Phase diagrams magnesium-lead

For some systems, discrete intermediate compounds rather than solid solutions may be found on the phase diagram, and these compounds have distinct chemical formulas for metal-metal systems, they are called intermetallic compounds. For example, consider the magnesium-lead system (Figure 9.20). The compound Mg2Pb has a composition of 19 wt% Mg-81 wt% Pb (33 at% Pb) and is represented as a vertical line on the diagram, rather than as a phase region of finite width hence, Mg2Pb can exist by itself only at this precise composition. 

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