JPS58167791A - Method for plating with resistant to sulfurization - Google Patents

Abstract

PURPOSE:To form an inexpensive silver Zn alloy film resistant to sulfurization and having electric characteristics equal to that of a silver contact film on a cathode, by passing a cylical reverse current through an electrolyte with a specific composition containing silver cyanide, Zn(CN)2, NaCN and NaOH. CONSTITUTION:An aqueous solution containing 1-30g/l one kind or more AgCN and K Ag(CN)2 as silver cyanide, 50-150g/l Zn(CN)2, 50-350g/l NaCN and 50-250g/l NaOH is used as an electrolyte. When cyclical reverse current is passed through this electrolyte, a plating film having a smoother surface as compared to an electrodeposition film obtained by DC electrolysis. When this silver. zinc alloy plating film is subjected to buff polishing, mirror surface gloss can be imparted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to obtain an inexpensive coating having electrical properties equivalent to those of a silver contact coating and sulfurization resistance, and to obtain an inexpensive coating of 1 m with specular gloss. This paper relates to a developed method for plating sulfur-resistant films.

Currently, silver plating is often used as a surface treatment for electrical connection parts such as terminals of electric machines. This has the drawback of increasing contact resistance and causing problems.

Therefore, the present inventors have developed a plating method that can be used for the same purposes as conventional silver plating, and can also produce a sulfide-resistant film, which we would like to propose here.

That is, 5 the present invention contains at least one of silver cyanide and silver potassium cyanide as silver cyanide in an amount of 1 to 30/1%.
Using an electrolyte containing 50 to 150/L of zinc cyanide, 50 to 35,024 sodium cyanide as a complexing agent, and 50 to 250 f/11 of sodium hydroxide as a conductive salt, the cathode was electrolyzed by periodic reversal current electrolysis. Silver/zinc alloy coating with good sulfidation properties (zinc content: 5%)
~70 whispers).

The first diagram shows the temporal change in the pulse current density used in the periodic reversal current electrolysis method, where T1 is the time width of the canted current pulse, Ts is the time width of the anode current pulse, and T is the nozzle repetition rate. It is a cycle.

The current densities of Naorindonocellus and Anotonozorus are equal.

The silver/zinc alloy plating according to the present invention uses so-called ordered IJ deposition in which the wrinkles of the metal are directly reflected in the composition of the electrodeposited material, so silver precipitation is at its limit in order to obtain a silver/zinc alloy plating film. conditions that are easy to reach.

That is, the concentration of silver cyanide needs to be lower than the concentration of zinc cyanide.

In this case, if the concentration of silver cyanide exceeds 30'/l, zinc will not eutectoid unless the average cathode current density is 2'1th" or higher in the stirred bath. The surface becomes rough.

On the other hand, if the concentration of silver cyanide is too low, the bath composition will not fluctuate during electrolysis, and electrolysis for a long time at a lower average cathode current density will be required to obtain electrodeposit with the same composition. Therefore, 1'4 or more is appropriate.

If the tt of zinc cyanide is increased too much, it will become saturated and the amount pumped out from the plating bath will increase, which is economically disadvantageous, so the amount of zinc cyanide is suitably in the range of sO to 150/l.

IJium (complexing agent cyanide) is necessary to bring the deposition potentials of silver and zinc closer together and create a situation where the alloy is more likely to be electrodeposited, but if the concentration is too high, the amount pumped out will increase, so A range of 350'/l is suitable.

(If the silver concentration in the bath is low, cyanide.) Reduce the amount of IJium, and if the silver concentration is high, increase the amount of sodium cyanide.

Sodium hydroxide stabilizes the cyanide bath and makes the bath conductive f
It is necessary to increase the concentration, and the appropriate concentration range is 50 to 2
5.t/l. Below this concentration range, the increase in conductivity is small, and above this concentration range, the amount of pumping increases, which is economically disadvantageous.

This plating bath does not require heating or cooling.

The sulfidation resistance of silver-zinc alloy plating is improved compared to silver plating when the zinc content is Ss or more, but this effect becomes significant when the zinc content is 20% or more. If the zinc content is 7)S or more, the properties as zinc plating become dominant, making it unsuitable as a substitute for silver plating.

The conditions for periodic reversal current electrolysis are the nine-Russ repetition period (T).
occupies 7 in the Ss, ie pulse repetition period from O-5ms
The average cathode current fIIW! where the time width ratio (Tη) of the node current nozzles is expressed by the 0.1 to 0.41st order equation. Conditions where the degree 1 is 0 and I Vdm'' or higher are suitable.

I = (IC@TI -IA@Ts)/T here I
cj! , the magnitude of the cathode current pulse, and the magnitude of the one-sided anode current pulse. However, ■□=Io.

The zinc content in silver-zinc alloy plating obtained by periodic reversal current electrolysis increases with the average-polar current density under conditions of constant silver cyanide concentration, stirring conditions, and bath temperature. On the other hand, if the average cathode current density is the same, the zinc content will not be affected by the pulse repetition period (T) or the 7-node current ratio (T to T), and the fM cyanide concentration will be increased. Stir vigorously. If conditions such as raising the bath temperature are made to facilitate electrodeposition, the zinc content will decrease.

According to the periodic reversal current electrolysis, the Jl deposits are electrolytically melted by the 7-node current nozzle, so that a plating film having a smoother surface can be obtained than the electrodeposited material obtained by If flow electrolysis. Further, the obtained silver/zinc alloy plating film can be given a specular gloss by hub polishing.

Hereinafter, the embodiment 2.3 will be described as follows.

Example 1 A copper plate of 3 cs
, Sodium cyanide 160v't1 Sodium hydroxide A1
In an electrolytic solution containing 00 f/l, the time width of the anode current pulse in the pulse repetition period is 0.2, and the average cathode current density is 0.0. Plating was carried out by changing the temperature from IA/d- to 1 person/dm.The bath was a static bath, and the bath temperature was 2.
The temperature was set at 5°C.

The zinc content in the obtained electrodeposit is shown in FIG. These electrodeposits have a smooth outer surface compared to those obtained by direct current electrolysis.
kf: Shown. After these samples were exposed to 1-hydrogen sulfide gas at 0° C. for 5 days, the contact resistance was measured under a load of 50 μm, and the results are shown in FIG. As can be seen from this figure, the contact resistance of the silver-zinc alloy plating containing 5 or more zinc is better than that of the silver plating with a zinc content of O, that is, the alloy plating containing 2' or more of zinc per 1%. The contact resistance is very small.

Example 2 A 3 cm x 3 cs copper plate was degreased and pickled, and the average cathode current was measured in an electrolytic solution containing 1 t/ls of silver cyanide, 50 t/l of zinc cyanide, 11 μm of sodium cyanide, and s o Vt of sodium hydroxide. Density 0-3 A/dm”
The ratio of the time width of the anode current pulse to the pulse repetition period is 0.1, and the pulse repetition period is 0.5.
Plating was performed by varying the time from ms to 5S. The bath was stirred at a relative velocity of 1.3 m/1 between the cathode and the plating solution, and the bath temperature was 25°C. The zinc content in the obtained electrodeposit and these samples were dissolved at 80°C in hydrogen sulfide gas.
Nikkei riot me, amount of generated sulfide film and load 50Of
Table 1 shows the results of determining the contact resistance at . As you can see, the amount of sulfide film and contact resistance of silver-zinc alloy plating are extremely small compared to silver plating.

Table 1 Example 3 A 33 x 3 ex copper plate was degreased and then pickled to give silver cyanide of 20'/l and potassium silver cyanide of 5'/l s.
Zinc diazide 150 t/l, sodium 7anide 3
50'/z, sodium hydroxide 250'/1 t-
The average cathode current density in the electrolyte containing 0-51'/
dg) "s" pulse repetition period f: 5 ma, and plating was performed while changing the ratio (TMr) frO of the time width of the anode voltage tIL pulse to the pulse repetition period from 1 to 0.4. The bath was a static bath, and the bath temperature was 25°C. The zinc content in the resulting electrodeposit is shown in Table 2.A silver-zinc alloy plating film with specular luster was obtained by cutting off these samples for 97 seconds. In addition, after exposing these samples to 1% hydrogen sulfide gas at 80°C for 5 days, the amount of sulfide film formed and the contact resistance at a load of 500F were investigated, and the results are also shown in Table 2. As you can see, the amount of sulfide film and contact resistance of *@zinc alloy plating are much smaller than that of silver plating.

Since the sheet/zinc alloy plating film according to the present invention has excellent sulfidation resistance, its use as a substitute for silver plating has often caused problems in the past in sulfidic atmospheres such as blast furnaces and sewage treatment plants. It is possible to significantly improve the sulfidation resistance of electrical parts such as automatic plugs9.
, it is possible to achieve one noble metal in total.

Further, since it is possible to easily impart a mirror-like finish by polishing, it is useful as a means for obtaining a sulfur-resistant mirror.

[Brief explanation of drawings]

Figure 1 is a current waveform diagram in periodic reversal current electrolysis, Figure 2
The figure is a graph showing the relationship between the average cathode current density and the zinc content in the electrodeposit, and FIG. 3 is a graph showing the relationship between the zinc content in the electrodeposit and the contact resistance after a hydrogen sulfide gas test. %ken applicant Yaskawa Electric Manufacturing Co., Ltd.

Claims (1)

[Claims] At least one kind of silver cyanide or silver potassium cyanide as silver cyanide, 1 to 30 times 50 to 150
m-pole Kfilil-zinc alloy by 5 periodic reversal current electrolysis using an electrolyte containing 50-350'/l sodium cyanide and 50-250 f/l sodium hydroxide. A method of plating a sulfur-resistant film, which is characterized by obtaining a film.