Table 1.

Thermodynamic parameters of the metal–silicate partitioning of Nb and Ta

Element (i)	a	b, K	c, K/GPa	d	${\epsilon }_i^O$	${\epsilon }_i^{Si}$	${\epsilon }_i^C$	${\epsilon }_i^S$	${\epsilon }_i^i$	lnγi0	N	R2
Nb	0	−10,314 (108)	−67 (7)	−0.39 (4)	−34.9	−6.1	−5.2	0	−0.7	−1.61	74	0.852
Ta	−2.71 (26)	−9,270 (607)	0	−0.18 (5)	−60.6	−8.7	−10.5	0	79.7	−3.22	72	0.906
O						−5			−1
Si									12.4

Parameters of Eq. 2 for Nb and Ta partitioning: a, b, and c represent the entropy, enthalpy, and volume change of reaction 1; values in parentheses are SEs (1σ) obtained from the least-squares regressions. ${\epsilon }_i^j$ is the interaction parameter of element j on element i and γ_i⁰ the activity coefficient of solute i at infinite dilution in liquid iron; interaction parameters in boldface are calculated from this study and other values are taken from metallurgy data (41). Interaction parameters and activity coefficients are reported at 1,873 K (details are given in SI Appendix). N is the number of data used in each thermodynamic modeling and R² the coefficient of determination of the fitted model.