RU2572914C2 - Method for depositing nickel-phosphorus coating on metal surfaces - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method comprising preparation of the said surface, depositing nickel-phosphorus coating from the electrolyte solution, comprising nickel and phosphorus ions, and adjusting the electrolyte solution to achieve required concentrations of the said ions, pH value and electrolyte volume. The nickel-phosphorus coating was deposited from an electrolyte solution of pH 3.5-5.0, comprising nickel sulphate, nickel chloride, sodium sulphate, sodium hypophosphite and boric acid at a temperature of 80-90°C. The electrolyte solution adjustment was performed throughout the duration of process by continuous dripping of the corrective agent having pH 5.5-7.5 into the said electrolyte at a rate of 2-7 ml/min. per one litre of electrolyte under continuous stirring; the corrective agent comprising the electrolyte mixed with 25-50 ml/l of a 50% solution of potassium hydroxide.

EFFECT: constant electrolyte volume and composition in terms of key ingredients maintained during depositing of nickel-phosphorus coating, stable rate of depositing, uniform chemical composition across the coating thickness, increased service life of the electrolyte.

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Description

The invention relates to methods for forming nickel-phosphorus films on the surface of a metal part from an electrolyte solution, in particular to electrolytes for forming nickel-phosphorus films, uniform in composition over the entire thickness, and can be used to produce ultra-black coatings used in optical information systems.

Known methods of forming films from electrolytes containing nickel and phosphorus ions are typically characterized by uneven film thickness, due to the instability of such electrolytes and a decrease in electrolyte volume during the process due to its boiling off at operating temperatures of 80-90 ° C. A decrease in electrolyte volume, a change in the composition of the components and pH affect the deposition rate of the film and its composition in thickness. It is necessary to control these parameters, adjust the composition and maintain the volume of electrolyte.

A known method of deposition of Nickel from an electrolyte, including the deposition of Nickel from sulfate electrolytes (US Pat. RU 2361967 C1, C25C 1/08 from 07/20/2009), with a solution pH of 4.5-5.5 at a process temperature of 59.5-60 ° C . The concentration of Ni ions is maintained by removing part of the spent electrolyte from the circulation system, and the pH of the solution is continuously measured and automatically maintained in the process by adjusting the acidity by adding a 36% NaOH solution. The disadvantage of this method is that when adjusting the pH, an excess of a solution of sodium hydroxide in the electrolyte forms poorly soluble white precipitates. The electrolyte becomes cloudy and needs to be replaced.

The closest to the achieved result is a method of forming nickel-phosphorus films on previously prepared surfaces of metal parts, which consists in nickel plating from an electrolyte solution containing nickel and phosphorus ions (US Pat. RU 2293137 C1, C23C 18/36 from 02.10.2007). The electrolyte contains nickel acetic acid, sodium hypophosphite and acetic acid, the process is carried out at a temperature of 83 ± 2 ° C and a pH of 4.1-4.3. The method allows to obtain nickel films up to 55-57 microns in 6-7 hours of planting. The solution is corrected after four hours of operation (once in a 6-7 hour cycle) according to the results of analysis for nickel and phosphorus content by adding the calculated amount of sodium hypophosphite and nickel sulfate to the electrolyte, and the pH of the electrolyte by adding NaOH solution.

The disadvantage of the described method is the heterogeneity in the thickness of the chemical composition of the applied nickel-phosphorus films, due to the fact that the correction of the electrolyte composition is carried out periodically (every 4 hours), while the concentration of the components of the electrolyte solution and its pH decrease continuously during the deposition process.

The objective of the invention is to develop a method of forming nickel-phosphorus films on the surface of a metal part having a uniform chemical composition in thickness, as well as increasing the continuous service life of the electrolyte.

The specified technical result is achieved in that the method of forming nickel-phosphorus films includes preparing the surface of a metal part, depositing nickel-phosphorus films from an electrolyte solution containing nickel and phosphorus ions, and correcting the electrolyte solution to the desired concentrations of nickel and phosphorus ions, pH and electrolyte volume. The nickel-phosphorus film is precipitated from an electrolyte solution having a pH of 3.5-5.0 and containing nickel sulfate, nickel chloride, sodium sulfate, sodium hypophosphite and boric acid, at a temperature of 80-90 ° C, and electrolyte correction is carried out throughout the process by continuous dropwise addition of a corrective additive having a pH of 5.5-7.5, at a flow rate of 2-7 ml / min per liter of electrolyte with constant stirring. In this case, an electrolyte is used as a corrective additive, to which 25-50 ml / l of a 50% potassium hydroxide solution was added.

The proposed method can significantly increase the duration of continuous operation and the performance of the electrolyte. In accordance with the present invention, the electrolyte for the deposition of nickel-phosphorus films has an increased duration of continuous operation due to the constant replenishment of nickel and phosphorus ions in the solution and maintaining a constant volume of electrolyte, which is confirmed by the absence of precipitation and turbidity of the electrolyte, a constant pH during the entire process of film deposition. In addition, the preparation of corrective additives, in contrast to the prototype, does not complicate the method, because its composition practically coincides with the composition of the electrolyte; it does not require additional parameter control (the content of nickel and phosphorus ions) in the process of deposition of a nickel-phosphorus film on the part.

An example implementation of the proposed method

The solution for the formation of nickel-phosphorus films consists of nickel sulfate, nickel chloride, sodium sulfate, sodium hypophosphite and boric acid and is prepared as follows: boric acid is dissolved in water heated to 70 ° C, nickel sulfate is added, and mixed until nickel sulfate is completely dissolved, Nickel chloride is added and everything is mixed. Sodium hypophosphite and sodium sulfate are dissolved in separate glasses in hot water at 70 ° C, which are poured into dissolved nickel sulfate with nickel chloride and boric acid and hot water is added up to 1 liter. Heat the resulting solution to a temperature of 80-90 ° C. The resulting electrolyte has a pH of 3.5-5.0.

A corrective additive is prepared similarly to an electrolyte, adding 25-50 ml of a 50% potassium hydroxide solution per 1 liter of electrolyte to the finished electrolyte. The solution is mixed well and the precipitate is allowed to settle, after which the solution is filtered. The resulting corrective additive has a pH of 5.5-7.5.

Then, a previously prepared metal part is lowered into the bath with the electrolyte heated to operating temperature. Surface preparation of metal parts is carried out in accordance with the requirements of a typical technological process (OST 107.460092.001-86). The onset of the film formation reaction is evidenced by the release of hydrogen bubbles on the part.

As soon as the part is placed in the electrolyte, the drip supply of the corrective additive to the surface of the electrolyte begins and continues throughout the entire process at a speed of 2-7 ml / min per liter of electrolyte. Drip supply to the surface of the electrolyte with constant mixing of the correction solution allows you to maintain a constant volume of electrolyte, pH 3.5-5.0 and a constant composition of Nickel and phosphorus. In this way, nickel-phosphorus films with a thickness of 50-60 μm were obtained at a growth rate of 0.1-0.5 μm / min. The time of continuous operation of the electrolyte is not limited. PH control is carried out using a pH meter model 2696 Y8-FULL NAME 00.001RE GOST 22261-94 with a combined electrode TU 4215-004-35918409-2009. The thickness and composition of the nickel-phosphorus film over the thickness were controlled by layer-by-layer etching by gallium ion etching using an FEI Quanta 3D PEG electron-ion microscope and confirmed that the nickel-phosphorus films obtained have a uniform chemical composition over the entire film thickness.

After the deposition was completed, the nickel-phosphorus film was etched in acid solutions to obtain an ultra-black coating. Super-coated parts are used as structural parts for parts of optical devices and information systems.

Thus, the developed method for the formation of nickel-phosphorus films allows maintaining a constant volume and composition of the electrolyte along the main components, which ensures the deposition of films at a constant speed and the same chemical composition throughout the thickness. Also, the method increases the continuous life of the electrolyte.

Claims (1)

A method of forming a nickel-phosphorus film on the surface of a metal part, including preparing the surface of the metal part, depositing a nickel-phosphorus film from an electrolyte solution containing nickel and phosphorus ions, and correcting the electrolyte solution to the desired concentrations of nickel and phosphorus ions, pH and electrolyte volume, characterized in that the nickel-phosphorus film is precipitated from an electrolyte solution having a pH of 3.5-5.0 and containing nickel sulfate, nickel chloride, sodium sulfate, sodium hypophosphite and boric acid one at a temperature of 80-90 ° C, and the correction of the electrolyte is carried out throughout the process by continuous dropwise addition of a correction additive having a pH of 5.5-7.5, at a flow rate of 2-7 ml / min per liter of electrolyte with constant stirring while an electrolyte is used as a corrective additive, to which 25-50 ml / l of a 50% potassium hydroxide solution is added.