2 PHASE REFINEMENTS OF THE STRUCTURES OF ALPHA-SI3N4 AND BETA-SI3N4 MADE FROM RICE HUSK BY RIETVELD ANALYSIS

The crystalline structures of alpha-Si3N4 and beta-Si3N4 made from rice husk were obtained at room temperature (300 K) from X-ray powder diffraction with CuK alpha radiation using Rietveld analysis for the two phase mixture. For alpha-Si3N4 at 300 K, crystal data: Mr = 140.285, the rhombohedral system, P31c, a = 7.7650(4) Angstrom, c = 5.6275(2) Angstrom, V = 293.85(2) Angstrom(3), Z = 4, Dx = 3.1709 g cm(-3), mu = 133.474 cm(-1) (lambda = 1.5406 Angstrom), F(000) = 280.0, the structure was refined with 29 parameters to R(b) = 2.42%, R(f) = 1.78% for 243 peaks. For beta-Si3N4 at 300 K, crystal data: Mr = 140.285, the hexagonal system, P6(3)/m, a = 7.6093(8) Angstrom, c = 2.9079(2) Angstrom, V = 145.81(2) Angstrom(3), Z = 2, Dx = 3.1951 g cm(-3), mu = 134.492 cm(-1) (lambda = 1.5406 Angstrom), F(000) = 140.0, the structure was refined with 17 parameters to R(b) = 3.02%, R(f) = 1.88% for 145 peaks. The whole diffraction was fitted and refined with 46 parameters to R(wp) = 6.98%, R(p) = 5.33% for 3301 step intensities and 'goodness of fit' S = 3.50.