The effect of mechanochemical activation and annealing on the structure and morphology of the WO₃–NiO system

Abstract

The present work investigates the processes of phase formation and morphological evolution in the WO₃–NiO system during mechanochemical synthesis followed by thermal annealing. The aim of the study was to determine the influence of milling time and annealing temperature on the phase composition and morphological characteristics of the materials, as well as to identify the conditions for the formation of nickel tungstate (NiWO₄).

The study was carried out using X-ray diffraction analysis, Raman spectroscopy, and scanning electron microscopy. It was shown that variations in milling time do not lead to phase transformations and are accompanied by preservation of a stable phase composition. Raman spectroscopy of non-annealed samples confirmed the presence of the monoclinic WO₃ phase. It was established that thermal annealing at temperatures of 500 °C and above results in the formation of the NiWO₄ phase.

Morphological studies revealed that the initial powders consist of large agglomerates of spherical nanoparticles. At 500 °C, a significant change in morphology and predominance of the NiWO₄ phase with NiO inclusions are observed, whereas further increase in annealing temperature promotes grain growth and enhanced structural ordering. At 1000 °C, large spherical grains with dendrite-like outgrowths are formed.

The obtained results expand the understanding of transition metal tungstate formation mechanisms and may be applied in the development of functional oxide materials for catalytic, photocatalytic, and energy-related applications.