Abstract: A protective sheath for a temperature sensing device for use in determining the temperature of molten metals. The temperature sensing device, such as a thermocouple, is encased in a molybdenum tube which is coated with successive porous layers of molybdenum, a plurality of layers of Al.sub.2 O.sub.3 -Cr.sub.2 O.sub.3 -Mo in a decreasing concentration of Mo in proceeding from the inner to the outer layers, and a layer of substantially pure Al.sub.2 O.sub.3 -Cr.sub.2 O.sub.3. The Al.sub.2 O.sub.3 -Cr.sub.2 O.sub.3 layer may be covered with an outer coating of a material, such as boron nitride, to protect the Al.sub.2 O.sub.3 -Cr.sub.2 O.sub.3 layer from attack by slag. Alternating layers of Al.sub.2 O.sub.3 -Cr.sub.2 O.sub.3 and boron nitride may be applied as outermost sacrificial layers.

Abstract: An immersion pyrometer having an outer casing comprising a mixture of graphite and a refractory metal oxide for contact with molten metal, an inner sheath enclosed by said outer casing, said inner sheath comprising a closed end metal tube wherein the closed end is in heat transfer contact with said outer casing, and a thermocouple within said inner sheath.

Abstract: A protective sheath for a temperature sensing device for use in determining the temperature of molten metals. The temperature sensing device, such as a thermocouple, is encased in a molybdenum tube which is coated with successive porous layers of molybdenum, a plurality of layers of Al.sub.2 O.sub.3 --Cr.sub.2 O.sub.3 --Mo in a decreasing concentration of Mo in proceeding from the inner to the outer layers, and a layer of substantially pure Al.sub.2 O.sub.3 --Cr.sub.2 O.sub.3. The Al.sub.2 O.sub.3 --Cr.sub.2 O.sub.3 layer may be covered with an outer coating of a material, such as boron nitride, to protect the Al.sub.2 O.sub.3 --Cr.sub.2 O.sub.3 layer from attack by slag. Alternating layers of Al.sub.2 O.sub.3 --Cr.sub.2 O.sub.3 and boron nitride may be applied as outermost sacrificial layers.