Tungsten nanoparticles

Wei X, Wang M-S, Bando Y, Golberg D (2011) Thermal stability of carbon nanotubes probed by anchored tungsten nanoparticles. Sd Technol Adv Mater 12 044605... 

Pis prepared with 4,4 -oxydianiline (ODA) and 3,3, 4,4 -benzo-phenone tetracarboxyhc dianhydride (BTDA) monomers, cf. Figure 6.1, can be loaded with 10 and 15 wt% tungsten nanoparticles that are treated with benzyl mercaptan. The 3,3, 4,4 -benzophenone tetra-carboxylic dianhydride and ODA monomers are reacted to form PI films that are flexible to the point of being creaseable. The nanocomposite films are effective as an electromagnetic radiation shield (5). 

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

Li Q, Walter EC, van der Veer WE, Murray BJ, Newberg JT, Bohannan EW, Switzer JA, Hemminger JC, Penner RM (2005) Molybdenum disulfide nanowires and nanoribbons by electrochemical/chemical synthesis. J Phys Chem B 109 3169-3182 Tenne R, Homyonfer M, Feldman Y (1998) Nanoparticles of layered compounds with hollow cage structures (inorganic fuUerene-like structures). Chem Mater 10 3225-3238 Shibahara T (1993) Syntheses of sulphur-bridged molybdenum and tungsten coordination compounds. Coord Chem Rev 123 73-147... 

Y. Koltypin, S. I. Nikitenko, and A. Gedanken, The sonochemical preparation of tungsten oxide nanoparticles, J. Mater. Chem. 12, 1107-1110 (2002). 

G. L. Frey, A. Rothschild, J. Sloan, R. Rosentsveig, R. Popovitz-Biro, and R. Tenne, Investigations of nonstoichiometric tungsten oxide nanoparticles, J. Solid State Chem. 162(2), 300 (2001). 

Section II is about the new structure and understanding of nanocatalysts. Chapters 4 and 5 provide insight for understanding the structure and reactivity of gold catalyst. Chapters 6 and 7 disclose new methods for making nanoparticle catalysts in a control way by using the sol-gel technique and dendrimer template, respectively. Chapter 8 reviews the synthesis, structure, and applications of tungsten oxide nanorods. 

At the simplest level, nanoparticles of hard substances are useful as polishing powders which are able to give very smooth, defect-free surfaces. Indeed, 50 nm nanoparticles of cobalt tungsten carbide are found to be much harder than the bulk material. Therefore, they can be used to make cutting and drilling tools that will last longer. 

The possibility of the incorporation of oxygen into the particle is particularly relevant for the carbides and nitrides of molybdenum and tungsten which possess a high affinity for this element.13,23 The oxygen may come from the carbonyl precursor, and result in oxycarbide or oxynitride formation in the core of the nanoparticle itself.16 Exposure to the ambient can also result in the formation of surface oxycarbides and oxynitrides with catalytic properties different from those of the pure nitride or carbide phase.15,24-26 However, heat treatment of these nanoparticles with a mixture of methane/hydrogen or ammonia/hydrogen should convert the surface to a pure nitride or carbide form. 

Abstract. Nanopowders of nonstoichiometric tungsten oxides were synthesized by method of electric explosion of conductors (EEC). Their electronic and atomic structures were explored by XPS and TEM methods. It was determined that mean size of nanoparticles is d=10-35 nm, their composition corresponds to protonated nonstoichiometric hydrous tungsten oxide W02.9i (OH)o.o9, there is crystalline hydrate phase on the nanoparticles surface. After anneal a content of OH-groups on the surface of nonstoichiometric samples is higher than on the stoichiometric ones. High sensitivity of the hydrogen sensor based on WO2.9r(OH)0.09 at 293 K can be connected with forming of proton conductivity mechanism. 

Nanoparticles of nonstoichiometric tungsten oxides W03 x are promising material to produce active elements for hydrogen sensors. High work temperature that causes degradation processes is a problem of exploitation of gas sensors based on nanoparticles of semiconductor oxides. 

Figure 1. TEM micrograph of nanoparticles.of nonstoichiometric tungsten oxide.

At the comparison of the Ols-spectra of the samples MS2 and NN2 it is seen (Fig. 3-2, Fig. 3-4, Table 1), that after anneal on air the OFF/O2 - ratio in the nonstoichiometric sample of tungsten oxide is higher than in the stoichiometric sample. High concentration of the OH -groups on the active element s surface can form a proton conductivity mechanism and cause a high sensitivity of the hydrogen sensor based on W02.9i (OH)0.09 nanoparticles at 293 K. 

Electrophoretic deposition (EPD) is a colloidal process in which the charged colloidal particles are driven by a dc electric field to deposit on a substrate, forming a condensed film. This process is a combination of electrophoresis and deposition (Sarkar and Nicholson 1996). It has a long history and the first application was in 1927 for Th02 and tungsten deposition on a platinum cathode. Recently, photocatalyst semiconductor nanoparticles/microparticles have also been assembled by this... 

Nanopowders of nonstoichiometric tungsten oxide W03 x were synthesized by EEC-method. According to the TEM data (Fig. 1) the mean size of nanoparticles is 10-35 nm, size distribution is normal (Gaussian). The nanoparticles have spherical shape, well-defined crystalline structure, their agglomeration is almost absent. The macropowders of stoichiometric tungsten oxide W03 was obtained at combustion of metal in oxygen. The macropowders of stoichoimetric (sample MS) and the nanopowders of nonstoichiometric (sample NN) tungsten oxides were examined conditioned on air (samples MSI and NN1 respectively) and annealed on air at 563 K (samples MS2 and NN2 respectively). 

Various electrode materials have been reported for use in constructing structurally small electrodes of different geometries and sizes [4-7], Common electrode materials, both modified and otherwise, include metals such as tungsten and aluminium, gold nanoparticle-deposited aluminum, various forms of carbon e.g. doped diamond, nanocrystalline diamond, pyrolyzed carbon, carbon fibers, and gold nanoparticles deposited on glassy carbon. 

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