Tridymite

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

Characterization of Unye bentonite after treatment with sulfuric acid

Abstract: Unye bentonite was found to consist predominantly of a dioctahedral smectite along with quartz, tridymite, cristobalite, and minor fractions of feldspar and anatase. A considerable amount of Al was retained as a constituent in acid-resistant impurities following the decomposition of the montmorillonite via acid treatment at an acid/clay ratio of 0.4. These impurities were mesoporous with a maximum surface area of 303.9±0.4 m2 g-1. A sharp decrease in the d001 lattice spacing of the montmorillonite to 15.33 A reflected the reduction of the crystallinity in the activated products. In addition, the increase in the ease with which newly formed hydroxyl groups were lost paralleled the severity of the acid treatment.

Silica polymorphs in lunar granite: Implications for granite petrogenesis on the Moon

Abstract: Granitic lunar samples largely consist of granophyric intergrowths of silica and K-feldspar The identification of the silica polymorph present in the granophyre can clarify the petrogenesis of the lunar granites The presence of tridymite or cristobalite would indicate rapid crystallization at high temperature Quartz would indicate crystallization at low temperature or perhaps intrusive, slow crystallization, allowing for the orderly transformation from high-temperature silica polymorphs (tridymite or cristobalite) We identify the silica polymorphs present in four granitic lunar samples from the Apollo 12 regolith using laser Raman spectroscopy Typically, lunar silica occurs with a hackle fracture pattern We did an initial density calculation on the hackle fracture pattern of quartz and determined that the volume of quartz and fracture space is consistent with a molar volume contraction from tridymite or cristobalite, both of which are less dense than quartz Moreover, we analyzed the silica in the granitic fragments from Apollo 12 by electron-probe microanalysis and found it contains up to 07 wt% TiO2, consistent with initial formation as the high-temperature silica polymorphs, which have more open crystal structures that can more readily accommodate cations other than Si The silica in Apollo 12 granitic samples crystallized rapidly as tridymite or cristobalite, consistent with extrusive volcanism The silica then inverted to quartz at a later time, causing it to contract and fracture A hackle fracture pattern is common in silica occurring in extrusive lunar lithologies (eg, mare basalt) The extrusive nature of these granitic samples makes them excellent candidates to be similar to the rocks that compose positive relief silicic features such as the Gruithuisen Domes

Phase compositions and microstructure of plasma sprayed wollastonite coating

Abstract: The phase compositions and microstructure of wollastonite coatings deposited onto Ti–6Al–4V substrates by plasma spraying were studied using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The plasma sprayed wollastonite coating was not homogeneous and had a rough surface. Some pores and microcracks existed in the coatings. The primary crystalline phase in the coating was triclinic wollastonite. Some crystalline wollastonite grains had dislocation. The glassy phase was also discovered with some small size crystals in the coating. In addition, tridymite (SiO2) and CaO were also found in the coating.