H. Rahier et al., Influence of the degree of dehydroxylation of kaolinite on the properties of aluminosilicate glasses, J THERM ANA, 62(2), 2000, pp. 417-427
The degree of dehydroxylation of kaolinite, D-TG and D-IR, respectively, is
characterized by thermogravimetric analysis (TG) and Fourier transform inf
rared spectroscopy (FTIR). The relation between DTG and DIR based on the in
frared absorptions at 3600-3700, 915, 810, and 540 cm(-1) is established. T
hree regions can clearly be distinguished: the dehydroxylation region (D-TG
<0.9), the metakaolinite region (0.9 <D-TG<1) and the 'spinel' region (D-TG
=1). The effect of the degree of dehydroxylation of kaolinite on the amount
of reactive material is measured by the reaction enthalpy, DeltaH, of the
low-temperature reaction of the dehydroxylated kaolinite with a potassium s
ilicate solution using differential scanning calorimetry (DSC). |DeltaH| in
creases almost linearly with DTG in the dehydroxylation region. In the meta
kaolinite region, DeltaH and thus the amount of reactive material, becomes
constant. |DeltaH| is sharply decreasing when metakaolinite transforms into
other phases in the 'spinel' region. No significant differences in the rea
ctivity of the dehydroxylates is detected with DSC. According to FTIR, the
use of partially dehydroxylated kaolinite is not influencing the molecular
structure of the low-temperature synthesized aluminosilicates, but residual
kaolinite is retrieved as an additive.