Incongruently melting phases

The first system is characterized by a partial miscibility of the liquid phases, the second one is instable with incongruent melting points at -54... 

The crystal growth of metal borides by gas-phase methods permits preparation of products at moderate T (1000-1500°C). This is an important advantage since most borides melt at high T (ca. 3000°C), which makes their crystal growth from melts difficult. In addition, the gas-phase methods lead to the formation of single crystals and solid films of incongruently melting borides. 

Keywords PCM phase change latent heat melting heat storage cold storage corrosion phase separation incongruent melting subcooling nucleator products. 

The effect of phase separation, also called semicongruent or incongruent melting, is a potential problem with PCM consisting of several components. Phase separation is explained in Figure 104 with a salt hydrate as example. 

Fig. 5.9 Phase diagram of the PEO-LiCFjSOj system. The 0.5/1 compound forms upon the incongruent melting of the 1/1 compound at 150 °C. From Vallee et al. (1992).

Fraser et al. (1983, 1985) deduced that, in several instances, the structure of the silicate melt should mimic the structural arrangement of the solid phase at liq-uidus. In incongruent melting processes, the structure of the liquid differs substantially from that of the solid phase of identical stoichiometry. 

Figure 7,8 Gibbs free energy curves and T-X phase relations for an intermediate compound (C), totally immiscible with pure components. Column 1 Gibbs free energy relations leading to formation of two eutectic minima separated by a thermal barrier. Column 2 energy relations of a peritectic reaction (incongruent melting). To facilitate interpretation of phase stability fields, pure crystals of components 1 and 2 coexisting with crystals C are labeled y and y", respectively, in T-X diagrams same notation identifies mechanical mixtures 2-C and C-1 in G-X plots.

From section 1.4, the variation of a mineral phase during incongruent melting is described by the following relationship... 

Person 1 Determine the phases present, the relative amounts of each phase, and the composition of each phase when the only incongruently melting intermetallic compound in this system is heated to 800°C. 

Fig. 3.33 Schematic drawing of phase diagram around GaAs composition. TJ denotes the incongruent melting temperature for stoichiometric GaAs and denotes the congruent melting temperature. The congruent melting composition is assumed to be in the As excess region.

Fig. 18. Comparison of the original (above) [4] and the revised (below) [5] phase diagrams of the Ce-Fe system. The change in the formation mode of CeFe2. from unequivocally incongruent-melting to nearly congruent-melting is to be noted.

Figure 12 Solid-liquid-phase diagram, showing incongruent melting.

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