Coating processes – Particles – flakes – or granules coated or encapsulated – Solid encapsulation process utilizing an emulsion or...
Reexamination Certificate
1997-11-03
2001-02-20
Nutter, Nathan M. (Department: 1711)
Coating processes
Particles, flakes, or granules coated or encapsulated
Solid encapsulation process utilizing an emulsion or...
C427S213310, C427S213340, C427S216000, C427S220000, C428S402000, C428S402240
Reexamination Certificate
active
06190731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to ultrafine and fine particles and methods for making and isolating such particles.
2. Discussion of the Related Art
Ultrafine particles are defined in the art as having diameters of about 100 nm or less. Such particles are therefore smaller than conventional powders, but larger than typical atom clusters. Ultrafine particles are of great interest due to their numerous applications, including use in the formation of ceramic and metal structures, conductive paths and/or conductive layers in electronic devices and the production of catalysts. For example, the use of ultrafine particles in forming ceramic and metal parts results in small grain size, thus providing the parts with optimal physical properties (e.g., strength and ductility). Also, in electronic devices, the small particles allow creation of finer conductor paths. Variations in processes used to produce ultrafine particles may also produce larger, so-called “fine” particles, which are defined as particles having diameters greater than 100 nm but less than 1500 nm. For many of the applications in which ultra ine particles are desired, fine particles may be equally useful.
It has been difficult, however, to obtain powder of ultrafine and fine particles without experiencing agglomeration into larger, less useful particles. Thus, those skilled in the art have attempted to isolate ultrafine and fine particles in a liquid suspension to prevent such agglomeration.
For example, U.S. Pat. No. 4,872,905 discusses a method of obtaining particles by utilizing a sputtering process and a liquid substrate. The metal particles generated from the target electrode encounter vapors of a heated liquid oil, are covered by the oil vapors, and are then captured by the liquid oil. A complex recovery process is required to obtain a usable end product. In particular, the liquid must be mixed with two solvents, such as kerosene and acetone, to thin out the oil and form a colloidal suspension. The acetone (or comparable solvent having a boiling point lower than both the other solvent and the oil) is removed by heating the solution, and the oil-covered particles then settle in the solution. This separation process may have to be performed up to four times. Moreover, prior to using the particles, the oil covering must be removed, for example by washing the particles in a solvent such as dioxane. Once the oil is dissolved, the particles will tend to agglomerate. Thus, while the method of this patent may offer a way of storing ultrafine or fine particles without agglomeration, it does not provide a means for producing isolated particles in a state that facilitates the actual use of the particles.
Another patent dealing with ultrafine and fine particles, U.S. Pat. No. 4,877,647, describes a method for obtaining a colloidal suspension of metal particles. Vaporized metal in a vacuum is captured by a solvent, which may be present as a gas or liquid. Typically, an external cooling set-up is provided, by which the solvent containing the captured metal atoms and atom clusters can be frozen to the interior of the vaporization vessel. The frozen matrix is slowly heated in the vessel to orm a colloidal suspension of metal particles in the solvent. A large excess of solvent is required to obtain the suspension, however, at least 30 to 1000 parts by weight of solvent. Preferred metal loadings range from 0.02 to 0.09 molar. Above this level, the metal particles will tend to agglomerate and precipitate. Thus, ultrafine and fine particles produced according to U.S. Pat. No. 4,877,647 are difficult to utilize in many applications, because they cannot be used separately and distinctly from the large amount of solvent required. Moreover, reduction of the amount of solvent results in undesirable agglomeration, thereby destroying the particles' usefulness.
The need therefore exists for methods of producing ultrafine and fine particles that remain isolated from one another, yet are in a state that facilitates handling and maximizes potential applications.
SUMMARY OF THE INVENTION
The present invention is directed to a method for isolating particles. The method involves the step of at least substantially encapsulating particles present as a highly dispersed colloidal suspension with an encapsulant material, such that the encapsulated particles remain independent and discrete upon separation from the suspension.
The present invention is also directed to a method for isolating ultrafine particles, including the steps of preparing a highly dispersed colloidal suspension of ultrafine particles of at least one metal in an organic solvent, adding to the suspension an encapsulant material such that the ultrafine particles are substantially encapsulated by the encapsulant material, and separating the encapsulated particles from the suspension.
The present invention is further directed to independent and discrete ultrafine and fine particles at least substantially encapsulated with an encapsulant material, wherein the encapsulant material is at least one compound selected from an amine, an ether, a thiol, a sulfide, a carboxylic acid, a hydroxy acid, a sulfonic acid, a polyhydroxy alcohol, an organosilane, a titanate, a zirconate, a zircoaluminate, a carboxylate, a sulfate, a sulfonate, an ammonium salt, a pyrrole, a furan, a thiophene, an imidazole, an oxazole, a thiazole, a pyrazole, a pyrroline, a pyrrolidine, a pyridine, a pyrimidine, a purine, a triazole, a triazine, and derivatives thereof, such that the particles remain independent and distinct.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention is applicable to particles of metal elements, nonmetal elements, inorganic compounds, and organic compounds, these particles capable of forming a highly dispersed colloidal suspension.
Solid elements such as boron, carbon, silicon and the Main Group metals, such as aluminum, beryllium, magnesium, etc., which are capable of forming atomic and cluster species in the gas phase, can form particles in a controlled fashion in a suitable medium to form colloidal suspensions.
Inorganic solid compounds, such as metal oxides, sulfides, selenides, tellurides, phosphides, antimonides, fluorides and other halide derivatives are known to form colloidal particles in suitable medium. Similarly, other inorganic compounds such as borides, carbides, nitrides and silicides form ultrafine particles in a controlled manner. Binary, ternary, and quaternary metal alloys, and the like, and intermetallic compounds can also form ultrafine particles using appropriate methods and conditions. Both organic and inorganic pigments, which may be produced by a variety of methods, require a great deal of physical and innovative effort to keep them well dispersed in a medium and produce them in a desired particle size and size distribution. The ability to keep such materials as discrete particles therefore enhances the efficiency of their production methods and improves their functional properties.
The initial step in producing isolated metal particles according to one embodiment of the present invention is formation of a highly dispersed colloidal suspension of metal particles in an organic solvent. One way to prepare such a suspension is described in U.S. Pat. No. 4,877,647, the entire disclosure of which is incorporated by reference herein.
The suspension may be prepared by first vaporizing a metal or metals to obtain metal atoms and atom clusters. The metal or metals preferably have an atomic number from 21 to 32, 39 to 50 and/or 72 to 82. The metal atoms and atom clusters are captured in a vaporized state in an organic solvent vapor. The atom- and atom cluster-containing solvent vapor is frozen or substantially frozen to form a matrix. The matrix is gradually warmed to room temperature without precipitat
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nutter Nathan M.
Tecle Berhan
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