Electrodeposition of crack-free Chromium coating from trivalent Chromium bath
Date Issued
2014
Date
2014
Author(s)
Tseng, Mao-Feng
Abstract
Trivalent chromium electrodeposition process has some problems such as instability of the electrolyte, difficulty to obtain thick coating and cracks penetrating through the deposition. In this study, a wide operating range in applicable current density had been obtained by adjusting concentration of the complexing agent in trivalent chromium bath. Hull-cell test had been operated in this study to examine the range in applicable current density. The surface morphology and cross-section of the deposited coatings were observed by SEM. The crystallinity of the deposition was examined by X-ray diffraction. In addition, hardness test had been operated to make more discussion about the relation between properties of the chromium coating and the parameters of electrodeposition process. The study reveals that adding urea would solve the problems of current efficiency decades with deposition time during trivalent chromium electrodeposition process. It is shown that the widest range in applicable current density is obtained from the bath containing 3.72M ammonium formate and 3.72M urea. After adding the thiosalicylic acid to the trivalent chromium bath, a thickness of 20μm, bright and crack-free coating can be obtained at a deposition rate of 0.33μm/min by applying current density of 80ASD.
Subjects
trivalent chromium electrodeposition
thiosalicylic acid
current density
deposition rate
crack-free
Type
thesis
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