Binary phase diagrams metals

Alloys. Many Ge alloys have been prepared and studied. Most have been made by melting Ge with another metal, much as germanides are made. Collections of binary phase diagrams and comments about many Ge alloys are available (25—28). 

When two metals A and B are melted together and the liquid mixture is then slowly cooled, different equilibrium phases appear as a function of composition and temperature. These equilibrium phases are summarized in a condensed phase diagram. The solid region of a binary phase diagram usually contains one or more intermediate phases, in addition to terminal solid solutions. In solid solutions, the solute atoms may occupy random substitution positions in the host lattice, preserving the crystal structure of the host. Interstitial soHd solutions also exist wherein the significantly smaller atoms occupy interstitial sites... 

Figure 4.17. The binary phase diagrams of the magnesium alloy systems with the divalent metals ytterbium and calcium (Ca is a typical alkaline earth metal and Yb one of the divalent lanthanides). Notice, for this pair of metals, the close similarity of their alloy systems with Mg. The compounds YbMg2 and CaMg2 are isostructural, hexagonal hP12-MgZn2 type.

An-An alloys. A summary ofthe phase diagrams for adjacent actinide metals is shown in the connected binary phase diagrams of Fig. 5.11. The structure of this diagram resembles that reported in Fig. 5.10 for the lanthanides notice, however, that such a sequence of interconnected diagrams could be used as a generalized diagram in a more limited way only, possibly for the heavier actinides from americium onward. 

Figure 5.11. Connected binary phase diagrams of the actinides. The binary phase diagrams (temperature vs. composition) for adjacent actinide metals are connected across the entire series (two-phase regions are in black, uncertain regions in grey). The transition from typical metallic behaviour at thorium to complex behaviour at plutonium and back to typical metallic behaviour past americium can be noticed (adapted from Hecker 2000).

The binary phase diagrams of the titanium oxides and sulphides are very complex with the formation of a very high number of intermediate phases (a similar behaviour is observed also for other intermediate transition metals such as vanadium). In the... 

Fig. 4. Interconnected binary phase diagrams of actinide metals (after Smith and Kmetko ). Two phase regions experimentally observed, assumed...

Consider the Mg-Ni binary phase diagram shown above. Note that in this system, inter-metallic compound formation is common for example, Mg2Ni, MgNi2 are stoichiometric compounds. 

Some years ago in a continuing effort to understand phase diagrams, I had discovered [3] the following empirical rules among more than 300 binary phase diagrams reported in the literature (Hansen, Elliot Shunk) [4,5,6], The metallic radii, Ra, Rb, used are from INTERATOMIC DISTANCES (The Chemical Society, London, 1958) [7] and the structural notation follows that described in Handbook of Lattice Spacing and Structure of Metals (Pearson, 1958) [8]).. 

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. 

Massalski, T.B., editor. Binary Alloy Phase Diagrams. Metals Park, OH Amer. Soc. Metals 1986. Mazzone, D., Rossi, D., Marazza, R., Ferro, R. J. Less-Common Met. 1982, 84,301. 

By combining the thermodynamic data with those on the structure of the equilibrium binary phase diagram, R. Pretorius et al 261,262 were able to improve the accuracy of predicting the sequence of compound-layer formation in the transition metal-aluminium systems. For this, they used the values of the standard enthalpies (heats) of formation of the compounds. 

The transition metals are used as metallization layers in Si device technology Upon heating, the thin (a few thousand A thick) transition-metal layers react uniformly with the Si substrate to form a silicide. From a typical transition-metal-Si binary phase diagram (see Fig. 1), the lowest T at which a liquid appears is greater than 900°C, which is above the process T used in integrated circuit fabrication. In Si device processing, silicide formation is therefore usually a solid-phase interaction. 

The change of halide ion results in weaker acidic properties for LnCl3 as compared with LnF3. This means that equilibrium (1.1.41) with the participation of alkali metal halide should be shifted to the left as compared with the fluoride complexes. That is, lithium chloride does not react with chlorides of the rare-earth elements with the formation of any compounds the binary phase diagrams are characterized by one simple eutectic. The same situation is observed for the binary diagrams for lithium- and rare-earth bromides. 

In contradiction to the binary phase diagram of TiAl the depletion layer in the metal subsurface zone after a 0.5 h oxidation at 900°C consists of a phase with a composition between 7-TiAl und arTi3Al. The analysis of this phase by electron diffraction reveals that this phase is equal to the recently reported new cubic phase (NCP) which is similar in compositions toTi3Al2,Ti2Al orTi5Al302 [17,18,19,20]. 

From studies of Schottky-barrier structures on crystalline Si, it has been shown that one of the least likely situations is an atomically sharp metal/Si interface with no interdiffusion. An examination of binary phase diagrams clearly indicates that coexisting adjacent metal/Si films are metastable at best. If no compounds are known to form, then diffusion should occur until the solubility limits are reached. If compounds exist in the binary phase diagram, then it is likely that they will form at the metal/Si interface. 

Practically all the remaining soft metallic ferromagnets are based on substitutional alloys of Ni-Fe and Co-Fe. Since at room temperature Fe is bcc, Ni is fee and Co is hep, the binary phase diagrams show a two-phase region in the middle of each diagram. 

Binary phase diagrams are very important for ceramics. The two most important cases for ceramics are the combination of a metal plus oxygen and the combination of two oxides. A model two-component system is shown in Figure 8.9 where we are now using the third dimension to display the data. 

First rare earth metal binary phase diagram study reported (Ce-Sn system)... 

Only Eu and Yb, among the rare earths, form immiscibility gaps with Sc in the liquid and solid. The difference in valence of these two rare earths and Sc is, perhaps, the main reason of this difference of interaction. The divalent state is more typical for Eu and Yb, whereas the other rare earths are usually trivalent. The same divalent state is characteristic for aUcaline earths which are immiscible with Sc in the liquid and solid too. Therefore, it is possible to predict the same type of binary phase diagrams of Sc with alkaline metals. These elements are even more different from Sc in the valence state and other characteristics (melting temperature, electronegativity, etc.) than are the alkaline-earth metals. 

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