US 6,586,046 B1 · Fluidized bed apparatus and method for treatment of nonspherical, nonequiaxed particles

Abstract

Apparatus and method for producing metallic flake having an environmental coating for use in oxidative and corrosive atmospheres. Fluidized bed techniques are utilized to perform a controlled oxidation of metallic particles that include aluminum. The fluidized techniques permit the formation of a thin, outer shell of alumina over the outer surface of the flake. Because the oxidation is controlled so that the selective oxidation produces a thin outer shell, the particle has good reflectance and the metallic core of the particle is unaffected by the oxidizing treatment. Although the techniques of the present invention are effective for producing a reflective surface on aluminum-containing iron alloys while the core particles can be either magnetically soft or hard, the techniques can be used to produce a reflective surface that is corrosion and oxidation resistant on any aluminum containing alloy. Apparatus that facilitates the controlled oxidation is also set forth.

Claims21

Dependent claims

A method for forming non-spherical aluminum-containing metallic particles to provide them with resistance to oxidation and corrosion, electrical insulation capabilities and sufficient brightness to provide heat reflectance and infrared radiation suppression, comprising the steps of:

placing a preselected mass of non-spherical, aluminum-containing particles in a tube having an upper end open to the atmosphere and a sealed lower end having at least one sealed connection;
placing the tube into a furnace;
introducing a non-oxidizing, fluidizing gas into the tube through the at least one sealed connection at a flow rate sufficient to provide a positive flow of gas out of the upper end of the tube and to fluidize the particles within the tube so that the fluidized particles are within a heating zone of the furnace;
then
heating the furnace so that a temperature within the tube is within a preselected range;
then
introducing an oxidant gas at a preselected rate into the tube through the at least one sealed connection;
and
forming a thin protective ceramic shell over external surfaces of the non-spherical particles as the oxidant reacts with the metal, the ceramic layer characterized by transparency for improved reflectance of at least 60% and resistance-to-environmental deterioration.

6 more elements

A method for treating non-spherical metallic particles to provide them with resistance to oxidation and corrosion in a fluidized bed comprising the steps of:

mixing a preselected mass of non-spherical, aluminum-containing metal particles with a preselected mass of inert spherical particles, the ratio of the mass of metal particles to inert particles being about 10:1 and lower, the spherical particles being sized so that the diameter of the inert spherical particles is about the same size as the average maximum dimension of the non-spherical particles;
placing the mixture into a suspension tube having an upper end open to the atmosphere and a sealed lower end having at least one sealed connection;
placing the suspension tube into a furnace;
introducing a non-oxidizing, fluidizing gas into the suspension tube at a flow rate sufficient to fluidize the mixture of particles within the tube so that the fluidized particles are within a heating zone of the furnace while substantially preventing oxidation of the metal particles;
heating the furnace until a temperature of the tube within the heating zone of the furnace is within a first preselected range;
then
introducing an oxidant gas at a preselected rate into the tube to react with the non-spherical metal particles to form a thin protective ceramic layer over external surfaces of the particle, the ceramic layer characterized by brightness for improved reflectance and resistance to environmental deterioration at elevated temperatures in corrosive and oxidative environments, while holding the temperature of the tube within the first preselected range for a preselected time and maintaining the flow of the fluidizing gas;
then
heating the furnace until the temperature of the tube within the heating zone of the furnace is within a second preselected range while maintaining the flow of the fluidizing gas;
then
stopping the flow of oxidant gas;
cooling the mixture of particles to about ambient temperature;
and
reducing the flow of fluidizing gas into the tube.

11 more elements

A non-spherical aluminum-containing metallic particle having a thin, reflective layer of transparent alumina forming a protective outer shell, formed by a process comprising the steps of:

mixing a preselected mass of non-spherical, aluminum-containing metal particles selected from the group consisting of FeAl and Fe CoAl with a preselected mass of inert spherical particles selected from the group consisting of alumina and silica and combinations thereof, the ratio of the mass of metal particles to inert particles being about 10:1 and lower, the spherical particles being sized so that the diameter of the inert spherical particles is about the same size as the average maximum dimension of the non-spherical particles;
placing the mixture into a tube;
placing the tube into a furnace;
introducing a non-oxidizing, fluidizing gas into the tube at a flow rate of about 4 CFH and sufficient to fluidize the mixture of particles within the tube so that the fluidized particles are within a heating zone of the furnace while substantially preventing oxidation of the metal particles;
heating the furnace until a temperature of the tube within the heating zone of the furnace is within a first preselected range of at least about 600° C. (1112° F.);
then
introducing an oxidant gas at a preselected rate of from about 0.01-10.0 l/min per 20 lbs. (9072 gram) of metal particles into the tube to form a thin protective alumina layer over external surfaces of the particles, the alumina layer characterized by reflectance of at least about 60% and resistance to environmental deterioration at elevated temperatures in corrosive and oxidative environments, while holding the temperature of the tube within the first preselected range of at least 600° C. (1112° F.) for a preselected time in the range of 1-4 hours and maintaining the flow of the reducing gas;
then
heating the furnace until the temperature of the tube within the heating zone of the furnace is within a second preselected range of between 760° C.-816° C. (1400° F.-1500° F.) while maintaining the flow of the fluidizing gas sufficient to maintain fluidization of the particles;
then
stopping the flow of oxidant gas;
cooling the mixture of particles to about ambient temperature;
and
reducing the flow of fluidizing gas into the tube.

11 more elements

Dependencies are inferred from the claim text.

Fluidized bed apparatus and method for treatment of nonspherical, nonequiaxed particles

Life of this patent

Fluidized bed apparatus and method for treatment of nonspherical, nonequiaxed particles

Life of this patent

Abstract

Claims21