Crystallinity phase field diagram

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

The difficulty in establishing a unique structural model for liquid crystalline side-chain polymers is the poor quality of x-ray data. X-ray analysis is the preferred method for structural investigations on a molecular level. It only shows a few reflections in the liquid crystalline phase and cannot be interpreted in a unique way. The alignment of samples in an external field, which yields fibre x-ray diagrams, has not led to much improvement as regards the idea of packing of polymers. However, it can lead to information about the orientation of the polymer and establishes the idea of small domains within the liquid crystalline phase. ... 

Combining the Flory-Hu jns theory for an isotropic mixing and a free energy for other liquid crystalline phases opens up the possibility of extending the theory to describe other Uquid crystalline phases such as smectic C. Such mean field theories have been appUed to phase diagrams of colloidal solutions [35], crystal and liquid crystal mixtures [82], and colloid and Uquid crystal mixtures [83]. 

Proteins are both colloids and polymers. Therefore, attempts have been made to understand the phenomenon of protein aggregation with the help of models from the polymer and colloid fields such as DLVO theory, describing the stability of colloidal particles, or phase behavior and attraction-repulsion models from polymers (De Young, 1993). For faster progress, more phase diagrams for equilibrium protein precipitation, in both the crystalline and the non-crystalline state, as well as more data on observations of defined protein oligomers or polymers, are required. 

Figure 11. Temperature-magnetic field (parallel to the basal plane) phase diagram of single crystalline copper metaborate 1 - incommensurate phase of helix magnet 2 - commensurate phase of weak ferromagnet.

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