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The Research on Preparation Technology and Sintering Behavior of Rare Earth Aluminates (Dy3Al5O12、 NdAlO3、LaAl11O18)

Author: WeiMiao
Tutor: ChenShaOu
School: Qingdao University
Course: Condensed Matter Physics
Keywords: rare earth aluminate sol-gel method coprecipitation method sintering behavior
CLC: TB383.3
Type: Master's thesis
Year: 2011
Downloads: 13
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Abstract


with garnet structure, NdAlO3 with perovskite structure and LaAl11O18 with plumbite structure are three kinds of the rare earth aluminates used widely in the industrials, especially composited with Al2O3, however there are few papers reported about their preparation and sintering behaviors. Therefore, the present paper paid attention to prepare DAG and NdAlO3 using sol-gel method and studied the influences of sintering temperature and dwell time on powder particle size. Furthermore, the sintering behavior of samples will provide guidance for rare earth aluminates to synthesis composite ceramics with alumina. We prepared LaAl11O18 with the higher melting point by sol-gel and coprecipitation methods respectively and compared the advantages and disadvantages of the two methods, in order to provide guidance for preparing pure phase aluminates.The pure-phase DAG powder was obtained at 900℃with a dwell time of 2 hours by sol-gel method and the average grain size for the powder was calculated to be about 30-50 nm. The sintering behavior proved that sintered compact was not in high densification. the average line expansion coefficient of green compact and sintered compact were 9.55×10-6/℃and 9.59×10-6/℃respectively. We adopted Arrhenius formula to calculate the sintering activation energy for DAG, the result were 92.81kJ/mol and 87.06kJ/mol respectively on the basis of shrinkage and relative density.The pure-phase NdAlO3 powder was obtained by sol-gel method through sintering at 850℃with a dwell time of 2 hours. The average size of particle obtained below 1100℃was about 500nm, which was calculated by laser particle analyzer. Then by studying sintering curves, it was found that the shrinkage of the NdAlO3 sample began at 989℃, and the maximum shrinkage ratio was 24.31%. The average line expansion coefficients of green and sintered compact were 11.18×10-6/℃and 11.4x10-6/℃respectively. Based on the sintering curves, the sintering activation energy cumulated by Arrhenius fitting method for NdAIO3 were 86.71 kJ/mol on relative shrinkage ratio and 126.7kJ/mol on relative density ratio apart.Using the sol-gel and coprecipitation methods, the pure-phase LaAl11O18 powders were obtained after sintering at 1500℃with a dwell time of 2 hours. The sintered powders prepared by the two methods were all needlelike, however there are different powders sizes which are 2μm length and 0.5μm diameter originated from the sol-gel method, at the same time observing serious reunion phenomenon in the powders, and 1μm length and 0.25μm diameter originated from the coprecipitation method, simultaneously appearing good dispersion.

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