Ultrafine preparation

Sephasorb HP (ultrafine, prepared by hydroxypropylation of crossed-linked dextran) can also be used for the separation of small molecules in organic solvents and water, and in addition it can withstand pressures up to 1400 psi making it useful in HPLC. These gels are best operated at pH values between 2 and 12, because solutions with high and low pH values slowly decompose them (see further in Chapter 6). 

A special use for meltblown olefin fiber is in filtration media such as surgical masks and industrial filters (78). The high surface area of these ultrafine filament fibers permits preparation of nonwoven filters with effective pore sizes as small as 0.5 p.m. 

Vapor-Phase Techniques. Vapor-phase powder synthesis teclmiques, including vapor condensation, vapor decomposition, and vapor—vapor, vapor—Hquid, and vapor—soHd reactions, employ reactive vapors or gases to produce high purity, ultrafine, reactive ceramic powders. Many nonoxide powders, eg, nitrides and carbides, for advanced ceramics are prepared by vapor-phase synthesis. 

Ultrafine powders can be prepared in high-temperature plasmas. Particles below 1 [Lm and larger particles with unusual surface structures are formed according to WaJdie [Trans. Inst. Chem. Eng., 48(3), T90 (1970)]. Energy costs are discussed. 

This method is one of the dry methods in which no chemical reaction is involved. Preparation of ultrafine particles by physical vapor deposition (PVD) dose not require washing and calcination, which are indispensable for chemical preparation such as in CP and DP methods. As waste water and waste gases are not by-produced, the arc plasma (AP) method is expected to grow in popularity as one of the industrial production methods for gold catalysts and as a clean preparation method. 

The liquid-phase reduction method was applied to the preparation of the supported catalyst [27]. Virtually, Muramatsu et al. reported the controlled formation of ultrafine Ni particles on hematite particles with different shapes. The Ni particles were selectively deposited on these hematite particles by the liquid-phase reduction with NaBFl4. For the concrete manner, see the following process. Nickel acetylacetonate (Ni(AA)2) and zinc acetylacetonate (Zn(AA)2) were codissolved in 40 ml of 2-propanol with a Zn/Ni ratio of 0-1.0, where the concentration of Ni was 5.0 X lO mol/dm. 0.125 g of Ti02... 

Particles with the lowest specific gravity are carried with the water towards the outside wall of the spiral. The spiral separates at its greatest efficiency when used in the size range of 10 to 200 mesh. Some particles will be recovered both above and below these size ranges, but occasionally, ultrafine and very coarse heavies will be lost in the tailings, as will be middlings or unliberated ore particles. The spiral will benefit, therefore, from the use of hydraulic classification as a feed preparation step. 

Okitsu K, Bandow H, Maeda Y, Nagata Y (1996) Sonochemical preparation of ultrafine palladium particles. Chem Mater 8 315-317... 

Kim D, Oh S, Lee J (1999) Preparation of ultrafine monodispersed Indium-Tin Oxide particles in AOT-Based reverse microemulsions as nanoreactors. Langmuir 15(5) 1599-1603... 

Arul Dhas N, Koltypin Y, Gedanken A (1997) Sonochemical preparation and characterization of ultrafine chromium oxide and manganese oxide powders. Chem Mater 9(12) 3159—3163... 

Cohen, B. S., R. G. Sussman and M. Lippmann, Deposition of Ultrafine Particles in Hollow Airway Casts of the Human Tracheobronchial Tree. In Preparation. 

Porous ultrafine tin oxide ethanol gas sensors92 in the form of a thin film have been prepared from tin alkoxide by the sol-gel process. The microstructural evolution of the tin oxide films, which affected the ethanol gas-sensing properties of the films, was investigated as a function of firing temperature and solution concentration. Theoretically, it was expected that ethanol gas sensitivity would increase monotonically with decreasing film thickness, but experimental results showed a maximum sensitivity at about 70 nm. The sudden decrease of the sensitivity below the thickness of 70 nm seemed to be due to the sudden decrease of film porosity, i.e., the sudden decrease of the number of the available sites for the oxidation reaction of ethanol molecules. Thus, it seemed that below the thickness of 70 nm, the sensitivity was governed by microstructure rather than by film thickness. 

Duff, D.G. and Baiker, A., Preparation and structural properties of ultrafine gold colloids for oxidation catalysis, in Preparation of Catalysts VI, Poncelet, G., Martens, J., Delmon, B., Jacobs, P.A., and Grange, P., Eds., Elsevier, Amsterdam, 1995, p. 505. 

An ultrafine diphtheria and tetanus toxoid preparation contains 15 Lf units of diphtheria and 10 Lf units of tetanus toxoids per 0.5-mL dose. In a dosage form containing 5 mL, how many Lf units of tetanus are present ... 

Synthesis by means of volatile compounds A number of halides (especially chlorides) of the transition metals display a high volatility and in the gaseous state they are easy to mix. They can be synthesized from oxides, or scrap metals, and chlorine they are highly reactive and can be utilized for the preparation of various compounds, either as powder or a coherent solid or as coatings. Mixtures, for instance, of TiCLj + CH4 + H2 have been used to prepare ultrafine TiC powder, to deposit TiC on graphite (at 1200-1300°C), etc. 

Leenaars, A. F. M. and A. J. Burggraaf. 1985. The preparation and characterization of alumina membranes with ultrafine pores 2. The formation of supported membranes. J. Coll. Interface Sci. 105(1) 27-40. 

Sonochemical Preparation of Ultrafine Powders and Nanostructured Materials... 

Ultrafine powders are usually considered to be particles with diameters between 1 -100 run [141]. A focus for recent work in material chemistry has been the preparation of such particles [142] because of their special properties optical, photocatalytic, electrochemical, magnetic, thermal resistance, high melting point and sintering abilities [143,144]. A variety of chemical and physical methods have been used for the synthesis of such materials including the decomposition of organometallics [145] and the controlled reduction of salts [146-148]. 

H. Shao, Y. Wang, H. Xu, X. Li, Hydrogen storage properties of magnesium ultrafine particles prepared by hydrogen plasma-metal reaction, Mater Sci. Eng. B 110 (2004) 221-226. 

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