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Powder coating

ALD particle coating with fluidized bed reactor (FBR)

We’ve talked about how atomic layer deposition (ALD) coating creates a strong, uniform, and pinhole-free barrier that protects even the most complex materials from corrosion and moisture. The same ALD coating method can also be used to coat materials such as fine powders.

And just to make sure that all readers are on the same page before we go further: when we talk about powder coating, it really means we coat the powder. We do not mean coating methods that use powder and electrostatic and thermal processes to replace conventional paint. That kind of powder coating is way too thick to be of any interest to us.

Coating fine powders

Fine powders are coated for multiple reasons – to improve their functionalization, to protect them from humidity and moisture, and to help prevent corrosion. Coating sensitive powders has helped industries such as LED lighting to improve product lifetime.

The best results for coating fine powders are achieved by ALD with fluidized bed reactor (FBR), as it’s the only reactor type that delivers conformal coating for single particles.

Why use a fluid bed and not a fixed bed? A fluid bed keeps the particles in motion. This allows for extensive mixing in all directions, and makes sure all particles are conformally coated.

A fixed bed basically keeps the particles stacked, leaving little to no room for the precursor gases to diffuse through the particle mass. This means that you’ll end up with particles that are partially coated, or not coated at all.

Illustration above: A fixed bed on the left, with stacked particles prevented from being conformally coated, and a fluid bed on the right, with fluidization enabling conformal coating of all particles.

The cross-section schematics above shows the Beneq ALD with FBR fluidization process (new features under patenting). Particles are kept fluid by a carrier gas and mechanical vibration. The residual gas analyzer (RGA) performs in-situ analysis, so you can see the results in real-time.

Beneq FBR in motion

We developed the Beneq ALD with FBR module to keep particle mass fluid by using not one method, but two:

By using gas flow through the reactor, and
By vibrating the reactor module itself.

We also designed observation windows in our FBR module so that you can observe the fluidization process. This is extremely useful when you’re setting the minimum fluidization flow, as it’s good to be able to see what’s happening. Once you’ve set the minimum fluidization velocity, it’s easy to scale up or down.

A stainless-steel reactor is also available for the high temperature depositions and production use. Both glass and stainless steel reactors can be used with the same FBR setup.

*The picture above shows the Beneq ALD with FBR module with openings on two sides for easy observation. The module is also easy to remove and clean.*

See in-situ

In addition to watching the fluidization, you can also see the actual results at the molecular level from the in-situ analysis provided by the residual gas analyzer (RGA). The RGA is integrated into the ALD system, which analyzes the results and provides real-time data on your PC.