Microspheres carbon

Yamaki, S., Isobe, T., Okuyama, T., Shinoda, T., Reversed-phase liquid chromatography on a microspherical carbon column at high temperature, /. Chromatogr. A, 728(1 2), 189, 1996. 

As mentioned in the previous section, hollow zeolite spheres of LTA, FAU, BEA, MFI can be prepared in the presence of polystyrene beads as templates by using an LBL self-assembly technique. Recently, several research groups have tried to adopt similar methods to synthesize zeolite-template composites on the surfaces of templates with various shapes and sizes, properties, and structures through self-assembly or in situ-crystallization approaches. Subsequent removal of the templates forms zeolite materials with analogical skeletons of the templates. Up to now, the reported templates include microspheres, carbon fibers, polyurethane foams, and microbe structures,[144,145] as well... 

Small glass spheres (microspheres), carbon nanotubes, and fullerenes can hold hydrogen if it is induced at high pressure and temperature. The hydrogen is held captive in the solid matrix when the temperature lowers. Hydrogen can be released by heating the solid. 

Sattarahmady N, Heli H, Moosavi-Movahedi AA (2010) An electrochemical acetylcholine biosensor based on nanoshells of hollow nickel microspheres-carbon microparticles-Nalion nanocomposite. Biosens Bioelectron 25 2329-2335... 

As previously stated, uranium carbides are used as nuclear fuel (145). Two of the typical reactors fueled by uranium and mixed metal carbides are thermionic, which are continually being developed for space power and propulsion systems, and high temperature gas-cooled reactors (83,146,147). In order to be used as nuclear fuel, carbide microspheres are required. These microspheres have been fabricated by a carbothermic reduction of UO and elemental carbon to form UC (148,149). In addition to these uses, the carbides are also precursors for uranium nitride based fuels. 

Most commercial lithium-ion cells maufactured today use graphitic carbons from region 1 of Fig. 2. These are of several forms, with mesocarbon microspheres and natural graphites being the most commonly used. The specific capacity of these carbons is near 350 mAh/g. 

For the preparation of spray-dried polyelectrolyte complexes, the polyanion was dissolved in dilute NH4HCO3 solution and mixed with the chitosan carbamate solution just before spray-drying. The excess NH4HCO3 decomposed thermally between 60 and 107 °C on the other hand, the carbamate function released carbon dioxide under the effect of the temperature at which the spray-drier was operated, thus regenerating chitosan at the moment of the polyelectrolyte microsphere formation (Fig. 5). 

By changing the ultrasound power, changes in the mesoporosity of ZnO nanoparticles (average pore sizes from 2.5 to 14.3 nm) have been observed. In addition to the changes in mesoporosity, changes in the morphology have also been noted [13]. Recently, Jia et al. [14] have used sonochemistry and prepared hollow ZnO microspheres with diameter 500 nm assembled by nanoparticles using carbon spheres as template. Such specific structure of hollow spheres has applications in nanoelectronics, nanophotonics and nanomedicine. 

They produced high performance electrets from thin polymer films metallized so as to yield high capacitance. Both electrical and mechanical properties of these transducers have been remarkable examples of how applications of science of solids, including knowledge of electron traps, conduction processes in insulators and the viscoelastic phenomena of semicrystalline polymers, can be combined.(6) Incidentally, similar ideas have been applied to optimization of the properties of particle microphones, through assemblies of perfectly microspherical polymer carbon systems. These have shown what limits of performance... 

A significant recent advance has been the development of microfiltration and ultrafiltration membranes composed of inorganic oxide materials. These are presently produced by two main techniques (a) deposition of colloidal metal oxide on to a supporting material such as carbon, and (b) as purely ceramic materials by high temperature sintering of spray-dried oxide microspheres. Other innovative production techniques lead to the... 

It was also found that the presence of some metal ions and borates can effectively accelerate the hydrothermal carbonization of starch, which shortens the reaction time to some hours. Thus, iron ions and iron oxide nanoparticles were shown to effectively catalyze the hydrothermal carbonization of starch (< 200 °C) and also had a significant influence on the morphology of the formed carbon nanomaterials [10]. In the presence of Fe2+ ions, both hollow and massive carbon microspheres could be obtained. In contrast, the presence of Fe203 nanoparticles leads to very fine, rope-like carbon nanostructures, reminding one of disordered carbon nanotubes. 

Li et al. reported first on the decoration of hydrothermal carbon spheres obtained from glucose with noble metal nanoparticles [19]. They used the reactivity of as-prepared carbon microspheres to load silver and palladium nanoparticles onto then-surfaces, both via surface binding and room-temperature surface reduction. Furthermore, it was also demonstrated that these carbon spheres can encapsulate nanoparticles in their cores with retention of the surface functional groups. Nanoparticles of gold and silver could be encapsulated deep in the carbon by in situ hydrothermal reduction of noble-metal ions with glucose (the Tollens reaction), or by using silver nanoparticles as nuclei for subsequent formation of carbon spheres. Some TEM images of such hybrid materials are shown in Fig. 7.4. 

First, the catalyst is meant to leach out of the capsules into a reaction solution. In this case, the capsules ate not meant to break open but are semipermeable to the catalyst, which diffuses into the reaction mixture over time. This method is t) pically used for metal catalysts or catalyst precursors where the metals leach out and perform the desired reaction. This method is useful because metal-catalyzed reactions typically require lower catalyst loading than organocatalysts (< 1 mol%), and highly loaded capsules can be isolated and reused until exhausted. Such metal catalysts are often touted for their decreased pyrophoricity relative to such catalysts as palladium on carbon (Coleman and Royer 1980 Bremeyer et al. 2002). One could simply use resins, microspheres, or other solid supports as catalyst reservoirs, but capsules are well suited because of their inherently higher surface areas (Royer et al. 1985 Wang et al. 2006). 

The fuel particles used in these studies were typical pyrolytic carbon-coated thorium-uranium dicarbide, (Th,U)C2, microspheres. The kernels, — 200/i in diameter, were prepared from Th02, U02, and C and converted to the carbide at temperatures below 2200°C., followed by a spheroidization above the melting point, 2450°-2500°C. The bare kernels were coated with a 30-50fi layer of low density (— 1.0 gram/cm.3) buffer pyrolytic carbon, followed by a 40-70/a layer of high density... 

A recent patent by Thomason [15] has revealed that ammonium zirconium carbonate when applied to a substrate such as glass, aluminium, or polypropylene can improve the adhesion of microsphere polymer-based adhesives. It is proposed that the zirconium after reacting with the substrate surface reacts with carboxyl groups at the surface of the polymer microspheres. 

Syntactic foamed plastics (from the Greek ovvxa C, to put together) or spheroplastics are a special kind of gas filled polymeric material. They consist of a polymer matrix, called the binder, and a filler of hollow spherical particles, called microspheres, microcapsules, or microballoons, distributed within the binder. Expoxy and phenolic resins, polyesters, silicones, polyurethanes, and several other polymers and oligomers are used as binders, while the fillers have been made of glass, carbon, metal, ceramics, polymers, and resins. The foamed plastic is formed by the microcapsular method, i.e. the gas-filled particles are inserted into the polymer binder1,2). 

The filler microspheres may be glass, polymeric, carbon, ceramic, or metallic. However, the main requirements are that the microspheres are spherical, non-cohesive, strong, intact, moisture and chemically resistant, and hydrolytically stable. They should be... 

Carbonized microspheres are a new type of hollow filler for syntactic plastics. They are very strong and bind well to the polymer matrix 37). 

The Carbosphere brand of filler is manufactured in USA by carbonizing BJO phenolic microspheres at 900 °C in an inert atmosphere. They are 5-150 pm (average 40 pm) in diameter, have wall thicknesses of 1-4 pm and bulk densities of 130 to 140 kg/m3 38). Four types of Kresosphere microspheres are produced in Japan. They are more than 95 % carbon and made by carbonizing microspheres made from wood resins (pitches) at 800-1100 °C in an inert medium (Table 7) 39). 

Shaver et al.40141 have shown that a considerable number of the initial microspheres are defective due to pores being eroded in the cell walls by oxidation during carbonization. The defective spheres are removed by sieving or by flotation fractionation, e.g. in acetone. 

Carbonized microspheres, even with defects in their shells, are stronger than glass microspheres. At a gas (nitrogen) pressure of 7 MPa, 43% of glass spheres, but only 5 % of carbon microspheres are damaged 39). Production of carbonized microspheres based on glass4Z) and polymers43) has been started in the USSR. 

A recent achievement worthy of note is the manufacture of microspheres containing an inert gas, e.g. nitrogen, or a volatile liquid, such as the freons The patent literature contains methods for producing microspheres based on poly(vinyl chloride) and poly(divinyl chloride), containing isobutane or carbon tetrachloride 52>, and based on poly(methyl methacrylate), containing neopentane . Microspheres containing liquid dyes and oils are also used to make syntactic foams 58>. 

Polymeric 47,61), inorganic, and carbon 37) hollow macrospheres are used too. They have densities of 200-500 kg/m3 and are larger than 1 mm. By using macrospheres and microspheres together the apparent density of a syntactic foam can be reduced, however its specific strength is also less than that of a foam made only with microspheres 18,62). 

Fig. 2. Influence of concentration (C) and diameter (D) of carbon microspheres on the fluidity (1, relative units) and the apparent density (2) of epoxy syntactic foams401. The A and B regions are the cast and molding compositions, respectively...

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