Composition, critical eutectic

The solubility of carbon in iron is reduced by the addition of phosphorus, but the temperature of formation of the eutectoid pearlite is not influenced by the presence of the phosphide. P. Goerens and W. Dobbelstein gave for the composition of the ternary eutectic E, Fig. 27, at 953°, l-96 per cent, of carbon, 6-89 per cent, of phosphorus, and 9145 per cent, of iron and J. E. Stead, respectively 1 92, 6 89, and 9149. In Fig. 26, A represents the iron-phosphorus eutectic, and B, the iron-carbon eutectic. They showed that when sat. solid soln. of iron phosphide in iron are heated or cooled they show no critical point at Ars, and the structure is not broken up even... 

My own criticism on the theories proposed for superplasticity can be summarized in one word, electrons , or more accurately the lack of electronic consideration. This is similar to the theoretical consideration brought forward in the study of LME (liquid metal embrittlement) described in the previous chapter - no electronic consideration. As shown in Table 2, all superplastic alloys of binary system are found either at eutectic or eutectoid compositions. This is illustrated in Fig. 14 in which a few binary phase diagram involving superplastic alloys are shown. However, the people who made efforts in the formulation of theories did not consider this well-known fact important enough to incorporate into their theory formulation [24], In fact, this observation is so consistent one should ask the question of the special attributes associated with eutectic or eutectoid composition. Or the fact that the intermetallic compounds with superelastic property are all of the peritectic type. It must be emphasized that to this date there is no report of finding superplasticity in congruently-melting compounds. 

A number of parallel future efforts are required in the Ti-B alloy system. The primary objective of future work is to eliminate primary TiB. Efforts to optimize processing to achieve the balance of first and second tier mechanical properties required for fracture-critical applications are also underway. Ti-B alloys may be considered as a matrix for continuously reinforced Ti MMCs, where the exceptional specific strength and stiffness of Ti-B alloys may help overcome current weaknesses in Ti-MMCs. In addition to the Ti-B alloys discussed here, exploration and development of similar in-situ eutectic composites are underway. Specifically, extensive efforts on the Ti-Si system are being pursed [12], and results similar to those reported here are now being obtained. These results are discussed in detail elsewhere in this volume. 

The composition and microstructure of a solid formed in a system showing a eutectic point depends critically on the composition of the liquid with respect to the eutectic composition. The situation will be explained by using the lead-tin (Pb-Sn) phase diagram described in Section 4.2.3. 

Rg- 6.3 Typical phase diagram of associating diblock copolymers in which macro- and microphase separation compete. Binodal (solid line), spinodal (dotted hne), and MST (broken line) are drawn. Critical points are indicated by CP. At the crossing of the spinodal and MST hues, Lifshitz points (LP) appear. At the stoichiometric composition where the number of A groups equals that of B groups, a eutectic point (E, E ) appears. (Reprinted with permission from Ref. [2].)... 

Binary organic mixtures with PAHs can form monotectic systems. Table 2 lists the monotectic and eutectic point of a few monotectic forming PAH systems. Monotectic systems are characterized by monotectic, eutectic and upper consolute temperatures, though the upper consolute temperature is often not reported. The monotectic temperature, tM, is the temperature at monotectic composition and the upper consolute temperature is the highest melting temperature of the mixture system, i.e. the critical point where the two liquid phases having identical composition become indistinguishable. 

Systems of type la (without critical phenomena in solid saturated solutions) (Figure 1.14). This is the simplest type of binary system. Most of the divariant (L-G, L-Sa, L-Sb, G-Sa, G-Sb) and monovariant equilibria (L-G-Sa, L-G-Sb, L = G) in the binary system (A-B) are the monovariant and nonvariant, respectively, with equilibria of one-component subsystems (A and B), spreading into two-component region of composition. Only the phase equilibria with two solid phases (invariant eutectic equihbrium (L-G-Sa-Sb) monovariant equilibria (L-Sa-Sb, G-Sa-Sb) and divariant equi-lihrium (Sa-Sb)) appear in the binary mixture as a result of an interaction of phase equilibria that extend fi om one-component subsystems. 

T and K - triple and critical points of component A and B f - eutectic equilibrium (L-G-Sa-Sb). Open circles - nonvariant points in one-component systems. Solid circles - nonvariant points in binary systems (p-T projection) and compositions of fluid (liquid, gas and critical) phases in binary nonvariant equilibria (p-T-x, T-x and p-x schemes). Diamonds - compositions of solid phases in binary nonvariant equilibria. Heavy lines - monovariant curves in one-component systems (A, B) solid lines - compositions of Uquid phases in monovariant equilibria of binary systems dashed lines - compositions of vapor (gas) phases in monovariant equUibria of binary systems dash-dotted lines - critical curves thin lines - isothermal cross-sections of the p-T-x diagram and tie-lines in T-x and p-x projections. For clarity, only tie-lines between fluid phases are shown in monovariant equilibria. 

Tranter(107) has studied a series of copoly(amides) based on hexamethylene diamine and dibasic acids. Only one of the copolymers, hexamethylene diamine and /7-phenylene dipropionic acid, gives a linear softening point-composition curve typical of isomorphic replacement. All the other copoly(amides) studied gave a minimum (eutectic type) softening point-composition diagram. However, from x-ray diffraction studies it was concluded that despite this type liquidus the second components dissolved in the lattice of the first until a critical concentration was reached. At this point the lattice structure changed rather abruptly. Now the second component was dissolved in the first, so that isodimorphism occurred. As a matter... 

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