Study On Manganese Dioxide Coating Solution For Tantalum Capacitors

In recent years,all kinds of military and civilian electronic products need to be thinner,lighter and smaller,which requires smaller components for using.Solid tantalum capacitors with cathode MnO₂ have the significant advantages of being large-capacity and easy to be made into small and chip-type components,therefore tantalum capacitors are widely used in various types of electronic products.The cathode MnO₂ is formed by impregnating/pyrolysis of manganese nitrate solution,and the manganese nitrate solution is called a coating solution.The performance of manganese nitrate solution has a huge impact on the formation of MnO₂ and the electrical properties of tantalum capacitors.In this study,three main factors of manganese nitrate solution,viscosity,surface tension and pyrolysis,which affected the forming of MnO₂,were detailed discussed.1.By testing the viscosity of 35%⁶0%manganese nitrate solution,it was found that the viscosity was 24.6cp or higher when the concentration was 50%or greater,and the coating effect was bad.When the concentration was 45%,the viscosity was 15.8cp,and the coating effect was better.When the concentration was 43%or less,the viscosity was 12.7cp or lower,and the coating effect was good.Furthermore,the formed MnO₂film had strong adhesive force and was difficult to drop.In addition,water-soluble viscosity reducer was added to manganese nitrate solution,and the viscosity of this solution was tested.The results showed that viscosity reducer did not greatly reduce the viscosity of manganese nitrate solution in high concentration（50%and greater）.Additionally,the coating effect was bad,and the formed MnO₂ film still dropped.2.By adding surfactants such as JFC-2,JFC-E and AEO₃ to coating solution and testing surface tension of these solutions,it was found that the surface tension decreased significantly when adding JFC-2 to coating solution.When adding 0.2%JFC-2 to a 45%manganese nitrate solution,the formed MnO₂ film became difficault to drop.In addition,ethanol and tert-butanol were added to coating solution,and then the viscosity and surface tension of these solutions were tested.The results showed that the surface tension of the solution with tert-butanol was lower,but its viscosity was higher.Additionally,the coating effect was bad,and the formed MnO₂ film was easy to drop.3.Peracetic acid,ammonium nitrate,and other catalysts were separately added to coating solution,and the DSC of these solutions were analyzed.The results showed that the temperature of losing water could be reduced by 30℃when adding 2%peracetic acid to coating solution,and the coating effect was good.Besides,the formed MnO₂film had strong adhesive force and was difficult to drop.When adding 2%ammonium nitrate to coating solution,the temperature of losing water could be reduced by15℃,and the pyrolysis temperature of Mn（NO₃）₂ could be reduced by 5℃.However,the formed MnO₂ film had week adhesive force and was easy to drop.When adding nickel nitrate and other catalyzers to coating solution,MnO₂ precipitate would be formed in short time at room temperature,so these catalyzers could not be used in actual production.