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      A low temperature synthetic route to nanocrystalline TiN

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          Abstract

          A simple chemical synthetic route has been developed to prepare nanocrystalline titanium nitride (TiN) in an autoclave, by the reaction of metallic Ti with NaNH2 at low temperature of 500-600 °C. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectra. The possible reaction mechanism of this process is also discussed. This method may be extended to the synthesis of other metal nitrides.

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          Most cited references 46

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          Rapid planetesimal formation in turbulent circumstellar discs

          The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are augmented a further order of magnitude by a streaming instability (Youdin & Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.
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            Ion pairing.

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              A Brønsted acid catalyst for the enantioselective protonation reaction.

              A highly reactive and robust chiral Brønsted acid catalyst, chiral N-triflyl thiophosphoramide, was developed. The first metal-free Brønsted acid catalyzed enantioselective protonation reaction of silyl enol ethers was demonstrated using this chiral Brønsted acid catalyst. The catalyst loading could be reduced to 0.05 mol % without any deleterious effect on the enantioselectivity.
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                Author and article information

                Affiliations
                [1 ] China University of Mining and Technology P.R. China
                [2 ] China University of Mining and Technology P.R. China
                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                sajc
                South African Journal of Chemistry
                S.Afr.j.chem. (Online)
                The South African Chemical Institute (Durban )
                1996-840X
                2011
                : 64
                : 0
                : 57-60
                S0379-43502011000100008

                http://creativecommons.org/licenses/by/4.0/

                Product
                Product Information: SciELO South Africa
                Categories
                Chemistry, Analytical
                Chemistry, Applied
                Chemistry, Inorganic & Nuclear
                Chemistry, Medicinal
                Chemistry, Multidisciplinary
                Chemistry, Organic
                Chemistry, Physical
                Electrochemistry

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