THERMAL-DESORPTION PROCESS OF WATER IN AMORPHOUS ALO(OH)CENTER-DOT-ALPHA-H2O FIBERS PREPARED BY AN ELECTROCHEMICAL METHOD

Amorphous fibres of similar to 30 mu m average diameter of AlO(OH).alp ha H2O, alpha less than or equal to 0.25, have been prepared by a spon taneous surface oxidation of AI-metal in air by an electrochemical rea ction method. These fibres present similar to 5.5 times lower value of the specific density (rho) than for the usual bulk sample obtained by the wet methods. The low rho = 0.17 Mg.m(-3) value is primarily the r esult of peculiarly modified interatomic and/or intermolecular distanc es (0.1 to 0.3 nm) in the fibres. On heating in a DTA (differential th ermal analysis) machine, the fibres desorb off the water, 2[AlO(OH).al pha H2O] --> Al2O3 + (2 alpha + 1)H2O, in two successive steps in two irreversible endothermic signals. The two signals appear at T-p simila r to 340 and 400 K in the DTA thermogram in heating the sample with th e heating rate of beta = 0.33 K.s(-1). Two distinct desorption signals also occur in the in-situ measurements of the thermograms in the ther mogravimetric analysis (TGA) or differential thermogravimetric analysi s (DTG). It has been found that the T-p varies with beta following a l inear ln(T-p(2)/beta) versus T-p(-1) Kissinger plot, whose slope Delta E/R (with R = 8.314 J.mol(-1).K-1 the gas constant) determines the va lue of the activation energy Delta E of the desorption process. A valu e of Delta E = 33.7 kJ.mol(-1) thus has been calculated from the plot for the prominent (the first signal) DTA thermogram. The results are d iscussed in correlation with the microstructure and the macroscopic an d/or microscopic properties.