Chemical, textural and structural evolution of Ni1-xO nanoparticles upon isothermal air heating
Résumé
The isothermal air heating (320 degrees C) of monolithic nanometric Ni1-xO (similar to 4 nm, 7% Ni3+) particles results in their sintering and concomitant loss of excess oxygen, leading to almost stoichiometric monolithic larger particles (similar to 7 nm, 0.5% Ni3+). By coupling crystallographic, thermal, textural and chemical analyses of the powders along heating, we could demonstrate that their evolutions in structure, texture and chemical composition are intimately linked and non-monotonous. First, while the particles/crystallites progressively coalesce and increase in size, their level of crystallographic strains increases until a saturation step in oxygen is reached (8 h). With time, this excess in oxygen is then progressively released, as well as the associated strains, and then the particles size and specific surface area stabilize (13 h). Beyond 13 h, the level of strains still monotonously decreases while a transient gain in oxygen/weight and a temporary decrease in crystallite size are observed before the final monolithic powder is produced (34 h). (C) 2016 Elsevier B.V. All rights reserved.