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Now showing 1 - 10 of 377
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    Significance of redox reactions in glass refining processes
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Yoshikawa, Hidemi; Kawase, Yoshinori
    The role of the redox reactions due to refining agents in the glass refining processes was examined. Α new approximate model for shrinkage (or growth) of gas bubbles in glassmelts in which redox reactions caused by refining agents were taken into account was developed. The proposed model is a modification of the quasi-stationary model by which the redox reactions due to refining agents can not be considered. It was found that the shrinkage (or growth) of gas bubbles in melts with refining agents is quite faster than that in those without refining agents. Numerical results for single-component and multicomponent gas bubbles indicate that the mechanism of the bubble shrinkage (or growth) in the refining process is significantly controlled by the oxidation of refining agents, which decreases (or increases) the oxygen concentration in the glassmelt and as a result causes the rapid oxygen transfer across the bubble/glassmelt Interface and hence the fast shrinkage (or growth) of the gas bubble. The applicability of the proposed model was examined using the computational results and experimental measurements in the literature. It was also found that the proposed model provides better predictions compared with the quasi-stationary model.
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    Verkehrsoptimierung (Traffic and Transport Optimization)
    (Oberwolfach-Walke : Mathematisches Forschungsinstitut Oberwolfach, 1999) Buckler Powell, Warren; Zimmermann, Uwe
    [no abstract available]
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    Mathematische Stochastik (Finance and Statistics)
    (Oberwolfach-Walke : Mathematisches Forschungsinstitut Oberwolfach, 1999) Heath, David C.; Schweizer, Martin
    [no abstract available]
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    Evaporation of fluorine, chlorine and selenium from glass melts and emission reducing measures
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Kirchner, Ulrich
    The simultaneous waste gas treatment of inorganic gaseous fluorine and chlorine Compounds as well as of gaseous selenium Compounds is still a big problem for many companies of the German glass industry. With the aid of an HVG/AiF research project investigations were carried out with the aim of characterizing the evaporation behaviour of fluorine, chlorine and selenium from industrially melted soda-lime-silica glasses (container glasses) and of correlating their behaviour with the operating data of the melting furnaces. The main effort, however, was put into investigating the absorption rates on an existing waste gas treatment plant depending on the kind and the quantity of the absorption agent. Moreover, the influence of the absorption temperature on the absorption rates was determined.
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    Influence of homologous substitutions of chemical components on the rheological properties and on isochomal workability of Silicate glass melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Yue, Yuanzheng; Brückner, Rolf
    Glass melts of various homologous Silicate glass series were investigated by means of the cylinder compression method with respect to their flow behaviour (Newtonian and non-Newtonian), stress generadon modulus (stiffness, brittleness) and critical deformadon rate (high-temperature tensile strength, isochomal workability). The experimental results show that decreasing CaO content and increasing basicity lead to the decrease of the brittleness of Silicate glass melts and to the increase of the critical deformadon rate, i.e. to the improvement of the isochomal workability of these melts. The mixed alkali effect of sodium potassium calcium Silicate glass melts at molar fracdon [K₂O]/[Na₂O+K₂O] = 0.5 has a favourable influence on the isochomal workability The correladon between flow behaviour and workability of glass melts is also discussed in the present paper. It could be shown that the ratio β = E2.8/E3.6 (E is the extinction of the hydroxyl band at 2.8 and 3.6 ηm, respectively) indicates the structural origin of the dependence of the mentioned rheological properties on the chemical compositions, at least within the homologous series.
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    Method for determining in-vitro dissolution rates of man-made vitreous fibres
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Guldberg, Marianne; Christensen, Vermund R.; Krøis, Winni; Sebastian, Klaus
    A "state-of-the-art" method for determining the in-vitro dissolution rate of man-made vitreous fibres (MMVF) is described. The dissolution rate is determined using an artificial lung fluid, adjusted to pH values of 7.5 or of 4.5, reflecting that the dissolution in vivo takes place both in the near-neutral lung fluid and in the acidic environment of the macrophages. The method is based on flow-through equipment and prescribes well-defined conditions using a ratio of the flow rate to surface area of 0.03 µm/s. The results obtained with this method correlate to results from in-vivo tests, and thus the method provides a tool for a comparative evaluation of the biodurability of different fibre types. The described method seems suitable to be estabhshed as a provisional standard test, until further investigations allow the definition of a final standard test. The empirically derived carcinogenicity index (KI) extrapolates the in-vitro results obtained for some fibre types at the neutral pH value to other very different fibre types. The proposed in-vitro method avoids these uncertain generalizations, as it is based on actually measured dissolution rates at pH values 7.5 and 4.5, respectively.
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    Bioactive coatings of glass-ceramics on metals
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Jana, Carsten; Wange, Peter; Grimm, Gabriele; Götz, Wolfgang; Nisch, Wilfried
    To combine the mechanical properties of high-strength base metals with the biological properties of bioactive materials, coatings of BIOVERIT® glasses and glass-ceramics on CoCr alloys and titanium have been produced. Different kinds of coating processes have been used: dipping, sputtering, plasma spraying, sintering and pasting. Dipping and pasting seem not to be suitable to produce layers because of cracks and low adhesion strength of the coatings (dipping) and the limitations in relation to the implant shape and the thickness of the layers (pasting). Using sputter techniques it is possible to produce dense layers ( < 10µim) with a high adhesion strength. Plasma spraying resuhed in layers with a thickness of 50 to 300µim, but during the plasma spraying process there is a partial evaporation of the highly volatile glass components. Sintering processes are very suitable to produce layers with a high adhesion strength; these layers are long term stable in simulated body fluid.
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    Phosphate glasses and glass-ceramics for medical applications
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Vogel, Jürgen; Wange, Peter; Hartmann, Peter
    Modified calcium phosphate glass Systems meet the requirements for the development of different biomaterials. Bioactive, longterm stable phosphate glass-ceramics and resorbable phosphate glasses were prepared in the Systems P₂O₅ - CaO - Al₂O₃ - Na₂O and P₂O₅ - CaO - MgO - Na₂O . Due to their high thermal expansion coefficients the bioactive phosphate glass-ceramics are excellently suited for coating metals. Using a salt-sintering process, porous resorbable glasses can be obtained. The properties of glassceramic coatings on cobalt/chromium alloys and the production of porous resorbable phosphate invert glasses are described.
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    Determination of coloring elements in the glass raw materials limestone and dolomite by flame atomic absorption spectrometry : Report of the International Commission on Glass (ICG) Technical Committee 2 "Chemical Durability and Analysis"
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Çorumluoğlu, Orhan; Guadagnino, Emanuel
    Α method is described for the determination of impurities such as iron, chromium, manganese, nickel, cobalt and copper in the glass raw materials limestone and dolomite. The proposed method involves the direct measurement technique in aqueous Solution by flame atomic absorption spectrometry. It has been proved to be an accurate and quick method for analyzing concentrations normally found in these raw materials.
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    Tracing of primary melt formation and reactions involved in glass batch melting
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Suwannathada, Pichanon; Hessenkemper, Heiko
    The primary melt formation and the reactions involved therein were traced by means of electrical conductivity measurement. After the temperature of the furnace had reached 1200 °C, 700 g of soda-lime-silica glass batches, either with or without carbon addidon, were loosely charged into an induction furnace. An electrical conductivity sensor connected with a thermocouple was put immediately into the batch; then the conductivity in terms of voltage drop and the temperatures were continuously recorded. Not only the changes in t h e reaction atmosphere were detected, but also at least four events leading to the occurrence of the primary melts could be identified. They were the double salt (Na₂Ca(CO₃)₂) with a soda-rich NaCa mixed crystal eutectic, the sodium distilicate-silica eutectic, the double salt melting temperature, and the soda melting temperature. The temperature at which the conductivity curve passed its original baseline is proposed as the primary melt formation temperature. The first highest sodium ion diffusion rate, or hopping region on the conductivity-temperature curve, is also proposed as the primary glass-forming melt temperature.