Originally Posted by commsysman
Electrolytic capacitors do not "dry up".
Interesting claim. Its been a number of years since I last tore an electrolytic capacitor apart. Back in the 1930s electrolytic capacitors did have liquid in them. My recollection that more recent versions used a jelled liquid that was more like a paste.
"An electrolytic capacitor is a capacitor that uses an electrolyte (an ionic conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other types, but with performance disadvantages."
My understanding of how electrolytic capacitors disputes the above.
"Electrolytic capacitors are capacitors in which one or both of the "plates" is a non-metallic conductive substance, an electrolyte. Electrolytes have lower conductivity than metals, so are only used in capacitors when metallic plate is not practical, such as when the dielectric surface is fragile or rough in shape or when ionic current is required to maintain the dielectric integrity. The dielectric material of electrolytic capacitors is produced from the anode metal itself in what is known as the forming (or anodizing process. During this process, current flows from the anode metal – which must be a valve metal such as aluminum, niobium, tantalum, titanium, or silicon – through a conductive bath of a special forming electrolyte to the bath cathode. The flow of current causes an insulating metal oxide to grow out of and into the surface of the anode. The thickness, structure and composition of this insulating layer determine its dielectric strength.
The above description is actually a little self-contradictory, but corrects itself in the second sentence:
"The dielectric material of electrolytic capacitors is produced from the anode metal itself in what is known as the forming (or anodizing process."
The anode is typically aluminum (hence the use of the word anodizing) or tantalum.
An electrolytic capacitor is not like a normal capacitor, which has two metal plates separated by an insulator material of some sort (mylar, polyester, etc.).
False. If you tear an electrolytic apart you will find two metal plates which are either aluminum or tantalum. They are separated by a layer that functions something like a wick, mechanically separating the metal plates and retaining and distributing the electrolyte. The actual dielectric is a thin oxide layer related to the material that the metal plates are made out of, IOW either aluminum oxide or tantalum oxide. Either of these materials combine a high dielectric constant with excellent insulating properties in thin layers.
"A tantalum capacitor is a type of electrolytic capacitor, a component of electronic circuits. It typically consists of a pellet of tantalum metal as anode, covered by an insulating oxide layer that forms the dielectric, surrounded by conductive material as a cathode. Tantalum capacitors are the main use of the element tantalum".
This electrolyte material undergoes a chemical reaction when a voltage of the correct polarity is applied. This chemical reaction forms a microscopically thin layer which acts as an insulator as long as the voltage is maintained, and the rest of the electroltyic material is connected physically to an outer metal can that acts as the negative connection of the capacitor.