In general, copper nanoparticles are easy to oxidize in the ambient conditions. That is the main obstacle for copper ink to use because the appearance of copper oxide will result in rising the sintering temperature and decreasing the conductivity. Therefore, preventing copper nanoparticles from oxidization becomes an important issue. In this study, the addition of hydrazine utilized as oxygen scanvenger decreases the oxygen concentration in the liquid media. This method could prevent the copper nanoparticles from the exposure of oxygen and copper nanoparticles could store more than two months without oxidation. If the reducing agent is stronger and the concentration of gelatin is appropriate, the size of CuNPs is smaller. When the CuNPs is oxidized, there are two different oxidation final states. If the concentration of gelatin is higher, the oxidation state is [Cu(gel)]2+ . If the concentration of gelatin is lower, the oxidation state is [Cu(OH)4]2-. After washing two times by DI water, the impurities could be totally removed. The shiny precipitate can not be redispersed by sonocation and can be taken by tweezers. The precipitation is centrifugation-induced sintering, and its conductivity is similar with silver paste.
