Ternary peritectic points

The vertical projection of the phase diagram of this system is shown in Figure 3.34. The phase diagram has four planes pc(A), pc(B), pc(C), and pc(ABC), which are the projections of the planes of primary crystallization of the compounds A, B, C, and ABC, respectively. The figurative point of the ternary compound ABC lies outside the plane of its primary crystallization. In contrary to the previous case, the phase diagram of this type has only one ternary eutectic point Ct and two singular points, which are the ternary peritectic points Ptj and Ptj. The boundary lines Ptj-et and Ptj-et represent the simultaneous crystallization of components B and ABC, and C and ABC, respectively. 

No peritectic point was noticed with lithium chloride and potassium or sodium chlorides. T. W. Richards and W. B. Meldrum (1917) have also studied ternary mixtures of lithium and sodium chlorides with potassium, rubidium, or caesium... 

The ternary invariant points (e.g., e and /in the above diagrams) that appear in a system without solid solution are either ternary eutectics or ternary peritectics. Whether it is eutectic or peritectic is determined by the directions of falling temperatures along the boundary curves. 

In the previous diagrams, points e and / for the congruently-melting compound are both ternary eutectic. On the other hand, for the incongruently-melting compound die point e is the ternary eutectic, whereas the point/is the ternary peritectic. 

At point m, a ternary peritectic reaction occurs isothermally. 

There are five ternary eutectic and one peritectic points. The crystallization path of all mixtures, figurative points of which lay inside the triangles BY-A3B2X3Y2-BX2 and A3B2X3Y2-P-BX2, starts with the primary crystallization of BY, A3B2X3Y2, or BX2, followed by the crystallization of the neighboring salt till the peritectic point P is reached. 

The section Ce2Se3-SnSe (fig. 16) is a quasi-binary section of the ternary system Ce-Sn-Se and belongs to a peritectic type with limited solid solutions based on SnSe (Murguzov et al. 1986). The parameters of the peritectic point are 70 mol% SnSe and 870 5°C. The ternary compound Ce2SnSe is formed according to the reaction... 

No invariant reaction exists inside the ternary system. A critical tie-line has been observed at 1220°C [1935Koe]. At this temperature the L-i-yi-i-y2 tie-line triangle degenerates to a straight line. The end points of this line are the critical point c and the upper point of the monovariant peritectic line Pc-ps- The... 

The liquidus curve and the invariant temperatures are known to good accuracy. This result will be an aid for understanding the thermodynamic behaviour of the ternary and quaternary phases. It has been possible to calculate the temperature of the metastable melting point of CoSbj (1283K instead of 1210K for the peritectic decomposition of the 1 2 phase). One can observ e that these temperatures are not so far and it could explain the problems occuring in the fabrication of the materials as well as the lack of 1 3 compounds for iron and nickel systems. 

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