Electrolytic Capacitor Anode Foil Corrosion Prevention
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Solution Overview
Problem
Conventional electrolytic capacitors using aluminum oxide films are prone to corrosion when dipped in formation solutions, especially when a negative voltage is applied, leading to reduced capacitance and reliability.
Innovation Solution
The method involves forming a capacitor element by winding an anode foil with a matrix of one metal and a metal oxide film, and a cathode foil of a different metal, applying positive voltage to the anode lead wire and negative voltage to the cathode lead wire while dipping in a chemical solution to prevent corrosion, using metal oxides like niobium oxide, tantalum oxide, or titanium oxide on the anode foil and titanium nitride on the cathode foil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum oxide film is formed on aluminum foil and dipped in formation solution, then capacitance can be maintained, but corrosion occurs on the cut surface especially when negative voltage is applied
Solution Approach 1:
The patent changes the material parameter of the oxide film from aluminum oxide to metal oxides with higher dielectric constants (niobium oxide, tantalum oxide, titanium oxide). This parameter change increases capacitance while the specific combination with titanium nitride cathode film prevents corrosion during formation, resolving the contradiction between maintaining reliability and preventing harmful corrosion effects.
Solution Approach 2:
The patent employs a composite structure combining metal oxide films (niobium oxide, tantalum oxide, or titanium oxide) on the anode foil with titanium nitride film on the cathode foil. This composite material approach provides both high capacitance through high dielectric constant materials and corrosion resistance through the stable titanium nitride layer, simultaneously addressing both requirements.
2Reliability
If metal oxide films with higher dielectric constant are used to increase capacitance, then capacitance increases, but corrosion and deposit formation occur on capacitor element surface
Solution Approach 1:
The patent changes the dielectric constant parameter by selecting metal oxides (niobium oxide, tantalum oxide, titanium oxide) with higher dielectric constants than aluminum oxide, thereby increasing capacitance. The specific selection of titanium oxide combined with titanium nitride cathode film prevents the corrosion and deposit formation that would otherwise occur, resolving the contradiction between increasing capacitance and preventing harmful effects.
Solution Approach 2:
The patent converts the potential harm of using high dielectric constant metal oxides (which tend to corrode and form deposits) into a benefit by combining them with titanium nitride film. The titanium nitride acts as a protective layer that prevents corrosion and deposit formation, allowing the high capacitance advantage of metal oxide films to be realized without the associated harmful effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents corrosion on the anode foil's cut surface, ensuring the formation of correct oxide films and maintaining capacitor integrity, as demonstrated by reduced corrosion rates in evaluated samples compared to conventional methods.
Implementation Method 1
applying a positive voltage to an anode lead wire electrically connected to the anode foil and applying a negative voltage to a cathode lead wire electrically connected to the cathode foil while dipping the capacitor element in a prescribed chemical solution stored in a formation vessel
Data Source
AI summary
As to each of a capacitor element employing an anode foil having a matrix made of a metal and a film, provided on the surface of the matrix, made of an oxide of a metal different from the metal of the matrix and a capacitor element employing an anode foil having a matrix made of a prescribed metal and a film of an oxide of the metal and a cathode foil having a matrix made of another metal different from the metal, formation treatment is performed on an end face of the anode foil exposing the surface of the metal forming the matrix by applying a positive voltage to an anode lead wire and applying a negative voltage to a cathode lead wire. Thus, an electrolytic capacitor resistant against corrosion or the like is obtained.