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Journal ArticleDOI

DTA of Kaolinite and Montmorillonite Under Water Vapor Pressures up to Six Atmospheres

01 Feb 1954-Clays and Clay Minerals (Springer Science and Business Media LLC)-Vol. 3, Iss: 1, pp 103-116
TL;DR: In this paper, at water-vapor pressure varying from approximately 0.0001 to 4,500 mm, the temperatures of the start of the endothermic peaks associated with exchange cations are shifted upward by increased gas (N2) pressure.
Abstract: Thermograms of kaolinite and montmorillonite were obtained at water-vapor pressures varying from approximately 0.0001 to 4,500 mm. of Hg with a variable pressure, dynamic gas, differential thermal analysis apparatus. The beginning of the kaolinite endotherm is shifted to a higher temperature with increasing water-vapor pressure. The sharp kaolinite exotherm is shifted to a lower temperature until at six atmospheres water-vapor pressure it makes a small broad peak at approximately 900° C. The dehydroxylation endotherm of montmorillonite is almost unaffected. The 900° C endotherm and the recrystallization exotherm are shifted to a lower temperature with increasing water-vapor pressure. The temperatures of the start of the endothermic peaks associated with exchange cations are shifted upward by increased gas (N2) pressure.
Citations
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Journal ArticleDOI
TL;DR: In this article, a technique has been developed for determining the reaction kinetics of infinitely thin disk-type specimens and the reactions are then strictly first order and the Arrhenius relation is obeyed.
Abstract: Previous studies of the kinetics of dehydroxylation of kaolinite and halloysite point to first-order reactions, in approximate conformity with the Arrhenius relation. Isothermal weight-loss measurements have shown that the rate constants are markedly dependent on factors such as specimen size, shape, and compaction. A technique has been developed for determining the reaction kinetics of infinitely thin disk-type specimens. The reactions are then strictly first order and the Arrhenius relation is obeyed. Activation energies of 65 and 55 kcal. per mole are obtained for kaolinite and halloysite, respectively. Comparison is made between the behavior of kaolinite and halloysite on the one hand and of macrocrystalline anauxite on the other. For anauxite, nucleation and growth of nuclei produce a sigmoid-type reaction curve, but for the fine-grained minerals it is believed that nucleation alone is the rate-controlling process. The dependence of the reaction rate on geometrical factors is attributed to the retention of water vapor within the powder specimen. The influence of water vapor on these reactions is discussed generally.

104 citations

Journal Article
TL;DR: In this article, high pressure DTA experiments show that the dehydroxylation of kaolinite in dry runs with P(Total) : p(argon) proceeds at 525"c and I bar to 627"c at 30.5 bars.
Abstract: High pressure DTA experiments show that the dehydroxylation of kaolinite in dry runs with P(Total) : P(argon) proceeds at 525"c and I bar to 627"c at 30.5 bars. Further increase in pressure slowly increases the dehydroxylation temperature, at 5270 bars it occurs at 670'C. Under conditions of P(Total) : p1"rOr, dehydroxylation occurs at 650.C at 46.5 bars and 520"C at 1088 bars after which it increases to 571'C at 5716 bars. The results are explained by postulating the presence of a liquid-like, "meta-liquid" phase, having a pressure-dependent H2O solubility. P-T relations of the kaolinite dehydroxylation reactions are best explained by assuming that they are metastable equilibrium reactions around a metastable invariant point at 625'C and 25 bars and a singular point at 640'C and 40 bars.

57 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the effect of pressure and interlayer-cation species on the dehydration temperature and rehydration hysteresis of Mg-exchanged montmorillonite.
Abstract: Dehydration of Ca- and Mg-exchanged montmorillonite was studied along H20 isochores in the hydrothermal diamond-anvil cell by in situ X-ray diffraction using a synchrotron radiation source. At-rressures between the H20 liquid-vapor (L-V) boundary and ~ 10 kbar, the dehydration temperature for the conversion from the 19 Ahydration state to the 15 A hydration state occurred over the temperature range 260-350 °C for Ca-exchanged montmorillonite and 200-250 °C for Mg-exchanged montmorillonite, with a slight increase with increasing pressure. For both materials, the rehydration from the 15 A to 19 A states occurred at the same temperature as dehydration at pressures along the H20 L-V boundary, thus showing no hysteresis. The rehydration hysteresis increased to nearly 75 °C at 6 kbar for Ca-exchanged montmorillonite and to the same amoUntat 2.5 kbar for Mg-exchanged montmorillonite. Dehydration experiments On Mg-exchanged montmorillonite along the isochores of 1.024 and 0.75 g/cm3 showed conversion from the 15 A hydrate to the 12.5 A hydrate at 590-605 dc. The 12.5 A hydrate only partially rehydrated after cooling to room temperature along those two isochores. In an experiment started from the 15 A state, in which the pressure was below the H20 L-V curve, dehydration occurred at 400-500 °C and rehydration at 430-350 dc. When our previous results on Na-exchanged montmorillonite are combined with the current experimental data, systematic trends can be found in the effect of pressure and interlayer-cation species On the dehydration temperature and rehydration hysteresis.

48 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the rate of recrystallization to forsterite has an inverse relationship to the speed of dehydration of fine and coarse powders and also of massive samples of serpentine.
Abstract: Dehydration and recrystallization reactions of fine and coarse powders and also of massive samples of serpentine under isothermal heating conditions in air are followed by thermobalance measurements and by X-ray diffraction intensities. The rate of recrystallization to forsterite is shown to have an inverse relationship to the rate of dehydration. This result is interpreted in terms of the damage inflicted on the crystal structure of serpentine by the dehydration reaction; the more slowly this reaction occurs, the more readily is forsterite formed as a result of the topotactic relationship between forsterite and serpentine. The surface layers of particles and massive samples of serpentine which dehydrate readily appear to be highly disordered and consequently recrystallize to forsterite very slowly. The corresponding phenomena exhibited by kaolinite are discussed and compared with those by serpentine.

31 citations

Journal ArticleDOI
TL;DR: When kaolinite is heated under pressures of self-generated H2O vapor from 04 to 32 atm, the dehydroxylation is best described by a nucleation and growth equation with m varying from 110 to 216 as the pressure is increased as discussed by the authors.
Abstract: When kaolinite is heated under pressures of self-generated H2O vapor from 04 to 32 atm, the dehydroxylation is best described by a nucleation-and-growth equation with m varying from 110 to 216 as the pressure is increased The temperature coefficient of the rate constant, expressed as an apparent activation energy, varies from 624 to 260 kcal/mol The H2O vapor evolved in a self-generated-atmosphere sample holder was automatically swept into a gas chromatograph at fixed intervals The measurement is specific for H2O

31 citations

References
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01 Jan 1945
TL;DR: The applications and limitations of this method to the study of various clays, bauxites, and aluminous minerals will be discussed in this article, including tables, illustrations, and photographs.
Abstract: Report issued by the Bureau of Mines discussing thermal analysis of clays and aluminous minerals. As stated in the introduction, "the applications and limitations of this method to the study of various clays, bauxites, and aluminous minerals will be discussed in this paper" (p. 1). This report includes tables, illustrations, and photographs.

25 citations

Book
02 Mar 2013
TL;DR: In this article, a differential thermal method for determining interval specific heats of ceramic materials is described, where the specific heat of the unknown is determined by comparing its temperature to that of quartz after each sample has been subjected to a definite heat treatment.
Abstract: A differential thermal method for determining interval specific heats of ceramic materials is described. The specific heat of the unknown is determined by comparing its temperature to that of quartz after each sample has been subjected to a definite heat treatment. This method shows the number of calories required to heat one gram of the material in question from 0 to t°C, accounting for all thermal processes which the material may undergo during the heating process. It shows the temperatures at which the various thermal processes begin and end as well as the quantitative figures for the more pronounced of these thermal processes. The kaolin, ball, flint, and diaspore clays undergo an endothermic reaction at about 575°C which amounts to “60 to 130” calories per gram of the air dried material. They undergo an exothermic reaction at about 960°C which amounts to about 25 calories per gram of the air dried material. About 510 calories are required to heat one gram of any firebrick body from 25 to 1200°C, the specific heat over this interval being about 43. About 500 calories are required to heat one gram of any kaolin or ball clay from 0–1000°C, the specific heat over this interval being about 5. About 290 calories are required to heat one gram of flint or feldspar from 0–1050°C, the specific heat over this interval being about 28. Instead of the kiln efficiencies being about 22% as was previously believed, this work proved them to be about 35%.

17 citations