نتایج جستجو برای: cristobalite
تعداد نتایج: 356 فیلتر نتایج به سال:
Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of...
With the recent eruption of the Icelandic volcano Eyafallajökull and resulting ash cloud over much of Europe there was considerable concern about possible respiratory hazards. Volcanic ash can contain minerals that are known human respiratory health hazards such as cristobalite. Short-term ash exposures can cause skin sores, respiratory and ocular irritations and exacerbation of pre-existing lu...
BACKGROUND Determination of quartz by Fourier transform infrared spectrometry (FTIR) is not specific: the obtained results are influenced by matrix components, some of which cause spectral interference. The aim of the study was to evaluate the effect of dust components responsible for spectral interference with quartz on the results of its determinations, and to develop methods to minimize the ...
OBJECTIVE To investigate the variation of the strength of gypsum-bonded dental investments with burnout temperature. METHODS The disc-rupture test was employed at burnout temperatures ranging from 450 to 800 degrees C for four products (Beauty Cast, Cristobalite, Novocast (all WhipMix) and Deguvest California (Degussa)). In this test, an investment disc is created inside an investment mold su...
Cryogenic heat-capacity measurements on coesite and stishovite provide thermodynamic properties from 5 to 350°K. The heat capacities (C,), entropies (SO), and Gibbs energy functions [-(Go H”,)/T] are 10.85, 9.65, 4.124, and 10.27, 6.64, 2.362 at 298015°K for coesite and stishovite, respectively, in Cal/( mole “K). Enthalpies of transition for phase changes were determined by solution calorimetr...
The hydrothermal formation of sodium hydroxyborate enclathrated sodalite synthesized from an initial ternary mixture of mullite, cristobalite and corundum has been investigated. Depending on temperature and pressure the compound Na7-5[AlSi04]6[B(0H)4]1.5 • 2H20 could be synthesized in form of polycrystalline powder as well as in form of single crystals. The kinetics of the sodalite growth could...
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