Synthesis and Sintering Behavior of Ultrafine (<10 nm) Magnesium Aluminate Spinel Nanoparticles

This article reports a comparative characterization of ultrafine MgAl2O4 spinel nanoparticles synthesized by polymeric precursor (Pechini) and coprecipitation methods. The nanoparticles were evaluated in terms of purity and surface cleanliness, size distribution, state of agglomeration, and sintering behavior. Powders synthesized by the Pechini technique were highly agglomerated and revealed a bimodal particle size distribution centered around 12 and 27nm. Thermal analysis and infrared spectroscopy measurements indicated that carbon species remained on the surface of the powders only to be released when temperatures exceeded 1000 degrees C. Isothermal sintering of such nanopowders at 1300 degrees C showed a maximum relative density of only 54%. MgAl2O4 synthesized via coprecipitation created small nanoparticles, around 5-6nm after calcination at 800 degrees C, with significantly less agglomeration. Compared with the precursor-derived powders, excellent sinterability of the coprecipitated powders was obtained under the same sintering conditions. Relative densities above 90% were obtained after only 10min, which further increased to greater than 95% after 20min with no sintering aids or dopants. The results highlight the importance of purity and processing control to exploit the beneficial high sinterability of nanoparticles.