Mechanochemical synthesis of M’MO4 oxides with the scheelite structure

The lattice parameters of the crystalline scheelite phases prepared by mechanochemical synthesis in M’O-MO3 systems were determined by x-ray diffraction. Analysis of x-ray intensities showed that all of the synthesized materials were deficient in the harder constituent. The M’/M atomic ratio was found to correlate well (r = 0.91) with the relative difference in Mohs’ hardness between the constituent oxides. The structural data obtained on the products of mechanochemical synthesis after ∼102 impacts agree with theoretical predictions for the first impact, according to which mass transfer is due to rolls forming in the contact region between colliding particles, and the product of mechanochemical synthesis is the result of relaxation in a layer of rolls and voids in the process of rapid quenching under negative pressure. Estimates show that, on account of the low temperature in the contact region, the rate of mass transfer by rolls is about 3 orders of magnitude faster than that of diffusive transfer, even though the latter is favored by the deformation intermixing and high vacancy concentration (2 to 3 orders of magnitude higher than that in melts). The termcold melting is in full measure applicable to the mechanochemical processes in question