Fusion entropy

Two other remarkable universalities emerge from the value of y. First, at a reference laboratory time scale of 1 h IO tq, we have a universal value of Sc O.Sfe. This implies Sc Tg)/sc Tm) — 0.7, where Sc Tm) is, of course, also the fusion entropy. This relation is independent of the precise identity of the moving subunit and holds very well. A second important universal feature emerges from the universal value of y/Tgi the cooperative size at Tg is nearly universal. 

Sm - Sc) = A/fm-c/Tg > 0 is the fusion entropy. If the equilibrium pressure between the crystalline phase and the melt under the given temperature is known to be Pe, then... 

The following are experimental data for diopside melting in its own melt (Kuo and Kirkpatrick, 1985). Diopside melting temperature is 1664 K. The fusion entropy is 82.76 J moC K Assume that the activation energy is 300 kj/mol. 

Table 4. Total Entropies of Fusion, Entropies of Fusion at Constant Volume and Volume Changes on Fusion ...

Fig. 29. The entropies of fusion (o) and the sum of the transition and fusion entropies ( ) of the DiFj compounds.

Trinitrotoluene (also known as y-TNT) is one of the main impurities in military and commercial grades of TNT. Chick and Thorpe (1971) characterized two polymorphs. Form I (mp 376.2 K) may be obtained by recrystallization from alcohol or solidification of the melt. Form II (mp 347.2 K) is produced in small quantities with difficulty from an undercooled melt. It readily converts to Form I by mechanical perturbation or even spontaneously. Chick and Thorpe also determined latent heats of fusion, entropies of fusion, specific heats, IR spectra. Due to the conversion induced by grinding no X-ray data were presented for either form. No crystal structures have been reported. 

Fusion enthalpy (kJ moP7 Crystallization entropy (J mor He (kJ mor7 Fusion entropy (J moF ... 

Fusion Entropy (kJmor ) Crystallization Enthalpy (kJmoP )... 

Degree of crystallinity Heat of fusion Entropy of fusion Density (crystalline)... 

Blundell [28] first demonstrated that the main features of crystallization for thermotropic longitudinal PLCs are (1) small crystallites ( 5 nm for quenched samples and about 10 nm across for annealed ones) (2) limited crystallinity (about 20% in wide angle X-ray diffraction (WAXD)) (3) low surface energy of the crystallites (4) little change of molecular conformation before and after melting and (5) low fusion entropy and enthalpy (sometimes no detectable endotherm on DSC thermograms). A model of small crystal size for extended chain polymers was proposed by Blundell [28]. 

From the latter equation the calculated boiling point of Cm is 3110°C. The derived heat of fusion, entropy of fusion, and average second-law entropy are 13.85 kJ mol , 9.16 JK mol , and 106.7 3.0 J K mol , respectively. Low-temperature condensed-phase thermodynamic parameters await the availability of long-lived isotopes. For excellent discussions of thermodynamic, electronic, and magnetic effects in curium and other actinide and lanthanide metals, the reader is referred to recent articles by Ward and Hill [34]. 

From the slope of a (1 — Tm/T ) versus (1 — c()) plot, along with the fusion entropy, Xfh he crystalline polymer blend can be determined. 

---