This thesis presents the measurements of thermodynamic properties of hematite (α-Fe 2 O 3 ), maghemite (γ-Fe 2 O 3 ), goethite (a-FeOOH), lepidocrocite (γ-FeOOH), feroxyhyte (δ-FeOOH), ferrihydrite (∼Fe(OH) 3 ), boehmite (γ-AlOOH), FeAlO 3 , [varepsilon]-Fe 2 O 3 , and hematite-corundum and goethite-diaspore solid solution.
The measured thermodynamic values for the bulk iron oxides are
[Table omitted.]
The upper limit on configuration entropy of maghemite was estimated as 2.0 J·K -1 mol -1 . The heat capacity above 273 K was fitted to a Maier-Kelley polynomial C p ( T in K) = a + b T + c T -2 . The C p polynomial coefficients are a = 1.246, b = 0.2332, c = 313900 (goethite, valid in temperature range 273-375 K), a = 59.76, b = 0.06052, c = -772900 (lepidocrocite, 273-390 K), a = 106.8, b = 0.06509, c = -1886000 (maghemite, 273-760 K).
The enthalpies of mixing (ΔH mix ) in the hematite-corundum and goethite-diaspore solid solution can be approximated by a polynomial ΔH mix = WX(1-X), where X is the mole fraction of the iron end-member, and W hematite-corundum = 58 ± 5 kJ·mol -1 , and W goethite-diaspore = 79 ± 14 kJ·mol -1 . The ΔH 0 f of FeAlO 3 from oxides at 298 K is 27.9 ± 1.8 kJ/mol. Its estimated standard entropy is 98.8 J/mol*K, and the ΔG 0 f at 298 K from oxides and elements is +19.1 ± 1.8 and -1144.2 ± 2.0 kJ/mol, respectively. The heat capacity of FeAlO 3 is approximated as C p ( T in K) = 175.8-0.002472 T - (1.958 × 10 6 )/ T 2 - 917.3/ T 0.5 + (7.546 × 10 -6 ) T 2 between 298 and 1550 K. The ternary phase is entropy stabilized. Static lattice calculations showed that the hypothetical LiNbO 3- , FeGaO 3- , FeTiO 3- , and disordered corundum-like FeAlO 3 structures are energetically metastable with respect to hematite and corundum.
The ΔG 0 f for 2-line ferrihydrite is best described by a range of -708.5--705.2 kJ·mol -1 , and ΔG 0 f for 6-line ferrihydrite by -711.0--708.5 kJ·mol -1 . The ΔH 0 f of feroxyhyte at 298.15 is -547.4 ± 1.3 kJ·mol -1 . The ΔH o f of [varepsilon]-Fe 2 O 3 is -797.7 kJ·mol -1 . Surface enthalpy (J·m -2 ) of boehmite is 0.52 ± 0.12, lepidocrocite 0.29 ± 0.13, maghemite 0.83 ± 0.18, hematite 0.75 ± 0.16, goethite 0.27 ± 0.12.
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