Young'S Modulus Of Different Illitic Clays During Heating And Cooling Stage Of Firing

Dynamical thermomechanical analysis of 5 illite-based clays from deposits in Slovakia, Estonia, Latvia, and Hungary is presented. The clays consist of illite (37-80 mass%), quartz (12-48 mass%), K-feldspar (4-13 mass%), kaolinite (0-18 mass%), and calcite (0-3 mass%). Young's modulus is measured during the heating and cooling stages of firing (25 degrees C -> 1100 degrees C -> 25 degrees C). The liberation of the physically bound water increases Young's modulus by similar to 70% for all studied clays. By increasing the temperature, dehydroxylation and the alpha -> beta transition of quartz take place without a significant effect on Young's modulus. Sintering, which starts at 800 degrees C, leads to an intensive increase in Young's modulus up to the highest temperature (1100 degrees C). The increase remains also in the early stage of cooling (1100 degrees C -> 800 degrees C). This increase of Young's modulus is also the result of solidification of the glassy phase, which is finished at similar to 750 degrees C. A sharp minimum of Young's modulus is observed at around the beta -> alpha transition of quartz. Then, Young's modulus still decreases its value down to the room temperature. The physical processes observed during heating and cooling do not differ in nature for the studied clays. Values of Young's modulus vary at around 8 GPa, up to 800 degrees C. During sintering, Young's modulus reaches values from 30 GPa to 70 GPa for the studied clays. The microstructure and composition given by the origin of the clay play a cardinal role for the Young's modulus of the final ceramic body.