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Factors affecting the microstructure and properties of nitrogen-carbon bonded silicon carbide products
- Aug 17, 2018 -

In general, the microstructure of the nitrogen-carbon bonded silicon carbide article obtained by the reaction sintering mainly depends on the layout of the silicon carbide particles in the green body formed by the reaction of the silicon powder with nitrogen. In the nitrogen-carbon bonded silicon carbide product, silicon nitride exists in two main forms, namely low temperature type α-Si3N4 and high temperature type β-Si3N4. Usually we consider both the alpha phase and the beta phase crystal structure as a hexagonal system.

 

In fact, in the nitrogen-carbon bonded silicon carbide product, α-Si3N4 is fibrous, mainly formed by the gas phase. The α-Si3N4 fibers are interlaced to form a dense network structure and thus have higher mechanical properties. β-Si3N4 is generally in the form of coarse particles or short rods. There is almost no change in the body during the nitriding process, and the formation of Si3N4 by the reaction of Si with N2 will make the structure of the article more compact.

 

So, what factors affect the performance of nitrogen-carbon bonded silicon carbide products? It should be known that the nitriding reaction of silicon powder is an exothermic reaction, and the reaction rate should be strictly controlled in the middle and high temperature nitriding stage. Otherwise, the speed is too fast, which may affect the further penetration of nitrogen into the green body, resulting in incomplete reaction and more residual silicon, thereby deteriorating material properties. The nitridation reaction rate of silicon mainly depends on the diffusion rate of nitrogen, and the diffusion rate of nitrogen has a certain relationship with temperature.

 

Normally, as the temperature increases, the rate of reaction increases. At the same temperature, the nitriding rate is in parabolic relationship with time. Therefore, if the nitriding temperature is too low, the reaction is greatly slowed down so that the reaction is incomplete. Therefore, in order to ensure the performance of nitrogen-carbon bonded silicon carbide products, it is necessary to strictly control the heating rate while ensuring the purity of nitrogen. The purity of nitrogen should be above 99.99%.

 

In general, factors affecting the properties of nitrogen-carbon bonded silicon carbide products include many aspects such as raw material particle size, purity, particle gradation, nitrogen purity, final reaction temperature, and amount of silicon powder added. Moreover, the influence of the size and content of silicon carbide particles on the toughness and strength of nitrogen-carbon bonded silicon carbide products is also very obvious.http://www.hshightec.com/