Rotary Bed Atomic Layer Deposition (Rotary ALD) is a mechanical agitation method specifically designed to overcome the limitations of static beds and the complexities of fluidization when coating powders. It uses physical rotation to tumble the powder, ensuring every surface is exposed to the precursor gases.

In a rotary system, the powder is placed inside a drum or cylinder that rotates within a vacuum chamber. This movement creates a constant "tumbling" effect—similar to a clothes dryer or a cement mixer—which prevents particle agglomeration and eliminates "dead zones" where precursors might not reach. (1) Mechanical Mixing: The drum rotates at a controlled speed (typically 10 to 100 RPM for lab scale. (2) Precursor Dosing: Gases are introduced through the axis of rotation or via a fixed delivery tube inside the drum. (3) Self-Limiting Reaction: Just like standard ALD, the gas reacts with the surface of the moving particles until all sites are occupied. (4) Purging: Inert gas sweeps through the tumbling bed to remove byproducts and excess precursor before the next cycle begins.  

Rotary ALD is particularly useful when working with cohesive powders or high-density materials (like certain metal oxides or catalysts) that are notoriously difficult to fluidize. It allows you to achieve the same Al2O3 or TiO2 conformal coating without the risk of "slugging" or "channeling" that often occurs in gas-fed columns.

The diagram of the general working mechanism of the rotary ALD process is shown below:

References:

M. W. Coile, et al., High-capacity rotary drum for atomic layer deposition onto powders and small mechanical parts in a hot-walled viscous flow reactor, J. Vac. Sci. Technol. A, 2020, 38, 052403.

K. Seong, et al., Rotary-type atomic layer deposition of aluminum oxide coating on micropowder for secondary battery anode applications, Thin Solid Films, 2025, 817, 140656. 

S. Adhikari, et al., Progress in Powder Coating Technology Using Atomic Layer Deposition, Adv. Mater. Interfaces, 2018, 5, 1800581.