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Composition Dependence (composition + dependence)

Distribution by Scientific Domains

Physics and Astronomy	38%
Polymers and Materials Science	30%
Chemistry	23%

Selected Abstracts

Molecular Dynamics Simulations of Amorphous Si,C,N Ceramics: Composition Dependence of the Atomic Structure

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003
Nicoletta Resta
We have performed classical molecular dynamics simulations of amorphous Si,C,N materials. The dependence of the local order and of the microstructure on the chemical composition was investigated. Our simulations show that for a stoichiometric nitrogen/silicon ratio equal to or higher than 4/3, the amorphous ceramic separates into different amorphous domains, namely C-rich, SiN-rich, and SiC-rich phases. Below this ratio, the material is composed of mixed structures, homogeneously spread within the material. For a very particular composition range, we found that carbon atoms crystallize into monoatomic graphitic layers surrounding the SiN-rich domains. [source]

ChemInform Abstract: Composition Dependence of the Enthalpies of Formation of NiAl.

CHEMINFORM, Issue 36 2001
Philip Nash
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Composition dependence of the OH-stretch-mode spectrum in lithium tantalate

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2004
C. Bäumer
Abstract The infrared absorption spectrum of the OH-stretch-mode in lithium tantalate is measured for crystals of different compositions. The spectrum exhibits two prominent lines which are representative for ideal and for Li-deficient sites in the crystal, respectively. Position, shape, and intensity of the two lines thus depend on crystal composition in a characteristic way. A comprehensive quantitative description is given which shows that the technique can be used as a sensitive non-destructive tool to rate the composition of lithium niobate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Composition dependence of positron annihilation lifetime for Al-Pd-Re-Ru quasicrystal and 2/1-AlPdRu approximant crystal

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
Y. Takagiwa
Abstract Quaternary icosahedral Al-Pd-Re-Ru (i -Al71Pd20(Re1,xRux)9 (X = 0.4, 0.55, 0.7, 0.85)) quasicrystals and its 2/1-AlPdRu approximant crystal, 2/1-Al71Pd20Ru9, were investigated by positron annihilation lifetime spectroscopy. The positron annihilation lifetimes measured here are significantly longer than those of defect-free states estimated by compositionally weighting the constituent elements. This result suggests that high densities of structural vacancies exist in both i -Al-Pd-Re-Ru quasicrystals and 2/1-AlPdRu approximant crystal. For i -Al-Pd-Re-Ru quasicrystals, composition dependence of the positron annihilation lifetime is compared with that of the electrical conductivity. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Studies on multiphased mixed crystals of NaCl, KCl and KI

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2009
M. Priya
Abstract Multiphased mixed crystals of NaCl, KCl and KI were grown by the melt method, for the first time. Densities and refractive indices of all the grown crystals were determined and used for the estimation of the composition in the crystal. Atomic absorption spectroscopic measurements were done to estimate the metal atom contents in the crystal. Lattice parameters and thermal parameters (Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency) were determined from the X-ray powder diffraction data. DC and AC electrical measurements were done at various temperatures ranging from 40 to 150°C. Activation energies were also estimated. The observed lattice parameters showed that the system exhibits three phases each nearly corresponds to NaCl, KCl and KI. The thermal and electrical parameters show a highly nonlinear bulk composition dependence. Results are reported. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Measurement of mutual diffusion coefficients of gases by the Taylor method: Measurements on H2,Air,H2,N2, and H2,O2 systems

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2002
Naoki Matsunaga
Abstract Mutual diffusion coefficients of hydrogen gas (H2) into air and its component gases (N2 and O2) have been measured in the temperature range of 30 to 180°C and at atmospheric pressure via the Taylor dispersion method. For a H2,N2 system, the composition dependence of the mutual diffusion coefficient has been studied with both H2 and N2 as the carrier gas. The mutual diffusion coefficients for the H2,air and H2,N2 systems are almost the same and smaller than that for the H2,O2 system by about 5%. The present data for the H2,N2 system, corrected to an equimolar composition, agree well with the accurate data reported by the groups of P. J. Dunlop and of R. J. J. Van Heijningen. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 182,193, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10025 [source]

RAFT polymerization of styrenic-based phosphonium monomers and a new family of well-defined statistical and block polyampholytes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2007
Ran Wang
Abstract We describe herein the first example of the controlled reversible addition-fragmentation chain transfer (RAFT) radical homo- and copolymerization of phosphonium-based styrenic monomers mediated with a trithiocarbonate-based RAFT chain transfer agent (CTA) directly in aqueous media. In the case of homopolymer syntheses the polymerizations proceed in a controlled fashion yielding materials with predetermined molecular characteristics as evidenced from the narrow molecular mass distributions (MMD) and the excellent agreement between the theoretical and experimentally determined molecular masses (MM). We also demonstrate the controlled nature of the homopolymerization of 4-vinylbenzoic acid with the same CTA in DMSO. We subsequently prepared both statistical and block copolymers from the phosphonium/4-vinylbenzoic acid monomers to yield the first examples of polyampholytes in which the cationic functional group is a quaternary phosphonium species. We show that the kinetic characteristics of the statistical copolymerizations are different from the homopolymerizations and proceed, generally, at a significantly faster rate although there appears to be a composition dependence on the rate. Given the inherent problems in characterizing such polyampholytic copolymers via aqueous size exclusion chromatography we have qualitatively proved their successful formation via FTIR spectroscopy. Finally, in a preliminary experiment we qualitatively demonstrate the ability of such pH-responsive block copolymers to undergo supramolecular self-assembly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2468,2483, 2007 [source]

Phase Characteristics and Piezoelectric Properties in the Bi0.5Na0.5TiO3,BaTiO3,K0.5Na0.5NbO3 System

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010
Shan-Tao Zhang
Lead-free 0.94Bi0.5Na0.5TiO3,(0.06,x)BaTiO3,xK0.5Na0.5NbO3 (x=0,0.06) ceramics were prepared. All these compositions have a structure close to the rhombohedral,tetragonal morphotropic phase boundary (MPB) and good electric properties at room temperature. No significant composition dependence of ferroelectric property can be established, whereas a dependence of piezoelectric properties can be observed, e.g. the piezoelectric coefficient (d33), planar coupling factor (kp), and field-induced strain (S) increase with increasing x when x,0.01 and then tend to decrease. The highest d33, kp, and bipolar strain are 118 pC/N, 0.29, and 0.32%, respectively, in the composition with x=0.01. The results not only indicate that BNT,BT,KNN lead-free piezoceramics can persist in the structure close to MPB in a wide composition range but that they may also be helpful for further investigation on lead-free piezoceramics. [source]

Cellulose Acetate- graft -Poly(hydroxyalkanoate)s: Synthesis and Dependence of the Thermal Properties on Copolymer Composition

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2004
Yoshikuni Teramoto
Abstract Summary: Several different series of cellulose acetate- graft -poly(hydroxyalkanoate)s (CA- g -PHAs) were synthesized over a wide range of compositions by the graft copolymerization of lactic acid, L -lactide, (R,S)- , -butyrolactone, , -valerolactone and , -caprolactone onto the residual hydroxyl positions of CA, by virtue of a suitable catalyst, solvent and procedure for each individual case. To achieve a diversity of molecular architectures of the respective graft copolymer series, the degree of acetyl substitution (acetyl DS) of the CA starting material was also varied, resulting in different levels of the intramolecular density of grafts. The CA- g -PHAs thus obtained were subjected to differential scanning calorimetric measurements and the relationship between their molecular structure and thermal transition behavior was estimated, in comparison with some semi-empirical equations available for polymer blends or comb-like polymers. In particular, the composition dependence of the Tgs of the graft copolymers was represented well in terms of a formula proposed by Reimschuessel for comb-like polymers, when CAs of acetyl DS ,2 were employed as a trunk polymer. The deviation of the glass transition data from the model function was discussed in connection with the manner of graft modification. [source]

Composition dependence of positron annihilation lifetime for Al-Pd-Re-Ru quasicrystal and 2/1-AlPdRu approximant crystal

Structure of strontium barium niobate SrxBa1,,,xNb2O6 (SBN) in the composition range 0.32 ,x, 0.82

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2006
Sergey Podlozhenov
The structure of strontium barium niobate crystals SrxBa1,,,xNb2O6 is comprehensively studied in the whole range of the tetragonal tungsten bronze phase (x = 0.32,0.82) using both powder and single-crystal X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show an explicit composition dependence which can be consistently explained using simple model calculations. The temperature dependence of the unit-cell parameters exhibits a remarkable anisotropy in a broad temperature region below the phase transition temperature. This proves that the electrostrictive contribution to the thermal expansion plays an important role in strontium barium niobate. [source]

Temperature-Dependent and Friction-Controlled Electrochemically Induced Shuttling Along Molecular Strings Associated with Electrodes

CHEMPHYSCHEM, Issue 10 2005
Eugenii Katz Dr.
Abstract The temperature and solvent composition dependence of the electrochemically stimulated rate of shuttling of the redox-active cyclophane, cyclobis(paraquat- p -phenylene), on a molecular string has been studied. The molecular string includes a ,-donor diiminebenzene-site that is associated on one side with an electrode, and stoppered on the other side with an adamantane unit. The cyclophane rests on the ,-donor site, owing to stabilizing ,-donor,acceptor interactions. Electrochemical reduction of the cyclophane units, to the bis-radical cation cyclophane, results in the shuttling of the reduced cyclophane towards the electrode, a process that is driven by the removal of the stabilizing donor,acceptor interactions, and the electrostatic attraction of the reduced product by the electrode. The latter process is energetically downhill, and is temperature-independent. Upon oxidation of the reduced cyclophane that is associated with the electrode, the energetically uphill shuttling of the oxidized cyclophane to the ,-donor site proceeds. The rate of this translocation process has been found to be temperature-dependent, and controlled by the solvent composition. The experimental results have been theoretically analyzed in terms of Kramers' molecular friction model. The theoretical fitting of the experimental results, using solutions of variable composition, reveals that the rate-constants for the uphill reaction in a pure aqueous solution follow the temperature-dependence of the viscosity of water. The results demonstrate the significance of friction phenomena in shuttling processes within molecular machines. [source]

AlGaN epitaxial layers grown by HVPE on sapphire substrates

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
V. Soukhoveev
Abstract Growth of AlxGa1,xN (x , 0.0-1.0) alloy layers by hydride vapor pahse epitaxy (HVPE) is reported. Crack-free undoped AlGaN layers from 0.1 to 2 ,m thick were grown on 2, SiC and 2,and 4, sapphire substrates. For AlxGa1,xN (x , 0.7-0.8) layers grown on sapphire, high-resolution symmetric/asymmetric X-ray diffraction (XRD) measurements resulted in ,-scan rocking curve widths ranging from 250 to 650 arcsec and from 1400 to 1900 arcsec, for the (00.2) and (10.2) reflections, respectively. Minimum XRD-estimated screw and edge dislocation densities in AlGaN layers grown on sapphire were <6 x 108 cm,2 and <2 x 109 cm,2, respectively. Raman studies revealed that the composition dependences of the phonon modes of HVPE-grown AlxGa1,xN layers are in a good agreement with the one, which have been observed for MOCVD-grown AlxGa1,xN alloys earlier. Grown layers had n-type electrical conductivity for the composition range up to x = 0.4. The layer became highly resistive for higher AlN contents. First results on 40 µm thick crack free AlGaN growth on SiC substrates are reported. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]