Nitrides reaction zone

Resistive Heating Combined with Reaction Zone. The simplest way to form nitride UFPs on a laboratory scale is to adopt the reactive gas condensation method with a resistive heating evaporator. UFPs of the Fe-N system were synthesized by evaporating iron from a tungsten basket heated to 1600-2300°C in NH gas pressure of 27 kPa (37). Crystalline phases of a-Fe, y-Fe including about 2.5wt% of nitrogen, and y -Fe4N depend on the NH3 gas pressure and the evaporation temperature. 

The dependence of combustion temperature and velocity for the Si-N2 system as a function of dilution with /3-Si3N4 powder is shown in Fig. 38. In this case, at constant gas pressure, remains constant and is equal to the dissociation temperature of silicon nitride, for dilutions up to 60 wt %. However, with increasing dilution, the combustion front velocity increases. Also, increasing the overall heat evolution, smaller dilution by nonmelted nitride powder promotes coalescence of liquid Si particles, leading to an increase in the average reactant particle size, as well as to formation of thin liquid Si films, which blocks nitrogen infiltration to the reaction zone (Mukasyan et al, 1986). The same effects were also observed for the AI-N2 and B-N2 systems (Mukasyan, 1994), which are characterized by dissociation of the final product in the combustion wave. 

I 1 Combustion Synthesis of Nitrides for Development of Ceramic Materials of New Generation 1.3.1.2 Role of Nitrogen Admission to the Reaction Zone... 

Fig. 8.1.2 Schematic model of nitriding zone of iron vapor and/or condensed iron particles in reactive plasma-metal reaction. (From Ref. 17, p. 412. with kind permission from The Japan Institute of Metals.)...

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