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281.
In this work we investigate the performance of high flux chemical vapour deposition (CVD) silica membranes for the separation of gas mixtures containing H2 and CO2 at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and O2 were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H2 and He) whilst the larger kinetic diameter gases (CO2 and N2) showed negative activation energy. The single gas permeation of H2 increased from 5.1 × 10−7 to 7.0 × 10−7 mol m−2 s−1 Pa−1 in the temperature range 100–400 °C, and H2/CO2 and H2/N2 selectivities reached 36 and 57 at 400 °C, respectively. The H2 purity in the permeate stream also increased with temperature for H2:CO2 binary gas mixture, thus being beneficial for H2 diffusion. H2 competitively permeated through the membrane at a several range of gas mixtures, and a saturation level was achieved at H2:CO2 60:40 feed concentration, where the diffusion of CO2 molecules became negligible delivering ∼99% H2 purity in the permeate stream. These results substantiate that the counter diffusion CVD method produced thin silica film membranes with a very precise pore size control, in particular suggesting a narrow pore distribution with average pore radius of about 3.1 Å. 相似文献
282.
Parthiban P Ramachandran R Aridoss G Kabilan S 《Magnetic resonance in chemistry : MRC》2008,46(8):780-785
The (1)H and (13)C NMR spectra of 2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ones (1-2), oximes (3-8) and O-benzyl oximes (9-12) were recorded. The chemical shifts were unambiguously assigned using 1D and 2D NMR spectral data. The results clearly indicate that the compounds exist in chair-boat conformation with equatorial and axial orientation of the aryl groups in the chair and boat forms, respectively. Since the molecules are flexible and dynamic in solution, the chair and boat forms are mutually interconvertible. In 3-12, because of the effect of oximation/oximination, all the protons in the heterobicyclic systems gave distinct signals except the benzylic protons of the boat form. In all synthesized compounds, the aryl group protons at C-6,8 are shielded by the aryl groups at C-2,4 and therefore appear in the lower frequency region than the aryl groups at C-2,4. 相似文献
283.
284.
P. Mythili T. Kanagasekaran G. Bhagavannarayana R. Gopalakrishnan 《Journal of Crystal Growth》2012,338(1):222-227
(0.5 mol%) Dysprosium (Dy) doped bismuth silicon oxide (BSO) single crystals were grown by the Czochralski technique under air atmosphere. Detailed analysis of Dy-doped BSO with pure BSO has been studied through optical analysis. The absorption edges of pure and Dy-doped BSO crystals are found to be 405 nm and 415 nm, respectively. The shift in the absorption edge is contributed to the defect centers created in the crystal with Dy-doping. The shifts observed in the Raman spectra on doping Dy are found to be lower, when compared with the pure BSO crystal. This effect can be correlated to the lattice distortion induced by the Dy doping. The oxide formation and intrinsic defects in the BSO crystal have been identified by photoluminescence analysis. Dielectric measurements reveal that higher permeability value in the BSO sample is due to the presence of charged defects, which can be related to the space charge polarization. There is a slight decrease in dielectric constant on doping with Dy. The piezoelectric value explains the defects formed in the crystal. On poling, d33 value of BSO and Dy-doped BSO are 32 pC/N and 40 pC/N, respectively. 相似文献
285.
N. Gopalakrishnan L. Balakrishnan A. Brindha G. Jayalakshmi 《Crystal Research and Technology》2012,47(1):45-52
The effect of film thickness and substrate orientation on ferromagnetism in Mn doped ZnO thin films have been studied. The Mn doped ZnO films of different thickness (15, 35 and 105 nm) have been grown on both Si (100) and Si (111) substrates. The structural, electrical, optical, elemental and magnetic properties of the films have been investigated by X‐ray diffraction (XRD), Hall Effect measurements, photoluminescence (PL), energy dispersive spectroscopy (EDS) and vibrating sample magnetometer (VSM), respectively. It is found that all the properties are strongly influenced by the film thickness and substrate orientation. The XRD analysis confirmed that the formation of high quality monophasic hexagonal wurtzite structure for all the grown films. The room temperature VSM measurements showed that the films of lower thickness have better ferromagnetism than that of the thicker films grown on both the substrates. Among the lower thickness films, the film grown on Si (111) substrate has higher saturation magnetization (291×10‐5 emu cm‐3) due to high density of the defects. The observed ferromagnetism has been well justified by XRD, Hall measurements and PL. The presence of Mn atoms in the film has been confirmed by EDS. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
286.
The diamond like carbon (DLC) films have been grown by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) in methane-argon plasma. In PECVD, the plasma sheath potential drop arising due to argon plasma was utilized to grow the DLC film on silicon (100) substrate at low temperature without using any external negative bias voltage. The growth process of the DLC film has been studied completely starting from nucleation to continuous film by atomic force microscopy. It was seen that the DLC film nucleates around surface defects on the substrate and that the film growth occurs by both adatom deposition and coalescence between nucleated islands. Raman spectrum confirms that the DLC film nucleates excessively in sp2 hybridized state and that during the growth process the fraction of sp3 CHx (x = 1 − 3) increases which leads to the amorphous nature of the film. Long range uniformity of the film was identified using scanning electron microscope. 相似文献
287.
S. An G. Gopalakrishnan Y. Shiroyanagi S.C. Parks T.J. Gramila L.N. Pfeiffer K.W. West 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):214
Electron drag between two two-dimensional electron systems has been measured in intermediate magnetic fields (/τ<ωckBT) with a relatively low electron density. We explore, in this sample, the unusual increase of drag in intermediate magnetic fields which was well characterized by a nearly temperature independent B3 dependence. The anomalous behavior of electron drag observed in higher density samples is found to persist for low sample density. 相似文献
288.
Rohini Mani Keka R. Chakraborty Joby E. Joy J. Gopalakrishnan A.K. Tyagi 《Journal of solid state chemistry》2010,183(6):1380-1387
We describe an investigation of the structure and dielectric properties of MM′O4 and MTiM′O6 rutile-type oxides for M=Cr, Fe, Ga and M′=Nb, Ta and Sb. All the oxides adopt a disordered rutile structure (P42/mnm) at ambient temperature. A partial ordered trirutile-type structure is confirmed for FeTaO4 from the low temperature (17 K) neutron diffraction studies. While both the MM′O4 oxides (CrTaO4 and FeTaO4) investigated show a normal dielectric property MTiM′O6 oxides for M=Fe, Cr and M′=Nb/Ta/Sb display a distinct relaxor/relaxor-like response. Significantly the corresponding gallium analogs, GaTiNbO6 and GaTiTaO6, do not show a relaxor response at T<500 K. 相似文献
289.
Kanagarajan V. Sureshkumar P. Thanusu J. Gopalakrishnan M. 《Russian Journal of Organic Chemistry》2009,45(11):1707-1713
One-pot condensation of thiourea (urea), diverse aromatic aldehydes, and ammonium acetate in the presence of repeatedly usable
heterogeneous catalyst NaHSO4-SiO2 in the absence of solvent under the microwave irradiation proceeds faster and with better yields of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones)
that under common heating. Compounds synthesized exist as a rule as two isomers distinguished by the position of the phenyl
ring: It is located in the major isomer nearly in the equatorial position, in the minor one, close to axial position. 相似文献
290.
R. Mohan Kumar N. Gopalakrishnan R. Jayavel P. Ramasamy 《Crystal Research and Technology》1999,34(10):1265-1268
The nucleation parameters, such as radius of the critical nucleus and critical free energy change have been evaluated for LAP single crystals. The interfacial tension determined by conducting the induction period measurements has been used for the evaluation of nucleation parameters. The determined interfacial tension is found to be comparable with theoretical literature values. 相似文献