There are many methods to take off the pitting on the deposited surface in the high concentration cupper cyanide baths.
One of these methods is to add some kind of surface active agent to the bath in order to decrease the surface tension of the bath, and easily separate the bubble of hydrogen gas from the depositing surface.
However, for this purpose the surface active agents must have necesarily the following characteristics:
1) Not to decompose at high temparature (ca. 75°C), and at high alkalinity (PH 12-13.)
2) Not to salt out in electrolyte of high concentration.
3) Not to decompose by electrolytic oxidation or reduction.
4) To reduce the surface tension of the electrolyte greatly by its addition even in small quantity.
From such point of view, we tested and studied nine surface active agents which are presumed to give good effect in alkaline and concentrated salt solution. The high concentration copper cyanide baths containing varying quantities of these surface active agents were made and satisfactory results were obtained in plating in three baths.
Conclusions are as follows:
1) Ionic surface active agents and polyalcohol ester type nonionic surface active agents can not be used in high concentration copper cyanide bath.
2) Polyoxyethylens lauryl alcohol ether, Polyoxyethylene sperm alcohol ether, Polyoxyethylene oleyl alcohol ether of relatively high polymerisation degree(p=20-50) and high purity (98%), decreased pits on the deposited surface without decomposition and salting out.
3) By addition of the agents in small quantity, makes it possible to reduce the surface tension of the bath to 50-30dyne/cm (30°C).
4) However, it is not possible to remove pitlike hollow caused by adheision of insoluble floating salt (copper complex salt) on the deposited surface and this salt must be removed completely by filtration.
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