| Aluminum titanate is one of the well-known thermal shock resistance materials with high melting point and low coefficient of expansion. However, it is thermal unstable and tend to decompose into TiO2 and corundum within the temperature interval of 750-1300°C. In order to overcome this drawback, great efforts have been devoted to add mineralizers, such as MgO, ZrO2 and V2O5, into the system to suppress the decomposition of aluminum titanate and improve its thermal stability. In this study, effects of MgO, ZrO2 and V2O5 mineralizers on decomposition crystalline phases, kinetics and properties of aluminum titanate are investigated. The crystalline structure of sintered samples was examined by X-ray diffraction (XRD). The content of crystalline phases was calculated by Rietveld quantification analysis. Microstructure of samples was examined by scanning electron microscope (SEM). The mechanical properties of specimens were measured by mechanical testing system. Mechanism and model of decomposition reaction were discussed to establish decomposition kinetic equation.The results show that a Al2-xMgx+yTii-yO5-0.5x-y solid solution is formed and the decomposition of Al2Ti05 is suppressed by adding MgO into Al2TiO5, resulting in the improvement of its thermal stability as well as the increase in bending strength and bulk density of Al2TiO5. The content of Al2Ti05 decreases with increase in decomposition time (except for 900°C). The decomposition rates at different temperatures are in the sequence of 1100℃> 1000°C >1200°C>900°C. The decomposition reaction is a chemical-reaction-controlled step, which is in accordance with the kinetic equation of first order reaction:F(G)= [(1-G)-2/3-1]= Kt. The kinetic equations of decomposition reaction at 900℃,1000 ℃,1100 ℃ and 1200℃ are (1-G)-2/3-1=2.20×10-4t; (1-G)-2/3-1=9.58×10-4t; (1-G)-2/3-1=1.30×10-3t; (1-G)-2/3-1= 9.30×10-4t, respectively.The addition of ZrO2 in Al2Ti05 leading to the formation of Al2-xMgx+yTi1-y05-1.5x-y solid solution, which suppresses the decomposition and improves the thermal stability of Al2TiO5 as well as the increase in bulk density and decreases in porosity of Al2TiO5. The content of Al2Ti05 decreases with increase in decomposition time (except for 900℃). The decomposition rate of Al2Ti05 with additive ZrO2 is larger than that with MgO addition. The decomposition rates at different temperatures are in the sequence of 1200℃> 1100℃ >1000℃> 900℃ from 6 h to 11 h and 1100℃>1200℃>1000℃> 900℃ from 11 hto 18 h,respectively. The decomposition reaction is a chemical-reaction-controlled step,which is in accordance with the kinetic equation of first order reaction:F(G)=[(1-G)-2/3-1]=Kt(or F(G)=(1-G)-2/3-1=Kt-9.82 x10-3).The kinetic equations of decomposition reaction at 900 ℃,1000℃,1100℃ and 1200℃are(1-G)-2/3-1=7.72×10-4t-9.82 ×10-3;(1-G)-2/3-1=1.32×10-3t；(1-G)-2/3-1=2.72×10-1t;(1-G)-2/3-1=1.76×10-1t,respectively.Addition of V2O5 into A12Ti05 form a stable liquid phase at 670℃,which promotes the sintering and increases bulk density of samples.However,V205 takes no effect on suppressing the decomposition of aluminum titanate.The decomposition rates at different temperatures are in the sequence 1100℃>1200℃>1000℃>900℃from 6 h to 11 h and 1100℃>1000 ℃>1200℃>900℃ from 11 h to 18 h.The kinetic equation can not be established because the aluminum titanate is totally decomposed at 1100℃.The decomposition reaction is a chemical-reaction-controlled step,which is in accordance with the kinetic equation of first order reaction:F(G):(1-G)-2/3-1=Kt.The kinetic equations of decomposition reaction at 900 ℃,1000℃ and 1200℃ are,(1-G)-2/3-1=2.63×10-3t;(1-G)-2/3-1=0.8-1t;(1-G)-2/3-1=0.40t,respectively.The SEM results show that aluminum titanate is in the shape of irregular multi-face,while α-Al2O3 deformed hexagonal sheet and rutile fine acicular or long columnar. |
PDF Full Text Request