Iron Oxide Surface Research Articles

Preparation of superhydrophobic nanoplate iron oxide surface on a carbon steel for anti-wetting applications

A simple route to fabricate a surface layer comprising Fe3O4 nanoplates on a carbon steel has been successfully demonstrated using etching treatment followed by annealing in oxygen atmosphere. Different sizes of the Fe3O4 (311) exposed nanoplates can be fabricated by varying the annealing temperature. Density Function Theory (DFT) calculation proved that the energy of Fe3O4 (311) surface was the lowest among all exposed facets, which make it most stable. The superhydrophobicity has been realized after modification with trimethoxy silane (HFTMS). Molecular dynamic simulation was further carried out to verify the excellent anti-wettability of the modified surface. In addition, the superhydrophobic surface exhibited a low adhesion with water and displays excellent performance in anti-corrosion, anti-icing and self-cleaning.

Phase evolution of the surface iron (hydr)oxides to the iron sulfide through anion exchange during sulfidation of zero valent iron

The naturally-formed iron (hydr)oxides on the surface of zero valent iron (ZVI) have long been considered as passivation layer and inert phases which significantly reduce the reaction activities when they are employed in environmental remediation. Although it seems there are no direct benefits to keep these passivation layers, here, we show that such phases are necessary intermediates for the transformation to iron sulfides through an anion exchange pathway during sulfidation of ZVI. The pre-formed (hydr)oxides undergo a phase evolution upon aging and specific phases can be effectively trapped, which can be confirmed by a combination of different characterization techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRPD), and X-ray absorption near edge structure (XANES) spectroscopy. Interestingly, after sulfidation, the resultant samples originated from different (hydr)oxides demonstrate different activities in the Cr(VI) sequestration. The XANES investigation of Fe K edge and Fe L2,3 edge indicates Fe remains the same after sulfidation, suggesting a non-redox, anion exchange reaction pathway for the production of iron sulfides, where O2- anions are directly replaced with S2-. Consequently, the structural characteristics of the parent (hydr)oxides are inherited by the as-formed iron sulfides, which make them behave differently because of their different structural natures.

Recent Advances on Drawing Technology of Ultra-Fine Steel Tire Cord and Steel Saw Wire

Steel tire cord and steel saw wire represent typical precision pearlitic steel wire rods of wire products; it is a very important solar energy material with a diameter about 50 μm. This paper mainly discusses the research progress of the wire rod drawing process, and its main contents are as follows: First section—the control of the wire rod surface quality is summarized, including the thickness of the surface decarburization layer, the phase composition and thickness of the surface iron oxide scale, and the removal of surface iron oxide scale. Then, the research progress of the wire rod water bath treatment process during sorbitization is summarized. In addition, the development of brass plating technology for steel wire is summarized, including copper plating technology, coating phase composition, etc. Furthermore, the development of steel wire drawing methods is summarized. Finally, the development of the dies used in steel wire drawings is summarized.

Formation of Environmentally Persistent Free Radicals (EPFRs) on the Phenol-Dosed α-Fe2O3(0001) Surface.

Environmentally persistent free radicals (EPFRs) are a class of toxic air pollutants that are found to form by the chemisorption of substituted aromatic molecules on the surface of metal oxides. In this study, we employ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) to perform a temperature-dependent study of phenol adsorption on α-Fe2O3(0001) to probe the radical formation mechanism by monitoring changes in the electronic structure of both the adsorbed phenol and metal oxide substrate. Upon dosing at room temperature, new phenol-derived electronic states have been clearly observed in the UPS spectrum at saturation coverage. However, upon dosing at high temperature (>200 °C), both photoemission techniques have shown distinctive features that strongly suggest electron transfer from adsorbed phenol to Fe2O3 surface atoms and consequent formation of a surface radical. Consistent with the experiment, DFT calculations show that phenoxyl adsorption on the iron oxide surface at RT leads to a minor charge transfer to the adsorbed molecule. The experimental findings at high temperatures agree well with the EPFRs' proposed formation mechanism and can guide future experimental and computational studies.

A Combined Experimental and Atomistic Investigation of PTFE Double Transfer Film Formation and Lubrication in Rolling Point Contacts

Solid lubricants such as polytetrafluoroethylene (PTFE) are used in rolling-element bearings (REBs) when conventional lubrication (i.e. by fluids or greases) cannot be applied owing to extreme operating conditions (e.g. high temperatures or vacuum). Often a double transfer film mechanism is used with a cage acting as a lubricant reservoir resupplying the REB with solid lubricant by cage wear. An increase in service life of such bearings requires a better understanding of the transfer processes in the sliding and rolling contacts. Here, we investigate the effect of PTFE resupply on friction and lubricant film formation in a steel/steel and steel/glass rolling contact by tribometry and classical molecular dynamics (MD). A ball-on-disk tribometer is enhanced by a pin-on-disk sliding contact that transfers PTFE to the disk. The experiment allows simultaneous in situ measurement of friction and film thickness by white light interferometry in the rolling point contact. Increasing the pin load results in an increased PTFE film thickness in the rolling contact accompanied by a significant decrease in friction. To elucidate the observed film transfer and friction mechanism, sliding MD simulations with a newly developed density-functional-based, non-reactive force field for PTFE-lubricated iron oxide surfaces are performed. A strong adhesion of PTFE chains to iron oxide drives transfer film formation, whilst shear-induced chain alignment within PTFE results in reduced friction. The simulations reveal an anti-correlation between PTFE film thickness and friction coefficient—in agreement with the experiments. These investigations are a first step towards methods to control PTFE transfer film formation in REBs.Graphic

Sulfur dioxide interaction with thin iron oxide films on low-index surfaces of iron

The adsorption of sulfur dioxide (SO2) at room temperature on iron oxide surfaces has been studied using core-level photoelectron spectroscopy. A variety of iron oxides, from adsorbate structure to thin film, with different stoichiometries and terminations were grown on common low-index single crystal iron surfaces to model a range of structures in the initial stages of atmospheric oxidation. This permits well-controlled comparisons of differences and similarities in SO2 interaction.Both non-dissociative and dissociative adsorption of SO2 were observed, to different relative and absolute coverages, on all surfaces. The only identified non-dissociated species is SO4. For all surfaces, at least some amounts of atomic sulfur are observed while only for the submonolayer adsorbate structure, also tentative dimerization of sulfur into S2 or formation of S-Osurface is observed. For the two oxides terminated by a complete well-ordered oxygen layer, the absolute sulfur coverage is low. The complete oxygen layer terminated oxide film exhibiting a moiré-pattern had a saturation coverage of one SO4 species per surface super cell, which indicates a tentative preferred adsorption site. The surface showing the highest SO4 formation is the Fe3O4(100) thin film surface with a corrugated row structure. The SO4 formation is suggested between surface oxygen atoms within the same row.

Mechanistic insights into the effect of structural factors on film formation and tribological performance of organic friction modifiers

The influence of molecular structure of organic friction modifiers (OFMs) on their adsorption behaviour on iron oxide surface immersed in PAO oil was investigated using neutron reflectometry (NR). The effects of carbon chain length and levels of unsaturation on film formation was studied using a series of fatty acids with 18–20 carbon atoms in the temperature range between 25 and 100 °C. The results revealed that saturated OFM molecules generate thicker films compared to its unsaturated counterparts. Further, a decrease in film thickness was observed with the degree of unsaturation with the exception of linolenic acid. The film thickness and grafting density of the OFM increased with temperature. A decreased film thickness for the binary additive system comprising GMO and saturated molecules suggested that the adsorption of OFMs on the surface is hindered in the presence of glycerol mono oleate (GMO). A lower boundary friction coefficient and wear exhibited by OFMs with longer chain and linear structure suggest that their tribofilms are more effective in withstanding shear. The tribofilm thickness measured using optical interferometry showed no correlation with the adsorbed layer thickness determined from NR data; this lack of correspondence is attributed to the load and shearing forces experienced by the OFM molecules at the contact surfaces during friction measurements.

On the role of surface oxygen during nascent single-walled carbon nanotube cap spreading and tube nucleation on iron catalysts

Single-walled carbon nanotubes (SWCNTs) are commonly grown in oxygen-rich environments. The precursor used as input for the SWCNT synthesis reaction typically provides oxygen atoms either as a pure gas or as an oxygen-containing compound. Similarly, metal oxide substrates are used to support the catalysts or as reactor wall materials and can transfer oxygen atoms while in contact with the catalytic particles. It has been proposed and experimentally observed that the interaction of the metal catalyst with specific promoters (e.g., oxygen, sulfur, hydrogen) triggers significant changes in the SWCNT properties during spreading, nucleation and growth. However, very few studies address the carbon-catalyst surface interactions in rich oxygen environments. Here we show that an increased surface oxygen concentration in the neighborhood of a spreading nascent carbon shell reduces the strength of interaction of the carbon shell with the iron catalyst's surface and increases the probability of carbon nucleation and SWCNT lift-off. The evolution of the carbon-surface interaction during the spreading and nucleation phases suggests that closed pentagons at the rim are preferentially formed in oxidized iron surfaces, and they exhibit the strongest and most stable interaction with the iron surface.

Cadmium Isotope Fractionation during Adsorption and Substitution with Iron (Oxyhydr)oxides.

Cadmium (Cd) isotopes have great potential for understanding Cd geochemical cycling in soil and aquatic systems. Iron (oxyhydr)oxides can sequester Cd via adsorption and isomorphous substitution, but how these interactions affect Cd isotope fractionation remains unknown. Here, we show that adsorption preferentially enriches lighter Cd isotopes on iron (oxyhydr)oxide surfaces through equilibrium fractionation, with a similar fractionation magnitude (Δ114/110Cdsolid-solution) for goethite (Goe) (-0.51 ± 0.04‰), hematite (Hem) (-0.54 ± 0.10‰), and ferrihydrite (Fh) (-0.55 ± 0.03‰). Neither the initial Cd2+ concentration or ionic strength nor the pH influence the fractionation magnitude. The enrichment of the light isotope is attributed to the adsorption of highly distorted [CdO6] on solids, as indicated by Cd K-edge extended X-ray absorption fine-structure analysis. In contrast, Cd incorporation into Goe by substitution for lattice Fe at a Cd/Fe molar ratio of 0.05 preferentially sequesters heavy Cd isotopes, with a Δ114/110Cdsolid-solution of 0.22 ± 0.01‰. The fractionation probably occurs during the transformation of Fh into Goe via dissolution and reprecipitation. These results improve the understanding of the Cd isotope fractionation behavior being affected by iron (oxyhydr)oxides in Earth's critical zone and demonstrate that interactions with minerals can obscure anthropogenic and natural Cd isotope characteristics, which should be carefully considered when applying Cd isotopes as environmental tracers.

Amplification effects of magnetic field on hydroxylamine-promoted ZVI/H2O2 near-neutral Fenton like system

This study has demonstrated an interesting amplification effect of magnetic field (MF) on the hydroxylamine (HA)-promoted zero valent iron (ZVI)/H2O2 Fenton-like system. Sulfamethoxazole (SMX) could be efficiently degraded at near neutral pH. Conditional parameters affecting the SMX degradation in the ZVI/H2O2/HA/MF system, e.g., pH and the dosages of ZVI, HA and H2O2, were investigated. Unlike the acid-favorable ZVI/H2O2 and ZVI/H2O2/HA systems, the MF-assisted system exhibited good performances even at pH up to 6.0 and highest degradation rate at pH of 5.0. •OH was still identified as the responsible oxidant. A mechanism involving the MF-enhanced heterogeneous-homogeneous iron cycle was proposed in the near-neutral ZVI/H2O2/HA system. Without MF, HA-induced reductive dissolution of the surface iron oxides occurred and thus leaded to homogeneous Fenton reactions. After the introduction of MF, the gradient magnetic field formed on the ZVI particles would induce the generation of concentration cells of Fe(II) and local corrosion of iron. Large amounts of aqueous and bounded Fe(II) catalyzed H2O2 to efficiently produce •OH, while HA maintained the surface and bulk cycles of Fe(II)/Fe(III). The result of study is expected to provide a green, energy-free method in improving the effectiveness of ZVI-based Fenton-like technologies at weak-acidic circumstances.

Core-shell-type Fe3O4@carbon nanoparticles and their fabrication using silanic/polymeric amino functionalization

A facile strategy for the fabrication of a carbon shell on Fe3O4 nanoparticles with a cluster structure has been proposed. Unlike the conventional solvothermal process using an autoclave, the proposed synthesis method could yield core-shell structured Fe3O4@C nanoparticles at low temperature and atmospheric pressure. This synthesis method was based on the chemical bonding among the terminal amine groups, introduced on the Fe3O4 surface, and carbonization by the catalytic reaction of glucose (carbon source) with sulfuric acid. The properties of the Fe3O4@C nanoparticles so obtained depended on the terminal amine groups that modified the iron oxide surface. The effects of the silane- and polymer-based amination on the fabrication of the carbon shell were investigated.

Deposition behavior of dissolved black carbon on representative surfaces: Role of molecular conformation

To understand the fate of colloidal or dissolved black carbon (DBC) in aquatic systems, a quartz crystal microbalance with dissipation (QCM-D) was applied to investigate deposition and release behaviors of DBC. The results suggested that DBC molecular composition and conformation were critical to the deposition processes on model surfaces, which were controlled by not only the classic Derjaguine-Landaue-Verweye-Overbeek (DLVO) interactions but also non-DLVO forces. The deposition rates of alumina, iron oxide and polyamide surfaces first increased due to the change of conformation and then decreased as the salt concentration increased. Correspondingly, the deposition layers first became more rigid and then got softer with the increase in the ionic strength. Both the pH values and calcium ion had distinctive effects on the deposition behaviors and viscoelastic properties due to their particular roles in DBC surface characteristic and molecular conformation. Overall, these results are meaningful to understand the environmental behaviors of DBC in aquatic systems.

Surface Observation of Laser-treated Carbon Steel and Application of Laser Ccleaning for Corroded Steel Member

A newly developed laser system is adopted in this study as a surface preparation method for corroded steel structures. To investigate the thermal effects of laser beam on steel material, carbon steel plates are treated by two different laser processing parameters. Then the surface condition, heat-affected zone, and iron oxide on laser-treated specimens are evaluated using optical microscope, SEM-EDX, and XRD. Moreover, a severely corroded steel member was used as laser irradiation target to verify the cleaning effects of laser beam. Results show that surface morphologies are varied according to laser processing parameters. Due to thermal effects, iron oxide was formed after laser irradiation, and higher laser power induced deeper heat-affected zone. The application of laser treatment for corroded steel member showing desirable surface cleanliness after laser irradiation. The laser surface treatment could be an alternative surface preparation method for steel structures in the construction field.

The adsorption of U(VI) on magnetite, ferrihydrite and goethite

During the long-term disposal of radioactive waste, ferrous waste containers and building materials are tending to corrode to produce a large number of iron oxides. The formed iron oxides would bring significant effects on the diffusion and migration of radionuclides through adsorption and reduction. This study aimed to evaluate the interaction of U(VI) on iron oxides under anaerobic conditions, where goethite, magnetite, and ferrihydrite were used as adsorbents. The results showed that the adsorption of U(VI) on iron oxides was chemical adsorption, and the adsorption capacity of U(VI) on ferrihydrite was much higher than that on goethite and magnetite. Humic acid (HA) promoted the adsorption of U(VI) on iron oxides under acidic conditions, while U(VI) adsorption was inhibited by HA in the neutral to alkaline conditions. The adsorption of U(VI) on iron oxides was an endothermic process, and higher temperature was beneficial for the adsorption. Surface complexation modeling (SCM) fitting revealed that monodentate inner complexes of ≡ FeOUO 2 + and ≡ FeOUO 2 ( OH ) 0 were mainly formed on the surface of iron oxides. Finally, the reduction of U(VI) to U(IV) on magnetite under anaerobic condition was confirmed by X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. • Interaction between U(VI) and iron oxides were studied under anaerobic condition. • Ferrihydrite has higher affinity for U(VI) than goethite and magnetite. • U(VI) was reduced to U(IV) on magnetite after reaction for long time.

Poly(ethylene glycol)-Alendronate-Coated Magnetite Nanoparticles Do Not Alter Cardiovascular Functions and Red Blood Cells' Properties in Hypertensive Rats.

In this study, magnetite nanoparticles were prepared and coated with poly(ethylene glycol) terminated by alendronate to ensure firm binding to the iron oxide surface. Magnetic nanoparticles, designated as magnetite coated with poly(ethylene glycol)-alendronate (Fe3O4@PEG-Ale), were characterized in terms of number-average (Dn) and hydrodynamic (Dh) size, ζ-potential, saturation magnetization, and composition. The effect of particles on blood pressure, vascular functions, nitric oxide (NO), and superoxide production in the tissues of spontaneously hypertensive rats, as well as the effect on red blood cell (RBC) parameters, was investigated after intravenous administration (1 mg Fe3O4/kg of body weight). Results showed that Fe3O4@PEG-Ale particles did negatively affect blood pressure, heart rate and RBC deformability, osmotic resistance and NO production. In addition, Fe3O4@PEG-Ale did not alter functions of the femoral arteries. Fe3O4@PEG-Ale induced increase in superoxide production in the kidney and spleen, but not in the left heart ventricle, aorta and liver. NO production was reduced only in the kidney. In conclusion, the results suggest that acute intravenous administration of Fe3O4@PEG-Ale did not produce negative effects on blood pressure regulation, vascular function, and RBCs in hypertensive rats.

Rice starch coated iron oxide nanoparticles: A theranostic probe for photoacoustic imaging-guided photothermal cancer therapy

In recent years, suitable bioactive materials coated nanoparticles have attracted substantial attention in the field of biomedical applications. The present study emphasizes experimental details for the synthesis of boiling rice starch extract (BRE) coated iron oxide nanoparticles (IONPs) to treat cancer by photoacoustic imaging (PAI)-guided chemo-photothermal therapy. The solvothermal method was used to synthesize IONPs. The physical immobilization method helps to coat BRE-loaded doxorubicin (DOX) molecules on the iron oxide surface. In vitro drug release was estimated in basic (pH 9.0), neutral (pH 7.2), and acidic (pH 4.5) media for varying time periods using ultraviolet-visible spectroscopy. The chemical and physical properties of the synthesized spherical BRE-IONPs were characterized using sophisticated analytical instrumentation. A magnetic saturation experiment was performed with BRE-IONPs for evaluating possible hyperthermia in targeted drug delivery. The biological activity of the synthesized BRE-IONPs was investigated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and acridine orange/propidium iodide fluorescence cell viability study. BRE-IONPs showed excellent photothermal stability, with a high photothermal conversion efficiency (η = 29.73%), biocompatible property, and high near-infrared region absorption for PAI-guided PTT treatment. This study will provide a better understanding of rice starch as a suitable bioactive coating material for possible theranostic applications.

Single Atom Catalysts: Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe2O3(11¯02) (Adv. Mater. Interfaces 8/2021)

Rhodium atoms adsorbed on a model iron oxide surface sinter to nanoparticles already at room temperature. Redispersion into isolated single atoms is induced by oxygen annealing. The resulting atoms are incorporated in the first subsurface layer of the oxide, rather than the surface. More details can be found in article number 2001908 by Gareth S. Parkinson and co-workers.

A study of alkali polyphosphate/borate/carbonate for high temperature lubrication of silicon steel using ball-on-disc tests

For hot metal forming at high temperatures, lubricant is required to reduce friction and wear, as well as improve the product surface quality. Inorganic compound has been regarded as a candidate to replace the traditional oil/water lubricant for the forming process. Friction and wear behaviour of three inorganic compounds, including sodium polyphosphate, sodium carbonate, sodium borate were evaluated under ball-on-disc tests at high temperature for high speed steel/silicon steel counterparts to simulate the hot rolling process. The results show that all the three compounds can reduce the friction and wear. Sodium polyphosphate is more corrosive with the oxide scale than others, which is believed to contribute to the descaling of red scale of silicon (Si) steel. Mechanisms by which the inorganic compounds improve the tribological behaviours were discussed here. Simulation results indicate that the molecules of sodium polyphosphate and sodium borate show a much higher binding energy on the iron oxide surface than that of sodium carbonate. The binding energy is mainly contributed from the ionic and the covalent interactions. The ionic part comes from the interaction between the Na+ cations and the oxide surface, while the covalent part comes from the chemical bonds between Fe and oxygen of the lubricants. Both of them contribute to the adhesion of the lubricants on the steel surface and are vital to the friction and wear performance of the lubricants.

Influence of Silica Coatings on Magnetite-Catalyzed Selenium Reduction.

The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.e., ∼2 maghemite surface layers), showing that Si adsorption follows a Langmuir isotherm up to 2 mM dissolved Si, where surface polymerization occurs. Furthermore, the effects of silica surface coatings on the redox-catalytic ability of magnetite are analyzed using selenium as a molecular probe. The results show that for partially oxidized nanoparticles and even under different Si surface coverages, electron transfer is still occurring. The results indicate anion exchange between silicate and the sorbed SeIV and SeVI. X-ray absorption near-edge structure analyses of the reacted Se indicate the formation of a mixed selenite/Se0 surface phase. We conclude that neither partial oxidation nor silica surface coatings block the sorption and redox-catalytic properties of magnetite nanoparticles, a result with important implications to assess the reactivity of mixed-valence phases in environmental settings.

Correlation between corrosion inhibition efficiency in sulfuric acid medium and the molecular structures of two newly eco-friendly pyrazole derivatives on iron oxide surface

The inhibition effect of newly synthesized eco-friendly pyrazole derivatives NPDM and NPD on the corrosion of the mild steel (MS) in 0.5 M H2SO4 solution was investigated by the open circuit potential (OCP) curves, potentiodynamic polarization (PP) curves and electrochemical impedance spectroscopy (EIS) along with weight loss (WL) measurements. Both compounds were confirmed to be good anti-corrosion inhibitors and their efficiency was in the order NPD > NPDM for a concentration of 10−3 M. The adsorption of the two compounds on MS surface was studied by SEM and various isotherm models. The adsorption of NPD appeared to obey the Langmuir model while that of NPDM followed Freundlich model. Corrosion inhibition was explained based on experimental results as well as computational studies. The influence of the molecular-electronic-structure on the inhibition activity was inspected by the DFT method. The global and local reactivity, before their adsorption onto the MS surface, were calculated at the B3LYP/6-311G(d,p) theoretical level for the neutral and cationic forms. The solvation hydration energy (∆GSolv) was also considered to evaluate the protection efficiency of both products. Molecular Dynamics Simulations (MDs) were carried out to model the interaction mechanism and the adsorption behavior of {10−3 M NPD or NPDM/α-Fe2O3(111)/0.5 M H2SO4} interfaces. Results derived from experimental (OCP, WL, PP and EIS) methods were supported by the theoretical investigations.