Glasses Tech

In a previous work (Morgan and London 1996), we proposed an optimized procedure for electron microprobe analysis (EMPA) of rhyolitic glasses using a broad (20 µm diameter), low-current (2 nA) fixed beam. Some important applications for EMPA of glass, such as vitreous inclusions in minerals and experimental run products, require smaller beam diameters that produce greater areal current densities (expressed as nA/µm2). For these situations, we have assessed the effect of areal current density on the migration of Na and its concomitant effects on other elements and their ratios during EMPA of granitic glasses. Anhydrous and hydrous glasses of a haplogranite composition (Ab38.23Or29.31Qtz33.37C0.10) were analyzed at 20 kV accelerating potential, using 2–50 nA beam currents, fixed beam diameters of 2–20 µm, and counting times scaled to yield similar analytical uncertainty at each condition (~2.6% relative for Na2O). (more glasses…)

This article reports on the use of ion chromatography (IC) to investigate extensively the release profiles of both cations and anions and characterize the relationship between composition and degradation for a ternary-based Na2O-CaO-P2O5 glass system developed as biomaterials. Studies are carried out on glasses with the formula 45P2O5-55(xCaO-Na2O) in deionized water, where x = 30, 35, and 40 mol%, using a cumulative release method, where the solution is changed at regular intervals. (more glasses…)

Many of the large structures of the cell, such as the cytoskeleton, are assembled and maintained far from equilibrium. We study the stabilities of various structures for a simple model of such a far-from-equilibrium organized assembly in which spherical particles move under the influence of attached motors. From the variational solutions of the many-body master equation for Brownian motion with motorized kicking we obtain a closed equation for the order parameter of localization. (more glasses…)

The concept that proteins exist in numerous different conformations or conformational substates, described by an energy landscape, is now accepted, but the dynamics is incompletely explored. We have previously shown that large-scale protein motions, such as the exit of a ligand from the protein interior, follow the dielectric fluctuations in the bulk solvent. (more glasses…)

We present a new, high-quality electron microprobe method for analyzing F in Fe-bearing minerals and glasses down to trace levels (<1000 ppm F). This method is empirically based and corrects for the problem of overlap of the FK peak onto the “shoulder” of the FeL 1 peak that arises when using synthetic multi-layered diffraction crystals. It also achieves high precision and accuracy while maintaining low detection limits and a small beam diameter. (more glasses…)

Coloured glasses produced commercially by Cebracê, São Paulo, were analysed by the thermoluminescent (TL) method, to verify the possibility of their use as high-dose dosemeters or irradiation indicators in industrial areas, due to their easy handling and their low cost. The samples were exposed to different radiation doses, using the Gamma-Cell 220 system (60Co) of IPEN. (more glasses…)

Cr K-edge X-ray absorption near-edge structure (XANES) spectra were recorded for silicate glasses of various compositions in the system CaO + MgO + Al2O3 + SiO2 ± TiO2, quenched from melts equilibrated as a function of oxygen fugacity (fO2) at 1400°C. The spectra vary systematically with fO2 (log fO2 ~0 to –16) indicating changes in the Cr oxidation state. The intensity of a shoulder on the absorption edge (attributed to the 1s 4s transition) was quantified using the corresponding peak in the XANES derivative spectrum and used to determine Cr2+/Cr. (more glasses…)

In an effort to improve the physical accuracy of models of the thermodynamics of silicate melts, we describe a systematic study of the extent of modifying cation mixing, using 17O 3QMAS NMR, in a series of Ca-Mg and K-Mg silicate glasses. (more glasses…)

A new calibration was performed for the molecular CO2 band at 2349 cm –1 in the infrared absorption spectra of rhyolitic glasses. Glasses with varying amounts of CO2 (730–3900 ppm by weight) and H2O (0.5–7.0 wt%) were synthesized in an internally heated pressure vessel at 200–800 MPa and 1100 and 1200 °C. The CO2 content of the glasses was measured by coulometric CO2-titration after thermal extraction at 1200 °C. It is shown that the entire CO2 content cannot be extracted from a rhyolitic glass at this temperature. Using the Lambert-Beer law, and taking into account the residual CO2 still present in the glasses after extraction, we have calculated a linear molar absorption coefficient of 1214 ± 78 L · cm –1/mol for the band at 2349 cm –1 . Strictly, this value is a practical absorption coefficient because the IR band intensity is related to the total CO2 content and not to the molecular CO2 content. (more glasses…)

The local structure of vanadium (V) in synthetic glasses of basaltic composition has been studied by means of high-resolution V K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to obtain quantitative data on distances, V coordination number (CN), and oxidation state. The compositions and experimental conditions were chosen so as to verify the effect of bulk-glass composition (using a diopside-anorthite composition, a sodium disilicate glass, and an iron-titanium-bearing basaltic glass) and V content (from 0.1 to 5 V2O5 wt%) on the structural role of V in these glasses. (more glasses…)