Transition pressure curve

Meiting (pressure) curve ( ) Transition (pressure) curve (in the strict sense)... 

Figure A2.5.1. Schematic phase diagram (pressure p versus temperature 7) for a typical one-component substance. The full lines mark the transitions from one phase to another (g, gas liquid s, solid). The liquid-gas line (the vapour pressure curve) ends at a critical point (c). The dotted line is a constant pressure line. The dashed lines represent metastable extensions of the stable phases.

Liquid helium-4 can exist in two different liquid phases liquid helium I, the normal liquid, and liquid helium II, the superfluid, since under certain conditions the latter fluid ac4s as if it had no viscosity. The phase transition between the two hquid phases is identified as the lambda line and where this transition intersects the vapor-pressure curve is designated as the lambda point. Thus, there is no triple point for this fluia as for other fluids. In fact, sohd helium can only exist under a pressure of 2.5 MPa or more. 

Although there have been few data collected, postshock temperatures are very sensitive to the models which specify y and its volume dependence, in the case of the Gruneisen equation of state (Boslough, 1988 Raikes and Ahrens, 1979a Raikes and Ahrens, 1979b). In contrast, the absolute values of shock temperatures are sensitive to the phase transition energy Ejp of Eq. (4.55), whereas the slope of the versus pressure curve is sensitive to the specific heat (see, e.g.. Fig. 4.28). 

It therefore follows that a transition from a rising to a falling part of a vapour pressure curve can occur only when the concentration of a specified component in the vapour is neither greater... 

The primary evidence for the conversion of gaseous monolayers at the air-water interface to other intermediate states lies in the abrupt changes found on the n-A isotherms of many film-forming compounds. So many of these isotherms have been reproduced in fine detail in a number of laboratories under a variety of conditions that they cannot possibly be rejected wholesale as artifacts. The sharp transitions from curves to plateaus, where the molecular area varies readily at constant surface pressure, may be related... 

In Figure 2 the ir-A and AV-A plots for SODS on O.OIM NaCl sub-solutions having different pH values are shown. In all cases, phase transitions from liquid-expanded to liquid-condensed state are evident ( ). Acidification of the subsolution Increases the transition pressure but the transition is less pronounced at the lowest pH studied. This is also accompanied by an expansion of the condensed part of the curve. Small negative surface potentials are observed over most areas. The highest potential is obtained for film spread on the pH 2.2 subsolution. For small areas, the surface potential attains a positive value. This may be related to reorientation of the dipole moments of the molecules which occur once a threshold surface concentration is exceeded (O. Mlnglns and Pethlca (7) studied the monolayer properties of SODS on various sodium chloride solutions (0.1, 0.01 and O.OOIM) at 9.5 C, and they showed that the monolayer is only stable on the more concentrated salt solutions (0.1 and O.OIM). In this work, no noticeable... 

The condition for valid results in this work is the fact that the system is in the gel-state that is, it is in a state of inner equilibrium, and not in the glass state. Measurements of Hellwege, Knappe, and Lehmann (5) on pure PVC show the expected discontinuity in the compressibility vs. pressure curve at the melting point transition in the glass state. It is inferred from this study that the glass temperature for pure PVC and for the plasticized, gel-type PVC does not rise above 110° C. at pressures of 200 atm. (Figure 7). Our study showed that the system is always in a state of inner equilibrium. 

Vaporization Transition Clausius-Clapeyron Equation For the liquid-vapor coexistence line ( vapor-pressure curve ), the Clapeyron equation (7.29) becomes... 

Fig. 6. Specific volume pressure curves for the l.c. polymer shown in Fig. 5. Thin dashed lines pressure dependence of the phase transformation temperatures l.c. to isotropic, Tc, and the glass transition temperatures, T , full line specific volume-temperature cut at 2000 bar (isothermal measurements)...

This paper deals with the degradation of substances like PVC, Tetrabromobisphenol A, y-HCH and HCB in supercritical water. This process is called "Supercritical Water Oxidation", a process which gained a lot of interest in the past. The difference between subcritical and supercritical processes is easy to recognize in the phase diagram of water. The vapor pressure curve of water terminating at the critical point, i.e. at 374 °C and 221 bar. The relevant critical density is 0.32 g/cm3. This corresponds to approx. 1/3 of the density of normal liquid water. Above the critical point, a compression of water without condensation, i.e. without phase transition is possible. It is within this range that supercritical hydrolysis and oxidation are carried out. The vapor pressure curve is of special importance in subcritical hydrolysis as well as in wet oxidation. 

Change other than solvation may occur in the stable solid phase. Thus rhombic sulfur (Chap. 17) is less soluble in suitable solvents than is monoclinic sulfur at temperatures below 95.5° C, the transition temperature between the two forms above this temperature the monoclinic form is the less soluble. The principles of thermodynamics require that the temperature at which the solubility curves of the two forms cross be the same for all solvents, and be also the temperature at which the vapor pressure curves intersect. 

Sometimes a transition between two crystalling phases occurs vei7 rapidly. That between orthorhombic sulfur and monoclinic i ulfur is rather slow, however, taking minutes or hours, and it is hence easy to superheat orthorhombic sulfur by heating it rapidly. If-this is done, the vapor pressure of the crystals increases as shown by the curve A, and at the point IP, where this curve crosses the vapor pressure curve of the liquid, the crystals melt. The temperature at P, 112.8° C, is... 

Figure 4. Proportional depletion by reaction with energy-dependent k2 E) and according to the Lindemann-Hinshelwood model (constant kz). The curve has been calculated at 999 K for ethane dissociation at the transition pressure.

Odd-even alternations have not been directly observed in k[A) curves, at least not in the G, LE and LC state. However, Sims and Zografi ), who systematically studied the pressure loss as a function of time upon keeping the film at constant A below the collapse pressure for the CjgCOOH- C20COOH series, found differences in film stability between odd and even-fatty acids. The odd-numbered ones were more resilient against pressure loss. On the other hand, up to the transition pressure, at any rate of compression there is a gradual increase of this pressure with the chain length ). 

Figure 1 shows mercury porosimetry curves on high dispjersive precipitated silica and on a low density xerogel previously examined [5]. The volume variation as a function of logarithm of pressure shows the same behavior. On both curves, one can see a sharp increase of the curve slope for a characteristic transition pressure P,. The value of this transition pressure is 45 MPa for precipitated silica and 27 MPa for the low density xerogel sample. The value of transition pressure Pt is dependent of the compressive strength of the sample. 

The curve of a sample submitted to the maximum available mercury pressure (200 MPa) is given on the figure 2 (curve b). It shows that above the characteristic transition pressure Pi, the volume variation is due to the mercury intrusion into the pore network which has been not completely destroyed at pressure below 45 MPa. During depressurization, the mercury extrudes with an hysteresis and a certain quantity of mercury remains entrapped. Back at the atmospheric pressure, the recovered sample initially white became gray and the microscope... 

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