System monotectic

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. 

Binary Alloys. Aluminum-rich binary phase diagrams show tliree types of reaction between liquid alloy, aluminum solid solution, and otlier phases eutectic, peritectic, and monotectic. Table 16 gives representative data for reactions in tlie systems Al—Al. Diagrams are shown in Figures 10—19. Compilations of phase diagrams may be found in reference 41. 

Al-Pb. Both lead [7439-92-17, Pb, and bismuth [7440-69-9] Bi, which form similar systems (Fig. 17), are added to aluminum ahoys to promote machinahility by providing particles to act as chip breakers. The Al—Pb system has a monotectic reaction in which Al-rich Hquid free2es partiahy to soHd aluminum plus a Pb-rich Hquid. This Pb-rich Hquid does not free2e until the temperature has fahen to the eutectic temperature of 327°C. SoHd solubiHty of lead in aluminum is negligible the products contain small spherical particles of lead which melt if they are heated above 327°C. 

Despite possible electron-acceptor B sp combining with the group I and II main-group elements, only metastable AIB2 phases, AgB2 and AUB2, are known, and the Ag-B and Au-B systems exhibit simple monotectics and eutectics, respectively. 

For the niobium-copper system different phase diagrams of the simple eutectic type (with the eutectic point very close to Cu) have been proposed, either with an S-shaped near horizontal liquidus line or with a monotectic equilibrium. It was stated that the presence of about 0.3 at.% O can induce the monotectic reaction to occur, whereas if a lesser amount of oxygen is present no immiscibility gap is observed in the liquid. 

Pb, where retrograde solubility for the solid in equilibrium with the liquid can also occur. As a critical value of n " is approached the liquid forms its own miscibility gap and the diagram then exhibits two forms of liquid invariant reaction, the lower temperature reaction being either eutectic or peritectic, while the higher temperature reaction becomes monotectic. Examples of such systems are Cu-Pb and Cu-Tl. When n becomes even larger, the top of the liquid miscibility gap rises above scale of the graph and there is little solubility of either element in the liquid. Such a diagram is typical of Mg systems such as Mg-Fe or Mg-Mn. 

C A ternary monotectic forms in the sulfur-rich portion of the system MoS2 + FeS2 + S(iiquid)= ternary monotectiC(iiquid) + v... 

C The binary monotectic liquid appears in the sulfur-rich portion of the Cu—S system liquid immiscibility occurs above 1.8 S (liquid) monotectic (liquid) analogous DTA experiments with added MoS2 contents showed no change of this temperature. 

C The ternary monotectic melt reaches the binary Cu—S system, the binary monotectic occurs liquid(cu-rich) + Cu2 S = binary monotectic(liquid) +v... 

C The ternary monotectic melt reaches the Cu—S system, the binary... 

Monotectic mixtures arise when the individual components have similar melting points, molecular volumes and polymorphic forms. Figure 17.12(a) represents a possible phase diagram for monotectic mixtures. A typical monotectic solution occurs when SSS is mixed with SOS. Lutton (1955) determined that the a form was present and associated with limited solid solution formation, and contrasted with the a forms of other glyceride mixtures that formed continuous solid solutions (Rossell 1967). It was found, for this system, that tristearin incorporates about 50% of the SOS into a solid solution on the other hand, SOS incorporates very little SSS into a solid solution. 

Figure 4. Phase behavior in binary systems (a) monotectic, continuous soiid soiution (b) eutectic (c) monotectic, partiai soiution and (d) peritectic (18).

Safonov et al. (331) determined the liquidus surface of the ternary In-Te-Cl system by DTA, X-ray diffraction, and crystal optical methods. Only one ternary compound, InTeCl, exists. The crystallization field of InTeCl occupies 6% of the diagram, which demonstrates the considerable thermodynamic stability of this compound. InTeCl melts congruently at 453°C. It forms part of the two pseudobinary systems In Tes-InCls and InCl-Te (82). Whereas the first consists of the two eutectic parts In Tes-InTeCl and InTeCl InCls, the latter is more complicated. It is composed of the monotectic system InTeCl-InCl and the eutectic system Te-InTeCl, where tellurium forms a solid solution with InTeCl containing from 100 to 82 atom% of Te at the eutectic temperature (82). 

Perepezko and coworkers have carried out an extensive series of measurements of nucleation in low-melting metal alloys, in most cases obtaining undercooling temperatures over a substantial range of compositions. In this way they have studied the alloy systems Sn-Pb, Cd-Pb, Sb-Pb 48.53-54 Cu-Pb, Pb-Bi,-" Sn-Bi,- 8 Ga-Bi, i Cd-Bi, Cd-Sb,-" and Cu-Te. Earlier work on the nucleation of alloys includes that of Cech and Turnbull on Cu-Ni and of Cech on Fe-Ni. These different studies encompass eutectic, peritectic, and monotectic binary crystallization and provide a rich variety of data for interpretation. 

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