In this study, a mixture of magnesium oxide and titanium dioxide was
mechanically activated in order to investigate the possibility of
mechanochemical synthesis of magnesium titanate. Mechanical activation was
performed for 1000 min in a high-energy vibro mill (type MH954/3, KHD
Humboldt Wedag AG, Germany). The mill is equipped with housing having a
horizontally placed shutter. The cylindrical stainless steel working vessel,
with inner dimensions of 40 mm in height and 170 mm in diameter, has working
elements consisting of two free concentric stainless steel rings with a
total weight of 3 kg. The engine power is 0.8 kW. Respecting the optimal
amount of powder to be activated of 50-150 g and the stoichiometric ratio of
the reactants in the equation presenting the chemical reaction of magnesium
titanate synthesis, the starting amounts were 20.2 g (0.5 mol) of MgO and
39.9 g (0.5 mol) TiO2. During the experiments, X-ray diffraction analysis of
the samples taken from the reaction system after 60, 180, 330, and 1000 min
of mechanical activation was performed. Atomic absorption spectrophotometry
was used for chemical composition analysis of samples taken at different
activation times. Based on the X-ray diffraction analysis results, it can be
concluded that the greatest changes in the system took place at the very
beginning of the mechanical activation due to the disturbance of the crystal
structure of the initial components. X-ray diffraction analysis of the
sample after 1000 min of activation showed complete amorphization of the
mixture, but diffraction maxima characteristic for magnesium titanate were
not identified. Therefore, the mechanical activation experiments were
stopped. Evidently, the energy input was not sufficient to overcome the
energy barrier to form a new chemical compound - magnesium titanate. The
failure to synthesize magnesium titanate is explained by the low negative
Gibbs energy value of -25.8 kJ/mol (despite the theoretical possibility that
the reaction will happen), as well as by the amount of mechanical energy
entered into the system during activation which was insufficient to obtain
the reaction product. Although the synthesis of MgTiO3 was not achieved,
significant results were obtained which identify models for further
investigations of the possibility of mechanochemical reactions of alkaline
earth metals and titanium dioxide.
Effect of Rare Earth Oxides on Microstructure and Corrosion Behavior of Laser-Cladding Coating on 316L Stainless Steel