Journal of Advanced Materials in Engineering (Esteghlal)

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In this study, the effect of different amounts of Y2O3 on the properties of mullite-zirconia composites was investigated. For this purpose, these composites were fabricated by reaction-sintering of alumina and zircon as raw materials. Besides, the slip casting method was used for forming these composites, and sintering process was carried out at 1600 °C. Then, the physical and mechanical properties, phase composition and the microstructure of these composites were investigated. The results showed that yittria addition up to 0.5 wt.% has no effect on the properties of these composites. Besides, addition of more than 0.5 wt.% yittria formed solid solution with zirconia grains and led to stabilization of tetragonal zirconia phase and increasing of its amount. Hence, yittria addition increases the hardness and bending strength of composite by stabilizing tetragonal zirconia phase and then, decreasing the micro-crack formation during zirconia phase transformation. As results show, addition of 0.75 wt.% yittria leads to a considerable increase in the bending strength.

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In this paper, the effect of MgCl2 addition on the kinetics of MA spinel formation was investigated. For this purpose, the stoichiometric mixture of MgCO3 and calcined aluminum was calcined at 1100 °C for 1 hr. Then, the calcined composition was wet-milled and after addition of 6% MgCl2 the compositions were pressed and fired at 1300 and 1500 °C for different times. Spinel phase content was determined using semi-quantitative phase analysis. With regard to Jander's equation, the rate constant was calculated, and the activation energy was obtained from Arrhenius equation. The results showed that the addition of MgCl2 leads to the acceleration of the spinel formation reaction. Besides, 55.71 Kcal/mol as the activation energy was calculated for the composition containing 6 wt.% MgCl2 compared with 93.06 Kcal/mol for the composition without MgCl2.

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In this study, the effect of different amounts of Y2O3 on the properties of mullite-zirconia composites was investigated. For this purpose, these composites were fabricated by reaction-sintering of alumina and zircon as raw materials. Besides, the slip casting method was used for forming these composites, and sintering process was carried out at 1600 °C. Then, the physical and mechanical properties, phase composition and the microstructure of these composites were investigated. The results showed that yittria addition up to 0.5 wt.% has no effect on the properties of these composites. Besides, addition of more than 0.5 wt.% yittria formed solid solution with zirconia grains and led to stabilization of tetragonal zirconia phase and increasing of its amount. Hence, yittria addition increases the hardness and bending strength of composite by stabilizing tetragonal zirconia phase and then, decreasing the micro-crack formation during zirconia phase transformation. As results show, addition of 0.75 wt.% yittria leads to a considerable increase in the bending strength