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The evaluators present in this publication spectroscopic data and level schemes from radioactive decay and nuclear reactions studies for all isobars with mass number A=65. Not much is known experimentally about {sup 65}V and {sup 65}Cr, although they are expected to decay by {beta}-emission. Spin/parity assignments for {sup 65}Mn, {sup 65}Fe, {sup 65}As, and {sup 65}Se are not firmly established.
Graphical abstract: Sensing response towards 250 ppm ethanol for the samples synthesized at different reaction temperatures at different operating temperatures. Highlights: ► Effect of reaction temperature on particle size of Cr{sub 2}O{sub 3}. ► No catalyst has been incorporated to enhance the response of the material. ► Synthesis of Cr{sub 2}O{sub 3} nanoparticles. -- Abstract: Nanoparticles of chromium oxide have been synthesized following a precipitation technique at reaction temperatures 5, 27 and 65 °C. Synthesized powders were characterized using X-ray diffraction, transmission electron microscope and Brunauer–Emmett–Teller techniques to carry out structural and morphological analysis. The reaction temperature has been found to be playing a crucial role in controlling particle size. It has been observed that Cr{sub 2}O{sub 3} nanoparticles synthesized at 27 °C were smaller as compared to those synthesized at 5 and 65 °C. Chromium oxide samples thus prepared were deposited as thick films on alumina substrates to act as gas sensors and their sensing response to ethanol vapour was investigated at different operable temperatures. It has been observed that all the sensors exhibited optimum response at 250 °C. The investigations revealed that sensing response of Cr{sub 2}O{sub 3} nanoparticles synthesized at 27 °C was exceptionally higher than that of Cr{sub 2}O{sub 3} nanoparticles synthesized at 5 and 65 °C.
Extensive research in recent years has explored the realm of porous carbon composites for various applications, including electrochemistry, structural materials, environmental remediation, and more. In particular, the fabrication of porous carbon composites using a metal-organic framework (MOF) and biochar (BC) for aqueous remediation is a fairly new avenue of research. In this study, a MOF-BC composite was synthesized with unmodified and chemically modified BCs using solvothermal synthesis. The composites were used as adsorbents to remediate heavy metals, such as lead (II) and chromium (VI), from aqueous environments. Here, it was verified that the MOF was homogeneously deposited onto the BC's surface using various material characterization techniques. Lead and chromium adsorption studies revealed a high adsorption capacity with greater than 99% removal for lead and ∼65% for chromium, respectively. Impressively, for lead, the highest observed experimental adsorption capacity of the MOF-chemically modified BC composite was 535 mg/g, compared to 240 mg/g for pristine BC. Meanwhile, the adsorption capacity of the same MOF-BC composite for chromium ions was low at 18 mg/g, compared to 80 mg/g for the chemically modified BC. The MOF-BC had a rapid adsorption rate, achieving equilibrium at only 150 min of reaction time for lead ions. MOF-BCs have higher adsorption for cationic lead through physisorption and ion-exchange mechanisms, whereas, for anionic chromium, removal is dominated only by physisorption mechanisms. The outcomes and methodological developments attained in this study offer a novel and compelling approach for synthesizing MOF-BC composites for aqueous remediation applications.
The high-pressure and high-temperature phase diagram of chromium has been investigated both experimentally (in situ), using a laser-heated diamond-anvil cell technique coupled with synchrotron powder X-ray diffraction, and theoretically, using ab initio density-functional theory simulations. In the pressure–temperature range covered experimentally (up to 90 GPa and 4500 K, respectively) only the solid body-centred-cubic and liquid phases of chromium have been observed. Experiments and computer calculations give melting curves in agreement with each other that can both be described by the Simon–Glatzel equation $T_{m}(P) = 2136K (1 + P/25.9)^{0.41}$ In addition, a quasi-hydrostatic equation of state at ambient temperature has been experimentally characterized up to 131 GPa and compared with the present simulations. Both methods give very similar third-order Birch–Murnaghan equations of state with bulk moduli of 182–185 GPa and respective pressure derivatives of 4.74–5.15. According to the present calculations, the obtained melting curve and equation of state are valid up to at least 815 GPa, at which pressure the melting temperature is 9310 K. Finally, from the obtained results, it was possible to determine a thermal equation of state of chromium valid up to 65 GPa and 2100 K.
The inherent crystallinity of metal–organic framework (MOF) catalysts offers the possibility to understand the structure of the active site at the molecular level. This property is often lacking in traditional amorphous supports. Cr-SIM-NU-1000, a MOF-supported Cr 3+ heterogeneous catalyst, is shown to be competent for ethylene polymerization after activation with AlEt 2 Cl (DEAC), producing crystalline linear polyethylene (PE). The polymer produced has a low polydispersity (D = 2.0), in marked contrast to the Phillips supported chromium catalyst, Cr@SiO 2 (D ~ 8–65). Cr-SIM-NU-1000 achieves a turnover frequency of 2.6 × 10 3 h –1 under 40 bar ethylene pressure at room temperature, with corresponding PE productivity of 1.3 × 10 5 g PE mol –1 Cr per h. Single crystal X-ray diffraction (SC-XRD) of the pre-catalyst was conducted by collecting a structure of alkyl aluminum (DEAC) co-catalyst treated Cr-SIM-NU-1000. This crystal structure provides insight into the interactions between DEAC co-catalyst and Cr active site, revealing a Cr–C bond after treatment with DEAC. Furthermore, DEAC is crystallographically resolved at the terminal oxy-ligands of the node and likely also exists within the window pores of the framework between nodes, based on electron density mapping. Cr-SIM-NU-1000 offers the opportunity to study a structurally well-defined olefin polymerization system, with atomically precise characterization of the pre-catalyst structure. Furthermore, this allows the proposal of a mechanism and feeds into future development of next-generation heterogeneous catalyst systems.
We have carried out {sup 63,65}Cu NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO{sub 2}. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.
The possibility of the BEST experiment on electron neutrino disappearance with intense artificial sources of electron neutrino {sup 51}Cr is considered. BEST has the great potential to search for transitions of active neutrinos to sterile states with Δm{sup 2} ∼ 1 eV{sup 2} and to set the limits on short baseline electron neutrino disappearance oscillation parameters. The possibility of the further constraints the oscillation parameters region with using {sup 65}Zn source is discussed.
Heavy metal pollution due to legacy waste from the Cold War nuclear proliferation remains a huge problem at federal and industrial sites. Microbial bioremediation is a cost effective method for removing heavy metals from soil and groundwater. This pilot research project looks at the reduction of chromium present at DOE's Savannah River Site and the ability of bacteria population to aid in the reduction of heavy metals. The purpose of this study was to characterize the growth pattern of Serratia marcescens strain 93-1399-1 in the presence of heavy metal hexavalent chromium (Cr [VI]) and its ability to convert Cr (VI) to the less toxic Cr (III). When S. marcescens was grown on LB agar with increasing concentrations of Cr (VI) as potassium dichromate, the bacteria survived at all concentrations tested up to 200 ppm. Growth curve of S. marcescens in Cr (VI) showed that the bacteria exposed to 25 pm grew in similarly to bacteria without Cr (VI), had reduced exponential growth at 50 and 100 ppm and the poor growth in 200 pp after 24 hours. Plate count assays showed that the 65% of the bacteria survived in 25 ppm of Cr (VI) but only 5% survived at 50 ppm. In preliminary chromium reduction assays, S. marcescens was grown for 24 hours in 25 ppm of Cr (VI). S. marcescens reduced 60% of the Cr (VI) to Cr (III) as compared to 4% reduction in broth alone. These data suggest that the S. marcescens strain may be useful in bio-remediating Cr (VI) at contaminated sites. Future studies will focus on identifying the genes responsible for Cr (VI) reduction. (authors)
The microstructure and properties of Cu-0.5Cr-0.03Zr-0.04Ti (wt.%) alloy subjected to cold rolling and aging were investigated using hardness and electrical conductivity measurement, tensile testing, and transmission electron microscopy. Plates subjected to 85% reduction in thickness showed significant improvement in the strength compared to solution treated and aged condition. By proper selection of aging temperature, ductility could be significantly improved without reduction in the strength. Aging of the cold rolled sheet at 420 °C for 1 h yielded an ultimate tensile strength and yield strength of 540 and 460 MPa, respectively. On the other hand, total and uniform elongation was 16 and 12%, respectively, with an electrical conductivity of 65 %IACS. The combination of properties achieved after cold rolling and aging is attributed to the higher dislocation density, ultrafine grains and nano-sized chromium precipitates.
We report on the electrical characterisation of a series of thin amorphous chromium oxide (CrO{sub x}) films, grown by dc sputtering, to evaluate their suitability for use as on-chip resistors in nanoelectronics. By increasing the level of oxygen doping, the room-temperature sheet resistance of the CrO{sub x} films was varied from 28 Ω/◻ to 32.6 kΩ/◻. The variation in resistance with cooling to 4.2 K in liquid helium was investigated; the sheet resistance at 4.2 K varied with composition from 65 Ω/◻ to above 20 GΩ/◻. All of the films measured displayed linear current–voltage characteristics at all measured temperatures. For on-chip devices for quantum phase-slip measurements using niobium–silicon nanowires, interfaces between niobium–silicon and chromium oxide are required. We also characterised the contact resistance for one CrO{sub x} composition at an interface with niobium–silicon. We found that a gold intermediate layer is favourable: the specific contact resistivity of chromium-oxide-to-gold interfaces was 0.14 mΩcm{sup 2}, much lower than the value for direct CrO{sub x} to niobium–silicon contact. We conclude that these chromium oxide films are suitable for use in nanoscale circuits as high-value resistors, with resistivity tunable by oxygen content.
The Savannah River Site (SRS) is preparing Tank 5F for closure. The first step in preparing the tank for closure is mechanical sludge removal. Following mechanical sludge removal, SRS performed chemical cleaning with oxalic acid to remove the sludge heel. Personnel are currently assessing the effectiveness of the chemical cleaning. SRS personnel collected liquid samples during chemical cleaning and submitted them to Savannah River National Laboratory (SRNL) for analysis. Following chemical cleaning, they collected a solid sample (also known as 'process sample') and submitted it to SRNL for analysis. The authors analyzed these samples to assess the effectiveness of the chemical cleaning process. The conclusions from this work are: (1) With the exception of iron, the dissolution of sludge components from Tank 5F agreed with results from the actual waste demonstration performed in 2007. The fraction of iron removed from Tank 5F by chemical cleaning was significantly less than the fraction removed in the SRNL demonstrations. The likely cause of this difference is the high pH following the first oxalic acid strike. (2) Most of the sludge mass remaining in the tank is iron and nickel. (3) The remaining sludge contains approximately 26 kg of barium, 37 kg of chromium, and 37 kg of mercury. (4) Most of the radioactivity remaining in the residual material is beta emitters and {sup 90}Sr. (5) The chemical cleaning removed more than {approx} 90% of the uranium isotopes and {sup 137}Cs. (6) The chemical cleaning removed {approx} 70% of the neptunium, {approx} 83% of the {sup 90}Sr, and {approx} 21% of the {sup 60}Co. (7) The chemical cleaning removed less than 10% of the plutonium, americium, and curium isotopes. (8) The chemical cleaning removed more than 90% of the aluminium, calcium, and sodium from the tank. (9) The cleaning operations removed 61% of lithium, 88% of non-radioactive strontium, and 65% of zirconium. The {sup 90}Sr and non-radioactive strontium were measured by different methods, and the differences in the fraction removed are not statistically significant. (10) Chemical cleaning removed 10-50% of the barium, chromium, iron, magnesium, manganese, and silicon. (11) Chemical cleaning removed only {approx}1% of the nickel.
Planar-patterned CrPt{sub 3} ordered L1{sub 2} nanodots with various bit sizes (D) from 220 to 55 nm were fabricated by the local irradiation of 30 keV of Kr{sup +} ions not by conventional physical etching. Patterned nanodots with bit size {<=} 65 nm show either dark or bright contrast, suggesting that they have single domain structure. Switching field distribution of nanodots was studied by taking magnetic force microcopy images, in the progress of the magnetization reversal. As-prepared CrPt{sub 3} film exhibited perpendicular hysteresis loop with the coercivity of 5.5 kOe. Compared with the as-prepared film, the average switching field (H{sub sf}) of the CrPt{sub 3} nanodots increased as 6.5, 8.5, and 9.2 kOe while the switching field distribution ({Delta}H{sub sf}) decreased as 6.8, 3.6, and 2.8 kOe, for the patterned nanodots with bit sizes of 220, 150, 65 nm, respectively. We found that the small {Delta}H{sub sf}/H{sub sf} is possible in the high density planar bit patterned media fabricated by ion irradiation.
The metal-to-insulator phase transition (MIT) in two-dimensional (2D) materials under the influence of a gating electric field has revealed interesting electronic behavior and the need for a deeper fundamental understanding of electron transport processes, while attracting much interest in the development of next-generation electronic and optoelectronic devices. Although the mechanism of the MIT in 2D semiconductors is a topic under debate in condensed matter physics, our work demonstrates the tunable percolative phase transition in few-layered MoSe 2 field-effect transistors (FETs) using different metallic contact materials. Here, we attempted to understand the MIT through temperature-dependent electronic transport measurements by tuning the carrier density in a MoSe 2 channel under the influence of an applied gate voltage. In particular, we have examined this phenomenon using the conventional chromium (Cr) and ferromagnetic cobalt (Co) as two metal contacts. For both Cr and Co, our devices demonstrated n-type behavior with a room-temperature field-effect mobility of 16 cm 2 V −1 s −1 for the device with Cr-contacts and 92 cm 2 V −1 s −1 for the device with Co-contacts, respectively. Further, with low temperature measurements at 50 K, the mobilities increased significantly to 65 cm 2 V −1 s −1 for the device with Cr and 394 cm 2 V −1 s −1 for the device with Co-contacts. By fitting our experimental data to the percolative phase transition theory, the temperature-dependent conductivity data show a transition from an insulating-to-metallic behavior at a bias of ∼28 V for Cr-contacts and ∼20 V for Co-contacts. This cross-over of the conductivity can be attributed to an increase in carrier density as a function of the gate bias in temperature-dependent transfer characteristics. By extracting the critical exponents, we find that the transport behavior in the device with Co-contacts aligns closely with the 2D percolation theory. In contrast, the devices with Cr-contacts deviate significantly from the 2D limit at low temperatures.
This paper focused on the factors affecting the respiration rate of the digestate taken from a continuous anaerobic two-stage process treating the organic fraction of municipal solid waste (OFMSW). The process involved a hydrolytic reactor (HR) that produced a leachate fed to a submerged anaerobic membrane bioreactor (SAMBR). It was found that a volatile solids (VS) removal in the range 40-75% and an operating temperature in the HR between 21 and 35 {sup o}C resulted in digestates with similar respiration rates, with all digestates requiring 17 days of aeration before satisfying the British Standard Institution stability threshold of 16 mg CO{sub 2} g VS{sup -1} day{sup -1}. Sanitization of the digestate at 65 {sup o}C for 7 days allowed a mature digestate to be obtained. At 4 g VS L{sup -1} d{sup -1} and Solid Retention Times (SRT) greater than 70 days, all the digestates emitted CO{sub 2} at a rate lower than 25 mg CO{sub 2} g VS{sup -1} d{sup -1} after 3 days of aeration, while at SRT lower than 20 days all the digestates displayed a respiration rate greater than 25 mg CO{sub 2} g VS{sup -1} d{sup -1}. The compliance criteria for Class I digestate set by the European Commission (EC) and British Standard Institution (BSI) could not be met because of nickel and chromium contamination, which was probably due to attrition of the stainless steel stirrer in the HR.
Nanosize grains of ~ 65 nm were developed with large misorientation angles of grain boundaries in surface region of normalized and tempered modified 9Cr-1Mo steel by ultrasonic shot peening (USSP) with hard steel balls of 3 mm diameter. The surface roughness and the depth of nanostructured surface region were found to increase with the duration of USSP from 0.5 to 5 min. Hot corrosion tests were performed for the Un-USSP and the samples USSPed for the durations of 0.25 and 1.5 min and also for the samples subjected to USSP and subsequently pre-oxidation at 600 °C for 4 h. The hot corrosion resistance at 600 °C under 100% NaCl coating was significantly improved by USSP for 1.5 min and subsequent pre-oxidation at 600 °C for 4 h. The results are discussed in terms of the formation of more uniform and effective protective iron–chromium oxide layer on the USSPed surface from the subsequent pre-oxidation treatment, prior to hot corrosion of the specimens under 100% NaCl coating at 600 °C.
In this work, the method of control of carbon content in the ultrafine-grained cemented carbide alloy was proposed. The treating of the WC-8Co-0.4VC-0.4Cr{sub 3}C{sub 2} compacts was made in a CO + CO{sub 2} gas mixture at CO concentrations from 0 to 80 vol.% during 50 min at the initial stage of the conventional sintering at a temperature of 700 °C. Conditions for increasing and decreasing the carbon content are CO concentrations of CO in gas mix more than 65 vol.% and less than 35 vol.%, respectively. It is shown that even a small deviation from the stoichiometric carbon content (0.3 wt.%) leads to an increase in porosity and a multiple decrease in the strength of the ultrafine-grained cemented carbide. A comparative analysis with literature data showed that the obtained ultrafine-grained solid alloy WC-8Co-0.4VC-0.4Cr{sub 3}C{sub 2} with stoichiometric composition is not inferior in hardness and toughness to the analogs obtained by hot pressing and electrospark sintering.