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Lviv Polytechnic National University
Lviv Polytechnic National University
Lviv Polytechnic National University
Lviv Polytechnic National University

The short-term effect and the limitation of  maximum temperatures influence in conditions of high-speed firing of ceramic tiles in roller furnaces of flow-conveyor lines raises an urgent task of controlling the processes of structure and phase formation  at burning in the direction of increasing the content of the crystalline component of the pot. Among the crystalline phases the particular attention deserves wollastonite,  its needle shape of the crystals provides a sufficient degree of deformation resistance of tiles at burning, and in the course of operation - high mechanical properties of ceramics.

In order to expand the raw material base of ceramic production, it was taken into consideration the possibility of using  polymineral semi-acid clays characterized by high content of coloring oxides, and calcium hydrosilicates in the form of synthetic tobermoryte for their use in the technology of ceramic tiles production.

The concentration influence of admixtures of calcium hydrosilicates in the form of synthetic tobermoryte on the sintering of masses in the system of «clay-tobermoryte» was investigated. It was established the following features: change of water absorption, fire combustion and the strength of the burned samples depending on the regime parameters of the technological process. It was discovered that the addition of tobermorite from 10 to 40 wt. % causes an increase in the amount of water absorption in the temperature range of 1000-1100 °C while reducing the fire combustion, the mechanical strength indexes increase as well. Such character of these properties change is due to the peculiarity of the crystalline structure of tobermorite admixtures and the processes of its recrystallization into wollastonite and anorthite at burning. The formation of anorthite occurs due to the interaction of an amorphous metacanolinite phase with calcium oxide, which is partially released at degeneration of tobermorite in wollastonite. These crystallization processes are a precondition for a significant reduction in the moist expansion of a ceramic tile. At the same time, the recrystallization of tobermorite at burning causes the stability of the structural viscosity of the tobermorite-clay mass in a wide temperature range, which is the determining criterion for assessing the deformation resistance at burning of ceramic tiles.

Based on the analysis of the change of structural viscosity during the heating of the experimental masses, the differential thermal and X-ray diffraction analysis methods, the interrelation of the physico-chemical processes of the formation of a ceramic pot with the content of the tobemorite admixtures was revealed. The obtained results are the basis for their usage in the technology of production of ceramic tiles.

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