Preparation Of Ultra-fine Flake Silver Powder And Its Application In Silver Paste Of Ceramic Capacitor Electrode

Silver paste is one of the most important materials in the production of ceramic capacitors.It is usually printed on the ceramic substrate by high-speed and high-resolution screen printing.After drying and high-temperature sintering,the electrode is formed.The conductive silver paste is mainly composed of silver powder,glass powder,organic carrier and additive.Compared with spherical silver powder,flake silver powder has more advantages.In this paper,ultra-fine flake silver powder for silver paste of ceramic capacitor electrode was prepared by chemical reduction in liquid phase.The conductive silver paste was prepared with the ultra-fine silver powder.The conductive properties of the ceramic substrate were studied by screen printing.The main results are as follows:1.Citric acid can promote the anisotropic growth of silver nucleus,make the silver nucleus form flake,and cooperate with sulfate to promote the growth of silver nucleus and the complexation of silver nucleus and silver.There is an optimal value in the formation of large silver powder.Different concentration of citric acid has great influence on the particle size of ultra-fine flake silver powder.With the increase of citric acid concentration,the particle size of silver powder increases gradually.When the amount of citric acid is 1.5 g/L,3 g/L,6 g/L,the particle size is 0.5?m,2?m,5?m respectively.The effect of FeSO₄·7H₂O content and adding method on the preparation of ultra-fine flake silver powder was studied.Increasing the amount of FeSO₄·7H₂O can increase the quantity and size of flake silver powder.2.Ascorbic acid as reducing agent shows better reducing effect than citric acid.When the initial concentration of AgNO₃ solution is 20 g/L,the concentration of ferrous sulfate heptahydrate solution is 80 g/L,the concentration of citric acid is 3 g/L,and the temperature is 25°C,the ultra-fine flake silver powder with good dispersibility and smooth surface is prepared.The vibrating density is 4.1 g·mL^-1,and the average particle size is 3.5?m.3.The dispersibility of silver powder has a significant effect on the printing performance of silver paste.The silver powder with fine particles and good dispersibility is suitable for screen printing.The thick silver paste film made of smooth flake silver powder is the most compact,with the largest adhesion and the best conductivity.The resistivity of sintered thick film is 0.20 m?·cm,and the adhesion is3.1 N.Moreover,the silver paste made of the flake silver powder has the best matching degree with the ceramic substrate.The connection is tight and there is no gap.The electrode electric performance made of the silver paste is the best.The capacitance of the capacitor made of the silver paste is large and the capacitance loss is small.