Showing papers in "Clay science in 1991"
TL;DR: In this article, the adsorption of ammonia by sepiolite containing water previously adsorbed, was studied in ambient atmosphere, and it was shown that the ammonia-adsorbing capacity increased as the relative humidity in the air was lowered.
Abstract: 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 0.32 mg/g in the relative humidity range of 60 to 80%
25 citations
TL;DR: Montmorillonite was synthesized by hydration of sodium, magnesium, and aluminosilicate glass under hydrothermal pressure of 100 MPa as discussed by the authors, and the water/solid ratio of starting mixtures was varied in the range 0.155 to 2.17.
Abstract: 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 nH 2 O, n=5 to 80, for Na 0.66 (Mg,Al) 4 (Si,Al) 8 O 20 (OH) 4 .nH 2 O. 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
16 citations
TL;DR: The absorption of various odorous vapors (adsorbates) by sepiolite, which adsorbed water previously, was studied by comparison with that of ammonia.
Abstract: The absorption of various odorous vapors (adsorbates) by sepiolite, which adsorbed water previously, was studied by comparison with that of ammonia Experiments were carried out at 25°C in ambient atmosphere or under the reduced pressure without air nor water The amounts of adsorbates, adsorbed on sepiolite in the air having 30% relative humidity, were found to be rather large They were about 015, 0011, and 00042 mmol/g, for ammonia, pyridine, and acetaldehyde, respectively, under the relative vapor pressure of these adsorbates, P/P 0 , of 10 −5 at 25°C
16 citations
TL;DR: In this paper, the hydration and dehydration process of laumontite have been investigated by gravimetry and X-ray powder diffractometry under the conditions of controlled relative humidity (RH) at 25°C.
Abstract: 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) 12H 2 O phase (The phase contains ca. 12 water molecules per unit cell). The cell parameters are a=14.71(1) A, b=13.09(1) A, c=7.46(1) A and β=112.1(1)° (0% RH). (2) 14H 2 O phase
14 citations
TL;DR: In this article, the reaction product of a kaolinite-DMSO intercalate with acrylic acid showed the basal spacing of 11.7 A, suggesting the formation of a new intercalation compound.
Abstract: Acrylic acid was intercalated between the layers of kaolinite by the use of a kaolinite-dimethylsulfoxide (DMSO) intercalation compound as the intermediate. The reaction product of a kaolinite-DMSO intercalate with acrylic acid showed the basal spacing of 11.7 A, 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
5 citations
TL;DR: In this article, the results of I.R., XRF and MAS-NMR techniques applied to characterize the intermediate phases namely metakaolinite and spinel have been reviewed and exhaustive analyses showed that no positive evidence has been obtained so as to conclude that the intermediate 980°C spinel is γ-Al 2 O 3.
Abstract: Analytical results of I.R., XRF and MAS-NMR techniques applied to characterize the intermediate phases namely metakaolinite and spinel 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-Al 2 O 3 . 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 AlO 4 content of 1000°C heated kaolinite by XRF analysis agrees closely with the theoretically expected global AlO 4 value of the 980°C reaction where Si-Al spinel and amorphous alumino silicate phases forms with the liberation of amorphous silica
4 citations
TL;DR: In this paper, the influence of trimethylsilyl groups on the surface areas of heat-treated TMS-magadiite and TMS kenyaite was investigated.
Abstract: Trimethylsilylated (TMS) magadiite and kenyaite were treated thermally and the influence of trimethylsilyl groups on the surface areas of the heat-treated products was investigated. The basal spacings of the TMS-magadiites treated up to 300°C were constant. When TMS-kenyaite was heat-treated, the basal spacing was kept at a constant value until 400°C. The specific surface areas of the products increased up to those temperatures. After the organic groups were burned, the interlayer spaces of the heat-treated TMS-magadiite and TMS-kenyaite were still expanded possibly by the presence of oxidized silyl groups in the interlayer spaces
3 citations
TL;DR: In this article, Hartree-Fock molecular orbital calculations are carried out for a system of linked [SiO 4 0] 4− and [AIO 4 ] 4− tetrahedra (denoted by a cluster).
Abstract: Ab initio Hartree-Fock molecular orbital (MO) calculations are carried out for a system of linked [SiO 4 0] 4− and [AIO 4 ] 4− tetrahedra (denoted by a cluster). The system is regarded as a model of the tetrahedral sheet of a clay. The effective charges from the Mulliken population analyses are almost constant when the number of tetrahedra in a cluster increases from 1 to 6. The MO calculation is extended for the system of a point positive charge located over the surface of a cluster
2 citations
1 citations
TL;DR: In this paper, the interaction between the talc layers is studied for a model system of two tetrahedral sheets, and the energy for the interlayer interaction is calculated under the periodic boundary conditions.
Abstract: The interaction between the talc layers is studied for a model system of two tetrahedral sheets. The upper sheet is a unit cell of tetrahedral sheet, [Si 4 O 10 ] 4− and the lower sheet an infinite hexagonal network of [SiO 4] 4− . Using the electrostatic and Lennard-Jones equations, the energy for the interlayer interaction is calculated under the periodic boundary conditions. It is concluded that the interaction between the above two silicate sheets is attractive
1 citations
TL;DR: An improvement in the crystallinity of an industrially synthesized nafluortaeniolite was performed by hydrothermal annealing with pure water or NaOH solutions as discussed by the authors.
Abstract: An improvement in the crystallinity' of an industrially synthesized nafluortaeniolite was performed by hydrothermal annealing with pure water or NaOH solutions. The temperatures and pressure applied were 300, 450 and 600°C, and 100MPa, respectively. The run duration was 7 days. By hydrothermal annealing, the particles of Na-fluortaeniolite less than about 2 μm disappeared and other grew to have the euhedral shape common to micas. The improvements in the size, form and perfection of crystals resulted from a pure water treatments, especially that at 600°C