State and forms of water in dispersed aluminum oxides and hydroxides.

The state and forms of water in dispersed aluminum oxides and hydroxides and products obtained during their treatment are investigated in this paper. It has been found that particles of dispersed aluminum oxides and hydroxides of various water forms are present on surface and in volume. Their classification based on the state of water and the values of Δ H of evaporation has been introduced: "surface-bound" water, "structural" water, and "single OH groups". For micron particles, the presence of predominantly "structural" water is exemplified for gibbsite (Al(OH) 3) and boehmite (AlOOH). For the defective structure of products of heat treatment of gibbsite in air at 250 and 800°С, a low dehydroxylation temperature and high values of Δ H of water evaporation have been found: 71.13 kJ/mol and 67.27 kJ/mol, respectively. For the γ-Al 2 O 3 nanopowder and the products of its treatment, the presence of "surface-bound", "structural" water, and water represented by "single OH groups" has been detected. It has been shown that the treatment of gibbsite or aluminum oxide in a supercritical aqueous fluid at a water/Al 2 O 3 molar ratio of less than 1.5 leads to the formation of tohdite 5Al 2 O 3 •H 2 O, the composition of which is characterized by a low content of structural water in the stable state over a wide temperature range. [Display omitted] • Temperature of reaction between steam and alumina determines the form of bound water. • Forms of water are classified as "surface-bound", "structural" and "single OH groups". • Density of the aqueous medium and water form determines the phase formed. • Products are bayerite, boehmite and todite, as well as γ-Al 2 O 3 and α-Al 2 O 3. • Exchange of oxide matrix with medium determines size and morphology of particles. [ABSTRACT FROM AUTHOR]