Thermodynamics of the Mg‐Mn‐O system—modeling and heat capacity measurements

Abstract

In this study, a thermodynamic description of the Mg-Mn-O system is presented.Phase diagram data, structural information, and thermochemical data are used in the assessment. All solution phases are modeled using the compound energy formalism. In addition, heat capacity measurement of the MgMn 2 O 4 and Mg 6 MnO 8 phases are reported. The thermodynamic description reproduces thermochemical, structural, and phase diagram data. K E Y W O R D SCalphad, heat capacity, metal-matrix composite, Mg

Oxidation Kinetics of Magnesium‐Manganese Oxides for High‐Temperature Thermochemical Energy Storage

“…Approximately 10 g of magnesium‐manganese oxide samples (2/3 MM, 1/1 MM, and 2/1 MM) were thermally reduced for 4 h at 1500 °C under a 1 SLPM (0.0167 standard liter s −1 or 744.05 μmole s −1 ) argon flow (99.999% pure). According to phase diagrams in previous studies, [ 23,24 ] the material is expected to form a solution of MgO and MnO under these conditions. After ensuring that the material had completely reduced (i.e., no oxygen evolution detected by the mass spectrometer), the furnace was cooled to the oxidation temperature.…”

“…This agrees with CALPHAD works in previous studies. [ 23,24 ] Some Mn 2 O 3 is also observed in samples quenched from 1000 °C. This is mostly likely due to oxidation of the sample during quenching.…”

“…This is mostly likely due to oxidation of the sample during quenching. Both the CALPHAD works [ 23,24 ] show Mn 2 O 3 in the temperature range of ≈500–900 °C.…”

Enhancing thermochemical energy storage density of magnesium‐manganese oxides

“…Samples of ~10 g were reacted according to redox condition 2, with 3 to 4 hours dwell times at both T RED and T OX to ensure complete reduction/oxidation. T OX was chosen as 600°C to guarantee the same starting oxidation states and because of the nature of the tube furnace: 600°C was achievable within a much more reasonable cooling time than lower temperatures. Oxygen release rate data during the reduction step was collected using mass‐spectrometry to measure the outlet gas composition and then integrated to calculate the total oxygen released for redox condition 2, defined as V O 2,2 .…”

“…These two opposing effects imply the existence of an optimum Mn/Mg ratio that maximizes energy density. Prior thermodynamic calculations show increased oxygen release capacities across all Mn/Mg ratios for the same reduction temperature at low , indicating that higher energy density can be achieved.…”