Search Results
Multi-method characterization of soda-lime glass corrosion : Part 2. Corrosion in humidity Report of the International Commissionon Glass (ICG) Subcommittee of Technical Committee 19 "Glass Surface Diagnostics"
As-received and cleaned soda-lime glass surfaces corroded in high relative humidity of 95 % at a temperature of 60 °C for times up to one week are investigated by means of TOF-SIMS, SNMS, XPS, NRA, ERD, RBS, GIXR, AFM, SEM and optical microscopy. Distinct differences in the corrosion behavior are observed for as-received and cleaned glass surfaces. Changes in element concentration in the glass interface and in the topography of the glass surfaces are described for different exposure times in humidity. They are combined with variations in density of the modified surface layer. Cleaning before the corrosion treatment drastically reduces degradation; cleaning after the corrosion treatment can restore the surface.
Open-pore sintered glass-ceramics as carrier material for biotechnological use
Open-pore carriers with defined open porosity up to 45 % for biotechnological use were manufactured by sintering and crystallization of glass powders of cordierite stoichiometry. The stop of the shrinkage caused by a surface crystallization of the glass ("sinter blockade") is utilized to stabilize a desired pore volume without filier or foaming aids. Glass powders of the stoichiometric composition of cordierite (2MgO · 2AI₂O₃ · 5SiO₂) with different grain size distributions were used as starting materials. The efficiency of the sinter blockade and thereby the stabilized porosity of the resulting compact mainly depends on the surface nucleation density at the Single glass particles which can be adjusted by powder processing. Furtheron, the chosen grain size distribution of the glass powders and the sintering process parameters (heating rate, temperature, heating time) are important factors to control the sintering behaviour. Samples of carrier bodies produced by this way are tested and evaluated quantitatively as carriers for biofilms in a biotechnological process for decomposition of pollutants in a synthetic model waste water system.
Low-temperature tensile deformation of flat glass containing metal particles to generate dichroism
Uniformly oriented metal particles shaped like prolate spheroids are produced by tensile deformation of flat glasses, containing small spherical particles of some 10 nm in diameters. The deformation is performed at temperatures only slightly above Tg. High tensile stresses up to 200 N/mm² and low velocities of deformation characterize the special conditions of this process. The method has been improved such as to exceed the previous limitation to relatively small values of the cross section of the specimens. Α unidimensional hydromechanical model including the conservation equations for momentum, mass and energy describes the glass deformation. The model has been solved numerically Α good agreement has been attained between experimental and theoretical results.
Local clouding of glass after machine dishwashing
The local clouding of glasses after dishwashing near the mouth rims on a coffee pot made from borosilicate glass, on a wine cup made from lead crystal glass and near the stem base on a wine cup made from barium Silicate glass has been found to be due to damage during manufacture. The examined clouding is different from the two well known types of filming and etching cloudiness related to the reactions of glass with water and detergent in the dishwasher. The intensive study on the wine cup of lead crystal glass shows that a phase Separation was induced during the flame treatment on the sharp rim and base. The aggregates of Pb-rich spheres scaled off when the thin covering of SiO2 rich skin was eroded away and consequently holes were formed on the glass surface on the micrometre scale, which resulted in light scattering and the clouding of the glassware. Evaporation species from warmer regions onto the colder areas of the glass surface could be observed, but they are not the reason for the local clouding in this study. Dendritic thin corrosion products caused by air exposure could be detected on the undisturbed glass surface as well.
Hat sich Georgius Agricola in seiner Abhandlung über Glaserzeugung am Ende seines Werkes „De re metallica" geirrt?
[no abstract available]
Mechanisms of the formation of gas bubbles in heat treatment of glass-silicate tiles
Theoretical research has been done into the mechanisms of the formation of gas bubbles which takes place during the sintering of the glass granulation product under the conditions of heating its upper layer. It is shown that in the bubble, there is a possibility of an inverse thermal distribution which will lead to a thermal jump on its boundary. At the thermal processing temperatures, the presence of CO2 increases the effect of absorption of the radiation conditioned by the spectral zones. Experimentally, it has been proved that a thermal field inversion takes place in the presence of an inner diffusing layer joined to a clearly transparent one for the thermal radiation of the material.
Origins of anomalous mixed-alkali effects in ion-exchanged glasses
Ion transport properties in ion-exchanged glasses are re-examined by a.c. impedance and infrared spectroscopies. In typical soda - lime-silica (float) glass it is shown that when Na+ ions are replaced by K+ ions, the region of highest resistivity resides in the surface, confirming the earlier result of Tomandl and Schaeffer. The existence of this anomalous impedance is correlated with cationinduced relaxations of the network (CIRON). This process enables the glass to accommodate larger ions at the expense of empty Κ sites (which in melt-grown glasses provide the stepping stones for ion migration). As a consequence of the structural relaxations, the compressive stresses stored within the surface of the glass may be smaller than expected, even when ion exchange occurs far below Tg and the effects of viscous flow can be neglected.
Fabrication of SiO2 glass fibres by thermoplastic extrusion
The fabrication of silica glass fibres by thermoplastie extrusion of nanosize and micron SiO2 powders has been investigated. The powders were mixed with a binder system, compounded for 3 h at 150 °C, and finally extruded through a die with a 500 μm-diameter die land. After debinding the green fibres at 500 °C, these were sintered for 1 h at 1100°C under air to yield glassy and crack-free silica fibres with a final diameter of 400 μm. The effect of the two different particle size distributions as well as the influence of varying powder loading (between 38 and 58 vol.%) on the rheological properties of the feedstocks were analysed using capillary rheometry. The debinding and sintering behaviour was also investigated using mercury intrusion porosimetry, thermal gravimetrie analysis and dilatometry.
Ratio of CaO/K20 > 2 as evidence of a special Rhenish type of medieval stained glass
The chemical compositions of more than 300 medieval stained glass samples of different local origin have been published so far. Regarding their characteristic components they can be classified into five types. About 80 % of all investigated samples proved to be potash-lime-silica glasses with roughly equal concentration of CaO and K₂O (type 1). But a small group of little more than 20 samples gave a ratio of CaO/K₂0 > 2 (type 2), all but three of which had been taken from two churches of the Rhine region (St. Catherine Church Oppenheim and Cologne Cathedral). Hence, it seems likely that a corresponding recipe was used there, which was nearly unknown elsewhere in Europe. Investigation of further objects of this region might be of interest for the history of technology.
Studies on viscosity of dried sodium water glasses by extrusion
Α study on viscosity and flow behavior of dried water glasses using an extrusion method is first reported. The rheological properties of water glass samples with water concentrations in the range from 22.2 to 36.4 wt% and also some glycerin-containing samples were studied. The extrusion method used enables the determination of viscosities in the range from 10^7 to 10^10 dPa s. By comparison to glass melts, relatively low temperatures in the range from 50 to 85 °C are used. During extrusion of dried water glasses, the viscosity decreases significantly with increasing shear rate. Lower water concentrations lead to a more pronounced deviation from Newtonian flow behavior. This is attributed to nonlinear flow behavior rather than to localized viscous heating effects by mechanical deformation work. Furthermore, the effect of composition on the viscosity-temperature dependence is studied. The higher the water concentration, the lower is the viscosity. Glycerin additions intensify this effect. Generally, the viscosity decreases with increasing temperature. Vogel-Fulcher-Tammann parameters are obtained by ftting the data of extrusion experiments and the corresponding Tg values.