<i>In Situ</i> Synthesis of β-Sialon Powder from Fly Ash

Abstract

β-Sialon powder was synthesized by in-situ carbothermal reduction-nitridation process, with fly ash and carbon black as raw materials. The influence of raw materials composition on synthesis process was investigated, and the phase composition and microstructure of the synthesized products were characterized by X-ray diffraction and scanning electronic microscope. The carbothermal reduction-nitridation reaction process was also discussed. It was found that increasing carbon content in a sample could promote the decomposition of mullite in fly ash and the formation of β-Sialon. The β-Sialon could be synthesized at 1550°C for 6h by heating the sample with the mass ratio of fly ash to carbon black of 100:56. The β-Sialon as-received in this study existed as granular with an average particle size of about 2μm. The carbothermal reduction-nitridation reaction process consisted of the nitridation processes of mullite, SiO2and Al2O3in fly ash as well as the conversion process of X-Sialon to β-Sialon.

A Review on Preparation of Non-Oxides Materials from Fly Ash

“…However, the main crystalline phases of sample containing lower carbon were composed of Al 2 O 3 and SiC. During the synthesis process of SiC-mullite spheres via microwave carbothermal [8][9][10] all reported the synthesis of β-Sialon from fly ash via carbothermal reduction process. The synthesis temperature and holding time were usually chosen as 1350-1550°C and 6-9h, respectively.…”

“…The chemical reactions to synthesize SiC-AlN and SiC-mullite composites from fly ash under N 2 atmosphere via carbothermal reduction reaction are as follows [4]: During the synthesis process of β-Sialon (z=3) from fly ash under N 2 atmosphere, O'-Sialon (Si 1.83 Al 0.17 O 1.17 N 1.83 ) and X-Sialon (Si 3 Al 6 O 12 N 2 ) could be formed, the following chemical reactions may be occur [2,8]…”

“…SiC based composites and β-Sialon (Si 6-z Al z O z N 8-z , 0<z<4.2) display many outstanding properties such as high hardness and strength, excellent resistance to thermal shock, oxidation and corrosion, and have been attracted much attention [1][2][3]. Recently, SiC-AlN [4], SiC-Al 2 O 3 [5], SiC-mullite (Al 6 Si 2 O 13 ) [6,7], β-Sialon [8][9][10][11][12], have been prepared from fly ash via in-situ carbothermal reduction reaction, which can not only reduce the production cost of SiC and β-Sialon, but also provide a new approach of high value-added-value utilization of fly ash.…”