Hydrothermal decomposition of NaCN, Na2[Zn(CN)4] and Na3[Cu(CN)4] (particulary, Na2[Cu(CN)3]) in aqueous solution using a batch-type autoclave was investigated at the temperature range of 373K to 423K, under pressurized condition of 1 MPa. The initial CN concentration in the sample solution was set at 1g dm−3. As a results, it was found that the rate of CN decomposition in NaCN solution increased with an increase in the temperature. The decomposition rate was found to be expressed by first-order reaction kinetics. For the metal cyanide complexes, the rate of CN decomposition increased in the following order Cu < Zn < Na, which was attributed to a decrease in the stability constant of metal cyanide complexes in the same order. It was recognized that the reaction products of formic acid, ammonia, and carbonate were formed in the decomposition of NaCN and Na2[Zn(CN)4] in the experimental condition.By contrast, formic acid, ammonia, carbonate, nitrous acid, and nitrogen were produced by the decomposition of Na3[Cu(CN)4]. Furthermore, it was found that the metal ions of Cu and Zn were precipitated as insoluble CuO and ZnO, respectively.
Pulse plating was used to prepare a zinc deposit from a zinc chloride bath with and without poly(ethylene glycols) and potassium benzoate as additives. The influence of additive and pulse plating parameters, namely, ton time=1 ms, Toff time=4 ms-19 ms and average current density=1 Adm−2-5 Adm−2 on grain size, surface morphology and preferred orientation was investigated. The surface morphology of zinc deposits was studied by scanning electron microscopy. The grain size and preferred orientation of zinc deposits were studied by X-ray diffraction. At constant ton time=1 ms, the grain size became finer with increasing Toff time from the electrolyte without the additives. On the other hand, a progressive decrease of the grain size was observed with the additives. The (1010) and (1120) orientations were strong preferred orientation at all pulse plating parameters from the electrolyte with and without additives. Current efficiency became high with an increase in average current density.