Melting point depression Phase diagrams

Figure 16.2 Experimental phase diagram of the sPP/EPDM blend as determined by a combination of DSC and light scattering techniques, exhibiting the combined LCST and UCST together with the melting-point depression. The UCST curve was determined after the blends were homogenized in the single phase below the T, but above the crystallization temperatures. The symbols represent the experimentally determined points and the lines are drawn by hand or polynomial hts to guide the eyes. (From Reference (6) with permission from Elsevier.)...

Figure 11 Phase diagrams of dodecyldimethylphosphine oxide in a family of homologous alkan-ols. That part of the phosphine oxide-water phase diagram linked to th dry phosphine oxide border is also shown. The form of these diagrams differs substantially from that of most surfactant—solvent systems (Fig. 10) in that the melting-point-depression region is expanded and the plateau region is small or nonexistent. (From Ref. 96.)...

Another example is given in Fig. 6.37, which shows the phase diagram of another copolyester based on p-hydroxybenzoic acid (HBA) and ethylene tereph-thalate. These polymers, first synthesized by Eastman-Kodak, USA, display a nematic mesomor-phism at a minimum of 40 mol% of HBA. The melting-point depression is also in this case relatively weak, possibly indicating blockiness in the monomer sequence. 

In pure titanium, the crystal structure is dose-packed hexagonal (a) up to 882°C and body-centered cubic (p) to the melting point. The addition of alloying dements alters the a—p transformation temperature. Elements that raise the transformation temperature are called a-stabilizers those that depress the transformation temperature, p-stabilizers the latter are divided into p-isomorphous and p-eutectoid types. The p-isomorphous elements have limited a-solubility and increasing additions of these dements progressively depresses the transformation temperature. The p-eutectoid elements have restricted p-solubility and form intermetallic compounds by eutectoid decomposition of the p-phase. The binary phase diagram illustrating these three types of alloy... 

The determination of purity by means of DSC is based on the assumption that impurities depress the melting point of a pure material according to the eutectic phase diagram behavior. 

A liquid-solid phase diagram established for blends of iPP/POE by means of DSC and LS is presented at the top left of Fig. 7.12, displaying four distinct regions isotropic (I), coexistence of crystal-isotropic (Ci +1), coexistence of crystal-crystal-isotropic (C1+C2 + I), and crystal-crystal (Ci + C2- -C3). Cj and C2 represent the a- and y-form crystals of iPP, respectively, while C3 is designated for POE crystals (31). The blend preparation is identical to the procedure conducted for sPP/POE blend specimens. These iPP/POE blends are found to be completely miscible in the melt state, showing little or no depression of the melting point with composition. 

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