Structure and phase formation

The effect of metal structure and phase formation on the kinetics of catalytic oxidation reactions was treated in detail by Savchenko et al. (see, for example, refs. 83, 84, 117 and 118). In metal surface layers both reconstruction of the metal proper (faceting) and processes associated with the formation of surface oxides can take place. In this case the first to form can be chemisorption structures (without breaking the metal-metal bond) and then the formation of two-dimensional surface oxides is observed. Finally, three-dimensional subsurface oxides are produced. An important role is played by the temperature of disordering the adsorbed layer. 

Levashov, E. A., Vijushkov, B. V, Shtanskaya, E. V, Borovinskaya, I. P., Ohyanagi, M., Hosomi, S., and Koizumi, M., Regularities of structure and phase formation of SHS diamond-containing functional gradient materials Operational characteristics of articles based on them. Int. J. SHS, 3,287 (1994). 

Mukasyan, A. S., Structure- and phase-formation of nitrides in SHS processes. D.Sc. Dissertation, Institute of Structural Macrokinetics, Russian Academy of Science (1994). 

Mechanism of Structure and Phase Formation of Silicon Nitride during Combustion of Ferrosiiicon in Nitrogen... 

Yuan Q, Deshinane C, Pesacreta T C and Misra R D K (2008) Nanoparticle effects on spherulitic structure and phase formation in polypropylene crystallized at moderately elevated pressures The influence on fracture resistance. Mater Sci Eng A480 181-188. 

We start with some elementary information about anisotropic intermolec-ular interactions in liquid crystals and molecular factors that influence the smectic behaviour. The various types of molecular models and commonly accepted concepts reproducing the smectic behaviour are evaluated. Then we discuss in more detail the breaking of head-to-tail inversion symmetry in smectic layers formed by polar and (or) sterically asymmetric molecules and formation of particular phases with one and two dimensional periodicity. We then proceed with the description of the structure and phase behaviour of terminally fluorinated and polyphilic mesogens and specific polar properties of the achiral chevron structures. Finally, different possibilities for bridging the gap between smectic and columnar phases are considered. 

Figure 8.20 Structure and phase sequence of prototypical bent-core mesogen NOBOW (8) are given, along with space-filling model showing one of many conformational minima obtained using MOPAC with AMI force field. With observation by Tokyo Tech group of polar EO switching for B2 smectic phases formed by mesogens of this type, banana LC field was bom. Achiral, polar C2v layer structure, with formation of macroscopic spontaneous helix in polarization field (and concomitant chiral symmetry breaking), was proposed to account for observed EO behavior.

The problem of a priory assessment of stable structure formation is one of the main problems of chemical physics and material science. Its solution, in turn, is directly linked with the regularities of isomorphism, solubility and phase-formation in general. Surely, such problems can be cardinally solved only based on fundamental principles defining the system of physical and chemical criteria of a substance and quantum-mechanical concepts of physics and chemistry of a solid suit it. 

At present the iron-based alloys diffusion saturation by nitrogen is widely used in industry for the increase of strength, hardness, corrosion resistance of metal production. Inexhaustible and unrealized potentialities of nitriding are opened when applying it in combination with cold working [1-3], It is connected with one of important factors, which affects diffusion processes and phase formation and determines surface layer structure, mechanical and corrosion properties, like crystal defects and stresses [4, 5], The topical question in this direction is clarification of mechanisms of interstitial atoms diffusion and phase formation in cold worked iron and iron-based alloys under nitriding. 

There have been few Raman investigations of catalyst preparation (of oxides, zeolites, or metals). Such experiments deliver information about molecular structures, and the formation of crystalline phases is detected at earlier stages by Raman spectroscopy than by XRD. Moreover, cells that allow for variable conditions are easily constructed. 

Ligands such as ammonia, amines, and polyhydric alcohols may be exchanged between an external aqueous phase and resins carrying ions capable of forming coordination complexes, thus providing a powerful technique for studying complex ion structure and complex formation equilibria. 

In this chapter, developments in the understanding of mullite over the last few decades are reviewed. A discussion of crystal structures and phase stability is presented to provide the reader with an overview of certain characteristics of this material. The next part of this chapter examines the effect of process chemistry on the synthesis and microstructure of mullite. The role of various synthetic methods that are used to modify mullite formation will be discussed, followed by a compilation of selected materials properties. 

The characteristic of datum (1) shows the shock effects on the starting graphite that resulted in more graphitized structures and diamond formation [25]. The datum (2) shows that the lattice strain in postshock sample II is more severe than that in postshock sample I. The data (3) and (4) suggest that defects play an important role in phase transition of graphite to diamond because the appearance of the diffraction line at 43.88° corresponds to the (111) reflection of diamond. 

These indicated that the formation of cordierite had great effected on the structure and phase state oft-Zr02 (k-ss). ... 

P8 M is not the only polymer forming the isotropic smectic phase. To date, we have observed formation of that phase for a half-dozen chiral polymethacrylates and polysiloxanes. Table 5.1 summarizes the chemical structure and phase behavior of synthesized side-chain homopolymers, which carry chirally substituted side chains derived from asymmetric esters of terephthalic acid and hydroquinone. Such a structure with alternating orientation of carboxylic link groups seems to favour the formation of the IsoSm phase, whereas isomeric derivatives of p-hydroxybenzoic acid, where all carboxylic links have the same orientation, form only conventional Sm A and Sm C phases. Molar mass of all the synthesized homo- and copoly(meth)acrylates is within the range of 1 to 2-10 g mol the poiysilox-anes have the average degree of polymerization, p 35. 

In most cases [2,6] influence of alloying elements on oxidation resistance of titanium is explained by formation of protective film with a structure and phase composition that differs from film formed on the unalloyed titanium. In our researches the phase composition of scale consisted mainly of oxide TiOi (rutile) for all alloys. The composition of scale did not practically depend on alloying and duration of exposure. Therefore the reason of rising heat-resistant in the alloys is presumably due to influence of their structure and phase composition on the scale formation. 

Surface processes are mainly inherent in PVD and UMS methods. In the case of the IBAD method, the path depth of gas ions reaches 100 nm. Therefore, their influence on the structure and phase composition is not confined to the film surface area and it covers approximately the same thickness (Figure 24.1). The main processes that occur in this case are as follows the film surface experiences the acceleration of surface diffusion and formation of radiation defects that serve as nuclei formation centers the film depth supports high flow of radiation defects that provides formation of such stoichiometric compounds as Me(N,0,C). 

In order to study in detail the mechanism of formation of a structure and phase composition of chromium film deposited under the nitrogen ion bombardment, the electron microscopic analysis of the objects whose thickness is <60 nm should be done. A precondition for the analysis of the grain... 

The combination of classical electrochemical measurements with ex situ transfer experiments into UHV [242], and in situ structure-sensitive studies such as electroreflectance [25], Raman and infrared (IR)-spectroscopies [29, 243], and more recently STM and SXS [39] provided detailed knowledge on energetic, electronic and structural aspects of (ordered) anion adsorption and phase formation. These experimental studies have been complemented by various theoretical approaches (1) quantum model calculations to explore substrate-adsorbate interactions [244-246] (2) computer simulation techniques to analyze the ion and solvent distribution near the interface [247] (3) statistical models [67] and (4) MC simulations [38] to describe phase transitions in anionic adlayers. 

A main field of activities is focused on structure and reactivity in two-dimensional adlayers at electrode surfaces. Significant new insights were obtained into the specific adsorption and phase formation of anions and organic monolayers as well as into the underpotential deposition of metal ions on foreign substrates. The in situ application of structure-sensitive methods with an atomic-scale spatial resolution, and a time resolution up to a few microseconds revealed rich, potential-dependent phase behavior. Randomly disordered phases, lattice gas adsorption, commensurate and incommensurate (compressible and/or rotated) stmctures were observed. Attempts have been developed, often on the basis of concepts of 2D surface physics, to rationalize the observed phase changes and transitions by competing lateral adsorbate-adsorbate and adsorbate-substrate interactions. 

---