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At least 1,513 records · Page 84
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DOE OSTI2020

Materials Data on Ta2Cr3Si by Materials Project

Ta2Cr3Si crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ta is bonded in a 12-coordinate geometry to four equivalent Ta, nine equivalent Cr, and three equivalent Si atoms. All Ta–Ta bond lengths are 3.00 Å. There are six shorter (2.86 Å) and three longer (2.89 Å) Ta–Cr bond lengths. All Ta–Si bond lengths are 2.86 Å. Cr is bonded to six equivalent Ta, four equivalent Cr, and two equivalent Si atoms to form distorted CrTa6Cr4Si2 cuboctahedra that share corners with four equivalent SiTa6Cr6 cuboctahedra, corners with fourteen equivalent CrTa6Cr4Si2 cuboctahedra, edges with six equivalent CrTa6Cr4Si2 cuboctahedra, faces with six equivalent SiTa6Cr6 cuboctahedra, and faces with twelve equivalent CrTa6Cr4Si2 cuboctahedra. There are two shorter (2.36 Å) and two longer (2.51 Å) Cr–Cr bond lengths. Both Cr–Si bond lengths are 2.49 Å. Si is bonded to six equivalent Ta and six equivalent Cr atoms to form SiTa6Cr6 cuboctahedra that share corners with twelve equivalent CrTa6Cr4Si2 cuboctahedra, edges with six equivalent SiTa6Cr6 cuboctahedra, faces with two equivalent SiTa6Cr6 cuboctahedra, and faces with eighteen equivalent CrTa6Cr4Si2 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti2Cr3Si by Materials Project

Ti2Cr3Si crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ti is bonded in a 3-coordinate geometry to four equivalent Ti, nine equivalent Cr, and three equivalent Si atoms. There are three shorter (2.95 Å) and one longer (3.02 Å) Ti–Ti bond lengths. There are six shorter (2.84 Å) and three longer (2.85 Å) Ti–Cr bond lengths. All Ti–Si bond lengths are 2.82 Å. Cr is bonded to six equivalent Ti, four equivalent Cr, and two equivalent Si atoms to form distorted CrTi6Cr4Si2 cuboctahedra that share corners with four equivalent SiTi6Cr6 cuboctahedra, corners with fourteen equivalent CrTi6Cr4Si2 cuboctahedra, edges with six equivalent CrTi6Cr4Si2 cuboctahedra, faces with six equivalent SiTi6Cr6 cuboctahedra, and faces with twelve equivalent CrTi6Cr4Si2 cuboctahedra. There are two shorter (2.31 Å) and two longer (2.49 Å) Cr–Cr bond lengths. Both Cr–Si bond lengths are 2.47 Å. Si is bonded to six equivalent Ti and six equivalent Cr atoms to form SiTi6Cr6 cuboctahedra that share corners with twelve equivalent CrTi6Cr4Si2 cuboctahedra, edges with six equivalent SiTi6Cr6 cuboctahedra, faces with two equivalent SiTi6Cr6 cuboctahedra, and faces with eighteen equivalent CrTi6Cr4Si2 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UCrFe by Materials Project

UCrFe is Frank-Kasper $\mu$ Phase-derived structured and crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. U is bonded in a 4-coordinate geometry to two equivalent U, six equivalent Cr, and six equivalent Fe atoms. Both U–U bond lengths are 2.78 Å. There are four shorter (2.94 Å) and two longer (3.13 Å) U–Cr bond lengths. There are four shorter (2.77 Å) and two longer (3.02 Å) U–Fe bond lengths. Cr is bonded to six equivalent U, two equivalent Cr, and four equivalent Fe atoms to form distorted CrU6Cr2Fe4 cuboctahedra that share corners with eight equivalent FeU6Cr4Fe2 cuboctahedra, corners with ten equivalent CrU6Cr2Fe4 cuboctahedra, edges with six equivalent CrU6Cr2Fe4 cuboctahedra, faces with six equivalent CrU6Cr2Fe4 cuboctahedra, and faces with twelve equivalent FeU6Cr4Fe2 cuboctahedra. Both Cr–Cr bond lengths are 2.22 Å. All Cr–Fe bond lengths are 2.54 Å. Fe is bonded to six equivalent U, four equivalent Cr, and two equivalent Fe atoms to form FeU6Cr4Fe2 cuboctahedra that share corners with eight equivalent CrU6Cr2Fe4 cuboctahedra, corners with ten equivalent FeU6Cr4Fe2 cuboctahedra, edges with six equivalent FeU6Cr4Fe2 cuboctahedra, faces with six equivalent FeU6Cr4Fe2 cuboctahedra, and faces with twelve equivalent CrU6Cr2Fe4 cuboctahedra. Both Fe–Fe bond lengths are 2.59 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr3C by Materials Project

Cr3C is Cementite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Cr sites. In the first Cr site, Cr is bonded in a 2-coordinate geometry to three equivalent C atoms. There are a spread of Cr–C bond distances ranging from 2.04–2.32 Å. In the second Cr site, Cr is bonded in a bent 150 degrees geometry to two equivalent C atoms. There are one shorter (2.02 Å) and one longer (2.05 Å) Cr–C bond lengths. C is bonded in a 6-coordinate geometry to eight Cr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrVCr by Materials Project

ZrCrV is Hexagonal Laves-derived structured and crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Zr is bonded in a 12-coordinate geometry to four equivalent Zr, six equivalent V, and six equivalent Cr atoms. There are two shorter (3.10 Å) and two longer (3.19 Å) Zr–Zr bond lengths. There are four shorter (2.96 Å) and two longer (3.04 Å) Zr–V bond lengths. There are two shorter (2.98 Å) and four longer (3.06 Å) Zr–Cr bond lengths. V is bonded to six equivalent Zr, two equivalent V, and four equivalent Cr atoms to form VZr6V2Cr4 cuboctahedra that share corners with eight equivalent CrZr6V4Cr2 cuboctahedra, corners with ten equivalent VZr6V2Cr4 cuboctahedra, edges with six equivalent VZr6V2Cr4 cuboctahedra, faces with six equivalent VZr6V2Cr4 cuboctahedra, and faces with twelve equivalent CrZr6V4Cr2 cuboctahedra. Both V–V bond lengths are 2.64 Å. All V–Cr bond lengths are 2.57 Å. Cr is bonded to six equivalent Zr, four equivalent V, and two equivalent Cr atoms to form CrZr6V4Cr2 cuboctahedra that share corners with eight equivalent VZr6V2Cr4 cuboctahedra, corners with ten equivalent CrZr6V4Cr2 cuboctahedra, edges with six equivalent CrZr6V4Cr2 cuboctahedra, faces with six equivalent CrZr6V4Cr2 cuboctahedra, and faces with twelve equivalent VZr6V2Cr4 cuboctahedra. Both Cr–Cr bond lengths are 2.50 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr2Cr3Si by Materials Project

Zr2Cr3Si is Hexagonal Laves-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Zr is bonded in a 12-coordinate geometry to four equivalent Zr, nine equivalent Cr, and three equivalent Si atoms. There are three shorter (3.08 Å) and one longer (3.13 Å) Zr–Zr bond lengths. There are six shorter (2.95 Å) and three longer (2.99 Å) Zr–Cr bond lengths. All Zr–Si bond lengths are 2.93 Å. Cr is bonded to six equivalent Zr, four equivalent Cr, and two equivalent Si atoms to form CrZr6Cr4Si2 cuboctahedra that share corners with four equivalent SiZr6Cr6 cuboctahedra, corners with fourteen equivalent CrZr6Cr4Si2 cuboctahedra, edges with six equivalent CrZr6Cr4Si2 cuboctahedra, faces with six equivalent SiZr6Cr6 cuboctahedra, and faces with twelve equivalent CrZr6Cr4Si2 cuboctahedra. There are two shorter (2.42 Å) and two longer (2.57 Å) Cr–Cr bond lengths. Both Cr–Si bond lengths are 2.57 Å. Si is bonded to six equivalent Zr and six equivalent Cr atoms to form SiZr6Cr6 cuboctahedra that share corners with twelve equivalent CrZr6Cr4Si2 cuboctahedra, edges with six equivalent SiZr6Cr6 cuboctahedra, faces with two equivalent SiZr6Cr6 cuboctahedra, and faces with eighteen equivalent CrZr6Cr4Si2 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrTaCr4 by Materials Project

ZrTaCr4 is Hexagonal Laves-derived structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Zr is bonded in a 12-coordinate geometry to four equivalent Ta and twelve equivalent Cr atoms. All Zr–Ta bond lengths are 3.05 Å. All Zr–Cr bond lengths are 2.92 Å. Ta is bonded in a 12-coordinate geometry to four equivalent Zr and twelve equivalent Cr atoms. All Ta–Cr bond lengths are 2.92 Å. Cr is bonded to three equivalent Zr, three equivalent Ta, and six equivalent Cr atoms to form a mixture of corner, edge, and face-sharing CrZr3Ta3Cr6 cuboctahedra. All Cr–Cr bond lengths are 2.49 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UCrNi by Materials Project

UCrNi crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to four equivalent U, six equivalent Cr, and six equivalent Ni atoms. There are two shorter (3.05 Å) and two longer (3.11 Å) U–U bond lengths. There are four shorter (2.89 Å) and two longer (3.04 Å) U–Cr bond lengths. There are four shorter (2.88 Å) and two longer (3.08 Å) U–Ni bond lengths. Cr is bonded to six equivalent U, two equivalent Cr, and four equivalent Ni atoms to form distorted CrU6Cr2Ni4 cuboctahedra that share corners with eight equivalent NiU6Cr4Ni2 cuboctahedra, corners with ten equivalent CrU6Cr2Ni4 cuboctahedra, edges with six equivalent CrU6Cr2Ni4 cuboctahedra, faces with six equivalent CrU6Cr2Ni4 cuboctahedra, and faces with twelve equivalent NiU6Cr4Ni2 cuboctahedra. Both Cr–Cr bond lengths are 2.45 Å. All Cr–Ni bond lengths are 2.55 Å. Ni is bonded to six equivalent U, four equivalent Cr, and two equivalent Ni atoms to form NiU6Cr4Ni2 cuboctahedra that share corners with eight equivalent CrU6Cr2Ni4 cuboctahedra, corners with ten equivalent NiU6Cr4Ni2 cuboctahedra, edges with six equivalent NiU6Cr4Ni2 cuboctahedra, faces with six equivalent NiU6Cr4Ni2 cuboctahedra, and faces with twelve equivalent CrU6Cr2Ni4 cuboctahedra. Both Ni–Ni bond lengths are 2.44 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrCrMo by Materials Project

CrMoZr crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Zr is bonded in a 12-coordinate geometry to four equivalent Zr, six equivalent Mo, and six equivalent Cr atoms. There are two shorter (3.20 Å) and two longer (3.22 Å) Zr–Zr bond lengths. There are four shorter (3.05 Å) and two longer (3.08 Å) Zr–Mo bond lengths. There are two shorter (3.04 Å) and four longer (3.10 Å) Zr–Cr bond lengths. Mo is bonded to six equivalent Zr, two equivalent Mo, and four equivalent Cr atoms to form distorted MoZr6Cr4Mo2 cuboctahedra that share corners with eight equivalent CrZr6Cr2Mo4 cuboctahedra, corners with ten equivalent MoZr6Cr4Mo2 cuboctahedra, edges with six equivalent MoZr6Cr4Mo2 cuboctahedra, faces with six equivalent MoZr6Cr4Mo2 cuboctahedra, and faces with twelve equivalent CrZr6Cr2Mo4 cuboctahedra. Both Mo–Mo bond lengths are 2.66 Å. All Mo–Cr bond lengths are 2.62 Å. Cr is bonded to six equivalent Zr, four equivalent Mo, and two equivalent Cr atoms to form distorted CrZr6Cr2Mo4 cuboctahedra that share corners with eight equivalent MoZr6Cr4Mo2 cuboctahedra, corners with ten equivalent CrZr6Cr2Mo4 cuboctahedra, edges with six equivalent CrZr6Cr2Mo4 cuboctahedra, faces with six equivalent CrZr6Cr2Mo4 cuboctahedra, and faces with twelve equivalent MoZr6Cr4Mo2 cuboctahedra. Both Cr–Cr bond lengths are 2.59 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf2Cr3Si by Materials Project

Hf2Cr3Si crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Hf is bonded in a 12-coordinate geometry to nine equivalent Cr and three equivalent Si atoms. There are six shorter (2.93 Å) and three longer (2.94 Å) Hf–Cr bond lengths. All Hf–Si bond lengths are 2.93 Å. Cr is bonded to six equivalent Hf, four equivalent Cr, and two equivalent Si atoms to form CrHf6Cr4Si2 cuboctahedra that share corners with four equivalent SiHf6Cr6 cuboctahedra, corners with fourteen equivalent CrHf6Cr4Si2 cuboctahedra, edges with six equivalent CrHf6Cr4Si2 cuboctahedra, faces with six equivalent SiHf6Cr6 cuboctahedra, and faces with twelve equivalent CrHf6Cr4Si2 cuboctahedra. There are two shorter (2.41 Å) and two longer (2.58 Å) Cr–Cr bond lengths. Both Cr–Si bond lengths are 2.55 Å. Si is bonded to six equivalent Hf and six equivalent Cr atoms to form SiHf6Cr6 cuboctahedra that share corners with twelve equivalent CrHf6Cr4Si2 cuboctahedra, edges with six equivalent SiHf6Cr6 cuboctahedra, faces with two equivalent SiHf6Cr6 cuboctahedra, and faces with eighteen equivalent CrHf6Cr4Si2 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr4(SeS)3 by Materials Project

Cr4(SeS)3 is Ilmenite-like structured and crystallizes in the trigonal R3 space group. The structure is three-dimensional. there are four inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to three equivalent Se2- and three equivalent S2- atoms to form a mixture of corner and edge-sharing CrSe3S3 octahedra. The corner-sharing octahedra tilt angles range from 46–48°. All Cr–Se bond lengths are 2.52 Å. All Cr–S bond lengths are 2.41 Å. In the second Cr3+ site, Cr3+ is bonded to three equivalent Se2- and three equivalent S2- atoms to form a mixture of corner and face-sharing CrSe3S3 octahedra. The corner-sharing octahedra tilt angles range from 46–50°. All Cr–Se bond lengths are 2.56 Å. All Cr–S bond lengths are 2.36 Å. In the third Cr3+ site, Cr3+ is bonded to three equivalent Se2- and three equivalent S2- atoms to form a mixture of corner, edge, and face-sharing CrSe3S3 octahedra. The corner-sharing octahedral tilt angles are 50°. All Cr–Se bond lengths are 2.54 Å. All Cr–S bond lengths are 2.42 Å. In the fourth Cr3+ site, Cr3+ is bonded to three equivalent Se2- and three equivalent S2- atoms to form a mixture of corner, edge, and face-sharing CrSe3S3 octahedra. The corner-sharing octahedral tilt angles are 48°. All Cr–Se bond lengths are 2.52 Å. All Cr–S bond lengths are 2.35 Å. Se2- is bonded in a rectangular see-saw-like geometry to four Cr3+ atoms. S2- is bonded in a distorted rectangular see-saw-like geometry to four Cr3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sm2CrFe16 by Materials Project

Sm2CrFe16 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent Sm sites. In the first Sm site, Sm is bonded in a 10-coordinate geometry to nineteen Fe atoms. There are a spread of Sm–Fe bond distances ranging from 3.01–3.30 Å. In the second Sm site, Sm is bonded in a 9-coordinate geometry to one Cr and eighteen Fe atoms. The Sm–Cr bond length is 3.18 Å. There are a spread of Sm–Fe bond distances ranging from 3.01–3.31 Å. Cr is bonded in a 1-coordinate geometry to one Sm and thirteen Fe atoms. There are a spread of Cr–Fe bond distances ranging from 2.31–2.76 Å. There are five inequivalent Fe sites. In the first Fe site, Fe is bonded in a 12-coordinate geometry to two Sm, one Cr, and nine Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.44–2.76 Å. In the second Fe site, Fe is bonded to two Sm, one Cr, and nine Fe atoms to form distorted FeSm2CrFe9 cuboctahedra that share corners with fourteen FeSm3CrFe8 cuboctahedra, edges with six FeSm3CrFe8 cuboctahedra, and faces with ten FeSm2CrFe9 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.44–2.63 Å. In the third Fe site, Fe is bonded to three Sm, one Cr, and eight Fe atoms to form FeSm3CrFe8 cuboctahedra that share corners with fifteen FeSm2CrFe9 cuboctahedra, edges with eight FeSm3CrFe8 cuboctahedra, and faces with ten FeSm2CrFe9 cuboctahedra. Both Fe–Fe bond lengths are 2.48 Å. In the fourth Fe site, Fe is bonded to three Sm and nine Fe atoms to form FeSm3Fe9 cuboctahedra that share corners with fifteen FeSm2CrFe9 cuboctahedra, edges with eight FeSm3CrFe8 cuboctahedra, and faces with ten FeSm2CrFe9 cuboctahedra. The Fe–Fe bond length is 2.65 Å. In the fifth Fe site, Fe is bonded in a distorted single-bond geometry to one Sm, one Cr, and twelve Fe atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrPO10 by Materials Project

CrO6PO4 is Silicon tetrafluoride-derived structured and crystallizes in the monoclinic Cc space group. The structure is zero-dimensional and consists of eight phosphoric acid molecules and eight CrO6 clusters. In each CrO6 cluster, Cr is bonded in a distorted tetrahedral geometry to six O atoms. There are a spread of Cr–O bond distances ranging from 1.61–2.39 Å. There are six inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Cr atom. In the second O site, O is bonded in a single-bond geometry to one Cr atom. In the third O site, O is bonded in a distorted single-bond geometry to one Cr atom. In the fourth O site, O is bonded in a single-bond geometry to one Cr atom. In the fifth O site, O is bonded in a single-bond geometry to one Cr atom. In the sixth O site, O is bonded in a single-bond geometry to one Cr atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiNbCr4 by Materials Project

TiNbCr4 is Hexagonal Laves-derived structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ti is bonded in a 12-coordinate geometry to four equivalent Nb and twelve equivalent Cr atoms. All Ti–Nb bond lengths are 2.99 Å. All Ti–Cr bond lengths are 2.86 Å. Nb is bonded in a 12-coordinate geometry to four equivalent Ti and twelve equivalent Cr atoms. All Nb–Cr bond lengths are 2.86 Å. Cr is bonded to three equivalent Ti, three equivalent Nb, and six equivalent Cr atoms to form a mixture of edge, face, and corner-sharing CrTi3Nb3Cr6 cuboctahedra. All Cr–Cr bond lengths are 2.44 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrTiCr4 by Materials Project

ZrTiCr4 is Hexagonal Laves-derived structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Zr is bonded in a 12-coordinate geometry to four equivalent Ti and twelve equivalent Cr atoms. All Zr–Ti bond lengths are 3.04 Å. All Zr–Cr bond lengths are 2.91 Å. Ti is bonded in a 12-coordinate geometry to four equivalent Zr and twelve equivalent Cr atoms. All Ti–Cr bond lengths are 2.91 Å. Cr is bonded to three equivalent Zr, three equivalent Ti, and six equivalent Cr atoms to form a mixture of corner, edge, and face-sharing CrZr3Ti3Cr6 cuboctahedra. All Cr–Cr bond lengths are 2.48 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Rational optimization of substituted α–MnO 2 cathode for aqueous zinc–ion battery

Density functional theory (DFT) is utilized to explore the effects of increasing concentrations of vanadium (V) and chromium (Cr) substitution on the discharge of α-MnO 2 cathode in hydrated zinc-ion batteries (ZIBs). During H + -intercalation and Zn 2+ -intercalation, Cr-substitution proves to be more effective than V-substitution in promoting discharge behaviors. Transitioning from Mn 0.875 Cr 0.125 O 2 , Mn 0.75 Cr 0.25 O 2 to Mn 0.625 Cr 0.375 O 2 is found to consistently enhance the discharge voltage, along with improved tunnel structure retention and volume expansion suppression. In comparison, the promoting effect of increasing V-substitution is relatively small at initial discharge stages and leads to degradation at later stages, primarily due to an increased concentration of unstable Mn 2+ ion. The superior effect of Cr-substitution is attributed to the unique atomic and electronic structures of substituted Cr 4+ and reduced Cr 3+ ions during discharge. These ions serve as active electron acceptors to limit the formation of Mn 3+ and Mn 2+ ions, and as anchors to stabilize the α-MnO 2 framework and intercalated H + /Zn 2+ ions, respectively. Finally, our study highlights fine-tuning through substitution to enhance the performance of α-MnO 2 -based cathode materials in ZIBs.

25 ENERGY STORAGE↗
DOE OSTI2023

Density functional study of atomic arrangements in CrMnFeCoNi high-entropy alloy and their impact on vacancy formation energy and segregation

Here, using the density functional theory-coupled Monte Carlo approach, we explored the chemical short-range order (SRO) and element segregation in equimolar CrMnFeCoNi alloy. We found that state-of-the-art approximation of random element distribution is only applicable at > 1100 K close to the melting temperature, while the Cr-Cr repulsion driving the system stabilization and accompanying the formation of cubic Cr sublattice, and mild Ni-Ni attraction are the most prominent pair interactions at lower temperatures. Chemical potential and vacancy formation energy calculations indicate that Cr is most sensitive to the local chemical environment, making Cr atoms most stabilized when the preferred SRO is introduced. While the vacancy formation is predicted equally probable among five constituting elements in the random solid solution, Cr and Ni atoms show the lowest vacancy formation energies in the structure with SRO. Furthermore, distinct element segregation was predicted in the vicinity of planar defects, including symmetric tilt grain boundary and stacking fault, which we correlated to the site- and chemistry-dependent atomic volume and bond lengths. It suggests that the local mechanical strain and bond energy induce the SRO development and element segregation: Namely, the system takes advantage of segregation of Ni atoms having large atomic volume or Cr-Cr pairs having elongated bond lengths to fill in the excess volume at defects that relaxes the mechanical strain field and optimizes bond energy distribution. The correlation between the SRO and properties of CrMnFeCoNi alloy needs further investigations, which is expected to greatly help understand and control the properties of high-entropy alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Reductive removal of pertechnetate and chromate by zero valent iron under variable ionic strength conditions

Radioactive technetium-99 (Tc) present in waste streams and subsurface plumes at legacy nuclear reprocessing sites worldwide poses potential risks to human health and the environment. This research comparatively evaluated efficiency of zero valent iron (ZVI) toward reductive removal of Tc(VII) in presence of Cr(VI) from NaCl and Na 2 SO 4 electrolyte solutions under aerobic conditions. In both electrolytes, anticorrosive Cr(VI) suppressed oxidation of ZVI at elevated concentrations resulting in the delay of initiation of Tc(VII) reduction to Tc(IV)). In the absence of Cr(VI), no such delay was observed in the analogous systems. At low ionic strength, retarded ZVI oxidation inhibited Tc(VII) reduction in part due to the competing thermodynamically more favorable reduction of Cr(VI) to Cr(III); this effect was particularly pronounced in the chloride medium at the ionic strength ? 0.1. Higher ionic strength favored reduction of both Tc(VII) and Cr(VI), which followed a second-order reaction rate in both electrolytes attributed to the more efficient iron oxidation as evident from x-ray diffraction and electron microscopy measurements. Magnetite was the primary iron oxide phase, and its higher fraction in the SO 4 2- solutions facilitated reductive removal of Tc(VII) and Cr(VI). In the Cl- matrix, Cr(VI) promoted further oxidation of magnetite as well as formation of chromite diminishing overall reductive capacity of this system and resulting in less effective removal of Tc(VII) compared to the SO 4 2- solutions.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗