Stabilization of metallic nickel particles obtained by chemical reduction in liquid by introducing high-molecular compounds at synthesis stage

Abstract

Highly dispersed nickel metal particles are used as a filler in electrically conductive adhesives. In this application, they partially or completely replace particles of noble metals. However, the size of the filler particles in electrically conductive adhesives should be in the range from 5 to 15 μm. The method of chemical reduction of salts in liquid was used to obtain particles of this type. As the synthesis of nickel particles with hydrazine is a patented technology, nickel chloride was used as a salt and sodium borohydride was used as a reducing agent. Various polymer stabilizers are used in this method to control the size of the resulting particles. Polyvinyl alcohol, polyethylene glycol, polyacrylic acid (and its salts) were used for nickel particles stabilization. Different concentrations of the above polymers were introduced at the synthesis stage. The sizes of the nickel particles that were obtained using polyvinyl alcohol and polyethylene glycol did not exceed 50 nm. The use of high-molecular polyacrylic acid (M = 200,000 g/mol) ensures production of 2±1 μm nickel particles. The most suitable size of nickel particles for the specified purposes is obtained by adding low-molecular polyacrylic acid (M= 3,000 g/mol) and is 6±1 μm at a 0.15 wt. % stabilizer concentration. A study of the electrokinetic potential of the stabilized systems showed that the electrostatic component does not play any major role and that the systems are stabilized due to the adsorption film of polyacrylic acid that forms on the surface of metallic nickel particles.This research was funded by the Moscow Polytechnic University in the framework of V. E. Fortov Grant.The authors express gratitude to Research sharing center named after D. I. Mendeleev of the Mendeleev university of chemical technology of Russia