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- ItemInfluence of modifier cations on the radiation-induced effects of metaphosphate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Ebeling, Polina; Ehrt, Doris; Friedrich, ManfredThe influence of different modifying cations on the radiation-induced defect generation in metaphosphate glasses was studied by optical absorption and electron paramagnetic resonance spectroscopy. For this task, several model glasses were prepared. These were simple metaphosphates of alkaline earths, aluminum and zinc. The synthesized glass samples were irradiated with X-rays and with UV light from an Xe/Hg lamp. The cation-dependent differences in the structure of the phosphate glasses were found to have a great influence on the concentration of some radiation-induced defects and thus on the optical absorption. The influence of the different cations became especially distinct under UV light Irradiation due to the selective interaction of the UV light with the glass samples. Some additional phenomena were observed for the irradiated zinc and magnesium metaphosphate glasses which were not found by the previously undertaken study of complex phosphate glasses.
- ItemApplication of electrical heating in forehearth channels(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Grössler, JürgenElectrical heating of forehearth channels can be either indirect with radiant heating elements installed above the glass surface, or direct utilizing immersed electrodes. Two types of heating elements are used, made of either silicon carbide or molybdenum disilicide. Electrodes are normally made of molybdenum, but tin oxide is also used, and platinum alloy may be required for some special applications. Direct electrical heating is also used in forehearths to supplement the traditional gas heating, and can provide a significant improvement in the thermal homogeneity of the glass at the end of the channel. Excellent results can also be obtained with full electrical heating. Whatever type of electrical heating is used, the relevant safety standards must be applied.
- ItemAnalysis of dissolution of a spherical gas bubble in a glass melt in the presence of a flow and a fast redox reaction(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Lertskrai, Supawan; Kalachev, LeonidModeling a process of dissoludon of a slowly moving gas bubble in a glass melt can be reformulated as a problem of dissoludon of a stadonary bubble in a flow. It is shown that in the presence of fast redox reaction (outside the bubble) the effect of the flow on the time of dissolution is negligible. Many authors omit the flow when modeling dissolution of bubbles in glass melts. This analysis specifies the conditions under which such omission can be justified. Due to the presence of fast reaction the problem is singularly perturbed. The boundary function method was used to obtain asymptotic approximation of the solution. Asymptotic results are compared with numerical computations performed for the original statement of the problem.
- ItemMeasurement and mathematical modelling of the heat transfer in the glass forming process, in consideration of the heat transfer coefficients and radiation influences(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Höhne, Diethard; Pitschel, Bettina; Merkwitz, Markus; Löbig, RicoDuring forming, glass to mould contact temperatures are the significant factor for the final glass surface quality. For a good characterization of this contact condition the heat transfer by conduction and radiation needs to be described in detail. Α laboratory testing unit was set up to investigate the influence of radiation emitted by different glass composidons and the influence of different mould materials used during forming. To support the experimental results, heat transfer conditions and temperatures were modelled at given boundary conditions using the CFD-Code FLUENT software program applying discrete models. Measurement and modelling results show that the radiation influence on heat transfer is strongly dependent on the spectral absorption coefficient of the glass which affects heat flux densities and surface temperatures. Results show up to 15 % higher heat flux density for amber glass compared to flint glass. In addition, internal glass temperature distributions are strongly affected. If glass throughput, type of forming tools and mould cooling settings are carefully adapted to the optical characteristics of the glass, an optimal surface quality and physical strength can be achieved, which may lead to significant economic benefits. Due to the complex interactions of the parameters which influence glass to mould heat transfer mathematical modelling proves to be essential for future developments in forming technology.
- ItemHigh-temperature spectroscopic study of redox reactions in iron-and arsenic-doped melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Schirmer, Henning; Müller, Matthias; Rüssel, ChristianGlasses with the basic composition 16Na2O - 10CaO - 74SiO2 doped with iron or with both iron and arsenic were studied by means of high-temperature UV-VIS-NIR spectroscopy. Increasing temperatures led to a shift of the UV absorption edge caused by Fe3+ -charge transfer bands to larger wavelengths. All other bands, especially the Fe2+ absorption band at around 1100 nm, decreased in intensity at higher temperatures. For glasses, solely doped with iron, the temperature dependency of the extinction coefficient was quantitatively determined. Glasses doped with both arsenic and iron showed a different behaviour: the intensity of the bands decreased up to a temperature of 600 to 650 °C and then increased again. This can be explained by the temperature-dependent redox reaction 2Fe3+ + As3+ ⇌ 2Fe2+ + As5+. Increasing temperatures lead to a shift of the reaction to the right. This reaction is in equilibrium at temperatures > 650 °C and gets frozen in at smaller temperatures, depending on the respective iron and arsenic concentrations. The latter is explained by a numerical simulation assuming the redox reactions to be controlled by diffusion.
- ItemHigh-temperature UV-VIS-NIR absorption and emission spectroscopy of soda-lime-silica glasses doped with Nd2O3(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Gödeke, Dieter; Müller, Matthias; Rüssel, ChristianAbsorption spectra were recorded from a glass with the basic composition 16Na2O ∙ 10CaO ∙ 74SiO2 doped with 4 wt% Nd2O3 at temperatures in the range from 25 to 1400°C. The effective width of the observed absorption peaks increased with increasing temperature, while the peak positions remained nearly constant. Some absorption coefficients decreased with temperature while that at a wavelength of 657 nm increased notably. Emission spectra were recorded from glass melts exhibiting a temperature gradient at the surface (cold surface). The spectra showed distinguished minima at those wavelengths where the absorption maxima occurred. Numerical simulation of the emission spectra assuming a constant temperature gradient at the surface is in agreement with the experimental spectra.
- ItemIR and Raman spectroscopic study of some strontium aluminosilicate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Peuker, Christel; Brzezinka, Klaus-Werner; Nofz, Marianne; Pilz, Walter; Geißler, HeinzVibrational spectra are measured for strontium aluminosilicate glasses with the composition (in mol%) x SrO ∙ y AI2O3 ∙ (100-x-y) SiO2 (33 ≤ x ≤ 40, 0 ≤ y ≤ 2) with a water content ranging from 0.014 to 0.14 mol ∙ l-1 . The OH bands systematically change with glass composition in both MIR and NIR regions. The ratio of the absorption coefficients α3550/α2800 increases with decreasing number of nonbridging oxygens per tetrahedron (NBO/T; Τ = Si, AI). This indicates an increasing amount of strongly hydrogen bonded OH groups (2800 cm-1) with NBO/T relative to the weakly bonded hydroxyls (3550 cm-1) within the compositional series. Intensity changes in the Raman and IR reflectance spectra also reflect the substitution of Al3+ for Si4+ in the network and the incorporation of Sr2+. The increasing intensity ratio of the Raman bands I945/I1070 with NBO/T indicates an increase of structural units relative to Q^3, as well as the weak shoulder at 870 cm-1 shows a rising amount of Q units. The growing intensity of the IR reflectance band at 930 cm-1 with NBO/T confirms the increasing amount of nonbridging oxygen in the glasses. Α depolarized Raman band at 330 cm-1 was assigned to an Sr-O vibration. For hydrated samples the significantly higher ratio of α3550/α2800 in relation to the basic glasses can be explained by structural changes in the samples due to the water enrichment procedure. The hydroxyl content of the basic and hydrated glasses can be estimated by the so called two-band method with composition independent extinction coefficients for the two IR bands at about 3550 and 2800 cm-1, ε3550 = 80 1 ∙ mol-1 ∙ cm-1 and ε2800 = 170 1 ∙ mol-1 ∙ cm-1, independent of the Al3+ content of the glasses.
- ItemSaving fuel by efficient crown insulation(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Lutskanov, Stan[no abstract available]
- ItemAmber chromophore formation in sulphur- and iron-containing soda-lime-silica glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Beerkens, Ruud G. C.During cooling of reduced soda-lime-silica glass melts, doped with iron oxides and sulphur species, ferrous iron (Fe2+) reacts with sulphite (SO3 2-), and the Fe3+ (ferric iron) and also the S2- (sulphide) concentration will increase. The sulphite concentration in the amber glass melt after fining is sufficient to produce ferric iron and sulphide, required for amber chromophore formation during the cooling process. The product of the concentrations of Fe3+ and sulphide will strongly increase during coohng below about 1000 K. This mechanism implies that a necessary condition for amber formation is the availability of sufficiently large iron concentrations in the presence of a sufficient sulphite content in the high-temperature glass melt. The formation of a chromophore, based on Fe3+ - S2- - 3O2- - nNa+ complexes in the silicate glass will lead to amber colouring. Α strong dependency of the amber intensity of the glass on the maximum temperature of melting, the alkali concentration of the glass, the total iron concentration and on the oxidation-state of the melt has been found experimentally. The charge of the networkmodifying alkali ions stabilizes the ferric iron-sulphide-oxide-alkali chromophores. In strongly reduced melts, hardly any sulphite can be formed and during cooling, the amber chromophore formation is limited. Experiments show a decrease in ferric iron concentrations and in the amber intensity when over-reducing glasses. Α decrease in the amber intensity of amber glasses with increasing water content is probably caused by lower sulphite retention after fining of waterrich melts.
- ItemTheory of the spectral transmittance of Christiansen filters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Hoffnnann, Hans-JürgenChristiansen filters are usually made of grains of transparent materials, such as glass, immersed in a fluid with matching refractive index. If the refractive index of the grains matches that of the fluid the spectral transmittance is maximum. It decreases with increasing difference between the refractive indices. Since a formula due to Raman and Shelyubskii, which is widely used in the literature to describe the spectral transmittance of such filters, has no scientific basis, a new theory is developed taking into account reflection and refraction at the boundaries between grains and fluid. The theory is applied to spheres distributed in the immersion fluid. In this ease, adjustable parameters are not required. For grains of arbitrary shape one needs a statistical description of the boundaries and their orientation. To simplify the procedure an adjustable parameter is introduced to account for such effects. The theory takes into account the aperture angles of the incident beam and of the detector to measure the transmittance. It predicts the dependence of the spectral transmittance as a function of the difference between the refractive indices, the average grain diameters and the thickness of the filter. The inhomogeneity of the refractive index of the glass grains can also be taken into account. The spectral transmittance curves published in the literature are qualitatively quite well described by the calculations. Exact fits, however, are not possible, since the aperture angles are generally not given for the published results. Therefore, experimental investigations controlling all necessary parameters are in progress.