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18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. there are three inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six equivalent SiO4 tetrahedra and edges with six MgO6 octahedra. There are four shorter (2.07 Å) and two longer (2.14 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 equivalent SiO4 tetrahedra and edges with six MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.12 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with four equivalent SiO4 tetrahedra, and edges with seven MgO6 octahedra. The corner-sharing octahedral tilt angles are 16°. There are two shorter (2.04 Å) and four longer (2.15 Å) Mg–O bond lengths. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with ten MgO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 47–61°. There are a spread of Si–O bond distances ranging from 1.65–1.72 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the second O2- site, O2- is bonded to five Mg2+ atoms to form edge-sharing OMg5 square pyramids. In the third O2- site, O2- is bonded in a trigonal planar geometry to one Mg2+ and two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 is Ilmenite-like structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent SiO4 tetrahedra, edges with six MgO6 octahedra, and edges with two equivalent SiO4 tetrahedra. There are four shorter (2.02 Å) and two longer (2.17 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 equivalent SiO4 tetrahedra and edges with six MgO6 octahedra. There are two shorter (2.33 Å) and four longer (2.34 Å) Mg–O bond lengths. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent SiO4 tetrahedra, edges with six MgO6 octahedra, and edges with two equivalent SiO4 tetrahedra. There are four shorter (2.02 Å) and two longer (2.17 Å) Mg–O bond lengths. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six MgO6 octahedra and edges with three MgO6 octahedra. The corner-sharing octahedra tilt angles range from 3–55°. There is one shorter (1.61 Å) and three longer (1.69 Å) Si–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 is Ilmenite-like structured and crystallizes in the trigonal P-3m1 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 MgO6 octahedra that share corners with four equivalent MgO6 octahedra, corners with two equivalent SiO4 tetrahedra, edges with four equivalent MgO6 octahedra, and edges with two equivalent SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. There are two shorter (2.07 Å) and four longer (2.11 Å) Mg–O bond lengths. In the second Mg2+ site, Mg2+ is bonded to six equivalent O2- atoms to form MgO6 octahedra that share corners with twelve equivalent MgO6 octahedra and corners with six equivalent SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. All Mg–O bond lengths are 2.24 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six MgO6 octahedra and edges with three equivalent MgO6 octahedra. The corner-sharing octahedra tilt angles range from 54–57°. There is one shorter (1.63 Å) and three longer (1.67 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three equivalent Mg2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Mg2+ is bonded in a 1-coordinate geometry to nine O2- atoms. There are a spread of Mg–O bond distances ranging from 1.96–2.48 Å. Si4+ is bonded to six O2- atoms to form corner-sharing SiO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There is four shorter (1.75 Å) and two longer (1.79 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Mg2+ and two equivalent Si4+ atoms to form a mixture of distorted edge, face, and corner-sharing OMg4Si2 octahedra. The corner-sharing octahedra tilt angles range from 0–55°. In the second O2- site, O2- is bonded to five equivalent Mg2+ and one Si4+ atom to form distorted OMg5Si octahedra that share corners with seventeen OMg4Si2 octahedra, edges with eight equivalent OMg5Si octahedra, and faces with four equivalent OMg4Si2 octahedra. The corner-sharing octahedra tilt angles range from 0–55°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 is Ilmenite-like structured and crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. there are five inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with two SiO4 tetrahedra, edges with five MgO6 octahedra, and edges with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–57°. There are a spread of Mg–O bond distances ranging from 2.05–2.14 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four equivalent MgO6 octahedra, corners with two equivalent SiO4 tetrahedra, edges with four equivalent MgO6 octahedra, and edges with two equivalent SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. All Mg–O bond lengths are 2.10 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with twelve MgO6 octahedra and corners with six SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–57°. There are two shorter (2.24 Å) and four longer (2.26 Å) Mg–O bond lengths. In the fourth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six SiO4 tetrahedra and edges with six MgO6 octahedra. There are four shorter (2.32 Å) and two longer (2.33 Å) Mg–O bond lengths. In the fifth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent SiO4 tetrahedra, edges with six MgO6 octahedra, and edges with two equivalent SiO4 tetrahedra. There are four shorter (2.02 Å) and two longer (2.13 Å) Mg–O bond lengths. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six MgO6 octahedra and edges with three MgO6 octahedra. The corner-sharing octahedra tilt angles range from 2–55°. There are a spread of Si–O bond distances ranging from 1.62–1.69 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six MgO6 octahedra and edges with three MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–56°. There is one shorter (1.62 Å) and three longer (1.68 Å) Si–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Mg2+ is bonded to six equivalent O2- atoms to form MgO6 octahedra that share corners with six equivalent SiO4 tetrahedra and edges with six equivalent MgO6 octahedra. All Mg–O bond lengths are 2.09 Å. Si4+ is bonded to four equivalent O2- atoms to form SiO4 tetrahedra that share corners with twelve equivalent MgO6 octahedra. The corner-sharing octahedral tilt angles are 53°. All Si–O bond lengths are 1.68 Å. O2- is bonded in a rectangular see-saw-like geometry to three equivalent Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.41 Å. In the second Mg2+ site, Mg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.43 Å. In the third Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 1.99–2.30 Å. In the fourth Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.30 Å. In the fifth Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.30 Å. In the sixth Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.30 Å. In the seventh Mg2+ site, Mg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.41 Å. In the eighth Mg2+ site, Mg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Mg–O bond distances ranging from 1.98–2.43 Å. There are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. In the second Si4+ site, Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. In the third Si4+ site, Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. In the fourth Si4+ site, Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Mg2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Mg2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted see-saw-like geometry to three Mg2+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Mg2+ and one Si4+ atom. In the seventh O2- site, O2- is bonded to three Mg2+ and one Si4+ atom to form distorted corner-sharing OMg3Si trigonal pyramids. In the eighth O2- site, O2- is bonded to three Mg2+ and one Si4+ atom to form distorted corner-sharing OMg3Si trigonal pyramids. In the ninth O2- site, O2- is bonded in a distorted see-saw-like geometry to three Mg2+ and one Si4+ atom. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to two Mg2+ and one Si4+ atom. In the eleventh O2- site, O2- is bonded in a distorted see-saw-like geometry to three Mg2+ and one Si4+ atom. In the twelfth O2- site, O2- is bonded to three Mg2+ and one Si4+ atom to form distorted corner-sharing OMg3Si trigonal pyramids. In the thirteenth O2- site, O2- is bonded to three Mg2+ and one Si4+ atom to form distorted corner-sharing OMg3Si trigonal pyramids. In the fourteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the fifteenth O2- site, O2- is bonded in a distorted see-saw-like geometry to three Mg2+ and one Si4+ atom. In the sixteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. Mg2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Mg–O bond distances ranging from 2.07–2.50 Å. Si4+ is bonded to six O2- atoms to form edge-sharing SiO6 octahedra. There is two shorter (1.77 Å) and four longer (1.87 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent Mg2+ and two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a 5-coordinate geometry to four equivalent Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 crystallizes in the orthorhombic Cmc2_1 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 MgO6 octahedra that share corners with three equivalent SiO6 octahedra, edges with two equivalent MgO6 octahedra, and edges with three equivalent SiO6 octahedra. The corner-sharing octahedra tilt angles range from 7–53°. There are a spread of Mg–O bond distances ranging from 2.02–2.12 Å. In the second Mg2+ site, Mg2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Mg–O bond distances ranging from 2.03–2.59 Å. Si4+ is bonded to six O2- atoms to form SiO6 octahedra that share corners with three equivalent MgO6 octahedra, edges with two equivalent SiO6 octahedra, and edges with three equivalent MgO6 octahedra. The corner-sharing octahedra tilt angles range from 7–53°. There are a spread of Si–O bond distances ranging from 1.73–1.90 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Mg2+ and two equivalent Si4+ atoms. In the second O2- site, O2- is bonded to three Mg2+ and two equivalent Si4+ atoms to form distorted OMg3Si2 square pyramids that share corners with five equivalent OMg3Si tetrahedra, corners with two equivalent OMg4Si trigonal bipyramids, edges with two equivalent OMg3Si2 square pyramids, an edgeedge with one OMg3Si tetrahedra, and edges with three equivalent OMg4Si trigonal bipyramids. In the third O2- site, O2- is bonded to four Mg2+ and one Si4+ atom to form distorted OMg4Si trigonal bipyramids that share corners with two equivalent OMg3Si2 square pyramids, corners with five equivalent OMg3Si tetrahedra, edges with three equivalent OMg3Si2 square pyramids, an edgeedge with one OMg3Si tetrahedra, and edges with two equivalent OMg4Si trigonal bipyramids. In the fourth O2- site, O2- is bonded to three Mg2+ and one Si4+ atom to form distorted OMg3Si tetrahedra that share corners with five equivalent OMg3Si2 square pyramids, corners with two equivalent OMg3Si tetrahedra, corners with five equivalent OMg4Si trigonal bipyramids, an edgeedge with one OMg3Si2 square pyramid, and an edgeedge with one OMg4Si trigonal bipyramid.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg2SiO4 by Materials Project

Mg2SiO4 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Mg2+ is bonded to four equivalent O2- atoms to form MgO4 tetrahedra that share corners with four equivalent MgO4 tetrahedra and corners with four equivalent SiO4 tetrahedra. There is two shorter (1.99 Å) and two longer (2.00 Å) Mg–O bond length. Si4+ is bonded to four equivalent O2- atoms to form SiO4 tetrahedra that share corners with eight equivalent MgO4 tetrahedra. All Si–O bond lengths are 1.65 Å. O2- is bonded in a trigonal planar geometry to two equivalent Mg2+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Using Multigrain Crystallography to Explore the Microstructural Evolution of the α-Olivine to γ-Ringwoodite Transformation and ε-Mg2SiO4 at High Pressure and Temperature

The introduction of multigrain crystallography (MGC) applied in a laser-heated diamond anvil cell (LH-DAC) using synchrotron X-rays has provided a new path to investigate the microstructural evolution of materials at extreme conditions, allowing for simultaneous investigations of phase identification, strain state determination, and orientation relations across phase transitions in a single experiment. Here, we applied this method to a sample of San Carlos olivine beginning at ambient conditions and through the α-olivine → γ-ringwoodite phase transition. At ambient temperatures, by measuring the evolution of individual Bragg reflections, olivine shows profuse angular streaking consistent with the onset of yielding at a measured stress of ~1.5 GPa, considerably lower than previously reported, which may have implications for mantle evolution. Furthermore, γ-ringwoodite phase was found to nucleate as micron to sub-micron grains imbedded with small amounts of a secondary phase at 15 GPa and 1000 °C. Using MGC, we were able to extract and refine individual crystallites of the secondary unknown phase where it was found to have a structure consistent with the ε-phase previously described in chondritic meteorites.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hydration-driven stabilization and volume collapse of grain boundaries in Mg2SiO4 forsterite predicted by first-principles simulations

Grain boundaries in mantle minerals are of critical importance to geophysical and geochemical processes of the Earth’s interior. One of the fundamental issues is to understand how the water (H 2 O) component influences the properties of grain boundaries in silicate materials. Here, we report the results of the structure and stability of several tilt grain boundaries in Mg 2 SiO 4 forsterite over the pressure range 0 to 15 GPa using density functional theory-based first-principles simulations. Here, the results suggest greater energetic stability and hydration-driven volume collapse (negative excess volume) at zero pressure for the majority of hydrous grain boundaries relative to the anhydrous (dry) ones. All the hydrous grain boundaries become increasingly favorable at elevated pressures as the calculated hydration enthalpy systematically decreases with increasing pressure. The hydrous components at the interfacial regions are predominantly in the hydroxyl form and, to a lesser extent, in the molecular H 2 O form. Their calculated ratio ranges from 1.6 to 8.7 among the different grain boundary configurations. Our structural analysis also reveals that the hydroxyls are bound to either both Mg and Si or to Mg only. In comparison, the molecular species are bound only to Mg sites. Besides direct oxygen-hydrogen bonding, intermolecular hydrogen bonding becomes important with compression. On the basis of our results, we suggest that local atomic rearrangements caused by dissociative adsorption of water facilitate efficient compaction of the boundary interfaces, which, in turn, results in greater relative stability of hydrous grain boundaries. This means that water prefers to be incorporated within the grain boundaries over the bulk of silicate materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Thin Water Films Enable Low-Temperature Magnesite Growth Under Conditions Relevant to Geologic Carbon Sequestration

Injecting supercritical CO2 (scCO2) into basalt formations for long-term storage is a promising strategy for mitigating CO2 emissions. Mineral carbonation can result in permanent entrapment of CO2; however, carbonation kinetics in thin H2O films in humidified scCO2 is not well understood. We investigated forsterite (Mg2SiO4) carbonation to magnesite (MgCO3) via amorphous magnesium carbonate (AMC; MgCO3·xH2O, 0.5 < x < 1), with the goal to establish the fundamental controls on magnesite growth rates at low H2O activity and temperature. Experiments were conducted at 25, 40, and 50 °C in 90 bar CO2 with a H2O film thickness on forsterite that averaged 1.78 ± 0.05 monolayers. In situ infrared spectroscopy was used to monitor forsterite dissolution and the growth of AMC, magnesite, and amorphous SiO2 as a function of time. Geochemical kinetic modeling showed that magnesite was supersaturated by two to three orders of magnitude and grew according to a zero-order rate law. The results indicate that the main drivers for magnesite growth are sustained high supersaturation coupled with low H2O activity, a combination of thermodynamic conditions not attainable in bulk aqueous solution. This improved understanding of reaction kinetics can inform subsurface reactive transport models for better predictions of CO2 fate and transport.

Kerisit, Sebastien N.↗
DOE OSTI2020

Liquid-Vapor Coexistence and Critical Point of Mg 2 SiO 4 From Ab Initio Simulations

Hypervelocity impact-driven vaporization is characteristic of late-stage planet formation. Yet the behavior and properties of liquid-vapor mixtures of planetary materials of interest are typically unknown. Multiphase equations of state used in hydrodynamic simulations of planet impacts therefore lack reliable data for this important phenomenon. Here, we present the first constraints on the liquid-vapor critical point and coexistence phase boundary of Mg2SiO4 computed from ab initio molecular dynamics simulations. We found that the vapor is depleted in magnesium and enriched in silica and oxygen, while the coexisting liquid is enriched in magnesium and depleted in oxygen, from which we infer vaporization is incongruent. The critical point was estimated from an equation of state fit to the data. The results are in line with recent calculations of MgSiO3 and together confirm that extant multiphase equation of state (EOS) models used in planetary accretion modeling significantly underestimate the amount of supercritical material postimpact.

58 GEOSCIENCES↗
DOE OSTI2020

Technical Performance of Refractory Liners for Molten Chloride Salt Thermal Energy Storage Systems

A chloride-based molten-salt system that uses a ternary blend of MgCl2/KCl/NaCl is investigated to provide higher temperature thermal energy storage capability. Despite higher thermal stability, molten chlorides present several unique challenges, including the design of internal refractory-ceramic liners to prevent the corrosion and thermal stress of alloy tank shells. This work discusses issues and potential solutions related to containment of molten chloride salt, specifically the optimization of the refractory material at the molten salt interface (hot face). The down-selected hot face candidate limits permeation of salt through the material and forms a highly stable secondary surface phase in equilibrium with the molten salt. A mortar is created using the corrosion resistant hot face brick. Brick and mortar composite are subjected to mechanical stress/strain analysis, in order to calculate composite material properties and better inform thermomechanical models. The U.S. Department of Energy Generation 3 (DOE Gen3) program seeks to develop higher efficiency CSP plants that can provide cost-competitive, flexible power in the U.S. electric grid. The proposed Gen3 Liquid Pathway CSP plant closely resembles the configuration of current nitrate salt power towers with two-tank storage (Gen2). The differences between Gen2 and Gen3 include the types of compatible materials used in salt storage tank construction. Stainless steel loses strength at Gen3 temperatures, and although nickel superalloys would be capable of withstanding sustained high temperatures, these materials are prohibitively expensive at scale. Uninsulated tank shells also pose a significant risk as common steels are highly susceptible to chemical attack from molten chloride salt. To address these concerns, refractory-ceramic based containment materials are proposed to line the inside of the hot and cold storage tanks. In doing so, stainless or carbon steel shells may be used in construction depending on the level of insulation provided. The composition of the internal liner requires careful consideration to maximize the efficacy of multiple parameters including corrosion resistance, strength at operating temperature, durability, and cost. This is particularly true for the material at the interface with the salt, known as the "hot face", which is responsible for protecting the insulating layers between the tank shell and the hot face brick layer. The molten salt in this system is superheated over 300 °C above its freeze temperature. Therefore, unlike other industrial processes which use refractory-lined vessels, it is not expected that a freeze plane will develop in the hot face. Therefore, the hot face must be designed to withstand chemical corrosion and inhibit permeation of molten salt into the insulating layers. A down selection was performed to identify a hot face candidate best equipped to maintain thermal, mechanical, and chemical integrity when exposed to molten salt over extended periods of time. Long-duration chemical capability experiments were conducted with the down selected hot face refractory fully immersed in molten chloride salt for up to 3000 hours. The average salt penetration does not exceed 100 microns. When extrapolated to 20 and 30 years of continuous exposure, the expected salt penetration depth is approximately 2.0 mm and 2.9 mm, respectively. A magnesium-rich secondary phases develops at the salt/refractory interface. X-ray diffraction identifies the material as forsterite (Mg2SiO4), which is reported to form synthetically in molten chloride salt solutions. These results suggest the selected hot face will adequately inhibit salt permeation. While there is optimism that the hot face brick will inhibit salt permeation, mortar joints are typically the weakest point of a refractory brick liner. From a thermochemical perspective, differing thermal expansion coefficients may result in the mortar and brick to grow independent of each other, creating gaps through which molten salt can penetrate. To address this issue, NREL has developed an in-house mortar composed of the down selected hot face brick that has been shown to be compatible with the salt. Compressive stress/strain analyses have been performed on the brick/ mortar composites to generate stress/strain curves. Modulus of elasticity and Poisson's ratio of the composite may be calculated from the stress/strain curves, in order to provide more representative data to finite element mechanical models for accurate approximation of stress on the tank shell and the amount of thermal expansion expected within the tank liner.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2025

Cation Disorder of ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ in Super‐Earth Mantles

Understanding the mineralogy of exoplanets is essential for unraveling their interior structures, dynamics, and evolution. For large super-Earths, the post-post spinel ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$, one of the major mantle phases, may undergo the order-disorder transition (ODT) at high temperatures. However, the ODT phase boundary of ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ has not been rigorously constrained. Additionally, fundamental thermodynamic properties of the disordered ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ remain poorly investigated. Here, we develop a unified machine learning potential (MLP) for ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ of ab initio accuracy under super-Earth mantle conditions. With the efficient MLP, we extensively calculate the free energy of post-post spinel ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ via the thermodynamic integration method. The results are used to constrain the ODT phase boundary. Furthermore, we report the P-V-T equation of state and Grüneisen parameters for post-post spinel ${\text{Mg}}_{\mathbf{2}}{\text{SiO}}_{\mathbf{4}}$ across various degrees of disorder. These thermodynamic properties are further applied to update the adiabatic thermal profiles and the mass-radius relation of super-Earths.

36 MATERIALS SCIENCE↗