Army

Device for applying coatings to particles in a fluidized bed

Introducing vibration from outside the vacuum chamber enhances coating properties and simplifies the process

Materials

(a) Schematic and (b) photo of experimental setup inside the vacuum chamber.

Small particles are often added to material systems to modify mechanical, dielectric, optical, or other properties. However, the particle often needs a coating to optimize its contribution to the material. For example, a nickel or copper coating can improve the anti-corrosion characteristics in carbon fiber-reinforced aluminum.

Sputtering is a common, inexpensive technique used to coat particles but must be done under a high vacuum. Vibration of the particles is a method added to sputtering that creates a fluidized bed and is a way to better ensure uniform coating. Unfortunately, vibration is not ideally compatible with maintaining a vacuum.

Army researchers have developed a novel method and apparatus for transferring vibratory motion from outside to inside the vacuum chamber to produce a fluidized bed. The method allows the use of non-vacuum rated vibratory sources, thus reducing complexity and cost.

The system also allows a wider variety of coatings to be produced on particles having a larger range of shapes and sizes. Sputter deposition using multiple sputter sources can be employed to produce single- and multi-layer coatings on the fluidized particles and simultaneous co-sputtering can also produce custom alloy coatings on the fluidized particles within this system.

The technique also allows for the coating of millions of particles whereas simpler shaking or tumbling techniques can only effectively agitate tens or hundreds of particles.  This technology has the potential to greatly increase the production processes for paint additives and pigments, reflective paints and coatings, dyes, metal matrix composites, polymer matrix composites, specialty metal alloys, specialty ceramics, time-release drugs, and passivated catalytic particles. Both sputter coating and fluidized bed processing are established and scalable manufacturing techniques, indicating that the particle coating methodology described here could be practically utilized for creating novel materials for engineering and industrial applications.

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