14 - Preparation of ultrafine powders by reaction-precipitation in impinging streams II: Nano copper and its surface improvement

Abstract

This chapter investigates the preparation of nano copper powder by reduction-precipitation in the submerged circulative impinging stream reactor (SCISR) with KBH4 (potassium borohydride) as the reducing agent, CuCI2 solution as the copper source, strong aqua ammonia as the complexant, and polyvinylpyrrolidone (PVP) as the dispersing agent. The preparation experiments are carried out in two stages. The major goal in the first stage is to make nano copper powder with a relatively uniform size distribution and determine the optimal or most feasible mole ratio of CuCl2 to KBH4. In the second stage the influences of various operating parameters on the mean size and the appearance of the produced nano copper are investigated to yield the optimal conditions. The effecting factors examined are the concentration of copper salt, the amount of PVP, the pH of the reaction mixture, the reaction temperature, and the impinging velocity. The chapter also investigates the surface improvement of the nano copper powder. Nano copper powder oxidizes very easily. The partial replacement of Cu by Ag to transform the nano copper powder into the Cu-Ag double metal powder is one of the most feasible methods for the surface improvement of nano copper. This can be achieved by reacting nano copper with Ag(NH3)2+ solution directly in the existence of polymer protecting agent to produce Cu-Ag double metal powder.