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- ItemManufacture of short-fibre reinforced glasses by extrusion and examinations regarding their structure and their mechanical properties(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Langhans, Klaus; Roeder, ErwinTechnical applications of glasses are mainly limited by their well-known tendency to brittle fracture. One promising possibility to improve the mechanical properties of glasses is the embedding of high-strength reinforcement fibres for increasing the strength and, first of all, the fracture toughness of these materials. Therefore, new fields of application for these glasses can be developed, where their many favourable properties become effective. In this paper the manufacture - by extrusion - of short-fibre reinforced glasses as well as structural and mechanical examinations of the thus produced specimens are represented. Due to the manufacturing process, extrusion results in a nearly unidirectional orientation of the fibres, parallel to the axis of the rod, with a corresponding high degree of reinforcement. After the explanation of the theoretical fundamentals of short-fibre reinforcement of brittle materials, the properties of the materials used for the experiments and the manufacture of the composites are described in detail. The subsequently illustrated examinations have clearly shown improvements of the mechanical properties of the glasses as well as good accordance with the theoretical considerations.
- ItemESR studies of iron-containing lithium, sodium and potassium silicate glasses before and after Irradiation with γ- and X-rays(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Schels, Thomas; Camara, Boubacar; Dannheim, HenningLithium, sodium and potassium silicate glasses containing different Fe2O3 amounts were irradiated with γ- and X-rays and investigated by using ESR. The well-known iron resonances at g = 4.2 and g = 1.99 show a characteristic behaviour at the transition from lithium to potassium and by changing the Fe2O3 concentration. The resonance at g = 4.2 decreases from lithium to potassium, whereas the resonance at g = 1.99 increases. The concordance of the intensity course of the two resonances with the preference of the alkali metals to take tetrahedral or octahedral coordination is an interesting support for the attribution of g = 4.2 to 4-fold coordinated Fe3+ and g = 1.99 to 6-fold coordination of this ion. γ- and X-rays induce the same defect centres (colour centres). These centres are characterized by a strong resonance at g = 2.01. All radiation defects have a strong dependence on the type of alkali metal - they increase from lithium to potassium - and on the Fe2O3 concentration of the glasses. In glasses which contain a very small quantity of Fe2O3 the irradiation induces more defects than in the corresponding iron-free glasses. With increasing Fe2O3 content the glasses become more resistant against irradiation and at a high concentration no more defects can be produced.
- ItemInfluence of the grain size of glass frits on the characteristics of glass enamels(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Paulus, Hildegard; Müller, Siglinde; Oel, Heribert J.Glass enamels, like porcelain decals, consist of a pigment in a glass flux (frit), but must be capable of being fired-on at low temperatures. Susceptibility to chemical attack and a reduction in the mechanical strength of the enamelled body are two disadvantages of enamels. An attempt to improve these properties by altering the fineness to which the glass frit is ground is described in this paper. Several glass frits were used, each ground to three different grades. The effect on colour, lustre, dishwasher durability and mechanical strength was investigated.
- ItemThermal shock behaviour of SiC-fibre-reinforced glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Klug, Thomas; Reichert, Jutta; Brückner, RolfThe preparation of two SiC-fibre-reinforced glasses with very different thermal expansion coefficients and glass transition temperatures is described and the influence of long-time temperature and thermal shock behaviour of these composites on the mechanical properties is investigated by means of bending test experiments before and after thermal treatments. It will be shown from experiments and calculations on stresses due to thermal expansion mismatch between fibre and glass matrix that not only best mechanical properties but also best thermal shock behaviour are connected with low tensile intrinsic stresses produced by thermal expansion mismatch during preparation. The thermal shock resistance of the best composite (SiC fibre/DURAN glass) does not show a significant decrease of flexural strength even after 60 shocks from 550 to 25 °C in water, while the bulk glass sample of the same dimension was destroyed by one thermal shock from 350 °C.
- ItemHigh-temperature IR spectra of nioboborate glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Quanzu, Yang; Zhongcai, Wang; Shizhuo, Wang; Donghui, LuThe structure of nioboborate glass melts in the system Nb2O5—B2O3—K2O has been studied for the first time by high-temperature IR spectra. The structure models of the glass melts and the glasses have been established.
- ItemSpectrophotometric analysis of ferrous, ferric and total iron content in soda-lime-silica glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Traverse, Jean-Pierre; Toganidis, Tryfon; Adès, ClaudeΑ study of the bands of charge transfer and of d-d transition was performed in view of quantitative analysis of ferrous, ferric and total iron content. For a given wavelength between 0.32 und 0.33 μm a linear relationship between the absorption and the total iron content can be found for all the redox states studied. Using the band at 1.06 μm allows [Fe2+] determination and by means of the band at 0.38 μm [Fe3+] can also be measured accurately if correction is made using the total iron content. The results of spectroscopic determinations are shown to be coherent with those of chemical analysis to within 1 to 3 %.
- ItemInvestigations concerning the recycling of filter dust from electrostatic precipitators in the glass industry(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Kircher, UlrichIn the container glass industry the recycling of filter dust was applied from the beginning of the waste gas treatment - first mainly in flint glass furnaces. It is reported about the experiences concerning handling, dusting, and refining behaviour. Moreover, the results of a research programme, investigating the danger of enrichment with toxic components in the molten glass, in the filter dust and in the residual emission are presented. These experiences were altogether positive - so that until now the filter dust in the container glass industry and meanwhile also in the flat glass industry has been completely recycled.
- ItemModelling of chemical and morphological changes of silicate fibres used in a Portland cement matrix(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Wojnárovits, Ilona; Fodor, MártaBasalt and glass wool materials were continuously eluated in saturated lime water and in 10^3 mol NaOH/m3 at 70 °C. The alkali resistance of fibres was investigated, in particular its dependence on the chemical composition of the fibres and on the nature of the reaction products formed on the fibre surface. For this purpose wet chemical and x-ray diffraction analysis, as well as scanning electron microscope and microprobe were employed. The higher alkali resistance of basalt fibres against both corrosive agents can be explained by their higher MgO and Fe2O3 as well as lower Na2 and K2O contents.
- ItemImportance of the Lorentz force in electrically heated glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Hofmann, Otto R.; Philipp, GerdIn all computations of the flow velocities and temperature distributions in electric glass melts the electromagnetic Lorentz force has been neglected. This force is caused by the interaction between electric current density and the magnetic flux density in the region around electrodes. For some examples of real glass melting furnaces the necessity of including the Lorentz force into flow modelling was demonstrated. Some problems, e.g. the thermal stability of the batch layer in furnaces with top electrodes and the residence-time distribution of tanks with horizontal electrodes, cannot be explained and interpreted realistically if this second driving force besides the buoyancy is neglected. Moreover, the method of physical modelling of the electrically heated glass melts remains doubtful as long as the similarity criteria also for the Lorentz force cannot be fulfilled.
- ItemTransient ionic conductivity in fused silica(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Varshneya, Arun K.; Jain, Vijay; Bihuniak, Peter P.Transient currents in doped and commercial type-I fused silica glasses were monitored by electrolyzing alkali ions (Na+ , Li+ and K+) through a sample disk in a U-tube dc non-blocking conductivity cell until steady state was achieved. The experiments were carried out either at 600 or 650 °C. Approach to steady state varied from sample to sample depending not only on the electrolyzing ion but also on the alumina/alkali ratio and the concentration of Li+ and Na+ impurity level in the silica. Results indicated that the transient behavior (current versus time) at a particular temperature was best expressed as a lg — lg plot showing two linear regions. The initial slope was attributed to the flushing of more mobile species and the final slope to the disappearance of interdiffusional coupling effects. The nature of the interdiffusional coupling, in some cases, was typical of the mixed-alkali effect in silicate glasses containing much higher levels of mixed alkali.