What electro-chemical mechanism used in electrolytic capacitor?

[SughiRam P.]

Hi,
I have a small doubt in polarized capacitor. One of the reason for using polarized caps is it is small in size compared to non-polarized for the same capacitance value. What is the process involved to get such a large capacitance value for polarized caps? some may say read about construction of tantalum or aluminum capacitors. But, my question is why can't we use aluminum oxide for non-polarized capacitor to make its size small? Is anodizing one plate while using aluminum oxide make its dielectric constant value high to get high capacitance?

 

[ArNvC]

The Al-oxide you are referring to is actually sometimes used in non-polarized capacitors...correct me if I am wrong...:|

 

[dick_freebird]

The oxide protects the plate metal from corrosion, if
you need to protect both plates then you double the
dielectric thickness yet only use one of the two Al2O3
layers for its purpose (anode). So you then need twice
the plate area, meaning about sqrt(2) times the radius
or twice the height or some combination in between.

I have nonpolarized aluminum electrolytics in the parts
bins, but keep very few around. Nowadays most of my
work is low voltage where ceramics give a better board
density (no can, no plug, low height surface mount...).