Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Utilizing binder to add green strength to preform
Reexamination Certificate
2002-02-11
2004-05-25
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Utilizing binder to add green strength to preform
C264S656000, C264S670000, C419S030000, C419S033000, C419S035000
Reexamination Certificate
active
06740287
ABSTRACT:
REFERENCES CITED
U.S. Patent Documents
2,939,199
09/1960
Strivens
264/63
4,006,025
02/1977
Swank, et al.
430/567
4,197,118
04/1980
Wiech
264/63
5,314,658
05/1994
Meendering, et al.
419/33
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND
1. Field of Invention
The present invention relates to the fabrication of articles from nanoparticulate materials. More particularly, the present invention relates to a method to overcome the problems of the prior art in controlling aggregation, contamination and pyrophoricity during handling of nanoparticulate materials and the fabrication of articles therefrom.
2. Description of Prior Art
In a broad sense, nanomaterials, nanocrystalline or nanostructured materials or simply nanostructures refer to dense materials with grain sizes in the nanometer (one billionth of a meter) range. The designation ‘nanoparticulates’ is generally applied to any particulate matter with an average dimension below one micrometer. In the literature, the terms nanoparticulates, submicrometer powders, nanopowders, nanoscale powders or nanocrystalline powders are often used interchangeably. The terms nanosuspension or nanodispersion usually refer to suspensions of discrete nanoparticulates, in either a liquid or in a solid matrix.
Nanoscale powders are not new. The use of lampblack, a carbon nanoscale powder with particle sizes in the 10-100 nm, to make Chinese ink, predates the Christian era by thousands of years. Nanoscale metal oxides have been used in the paint industry for centuries, whereas nanoscaled silica powders are used as filler additives to tailor the rheological properties of a variety or organic suspensions. In the hardmetal industry ultrafine carbide and nitride powders are used to make cutting tools with increased strength and extended economic life over those produced from conventional powders. More recently, the use of oxide nanopowders in optics, electronic, and in cosmetics for UV protection is well established.
It is well known that a decrease in particle size results in enhanced sintering kinetics of particulate materials. When particle size reaches the nanometer range, full densification is often possible at substantially lower temperatures than those needed for sintering coarse-grained particulates. This is because nanoparticles imply shorter diffusion lengths while promoting boundary diffusion mechanisms. In addition to savings in energy, lower sintering temperatures also result in reduced contamination, stresses and cracking during cooling.
The enhanced sintering kinetics of nanoparticulate materials are already exploited in the microelectronic packaging industry, where metal alloy nanopowders are incorporated in cold-weldable welding pastes to achieve ductile and electrically conductive metal to metal bonds.
In the refractory metal industry, a decrease of several hundreds of degrees in the sintering temperature is achievable when standard 2 &mgr;m tantalum powder used to produce tantalum capacitors is replaced with a 50 nm nanopowder.
Aside from geometric considerations, the prefix ‘nano’ also implies dramatically improved material properties as inferred from the well-known Hall-Petch relationship according to which a material's strength increases proportionally to the inverse square root of its grain diameter.
Hence, interest has been growing in nanoparticulate materials stemming from the fact that novel phenomena are being discovered at the nanoscale level, and there is immense potential for improving structural and functional properties of components and devices by ‘nanostructuring’ as nanostructures can generate superplastic or ultra-high strength, tough materials. Extrapolations based on reducing grain size have produced forecasts of 2-7 times higher hardness and 2-3 times the tensile strength of parts produced from conventional powders.
For example the yield strength of an 80 nm iron nanopowder sintered to 99.2% of theoretical density is about 2.4 GPa, roughly five times that of conventional iron with a particle size in the 25 &mgr;m range.
The improved material properties of nanostructures have already found applications in many different fields of industry and technology. For example nanograined powders are already used in hydrogen storage technology. Another fast growing field of application is that of nanopowder-polymer composites for microelectronic applications. Using metallic nanopowders dispersed in polymers allows the fabrication of electrically conductive adhesives, radio frequency shielding polymers, and magnetic polymeric layers. Another area of strong interest is the fabrication of lightweight electrical wires using conductive nanopowders in a polymer matrix. These extrinsically conductive polymer wires with nanoparticulate fillers exhibit improved electrical percolation. Since the volume of filler material needed to provide conductivity can be reduced by over 50%, the intrinsic flexibility, strength and toughness of the polymer matrix material is retained.
The use of nanopowders as reinforcing phase in nanocomposites is a fast developing technology where the vastly increased interfacial area between the nanoparticles and the matrix material leads to improvements in the amount of energy absorbed during mechanical stress. This is especially useful in applications such as ballistic armor protection, where improved energy absorption under high strain rate conditions leads to increased ballistic impact resistance. Furthermore the reduction in the amount of filler phase necessary to reinforce the polymer matrix reduces overall component weight.
The fine size of nanoparticulates also allows for the design of strengthened optically transparent components such as aircraft canopies. In this case the nanoparticle reinforcing agent is so fine that interference with the wavelengths of the visible light spectrum is minimized or eliminated.
Another exciting field of application is that of lithium ion batteries where nano-vanadium pentoxide has been shown to possess electrochemical properties that are different from those of commercial coarse-grained V
2
O
5
powders, and these properties can be attributed to the structure of the nanoparticles. The discharge-charge voltage curve of nano-V
2
O
5
is continuous whereas, in contrast, coarse-grained V
2
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5
has a stepwise curve which is unsuitable for lithium ion batteries. For the same number of discharge charge cycles, the capacity of nano-V
2
O
5
is 60% higher than that of commercial powder. Furthermore irreversible losses are also much smaller when using nano-V
2
O
5
.
In the area of materials joining, copper, gold, nickel, tin and solder powders are routinely formed into pastes and used for electronics interconnects. The pastes are printed on ceramics such as aluminum oxide, and more recently aluminum nitride, to produce highly dense, so called thick film circuits. The requirement to shrink circuits and increase functionality has resulted in a continuing search for new and improved processes. One of the latest developments is in copper based pastes that can be applied to ceramic substrates at temperatures substantially below those currently used to manufacture thick film circuits. Lower temperatures are desirable because many electronic components are degraded by excessive temperatures. The lower sintering temperatures also allow environment-unfriendly lead based solder pastes to be phased out. Nanoparticulate-based joining formulations offer the potential to tailor the metallurgy and to lower the brazing temperature.
Nanoaluminum powders are also advantageously used in solid propellant formulations, doubling the burning rate as compared with that of compositions based on micrometer size aluminum. High burning rates increase thrust and speed of response. Adding nanoaluminum to hydrogen and kerosene burning with liquid oxygen increases the amount of energy released, resulting in smaller fuel tanks and shorter, lighter weight rockets.
There are many methods to produce nan
Billiet Romain Louis
Nguyen Hanh T.
Fiorilla Christopher A.
Foley and Lardner
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