Showing papers on "Tridymite published in 1971"
Patent•
28 Jul 1971
TL;DR: In this paper, the authors show that when exposed to elevated temperatures, the nuclei promote the formation of the outer layer of uniformly fine crsytalline silica which imparts thermal dimensional stability for extended periods of use at elevated temperatures.
Abstract: Quartz glass element, such as a diffusion tube useful in the production of semiconductor elements, capable of forming an outer layer of uniformly fine crystalline silica such as cristobalite or tridymite when heated to a temperature at which such crystalline silica forms containing crystallization promoting nuclei having a rate of diffusion in quartz glass less than that of sodium at elevated temperatures. Such nuclei are preferably present in the outer half of the element wall. When the quartz glass element is exposed to elevated temperatures, the nuclei promotes the formation of the outer layer of uniformly fine crsytalline silica which imparts thermal dimensional stability for extended periods of use at elevated temperatures.
41 citations
TL;DR: In this article, a large number of specimens of α-quartz, α-cristobalite, chalcedonies, opals, quartzines, and agates were examined.
Abstract: Examination of a large number of specimens of α-quartz, α-cristobalite, chalcedonies, opals, quartzines, and agates shows that the so-called amorphous forms of silica do not represent any particular specificities, but are simply amorphous mixtures, more often than not, for example, α-quartz with tridymite, on the α-quartz base (chalcedonies, opals). In chalcedonies the tridymitic constituent is somewhat larger than in opals. Another large group of opals is but an altered α-cristobalite, high in molecular water. The α-quartz opals characteristically contain far less water. — Authors.
8 citations
TL;DR: In this paper, a Tertiary tholeiitic dyke intruded into sedimentary rocks of Lower Carboniferous age is locally rich in xenoliths of siliceous and argillaceous rocks possibly of Upper Old Red Sandstone age.
Abstract: Synopsis A Tertiary tholeiitic dyke intruded into sedimentary rocks of Lower Carboniferous age is locally rich in xenoliths of siliceous and argillaceous rocks possibly of Upper Old Red Sandstone age. The xenoliths and the country rocks have suffered thermal metamorphism with the production of glass, tridymite, cordierite, pyroxenes and biotite in the former and tridymite, cordierite, biotite and lime-garnet in the latter. From considerations of the stability fields of tridymite, melt-products and the solidus of dolerite, it is estimated that the PT conditions under which the presently exposed levels of the dyke crystallised were approximately 500 bars and 1,000° C, possibly representing a cover in Tertiary times some 6,200 ft (1,900 m) thick.