Condensed transition point

The SJ-S2-V point is the transition point of the substance, the Sj-L-V and Sj-L-V points are melting points, and the SJ-S2-L point is a condensed transition point (7). Whether all these points can be experimentally attained depends on the empirical details of the system itself. 

At a given (low) temperature and pressure a crystalline phase of some substance is thermodynamically stable vis a vis the corresponding amorphous solid. Furthermore, because of its inherent metastability, the properties of the amorphous solid depend, to some extent, on the method by which it is prepared. Just as in the cases of other substances, H20(as) is prepared by deposition of vapor on a cold substrate. In general, the temperature of the substrate must be far below the ordinary freezing point and below any possible amorphous crystal transition point. In addition, conditions for deposition must be such that the heat of condensation is removed rapidly enough that local crystallization of the deposited material is prevented. Under practical conditions this means that, since the thermal conductivity of an amorphous solid is small at low temperature, the rate of deposition must be small. 

A somewhat similar phenomenon is observed with substituted ureas, which also have two condensed films stable at the same pressure but within different temperature ranges. Here rise of temperature at the transition point produces a diminution of area, and pressure lowers the transition point. 

There is a series of arsenatophosphates corresponding with each of the three forms of condensed potassium arsenate and phosphate, the transition points and melting point of which vary systematically with composition (see Fig. 10). A chain structure for the a-form of potassium arsenate and arsenophosphate may be inferred from their isomorphism with (KP03)xB. The 7-forms also contain high-molecular anionic chains for, when they are hydrolyzed, monoarsenate and polyphosphates with chain length up to n = 6 are formed, depending on their phosphorus content. No metaphosphate is produced, however. 

Try running your hand along the outside of such a condenser. Feel for the point on the surface of the shell where there is a noticeable drop in temperature. The upper part of the shell will be hot. The lower part of the shell will be cold. The transition point corresponds to the liquid level of condensate in the shell. The condensate level will always be higher toward the shell outlet nozzle. Again, this all applies only to condensers in total condensing service. 

Notice that the phase transitions—condensation at point B and evaporation at point D—take place at boundaries on the phase diagram the system cannot move off these boundaries until the transitions are complete. 

In selective separation of hydrocarbons from their mixtures with air or from their aqueous solutions, it makes sense to use membranes based on rubbery polymers, whose permeability increases with the decrease in glass transition point. Permselectivity of rubbery polymers is dominated by the sorption component, which increases with condensability of the hydrocarbon penetrant. Higher activity of the component being separated in the feed mixture results in plasticization of the membrane and can make it swell. This can produce a non-monotonic dependance of selective properties of the membrane on activity of the component being separated. As a rule, permselectivity for mixtures of penetrants is significantly lower than their ideal values. Negative values of sorption heat of easily condensable hydrocarbons can result in existence of non-monotonic temperature dependencies of mass transfer coefficients. 

Tables which show only values for the stable phases at 1 bar pressure are multiphase tables. Multiphase tables can always be recognized by the presence of solid lines, indicating phase transitions, on the table. They are prepared in a manner similar to tables for condensed phases. The functions are evaluated in the same manner as for a solid up to the first transition point then the enthalpy and entropy of transition are added and the integration is continued using the heat capacities of the next phase. At each transition, the above process is repeated.

Typical results are shown in Fig. 6 for U-methane in graphite pores of H =7.5 at T=114 K. At p/ps=l the system is solid-like at this temperature, but a discrete change in density occurs around p ps ca.0.5. The self diffiisivity along axial direction also shows drastic change at this point. Further examination of various characteristics of molecular state such as snapshots, in-plane pair correlations and static structure factors confirmed that this change in density is the result of a phase transition from solid-like state to liquid-like one, or melting. Since the critical condensation condition for this pore is far lower than this transition point to stay around p ps= ca.0.2, the liquid-like state is not on metastable branch but thermodynamically stable. Thus a solid-liquid coexistence point is found for this temperature. 

The adsorption and desorption isotherms have been calculated for the Nj sorption at 77K in cylindrical pores of MCM-41 materials in the range 1-12 nm. The points of spinodal and equilibrium transitions are plotted in Fig. 2. There are several features worth noticing. As the pore size increases, the line of spinodal desorption saturates at the value corresponding to the spinodal decomposition of the bulk liquid. The line of equilibrium capillary condensation asymptotically approaches the Kelvin equation for the spherical meniscus and the line of spontaneous capillary condensation asymptotically approaches the Kelvin equation for the cylindrical meniscus. This asymptotic behavior is in agreement with the classical scenario of capillary hysteresis [12] capillary condensation occurs spontaneously after the formation of the cylindrical adsorption film on the pore walls while evaporation occurs after the formation of the equilibrium meniscus at the pore end. Most interestingly, the NLDFT predictions of equilibrium and spontaneous capillary condensation transitions for pores wider than 6 nm are approximated by the semi-empirical equations of the Deijaguin-Broekhoff-de Boer theory [13]. 

Phosphorus crystallizes in at least five polymorphic forms. The white form is metastable and is prepared by condensing the vapour. There are apparently two closely related modifications of white P, with a transition point at —77°C. The... 

Law of Successive Reactions.— When sulphur vapour is cooled at the ordinary temperature, it first of all condenses to drops of liquid, which solidify in an amorphous form, and only after some time undergo crystallisation or when phosphorus vapour is condensed, white phosphorus is first formed, and not the more stable form, violet phosphorus. It has also been observed that even at the ordinary temperature (therefore much below the transition point) sulphur may crystallise out from solution in benzene, alcohol, carbon disulphide, and other solvents, in the monoclinic form, the less stable crystals then undergoing transformation into the rhombic form a similar behaviour... 

The sextuple point is the point of intersection of the curves of six univariant systems, viz. four solubility curves with three solid phases each, a vapour-pressure curve for the system two reciprocal salt-pairs — vapour and a transition curve for the condensed system two reciprocal salt-pairs—solution. If we omit the vapour phase and work under atmospheric pressure (in open vessels), we find that the transition point is the point of intersection of four solubility curves. 

The pressure exponent or pressure sensitivity parameter (v or n) is shown in Fig. 6. At very high and low pressures, the condensed-phase kinetically controlled regimes seen earlier in Fig. 3 are also apparent in Fig. 6 where the pressure sensitivity goes to zero. The low-pressure transition point can be seen to be sensitive to fg, Qr, and Q, increasing with each of those parameters, whereas the high-pressure transition point is not. In the important intermediate pressure range, the pressure sensitivity is relatively constant at around 0.8 for small Eg and 1 for... 

The tables for solid and liquid substances end either with a phase transition point or with an upper calculation limit, below which data were available. The final temperature is always a calculation limit in the case of gaseous substances. With condensed substances there are the following special cases for the final temperature T ... 

The dependencies of FI on B for various 0c values, calculated with Eqs. (2.118) and (2.120), are shown in Fig. 2.22. In agreement with the models given in [I, 104, 105, 119-128], the curve exhibits a sharp inflection accompanied by an increase in the slope at the condensation onset point. In contrast to curves presented in Fig. 2.21, the saturation of the monolayer does not move these curves towards that calculated for the case when no phase transition takes place. We find, that the lower the 0c-value, the steeper is the dependence of FI on B, which seems incorrect. For example, for 0c = 0.01 (not shown in Fig. 2.22) the FI (B)-curve coincides... 

Beyond this phase transition point, the creation and growth of condensed phase domains is observed. The shape of these domains is very similar to those of pure DPPC domains, as one can see from the images given in Fig. 4.51. The BAM images were taken at different times after the start of the penetration experiments and the letters correspond to the respective moments in the rt(t) curve. The aggregation of DPPC into condensed phase domains is induced even if the initial surface DPPC concentration is less than 50% of the critical adsorption T. ... 

If, therefore, we consider a given pressure, molecules of a pure substance wiU pass all into one phase or all into the other, except at a single temperature where a given pair of phases can coexist, that is at the melting-point, condensation point, or transition point. At this equilibrium temperature, since G = G, G remains at its minimum for all values of a. Thus the equilibrium does not depend upon the relative amounts of the two phases present. 

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