Thermodynamics lanthanide metals

Unlike the di-f dihalides, such compounds differ little in energy from both the equivalent quantity of metal and trihalide, and from other combinations with a similar distribution of metal-metal and metal-halide bonding. So the reduced halide chemistry of the five elements shows considerable variety, and thermodynamics is ill-equipped to account for it. All four elements form di-iodides with strong metal-metal interaction, Prl2 occurring in five different crystalline forms. Lanthanum yields Lai, and for La, Ce and Pr there are hahdes M2X5 where X=Br or I. The rich variety of the chemistry of these tri-f compounds is greatly increased by the incorporahon of other elements that occupy interstitial positions in the lanthanide metal clusters [3 b, 21, 22]. 

Nitridoborates of lanthanum and the lanthanides were obtained from reactions of lanthanide metal or lanthanide metal nitride with layer-like (a-)BN at elevated temperatures (3>1200°C). These reactions require elaborated techniques in the inert gas sample-handling and the use of efficient heating sources, such as induction heating. Only some compounds remain stable in this high-temperature segment, and the yields of such reactions are often limited due to the competing stability of binary phases, allowing only the most (thermodynamically) stable compounds to exist. 

Figure 7.10 Thermodynamic data (b)-(d) needed in analysis of the enthalpy of formation of the binary lanthanide metal compounds given in (a), (b) Sum of first, second and third ionization enthalpies of lanthanide metals (c) atomization enthalpy of lanthanide metals (d) derived lattice enthalpy of lanthanide trichlorides.

High Temperature Thermodynamic Functions for the Lanthanide Metals ... 

Nd202C03 (a metal oxide carbonate) has also been reported as a strong candidate for a CO2 sensor (Djerdj et al, 2009) and gives an impressive response of 7.5 to 3000 ppm CO2 at an operating temperature of 350°C in 50% relative humidity air. The material also displays an impressive dynamic with sub-100 ppm concentrations of CO2 being readily detectable. However, the authors do not comment on the long-term stability of the material although it is well-known that oxides of the lanthanide metals are the most thermodynamically stable. 

Thermodynamic data for lanthanide metals S-S = transformation to bcc structure S-L = melting. From layaraman (1965) Melting and transformation temperature from ch. 2, tables 2.15 and 2.14, respectively. 

In general, the Bl-type actinide compounds show a large difference between the transition pressure on pressure increase and the transition pressure on pressure decrease (Dabos-Seignon and Benedict 1990). This hysteresis is probably due to delayed establishment of thermodynamic equilibrium. It has been shown in some lanthanide metals (Kruger et al. 1990) that a slight temperature increase reduces the width of this hysteresis zone and that the equilibrium transition pressure has some intermediate value. 

From the latter equation the calculated boiling point of Cm is 3110°C. The derived heat of fusion, entropy of fusion, and average second-law entropy are 13.85 kJ mol , 9.16 JK mol , and 106.7 3.0 J K mol , respectively. Low-temperature condensed-phase thermodynamic parameters await the availability of long-lived isotopes. For excellent discussions of thermodynamic, electronic, and magnetic effects in curium and other actinide and lanthanide metals, the reader is referred to recent articles by Ward and Hill [34]. 

Table 8.17 Thermodynamic data for species of the lanthanide metals at 25 °C and comparison with data available In the literature.

The thermodynamic data for the standard state (elemental solids) and trivalent ions of the lanthanide metals are taken from Bard, Parsons and Jordan (1985). The enthalpy of formation for some of the trivalent ions is taken from Merli, Rorif and Fuger (1998). The data are listed in Table 8.53. They have been utilised in deriving the thermodynamic data Usted in Table 8.17. 

I 8 Scandium, Yttrium and the Lanthanide Metals Table 8.53 Literature thermodynamic data for lanthanide species at 25 ... 

For all three halates (in the absence of disproportionation) the preferred mode of decomposition depends, again, on both thermodynamic and kinetic considerations. Oxide formation tends to be favoured by the presence of a strongly polarizing cation (e.g. magnesium, transition-metal and lanthanide halates), whereas halide formation is observed for alkali-metal, alkaline- earth and silver halates. 

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