Phase diagrams ceramic systems

In addition to all the metallic phase diagrams, a series of volumes devoted to ceramic systems have been published since 1964 by the American Ceramic Society and is still continuing. The original title was Phase Diagrams for Ceramists, now it is named Phase Equilibria Diagrams. Some 25,000 diagrams, binary and ternary mostly, have been published to date. There is no compilation for polymeric systems, since little attention has been devoted to phase diagrams in this field up to now. 

Figure 4.20 Tetrahedron space model for the phase diagram of the quaternary system A-B-C-D. The isotherms T], 72, T3 are shown for the primary phase volume of component A [17]. Reprinted with permission of The American Ceramic Society, www.ceramics.org. Copyright [1984]. All rights reserved.

FIGURE 3.14 Ternary phase diagram of (Zr,Y)02-La203-Mn304 system at 1400°C in air. (Zr,Y)02 denotes 3 mol% Y203-Zr02. Symbols + are the experimental data. (From Jiang, S.P. et al., J. Euro. Ceram. Soc., 23 1865-1873, 2003. With permission.)... 

Figure 2.19 Perspective drawing of a ternary system with a simple eutectic and no ternary compound. Reprinted, by permission, from Phase Diagrams for Ceramists, Vol. 1, p. 15. Copyright 1964, The American Ceramic Society.

Much of what we need to know abont the thermodynamics of composites has been described in the previous sections. For example, if the composite matrix is composed of a metal, ceramic, or polymer, its phase stability behavior will be dictated by the free energy considerations of the preceding sections. Unary, binary, ternary, and even higher-order phase diagrams can be employed as appropriate to describe the phase behavior of both the reinforcement or matrix component of the composite system. At this level of discussion on composites, there is really only one topic that needs some further elaboration a thermodynamic description of the interphase. As we did back in Chapter 1, we will reserve the term interphase for a phase consisting of three-dimensional structure (e.g., with a characteristic thickness) and will use the term interface for a two-dimensional surface. Once this topic has been addressed, we will briefly describe how composite phase diagrams differ from those of the metal, ceramic, and polymer constituents that we have studied so far. 

Ondik, H.M. and HF. McMurdie Phase Diagrams pr Zirconium and Zirconia Systems, The American Ceramic Society, Westerville, OH, 1998. 

Fig. 8. Phase diagram for the Zr02-Y203 system. From ref. [19]. Reprinted by permission of the American Ceramic Society.

This approach has been applied for Si-Al-O-N ceramics. The results can explain the existence of the amorphous phase in the grain boundaries (Fig. 24), depending on the overall composition of the system ([equ% O] = 16, 12, 8 and [equ% Al] = 10.6) and on the strength of interaction (Ap). In a strict sense it must be concluded that the conventional phase diagrams of Si3N4 ceramics are incomplete representations of materials containing an amorphous intergranular phase. 

Common approaches for the tailoring of nonmetallic (ceramic) materials properties involve topochemical methods (those where the crystal structure remains largely unaffected) and the preparation of phases in which one or more sublattices are alloyed. In principle, such materials are within the realm of CALPHAD. On the other hand, as has already been stated, extrapolation does not really aid the discovery of new or novel phases, with unique crystal structures. Furthermore, assessed thermochemical data for the vast majority of ceramic systems, particularly transition metal compounds, are presently not available in commercial databases for use with phase diagram software. This does not necessarily preclude the use of the CALPHAD method on these systems However, it does require the user to carry out their own thermodynamic assessments of the (n — 1 )th-order subsystems and to import that data into a database for extrapolation to nth-order systems, which is not a trivial task. 

Karlin, S., Colomban, P., Phase diagram, short range structure and amorphous phases in the Zr02-Ge02(-H20) system, J. Am. Ceram. Soc., 82, 735, 1999. 

The diagram indicates that the mixes for the manufacture of steatite ceramics lie away from the theoretical composition of enstatite, which is a binary phase in the system MgO —Si02- The maximum enstatite content should be attainable through... 

FIG. 189. Phase diagram of the system MgO—AI2O3—S1O2 with plotted regions showing the composition of ceramic materials (from Kingery, 1960). 

The most significant ceramic dielectrics can be found in the system BaO—Ti02, the phase diagram of which is shown in Fig, 192,... 

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