Mechanochemistry of Bi2O3. 1. Defect Structure and Reactivity of Mechanically Activated Bi2O3

The regularities of the mechanical activation of α-Bi2O3, the nature and thermal stability of defects resulting from the activation, and an increase in the reactivity of the oxide have been analyzed with the use of X-ray diffraction, measurement of specific surface area, and synchronous thermal analysis combined with mass spectrometry. The process of Bi2O3 mechanical activation may be divided into two stages. At the stage of the fracture of particles, their specific surface area grows to S = 3.2 m2/g, while the particle size and size L of the coherent-scattering region decrease to 100 and 40 nm, respectively. At the stage of friction, S somewhat decreases, while L remains unchanged. After grinding in air, a phase of Bi2O2CO3 is observed in addition to the main phase of monoclinic α-Bi2O3, with the former phase resulting from sorption of CO2 from air. When an activated sample is heated, bismutite decomposes with CO2 liberation in a wide temperature range. For an activated sample of nanosized oxide, heat absorption due to the α-Bi2O3 → δ-Bi2O3 phase transition begins at a temperature that is 10°C lower than the usual one. The reactivity of activated Bi2O3 has been determined by the example of its reduction in the atmosphere of CO. The mechanical activation increases Bi2O3 conversion upon reduction at 600°C by 2.5 times and decreases the temperature of the reduction onset by nearly 100°C.