Fracture Toughness of Ceramics Fired at Different Temperatures

  • Peter SIN Constantine the Philosopher University in Nitra
  • Renno VEINTHAL Tallinn University of Technology
  • Fjodor SERGEJEV Tallinn University of Technology
  • Maksim ANTONOV Tallinn University of Technology
  • Igor STUBNA Constantine the Philosopher University in Nitra
Keywords: ceramics, fracture toughness, mechanical strength, solid-state sintering, liquid-state sintering, dehydroxylation


The fracture toughness test was performed at room temperature on sets of 5 ceramic samples made from material for high voltage insulators (kaolin 36 wt. %, Al2O3 30 wt. %, clay 12 wt. % and feldspar 22 wt. %) fired at temperatures 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1250, 1300, 1400, 1500 °C at heating and cooling rate of 5 °C/min. The precrack was made to each sample by indentation under the loads 10 N 200 N, the dwell time was 45 s and the loading rate was 10 N/s. Results of the fracture toughness tests were in accordance with changes of structure of the samples after the partial firings. Fracture toughness from 20 °C to 500 °C is almost constant and it varies between 0.1 MPa·m0.5and 0.2 MPa·m0.5. Dehydroxylation (420 °C 600 °C) does not influence the value of fracture toughness. At temperature interval where we assume sintering (700 °C 1250 °C) we observe exponential dependence of fracture toughness up to 1.5 MPa·m0.5. From comparison of the fracture toughness, Young’s modulus and flexural strength follows a correlation and proporcionality of these mechanical properties.