Amorphous eutectic temperature

To freeze a substance, it must be cooled to such a temperature at which the water and the solids are fully crystallized, or at which areas of crystallized ice and solids are enclosed in zones in which amorphous concentrated solids and water remain in mechanically solid state (see Section 1.1.2). In the zone of freezing, the ice crystals are growing first, thus concentrating the remaining solution, which can vary the pH value. In many substances a eutectic temperature can be determined, but in many others this value does not exist. The crystallization depends on several factors which influence each other cooling velocity, initial concentration, end temperature of cooling, and the time at this temperature. In several products no crystallization takes place and the product remains in an amorphous, glasslike phase, or a mixture of both occurs. 

After cooling, the stable / -phase is embedded in an amorphous phase, from which an oxide nitride can be precipitated during a devitrification heat treatment, which is done just below the eutectic temperature. But even after... 

Freezing the product below its eutectic temperature (for crystalline materials) or below its glass transition temperature (for amorphous materials) ... 

Tx also shows a similar compositional dependence as that for Hy. As shown in fig. 6, as the M content increases from 8 to 20%, Tx increases from 498 to 715 K for Al-Si-(Cr,Mn,FeorCo) alloys and from 370 to 575 K for Al-Si-Ni alloys. On the other hand, the increase in Tx of Al—Ge-M alloys with increasing M content is considerably smaller than that of Al-Si-M alloys, and the increase of Tx with increasing M content from 8 to 15% is as small as about 50 K. Furthermore, Tx is higher by 50 to 150K for Al-Si-M alloys than for Al-Ge-M alloys. This difference is probably because the eutectic temperature of the Al-Si alloy is higher by 153 K than that of the Al-Ge alloy, Massalski (1986). The Tx values of Al—Si—M alloys are considerably higher for Al-Si-(Cr,Mn,FeorCo) alloys than for Al-Si-Ni and the Al-Si-M (M=Cr, Mn, Fe or Co) alloys have nearly the same Tx values. No distinct change in Tx with Si and Ge content is observed as shown in fig. 7. Thus, the Hy and Tx of Al-Si-M and Al-Ge-M amorphous... 

On cooling a typical copolymer melt, one observes, after the customary supercooling, crystallization of pure A. The melt must thus increase to some degree in concentration B as predicted by the liquidus line of Fig. 4.23. But in copolymer systems, one neither reaches the liquidus concentration, nor observes the eutectic point. The system freezes to a metastable state before the eutectic temperature is reached. Usually only one component crystallizes in random copolymers. All of the component B and a large fraction of A remain in the amorphous portion of the semicrystalline sample. For a more extensive discussion of the irreversible melting of homopolymers and copolymers see Ref. 57, Chapters IX and X. 

All attempts to form crystals in ultraphosphate systems with K2O-P2O5 ratios of 0.5 or less have been unsuccessful. Thermal analyses reveal an endothermic region extending from about 200 °C to the eutectic temperature at 450 °C. This amorphous region becomes more and more pronounced as M2O-P2O5 ratios are decreased to 0.5, where the total system is amorphous. 

Smith et al. [64] prepared a series of PET/PTT copolyesters, and found that addition of the other component suppressed the melting point of the respective homopolymer. Between 37 and 60 % PTT content, the copolymers became amorphous and did not show any melting endotherms in the differential thermal analyzer scans. A similar behavior was observed by Balakrishnan and coworkers [102] in PET/PTT copolyesters prepared by the transesterification of PET with PDO, and by the copolymerization of EG and PDO with DMT [103, 104], The non-crystallizing behavior of copolymers with intermediate contents of the respective component is similar to that of a eutectic mixture, indicating formation of random copolyesters. The 7 g and solubility temperature of the copolyesters were, however, continuous and went through minima with increasing PTT content [64],... 

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