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

Resumo

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.