Abstract
The structures and surface states of chromium coatings electrodeposited by applying rippled direct current of various frequencies have been investigated by microscopy and X-ray diffraction. The current applied was obtained by amplifying and rectifying signals of a RC-oscillator. The bath was of Sargent type (50°C) and the cathode current density was 30A/dm2. The surface of chromium coatings varied from gray to bright via milky gray with increasing ripple frequency, and this was closely related to the current interruption time in unit Hertz. The gray chromium was of bcc and hcp mixed structures and the ratio of the hcp chromium increased in proportion to the current interruption time in unit Hertz. In previous works, it was found that the necessary factors for the deposition of the hcp type chromium were 1) high concentration of chromium acid in the bath, 2) low temperature of the bath, 3) high current density, and 4) use of pulsating and rippled current. But from the result of this paper, it was found that the application of rippled current with a long current interruption time (0.4msec. in minium) made it possible to deposit the hcp type chromium. The hardness of the coating decreased with increasing the ratio of the hcp type chromium.
