In this paper, the influence of precursors (CA, C 7 A 3 Z, C 12 A 7 , C 6 SrA 3 Z, C 7 A 2 FZ and commercial calcium aluminate cement 'Gorkal 70') on the structure, microstructure and thermal stability characterizations of C 3 AH 6 through hydration was investigated. The materials were characterized by X-ray diffraction, differential thermal analysis-thermogravimetric analysis-evolved gas analysis and scanning electron microscopy combined with energy-dispersive spectroscopy 24 h and 72 h after starting the hydration process. Results of investigation confirmed the influence of precursor on shape and grain size of C 3 AH 6 . The CaO/Al 2 O 3 mass ratio of precursors before the hydration process affects the size of C 3 AH 6 crystals: the higher the CaO/Al 2 O 3 value, the larger the size of the crystals of C 3 AH 6 . Moreover, the presence of Sr and Fe affects the formation of stable C 3 AH 6 crystals.

Low-melting frits are most often applied in the form of coatings for ceramic building materials, i.e., roof tiles and brick façade. A thin layer of glaze or sintered engobe improves decorative and functional properties of the final product. The roof tiles are fired in the low temperature range (1000-1200°C). There are expected solutions which will allow obtaining a smooth layer of glaze without deteriorating mechanical and chemical properties. Thus, it is important to find a solution that meets the above requirements. The aim of this study was to analyze the effect of bismuth (III) oxide on the properties of low-melting different commercial frits used as a main component of glaze for ceramic roof tiles. Three commercial frits were modified with the addition of bismuth (III) oxide in the amount of 5 and 10 wt%. In the first stage, the results of the dilatometric and high-temperature microscopy analysis are shown. Keywords Low-melting frits. Ceramic roof tiles. Low-melting glaze. Bismuth (III) oxide Bi 2 O 3