Parametric analysis on the apparent purity of Ni powder synthesized via hydrazine-reduction of aqueous NiSO4

The present research focuses on the synthesis of high-purity nickel powder through solution-based chemical reduction using hydrazine hydrate as a reducing agent. A series of synthesis experiments were carried out with variations in the concentration ratio of hydrazine to nickel ions ([N2H4]/[Ni2+] = 5–15), the concentration ratio of hydroxyl ions to nickel ions ([OH−]/[Ni2+] = 10–20), temperature (T = 60–80 °C), and reaction time (t = 30–90 min). The Taguchi L9 design of experiments and analysis of variance (ANOVA) was used to identify the role of the hydroxyl-to-nickel ion ratio ([OH⁻]/[Ni2⁺]) in determining the apparent purity of the nickel powder. The highest apparent nickel powder content, which was 92.75 %, was obtained in the experiment with [N2H4]/[Ni2+] = 5, [OH−]/[Ni2+] = 12.5, T = 60 °C, and t = 30 min. The optimum conditions that significantly influence the apparent purity of nickel powder derived from data processing are used as the basis for the second stage of the experiment to determine the effect of the [OH−]/[Ni2+] ratio on particle size, morphology, and purity of the synthesized nickel powder. It was found that higher hydroxyl concentrations lead to finer particles, and the morphology of nickel particles is linked to their apparent purity, with the chain of beads of nanoparticle aggregates morphology achievable when [OH−]/[Ni2+] = 12.5 and [OH−]/[Ni2+] = 15. The presented results may contribute to filling the gap in the knowledge to synthesize high-purity nickel powder with controlled size and morphology, which can be used in various applications such as catalysts, conductive fillers, and advanced electrodes.