The composition of gases evolved during heating of chromium electroplates obtained from Cr(III) sulfate solutions

摘要

The effect of conditions of chromiumdeposition(acidity, current density, and temperature) on thehydrogen content in chromium deposits obtained from thesolutions (g/l) : (1)25 Cr2(SO4)3·6H2O, 7 to 10 Na2C2O4, 40H3BO3, 100Na2SO4, and 0.1 or 1.5 SAA and (2) 100 or 200Cr2(SO4)3·6H2O, 20 or 40 Na2C2O4, 100Al2(SO4)3·18H2O,and 80Na2SO4 are researched. In solution no.1, the content ofhydrogen can be changed from 2 to 45 cm3/g by the appropriatechoice of SAA concentration. The hydrogen content in chromiumdeposits obtained from solution no.2 was approx. 20 cm3/g andslightly depended on the conditions of electrolysis. According tothe data of thermodesorption mass-spectrometric (mass-thermographical) analysis, upon heating the chromium deposits to400℃, CO2 and H2O evolve along with hydrogen. Carbondioxide is formed as a result of the thermal decomposition ofH2C2O4 or the products of its partial cathodic reduction, whileH2O evolves from chromium and aluminum hydroxides.