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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on MgMn2O4 by Materials Project

MgMn2O4 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 pentagonal pyramids that share corners with six equivalent MnO6 octahedra, edges with six MnO6 octahedra, and edges with two equivalent MgO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 5–20°. There are a spread of Mg–O bond distances ranging from 2.13–2.29 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 pentagonal pyramids that share corners with twelve MnO6 octahedra, edges with two equivalent MgO6 pentagonal pyramids, and faces with two equivalent MnO6 octahedra. The corner-sharing octahedra tilt angles range from 41–55°. There are a spread of Mg–O bond distances ranging from 2.08–2.29 Å. There are three inequivalent Mn3+ sites. In the first Mn3+ site, Mn3+ is bonded to six O2- atoms to form distorted MnO6 octahedra that share corners with five MgO6 pentagonal pyramids, edges with six MnO6 octahedra, an edgeedge with one MgO6 pentagonal pyramid, and a faceface with one MgO6 pentagonal pyramid. There are a spread of Mn–O bond distances ranging from 1.88–2.34 Å. In the second Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with four equivalent MgO6 pentagonal pyramids, edges with six MnO6 octahedra, and edges with two equivalent MgO6 pentagonal pyramids. There are a spread of Mn–O bond distances ranging from 1.98–2.18 Å. In the third Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with four equivalent MgO6 pentagonal pyramids, edges with six MnO6 octahedra, and edges with two equivalent MgO6 pentagonal pyramids. There are a spread of Mn–O bond distances ranging from 1.97–2.24 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to one Mg2+ and three Mn3+ atoms to form distorted OMgMn3 trigonal pyramids that share corners with four OMg2Mn3 trigonal bipyramids, corners with six OMgMn3 trigonal pyramids, edges with four OMg2Mn3 trigonal bipyramids, and an edgeedge with one OMgMn3 trigonal pyramid. In the second O2- site, O2- is bonded to one Mg2+ and three Mn3+ atoms to form distorted OMgMn3 trigonal pyramids that share corners with four OMg2Mn3 trigonal bipyramids, corners with six OMgMn3 trigonal pyramids, edges with four OMg2Mn3 trigonal bipyramids, and an edgeedge with one OMgMn3 trigonal pyramid. In the third O2- site, O2- is bonded to two Mg2+ and three Mn3+ atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with five OMg2Mn3 trigonal bipyramids, corners with four OMgMn3 trigonal pyramids, edges with four OMg2Mn3 trigonal bipyramids, and edges with four OMgMn3 trigonal pyramids. In the fourth O2- site, O2- is bonded to two Mg2+ and three Mn3+ atoms to form OMg2Mn3 trigonal bipyramids that share corners with five OMg2Mn3 trigonal bipyramids, corners with four OMgMn3 trigonal pyramids, edges with four OMg2Mn3 trigonal bipyramids, and edges with four OMgMn3 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgMn2O4 by Materials Project

MgMn2O4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Mg2+ is bonded to four equivalent O2- atoms to form MgO4 tetrahedra that share corners with twelve equivalent MnO6 octahedra. The corner-sharing octahedral tilt angles are 58°. All Mg–O bond lengths are 2.02 Å. Mn3+ is bonded to six equivalent O2- atoms to form MnO6 octahedra that share corners with six equivalent MgO4 tetrahedra and edges with six equivalent MnO6 octahedra. All Mn–O bond lengths are 2.06 Å. O2- is bonded to one Mg2+ and three equivalent Mn3+ atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgMn2O4 by Materials Project

MgMn2O4 is Spinel-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are six inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to four O2- atoms to form MgO4 tetrahedra that share corners with three MgO6 octahedra and corners with nine MnO6 octahedra. The corner-sharing octahedra tilt angles range from 56–61°. There are three shorter (2.02 Å) and one longer (2.05 Å) Mg–O bond lengths. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six MnO4 tetrahedra, edges with two MgO6 octahedra, and edges with four MnO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.14 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent MgO4 tetrahedra, corners with four MnO4 tetrahedra, an edgeedge with one MgO6 octahedra, and edges with five MnO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.11 Å. In the fourth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six MnO4 tetrahedra, edges with two MgO6 octahedra, and edges with four MnO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.14 Å. In the fifth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six MnO4 tetrahedra, edges with two MgO6 octahedra, and edges with four MnO6 octahedra. There are four shorter (2.07 Å) and two longer (2.11 Å) Mg–O bond lengths. In the sixth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share a cornercorner with one MgO4 tetrahedra, corners with five MnO4 tetrahedra, an edgeedge with one MgO6 octahedra, and edges with five MnO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.11 Å. There are twelve inequivalent Mn3+ sites. In the first Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent MgO4 tetrahedra, corners with four MnO4 tetrahedra, edges with three MgO6 octahedra, and edges with three MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–2.07 Å. In the second Mn3+ site, Mn3+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with six MgO6 octahedra and corners with six MnO6 octahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Mn–O bond distances ranging from 2.01–2.10 Å. In the third Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three equivalent MgO4 tetrahedra, corners with three equivalent MnO4 tetrahedra, edges with two MgO6 octahedra, and edges with four MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.98–2.07 Å. In the fourth Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent MgO4 tetrahedra, corners with four MnO4 tetrahedra, edges with three MgO6 octahedra, and edges with three MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–2.07 Å. In the fifth Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with six MnO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four MgO6 octahedra. There is two shorter (1.94 Å) and four longer (2.01 Å) Mn–O bond length. In the sixth Mn3+ site, Mn3+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with six MgO6 octahedra and corners with six MnO6 octahedra. The corner-sharing octahedra tilt angles range from 55–63°. There are two shorter (2.02 Å) and two longer (2.05 Å) Mn–O bond lengths. In the seventh Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with six MnO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four MgO6 octahedra. There is two shorter (1.94 Å) and four longer (2.01 Å) Mn–O bond length. In the eighth Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one MgO4 tetrahedra, corners with five MnO4 tetrahedra, edges with three MgO6 octahedra, and edges with three MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–2.08 Å. In the ninth Mn3+ site, Mn3+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with six MgO6 octahedra and corners with six MnO6 octahedra. The corner-sharing octahedra tilt angles range from 56–62°. There are two shorter (2.02 Å) and two longer (2.05 Å) Mn–O bond lengths. In the tenth Mn3+ site, Mn3+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one MgO4 tetrahedra, corners with five MnO4 tetrahedra, edges with three MgO6 octahedra, and edges with three MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–2.06 Å. In the eleventh Mn3+ site, Mn3+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with six MgO6 octahedra and corners with six MnO6 octahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Mn–O bond distances ranging from 2.01–2.10 Å. In the twelfth Mn3+ site, Mn3+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with three MgO6 octahedra and corners with nine MnO6 octahedra. The corner-sharing octahedra tilt angles range from 57–63°. There are one shorter (2.04 Å) and three longer (2.05 Å) Mn–O bond lengths. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded to two Mg2+ and two Mn3+ atoms to form distorted OMg2Mn2 trigonal pyramids that share corners with two OMgMn3 tetrahedra, corners with two OMn4 trigonal pyramids, and edges with two OMgMn3 trigonal pyramids. In the second O2- site, O2- is bonded to one Mg2+ and three Mn3+ atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids. In the third O2- site, O2- is bonded to two Mg2+ and two Mn3+ atoms to form distorted OMg2Mn2 trigonal pyramids that share corners with two OMgMn3 tetrahedra, corners with two OMn4 trigonal pyramids, and edges with two OMg2Mn2 trigonal pyramids. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the fifth O2- site, O2- is bonded to two Mg2+ and two Mn3+ atoms to form a mixture of distorted edge and corner-sharing OMg2Mn2 trigonal pyramids. In the sixth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the eighth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Mn3+ atoms. In the ninth O2- site, O2- is bonded to two Mg2+ and two Mn3+ atoms to form a mixture of distorted edge and corner-sharing OMg2Mn2 trigonal pyramids. In the tenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the eleventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the twelfth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Mn3+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Mn3+ atoms. In the fourteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the fifteenth O2- site, O2- is bonded to two Mg2+ and two Mn3+ atoms to form a mixture of distorted edge and corner-sharing OMg2Mn2 trigonal pyramids. In the sixteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mg2+ and two Mn3+ atoms. In the seventeenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Mg2+ and two Mn3+ atoms. In the eighteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the nineteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mg2+ and three Mn3+ atoms. In the twentieth O2- site, O2- is bonded to two Mg2+ and two Mn3+ atoms to form a mixture of distorted edge and corner-sharing OMg2Mn2 trigonal pyramids. In the twenty-first O2- site, O2- is bonded to four Mn3+ atoms to form distorted OMn4 trigonal pyramids that share corners with two OMgMn3 tetrahedra, corners with two OMg2Mn2 trigonal pyramids, edges with two OMgMn3 tetrahedra, and an edgeedge with one OMgMn3 trigonal pyramid. In the twenty-second O2- site, O2- is bonded to one Mg2+ and three Mn3+ atoms to form distorted OMgMn3 tetrahedra that share a cornercorner with one OMgMn3 tetrahedra, corners with three OMn4 trigonal pyramids, an edgeedge with one OMgMn3 tetrahedra, and edges with two OMgMn3 trigonal pyramids. In the twenty-third O2- site, O2- is bonded to one Mg2+ and three Mn3+ atoms to form distorted OMgMn3 trigonal pyramids that share corners with two OMg2Mn2 trigonal pyramids, edges with two OMgMn3 tetrahedra, and an edgeedge with one OMn4 trigonal pyramid. In the twenty-fourth O2- site, O2- is bonded to one Mg2+ and three Mn3+ atoms to form distorted OMgMn3 tetrahedra that share a cornercorner with one OMgMn3 tetrahedra, corners with three OMn4 trigonal pyramids, an edgeedge with one OMgMn3 tetrahedra, and edges with two OMgMn3 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgMn2O4 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2022

A Simplified Numerical Approach to Characterize the Thermal Response of a Moving Bed Solar Reactor

Abstract Concentrated solar thermochemical storage in the form of a zero-emission fuel is a promising option to produce long-duration energy storage. Solar fuel is produced using a cavity reactor that captures concentrated solar radiation from a solar field of heliostats. In this paper, heat transfer model of a tubular plug-flow reactor designed and manufactured for a solar fuel production is presented. Experimental data collected from a fixed bed tubular reactor testing are used for model comparison. The system consists of an externally heated tube with counter-current flowing gas and moving solid particles as the heated media. The proposed model simulates the dynamic behavior of temperature profiles of the tube wall, gas, and particles under various gas flowrates and residence times. The heat transfer between gas–wall, solid particle–wall, and gas–solid particle is numerically studied. The model results are compared with the results of experiments done using a 4 kW furnace with a 150 mm heating zone surrounding a horizontal alumina tube (reactor) with 50.8 mm outer diameter and thickness of 3.175 mm. Solid fixed particles of magnesium manganese oxide (MgMn2O4) with the size of 1 mm are packed within the length of 250 mm at the center of the tube length. Simulation results are assessed with respect to fixed bed experimental data for four different gas flowrates, namely, 5, 10, 15, and 20 standard liters per minute of air, and furnace temperatures in the range of 200–1200 °C. The simulation results showed good agreement with maximum steady state error that is less than 6% of those obtained from the experiments for all runs. The proposed model can be implemented as a low-order physical model for the control of temperature inside plug-flow reactors for thermochemical energy storage applications.

Engineering↗
DOE OSTI2022

Implementation of a Model Predictive Control Strategy to Regulate Temperature Inside Plug-Flow Solar Reactor With Countercurrent Flow

Abstract Solar-driven thermochemical energy storage systems are proven to be promising energy carriers (solar fuels) to utilize solar energy by using reactive solid-state pellets. However, the production of solar fuel requires a quasi-steady-state process temperature, which represents the main challenge due to the transient nature of solar power. In this work, an adaptive model predictive controller (MPC) is presented to regulate the temperature inside a tubular solar reactor to produce solid-state solar fuel for long-term thermal storage systems. The solar reactor system consists of a vertical tube heated circumferentially over a segment of its length by concentrated solar power, and the reactive pellets (MgMn2O4) are fed from the top end and flow downwards through the heated tube. A countercurrent flowing gas supplied from the lower end interacts with flowing pellets to reduce it thermochemically at a temperature range of 1000—1500 °C. A low-order physical model was developed to simulate the dynamics of the solar reactor including the reaction kinetics, and the proposed model was validated numerically by using a 7-kW electric furnace. The numerical model then was utilized to design the MPC controller, where the control system consists of an MPC code linked to an adaptive system identification code that updates system parameters online to ensure system robustness against external disturbances (sudden change in the flow inside the reactor), model mismatches, and uncertainty. The MPC controller parameters are tuned to enhance the system performance with minimum steady-state error and overshoot. The controller is tested to track different temperature ranges between 500 °C and 1400 °C with different particles/gas mass flowrates and ramping temperature profiles. Results show that the MPC controller successfully regulated the reactor temperature within ± 1 °C of its setpoint and maintained robust performance with minimum input effort when subjected to sudden changes in the amount of flowing media and the presence of chemical reaction.

Engineering↗
DOE OSTI2023

Experimental Performance of a Nonlinear Control Strategy to Regulate Temperature of a High-Temperature Solar Reactor

Abstract Despite the significant potential of solar thermochemical process technology for storing solar energy as solid-state solar fuel, several challenges have made its industrial application difficult. It is important to note that solar energy has a transient nature that causes instability and reduces process efficiency. Therefore, it is crucial to implement a robust control system to regulate the process temperature and tackle the shortage of incoming solar energy during cloudy weather. In our previous works, different model-based control strategies were developed namely a proportional integral derivative controller (PID) with gain scheduling and adaptive model predictive control (MPC). These methods were tested numerically to regulate the temperature inside a high-temperature tubular solar reactor. In this work, the proposed control strategies were experimentally tested under various operation conditions. The controllers were challenged to track different setpoints (500 °C, 1000 °C, and 1450 °C) with different amounts of gas/particle flowrates. Additionally, the flow controller was tested to regulate the reactor temperature under a cloudy weather scenario. The ultimate goal was to produce 5 kg of reduced solar fuel magnesium manganese oxide (MgMn2O4) successfully, and the controllers were able to track the required process temperature and reject disturbances despite the system's strong nonlinearity. The experimental results showed a maximum error in the temperature setpoint of less than 0.5% (6 °C), and the MPC controller demonstrated superior performance in reducing the control effort and rejecting disturbances.

Energy & Fuels↗