NBSiC Thermocouple Protective Tube

Silicon nitride‑bonded silicon carbide (Si₃N₄‑bonded SiC) is a porous material that offers exceptional thermal shock resistance, making it particularly suitable for applications involving frequent furnace start‑up/shut‑down cycles and rapid temperature fluctuations. Its maximum continuous service temperature is 1450 °C, and it provides a cost‑effective solution for a wide range of medium‑ to high‑temperature heat‑treatment furnaces.

The material is produced by mixing silicon carbide grains with metallic silicon powder, which is then formed, dried, and dewaxed. The green body is sintered in a high‑purity nitrogen atmosphere at 1400–1500 °C. During this process, the SiC particles act as a skeleton, while the metallic silicon reacts in situ with nitrogen to form Si₃N₄ as the bonding phase. This nitride phase firmly encapsulates and bridges the SiC grains, creating an integral tubular structure. The process features very low shrinkage, high dimensional precision, and excellent production yield. The resulting tubes have moderate porosity, outstanding thermal shock resistance, and are well suited for high‑volume manufacture of thermocouple protection sheaths.

Si₃N₄‑bonded SiC protection tubes are widely employed in industrial processes that demand robust thermal‑shock performance, such as in batch‑type furnaces, continuous annealing lines, large‑scale sintering equipment, and ceramic kilns. They are also used in metal heat‑treatment, foundry, and other medium‑high temperature applications where cost and durability are key considerations. However, for atmospheres containing strong alkalis, aggressive molten salts, or molten zinc/lead, alternative protection schemes (e.g., double‑wall designs with alumina liners) must be applied to ensure reliable service life.

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