expensive palladium salt is used in the activation solution, which leads to a significant increase in the cost of the surface preparation process.

- as a sensitizing solution, a system based on tin salts is used, which is highly unstable during operation, as a result of which the solution must be changed frequently.

A known method of chemical metallization of combined cermet materials, including surface treatment of parts in a sorption stabilization solution, sensitization, and activation in a solution containing palladium chloride and hydrochloric acid. [RU 2350687, 03/27/2009].

The disadvantages of the method are:

- a large number of technological operations of surface pretreatment, such as sensitization and activation.

- an expensive palladium salt is used in the activation solution, which leads to a significant increase in the cost of the surface preparation process.

- as a sensitizing solution, a system based on tin salts is used, which is highly unstable during operation, as a result of which the solution must be changed frequently.

A known method of preparing the surface of parts made of ferrites, ceramics and ferritoceramics for the application of metal coatings, including degreasing, washing in hot running water, washing in cold water, chemical etching, washing in cold running water, sensitization, washing in cold running water, washing in cold distilled water, activation in a solution of palladium chloride and hydrochloric acid at a temperature of 12-15°C.

[RU 2219284, 20.12.2003].

The disadvantages of the method are:

- a large number of technological operations of surface pretreatment, such as sensitization and activation.

- an expensive palladium salt is used in the activation solution, which leads to a significant increase in the cost of the surface preparation process.

- as a sensitizing solution, a system based on tin salts is used, which is highly unstable during operation, as a result of which the solution must be changed frequently.

The closest analogue of the proposed method is a method of chemical nickel plating of the surface of the aluminum-silicon carbide metal-matrix composite material, including degreasing, first washing, etching is carried out in an aqueous solution containing 20-35 wt. % hydrofluoric acid and 10-35 g/l ammonium fluoride, for 15-30 s at a solution temperature of 10 to 40°C, second washing, nickel chemical precipitation, third washing and drying. [RU 2544319, 12/17/2013].

The disadvantages of the method are:

- the need to pre-degrease the surface,

- the etching solution contains ammonium fluoride, which is very toxic.

The technical result of the invention is to ensure the continuity and uniformity of the Nickel coating, its adhesion with the combined surface of MMCM AlSiC, as well as to simplify the process by eliminating the stages of sensitization and activation.

The technical result is achieved by the fact that the method of chemical nickel plating of the surface of the aluminum-silicon carbide metal-matrix composite material includes pickling, washing, chemical nickel deposition, washing and drying. The first etching is carried out in an aqueous solution of alkali containing 50 g/l of sodium hydroxide for 2-60 seconds at a temperature of 60-70°C, and the second etching in a solution containing 800 ml/l of nitric acid and 200 ml/l of hydrofluoric acid, for 5-60 sec. at a temperature of 18-25°C. In this case, after the first etching, washing is carried out in hot water for 10-15 minutes. and in cold water for 15-30 seconds, and after the second etching, washing is carried out only in cold water for 15-30 seconds. Nickel chemical precipitation is carried out in a sulfuric acid solution with sodium hypophosphite for chemical nickel plating with an acid pH of 4.2-4.4 at a temperature of 80-84°C.

The optimum solution temperature for the first pickling is 60-70°C. At a lower temperature, the etching process proceeds much more slowly, and at a higher temperature, the quality of the surface deteriorates. An increase in the amount of caustic soda leads to increase the speed of the etching process, and a decrease in the amount of caustic soda to a decrease in the speed of the process and to an increase in processing time up to several minutes.

The optimum solution temperature for the second pickling is 18-25°C. At higher temperatures, the etching process becomes uncontrollable. It is not advisable to cool the solution below room temperature, since this does not affect the process in any way. An increase in the concentration of nitric acid and a decrease in hydrofluoric acid leads to a slowdown in the etching of silicon carbide, an increase in the concentration of hydrofluoric acid and a decrease in nitric acid leads to intensive etching of silicon carbide and aluminum.

The optimum pH of an acidic chemical nickel plating solution is 4.2-4.4. At pH less 4.2, the deposition process slows down, at a pH greater than 4.4, the solution becomes cloudy and metallic nickel is restored on the walls of the bath.

The optimal temperature of the chemical nickel plating solution is 82 ± 2°C, at a higher temperature sodium hypophosphite decomposes, nickel begins to be reduced in the volume of the solution and creates large nickel deposits on the surface of the part, at a lower temperature the process speed slows down or the nickel reduction process does not start.

The invention is illustrated by drawings.

Figure 1 shows photographs of the base of MMCM AlSiC without coating, made using a microscope with a magnification of X7, X45, X70.

Figure 2 shows photographs of the AlSiC MMCM base with a prepared surface for coating according to the proposed method, taken using a microscope with a magnification of X7, X45, X70.

Figure 3 shows photographs of the base of MMCM AlSiC with a surface coated with chemical Nickel thickness of 18 μm according to the proposed method, made using a microscope with a magnification of X7, X45, X70.

Figure 4 shows photographs of the AlSiC MMCM base with a surface coated with 18 μm chemical nickel, 1 μm galvanic nickel and 3 μm gold, taken using a microscope with a magnification factor of X7, X45, X70.

Example.

Chemical nickel plating of the surface of a heat-removing base made of MMCM AlSiC with an area of 23 cm ² and a thickness of 1.5 mm, for a microwave module.

An alkaline solution is prepared for the first etching: 50 g of sodium hydroxide is added to 1 liter of water and stirred until the latter is completely dissolved, then heated to 65°C. The item, fixed on a wire or in a fluoroplastic basket, is immersed in the prepared solution. The process proceeds with rapid gas evolution, simultaneous degreasing and etching of the part occurs. Etching takes place within 2-60 seconds, depending on the dimensions (thickness) of the part. For large parts (thickness ≥2 mm) etching from 5 to 60 seconds. For medium-sized parts (thickness 1-2 mm) etching from 5 to 40 seconds. For small parts (thickness <1 mm) etching from 2 to 3 seconds. After etching in an alkaline solution, the part is washed in hot running water for 10-15 minutes, then in cold running water for 15-30 seconds.

Prepare a solution for the second pickling: add 800 ml of nitric acid to 200 ml of hydrofluoric acid and mix. The item is immersed in the prepared solution. Etching takes 5-60 seconds, depending on the dimensions (thickness) of the part. For large parts (thickness ≥2 mm) etching from 5 to 60 seconds. For medium-sized parts (thickness 1-2 mm) etching from 5 to 40 seconds. For small parts (thickness <1 mm) etching from 5 to 8 seconds. After etching, the part is washed in cold running water for 15-30 seconds. (see Fig.2)

Sulfuric acid solution is prepared with sodium hypophosphite for chemical nickel plating with an acid pH of 4.2-4.4 and heated to 82±2°C. The item is immersed in heated chemical nickel solution. The duration of the process depends on the required coating thickness (coating speed 6-9 µm/h). The part coated up to 18 microns is washed in hot running water for 10 seconds. and in cold running water for 10 sec. Drying of the coated part is carried out by dehydration in acetone for 5 seconds. and in an oven at 100°C.

The coating on the product was solid and uniform . No peeling of the coating is observed.

Since the surface of the MMCM AlSiC base and the nickel coating have a similar gray color, it becomes more difficult to assess the continuity of the coating. Therefore, to visualize the continuity of the coating, on the base, coated with 18 microns of chemical nickel, 1 micron of electroplated nickel and 3 microns of gold were applied (see Fig.4). Because the gold is yellow in FIG. 4 clearly shows that the coating is continuous, without gaps.

Thus, the method of surface preparation and chemical nickel plating of parts from MMCM AlSiC using the above solutions makes it possible to combine the processes of degreasing and etching, to apply high-quality nickel coatings without additional processes of sensitization and surface activation.

The quality of the nickel coating was assessed by checking adhesion (heating at 200°C in a BINDER FED 720 oven) and visually under an Altami CM0745 microscope for coating defects (bulging, peeling, non-coverage, etc.).

Claims (2)

1. A method for chemical nickel plating of the surface of a metal-matrix aluminum-silicon carbide composite material, including etching, washing, nickel chemical precipitation, washing and drying, characterized in that, during etching, the first etching is carried out in an aqueous solution of alkali containing 50 g/l of sodium hydroxide, in for 2-60 s at a temperature of 60-70°C and a second etching in a solution containing 800 ml/l of nitric acid and 200 ml/l of hydrofluoric acid for 5-60 s at a temperature of 18-25°C, while after the first etching, washing is carried out in hot water for 10-15 min and in cold water for 15-30 s, and after the second etching, washing is carried out in cold water for 15-30 s, chemical precipitation of nickel is carried out in an acidic solution with a pH value 4.2-4.4. 2. The method according to claim 1, characterized in that the chemical deposition of nickel is carried out at a temperature of from 80 to 84°C.

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