Bayerite thermal decomposition

The thermal decomposition of gibbsite was chosen to illustrate the application of modem instrumental and computing techniques to preparative controlled reaction rate methods for making reproducible catalysts or catalyst supports of high surface area at atmospheric pressure. Gibbsite is one form of aluminium trihydroxide, Al(OH)3, the other being the mineral bayerite [6]. The thermal decomposition of gibbsite is complex, and is influenced both by crystallite size and water vapour pressure. Two processes, which may overly under certain conditions, have been identified [7] ... 

Among the wide variety of the phases formed by the thermal decomposition of aluminum hydroxides we shall consider only alumina forms which derive from pseudoboehmite, boehmite and bayerite. Information about these structures is rather poor. With the exception of the spinel form (t -, y-), the species are mainly characterized by the dimensions of the unit cell and by some indications on their crystallographic system [20]. The structure of y-AbOs was considered as a tetragonal distorted spinel lattice (a superstructure with one unit cell parameter tripled in the case of 8-AI2O3) and is depicted by the formula A18/3 [ ] 1/3 O4, where [ ] is a cation vacancy. This formula is consistant with the constraints of stoichiometry and electrical neutrality. It is difficult to know the exact distribution of the cations in the octahedral or tetrahedral sites despite an abundance of work on this subject [21-23]. The 0-phase, isomorphous with... 

In the 1950s, de Boer and his co-workers (de Boer et al., 1954, 1956 de Boer, 1957) used a variety of techniques in their studies of the thermal dehydration of gibbsite and bayerite and a more detailed picture was obtained of the conditions under which the two decomposition routes were manifested. For example, it was shown that relatively well-crystallized boehmite could be produced by the treatment of gibbsite or bayerite in saturated steam at temperatures of c. 165°C. These and other findings provided qualitative confirmation that the formation of boehmite involved an intragranular hydrothermal transformation. 

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