Home About us Contact
|
Home About us Contact | ||
|
|
||
High Silica Contents (high + silica_content)
Selected AbstractsCOLD NEUTRON PROMPT GAMMA ACTIVATION ANALYSIS,A NON-DESTRUCTIVE METHOD FOR CHARACTERIZATION OF HIGH SILICA CONTENT CHIPPED STONE TOOLS AND RAW MATERIALS,ARCHAEOMETRY, Issue 1 2008ZS. KASZTOVSZKY Recently, several archaeometrical projects have been started on the prehistoric collection of the Hungarian National Museum. Among the analytical methods applied, non-destructive prompt gamma activation analysis has a special importance. We have also tested the potential of this method on chipped stone tools, with the aim of determining their exact provenance. On the basis of major and trace element components, characterizations of stone tools and their raw materials,silicites (flint, chert, radiolarite and hornstone) as well as volcanites (felsitic porphyry and obsidian),were performed. We discuss some important results concerning each group, as case studies. Compiling the data set of different PGAA analysis series, compositions of 110 samples are reported, including 76 archaeological pieces. In the future, we plan to extend the number of investigated objects in each class. [source] Thermochemistry of Glasses in the Y2O3 -Al2O3 -SiO2 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Yahong Zhang Enthalpies of drop solution in molten 2PbO-B2O3 at 1078 K were measured for glasses along the 2YAlO3 -3SiO2 and return ½Y3Al5O12 -3SiO2 joins. The onset glass transition temperature increases slightly with increasing silica content and Y/Al. Enthalpies of mixing were calculated on the basis of amorphous end members. Strongly negative heats of mixing support the absence of miscibility gaps except possibly for very high silica content, consistent with experimental phase analyses, which indicate much narrower miscibility gaps compared with the phase diagrams calculated on the basis of previous data and the CALPHAD formalism. [source] High-Si phengite, mineral chemistry and P,T evolution of ultra-high-pressure eclogites and calc-silicates from the Dabie Shan, eastern ChinaGEOLOGICAL JOURNAL, Issue 3-4 2000Robert Schmid Abstract A suite of coesite,eclogites and associated calc-silicate rocks from the ultra-high-pressure (UHP) belt in the Dabie Shan (eastern China) was investigated petrologically. Field relations and the presence of UHP minerals such as coesite, omphacite and high-Si phengite in the eclogites and the enclosing calc-silicates testify to a common metamorphic evolution for these two lithologies. Except for one sample, all bear phengite with unusually high silica contents (Si up to 3.7 per formula unit). Phengite occupies various textural positions indicating that different metamorphic stages are reflected by these white micas, which correlate with distinct mineral zonation patterns. Using the latest thermobarometric calibrations for eclogite-facies rocks, maximum pressure,temperature (P,T) conditions of 40,48 kbar at <,750°C were estimated for the peak-metamorphic mineral assemblages. These P,T conditions were calculated for both eclogitic garnet porphyroblasts with diffusion-controlled zoning as well as garnet porphyroblasts with prograde growth zonation patterns. Most samples were affected by a strong retrograde overprint mainly under eclogite- and amphibolite-facies conditions. Thermobarometry using mineral sets from different textural positions reveals cooling and decompression of the UHP rocks down to <,20 kbar at <,600°C for the bulk of the samples. Decompression and heating indicated by a few samples is interpreted to result from mineral chemical disequilibrium or late thermal influence. These new data show that subduction of continental crust in the Dabie Shan was deeper than previously thought, and also that some cooling and decompression took place at upper-mantle depths. Copyright © 2000 John Wiley & Sons, Ltd. [source] Preparation and properties of high molecular weight polyethoxysiloxanes stable to self-condensation by acid-catalyzed hydrolytic polycondensation of tetraethoxysilaneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2003Yoshimoto Abe Abstract The acid-catalyzed controlled hydrolytic polycondensation of tetraethoxysilane (TEOS) provided polyethoxysiloxanes with weight-average molecular weights of 2300,11,700, which depended on the reaction molar ratios of the water, catalyst, and solvent to TEOS. They were soluble in common organic solvents and stable to self-condensation and were characterized with high silica contents of up to 67%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2250,2255, 2003 [source] | ||||||||||