Temperature crystalline phase

Now it is well established that [bmim] cation in the liquid state has a tt—gt equilibrium of the NCCC and CCCC angles of the butyl group as already shown in Fig. 1 (Hamaguchi Ozawa, 2005 Ozawa et al., 2003). Recently, Endo et al. (Endo et al., 2010) reported that three low-temperature crystalline phases of [bmim] [PFe] closely correlate with the conformational changes of [bmim] cation. Subsequently, Su et al. Su et al., 2009) reported the phase transitions of [bmim][PF6] using HP-DTA up to 1.0 GPa. The transition from the liquid to crystalline phases was reported to occur at 0.1 GPa. However, detailed information on the transformed crystalline phase of [bmim][PF6] still requires further study. We suppose that the conformational analysis of [bmim] cation in its relation to the phase transition behavior is helpful to obtain the structural information of the high pressure phases. 

Data for illite (not shown in Fig. 9) indicate a slight expansion in the temperature range 450-800°C followed by a rapid continuous shrinkage. PO] Expansion is attributed to the development of the anhydrite structure, and the shrinkage to loss of structure of the phase. The high rate of shrinkage correlates with the relatively lower development of high temperature crystalline phases. 

At a sufficiently low temperature, the phase nucleated will be crystalline rather than liquid. The theory is reviewed in Refs. 1 and 7. It is similar to that for the nucleation... 

The parameter /r tunes the stiffness of the potential. It is chosen such that the repulsive part of the Leimard-Jones potential makes a crossing of bonds highly improbable (e.g., k= 30). This off-lattice model has a rather realistic equation of state and reproduces many experimental features of polymer solutions. Due to the attractive interactions the model exhibits a liquid-vapour coexistence, and an isolated chain undergoes a transition from a self-avoiding walk at high temperatures to a collapsed globule at low temperatures. Since all interactions are continuous, the model is tractable by Monte Carlo simulations as well as by molecular dynamics. Generalizations of the Leimard-Jones potential to anisotropic pair interactions are available e.g., the Gay-Beme potential [29]. This latter potential has been employed to study non-spherical particles that possibly fomi liquid crystalline phases. 

Eig. 15. Time—temperature transformation ia a thin-phase change layer during recording/reading/erasiug (3,105). C = Crystalline phase A = amorphous phase = melting temperature = glass-transition temperature RT = room temperature. 

Research has led to alloys which undergo laser-induced crystallization within about 50 ns. This is possible, for example, with TeGe alloys, which also possess the necessary temperature stability up to 180°C and exhibit sufficient reflection (crystalline phase) and transmission characteristics (amorphous phase), respectively. TeGe alloys have not found a practical use because of the formation of depressions in the memory layer typical for them after repeated... 

The existence of tridymite as a distinct phase of pure crystalline siUca has been questioned (42,58—63). According to this view, the only tme crystalline phases of pure siUca at atmospheric pressure are quart2 and a highly ordered three-layer cristobaUte having a transition temperature variously estimated from 806 250°C to about 1050°C (50,60). Tridymites are considered to be defect stmctures in which two-layer sequences predominate. The stabihty of tridymite as found in natural samples and in fired siUca bricks has been attributed to the presence of foreign ions. This view is, however, disputed by those who cite evidence of the formation of tridymite from very pure siUcon and water and of the conversion of tridymite M, but not tridymite S, to cristobahte below 1470°C (47). It has been suggested that the phase relations of siUca are deterrnined by the purity of the system (42), and that tridymite is not a tme form of pure siUca but rather a soHd solution of minerali2er and siUca (63). However, the assumption of the existence of tridymite phases is well estabUshed in the technical Hterature pertinent to practical work. 

Cristobahte can also form on vitreous siUca at temperatures as low as 400°C when the pressure is equal to 35 MPa (<350 atm) and the glass is immersed in weak NaOH solutions (108). In stronger NaOH solutions, quart2 is formed. The formation of the crystalline phases is a result of the hydrolysis of the anions present. No crystallisation occurs with HF, H2SO4, and H PO in KHSO solutions or in pure water. 

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