Passivation of aluminium electrolytic capacitors is an essential part of capacitor design to improve reliability and reduce leakage. As such, the choice of a suitable inert anode material is of paramount importance. This paper presents an overview of the various considerations to be taken into account when selecting an inert anode, and also discusses the merits of each material with respect to their respective performance.
The choice of an inert anode material depends largely on cost and performance. An inert anode material is typically anodized to provide a low-surface-energy layer that resists oxidation, thus ensuring excellent protection against corrosion and other degradation mechanisms. The anodized layer is typically much thicker than that used in electrolytic capacitors, which are typically only a few hundred nanometers thick. Common inert anode materials are aluminium, titanium, tantalum, and niobium.
Aluminium is the most common inert anode material used in aluminium electrolytic capacitors. It is relatively low cost, abundant, and corrosion-resistant, making it an ideal choice for passivating any capacitor. In addition, aluminium has a high dielectric breakdown strength and can be formed into a wide range of geometries for optimized capacitor performance.
Titanium is becoming increasingly popular as an inert anode material due to its superior corrosion resistance and thermal energy efficiency. It is also highly resistant to oxidation, and in some cases, may even be coated with a protective oxide layer to further improve durability. Furthermore, titanium is also much easier to machine than aluminium, allowing for cost-effective production.
Tantalum is a rare and expensive inert anode material with an exceptionally high dielectric breakdown strength. It is also extremely corrosion-resistant, oxidation-resistant, and non-hygroscopic, making it an ideal choice for high-performance capacitors. However, tantalum can be expensive, challenging to machine, and difficult to source.
Finally, niobium is a very hard and strong inert anode material. It is extremely corrosion-resistant, thermal shock-resistant, and oxidation-resistant, making it the perfect choice for applications involving high temperatures or extreme electrical conditions. Additionally, niobium has a relatively low cost compared to other inert anode materials.
Ultimately, the selection of an inert anode material will depend on the intended application. While aluminium may be the preferred choice for general-purpose aluminium electrolytic capacitors, an alternative anode material may be more suitable for more demanding applications. However, regardless of the anode material used, careful attention must be paid to the anodizing process to ensure the highest quality and most reliable product possible.
