Dielectric vs Electrolyte

Dielectric vs Electrolyte purpose in a capacitor

Hello,
I have confused about what is dielectric and electrolyte. If I understand right, the dielectric blocks the flow of electrons and ions, but the electrolyte allows only the ions pass (and not to the electrons)? So the non electrolitic capacitor have dielectric only, but in otherwise an electrolytic capacitor which has electrolyte between their plates must have a dielectric to block the ions pass or
the electrolyte is different type of dielectric and there is no need to exists in an electrolytic capacitor?

Electrolytic capacitor has a thin oxide layer as dielectric, review the drawing in a recent thread https://www.edaboard.com/showthread.php?t=366714&p=1570040&viewfull=1#post1570040

More information in this Wikipedia article https://en.wikipedia.org/wiki/Electrolytic_capacitor

Capacitor, by definition is two conductive plates separated by a dielectric.

in the case of electrolytic, the electrolyte can be considered one of the conductors.

the oxide layer is the dielectric, and also a semiconductor. That why if you run the voltage the wrong way, they conduct, heat up and explode.

Re: Dielectric vs Electrolyte purpose in a capacitor

diamadiss said:

the electrolyte is different type of dielectric and there is no need to exists in an electrolytic capacitor?

Click to expand...

The electrode is commonly Al; it has a thin oxide layer that acts as the dielectric. The thickness of the oxide layer determines the voltage rating and also the capacitance.

Unfortunately the native oxide layer is rather porous and that makes a lousy capacitor. We use electrolytes (soap like; contains borates, phosphates etc) that block the pores and improves the performance. However, under reverse voltage, the pores get deprotected and the capacitor fails. But the electrolyte is NOT the dielectric. It becomes an extension of the other foil. Ta also has a similar oxide layer (that makes soldering Al very difficult if not impossible).

Re: Dielectric vs Electrolyte purpose in a capacitor

c_mitra said:

The electrode is commonly Al; it has a thin oxide layer that acts as the dielectric. The thickness of the oxide layer determines the voltage rating and also the capacitance.

Unfortunately the native oxide layer is rather porous and that makes a lousy capacitor. We use electrolytes (soap like; contains borates, phosphates etc) that block the pores and improves the performance. However, under reverse voltage, the pores get deprotected and the capacitor fails. But the electrolyte is NOT the dielectric. It becomes an extension of the other foil. Ta also has a similar oxide layer (that makes soldering Al very difficult if not impossible).

Click to expand...

First of all thanks for the replies.
The dielectric and the electrolyte have the same conductive characteristics? For instance the dielectric and the electrolyte block the flow of electrons and allow the pass of the ions?

Re: Dielectric vs Electrolyte purpose in a capacitor

diamadiss said:

The dielectric and the electrolyte have the same conductive characteristics? For instance the dielectric and the electrolyte block the flow of electrons and allow the pass of the ions?

Click to expand...

The dielectric is a thin Al2O3 layer on the Al electrode. It does not allow electrons or ions to flow.

Al that is exposed to the elements is often anodised; this is a process in which the Al2O3 oxide layer is made thicker and pores sealed with chemicals. Very thick Al2O3 layers are used in cooking pans and other stuff.

If you use an Al electrode in a solution (electrolyte) it will act as a rectifier (because of the presence of the oxide film). If the electrolyte contains PO4 or BO3, you will see the capacitor effect.