The Special Nano-sio <sub> 2 </ Sub> Sol In Aluminum Electrolytic Capacitor Applications

Aluminum foil electrochemical forming and preparation of working electrolyte are the key techniques in Aluminum electrolytic capacitor R&D. In this paper, a kind of working electrolyte containing nano size silica glycol sols was prepared. We found that the Aluminum electrolytic capacitors using this kind of working electrolyte achieved the excellent electrical behaviors, such as low tgδ, low Il (leakage current) and high working voltage. The gelating of nano size silica glycol sols is a serious problem to be solved. In this paper orthogonal experimental design was used to seek the optimized conditions to prepare steady nano size silica glycol sols. Firstly, the silica water sols was prepared use the Na2SiO3 reaction with cation exchange resin, Secondly the H2O in the sols was replaced by HOCH2CH2OH , then the silica glycol sols was yield. After experiment in orthogonal method, we found that under this given conditions a clear and steady nano size silica glycol sols was prepared. The condition is: concentration of Na₂SiO₃ is 35%; CH₃Si(OC₂H₅)₃ is 2.5%; aging temperature is 60℃; aging time is 1 hour; under 90℃H2O is replaced by glycol by vacuum evaporation; pH between 5 7; SiO₂ concentration in glycol sols is 5%. The deleterious ions such as Cl-, SO42-have not been detected in the yield sols. We got the working electrolyte (I) by mix the silica glycol sols and other ingredients together, and another working electrolyte (II) containing no silica particles as contrast sample. Under 30℃, the conductivity of electrolyte (I) is 1830μS/cm is higher than that of electrolyte (II) is 1800μS/cm. The reason is, considered in this paper, the ionization of hydroxide in the surface of SiO₂ particles made the free charge in the electrolyte increased. So, the conductivity of electrolyte (I) is higher than that of contrast sample. The Us (spark voltage) of electrolyte (I) is 520V , voltage increase rate during aging process is 4.24V/s; these factors of electrolyte (II) are 460V and 1.83V/s. The reason is: the negative charged SiO₂ particles is adsorbed by anode at the weak point of the Oxide layer. The SiO₂ particles become a part of the Oxide layer, so it accelerates heal up speed of the Al2O3 film on the anode. Capacitors using electrolyte (I) and (II) were assembled. After 425V aging, tgδand Il of capacitors using electrolyte (I) were 4.86% and 4.0μA , these factors of...