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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 SO 3 from the vitreous phase.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Abstract. One of the most important performance characteristics of masonry units is their high thermal insulation. There are many different ways to improve this parameter, however the most popular methods in case of ceramic masonry units are: addition of pore-creating raw materials and application of proper hole pattern. This study was an attempt to improve thermal insulation of ceramics by applying thermal insulation additives. Perlite dust created as a subgrain from expansion of perlite rock was used. Perlite subgrain is not very popular among consumers, that's why it's subjected to granulation to obtain coarse grain. The authors presented concept of direct application of perlite dust for the production of building ceramics with improved thermal insulation. Fineness of this additive is asset for molding of ceramic materials from plastic masses. Based on the results it was found that about 70% perlite by volume can be added to obtain material with a coefficient of heat conductivity of 0,37 W/mK. Higher content of this additive in ceramic mass causes deterioration of its rheological properties. Mass loses its plasticity, it tears up and formed green bodies are susceptible to deformation. During sintering perlite takes an active part in compaction process. Higher sintering dynamics is caused by: high content of alkali oxides in perlite and glass nature of perlite. Alkali oxides generate creation of liquid phase which intensifies mass compaction processes. Active role of perlite in sintering process causes good connection of its grains with clay groundwork which is important factor for mechanical parameters of ceramic materials. It was also noted that addition of perlite above 40% by volume of mass effectively neutralized negative effect of efflorescence in ceramic materials.

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