Fe Cr Oxide Research Articles

The Influence of Pretreatment of Carbon Support on the Catalytic Activity of Fe–Cr Oxide Systems in the Oxidative Dehydrogenation of Ethane

The Influence of Pretreatment of Carbon Support on the Catalytic Activity of Fe–Cr Oxide Systems in the Oxidative Dehydrogenation of Ethane

Passivation Behavior of Chromium Alloyed High-Strength Rebar in Simulated Concrete Pore Solution

In this study, SEM, AFM, TEM, XPS, and electrochemical tests are used to study the passivation behavior of chromium alloyed high-strength rebar in simulated concrete pore (SCP) solutions with different pH values. The results show that after passivation in SCP solution with different pH values, the passivating film on the surface of the chromium alloyed rebar primarily consists of a layer of nanoscale oxide particles, which makes the passive film exhibit a p-n type semi-conductor, and the passive film presents a rhombohedral crystal structure. As the pH value of the SCP solution decreases, the nanoscale oxide particles on the surface of the rebar become denser, which leads to a reduction in the carrier density (Nq and Na) of the passive film and an increase in film resistance (R2) and charge transfer resistance (R3), thus increasing the corrosion resistance of the passive film. The passive film on the surface of the chromium alloyed high-strength rebar predominantly exhibits a three-layer structure, the outer passive film layer is composed of Fe oxides, the stable layer of the passive film is composed of Fe oxides and Cr oxides, and the growth layer of inner passive film is composed of Cr oxides. Compared with passivation 10 d in SCP solutions with pH 13.5 and pH 12.5, the passive film on the surface of the rebar has good stability at pH 10.5, which indicates that the addition of Cr is beneficial to promote the corrosion resistance of the rebar.

Using Mössbauer Spectroscopy to Evaluate the Influence of Heat Treatment on the Surface Characteristics of Additive Manufactured 316L Stainless Steel.

The oxidation behaviour of iron-based 316L stainless steel was investigated in the temperature range of 700 to 1000 °C. The test specimens in the shape of plates were produced by selective laser melting. After fabrication, the samples were sandblasted and then annealed in air for different periods of time (0.5, 2, 8, 32 h). Under the influence of temperature and time, stainless steels tend to form an oxide layer. Scanning electron microscopy, energy dispersive analysis, and X-ray diffraction were employed to analyse the composition of this layer. Notably, a thin oxide layer primarily composed of (Fe-Cr) formed on the surface due to temperature effects. In addition, with increasing temperature (up to 1000 °C), the oxide of the main alloying elements, specifically Mn2(Fe-Cr)O4, appeared alongside the Fe-Cr oxide. Furthermore, the samples were subjected to conversion X-ray (CXMS) and conversion electron (CEMS) Mössbauer spectroscopy. CXMS revealed a singlet with a decreasing Mössbauer effect based on the surface metal oxide thickness. CEMS revealed the presence of Fe3+ in the surface layer (0.3 µm). Moreover, an interesting phenomenon occurred at higher temperature levels due to the inhomogeneously thick surface metal oxide layer and the tangential direction of the Mössbauer radiation towards the electron detector.

Comparing Electrochemical Passivation and Surface Film Chemistry of 654SMO Stainless Steel and C276 Alloy in Simulated Flue Gas Desulfurization Condensates.

This research examines the behavior of electrochemical passivation and the chemistry of surface films on 654SMO super austenitic stainless steel and C276 nickel-based alloy in simulated condensates from flue gas desulfurization in power plant chimneys. The findings indicate that the resistance to polarization of the protective film on both materials initially rises and then falls with either time spent in the solution or the potential of anodic polarization. Comparatively, 654SMO exhibits greater polarization resistance than C276, indicating its potential suitability as a chimney lining material. Mott-Schottky analysis demonstrates that the density of donors in the passive film formed on 654SMO exceeds that on C276, potentially due to the abundance of Fe oxide in the passive film, which exhibits the characteristics of an n-type semiconductor. The primary components of the passive films on both materials are Fe oxides and Cr oxides. The formation of a thin passive film on C276 in the simulated condensates is a result of the low Gibbs free energy of nickel oxide and low Cr content. The slower diffusion coefficient of point defects leads to the development of a thicker and more compact passive film on the surface of 654SMO.

Redox regulation of layered Fe-Cr hydroxides during Cr(VI) reduction by sulfate green rust: The overlooked electron conductivity and reactivity of Fe(III)-Cr(III) residues

In this study, unique layered Fe(III)-Cr(III) oxides were formed during the Cr(VI) removal by sulfate green rust (GRSO4). Solid state characterization confirmed that the hexagonal plate and layered structure of GRSO4 remained after fast reduction of Cr(VI). Then, sodium dithionite was further employed to reduce the Fe(III) to Fe(II) in these layered Fe(III)-Cr(III) oxides, enabling stable Fe(II)/Fe(III) cycle in the hexagonal plates. As the Fe(II) content increased in the layered Fe(III)-Cr(III) oxides, there was no significant Fe(II) and Cr(III) release into the solution and the GR-like plate remained intact, indicating that this hexagonal layer Fe-Cr oxides has stable structure during the reduction of Fe(III). Interestingly, better crystallinity was observed at higher Fe(III) reduction rate, and the layered metal oxide structure was confirmed with a basal spacing of 0.935 nm when ∼ 100 % of Fe(III) was reduced to Fe(II). Multiple treatment cycles experiment demonstrated that Cr(III) loading on the layered Fe(III)-Cr(III) oxides could be increased in the following 6 runs of Fe(II)/Fe(III) redox cycle. This study provides new evidence to confirm the electron conductivity and redox reactivity of the Fe(III)-Cr(III) residues under ambient condition, which might help to formulate novel strategies for elimination of Cr(VI) or related heavy metals.

Corrosion product film formation mechanism of 110H-13Cr casing steel in simulated ultra-high-temperature gas environment for shale oil production

This study investigated the corrosion film formation mechanism of 110H-13Cr at 350 °C in the coexistence of four gases, including H2, H2S, CO2 and H2O, by using techniques such as SEM, EDS, XRD and RAMAN, along with thermodynamic calculations. The results indicate that the average corrosion rate of 110H-13Cr is only 0.0573 mm/a. In this environment, the 110H-13Cr steel spontaneously reacts with H2S and H2O. The corrosion products consist of an easily removable outer Fe(1-x) S film and a dense inner Fe-Cr oxide film. The corrosion film formation process comprises an interfacial reaction stage and an element diffusion stage.

Heavy minerals as indicators of source material in soils on carbonates

The origin of the soils formed on carbonate rocks remains uncertain, as they are probably of polygenetic origin. Of particular interest are the elevated contents of some trace elements detected in these soils, as they can hardly be attributed to insoluble residues of carbonate rock. The aim of this study was to uncover the relationship between heavy minerals in bedrock and soil and to identify other sources that influence the mineral and chemical composition of soil. We investigated representative samples of soils and dolomite bedrock as well as sandstones and marlstones from the nearby flysch basin as an expected source of the aeolian contribution. XRD and SEM/EDS showed that mineral diversity is higher in soils compared to the dolomites. Heavy minerals found in dolomite insoluble residue include sphalerite, Ti-oxide (probably rutile), zircon, fluorite, pyrite, minerals of REE phosphates and apatite group, interpreted as terrigenous detrital material. The mineral composition of soil heavy fraction is only partly following insoluble residues of bedrock and indicates possible aeolian contribution. Comparison with nearby flysch sandstones and marlstones showed similarities in mineralogical diversity by the presence of chromite and Fe-Cr(Mn) oxides (probably carmichaelite). Other minerals present in soils and flysch layers, such as Ti-oxide (probably rutile), zircon, REE phosphates, and pyrite grains, however, show similarities in mode of occurrence and transport indications. Signs of aeolian transport on the grains detected in soils were further confirmed by SEM/EDS.

The Role of Oxygen Reduction Reaction in Determining Pit Stability of FeCr Alloys

Pitting corrosion is one of the most dangerous forms of corrosion, leading to sudden catastrophic failures in engineering system. Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film. Here the ORR kinetics on conventional and high Cr content FeCr alloys made by arc-melter were investigated by experimental and computational methods. DFT calculations suggested that the overpotentials for the ORR on FeCr oxides are in the order Cr2O3 > Fe3O4 > Fe2O3 > FeCr2O4, which was experimentally confirmed on the FeCr alloys by rotating disc electrode experiments in both O2 saturated 0.1 M NaOH and 3.5 wt% NaCl. Koutecký-Levich analysis demonstrated that ORR follows a 4-electron pathway on all surfaces investigated. Moreover, the investigation of the Pourbaix diagrams of FeCr revealed that at potentials where pitting corrosion initiates the main constituents of the passive films should be a mixture of Fe2O3 and Cr2O3, rather than FeCr2O4, which is proved to be a good ORR catalyst. The results support the postulation that one role Cr additions play in the prevention of pitting corrosion is to suppress the ORR reaction.

Understanding the effect of dolomite additive on corrosion characteristics of straw biomass ash through experiment study and molecular dynamics calculations

Experiments and molecular dynamics calculations were conducted to study the corrosion characteristics of straw biomass ash with dolomite as an additive. The results showed that the corrosion of metal by straw ash followed a parabolic law with respect to time, and this corrosion gradually reduced after adding dolomite. At 650 °C, the surface of straw ash almost completely sintered and melted and was composed of SiO2, KCl, K2Si4O9 and K2CrO4. The corrosion layer contained cracks and many acicular Fe–Cr oxides. After adding 5% dolomite, the corrosion rate decreased by 57.74%. The ash layer loosened and was mainly composed of CaMgSi2O6, CaSiO3 and MgSiO3. No evident cracks were observed in the corrosion layer. As the temperature increased, the absolute value of the binding energy of KCl on the Fe2O3 and dolomite surfaces increased. Moreover, stronger chemical interactions were observed between the K+, Cl−, and dolomite. On the same surface, the diffusion coefficient of K+ was higher than that of Cl−. At the same temperature, the diffusion coefficient of K+ and Cl− on the dolomite was greater than on the Fe2O3. KCl was more likely to combine with dolomite than with the metal surface, alleviating the metal corrosion caused by biomass ash.

STEM and HRTEM study on matrix microstructure and oxide particles in 11Cr ferritic/martensitic ODS steel

Fe–Cr oxide dispersion strengthened (ODS) steel is one of the candidate structural materials for high burn-up fuel cladding of sodium-cooled fast reactor and fusion reactor blanket due to its superior high temperature strength and excellent resistances to corrosion, creep and irradiation. The matrix structure and oxides in 11Cr ferritic/martensitic (F/M) ODS steel (Fe–11Cr–0.13C–1.3W–0.4Ni–0.3Ti–0.35Y2O3) have been characterized by scanning transmission electron microscopy (STEM) and high resolution transmission electron microscopy (HRTEM). The matrix of 11Cr F/M ODS steel is composed of tempered martensite (major) and residual ferrite (minor). The dispersion morphology of oxides of residual ferrite is much better, relative to that of tempered martensite, because the oxides in the former have much smaller mean diameter and inter-particle spacing and, however, significantly higher number density and volume fraction. For tempered martensite and residual ferrite, phase identifications on 41 and 69 nanoparticles with peak number fraction and, consequently, most significant contributions to the macroscopic properties, were accomplished, respectively. The proportions of Y–Ti–O, Y–Cr–O, TiO2 and Y2O3 in tempered martensite are 58.5%, 12.2%, 19.5% and 9.8%, respectively. The proportions of Y–Ti–O, Y–Cr–O, TiO2 and Y2O3 in residual ferrite are 65.3%, 8.7%, 15.9% and 10.1%, respectively. There is no considerable difference in phases and their corresponding number fractions of nanoparticles between tempered martensite and residual ferrite. Coherency and crystallographic orientation relationship between the lattice of oxides and that of the residual ferrite matrix are ubiquitous and, moreover, such coherency and crystallographic correlation between the lattice of oxides and that of the tempered martensite matrix were only occasionally detected. The mechanisms of the formation and polymorphic transition of various kinds of oxides, the structure origins of the much better dispersion morphology of the nanoparticles of residual ferrite, relative to that of tempered martensite, and, moreover, the strengthening mechanisms in the 11Cr F/M ODS steel were discussed.

Phase Changes in the Surface Layer of Stainless Steel Annealed at a Temperature of 550 °C.

Stainless steels have the advantage of forming a protective surface layer to prevent corrosion. This layer results from phase and structural changes on the steel surface. Stainless steel samples (1.4404, 316L), whose alloying elements include Cr, Ni, Mo, and Mn, were subjected to the study of the surface layer. Prism-shaped samples (25 × 25 × 3) mm3 were made from CL20ES stainless steel powder, using selective laser melting. After sandblasting with corundum powder and annealing at 550 °C for different periods of time (2, 4, 8, 16, 32, 64, 128 h), samples were studied by conversion X-ray Mössbauer spectroscopy (CXMS), conversion electron Mössbauer spectroscopy (CEMS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The main topics of the research were surface morphology and elemental and phase composition. The annealing of stainless steel samples resulted in a new surface layer comprising leaf-shaped crystals made of chromium oxide. The crystals grew, and their number increased as annealing time was extended. The amount of chromium increased in the surface layer at the expense of iron and nickel, and the longer the annealing time was set, the more chromium was observed in the surface layer. Iron compounds (BCC iron, mixed Fe-Cr oxide) were found in the surface layer, in addition to chromium oxide. BCC iron appeared only after annealing for at least 4 h, which is the initial time of austenitic-ferritic transformation. Mixed Fe-Cr oxide was observed in all annealed samples. All phase changes were observed in the surface layer at approximately 0.6 µm depth.

Activated Carbon from Used Motor Oils: Synthesis and Application as Supports of Nanosized Fe–Cr Oxides

Activated Carbon from Used Motor Oils: Synthesis and Application as Supports of Nanosized Fe–Cr Oxides

Products of molten corium-metal interaction in chernobyl accident: Composition and leaching of radionuclides

During initial stages of severe nuclear accident at Chernobyl NPP on 26 April 1986 interaction between U-oxide fuel and Zr-cladding has occurred and a corium melt (Zr–U–O) formed in localized part(s) of reactor core. In this paper, we describe the properties of unique set of samples formed during interaction of the corium melt with steel in the core that was expelled from the reactor shaft into reactor premises and subsequently oxidized. These samples primarily consist of Fe–Cr oxides with inclusions of U- and Zr-based oxides. Uranium is heavily oxidized, forming U4O9 and U3O8. Nb/Zr ratio of the inclusions and presence of substantial Ni in the oxide matrix permitted us to identify precursor materials of the studied samples. The studied material was formed in two principal stages: interaction of liquefied fuel with Zr from walls of technological channels and/or guide rod, and subsequent reaction with steel parts located in a very well-defined part of the core – the bottom part of the guide rod and/or graphite/guide rod socket on the reactor base plate. The differences in texture between the samples are ascribed to a cooling regime and substrate on which the ejected melts were cooled. Submicron particles of fission products (Pd, Ru, Tc, etc.), very rare for Chernobyl samples, are scattered within the Fe–Cr oxide matrix. Their preservation was the result of highly oxidative conditions. Leaching of 137Cs and Am in hot aqueous fresh and saline solutions was studied. High leach rates of these nuclides is ascribed to highly oxidized state of U-containing phases. Results of the current study are compared with experiments on molten corium – vessel steel interaction and provide new details on progression of the Chernobyl NPP core destruction shortly before and during the explosion.

Design of highly selective heterogeneous catalyst for CO2-mediated ethane oxidative dehydrogenation based on nonoxidative catalysis in stainless-steel reactor

Highly selective and active phases in the ethane dehydrogenation were formed on the inner wall of stainless-steel reactor after its long-term using in the process at 650–750 °C. The conversion of ethane at 650 °C reached up to 40% with ethylene selectivity closed to 90%. Fe-Cr-Ni and Fe-Cr oxides catalysts supported on carbon were created for CO2–mediated oxidative dehydrogenation of ethane (ODE) based on SR-XRD analysis of the inner wall of the steel reactor. In the case of Fe-Cr-Ni/C catalyst, the ethylene selectivity decreased and the catalyst was rapidly deactivated by coke deposits. On Fe-Cr/C catalyst, the ethylene selectivity was 82% and ethane conversion was above 20% at 700 °C. It was found that phase FeCr2O4 forms on the surface of Fe-Cr/C catalyst, which, as we assume, is responsible for high stability of the catalyst and its high selectivity of ODE with CO2.

Effect of the grain size on the corrosion behavior of CoCrFeMnNi HEAs in a 0.5 M H2SO4 solution

This work investigated the corrosion behavior of the equiatomic CoCrFeMnNi high entropy alloy (HEA) in a 0.5 M H2SO4 solution. The grain size of the HEA was adjusted by annealing. The electrochemical analysis showed that the corrosion resistance of the CoCrFeMnNi HEA increases first and then decreases with the increase of grain size. When the grain size is lower than a certain value, increasing the grain size can improve the corrosion resistance. Fine-grained (≤1.24 μm) HEA forms abundant grain boundaries, which promotes the occurrence of galvanic corrosion at the grain boundaries with inter-grains, resulting in reduced corrosion resistance. However, coarse-grained (≥145.9 μm) HEA provides too few ionic diffusion channels to form a stable and continuous passive film, which also reduces the corrosion resistance. Nanoindentation and XPS tests showed that a high content of Fe (Ⅲ) oxides and Cr (Ⅲ) oxides are formed on the medium-grained HEA, which improves the chemical stability and mechanical strength of the passive films. Thus, the corrosion resistance of medium-grained HEA is much better than those of fine-grained and coarse-grained HEA.

Highly enhanced foams for stability and decontamination efficiency with a fluorosurfactant, silica nanoparticles, and Ce(IV) in radiological application

The stability and decontamination efficiency of foams containing a fluorosurfactant, stabilizer, and the chemical reagents with HNO3 and Ce(IV) for the decontamination of Fe–Cr oxide layers containing 60Co radionuclides were tested to find their optimum formulation. The stability of foams containing 2 M HNO3 and 0.5 M Ce(IV) with 1 wt% silica nanoparticles (NPs) is higher for Zonyl TBS (an anionic fluorosurfactant) than for other surfactants such as SDS (anionic) and CTAB (cationic). This result indicates that Zonyl TBS is more suitable for the harsh conditions required for the use of the oxidant Ce(IV) and silica NPs, indicating that this formulation is conducted for the decontamination test. After three repetitions of the decontamination test, performed by re-injecting air into the decontamination foam, approximately 73% of 60Co was removed from the corroded specimen (SUS 304) by the foam containing 1% v/v Zonyl TBS; this removal value is close to that obtained with the chemical decontamination solution alone, i.e., 80%. The results of secondary waste showed that the decontamination foam contains only 70 ml of chemical decontamination solution and 280 ml of injected gas, indicating that decontamination foam decreased the generated secondary waste by 80%, compared to the use of 350 ml chemical decontamination solution. Moreover, the results indicate that the use of silica NPs and the TBS surfactant enhances foam stability, particularly because of the resistance to harsh conditions of the surfactant due to its low pKa and strong C–F bonding.

Experimental and Modelled Reactions of CO2 and SO2 with Core from a Low Salinity Aquifer Overlying a Target CO2 Storage Complex

CO2-induced reactions in low salinity aquifers overlying CO2 storage sites are of interest to understand potential reactions or impacts in the possible case of a leak. Previous investigations of overlying aquifers in the context of CO2 storage have focused on pure CO2 streams, however captured industrial CO2 streams may contain ancillary gases, including SO2, O2, NOx, H2S, N2, etc., some of which may be more reactive than CO2 when dissolved in formation water. Eight drill cores from two wells in a low salinity sandstone aquifer that overlies a target CO2 storage complex are characterised for porosity (helium, mercury injection, or micro CT), permeability, and mineral content. The eight Hutton Sandstone cores are variable with porosities of 5.2–19.6%, including carbonaceous mudstones, calcite cemented sandstones, and quartz rich sandstones, common lithologies that may be found generally in overlying aquifers of CO2 storage sites. A chlorite rich sandstone was experimentally reacted with CO2 and low concentrations of SO2 to investigate the potential reactions and possible mineral trapping in the unlikely event of a leak. Micro CT characterisation before and after the reaction indicated no significant change in porosity, although some fines movement was observed that could affect permeability. Dissolved concentrations of Fe, Ca, Mn, Cr, Mg, Rb, Li, Zn, etc., increased during the reaction, including from dissolution of chlorite and trace amounts of ankerite. After ~40 days dissolved concentrations including Fe, Zn, Al, Ba, As and Cr decreased. Chlorite was corroded, and Fe-rich precipitates mainly Fe-Cr oxides were observed to be precipitated on rock surfaces after experimental reaction. Concentrations of Rb and Li increased steadily and deserve further investigation as potential monitoring indicators for a leak. The reaction of chlorite rich sandstone with CO2 and SO2 was geochemically modelled over 10 years, with mainly chlorite alteration to siderite mineral trapping 1.55 kg/m3 of CO2 and removing dissolved Fe from solution. Kaolinite and chalcedony precipitation was also predicted, with minor pyrite precipitation trapping SO2, however no changes to porosity were predicted.

Micro-structural evolution of oxide scales formed on a Nb-Stabilizing heat-resistant steel at the initial stage in high-temperature water vapor

Early oxidation behavior of a Nb-Stabilizing heat-resistant steel in water vapor at 700 °C for 336 h was investigated. Micro-characterization methods including in-depth XPS, SEM/EDS, FIB were employed to acquire the composition and distribution of oxidation products. The results showed that the oxidation kinetics of this heat-resistant steel almost followed a parabolic law at 700 °C, indicating the oxidation was controlled by the ion diffusion. Surfaces of oxidation products on TP347HFG were gradually from compact to loose with a longer exposure. Oxide scales were mainly composed of layered (Mn, Fe)Cr2O4 and Cr2O3 and scattered Nb2O5. Contents of Mn at the surface were much higher than other positions, confirming that Mn diffuse much faster than Fe and Cr. During the initial oxidation stage, NbC was transformed into Nb2O5, which was covered by Fe–Cr oxide scales. The growth of oxide scales on TP347HFG is suggested.

Effect of in-situ oxidation on the nanomechanical evolution of Fe-base coating with ceramic particles produced by internal rotating plasma spraying

In this work, we investigated FeCrMo coatings with 35 wt% ceramic, which were produced on a cylinder surface by an internal rotating plasma spraying and oxidized in air. The ceramic particles consisted of 80 wt% alumina and 20 wt% zirconia, which can improve the mechanical properties of the coating. For microstructural characterization, scanning electron microscopy was combined with energy dispersive X-ray analysis and electron probe micro analysis, and the nanomechanical properties were measured by a nanoindentation tester. The structure of Fe-base coating matrix consists of Al 2 O 3 , ZrO 2 and a small amount of mixed Fe–Cr oxides, and the ceramic particles exhibit a uniform distribution. During oxidation, a mixed oxide layer containing Fe 2 O 3 and Fe 3 O 4 forms on the surface of the Fe-base coating, and the thickness of the oxide layer increases with increasing oxidation temperature. Due to the in-situ oxidation, the nanohardness and Young's modulus of the Fe-base coating decreased with increasing oxidation temperature. The nanohardness evolution of Fe-base coatings oxidized at different temperatures is discussed.

Removal behavior of Cu(II) during Cr(VI) reduction by cast iron powder in absence and presence of ultrasound

ABSTRACTCu(II) is an important and typical heavy metal ion in the wastewater containing Cr(VI), and its removal during Cr(VI) reduction by zero valent iron (ZVI) may make it separately be recovered as a kind of copper resource. In this study, the removal behavior of Cu(II) during Cr(VI) reduction by cast iron powder in absence and presence of ultrasound was investigated by atomic absorption spectrometry (AAS), X-ray powder diffractometer (XRD), scanning electron microscope-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The AAS tests indicated that the ultrasound could not only obviously enhance the removal of Cu(II) but also improve the reduction rate of Cr(VI). The XRD and SEM-EDS analyses showed that Cu(II) in the solution was reduced to metallic copper and then was deposited at the surface of ZVI. The ultrasound could remove the Fe-Cr oxides and hydroxides at the ZVI surfaces, resulting in the active surfaces of iron increased. The XPS analyses demonstrated that the surface of metallic copper would be transformed into the film of copper oxide (CuO) in the ultrasound system. The obtained metallic copper and copper oxide could be recovered alone by traditional method of the acid pickling.