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Zinc Phosphate stripping for coating weight

Q. Hello Community,

Tetrasodium EDTA
tetrasodium_edta

on Amazon or eBay
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surfaces IAW defense specification TT-C-490. In this spec it requires us to strip the phosphate with a solution that is not stripping this coating at all. My supplier has not been able to close the gap on this and I am hoping there is some information in the community that can help.

I there a commonly used process for stripping phosphate on steel that I could use to determine this?
Is there a certain concentration i should be using for this formulation?

Spec Callout----

A.4.6 Zinc phosphate stripping (types I and V) for coating weight determination on steel. The phosphate coating shall be completely removed by immersion in a sodium hydroxide/tetrasodium ethylenediamine-tetraacetic acid (EDTA) solution for 15 minutes at 70 °F (21 °C). The solution can be formulated by adding 125 grams of sodium hydroxide and 125 grams of tetrasodium EDTA to 750 mL deionized water. Upon removal from stripping solution, rinse the samples in water, dry the test specimens and reweigh to the nearest milligram. Repeat this process, in five minute increments, until a constant weight is obtained.

Matt C
- Lansing Michigan
October 3, 2024

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A. Try solution of chromic acid 50 g/L at about 74 °C for 15 minutes. Repeat until you have constant weight. Do not use this solution again.
Good luck.

Alex Sirota
Plating Engineer - Lod, Israel
November 25, 2024

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