Composition, structure, and property relationship in cordierite ceramics

Cordierite ceramics (Mg2Al4Si5O18) are perfect materials for some specific electrical and thermal applications due to their outstanding properties. Having low thermal expansion coefficient and low dielectric constant, high chemical and electrical resistivity make them suitable for extreme condition applications. The effect of composition on the final properties of cordierite is a considerable issue since even minor changes influence the majority of the properties. In this study, four cordierite compositions were chosen from the cordierite region in the phase diagram and their characteristics were observed. The effect of solidus and liquidus temperature on densification and final properties of cordierite ceramics were investigated. The MgO amount was increased to lower these temperatures. Samples were sintered at 1300 and 1350℃. Physical, mechanical, thermal, and dielectric properties were measured and compared with each other. C4 samples with the highest MgO and lowest Al2O3 content had the lowest sintering and densification temperature, yet the highest densification. It also had a density of 2.42 g/cm3, 0.53 percent open porosity, and 1.55 percent closed porosity. Phase analysis proved α-cordierite phase formation as the major phase in all samples. C4 samples showed highest thermal conductivity and thermal diffusivity -which were 1.23 W/m∙K and 0.16 mm2/s, respectively- among the samples as a result of a small amount of open porosity presence. Three-point bending test results indicated that flexural strength of samples varied between 43-73 MPa and they increased with porosity absence. Highest dielectric constant and lowest dielectric loss at 1-5000 kHz frequencies were obtained as 5.2 and 0.003, respectively in the C4 sample. Microstructure and elemental analyses proved the existence of isolated and closed pores and homogeneous elemental distribution in all samples. It was proved that adjusting solidus and liquidus temperatures eliminates an extra melting-quenching process and at 1300℃, cordierite ceramics with the above-mentioned properties can be produced.