Voltage-temperature phase diagram

With an increasing external field a series of the field-induced phase transitions BP I — cholesteric, BP II cholesteric, and then cholesteric —> nematic are observed. This is illustrated by Fig. 6.27 [91] where the voltage-temperature phase diagram is presented for a mixture (47-53 mol.%) of... 

FIGURE 6.27. Voltage-temperature phase diagram for 47-53 mol.% mixture of CB15 and 60CB [91]. 

Figure 7.13. Voltage-temperature phase diagram for a 49.6% mixture of chiral CB15 nematic E9. The helical phase is labeled chol the structure BPE was not yet determined in this article (from Porsch and Stegemeyer [113]).

Figure 7.14. Schematic voltage temperature phase diagram for a 49.8% mixture of CB15 in E9. The shaded region is the coexistence region in which crystals of different shapes appear. C is the helical phase H is the hexagonal BPH phase (from Pier-anski et al. [115]).

With increasing external field a series of field-induced phase transitions is observed BP,—>cholesteric, BP,->cholesteric, and then cholesteric—>nematic [52]. This is illustrated in Fig. 8 [42] which shows a voltage-temperature phase diagram for a mixture (47-53 mol%) of chiral 15-CB with 4-n-hexyloxycyanobiphenyl (60-CB). BPj loses its stability, first transforming into the cholesteric phase, because the transition enthalpy AH, is extremely small ( 50 J mol" ) for the BPj-Ch transition. This enthalpy, normalized to a unit volume (0.2 J cm ) and compared with the difference in electrostatic energy density between the two phases Se (Se = ggp, - fch 0.2) ex-... 

Figure 8. Voltage-temperature phase diagram for a 47-53 mol% mixture of 15-CB and 6-OCB [42],...

Figure 9. Voltage-temperature phase diagram obtained on heating 14P1M7 [56]. Cell thickness 2 im.

Chapters 7 to 9 apply the thermodynamic relationships to mixtures, to phase equilibria, and to chemical equilibrium. In Chapter 7, both nonelectrolyte and electrolyte solutions are described, including the properties of ideal mixtures. The Debye-Hiickel theory is developed and applied to the electrolyte solutions. Thermal properties and osmotic pressure are also described. In Chapter 8, the principles of phase equilibria of pure substances and of mixtures are presented. The phase rule, Clapeyron equation, and phase diagrams are used extensively in the description of representative systems. Chapter 9 uses thermodynamics to describe chemical equilibrium. The equilibrium constant and its relationship to pressure, temperature, and activity is developed, as are the basic equations that apply to electrochemical cells. Examples are given that demonstrate the use of thermodynamics in predicting equilibrium conditions and cell voltages. 

Wh/kg. As indicated in the sodium-sulphur phase diagram given in Fig. 8.15, sodium pentasulphide and sulphur are not mutually soluble at the temperature of cell operation, so that two liquid phases are present in the cathode compartment and the cell voltage is invariant. As the discharge progresses and the available elemental sulphur is consumed, a series of reactions commences as the sodium pentasulphide is converted to lower polysulphides, all of which are mutually soluble ... 

The newly introduced variable Qp is the spatial temperature gradient. As the cell voltage steady-state system is completed by the three implicit algebraic correlations (12-14) for the unknowns Asteady-state system can be visualized in a phase diagram, where 0 is plotted against 0. The result for the parameter values listed in Tab. 3.1 is shown in Fig. 3.2. 

The importance of phase diagrams to materials scientists, physicists, and chemists is difficult to overemphasize as the physical, mechanical, and chemical properties of a material depend upon its underlying structure and composition. A phase diagram is a description of the equilibrium structure and composition of a material as a function of selected (often) exogenous variables such as pressure, temperature, voltage, and so on. 

The incremental capacity of an insertion electrode material used in ambient temperature batteries can be estimated from voltage spectroscopy measurements which can help to the determination of phase diagram of the insertion compotmd [1], In the first section, we examine the various aspects of electrochemical lithium insertion into a number of electrode materials. The experimental techniques of solid-state electrochemistry are presented in the second section. Voltage spectroscopy and phase diagram during Li intercalation into cathode materials are investigated. Finally, the experimental determination of the diffusion coefficient of ions in solid materials is investigated. 

A circuit diagram for a typical thyratron-operated relay is shown in Fig. 5-29. When the bath temperature is low, the external circuit (to the mercury contactor) is open and current is passed by the thyratron, since the voltages at the plate and grid are in phase. However, when the external circuit is closed, a larger out-of-phase voltage... 

Fig. 16. Electrostriction of a ferroelectric LC-elastomer (43). Big diagram Thickness variation Ah as a function of the applied ac voltage (/ac- Interferometric data were obtained at the fundamental frequency of the electric field (piezoelectricity, first harmonic -t) and at twice the frequency (electrostriction, second harmonic o). Sample temperature 60°C. Inset Electrostrictive coefficient a (-I-) versus temperature. At the temperature where the non-cross-linked polymer would have its phase transition Sc -Sa (about 62.5 0, the tilt angle of 0° is unstable. That is why the electroclinic effect is most effective at this temperature. An electric field of only 1.5 MV/m is sufficient to induce lateral strains of more than 4%.

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