Inductive heating of ZrO2 crucible

Above about 700 deg Centigrade, zirconia is a passable electrical (oxygen ion) conductor and the resistance decreases as the temperature increases.

But why heat it inductively? Zirconia is a poor thermal conductor and has low tensile strength, so it is very prone to thermal shock. Depending on the size of the crucible and the contents, you will be limited to a heating rate of about 200 deg C to about 600 deg C per hour.

Most ZrO2 crucibles and tubes used as suseptors are preheated. Optical fiber is produced by pulling a glass fiber from a spinneret through an inductively heated zirconia tube. The investment casting industry also uses inductive heating & ZrO2 crucibles

- they melt the superalloy - dump the melt and drop in a cold ingot in a 2 minute cycle.

- and yes they get a quite a few cycles from one crucible (not bad for a material with lousy thermal shock resistance) Both tubes and crucibles are fairly coarse grained materials. The tubes are Yittria stabilized and surrounded by grog and a preheat furnace - thermal shock is a big problem for the tubes.

- The crucibles are not designed to be susept, but are designed for thermal shock & corrosion resistance. A good suspetor unit would be a SiC sleeve fitted over a ZrO2 insert with some fiber or grog spacer to prevent the ZrO2 from cracking the SiC sleeve. I have a feeling that reduced ZrO2 will quickly replenish the O2 in air and direct inductive heating of a fully stabilized ZrO2 unit will cause severe thermal shock problems.

What's you application? what type of corrosion and thermal shock resistance do you need??

Gregg

Good point. Being a ceramicist, I naturally think first of a fully dense, fine grain material. But a coarse grain porous castable refractory is a different matter entirely. And as you say, it is commonly packed in grog, so even if it cracks (some more), it won't go anywhere.

Cheers

AW