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What is the reaction of a petroleum product on zinc plated part?

June 26, 2015

Q. We are using doing Non cyanide Alkaline Zinc plating and Trivalent (Non-Silver) black passivation with organic top coat for a sheet metal component. During assembly, we are dipping the plated part in a petroleum based oil (Thewalt T14). In few parts, there is a white coloration observed after the oil dipping.

59918

Kindly let me know what would be the reaction of any petroleum product with the zinc plated part?

Srinivasan Rajagopalan
- Coumbatore, India

A. Hi Srinivasan. I can't successfully google "Thewalt T14", so I don't know exactly what it is -- but I assume it is a rust-preventative oil that would be selected to be compatible with zinc plating?

The general answer, as I understand it from reading rather than practical experience, is that zinc plating is compatible with gasoline and some oils, but is attacked by sulfurous fumes so it is not acceptable for diesel fuels and some other oils that may contain significant sulfur.

Still, the general pattern of this looks to me somewhat like an emulsion, so I wonder if it is the "organic top coat" and "Thewalt T14" that are not compatible?

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2015

June 28, 2015

Thank you for your reply.

I will check whether the Thewalt T14 oil has got any sulfur. Also will try without using organic top coat.

Regards

Srinivasan Rajagopalan [returning]
- Coimbatore, India

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