Casting Day Fuzzy Feeling

This entry is part 14 of 15 in the series Dog's Head
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So I posted about my ceramic shield. I thought this was a wonderful thing – addressing a flaw in other ‘amateur’. electric furnace designs. I may have even revelled in my brilliance in that post (I did refer, at one point, to a likeness with the heat shields on the Space Shuttle).

Gratuitous photo of a space shuttle. But not The Space Shuttle…this is the Russian one. It suddenly occurred to me that this might be a hoax. I REALLY hope not.


“What material can resist high temperatures, but does not conduct electricity”

My (Wrong) answer: “Regular old clay ceramic, e.g. bathroom tiles”

So, on casting day, I was a little unnerved to feel the slight tingling fuzzy sensation of electricity in my hand when I nonchalantly scooped dross off the melt with a metal ladle as the furnace furnaced away. Which was weird, because as far as I was concerned I had “all-powerful” CERAMIC between me and 240AC.

Ceramic Insulators on Telephone Pole

But here is something:

At 1000°C, bathroom tiles are different from regular bathroom tiles…they conduct electricity.

Oh dear.

I found this paper: Temperature dependence of electrical conductivity of a green porcelain mixture“. It was the most relevant I found to my cause, because since it’s about porcelain clay ceramic, not AlN ceramics, SiN ceramics, carbon-ceramics, or a million other engineering ceramics. It turns out ceramics, as a subject matter, is a deep kettle of fish.

Acronym of the week is Field Assisted Sintering Technology (FAST): a boon if you are in the bathroom tile production or weapons business, but something you-probably-would-never-have-known-about-but-would-have-been useful-to-know if you were thinking that bathroom tiles were going to separate you from 240V AC at 1000°C.






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