US 5,284,676 AGranted

Pyrolytic deposition in a fluidized bed

AssigneeCarbon Implants, Inc.

InventorsJames A. Accuntius, David S. Wilde

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Abstract

Precise control of pyrocarbon being coated upon an object in a fluidized particle bed is achieved by monitoring the pressure difference between a region above the bed and a region in the lower portion of or just below the bed. Measurement of such pressure differential has been found to be truly representative of bed size in such a coater, and bed size is recognized to be a most important factor in achieving the desired characteristics of the substance being deposited. By adjusting bed size in response to changes in the pressure difference being monitored, a substantially constant bed size is readily achieved; alternatively, the pressure difference can be caused to gradually change in accord with a predetermined program. In either instance, adjustments are effected by adding additional particles to the bed or by changing the rate at which particles are withdrawn, and precise coating characteristics, e.g. thicknesses within very close tolerances, are achievable.

Claims14

Dependent claims

A method of carefully controlling the deposition of a substance onto a substrate while being levitated in a fluidized bed of particles, said deposition being carried out in an enclosure through which a gaseous atmosphere is caused to flow upward, which method comprises

establishing a bed of particles in fluidized condition in said enclosure with at least one substrate to be coated being levitated within said fluidized bed, said levitation being effected by the upward flow of said gaseous atmosphere,
heating said particles and said substrate to a desired temperature and including a pyrolytically decomposable component within said gaseous atmosphere such that pyrolysis of said component occurs to cause the desired pyrolytic substance to be deposited upon said substrate and upon said particles, both of which are being levitated,
withdrawing particles from said bed in a controlled manner,
adding feed particles to said bed in a controlled manner, which feed particles have an average size that is less than the average size of the particles being withdrawn,
monitoring the pressure at a predetermined location within or below said bed and the pressure above said bed to determine the difference in pressure therebetween, and
changing either the rate at which particles are withdrawn from said bed or the rate at which particles are fed to said bed or both in response to said determined pressure difference so as to precisely regulate deposition over an extended period of time and thereby produce a precise coating upon said substrate being coated.

3 more elements

Dependencies are inferred from the claim text.