Determination of the Growth Time Period of Loose Zinc Deposit Using Interval Analysis Methods
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TION PROCESSES AND PROPERTIES OF POWDERS
Determination of the Growth Time Period of Loose Zinc Deposit Using Interval Analysis Methods V. S. Nikitina, *, T. N. Ostaninaa, S. I. Kumkovb, V. M. Rudoya, and N. I. Ostanina aUral
Federal University named after the first President of Russia B. N. Yeltsin, Yekaterinburg, Russia Krasovskii Institute of Mathematics and Mechanics (IMM UB RAS), Yekaterinburg, Russia *e-mail: [email protected]
bN.N.
Received October 22, 2019; revised January 27, 2020; accepted January 31, 2020
Abstract—A characteristic of obtaining metal powders by direct current electrolysis is changes in the morphology of particles over the loose deposit layer thickness up to the formation of large spherulites. Deposits should be periodically removed from the cathode in order to obtain a powder with homogeneous composition. This paper justifies the choice of the parameter describing the change in loose deposit properties and proposes a method for determining the periodicity of its removal from the cathode. Loose zinc deposits were obtained at 25°C from zincate electrolyte containing 0.3 mol L–1 of ZnO and 4 mol L–1 of NaOH at a current setpoint exceeding six times the limiting diffusion current calculated using the smooth electrode. Electrode potential, deposit thickness and evolved hydrogen volume were measured directly in the process of electrolysis. Current redistribution between the metal reduction and hydrogen evolution leads to a change in the structure of loose deposit particles. It is shown that the differential current efficiency of zinc is the parameter describing the change in the loose zinc deposit density. Its value should not exceed 0.96, in order to ensure deposition of loose deposit with homogeneous properties. A further increase in current efficiency will lead to the formation of aggregates at the deposit growth front. It is proposed to determine the periodicity of loose deposit removal from the cathode using the empirical equation for the time dependency of differential current efficiency of zinc. The mathematical and statistical analysis of the data obtained in six replicates was carried out. The interval approach made it possible to significantly narrow the range of permissible differential current efficiency values and, as a consequence, to determine empirical equation coefficients with acceptable accuracy and calculate the growth time period of a deposit with homogeneous structure. The obtained approach can be used to estimate the time period of loose metal deposition accompanied by hydrogen evolution. Keywords: zinc powders, electrodeposition, current efficiency, growth time period, process parameters, estimation, interval analysis methods DOI: 10.3103/S1067821220050119
INTRODUCTION The most important component of the technology of the powder metal industry is manufacturing of raw materials—metal powders. The most universal methods for their preparation are physicochemical methods, in particular, electrolysis of metal salts [1, 2]. After separation of loose deposits of me
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