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-----Test procedure for sodium dichromate solution for galvanizing?
January 7, 2011
I want to know the actual lab test procedure for Dichromate Bath.
What can be checked
1) The Percentage of Chromium in respect of total volume ?
or
2) Percentage of dichromate in respect of total volume ?
and What would be first time preparation ration for water and Dichromate powder/Chromic Acid ?
Very confusing please advice.
Galvanizer - Haridwar, U.K. , India
January 13, 2011
Sir:
Sodium Dichromate it the preferred chemical rather than chromic acid (Cr03). In a new batch add acetic acid
⇦ on
eBay
or
Amazon [affil link] (glacial) and enough HCl to bring the pH down to about 4.5. Readjust pH periodically with con. HCl to maintain pH between about 4 to 4.5. Avoid below pH 3 or above pH 5. pH 3 or lower gives product brown color. pH 5 or above does not work. Zinc +2 ion can be titrated with disodium EDTA with suitable indicator in basic pH buffer. Total dissolved solids can be measured by a conductivity meter. Properly made up a chromate solution of sufficient size for the product can last several years and pass a 40 hour salt-spray test.
Regards,
Galvanizing Consultant - Hot Springs, South Dakota, USA
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