Topic
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 paper, the effect of pure oxides, fluorides, chlorides, borates, phosphates, carbonates, and other compounds on the inversion of quartz to cristobalite and tridymite at temperatures between 1000 and 1500°C.
Abstract: The action of a considerable number of pure oxides, fluorides, chlorides, borates, phosphates, carbonates, and other compounds and of certain mixtures, as well as the effect of several minerals in promoting or accelerating the inversion of quartz to cristobalite and tridymite at temperatures between 1000 and 1500°C. has been studied. Alkali oxides are found to be superior to all other substances, and they are effective in amounts of less than 0.1%. Acid oxides, such as BIOs or Plot., seem to have little or no value as catalysts for this inversion. Possible mechanisms for the inversion process are presented, and some applications of controlled inversion in the heat treatment of ceramic bodies are mentioned. A few data are also given on the temperature of the “low-high’ change in cristobalite.
11 citations
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TL;DR: In this article, the Hartree-Fock STO-3G calculations have been performed on several tetracoordinated silica polymorphs: low and high quartz, low and idealized high cristobalite and prototype tridymite.
Abstract: Periodic Hartree-Fock STO-3G calculations have been performed on several tetracoordinated silica polymorphs: low and high quartz, low and idealized high cristobalite and prototype tridymite. The optimized structural parameters are in overall good agreement with experimental data. In the particular case of α-quartz, the SiO4 tetrahedra are found to be irregular. The optimized values of the two different SiO bond lengths are respectively 1.608 A and 1.613 A. The potential energy versus tilt angle curves suggest a picture of the high temperature phases in terms of delocalized oxygen atoms which is consistent with a disordered structure. Finally, the bonding in silica polymorphs is discussed from electron density maps and Mulliken population analysis.
11 citations
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TL;DR: In this paper, the nanostructure and water species in the body frame and spicules of Euplectella aspergillum, collected from the sea floor around Cebu Island was characterized in detail by thermogravimetric differential thermal analysis, nuclear magnetic resonance spectroscopy, Raman and infrared spectroscopies, and X-ray diffraction method.
Abstract: The nanostructure (atomic-scale structure) and water species in the body frame and spicules of the marine glass sponge, Euplectella aspergillum, collected from the sea floor around Cebu Island was characterized in detail by thermogravimetric differential thermal analysis, nuclear magnetic resonance spectroscopy, Raman and infrared spectroscopies, and X-ray diffraction method. The structural features of the nanostructure in the body frame and spicules were essentially similar to each other, although these were different from those of inorganic amorphous silica materials, such as silica gel and silica glass. In addition, the averaged short and medium range structures of the sponge may be similar to those of tridymite. The water content and water species included in the body frame and spicules were almost the same. More than half of the contained water was physisorbed water molecules, and the rest was attributed to Q3 and Q2 silanol groups. Most of the water species may be present at the surface and involved in hydrogen bonding.
11 citations
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11 citations
05 Jul 2010
TL;DR: In this article, the loci of alkali-silica reaction (ASR) of reactive silica minerals (cristobalite, tridymite) and interstitial glass in the volcanic aggregates in concrete were identified.
Abstract: Petrographic diagnosis of alkali-aggregate reaction in concrete was introduced. Combined use of polarizing microscopy and scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) analysis on polished thin section well identified the loci of alkali-silica reaction (ASR) of reactive silica minerals (cristobalite, tridymite) and interstitial glass in the volcanic aggregates in concrete. Slowly cooled volcanic rocks oversaturated with silica contained silica minerals, nearly comparable with the calculated normative quartz in CIPW norm. Interstitial glass in volcanic rocks becomes enriched in SiO2 with diminishing content by cooling of magma, which suggests that reactive rhyolitic glass can be formed in andesite and even basalt oversaturated with silica. Fly ash glass in ASR-affected concrete was also analyzed. SEM-EDS analysis revealed compositional trend lines of ASR gel, which reflects position of gel, evolutionary stage and environments of ASR in concrete.
11 citations