YOUNG'S MODULUS OF PREFIRED QUARTZ PORCELAIN IN A TEMPERATURE RANGE OF 20-1200 °C

Green samples (50 w/% of kaolin, 25 w/% of quartz and 25 w/% of feldspar) are prefired up to 400-1200 degrees C and analyzed during their second firing. Thermogravimetry, thermodilatometry and dynamic thermomechanical analyses are performed in a range from room temperature to 1100 degrees C. In the samples prefired at temperatures of up to 400 degrees C and 500 degrees C, the release of physically bound water has a significant influence on Young's modulus, increasing its values by approximate to 25 % and 6.5 %, respectively, between room temperature and 200 degrees C. In the samples prefired at temperatures above 500 degrees C. the alpha -> beta transition of quartz governs Young's modulus in a temperature interval of 500-700 degrees C. Young's modulus increases by 29-40 % in the samples prefired at 600-1200 degrees C due to the closing of the cracks located around quartz grains. The presence of a glassy phase is not necessary for the steep increase of Young's modulus around the alpha -> beta transition of quartz. At high temperatures, an increase in Young's modulus is caused by solid-phase sintering (above 800 degrees C), formation of Al-Si spinel (approximate to 950-980 degrees C) and crystallization of mullite (above 1050 degrees C).