The high price of precious metals in recent years has prompted the widespread use of ultra-fine nickel powder and copper powder in internal electrodes and terminal electrodes of multilayer chip ceramic capacitors (MLCC). However, the use of nickel powder as the internal electrode material has the problems of partial oxidation of the nickel powder and mismatch of shrinkage of the nickel layer and BaTiO_3. Copper powder is easily oxidized during sintering and has a high sintering temperature.
In this paper, the surface modification of ultra-fine nickel powder and copper powder is performed to solve these problems.
In the modification experiment of nickel powder, a composite nickel powder coated with a Ni-B-O-based anti-oxidation film was prepared by the NaBH_4 reduction method. The effects of various reaction conditions on the oxidation resistance of the modified nickel powder were examined. The single-factor analysis method was used to determine the optimal modification process conditions, such as 10g of nickel powder, 0.6mol·L ~ (-1) of NaBH_4, reaction temperature of 45 ℃, pH = 111, and NaBH_4 added flow rate of 3mL · min ~ (-1), reaction time 30min, stirring speed 200r · min ~ (-1). The initial oxidation temperature of the modified nickel powder prepared under the optimal conditions is 355 ° C, which is 78 ° C higher than the initial oxidation temperature of the original nickel powder, and its shrinkage performance is also improved, and it has good electrical conductivity and tap density. In the modification experiment of copper powder, the original copper powder was sensitized and activated, and then the copper-silver bimetal powder was prepared by electroless silver plating method. The effects of various reaction conditions on the oxidation resistance of copper-silver bimetal powder were investigated. The single-factor analysis method was used to determine the optimal modification conditions, such as 2.5 g of copper powder, 0.5 mol·L ~ (-1) of silver ammonia solution, and 2.5 mol·L ~ (-1) of hydrazine hydrate. , PVP is 0.75g, reaction temperature is 50 ° C, pH = 111, the flow rate of silver ammonia is 3mL · min ~ (-1), reaction time is 30min, and stirring speed is 100r · min ~ (-1). Under the optimal conditions, electroless silver plating was performed twice on the activated copper powder to prepare a coated copper-silver bimetal powder. The results show that the oxidation rate of the secondary-coated copper-silver bimetal powder is 4.5% lower than that of the original copper powder by heating at 400 ° C for 30min in the air atmosphere. It also reduces the sintering temperature and the electrical conductivity. The original copper powder is good.