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• Main Authors: Shih-Chung Lin, 林世忠
• Other Authors: Hsing-I Hsiang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/83080749392747708634

碩士 === 國立成功大學 === 資源工程學系碩博士班 === 92 === This study used precipitation method to synthesize titania gel, and then the gels were aged for various time to get two kinds of titania: unaged and aged gels. Effects of the aging on the properties of gel powders (crystalline phase, thermal behaviors), anatase crystallite growth and anatase to rutile transformation in calcination were investigated in this study. The activation energy of anatase crystallite growth and anatase to rutile transformation were also calculated to know and explain the mechanisms. The crystalline phases of the gels with and without aging treatment were amorphous and anatase, respectively. Much larger amounts of H2O, OH-, and NH4+ existed in unaged gel than in aged gel. The amounts of H2O, OH-, and NH4+ in gel powders decreased with increasing aging time. Anatase of unaged gel powder owned faster crystalline growth rate and worse aggregation during calcination than that of aged gel powder due to the existence of much more amounts of OH- in unaged powder. The mechanism of anatase crystalline growth was controlled by oriented attachment. Anatase owned faster crystalline growth rate and lower activation energy of crystallite growth ( 50 kJ/mol ) for unaged gel powder. The temperature of anatase to rutile transformation was lowered and the mechanism of transformation was interface controlled. Amounts of OH- in gel powder decreased with increasing aging time. Therefore, the crystallite growth rate of anatase during calcination for aged gel powder was slower than unaged gel powder. Aging process decreased the extent of aggregation of powders after calcination. The rate controlled step for anatase crystallite growth was grain boundary diffusion. Activation energy of anatase crystalline growth ( about 200-250 kJ/mol ) for aged gel powder was higher than unaged gel powder. Based on the above results, pure and small crystallite size of anatase powder can be obtained by aging treatment due to the less aggregation and higher activation energy of anatase crystalline growth. The mechanism of anatase to rutile transformation was diffusion controlled.