Lanthanide melting temperatures

We assume, in this case, that the conduction band has become normal (that is, it has no longer any 5 f character). Thus, physical properties may be usefully compared with those of the lanthanides. In Table 5 we report known basic properties (metallic radii, crystal structures, melting temperatures and enthalpies of sublimation) of the transplutonium metals. 

The skutterudites do not melt congruently and involve pnicogens (P, As, Sb) that generally have high vapor pressures at the formation temperatures of the compounds. The high melting temperatures of Fe, Ru and Os coupled with the reactivity of the lanthanide metals with convenient crucible materials (e.g., Si02) makes the synthesis of many of these compounds difficult. As a result, variations in the reported properties of a particular lanthanide skutterudite compound can often be traced to differences in sample composition and quality. 

The selected transition and melting temperatures for the lanthanide trihalides, in K... 

Table V. Melting temperatures and sublimation enthalpies of lanthanides and actinides...

The lanthanides make soft metals. Figure 14-1 illustrates the linear increase in melting temperature for each of the elements from lanthanum to lutetium. 

Because they have similar sizes, the alloys of these elements are soft and malleable. Examining the melting temperature is one of the best ways to see differences between the lanthanide atoms. 

Fig. 4. The allotropy, transformation and melting temperature of the lanthanides. Note that room temperature is the baseline. Below room temperature the scale is in degrees Kelvin (K) and above room temperature it is in degrees Celsius because this is the common usage. N.T. means no transformation occurs in the temperature direction from room temperature. The low-temperature transformations (<400X or <673 K) exhibit hysteresis and thus an arrow next to the transformation point indicates the direction in temperature which was used to measure the given point (usually away from room temperature). P means a partial transformation and that the transformation does not go to completion unless some unusual means are employed.

The heat of solution, Hs, of hydrogen in the heavy lanthanides has been determined for the system RH(D)o.2 from equilibrium measurements in the a 3 reaction and is given in table 11. The strongly decreasing tendency of with increasing Z of the rare earth conelates with the decieasii atomic volume and with the increasing melting temperature of R. 

The densities of the liquid lanthanides, at their respective melting temperatures, are shown as a function of atomic number in fig. 1. With the exception of the divalent liquid metals, Eu and Yb, the densities are seen to increase linearly with Z. It is also notable that the density increases at approximately twice the rate that the atomic weight increases, implying a contraction of the atomic core with increasing Z this has been called the lanthanide contraction . 

Fig. 1. Density, p, of the liquid lanthanides at their respective melting temperatures. Data are from table 1.

We remark that europium and ytterbium are divalent both have molar volumes, melting and boiling temperatures which are different from the other lanthanides. Consequently they exhibit a completely different behavior when alloyed with rare earths. The binary phase diagrams based on europium and ytterbium exhibit a large miscibility gap in the liquid state. The boiling temperature under the normal pressure of europium and ytterbium is lower than the melting temperature of some other rare earth elements this is the case in the binary alloys Eu—Lu, Yb-Gd to Lu, Yb-Sc and Yb-Y. 

With Cu, the compound which exhibits the highest melting temperature is RCug or AnCug for the first six elements of the lanthanide series, La —> Sm, and also for Th. In the middle of the lanthanide series (Gd — Dy) the compound is R2CU9, and at the end of the series and also with Sc, it is RCu. The temperature and the enthalpy of fusion, and the heat content of some R-Cu compounds have recently been obtained by Qi et al. (1989a,b). 

With Ag, the compound which possesses the highest melting temperature has the formula R Agsi for the early elements of the lanthanide series (La — Nd), it has the formula RAg for the other lanthanide elements (except Eu and Yb) and also for Y and Sc. The stoichiometry of this compound is Ag3Th and Aga.ePu for the actinides. 

The compounds with the highest melting temperatures are LaZng, Ln2Zni7 for Ln = Ce, Nd and lastly LnZn for Ln = Sm —> Lu for the lanthanide elements ThZn2, U2Zni7... 

With Ga, the stoichiometry of the compound with the highest melting temperature is RGa2 or AnGa2 for the first elements of the lanthanide series (La— Ho) and for... 

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