ISSN:0005-9021    

DOI:10.1002/bbpc.19900940602

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn this review the physico‐chemical fundamentals of the atmospheric corrosion of iron are discussed, as they result from a number of electrochemical and spectroscopic techniques, which have been applied in order to analyze the corrosion mechanism of the atmospheric corrosion during wet‐dry‐wet transitions. — Afterwetting a dry corroded metal surfacethe cathodic partial reaction of the corrosion process is given by the reduction of Fe3+‐ to Fe2+‐states within the lattice of γ‐FeOOH. If the corrosion potential is rather negative, then also magnetite is formed. As a consequence of the formation of Fe2+states the electronic conductivity of oxide crystals close to the metal/oxide interface is increased. This results in an acceleration of the kinetics of the oxygen reduction. It could be shown, that oxygen is reduced predominantly at the oxide/electrolyte and not at the metal/electrolyte interface and therefore the rate of the oxygen reduction is determined by the electronic properties of the oxide crystals, the kinetics of the electron‐transfer reaction being very fast at oxides, which are highly doped with Fe2+states. If themetal surface is covered with a thick electrolyte layer, then the charge transfer reaction is so fast within the reduced oxide scale, that the overall rate of the oxygen reduction is given by the diffusion of oxygen through the water filled pore system of the scale and by the surface area of the highly doped oxide scale, which allows an electron transfer to occur at the oxide/electrolyte interface. The size of this effective surface area is determined by the amount of the reduction of the oxide scale immediately after wetting the dry metal surface.During drying, oxygen diffuses rapidely into the pore system of the oxide scale by gas diffusion. Then the corrosion rate is increased dramatically due to the fast oxygen reduction at the electron‐conducting large surface area oxide cathode. Due to the fast corrosion a dense oxide layer is formed on top of the metal surface and the surface is passivated. The corrosion stage of drying is terminated by a reoxidation of the oxide scale by oxygen, which causes the rate of the oxygen reduction to decrease as the electronic conductivity of the oxid

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940603

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe kinetics of the reaction between ethoxy (C2H5O) radicals and O2have been studied using a combined laser photolysis/LIF technique for the generation and detection of C2H5O. In the temperature range 295–411 K the rate coefficient has been found to be.Product investigations using a chemical titration of HO2by NO and subsequent quantitative detection of OH by LIF indicate the dominance of the HO2formation channel, viz.with ϕ HO 2= 0.89 (−0.12+0.22). Energy correlations show that these products are formed by a direct metathesis reaction only. It is suggested, that the low pre‐exponential factor in the Arrhenius expression may be the result of a more complex than linear configuration of the moiety in the transition state and/or of

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940604

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe reactions of CH2(ã1A1) with CH3C2H, HCN, CO2, N2O and COS are investigated at room temperature. CH2(ã1A1) is generated by pulsed laser photolysis of CH2CO. Overall removal rate constants are derived from concentration profiles under first order reaction conditions using direct, time resolved LIF detection of CH2(ã1A1). The second order rate constants are found in units of 1013cm2/mol s to be 24, 18, 2.0, 3.8 and 20, respectively. — The contributions of physical quenching to the removal of CH2(ã1A1) are determined by monitoring directly the formation of CH2(X̃3B1) with the LMR absorption technique. The branching ratios of collision induced intersystem crossing versus total consumption of1CH2are 0.24, 0.32, 0.67, 0.46 and 0.29 for the five rea

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940605

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

年代:1990

数据来源: WILEY

摘要:

AbstractWe consider the autocatalytic synthesis of MDV‐1 RNA by Q beta replicase, which proceeds by template‐instructed replication. We predict the effect of a particular point mutation in the sequence on the overall doubling time and conjecture its role on the recognition step. The mutation considered destabilizes the folding of the internal recognition site. The theoretical analysis is based on the calculation of nonequilibrium re‐folding events which occur in the RNA chains as they are being synthesized. Free‐energy minima are irrelevant. In order to test the theoretical findings, we incubate both the natural template and the mutant simultaneously, in the presence of the replicase. The experiment reveals that the mutation facilitates the enzyme‐template interaction, thus enhancing recognition. However, examining the exponential phase of the replication kinetics, where the enzyme is in large excess with respect to the RNA species, we can conclude that the mutant presents a larger overall doubling time, in good agreement with our theoretical

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940606

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

年代:1990

数据来源: WILEY

摘要:

AbstractPartition of 2‐butanol, water, NaCl and KCl between the aqueous and alcoholic phases at 298.15 K is considered. Extraction of chlorides is represented as a formation of partially dissociated complexes in the alcoholic phase. The equilibrium constant for formation of the Na+(2‐BuOH)2Cl−complex is 0.11 and for formation of the K+(2‐BuOH)2Cl−complex is 0.16. Detailed thermodynamic analysis of the investigated systems is presented by evaluating activities of components from the mass‐action and Gibbs‐Du

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940607

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

年代:1990

数据来源: WILEY

摘要:

AbstractA thermodynamic model of stepwise hydration of ions in aqueous solutions has been developed. It is applied to the activity and osmotic coefficients of the alkali halogenides at 25°C. The hydration at infinite dilution can be decomposed into ion specific contributions. Together with a distance of closest approach in the Debye‐Hückel term it is possible to describe the activity and osmotic coefficients within the experimental error limits up to 1 molal soluti

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940608

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe Debye‐Hückel theory, including a closest distance of approach between cations and anions, has been extended to ternary solutions of 1: 1 electrolytes. Together with a thermodynamic model of stepwise hydration this allows the calculation of the Gibbs energy of ternary solutions without any ternary mixing parameter. The agreement between theory and experiment is good up to 1 molal solutio

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940609

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

年代:1990

数据来源: WILEY

摘要:

AbstractPhotoetching of holographic gratings was performed on materials belonging to two families of compounds, exhibiting bidimensional and tridimensional structures. Fringes of poor quality only could be obtained on the Van der Waals face of quasi‐two dimensional (layered) semiconductors due to their high resistance to photocorrosion (WSe2), or large diffusion length of minority carriers along this face (InSe), while good morphological and optical contrasts were obtained on the surface of II — VI semiconductors. — Using a laser scanning setup, the photoresponse of Schottky diodes which were made from these semiconductors was used to convert optical information into electrical signal. The photoetched part exhibits an improved photoresponse, which produces electrical contrast between the two parts. This observation is used to transform optical information into an electrical signal. The diffusion length of minority carriers was determined from this photocurrent profile. Some applications for this method for holography and for optical data recording and its retrieval are discussed. Guidelines for materials' selection for this kind of application are pro

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940610

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

年代:1990

数据来源: WILEY

摘要:

AbstractSynchrotron small angle X‐ray scattering (SAXS) measurements were performed on water/AOT/n‐hexane w/o microemulsions withw0( = [H2O]/[AOT]) values ranging from about 0 to 100. The volume fraction of solute and the temperature were varied in a wide range. The scattering behaviour (form and structure factor) could be explained on the basis of a pseudo hard sphere model, where the spheres were allowed to be spheroidally deformed to a certain extent. We have shown that these deformations become larger as the lower consolute point of the mixture is approached. Furthermore, we have demonstrated that the radius of gyration is temperature independent, and that it depends linearly onw0. Thew0‐dependence of the scattering intensity could be explained on the basis of the droplet

ISSN:0005-9021    

DOI:10.1002/bbpc.19900940611

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

年代:1990

数据来源: WILEY