T. Stanimirova et al., Thermal decomposition products of hydrotalcite-like compounds: low-temperature metaphases, J MATER SCI, 34(17), 1999, pp. 4153-4161
Synthetic hydrotalcite-like samples with composition [M-1-Al-2+(x)x(3+)(OH)
(2)](CO3)(x/2) . nH(2)O, where M = Mg, Ni, x = 0.25 and 0.33, n = 2x and 1.
5x, are studied by XRD, DTA, TG and IR spectroscopy after heating in the te
mperature interval 120-260 degrees C and rehydration in air and water. Stru
ctural models of the two metaphases obtained are proposed. Metahydrotalcite
-D (HT-D) is formed at 140-180 degrees C by the reversible dehydration of t
he interlayer. Metahydrotacite-B (HT-B) is formed at temperatures 240-260 d
egrees C as a result of the dehydroxilation of a part of OH groups of the b
rucite-like layer and inclusion of two oxygenes from the CO3-group in the s
ame layer. The HT-B has a specific crystal structure. Rehydration does not
restore the initial structural state but leads to the formation of a phase
(HT-B-r) characterized with increased thickness of the interlayer, high con
tent of water and a low temperature of dehydration. The properties of HT-B
depend on the ratio M2+:Al of the initial sample. The substitution Mg <----
> Ni does not influence the properties of the metaphases in the low tempera
ture region. (C) 1999 Kluwer Academic Publishers.