Black spots in galvanized metal
Black spots in galvanized metal
(OP)
I'm looking to identify the black spots that are created when galvanized sheet metal (HVAC duct material) is heated to 600-800 degrees C (medium cherry). As the metal is heated sparks fly off the surface and white powderey residue remains, which I assume is zinc oxide as it turns yellow when hot and white after cooling. But the material of interest is the small black spots that form in a random way on the surface. These black areas exhibit the unusual electrical characteristic of negative resistance when placed in a proper circuit, but the composition of this material is unknown, and identification is the first step toward being able to produce it more consistently. The attached image shows several examples that I hope are helpful in identifying the black material. Thanks for any assistance.
RE: Black spots in galvanized metal
Well I am no expert but the black spots just look like corrosion on the base metal surface, iron oxide? maybe.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Black spots in galvanized metal
why are you baking at 600-899 c when the melting point of zinc alloy is at 420 c, what is left cooked zinc alloy.
by the way investigate about the toxicity of zinc alloy.
RE: Black spots in galvanized metal
RE: Black spots in galvanized metal
RE: Black spots in galvanized metal
The temperature range 600-to-800C [in air or similar] is entirely unsuited for any carbon or alloy steel... and the galvanized coatings will do exactly as described... and spot rust will 'pop-up' in bare areas.
This temperature range is best suited for BARE A286... or maybe... SStl 321A... or nickel alloys 600 or 625.
Note1. IVD aluminum coatings over the SStl may help the duct survive in a externally corrosive environment.
Regards, Wil Taylor
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