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Thermodynamic phase

Both extreme models of surface heterogeneity presented above can be readily used in computer simulation studies. Application of the patch wise model is amazingly simple, if one recalls that adsorption on each patch occurs independently of adsorption on any other patch and that boundary effects are neglected in this model. For simplicity let us assume here the so-called two-dimensional model of adsorption, which is based on the assumption that the adsorbed layer forms an individual thermodynamic phase, being in thermal equilibrium with the bulk uniform gas. In such a case, adsorption on a uniform surface (a single patch) can be represented as... [Pg.251]

The thermodynamic phase stability diagrams appear to be preferred by corrosion scientists and technologists for the evaluation of gas-metal systems where the chemical composition of the gaseous phase consisting of a single gas or mixture of gases has a critical influence on the formation of surface reaction products which, in turn, may either stifle or accelerate the rate of corrosion. Also, they are used to analyse or predict the reason for the sequence of formation of the phases in a multi-layered surface reaction product on a metal or alloy. [Pg.1094]

A detailed explanation of the construction of thermodynamic phase stability diagrams may be found in References 22-25. In this section the basic principles of construction and interpretation for the specific situation of gas-metal equilibria will be addressed using a hypothetical system. [Pg.1114]

Table 7.37 Data for the construction of thermodynamic phase stability diagram M-S-0 at 1 000 K... Table 7.37 Data for the construction of thermodynamic phase stability diagram M-S-0 at 1 000 K...
Fig. 7.72 A thermodynamic phase stability diagram for Al-O-S species in the eqilibrium with liquid Na2S04 at 1 000°C as a function of the oxygen activity and the acidity of the salt (after... Fig. 7.72 A thermodynamic phase stability diagram for Al-O-S species in the eqilibrium with liquid Na2S04 at 1 000°C as a function of the oxygen activity and the acidity of the salt (after...
Fig. 7.79 Five possible reaction paths on a schematic thermodynamic phase stability diagram, and the corresponding distribution of phases in the reaction systems (after Stringer... Fig. 7.79 Five possible reaction paths on a schematic thermodynamic phase stability diagram, and the corresponding distribution of phases in the reaction systems (after Stringer...
Fig. 7.80 A schematic thermodynamic phase stability diagram for the A-C-O system, showing three reaction paths. Paths 2 and 3 are only possible if gaseous diffusion in pores in the oxide product results in a carbon activity increase through the scale, as shown in Fig. 7.81 (after... Fig. 7.80 A schematic thermodynamic phase stability diagram for the A-C-O system, showing three reaction paths. Paths 2 and 3 are only possible if gaseous diffusion in pores in the oxide product results in a carbon activity increase through the scale, as shown in Fig. 7.81 (after...
Let us mention some examples, that is, the passivation potential at which a metal surface suddenly changes from an active to a passive state, and the activation potential at which a metal surface that is passivated resumes active dissolution. In these cases, a drastic change in the corrosion rate is observed before and after the characteristic value of electrode potential. We can see such phenomena in thermodynamic phase transitions, e.g., from solid to liquid, from ferromagnetism to paramagnetism, and vice versa.3 All these phenomena are characterized by certain values... [Pg.218]

Passivation currents, fluctuations in, 293 Passivation potential, and thermodynamic phase formation, 218 Passive film... [Pg.636]

Thermal desorption spectra, 171 Thermodynamic equilibrium, phase transitions at, 219 Thermodynamic phase formation, passivation potential and, 218 Time resolved measurements in the microwave frequency range, 447 photo electrodes and 493 Tin... [Pg.643]

For two-phase flow, additional assumptions are made that thermodynamic phase equilibrium exists before and after the restriction (or expansion), and that no phase change occurs over the restriction. Romie (Lottes, 1961) wrote the equation for the momentum change across an abrupt expansion as... [Pg.241]

Fig. 21 Schematic summary of thermodynamic phase behaviour for neat, composition-ally symmetric PI-fc-PS-fc-PDMS (ISD) and PS-fc-PI-fc-PDMS (SID) terpolymers. Heating PI-fc-PS-fc-PDMS or decreasing molecular weight causes transition from three-domain lamellae to hexagonally packed two-domain cylindrical morphologies, followed by disordering. PS-fc-PI-fc-PDMS disorders directly from three-domain lamellar state. From [88], Copyright 2002 American Chemical Society... Fig. 21 Schematic summary of thermodynamic phase behaviour for neat, composition-ally symmetric PI-fc-PS-fc-PDMS (ISD) and PS-fc-PI-fc-PDMS (SID) terpolymers. Heating PI-fc-PS-fc-PDMS or decreasing molecular weight causes transition from three-domain lamellae to hexagonally packed two-domain cylindrical morphologies, followed by disordering. PS-fc-PI-fc-PDMS disorders directly from three-domain lamellar state. From [88], Copyright 2002 American Chemical Society...
Liquid crystals are thermodynamic phases composed of a great many molecules. These molecules, termed mesogens, possess a free energy of formation, of course. LCs (their structure, properties, everything that gives them their unique identity), however, are not defined at the level of the constituent molecules any more than a molecule is defined at the level of its constituent atoms. LCs are supermolecules. How do they differ from supramolecular... [Pg.460]

Figure 8.24 Illustration of layer structure and symmetries observed for NOBOW thermodynamic phase (majority domains) in freely suspended films, (a) Films of even-layer number have achiral, nonpolar C symmetry, (b) Films of odd-layer number have chiral and polar C2 symmetry, with net polarization normal to tilt plane (lateral polarization). Figure 8.24 Illustration of layer structure and symmetries observed for NOBOW thermodynamic phase (majority domains) in freely suspended films, (a) Films of even-layer number have achiral, nonpolar C symmetry, (b) Films of odd-layer number have chiral and polar C2 symmetry, with net polarization normal to tilt plane (lateral polarization).
This rather amazing result at first seems impossible. As indicated in Figure 8.37, the ShiCaPf structure is composed of heterochiral adjacent layer pairs. By pure symmetry it must be the case that the unichiral molecules have a lower free energy in either the (+) or the (—) layers. The free-energy difference between these diastereomeric layer structures could be small. But, the layers possess a collective free energy. A priori it is expected that the thermodynamic phase would possess only layers of the lower free-energy chirality. [Pg.514]

Most liquids respond to a temperature rise through a thermodynamic phase change to gas. For ignition to occur, the fuel concentration in air must be in a range that defines a flammable mixture. These bounding limits are commonly referred to as the lower flammability limit (LFL) and upper flammable limit (UFL). These are the lowest and highest fuel concentrations in air (by volume) that will support flame propagation. Fuel concentrations below the LFL or above the UFL are too lean or rich, respectively, and will not support combustion. [Pg.409]

Aging and nonequilibrium dynamics indicate but give by no means evidence for a thermodynamic phase transition at finite temperamre to a low-temperature... [Pg.228]

D. H. E. Gross, Microcanonical Thermodynamics, Phase Transitions in Small Systems, World Scientific Lecture Notes in Physics, World Scientific, Singapore, 2001. [Pg.114]

From a thermodynamic viewpoint, we may imagine that, in an actinide metal, the model of the solid in which completely itinerant and bonding 5 f electrons exist and that in which the same electrons are localized, constitute the descriptions of two thermodynamic phases. The 5f-itinerant and the 5 f-localized phases may therefore have different crystal properties a different metallic volume, a different crystal structure. The system will choose that phase which, at a particular T and p (since we are dealing with metals, the system will have only one component) has the lower Gibbs free-energy. A phase transition will occur then the fugacity in the two possible phases is equal e.g. the pressure. To treat the transition, therefore, the free energies and the pressures of the two phases have to be compared. We recall that ... [Pg.103]

Domarfska, U. and Bogel-Lukasik, R., Solubility of ethyl-(2-hydroxyethyl)-dimeth-ylammonium bromide in alcohols (C2-CJ2), Fluid Phase Equilib., 233, 220, 2005. Doman ska, U., Thermophysical properties and thermodynamic phase behavior of ionic liquids, Thermochim. Acta, 448,19, 2006. [Pg.62]

Domariska, U., Zolek-Tryznowska. Z., and Krolikowski, M., Thermodynamic phase behavior of ionic liquids, /. Chem. Eng. Data, 52, 1872, 2007. [Pg.65]

Three-component systems, or ternary systems, are fundamentally no different from two-component systems in terms of their thermodynamics. Phases in eqnilibrium must still meet the equilibrium criteria [Eqs. (2.14)-(2.16)], except that there may now be as many as five coexisting phases in eqnilibrinm with each other. The phase rule still... [Pg.165]

The above requirement implies that polymer fractionation by TLC is caused not by simple polymer precipitation but by thermodynamic phase-separation of... [Pg.194]

Semenova, M., Pavlovskaya, G., Tolstoguzov, V. (1991a) Light scattering and thermodynamic phase behaviour of the system 11S globulin - K-carrageenan - water. Food Hydrocolloids, 4, 469 179... [Pg.112]

Let us begin with a formal definition of thermodynamic phase ... [Pg.209]

Helium One could hardly imagine a simpler elemental substance than helium, which is viewed at the microscopic level as consisting of spherically symmetric closed-shell 2-electron atoms that interact most weakly of all known atoms. It is therefore surprising that helium exhibits thermodynamic phase behavior that is spectacularly unusual and perplexing. [Pg.226]

With the help of (12.89), it is now possible to establish some simple theorems concerning the possibility of stationary points (e.g., maxima, minima, or horizontal inflections) in thermodynamic phase diagrams. In each case, we suppose that Rh Rj are chosen from any set of/+l intensive variables (spanning at least/ — 1 dimensions), and that iy are... [Pg.416]


See other pages where Thermodynamic phase is mentioned: [Pg.412]    [Pg.1111]    [Pg.95]    [Pg.643]    [Pg.410]    [Pg.196]    [Pg.484]    [Pg.98]    [Pg.189]    [Pg.99]    [Pg.42]    [Pg.511]    [Pg.514]    [Pg.57]    [Pg.24]    [Pg.71]    [Pg.215]    [Pg.298]    [Pg.233]    [Pg.5]    [Pg.128]    [Pg.291]   
See also in sourсe #XX -- [ Pg.168 ]




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