DSpace :: Browsing by Author "Geotti-Bianchini, Franco"

Browsing by Author "Geotti-Bianchini, Franco"

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Analysis 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, Martina
The 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. A 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.
Angular emissivity at room temperature and spectral reflectance at near normal incidence of float glass, borosilicate glass and glass-ceramics
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Lohrengel, Joachim; Rasper, Manfred; Geotti-Bianchini, Franco; De Rio, Luca
An accurate investigation of the emissivity of uncoated flat glass (necessary to calculate the solar factor and the U value of glazing according to standardized procedures) was performed in agreement with Groupement Europeen des Producteurs de Verre Fiat, in support of CEN and ISO standardization activities. The total angular emissivity of a range of uncoated float glass samples was determined between 10 and 80 °C with an uncertainty of 0.5%. Both the normal and the hemispherical emissivity were nearly identical for all the samples investigated. No significant differences between the top and the bottom side were observed. Measurements were also extended to borosilicate glass and glass-ceramic plates used for fire-resistant glazing, determining their thermal conductivity and angular emissivity behaviour. In order to obtain addidonal information, also the spectral reflectance curves at near normal incidence between 2000 and 200 c m ⁻¹ were obtained using a spectroradiometer. The fact that almost identical curves were obtained for a wide range of float glasses (both sides) as well as for the fire-resistant materials confirms the correctness of the close emissivity values found. On the basis of the resuhs obtained, a Standard value of εn = 0.900 and a εh/εn ratio = 0.936 is suggested for both float glass and for the two other materials.
CEMS 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, Amedeo
Tin 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.
Influence 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, Dal
The 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).
Influence 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).
Infrared spectroscopic analysis of water incorporated in the structure of industrial soda-lime-silica glasses
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Geotti-Bianchini, Franco; De Riu, Luca
The paper illustrates a method for the determination of the water content of glasses by infrared transmittance spectroscopy from the exdnctions of the bands due to free and hydrogen-bonded hydroxyl groups dissolved in the glass. The procedure is discussed in detail, highlighting the sources of random and systematic errors and what can be done to improve the interlaboratory reproducibihty. The ratio of the intensities of the two bands at 2.8 and 3.6 µm is investigated accurately for a range of industrial soda-lime-silica glasses. In the case of containers and float glass it is nearly constant, but it varies widely for other products, such as household appliances, car headlamps and hand worked arücles, probably due to differences in the glass formulation. Accordingly, caution should be exerted in using the simplified method based on the measurement of the first band only, implying a constant rado. Finally, evidence of molecular water in the dealkalized surface layers of commercial articles is obtained using infrared reflectance spectroscopy.
Intercomparison of IR transmittance measurements on water-containing glasses : Report of the International Commissionon Glass (ICG) Technical Committee14 "Gases in Glass"
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Geotti-Bianchini, Franco; Preo, Martina; Smith, lan H.; Nijnatten, Peter van; Geißler, Heinz; Bucher, Greg
A previous paper illustrated a procedure recommended by Technical Committee 14 (TC 14 "Gases in Glass") of the International Commission on Glass (ICG) for the determination of the water content of soda-lime-silica glasses by infrared transmittance spec-troscopy. The present paper describes the results of an intercomparison of spectral transmittance measurements performed by TC 14 in order to check the interlaboratory reproducibility that can reasonably be expected when a range of industrial laboratories determines the water content of a given sample. Three samples were circulated within a group of 10 laboratories and for each of them17 spectral transmittance curves were reported, using various spectrophotometers. From each spectrum the corresponding water content value was calculated, using the TC 14 procedure. A statistical elaboration of the results is presented. The spectral transmittance values were affected by a significant spread, with maximum relative deviations up to 14.4 % (maximum relative standard deviation 4.5 %).The spread affecting the corresponding calculated water contents was much smaller, with maximum relative deviations within 4.8 % (maximum relative standard deviation 1.3 %).
Measured 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, Joachim
International 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.
Measured 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, Joachim
The 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.
New interpretation of the IR reflectance spectra of SiO2-rich films on soda-lime glass
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Geotti-Bianchini, Franco; De Riu, Luca; Gagliardi, Giovanni; Guglielmi, Massimo; Pantano, Carlo G.
A new interpretation of the reflectance spectra of weathered or silica-coated soda-lime glass between 1250 and 900 cm^-1 is suggested. Traditionally, the presence and intensity of each spectral band observed were attributed to the concentration of a given chemical species in the film. Contributions due to the substrate and to the film thickness were excluded. On the basis of a more rigorous model, with the help of mathematical and physical simulations, it is shown that the penetration depth is much higher than previously assumed. Accordingly, all the spectral features observed for coatings or weathered films are a function not only of the nature of the film, but also of film thickness and type of substrate.
Parameters 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, Franco
Poor 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.
Parameters 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, Franco
The 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.
Recommended 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.
Spectrophotometric determination of the normal emissivity of coated flat glass Report of the International Commission on Glass Technical Committee 10 "Optical Properties of Glass"
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Nicoletti, Fabiano; Geotti-Bianchini, Franco; Polato, Pietro
The results of the activity of TC 10 of the International Commission on Glass aimed at assessing the reproducibility and accuracy of the determination of normal emissivity from IR reflectance measurements with commercial spectrophotometers are presented. Eight European and American flat glass producers and two glass institutes participate in the activity. Two intercomparisons of near normal spectral reflectance are performed on 4 samples, representative of the current production. The circulated samples are subsequently calibrated in a metrological laboratory. The results show that even with a free integration procedure and reference mirror a satisfactory reproducibility can be achieved (the maximum discrepancy in computed U values between the participants being within 0.1 W/(m2 K)). The agreement significantly improves by using a common reference mirror, showing the importance of the availability of reference mirrors calibrated by some metrological source. After discussing the effect of the integration procedure on the resulting emissivity, a new 30 selected ordinates method is developed and transmitted to ISO (to be incorporated into the standard for the computation of the U values of double glazings).
Study of the high-temperature spectral behavior of container glass
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Endrýs, Jiří; Geotti-Bianchini, Franco; De Riu, Luca
The spectral absorption coefficients of container glasses in the wavelength region from 0.4 to 4.5 µm and in the temperature range from room temperature to 1400 °C were measured by a single-beam spectrophotometer by means of the transmission method. From the measured absorption coefficients radiative thermal conductivities in the temperature ränge from 600 to 1400 °C were calculated by means of Rosseland's diffusion approximation. The intensity of the band at 2.8 µm due to dissolved hydroxyl groups in glass was also calculated. While most previous measurements were performed on model glasses with a very simple basic composition, molten in laboratory furnaces from pure raw materials, the glasses investigated in this paper are the most frequently used types of container glasses with a complex composition and different chromophores. The influence of different coloring agents and dissolved water on the spectral behavior and radiative thermal conductivity of glass were studied, checking how the spectra change from room temperature to high temperature.
Thermal conductivity of float glass at room temperature
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Geotti-Bianchini, Franco; Lohrengel, Joachim
When 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.
Water content of sulfate-fined industrial soda-lime glass and its influence on workability
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Geotti-Bianchini, Franco; De Riu, Luca
The aims of the paper are: a) to systematically determine by IR spectroscopy the water content of sulfate-fmed industrial soda-lime glass (mainly Container and float, besides that household and technical glass) produced in Italy; b) to highlight the influence of redox State , melting conditions, batch and cullet addition on the water content; c) to check the consistency with time and between different feeders of the water content in the glass produced by a given furnace; d) to assess possible correlations between water content and workability in Container glass. The water content ranges between 300 and 400 ppm in conventionally fired glass, with electrical melting it decreases to 150 to 200 ppm, with oxycombustion it increases to 500 to 600 ppm. In the case of conventional flame melting the main factor influencing the water content is the redox State , due to a water/sulfate exchange. When a glass with a given color and redox State is produced in a given furnace, the daily oscillations of the OH level are moderate, with negligible effects on viscosity. In all the workability problems analyzed the contribution of water content oscillations was negligible as compared to other factors. According to the results obtained, significant water-related viscosity variations are expected to take place only when the meldng atmosphere or the redox conditions are significantly altered.

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