Bright chromium electrodeposition from tetrachromate baths - contg sodium tetrachromate prepd by oxidising sodium bichromate with chromic acid and aluminium hexafluoride ion brighteners

摘要

Tetrachromate baths for bright and hard Cr electrodeposition contain (1) Na2Cr4O13, formed by oxidn. of Na2Cr2O7, esp. as the dihydrate, with H2CrO4, and (2) AFP63 circled negative ions as brighteners. Sum of all catalysts and brighteners dissolved in electrolyte is 0.4-2.6 wt. % w.r.t. total CrO3 content. Prepn. pref. takes place in 2 steps. A homogeneous intermediate of Na2Cr2O7, catalyst and brightener is formed in 1st step, followed by reaction with excess, granulated CrO3.