The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Masami Kanzaki - One of the best experts on this subject based on the ideXlab platform.
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Crystal structure of a new high-pressure polymorph of Topaz-OH
American Mineralogist, 2010Co-Authors: Masami KanzakiAbstract:A new high-pressure form of Topaz-OH (denoted here Topaz-OH II) was obtained at 14 GPa and 1400 °C. The X-ray diffraction pattern of this phase can be indexed by an orthorhombic cell with a = 4.72318(5), b = 8.91480(9), and c = 2.77276(3) A. The lengths of a and b are similar, but c is approximately a third of that for a previously reported Topaz-OH (denoted Topaz-OH I). The structural formula of Topaz-OH II can be written as (Al0.68Si0.32)(O0.66(OH)0.34)2, suggesting significant cation disorder in the structure. The crystal structure of Topaz-OH II is solved using powder synchrotron X-ray diffraction data, and refined with constraints provided by a separate multi-nuclear NMR study. The structure has similarities with Topaz-OH I and diaspore ( α-AlOOH) structures, having partially occupied double edge-shared octahedral chains, and 2 × 1 tunnels with partially occupied tetrahedral
Rongqing Zhang - One of the best experts on this subject based on the ideXlab platform.
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a tin mineralized Topaz rhyolite dike with coeval Topaz granite enclaves at qiguling in the qitianling tin district southern china
Lithos, 2013Co-Authors: Rucheng Wang, Jianjun Lu, Wenlan Zhang, J. Chen, Rongqing ZhangAbstract:Abstract The Qiguling Topaz rhyolite is present as a dike within the Qitianling biotite granite batholith of the Nanling Range of southern China. Here, the rhyolitic dike, 4.5 m wide and 500 m long, contains enclaves of Topaz granite. These rhyolites contain up to 72 wt.% SiO 2 , have alumina saturation index (ASI) > 1.1, and have groundmasses with estimated fluorine contents of approximately 1.5 wt.%. Textural relationships provide evidence of a quenched silicate melt that contains quartz, K-feldspar, albite, and zinnwaldite phenocrysts in a groundmass containing abundant Topaz. The rhyolites in the study area are also strongly enriched in tin (90–2700 ppm), and generally have a close association between cassiterite and zinnwaldite, although cassiterite is also present as sponge-textured fills between rock-forming minerals. Granite enclaves and their hosted rhyolite have similar major geochemical compositions and mineralogies to each other. Zircon U–Pb dating indicates that the Topaz rhyolite (147–150 Ma) and Topaz granite enclaves (154 Ma) were formed contemporaneously, with ages that overlap within analytical uncertainty. In addition, the major and trace element compositions of the rhyolite and their granite enclaves are dissimilar to those of the hosting Qitianling biotite granite. This discovery of granite enclaves within rhyolite dikes suggests the presence of a Topaz-bearing granite body at depth that may host tin mineralization. The expected hidden tin granite may be of great interest in the further exploration.
S.s. Voss - One of the best experts on this subject based on the ideXlab platform.
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Topaz II Reactor Modifications Overview
AIP Conference Proceedings, 1994Co-Authors: Roy A. Haarman, S.s. Voss, Veniamin UsovAbstract:A proposed launch of the Russian Topaz II power system by the United States will require compliance with U.S. environmental, safety and health (ES&H) regulations. Recent work done by the Topaz II Flight Safety team in assuring ES&H compliance for a proposed Topaz II flight program has identified some modifications that are necessary to meet United States (U.S.) requirements. There are also some components, particularly in the electronic control area, where more modern components can improve the operability and reliability of the mission. This paper describes the overall approach to considering modifications on the existing Topaz II system from both the ES&H and operational aspects, and provides a brief description of each of the proposed modifications.
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Topaz II Design Evolution
AIP Conference Proceedings, 1994Co-Authors: S.s. VossAbstract:The United States (U.S.) has begun a journey to purchase, understand the workings of, and possibly launch the Russian developed Topaz II space nuclear power system. In support of this work, the U.S. Topaz II team has been working closely with the Russian technical specialists to learn how the Russian Topaz II system was developed and to understand the major programmatic and technical changes. It is important to know what drove the major system design and test changes ‐ were they programmatic or were they technical? The purpose of this paper is to provide an overview on what the U.S. has learned to date about the evolution of the Topaz II system and its flight readiness.
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The Topaz II space reactor response under accident conditions
1993Co-Authors: S.s. VossAbstract:The Topaz II is a single-cell thermionic space reactor power system developed by the Russians during the period of time from {approximately}1969 to 1989. The Topaz II has never been flight demonstrated, but the system was extensively tested on the ground. As part of the development and test program, the response of the Topaz II under accident conditions was analyzed and characterized. The US Topaz II team has been working closely with the Russian specialists to understand the Topaz II system, its operational characteristics, and its response under potential accident conditions. The purpose of the technical exchange is to enable a potential launch of a Topaz II by the US. The information is required to integrate the system with a US spacecraft and to support the safety review process. The purpose of this paper is to provide a brief overview of the system and its response under actual and postulated accident conditions.
Roberto Compagnoni - One of the best experts on this subject based on the ideXlab platform.
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intermediate alkali alumino silicate aqueous solutions released by deeply subducted continental crust fluid evolution in uhp oh rich Topaz kyanite quartzites from donghai sulu china
Journal of Petrology, 2007Co-Authors: Maria Luce Frezzotti, Simona Ferrando, Luigi Dallai, Roberto CompagnoniAbstract:Minerals, fluid inclusions and stable isotopes have been studied inultrahigh-pressure (UHP) OH-rich Topaz^kyanite quartzitesfrom Hushan (west of Dongai), in southern Sulu (China). Thequartzites underwent a metamorphic evolution characterized by apeak stage (3 5GPa and 730^8208C) with the anhydrous assem-blage coesiteþkyanite I, followed by an early near-isothermaldecompression stage (2 9GPa and 705^7808C) with growth ofkyanite II, muscovite, and OH-rich Topaz, and by decompression-cooling stages, represented by paragonite (19GPa and 700^7808C)and pyrophyllite (0 3GPaand4008C) on kyanite (I and II) andOH-rich Topaz, respectively.These rocks may exhibit unusually lowd
T V Vakalova - One of the best experts on this subject based on the ideXlab platform.
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Topaz activated solid phase sintering of mullite
Refractories and Industrial Ceramics, 2005Co-Authors: T V Vakalova, A V Ivanchenkov, V M PogrebenkovAbstract:The solid-phase Topaz-activated sintering of mullite from stoichiometric mixtures of pure aluminum and silicon oxides is studied. The role of Topaz in the mechanism of synthesis and sintering of mullite is discussed in detail.
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Kinetics of the solid-phase synthesis of mullite in the presence of Topaz
Refractories and Industrial Ceramics, 2005Co-Authors: T V Vakalova, A V Ivanchenkov, V M PogrebenkovAbstract:Results of a kinetic study of solid-phase interactions in stoichiometric oxide mixtures of mullite composition are reported. The mechanism of mullitization, irrespective of the oxide form (crystalline or amorphous), is diffusive in character. Topaz added in small quantities accelerates the process through generating surface and structure imperfections and activating the diffusion of reactants owing to the assistance of gaseous fluorides released by Topaz. The secondary mullite produced by thermal degradation of Topaz facilitates the formation of nucleation centers for topochemical reactions and activates the mullite crystallization.
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Synthesis of mullite from Topaz, refractory clay, and clay-Topaz compositions
Refractories and Industrial Ceramics, 2004Co-Authors: T V Vakalova, A V Ivanchenkov, V M Pogrebenkov, O. A. KonovalovaAbstract:Results of a study of the phase formation in Topaz-containing rocks and clay-Topaz compositions are reported. The percentage of Topaz in its mixtures with refractory clay is shown to be an important factor controlling the formation of crystalline phases.
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Synthesis of mullite from oxides doped with Topaz
Refractories and Industrial Ceramics, 2004Co-Authors: T V Vakalova, A V Ivanchenkov, V M Pogrebenkov, Evgeny V. AlekseevAbstract:Results of a study of the mullitization in stoichiometric pure oxides Al2O3 and SiO2 doped with Topaz are reported. A mineralizing Topaz-mediated effect is manifested in the activated synthesis of mullite of short prismatic habit involving products of thermal degradation of Topaz (mullite and volatile fluorides). The volatile active fluorides enhance structural imperfections in the reactants and promote their high-temperature interaction. Mullite produced by thermal degradation of Topaz plays the role of a seeding agent in the solid-state synthesis of mullite from oxides.
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Effect of Topaz on the synthesis of mullite in mixtures of kaolinite and alumina
Refractories and Industrial Ceramics, 2004Co-Authors: T V Vakalova, A V Ivanchenkov, V M Pogrebenkov, Evgeny V. AlekseevAbstract:The synthesis of mullite in mixtures of kaolinite and alumina in the presence of small amounts of Topaz is studied. Topaz is shown to activate the synthesis of both the primary (from kaolinite) and secondary mullite (through binding silica produced by thermal degradation of kaolinite), decrease the temperature of synthesis by 100°C, and increase the total yield of mullite. Products of the thermal degradation of Topaz — mullite and gaseous chemically active fluoride compounds — are shown to play the role of mineralizing agents.
