Tridymite

About: Tridymite is a research topic. Over the lifetime, 840 publications have been published within this topic receiving 14831 citations.

[Studies of structure-determined biological aggressiveness of chrysotile asbestos. I. Model of chrysotile crystalline structure]

Abstract: Chrysotile is built out of two kinds of layers placed alternately, namely tridymite (silico-oxygenic) and brucite. A tridymite layer is composed of silico-oxygenic tetrahedrons laid planary in the pseudohexagonal order, while magnesium ions coordinated octahedrally in hydroxyl groups produce a brucite layer. Two layers are bound in a chrysotile molecule through substitution of a part of hydroxine groups of the basis of the brucite layer by oxygen ions from the vertex of the tridymite layer tetrahendrons. The size of an elementary chrysotile cell is as follows: a = 5.3A, b = 9.2A, c = 7.3A, beta = 93 Positions (x, y, z) of all atoms in the elementary chrysotile cell were calculated. In calculations hydrogen atoms were neglected because of small atomic dissipation factor (contribution to the structure) and difficulties in their precise location in the elementary cell. The elementary chrysotile cell is composed of two molecules Mg3 [Si2O5] (OH)4. Crystallographic axes of chrysotile structure were directed in relation to the fibre axis. The values of the elementary chrysotile fibre radii are as follows: R = 208A (starting value) and r = 18.2A (minimum value) A theoretic chrysotile pulverulent diffraction pattern was calculated and drawn. The theoretical pulverulent diffraction pattern of chrysotile was compared with chrysotile diffraction pattern in the card JC PDS21-543. A great similarity between the two diffraction patterns was found.

Binder for chemically resistant concrete - contg. quartz sand tridymite and/or cristobalite and sodium and/or potassium oxide

Abstract: Binder for chemically resistant concrete comprises 30-80 % wt. quartz sand with specific surface area 1000-5000 cm2/g and 20-70 % wt. of tridymite and/or cristobalite particles contg. on the surface 0.5-6% mole Na2O and/or K2O. Binder is made by heating at 1000-1550 degrees C a mixt. of quartz sand and 0.7-15% of >=1 of Na2CO3, K2CO3, NaOH, KOH to form the tridymite and/or cristobalite contg. Na2O and/or K2O. Cooled mixt. is ground and mixed with ground quartz sand. Used for producing finishing blocks and panels bearing structural members for use in chemically aggressive environment. The binder has increased water resistance and is more economically produced with lower energy consumption.

Wholly aromatic liquid crystalline polyester resin composition with excellent blister resistance

Abstract: PURPOSE: A wholly aromatic liquid crystal polyester resin composition is provided to have excellent blister resistance without loss of flowability, heat resistance, and mechanical properties. CONSTITUTION: A wholly aromatic liquid crystal polyester resin composition comprises a wholly aromatic liquid crystal polyester resin with a melting point of 300-450 °C; filler for reinforcing physical properties; and powder type inorganic filler with a powder type. The filler for reinforcing physical properties is one or more selected from glass fiber and carbon fiber. The powder type inorganic filler is one or more selected from calcium carbonate, quartz, tridymite, cristobalite, coesite, stishovite, talc, mica, and carbon black.

Vapor-Phase Garnet at Yucca Mountain, Nevada: Geochemistry and Oxygen-Isotope Thermometry

Abstract: About 20 vapor-phase garnets were studied in two samples of the Topopah Spring Tuff from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350-m-thick, devitrified, moderately to densely welded ash flow that is compositionally zoned from high-silica rhyolite to quartz latite. During cooling of the tuff, escaping vapor produced lithophysae (former gas cavities) lined with an assemblage of tridymite, cristobalite, alkali feldspar, and locally, hematite and/or garnet. Vapor-phase topaz and economic deposits (such as porphyry molybdenum-tungsten) commonly associated with topaz-bearing rhyolites (characteristically enriched in fluorine) were not found in the Topopah Spring Tuff at Yucca Mountain. The garnets are not primary igneous phenocrysts, but rather crystals that grew from a fluorine-poor magma-derived vapor trapped during emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter, and fractured. The garnets also contain inclusions of tridymite. Electron-microprobe analyses of the garnets reveal that they are almandine-spessartine (48.0 and 47.9 mol percent, respectively), have an average chemical formula of (Fe{sub 1.46}, Mn{sub 1.45}, Mg{sub 0.03}, Ca{sub 0.10}) (Al{sub 1.93}, TiO{sub 0.02}) Si{sub 3.01}O{sub 12}, and are homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have {delta}{sup 18}O values of 7.2 and 7.4{per_thousand}. The coexisting tridymite, however, has {delta}{sup 18}O values of 17.4 and 17.6{per_thousand} values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a {delta}{sup 18}O of 11.1{per_thousand} which, when coupled with the garnet {delta}{sup 18}O values in a quartz-garnet fractionation equation, indicates vapor-phase crystallization at temperatures of almost 600 C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50-70 C) of calcite, quartz, and opal secondary mineralization, formed from percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.