Reaction heat utilization potential in mullite and spinel based ceramics synthesis and sintering

Typically synthesis of technical ceramics, such mullite and spinels, requires high temperatures and long sintering times. Traditional production routes consume lot of energy, which increases the cost of products and have high environmental burden. Therefore low-energy intensity processing routes are sought for. Self-propagating High-temperature Synthesis (SHS) is offering one energy efficient route for making advanced composites and intermetallic compounds. The SHS process is traditionally limited only to highly exothermic reactions where the released combustion energy is exploited. Present work studies the potential of utilization the heat released from the exothermic reactions in ceramic synthesis and sintering. For example the initialization of the endothermic reaction of mullite formation reaction is studied. Exothermically reactive raw material (aluminium powder) is examined for less external energy requiring synthesis of mullite and magnesium aluminate spinel based ceramics. Thermodynamics calculations and the analysis of the energy balance compared to the conventional sintering bonding are presented for selected materials. In addition thermogravimetry (TGA) combined to Differential Scanning Calorimetry (DSC) is used for examination of thermal behaviour of raw materials and reacted materials. X-ray diffractometry (XRD) and scanning electron microscope (SEM) studies are used for phase structure analysis.