| Research Abstract |
Of many ceramic raw materials kaolin minerals, fibrous clay minerals (sepiolite and palygorskite) and zeolites (natrolite and laumontite) were investigated.
1. Kaolin minerals kinetic analysis of the dehydration of dickite was performed using TG data. A computer-system for analyzing a complex reaction kinetically was developed. Using this system, the dehydration of four dickite samples, different in crystallinity, was analyzed. As a result, it was found that the dehydration of this mineral consists of the lower temperature (290-630 ^ﾟC) - and the higher temperature (520-780 ^ﾟC) reactions, of which activation energy and reaction mechanism are 126-164 KJ/mol, diffusion process, and 210-260 KJ/mol, first order or phase boundary reaction, repectively. Further, it was recognized that the (W_A/W_B) ratio has a positive or negative relationship to the crystallite size of the sample. Here, W_A : the dehydration amount in the lower or higher temperature region, W_B : the total dehydration amoun
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2. Fibrous clay minerals Two-step dehydration of bound water of sepiolite was studied in detail by variuos analytical techniques, giving the results that the first step dehydration is controlled by the water separation process from the Mg atoms at the edges of channels, while, after the folding of sepiolite crystals, the rate is determined by the water diffusion process in the folded channels. It was confirmed that palygorskite dehydrates essentially in three steps, not in four steps.
3. Zeolites (1) The dehydration mechanism of natrolite and its K-exchanged form was studied, with the results that the dehydration in natrolite proceeds at a constant rate in a single direction parallel to C, While in K-form the dehydration is instantly completed in each particle, then proceeds particle by particle. (2) Laumontite was found to exist in three phases under relative-humidity controlled atmosphere, i. e., 12H_2O phase (containing 12 water molecules per unit cell) (0% RH), 14H_2O phase (50% RH), and 16-18H_2O phase (100% RH) . Less
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