Thermodynamic properties of iron oxides and hydroxides; III, Surface and bulk thermodynamic properties of lepidocrocite (gamma -FeOOH) to 500 K
Thermodynamic properties of iron oxides and hydroxides; III, Surface and bulk thermodynamic properties of lepidocrocite (gamma -FeOOH) to 500 K
European Journal of Mineralogy (February 1998) 10 (1): 31-41
Experimental measurements of the heat capacity of lepidocrocite are consistent with the equation: C (sub p) degrees = 65.205 + 0.067665T - 0.81564 X 10 (super 6) /T (super 2) (298.15-500 K), which yields a value of the standard heat capacity at 298.15 K: C (sub p) degrees = 76.2 + or - 1.5 J/mol K. Measured enthalpies of dehydration of lepidocrocite to disordered maghemite and of its transition reaction to goethite result in a standard enthalpy of formation of lepidocrocite at 298.15 K: Delta (sub f) H degrees = -556.4 + or - 2.0 kJ/mol. Standard entropy at 298.15 K was estimated as S degrees = 62.5 + or - 5.0 J/mol K. Standard Gibbs energy of formation at 298.15 K and the solubility product of lepidocrocite were calculated as: Delta (sub f) G degrees = -486.3 + or - 2.5 kJ/mol and pK (sub sp) = 41.4 + or - 0.6.
