Phase-change media

Gidon, S., Lemonnier, O., Rolland, B., Bichet, O., and Dressier, C., Electrical Probe Storage Using Joule Heating in Phase Change Media, Appl. Phys. Lett., Vol. 85, 2004, pp. 6392-6394. 

Mustafa, M. M., and Wright, C. D., An Analytical Model for Nanoscale Electrothermal Probe Recording on Phase-Change Media, J. Appl. Phys., Vol. 99, 2006, pp. 03430101-03430112. 

The use of a phase-change media circumvents many of these problems. A material slightly above its liquid/solid-phase transition temperature may be ejected from a jet-printing nozzle the droplet solidifies quickly upon contact with a cooler surface. The feature size will then depend more on the cooling rate and less on the material s wetting properties, because a frozen droplet cannot spread. In this situation, the substrate temperature controls the printed feature size for materials having excellent wetting properties. 

From the perspective of a materials scientist, tellurium is certainly the most attractive element, and it has found applications mainly in the electronics industry because of its p-type semiconducting properties. It can also be used for the synthesis of so-called II-VI semiconductors (such as MgTe) or may be alloyed to yield superior intermetallic phases. In addition, some Te alloys are under investigation in the realm of phase-change media for rapid data storage [273]. 

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. 

Coolant may be water or another phase-change medium. Use of water simplifies the stack design, because water is already used in both anode and cathode compartments. 

Figure 4.11. Diagrammatic sketches of atomic lattice rearrangements as a result of dynamic compression, which give rise to (a) elastic shock, (b) deformational shock, and (c) shock-induced phase change. In the case of an elastic shock in an isotropic medium, the lateral stress is a factor v/(l — v) less than the stress in the shock propagation direction. Here v is Poisson s ratio. In cases (b) and (c) stresses are assumed equal in all directions if the shock stress amplitude is much greater than the material strength.

The dependences of electron mobility on medium density and on phase change are complex and poorly understood. In Ar, Kr and Xe, the mobility increases by a factor of about 2 in going from the liquid to the solid phase. This has generated speculation that long-range order is not necessary for high electron mobility. On the other hand, electron mobility in Ne increases from 10-3 to 600 cm2v 1s 1 on solidification at 25.5 K (see Allen, 1976). In liquid He, the electron mobility above the A-point (2.2 K) varies approximately inversely with the viscosity, consistent with the bubble model. Below the A-point, the mobility... 

In the disc method, the powder is compressed by a punch in a die to produce a compacted disc, or tablet. The disc, with one face exposed, is then rotated at a constant speed without wobble in the dissolution medium. For this purpose the disc may be placed in a holder, such as the Wood et al. [Ill] apparatus, or may be left in the die [112]. The dissolution rate, dmldt, is determined as in a batch method, while the wetted surface area is simply the area of the disc exposed to the dissolution medium. The powder x-ray diffraction patterns of the solid after compaction and of the residual solid after dissolution should be compared with that of the original powder to test for possible phase changes during compaction or dissolution. Such phase changes would include polymorphism, solvate formation, or crystallization of an amorphous solid [113],... 

Other independent variables (changes in temperature or medium composition) should produce effects analogous to pressure and therefore induce phase changes and shifts in association equilibria. Combination of these different variables could be used to investigate protein-subunit interactions and conformational changes, to determine the fundamental physical-chemical parameters of these changes. 

Fourier s equafion does nof fake into account convection, which in the case of food freezing governs heat transfer befween fhe food surface and fhe refrigerafing medium, for example cold air in the case of a fluidized bed. Second, and more importanfly, if cannof accounf for fhe removal of lafenf heaf and fhe resultant phase change. Of the models available to predict freezing time. Plank s equation (Plank, 1913, 1941) is one of fhe simplesf and most widely used and is derived in many standard texts (Singh and Heldman, 2001 Smith, 2003). The principal... 

Density is a factor in the solvating power of a supercritical fluid the more dense the fluid, the more powerful its solvent strength. Since changing the temperature and pressure within the supercritical phase changes the density, a supercritical fluid can be made to possess a wide range of solvent power. This property together with its increased diffusion and lower viscosity makes supercritical fluid an attractive extraction medium. 

A second method of process intensification for recuperative reactors is to enhance performance by using a reactive coolant or heating medium, since the heat effects associated with reactions are usually much larger than those available with phase changes or simpler heating and cooling procedures. The coupling of an exothermic auxiliary heat source reaction with the desired endothermic reaction, or vice... 

The enthalpy conservation equation of the multiphase medium, obtained from the sum of the appropriate balance equations of the constituents includes the heat effects due to phase changes and hydration (dehydration) process, as well as the convectional and latent heat transfer,... 

Kinetics and Phase Behavior - Table IV represents a simplified picture of the situation however, some polymerizations go through several phase changes in the course of the reaction. For example, in the bulk polymerization of PVC, the reaction medium begins as a low viscosity liquid, progresses to a slurry (the PVC polymer, which is insoluble in the monomer, precipitates), becomes a paste as the monomer disappears and finishes as a solid powder. As might be expected, modelling the kinetics of the reaction in such a situation is not a simple exercise. 

Light is changed in phase in traversing a medium some light may be lost from the transmitted beam by extinction. Both the phase change and the extinction may be described by a complex refractive index ... 

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