Journal
CERAMICS INTERNATIONAL
Volume 45, Issue 17, Pages 22829-22840Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2019.07.325
Keywords
Coal gangue; Coal-coke powder; CRN reaction; Fusible components; beta-SiAlON
Categories
Funding
- National Natural Science Foundation of China [21506121, U1610254]
- key scientific and technological project of Shanxi province [MC2014-06]
- China Scholarship Council
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The synthesis of SiAlON materials by the carbothermal reduction-nitridation (CRN) method paves the way for utilization of coal gangue with significant economic benefits. Excessive carbon (C), which provides a high residual C content in the product, is added to the raw materials to ensure a high yield of SiAlON. The industrial solid waste of coal-coke powder is used as a reductant. In this study, the effects of the reducing environment and C content on the CRN reaction of coal gangue using corundum and graphite crucibles are investigated and a method to reduce the amount of C added to the raw materials is proposed. The process is carried out under a N-2 flow in the range of 1300-1500 degrees C with a holding time of 3 h. The effects of fusible components including CaO, Fe2O3, and MgO on the CRN reaction and micromorphology are discussed. The graphite crucible considerably promotes the conversion of mullite to beta-SiAlON and is effective for the reduction in residual C content in the product. When the graphite crucible is used, the mullite wholly transforms to beta-SiAlON and corundum, and beta-SiAlON and AlN at 1400 degrees C when the C contents in the raw materials are 11% and 18%, respectively. The content of residual C in the product is approximately 1% (or lower). The beta-SiAlON content decreases with the additions of CaO and MgO in the raw materials owing to sintering and melting. The addition of Fe2O3 promotes the formation of beta-SiAlON whiskers according to the vapor-liquid-solid mechanism. These results would be useful in parameter optimization for a cleaner production of beta-SiAlON powder using the CRN method.
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