摘要:

AbstractWhen lead chloride is deposited onto substrates at temperatures below 150 K, a non‐crystalline film is formed. This material crystallizes at temperatures above 260 K, as could be demonstrated by UV‐VIS‐spectroscopy. In order to determine whether or not the deposited material consists of extremely small crystals with a high degree of disorder or of a genuine amorphous phase, it was investigated by electron diffraction. We describe the procedure which we applied for the determination of the elastically scattered intensity as a function of the scattering vector. From this function, the reduced radial distribution function was determined. The results were compared with those reported about crystalline and molten lead chloride. The short range order in the cold condensed material is different from that in the crystal and that in the melt. Hence, cold condensation of lead chloride leads to the formation of an ionic

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980602

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe vapor pressure of liquid PCl3was determined by the Knudsen effusion method. The pressure was found to follow the relation log10P[kPa]= −1800/T+7.371 between 240 and 278

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980603

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe prediction of Vapor‐liquid Equilibrium data (VLE) from excess enthalpy data (HE) for alkanol/alkane mixtures by means of the Hanks‐Gupta‐Christensen (HGC) method is examined. The Extended Real Associated Solution model (ERAS) for the excess Gibbs energy which combines the Kretschmer‐Wiebe linear association model with Flory's equation of state for chainlike molecules is used. In this prediction, the parameters of the ERAS model are evaluated by fitting the experimentalHEdata to the algebraic equation for theHEof this model. Results from this study indicate that the ERAS model leads to VLE predictions which are more accurate than those previously obtained when the HGC method was used in conjunction with the Continuous Linear Association model or the Wiehe‐Bag

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980604

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

年代:1994

数据来源: WILEY

摘要:

AbstractNMR spin‐lattice relaxation timeT1and phase diagrams of deuterosubstituted tetrahydrofurans (THF‐hg, THF‐h4d4, THF‐d8) in D2O and D2O/salt (Salt = MeCl, Me = Na, K, Rb, Cs; CaCl2, AlCl3; MeOH, Me = Na, K) mixtures have been studied close to their lower critical solution points. It has been found that deuteration of THF leads to a shrinkage of the closed‐loop phase diagram THF‐h8‐xdx/D2O. It is an opposite and much stronger effect to the well‐known replacement of H2O by D2O in the system THF‐h8/H2O (D2O). The lower and the upper critical solution points (TC,L,TC,U) shift from 63.7 °C and 143.5 °C in THF‐h8/D2O to 84.5 °C and 128.5 °C in THF‐h4d4/D2O respectively, and they disappear in THF‐d8/D2O mixtures. This phenomena has been studied by precise (±0.01 °C) measurements of dependencies ofT1(2H) of THF and D2O deuterons on temperature. An increase of activation energies (Ea) of reorientational motion of THF‐d8has been found by introduction of ions into the solutions. The theoretical modeling of phase diagrams using renormalization‐group and decorated lattice methods shows that the observed changes ofTC,Lcan not be considered as a pure energetical effect where onlyEachanges due to additional interaction of polar molecules with the electric field of ions. The entropic contribution, viz. the appearance of additional orientations has

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980605

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

年代:1994

数据来源: WILEY

摘要:

AbstractCrystal structures of chloral 4‐bromo‐, 4‐methyl‐, 2,4‐dichlorobenzylhemiacetals, and iso‐butylhemiacetal were determined by the single crystal X‐ray method at room temperature. Two modifications were found for the 2,4‐dichlorobenzyl derivative. A chiral chain of molecules formed by OH … O hydrogen bonds (H‐bonds) along a 21axis is common to the crystals studied, except for iso‐butyl derivative where a centrosymmetric dimer is formed by H‐bonds. Conformation analyses were made using molecular mechanics. The crystal structures and IR spectra indicated that the H‐bonds in these crystals except for the 2,4‐dichlorobenzyl derivate were bifurcated ones. An intramolecular OH…Cl interaction was found in the iso‐butyl derivative. The relationship between the35Cl NQR spectrum and the mo

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980606

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe nuclear spin‐lattice relaxation times of14N have been measured as a function of temperature for liquid 3,5‐dimethylpyridine. These results together with the values of the13C spin‐lattice relaxation times and the factor of nuclear Overhauser enhancement for the ring C2,6and C4carbons presented previously [15], have been analyzed in terms of relative influence of molecular shape and attractive dipolar forces on anisotropy of the molecular reorientations. Principal components of the rotational diffusion tensor have been deter

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980607

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe method of the Pendant Drop or Standing Bubble is applied to measure interfacial tensions between water and nonpolar fluids to high temperatures and pressures. The high pressure cell with two sapphire windows and the auxiliary equipment with several feed autoclaves is described. The shapes and sizes (about 2 mm) of drops and bubbles are recorded with microscope and video camera. A digital image processing procedure was developed which permits fast, objective and precise determination of the contour parameters.The six gases helium, neon, argon, nitrogen, methane, and propane have been investigated to 473 K (with nitrogen to 573 K) and (in part) to 2800 bar. Gas densities came close to liquid density values. For comparison, water plus liquid n‐hexane, n‐decane, and toluene was investigated to 473 K and 3000 bar. For these liquid hydrocarbons, the interfacial tensionγalways increases with pressure. At 373 K for water‐n‐hexaneγis 41.8 mN/m at 100 bar and 47.3 mN/m at 2600 bar, respectively. In the water‐gas systemsγdecreases with pressure and passes through a flat minimum around 1000 bar. For water‐nitrogen at 373 K γ = 52.5, 46.5 and 48.3 mN/m at 200, 1400 and 2800 bar. Only with water‐heliumγincreases continuo

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980608

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

年代:1994

数据来源: WILEY

摘要:

AbstractIt has been shown that the trans‐gauche rearrangement of the CH2OH group and the jump motion of an OH group proton between two equilibrium sites in a hydrogen bond are the motions contributing to the observed proton spin‐lattice relaxation times of anhydrous polycrystalline α‐D

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980609

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

年代:1994

数据来源: WILEY

摘要:

AbstractSelf‐diffusion coefficients of urea have been measured at 25.0 °C in aqueous solutions and in mixtures of water with 1‐propanol, as a function of the urea concentration and of the mixed solvent composition. The hydrodynamic radius of urea has been calculated. It has been found that both in aqueous solutions as well as in 1‐propanol‐water mixtures dimers of urea, if they exist, do not play any role in the diffusion processes. Diffusion is, however, a collective process and motions of urea depend on the numbers of neighbours, therefore they are very sensitive on the structure of the solvent. The results have also confirmed the previous supposition that urea does not affect the water structure, but it does fit the water structure quite well. It has been also found that the solvation of urea is determined by the structure of the mixed

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980610

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe electrooxidation behaviour of anthracene and 9,10‐diphenylanthracene on poly(vinylferrocenium) coated Pt electrodes was investigated and compared with that on uncoated Pt surface using cyclic voltammetry in acetonitrile/0.1 M TBAP solutions. IR spectroscopy was used to detect the changes occurring in the structure after the electrode reaction. The formation of the quinone and hydroxy substituted type products was revealed if the electrode potential was cycled between + 1.50 and 0.00 V. The catalytic oxidation of anthracene rings were observed if the potential cycling was kept between + 1.50 V and −2.3

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980611

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

年代:1994

数据来源: WILEY