Quasicrystalline state

While some specific role of the K+ cation may account for the increased reactivity of benzothiophene with increasing amounts of KOH in the hydroxide mixture, the possible role of the total base, KOH, cannot be neglected. Potassium hydroxide is a stronger base and nucleophile in this system than NaOH is (10), and the increased basicity and nucleophilicity could account for increased reactivity toward benzothiophene decomposition. The chemical nature of ionic melts is not fully understood. While the hydroxide melts are believed to be fully dissociated (H), explanations have also been given for the formation of "quasicrystalline states (12), where order within the melt exists and dissociation is not complete. It is difficult to deduce how much independent freedom K+ and 0H have and if either the K+ cation or KOH or both are the important species. 

Since the initial discovery of metastable quasicrystals, many ternary inter-metallic compounds have been produced in the quasicrystalline state, which are thermodynamically stable at room temperature. These have been obtained... 

Quasicrystalline phases have received much attention since first reported by Shechtman et al. [3.92] in 1984 for Al-Mn. Within the last few years, various preparation techniques have been applied for the preparation of alloys in the quasicrystalline state. Liquid-phase quenching [3.92, 93] and relatively slow cooling from the melt [3.94], sputter or vapor deposition [3.95,96], ion-beam techniques [3.97-100], heat treatment of the amorphous phase [3.93,101, 102], and solid-state reaction during interdiffusion [3.103-106]. Recently it was demonstrated that the quasicrystalline phase can be produced by mechanical alloying [3.107-112],... 

Mechanical Properties of Boundary Film of Liquid. The mechanical properties of liquids in the bulk (including viscosity) differ from the properties in a thin boundary film, for each liquid there is some characteristic limiting film thickness below which the liquid changes over a quasisolid or quasicrystalline state. According to Akhmatov [35, p. 279], this limiting film thickness is 0.08 /xm for myristic acid, 0.058 jum for oleic acid, and 0.05-0.1 jum for high-molecular-weight unsaturated fatty acids. 

The molecules in the pure liquids and in their solution are considered to be solid-like, in a quasicrystalline state, where the molecules do not translate fully in a chaotic manner as in a gas, but where each molecule tends to stay in a small region, a more or less fixed position in space about which it vibrated back and forth. The quasicrystalline picture of the liquid state supposes molecules to sit in a regular array in space, called a lattice, and therefore liquid and liquid mixture models based on this simplified picture are called lattice models. 

Monocrystalline Quasicrystalline Polycrystalline Semicrystalline Amorphous and glassy state LRO NoncrystaUographic rotational symmetry, no LRO Crystallites separated by grain boundaries Crystalline regions separated by amorphous regions No LRO, no rotational S3fmmetry, does possess short-range order (SRO)... 

The structure of amorphous metals, quasicrystals, and crystalline inter-metallic compounds can be modelled by atom clusters with icosahedral arrangement [3.113-117]. The differences between the various phases result from a different arrangement of the individual atom clusters. Therefore, it is evident that there exists a close relation between the different states of matter, and that the different phases corresponding to minima of the free enthalpy can be quite easily transformed into each other. For example, rapid cooling from the melt results in an amorphous alloy for high quenching rates, and a quasicrystalline... 

Amorphous powder formed by mechanical alloying for 510 h at intensity 5 was further milled at intensity 7 for 25 h. The typical broad diffuse maximum of the amorphous state disappeared, and the characteristic intensity distribution of the quasicrystalline phase showed up in the X-ray diffraction pattern. Therefore, additional milling at higher intensity led to an amorphous-to-quasicrystal transition. Amorphization can also be achieved for crystalline starting powder mechanically alloyed for 206 h at intensity 9 by a further milling for 433 h at intensity 3 [3.108]. 

Unique nanocrystalline microstructures can be produced by controlled crystallization of the fully amorphous product, including nanocrystalline precipitates homogeneously distributed in an amorphous alloy matrix. In some systems, both the strength and ductility increase in this partially crystalline state [24], Other alloys produce nanocrystalline intermetallic or quasicrystalline precipitates, providing a credible path for increasing the specific stiffness. Thus, a significant effort is required to study the kinetics of crystallization, the devitrification pathways and the microstructures and properties that may be produced upon devitrification. The potential for exploration of novel compositions and microstructures in this class of materials is clearly promising. 

Rapid solidification processes are successfully used for A1 alloys to form a dispersion particles of intermetallic phases, which resist coarsening and strengthen the alloys at elevated temperatures. It has recently been shown that metastable intermetallic phases with a quasicrystalline structure, mainly of the icosahedral type, can also be produced by rapid solidification [23], As distinct from a crystalline state, translational long-range order is absent in quasicrystals, but there is rotational symmetry with 5-, 8-, 10- or 12-fold axes, which is forbidden in crystalline materials. The absence of translational symmetry in all three orthogonal directions is characteristic of the icosahedral structure [24],... 

Determination of crystalline and amorphous states, determination of crystal anisotropy, defects and defect structures, characterization of quasicrystalline, microcrystalline, nanocrystalline and amorphous materials... 

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