 Sintered alumina was developed by Siemens in Germany to counteract this.Sintered alumina is a superior material to mica or porcelain because it is a relatively good thermal conductor for a ceramic, it maintains good mechanical strength and (thermal) shock resistance at higher temperatures, and this ability to run hot allows it to be run at "self cleaning" temperatures without rapid degradation.It also allows a simple single piece construction at low cost but high mechanical reliability.