Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
1996-06-12
2002-01-08
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
Reexamination Certificate
active
06337060
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fine particles of hydrophilic diamond which can effectively provide a single layer of particles when used in lubrication, surface mondification, abrasive applications, etc. The invention also relates to a method of effectively producing such diamond.
BACKGROUND OF THE INVENTION
Diamond fine powders less than one micrometer in nominal average particle size (APS) are available on the market as a grinding medium, and even superfine powders of 5 nm (nanometers) for lubrication, surface modification and polishing applications. They are often used with a specific dispersion medium, in order to achieve a uniform deposit of single particle thickness on a support body, or a regular distribution of separate particles in the matrix.
Diamond particles are often at a decreased surface energy level due to the combination with different atoms or groups, although the surfaces may be sometimes made up of carbon atoms joined with each other. Thus the physical and chemical properties of diamond particles are affected by the surface state, increasingly with the decrease in particle size, and essentially for submicron sizes, in addition to their bulk properties. So the dry agglomeration and affinity to aqueous or oily medium of particles, in particular, depend essentially on the atoms or groups, adsorbed or combined with carbon atoms in the surface layer. Possible atoms and groups are collected and out-lined, along with techniques for providing them, by N. V. Novikov in “The Physical properties of diamond”, Naukova Dumka (1987).
Diamond fine powders are commonly prepared by crushing coarser particles of either natural or synthetic origins, the latter being produced by static compression at high temperatures on a hydraulic press or dynamic compression by means of explosive detonation. They, natural or synthetic, assume a set of specific properties which vary with the different set of physical and chemical processes they were subjected on the way to the end products.
Diamond from a hydrostatic press, for example, contains metallic or nonmetallic substances which derive from the flux and specimen accommodation materials employed in the process, and which exist in the crystals as an impurity. Some kinds of impurity may be removed and the powder be purified to a degree, as the particles undergo chipping or splitting during the crushing process, preferentially at crystal defects and expose the foreign substance within, which is to be dissolved during the acid treatment. However there are other impurities, including chromium from the crushing machine and graphite remaining unconsumed and trapped in the particles which then are exposed or released by the breakdown. As insoluble to the acids, they accumulate in the solution and accompany with the finest fraction when recovered. As a result, the class zero diamond powders, which contain the undersize end, often exhibit a light to dark grayish color due to those impurities.
As for the dynamic compression synthesis technique, whose mechanism has not fully been understood, diamond fine powders contain impurities whose origin is not always identified. However there are some elements, beside graphite, which should evidently derive from the specimen receptacle material or, at least, matrix material for the process.
Synthetic diamonds in general may be somehow more hydrophilic than natural ones as a result of the treatments the former undergo, before it is isolated as separate particles, with or in various chemical solutions which can leave oxygen atoms or hydroxy groups, combined with carbon atoms on the particle surface. Although such quality even causes a trouble in establishing a reproducible size grading of micron sizes by affecting Stokes's relationship between particle size and sedimentation rate in the elutriation process. If so, the treated diamond particles in general are not in a surface state which would form a stable suspension or dispersion in a polar solvent such as water and alcohol.
Besides oxygen and hydroxy atom and group, presence of several elements as impurities has been recognized by ICP spectrometry or inorganic qualitative analysis. They include Si, Al, Fe, Cr, Mn, Cu, Ca, S and C. It appears that some of them are somehow interactive with the surface of diamond particles whichever the production process is, and causes agglomeration of said particles in the aqueous environment. Thus impurities make most fine diamond powders so far available tend to form an agglomeration, which is almost impossible to completely break down in polar or nonpolar medium, even under ultrasonic vibration. It is further observed that such fine particles, once separated, readily gather and form again an agglomeration and begin to sediment.
Diamond fine powders are promising materials for the use in tribologic and abrasive applications as well as surface modification, if they can be successfully separated into single particles and distributed in a matrix or spread on a carrier body. While it is understood that such quality can be achieved by either eliminating the above said interaction or by improving the wettability of the diamond surface with the medium employed, no effective techniques have been available for the purposes.
Metal or ceramic materials coated with diamond fine particles could be useful as a wear resistant material. It is essential, however, to keep the diamond particles in stable suspension, with the diamond concentration or particle distribution unvarying over the deposition process, for example.
Therefore one of the principal objects of the invention is to provide diamond fine particles with a surface nature so improved as to form a stable, uniform suspension or dispersion in a common medium such as water and alcohol.
Another object is to provide an effective technique for producing hydrophilic diamond fine particles by chemically modifying the particle surface nature, while removing at the same time contaminants and foreign materials which coexist with the diamond.
DETAILED DESCRIPTION OF THE INVENTION
In the invention diamond particles are treated by boiling in the treatment fluid of sulfuric acid solution, which is in particular of concentrated or fuming nature, at a temperature more than 200° C., which is preferably 250° C. or more. Thus hydrophilic diamond fine particles are left and recovered with hydrophilic atoms and/or groups formed on the surface, while contaminants and foreign matters are removed from among the particles or from the surface as chemically decomposed and dissolved into the solution.
Said treatment fluid may further comprise one or more of nitric, perchloric and permanganic and other inorganic acid as an oxidizer, as well as potassium or other metal nitrate. They are used essentially in combination with concentrated or fuming sulfuric acid, in order to achieve a corresponding effect at lower temperatures.
Results are more appreciable and the increase in suspension stability is greater with finer particles. Coarser particles are more susceptible to the gravity and thus are more difficult to hold a good suspension in a medium for a sufficient time. Thus the method of the invention employs average particle sizes of—or less than 2 &mgr;m (micrometer), and the diamond particles as treated hold suspension practically without sedimentation in purified water for, at: least, 30 minutes with the 2 &mgr;m size and more than 2 hours with 1 &mgr;m or less size. Further finer particles can exhibit a further longer suspension holding time of, for example, more than 24 hours for a size of 200 nanometers or less. A suspension time of 6 hours or more also is achieved with such ultrafine particles in a pH 4.0 acidic aqueous solution of inorganic acid. Hydrophilic diamond surface which allows such good suspension is produced by the method of the invention at a good reproducibility.
Since polar media such as water and alcohol are commonly used for distributing diamond particles in, the latter should be more favored as versatile if, and when, they are of hydrophilic nature and, at the same
Hatta Akimitsu
Hiraki Akio
Hosomi Satoru
Ishizuka Hiroshi
Ito Toshimichi
Hendrickson Stuart L.
Larson & Taylor PLC
The Ishizuka Research Institute Ltd.
LandOfFree
Hydrophilic diamond particles and method of producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydrophilic diamond particles and method of producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrophilic diamond particles and method of producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2851451