Protective tube for thermocouple and method of producing same

Details Protective tube for thermocouple and method of producing same Protective tube for thermocouple and method of producing same

1987-03-17

1989-01-10

Marcus, Stephen

Pipes and tubular conduits

Distinct layers

374139, 374208, 428 346, 501 97, H01L 3502

Patent

active

047966718

ABSTRACT:
A protective tube for a thermocouple for measuring the temperature of molten metal, comprising two layers, an inner layer being made of a silicon nitride or sialon ceramic having a bending strength of 50 kg/mm.sup.2 or more, a density of 90% or more based on a theoretical density and a thermal shock temperature .DELTA.T of 400.degree. C. or more, and an outer layer being formed on the silicon nitride or sialon ceramic and containing BN and SiO.sub.2. The silicon nitride of sialon ceramic comprises 70 weight % or more of Si.sub.3 N.sub.4 having 65 weight % or more of an .alpha.-phase content, 20 weight % or less of one or more oxides of elements of Group IIIa of the Periodic Table, 20 weight % or less of Al.sub.2 O.sub.3, and optionally 15 weight % or less of AlN or AlN solid solution, and the outer layer is composed mainly of BN-SiO.sub.2 -Al.sub.2 O.sub.3 -Y.sub.2 O.sub.3. This protective tube is produced by coating ceramic powder comprising BN and SiO.sub.2 before sintering. This protective tube can enjoy an extremely long life.

REFERENCES:
patent: 4430518 (1984-02-01), Nakajima et al.
patent: 4547470 (1985-10-01), Tanase et al.
patent: 4558018 (1985-12-01), Matsuhiro et al.
patent: 4568516 (1986-02-01), Alderborn et al.
patent: 4699890 (1987-10-01), Matsui
F. Lieneweg, "Handbuch der technischen Temperaturmessung", 1976, Verlag Vieweg, p. 199.
L. V. Kortvelyessy, "Thermoelement Praxis", Vulkan-Verlag, 1981, p. 211.

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