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The Electrocrystallization of Metals. Investigation of Zinc

D. M. Dražić ; Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia, Yugoslavia
S. Hadži Jordanov ; Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia, Yugoslavia
Z. Nagy ; Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia, Yugoslavia


Puni tekst: engleski pdf 19.284 Kb

str. 199-211

preuzimanja: 109

citiraj


Sažetak

In electrodeposition of zinc depending on the condition of
deposition, various effects of electrocrystallization can be observed.
In acid solution of zinc sulfate the considerable surface diffusion
overpotential appears at lower values of the total overpotential,
indicating the surface diffusion of actions as the rate
determining step. An interesting dependence of exchange current
density on pH with a minimum at pH - 2 indicate the probable
change in structure of the reacting particle. The mechanism of the
reaction is evaluated.
In alkaline zincate solutions no surface diffusion limitations
can be detected. However, due to the rather low zincate ion concentration
and high exchange current density zinc deposition
proceeds practically always under the diffusion control.
Morphology of zinc deposited depends considerably on the
value of the electrode potential. This can be seen from the experiments
in which the deposition morphology was observed with
a scanning electron microscope. It was found possible to disrupt
the deposition repeatedly for microscopic observation and than
continue deposition. At low overpotentials (up to 50 mV) epitaxial
layer type growth was observed with the linear increase of the
microstep width with time. For this effect a theory is proposed
which accounts also for the observed effects of substrate orientation.
At larger overpotentials (50-100 mV) boulder type deposit was
observed, most of which were not epitaxial with the substrate.
They are suggested to be originated by nucleation. The boulder
density per cm2 is first sharply increasing, and then slowly
decreasing with time. A statistical calculation for this is given
based on the model that large boulders consume the smaller ones.
With further deposition a small fraction of the boulders develop
into dendrites, their number being limited by the available total
current.

Ključne riječi

Hrčak ID:

197061

URI

https://hrcak.srce.hr/197061

Posjeta: 246 *