Phase rule cooling curve

At the time, the most promising approach appeared to be that of a method which referred to the phase rule. Determination of time-temperature cooling curves is an admirable procedure if the substance is crystalline, is completely stable and crystallizes rapidly from its melt. None of the antimalarials studied possessed all these properties. 

Since polymer solutions obey the rule of phases, it is expedient to use a traditional thermal analysis of the cooling curves in stud3ung their phase state. A peculiarity of the polymer-solvent system is its propensity to form solid solutes under definite ratios of components, which has been confirmed by X-ray diffraction analysis [69]. 

During cooling the mixture of the composition x(A), at Tpc solid solution Ass with the composition x (A) starts to crystallize. On further cooling, the composition of the saturated liquid follows the upper curve, while the composition of the solid solutions follows the lower one. The amounts of the saturated liquid L and the solid solution Ass change according to the lever rule. At the lower curve, the liquid phase disappears and the mixture solidifies. 

Eutectic Mixture What happens when we cool a melt having a composition When the temperature is lowered and the boundary of the two-phase region solid/ liquid is reached, a very B-rich mixed crystal p begins to separate from the melt. Further cooling causes more and more solid substance to crystallize whereby the ratio of melt to mixed crystal is determined by the lever rule. In the process, the melt is constantly depleted of B because almost pure B (mixed only with a bit of A) precipitates. When the system reaches the temperature and thereby the horizontal line, the residual melt with the composition Xg solidifies. The fi(x) curves (Fig. 14.11) are applied again here for the purposes of illustration. 

Stance see Fig. 2.2. The most striking properties, however, are those exhibited by liquid helium at temperatures below 2.17 K. As the liquid is cooled below this temperature, instead of solidifying, it changes to a new liquid phase. The phase diagram of helium thus takes on an additional transition line separating the two phases into liquid He I at temperatures above the line and liquid He II at lower temperatures. The low-temperature liquid phase, called liquid helium II, has properties exhibited by no other liquid. Helium II expands on cooling its conductivity for heat is enormous and neither its heat conduction nor viscosity obeys normal rules (see below). The phase transition between the two liquid phases is identified as the lambda line, and the intersection of the latter with the vapor-pressure curve is known as the lambda point. The transition between the two forms of liquid helium, I and II, is called the X... 

---