Ferroboron nitriding

Figure 7.30 SEM images of particles of products of ferroboron nitriding with addition of 10% of amorphous boron (a-d) outer part of the combusted sampie.

Combustion of Ferroboron in Nitrogen and Synthesis of Boron Nitride... 

Figure 7.29 SEM images of original ferroboron particles (a) and products of nitriding with a stopped combustion front (quenched) (b).

The microstructure of products of ferroboron combustion in nitrogen has various morphological forms. At the same time, a significant difference is visible in shape of particles of external and central parts of the burned sample. The presence of amorphous boron in the original material influences the process of nitride formation because (according to XRD analysis) amorphous boron contains boric acid which decomposes during combustion forming boric anhydride and water. 

The results obtained by [2001War] showed that complete nitridation of ferroboron precmsor in a mixture of NH3 + H2 under ambient pressure with BN formation can be achieved at 400°C with 20 vol.% NH3. The nitrided product consists of amorphous BN, Fe and metastable Fe nitrides. An alternative route using 100 vol.% N2 is also possible, but a higher reaction temperature (>1430°C) is needed. The product from the high temperature route contains partially crystallized ABN, Fe and virtually no metastable Fe nitrides [2001War]. 

War] Warner, T, Liu, C., Fray, D.J., Synttiesis of Boron Nitride from Ferroboron Part I -Nitriding , Mater. Sci. Technol, 17(9), 1039-1044 (2001) (Experimental, Calculation, Phase Relations, 17)... 

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