Nickel was electroplated by using a jet flow device. For the normal Watts bath (containing 240g/l of nickel sulfate, 45g/l of nickel chloride, and 30g/l of boric acid at pH=4), the maximum available current density (i_m) was found to be 90Amp/dm² at 45°C or 180Amp/dm² at 60°C when the electrolyte was supplied at a jet flow rate of 200cm/sec. (average value in nozzle).
At higher current densities, deposition of nickel was perfectly restrained.
The deposition rate attained to its maximum value (not limiting current value) at E_p (about -1.5V vs SCE), followed by a marked decrease at less noble potentials.
The effects of pH, flow rate, and nickel concentration on i_m were discussed with respect to codeposition rate of hydrogen and the resultant increase of pH in the diffusion layer around the cathode.
No remarkable difference in i_m was observed between the Watts bath and sulfamate bath, both of which were of the same concentration of nickel.

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Studies were made on the stability of the 2nd intermediate, which had been produced by reducing reaction of Pd (II) with Sn (II) in hydrochloric acid solutions, and also on its activity as an active center of reduction process of copper with formaldehyde in basic tartrate solutions.
The stability of intermediate was evaluated by spectrophotometric method, and its activity was evaluated by the hydrogen gas evolution rate in the course of reduction process of copper.
The results obtained were as follows:
(1) The stability of the 2nd intermediate was higher with the increase in the ratio of Sn (II)/Pd (II) and the increase in Cl^- concentration in the reaction mixture. This phenomenon was identical with that of the 1st intermediate.
(2) The activity of the 2nd intermediate was higher than that of the 1st one. It largely depended on the desorption of adsorbed Sn (II) from the surface as far as the intermediate was stable.
(3) The measurement of hydrogen evolution rate would afford a convenient method for evaluating the activity of intermediate.

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Results of basic research and experiments on chromium diffusion coating of nickel superalloys were reported in the previous papers for the purpose of obtaining high corrosion resistance of gas turbine blades.
In this paper, there are discussed inner diffusion behavior indispensable to evaluation of surface concentration of chromium and thickness of surface layer at the time of designing turbine blades which will be exposed to high temperature atmosphere for long hours.
The results obtained were as follows:
(1) Interdiffusion coefficient of chromium and base metal of nickel superalloys extremely depended on chromium concentration; its value was lower with the increase of the chromium concentration.
(2) The dependence of the diffusion coefficient on temperature conformed to an Arrhenius type equation within the error of 5% at maximum.
(3) There were no great differences among the diffusion coefficients of several kinds of alloy materials. However, the base metal of higher nickel content gave higher value of coefficient. The materials were arranged in decreasing order of coefficient as follows:
Ni>Inco X>Inco 700>U -500 (at higher than 1000°C)
Ni>U -500>Inco X>Inco 700 (at lower than 1000°C)
(4) When gas turbine blades with chromium diffusion coating were used in high temperature (900°C) gas, the surface layer was gradually corroded, and the surface concentration of chromium decreased to 45% after the use of 20, 000hrs.

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