Journal of the American Ceramic Society, Vol.103, No.8, 4167-4177, 2020
Low-temperature sintering of magnesium aluminate spinel doped with manganese: Thermodynamic and kinetic aspects
This work describes the role of manganese (Mn) as a sintering aid for magnesium aluminate (MgAl2O4) nanoparticles. Mn-doped MgAl2O4 nanoparticles, synthesized by coprecipitation method, showed increased surface area when contrasted to undoped MgAl2O4. Fast firing of compacted-doped nanoparticles achieved high degree of densification at temperatures as low as 1100 degrees C with very moderate grain growth, resulting in average sizes at the nanoscale (similar to 60 nm). Differential scanning calorimetry was used to quantify the exothermic heat effects of sintering, which combined with quantitative microstructural evolution analysis enabled calculation of both surface and grain boundary energies. The results revealed that Mn effectively reduces the surface and grain boundary energies which led to dihedral angle broadening and consequently increased sintering stress. Experimental data also revealed a concomitant decrease in the activation energy of sintering with Mn doping which dropped from 644 kJ/mol for undoped MgAl2O4 to 285 kJ/mol, informing Mn acts as a sintering aid in a thermokinetic manner.