High pressure anomalies

Ordinary water behaves very differently under high temperature and high pressure. Early studies of aqueous solutions under high pressure showed a unique anomaly that was not observed with any other solvent.11 The electrolytic conductance of aqueous solutions increases with an increase in pressure. The effect is more pronounced at lower... 

Detailed reviews of the physical properties of fullerenes under pressure already exist [13,14] and only a few important parameters will be discussed here. Since fullerene molecules have been found to be very incompressible the primary effect of high pressure is to decrease the intermolecular distance, which leads to changes in most physical properties. To a first approximation, solid molecular fullerites can be described as three-dimensional graphite , in the sense that the molecular interaction is similar to the interlayer interaction in graphite, and because compression can occur in three dimensions the bulk modulus B is close to one third of that of graphite. However, the molecular reorientation from a P-oriented to an H-oriented structure with increasing pressure leads to anomalies... 

Aluminum compressed air cylinder safety has been an important issue in recent years. Safety procedures regarding the use, care and maintenance of compressed air cylinders have been in placed to ensure the public safety. Many attentions have been paid especially so-called sustained-load cracking (SLC) failures. SLC is a metallurgical anomaly that occasionally develops in high-pressure cylinders made generally from aluminum alloys. 

Since the Navier s slip hypothesis of the last century, most experiments have failed to obtain positive evidence for a slip boundary condition on macroscopic scales in low molar mass liquids. However, Navier s notion of slip turns out to be extremely useful and convenient for the latest description of flow anomalies of highly entangled polymer melts including linear polyethylenes (LPE). The ability of a melt/solid interface to possess two profoundly different states as shown by Fig. 4a,b clearly reveals the potential role of interfacial slip in governing various melt flow phenomena in high pressure extrusion. Before reviewing recent experimental studies that have elucidated the molecular origins of different flow... 

The anomalies have some important consequences. The expansion of the system due to ice formation can cause high pressures. Nearly everybody knows about the bursting of water pipes that become frozen. Some... 

The AV data of Fig. 5.1 that are satisfactorily accounted for by Eqs (5.5)-(5.8) are fewer in number than the anomalous cases of Table 5.1. This is a rather unsatisfactory situation, even though most of the anomalies can be explained away - indeed, deviations from the predictions of Eqs (5.5)-(5.8) can often provide important mechanistic information. More AV data are clearly desirable, but the prospects for further successful experiments are poor. The measurements of AV summarized in Fig. 5.1 and Table 5.1 were obtained at high pressures by radiochemical tracer methods for the slowest reactions [12, 17, 25], NMR linebroadening techniques for the faster cases [11, 13, 15, 19-22, 34], and stopped-flow circular dichroism [13, 14, 18] for moderately rapid reactions of reactants that could be prepared as resolved enantiomers. There are, however, many self-exchange reactions that are inaccessible to these techniques. For example, rates of electron transfer in couples where both reactants have unpaired electrons generally cannot be studied by NMR methods, while other couples that undergo electron transfer at intermediate rates may not be resolvable into optical isomers or be amenable to radiochemical sampling procedures under pressure. 

Internal Corrosion of Aluminum Compressed Air Cylinders The safety of aluminum compressed air cylinders has been an important problem in recent years. Safety procedures regarding their use and maintenance are necessary to ensure public safety. Sustained-load cracking (SLC) is a common failure mode of these cylinders. SLC is a metallurgical anomaly that develops occasionally in high-pressure cylinders made of aluminum alloys. 

The negative sloping liquidus line at low pressures, unique among the rare earth metals, is also an obvious anomaly. Not obvious from a P—T diagram is the fact that in cerium, one has an element which is both an antiferromagnet (/ -Ce) and a superconductor at high pressures, see fig. 12b (a-, a - and a"-Ce). Cerium is indeed a fascinating element. 

Figure 9.3 Log CRSS) versustemperaturefor 110 (110) slip in spinel of various stoichiometries. The low-temperature data represent either high-pressure confinement experiments or hardness tests. Note the yield stress anomaly for n = 1.1 crystals [18].

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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