High-pressure behavior

It is rather likely that pressure-induced phase transformations can also occur in hydrogenated multicomponent industrial titanium alloys. However, there were no available data on the high-pressure behavior of such alloys. 

Models based on chemisorption and kinetic parameters determined in surface science studies have been successful at predicting most of the observed high pressure behavior. Recently Oh et al. have modeled CO oxidation by O2 or NO on Rh using mathematical models which correctly predict the absolute rates, activation energy, and partial pressure dependence. Similarly, studies by Schmidt and coworkers on CO + 62 on Rh(l 11) and CO + NO on polycrystalline Pt have demonstrated the applicability of steady-state measurements in UHV and relatively high (1 torr) pressures in determining reaction mechanisms and kinetic parameters. 

Based on the studies of alkane dissociation at high pressures, two conclusions were reached regarding the applicability of molecular beam studies for predicting high pressure behavior . First, the effects of vibr-... 

Pressure Dependencies Equation 3.95 predicts the binary diffusion coefficient to scale as p l, which is generally true except as the pressure approaches or exceeds the critical pressure. The Takahashi formula [392], which can be used to describe the high-pressure behavior, is discussed below. The Chapman-Enskog theory also predicts that Vji, increases with temperature as T3/2. However, it is often observed experimentally the temperature exponent is somewhat larger, say closer to 1.75 [332], An empirical expression for estimating T>jk is due to Wilke and Lee [433]. The Wilke-Lee formula is [332]... 

Transition-state theory is based on the assumption of chemical equilibrium between the reactants and an activated complex, which will only be true in the limit of high pressure. At high pressure there are many collisions available to equilibrate the populations of reactants and the reactive intermediate species, namely, the activated complex. When this assumption is true, CTST uses rigorous statistical thermodynamic expressions derived in Chapter 8 to calculate the rate expression. This theory thus has the correct limiting high-pressure behavior. However, it cannot account for the complex pressure dependence of unimolecular and bimolecular (chemical activation) reactions discussed in Sections 10.4 and 10.5. 

Implications for the interpretation of recent laboratory [11,12] and atmospheric [13] spectroscopic observations, as well as current measurements of high pressure behavior of oxygen [14], are amenable to be discussed in this framework. This work provides also the ground for the interpretation of complicated band features in rotational spectra, as exemplified by the case of oxygen. Still appears to be valid the statement [15,16] that spectral analysis alone is not sufficient to extract information on structure and bonding, and the combined use of scattering and gaseous properties information is therefore confirmed to be crucial". 

Cohen, A. J., and R. G. Gordon (1976). Modified electron-gas study of the stability, elastic properties, and high-pressure behavior of MgO and CaO crystals. Phys. Rev. B14, 4593-605. 

Mehl, M. J., R. J. Hemley, and L. L. Boyer (1986). Potential-induced breathing model for the elastic moduli and high pressure behavior of the cubic alkaline earth oxides. Phys. Rev. B33, 8685-96. 

Models I or II, demonstrate the importance of carefully investigating the high pressure behavior associated with a model when developing potentials for the simulation of detonations. 

Hemley RJ, Prewitt CT, Kingma KJ (1994) High-pressure behavior of silica/ PJ Heaney, CT Prewitt, GV Gibbs (eds) Silica—Physical Behavior, Geochemistry, and Materials Applications. Rev Mineral 29 41-81... 

Bridgman PJ (1939) The high pressure behavior of miscellaneous minerals. Am J Sci 237 7-18 Brown, JM (1999) The NaCl pressure standard. J Appl Phys 86 5801-5808... 

Material Constants, Elastic wave velocities have been obtained for oil shale by ultrasonic methods for various modes of propagation. Elastic constants can be inferred from these data if the oil shale is assumed to be a transversely isotropic solid (9). This is a reasonable approximation considering the bedded nature of the rock. Many of the properties of oil shale depend on the grade (kerogen content), which in turn is correlated with the density ( 10). The high pressure behavior of oil shale under shock loading has been studied in gas-gun impact experiments (11). 

In Table 3, the compressibility of the lattice parameters and of the polyhedral building units are reported, along with other structural parameters useful to understand the high-pressure behavior of Cs-annite, Rb-annite and phlogopite. The points outlined below show the effect of how different structural units of trioctahedral micas relate with one another, and then respond as a whole to pressure ... 

For NbON, the data (not shown for reasons of brevity) predict a very similar high-pressure behavior. This is not unexpected because both Ta + and Nb " have identical Shannon ionic radii (seven-fold coordination) of 0.69 A, as given in Table 1.1. Beyond 27 GPa, NbON also adopts the cotunnite structure - as expected - but the density-of-states is nonzero at the Fermi level, such that cotunnite-like NbON will have metallic properties [382]. Similar cases of metalization for insulating (or semiconducting) materials imder pressure have already been reported [383]. 

Indium Antimonide. Among the binary semiconductors, InSb has received extensive attention in the experimental and theoretical studies due to the complex transition mechanisms involved in its high-pressure behavior [165]. The traditional phase diagram in InSb [166] was substantially revised recently [167, 168]. Two high-pressure phases of InSb are the site-ordered orthorhombic Cmcm and Immm structures, the transition between which proceeds via an intermediate site-disordered orthorhombic phase with Imma symmetry [167]. At room temperature, the transition sequence in InSb depends on the pressurization rate. At slow loading, zincblende strucmre transforms into Cmcm at 2 GPa, whereas rapid loading rates lead to a direct zincblende Immm transition at 3 GPa [167]. The zincblende Cmcm transformation seems to be reversible and the phases other than zincblende have not been observed at ambient conditions in InSb. 

The high-pressure behavior of boron carbide was studied solely due to the presumption that it belonged to the class of the so-called inverted molecular solids [208], which is revealed through the higher compressibility of BjiC icosahedra than that of space between them [209]. However, the inverted molecular behavior of boron carbide has been disputed recently based on the ab initio density-functional calculation of its vibrational properties [210]. Not much is known about... 

A. San-Miguel, P. Keghelian, X. Blase, P. Melinon, A. Perez, J.P. Itie, A. Polian, E. Reny, C. Cros, M. Pouchard, High pressure behavior of silicon clathrates a new class of low compressibility materials. Phys. Rev. Lett. 83, 5290-5293 (1999)... 

Cerium metal is discussed in ch. 4 and only a brief mention of its high pressure behavior will be made here (for references see the list in ch. 4). Cerium can exist at atmospheric pressure in the fee (y) or dhep (iS) form and undergoes an isostructural transition near 100 K to another fcc-form referred to as o-Ce. The y-a Ce transition occurs at 7 kbar at room temperature and this transition is accompanied by about 8% volume decrease. This is one of the most widely studied transitions as a function of pressure and temperature and is believed to involve a valence change from 3 towards a higher valence state (3.7 ). The y to a transition line terminates at a critical point the very first example in which a solid - solid transition was shown to exhibit a liquid-vapor-like critical point. A pressure-induced phase transition near 50 kbar, initially reported to be yet another isostructural transition has been shown to be from fee (a-Ce) to an orthorhombic phase with the a-U structure. Stager and Drickamer (1964) have reported a pronounced resistance anomaly near 120 kbar indicative of a phase transition, but the nature of this transition is unknown. The fusion behavior of Ce is again unique in that it exhibits a minimum. 

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