Production of metallic nickel particles of a given size from nickel (II) salts using sodium borohydride

Abstract

Fine nickel particles offer an innovative material which can be used, in particular, as a filler in conducting compositions. However, for successful practical application in the above area the size of such particles should not exceed 12 μm. The method of chemical reduction of salts in liquid phase was selected to produce metallic nickel particles with controlled size. Nickel chloride was used as a salt, and sodium borohydride with its high reduction activity – as a reducing agent. The synthesis was carried out in aqueous medium at room temperature with the [BH4–]/[Ni2+] ratio equal to 3.5 mol/mol. The authors looked at the hydrolysis of sodium borohydride in solutions with varying concentrations of alkali and thus determined what concentration of sodium hydroxide would be optimum to stabilize the sodium borohydride solution. Kinetic dependencies of pH and the optical density of the reaction mixture were obtained. Their comparison and analysis helped time-space the processes of nucleation and synthesis suggesting that that was an autocatalytic reaction. The obtained results helped establish that the optimum range of nickel chloride concentrations is 15 to 20 mmol/L. An optical microscope was used to obtain microphotographs of the synthesized particles and determine their sizes as a function of the concentration of the initial salt and the storage time. It was established that the maximum size of the obtained particles in the nickel chloride concentration range of 5 to 20 mmol/L after a week after synthesis was 10 μm. At the same time, when the nickel chloride concentration is 15 to 20 mmol/L, the most probable size of the particles after a week after synthesis is 4–6 μm.This research was funded by the D. Mendeleev University of Chemical Technology of Russia. Project number: G-2020-019.