Synthesis and chemical reactivity of polyol prepared monodisperse nickel powders

• Published in: Solid state ionics 1996-12, Vol.93 (1), p.33-50
• Main Authors: Hegde, M.S., Larcher, D., Dupont, L., Beaudoin, B., Tekaia-Elhsissen, K., Tarascon, J.-M.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Nickel powder; Oxidation; Particles; Polyol; Powder production; Powders; Reactivity
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/S0167-2738(96)00516-4

Monodisperse 1350 Å Ni powders are prepared according to the polyol process using polyvinylpyrrolidone (PVP) as a protective agent. Smaller size monodisperse Ni powders (300 Å) have presently been made from Ni(OH) 2 in ethylene glycol (EG) and PVP using Pd or Pt as nucleating agents. Thermogravimetric Analysis (TGA) and Temperature Programmed Desorption (TPD) measurements in air showed that ethylene glycol chemisorbed on the Ni surface protects the fine particles from air oxidation up to 180 °C. The oxidation peak temperature is reduced from 650 °C for Ni of 1 to 2 μm to 260 °C for Ni of 300 Å. The unseeded pure Ni powder undergoes stoichiometric oxidation to become NiO with a 27% weight gain while the oxygen uptake is 18.6% for 300 Å Ni particles seeded with 1% Pd. In that case, the formation of a new (Ni 1− x Pd x O 1− y ) type oxide crystallizing in a tetragonal structure similar to PdO is suggested. While the Ni particles of 1350 Å mean size followed a parabolic oxidation law ( % oxide formed ∞ t 1 2 ), 300 Å Ni particles followed a cubic law ( % oxide ∞ t 1 2 ). For Ni seeded powders with 1% Pt, the oxygen uptake is only 15.7%; the remaining Ni not undergoing oxidation is an Ni 1− x Pt x , alloy phase. A model calculation shows that 300 Å Ni particles grow around 70 Å Pd or 60 Å Pt nuclei and that the particles are covered by half an EG monolayer.