Mechanical testing of cordierite porous ceramics using high temperature diametral compression

In this study, the high temperature mechanical behavior of cordierite porous disks prepared by the starch consolidation forming method was evaluated. In this method, due to the swelling and gelatinization properties of starch in aqueous suspension at a temperature between 55 and 85 °C, the starch granules perform as both consolidator/binder of the green body and pore former at high temperature. Aqueous suspensions (29.6 vol.%) of a cordierite precursor mixture (talc, kaolin, and alumina) with the addition of potato or cassava starches (11.5 vol.%) were prepared by intensive mechanical mixing, homogenization, and vacuum degasification. Green disks were formed by thermogelling of the aqueous suspensions at 85 °C for 4 h followed by additional drying at 50 °C for 24 h. They were characterized by bulk density and apparent porosity measurements, and microstructural analysis by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Porous cordierite materials were obtained by calcination at 650 °C for 2 h and reaction-sintering at 1330 °C for 4 h, employing specific, controlled heating schedules in both treatments. Cordierite disks were characterized by bulk density and apparent porosity measurements, and microstructural analysis by SEM. Mechanical behavior was evaluated in diametral compression using a servohydraulic testing machine at room temperature (RT), 800, 1000, and 1100 °C. Apparent stress–strain relationships were obtained from load–displacement curves, and mechanical parameters, such as fracture strength (σF), apparent Young modulus (Ea), and yield stress (σY), were determined. Moreover, crack patterns were also evaluated. The obtained results were analyzed in function of the developed microstructures, considering the presence of a silicate glassy phase and a complex porosity, and the testing temperature.