Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
2001-05-18
2003-04-29
Beck, Shrive P. (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C427S215000, C427S216000, C427S569000
Reexamination Certificate
active
06555160
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for coating particle substrates, the coated particle substrate and to applications and uses thereof. More particularly, the invention relates to coating particle substrates with a metal oxide-containing material, such material preferably being an electrically conductive and/or ferromagnetic oxide-containing material and such coated substrate.
In many electronic and/or ferromagnetic applications it would be advantageous to have an electrically, electronically conductive; electro mechanical and/or ferromagnetic metal oxide coating which is substantially uniform, has high and/or designed electronic conductivity, and/or ferro magnetic properties and has good chemical properties, e.g., morphology, stability, etc.
A number of techniques have been employed to provide certain metal oxide coatings on substrates. The CVD process is well known in the art for coating a single flat surface, which is maintained in a fixed position during the contacting step. The conventional CVD process is an example of a “line-of-sight” process or a “two dimensional” process in which the metal oxide is formed only on that portion of the substrate directly in the path of the metal source as metal oxide is formed on the substrate. Portions of the substrate, particularly internal surfaces, which are shielded from the metal oxide being formed, e.g., such as the opposite side and edges of the substrate, pores or channels which extend inwardly from the external surface and substrate layers which are internal or at least partially shielded from the depositing metal oxide source by one or more other layers or surfaces closer to the external substrate surface being coated, do not get uniformly coated, if at all, in a “line-of-sight” process. Such shielded substrate portions either are not being contacted by the metal source during line-of-sight processing or are being contacted, if at all, not uniformly by the metal source during line-of-sight processing. A particular problem with “line-of-sight” processes is the need to maintain a fixed distance between the source and the substrate. Otherwise, metal oxide can be deposited or formed off the substrate and lost, with a corresponding loss in process and reagent efficiency.
In an attempt to overcome the limitations of the “line-of-sight” processes it has been proposed to contact a three dimensional substrate with a metal oxide precursor wherein the precursor preferably forms a liquidous metal oxide precursor on the substrate. The formed coated substrate is subjected to oxidation conditions to convert the metal oxide precursor to the metal oxide coated substrate (U.S. Pat. No. 5,326,633 [1994], U.S. Pat. No. 5,603,983 [1997], U.S. Pat. No. 5,633,081 [1997] and U.S. Pat. No. 5,756,207 [1998] granted to Clough et al.) While these processes represent a significant advance over the prior art CVD “line-of-sight” processes described above, the Clough et al. processes typically require total times for contacting, equilibration and oxidation in the range of minutes to hours.
It has been desirable to further improve the processes for producing metal oxide coated substrate particles particularly under fast reaction processing conditions which significantly reduce the processing times required for producing metal oxide coated particle substrates and to produce unique metal oxide coated substrates having improved properties
BRIEF SUMMARY OF THE INVENTION
A new process, e.g., a “non-line-of-sight” or “three dimensional” process, useful for coating of three dimensional particle substrates has been discovered. As used herein, a “non-line-of-sight” or “three dimensional” process is a process which coats surfaces of a substrate with a metal oxide coating which surfaces would not be directly exposed to metal oxide-forming compounds being deposited on the external surface of the substrate during the first line-of-sight contacting step. In other words, a “three dimensional” process coats coatable substrate surfaces which are at least partially shielded by other portions of the substrate which are closer to the external surface of the substrate and/or which are further from the metal oxide forming source during processing, e.g., the internal and/or opposite side surfaces of for example glass, ceramic or mineral particle substrates such as fibers, spheres, flakes or other shapes or surfaces including porous shapes.
A new fast reaction, elevated temperature process for at least partially coating a three dimensional substrate having shielded surfaces with a metal oxide, preferably an electrically conductive or ferromagnetic metal oxide coating on at least a part of all three dimensions thereof and on at least a part of said shielded surfaces thereof has been discovered. In brief, the process comprises contacting the substrate particles with a metal oxide precursor, for example, stannous chloride, stannic chloride, stannous oxide, zinc chloride, cuprous chloride, ferric chloride or titanium tetrachloride in a liquid form and/or in a solid form, to form a metal oxide precursor/substrate reactant mixture; preferably contacting the substrate also with at least one interacting component, i.e., a conductivity interactive or a ferromagnetic interacting component and contacting the reactant mixture with an oxidizing agent under fast reaction short residence time, higher temperature condition to form a metal oxide coated substrate and recovering such coated substrate, preferably a semi conductor or ferromagnetic oxide-containing coated substrate more preferably an n-type oxide semi conductor, more particularly a doped semiconductor and/or semi conductor having a defect and/or non-stoichiometric structure which enhances conductivity. The contacting of the substrate with the metal oxide precursor and optionally with the interacting component to form the reactant mixture takes place prior to substantially deleterious oxidation of the metal oxide precursor. In a particularly preferred embodiment, the reaction mixture is introduced directly into a high temperature oxidizing reaction zone under fast reaction processing conditions. The coated substrate is then recovered by conventional means.
The process can provide unique coated substrates including single and mixed oxides which have application designed electrical conductivity or magnetic properties and/or pearliest or transparent properties so as to be suitable for use as components such as additives in a wide variety of applications. Substantial coating uniformity, e.g., in the thickness of the metal oxide coating and in the distribution of interacting component in the coating, is obtained. Further, the present metal oxide coated substrates in general have outstanding stability, e.g., in terms of electrical or magnetic properties and morphology and are thus useful in various applications.
DETAILED DESCRIPTION OF THE INVENTION
The present coating process comprises forming a reactant mixture by contacting a substrate with a metal oxide precursor, such as metal chloride forming components, metal complexes and mixtures thereof and contacting the reactant mixture with an oxidizing agent, at fast reaction, elevated temperature process conditions, preferably oxidizing and hydrolyzing conditions, effective to form a metal oxide containing coating on the substrate. The reactant mixture preferably comprises at least one conductivity or magnetic interacting component, hereinafter referred to as interacting or interactant component, such as at least one dopant compound, in an effective amount to form an interacting component-containing coating, such as a dopant component-containing coating, on at least a portion of the substrate. The reactant mixture, preferably with an interacting component, for example a dopant component, are contacted with at least one oxidizing agent at conditions effective to convert the metal oxide precursor to metal oxide and form a metal oxide-containing coating, preferably a semi conductor, or magnetic metal oxide-containing coatin
Beck Shrive P.
Blanton Rebecca A.
Ensci Inc
Uxa FranK J.
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