JPS616291A - Plating method of nickel-tungsten alloy - Google Patents

Abstract

PURPOSE:To execute electrodeposition of an Ni-W alloy contg. W at a high rate by using a bath prepd. by adding a specific amt. of citric acid and aq. ammonia to a plating bath contg. nickel sulfamate and sodium tungstate and executing electrolysis under specific conditions. CONSTITUTION:The citric acid of the equiv. of the molar number of Ni and W in total or above is added to the plating bath into which Ni is incorporated at 0.2-0.4M/l in the form of nickel sulfamate and W at 0.2-0.4M/l in the form of sodium tungstate. The aq. ammonia is added to such soln. and the pH is adjusted to 6-7. The electrolysis is executed by using such plating bath at 60- 80 deg.C bath temp. and 10-30A/dm<2> cathode current density. The industrial plating of the Ni-W alloy having high film hardness is made possible at a high rate of about >=40% concn. of W by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of plating a nickel-tungsten alloy containing 40 to 50% tungsten. Conventionally, the plating bath for producing a nickel-tungsten alloy has been known to be an ammonia alkaline bath containing nickel sulfate, sodium tungstate and citrate, and having a pH of 8 to 9.

For example, according to page 171 of the book New Alloy Plating Method by B. M. Vyacheslavov, nickel 13g//
Sodium citrate added as 117 nickel sulfate
200g/l Ammonium chloride 50g/l Cathode current density 20A/dm” Bath temperature
It is stated that a nickel-tungsten alloy plating containing up to 83% tungsten can be obtained from a 90°C bath.

However, when an ammonia-alkaline bath with a pH of 8 to 9 is used at a high temperature of 70°C or higher, it not only emits a marked ammonia odor, harms the working environment, and is extremely inconvenient in practice, but also causes the bath to evaporate due to ammonia evaporation. The inventor of the present invention has confirmed through follow-up experiments that there is a drawback that the tungsten changes and becomes unstable, and that it is difficult to obtain an alloy plating containing 40% or more of tungsten. The inventor of the present invention uses a bath that frequently emits ammonia odor during work and has a stable bath composition, especially tungsten.
As a result of intensive research in pursuit of a plating bath capable of electrodepositing a nickel-tungsten alloy containing a high percentage of 0% or more, we found that when adding nickel to the bath in the form of sulfamate instead of sulfate, the pH should be adjusted. It was discovered that it is possible to obtain a practical plating bath for electrodepositing a nickel-tungsten alloy that is neutral in the range of 6 to 7, does not generate an ammonia odor during operation, and contains a high percentage of tungsten of 40 to 50%. The present invention was completed.

Next, to explain the structure of the present invention, nickel is sulfamic acid nickel, Ni(NH2SO3)2.
It is added to the plating bath in the form of 4H20 and its concentration range: is. , 2 to 0.4 indulgences.

Tungsten is sodium tungstate Na2VJ0
It is added to the plating bath in the form of 4.2H20 and its concentration ranges from 0.2 to 0.4 mal/l. Next, citric acid is added in an amount equivalent to or more than the total number of moles of nickel and tungsten. Add ammonia water to this solution to adjust the pH to 6-7.
A component of the present invention is to conduct electrolysis at a cathode current density of 10 to 30 A/dm 2 at a bath temperature of 60 to 80° C. using a plating bath prepared in the following manner.

As the anode, a nickel anode, a platinum-coated titanium electrode, or an insoluble anode made of stainless steel or the like can be used.

The concentration range of each component in the plating bath is 0.2 to 0.4M for both nickel sulfamate and sodium tungstate.
A range of 0.2 M/l or less is not preferable because the bath composition tends to change during work and it becomes difficult to obtain a stable alloy composition. I don't like it because it's expensive.

The concentration of citric acid must be equal to or higher than the total number of moles of nickel and tungsten; a concentration lower than this is not preferred because the bath becomes unstable.

The pH of the bath must be neutral, between 6 and 7. If the pH is less than 6, the current efficiency will decrease, which is preferable, and if it is more than 7, an ammonia odor will be emitted during the operation, which is not preferable.

The bath temperature needs to be 60 to 80°C; if it is below 60°C, the content of tungsten in the deposit will be below 40%, which is not preferable. Further, if the temperature exceeds 80°C, the citric acid in the bath undergoes anodic oxidation and is decomposed and consumed, which is not preferable. If the current density is less than Pi IOA/dm2, the tungsten content in the plating film will be less than 40%, which is not preferable.
Moreover, if it exceeds 80AΔh2, cracks will occur in the plating film, which is not preferable.

The above is an explanation of the reasons for the constituent elements of the present invention.

Next, the effects of the present invention will be explained.

The nickel-tungsten alloy plating obtained by the present invention can be a bright plating containing 40 to 50% by weight of tungsten, and its hardness is Hv 630 to 780 Te, and after heat treatment at 400°C for 1 hour, the hardness is HvlO0.
0 to 11oo, and after heat treatment at 600'C for 1 hour, h
High hardness of Hv 1200-135o is obtained.

It also has excellent acid resistance, and according to the 8NHC7 immersion test, it showed 15 to 20 times more corrosion resistance than electroless nickel plating and 200 times more than hard chrome plating.

The research conducted by the present inventors has demonstrated that nickel-tungstate alloy plating having the properties described above can be obtained extremely easily and industrially using the plating bath according to the present invention.

The nickel-tungsten alloy plating according to the present invention has excellent hardness at high temperatures, so when used for plating glass molds, excellent durability and mold release acid can be obtained.Also, since it has excellent hydrochloric acid resistance, The inventor's research has revealed that the present invention has an excellent effect when applied to plating molds for chlorinated plastics, where corrosion due to the generation of hydrogen chloride is a problem.

As explained above, the present invention exhibits extremely excellent industrial effects.

Next, an example will be given and explained.

Example 1 Nickel sulfamate 0.25M/l Sodium tungstate 0.25M/l citric acid
0.5 M/l pH 6.5 (adjusted with aqueous ammonia) Using the above plating bath at a bath temperature of 75°C, with an 18-8 stainless steel plate as an anode and a mild steel plate as a cathode, a cathode current density of 20
Electrolysis was carried out at A/dm for 15 minutes to obtain a shiny nickel-tungsten alloy plating with a thickness of 25 μm. Quantitative analysis of this plated layer by EPMA revealed that the composition was 58% nickel and 42% tungsten. The hardness of the plating film is HV 680, and this is heated to 600℃1.
After heat treatment for several hours, the hardness was 1200 Hv.

Example 2 Nickel sulfamate 0.8 M/l Sodium tungstate 0.85 M/l citric acid
0.70M/l pH 6.8 (adjusted with ammonia water) Bath temperature 78℃ Using the above plating bath, a cathode current density of 15A/dm2 with a glass mold made of SUS 403 as the cathode and a stainless steel wire as the anode. Plating for 10 minutes at
A bright nickel-tungsten alloy plating of μ was obtained. When this mold was heat treated at 400° C. for 1 hour, its hardness was 1030. This mold showed excellent mold releasability and durability when used continuously in the glass molding process1.
．． Ta.

As is clear from the above examples, the present invention enables industrial production of nickel-tungsten alloy plating containing a high percentage of tungsten of 40% or more. This is an invention of great industrial significance.

1 penalty Country

Claims (1)

[Claims] Contains 0.2 to 0.4 M/l of nickel sulfamate, 0.2 to 0.4 M/l of sodium tungstate, and citric acid equivalent to or more than the total amount of nickel and tungsten, and adjusts the pH to 6 to 7 with aqueous ammonia. Using the same plating bath,
Bath temperature 60-80℃, cathode current density 10-30A/dm
A method for plating a nickel-tungsten alloy, characterized by electrolyzing at ^2.