Hydrothermal Preparation Of Ultrafine Copper And Its Properties

Copper powder is one of the ideal substitution products of the PdAg electrode of multilayer ceramic capacitors(MLCC). It is excellent in price and electrical conductivity for preparing MLCC. However, copper powder is active in chemical property and can be oxidized easily in the air. Hence, a new technique of preparing copper powder which has excellent antioxidation ability and uniformity has been studied.The contrast experiment of chemistry reducing process and hydrothermal treatment were studied. The results showed that the crystallinity of copper powders prepared by hydrothermal method clearly increased, and the grain size distribution became narrow comparing with the copper powder prepared by reducing process.The precursor obtained by reducing process has many lattice defects and is inferior in uniformity. Hence we put it under the hydrothermal environment to improve its characteristic. The Optimized experiments were used to explore the optimal hydrothermal conditions in order to prepare Cu powders which have excellent properties. The optimal parameters of hydrothermal experiment as follows: the temperature is 240℃, the time of reaction is 10h and the volume ratio of solution filling is 80 % . The starting oxidation temperature of copper powders prepared by hydrothermal method is about 210℃and average particle size is about 0.7μm.The Cu powders were immerged in BTA solution to improve the antioxidition capability. The BTA thin films are nonconductive and were formed on the surface of copper powders. Hence, the chemical property of copper powders is more stable, and the starting oxidation temperature increased to 299℃.The mechanism of hydrothermal process has also been studied. Under the hydrothermal conditions, a small quantity of Cu2+ in solutions were carried to the copper lattice due to the diffusion and convection, then the Cu2+ move to the positions of lattice defect. The crystallization reaction happened and copper powders got a good crystallinity and an excellent antioxidation. The model of primary battery theory was built to explain the mechanism of improving uniformity of copper powders. As the two different particles closing up, primary battery reaction happened because of the...