Neighbouring phase

In order to make compatible the variation of the E (r)-modulus with its neighbour phases, this modulus should be expressed by three terms i.e. 

Points hilling directly on the phase boundaries represent conditions which require that two neighbouring phases coexist at equilibrium ... 

The backscattered electron yield increases significantly with atomic number Z. In other words, on a backscattered electron image, the higher the atomic number, the brighter the phase will appear. Contrast is obtained if the mean atomic numbers of 2 neighbouring phases differ by more than 0.05 Z, the mean atomic number of a phase being calculated from the mass concentration of its various constituents by the formula Z TC, Zj. 

If a phase is unstable with respect to phases infinitesimally different from it, then it will disappear and give rise to one or more neighbouring phases. This process will be repeated until we arrive at a phase which is stable with respect to adjacent phases. In fact, since all matter undergoes molecular fluctuations, small amounts of phases infinitesimally different from the initial phase will be formed continuously, and so by means of such fluctuations, the system will be transformed spontaneously into a perturbed state. If a phase is not stable with respect to the perturbed state, then the phase will disappear. 

II is enriched with molecules, which have tetrahedrally ordered four nearest neighbours and up to 6 molecules in the first coordination shell. Phase III seems to be an analogue of HDA. Contrary to the phases I and II, first and second coordination shells of molecules in phase III is not clearly divided. Phases I, II and III are enriched with tetrahedrally ordered molecules. There is a noticeable drop of tetrahedral order in phase IV and it consists mainly of molecules with highly anisotropic distribution of the nearest neighbours. Phase IV may be considered as analogue of VHDA. 

Many physical and chemical processes occur at the boundary between two phases, while others are initiated at that interface. The change in concentration of a given substance at this interface as compared with the neighbouring phases is referred to as adsorption. Depending on the type of phases in contact, we can consider this process in the following systems liquid/gas, liquid/liquid, solid/liquid and liquid/liquid. Adsorption is also possible even between solid and solid materials [1]. 

The interface is a layer between two different phases of a composite material. The structure and composition of that particular layer, known as the interfacial transition zone (ITZ), depend on the properties of both neighbouring phases and also on conditions of mixing, hydration, curing and ageing of the materials. 

The interface in concrete is formed partly by two neighbouring phases or, more often, predominantly by one of them, but in this region strong... 

Chemical reactions have been observed at the surface of siliceous grains and limestone grains, but of a different origin in both cases. Due to the reactions, an interface layer is created in most cases and its properties are different from neighbouring phases. Besides moderate chemical reactions that improve bonding and help to increase the density of the interface, the alkali-aggregate reaction (AAR) may appear in certain conditions and in an extreme case it may ruin the material s structure. The nature and effects of AAR are described in Section 4.2.2. 

RS molecules are designed to accumulate at the interfaces forming a self-assembling layer there and to react with the neighbouring phases. Therefore these characteristics were analysed when the performance of the synthesised RS molecules were evaluated. The applicability of these new additives was tested in various types of polymer composites. The characterisation of the new systems was performed using methods of analytical and colloid chemistry. 

The increase of adhesion owing to the RS interfacial layer is reflected in the macroscopic properties of various multicomponent systems [3, 4, 10]. Direct verification of the chemical bonds between RS molecules and the neighbouring phases were carried out using X-ray photoelectron spectroscopy and DSC methods. These results have been published elsewhere [11]. 

Increase the adhesion at the interfaces through bonding the neighbouring phases to each other with chemical bonds. 

There are certainly more phases to be expected upon increasing the number of components. Simultaneously, however, will their stabihty be only marginally distinct from the neighbouring phases and their characterization will therefore more and more rely on high-resolution methods. 

Generally, the term adsorption is used to describe accumulation, i.e. a concentration rise close to a surface, or to an interface between neighbouring phases. In principle, the opposite of accumulation, i.e. the negative adsorption (depletion) of substances at a surface, also exists. However, this case is considered infrequently. 

The transitions between the blue phase region and its neighbouring phase, the cholesteric and the isotropic phase, are both of first order. The transitions between the various blue phases are weakly first order. 

It has also been noticed that within some temperature interval around the transition points and NI the two neighbouring phases are not strictly homogeneous, but each phase contains embryos of the other phase. The relative amount of the phase existing in an embryonic form remains very small up to temperatures very close to the transition point, but it is detectable by NMR. Figure 1 shows several proton NMR spectra of DDA9-L representative of (A) the isotropic phase with a small nematic fraction, (B) nematic phase with a small isotropic fraction (1-2 %), (C) pure nematic phase homogeneously oriented, (D) unoriented nematic phase, or solid phase above the cold crystallization temperature, (E) solid phase with some nematic fraction, and (F) solid phase near room temperature. It is interesting to note that the sharp peak at the centre of spectrum B, which could not be obtained in the line shape simulation procedure reported in... 

The text will have fulfilled its purpose in an ideal marmer, if it not only conveys to the reader the elegance and power of the defect concept, when it not only puts him or her in the position of being able to recognize the common aspects of different properties and processes such as doping and neighbouring phase effects, ionic and electronic conductivity, passivation and corrosion of metals, diffusion and reaction processes, synthesis kinetics and sintering kinetics in solids, electrode reactions and... 

We have previously established (i) that, at finite temperatures, ionic and electronic point defects are required as local chemical excitations at equiUbrium, (ii) that we can write ideal mass action laws in all cases for low concentrations of defects, and (iii) that we know what parameters influence our mass action constants. We can now turn to a specific consideration of defect chemistry. Let us consider first internal defect reactions and pure single crystals By internal defect reactions in pure substances we mean processes that occur as a consequence of nonzero temperature in the otherwise perfect crystal without neighbouring phases being involved. (For two of these reaction tjrpes, however, we will need surfaces as sinks or sources of monomeric units, i.e. of lattice molecules.) In binary systems such processes leave the composition within the sohd undhanged. If we refer to the Dalton composition , we also speak of the intrinsic case. 

Impurities are meant here (see Section 5.6). In AgCl or NaCl the equilibrimn with the neighbouring phase (treated in Section 5.5.2) signiffcantly affects — relatively speaking — only the electrons as minority defects, whose concentration is small with respect to that of the silver defects. However, the latter is relevant for the Sn02 example in Fig. 5.36. 

Moreover, it is possible to regard the interaction with Pb as a constituent of the neighbouring phase, in, for example, the form... 

To cut a long story short Provided internal defect-chemical equilibrium is established, it is sufficient to formulate a single reaction, that expresses the interaction of the neighbouring phase with the bulk, e.g. Eq. (5.98c). Naturally, if we have some knowledge of the material we will prefer the formulation that involves the major defects, i.e. those encountered in the majority in the material. 

Ch (x) = C (x). Typical potential differences are of the order of a few lOOmV. A value of 250 mV corresponds to a concentration influence of a factor e 10 at 300 K In ideally pine AgCI, for (x=0) — oo = 250mV, the number of interstitial ions at the contact is reduced by 4 orders of magnitude with respect to the bulk value of level 10 the vacancies are increased by 4 orders of magnitude. Naturally the value of the interfacial potential is determined by chemical interaction and, hence, will be strongly dependent on the neighbouring phase and on temperature. 

The last ( and actually redimdant) step is the interaction with the neighbouring phase (chemical process C ). Here we formulate the interaction with oxygen ... 

In the literature the interaction with the neighbouring phase, the differing thermostatics of the core and also the potential jump are usually neglected in the treatment of space charge chemistry. If, in such greatly simplified approximations, we allow s to approach zero, we obtain the results associated in the literature with the model of Poppel and Blakely [258], while additional neglect of the finite number of sites is associated with the model by Kliewer and Kohler [259]. In the latter case the... 

For Cv(x) and Ci(x) the parameter AG must be replaced by AG (= AG 2F( — (x))). In the case of bulk concentration the relevant potential difference is o - qq- Evidently it follows that a()G -I- aIg = AvG + AiG = ApGS, while the difference AvG - AiG is determined by ln(ao" Kog) and the space charge potential. The latter follows from the electroneutrality of the bulk, he. from Cvoo = Cioo. The effect of a neighbouring phase on the defect concentrations can be seen immediately from the above reactions. If 0" is stabilized by the neighbouring phase there is a tendency for [Vb(x)l to increase and for [0( (x)] to get smaller. In Kliewer s approximation og and ao" are tacitly taken as constant and these can be included in the AG values. The result is then a relationship of the form (5.256). The sum of these AG values is then again ApG°, while the difference is given directly by 2zF( — 4>oo)- This consideration also applies if there are additional vacancy defects in the core. It is important that the definition of the AG -values refers to the same defect species. 

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