光沢カドミウムメッキにおける光沢生成に及ぼす添加剤の影響について

Abstract

Effect of addition agents on the formation of bright cadmium deposits from the cadmium cyanide baths has been studied.Cathode polarisation measurements were carried out in the presence of several addition agents and, at the same time, the deposits obtained from these baths were analyzed by electron diffraction method and also by microscopic method, in order to elucidate the characteristics of the crystal structures with respect to the formation of bright deposits.The results obtained are as follows:1) The presence of very small amounts of metallic salts, such as Ni, Co, Fe, Cu, Zn and Hg, in the cadmium cyanide baths, did not remarkable affect the deposition potentials of cadmium, while they gave more positive values of hydrogen deposition potentials in the case of Ni, Co and Fe.2) Addition of organic compounds, such as gelatin, peptone, dextrine, turkey red oil, heliotropine and coumarin, generally resulted in higher polarisation potentials of cadmium to give 30-100mV. at 1amp./dm2.3) Addition of organic compounds in conjunction with metallic salts usually made the cathode potentials more negative to give 70-150mV. at 1amp./dm2.4) In the absence of addition agents, cadmium cyanide baths gave the matt deposits which usually have no preferred orientation of the crystals. Metallic salts were ineffective in changing the grain size or the preferred orientation of the crystals.5) Most organic compounds tested had an effect on the crystal growth of the deposits as revealed by the ability to reduce the grain size and to change the type and/ or degree of the preferred orientation of the crystals.6) Use of organic compounds in conjunction with metallic salts had a marked effect on the crystal growth to bring the bright deposits which have the specific preferred orientation of the crystals.Even though there was no direct relationship between the degree or the type of the preferred orientation and the brightness of the deposits, the main effect in promoting brighter deposits appears that the crystal habits are altered so as to lead to the development of the smooth surface which has fine grains and the preferred orientation of crystals in the deposits.