Mechanochemical solid-gas reactions: Kinetics and products of interaction between Zr and CO

The kinetics of CO absorption and variations in the composition and crystal structure of a solid phase were studied in detail for a mechanochemical reaction between Zr and CO. It is established that, after mechanical treatment of a Zr powder in a CO atmosphere at room temperature, the amount of absorbed CO molecules is comparable with the number of Zr atoms. It is shown that mechanical loading leads to the trapping of CO molecules by grain boundaries, followed by the penetration of C and O atoms into the volume of microcrystallites. In the course of volume saturation with C and O atoms, the structure of Zr varies in the following sequence: hcp Zr --> fcc ZrOxCy{0.42 < (x + y) less than or equal to 1} --> t-ZrO2 + fcc ZrC + C. Until half conversion, the mechanochemical reaction Zr + CO exhibits a self-accelerating character: N(CO) = (G(0)/2A)D-2, where D is the energy supplied during the mechanical treatment of Zr [J/g]; A = 250 J/m(2) is the work of formation of grain boundaries; and G(0) = 2 x 10(-3) (mol g)/(MJ m(2)) is the specific energy yield of CO sorption. The reaction yield drops sharply at P(CO) < 80 torr.