Levitation, Coating and Transport of Particulate Materials
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Guy E. Rindone, editor
LEVITATION, COATING AND TRANSPORT OF PARTICULATE MATERIALS* CHARLES D. HENDRICKS Lawrence Livermore National Laboratory, P. 0. Box 5508, Livermore, California ABSTRACT Several processes in various fields require uniformly thick coatings and layers on small particles. The particles may be used as carriers of catalytic materials (platinum or other coatings), as laser fusion targets (various polymer or metallic coatings), or for biological or other tracer or interactive processes. We have devisea both molecular beam ano electro-aynamic techniques for levitation of the particles during coating and electrodynamic methods of controlling and transporting the particles between coating steps and to final use locations. Both molecular beam ano electrodynamic techniques are cescribea and several advantages ano limitations of each will be discussed. A short movie of an operating electrooynamic levitation ano transport apparatus will oe shown. INTRODUCTION Many scientific, industrial and consumer oriented uses for particulate materials benefit from the application of uniform coatings ana layers of various types and compositions. Powders are given protective coatings against moisture incursion, candies and decorative particles are providea with various layers for color and taste properties. Medications are multiple layer for Particles used for catalysis must be coated time release characteristics. with the finely divided catalyst. The cascade developer process used in many xerographic reproduction systems utilizes carrier beads which are coateu to provide charging ano carrier functions for the toner material. Some inertial confinement fusion targets reouire coatings and layers of various materials. These are only a few examples of a very large number of processes, applications and uses in which uniform coatings and layers are either aesirable or necessary. For several years in our work on laser fusion targets we have been developing techniques for coating spheres used for ICF targets. The spheres have been metal, glass andipolymer materials. In order to have a perspective on the problems faced in our coating development, consioer the quality parameters of the spheres and the coatings to be depositea. The finished product must have a very Smooth surface -- peak to valley roughness of a few hundred Angstroms with not more than half a dozen peaks of a thousand Angstroms altitude. Because a coating generally will, at best, replicate the substrate surface, the spheres which are to be coated must meet the same quality criteria as the coatings. If we examine the reasoning behino the surface smoothness criteria, we find that the real concern is that
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outer surface por = constant for all 0,
* Work performed under the auspices of the U. S.
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(i)
Department of Energy by the Lawrence Livermore National Laboratory under contract number Wl-7405-ENG-48.
60 to ensure symmetry of the implosions. It is obvious that the condition stated in Equation (1) is impossible to fulfill and the real Question becomes
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