Effect of Cobalt Doping on Synthesis and Sintering Properties of MgAl2O4 Spinel Nanopowders

In this study, magnesium aluminate spinel (MgAl 2 O 4 ) has been synthesized with inorganic nitrate salts route in the presence of 1 wt.% cobalt addition. Microstructure, phase transformation, densification and sintering behavior of the pure and Co-doped powders have been investigated. The synthesis process was proceeding during calcination of the prepared gel at different temperatures 700-900 °C. Samples were prepared from granulated powders using uniaxial pressing at 200 MPa with consequent sintering at 1500-1650 °C. Phase study and microstructure observations indicate the crystallization improvement of nanopowders at the presence of cobalt addition for all of the calcination temperatures in comparison with the pure MgAl 2 O 4 . Maximum relative density for pure sample achieved about 95% of its theoretical value, while it was about 98% for the Co-doped sample by sintering at 1600 °C. Pore trapping was observed for sintered samples at 1650 °C due to increase in the grain boundary mobility at high temperature. The values of Vickers hardness for both samples decreased from about 15 to 13 GPa during increasing the sintering temperatures from 1500 to 1650 °C as a result of the grain growth occurrence.