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study of structural modification in extruded and heat-treated lithium disilicate glasses by the method of radiation color centers chronospectroscopy
Samples of extruded and non-extruded lithium disilicate glasses were studied. Extruded glass samples were cut out along and across the extrusion axis of fmished cylindrical rods. For all the samples, spectra of radiation-induced absorption, Δα(E), were measured for various time instants after the cessation of X-irradiation. On the data basis obtained, kinetic dependences. Δα = f(t), were plotted and analyzed. In the diagram "Δα versus lgt", they are represented by straight hnes. Each of them is falling down with its own constant slope a. These a's are rate parameters of the decay of radiation color centers (CCs). They appear to be functions of average distances between recombinating electron and hole CCs. The above α-parameter decreases when passing from the longitudinal cut extruded glass sample to the sample of the non-extruded glass and finally to the transversely cut extruded glass sample. These data mean that, in the course of extrusion, the glass structure becomes less dense in the axial direction of extruded glass rods and more dense in the radial one. Α 4-hour heat treatment at 465 °C (≈5°C above the glass transformation temperature, Tg) eliminated the above anisotropy of radiation properties in extruded glasses and forced their anisometric structures to return to the isometric State characteristic of the non-extruded glass.
Chemical composition of medieval glass from excavations in West Germany
Investigations of excavated glass fragments from the Roman-Frankish cemetery at Krefeld-Gellep, the Carolingian imperial palace with glassworks at Paderborn, the monasteries and towns of Corvey, Höxter and Brunshausen-Gandersheim and several glassworks in the Bramwald, Hils, Spessart and Eichsfeld areas allow conclusions on the sequence of major medieval glass types. Exhaustion of Imports of trona-soda or soda raw glass and increased needs caused the introduction of woodash as domestic alkali and earth alkali source for glass manufacture at about 800 AC. Early woodash glass from 800 to 1000, woodash glass from about 1000 to 1400 and woodash-lime glass from about 1400 to post-medieval times were the major glass types. They were accompanied by minor Imports of soda-lime and soda-ash glass objects, the latter since about 1300. From about 1100 to 1400 woodash-lead and lead glass have been produced from the P bO byproducts of the silver metallurgy. Galena from the Harz Mountains was a major source of lead for lead glass in northwestern Europe. The average production of a medieval glassworks was in the order of 15 t glass per year and its requirements for ash and fuel about 30001 wood. The number of glassworks in Germany during the late medieval period (moving after 5 to 30 years from one to another location) is tentatively estimated to be in the order of 40. Their main furnaces were constructed for about 1400 C working temperature. The occurrence of the medieval chemical glass types in a sequence allows some rough dating of glass fragments.
Oriented mica glass-ceramic by extrusion and subsequent heat treatment
Glass-ceramics with oriented mica crystals have been produced by extruding a fluorophlogopite glass and subsequent therma treatment. During extrusion predominantly the intermediate phase norbergite (Mg₃F₂SiO₄) and besides small quantities of phlogo pite mica crystals (Na/KMg₃F₂Si₃AlO₁₀) crystallized. Heat treatments at temperatures around the maximum crystallization rat resulted in an oriented crystallization of phlogopite as proved by electron microscopy and XRD analysis. The plate-like crystals ar aligned with their basal planes parallel to the direction of extrusion. The degree of orientation was studied by X-ray pole figur measurements. The (003) planes show strong ring-fibre texture. The degree of orientation decreased if the crystallization was realize at lower temperatures and lower crystallization rates. The alignment mechanism is discussed.
Which rheological parameters control the isochomal workability of glass melts from the Container glass industry?
Two species of brown glass which were characterized by industrial workability and quality criteria as "good" and " bad ", respectively, were investigated by the cylinder compression method and by the Christiansen method. Significant differences between the two species were found by means of the two methods in such a manner that the "good" brown glass samples indicate a better homogeneity and the corresponding melts a larger critical deformation rate, hc and therefore, a better isochomal workability than the " bad " brown glasses and melts. Additionally, the former ones show a larger ratio Fe²⁺/F_total with the consequence that they have a lower Newtonian viscosity at the same temperature. In contrast to the brown glass melts no clear differences in the rheological properties and isochomal workability could be detected between white Container glass melts which have also been characterized as "good" or as "bad". The white Container glass melts are classified to be less workable at equal viscosities than the brown glass melts. The stress generation modulus, E_max, and the normalized non-Newtonian viscosity, η/η0T, are less sensitive properties with respect to the redox State of the melts and to the homogeneity than the hc values. With the results of this study the limits of the sensitivity of the various properties resulting from the cylinder compression method were reached.
Laser glass level measurement - Possibilities and perspectives using the Horn System
[no abstract available]
Öfen zur vollelektrischen Schmelze von Glas in Deutschland
Die HVG verschickte im November 1993 einen Fragebogen an alle Betreiber von vollelektrischen Wannen in Deutschland mit einem Durchsatz von mehr als 10 t/d. 24 ausgefüllte Fragebögen wurden der HVG bis zum April 1994 zurückgesandt. Auch 6 vollelektrische Öfen von Nichtmitgliedern sind in die Auswertung mit aufgenommen. Ausgewertet wurden die Wannengröße (Durchmesser und Badtiefe), Art und Material der Heizelektroden, Gemengeeinlage, Gesamtscherbenanteil, Glasart und gefertigtes Erzeugnis, Schmelzleistung und spezifischer Wärmeverbrauch. In 8 Wannen wird Borosilicatglas erschmolzen, in 6 Kalk-Natronsilicatglas, in 4 Bleikristall- und in 2 Kristallglas, in 2 weiteren C-Glas und in einer Opalglas. Gefertigt werden Glasbehälter, Rohre, Wirtschaftsglas, Fasern, Streuscheiben und Beleuchtungsglas. Sowohl bei der Wannenfläche als auch bei der Badtiefe läßt sich in Abhängigkeit von der maximalen Tagestonnage eine gemeinsame Tendenz bei fast allen Öfen erkennen. Der spezifische Wärmeverbrauch sinkt mit steigendem Durchsatz bzw. größerem Wannenvolumen, da das Verhältnis von Oberfläche zu Wanneninhalt besser wird damit die Wandverluste anteilmäßig geringer werden. An 20 Wannen werden Molybdänelektroden und an 4 Wannen Zinnoxidelektroden eingesetzt. Diese Heizelektroden sind an 9 Wannen als Seiten- und Bodenelektroden eingebaut, an 7 Wannen als Seitenelektroden, an 5 Wannen als Bodenelektroden und an 3 Wannen als Topelektroden.
Determination of the rheological properties of high-viscous glass melts by the cylinder compression method
A detailed description of the cylinder compression method and its application on the viscoelastic behaviour of glass melts is given with the help of closed solutions and equations in contrast to algorithmic methods, like e.g. the finite element method. Special attention is paid to the system deformation and system deformation rate of the testing equipment and to the dissipation of mechanical energy within the specimen and the heat flow from the specimen. The limits of this treatment are discussed with respect to the applicability of the theoretical basis (Gent and Nadai equation) and with respect to the experimental determination of the rheological properties of glass melts. On this basis the pure non-Newtonian viscosity, ηnN, can be determined. If very small differences have to be ascertained in the rheological behaviour of glass melts due to small differences in composition or in melting history (e.g. redox condition or bad/good workability), the same conditions concerning the mechanical and thermal equipment and even the same geometry of the glass specimens have to be strictly maintained. Comparison between different glass melts should be made rather on the basis of equal (Newtonian) equilibrium viscosity, η₀, (isochomal conditions) and not on equal temperature. Owing to large thermal effects, the slope of the viscosity-temperature curve at η₀ plays a certain role, particularly for the forming process.
Chemical surface and thin film analysis in glass coating
After a short overview of recent analytical techniques for compositional surface analysis and the determination of concentration depth profiles, the principle, the Instrumentation and the Performance of the routinely used electron spectroscopic and mass spectrometric methods, namely photo- and Auger electron spectroscopy as well as secondary ion and secondary neutral mass spectrometry, are described. The application of these techniques to electrically insulating surfaces and layer structures is particularly emphasized by corresponding practical examples. Secondary neutral mass spectrometry is specifically addressed with regard to the potentialities of the novel high-frequency mo d e of electron-gas secondary neutral mass spectrometry for quantitative composition analysis and high-resolution depth profiling of electrically nonconducting sample structures.
Modelling of time strength behaviour of soda-lime-silica glass in moist environments
The time strength behaviour of alkali silicate glasses depends on the environmental media and external stresses during aging as well as on the type of initial crack (kind of damage). An extended crack growth model based on the competing processes of crack growth and its retardation due to stress-enhanced alkali leaching in moist media has been implemented on a computer. Considering residual contact stresses, this model is able to simulate crack arrest, strength increase (or decrease, respectively) during aging under load, static and dynamic fadgue including strength distribudons of various soda-lime-silica glass applicadons. Lifetime predicdon of static fatigue can be improved up to about 10 years.
First practical experiences with an SCR DeNOx facility in a container glassworks
The German Federal Minister for Environment, Nature Protection and Reactor Safety (BMU) and the State Ministry for Environmental Affairs in Hannover sponsor projects in shop-floor size which demonstrate how equipment can be adopted to the latest technical developments to reduce environmental damages. At PLM Glashütte Münder such a project is being sponsored and expertly ac companied by the German Federal Bureau for Environment with funds being made available by the BMU and the State of Lower Saxony An important feature of the project is the technology to reduce NOₓ, values with the help of the Selective Catalytic Reduction (SCR) process. The DeNOx facility has been equipped with two ammonia water storage tanks having a capacity of 30 m³ each. The direct vaporizer is installed before the SCR reactor. The ammonia water is finely sprayed in with the two-material nozzle technique and mixed evenly with the flue gas volume flow. An analysis measuring device before and after the SCR reactor measures the relevant NOₓ values, these values are transformed into a signal which controls a valve supplying the required quantity of ammonia water. The conditioned flue gas volume is sent to the SCR reactor via guide systems. The reactor is equipped with two layers of catalyzers. To avoid bridge formation of dust that still accumulates in the purified gas flow, dust blowers are positioned above each catalyzer layer, which are activated at set intervals. First practical results show that with this technology NOₓ emissions can be reduced to values below 500 mg/m³ flue gas, where the NOₓ concentrations are based on dry flue gas in standard condition (1013 mbar, 273 K) with 8 % O₂.