Thermal Shock Resistance of Mullite obtained from Kaolin and Tri-hydrated Alumina
Zahra Malou, Mohamed Hamidouche and Belhouchet Hocine
In this work we have studied the thermal shock behavior of mullite prepared locally under different conditions. The initial powders used are 60% of trihydrate alumina (Gibbsite) and 40% of natural Kaolin. The specimen shaping was obtained by uniaxial pressing the mixture powders under three pressures (100, 80 and 70) MPa. After debinding at 600°C, pre-cooked samples were sintered at 1600°C for 1h.
Differential thermal analysis coupled with thermogravimetric analysis, conducted on the mixture kaolin-gibbsite, revealed different microstructural transformations and reactions occurring during heating. The spectra X-ray diffraction showed the presence of mullite. Observations of the microstructures showed a bi-modal morphology of the mullite grains.
A water-quenching technique was used for the thermal shock tests.The Mullite specimens were heated at different temperatures (100 °C to 500 °C), and held at each temperature for 10 min. Then, the heated specimens were dropped by free fall into a water bath, which was maintained at 25°C with a thermostat. The residual strengths of the quenched specimens were determined in a three-point bending test. The results showed that the quenching critical temperature difference ΔTc depends on density and porosity of the samples.
Keywords: Kaolin, Mullite, thermal shock, strength, density