SYNTHESIS AND THERMOGRAVIMETRIC ANALYSIS OF AMORPHOUS BOEHMITE FIBERS

Amorphous fibres of boehmite Al=O [GRAPHICS] are synthesised using an electrochemical surface oxidation reaction of an amorphous Al plate in open air at room temperature. The microstructure es of the samples, m easured at selected periods of time of reaction, demonstrate a very ra pid growth in the separated fibres with a highly exothermic reaction. Two broad haloes occur in the X-ray diffractogram of the sample, at sc attering vectors k(1) = 25.5 nm(-1) and k(2) = 6.3 nm(-1), intrinsic t o amorphous solids. Thermogravimetric analysis together with infrared studies determine the chemical composition of the sample to be AlO(OH) . xH(2)O, with x approximate to 0.25. The water in this example is hy drogen bonded with the AlO(OH) molecule in a particular fashion so tha t they form a correlated structure at molecular scale. As a result, it s controlled thermal desorption at 320 to 350 K modifies the 2AlO(OH) --> Al2O3 + H2O thermal desorption transformation, which occurs at sub sequently higher temperatures. The presence of the hydrogen bonding is clearly evidenced by a significantly modified (lowered) value for the symmetric or asymmetric stretching vibration frequency of the [GRAPHI CS] group in the IR spectrum at 1022 or 1125 cm(-1) in comparison to 1 070 or 1150 cm(-1) found for a gel derived boehmite sample. The OH fun ctional group in the AlO(OH) molecule exhibits three characteristic vi bration bands at approximate to 600, 1640 and 3460 cm(-1).