An expendable immersion thermocouple having a cup-shaped body member for supporting the thermocouple and providing a cavity into which a refractory cement is poured to secure the thermocouple in place. The refractory cement is nonhomogeneous and has a surface region which is substantially composed of a high temperature refractory material such as alumina.

In an expendable immersion thermocouple for the measurement of the temperature of molten metal having a thermocouple enveloped in a protective tube which projects from the face of a body member for contact with said molten material and in which said tube is secured in said body member by a mass of refractory cement including a mixture of refractory material having differing thermal characteristics and having a surface which also is exposed to said molten material when immersed, the improvement comprising a layer of high refractory material comprising alumina or magnesia within the exposed surface of said refractory cement.