Equilibrium melting point

For a pure substance, the melting point is identical to the freezing point It represents the temperature at which solid and liquid phases are in equilibrium. Melting points are usually measured in an open container, that is, at atmospheric pressure. For most substances, the melting point at 1 atm (the normal melting point) is virtually identical with the triple-point temperature. For water, the difference is only 0.01°C. 

The copolymers consist of strictly alternating sequences of diene and olefin. C-NMR measurements Showed the microstructure of the butadiene units in BPR to be exclusively of the trans-1,4 configuration (Figure 8). The isoprene units in isoprene-ethylene copolymer (IER) contain 84 % trans-1,4, 15 % cis-1,4, and 1 % 3,4 structures (Figure 9). Spontaneous crystallization in unstretched BPR samples was detected by dilatometry and confirmed by X-ray diffraction and DSC measurements. The extrapolated equilibrium melting point is about -10 °C. 

PTT is a semicrystalline polymer with a DSC peak melting point of 228 °C (Figure 11.5). The equilibrium melting points, 7m°, obtained from the... 

Generally, the crystalline melting point of a polymer corresponds to a change in state from a solid to a liquid and gives rise to an endothermic peak in the DSC curve [3,9], The equilibrium melting point may be defined as... 

The extrapolated equilibrium melting point of orthorhombic HDPE crystals is 146 147 C. Actual measurements of slowly crystallized samples give the highest melting point. Tm. at 133- 138°C. 

Fig. 5.34 Schematic of the growth rate in the three regimes of the Lauritzen Hoffman theory. Here AT = 7 J, - T where J 2, is the equilibrium melting point and Tc is the crystallization temperature,...

This difference in behavior must reflect the difference in energetic barrier in the different cases, perhaps due to differences in the degree of thickening required in the transition between the different forms, the proximity to the equilibrium melting point and also perhaps to differences in the initial lamellar thickness. 

Fig. 4.2 Melting behaviour of sulphathiazole. (a) 175 °C, which is the melting point for commercially available Form II, (b) some Form II crystals melting at 175 °C, while others transform to the stable modification, (c) 200 °C, at which point some of the stable form begins to melt, (d) the equilibrium melting point (Kuhnert-Brandstatter 1971) for the higher melting form. (From Kuhnert-Brandstatter 1971, with permission.)...

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