Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Reexamination Certificate
1997-12-15
2001-09-11
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
C205S210000, C205S270000, C205S271000, C205S283000, C205S291000, C205S269000, C205S263000
Reexamination Certificate
active
06287445
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to coating of particles, and more particularly electrolytic plating of metals and alloys onto small electrically conductive particles.
It is known to coat particles by such techniques as sputtering, spraying, electroless (autocatalytic) plating, coating with metal organic resonates, and electrolytic plating.
Electrolytic plating of particles involves placing a cathode and an anode in an appropriate electrically conductive solution, placing electrically conductive particles in the solution and in electrical contact with the cathode, and causing an electrical current to pass from the cathode to the anode. The passage of the electrical current through the solution causes reduction of ions in the solution, which results in deposition of a coating material on the particles in electrical contact with the cathode.
One technique for electrolytic plating of particles is described in Lashmore et al., U.S. patent application Ser. No. 08/317,532, filed Oct. 4, 1994, now U.S. Pat. No. 5,603,815, the entire disclosure of which is hereby incorporated herein by reference. In this technique, a bed of particles are placed in a cathodic container that is vibrated during the plating process. The vibration of the container causes fluidized motion of the bed of particles while the particles remain in electrical contact with the cathode, which avoids agglomeration of the particles and thereby enables accurate control of the volume ratio of the coating material to particle material on each of the particles.
By selecting an appropriate volume ratio of coating material to particle material and controlling the ratio for each of the particles, it is possible to engineer the physical and mechanical properties of the composite particles and articles formed from the composite particles. This technique is described in detail in Beane et al., U.S. Pat. No. 5,453,293, the entire disclosure of which is hereby incorporated herein by reference.
SUMMARY OF THE INVENTION
The invention provides an apparatus and method for coating particles in a rotating container. A cathode forms an electrically conductive inner surface of a side wall of the container. An anode is positioned relative to the cathode so as to permit both the cathode and the anode to be immersed together in an electrically conductive fluid. A motor is connected to the container and arranged to cause the container to rotate so as to generate a centrifugal force. Particles are placed in the container, the container is filled with the electrically conductive fluid, and electrical current is caused to pass from the cathode to the anode through the electrically conductive fluid while the container is rotated. The particles rest against the electrically conductive inner surface of the side wall of the container while the electrical current passes from the cathode to the anode, so as to result in deposition of a coating material from the electrically conductive fluid onto the particles.
By providing for generation of a centrifugal force such that the particles rest against the electrically conductive inner surface of the side wall of the container, the invention provides a reliable way to coat small particles (e.g., less than 100 &mgr;m in diameter), which might otherwise make only intermittent electrical contact with the cathode surface due to the tendency of viscous friction to resist the gravitational force on the small particles. This is especially important where the small particles have a low density. Because each of the particles tends to remain in electrical contact with the cathode surface, the invention makes it possible to achieve a high degree of uniformity in the ratio of coating material to particles material on a particle-by-particle basis. The invention is especially effective where the current efficiency through the solution is less than 100 percent. This is because hydrogen might evolve during the deposition process and adhere to the particles, and the centrifugal force resists the tendency of the hydrogen to cause the particles to rise up in the solution and break electrical contact with the cathode surface.
Numerous other features and advantages of the invention will become apparent from the detailed description, drawings, and claims.
REFERENCES:
patent: 2102819 (1937-02-01), Ronci
patent: 3591466 (1971-07-01), Heiman
patent: 3783110 (1974-01-01), Ahmad
patent: 5565079 (1996-10-01), Griego
patent: 5698081 (1997-12-01), Lashmore et al.
patent: 1596970 (1970-07-01), None
patent: 53-73433 (1978-06-01), None
patent: 59-35699 (1984-02-01), None
patent: 629034 (1978-09-01), None
Beane Glenn L.
Lashmore David S.
Materials Innovation Inc.
Wasserman Fran S.
Wong Edna
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