Cryogenic grinding of tantalum for use in capacitor manufacture

Abstract

An electrolytic capacitor comprising an anode comprised of cryogenically milled anode material is described. The cryogenic milling process prepares the active anode material for anode fabrication. The capacitor further comprises a casing of first and second casing members secured to each other to provide an enclosure. A feedthrough electrically insulated from the casing and from the casing and extending there from through a glass-to-metal seal, at least one anode electrically connected within the casing, a cathode, and an electrolyte. The cathode is of a cathode active material deposited on planar faces of the first and second casing members.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a divisional application of U.S. patent application Ser. No. 13 / 932,034, filed on Jul. 1, 2013, which claims priority from U.S. Provisional Application Ser. No. 61 / 665,936, filed Jun. 29, 2012.TECHNICAL FIELD[0002]The present invention relates to the manufacture of capacitors, more specifically, to the processing of materials that comprise the anode of an electrolytic capacitor.BACKGROUND OF THE INVENTION[0003]As more and more medical applications are investigated and implemented to aid and assist the human body, devices needed to deliver the desired therapy are becoming increasingly more sophisticated, both functionally and in terms of their structural makeup. Modern implantable devices require power sources that are smaller in size, but powerful enough to meet the therapy requirements. For example, a cardiac defibrillator has a battery powering circuits performing such functions as, for example, the heart sensing and ...

AI Technical Summary

Benefits of technology

[0015]Specifically, at about −198° C., tantalum undergoes a phase change in which the ductile metal transitions into a body centered cubic (BCC) crystalline structure. At this temperature tantalum becomes embrittled which facilitates its milling without the need to expose it to gas, such as hydrogen gas of the prior art. Thus, the potential to adversely alter the surface oxidation state or phase of the material through exposure to a gas is reduced.

[0016]In contrast to the prior art, the anode active material, such as tantalum, is milled in its frozen embrittled state. Since the hydrogen embrittlement and sequential de-hydride steps are eliminated, the surface properties and electrical resistance of the anode material can be better controlled. Furthermore, the need to subject the material to additional, potentially environmentally harmful processing steps such as de-oxidation and acid leach is also eliminated.

[0017]Thus, the material preparation process of the present invention improves control of the material properties of capacitor anode materials, particularly tantalum. In addition, the material preparation process of the present invention eliminates added processing steps, which therefore increases material preparation speed as well as reduces the potential of introducing contamination and error within the material.

Problems solved by technology

In comparison, the prior art material preparation process shown in FIG. 4 is a multi-step process that is both time consuming and cumbersome.

In addition, the anode material produced by the prior art process is susceptible to possible compositional inconsistencies and contamination.

The prior art anode material preparation process is a cumbersome process that comprises as many as 13 steps.

Such a complex process is not conducive to producing a material having consistent properties.

At room temperature, tantalum is a ductile material that makes milling of the material difficult.

However, the hydrogen embrittlement process modifies the material such that its surface properties, in particular its surface oxidation state is not ideal.

However, if diffusion of oxygen is not correctly controlled, and too much oxygen diffuses into the surface of the tantalum, a less desirable phase of tantalum oxide is formed.

Such undesirable phases of tantalum oxide typically have a reduced electrical resistivity, which tends to increase the current leakage.

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