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Tridymite
About: Tridymite is a research topic. Over the lifetime, 840 publications have been published within this topic receiving 14831 citations.
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TL;DR: In this article, the surface contribution to the interfacial chemistry involved in the preparation of potassium-modified metal oxide catalysts has been revealed by examining industrial 5 wt.% K+ silica-alumina versus silica and previously examined alumina.
Abstract: The surface contribution to the interfacial chemistry involved in the preparation of potassium-modified metal oxide catalysts has been revealed by examining industrial 5 wt.% K+ silica–alumina versus silica and previously examined alumina. The investigation was conducted by means of potassium and nitrogen adsorption measurements, insitu IR spectroscopy, X-ray diffractometry and photoelectron spectroscopy, which allowed definition of the adsorptive and thermochemical events occurring during the impregnation, drying and calcination steps of the preparation. The oxide surface chemistry influences the adsorption amounts attained during the impregnation from aqueous K2CO3 solutions: non-specific and specific adsorption on silica (7 K+ nm−2) and only weaker specific adsorption on silica–alumina (1.1 K+ nm−2) related to the low content of very well dispersed silica. On both carriers, the presence of potassium leads to the lower amount and weaker stability of the surface hydroxy groups owing to synergetic effects with absorbed carbonate. During calcination, K+ greatly enhances the crystallization of silica into crystoballite at 973 K and tridymite at 1273 K, which is accompanied by a strong decrease in surface area, a better dispersion of K+ and an increase in surface basicity, by comparison with silica–alumina. No specific effect can be observed on silica–alumina during transformation of the boehmite form into the γ-alumina-type structure; the presence of very well dispersed silica in alumina decreases the CO2 adsorption capacity observed on pure alumina.
18 citations
TL;DR: Calcic plagioclase is the dominant luminescent mineral in crystalline rocks and breccias, as are trace grains of potassium feldspar and minor amounts of cristobalite and tridymite, which give evidence of disordering on the angstrom scale.
Abstract: Calcic plagioclase is the dominant luminescent mineral in crystalline rocks and breccias. Minor amounts of cristobalite and tridymite are also luminescent, as are trace grains of potassium feldspar. Two types of intergrowths of potassium feldspar with a silica phase, possibly quartz, were found in the breccias. Luminescence spectra of plagioclase show significant similarities to, and differences from, spectra of terrestrial plagioclase. Shock damage in the breccias is reflected in systematic changes in the plagioclase spectra, thus giving evidence of disordering on the angstrom scale. Associated extinction patterns seen between crossed Nicol prisms give evidence of disordering on the micrometer scale.
18 citations
TL;DR: In this article, the rates of dissolution in dilute sodium hydroxide solution of a series of size-graded powders of the four common polymorphic forms of silica (quartz, tridymite, cristobalite and vitreous silica) have been studied and found to be in keeping with their physical properties.
Abstract: The rates of dissolution in dilute sodium hydroxide solution of a series of size-graded powders of the four common polymorphic forms of silica (quartz, tridymite, cristobalite and vitreous silica) have been studied and found to be in keeping with their physical properties. The effect of variation of particle size on the dissolution of quratz has been related to the ‘amorphous layer’. The results provide no support for the ‘solubility theory’ of silicosis.
18 citations
31 Aug 2007-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the authors provided relevant data at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10−9 and 10−4 K at intermediate oxygen partial pressures and temperatures relevant to sulfide smelting and nonferrous metallurgy.
Abstract: At present, there is a scarcity of data on the activities of iron oxides in the FeO-Fe2O3-CaO-SiO2 slag system at intermediate oxygen partial pressures and temperatures relevant to sulfide smelting and nonferrous metallurgy. The present study provides relevant data at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10−9 and 10−4 atm. The experiments were carried out by equilibrating the slag in a CO-CO2 gas mixture in a platinum crucible, after which the phases of all the experimental samples, including the platinum foil, were analyzed by electron probe microanalysis (EPMA). Where only liquid phase or liquid phase and tridymite (SiO2) were observed, wet chemical analysis was used to determine the ratio of (mass pct Fe2+)/(mass pct Fe3+). Activity and activity coefficients for FeO (liquid) and FeO1.33 (solid) were calculated. Tendencies of the effect of the (CaO/SiO2) ratio, temperature, and oxygen partial pressure on these thermochemical quantities are discussed in this article.
18 citations
TL;DR: In this article, the existence of atomic hydrogen besides intense Al-centers was ascertained in ESR spectrum measurements of a variety of natural quartzes after irradiation at 77 K. The remarkable decrease of Al-hole center signals, coincident with the complete disappearance of ESR-signal due to atomic hydrogen, was observed upon heating to room temperature.
18 citations