Microwave assisted solid state reaction synthesis of MgAl2O4 spinel powders

Stoichiometric MgAl2O4 spinel powders were synthesized by microwave assisted solid-state reaction (MWSSR powders) in a domestic microwave (MW) oven (2.45 GHz frequency, 700 W power) from aluminum tri-hydroxide and caustic MgO in the presence of carbon black (10–50 wt.% with respect to total raw mix). 20% C was found to be sufficient to produce spinel powder with 82% spinel content within 100 min while 50% C was able to produce 93% spinel containing powder within the same time. In conventional solid-state reaction (CSSR), in order to obtain the powder with the same amount of spinel phase (i.e., ∼93%), the above raw mix was calcined at 1350 °C for 1 h and the total heating and cooling cycle time was more than 24 h. For the purpose of better comparison, three other stoichiometric MgAl2O4 powders were also prepared following conventional combustion synthesis using urea (CUCS powder) or sucrose (CSCS powder) as a fuel, and microwave assisted combustion synthesis using urea as a fuel (MWUCS powder), respectively. Effects of synthesis route on the powder properties were assessed by means of XRD, SEM, BET surface area, and particle size analysis. Among the various powders studied, the MWSSR powder was found to be superior as far as saving in processing time and power is concerned in addition to good sintering characteristics in terms of bulk density (B.D), apparent porosity (A.P) and water absorption (W.A).