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There is a fairly large range of waste that is partially or fully vitrified e.g.,: fly ashes, granulated slag, glass cullet. As long as they are not loose, after milling these wastes are an interesting raw material for the production of sintered ceramics. In this application, attention is usually paid to their fluxing effect during sintering, due to the high content of alkali oxides and iron oxide. The high entropy of these raw materials resulting from the large proportion of glassy phase is usually neglected. In this paper, we shown that during the sintering of glassy wastes their entropy decreases, which is mainly the result of their devitrification and previous glass transformation. Both the sintering process and the processes associated with the drop in glass entropy are exothermic. Their simultaneous coexistence causes that they can accelerate each other. The influence of high entropy of vitreous wastes on the acceleration of the sintering process was demonstrated with use of thermal studies such as DTA/TG and high temperature microscopy. The fly ash, ground cullet and their mixture were used as glassy wastes. [ABSTRACT FROM AUTHOR]

The object of this study is to investigate the thermal properties of fly ashes from the last, farthest dedusting zone in terms of their use as ceramic masses additives. Siliceous fly ash is valuable additive to ceramic mass, which not only reduces its plasticity, but also actively affects sintering process and shapes the properties of the final material. The finest fly ash fractions are potentially useful flux materials in ceramics; however, a significant limitation in their use is due to thermal expansion/bloating occurring during high-temperature sintering. The bloating mechanism of fly ashes was investigated in relationship to their chemical composition with the use of DTA/TG/EGA analysis as well as high-temperature microscope. Chemical and phase compositions were studied by X-ray fluorescence and X-ray diffraction. Based on the results obtained, it can be concluded. The results indicate that bloating mechanism is caused by the co-occurrence of two phenomena accompanying sintering: appearance of high amount of liquid phase and simultaneous gas release from sintered material. The dominant mechanism is the simultaneous release of sulfur (IV) oxide and oxygen as a result of the redox reaction of removing SO3 from the vitreous phase. [ABSTRACT FROM AUTHOR]

Oxyfluoride glasses are the basic materials for obtaining transparent glass-ceramic (TGC) which can be used in a wide range of optoelectronics devices such as: amplifiers, up-conversion, telescopes, laser sources. Oxyfluoride TGC is obtained by the control heat treatment of the parent glass due to low phonon nanocrystalline phases. The oxyfluoride glasses from the sodium-lead-silica system were the object of investigation. The influence of fluoride content on the thermal properties of glasses was analyzed. Thermal characteristics of glasses like the transition temperature T, the temperature for the crystallization onset T, and the maximum crystallization temperature T, thermal stability parameter were determined by DTA/DSC method. The linear expansion coefficients of oxyfluoride glasses as a function of temperature were measured using a thermo-mechanical analyzer (TMA 7 Perkin-Elmer). The effect of crystallization on the thermal expansion coefficient and softening temperature T was found. [ABSTRACT FROM AUTHOR]