出现于β-A1_2TiO_5的固相合成及热分解过程中的待定归属相

STUDY ON THE NON-IDENTIFIED PHASE OCCURED IN SOLID-STATE SYNTHESIS AND THERMAL DECOMPOSITION PROCESS OF β-Al_2TiO_5

在由-αA l2O3和T iO2合成-βA 12T iO5时,文献报道有待定归属相(称作x相)先于-βA 12T iO5出现在煅烧后的混合物内,该x相表现出中间产物相特征,据说它在混合物内的含量随煅烧温度升高而增大,1 400℃时出现-βA 12T iO5,且x相与未转化反应物均转变成-βA 12T iO5。研究煅烧共凝胶法前驱体制备-βA 12T iO5的固相反应以及-βA 12T iO5的热分解过程,以了解该待定归属相的生成、演变规律。同文献报道的x相相比该相的初始生成温度、转化为-βA 12T iO5的温度均有明显降低,1 150℃煅烧共凝胶法前驱体所获产物的XRD图谱(18°≤2θ≤58°)内出现3个归属该x相的衍射峰,它们的峰中心分别位于2θ=41.2,°44.0,°24.9°(按相对峰强大小排列)。M gO掺杂使该x相与少量-βA 12T iO5相共同出现于1 150℃及1 200℃煅烧物内。1 250℃煅烧使该相失稳,转变为-βA 12T iO5,同时使未转化的金红石、-αA l2O3完成固相反应。对比表明x相的转变温度具有阈值特征,前驱体的微细化使之大大降低。本研究首次发现,伴随-βA 12T iO5在1 100℃下的热分解,该待定归属相重新出现,说明该相随热过程条件改变具有生成-消亡-重新生成的可逆性。它的消亡及重新生成体现出同-βA 12T iO5此消彼长的相关性。它应该是除-βA 12T iO5、A 12T i7O15以外的第三种铝、钛复合氧化物。

It has been reported that a non-identified phase had been determined from the sintered mixture prior to the forming of β-Al2TiO5 phase. This material disappered at a higher sintering temperature and showed an intermediate phase feature. In order to know the forming and changing behavior of the phase （denoted as x phase）,products calcined from monophase Al2O3TiO2 precursors at different temperatures and the thermally treated samples by sintering phase pure β-Al2TiO5 at 1 100℃ have been studied. Compared with the x phase reported,the forming temperature of the phase from Al2O2-TiO2 precursors evidently lowered and so did its transforming temperature. Three XRD peaks at 2θ=41.2°,44.0°,and 24.9° have been discriminated to belong to the phase from the patterns of the samples calcined the precursors at 1 150 ℃. This phase coexisted with β -Al2TiO5 in MgO doping samples calcined at 1 150 ℃ and 1 200 ℃,separately. By a calcining of 1 250 ℃ the x phase has been destabilized and transformed into β-Al2TiO5,and the solid-state reaction between unreacted α-Al2O3 and rutile residue has been fulfilled,too. Fine precursor shows a clearly lowered x phase trasforming temperature,suggestted that the temperature is of threshold characteristic. Reappearing of the phase in partly decomposed β-Al2TiO5 has been noticed by this study,demonstrated an appearing-trnsforming-reappearing feature of the x phase resulted from thermal condition change and confirmed its reversibility. It has been seen that decline of the phase accompanied with growth of β-Al2TiO5 when raising calcining temperature, and vice versa in thermal treatment of β-Al2TiO5. It is likely that this non-identified phase should be a new Al-Ti-O composite oxide except β-Al2TiO5 and Al2Ti7O15.