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991.
Andrey Tsyganok 《Journal of solid state chemistry》2006,179(6):1830-1841
A comparative study on two different methods for preparing Mg-Al layered double hydroxides (LDH) containing various divalent transition metals M (M=Co, Ni, Cu) has been carried out. The first (conventional) method involved coprecipitation of divalent metals M(II) with Mg(II) and Al(III) cations using carbonate under basic conditions. The second approach was based on the ability of transition metals to form stable anionic chelates with edta4− (edta4−=ethylenediaminetetraacetate) that were synthesized and further introduced into LDH by coprecipitation with Mg and Al. The synthesized LDHs were characterized by X-ray diffraction (XRD) and X-ray fluorescence (XRF) methods, thermogravimetry with mass-selective detection of decomposition products (TG-MSD), Fourier transform infrared (FTIR) and Raman spectroscopy techniques. The results obtained were discussed in terms of efficiency of transition metal incorporation into the LDH structure, thermal stability of materials and the ability of metal chelates to intercalate the interlayer space of Mg-Al LDH. Vibrational spectroscopy studies confirmed that the integrity of the metal chelates was preserved upon incorporation into the LDH. 相似文献
992.
Belokon YN Gutnov AV Moskalenko MA Yashkina LV Lesovoy DE Ikonnikov NS Larichev VS North M 《Chemical communications (Cambridge, England)》2002,(3):244-245
A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. This is the first report of the asymmetric synthesis of cyanohydrin derivatives using a cyanide source which is non-volatile and inexpensive. 相似文献
993.
Choukourov A Biederman H Slavinska D Hanley L Grinevich A Boldyryeva H Mackova A 《The journal of physical chemistry. B》2005,109(48):23086-23095
Plasma polymerization of allylamine is performed both in continuous wave and pulsed mode. Chemical derivatization is applied to determine primary and secondary amine concentration. Primary amines are efficiently formed, but secondary amines are more abundant. A polymerization mechanism is proposed to account for the difference in amine content obtained from comparison between continuous wave and pulsed mode plasma polymerization. The AFM measurements performed on ultrathin (1-10 nm) plasma polymers confirm the continuity of films and that the film growth on silicon occurs via a layer-by-layer mechanism because no islandlike structures were detected. 相似文献
994.
995.
Surface properties of porous carbon obtained from polystyrene sulfonic acid-based organic salts 总被引:2,自引:0,他引:2
Hines D Bagreev A Bandosz TJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3388-3397
Pyrolysis ofpolysterene sulfonic acid-co-maleic acid salts at 800 degrees C resulted in formation of new materials consisting of porous carbon and metal species dispersed on the surface. After hydrochloric acid treatment, the metal oxides/salts were removed. Obtained materials were characterized using adsorption of nitrogen, thermogravimetric analysis, Raman spectroscopy, and scanning electron microscopy with energy dispersive analysis of X-rays. The results showed highly developed porous structures in the range of micro- and mesopores. The porous features of new materials resemble those characteristics for carbon foams. The differences in the porous structure are linked to the type of transition metal used for the modification of the initial polymer and the chelation process. Macro- and mesopores are spherical/cylindrical in shape, and they are likely formed when release of pyrolysis gases, such as CO2, NO2, SO2, H2S, and CxHy, occurs. Moreover, reduction of metal, its migration to the surface, and agglomeration contribute to development of porosity. Depending on the reactivity of the metal used for cation exchange (Fe, Co, or Ni) either sulfides (nickel and cobalt) or oxides (cobalt and iron) are formed on the carbon surface. 相似文献
996.
997.
Alexander A. Kaminskii Oliver Lux Victor G. Ralchenko Andrey P. Bolshakov Hanjo Rhee Hans J. Eichler Akira Shirakawa Hitoki Yoneda 《固体物理学:研究快报》2016,10(6):471-474
We determined, for the first time, the room temperature phonon energy related to the F2g vibration mode (ωSRS(12C) ~ 1333.2 cm–1) in a mono‐crystalline single‐isotope CVD 12C‐diamond crystal by means of stimulated Raman scattering (SRS) spectroscopy. Picosecond one‐micron excitation using a Nd3+:Y3Al5O12‐laser generates a nearly two‐octave spanning SRS frequency comb (~12000 cm–1) consisting of higher‐order Stokes and anti‐Stokes components. The spacing of the spectral lines was found to differ by ΔωSRS ~ 0.9 cm–1 from the comb spacing (ωSRS(natC) ~ 1332.3 cm–1) when pumping a conventional CVD diamond crystal with a natural composition of the two stable carbon isotopes 12C (98.93%) and 13C (1.07%). (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
998.
Tatyana A. Bolshova Vladimir M. Shvartsberg Oleg P. Korobeinichev Andrey G. Shmakov 《Combustion Theory and Modelling》2016,20(2):189-202
On the basis of a multi-step kinetic mechanism for flame inhibition by organophosphorus compounds including more than 200 reactions, a skeletal mechanism for flame inhibition by trimethylphosphate was developed. The mechanism consists of 22 irreversible elementary reactions, involving nine phosphorus-containing species. Selection of the crucial steps was performed by analysing P-element fluxes from species to species and by calculating net reaction rates of phosphorus-involving reactions versus the flames zone. The developed mechanism was validated by comparing the modelling results with the measured and simulated (using the starting initial mechanism) speed and the chemical structure of H2/O2, CH4/O2 and syngas/air flames doped with trimethylphosphate. The mechanism was shown to satisfactorily predict the speed of H2/O2/N2 flames with various dilution ratios, CH4/air and syngas/air flames doped with trimethylphosphate. The skeletal mechanism was also shown to satisfactorily predict the spatial variation of H and OH radicals and the final phosphorus-containing products of the inhibitor combustion. Further reduction of the skeletal mechanism without modification of the rate constants recommended in the starting mechanism was shown to result in noticeable disagreement of the flame speed and structure. 相似文献
999.
Dr. Craig A. Bell Jiayi Yu Dr. Ian A. Barker Dr. Vinh X. Truong Zhen Cao Prof. Andrey V. Dobrinyin Prof. Matthew L. Becker Prof. Andrew P. Dove 《Angewandte Chemie (International ed. in English)》2016,55(42):13076-13080
In most synthetic elastomers, changing the physical properties by monomer choice also results in a change to the crystallinity of the material, which manifests through alteration of its mechanical performance. Using organocatalyzed stereospecific additions of thiols to activated alkynes, high‐molar‐mass elastomers were isolated via step‐growth polymerization. The resulting controllable double‐bond stereochemistry defines the crystallinity and the concomitant mechanical properties as well as enabling the synthesis of materials that retain their excellent mechanical properties through changing monomer composition. Using this approach to elastomer synthesis, further end group modification and toughening through vulcanization strategies are also possible. The organocatalytic control of stereochemistry opens the realm to a new and easily scalable class of elastomers that will have unique chemical handles for functionalization and post synthetic processing. 相似文献
1000.