Pore structure and kinetics of the thermal decomposition of Al(OH)₃

Abstract

The isothermal decomposition of gibbsite (aluminum hydroxide) was studied under controlled, pure water vapor pressures from 50 to 3,000 Pa over the temperature range from 458 to 508 K; the effect of sample particle size was also investigated. The partial conversion to boehmite (AIOOH) and the subsequent formation of a p-transition alumina product phase were followed with respect to the reactor operating conditions. Nitrogen and water vapor adsorption measurements were used to evaluate the chemical kinetics of the formation of p-alumina in terms of an interface velocity, and to interpret the observed dependencies on temperature and water vapor pressure. An adsorption /decomposition model is presented for these kinetics. The interpretation is consistent with the observation that decomposition rate is inversely proportional to the square of the water vapor pressure. The apparent activation energy of 342 f 15 kJ/mol includes a water adsorption energy, as well as the chemical decomposition contribution of 260 * 20 kJ/mol.

Synthesis and photoactivity of anatase porous single crystals with different pore sizes

“…It can be seen that all samples show the type IV isotherm, which is consistent with the porous feature demonstrated by SEM micrographs. Desorption curves of samples exhibit the hysteresis loop of type E which can be attributed to the inkwell-type pore structure formed by the close-packed template spheres inside anatase crystal [21,22]. The PSCs exhibit relatively narrow pore size distributions (Fig.5), in agreement with the results observed from SEM images.…”

An Unreacted Shrinking Core Model for Calcination and Similar Solid-to-Gas Reactions

“…Candela and Perlmutter (1986) reported E = 260±20 kJ/mol as the activation energy for gibbsite decomposition, and this is reasonably consistent with the value presented by Stacey (1987), 272±12 kJ/mol. The E value estimated by Lopushan et al (2007) was 150±12 kJ/mol, obviously not in agreement with either previous study.…”

“…The calcination of gibbsite particles (75 µm) at 473K and different water vapour pressures (100-3200 Pa) was studied by Stacey (1987) conversions, respectively. Candela and Perlmutter (1986) estimated the value of n as -2 in their investigations conducted in pure water vapour atmospheres at pressures from 50 to 3000 Pa over a temperature range from 458 to 508K. The negative value of n means that increasing the water vapour concentration reduces the rate of gibbsite conversion.…”

The nature and impacts of fines in smelter-grade alumina

“…requires about 260 kJ of energy per mole of gibbsite [7]. In both cases, another 90-112 kJ of energy per mole of Al 2 O 3 is needed to lift the temperature to the electrolyte temperature at which it dissolves [6].…”