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Pure SiO2 (pure + sio2)

Distribution by Scientific Domains
Polymers and Materials Science40%
Physics and Astronomy40%

Selected Abstracts

Tribology,Structure Relationships in Silicon Oxycarbide Thin Films

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2010
Joseph V. Ryan
Silicon oxycarbide is a versatile material system that is attractive for many applications because of its ability to tune properties such as chemical compatibility, refractive index, electrical conductivity, and optical band gap through changes in composition. One particularly intriguing application lies in the production of biocompatible coatings with good mechanical properties. In this paper, we report on the wide range of mechanical and tribological property values exhibited by silicon oxycarbide thin films deposited by reactive radio frequency magnetron sputtering. Through a change in oxygen partial pressure in the sputtering plasma, the composition of the films was controlled to produce relatively pure SiO2, carbon-doped SiC, and compositions between these limits. Hardness values were 8,20 GPa over this range and the elastic modulus was measured to be between 60 and 220 GPa. We call attention to the fit of the mechanical data to a simple additive bond-mixture model for property prediction. Tribological parameters were measured using a ball-on-disk apparatus and the samples exhibited the same general trends for friction coefficient and wear rate. One film is shown to produce variable low friction behavior and low wear rate, which suggests a solid-state self-lubrication process because of heterogeneity on the nanometer scale. [source]

Grain-Boundary Viscosity of BaO-Doped SiC

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000
Giuseppe Pezzotti
Internal friction characterization of the viscosity of a residual SiO2/BaO glass, segregated to grain boundaries of polycrystalline SiC, is presented. The anelastic relaxation peak of internal friction, arising from viscous slip along grain boundaries wetted by a glass phase, is analyzed. Two SiC polycrystals, containing SiO2/BaO glasses with different compositions, are studied and compared with a SiC polycrystal containing only pure SiO2. The internal friction peak is first analyzed with respect to its shift upon frequency change. This analysis allows quantitative assessment of both the intrinsic viscosity and the activation energy for viscous flow of the grain-boundary phase. Both parameters markedly decrease with increasing amounts of BaO dopant, which is consistent with data reported in the literature on SiO2 and SiO2/BaO bulk glasses with the same nominal composition. Analysis of the peak morphology is also attempted, considering the evolution of peak width while varying the grain-boundary glass composition. Moreover, the role of microstructural parameters, such as the distributions of grain size and grain-boundary angles, on the broadening of the internal friction peak is addressed, and a procedure is proposed that allows quantitative evaluation of the activation energy for viscous flow of intergranular glass merely from the width of the internal friction peak. [source]

First discovery of stishovite in an iron meteorite

METEORITICS & PLANETARY SCIENCE, Issue 11 2003
Dan Holtstam
The mineral occurs intimately mixed with amorphous silica, forming tabular grains up to ,3 mm wide, with a hexagonal outline. It was identified using X-ray diffraction and Raman microspectroscopy. The unit-cell parameters of stishovite are a = 4.165(3) Å and c = 2.661(6) Å, and its chemical composition is nearly pure SiO2. Raman spectra show relatively sharp bands at 231 and 754 cm,1 and a broad band with an asymmetric shape and a maximum around 500 cm,1. The rare grains are found within troilite nodules together with chromite, daubreelite, and schreibersite. From their composition and morphology, and by comparisons with silica inclusions in, e.g., the Gibeon IVA iron, we conclude that these rare grains represent pseudomorphs after tridymite. The presence of stishovite in Muonionalusta is suggested to reflect shock metamorphic conditions in the IVA parent asteroid during a cosmic impact event. [source]

A micron-sized nanoporous multifunction sensing device

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2009
L. Moreno i Codinachs
Abstract In this work, a capacitive sensor based on Anodic Aluminium Oxide (AAO) porous structures has been developed. In some cases, the pores have been also conformally coated with a high chemical pure SiO2 by means of Atomic Layer Deposition (ALD). Temperature measurements have been done in DI water obtaining a response of 5 nF/°C. pH measurements have been performed and the responses obtained are between 0.2 and 1 nF/pH. The reproducibility of the sensors has been found to be high and a larger hysteresis effect has been observed in the samples with alumina pores rather than in the SiO2 ones. The hysteresis seems to be related to the charging of the oxide upon application of a voltage. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A mass spectrometric study of Al2O3 -SiO2 melts using a Knudsen cell

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2001
Johan Björkvall
The thermodynamic activities of SiO2 in Al2O3 -SiO2 liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863,2169,K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF2 standard. The mass spectra obtained for pure SiO2 were in agreement with earlier data. The activities of silica, measured in the present work at 2150,K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al. Copyright © 2001 John Wiley & Sons, Ltd. [source]