Equilibrium melting temperature structure

The equilibrium, room temperature structure of pure cobalt is hep. The fee structure is stable at high temperatures (422 °C to 1495 °C) and has been retained at room temperature by rapid solidification techniques [101], X-ray diffraction analysis was used to probe the microstructure of bulk Co-Al alloy deposits containing up to 25 a/o Al and prepared from solutions of Co(II) in the 60.0 m/o AlCfi-EtMelmCl melt. Pure Co deposits had the hep structure no fee Co was observed in any of the deposits. The addition of aluminum to the deposit caused a decrease in the deposit grain size and an increase in the hep lattice volume. A further increase in the aluminum content resulted in amorphization of the deposit [44], Because the equilibrium... 

Floudas et al. [135] also studied the isothermal crystallization of PEO and PCL blocks within PS-b-PEO-h-PCL star triblock copolymers. In these systems the crystallization occurs from a homogeneous melt Avrami indexes higher than 1 are always observed since the crystallization drives structure formation and does not occur under confined conditions. A reduction in the equilibrium melting temperature in the star block copolymers was also observed. 

What is important to the present study is to examine the effect of PEC comonomer, not i-PS copolymer structure, on the thermodynamics of interaction with i-PS. Consequently, we limited crystallization temperatures to values less than 180 °C to Inhibit the Tb enhancement process. As can be seen from Figures 5 and 6, good straight lines, which appear to follow Equation 6, can be drawn through the solid data points corresponding to these lower crystallization temperatures, and reasonable equilibrium melting temperatures result from the intersection of these lines with the Tb = Tc lines for each blend fraction of PEC. 

The kinetic restraints that are placed on the crystallization of polymers make it difficult, if not impossible to directly determine their equilibrium melting temperatures. The directly observed melting temperatures are primarily a reflection of the structure and morphology of the actual crystalline systems. The primary factors involved are the crystallite thickness, the interfacial free energy, and the influence, if any, of the noncrystalline region. There are, however, indirect methods by which to estimate the value of T. One of these is a theoretical method. The others are based on extrapolative procedures. To properly use the T values that are tabulated, and to understand their limitations, the basic assumption involved and the problems in execution need to be recognized. 

When a crystallizable polymer is cooled below its equilibrium melting temperature, the hierarchical structure formed can be probed by in situ scattering. Crystallization mechanisms can be determined by comparing the time evolution of the degi ee of crystallinity (wc) determined from WAXS and the total integrated scattering intensity or invariant during crystallization [27,38] from SAXS. 

The melting point must be equivalent in both samples at the extreme condition (infinite lamellar length), provided the native structure is of the same type, since the melting point (T ,) is thermodynamically defined as T = AH,JAS , where AH and AS are the enthalpy and the entropy of melting, re jectively. The 185 °C equilibrium melting temperature is rather amilar to the reported values... 

TABLE 21.5 Equilibrium Melting Temperature (7 ) and Folding Surface Free Energy (Oe) for PLLA Having Different Folding Snrfac Structures [62, 67, 272, 276-287]... 

---