Solid solutions intermediate

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... 

In Fig. 2.19, on the contrary, we observe that intermediate solid phases with a variable composition are formed (non-stoichiometric phases). In the diagrams shown here we see therefore examples both of terminal and intermediate phases. (For instance, the Hf-Ru diagram shows the terminal solid solutions of Ru in a and (3Hf and of Hf in Ru and the intermediate compound containing about 50 at.% Ru). These phases are characterized by homogeneity ranges (solid solubility ranges), which, in the case of the terminal phases, include the pure components and which, generally, have a variable temperature-dependent extension. 

Figure 5.4. The niobium-hydrogen system. A small part (from 40 to 50 at.% H) of the diagram is shown in the low- and very-low-temperature region. Notice the complex equilibria and the high number of intermediate solid solution phases. Other phases are formed in the composition ranges not shown in figure the q (11 to 39 at.% H) and 0 (21 to 41 at.% H) solid solutions in the Nb-richer part and the nearly stoichiometric 6 phase ( NbH2, cF12-CaF2-type).

The Cu-Zn system (see Figure 2.7) displays a number of intermediate solid solutions that arise due to limited solubility between the two elements. For example, at low wt% Zn, which incidently is the composition of alloys known as brass, the relatively pure copper a phase is able to accommodate small amounts of Zn as an impurity in the crystal structure. This is known as a terminal solid phase, and the solubility limit where intermediate solid solutions (such as a + /S) begin to occur is called the solvus line. Some of the three-phase transformations that are found in this diagram include a peritectic (5 - - L -> e) and a eutectoid (5 -> y - - e). Remember that these three-phase transformations are defined for equilibrium coohng processes, not heating or nonequihbrium conditions. 

Pokkuluri et al. have recently addressed the question of the directionality of free volume in their studies on the solid state di-Ti-methane rearrangement of methyl 2-benzoyl-l,4-dihydrol,4-ethenonaphthalene-3-carboxylate, 30 [150]. The title compound gives two different sets of products upon solution and solid state irradiation, both resulting from di-Ti-methane process involving 1,3-diradical intermediate (Scheme 14). Strikingly, the solid state products derive via less stable 1,3-diradical intermediates, 31 and 32 whereas the... 

As SeCl and a/yS-SeBr are the only known subhalides of selenimn and no binary compound exists in the Se-I system, the ternary system Se-Te-I was investigated. No distinct new phase is observed, but there is a region of intermediate solid solution a-Tei. Se I with x s 0.18 (228). 

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