XRD patterns of samples sintered at

XRD patterns of samples sintered at various temperatures are displayed on Fig. 3b. At 125°C, small broad peaks are evidenced which are the first signature of the genesis of a crystallization phenomenon. Above this temperature, from 150°C to 400°C, the peak intensity increases progressively up to 400°C with sharper peaks, indicating that crystallization has continued and/or that crystal size increases with sintering temperature. As a confirmation, crystallite sizes, obtained from Scherrer equation applied to XRD FWHM data indicate an average size evolution from 3 nm to 18 nm for sintering temperatures of 150 and 400°C respectively. He pycnometry measurements, along with XRD patterns, indicate that the formation of boehmite progressively occurs from 150 to400°C from the amorphous Al(OH)3, 0.5H2O powder, both visible in the XRD peak width and skeletal density increase. Since the only phase forming during sintering is AlOOH (having a theoretical density of 3.05 g.cm−3) and skeletal density for samples sintered in the range 150°C ~T ~380°C is progressively increasing, still below that of AlOOH, it means they are composed of mixed amorphous Al(OH)3 and crystallized AlOOH. This progressive evolution from amorphous to crystallized phase occurring up to 400°C allows producing samples with mixed composition of controlled crystallinity.This is an important asset of the present work since the preparation of mechanically coherent boehmite pellet is made difficult due to the layered structural nature [27], making it brittle. Thus,the resulting pellets after sintering most often break, by delamination, due to pressure release. This is why a careful slow pressure release is necessary to preserve the mechanical cohesion of the sample. In the case of samples sintered at temperatures lower than 400°C leading to a partial crystallization of the sample permits the preparation of cohesive samples. It appears that the presence of an amorphous phase allows for a stress absorption in the sample, and therefore allows to prepare cohesive samples.