Factors Governing the Formation of Oxygen-Containing Copper Powders in a Plasma-Solution System

The formation of precipitation under the action of a direct current atmospheric pressure discharge in air on a copper (II) nitrate solution was investigated. The discharge was excited by applying a high voltage to two pointed titanium electrodes placed above the liquid anode and liquid cathode in the H-shaped cell. The one of the advantages of such design is the absence of the contact of the electrodes and liquid phase that can affect on the precipitation composition. The studies were carried out at initial concentrations of 0.005 and 0.1 mol·L−1 of Cu(NO3)2 and discharge currents from 30 to 70 mA. Under the discharge action of the discharge, the formation of colloidal solutions occurs only in the anode part of the discharge. Turbidimetry kinetic measurements showed that the process includes two stages. In the first stage (slow), insoluble copper compounds are formed, the coagulation of which and an increase in concentration leads to the second stage (fast). When the precipitate is calcined, crystalline monoclinic CuO is formed. The size of the aggregates of the sediment particles was less than 1 μm. It is assumed that the process is initiated by solvated electrons generated in the anodic part of the discharge. Their reactions with water molecules lead to the formation of hydroxide ions. These ions, reacting with copper ions, lead to the formation of their insoluble hydroxo compounds.