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The thermodynamic quantities associated to the transformation from graphite to multiwalled carbon nanotubes (MWCNTs) were determined by electromotive force (emf) and differential scanning calorimetry (DSC) measurements. From the emf versus T data of galvanic cell Mo|Cr(3)C(2), CrF2, MWCNTs|CaF2 s.c.|Cr(3)C(2), CrF2, graphite|Mo with CaF2 as solid electrolyte, Delta(r)H(T) degrees= 8.25 +/- 0.09 kJ mol(-1) and Delta(r)S(T) degrees= 11.72 +/- 0.09 JK(-1) mol(-1) were found at average temperature T = 874 K. The transformation enthalpy was also measured by DSC of the Mn(7)C(3) formation starting from graphite or MWCNTs. Thermodynamic values at 298 K were calculated to be: Delta(r)H(298) degrees = 9.0 +/- 0.8 kJ mol(-1) as averaged value from both techniques and Delta(r)S(298) degrees approximately Delta(r)S(T) degrees. At absolute zero, the residual entropy of MWCNTs was estimated 11.63 +/- 0.09 JK(-1) mol(-1), and transformation enthalpy Delta(r)H(0) degrees approximately Delta(r)H(298) degrees. The latter agrees satisfactorily with the theoretical calculations for the graphite-MWCNTs transformation. On thermodynamic basis, the transformation becomes spontaneous above 704 +/- 13 K.

A set of thermodynamic properties of the Fe-rich part of the Fe/rare earth (RE) systems is presented for almost all the elements in the rare earth series. This set of data comes entirely from electromotive force (emf) vs T experimental measurements obtained by galvanic cells with a CaF2 single crystal as the electrolyte. The standard enthalpy and entropy of formation of RE2Fe17 intermetallics have been obtained and compared with previous results found for the RE2Ni17 intermetallics. The enthalpy of formation of RE2Fe17 intermetallics is decidedly less exothermic than the enthalpy of formation of RE2Ni17 with the exception of the value of Pr2Fe17, which is endothermic. The RE2Fe17 entropy of formation is always positive contrary to the values of RE2Ni17. For comparison purposes, the thermodynamic data of Y2Fe17 and Dy2Co17 have also been determined. The RE solubility in Fe has been evaluated by the shift of the bcc Fe(110) plane spacing with respect to pure Fe as shown by corresponding X-ray diffraction (XRD) data. Along the RE series, the atomic fraction of RE in the Fe solid solution changes from (1.2 ± 0.1)·10-4 for Er to (9.2 ± 0.2)·10-4 for Ho. The values of the thermodynamic activity of RE coexisting between the RE2Fe17-rich phase and the Fe solid solution are reported along the series, and the related partial excess free energy is given as electronic and dilatation contributions. The electronic partial excess free energy of RE2Fe17 intermetallics is practically independent of the dilatation term contrary to the RE2Ni17 intermetallics.

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