CH503361A - Electrolyte for electrolytic condensers - containing dicarboxylic acids - Google Patents

Abstract

Electrolyte for condensers with aluminium electrodes, which can be used in a wide range of temps. (-55 degrees to + 100 degrees C), consists of an aqs. soln. of a dicarboxylic acid, such as adipic acid, with addition of phosphonic acid or a phosphate. The evolution of gases depends on the phosphate concentration (decreases with the latter), but is lower than in the case of conventional electrolytes.

Description

  

  
 



  Electrolytic capacitor
The present invention relates to an electrolytic capacitor with an aluminum electrode.



   The electrolyte used in such capacitors is usually a mixture of an organic and an inorganic acid, such as boric acid, in water solution together with ammonia and glycol, the main purpose of the latter element being to lower the freezing point of the electrolyte.



   However, capacitors with an electrolyte of this composition have the disadvantage that they only work satisfactorily within a limited temperature range. At low temperatures the electrolyte usually has too high a resistance, and in view of this it is important to note that any measures that can be taken to reduce the resistance, such as increasing the water content and adding alkali, deteriorate the capacitor result at high temperatures. At high temperatures, the dielectric layer is attacked by the electrolyte, which can be recognized by the formation of gas.

  Even without the above-mentioned measures, the gas formation can be of such magnitude that special design measures have to be taken to create a gas outlet so that the capacitor housing does not burst.



   With a known electrolyte composition, gas formation is avoided. This electrolyte consists of a mixture of boric acid, glycol and ammonia with an addition of phosphoric acid or a phosphate. However, capacitors with this electrolyte cannot be used at low temperatures, especially because the specific resistance of this electrolyte is quite high, in the order of magnitude of 5000 ohms at room temperature.



   The invention relates to an electrolytic capacitor with an aluminum electrode which is intended to work at both low and high temperatures and has a relatively low specific resistance. The electrolyte used therein is of the same kind as the above-mentioned electrolytes and consequently contains an organic acid in water solution together with an addition of phosphoric acid or a phosphate as an electrolyte. The invention is characterized in that the organic acid is a dicarboxylic acid and the concentration of the phosphate ions, calculated as PO 1, is between 0.01 wt / o and 1 wt / o of the electrolyte.



   It is convenient to use ammonia to neutralize the electrolyte to a pH between 4 and 9. An example of the composition of the electrolyte according to the invention is as follows.



     Adipic acid 81 g ammonia 70 ml glycol 110 ml water 250 ml diammonium phosphate 0.2 g
This electrolyte has a specific resistance of 25 Ohmcm at room temperature and provides a capacitor that can be used advantageously in the temperature range between -55 ° C. and + 100 ° C.



   With regard to the phosphate content, it should be noted that certain aluminum oxide layers strongly absorb phosphate ions, and it is therefore necessary to take into account a sufficient excess of phosphate for this absorption when deciding on the composition of the electrolyte, so that the composition of the electrolyte in the working state of the capacitor correct is.

  The influence of Ide's phosphate content on the gas formation is shown in the figure of the accompanying drawing, in which curves of the gas formation can be seen in an aluminum foil that is immersed in electrolytes with different concentrations of Ide's phosphate.An etched foil of 1 dm2 made of aluminum with a purity of 99.99 / o was immersed in different baths of the electrolyte with a composition according to the example given above and with different phosphate concentrations. The temperature of the electrolyte was kept at 85 ° C., and the gas formed was collected and measured at regular time intervals. The time in hours is plotted on the X-axis and the volume of the gas is given in ml on the Y-axis.

  The percentages on the curves relate to the phosphate concentration in each individual case. The straight line B refers to an electrolyte that contains boric acid in ethyl glycol and neutralized with ammonia. The specific resistance of the electrolyte is 550 Ohmcm. The curves A relate to the electrolytes according to the invention.



   As the curves show, the lowest gas formation is achieved at a PO concentration of about 0.05 wt / o, but a concentration of 0.01 wt / o results in less gas formation than the conventional ammonium borate electrolyte, and this is also the case with a PO concentration of
4 0.5 o / o by weight and above.

 

Claims (1)

PATENT CLAIM Electrolytic capacitor with aluminum electrode which contains an organic acid in water solution together with an addition of phosphoric acid or a phosphate as electrolyte, characterized in that the organic acid is a dicarboxylic acid and the concentration of the phosphate ions, calculated as PO 4, is between 0.01 wt .O / o and 1% by weight Indes Elektro 4 lytes.