Reaction kinetic phase diagram

Glass transition determinations Decomposition reaction Reaction kinetics Phase diagrams Dehydration reactions Solid-state reactions Heats of absorption Heats of reaction Heats of polymerization Heats of sublimation Heats of transition Catalysis... 

This type of reaction represents the ultimate control solid-state synthetic chemists seek, namely, the bottom-up abUity to build a compound atom by atom. Harris et al. (2003) took advantage of the two dimensional nature of Bi2Te3 and TiTe2, such that their S5mthetic challenge was layer by layer. The secret to their success lies in the fact that two important principles control any synthetic efforts thermodynamics and kinetics. Phase diagrams, which are discussed in Chapter 11, owe allegiance to thermodynamics... 

Differential thermal analysis is the monitoring of the difference in temperature between a sample and a reference compound as a function of temperature. These data can be used to study heats of reaction, kinetics, phase transitions, thermal stabilities, sample composition and purity, critical points, and phase diagrams. 

Our principal goal in devising thermodynamic models for the chemical behaviour of crystalline solutions is to provide a realistic basis for the calculation of reaction equilibria, phase diagrams or reaction kinetics. We recognise in this that the activities of the chemical components of crystalline solutions are usually unequal to the mole fractions of those components, and we attempt in forming our models to express chemical activity as a fimction of composition and of some minimum number of additional variables, preferably not a function of composition. 

Nitrides, Phosphides, and Arsenides. The phase diagram for the Cr-N system between 900 and 1350°C has been constructed and thermodynamic relationships in this system have been calculated. These latter studies indicated the extreme sensitivity of the kinetics of Cr-N reactions to oxygen impurity. ... 

A final caveat that must be applied to phase diagrams determined using DFT calculations (or any other method) is that not all physically interesting phenomena occur at equilibrium. In situations where chemical reactions occur in an open system, as is the case in practical applications of catalysis, it is possible to have systems that are at steady state but are not at thermodynamic equilibrium. To perform any detailed analysis of this kind of situation, information must be collected on the rates of the microscopic processes that control the system. The Further Reading section gives a recent example of combining DFT calculations and kinetic Monte Carlo calculations to tackle this issue. 

Note that even in those cases where multiple compound layers were present at the A-B interface, two layers were dominating. For example, G. Hillmann and W. Hofmann and O. Taguchi et al. observed the formation of all six intermetallics shown on the equilibrium phase diagram in the reaction zone between zirconium and copper, with two Cu-rich compounds occupying more than 90 % of the total layer thickness and layer-growth kinetics deviating from a parabolic law. When investigating... 

Section 4.4 extends the proposed methodology to reactive membrane separation systems being controlled by vapor-liquid mass transfer and finite chemical reaction kinetics, simultaneously. For this general case the term kinetic arheo-trope is introduced for the singular points obtained in phase diagrams. 

At kinetically controlled reactive conditions (Da = 1), Fig. 4.28(b) shows that the stable node moves into the composition triangle, as in reactive distillation (Fig. 4.27(b)). This point is termed the kinetic arheotrope because its location in the phase diagram depends on the membrane mass transfer resistances and also on the rate of chemical reaction. The kinetic arheotrope moves towards the B vertex with increasing C-selectivity of the membrane. At infinite Damkohler number, the system is chemical equilibrium-controlled (Fig. 4.28(c)), and therefore the arheotrope is located exactly on the chemical equilibrium curve. In this limiting case, it is called a reactive arheotrope . 

Fig. 4 shows a simple phase diagram for a metal (1) covered with a passivating oxide layer (2) contacting the electrolyte (3) with the reactions at the interfaces and the transfer processes across the film. This model is oversimplified. Most passive layers have a multilayer structure, but usually at least one of these partial layers has barrier character for the transfer of cations and anions. Three main reactions have to be distinguished. The corrosion in the passive state involves the transfer of cations from the metal to the oxide, across the oxide and to the electrolyte (reaction 1). It is a matter of a detailed kinetic investigation as to which part of this sequence of reactions is the rate-determining step. The transfer of O2 or OH- from the electrolyte to the film corresponds to film growth or film dissolution if it occurs in the opposite direction (reaction 2). These anions will combine with cations to new oxide at the metal/oxide and the oxide/electrolyte interface. Finally, one has to discuss electron transfer across the layer which is involved especially when cathodic redox processes have to occur to compensate the anodic metal dissolution and film formation (reaction 3). In addition, one has to discuss the formation of complexes of cations at the surface of the passive layer, which may increase their transfer into the electrolyte and thus the corrosion current density (reaction 4). The scheme of Fig. 4 explains the interaction of the partial electrode processes that are linked to each other by the elec-... 

The solid materials obtained by these methods are always governed by the general thermodynamic laws represented by the phase diagrams. In contrast, the methodologies included in the phrase Chimie Douce involve kinetic control of the solid synthesis when non-reversible reactions are used. Therefore, solids prepared by this route are not the most... 

The enormous variety of possible surface reactions still reveals many open questions regarding exact reaction pathways, kinetics, and/or structural iirformation. The seemingly simple water formation reaction from H2 and O2 over a Pt-catalyst already shows many different reaction pathways. Regarding this reaction, we have performed periodic DFT calculations and thermodynamic considerations to evaluate the corresponding (a,7 ,A(zi)-surface phase diagram for Pt(lll) on contact with an aqueous electrolyte. Our work determined that below 0.95 V no stable and ordered oxygen overlayer forms, and that between 0.95 and 1.20 V the... 

Finally, the inexperienced reader should note that phase equilibrium diagrams only tell what will eventually happen—at equilibrium. These diagrams do not contain information relating to the kinetics of the reactions. In general, however, reactions involving alkali oxides are relatively fast for ceramic systems. If, for example, the phase diagram reveals liquid... 

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