Exothermic assisted synthesis of mullite and spinel based ceramics

Typically synthesis of oxide ceramics requires high temperatures and long heat treatment times consuming a lot of energy which increases the cost of products and the environmental burden. In order to produce more economical and more environmental friendly oxide ceramics low-energy intensity processes are sought for. The potential of mine tailings as a secondary raw material source has been acknowledged widely. Compositions of mine tailings vary, including typically SiO2, MgO, Al2O3 and CaO as the main components. Presented study is a part of the research aiming to utilize selected mine tailings based minerals in production of porous ceramics by low energy intensity processes. In this part of the study the exothermic reaction assisted synthesis of oxide ceramics are studied and compared to the basic sintering bonding. The goal is to examine exothermically reactive raw materials (e.g. aluminium powder) for less energy intensity synthesis of mullite and spinel based ceramics. Thermodynamic calculations and evaluations are presented for selected mixtures. The thermal behaviour of raw materials and thermal evolution of mixtures was studied by using thermogravimetry (TGA) giving a simultaneous Differential Scanning Calorimetry signal (DSC). Phase structure evolution was analysed by an X-ray diffractometry (XRD) and morphology of raw materials and final products were analysed by scanning electron microscope (SEM).