High Voltage Capacitor Anode Deoxidation for Volumetric Efficiency
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Solution Overview
Problem
High voltage electrolytic capacitors face limitations in volumetric efficiency and D.C. leakage stability due to the growth of crystalline phases and native oxide in anodic oxide films, which are exacerbated by the use of coarse powders and complex deoxidizing processes like Y-sintering and MgO coating, leading to contamination and inefficient equipment maintenance.
Innovation Solution
A method involving two deoxidizing processes using a reducing agent with higher oxygen affinity than the valve metal, such as magnesium, to form a cover oxide layer, followed by sintering and subsequent removal of the oxide layer, allowing for improved surface diffusion and reduced oxygen content, thereby enhancing anode morphology and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thick dielectric films are grown to withstand high application voltages, then voltage resistance is improved, but volumetric efficiency deteriorates due to non-linear CV characteristics
Solution Approach 1:
The patent changes the chemical composition parameters of the anode by reducing bulk oxygen content through deoxidizing treatments. This modifies the anodic oxide film formation characteristics, enabling more linear CV relationships that maintain volumetric efficiency even at high formation voltages required for thick dielectric films
Solution Approach 2:
The patent applies localized deoxidizing treatments to specific regions of the anode where oxygen content is highest. By creating zones with different oxygen concentrations, the anodic oxide film grows more uniformly without excessive thickness in critical areas, improving volumetric efficiency while maintaining voltage resistance
2Strength
If formation voltage is increased to grow thick dielectrics, then voltage resistance is improved, but D.C. leakage stability deteriorates due to crystalline phase precipitation
Solution Approach 1:
The patent applies preliminary deoxidizing treatments before anodization to remove bulk oxygen that would otherwise form crystalline phases during high voltage formation. By pre-removing oxygen sources, the anodic oxide film remains amorphous and stable even at high formation voltages, preventing D.C. leakage instability
Solution Approach 2:
The patent converts the harmful effect of high formation voltage (which causes crystalline phase precipitation and instability) into a benefit by first removing bulk oxygen. The same high voltage that would normally create instability instead promotes uniform amorphous oxide growth when bulk oxygen is eliminated, improving both voltage resistance and D.C. leakage stability
3Volume of moving object
If Y-sintering process is used to reduce oxygen content, then volumetric efficiency is improved, but device complexity and maintenance difficulty increase
Solution Approach 1:
The patent segments the deoxidizing process into separate, independent steps that can be performed using conventional equipment. Instead of requiring integrated Y-sintering equipment, the process divides deoxidization into discrete treatment stages, simplifying device requirements while achieving the same oxygen reduction and volumetric efficiency improvements
4Reliability
If MgO coating is applied to prevent reoxidation, then protection against oxygen is improved, but contamination occurs and productivity decreases
Solution Approach 1:
The patent extracts and removes the MgO coating layer after it has served its protective function during deoxidizing. By removing the coating, the anode surface is freed from contamination that would otherwise require extensive cleaning, maintaining protection against reoxidation during processing while eliminating productivity losses from contamination and maintenance
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
The method achieves increased volumetric efficiency and significantly reduces D.C. leakage, maintaining stability even after a 2000-hour life test, with improved productivity using conventional equipment and avoiding the contamination issues of previous methods.
Implementation Method 1
heating the anodes above the melting point of the reducing agent but below the temperature conventionally used for sintering of valve-metal anodes. During the heating, vaporized reducing agent deposits on the anode surface and reacts with oxygen in Ta(Nb) thereby creating a cover oxide layer of MgO
Implementation Method 2
vaporized reducing agent deposits on the anode surface
Implementation Method 3
vaporized reducing agent deposits on the anode surface
Implementation Method 4
the cover oxide layer is chemically leached from the anode surface with material such as a diluted solution of sulfuric acid and hydrogen peroxide
Implementation Method 5
the improvement is believed to be due to surface diffusion of the Ta atoms as an alternative to the bulk diffusion of Ta atoms which dominants at conventional sintering temperatures
Implementation Method 6
thick dielectric films are grown
Data Source
AI summary
A process for the manufacturing valve metal anodes is provided. The process includes:providing a valve metal powder;pressing the valve metal powder to form a pellet;first deoxidizing the pellet with a first reducing agent to form a first oxide of reducing agent on the pellet;removing the first oxide of reducing agent from the pellet to form a deoxidized pellet;sintering the deoxidized pellet to form a sintered pellet;second deoxidizing the sintered pellet with a second reducing agent to form a second oxide of reducing agent on the sintered pellet; andremoving said second oxide of reducing agent.