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Black powder come from nickel-plated grid after high temperature exposure

Hi everyone,

I'm a technician and I work in an analysis laboratory.

I'm testing a grid (used on the cooker) made of (after EDS analysis) iron (99% in the bulk) and trace of carbon (difficult to reveal due to limit of EDS detector). On the surface there is a nickel-plated layer of about 10 microns and a thin layer of chrome (plus some trace of sulfur in both layer).

After an exposure to high temperature (more than 500 °C) the grid loses its shining appearance and becomes coloured: from blue-violet to red-yellow. In the same time, in the area exposed to the higher temperature there is a production of some black powder that seems to be nickel carbonate (EDS show an high content of Ni, C and O). Some further analysis of the clean region displayed some hump, blister that in some case explode revealing a rough substrate.

Can anyone help me? Thanks in advance

Dr. Cristian Zanchetta
- Italy
2007

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Hi. Bright nickel plating usually involves sulfur-bearing organic brighteners which don't sustain 500 °C without decomposition. For high temperature nickel you should probably use a brightener-free nickel sulphamate plating bath.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2013