Compressibility, crystals

Their special field of investigation dealt with the electrical and thermal properties of metals. More recently considerable attention has been paid to the question of the nature of the interatomic forces in metals, which are significant for properties such as density, compressibility, crystal energy, and hardness and it has been found possible to treat this problem in a reasonably satisfactory way for the case of the alkali metals, with a single valence electron per atom.8... 

Fig. 1. The piezoelectric effects, (a) generated Vby an applied force, (b) compressed crystal by an applied voltage.

Bhateja SK, Pae KD. Effects of hydrostatic-pressure on compressibility, crystallization, and melting of polymers. J Macromol Sci—Rev Macromol ChemPhys 1975 C 13(1) 77-133. 

Figure 4.18 Typical e dependence of the crystallization behavior directly observed by optical microscopy on samples elongationally crystalhzed by 2D compression at Tc = 150°C. f is crystallization time. At f = 0, a sample was just compressed. Crystallized at (a) quiescent field, = 0s (b) e(S) = 3s (c) e(S) = 70s and (d) e(L) = 1.3x10 s" . (a, b) Scale bar is 100 pm. (c, d) Scale bar is 500 pm. (See color insert.)...

An indirect estimate of surface tension may be obtained from the change in lattice parameters of small crystals such as magnesium oxide and sodium chloride owing to surface tensional compression [121] however, these may represent nonequilibrium surface stress rather than surface tension [68]. Surface stresses may produce wrinkling in harder materials [122]. 

No system is exactly unifomi even a crystal lattice will have fluctuations in density, and even the Ising model must pemiit fluctuations in the configuration of spins around a given spin. Moreover, even the classical treatment allows for fluctuations the statistical mechanics of the grand canonical ensemble yields an exact relation between the isothemial compressibility K j,and the number of molecules Ain volume V ... 

Dryers. A drying operation (see Drying agents) needs to be viewed as both a separation and a heat-exchange step. When it is seen as a separation, the obvious perspective is to cut down the required work. This is accompHshed by mechanically squeezing out the water. The objective is to cut the moisture in the feed to the thermal operation to less than 10%. In terms of hardware, this requires centrifuges and filters, and may involve mechanical expression or a compressed air blow. In terms of process, it means big crystals. 

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

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