Non-oxidative copper nano and fine particles for electroconductive materials

Metallic copper nano and fine particles have been successfully prepared by a wet process using a biopolymer as an anti-oxidation reagent. Copper oxide (CuO) and copper sulfate (CuSO₄) were the metal sauces used in this study. Hydrazine was used as the reducing reagent in order to obtain copper metal atoms. Uniform sized metallic copper particles were obtained by this process. Detailed TEM observation revealed that the obtained copper nanoparticles were covered by a continuous thin gelatin layer with the thickness of a couple of nanometers, which prevented oxidation of the obtained metallic copper particles for months. On submicron-sized fine particles, the gelatin layers were very condensed and showed a smooth surface. These organic layers show a sharp gray amorphous contrast in the TEM image. On the other hand, room temperature reduction of Cu²⁺ surprisingly gave very small copper nanoparticles with the size in a single digit nm level, but they form uniform-sized submicron sized secondary aggregations. The obtained particles can be kept non-oxidized for months in an ambient condition (under air). These particles could be successfully dispersed into an organic media to form stable electroconductive pastes, by using several physical dispersing steps and an organic coating polymer. Monodispersed particle pastes were obtained to form a continuous particle thin layer. These particles and pastes can be applied to printable electronics in the near future.