期刊
PHASE TRANSITIONS
卷 93, 期 6, 页码 596-605出版社
TAYLOR & FRANCIS LTD
DOI: 10.1080/01411594.2020.1765245
关键词
Alumina nanoparticles; annealing; Al-27-MAS NMR; Al-O speciation; transition alumina phases
资金
- Council of Scientific and Industrial Research, New Delhi, India
Alumina nanoparticles were synthesized by thermal dehydration of Al(OH)(3) (gibbsite), which shows the sequential formation of AlOOH (bohemite), gamma, delta, theta, and alpha-alumina phases upon heat treatment in the temperature range: 150-1150 degrees C. Alumina nanoparticles were characterized by X-ray diffraction and Al-27 MAS-NMR studies to investigate the structural transitions, in particular, the changes in Al-O speciation as a function of heat treatment. gamma-alumina is produced by annealing bohemite at 400 degrees C, and transforms into alpha-alumina via the formation of delta and theta-alumina as the intermediate phases. The formation of theta and alpha-alumina starts at 1020 degrees C and the concentration of these phases increases upon annealing at 1100 degrees C, while the concentrations of gamma and delta-alumina decreases steadily. The heat treatment at 1150 degrees C produces alpha-phase (84%) and the remnant theta-phase (16%). Al-27 MAS-NMR revealed the existence of two types of Al-O speciation i.e. AlO4 and AlO6 structural units whose relative concentration depends upon the transition alumina phases.
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