Layered Emitter Coating Structure for Crack Resistance with PDAG Coatings

Abstract

A thermal management apparatus includes an electrohydrodynamic fluid accelerator in which an emitter electrode and another electrode are energizable to motivate fluid flow. The emitter electrode is a layered structure including an electrode core material and an outermost coating that is susceptible to micro-cracking or corona erosion. A barrier material is provided in a sublayer to protect the underlying electrode core material. An adhesion promoting layer may be used between the barrier material and the electrode core material or between other layers of the structure. solid solution. A method of making an EHD product includes positioning the layered electrode relative to another electrode to motivate fluid flow when energized.

Description

BACKGROUND[0001]1. Field of the Invention[0002]This application relates generally to electrodes in electrohydrodynamic or electrostatic devices such as electrohydrodynamic fluid accelerators and electrostatic precipitators, and particularly to classes of materials that can be used to form such electrodes.[0003]2. Description of the Related Art[0004]Many electronic devices and mechanically operated devices require air flow to help cool certain operating systems by convection. Cooling helps prevent device overheating and improves long term reliability. It is known to provide cooling air flow with the use of fans or other similar moving mechanical devices; however, such devices generally have limited operating lifetimes, produce noise or vibration, consume power or suffer from other design problems.[0005]The use of an ion flow air mover device, such as an electrohydrodynamic (EHD) device or electro-fluid dynamic (EFD) device, may result in improved cooling efficiency, reduced vibration...

AI Technical Summary

Benefits of technology

[0029]In some implementations, an emitter electrode material includes palladium solvent metal and a silver solute material. Palladium exhibits many desirable characteristics such as high strength and conductivity, while silver is an excellent catalyst for ozone. In the solid solution, some palladium atoms are displaced by silver at the surface of the electrode, and, in some cases through at least a substantial portion of the bulk of the electrode. Thus, the materials characteristics of the electrode are substantially similar to those of pure palladium, with the addition of an ozone reducing catalytic effect provided by sufficient concentration of silver atoms at the electrode surface.

[0076]Advantages of use of an EHD device for thermal management in such devices includes, e.g., substantially silent operation, reduced power consumption, reduced vibration, reduced thermal solution footprint and volume, and form factor flexibility, e.g., capability to utilize space around other electronics.

Problems solved by technology

It is known to provide cooling air flow with the use of fans or other similar moving mechanical devices; however, such devices generally have limited operating lifetimes, produce noise or vibration, consume power or suffer from other design problems.

Elevated ozone levels have been associated with respiratory irritation and certain health issues.

For example, EHD device performance reduction or failure can be caused by gradual coating of the emitter with silica.

Still other EHD devices produce unacceptable concentrations of ozone in the air transported through the device.

Additionally, some electrodes may be susceptible to oxidation, corona erosion, or accumulation of detrimental materials.

However, pure metals are often deficient in some regard with respect to other desirable materials characteristics.

While each of the elements present in the alloy will contribute in some way to the overall characteristics required, alloys of such metals do not always provide the same desirable characteristics as the pure metals would alone and such compound characteristics are not always readily predictable.

The alloy no longer contains either pure lead or pure tin so the beneficial effects of these elements may be altered, diminished or lost.

While some phases formed on alloying may present other beneficial materials characteristics, such beneficial properties are not readily determinable or predictable without extensive testing as the new phases do not present the same properties as the pure components.

Silver, however, does not generally exhibit long life in the emitter wire corona environment.

However, the difference in the size of the Pd and Ag atoms can generate some degree of stress in such a solid solution coating due to the strain on the lattice.

It has been found that these stresses within the AgPd solid solution coating can result in micro-cracking of the surface in some cases, which can accelerate deterioration of the electrode and electrode failure.

The micro-cracks in the solid solution coating expose the underlying core material of the emitter electrode which can be more susceptible to corona plasma induced degradation.

Both of these metals exhibit high strength and conductance, yet typically oxidize in the type of plasma environment commonly found in an EHD device.

However, non-metal materials such as carbon graphite are known to have relatively low friction coefficients.

The electrode includes an electrode core material and a coating about the core material, the coating being susceptible to adverse effects from a plasma discharge environment, e.g., following micro-crack formation, pinhole formation, defect formation, corona erosion or consumption of a portion of the coating.

The layered emitter electrodes include: an electrode core material, a coating about the core material, the coating being susceptible to adverse effects from a plasma discharge environment, e.g., micro-crack propagation, pinhole formation, coating defect formation and corona erosion.

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