Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
1995-06-07
2001-02-20
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
C423S440000, C423S447200, C423S414000, C428S366000, C428S367000
Reexamination Certificate
active
06190634
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is in the field of nanometer scale materials.
Examples of nanomaterials include hollow carbon graphite tubes with diameters between 1 and 75 nm, and lengths up to one micron. Such nanotubes are produced, for example, in reactors at 550-850° C. by mixing hydrogen and carbon-containing gases in the presence of a catalyst. Strategies used to prepare filled nanotubes include in-situ arc growth using metal/carbon composites and the loading of nanotubes using liquid reagents. In addition, graphitecoated, partially-hollow lanthanum carbide particles with overall diameters between 20 and 40 nm have been made.
In contrast to nanoscale materials, whiskers are crystalline solid structures generally having diameters between 1-100 microns, although diameters as small as 0.1 microns have been observed.
SUMMARY OF THE INVENTION
The invention features a carbide article consisting essentially of covalently bonded elements M
1
, M
2
and C having the molar ratio M
1
:M
2
:C::1:y:x. The first element M
1
is selected from the first element group consisting of titanium, silicon, niobium, iron, boron, tungsten, molybdenum, zirconium, hafnium, vanadium, tantalum, chromium, manganese, technetium, rhenium, osmium, cobalt, nickel, a lanthanide series element, scandium, yttrium, and lanthanum. The second element M
2
is selected from a second element group consisting of nitrogen, boron, phosphorus, zinc, aluminum, copper, germanium, cadmium, indium, tin, lead, thallium, and the elements in the first element group, provided that the first and second elements are not the same. The value of y is between 0 and 0.9 (e.g., y is 0 or y is between 0.1 and 0.9). The third element C is sp
3
hybridized carbon, and the value of x is between 0.1 and 2.1 (e.g., between 0.9 and 1.1). The article has an aspect ratio of between 10 and 1000 (e.g., between 50 and 500, or between 100 and 1000), and has a shorter axis of between 1 and 40 nanometers (e.g., between 1 and 30 nm).
In certain embodiments, the article has a single crystal structure, a polycrystalline structure, or an amorphous structure. Preferably, element M
1
is selected from the group consisting of titanium, silicon, niobium, iron, boron, tungsten, molybdenum, or gadolinium, or from the group consisting of titanium and silicon. Preferably, second element M
2
is selected from the group consisting of boron and nitrogen, wherein y is greater than 0 (e.g., between 0.1 and 0.9). In one aspect, the article is a nanorod.
The nanoscale carbide articles of the invention are useful materials having metallic, semiconducting, insulating, superconducting, or magnetic properties, or a combination thereof. The novel dimensions of the disclosed articles permit the building of nanostructures and superior metallic, ceramic, and polymer composites. For example, the tensile strength (kg/mm
2
) of the disclosed nanorods is greater than that of the corresponding whisker. Some embodiments have a lower density of stacking faults, as measured by TEM and normalized to diameter, than prior larger materials. For example, SiC nanorods disclosed herein have a lower density of stacking faults than the SiC whiskers as described by G. McMahon et al.,
J. Mater. Sci
. 26:5655-5663 (1991). The invention encompasses not only the individually identified carbide articles, but also other nanoscale materials that are made according to processes disclosed herein. The invention also encompasses the methods disclosed herein for making carbide articles such as nanorods.
Other features or advantages of the present invention will be apparent from the following detailed description of the invention, and also from the appending claims.
Terms
As used herein, the term “carbide” means a compound of carbon and one or two elements more electropositive than carbon, excluding hydrogen. The atoms in a carbide are covalently bound, the carbon atoms being generally sp
3
hybridized as in Ta
2
C and Cr
3
C
2
. In contrast, pure graphitic carbon (e.g., nanotube starting material) is sp
2
hybridized. Examples of binary carbides include TiC
x
, NbC
x
, and SiC
x
(wherein x is between 0.5 and 1.1), Fe
3
C
x
(wherein x is between 0.8 and 1.2), and BC
x
(wherein x is between 0.1 and 0.3). Additional examples of binary carbides include ZrC
x
, HfC
x
, VC
x
, TaC
x
, CrC
x
, MoC
x
, WC
x
, NiC
x
, LaC
x
, CeC
x
, PrC
x
, NdC
x
, SmC
x
, GdC
x
, DyC
x
, HoC
x
, ErC
x
, and YbC
x
. Examples of ternary carbides include carbonitrides, carboborides, and carbosilicides and others such as TiN
y
C
x
, MoN
y
C
x
, and SiN
y
C
x
, TiB
y
C
x
, TiTa
y
C
x
, TiSi
y
C
x
, TiNb
y
C
x
, MoSi
y
C
x
, MoB
y
C
x
, MoGa
y
C
x
, MoAl
y
C
x
, FeB
y
C
x
, FeSi
y
C
x
, FeNi
y
C
x
, SiB
y
C
x
, TaSi
y
C
x
, WSi
y
C
x
, ZrSi
y
C
x
, NbSi
y
C
x
, CrSi
y
C
x
, NdB
y
C
x
, and WCo
y
C
x
. The values of x and y are, respectively, between 0.1 and 2.1 and between 0 and 0.9. Where y is 0, the carbide is a binary carbide consisting essentially of carbon and M
1
having the formula ratio of M
1
C
x
. Where y is greater than 0 (e.g., between 0.1 and 0.9), the carbide is a ternary carbide consisting essentially of carbon, M
1
, and M
2
having the formula ratio M
1
M
2
y
C
x
.
As used herein, the term “article” includes nanorods, sheets, cages, shaped forms, and irregular crystalline or amorphous forms, such as dendritic or starburst forms. An article, such as a sheet, may be substantially planar, wavy, corrugated, or helical. An article may have one or more pores, grooves, or other textured topology.
As used herein, the term “nanorod” means a space-filling article with an aspect ratio of at least 10 (e.g., at least 50, at least 100, or at least 500). In general, the aspect ratio is between 25 and 1000, (e.g., between 100 and 1000, between 50 and 500, between 100 and 500, or between 500 and 1000). A nanorod has a shorter axis of between 0.1 and 80 nm (e.g., between 1 and 40 nm, and preferably between 2 and 30 nm). In other words, the length of a nanorod is between 0.02 and 50 &mgr;m, and preferably between 0.5 and 25 &mgr;m. The disclosed nanorods are solid, being neither hollow with one or two open ends, nor hollow with two sealed ends.
There may be impurities in or on the carbide lattice material such as oxygen (up to 10%), halogen (up to 2%), silicon (up to 5%), tellurium (up to 1%), and SP
2
hybridized carbon (up to 5%). The sources of these impurities are typically the reactants (metal oxide, transport molecules and transport agents) used in forming volatile metal and nonmetal species. These impurities are covalently bonded within the lattice, covalently bonded to or physically adsorbed to the surface of the nanorod, or located in interstitial sites (caged) within the lattice. In some embodiments, the presence of some impurities is desirable. For example, the presence of silicon is desirable to enhance or impart greater strength or fracture resistance for applications in intercombustion engines and gas turbines. It is believed that the term “consisting essentially of” allows for the above-described impurities.
As used herein, the term “short axis” is equivalent to “diameter,” meaning the shortest dimension or cross-sectional thickness of a nanorod. Where a nanorod is, e.g., helical or networked, the diameter is always measured across the thickness of the rod, and not the overall diameter of the helix or the network, which is generally much greater than the diameter of the nanorod. In general, the diameter of a nanorod is substantially the same along the length of the nanorod. In some embodiments, a nanorod may have pores, grooves, or a fluctuating diameter (in an embodiments with a fluctuating diameter, the diameter is the average diameter).
As used herein, the term “length” means a longitudinal dimension (or approximation) of the nanorod that is orthogonal to the diameter of the nanorod. Length is not the overall size of a helix or overlapping network, which (if made of only one nanorod) is generally shorter than the length of the nanorod. If a helix or network is made of more than one nanorod, the length
Dai Hongjie
Lieber Charles M.
DiMauro Peter
Fish & Richardson P.C.
Griffin Steven P.
President and Fellows of Harvard College
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