Binary alloys alkaline earth metals

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.

Figure 5.14. Compound formation capability in the binary alloys of Sc, Y, light trivalent lanthanides (as exemplified by La), heavy trivalent lanthanides (exemplified by Gd) and of the actinides (exemplified by Th, U and Pu). The different partners of the 3rd group metals are identified by their position in the Periodic Table. Notice that a sharper subdivision between compound-forming and not forming metals will result from a shifting of Be and Mg from their position in the 2nd group towards the 12th group (see 5.12.3). The behaviour of the divalent lanthanides Eu and Yb is shown in Fig. 5.7 where it is compared with that of the alkaline earth metals.

From a biological point of view, potassium is an essential element in all forms of life. Each organism has a closely maintained potassium level and a relatively fixed potassium-sodium ratio. For instance, in the human body, the ratio of potassium between the cell and plasma is ca. 27/1. Potassium is the primary inorganic cation within living cells, and sodium is the most abundant cation in extracellular fluids. Moreover, potassium is a chief element of fertilizers. Potassium forms alloys with all the alkali metals. Complete miscibility exists in the K-Rb and K-Cs binary systems. The latter system forms an alloy eutectic melting at ca. -38°C. Modification of the system by the addition of sodium results in a ternary eutectic melting at ca. -78°C. Potassium is essentially immiscible with all of the alkaline-earth metals (when they are liquid), as well as with molten zinc, aluminum, and cadmium. 

There are no data about the interaction of scandium with the alkaline metals. Taking into consideration the large differences in the melting temperatures of Sc and lA elements the occurrence of immiscibility gaps in liquid and solid binary alloys are possible as they occur in the Sc-E (E = alkaline-earth element) alloys (see sect. 2.2). The absence of binary compounds in these systems is very likely. 

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