Mo Mn Research Articles

In-situ deformation inhomogeneity and damage evolution of mixed-grain structure with tempered sorbite/bainite in Fe–Cr–Mo–Mn steel

The inhomogeneous tempered sorbite/bainite (TS/B) with various morphologies and orientations play a significant role in deformation coordination and damage evolution. In this paper, the influence of distinct morphologies and orientations of the mixed-grain structure with TS/B on the deformation heterogeneity were extensively investigated by in-situ tensile testing. Furthermore, a multi-scale model of dislocation density-based crystal plasticity (CP) coupled with the phase field method (PFM) was developed to illustrate the damage nucleation and its evolution via the representative volume element (RVE) modelling. The results shows that mixed-grain structure with TS/B exhibits non-homogeneous deformation during the tensile process, and the coarse grains bear the main plastic deformation, resulting in cross-slip traces and the wrinkling phenomenon at the grain boundary and the interior of coarse grains. Furthermore, the activation of slip systems was determined through slip trace analysis, and the slip transfer behavior between adjacent microstructure was analyzed. According to the critical resolved shear stress (CRSS), the {123}<111> slip system was determined to be the most activated slip system during the in-situ deformation. Hard-orientated lath-shaped B (M1) is more prone to accumulate low angle grain boundaries (LAGBs) than hard-orientated TS (M2) and soft-orientated granular B (M3), resulting in higher orientation rotation degree and geometrically necessary dislocations (GNDs) density of M1 than M2 and M3. The M1 exhibits the nucleation of damage during the initial deformation stage. In addition, compared with the M2 and M3, the Schmid factor (SF) of M1 dominates the transformation from hard orientation to soft orientation and the higher value of damage factor (φ) of M1 results in the more activated slip systems and local damage at high strain levels. This study provides new insights into elucidate the effects of TS/B morphologies and orientations on deformation heterogeneity and damage evolution in large-scale forged spindles for offshore wind power.

Effect of Mn content on mechanical properties and corrosion resistance of Ti–8Mo-xMn alloys through the vacuum sintering process

This study mixed various powders (Ti, Mo, and Mn) according to the nominal Ti–8Mo-xMn (x = 1, 3, 5 wt%) composition, and vacuum sintered the compacts of the Ti–Mo–Mn alloys at 1220 °C, 1240 °C, 1260 °C, and 1280 °C for 1 h. The experimental results show that the Ti–8Mo–3Mn alloys sintered at 1260 °C had better comprehensive properties, with a relative density of 96.71 ± 0.14 %, transverse rupture strength (TRS) of 1624.4 ± 29.2 MPa, and hardness of 67.8 ± 0.4 HRA. However, due to the microstructure evolution and increased amount of Mn in the Ti–8Mo-xMn alloys, the TRS shows a significant increase. Consequently, the suitable Mn content of the Ti–8Mo–3Mn alloys, which proves advantageous to the TRS, results from the uniformly distributed lamellar-like Widmanstätten microstructure and the basket-net microstructure. Moreover, the Ti–8Mo-xMn alloy does not have intermetallic compounds, and only consists of two phases, α-Ti and β-Ti. Furthermore, the sintered Ti–8Mo–3Mn alloys possess the suitable corrosion current (Icorr was 4.56 × 10−5 A cm−2) and polarization resistance (Rcorr was 569.76 Ω cm2) in 0.1 N H2SO4 solutions, which confirms that sintered Ti–8Mo–3Mn alloys can improve mechanical properties.

Effects of Zr Addition on the Microstructural Evolution, Mechanical Properties, and Corrosion Behavior of Novel Biomedical Ti-Zr-Mo-Mn Alloys.

β-Type Ti alloys have been widely investigated as implant materials owing to their excellent mechanical properties, corrosion resistance, and biocompatibility. In the present work, the effects of Zr on the microstructure, mechanical properties, and corrosion behaviors of Ti-Zr-Mo-Mn alloys were systematically studied. With the increase of Zr content, the phase composition gradually changed from intragranular-α + β of (TZ)5:1MM alloy to grain-boundary-α + β of (TZ)2:1MM alloy and finally transferred to a single β phase structure of (TZ)1:1MM alloy. The (TZ)1:1MM alloy exhibited a good mechanical combination with a yield strength of 750.8 MPa, an elastic modulus of 61.3 GPa, and a tensile ductility of 14.6%. Moreover, the addition of Zr can effectively stabilize the passivation film and reduce the sensitivity of microgalvanic corrosion in simulated body fluid, leading to enhanced corrosion resistance in the TZMM alloys. X-ray photoelectron spectroscopy analysis together with the ion-sputtering technique revealed that the passivation films formed on TZMM alloys possessed a bilayered structure (outer Ti+Zr mixed-oxide layer and inner Zr-oxide-rich layer), in which the inner Zr oxide layer plays an important role in the corrosion resistance of the TZMM alloys. In vitro biocompatibility evaluations demonstrated that the TZMM alloys can support cell adhesion and proliferation with high biocompatibility comparable to that of CP-Ti, while in vivo biocompatibility evaluations validated the bone osteointegration ability of TZMM alloys after long-term implantation. The above results indicate that novel TZMM alloys are promising candidates for implant material.

Identification of Carbides and Phase Transformations in Sintered Fe–Mo–Mn–C Alloys Produced under a Slow Continuous Cooling

Different sintered alloys were produced by sintering and slow cooling of powder compacts made from pre-alloyed Fe-0.50Mo-0.15Mn powder mixed with varied graphite powder contents (0.30–1.20 wt.% with 0.15% increment). According to microstructures, sintered alloys were divided into sintered hypo-eutectoid, near eutectoid, and hyper-eutectoid alloys. By using Groesbeck color tinting and X-ray diffraction technique, the common phase transformation products of these sintered alloys were found to include ferrite and carbides. The sintered hypo-eutectoid alloys had microstructures consisting of polygonal ferrite grains and two forms of ferrite + carbide mixtures, such as ferrite + M23C6 carbide and ferrite + M3C carbide. In sintered near-eutectoid alloys, only ferrite + M3C carbide mixtures occupied microstructures. In sintered hyper-eutectoid alloys, large proeutectoid M23C6 carbide formed first and followed by abnormal ferrite, degenerate ferrite + M23C6 pearlite, lamellar ferrite + M23C6 pearlite, Widmanstätten M3C carbide, inverse bainite (ferrite + M3C) and upper bainite (ferrite + M3C).

Enhancing hydrogen evolution reaction performance of transition metal doped two-dimensional electride Ca2N

Two-dimensional electride Ca2N has strong electron transfer ability and low work function, which is a potential candidate for hydrogen evolution reaction (HER) catalyst. In this work, based on density functional theory calculations, we adopt two strategies to improve the HER catalytic activity of Ca2N monolayer: introducing Ca or N vacancy and doping transition metal atoms (TM, refers to Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ru, Hf, Ta and W). Interestingly, the Gibbs free energy ΔGH∗ of Ca2N monolayer after introducing N vacancy is reduced to -0.146 eV, showing good HER catalytic activity. It is highlighted that, the HER catalytic activity of Ca2N monolayer can be further enhanced with TM doping, the Gibbs free energy ΔGH∗ of single Mo and double Mn doped Ca2N are predicted to be 0.119 and 0.139 eV, respectively. The present results will provide good theoretical guidance for the HER catalysis applications of two-dimensional electride Ca2N monolayer.

Molybdenum–Manganese hydroxide microcubes based electrode via hydrothermal method for asymmetric supercapacitor

An electrode with multi electron surfaces facilitates more redox sites during charge storage reaction in the case of transition metal oxides used in supercapacitor application. Molybdenum (Mo) oxide and manganese (Mn) oxide have high theoretical capacitance; this study focused on depositing Mo–Mn together in a single mixed metal oxide. Here, Mo–Mn hydroxide was deposited on Ni-foam by a single-step hydrothermal method. The X-ray photoelectron spectroscopy confirms the presence of Mo and Mn in 4+ and 3+ oxidation states, respectively. The different size of Mo–Mn hydroxide microstructures was observed with varying deposition time. The porous cubes-like microstructure exhibited high areal capacitance of 88.6 mF cm−2 with energy density of 3.08 μWh·cm−2 at 125 μW cm−2 power density within a kinetic potential. This microcubes-like structures and activated carbon were used as positive and negative electrodes, respectively, to fabricate an asymmetric supercapacitor (ASS) device. The ASS device showed capacitance retention of 87% (∼5,000 cycles) and excellent Coulombic efficiency (96%) with energy density of 5.6 μWh·cm−2 at 1.12 mW cm−2 power density at 1.8 V potential.

Hydrogen absorption-desorption characteristic of (Ti0.85Zr0.15)1.1Cr1-xMoxMn based alloys with C14 Laves phase

The microstructure and hydrogen absorption-desorption characteristic of (Ti0.85Zr0.15)1.1Cr1-xMoxMn (x ​= ​0.05, 0.1, 0.15, 0.2 ​at.%) alloys were investigated. The results showed that the corresponding alloys were determined as a single phase of C14-type Laves structure. With the increase of Mo content, the maximum and reversible hydrogen absorption capacity decreased, the slope factor Hf increased. Among the studied alloys, (Ti0.85Zr0.15)1.1Cr0.95Mo0.05Mn had the best overall properties for practical application of hydrogen storage materials. The maximum and reversible hydrogen storage capacity were 1.76 ​wt% and 1.09 ​wt%, the slope factor Hf was 0.51, and its dissociation enthalpy (ΔHd) and entropy change (ΔSd) were 23.1 ​kJ ​mol−1H2, 93.8J ​K−1mol−1H2 at 303K, respectively. By studying the dissociation pressures of the synthesized metal hydrides, it was found that Mo had a special effect on the dissociation pressure of Ti–Zr–Cr–Mo–Mn alloys. Among the four alloys, (Ti0.85Zr0.15)1.1Cr0.95Mo0.05Mn alloy had the largest hydrogen absorption capacity and the fastest hydrogen desorption rate, which can meet the commercialization demand of hydrogen fuel cell hydrogen supply system.

Garnet and scheelite chemistry of the Weijia tungsten deposit, South China: Implications for fluid evolution and W skarn mineralization in F-rich ore system

Fluid evolution is an essential subject in the studies of hydrothermal ore-forming processes. Garnet and scheelite prevail in W-bearing skarn deposits and record plentiful information on W skarn mineralization. In-situ LA-ICP-MS trace element analyses have been carried out on the garnet and scheelite from the F-rich Weijia W deposit in South China to constrain the processes of fluid evolution and W skarn mineralization. The Weijia W deposit mainly consists of calcic and magnesian skarns and was formed through six stages of alteration and mineralization. Two stages of fluid exsolution are recognized in the magmatic-hydrothermal system. The earlier exsolved fluids are Cl-rich with rightward-sloping REE patterns and result in pre-ore skarnization. The later exsolved fluids are F-rich with relatively flat REE patterns and are responsible for W mineralization. The pre-ore garnets are LREE-enriched and HREE-depleted whereas the syn-ore garnets are LREE-depleted and HREE-enriched with lower δEu values than the former, denoting a transition from wall rock-controlled to magmatic fluid-dominated fluid-rock interaction. Combined with the skarn occurrences, mineral assemblages, and garnet textures, it is revealed that the mechanism of skarn formation shifts from more diffusive metasomatism under lower water/rock ratios to more advective metasomatism at higher water/rock ratios. The advective metasomatism with a high flux of ore-forming fluids is hydrodynamically favorable for the consequent W mineralization. The earliest-formed scheelite is akin to the host granite porphyry in REE patterns and can reflect the features of initial mineralizing fluids. It has high ΣREE (1255–5059 ppm), Y (616–1416 ppm), Nb (585–2629 ppm), Ta (14–248 ppm), Mn (up to 1977 ppm) and low Mo (mostly < 1000 ppm) contents, indicating that the primary F-rich magmatic fluids are reduced and enriched in REEs, Y, Nb, and Ta. The contents of ΣREE, Y, Nb, and Ta in scheelite are decreasing with the evolution of the F-rich mineralizing fluids. The latest-formed scheelites have distinctly lower ΣREE (2.9–140 ppm), Y (0.01–4.1 ppm), Nb (1.7–77 ppm), and Ta (0.04–0.19 ppm) contents and higher (La/Yb)N ratios and δEu values. They show 1:1 positive correlation of EuN vs. EuN* and have high Mo (up to 129466 ppm) and low Mn (as low as 3.4 ppm) contents, implying involvement of meteoric waters in the evolved ore-forming fluids and an oxidizing condition. Fluid-rock interaction, mineral precipitation, and fluid mixing largely control the process of fluid evolution. Fluorine consumption due to the formation of fluorite and the other F-rich minerals is vital for the compositional evolution of F-rich mineralizing fluids. The decrease of F concentration in fluids will depress the solubilities of REEs, Y, Nb, and Ta and enhance the LREE/HREE fractionation. Greisenization and skarnization induced the neutralization of the acidic W-bearing fluids and the liberation of Ca from the granite porphyry and carbonate strata and then triggered the scheelite precipitation. The carbonate strata contain abundant Ca and the granite porphyry is poor in Ca, and thus the economic W mineralization dominantly occurs in the skarns.

Stable Divisorial Gonality is in NP

Divisorial gonality and stable divisorial gonality are graph parameters, which have an origin in algebraic geometry. Divisorial gonality of a connected graph G can be defined with help of a chip firing game on G. The stable divisorial gonality of G is the minimum divisorial gonality over all subdivisions of edges of G. In this paper we prove that deciding whether a given connected graph has stable divisorial gonality at most a given integer k belongs to the class NP. Combined with the result that (stable) divisorial gonality is NP-hard by Gijswijt et al., we obtain that stable divisorial gonality is NP-complete. The proof consists of a partial certificate that can be verified by solving an Integer Linear Programming instance. As a corollary, we have that the total number of subdivisions needed for minimum stable divisorial gonality of a graph with m edges is bounded by mO(mn).

Single-atom doping of MoS2 with manganese enables ultrasensitive detection of dopamine: Experimental and computational approach.

Two-dimensional transition metal dichalcogenides (TMDs) emerged as a promising platform to construct sensitive biosensors. We report an ultrasensitive electrochemical dopamine sensor based on manganese-doped MoS2 synthesized via a scalable two-step approach (with Mn ~2.15 atomic %). Selective dopamine detection is achieved with a detection limit of 50 pM in buffer solution, 5 nM in 10% serum, and 50 nM in artificial sweat. Density functional theory calculations and scanning transmission electron microscopy show that two types of Mn defects are dominant: Mn on top of a Mo atom (MntopMo) and Mn substituting a Mo atom (MnMo). At low dopamine concentrations, physisorption on MnMo dominates. At higher concentrations, dopamine chemisorbs on MntopMo, which is consistent with calculations of the dopamine binding energy (2.91 eV for MntopMo versus 0.65 eV for MnMo). Our results demonstrate that metal-doped layered materials, such as TMDs, constitute an emergent platform to construct ultrasensitive and tunable biosensors.

Evaluation of energy-dispersive X-ray spectrometer with transition-edge sensor microcalorimeter on scanning transmission electron microscope for detection of low-concentration phosphorus in Fe–P alloy

An energy-dispersive X-ray spectrometer using a transition-edge sensor microcalorimeter with a scanning transmission electron microscope was applied to detect low concentrations of phosphorus (P) in an Fe–P–Mo–Mn alloy. The high energy resolution of 7.2 ± 0.9 eV was demonstrated in the measurements of P Kα signals, which were not visible in the spectra for a conventional silicon drift detector. The P detection limit estimated from the minimum mass fraction improves with the measurement time and is expected to be below 0.005 wt%.

Preparation and mechanism of active Mo–Mn metallization on ZTA particles surface and interfacial bonding of reinforced iron matrix composite

ZrO2 toughened Al2O3 particles (ZTAp) have poor wettability with iron, and therefore some defects are easily formed at the interface between ZTAp and iron matrix, which may lead to material failure. This paper illustrates that the ZTAp were modified on the surface by the active Mo–Mn metallization, and thus, they were used as the reinforcing phases to prepare the iron-matrix composite (ZTAp/Fe composite). It is concluded that the sponge-like skeleton structure was formed on the surface of ZTAp after the metallization. The interface of ZTAp/Fe composite, which has been proved to have bearing and transitional capacity by scratch test, was formed by chemical bonding with elemental diffusion, besides mechanical bonding. The metallization mechanism of elemental diffusion can be explained by the migration of glass phase, and the elements diffusion between the interface and iron matrix is to form solid solution.

The striking influence of oxophilicity differences in heterometallic Mo-Mn oxide cluster reactions with water.

Mixed-metal oxides have proven to be effective catalysts for the hydrogen evolution reaction, often outperforming either of the binary metal oxides. The reactivity of MnxMoOy - (x = 1, 2; y = 3, 4) clusters toward H2O was investigated via time-of-flight mass spectrometry with clear evidence of cluster oxidation and corresponding H2 production, specifically for MnxMoO3 - (x = 1, 2) clusters. Unlike previously studied MoxOy - clusters, which assumed a broad distribution of stoichiometries (typically x ≤ y ≤ 3x), both MnMoOy - and Mn2MoOy - preferentially formed y = 3 and 4 compositions in significant quantities under our source conditions. The electronic and molecular structures of the MnxMoOy (x = 1, 2; y = 3, 4) anion and neutral clusters were probed with anion photoelectron spectroscopy and analyzed with supporting density functional theory calculations. Our studies suggest that both metal centers are involved in initial cluster-water complex formation, while Mo is the center that undergoes oxidation; hence, reactivity terminates when Mo is saturated in its highest oxidation state of +6. Across these four clusters, Mn remains relatively reduced and is stable in a high-spin electronic configuration. The preferential reactivity of water molecules toward the Mo center rather than Mn is rationalized by the much lower relative oxophilicity of Mn.

Influence of ceramic substrate porosity and glass phase content on the microstructure and mechanical properties of metallized ceramics via an activated Mo-Mn method

With the development of power electronics, metallizing of ceramics has been developed and employed in many industrial applications. This paper describes the effect of porosity, mean pore size and glass phase content of Al2O3 substrate on the microstructure evolution and mechanical properties of metallized ceramics obtained by an activated Mo–Mn method. The interface reaction as well as the joining strength between Al2O3 ceramic and Mo–Mn layer were investigated systematically using X-ray diffraction, SEM, energy dispersive X-ray analysis et al. The overall porosity affects the ‘absorptivity’ of the substrate towards the glass phase in the metallized layer, while the glass phase content affects the diffusion depth of the Mn-containing phase. The results show that the distribution of the Mn-containing glass phase in the alumina substrate determined the failure characteristics of specimens under bending and tension conditions. The mean pore size determines the magnitude of capillary force responsible for the diffusion of Mn-containing glass phase into the ceramic substrate. The thickness of the Mo–Mn layer reduced and the thickness of the transition region increased at high alumina porosity. This resulted in a decrease of tensile strength, and an increase of flexural strength growth rate GR for specimens after metallization. The tensile strength of metallized specimens monotonously increased with the glass phase content, while the flexural strength first increased and then decreased. A tensile strength of 1990 ± 75 N, a flexural strength of 9499 ± 346 N and a He leakage rate of 3.5 × 10−11 Pa m3 s−1 were obtained in the optimized specimens after metallization.

Trapping of an Heterometallic Unsaturated Hydride: Structure and Properties of the Ammonia Complex [MoMnCp(μ-H)(μ-PPh2)(CO)5(NH3)

Complexes displaying multiple bonds between different metal atoms have considerable synthetic potential because of the combination of the high electronic and coordinative unsaturation associated to multiple bonds with the intrinsic polarity of heterometallic bonds but their number is scarce and its chemistry has been relatively little explored. In a preliminary study, our attempted synthesis of the unsaturated hydrides [MoMCp(μ-H)(μ-PR2)(CO)5] from anions [MoMCp(μ-PR2)(CO)5]− and (NH4)PF6 yielded instead the ammonia complexes [MoMCp(μ-H)(μ-PR2)(CO)5(NH3)] (M = Mn, R = Ph; M = Re, R = Cy). We have now examined the structure and behaviour of the MoMn complex (Mo–Mn = 3.087(3) Å) and found that it easily dissociates NH3 (this requiring some 40 kJ/mol, according to DFT calculations), to yield the undetectable unsaturated hydride [MoMnCp(μ-H)(μ-PPh2)(CO)5] (computed Mo–Mn = 2.796 Å), the latter readily adding simple donors L such as CNR (R = Xyl, p-C6H4OMe) and P(OMe)3, to give the corresponding electron-precise derivatives [MoMnCp(μ-H)(μ-PPh2)(CO)5(L)]. Thus the ammonia complex eventually behaves as a synthetic equivalent of the unsaturated hydride [MoMnCp(μ-H)(μ-PPh2)(CO)5]. The isocyanide derivatives retained the stereochemistry of the parent complex (Mo–Mn = 3.0770(4) Å when R = Xyl) but a carbonyl rearrangement takes place in the reaction with phosphite to leave the entering ligand trans to the PPh2 group, a position more favoured on steric grounds.

Mn2(Fe0.8Mo0.2)MoO6: A Double Perovskite with Multiple Transition Metal Sublattice Magnetic Effects

Transition-metal-only perovskite oxides can introduce additional magnetic functionality with robust magnetoelectric properties but are rare. In this work we prepared a new transition-metal-only perovskite Mn2(Fe0.8Mo0.2)MoO6 at high pressure and temperature. Uniquely, Mn2(Fe0.8Mo0.2)MoO6 was discovered as a line phase upon composition modulation that was motivated from the above-room-temperature multiferroic Mn2FeMoO6 corundum phase. It exhibits ferrimagnetic Fe–Mo sublattice (TC = 194 K) and Mn sublattice antiferromagnetic (Tm ∼ 45 K) transitions. Below Tm the two sublattice orderings are coupled and give rise to canted components in both. A first-order field-induced transition is also observed below 45 K. Mn2(Fe0.8Mo0.2)MoO6 is a Mott variable range hopping semiconductor. These findings for the first time show that either an exotic perovskite or a corundum phase can be achieved by composition modulation besides the pressure effect.

Electrochemical, top-down nanostructured pseudocapacitive electrodes for enhanced specific capacitance and cycling efficiency.

Stabilization of the electroactive redox centers on ideally polarisable conductive electrodes is a critical challenge for realizing stable, high performing pseudocapacitive energy storage devices. Here, we report a top-down, electrochemical nanostructuring route based on voltammetric cycling to stabilize β-MnO2 on a single walled carbon nanotube (CNT) scaffold from a MnMoO4 precursor. Such in situ nanostructuring results in controlled disintegration of an ∼8 μm almond like structure to form ∼29 nm β-MnO2 resulting in a 59% increase in the specific surface area and a 31% increase in the porosity of the pseudocapacitive electrode. Consequently, the specific capacitance and areal capacitance increase by ∼75% and ∼40%, respectively. Such controlled, top-down nanostructuring is confirmed through binding energy changes to Mo 3d, C 1s, O 1s and Mn 2p respectively in XPS. Furthermore, Raman spectral mapping confirms the sequential nanostructuring initiating from the interface of CNTs with MnMoO4 and proceeding outwards. Thus, the process yields the final CNT/β-MnO2 electrode that is electrically conductive, facilitates rapid charge transfer, and has increased capacitance and longer stability. Furthermore, the charge-transfer resistance and equivalent resistance are significantly lower compared to conventional activated carbon based electrodes.

Trace metal cycling and 238U/235U in New Zealand’s fjords: Implications for reconstructing global paleoredox conditions in organic-rich sediments

Reconstructing the history of ocean oxygenation provides insight into links between ocean anoxia, biogeochemical cycles, and climate. Certain redox-sensitive elements respond to changes in marine oxygen content through phase shifts and concomitant isotopic fractionation, providing new diagnostic proxies of past ocean hypoxia. Here we explore the behavior and inter-dependence of a suite of commonly utilized redox-sensitive trace metals (U, Mo, Fe, and Mn) and the emerging “stable” isotope system of U (238U/235U, or δ238U) in New Zealand fjords. These semi-restricted basins have chemical conditions spanning the complete redox spectrum from fully oxygenated to suboxic to intermittently anoxic/euxinic. In the anoxic water column, U and Mo concentrations decrease, while Fe and Mn concentrations increase. Similarly, signals of past euxinic conditions can be found by U, Mo, Fe, and Mn enrichment in the underlying sediments. The expected U isotopic shift toward a lower δ238U in the anoxic water column due to U(VI)–U(IV) reduction is not observed; instead, water column δ238U profiles are consistent in fjords of all oxygen content, falling within previously reported ranges for open ocean seawater (δ238U=−0.42±0.07‰). Additionally, surface sediment δ238U results show evidence for competing U isotope fractionation processes. One site indicates increased export of 238U from seawater to the underlying sediments (fractionation between aqueous seawater U and particulate sediment U, or ΔU(aq)−U(solid)=−0.25‰), consistent with redox-driven fractionation. Another site suggests potential U(VI) adsorption-driven fractionation, reflecting increased export of 235U from seawater to sediments (ΔU(aq)−U(solid)=0.25‰). We discuss several potential factors that could alter δ238U in waters and sediments beyond redox-driven shifts, including adsorption to organic matter in waters of high primary productivity, reaction rates for competing processes of U adsorption and release, and isotopic constraints of U coming into the system from terrestrial environments. These potential complications should be understood and constrained through observations, experiments, and models before future application of δ238U as a global paleoredox tracer can achieve its full potential.

A flux-core wire for hardfacing sealing surfaces of stop valves

A new flux-cored wire producing the deposited metal of high-chromium steel of the Fe–Cr–Ni–Mo–Mn–Si–Nb–Ti–B alloying system is described. The structure of the deposited metal and the composition of the hardening phases are determined. The role of borides in increasing the wear resistance and stability of the properties of the metal in hardfacing is analysed.

PASSIVATION BEHAVIOR OF Fe-BASED AMORPHOUS METALLIC COATING IN NaCl AND H2SO4 SOLUTIONS

Amorphous alloy is a new type of material that exhibits exceptional properties or combinations of properties that are often not achievable in conventional crystalline materials. Fe-based amorphous alloys has attracted significant attention over the last few decades because of their low cost and enhanced mechanical performance. *国家自然科学基金项目51274151和51025415,中国博士后科学基金项目2014M551447,黑龙江省自然科学基金项目QC2013C056 和黑龙江省教育厅科学技术研究项目12541079资助 收到初稿日期: 2014-05-21,收到修改稿日期: 2014-08-26 作者简介:王 勇,男, 1979年生,副教授,博士 DOI: 10.11900/0412.1961.2014.00272 第49-56页 pp.49-56