There are four primary phase fields, one for each of the solids, A, B, C and D. 3.6 shows a congruently melting ternary phase, D (a compound of A, B and C), and its influence on the shape of the liquidus surface. Clearly, maximum liquid content occurs at point c, and decreases as the system cools in the direction cme.įig. The relative amounts of A, C and liquid can now be determined from the line portions 圜, zA and yz, respectively. Similarly, point z can be located by translating line xA. By translating the line xC such that it passes through the original composition, c, an intersection y on the line AC can be found. Construction lines xA and xC can be drawn to construct the triangle xAC. As before, it may be of interest to know the amount of any phase present at a particular temperature, x, for a fixed bulk composition, c. 3.5B to illustrate the application of the lever rule in ternary systems. Further cooling causes compositional changes in the liquid along me resulting in all solids (A, B and C) coexisting at the eutectic temperature. Solid C crystallises in its primary phase field at c and the liquid composition alters in the direction cm where A crystallises at m. The cooling behaviour within such a system is illustrated by example in Fig. This occurs at the minimum temperature on the liquidus ‘surface’. 3.5, a ‘ternary eutectic’ is shown at e′. In addition to the binary eutectics located on the binary edges of the diagrams in Fig. The cooling characteristics of phases in the ternary system can be described in a similar way to that previously discussed for binary systems. (A) and (B) Alternative representations of the ternary system A–B–C. It can be seen that ternary phases lie within the boundary of the diagram, illustrating the contribution of each of the components in the phase composition.įig. On the diagram, this composition can be fixed in several ways, but the simplest and often most convenient way is to plot the composition using percentages of only two of the components the third is automatically fixed by the geometry of the diagram. Additionally, the components can participate to provide ternary or three-component phases where the fractional contribution of all components must add up to unity, for example, a phase with the composition A 3BC 2 has 50% A, 16.7% B and 33.3% C. Each edge of the ternary diagram between pairs of end-members is a binary system in its own right, as is a vertical section between two compatible phases, and has all the normal properties of a binary system. But first, some explanation of interpreting compositions from ternary diagrams will be given. We shall therefore focus on isothermal sections, an example of which is illustrated in Fig. However, it is sometimes easier and more relevant to discuss isothermal sections of the complete diagram, particularly for subsolidus properties or, as is useful in some cases, a vertical section between two compatible phases.
#Ternary diagram heaviest component how to
A practical example of how to use this is given in Section 3.4.2 for the CaO–Al 2O 3–SiO 2 system. 3.5B) arrows on the bold phase field boundary lines indicate the direction of falling temperature, and double arrow where this becomes a reaction curve. The conventional way of expressing detail in the complete system is by the use of isothermal contour lines on the liquidus surface ( broken lines in Fig. 3.5A) rather than lines as in the binary system. However, in three dimensions the diagram is more complex with surfaces emerging ( Fig. Ternary diagrams represent three-component systems and are conveniently presented as triangular diagrams where each side corresponds to an individual binary system.
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