SB拟薄水铝石焙烧产物的晶体结构特性及相转变

STRUCTURAL CHARACTERISTICS AND PHASE TRANSITION OF CALCINED SB PSEUDO-BOEHMITE

采用XRD、DTA、MAS NMR测定方法,对SB拟薄水铝石500至1200℃焙烧产物,特别是其中γ Al_2O_3、δ-Al_2O_3和θ-Al_2O_3代表性样品,有关晶体结构特性及变化情况进行了考察。提出了晶轴比a_(440)/C_(311)、400衍射对称度和400与440两衍射峰间距加宽值。对γ-Al_2O_3至δ-Al_2O_3再至θ-Al_2O_3相变过程的表征,发现在相变过程中,四方形晶体c轴逐渐加长的规律性。MAS NMR结果表明,上述相变过程及四方形晶体c轴逐渐加长的情况,应归因于晶格内部铝离子位置分布的变化。

The crystal structural characteristics and phase transition of SB pseudoboehmite (particularly with γ-Al_2O_3, δ-Al_2O_3 and θ-Al_2O_3 as representative samples) calcined at 500～1200℃ have been examined by means of XRD, DTA and MAS NMR. It is suggested that the crystal axes ratio a_(440)/C_(311), the symmetry of 400 diffraction peak and the increment of distance between 400 and 440 diffraction peaks can be uses to characterize the phase change for γ-Al_2O_3 to δ-Al_2O_3 and to θ-Al_2O_3. It has also been found that the regularity of tetragonal crystal c axis is elongated gradually during the phase change process. The results of MAS NMR illustrate that the phase change process and the elongation of tetragonal crystal c axis are due to the variation of aluminium ion distribution within the lattice.