Silicothermal synthesis and densification of x-sialon in the presence of metal oxide additives |
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| Affiliation: | 1. Department of Materials Science and Engineering, Anadolu University, Iki Eylul Campus, 26550 Eskisehir, Turkey;2. Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany;3. Science Consulting International, Niersteinerstr. 1, 70499 Stuttgart, Germany;1. Key Laboratory of Liquid-Solid Structure Evolution and Processing of Materials, Ministry of Education, School of Materials Science and Engineering, Shandong University, Jinan 250061, PR China;2. Shandong Provincial Key Laboratory of Engineering Ceramics, School of Materials Science and Engineering, Shandong University, Jinan 250061, PR China;3. Normal college, Shihezi University, Shihezi 832003, PR China;1. School of Materials Science and Engineering, Nanchang Hangkong University, Jiangxi Province, 330063, PR China;2. Department of Mechanical Engineering, Jiangxi Technical College of Manufacturing, Jiangxi Province, 330095, PR China;1. Materials Science and Nanotechnology Program, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand;2. School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand;3. Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand;4. Nanotec-KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Khon Kaen 40002, Thailand |
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| Abstract: | The effect is reported of seven inorganic oxide additives on both the formation mechanism and the densification of X-sialon prepared by a silicothermal process. The oxides were added to the starting mixture of halloysite clay, alumina and elemental silicon at a level of 1 wt% of the calculated final product, and fired in nitrogen at 1200–1500°C. The formation of X-sialon was monitored by thermal analysis, powder XRD and 27Al and 29Si solid state MAS NMR. The effects of the additives are temperature dependent, and influence the various stages of the reaction by differing degrees. The oxides which best promote the formation of crystalline X-sialon (Y2O3, CaO and MgO) are also those which facilitate the conversion of initially-formed Si3N4 to SiO2N2 and SiO3N units, the latter being particularly enhanced by Y2O3, Fe2O3 enhances the initial nitridation of Si but suppresses X-sialon formation by stabilising the preceding mullite phase. Densification is most enhanced by Y2O3, CaO and CeO2; MgO exerts its maximum effect on sintering at lower temperatures. The beneficial influence of MgO and Y2O3 on both X-sialon formation and sintering is due to the formation of liquid phases. |
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