Chemical Reaction, Substructure, and Mechanical Behavior of Spinel MgAl2O4, Mullite, and Forsterite Nanocrystallines by Applying Mechanochemical Process and Subsequent Three-Step Heat Treatment

This research aimed to evaluate the formation reaction, substructure, crystallite size, and mechanical behavior of spinel MgAl2O4, mullite, and forsterite nanocrystalline using a combination of mechano-chemical and three-step heat treatment. The main aim was achieved by decreasing the annealing temperature to the level of nanostructures and high mechanical strength by considering three-step heat treatment. We conducted the mechanism of these phases by considering low milling and declining annealing temperatures. More specifically, phase transformation was conducted with proper activation energy to form the nanocrystalline at 1050 oC. The obtained crystallite sizes for spinel MgAl2O4, mullite, and forsterite nanocrystallites were 49.5, 70.71, and 47.8 nm, respectively, and their substructure verified the formation of 50 nm nanocrystalline. It was revealed that mechanical strengths were in order of increasing 378.33, 216.33, and 179.66 MPa. Interestingly, spinel MgAl2O4 was outstanding compared to mullite and forsterite due to the strong comparison between ionic and covalent bonds and the breaking of silicate networks by alumina and magnesia in mullite and forsterite structures. Declining the annealing temperature by three-step heat treatment proved to help develop spinel, mullite, and forsterite, and enhance their mechanical strengths as potential substrates for porous materials, ceramics, and refractory industries.