| 摘要 |
Micro-cracked chromium plate, i.e. plate having at least 750 cracks per lineal inch, is formed by electro-depositing chromium for a sufficient period until internal stress of the deposit causes cracking using a cathode C.D. of from 20 to 1500 amps./sq.ft. and an aqueous bath at a temperature of 90 to 115 DEG F. and comprising less than 250 g/l of dissolved CrO3, dissolved sulphate ion, dissolved fluoride ion, and dissolved selenate ion. Preferably the bath contains 0.1 to 2.5 g/l sulphate ion, sufficient simple or complex fluoride ion to give a dissolved fluorine content of 0.01 to 3 g/l, and 0.007 to 0.1 g/1 of dissolved selenate ion. Typically the fluorine content is supplied as hydrofluoric, hydrofluosilicic or fluoboric acids or their sodium salts, or the reduced reaction product of hexavalent chromium and either hydrofluosilicic acid or hydrofluoric acid and silica as in Specification 829,429; or by fluoaluminates, fluotitanates or fluozirconates while the selenate ion is supplied as Na2SeO4. A plating of 0.025 to 0.1 mm may be obtained. |
