Powder Surface Treatment or Coating

Dealing with powders, it is necessary to either (1) drop or blow substrates through the luminous gas phase or (2) contain powders in the bottom of reactor and tumble the reactor wall in a marmer similar to that of wet clothes in a drier. 

The first method is a sure way to expose the surface of powder uniformly if one pass is sufficient to achieve the surface modification, but it is not easy to recycle the substrate in the luminous gas phase in vacuum. Therefore, the main issue in this approach is how to repeat the interaction of surface with the luminous gas phase efficiently, which entirely depends on the flow dynamics of powders. Multiple-step operation requires multiple discharge systems or repeated operation. The generation of discharge is more or less the same as the conventional modes used in LCVD reactors. External radio frequency electrodes or coil with glass tube is the most 

The second method is the tumbler treatment or coating of powders. So far as the handling of substrate is concerned, the tumbler coating of powder and the tumbler coating of small-size substrates are the same. However, many detailed factors involved in these reactors are not the same, and it is better to deal with these two processes separately. 

Powders generally pack rather densely, particularly in comparison to small-size substrate, and the interaction of luminous gas (for deposition) with powder surface is limited to more or less the top powder layer. Consequently, the mixing by tumbling action is important to treat powder uniformly. The mixing along the axis of tube is also an important factor. If dilferent color powders are placed in different 

In principle, the rotating speed could be raised so that a considerable portion of powders is in gas phase however, it causes difficulty in feeding monomer and establishing a uniform distribution of deposition rate along the axis of tube length. In other words, maintaining powders in the gas phase is not the prime purpose of the tumbler reactor. 

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