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

In this study, magnesium aluminate spinel (MgAl2O4) 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 degrees C. Samples were prepared from granulated powders using uniaxial pressing at 200 MPa with consequent sintering at 1500-1650 degrees 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 MgAl2O4. 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 degrees C. Pore trapping was observed for sintered samples at 1650 degrees 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 degrees C as a result of the grain growth occurrence.

Automated summary

In this study, magnesium aluminate spinel was synthesized with cobalt addition, which improved the crystallization and densification of nanopowders but also led to increased grain boundary mobility and decreased hardness at high temperatures.