RU2489525C2 - Method of applying nickel coating on steel and copper components in nickel plating electrolyte - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves chemical and electrochemical purification of a nickel plating electrolyte containing nickel sulphate, sodium chloride and boric acid, and applying a nickel coating from said electrolyte, wherein chemical purification of the electrolyte is carried out by bringing pH of the electrolyte to 5.5 with 5% sulphuric acid solution and heating to temperature of 80-90°C, and the nickel coating is applied at electrolyte pH 3.5-5.5, wherein the electrolyte further contains sodium sulphate and magnesium sulphate, wit the following concentration of components, g/l: nickel sulphate 140-200, sodium chloride 5-15, boric acid 18-35, sodium sulphate 70-125, magnesium sulphate 20-50.

EFFECT: low power consumption of the nickel plating process, high quality of the nickel coating and longer service life of components in aggressive media.

Description

The invention "A method for applying a nickel coating to steel and copper parts in a nickel plating electrolyte" relates to the electrical industry and can be used in the production of alkaline nickel-cadmium batteries.

Nickel plating is the most popular electroplating process. Attractive appearance, high corrosion resistance and mechanical properties speak in favor of a wider use of nickel with decorative, protective and functional purposes. Nickel deposited directly on steel or copper has the character of a cathode coating and, therefore, protects against mechanical damage. The discontinuity of the coating contributes to the formation of corrosive pairs in which steel or copper is a soluble electrode. As a result, corrosion occurs under the coating, which destroys the steel or copper substrate and leads to peeling of the nickel coating. In order to prevent this phenomenon, steel or copper must be coated with a dense nickel layer without porosity, therefore, in the manufacture of parts for nickel-cadmium batteries, those parts that are exposed to aggressive environments are covered with a dense nickel layer.

A known method of nickel plating of parts [1], in which products of steel and alloys based on copper, zinc and aluminum in sulfate electrolytes with the addition of special brighteners are subjected to electrolytic nickel plating, and a multilayer coating is applied to protect against corrosion.

The disadvantages of this method are the complexity, low technology, the inability to obtain a uniform coating of nickel on the embossed surface of the parts and nickel plating of narrow and deep holes, cavities, slots, threaded connections.

A known method [2] of nickel plating of parts from steel, copper and copper alloys, including deposition on the cathode, which is the product of positively charged metal ions from aqueous solutions and their compounds when passing through a solution of direct current, and the nickel plating process is carried out with insoluble anodes from metal or alloy stable in this electrolyte, the electrolyte is poured into the bath, heated to 45 ° C and the electrolyte is worked out at a current density of 0.1-0.2 A / dm ² , the distance between the anode and cathode is set from 10 to 100 mm, the parts are loaded at a current of 0.1-0.2 A / dm ^2, and as the bath is filled with parts, the current is increased to the required level, the nickel build-up speed at a current output of 90% is from 20 to 40 μm / h at a current density of 2-4 A / dm ² , at the end of the nickel plating process, the parts are unloaded from the bath, washed in cold running water, and then in hot running water, followed by drying.

The known method is also laborious, non-technological, does not allow to obtain a uniform nickel coating on parts of complex configuration and relief, the quality of electrolytic nickel coatings depends on the thoroughness of surface preparation and the presence of pores, defects and cracks on the surface of the parts.

The closest technical solution to the proposed and therefore adopted as a prototype is a method in which first a nickel plating electrolyte is prepared, then the electrolyte is chemically cleaned by adjusting the pH to 5.0 with a 20% sulfuric acid solution and heating the electrolyte to a temperature of 65-70 ° C, after which 0.3-0.5 g / l of potassium permanganate is first introduced into the electrolyte and stirring for 2-3 hours and then 3 g / l of activated carbon and stirring for 5-7 hours, and during electrochemical cleaning, the electrolyte ita begins at a cathodic current density of 0.05-0.1 A / dm ² and a temperature of 50 ° C, and then it is abruptly increased to 0.6 A / dm ² , and after applying nickel coatings, the parts are washed with cold and hot water and dried [3].

The disadvantage of this method is that the complex cleaning technology and the introduction of additives into the nickel-plating electrolyte according to the specified method, the high complexity and energy consumption for mixing and filtering the nickel-plating electrolyte lead to an increase in the final cost of nickel-plated parts.

An object of the invention is to develop a cost-effective method of applying a nickel coating to steel and copper parts in a nickel electrolyte for use in the manufacture of nickel-cadmium batteries with increased cyclic and resource characteristics.

The specified technical result is achieved by the method of applying a nickel coating to steel and copper parts in a nickel electrolyte by preparing a nickel electrolyte containing nickel sulfate 140-200 g / l, sodium sulfate 70-125 g / l, sodium chloride 5-15 g / l and boric acid 18-35 g / l, chemical cleaning of the nickel electrolyte, bringing it with a 5% sulfuric acid solution to pH 5.5 and heating to a temperature of 80-90 ° C, working out the electrolyte with current, applying a nickel coating from nickel electrolyte with acid STI equal to pH 3,5-5,5 and containing in its composition an additive of magnesium sulfate at a concentration of 20-50 g / l

The proposed method for applying a nickel coating to steel and copper parts in a nickel electrolyte is as follows.

рабочего объема бака и перемешивается в течение 20 минут с помощью сжатого воздуха, после чего электролит никелирования подвергают химической и электрохимической очистке от органических и неорганических примесей, причем для химической очистки в электролит наливается расчетное количество 5%-ного раствора серной кислоты, доводится рН до 5,5 и нагревается до температуры 80-90°С, для достижения полноты осаждения электролит никелирования перемешивается в течение 2-3 часов сжатым воздухом. Далее наливается дистиллированная вода до рабочего объема бака и дополнительно перемешивается сжатым воздухом в течение 30-40 минут. Затем электролит никелирования отстаивается в течение 2-6 часов, отстоявшийся электролит фильтруют через фильтровальную установку в рабочую ванну. В дальнейшем осуществляется электрохимическая очистка для удаления примесей меди, железа, цинка и свинца, для чего рН электролита доводится до 2-2;5 единиц 5%-ным раствором серной кислоты, после чего на анодные штанги помещаются никелевые аноды из расчета один анод на 0,5-0,6 м длины штанги, а на катодные штанги -максимальное количество катодов из листовой стали, очистка проводится при катодной плотности тока 0,2 А/дм² и температуре 40±10°С в течение 4-5 часов, появление светлого никелевого покрытия на пластинах указывает на окончание процесса очистки. После окончания процесса очистки электролит никелирования корректируют 3%-ным раствором едкого кали до рабочего интервала и приступают к работе.The required amount of nickel sulfate, magnesium sulfate, sodium chloride and boric acid is weighed. The components are poured into the tank for the preparation of nickel electrolyte. Subsequently, 480 l of sodium sulfate solution with a temperature of 20 ± 5 ° C is poured into the tank. Then distilled water is poured into the nickel plating electrolyte tank $${}_{\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$\mathrm{four}$}\right.}$$

the working volume of the tank and is mixed for 20 minutes using compressed air, after which the nickel-plated electrolyte is subjected to chemical and electrochemical purification from organic and inorganic impurities, and for chemical cleaning, the calculated amount of a 5% sulfuric acid solution is poured into the electrolyte, the pH is adjusted to 5 5 and is heated to a temperature of 80-90 ° С, in order to achieve complete deposition, the nickel-plating electrolyte is mixed for 2-3 hours with compressed air. Then distilled water is poured to the working volume of the tank and is additionally mixed with compressed air for 30-40 minutes. Then, the nickel-plating electrolyte settles for 2-6 hours, the settled electrolyte is filtered through a filter unit into the working bath. Further, electrochemical cleaning is carried out to remove impurities of copper, iron, zinc and lead, for which the pH of the electrolyte is adjusted to 2-2; 5 units with a 5% solution of sulfuric acid, after which nickel anodes are placed on the anode rods at the rate of one anode per 0 , 5-0.6 m length of the rod, and on the cathode rods - the maximum number of cathodes made of sheet steel, cleaning is carried out at a cathodic current density of 0.2 A / dm ² and a temperature of 40 ± 10 ° C for 4-5 hours, the appearance light nickel coating on the plates indicates the end of the cleaning process and. After the end of the cleaning process, the nickel-plating electrolyte is adjusted with a 3% potassium hydroxide solution to the working interval and set to work.

Nickel grades NPA1, NPA2, NPAN, NPANE are used as anodes.

Nickel electrolyte analysis for the content of the main components is performed at least twice a month, impurities - at least once a month. Nickel plating electrolyte must meet the following indicators:

nickel sulfate - 140-200 g / l;

sodium sulfate - 70-125 g / l;

magnesium sulfate - 20-50 g / l;

sodium chloride - 5-15 g / l;

boric acid - 18-35 g / l;

iron - not more than 0.1 g / l;

zinc - not more than 0.01 g / l;

lead - not more than 0.01 g / l;

copper - not more than 0.02 g / l;

pH is 3.5-5.5.

The quality control of the Nickel coating is carried out by external inspection of parts and verification of compliance with the technological regime in the coating process.

The nickel plating process is carried out in steel bathtubs lined with plastic sheet. Suspension devices have reliable contact with the part and the bar. Before starting the nickel plating process, the rods are thoroughly cleaned, the system of heating and mixing of the electrolyte is turned on. When the temperature reaches 40 ° C, heating and mixing are turned off and the calculated number of parts is suspended so that they do not come into contact with each other. Once a month, nickel anodes are removed from the covers, cleaned with wire brushes to a metallic luster and washed with water.

The rate of growth of Nickel when the current output equal to 90%, is 7-9 microns / h at a current density of 0.5-1 A / DM ² . At the end of the nickel plating process, the parts are unloaded from the bath, washed in cold running water, and then in hot running water, followed by drying.

The application of Nickel coating occurs at a temperature of 20-40 ° C and a current density of 0.5-1 A / DM ² . The anodes in the working bath are used of the brands NPA1, NPA2, NPAN, NPANE, and they are hung in covers made of KS-34 fabric. The ratio of the anode and cathode surfaces 2: 1 allows you to get maximum labor productivity and the best quality of the Nickel coating.

The removal of low-quality nickel coatings from parts is carried out chemically in a solution consisting of two volumes of nitric acid and one volume of sulfuric acid.

The choice of the heating temperature of the electrolyte and its acidity during chemical cleaning, as well as the working range of the acidity of the nickel electrolyte during coating and the concentration of magnesium sulfate additive, are dictated by the following considerations.

At a temperature of heating of nickel electrolyte below 80 ° C, incomplete dissolution of all components of nickel electrolyte (especially boric acid) takes place, which makes it impossible to use, and at a temperature of heating above 90 ° C there is an irrational use of energy resources and, as a result, an increase in the cost of nickel-plated parts.

The indicated acidity of nickel plating electrolyte, equal to pH 5.5, is optimal for carrying out its chemical cleaning and ensuring the rational use of expensive materials in preparation, as well as increasing the service life of the working bath with nickel plating electrolyte.

When the working acidity of the electrolyte is less than pH 3.5, a shiny coating with many cracks forms and abundant hydrogen is generated at the cathode, which leads to a deterioration in the quality of the nickel coating due to its insufficient thickness and high porosity, and when the working acidity of the electrolyte is greater than pH 5, 5, the electrolyte is alkalized to form nickel hydroxide sludge in the coating composition.

The indicated concentration of magnesium sulfate additive equal to 20-50 g / l is optimal for the nickel process and for a softer, brighter and more easily polished precipitation.

The advantages of the method are to reduce the energy intensity and cost of the nickel plating process, increase the quality of the nickel coating and increase its service life by almost an order of magnitude compared to traditional coating methods by reducing the working temperature of nickel plating by 5-10 ° C relative to the prototype, the use of magnesium sulfate and nickel anodes of the NPAN and NPANE brands, which allows to reduce the consumption of expensive materials during nickel plating by 49%.

The use of this invention in industry improves the protective and decorative properties of nickel-plated parts, which entails the manufacture of nickel-cadmium batteries and batteries based on them with high performance.

PUBLICATIONS TAKEN INTO ACCOUNT WHEN DRAWING IN THE APPLICATION

1. Yampolsky A.M. Modern Nickel Technology, L. 1950

2. Liner V.I. Modern electroplating. M. 1967

3. Patent of Russia N 2089675, decl. 10.24.1996 g.

Claims (1)

The method of applying a nickel coating to steel and copper parts, including chemical and electrochemical cleaning of a nickel plating electrolyte containing nickel sulfate, sodium chloride, boric acid, and applying a nickel coating from said electrolyte, characterized in that the electrolyte is chemically cleaned by 5% reduction of the electrolyte a solution of sulfuric acid to pH 5.5 and heating to a temperature of 80-90 ° C, and the deposition of a Nickel coating is carried out at a pH of electrolyte 3.5-5.5, while the electrolyte additionally contains um sodium sulphate and magnesium sulphate with concentrations of the components, g / l:
nickel sulfate 140-200 sodium chloride 5-15 boric acid 18-35 sodium sulfate 70-125 magnesium sulfate 20-50