Pressure effects on crystallization

Goto, T., Sato, J. Syono, Y. (1982) Shock-induced spin-pairing transition in Fe203 due to the pressure effect on the crystal field. In High-Pressure Research in Geophysics. (S. Akimoto M. H. Manghani, eds D. Reidel Publ. Co., Dortrecht), pp. 595-609. 

Mao, H.-K. Bell, P. M. (1972a) Optical and electrical behaviour of olivine and spinel (Fe2Si04) at high pressure. Interpretation of the pressure effect on the olivine absorption bands of natural fayalite to 20 kb. Crystal field stabilization of the olivine-spinel transition. Ann. Rept. Geophys. Lab., Yearb. 71, 520-8... 

Horsewill et al. (1994) examined the hydrostatic pressure effect on the proton transfer in crystals of a carboxylic acid dimer. Under a hydrostatic pressure, the distance of hydrogen bonds becomes shorter, and this is accompanied by a decrease in the potential barrier to proton transfer. The temperature dependence of the rate of the proton transfer turns out to be of a non-Arrhenius type. The influence of phonon-assisted tunnelling becomes evident as the external pressure increases, especially at lower temperatures. 

Figure 3 Transitiometric investigation of the pressure effect on the isobaric thermal expansivities a. of gaseous, liquid, and solid substances (a) comparison between calculated ana experimental data of methane at 333 K (bl) quinoline as a simple fluid (b2) water as the associated liquid (cl) effect of temperature on medium-density polyethylene (MDPE) (c2) evolution of with the crystallinity (points represent the experimental data and the lines were obtained by the least squares fitting of data) (c3) comparison between the experimental a for three polyethylenes with different degrees of crystallinity and the predicted values for crystal and amorphous phases obtained by extrapolation from linear fitting of the experimental data...

The pressure effect on the melting/crystallization temperature of an MDPE sample, in the pressure range from 50 to 200 MPa, is illustrated in Figure 5. The isobaric temperature scans were performed at a rate of 0.833 mK s either in ascending or... 

Figure 5 Heat flow curves obtained on heating and cooling at a rate of0.833 mK s for the mercury-pressurized MDPE. The base lines were shifted for the sake of clarity on the pressure effect on the melting/crystallization temperatures...

Figure 6 Pressure effect on the temperature-induced and gas-assisted melting of tetracosane and PVDF (for more details and explanations, see refs. 26 and 29) (al) and (a2) heat rate evolution during fusion in the presence of supercritical CH and C 2 2 (VF), respectively (bl) fluid phase equilibria in the tetracosane/methane system and (b2) partial p—T phase diagram for the PVDF-VF and PVDF-N2 systems. Note the depression in the melting/crystallization temperatures in the pressure range up to 30 MPa for the tetracosane/CH and PVDF/VF systems...

It is important to note that the difference in free energy between polymorphs is identical in different solvents at the same temperature, assuming that the activity coefficient in each solvent is independent of concentration. Hence, the thermodynamic stability relationship between polymorphs depends only on the temperature at constant pressure and is completely independent of the solvent. This is an important point to emphasize because crystallizations from different solvents frequently yield different polymorphs. In these instances, the solvent is not changing the relative thermodynamic stabilities of the polymorphs. These observations are the result of kinetic and/or molecular recognition effects on crystallization processes, which are discussed in subsequent sections of this chapter. 

A number of other techniques have been applied to the analysis of metal complex luminescence. Pressure effects on luminescence of coordination complexes in single crystals (either pure or doped) can also provide information of value in evaluating excited-state distortion or metal-metal interactions of ordered solid matrices." " The magnitude of transition dipole moments and polarizability can be determined using Stark spectroscopy, and Bublitz and Boxer wrote a recent review of the technique. Two-photon excitation of transition metal complex chromophores has also been observed to yield luminescence. Recent work in this area has been reviewed by Lakowitz and co-workers. ... 

Gryk W, Dujardin C, Joubert M-F, Ryba-Romanowski W, Malinowski M, Grinberg M (2006) Pressure effect on luminescence dynamics in Pr + 3 -doped LiNb03 and LiTa03 crystals. J Phys Cond Matter 18 117... 

Friedl C, Costa FS, Cook P, Talwar K, Antanovski LK (2004) Method and apparatus for modeling injection of a fluid in a mold cavity. US Patent, US 6816820 B1 Fulchiron R, Koscher F, Poutot G, Delaunay D, Regnier G (2001) Analysis of the pressure effect on the crystallization kinetics, dilatometric measurements and thermal gradient modeling. J Macromol Sci—Physics 40 297-314... 

In further refinement, one could consider additional pressure effects on C for some ions. (One might expect that the Slater-Condon-Shortley parameter would be more affected by pressure than F. ) Alternatively one might assume with Stout that the higher energy Cg) levels are more spread out by the crystal field than the 2 levels. One could then calculate the covalency parameter e for these as a function of pressure. 

Figure 15.27. (a)-(e) The pressure effect on the heat capacity and a.c. susceptibility of i -phase crystals of p-NPNN. (f) The pressure dependence of the magnetic transition temperatures of ferromagnetic p-NPNN and antiferromagnetic TANOL and TVP. 

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