Abstract
General properties of the black chromium electrodeposit obtained from the chromic acid bath (CrO3 2.5-4M/l, CH3COOH 0.05M/l, CO(NH2)2 0.05M/l) were investigated. The surface and cross-section of these deposits were examined microscopically. The apparent specific gravity was measured as compared with the other chromium electrodeposits. The structure of these deposits were analysed by the Xray diffraction method. The analytical method of urea contained in the chromic acid bath were established.
(1) The black chromium electrodeposit are grain-like having large cracks.
(2) The apparent specific gravity of the deposit is lighter than the other chromium electrodeposits and the Cr content of the deposit is about 70%, which suggests that the black chromium electrodeposit consists partly of Cr oxide.
(3) The Xray diffraction pattern shows that these deposits consist of the two different types of the stracture, i. e. B. C. C. and H. C. P.
(4) The gravimetric method using Xanthydrol is suitable for the analysis of urea in the black chromium plating bath.
