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Abstract

[0081] A thermocouple lance for measuring temperatures in molten metals has a protective sheath of multi-layered structure that makes it possible to improve the life expectancy of repetitive measuring devices. The thermocouple lance has a protective sheath with one closed end and one opened end wherein porous heat-resisting ceramic filler is compacted. Embedded in the filler is a pair of W--Re alloy wires dissimilar in their composition from each other. The protective sheath has a layered structure made from cermet layers each having a molybdenum matrix and other layers of at least one boundary layer selected from the class consisting of C, MgO, CaO, Al.sub.2 O.sub.3 and ZrO.sub.2, the cermet layers and boundary layers overlapping each other in alternate layers. At least the outermost shell layer of the protective sheath is made of a cermet layer composed of any one of Mo--ZrN, Mo--ZrB.sub.2, Mo--ZrO.sub.2, Mo--ZrC and composite thereof. In one embodiment, a protective sheath is composed of layers in which are embedded filaments oriented predominantly in the circumferential direction of the sheath, and boundary layers which are provided between confronting surfaces of any adjoining filament-embedded layers, the boundary layer being weaker in bonding power than the filament-embedded layers. The filaments are of carbon or ceramic whereby the protective sheath may be enhanced in strength against the tensile stress that will occur due to the temperature difference in the protective sheath.

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First Claim