Metastable phase diagram

Figure 5.14 Calculated (a) stable and (b) metastable phase diagrams for the Sn-Sb system.

Figure 11.1. Calculated (a) metastable phase diagrams in the Ni-Ti system, (b) some combinations of these digrams and (c) comparison of calculated and observed stable diagram (Ansara 1979).

Herein, we expand on the discussion of our recently observed isothermal amorphous-amorphous-amorphous transition sequence. We achieved to compress LDA in an isothermal, dilatometric experiment at 125 K in a stepwise fashion via HDA to VHDA. However, we can not distinguish if this stepwise process is a kinetically controlled continuous process or if both steps are true phase transitions (of first or higher order). We want to emphasize that the main focus here is to investigate transitions between different amorphous states at elevated pressures rather than the annealing effects observed at 1 bar. The vast majority of computational studies shows qualitatively similar features in the metastable phase diagram of amorphous water (cf. e.g. Fig.l in ref. 39) at elevated pressures the thermodynamic equilibrium line between HDA and LDA can be reversibly crossed, whereas by heating at 1 bar the spinodal is irreversibly crossed. These two fundamentally different mechanisms need to be scrutinized separately. 

Thermodynamics of Metastable Phase Equilibria and Metastable Phase Diagrams... 

Figure 6.3. The metastable phase diagram for the polyure-thane-poly(methyl methacrylate) SIN at 60°C. The PMMA gels at and above the plane Gj- U -PU. The intersection of the PMMA gelation plane and the surface along the curve A represents the condition of simultaneous phase separation and PMMA gelation.

Figure 6.4. The metastable phase diagram, same compositions as Figure 6.3, illustrating the PU gelation plane, G2-MMA-PMMA.

The important points developed in this section are that sequential IPN synthesis tends to make dual phase continuous materials. Eor both sequential and simultaneous syntheses, a metastable phase diagram can be developed to study the kinetics of phase separation and gelation, so that better control of the morphology can be attained. The thermoplastic IPNs depend on equal volume and viscosity ratios to attain the dual phase continuity. 

Fig. 7. C-Cu-Fe. (7Fe) projection with lines of double saturation in the Cu-Fe-Fc3C metastable phase diagram...

She] Shevchuk, L.A., Dudetskaya, L.R., Gurinovich, V.I., Stmcture of Silicon Steels and Metastable Phase Diagram of Iron-Carbon-Sihcon Alloys (in Russian), Izv. Akad. Nauk BSSR, 3, 54-61 (1972) (Experimental, Phase Diagram, Morphology, 9)... 

As shown in Fig. 6.3, Mishra et al. (1995) presented a tetrahedron as the spatial form of their metastable phase diagram, the comers of which represented MMA, PMMA, urethane prepolymer U , and PU. The PMMA contained 0.5 % tetraethylene glycol dimethacrylate, causing it to gel after about 8 % conversion see the Gi- U -PU plane. The phase separation curve for the ternary system MMA-PMMA- U (front triangle) on polymerization of only the MMA is indicated by the points C-D-A-E. Similarly, the phase separation curve for the MMA-PMMA-PU system (see rear triangle. Fig. 6.3) is represented by the points J-B-K-L. Thus, the entire tetrahedron volume is divided into two regions one phase separated and the other single phased, separated by the curvilinear constmction C-D-A-E-L-B-J. This surface exhibits a characteristic sail-like shape. 

A metastable phase diagram is different from the stable type. The G(x, T) function of the metastable phases is not located at a minimum position, but at a secondary minimum. Under the condition r(T)>Tp(T) (the critical time), metastable phases transform to stable phases. A method to attain a metastable phase is that the stable phase in the (x T,) state under the condition r(T) < fp(T) changes to the ( 2, T2) state (it is also allowed that only x or T changes). In order to obtain a metastable phase, the corresponding Tp T) must be realized technologically. When long-distance diffusion of atoms is required for crystallization of a liquid, amorphous alloys can be obtained by quenching the liquid under the condition of r(T)polymorphous transformation, only a solid solution will be... 

Fig. 13. A tetrahedron metastable phase diagram for the SIN polymerization of poly(methyl methacrylate) and polyurethane.

The finding that the VHDA HDA transformation is continuous [65], as opposite to the pressure-induced, apparently discontinuous LDA-HDA transformation, has implications for our understanding of the metastable phase diagram of amorphous supercooled and glassy water. It seems counterintuitive that a continuous amorphous-amorphous transition at 140K changes character into a discontinuous liquid-liquid transition when performed above Tg. On the other hand, it seems quite possible that a first-order-like amorphous-amorphous transition develops into a first-order liquid-liquid transition when performed above Tg. Since first-order... 

Fig. 6. Metastable phase diagram of the quaternary system (NaCl- KQ - Na2B407 - K2B4O7 -H2O) at 308.15 K. (a), dry-salt phase diagram (b), water-phase diagram.

Fig. 8. Comparison of the metastable phase diagram at 308.15 K in solid line and the stable phase diagram at 298.15 K in dashed line for the quaternary system (NaCl - KCl - Na2B407-K2B4O7 - H2O). - metastable experimental points -o-, stable experimental points.

Figure 13.21 Metastable phase diagram for the poly(methyl methacrylate)-polyurethane SIN polymerization. The four corners of the tetrahedron represent the pure monomers and polymers indicated.

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