Study On The Technology And Performance Of Silver Powder For Electronic Paste Prepared By Chemical Reduction Method

As the conductive phase in the electronic paste,ultra-fine silver powder is required narrow distribution particle size,high tap density,and smooth surface.With the progress of milling and slurry sintering technology,silver powder has been developed from micron to micronanoscale.Solar battery power generation is a green and renewable resource,and silver powder is manufactured using liquid phase reduction method.Due to the difficulty of prepared the silver powder used in electronic paste,result the low domestic market share of this silver powder.The preparation of ultra-fine silver powder by liquid-phase precipitation conversion method could obtain ultra-fine silver powder with uniform particle size and smooth surface,which was rarely used in practical applications.Through the liquid-phase precipitation conversion method,silver powder has excellent performances by using reduction from NaBH₄ to AgCl and ascorbic acid to Ag₂CO_3.AgCl was reduced by NaBH₄,and it could be completely reduced when NaBH₄was treble amount of AgCl,and the gas generated during the reduction refined fine particle by crushing and shearing action.With the increasing of concentration and amount of NaBH₄,the average particle size and specific surface area of silver powder were decreased,dispersion became worse.Cl^-can be used nucleation control agent,combining with the CTAB surfactant induces of the silver powder to grow from flake structure into micro-nanometer-like spherical silver powder.The AgCl particles are coated with a dispersant and the silver powder precipitated in situ.Using L₁₈3⁷orthogonal experiment for optimization,the optimal process combination was:reducing agent 3.5 times,concentration 0.6 mol/L,temperature 45°C,pH=11,dispersant 5%CTAB,stirring 350 r/min.With the optimized process,the surface-smoothed spherical silver powder was prepared which average particle size was 0.39?m,Span=0.513,specific surface area was 1.355 m²/g,AF₅₀=0.924,burn rate was 0.6703%,and bulk density was 1.23 g/m L.The reduction of Ag₂CO₃ with ascorbic acid could be completely reduced when the reducing agent was 2 times.The dispersants PVP,Tween80 and CTAB aggregated to form loose Ag₂CO₃ particles,the gas generated during the reduction stirred the silver powder to reduce agglomeration.The particle size of Ag₂CO₃ has little effect on the particle size of the reduced silver powder,and silver powder was precipitated in situ.With the increasing of reducing agent concentration and temperature,silver powder particle size and specific surface area were an increasing trend.The dispersant was used as a dispersant through steric hindrance and chemical adsorption.The ellipsoidal smooth-dispersed silver powder was obained prepared with CTAB as a dispersant at 50°C.Using L₁₈3⁷ orthogonal experiment for optimization,the optimal process combination is:amount of reducing agent was 2 times,Ag⁺concentration was0.1 mol/L,reducing agent concentration was 1.0 mol/L,dispersant was 10%CTAB,temperature is 50°C,stirring rate is 350 r/min.Under the optimal process,elliptical and spherical ultra-fine silver powder was obtained:average particle size 0.39?m,specific surface area 1.4762 m²/g,AF₅₀=1.007,silver powder which had smooth surface,good dispersibility,burning rate of only 0.2994%,loose packing density1.48g/mL.