Phase-change properties

Phase-change media An optical recording material consisting of an alloy that has two metastable phases with different optical properties. Phase-change media can be rewritable or write-once. 

The preparation of the reflecting silver layers for MBI deserves special attention, since it affects the optical properties of the mirrors. Another important issue is the optical phase change [ ] at the mica/silver interface, which is responsible for a wavelength-dependent shift of all FECOs. The phase change is a fimction of silver layer thickness, T, especially for T < 40 mn [54]. The roughness of the silver layers can also have an effect on the resolution of the distance measurement [59, 60]. 

Calorimetry is the basic experimental method employed in thennochemistry and thennal physics which enables the measurement of the difference in the energy U or enthalpy //of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or AH) is called a calorimeter. In the first section the relationships between the thennodynamic fiinctions and calorunetry are established. The second section gives a general classification of calorimeters in tenns of the principle of operation. The third section describes selected calorimeters used to measure thennodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

Section IB presents results that the analytic properties of the wave function as a function of time t imply and summarizes previous publications of the authors and of their collaborators [29-38]. While the earlier quote from Wigner has prepared us to expect some general insight from the analytic behavior of the wave function, the equations in this secbon yield the specific result that, due to the analytic properties of the logarithm of wave function amplitudes, certain forms of phase changes lead immediately to the logical necessity of enlarging... 

If a dye is used which changes its properties by illumination, eg, its shape like the a2oben2ene, the phase change temperature can be lowered. The writing process then is nearly isothermal which helps to reduce spot diameters. 

Another property pecuHar to SMAs is the abiUty under certain conditions to exhibit superelastic behavior, also given the name linear superelasticity. This is distinguished from the pseudoelastic behavior, SIM. Many of the martensitic alloys, when deformed well beyond the point where the initial single coalesced martensite has formed, exhibit a stress-induced martensite-to-martensite transformation. In this mode of deformation, strain recovery occurs through the release of stress, not by a temperature-induced phase change, and recoverable strains in excess of 15% have been observed. This behavior has been exploited for medical devices. 

Micellar properties are affected by changes in the environment, eg, temperature, solvents, electrolytes, and solubilized components. These changes include compHcated phase changes, viscosity effects, gel formation, and Hquefication of Hquid crystals. Of the simpler changes, high concentrations of water-soluble alcohols in aqueous solution often dissolve micelles and in nonaqueous solvents addition of water frequendy causes a sharp increase in micellar size. 

Commercial appHcations of calcium chloride and its hydrates exploit one or more of its properties with regard to aqueous solubiUty, hygroscopic nature, the heat gained or lost when one hydrated phase changes to another, and the depressed freezing point of the eutectic solution at a composition of about 30% by weight calcium chloride. 

In this chapter we define what is meant by a shock-wave equation of state, and how it is related to other types of equations of state. We also discuss the properties of shock-compressed matter on a microscopic scale, as well as discuss how shock-wave properties are measured. Shock data for standard materials are presented. The effects of phase changes are discussed, the measurements of shock temperatures, and sound velocities of shock materials are also described. We also describe the application of shock-compression data for porous media. 

The composition of a production fluid is usually not well defined. In most cases, only a specific gravity is known. Compositions are important to the prediction of physical properties of the fluid as it undergoes phase changes. Estimations can be made based only upon specific gravity, however, for good reliability, molecular compositions should be used wlien available. 

Many metals and metallic alloys show martensitic transformations at temperatures below the melting point. Martensitic transformations are structural phase changes of first order which belong to the broader class of diffusion js solid-state phase transformations. These are structural transformations of the crystal lattice, which do not involve long-range atomic movements. A recent review of the properties and the classification of diffusionless transformations has been given by Delayed... 

As mentioned earlier, the physical properties of a liquid mixture near a UCST have many similarities to those of a (liquid + gas) mixture at the critical point. For example, the coefficient of expansion and the compressibility of the mixture become infinite at the UCST. If one has a solution with a composition near that of the UCEP, at a temperature above the UCST, and cools it, critical opalescence occurs. This is followed, upon further cooling, by a cloudy mixture that does not settle into two phases because the densities of the two liquids are the same at the UCEP. Further cooling results in a density difference and separation into two phases occurs. Examples are known of systems in which the densities of the two phases change in such a way that at a temperature well below the UCST. the solutions connected by the tie-line again have the same density.bb When this occurs, one of the phases separates into a shapeless mass or blob that remains suspended in the second phase. The tie-lines connecting these phases have been called isopycnics (constant density). Isopycnics usually occur only at a specific temperature. Either heating or cooling the mixture results in density differences between the two equilibrium phases, and separation into layers occurs. 

As with other properties of solids, the increased relative significance of surface energy in very small (i.e. micrometre-sized) crystals influenced the melting points [2,16,17] and diffusion at this temperature. Quantitative studies of rates of melting of solids are impracticable since superheating is effectively forbidden and the rate of the endothermic phase change is determined by the rate of heat supply and the thermal conductivity of the solid. 

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