Tomáš Húlan

Assessing the frost resistance of illite-based ceramics through the resonant frequency of free vibration and internal damping

Experimental samples with porosity ranging from 6 % to 50 % were prepared by sacrificing template method from illite-rich clay. The frost resistance was assessed by measuring the shift in resonant frequency of free flexural vibration of prismatic samples and by the change of internal damping due to freeze-thaw cycles. Resonant frequency was determined by the impulse excitation technique and internal damping of the material was evaluated from the width of resonant peak. Samples were saturated with water and subjected to freeze-thaw cycles in the temperature range from –22 to 20 °C. Resonant frequency and internal damping were measured after 50, 100, 200, and 300 freeze-thaw cycles. Resonant frequency drops with increasing number of freeze-thaw cycles, and the effect is more pronounced in the case of samples with higher porosity. Internal damping of material was not found to be a suitable quantity for assessing the frost damage.

Building ceramics with an addition of pulverized combustion fly ash from the thermal power plant Nováky

Pulverized combustion fly ash (PFA) from the Power plant Novaky (Slovakia) is analyzed for its potential use in the production of building ceramics. Three materials are used to prepare the mixtures: illite-rich clay (IRC), PFA and IRC fired at 1000 °C (called grog). The mixtures contain 60 % of IRC and 40 % of a non-plastic compound (grog or PFA). A various amount of the grog is replaced by PFA and the effect of this substitution is studied. Thermal analyses (TGA, DTA, thermodilatometry, and dynamical thermomechanical analysis) are used to analyze the processes occurring during firing. The flexural strength and thermal conductivity are determined at room temperature after firing in the temperature interval from 800 to 1100 °C. The results show that an addition of PFA slightly decreases the flexural strength. The thermal conductivity and porosity are practically unaffected by the presence of PFA. Thus, PFA from the Power plant Novaky is a convenient non-plastic component for manufacturing building ceramics.