Mechanical, dielectric and photoluminescence properties of alumina–mullite composite derived from natural Ganges clay

•An allumina–mullite composite was derived from the alluvial clay of the Ganges.•Good Vicker's strength and density reveal structural applications.•Charge storage on the interface results in a higher dielectric constant.•Prominent PL emission bands for oxygen vacancies ensure optical applications.

A highly dense mullite–alumina composite was developed utilizing external alumina and clay aggregates from the Ganges (India) bed in order to obtain a low-cost multifunctional composite. Thermal evaluation and phase formation were investigated by simultaneous differential thermal and thermo-gravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Both equiaxed and elongated whiskers of mullite were present along with alumina platelets. Mechanical characteristics of the mullite composites were measured in terms of relative density and Vicker's hardness and were found to be ~ 89% and ~ 4.5 GPa at 1400 °C. Dielectric constant of the composite was found to be ~ 18 at 1400 °C which is higher than that of pure alumina or mullite. Structural defects and peculiar morphologies of the composite caused photoluminescence bands at around 310, 347, 436 and 460 nm. Due to its remarkable density, Vicker's hardness, improved dielectric properties and prominent photoluminescence, the composite can be used as a multifunctional composite with structural, electrical and optical applications.