Study of phase transformation of nano Al2O3 compacts derived by hydrolysis and subsequent thermal sintering of Al powders

Al2O3 compacts with various phases were prepared by hydrolysis and spark plasma sintering (SPS) process of Al powder. The bayerite (beta-Al(OH)(3)) phase was derived by hydrolysis of commercial Al powder with micron size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate nano powder into dense compacts with a rapid heating rate of about 100 degreesC per min. under the pressure of 50 MPa. After compaction in the temperature ranges from 350 degreesC to 1100 degreesC, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows the phase transition of AI(OH)(3) --> eta-Al2O3 --> theta-Al2O3 --> alpha-Al2O3 sequences. On the other hand, the bohernite experiences the phase transition from AlO(OH) to gamma-Al2O3 at 350 degreesC showing AlO(OH) --> gamma -Al2O3 --> delta-Al2O3 --> theta-Al2O3 --> alpha-Al2O3 sequences.