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Production of nickel nanoparticles from a nickel precursor via laser pyrolysisRelated Patent Categories: Specialized Metallurgical Processes, Compositions For Use Therein, Consolidated Metal Powder Compositions, And Loose Metal Particulate Mixtures, Processes, Producing Or Purifying Free Metal Powder Or Producing Or Purifying Alloys In Powder Form (i.e., Named Or Of Size Up To 1,000 Microns In Its Largest Dimension)Production of nickel nanoparticles from a nickel precursor via laser pyrolysis description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060225534, Production of nickel nanoparticles from a nickel precursor via laser pyrolysis. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/618,288, filed Oct. 13, 2004, which is hereby incorporated by reference in its entirety. FIELD OF THE INVENTION [0002] The present invention relates to a process for producing nickel nanoparticles. BACKGROUND OF THE INVENTION [0003] There is an intense and growing interest in the development of nanostructured magnetic materials, motivated primarily by the immense potential of these materials in a broad range of applications including data storage, spintronics, biomedicine, and telecommunications (Pileni, Advanced Functional Materials 11:323 (2001); Leslie-Pelecky and Rieke, Chem. Mater. 8:1770 (1996); Skomski, J. Phys. Condens. Matter. 15:R841-R896 (2003); Prasad, Nanophotonics John Wiley & Sons, New York (2004)). The synthesis and characterization of such materials are also important for basic science in that they can provide insight into the fundamentals of surface chemistry and magnetic interactions at the nanoscale. Magnetism in the transition elements has been investigated for decades, with the ferromagnetic series--Fe, Co, and Ni--being by far the most extensively studied systems. One fascinating discovery, surface-enhanced magnetism, in which the magnetic moments of small clusters of the ferromagnetic series exceeded their bulk values, occurred in the last decade (Apsel et al., Phys. Rev. Lett. 76:1441 (1996); Billas et al., Science 265:1682 (1994)). These magnetic moments in fact, exhibited dramatically higher values at a certain magic number of atoms. Ever since this discovery, an extraordinary amount of attention has been devoted to understanding the dependence of magnetic properties on particle size and surface treatment. In the development of nanostructured magnetic materials, it is important to control the structure, size, composition, surface characteristics, and self-assembly of the nanoparticles, and to understand how these properties impact the bulk magnetic behavior. [0004] The magnetic behavior of a material depends on numerous factors including the sizes, shapes, and orientations of grains within it, the structure of the grain boundaries, the magnitude and direction of internal stress, the crystallographic phases, the concomitant presence of any other phase, and the overall size and shape of the specimen (Vincent and Sangha, GEC J. Res. 13:2 (1996)). All of these factors can be affected by the particle synthesis procedure. Thus, different methods of preparation are expected to result in different overall properties. This is especially true in nanomaterials because of their high surface to volume ratios. Over the years, a variety of procedures have been developed for the preparation of nanomagnetic materials, including hot colloidal synthesis (Murray et al., IBM J. Res. Dev. 45:47 (2001)), microemulsion (Feltin and Pileni, Langmuir, 13:3927 (1997)), sol gel (Leite et al., J. Nanosci. Nanotechnol. 2:89 (2002)), laser ablation (Jonsson et al., J. Appl. Phys. 79:5063 (1996)), and mechanical milling (Gonzalez et al., Euro. Phys. Lett. 42:91 (1998)). Each of these has advantages and disadvantages relative to the key criteria of controlling particle size, shape, dispersibility in desired solvents, yield, production rate, and processability. It is universally agreed upon that a stable dispersion of uniformly sized particles is desirable for many purposes. [0005] Because of their important potential applications (Hyeon, Chem. Commun. pp. 927-934 (2003)) as pigments, catalysts (Weber et al., J. Nanoparticle Res. 5(3-4):293-298 (2003); Guo et al., Phys. Chem. Chem. Phys. 3(9):1661-1665 (2001)), components of magnetic data storage media (Teng and Yang, J. Am. Chem. Soc. 125(47):14559-14563 (2003)), and elements of chemical and biological sensors (Carpenter, J. Magn. Magn. Mater. 225:17-20 (2001)), the synthesis of nickel-based nanophase materials has attracted considerable interest. Ultrafine magnetic particles (Shi et al., Science 271:937-941 (1996); Majetich and Jin, Science 284:470-473 (1999)) can also be used in magnetic inks and other magnetic fluids (ferrofluids) (Raj et al., J. Magn. Magn. Mater. 149:174-180 (1995)) and in biomedical applications (Berry and Curtis, J. Phys. D: Appl. Phys. 36(13):R198-R206 (2003); Tartaj et al., J. Phys. D: Appl. Phys. 36(13):R182-R197 (2003); Halbreich et al., Biochimie 80(5-6):379-390 (1998); Scherer et al., Gene Therapy 9(2):102-109 (2002); Pankhurst et al., J. Phys. D: Appl. Phys. 36(13):R167-R181 (2003)). Magnetic nanoparticles are also ideal systems for fundamental research in several areas including superparamagnetism, magnetic dipolar interactions, and magnetoresistance. As a result, a significant amount of work has been done to study the preparation and magnetic properties of such particles. A number of techniques have been used for the production of metallic magnetic nanoparticles, such as inert gas evaporation/condensation (Choi et al., Mater. Lett. 56:289-294 (2002); Jonsson et al., J. Appl. Phys. 79(8):5063-5065 (1996); Ullmann et al., J. Nanoparticle Res. 4:499-509 (2002); Wu and Xie, Mater. Lett. 57:1539-1543 (2003)), sonochemisty (Kataby et al., Appl. Surf Sci. 201:191-195 (2002); Jung et al., J. Phys. Chem. Solids 64:385-390 (2003)), coprecipitation (Ge et al., NanoStruct. Mater. 8(6):703-709 (1997); Li et al., Ceram. Int. 28:165-169 (2002)), wet chemical methods (Teng and Yang, J. Am. Chem. Soc. 125(47):14559-14563 (2003); Dubios et al., J. Mol. Liq. 83:243-254 (1999); Bermejo et al., Powder Technol. 94:29-34 (1997); Sun et al., Chem. Mater. 11:7-9 (1999); Chen and Hsieh, J. Mater. Chem. 12:2412-2415 (2002); Hou and Gao, J. Mater. Chem. 13:1510-1512 (2003); Wu and Chen, Chem. Lett. 33(4):406-407 (2004)), microemulsion methods (Guo et al., Phys. Chem. Chem. Phys. 3(9):1661-1665 (2001)), the polyol process (Wu and Chen, J. Colloid Interface Sci. 259:282-286 (2003)), and laser-driven thermal methods (Ullmann et al., J. Nanoparticle Res. 4:499-509 (2002); Miguel et al., IEEE Trans. Magn. 38(5):2616-2618 (2002); Veintemillas-Verdaguer et al., Mater. Lett. 57:1184-1189 (2003); Martelli et al., Appl. Surf Sci. 186:562-567 (2002)). [0006] There are very few reports on vapor-phase synthesis of nickel nanoparticles with diameters below 100 nm, though larger (micron diameter and larger) particles are synthesized commercially in tonnage quantities by thermal decomposition of nickel carbonyl. He et al. reported a UV laser-assisted gas-phase photonucleation process to generate nickel ultrafine particles (UFPs) at ambient temperature with Ni(CO).sub.4 as precursor (He et al., NanoStruct. Mater. 8(7):879-888 (1998)). Ni(CO).sub.4 has a high vapor pressure and decomposes cleanly to give pure nickel, and is therefore used in vast quantities in commercial nickel refining. However, its high toxicity has limited its use as a gaseous precursor in laboratory studies. [0007] The present invention is directed to overcoming these deficiencies in the art. SUMMARY OF THE INVENTION [0008] The present invention relates to a process for producing nickel nanoparticles. The process involves heating a nickel precursor generated in situ in the presence of a carrier gas under conditions effective to decompose the nickel precursor and produce nickel nanoparticles. [0009] CO.sub.2 laser pyrolysis of different chemical vapor deposition (CVD) precursors has proven to be a successful method for preparation of nanoparticles of a variety of materials (Cannon et al., J. Am. Ceram. Soc. 65(7):324-330 (1982); Cannon et al., J. Am. Ceram. Soc. 65(7):330-335 (1982); Li et al., Langmuir 19(20):8490-8496 (2003); Li et al., Langmuir 20(11):4720-4727 (2004), which are hereby incorporated by reference in their entirety) and suggest the possibility of using this method to produce nanopowders with primary particle diameters from 5 to 50 nm at production rates of hundreds of mg per hour in a small bench-scale reactor system. The present invention discloses a method of preparing nickel nanoparticles by laser-driven decomposition of a nickel precursor, such as nickel carbonyl. In this method, an infrared laser rapidly heats a dilute mixture of nickel carbonyl and a photosensitizer in a carrier gas, to decompose the precursor and initiate particle nucleation. To produce nickel nanoparticles, nickel carbonyl was generated in situ from activated nickel powder and CO at room temperature, in order to avoid maintaining an inventory of the highly toxic Ni(CO).sub.4. During the synthesis process, laser heating allows for rapid cooling of the freshly nucleated particles by mixing with unheated gas. By varying the precursor flow rate, laser energy, and unheated gas flow rate to change the residence time, precursor concentration, and reaction temperature, the average particle size can be controlled over a range of primary particle diameters from 5 to 50 nm. The particle size and crystalline structure have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen physisorption surface area measurement (the BET method), and X-ray photoelectron spectroscopy (XPS). For nanosize nickel, which has a low tendency to oxidize, very high surface area powders with mean particle diameter below 10 nm sometimes oxidize violently upon exposure to air. Therefore, conditions that produce somewhat larger particles, 10.about.20 nm in average size, were used for studying the effects of reactor operating parameters on particle size and morphology. Magnetization measurements, on the other hand, are presented for smaller particles, 5-8 nm in diameter, since these are the ones that exhibit superparamagnetism and have the most interesting magnetic behavior. [0010] In addition, the present invention discloses a method of using laser-driven decomposition of nickel carbonyl vapors to produce particles in the form of an aerosol, followed by exposure to a solvent containing an appropriate surfactant to yield a stable dispersion of particles. This method is scalable and yields a substantially monodisperse distribution of particles at a relatively high rate of production. The particles produced by this method are subjected to a detailed characterization using transmission electron microscopy, atomic force microscopy, energy dispersive spectroscopy and dc magnetization. The particles have an average diameter of 5 nm, and the observed magnetization curves show no hysteresis above 200 K. The normalized magnetization curves follow a scaling law proportional to the quotient of the applied field over temperature. This data indicates the presence of randomly oriented superparamagnetic particles. The measured magnetization is significantly smaller than that of the bulk, probably due to an effective surface anisotropy and spin canting. The coercivity is the same in either direction of the applied field which indicates that there is negligible exchange coupling between the nickel particles and any possible antiferromagnetic oxide layer on their surfaces. [0011] The present invention combines the advantages of high purity and high throughput achieved in aerosol synthesis with stabilization by surface treatment, as used in colloidal chemistry, to obtain a reasonably stable dispersion of nickel nanoparticles. The method of the present invention is clean in that there are no side products that could adhere to the surface of the particles. Thus, the particles are devoid of any magnetic dead layers, which may be detrimental to the magnetic properties. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 is a schematic drawing of the reactor system for producing Ni nanoparticles by laser-driven decomposition of Ni(CO).sub.4. [0013] FIG. 2 is a schematic drawing of the reactor. [0014] FIG. 3 illustrates the nickel nanoparticle production rate and average size vs CO flow rate. [0015] FIG. 4 shows the TEM image and selected area electron diffraction (SAED) pattern from nickel particles with 100 sccm CO flow rate. [0016] FIG. 5 shows the TEM image and selected area electron diffraction (SAED) pattern from nickel particles with 250 sccm CO flow rate. [0017] FIG. 6 shows the XRD pattern from nickel samples with 100 sccm CO flow rate. [0018] FIG. 7 shows the XRD patterns for nickel samples produced using He and Ar as sheath and purge gas. [0019] FIG. 8 shows the TEM image and SAED pattern from nickel particles produced with He sheath and purge gas. [0020] FIG. 9 shows the TEM image and SAED pattern from nickel particles produced with Ar sheath and purge gas. Continue reading about Production of nickel nanoparticles from a nickel precursor via laser pyrolysis... 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