Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2002-05-17
2003-05-13
Le, H. Thi (Department: 1773)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C148S514000, C148S516000, C428S323000, C428S327000
Reexamination Certificate
active
06562495
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to non-stoichiometric substances and more particularly to nanostructured non-stoichiometric substances and products incorporating such substances.
BACKGROUND OF THE INVENTION
Most compounds are prepared as stoichiometric compositions, and numerous methods of preparing substances for commercial use are motivated in objective to create stoichiometric compounds. For example, producers of titania fillers, copper oxide catalysts, titanate dielectrics, ferrite magnetics, carbide tooling products, tin oxide sensors, zinc sulfide phosphors, and gallium nitride electronics all seek stoichiometric compositions (TiO
2
, CuO, BaTiO
3
, NiFe
2
O
4
, TiC, SnO
2
, ZnS, and GaN, respectively).
Those skilled in the art will note that conventional powders of oxides and other compounds, when exposed to reducing atmospheres (e.g. hydrogen, forming gas, ammonia, and others) over a period of time, are transformed to non-stoichiometric materials. However, the time and cost of doing this is very high because the inherent diffusion coefficients and gas-solid transport phenomena are slow. This has made it difficult and uneconomical to prepare and commercially apply stable non-stoichiometric forms of materials to useful applications.
Limited benefits of non-stoichiometric materials have been taught by others; for example, Sukovich and Hutcheson in U.S. Pat. No. 5,798,198 teach a non-stoichiometric ferrite carrier. Similarly, Menu in U.S. Pat. No. 5,750,188 teaches a method of forming a thin film of non-stoichiometric luminescent zinc oxide. The film is a result of a thermodynamically favored defect structure involving non-stoichiometric compositions where the non-stoichiometric deviation is in parts per million.
SUMMARY OF THE INVENTION
This invention includes several methods of making non-stoichiometric submicron and nanostructured materials and devices from both stoichiometric and non-stoichiometric precursors. This invention also includes methods of making stoichiometric materials and devices from non-stoichiometric precursors. In one aspect, the invention includes an improved sintering technique utilizing submicron non-stoichiometric powders. The invention also includes a variety of other applications for submicron non-stoichiometric materials, including catalysis, photonic devices, electrical devices and components, magnetic materials and devices, sensors, biomedical devices, electrochemical products, and energy and ion conductors.
In one aspect, this invention includes a variety of methods of producing a non-stoichiometric material. According to one method, a submicron powder of a stoichiometric material is transformed into a non-stoichiometric powder. The submicron powder may also be a nanopowder. If desired, the submicron non-stoichiometric powder may be sintered into a bulk substance. This invention excludes from its scope the non-stoichiometry that naturally results from the randomly occurring thermodynamic defects in a bulk crystal of the theoretical stoichiometry which are typically on the order of a few hundred parts per million. As used herein, non-equilibrium means thermodynamic non-equilibrium.
According to another method, a non-stoichiometric submicron material is produced by quenching a high-temperature vapor of a precursor material to produce a non-stoichiometric submicron powder. A vapor stream of the high temperature vapor flows from an inlet zone, and this stream is passed through a convergent means to channel the vapor stream through an area where flow is restricted by controlling the cross-section of the flowing stream. The vapor stream is channeled out of the flow restriction through a divergent means to an outlet pressure which is smaller than the inlet pressure. This quenches the vapor stream. The inlet and outlet pressures are maintained, creating a pressure differential between them. The pressure differential and the cross-section of the flow restriction are adapted to produce a supersonic flow of the vapor stream. This method may further comprise sintering the resulting powder.
According to yet another method, a nanoscale starting material comprising more than one element is provided. At least one of these elements is an electropositive element. A dopant element with valency different than the electropositive element is added, and the mixture is heated to a selected temperature, preferably greater than the solid state reaction temperature, for a time sufficient to allow intermingling of the dopant element and the given electropositive element.
According to still another method, two nanopowders are mixed in a ratio selected to produce a desired non-stoichiometric composition. The first nanopowder comprises a plurality of materials, and the second comprises a subset of those materials. The materials comprising the first nanopowder maybe metallic, semimetallic, non-metallic, or any combination thereof. The mixture is heated in a selected atmosphere to a temperature to produce a solid state reaction. The atmosphere may participate in the solid state reaction. This invention also includes the materials produced via the above methods.
In another aspect, this invention includes a submicron non-stoichiometric material where the value for a selected physical property of the submicron non-stoichiometric material is greater than 10% different from that for a stoichiometric form of the submicron non-stoichiometric material. Alternately, the relative ratios of the components of the material differ by more than 1% from the stoichiometric values, preferably 2% from the stoichiometric values, and more preferably 5%. The material may be a nanomaterial or a nanopowder.
This invention also includes a submicron material wherein a domain size of the material is less than 500 nm, and the material is non-stoichiometric. Preferably, the domain size is less than 100 nm. Alternately, a domain size may be less than 5 times the mean free path of electrons in the given material, or the mean domain size maybe less than or equal to a domain size below which the substance exhibits 10% or more change in at least one property when the domain size is changed by a factor of 2. The material may be a powder or a nanopowder.
In another aspect, this invention includes a method of determining the non-stoichiometry of a material. A stoichiometric form of the material and the material whose stoichiometry is to be ascertained (the “unknown” material) are heated separately in a reactive atmosphere to 0.5 times the melting point of the material. The weight change per unit sample weight for the unknown material is monitored. In addition, the weight change per unit sample weight of the unknown material is compared to the weight change per unit sample weight of the known material.
In another aspect, this invention includes a method of conducting combinatorial discovery of materials where non-stoichiometric forms of materials are used as precursors.
In another aspect, this invention includes a method of making a non-stoichiometric nanoscale device by fashioning a non-stoichiometric nanoscale material into a device. Alternately, a device is fashioned from a stoichiometric material and the stoichiometric material converted into a non-stoichiometric form. The stoichiometric material may be an electrochemical material, a photonic material, or a magnetic material. The non-stoichiometric material may be electroded; and the electrode may comprise a non-stoichiometric material. This invention also includes stoichiometric devices with non-stoichiometric electrodes. The non-stoichiometric materials may further be a nanomaterials.
In another aspect, this invention includes a method of producing a stoichiometric material from a non-stoichiometric powder. The powder is processed into the shape desired for a stoichiometric material and further processed to produce stoichiometric ratios among its components. This invention also includes a method of producing a stoichiometric device via the same method.
In another aspect, this invention also includes an improved method of producing sintered ma
Miremadi Bijan
Yadav Tapesh
Hogan & Hartson LLP
Langley Stuart T.
Le H. Thi
NanoProducts Corporation
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