Of the impervious ceramic materials the highly refractory Alsint, having an alumina content of 99.7% (the rest is mainly MgO) is best suited for furnace constuction.

•Refractoriness up to 1700°C.

•Good thermal shock resistance because of its high thermal conductivity and high mechanical strength.

•Good electrical resistance at high temperatures.

Use is recommended in case of:
•High working temperature, chemical attack (for example, hydrogen and other reducing gases).

•Demand for very pure furnace atmosphere.

•Thin-walled constructions having a high thermal-shock resistance.

•If great differences in temperature are to be expected, thin-walled tubes are more suitable. Smaller wall thicknesses will speed temperature equalisation.

With furnace elements that must withstand high mechanical stress and which must therefore have thick walls, the wall thickness should be reduced at least in the zone of high temperature differences.