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How can I convert the chromium content of my quench tank to chromate content?

A passivation coating provides galvanized steel with excellent resistance to the formation of wet storage stain. It also offers the benefit of decreasing the reaction between the zinc coating and concrete, which increases the bond strength of galvanized rebar in cement structures. A passive chromate coating can be created by quenching newly galvanized steel in a chromate quench tank. The amount of chromate ions desired in the quench bath depends upon the galvanizers needs and experience with their own quench tank. If a galvanizer does not want to rely on an in-house test to determine the amount of chromate in their quench tank, an outside laboratory may be called upon.

These independent laboratories often report the amount of chromium in the bath and not the amount of chromate ions present, which is of real interest to the galvanizer. Therefore, the galvanizer will need to know how to use the number reported back to them and convert it into information that is useful to him or her. In order to convert your chromium content into chromate ion content, you must know if the bath uses sodium dichromate or chromic acid flake. Once this and the chromium content are known, the following calculations can be made.

If sodium dichromate is used:

Table comparing various Zinc Coatings
Table comparing various Zinc Coatings

Where:

Welding Table2
Welding Table

Simplified:

Table5

If chromic acid flakes are used:

Table3

Where:

Table4

Simplified:

Table6

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