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The Study On Preparation Of Cu-Ag, Ni-Ag Bimetal Powders And CaZrO3 Plating Nickel Powders

Posted on:2010-03-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:R XuFull Text:PDF
GTID:1101360278954026Subject:Metallurgical Environmental Engineering
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Recent years,the application scopes of copper and nickel powders were broadened with the rapid development of inner electrode utilizing base metal for MLCC(multilayer ceramic capacitors).In order to avoid electromagnetism interference and electromagnetism wave radiating, nickel powders become a main material of electric paint because of its excellent electromagnetism wave shielding properties in the scopes of electron,electrical facility,communications,modern electron war, warship,nuke and so on.Copper and nickel powders are apt to be oxidated in high temperature,to form an insulated oxide film,so the oxidation problem of them must be solved.This dissertation aimed to solve anti-oxidation of copper and nickel powders in high temperature.On the basis of thorough review of large amount of references on surface modification and theory analysis,a novel electroless plating method—silver salt dripping method has been proposed and used for the preparation of Cu-Ag and Ni-Ag bimetals.The surface modification of nickel powders has been carried out by using chemical precipitation to coat Ni powders with CaZrO3.The details are summarized as the followings.Copper and nickel powders have stronger activity than silver,their displacement reaction with silver makes against forming a smooth silver layer.Through thermodynamic analysis,N2H4 was selected as the reducing agent and possibility of restraining the displacement reaction was studied.The dispersibility of Cu powder and Ni powder suspended solutions was investigated by measuring Zeta potential and turbidity of the suspended solutions.First,dispersion stability of Cu powder respectively using PVP and sodium Tartrate as a dispersant,Cu powder possesses good dispersion property both in PVP-water-ethanol system and sodium Tartrate-water system.The system stabilization is based on electrostatic repulsion with sodium Tartrate acting as dispersant,and based both on electrostatic repulsion and spatial position resistance with PVP as dispersant.Secondly,dispersion stability of nickel powder was discussed in the system of PVP-water-ethanol and sodium Tartrate-water, experiments show that both of them possessed good dispersion effect.During the preparation of Cu-Ag bimetal via electroless plating,first of all,the sensitization and activation process on copper powder surface were studied using AgNO3 as an activating agent instead of conventional PdCl2,and the activation mechanism was determinate.The effects of pH, reaction temperature,dosage of PVP,concentration of N2H4 on anti-oxidation property of bimetal and residual Ag+ concentration were studied.Experiments show that the optimal conditions are as the followings:the copper-suspended solution compositions are ethanol 333mL/L,the activated copper powers 33.3g/L,pH 10.0,dosage of PVP 10g/L,N2H4 2.5mol/L;the copper-suspended solution volume is 150mL; reaction temperature is 50~55℃;the N2H4 concentration and volume of silver ammine solution are 0.5mol/L and 78.1mL respectively.The results show that the dipping mode of silver ammine solution can prevent silver from precipitating as separate particles.Prepared bimetal powders possess good dispersion property and good anti-oxidation at room and high temperature.A continuous film is formed on the surface of copper particles applied Ag coating two times,and the oxidation mass increase reduced from 23.78%of uncoated copper powders to 1.20%.Bimetal powders possess better electric performance in air atmosphere.During the preparation of Ni-Ag bimetal via electroless plating,the effects of pH,reaction temperature,dosage and feed mode of PVP, concentration of N2H4 and dispersion system on bimetal anti-oxidation properties and residual Ag+ concentration were studied.Experiments show that the optimal conditions were as the followings:the nickel-suspended solution compositions are ethanol 417mL/L,the nickel powers 25g/L,pH 11.0,dosage of PVP 8.33 g/L,N2H4 2.5mol/L;the copper-suspended solution volume is 120mL;reaction temperature is 60℃;the N2H4 concentration and volume of silver ammine solution are 0.5mol/L and 51mL respectively.Ni-Ag bimetal powders possess good dispersion property.The initial oxidation temperature notably rises from 290.45℃to 389.36℃.CaZrO3-coated nickel powders have been synthesized in methanol-water solvent.The effects of the amount of modification agent and dispersant,mixing speed,feed mode and flow rate of modification agent,heat treatment temperature of the composite nickel powder precursor,mixing time,reaction temperature and surface treatment of the origin Ni on composite nickel powders' properties were investigated. Through analysis of the experiment data,the optimum conditions were as the followings:the mass ratio of modification agent counted by CaZrO3 to original nickel powder is 5.9 to 100;both precipitation agents solution and zirconium-calcium solution are dripped at the meantime into the Ni-particle-dispersed methanol solution,with the flow rate of 0.65mL·min-1 respectively,H2O is 60mL and CH3OH is 126mL in methanol-water solvent,reaction temperature is 55℃,reaction time is 90 min,mixing speed is 350r/min,heat treatment temperature of the composite nickel powder precursor is 690℃.Composite nickel powders obtained under the optimum conditions were characterized by TG-DTA,SEM and the electric conductivity.It was approved that those composite nickel powders not only afforded the strong resistance to oxidation,but also had high electric conductivity.In addition,these powders have displayed good dispersion property.These features of CaZrO3-coated Ni powders have a good agreement with the demand of internal electrode material of MLCC.
Keywords/Search Tags:copper powders, nickel powders, electroless plating, chemical precipitation method, anti-oxidation
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