Mechanism Of The High-temperature Reaction Of Al₂O₃-Si System Materials In Different Atmosphere

In recent years, nonoxide Refractory has become the focus on the field of refractory and led the developing trend of the new refractory in the future. In all members of Non-oxide Refractory, Sialon has been paid more attention due to its excellent performances. At present, there are mainly two ways to produce Sialon refractory. One way is the hot-pressing process using chemical starting materials, and another is Carbothermal Reduction and Nitridation process using natural starting materials. Both ways have Al₂O₃ and Si as the main contents in the above starting materials. In this paper, we made thermodynamic calculation on the possible reactions of Al₂O₃-Si system in pure N2 atmosphere and C-immerging condition. According to AlN-Al₂O₃-Si₃N₄-SiO₂ phase diagram, four groups of samples, whose starting materials is corundum and industrial Si in the different ratio, fired at five temperature points of 1400℃,1450℃, 1500℃,1550℃and 1600℃in pure N2 atmosphere and C-immerging condition, respectively. By using XRD analyzing technique, phase constitutions of the fired samples have been detected. Such important issues as influence of formula and synthesized temperature on synthesis are investigated. Hence the related dynamic mechanism of Al₂O₃-Si system Sialon has been tentatively explained. The following results can be included from this research.In the Samples which are the high-temperature synthesized in highly pure N2 atmosphere. Besides the phases of Al₂O₃ and Si which come from the start materials, the mainly synthsised phases areβ-Sialon and Si₃N₄. The value of Z of the new phaseβ-Sialon(Si6-ZAlZOZN8-Z,02O₃ are respectively nitridated to Si₃N₄ and AlN, and both of which then react with Al₂O₃ to synthesizeβ-Sialon.In the Samples which are high-temperature synthesized in the C-immerging condition, besides phase Al₂O₃ and Si which come from start materials, the mainly synthsised phases are SiC and OËŠ-Sialon, otherwise there is the existing phase of SiO₂ in the samples which are synthsised at lower temperature point (1400℃and 1450℃), and there is the existing phase of X phase in the fired samples which are synthsised at higher temperature point (1500℃, 1550℃and 1600℃). In the C-immerging condition, the synthsising mechanism of new phases is that Si is nitridated to Si₃N₄, or Si is reacted with CO to produce SiO₂ and SiC. Then SiC and Si₃N₄ is transformed to Si₂N₂O, respectively. Meanwhile, Al₂O₃ and Si₂N₂O synthesized to form solid solution OËŠ-Sialon. As the fired temperature increased, the phase of Al₂O₃ will be further...