Glastechnische Berichte : Zeitschrift für Glaskunde

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Einfluß der Eisenoxide auf die Kristallisation von Basaltfasern
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Wojnáravits, Ilona; Barna, Árpád
The influence of iron oxide on the crystallization of basalt wool, made by melting in a cupola furnace, has been investigated. The changes in structure and morphology caused by heat treatments in air, argon gas, and vacuum have been observed by x-ray diffraction, transmission and scanning electron microscopy. It has been shown that the action of air in initiating crystallization is related to a change in the oxidation of iron. To produce a high resistance to heat in the basalt wool a high value of the ferrous: ferric ratio is desirable because ferric ions aid both nucleation and growth of crystals.
Erlaubte Biegespannung in Glasbauteilen im Dauerlastfall : Ein Vorhersagekonzept aus dynamischen Labor-Festigkeitsmessungen
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Exner, Gerhard
The strength of glasses and glass ceramics is not an intrinsic property like density but depends especially on the mechanical condition of and tensile stress present in the surface, the maximum permissible probability of fracture, the time distribution of loading particularly the duration of the effective tensile stress, and the surrounding medium. A concept is proposed for dealing with the problem of evaluating the strength of intermittently loaded structural glass components. Whilst surface quality in relation to strength requires at least one of a series of measurements in the laboratory, factors for the area, the probability of failure and the effect of time could be defined. Equations that permit this are reported and are valid for the Weibull model with two parameters. An example is given to provide a detailed explanation of the foregoing; diagrams make the assumptions clear. The theoretical basis is being referred to in full so that the limits of application are able to be evaluated.
Das 100 Jahre alte Thermometerproblem und der „Mischalkalieffekt"
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Dietzel, Adolf
Das Thermometerproblem bei den alten Soda-Pottasche-Gläsern, d. h. die Nullpunktsdepression bei vorheriger Erwärmung und die langsame „Erholung" (säkularer Anstieg), wird erläutert. 1883 erkannte Weber [1], daß diese thermische Nachwirkung nur dann auftritt, wenn Na₂O und K₂O gleichzeitig im Glas enthalten sind; sie ist geringfügig, wenn nur ein Alkali vorhanden ist. Systematische Versuche von Schott [2] führten dann zu dem weltberühmt gewordenen Normalthermometerglas 16 III, das seit 1885 unverändert hergestellt wird. Für das Auftreten der Depression wird bisher der sogenannte Mischalkalieffekt verantwortlich gemacht, für den es aber auch keine einleuchtende Erklärung gab. An anderer Stelle wird gezeigt, warum dieser Mischeffekt um so größer ist, je größer der Unterschied der Fremdkationen-Feldstärken ist. In der vorliegenden Arbeit wird gefolgert, daß das Thermometerproblem geradezu auf einem Anti-Mischeffekt beruht, d. h. eine Nullpunktsdepression muß um so größer sein, je kleiner der Feldstärkenunterschied ist. Bei Borosilicat-Thermometergläsern mit sehr hohem SiO₂-Gehalt liegen die Verhältnisse anders; hier kommt es lediglich zur kurzfristig reversiblen elastischen Deformation des SiO₄-Netzwerks und damit zu keiner nennenswerten Nullpunktsdepression. The 100 year old thermometer problem and the „mixed alkali effect" The problems with thermometers made of the old soda-potash glasses, namely zero point depression after previous heating and the slow recovery (secular rise), are described. Weber [1] showed in 1883 that these thermal after effects only occurred when the glass contained both Na₂O and K₂O; they are insignificant if the glass contains only one alkali. Systematic investigations by Schott [2] led to the world famous standard thermometer glass 16 III which has been made, unchanged, since 1885. The occurrence of zero point depression was previously attributed to the so-called mixed alkali effect but no detailed explanation was given. It has been shown elsewhere that this mixed alkali effect becomes greater as the difference in the foreign cation field strength becomes larger. In this work it is argued that the thermometer problem must be attributed to an „anti-mixed-alkali" effect, that is that the zero point depression must become greater the smaller the difference in field strength. Borosilicate thermometer glasses of high silica content show different behaviour; here there is only a brief reversible elastic deformation of the silicate network and thus no significant zero point depression. Le problème des thermomètres vieux de 100 ans et „l'effet alcalin mixte" Le problème des thermomètres en verre sodopotassique, c'est-à-dire la dépression du zéro lors de l'échauffement précédent et la lente «restauration du zéro» (ascension séculaire), est éclairci. En 1883, Weber [1] s'aperçut que cet effet thermique n'avait lieu que lorsque le verre renfermait simultanément Na₂O et K₂O; cet effet est peu important avec un seul alcalin. Des essais systématiques de Schott [2] aboutirent par la suite au célèbre verre pour thermomètre 16 III, qui continue d'être fabriqué depuis 1885. Jusqu'à présent, on rendait responsable de cette dépression ce qu'on appelle l'effet alcalin mixte, sans pour autant fournir d'explication claire. Par ailleurs, on a montré que cet effet mixte est d'autant plus grand que la différence des intensités de champ des cations étrangers est grande. Dans cette étude, on conclut que le problème des thermomètres réside dans un anti-effet mixte, c'est-à-dire une dépression du zéro qui doit être d'autant plus grande que la différence des intensités de champ est petite. Avec les verres de thermomètre borosihcatés à tres forte teneur en SiO₂, il en va tout autrement; il ne se produit dans ce cas qu'une déformation élastique réversible de courte durée du réseau de SiO₄ et par conséquent aucune dépression du zéro notable.
Modelluntersuchung zum Bildungsmechanismus fototroper Silberhalogenidphasen in Gläsern
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Pascova, Radost; Gutzow, Iwan
The mechanism of formation of the phototropic silver chloride phase in commercial glasses has been investigated in a water soluble sodium borate melt. Electron microscopy, x-ray diffraction and nephelometric techniques have been used to make a detailed study of the kinetics of phase formation. The variation of silver chloride solubility in the melt with temperature has been determined and it is shown that the formation of photo-active AgCl can be treated by classic nucleation theory as a binodal liquid-liquid phase separation and as a special case of Ostwald ripening.
Wasserglas — Herstellung und Anwendung
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) von Laufenberg, Jürgen; Novotny, Rudolf
The technologies of glass and soluble silicate manufacture have many points in common. Thus a Siemens-Martin regenerative furnace is used to melt batch as well as to prepare the solid silicate. Improvements in primary energy use and waste gas heat recovery in the high temperature process have been given priority in both industries. The basic differences between the processes depend on the composition of the batch which contains SiO₂, CaCO₃ and Na₂CO₃ as major components in ordinary glasses but only SiO₂ and Na₂CO₃ for soluble silicate. Glasses are normally made into a wide variety of end products but soluble silicate is dissolved and sold in liquid form. Aqueous sodium silicate solutions find many applications in chemistry (e.g. fillers, detergents, binders) and technology (consolidating floors).
Fotoakustische Messungen an fototropen Gläsern
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Gliemeroth, Georg
The technique of making photo-acoustic measurements has been used on phototropic glasses. The basic relations between the photo-acoustic signal and its absorption show that a photochemical loss is involved, as occurs in botanical processes. Analysis of how the photochemical loss depends on the extinction induced by ihumination in defined conditions of preparation of the phototropic glass indicates that the formation of the colloidal silver on the surface of silver halide particles, caused by illumination, has variable energy requirements which depend on the degree of crystallinity of the silver halide. The sample's history of illumination influences the photo-acoustic signal but this effect can be excluded by suitable precautions.
Reaktionen im glasbildenden System Na₂O-Rb₂O-SiO₂ zwischen 500 und 700 °C
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Daemgen, Rainer Michael; Frischat, Günther Heinz
The reaction profiles between different compositions in the system Na₂O-Rb₂O-SiO₂ were determined between 500 and 700 °C, that is somewhat above T_g. In quasi-binary reactions, for example in the section Na₂O · 3 SiO₂/Rb₂O · 3 SiO₂, Rb⁺-Na⁺ ion exchange occurs with a strongly concentration dependent diffusivity D_Rb,Na. Reactions in other directions are more complex. Although there is also a quasi binary Rb⁺-Na⁺ ion exchange at some distance from the original boundary, SiO₂ takes part in the reaction near the boundary. This shows itself in concentration jumps or uphill diffusion of the alkalis, especially of sodium. A structural mechanism for this type of reaction is developed. Lastly reaction paths in the ternary system are determined and discussed.
Fast and accurate analysis of silver and halides in glasses by stepwise Potentiometrie titration
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Baucke, Friedrich G. K.
An analysis of silver and halides in glasses is reported. The method requires only one decomposition of the glass, followed by the conversion of the silver chloride and/or bromide precipitates into silver iodide by a known addition of excess potassium iodide and subsequent stepwise potentiometrie titration of the halides with silver sulphate. The time required for the complete analysis of the ground glass is 2 h. Presence of silver and iodide in the glass necessitates an additional, independent, determination of one of these elements. Experimental conditions are given and discussed, the reproducibility of the method is reported.
Glasschmelzen mit Gas aus Kohle
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Günther, Rudolf
The high price of fuel oil and its dependence on politics point towards the melting of glass with gas from coal. The previously commonly used producer gas had, on economic grounds, to be preheated to 1000 °C. The four regenerators thus required led to a very awkward furnace design. A simple calculation shows that without preheating a calorific value of only about 10 000 kJ/m³ (gas in standard state) can be obtained. For the size of installation needed for a glass works only gasification of the coal with a mixture of O₂ and H₂O or the water gas process can be considered. For the latter a continuous system must be developed. Several variants are mentioned. These processes are only economic when the cost per unit of energy is considerably lower for coal than for oil.
Berechnungen zum Einfluß der Rohstoffvorwärmung auf den Wärmehaushalt von Glasschmelzöfen
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Barklage-Hilgefort, Hansjürgen; Trier, Wolfgang
A quantitative model is proposed to describe the combined furnace/preheater unit. To describe the combustion space a closed equation is derived which is based on the differential equation for heat transfer between flame and surroundings. The well known recuperator formula is used to describe both air and raw material preheating. The individual parts of the installation are characterized by their heat transfer coefficients; for the furnace there is one for the heat transferred to the charge and one for heat lost to the surroundings. Although improvements to air preheating and heat insulation must be desirable the state of furnace technology means that only small improvements are to be expected, yet raw material preheating has significant advantages. By introducing raw material preheating either a parallel or a series linking of the air and batch preheating may be envisaged. According to the heat transfer conditions both kinds of link can be shown to exhibit optimum sets of parameters. For parallel connexion there is also an optimum distribution of waste gas flows between the individual units. Parallel connexion would have greater advantages in terms of thermal efficiency but, because of higher waste gas and batch temperatures, would be more difficult to realize in practice. It is consequently important to preheat as large a proportion of the batch materials as possible.
Theoretische Analyse des Düsenschwellphänomens beim Strangpressen einer Alkali-Kalksilicatglasschmelze : Teil 2. Rechenergebnisse und Vergleich mit experimentellen Befunden
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Achten, Norbert; Roeder, Erwin
With the aid of the computer model described in part 1 of the present paper [2] the thickening of the rod observed in the extrusion of rod from an alkali-lime-silica glass melt was calculated approximately for circular cross-sections. Besides the distribution of the streamlines and the profile of the rod together with the final diameter, the axial and radial velocities and the pressure distribution in the channel of the die and in the emerging rod were determined and are shown graphically. The influences of extrusion temperature and thus viscosity as well as extrusion pressure were investigated. The available data are used to provide an explanation of the occurrence of swelling at the orifice. Comparison of experimental and calculated rod diameters showed a relative discrepancy of less than 5 %. This shows that the numerical method used is suitable for the solution of the problem.
Theoretische Analyse des Düsenschwellphänomens beim Strangpressen einer Alkali-Kalksilicatglasschmelze : Teil 1. Erstellung des Rechenmodells und numerische Lösung des Randwertproblems
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Achten, Norbert; Roeder, Erwin
The differential equation for the stream function, based on the Navier-Stokes equations, together with appropriate boundary conditions provides the basic mathematical background for a theoretical treatment of the die swell phenomenon. The solution of the boundary value problem is achieved by a numerical method which allows, in addition to the pattern of streamlines, calculation of the axial and radial velocity and pressure distributions in the die channel and in the extruded bar, and of its final diameter. The results of this theoretical analysis will be compared with experimental measurements in part 2.
Beschichtung großflächiger Glasscheiben durch Kathodenzerstäubung
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Gläser, Hans-Joachim
Coating technology has developed considerably in recent years by the use of cathode sputtering which is tending to become used for coating large glass panels throughout the world. The outstanding advantages of this technique are high capacity, good layer uniformity, economical consumption of coating material, and lack of environmental problems. The physical phenomena involved in coating by cathode sputtering, the types of cathode used for coating large flat surfaces, the production process and the possible applications of available types of installation, namely semi-continuous flow systems and batch systems, are discussed.
Besondere Anforderungen an die Herstellung gepreßter Scheinwerfergläser
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Daniels, Manfred
Design and constructional details of signal and head lamp lenses are essentially determined by function and design. Whilst signal and head lamp lenses must meet requirements of standards for colour, transmission, light distribution, etc., car head light lenses especially must also satisfy requirements of style and form. Production technology, especially requirements related to glass feeding, press and machine technology, and tool design are discussed here.
Zusammensetzung der Abgase hinter Glasschmelzwannen
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Roggendorf, Hans; Waldecker, Gerd Georg; Scholze, Horst
The compositions of waste gases from glass tanks melting soda-lime-silica glasses have been calculated by thermodynamic methods. The concentrations of up to 39 compounds in the system N₂-CO₂-H₂O--O₂-SO₂-Na₂O-HCl, also including condensed phases, have been determined. Condensation temperatures of Na₂SO₄ predicted by calculation were confirmed experimentally in synthesized mixtures of waste gases. Thermodynamic calculations and measurements of condensation temperatures both showed that the Na₂O and SO₂ contents of the gases largely determine the condensation behaviour, Na₂O having the greater influence. Other components such as N₂, CO₂, H₂O, and O₂ at the relevant concentrations have negligible influence in practice. HCl has a marked influence only in extreme condhions such as high HCl concentration and very low Na₂O concentration.
Der Spessart: die „Urheimat" der alten Glasmachersippe Stenger?
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Stenger, Ernst G.
In 1406 the glassmakers in and around the Spessart were granted a guild charter. In this document the name Stenger occurs six times among the names of forty glassmakers. Arguments are explained as to whether the Spessart can be considered the ancestral home of the Stenger family of glassmakers.
Bestimmung der Leistungsdichte- und Temperaturverteilung in elektrischen Glasschmelzwannen
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Endreß, Herbert
The flow of the melt, which cannot be determined directly, is of fundamental importance in the technology of melting glass electrically. It can be estimated from measurement of the spatial electrical field and power density distributions as well as the temperature distribution for which measurement point by point with a probe is described. Four potential measuring points arranged according to a co-ordinate system and a temperature sensor are combined in the probe. The data are obtained by a co-ordinate transformation together with analogous switching and impedance transformation using amplifiers. The errors in measurement are independent of electric potential, the field strength, the ahgnment of the probe, and the glass temperature in a glass melt with a known homogeneous electric field. The probe being out of balance or unsymmetrical causes errors; only the asymmetry error can be reduced appreciably. The usefulness of the method of measurement is shown using data measured on an electric vertical melting furnace producing illuminating ware.
Positiver Temperaturkoeffizient des Elastizitätsmoduls von Gläsern
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Coenen, Matthias
The temperature coefficient of the elastic properties of glasses is of great importance for glass components used as transmitters in control circuits, for compensation of thermal expansion. Glasses can have many advantages over other materials such as the wide range of compositions, electrical and thermal insulation, transparency, lack of reflection, workability, resistance to temperature, homogeneity, reproducibility of mechanical, electrical and magnetic losses, chemical durability, impermeability to gases, ease of sealing, etc. A positive sign is not normally found for the temperature coefficient of the elastic moduli of glasses. It is shown that the anomaly is a consequence of the glass structure and depends on an entropy effect.
Einschmelzverhalten von Flachglasgemengen unter Einsatz von Tonerdehydrat, Nephelinsyenit und Calumite
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Gebhardt, Franz; Arnolds, Jakob L.; Klinger, Otto-Eberhard
This work concerns the melting of flat glass batches with increases in alumina content from 0,35 to 0,45 to 0,7 % AI₂O₃. The alumina was provided by hydrated alumina, nepheline syenite and Calumite. The introduction of blast furnace slag (Calumite) showed the most advantageous melting behaviour. The use of Calumite had advantages over the other sources particularly through a decrease of the soda ash in the batch. Nepheline syenite showed no advantage over hydrated alumina either in melting behaviour or viscosity-temperature relation.
Zum Einfluß der Schneidgeschwindigkeit auf Elementarvorgänge beim Schleifen optischer Gläser
(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1983) Schinker, Martin G.; Döll, Walter
Individual scratches were produced by single diamond tools over a wide range of velocities, from 1 μm/s to 100 m/s, on the surfaces of several optical glasses with very different physical properties, in dry surroundings at room temperature. By means of specially developed apparatus it is possible to make scratches at defined and predetermined velocities and to observe directly by microscope the processes in the diamond/glass contact area. Thereby, together with numerous scanning electron microscope investigations of individual scratches, can the deformation, flow, and fracture processes during crack formation be analyzed in more detail. The results obtained, especially a velocity dependent transition in the plastic behaviour from isothermal to adiabatic flow and the related brittle fracture behaviour of the glass in the contact zone, as well as model concepts are discussed.

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