Analytical results of I.R., XRF and MAS-NMR techniques applied to characterize the intermediate phases namely metakaolinite and spinel phase have been reviewed. The exhaustive analyses showed that no positive evidence has been obtained so as to conclude that the intermediate 980°C spinel is γ-Al₂O₃. The major drawback in arriving to a definite conclusion is probably due to unaccountability of the co-existence of a substantial amount of amorphous alumino silicate phase at 980°C. The measured AlO₄ content of 1000°C heated kaolinite by XRF analysis agrees closely with the theoretically expected global AlO₄ value of the 980°C reaction where Si-Al spinel and amorphous alumino silicate phases forms with the liberation of amorphous silica. Lastly metakaolinite does not have any fixed structure. It transforms to mullite in two parallel paths as explained from I.R. studies of successive heated kaolinites. First path corresponds to nucleation of mullite in amorphous alumino-silicate matrix and subsequent growth thereof which is related to the observation that the ratio of AlO₄ to AlO₆ does not change too much between the temperature range 1000°C to 1400°C in some kaolinite where mullitization predominantly takes place following this path.
The second path corresponds to the polymorphic transformation of cubic to orthorhombic form where the global AlO₄/AlO₆ ratio of 1000°C heated kaolinite changes and subsequently attains to the value close to 3: 2 mullite.

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Montmorillonite was synthesized by hydration of sodium, magnesium aluminosilicate glass under hydrothermal pressure of 100 MPa. The water/solid ratio of starting mixtures was varied in the range 0.155 to 2.17. If complete conversion from glass to montmorillonite is assumed, the ratios correspond to 4 (OH) and nH₂O, n=5 to 80, for Na_0.66 (Mg, Al) ₄ (Si, Al) ₈O₂₀ (OH) ₄·nH₂O. The synthesis temperature ranged from 250 to 475°C. Run products were analyzed by X-ray diffraction.
Yield of montmorillonite and its crystallinity increased drastically at the water/solid ratio of 0.310 (i.e.n=10) but were saturated in more water-rich conditions. The interlayer spacings of as-grown samples before humidity-adapted de-intercalation indicated that the number of water-layers depended on the water/solid ratio: one water-layer for n <20, two for n>20, and three in excess-water synthesis.
From variations of full width at half maximum (FWHM) of 001 and 11, 02 reflections depending on the hydration of glass, the following growth mechanism for montmorillonite is suggested: two-dimensional fragments were formed by an initial hydration of the glass and appeared to be slightly interstratified by one another. Further hydration did not increase the dimensions of the fragment or the degree of interstratification, although the number of such poorly crystallized fragments was increased.

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Acrylic acid was intercalated between the layers of kaolinite by the use of a kaolinitedimethylsulfoxide (DMSO) intercalation compound as the intermediate. The reaction product of a kaolinite-DMSO intercalate with acrylic acid showed the basal spacing of 11.7 Å, suggesting the formation of a new intercalation compound. The IR spectrum of the product exhibited that the profiles arising from the interaction between the kaolinite layers and the interlayer organic species changed as compared with the kaolinite-DMSO system. X-ray fluorescence analysis showed the presence of DMSO, indicating the coexistence of both DMSO and acrylic acid between the layers. This finding was supported by the ¹³C CP/MAS NMR spectrum of the product. By the heat treatment of the product at 250°C for 1 h, acrylic acid was not polymerized possibly because of its complicated arrangement with co-existed DMSO.

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Several previous studies of the hydration and dehydration process of laumontite have been performed, however, they have been carried out at room temperature without humidity-controlled conditions. The process is investigated by gravimetry and X-ray powder diffractometry under the conditions of controlled relative humidity (RH) at 25°C. The results show that laumontite has the following three phases in the atmosphere from 0 to 100%RH.(1) 12H₂O phase (The phase contains ca. 12 water molecules per unit cell). The cell parameters are a=14.71 (1)Å, b=13.09 (1)Å, c=7.46 (1)Å and β=112.1 (1)°(0% RH).(2) 14H₂0 phase. The cell parameters are a=14.77 (1)Å, b=13.09 (1)Å, c=7.58 (1)Å and β=112.0 (2)°(50%RH).(3) 16-18H₂0 18H20 phase. The cell parameters are a=14.90 (2)Å, b=13.19 (1)Å, c=7.55 (1)Å and β=110.2 (1)°(100% RH).

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The adsorption of ammonia by sepiolite containing water previously adsorbed, was studied in ambient atmosphere.
The ammonia-adsorbing capacity of sepiolite grains, treated with water vapor, increased as the relative humidity in the air was lowered. The apparent ammonia adsorption isohume on sepiolite follows Freundlich's one. The amount of ammonia adsorbed on sepiolite grains was about 1.68 mg/g at 9.0% relative humidity in the air containing 10 ppm ammonia at 25°C, and it was about 0.32mg/g in the relative humidity range of 60 to 80010. It may be concluded that ammonia is adsorbed on the unoccupied pores in the channel inherent in the sepiolite structure and also on the water molecular layer covering the pore in the channel as well as on the outer surface of sepiolite. The former adsorption is remarkable when the relative humidity is below or equal to 9.0%, and the latter above 9.0%. The difference of ammonia adsorption between these cases, reflects the above-mentioned adsorption mechanisms.
The ammonia-adsorbing capacity of sepiolite powders, dried at 110°Cfor three days, decreased with the temperature in the air with the dew point of-9.0°C (PH2O=285 Pa). The apparent ammonia adsorption isotherm on sepiolite powders in the air also follows Freundlich's one. The amounts of ammonia, adsorbed on sepiolite powder were about 1.55 and 0.88 mg/g at 10 and 25°C, respectively, in the air with 285 Pa water vapor containing 10 ppm ammonia. It decreased gradually in the temperature range of 10 to 50°C, and reached about 0.65mg/g at 50°C. The amounts of ammonia adsorbed by coconut-shell active carbon was about 0.15 and 0.12mg/g at 10 and 25°C, respectively, in the same atmosphere. Therefore, those by the sepiolite were about ten and seven times higher than those of the carbon at 10 and 25°C, respectively.

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