Boron nitride-boron carbide-graphite composite heating element used for high temperature electric heating

Abstract

The invention discloses a boron nitride-boron carbide-graphite composite heating element used for high temperature electric heating, which is composed of a graphite matrix, a boron carbide intermediate layer coated on the outer surface of the graphite matrix and a boron nitride surface layer coated outside the boron carbide intermediate layer. The profile of the graphite matrix can be designed and treated according to the requirements of the electric heating equipments, the graphite matrix requires high temperature pretreatment; the boron carbide intermediate layer is coated on the surface of the graphite matrix, the thickness is 0.02-1mm, and the boron carbide intermediate layer can be prepared by chemical vapor deposition; the boron nitride surface layer is coated outside the boron carbide intermediate layer, and the thickness is 0.1-10mm, and the boron nitride surface layer is prepared by chemical vapor deposition. The boron nitride-boron carbide-graphite composite heating element can realize the electric heating requirements under the temperature of 2000-2800 DEG C, and has the advantages of stable electrical resistivity of the heating element, long usage life, accurate temperature control and less high temperature environmental pollution.

Description

technical field [0001] The invention relates to a boron nitride (BN)-boron carbide (BN) for high temperature electric heating 4 C) - graphite composite heating element, which belongs to the technical field of high temperature heating elements. Background technique [0002] In recent years, with the development of high-temperature materials, especially the development of ultra-high-temperature ceramics and Si-B-C-O-N materials, materials need to be synthesized and sintered at higher temperatures (2000°C-2800°C). Characterization and testing of performance and service performance, such as differential thermal gravimetric research of precursors, testing of thermal expansion coefficient and thermal conductivity, testing of high-temperature mechanical properties of materials, etc. The preparation and testing of these materials require equipment that can accurately control A heating device with a uniform temperature field and no gas pollution. At present, the heating methods of t...

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Problems solved by technology

When the temperature is higher than 1600°C, the quartz coating will undergo a carbothermal reduction reaction with the graphite material, and gaseous SiO will be volatilized or SiC and other substances will be generated, making the thermal expansion coefficient of the surface coating uneven and the resistivity of the heating element unstable. And it will lead to a decrease in the density of the coating

When the temperature is higher than 1800°C, the quartz coating melts, so the quartz coating cannot meet the requirements of the super high temperature heating element surface coating

Therefore, the existing graphite surface coating and modification technology cannot meet the needs of graphite heating elements used at 2300°C-2800°C. The main problem is that the graphite coating will interact with the oxides in the surface coating at high temperatures. reaction, leading to coating failure

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