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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Magnetostriction and damping of forced vibrations in Fe-Mo single and polycrystal alloys

Magnetostriction and damping of forced vibrations in Fe-Mo single and polycrystal alloys is studied and analyzed with respect to existing approaches and experimental data. In this work, our data suggest that a more complex dependence (compared with linear dependence predicted by Smith and Birchak) between damping capacity and magnetostriction takes place for this and possibly other Fe-based ferromagnetic alloys. We believe that more factors related to the structural changes, brought about by the additions (elements added to Fe), which can affect phase stability as well as magnetic and electric contributions influencing property response, should be considered to provide a better correlation between the magnetic and magnetomechanical characteristics of this alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sintering inhibition enables hierarchical porosity with extreme resistance to degradation during redox cycling of Fe-Mo foams

High-temperature (800 ºC) steam-hydrogen redox cycling, relevant to grid-scale energy storage, is studied for iron-based freeze-cast lamellar foams. In contrast to previously studied Fe, Fe-Ni, and Fe-Co foams that rapidly degrade, Fe-25Mo foams feature a much-enhanced structural damage resistance. Utilizing in-situ x-ray diffraction, microscopy, and x-ray tomography, strong sintering inhibition is observed in Fe-Mo foams, creating a hierarchically porous lamellar structure. This leads to (i) wide channels between lamellae, enabling high macroscopic porosity (~78%) which can accommodate gas flow as well as volumetric expansion without lamellar contact, and (ii) microporosity within lamellae, providing additional free volume to accommodate expansion during oxidation, limiting both swelling of the lamellae and the formation of Kirkendall pores. Finally, these combined effects enable a near-complete reversibility of the microstructure during cycling, preventing damage produced via internal lamellar buckling, cracking, contacting and sintering, with a remarkably high porosity (65%) remaining after 50 consecutive redox cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Elucidating the role of $\mathrm{Fe}$-$\mathrm{Mo}$ interactions in the metal oxide precursors for Fe promoted $\mathrm{Mo/ZSM}$-5 catalysts in non-oxidative methane dehydroaromatization

Literature shows that adding Fe as a separate phase to MoO 3 /ZSM-5 catalysts can improve benzene selectivity in methane dehydroaromatization (MDA), but only when added in small quantities, making it difficult to characterize the state of Fe in the catalyst and understand the role of Fe-Mo interactions on the catalytic properties. We explore how the nature of the Mo-Fe interactions in the catalyst precursor can influence the stability and product selectivity in MDA, by employing for the first time Fe 2 (MoO 4 ) 3 /ZSM-5 as a catalyst precursor in MDA. We have compared the activity of Fe 2 (MoO 4 ) 3 /ZSM-5 with monometallic MoO 3 /ZSM-5 and mixed MoO 3 + Fe 2 O 3 /ZSM-5 containing equivalent Mo and Fe loadings and found that Fe 2 (MoO 4 ) 3 /ZSM-5 shows higher benzene selectivity than the mixed MoO 3 + Fe 2 O 3 /ZSM-5 catalyst and exhibits higher stability in reaction compared to the monometallic MoO3/ZSM-5 catalyst. Structural characterization suggests that Fe 2 (MoO 4 ) 3 partially segregates to Fe 2 O 3 and amorphous MoO x during thermal pretreatment. The MoO x species migrate into the zeolite channels during pretreatment, while Fe oxides remain on the external surface of the zeolite. Gas adsorption/desorption techniques and density functional theory calculations demonstrate that the preexisting Fe 2 O 3 phases on the external surface of the zeolite in the mixed MoO 3 + Fe 2 O 3 /ZSM-5 precursor trap (MoO 3 ) 3 clusters preventing them from migrating into the zeolite channels during pretreatment, whereas gradual formation of amorphous MoOx together with the segregation of the Fe 2 O 3 phase when using the Fe 2 (MoO 4 ) 3 precursor diminishes trapping of (MoO 3 ) 3 and consequently enhances migration and anchoring of the MoO x species in the zeolite channels, boosting selectivity to benzene. Characterization of used catalysts suggests that the presence of Fe promotes formation of structured carbon nanofibers which reduce the rate of catalyst deactivation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Significance of pH and iron-sulfur chemistry for molybdenum sequestration under sulfidic conditions

Molybdenum (Mo), a redox-sensitive trace metal, plays an important role in recording ancient oxygenation and deoxygenation events as a paleoredox proxy. The mobility and reactivity of Mo in aqueous conditions are closely tied to the chemistry of reduced sulfur and iron species. However, our current knowledge on the formation, structure, stability, and condensation pathways of FeMoS clusters in aqueous settings remains limited, which has driven the current study. In this study, we conducted systematic experiments investigating the interactions between dissolved Mo (initially introduced as molybdate, MoO 4 2– , or tetrathiomolybdate, MoS 4 2– ), ferrous iron (Fe 2+ ), and sulfide (ΣH 2 S aq ) in variously defined abiotic sulfidic systems to determine the external conditions (i.e., pH, and reactant concentrations and ratios) necessary for the formation of solid-phase Fe-Mo sulfides. Solution samples of each system were monitored using ultraviolet-visible spectroscopy (UV–vis) to track the degree of thiolation of dissolved Mo species. Precipitates were analyzed using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to determine their elemental compositions and valences, and structure (i.e., crystalline or amorphous), respectively. All FeMoS precipitates were amorphous and contained 76–90% Mo(IV) and 10–24% Mo(V) with a trend toward lower Mo(IV):Mo(V) ratios with increasing pH. The degree of Mo thiolation, which was strongly dependent on solution pH and Fe 2+ concentrations, greatly affected the amount of Mo sequestered (i.e., an increased degree of Mo thiolation in solution led to an increased amount of Mo in the final FeMoS precipitate). Furthermore, these findings suggest that changes in pH and Fe 2+ concentrations may be responsible for the sulfide-independent variations in Mo behavior observed in euxinic basins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Fe7Mo6 by Materials Project

Fe7Mo6 is Frank-Kasper $\mu$ Phase structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to four Mo and twelve Fe atoms. There are one shorter (2.66 Å) and three longer (2.83 Å) Mo–Mo bond lengths. There are a spread of Mo–Fe bond distances ranging from 2.66–2.87 Å. In the second Mo site, Mo is bonded in a 6-coordinate geometry to nine Mo and six equivalent Fe atoms. There are a spread of Mo–Mo bond distances ranging from 2.75–3.03 Å. There are three shorter (2.68 Å) and three longer (2.71 Å) Mo–Fe bond lengths. In the third Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Fe atoms. The Mo–Mo bond length is 2.52 Å. All Mo–Fe bond lengths are 2.60 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to seven Mo and five Fe atoms to form a mixture of edge, face, and corner-sharing FeFe5Mo7 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.37–2.39 Å. In the second Fe site, Fe is bonded to six equivalent Mo and six equivalent Fe atoms to form FeFe6Mo6 cuboctahedra that share corners with twelve equivalent FeFe5Mo7 cuboctahedra, edges with six equivalent FeFe6Mo6 cuboctahedra, and faces with eighteen equivalent FeFe5Mo7 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe4Mo by Materials Project

MoFe4 is alpha Samarium-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Mo is bonded to four equivalent Mo and eight equivalent Fe atoms to form MoFe8Mo4 cuboctahedra that share corners with four equivalent MoFe8Mo4 cuboctahedra, corners with eight equivalent FeFe12 cuboctahedra, edges with twenty-four FeFe8Mo4 cuboctahedra, faces with eight equivalent MoFe8Mo4 cuboctahedra, and faces with ten FeFe8Mo4 cuboctahedra. All Mo–Mo bond lengths are 2.61 Å. All Mo–Fe bond lengths are 2.76 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to four equivalent Mo and eight Fe atoms to form FeFe8Mo4 cuboctahedra that share corners with twelve FeFe8Mo4 cuboctahedra, edges with eight equivalent MoFe8Mo4 cuboctahedra, edges with sixteen FeFe12 cuboctahedra, faces with four equivalent MoFe8Mo4 cuboctahedra, and faces with fourteen FeFe8Mo4 cuboctahedra. There are four shorter (2.53 Å) and four longer (2.61 Å) Fe–Fe bond lengths. In the second Fe site, Fe is bonded to twelve Fe atoms to form FeFe12 cuboctahedra that share corners with four equivalent MoFe8Mo4 cuboctahedra, corners with eight FeFe8Mo4 cuboctahedra, edges with four equivalent MoFe8Mo4 cuboctahedra, edges with twenty FeFe8Mo4 cuboctahedra, a faceface with one MoFe8Mo4 cuboctahedra, and faces with seventeen FeFe8Mo4 cuboctahedra. There are four shorter (2.46 Å) and four longer (2.61 Å) Fe–Fe bond lengths.

36 MATERIALS SCIENCE↗