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How much mileage can one get out of a pound of Chromic Acid in a conversion bath?

2006

Anyone have any ideas on how much mileage one can expect to get out of a electroless chromic acid conversion bath?

In other words, for every pound of CrO3, how much will be used up before I need to scrap the bath. ( Or how much Chromium is left over in the bath that's scrapped, percentage wise.)

Thanks

Jim Williamson
chemicals - Columbus, Ohio, USA

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2006

Sir:
Your question is an interesting one. About 25 years ago in Montreal I did substantial work to determine the best hex. chrome for hot dip galvanizing. CrO3 consistently gave very bad results as the source of hex. chrome. The coatings were sometimes green, or yellow, or red, or black and ALWAYS ugly and streaky (vertical). After two weeks of intensive work we found a colorless hex. chrome coating at 0.1% Cr+6 and with the correct hex chrome source and additives. If there was a place on the lower side of the product it dried into a light blue coating. In the Canadian Government 40 hour salt spray test the product always easily passed. As far as scraping the bath; the resulting 20,000 gallon tank kept doing a good job for at least 7 years and then I lost track of them.
Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA