Energetics of manganese oxides
- Princeton Univ., NJ (United States)
The energetics of some manganese oxides: pyrolusite MnO{sub 2}, bixbyite Mn{sub 2}O{sub 3}, hausmannite Mn{sub 3}O{sub 4} and manganosite MnO were studied by transposed temperature drop calorimetry and high temperature drop solution calorimetry in molten 2PbO {center_dot} B{sub 2}O{sub 3} at 977 K. The enthalpies of oxidation at 298 K in the Mn-O system, determined by appropriate thermodynamic cycles, are (in kJ/mol O{sub 2}): {minus}441.4 {+-} 5.8 for the reaction 6 MnO + O{sub 2} {ge} 2 Mn{sub 3}O{sub 4}, {minus}201.8 {+-} 8.7 for 4 Mn{sub 3}O{sub 4} + O{sub 2} {ge} 6 Mn{sub 2}O{sub 3} and {minus}162.1 {+-} 7.2 for 2 Mn{sub 2}O{sub 3} + O{sub 2} {ge} 4 MnO{sub 2}. These values agree very well with previous data obtained by equilibrium pO{sub 2} measurements and indicate that direct calorimetric measurements are well suited to obtain reliable enthalpy of formation data for oxides containing manganese in the 2+, 3+ and 4+ states. The phase diagram of the Mn-O system was calculated using these new values of enthalpies.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States)
- OSTI ID:
- 479334
- Report Number(s):
- CONF-951155--; ISBN 1-55899-301-0
- Country of Publication:
- United States
- Language:
- English
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