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

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In this study, the effect of nano-titania addition on the mechanical strength of mullite-bonded alumina-siliconcarbide nano-composites was investigated. To this end, the gel-casting process via nano-silica sol was used for shaping the nano-composite.The firing temperature of composition was determined by use of STA. The compressive and bending strengths of samples were measured after firing at 1300 °C. Besides, the physical properties, phase composition and microstructure of the composites were evaluated after firing. The results showed that the use of nano-titania up to 1 wt.% had a higher effect on improvement of nano-composite mechanical strength. The nano-titania addition led to increasing of mullite phase and higher growth of its needle-like grains. Enhancing of ceramic bonds between grains and the improvement of mechanical strength were obtained by increasing the mullite phase.

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In this study, the composition of magnesium aluminate spinle and the converter mud were used as raw materials to in-situ formation of hercynite phase in magnesite-hercynite refractory bricks. The pressed samples were sintered at 1400 and 1500℃ and then, the phase composition of bricks was evaluated after firing at 1400℃. Besides, the effect of nano-magnesia particles addition on the properties of magnesia-hercynite refractory bricks was examined. Hence, the physical peroperties, thermal shock resistance and microstructure of refractory bricks were evaluated. The phase composition results showed that hercynite is well-formed in the refractory matrix, which leads to bonding formation and its increase between magnesia particles. The evaluation of results indicated that the addition of nano-magnesia particles can reduce the porosity of brick via increasing particles packing. In this relation, 1 wt. % nano-magnesia addition was determined as optimum content. Further addition of nano-magnesia leads to increasing of porosity via agglomeration of particles. Due to the high surface area of used nano-magnesia particles, the adequate sintering of refractory brick containing nano-magnesia take places at 1400℃. This leads to increasing of particles bonding and then, increasing mechanical strength, but it can not affect the thermal shock resistance of refractory bricks. The microstructural evaluations showed the lower porosity and further particles bonding with addition of nano-magnesia optimum content.