摘要:

AbstractIn cholesteric liquid crystals with high chirality up to three thermodynamically stable blue phases (BPI, BPII and BPIII) occur in a narrow temperature range below the isotropic phase. The BPI and BPII are characterized by a three‐dimensional helicoidal structure of cubic symmetry with lattice constants of the order of several hundred nanometers.An applied electric field causes a i) change of the BP lattice constants(electrostrictive effect)and ii) a field‐induced birefringence(electrooptical effect).At high fields, new field‐induced phases with different symmetries compared to the zero field blue phases were observed.To get further informations about the molecular arrangement within the blue phases, the electrooptical effect has been studied with a modified microscope‐interferometer in BPs of systems with positive and negative dielectric anisotropy. For the first time an electrooptical effect has been observed also in field‐induced bl

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990602

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe time evolution of oxygen stoichiometry profiles in Fe‐doped SrTi03single crystals has been detected and analyzed in‐situ using an optical absorption technique. The profiles can be fitted according to Fick's second law by a constant chemical diffusion coefficient. The data obtained are in good agreement with earlier results from integral detection techniques and can be quantitatively understood by including the influence of internal coupling reactions to bare ambipolar transport via short range interact

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990603

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractKnudsen cell mass spectrometry has been employed to investigate thermodynamically the fcc solid ternary Fe1‐x(Ni0.86Cr0.14)xalloys. The “Digital Intensity‐Ratio” (D.I.R.)‐method has been applied for the determination of the thermodynamic excess properties. Fcc solid ternary Fe1‐x(Ni0.86Cr0.14)xalloys are characterized by negative molar excess Gibbs energies GE, negative molar excess entropiesSE, and exothermic molar heats of mixingHE. At 1673 K the minimumHEvalue is ‐2830 J/mol (28 at.% Fe), the minimum GEvalue is ‐2390 J/mol (29.5 at.% Fe), and the minimum SEvalue is ‐0.27 J/(mol K) (28 at.% Fe). At 1673 K the thermodynamic activities of Fe show slight negative deviations from the ideal behavior for alloys with a Fe‐content of less than 70 at.%, and ideal behavior for the Fe‐

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990604

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe thermodynamic parameters for solution of hydrogen at infinite dilution and the (a+B) plateau thermodynamic properties for hydrogen absorption at moderate temperatures for a series of Pd‐based f.c.c binary alloys with relatively low solute metal content have been correlated from the viewpoint of whether the alloy lattice is expanded or contracted to parent Pd lattice. Newly determined data for Pd‐Zn, Pd‐Sb, Pd‐Bi, Pd‐Cr, Pd‐Mo and Pd‐Mn alloys are included. When alloys with solute metals in the same groups are compared, the lattice parameters of Pd binary alloys with the 4 d and 5 d transition elements are, in general, larger than those with the 3 d elements. The relative partial molar enthalpy, ΔH0H, at infinite dilution becomes more exothermic with an increase of lattice parameter for the lattice‐expanded alloys with the exception of Pd‐Pt alloys. Conversely, for contracted alloys, with the exceptions of Pd‐Li, Pd‐Zn, Pd‐Al and low Ti content Pd‐Ti alloys, the enthalpy becomes less exothermic with increasing lattice contraction. The dilute phase solubility at the same temperature as reflected by the relative chemical potential of dissolved hydrogen at infinite dilution, Δμ0H, increases with increasing lattice expansion for the expanded alloys, with the exceptions of Pd‐Pt and Pd‐Nb (Ta), whereas for the contracted alloys, the solubility decreases with increasing lattice contraction, with the exception of the Pd‐Li alloys. The standard free energy change, ΔG0plat'for B‐hydride formation in the expanded alloys decreases with increase of lattice expansion with the exceptions of the Pd‐Pt, Pd‐Zr, Pd‐Sb, Pd‐Nb(Ta) and Pd‐Mn alloys. For the contracted alloys, the B‐hydride becomes less stable with increasing lattice contraction except for the Pd‐Li alloys. The isobaric hydrogen solubilities in Pd alloys at relatively high pressures may be attributed to the influence of the solute metal atoms on the Pd band structure and to the exclusion of H from site occupation due to solute atoms in the nearest neighbor shells; both of these effects are i

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990605

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reorientational behaviour of cyclohexane molecules in the rotator phase has been investigated with a Monte Carlo simulation on a system of 108 molecules in a cubic box with periodic boundary conditions. Different starting configurations have been tested, including also a special model where the molecules are aligned parallelly to the four cubic threefold axes. This model is characterized by a low potential energy. The discrete molecular orientations of this model are maintained at 195 K, that is, in the immediate neighbourhood to the low‐temperature solid II‐solid I transition. At higher temperatures no preferred orientations can be detected, irrespective of the employed starting set up. Both the molecular three‐fold axes and the angles between them of neighbouring molecules are distributed randomly. Therefore the Frenkel model of a discrete number of preferred orientations is disco

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990606

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electrical double layer at Au(100) and Au(111) electrodes in acetonitrile containing tetraethylammoniumper‐chlorate (TEAP) was studied by means of differential capacitance and in‐situ FTIR spectroscopy measurements. For both surfaces, a preponderant capacitance maximum was observed at a positive charge of about 8 μC cm−2. Two types of acetonitrile molecules were identified in the interfacial infrared spectra. One of these concerns adsorbed acetonitrile with a strongly blue shifted vCN mode at 2337 cm−1. The potential dependence of the spectra provides a clear evidence for dielectric saturation of the solvent and specific adsorption of the ions at large electrode charges. The spectra also indicate that the maximum ability of the solvent to reorientate in the interfacial field is in an adsorption geometry with the molecular axis inclined with respect to the surface. The data are discussed in context of the current models of the double layer, and compared with the related literature data obtained in an aqueous ele

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990607

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe particle size distribution function and the total number of stable clusters formed at solid surfaces during the initial stage of the CVD process, have been modeled. This is done on the basis of a kinetic scheme for nucleation in which the elementary steps are the attachment and the detachment of monomers to and from the clusters. The model is solved in terms of the eigenvalues of the associated kinetic matrix. It is shown that the microscopic growth law of the nucleus directly stems from the kinetics through the rate constants for monomer addition to the nucleus. A relationship between the particle size distribution function and the nucleation kinetics is derived that is used to process experimental data on the size distribution of diamond crystallites at the Si substrate. The overall activation energy for nucleation is obtained from the Arrhenius plot of the eigenvalues extracted from the experimental kinetics. The rate equation approach shows that the observed induction period of the nucleation kinetics can indeed be related to the dimension of the nuclei.

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990608

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractExperimental evidence is presented demonstrating that the slowing down of the diffusion process in binary liquid mixtures with a miscibility gap approaching the temperature of phase separation at constant noncritical composition and approaching the critical point along the liquid/liquid coexistence curve is caused by an increase of the correlation length of local composition fluctuations. This conclusion is drawn from dynamic light scattering data obtained with the system 2‐butoxyethanol/water in the vicinity of its lower critical point. The (hydrodynamic) correlation length is calculated from the diffusion coefficient data in combination with viscosity data taken from the literature using the analogue of the Stokes‐Einstein relat

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990609

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe method of scavenging free radicals sampled through a rarefied free‐jet from stationary low‐pressure high‐temperature reaction systems (flames, pyrolysis) in the condensed phase of dimethyl disulfide (DMDS) has been studied systematically. For this purpose the flat open condensing device originally used has been replaced by a condensation trap consisting of two stainless‐steel hemispheres cooled with liquid nitrogen. The scavenging products were separated and identified by GC/MS. The condensing efficiencies of the scavenger DMDS and condensable substances from the reaction system were so determined as to make the scavenging R+CH3SSCH3RSCH3+CH3S a quantitative method of radical analysis. It is shown that with a sufficient excess of DMDS the scavenging reaction takes place to 90‐100% for hydrocarbon radicals with two or more C atoms, with a slight interference from addition reaction of radicals to condensable unsaturated products from the reaction system. The type of reactions with mono‐ and divalent radicals and carbenes in the solid DMDS matrix are investigated. Consecutive reactions during warming‐up are also studied and discussed. It is stated that this scavenging method is well suited for the analysis of all hydrocarbon radicals heavier than ethyl, provided that the scavenging products can be separated and identified, which might become a problem with heavy polycyclic arom

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990610

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reactions of NH2(X̄2B1) with the hydrocarbons methane (1), ethane (2) and propane (3) were investigated behind incident shock waves at temperatures between 1500 K and 2100 K. The decay of NH2was measured by laser absorption. NH2was formed by the thermal decomposition of hydrazine. The following rate constants were obtained for the temperature range mentioned:k1= (1.2±0.6)·1013exp(‐(63.4±3.4) kJ/mol/RT) cm3mol−1s−1k2= (9.7±0.3)·1012exp(‐(48.0±1.8) kJ/mol/RT) cm3mol−1s−1k3= (1.7±0.4)·1013exp(‐(44.6±2.0) kJ/mol/RT) cm3mol−1s−1.These measurements extend the results obtained at low temperatures by Demissy and Lesclaux (330 K–250 K) and by Hack et al. (400 K–1080 K) into the range of interest for combustion processes.The apparent energies of activation fit rather well into an Evans Polanyi plot. They correlate with the energies of activation of the corresponding reactions of OH(X2II)

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990611

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1995

数据来源: WILEY