Is the chemistry different if you melt them in a reduction chamber, for example a gas-fired kiln, and cool in an absence of oxygen? Or does the O “stick around” because it’s bonded to Si or Al?

Something else to check: the switch that powers it. If you flip the switch and don’t hear the motor trying to turn, and you’ve already found the power reset on the disposal, it’s worth checking the switch VERY CAREFULLY with a multi-meter. Switches can wear out with use over time (I’ve had this happen 3 or 4 times with disposals and light switches).