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- ItemThermal conductivity of float glass at room temperature(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Geotti-Bianchini, Franco; Lohrengel, JoachimWhen the heat transfer coefficient of multiple glazings is to be determined, it is important to know the exact thermal conductivity value of the glasses used for building purposes. The values given for flat glass lie between 0.8 and 1.15 W/(m K ) . The thermal conductivity of 11 float glass samples of 4 different colours, manufactured in 5 European countries, has been determined in the temperature range between 10 and 90 °C with an uncertainty of less than 1.5 %. At 10 °C, the mean value of all glasses investigated amounts to 1.022 W/ (m K); the individual values vary between 1.033 and 1.017 W/(m K) . On the basis of the composition, the basicity and the density, the measurement results could be well interpreted by known theoretical considerations. The slight variation of the thermal conductivity values obtained by measurement is in agreement with the values calculated from the composition and the density and can be explained by the fact that all float glasses are of nearly the same composition. By interpolation of the measurement data, coefficients could be determined to calculate the thermal conductivity from the oxide composition. The investigation has shown that - at 10 °C - a value of 1.02 W/(m K) can be applied for the thermal conductivity of flat glasses used for building purposes, independent of their colour or manufacturer.
- ItemCEMS study of tin in the hot end coatings of glass containers(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Geotti-Bianchini, Franco; Preo, Martina; Principi, Giovanni; Maddalena, AmedeoTin oxide coatings are applied to glass containers as adhesion promoters for the organic lubricants. Here, room temperature conversion electron Mössbauer spectroscopy (CEMS) is used to analyse a range of tin oxide coated containers. Readable CEMS curves could be obtained even for the thinnest (30 CTU or about 6 nm) coatings. The hyperfine parameters calculated from the spectral curves show that tin is tetravalent in crystalline form with a preferential grain orientation, which is reduced on annealing. The presence of tin in other oxidation states and dissolved in the matrix was excluded.
- ItemMeasured angular distribution of the emissivity and calculated radiation heat transfer of architectural coated flat glass Part 1. Theory(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) Geotti-Bianchini, Franco; Lohrengel, JoachimInternational standards for the calculation of the central U value of coated multiple glazings are based on a model of radiative heat transfer allowing the behaviour at all angles to be predicted from emissivity measured at normal incidence. In order to provide a background for such standards, a theoretical and experimental study of the angular variation of total directional emissivity at room temperature of the relevant materials (including uncoated float glass and typical architectural coatings) has been undertaken in cooperation with TC 10 of the International Commission on Glass and with the Light and Energy Group of the Groupement Europeen des Producteurs de Verre Fiat. After illustrating the equations which correlate the optical constants with angular reflectivity and emissivity, the possibility of mathematically correlating the normal emissivity with the hemispherical and effective emissivity for different materials is discussed.
- ItemMeasured angular distribution of the emissivity and calculated radiation heat transfer of architectural coated flat glass Part 2. Results and discussion(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) Geotti-Bianchini, Franco; Lohrengel, JoachimThe angular emissivity curves of 10 representative architectural coatings and of uncoated float glass are measured at 283 Κ with the help of an angular emissometer up to an angle of 70°. The experimental values can be fitted with the help of Fresnel's equations for a single, optically thick material, and extrapolated up to 90°. The obtained curves are integrated and the results compared with the values computed according to several drafts of standards in course of approval. The principle of computing the hemispherical and effective emissivity from normal emissivity with the help of a suitable multiphcative coefficient is found to be in substantial agreement with the experimental evidence.
- ItemInfluence of alumina content and modifiers on phase separation in soda-lime-silica glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Geotti-Bianchini, Franco; De Riu, Luca; Sglavo, Vinvenzo M.; Maschio, DalThe phase Separation behaviour of industrial soda-lime-silica glass is studied by visible light scattering. The main aspects which differentiate industrial glass from the ternary glass (composition in wt%): 76 SiO₂, 13 Na₂O, 11 CaO are considered. The obtained results show that the simple ternary glass easily develops phase Separation upon annealing at suitable temperature levels. Conversely, Container glass is stabilized against demixtion by the presence of a significant AI₂O₃ concentration, a significantly lower SiO₂ content and a more complex chemical formulation (partial Substitution of SiO₂, Na₂O and CaO with AI₂O₃, K₂O and MgO, respectively, as well as minor ingredients).
- ItemInfluence of water dissolved in the structure of soda-lime-silica glass on melting, forming and properties: state-of-the-art and controversial issues Report of the International Commission on Glass (ICG) Technical Committee 14 "Gases in Glass"(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Geotti-Bianchini, Franco; Brown, John T.; Faber, Anne J.; Hessenkemper, Heiko; Kobayashi, Sho; Smith, Ian H.The paper summarizes the information available about the water content of soda-lime-silica glass, the factors that influence it and the influence exerted by water in glass on redox and sulphur retention, on fming, on the melting and forming behaviour, workability and the physical and chemical properties of the melt. Such issues were discussed by the authors in their presentations at the first Forum on Water in Glass, organized in 1997 by Technical Committee 14 (TC 14 "Gases in Glass") of the International Commission on Glass (ICG). The present paper reports the conclusions of the final discussion, highlighting the issues on which consensus was reached (IR spectroscopy is suitable to monitor the water content; the water content of conventionally fired Containers is 300 to 400 ppm and daily oscillations are moderate; water, redox and sulphur interact mutually; water lowers the viscosity; the influence of water content variations on the radiative thermal conductivity is moderate) and the still controversial issues (influence of water and hydroxides in the batch on the final water content; influence of water in the batch and atmosphere on the redox State of the glass; influence of oscillations of OH level on the workability; influence of OH level on ease of forming, product quahty and strength).
- ItemParameters affecting the workability of container glass Part 1. Description of the problem - Melting history, rheology and influence of microstructure(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Geotti-Bianchini, FrancoPoor workability designates sporadic cases in which the forming behaviour of container glass varies unpredictably, impairing quality, productivity and sometimes strength. The literature offers several plausible suggestions to explain such a poor reproducibility of the rheological behaviour, generally associated with physicochemical parameters of the glass which are not routinely analyzed and which are supposed to vary with "melting history" (temperatures, raw materials, melting atmospheres) and to influence viscosity by altering the structure of "flow units", while the analytical composition remains unchanged. Alternative hypotheses are based on various not properly controlled process parameters, such as gob temperature distribution or plunger and mould condition including lubrication. Moreover, recent advances in rheology show that during the most critical stages of the forming process viscosity may change drastically with the deformation rate, providing a further plausible explanation for the observed irregular forming behaviour. One of the most promising physicochemical parameters is the possible presence of microstructure (phase separation, clustering, microcrystals). While in model glasses the correlation between microstructure and rheology is well-established, both at equilibrium and at high shear rates, there is still a lack of conclusive evidence about the presence of microstructure in industrial multicomponent glass.
- ItemRecommended procedure for the IR spectroscopic determination of water in soda-lime-silica glass : Report of the International Commission on Glass (ICG) Technical Committee 14 "Gases in Glass"(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Geotti-Bianchini, Franco; Geißler, Heinz; Krämer, Fritz; Smith, Ian H.The paper illustrates a procedure recommended by Technical Committee 14 (TC14 "Gases in Glass") of the International Commission on Glass (ICG) for the determination of the water content of soda-lime-silica glass by infrared transmittance spectroscopy, based on the two bands at 2.8 and 3.6 μm using as extincdon coefficients 70 and 150 l/(mol · cm), respectively As shown by the result of two intercomparisons, the agreement on the determined water concentration values can be quite satisfactory, within ±20 ppm, provided the procedure to evaluate the spectral curves is closely specified. The selected extinction coefficients are in reasonable agreement with recent evidence obtained using Nuclear Reaction Analysis.
- ItemAnalysis of polyethylene-based cold end coatings on glass : Containers with contact angle and IR spectroscopy(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Geotti-Bianchini, Franco; Preo, MartinaThe aim of cold end coating is to protect the glass surface from abrasive wear with the help of a suitably anchored film of organic material which decreases friction, by preventing direct glass to glass contacts. At present, routine controls on cold end coatings are limited to a lubricity test, i.e. the determination of the slide angle. Α laboratory procedure based on the determination of the contact angle with water is described in this work. It allows one to estimate the coverage with cold end coating locally from the waterrepellence caused by the organic deposit. This method can be used to investigate a ränge of problems associated with glass wettability, including label adhesion, acid etching and washing residues. The contact angle correlates well with the slide angle. Qualitative information on the nature of cold end coatings is obtained by extracting the glass with volatile organic solvents such as methylene chloride, evaporating them and analyzing the residue with infrared spectroscopy. In the case of a coating with RP 40 LT the IR curves show the presence of Polyethylene partially oxidized in order to improve adhesion to the glass surface, besides Polyethylene glycol added as an emulsifying agent. If the cold end coated container is rinsed with water, the glycol dissolves, but the Polyethylene derivative remains strongly anchored. Such bond withstands even drastic washings with water and detergents, alkali or oxidizing acids. Even when the glass is extracted with organic solvents, only a fraction of the deposit is dissolved. Therefore, even a quantitative analysis of the IR spectrum of the extract provides values smaller than the true coverage due to incomplete extraction.
- ItemParameters affecting the workability of container glass Part 2. Influence of dissolved gases and of other parameters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Geotti-Bianchini, FrancoThe hypotheses associated with variations of dissolved gases, structure, macroinhomogeneity (or cordiness), surface composition gradients and radiant heat transfer properties are presented in some detail in the second part of the review. While each of the physicochemical parameters considered was shown to be potentially influential by laboratory experiments, there is still no general agreement on the factors which are most relevant in practice. The most popular candidates are microstructure formation and variations of the content of dissolved gases; however, so far no conclusive evidence has been obtained. The influence of such parameters on stress-induced viscosity variations is also not well clarified. In order to decide what should be improved in the melting practice to achieve a better control of the forming behaviour, it is essential to solve the alternative with suitable experiments on carefully selected production samples.