Conventional and spark-plasma sintering of cordierite powders synthesized by sol–gel methods

Cordierite powders synthesized by colloidal and alkoxide sol–gel methods were conventionally and spark-plasma sintered. The powders for the sintering investigations were obtained by calcination of the gels at a temperature where α-cordierite is formed (crystalline powders) or at a temperature where densification without crystallization of silica-containing component occurred (amorphous powders). All the calcinated gels were ground for 3 h, uniaxial pressed at 400 MPa and sintered conventionally at 1400, 1430 and 1450 °C for 2 h. In order to improve the sintering behavior of the cordierite powders, spark-plasma sintering (SPS) was applied. The microstructures and the phase composition of the obtained cordierite materials were analyzed using scanning electron microscopy (SEM) and X-ray diffraction analysis and the mechanical properties of the materials were determined. It was shown that the sinterability of the colloidal powders was much better than that of the alkoxide powders. Conventional sintering at 1400 °C of the crystalline powder produced by the colloidal method gave the material of the best mechanical properties. The sinterability of the crystalline alkoxide cordierite powder was highly improved by spark-plasma sintering at a lower sintering temperature (1350 °C), for a very short period of time (7 min). The density of the obtained material was very close to the theoretical density of α-cordierite and the mechanical properties were better than those of materials obtained by conventional sintering.