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- ItemCollaborative study into the analysis of total selenium and selenium valence states in glass - a general method by hydride generation atomic absorption spectrometry and photometry : Report of the International Commission on Glass (ICG) Technical Committee 2 "Chemical Durability and Analysis"(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Guadagnino, Emanuel; Çorumluoğlu, OrhanWhilst the determination of total selenium in glass is of great relevance to environmental purposes, the measurement of the oxidation states of selenium which may arise under different redox conditions may contribute to clarify the mechanisms of colour formation. In the proposed method, the determination of total selenium is carried out by hydride generation atomic absorption spectrometry (HGAAS) on three different glasses covering the range of selenium content between 10 and 130 mg/kg of glass. To prevent losses during the decomposition step, selenium is converted into a nonvolatile form as selenate (Se6+). When the sample is decomposed, the HCl Solution (c(HC1) = 10 mol/l) is made and selenium is pre-reduced to Se4+ by heating for 2 h at 80 °C. The determination of selenium oxidation states requires a stepwise approach. The measurement of Se0 is based on its insolubility in HF. After the sample is decomposed, Se0 is filtered off, dissolved from the filter with a HBr-Br2 mixture and finally measured by HGAAS. Se4+ and Se6+ are recovered in the filtrate of the same sample and determined together after conversion of Se4+ into Se6+. Se4+ is determined in the same filtrate by photometry with o-phenylenediamine (OPDA).
- ItemPostmortem analyses of salvaged conventional silica bricks from glass production furnaces(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Wereszczak, Andrew; Wang, Hsin; Karakus, Musa; Curtis, Warren; Aume, Victor; VerDow, DennisThe microstructure, phase content, and thermal conductivity of salvaged conventional silica bricks from float glass and TV-panel glass production furnaces were examined as a function of position through the brick, and compared with the original, unaltered brick materials. The silica brick from the float glass furnace was in service for approximately 10 years while that for the TV-panel glass furnace was for approximately 6 1/2 years. The microstructure and phase content in both salvaged bricks showed gradients, from tridymite at the bricks' cold-face ends, to cristobalite at their hot-face end even though both bricks were an initial mixture of tridymite and cristobalite to begin with. The thermal conductivity of both bricks had increased as a consequence of these phase and microstructural changes. Α thermal analysis model predicted that such changes would result in an increase in the bricks' cold-face temperature and heat content during service. The initially-produced temperature gradients and environment caused microstructural changes in the silica brick; however, the cause-and-effect relationship between temperature/environment and microstructural changes in the brick likely became mutually reversible once the microstructural changes initiated and the thermal conductivity of the brick started to change as a consequence.
- ItemRedox equilibria of polyvalent elements in binary Na2O · xSiO2 melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Gönna, Gordon von der; Rüssel, ChristianGlass melts with the basic compositions (in mol%) of 15 Na2O ∙ 85 SiO2 and Na2O ∙ 2 SiO2 were doped with oxides of various polyvalent elements. At temperatures in the range of 800 to 1550°C, square-wave voltammograms were recorded, which exhibit distinct maxima attributed to respective reduction processes. The following redox steps were observed: Sb5+/Sb3+, Sb3+/Sb0, As5+/As3+, As3+/As0, Cu+/Cu0, V5+/V4+, V4+/V3+, Cr6+/Cr3+, Cr3+/Cr2+, Fe3+/Fe2+ and Ti4+/Ti3+. Peak potentials measured in the Na2O ∙ 2 SiO2 glass depended linearly on temperature, while those of the 15 Na2O ∙ 85 SiO2 melt were affected by the crystallization of cristobalit at temperatures < 1300°C. Redox equilibria in the alkali-rich Na2O ∙ 2 SiO2 melt were generally shifted to the oxidized state by comparison to those measured in the 15 Na2O ∙ 85 SiO2 melt.
- ItemChemical indexes and in-vitro solubility(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Meringo, Alain de; Lafon, Fabrice; Furtak, Hans; Hanton, DanielDifferent chemical indexes have been proposed in the literature, in order to predict the influence of the chemical composition of mineral fibers on their properties. One of these properties is the acellular in-vitro dissoludon behavior (noted thereafter: solubility) in synthetic lung fluids at pH 7.4, which has been shown to be a reliable predictor of the results of expensive chronic long-term in-vivo tests conducted up to now with fibers [1 and 2]. This in-vitro solubility has been reported as being a function of the chemical composition [3 and 4]. The aim of this investigation was to assess if the in-vitro solubility could easily be predicted through conventional chemical indexes already reported in the literature; such as the following: - nonbridging oxygen (NBO) as calculated by Moore and Brown [5]; - optical basicity (OB) as defined by Baucke and Duffy [6]; - free enthalpy (ΔG°) of hydration as evaluated from tables in Paul [7]; - "Kanzerogenitätsindex" (KI) as defined in [8]. The relationship between the acellular in-vitro solubility expressed as KDISSiO2 or KDISCaO and these four different indexes has been analyzed. Nene of these indexes could be reliably used to prediet the in-vitro solubility at pH 7.4 for a broad range of composidons. KI is an acceptable indicator of in-vivo biopersistence [9], in a narrow range (15 to 40). It is the best of all the analyzed indexes giving a general trend for the solubility. The calculated correlation coefficient between KI and KDISSiO2 is then 0.78. This work shows that calculated indexes derived from the literature are not sufficient to prediet the results of in-vitro dissolution tests; and thus the need for a reliable standardized in-vitro test method is emphasized.
- ItemAnalysis of glass science and industry in the Czech Republic(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Kasa, StanislavThis article analyses glass science, research and the glass industry in the Czech Republic from 1996 to 1998. It contains the principal economic data and the geographical distribution of the Czech glass industry, as well as its structure regarding the manufacture of individual products. The final chapter deals with the current state of glass science and research in the Czech Republic. Also included are the main research institutes, together with their respective fields of research.
- ItemInfluence of various atmospheres on the surface properties of silicate melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Kucuk, Ahmet; Clare, Alexis G.; Jones, Linda E.The surface tension of a soda-lime-silica glass melt and some commercial glass melts including an E-glass, a TV panel glass, and a soft borosilicate was measured under various atmospheres. The atmospheres included dry argon, dry air and wet air with varying amount of water vapor using the sessile drop and pendant drop arrangements. In general, the surface tension of melts decreased in the order: dry argon, dry air and wet air. OH- groups from the water vapor in the atmosphere behave as a surface-active species according to the Gibbs adsorption equation and form a monolayer on the surface with certain number of molecules according to the Langmuir adsorption theorem. The number of OH- -like molecules in the monolayer is higher for the melts containing high ionic strength ions.
- ItemExperimental and industrial evaluation of a new fused cast modular checker design for decreasing regenerator plugging(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Boussant-Roux, Yves; Citti, Olivier; Miller, Michelle; Chaudourne, SergeThe plugging of regenerators of glass furnaces resulting from deposition of condensated gases is an important concern of glassmakers since it always leads to a reduction of the regenerative efficiency and sometimes causes strong corrosion of the refractories. SEPR has been working on technical solutions for regenerator problems for a long time. Special products like ER 5312 RX (β''' alumina, 85 % AI2O3) have been developed to protect the top of the packing and increase regenerator life. To improve fuel savings, type 4, a corrugated surface product, was introduced to the market in 1989. This product has since become the standard solution for cruciform packing. In 1997, to meet glass-maker's requirements, SEPR designed a new packing solution aimed at decreasing regenerator plugging risks. This new solution consists of a combination of two products: type 6 and type 4. Type 6 is designed for large flue sizes (up to 350 mm) and reduces plugging in the sulfate condensation zone. Type 4 is used at the top of the packing to maintain high thermal efficiency. Α complete thermal characterization of the new checker, based on laboratory tests and industrial on-site measurements, and including computer model development and adjustment, was performed. This paper presents the technical benefits of this new solution and the results of both laboratory experiments and industrial experience.
- ItemKinetics of phase separation in a 6.5 Na2O ∙ 33.5 B2O3 ∙ 60 SiO2 glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Flügel, Alexander; Rüssel, ChristianIndustrially melted glasses with the composition (in mol%) 6.5 Na2O ∙ 33.5 B2O3 ∙ 60 SiO2 were thermally treated at temperatures in the range of 660 to 750 °C. This resulted in phase separation, i.e. in the formation of a silica- and a sodium borate-rich phase with an interconnected microstructure. Both, the volume content of the borate-rich phase and the mean structure thickness (the correlation length) increased with time as well as with temperature. The volume content approached to a limiting value at constant temperature. The correlation length increased with time according to a power law (~ t^1/n). By contrast to previous studies, n was in the range of 1 to 1.2 within the temperature range and time scale studied. The correlation lengths were much larger (up to 12 µm) and the viscosities much lower than in most previous studies. The kinetic law was explained as controlled by visous flow.
- ItemNickel sulphide: new results to optimise the heat soak test for thermally toughened building glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Kasper, Andreas; Bordeaux, Frédéric; Duffrène, LucasThe spontaneous failure of tempered facade glazings has been known as a security and reputation problem of these beautiful parts of the surface of modern buildings since the late fifties. By kinetic investigations on synthetic nickel sulphides and by statistical analysis of the breakage of heat soak test ovens it is shown that this problem can be solved. If the test is done in a right and careful way, at temperatures of (290 ± 10) °C, holding time need not be longer than 2 to 3 h to fulfil the implicit requirements of the German Standard (DIN 18516). On the other hand, literature data show that it should be possible to further shorten this holding time if it were possible to heat up faster and more homogeneously the glass to be tested.
- ItemInfluence of mixed alkali oxides on some melt properties of TV screen glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Hwang, Jong-Hee; Park, Jeong-Hyun; Kim, Ki-Dong; Choi, Sang-SamThe influence of K2O/R2O (R2O = Na2O+K2O) on some melt properties was studied in alkali-alkaline earth-silicate TV screen glasses. Viscosity, surface tension, electrical resistivity, volatilization and devitrification of glass melts were determined. No mixed alkali effect was observed in viscosity, surface tension and liquidus temperature. They showed a linear behavior with increase of K2O/R2O. On the other hand, electrical resistivity and weight loss by volatilization showed a strong mixed alkali effect against relative alkali concentration. According to the dependence of viscosity, electrical resistivity and volatilization on K2O/R2O, the slope change of those properties took place at K2O/R2O = 0.4 to ≈ 0.5. The compositional dependence of viscosity, surface tension and liquidus temperature was discussed in terms of field strength, polarizability and material diffusion, respectively. Α correlation was also discussed between the dependence of properties on K2O/R2O and the production process of TV screen glass. In conclusion, from the viewpoint of both production and application of TV glasses it was suggested that the mole fraction of K2O/R2O should lie between 0.2 and 0.5.