Search results for "Chemical potential"
showing 10 items of 21 documents
Studies of the Phosphatization of Steel and its Corrosion Products
1986
The reaction of phosphoric acid with steel is a basic process in many technological procedures. A typical example is the pretreatment of steel surfaces for the application of coatings. The aim of the treatment is to clean the surface, to produce a homogeneousr tight, and smooth cover and to provide a reliable adhesion between the steel substrate and the coating. This example points out that the phase composition of the layer formed is of great interest, and that reactions with residues on the surface, such as oxides and corrosion products, have to be considered, too. The same holds for phosphate layers formed in order to modify the mechanical or corrosion behavior of steel surfaces. Because…
Electrochemically shape-controlled transformation of magnetron sputtered platinum films into platinum nanostructures enclosed by high-index facets
2017
Abstract A new method based on transformation of magnetron sputtered platinum thin films into platinum nanostructures enclosed by high-index facets, using electrochemical potential cycling in a twin working electrode system is reported. The controllable formation of various Pt nanostructures, described in this paper, indicates that this method can be used to control a selective growth of high purity Pt nanostructures with specific shapes (facets or edges). The method opens up new possibilities for electrochemical preparation of nanostructured Pt catalysts at high yield.
Excitation levels and magic numbers of small parahydrogen clusters (N⩽40)
2008
The excitation energies of parahydrogen clusters have been systematically calculated by the diffusion Monte Carlo technique in steps of one molecule from 3 to 40 molecules. These clusters possess a very rich spectra, with angular momentum excitations arriving up to L=13 for the heavier ones. No regular pattern can be guessed in terms of the angular momenta and the size of the cluster. Clusters with N=13 and 36 are characterized by a peak in the chemical potential and a large energy gap of the first excited level, which indicate the magical character of these clusters. From the calculated excitation energies the partition function has been obtained, thus allowing for an estimate of thermal e…
A thermodynamical model of inhomogeneous superfluid turbulence
2007
In this paper we perform a thermodynamical derivation of a nonlinear hydrodynamical model of inhomogeneous superfluid turbulence. The theory chooses as fundamental fields the density, the velocity, the energy density, the heat flux and the averaged vortex line length per unit volume. The restrictions on the constitutive quantities are derived from the entropy principle, using the Liu method of Lagrange multipliers. The mathematical and physical consequences deduced by the theory are analyzed both in the linear and in the nonlinear regime. Field equations are written and the wave propagation is studied with the aim to describe the mutual interactions between the second sound and the vortex t…
Thermodynamics of Electrochemical Systems
2004
A discussion of the fundamentals of thermodynamic theory describing electrochemical systems is presented. The basic relationships are deduced as properties of the electrochemical potential. The theory introduces an observable electric potential that is defined at every position within the electrochemical system as the potential of a reversible electrode placed there. To provide a good test of the formalism, five systems have been studied including equilibrium and nonequilibrium. The formalism emphasizes the advantages of the electric current density in order to characterize one of the degrees of irreversibility and the electrical equilibrium. Finally, the electrostatic potential is discusse…
Ion transport through polyelectrolyte multilayers under steady-state conditions
2004
Abstract The permeability of a self-assembled polyelectrolyte multilayer to small ions under the influence of an applied potential difference is studied as a function of the number of layers and the nature of the supporting electrolyte. The multilayer is described as a series of homogeneously charged membranes with alternating sign of their fixed charge. Ion transport is described on the basis of the diffusion equation and the assumption of (Donnan) electrochemical equilibrium at the boundaries between layers. The calculated steady-state current–voltage curves are found to be in good agreement with experimental linear sweep voltammograms (at low sweep rate). The permeability of polystyrenes…
Measurement of higher cumulants of net-charge multiplicity distributions in Au+Au collisions at √sNN = 7.7-200 GeV
2016
We report the measurement of cumulants (Cn,n = 1,...,4) of the net-charge distributions measured within pseudorapidity (|η| < 0.35) in Au + Au collisions at √sNN = 7.7–200 GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g., C1/C2, C3/C1) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmono…
Entropy theory and glass transition: A test by Monte Carlo simulation
1997
This article reviews the results of a test of the Gibbs-DiMarzio theory by Monte Carlo Simulation. The simulation employed the bond-fluctuation model on a simple cubic lattice. This model incorporates two kinds of interactions: the excluded volume interaction among all monomers of the melt and an internal energy of the chains, which favors large bonds and makes the chains stiffen with decreasing temperature. The stiffening of the chains leads to an increase of their volume requirements, which competes with the packing constraints at low temperatures. This competition strongly slows down the structural relaxation of the melt and induces the glassy behavior. The model therefore takes into acc…
Garnet as a monitor for melt–rock interaction: Textural, mineralogical, and compositional evidence of partial melting and melt‐driven metasomatism
2021
International audience; In this study, we focus on a partially melted garnet-bearing granulite from the Salvador–Esplanade Belt (Salvador da Bahia, Brazil), and examine the behaviour of major and trace elements during partial melting and melt-driven metasomatism. Phase equilibria modelling and U–Th– Pb geochronology show that the sample underwent partial melting during the heating segment of the decompression path from ~1.2 GPa and 675–700° C to ~0.8 GPa and 790°C at c. 2.06 Ga. During the final stage of decompression, from 0.8 to ~0.5 GPa, physical segregation of melt resulted in the establishment of chemical potential gradients and mass transfer between the host granulite and the leucosom…
Polysubstituted ferrocenes as tunable redox mediators
2018
A series of four ferrocenyl ester compounds, 1-methoxycarbonyl- (1), 1,1’-bis(methoxycarbonyl)- (2), 1,1’,3-tris(methoxycarbonyl)- (3) and 1,1’,3,3’-tetrakis(methoxycarbonyl)ferrocene (4), has been studied with respect to their potential use as redox mediators. The impact of the number and position of ester groups present in 1–4 on the electrochemical potential E1/2 is correlated with the sum of Hammett constants. The 1/1+–4/4+ redox couples are chemically stable under the conditions of electrolysis as demonstrated by IR and UV–vis spectroelectrochemical methods. The energies of the C=O stretching vibrations of the ester moieties and the energies of the UV–vis absorptions of 1–4 and 1+–4+ c…