Peterson, Kristina M., Heaney, Peter J., and Post, Jeffrey E. 2016. "A kinetic analysis of the transformation from akaganeite to hematite: An in situ time-resolved X-ray diffraction study." Chemical Geology, 444 27–36. https://doi.org/10.1016/j.chemgeo.2016.09.017.
The nucleation and growth of akaganeite and its transformation to hematite under hydrothermal conditions were monitored over a temperature range of 80 to 200 degrees C using time-resolved synchrotron X-ray diffraction. In each experiment, akaganeite was the first phase to form and hematite was the final phase. No intermediate phases were identified. The induction time to akaganeite nucleation was similar to 5525 s and 537 s at 80 degrees C and 100 degrees C, respectively, yielding an activation energy of 129 /- 15 kJ/mol. However, akaganeite nucleated at a constant temperature of 123 /- 5 degrees C when the heater set point was 150 degrees C or higher, suggesting an activation energy for akaganeite nucleation of 0 kJ/mol between 150 and 200 degrees C. Hematite nucleation induction times decreased with increasing temperature from 1723 s to 110 s between 150 and 200 degrees C. Based on a JMAK analysis, the activation energies for the crystal growth and dissolution of akaganeite were 74 /- 8 kJ/mol and 125 /- 7 kJ/mol, respectively. Our calculated activation energies for hematite nucleation and crystal growth were 80 /- 13 kJ/mol and 110 /- 21 kJ/mol, respectively. (C) 2016 Elsevier B.V. All rights reserved.
