Surface Oxidation Research Articles

Corrosion Behavior of 20G and TP347H in Molten LiCl-NaCl-KCl Salt.

The corrosion behavior of 20G and TP347H materials was investigated in molten LiCl-NaCl-KCl salt. The corrosion rates of these materials in molten chloride salt are high and are strongly affected by the alloying surface oxide formation. The 20G shows uniform surface corrosion with almost no protective oxide formation on the surface. In contrast, the austenitic steel TP347H exhibits better corrosion resistance in molten chloride salts due to its high Cr content. Owing to the highly corrosive nature of molten chloride salts, the Cl- in molten salt could react with oxides and alloy, inducing intergranular corrosion of austenitic steel in molten chloride salt environments.

Redox behavior of unsubstituted cobalt phthalocyanine in nanostructured Langmuir-Schaefer films

Although the properties of unsubstituted metal tetrapyrroles in solutions have received attention in numerous work, the physico-chemistry of their thin films remains poorly investigated. In this work, we constructed thin films of unsubstituted cobalt phthalocyanine on the surface of quartz plates and indium tin oxide (ITO) electrodes using the Langmuir-Schaefer (LS) and drop casting techniques. In LS films, CoPc species are involved in strong intermolecular interactions, which result in formation of CoPc nanostructures and prominent changes in the ultraviolet-visible spectrum. Electrochemical reduction of CoPc in LS films at −0.9 V (versus silver chloride electrode) results in formation of Co(I) species. In contrast to the highly reactive nature of Co(I)Pc in solution, these species generated in thin films are relatively resistant to dioxygen due to the dense packing of CoPc units. These findings can further the development of CoPc-based resistive sensors utilizing not only common Co(II), but also Co(I) species, which may possess different sensitivity toward analytes.

Spatiotemporal variability of surface ozone and associated meteorological conditions over the Arabian Peninsula

This study investigates the spatiotemporal variability of surface ozone (O3) over the Arabian Peninsula (AP) between 2005 and 2019, focusing on the Arabian Gulf (AG). The analysis explores the relationship between surface O3 data from the Copernicus Atmosphere Monitoring Service (CAMS) with boundary layer height (BLH), 2 m temperature (T2M), downward ultraviolet radiation at the surface (UVB), and 10 m wind speed (WS) and direction from the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5). Also, the study considers Carbon Monoxide (CO) and Nitrogen Oxides (NOx) surface emissions from the Tropospheric Chemical Reanalysis version 2 (TCR-2). Furthermore, it investigates the impact of El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on surface O3 variations on a seasonal scale. Surface O3 observations from 15 ground-based stations across the AP were used to evaluate CAMS-O3, showing a good agreement between CAMS and the observations. The analysis of mean diurnal variations of CAMS-O3 and ERA5 reveals that surface O3 is highest over the eastern parts of the AP, mainly the AG, peaking during summer, followed by spring, fall, and winter. This seasonal cycle is also observed, to a large degree, in BLH, T2M, UVB, and WS. The results also reveal insignificant correlation between surface O3 and ENSO, but stronger correlation with IOD, especially over the AG during summer and fall. The analysis indicates that elevated T2M and UVB during daytime and elevated BLH during nighttime are significant contributors to increased levels of O3 over the AG.

Microstructural evolution and thermal stability of Al–Zn–Mg–Cu–Si–Zr alloy fabricated via spark plasma sintering

We investigated the microstructural evolution and thermal stability of Al–Zn–Mg–Cu–Si–Zr alloy fabricated via high-energy ball milling (HEBM), spark plasma sintering (SPS), and heat treatment at 500 °C. HEBM induces the Al2O3 surface oxide to penetrate the powder interior, and the surface oxide is transformed into MgO particles along the grain boundaries during the sintering process, depleting the Mg solid solution in the matrix. HEBM caused the formation of Mg-free phases and accelerated the transformation of Zr into the Si2Zr phase. Heat treatment promoted the transformation of Zr to the Si2Zr phase in the Zr/Si2Zr coupled particles and caused the coarsening of the secondary phase. The MgO particles present along the grain boundaries suppressed the grain growth of the sintered alloy until fine MgO was transformed into coarse MgAl2O4. The microhardness of the sintered alloy was significantly increased by the application of HEBM, mainly owing to strengthening by grain refinement and oxide dispersion. The Al–Zn–Mg–Cu–Si–Zr sintered alloy maintained high microhardness values even after heat treatment at 500 °C for 168 h, indicating the excellent thermal stability of the alloy compared to the Zr-free Al–Zn–Mg–Cu–Si alloy.

Polystyrene microplastics facilitate formation of refractory dissolved organic matter and reduce CO2 emissions

Microplastics, as a type of anthropogenic pollution in aquatic ecosystems, affect the carbon cycle of organic matter. Although some studies have investigated the effects of microplastics on dissolved organic matter (DOM), the impact of alterations in the chemical properties of microplastics on refractory DOM and carbon release remains unclear. Here, we observed that microplastic treatments (e.g., polystyrene, PS) altered the composition and function of microbial community, notably increasing the abundance of microbial families involved in consuming easily degradable organic matter. During the process in which microbial community decomposed organic matter into DOM, PS underwent surface oxidation. The oxidized PS aggregated with DOM and microorganisms through electrostatic interactions and chemical bonds. Moreover, these interactions between oxidized PS and microbial community affect the utilization of organic matter, resulting in a significant decrease in CO2 emissions. Specifically, total CO2 emissions decreased by approximately 23.76 % with 0.1 mg/L PS treatment and by 44.97 % with 10 mg/L PS treatment compared to those in PS-free treatments over the entire reaction. These findings underscored the significance of the chemical properties of PS in the interactions among DOM and microorganisms, emphasizing the potential impact of PS microplastics on the carbon cycle in ecosystems.

Insights into Electrochemical CO2 Reduction on Metallic and Oxidized Tin Using Grand-Canonical DFT and In Situ ATR-SEIRA Spectroscopy.

Electrochemical CO2 reduction (CO2R) to formate is an attractive carbon emissions mitigation strategy due to the existing market and attractive price for formic acid. Tin is an effective electrocatalyst for CO2R to formate, but the underlying reaction mechanism and whether the active phase of tin is metallic or oxidized during reduction is openly debated. In this report, we used grand-canonical density functional theory and attenuated total reflection surface-enhanced infrared absorption spectroscopy to identify differences in the vibrational signatures of surface species during CO2R on fully metallic and oxidized tin surfaces. Our results show that CO2R is feasible on both metallic and oxidized tin. We propose that the key difference between each surface termination is that CO2R catalyzed by metallic tin surfaces is limited by the electrochemical activation of CO2, whereas CO2R catalyzed by oxidized tin surfaces is limited by the slow reductive desorption of formate. While the exact degree of oxidation of tin surfaces during CO2R is unlikely to be either fully metallic or fully oxidized, this study highlights the limiting behavior of these two surfaces and lays out the key features of each that our results predict will promote rapid CO2R catalysis. Additionally, we highlight the power of integrating high-fidelity quantum mechanical modeling and spectroscopic measurements to elucidate intricate electrocatalytic reaction pathways.

Efficient Air-Processed MA-Free Perovskite Solar Cells by SH-Based Silane Interface Modification.

Air-processed perovskite solar cells (PSCs) with high photoelectric conversion efficiency (PCE) can not only further reduce the production cost but also promote its industrialization. During the preparation of the PSCs in ambient air, the contact of the buried interface not only affects the crystallization of the perovskite film but also affects the interface carrier transport, which is directly related to the performance of the device. Here, we optimize the buried interface by introducing 3-mercaptopropyltrimethoxysilane (MPTMS, (CH3O)3Si(CH2)3SH) on the nickel oxide (NiOx) surface. The crystallization of the perovskite film is improved by enhancing surface hydrophobicity; besides, the SH-based functional group of MPTMS passivates the uncoordinated lead at the interface, which effectively reduces the defects at the bottom interface of perovskite and inhibits the nonradiative recombination at the interface. Moreover, the energy level between the NiOx layer and the perovskite layer is better matched. Based on multiple functions of MPTMS modification, the open circuit voltage of the device is obviously improved, and efficient air-processed methylamine-free (MA-free) PSCs are realized with PCE reaching 21.0%. The device still maintains the initial PCE of 85% after 1000 h aging in the glovebox. This work highlights interface modification in air-processed MA-free PSCs to promote the industrialization of PSCs.

Epoxy-ended hyperbranched polymer-grafted graphene oxide for cold-mixed epoxy asphalt modification

ABSTRACT To improve the compatibility of asphalt-epoxy and mechanical properties of cold-mixed epoxy asphalt (CEA), epoxy-ended hyperbranched polymer (EHBP) was grafted on the surface of graphene oxide (GO) nanoplates to synthesize GOEHBP as a compatilizer. The chemical structures and micromorphology of GOEHBP were analysed through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, thermo gravimetric analysis and transmission electron microscopy. The CEA modified by EHBP and GOEHBP was investigated by tensile test, dynamic thermomechanical analysis, viscosity test, fluorescence microscope experiment, FTIR analysis and XPS analysis. The results showed that the EHBP was successfully grafted onto the surface of GO via chemical reaction, and the GO was partially reduced. The mechanical properties of CEA modified by EHBP are obviously improved, and the elongation at break was increased by 74.5%. The glass transition temperature of CEA modified by GOEHBP was increased to 62.58°C. At high temperature (≥40°C), the E′ of CEA modified by GOEHBP was larger than that of the CEA, indicating that GOEHBP can improve the high-temperature deformation resistance of CEA. The addition of GOEHBP can improve the compatibility of asphalt-epoxy, thus improving the toughness of CEA.

Vacancy Ordering in Ultrathin Copper Oxide Films on Cu(111).

Oxide thin films grown on metal surfaces have wide applications in catalysis and beyond owing to their unique surface structures compared to their bulk counterparts. Despite extensive studies, the atomic structures of copper surface oxides on Cu(111), commonly referred to as "44" and "29", have remained elusive. In this work, we demonstrated an approach for the structural determination of oxide surfaces using element-specific scanning tunneling microscopy (STM) imaging enhanced by functionalized tips. This approach enabled us to resolve the atomic structures of "44" and "29" surface oxides, which were further corroborated by noncontact atomic force microscopy (nc-AFM) measurements and Monte Carlo (MC) simulations. The stoichiometry of the "44" and "29" frameworks was identified as Cu23O16 and Cu16O11, respectively. Contrary to the conventional hypothesis, we observed ordered Cu vacancies within the "44" structure manifesting as peanut-shaped cavities in the hexagonal lattice. Similarly, a combination of Cu and O vacancies within the "29" structure leads to bean-shaped cavities within the pentagonal lattice. Our study has thus resolved the decades-long controversy on the atomic structures of "44" and "29" surface oxides, advancing our understanding of copper oxidation processes and introducing a robust framework for the analysis of complex oxide surfaces.

Electrochemical Stability of MXenes in Water Based on Constant Potential AIMD Simulations.

MXene has been recently explored as promising electrocatalytic materials to accelerate the electrocatalytic process for hydrogen evolution, but their dynamic stability under electrochemical conditions remains elusive. Here we performed first-principles ab initio molecular dynamics calculations to reveal the electrochemical stability of Ti2CTx MXene in different aqueous environments. The results revealed the high vulnerability of the pure and vacancy-defected Ti2CO2 MXene towards water attack, leading to surface oxidation of MXene under neutral electrochemical conditions that formed adsorbed oxygen species to Ti and the dissociated proton in solution. The surface oxidation of Ti2CO2 could be prevented in the acid condition or in the neutral condition under the negative potential. Differently, the fully F- or OH-functionalized Ti2CF2 and Ti2C(OH)2 as well as the mixed functionalized Ti2C(O0.5OH0.5)2 and Ti2CO1.12F0.88 are highly stable under various electrochemical conditions, which can effectively prevent close contact between water molecules and surface Ti atoms via electronic repulsion or steric hindrance. These findings provide atomic level understanding of the aqueous stability of MXene and provide useful strategies to prevent degradation and achieve highly stable MXenes.

A comparative study of electrochemical stability and biocompatibility of TiN nanowires and thin films for neural-electrode application

Neural-electrode devices with adequate charge injection capacity, long operating lifetime and excellent biocompatibility with interfaced tissues are essential to treat chronic neurological disorders. The device's efficiency hinges on the electrochemical properties of the electrode material, prompting extensive research on diverse material surfaces. Here, we investigate the electrochemical stability and biocompatibility of titanium nitride (TiN) nanowires (NWs) synthesized previously through the novel plasma enhanced chemical vapor deposition (PECVD) utilizing lower temperature as compared to conventional methods. These TiN-NWs were compared with TiN thin films, shedding light on their respective performances. TiN-NWs electrode revealed far superior electrochemical stability over 1000 cycles, achieving a capacitance retention of 93 % as compared to 68 % to that of TiN film electrode, under ambient conditions with dissolved oxygen. Additionally, impedance of TiN-NWs showed almost no change with cycling as compared to the film electrode. Moreover, our in-vitro cell culture spanning 20 days exhibited excellent biocompatibility for both substrates. Interestingly, cell distribution on the NWs appeared more dispersed with fewer clusters, potentially facilitating controlled electrical stimulation. These findings not only highlights the potential use of TiN-NWs for chronic stimulation of neurons, but also shows that surface morphology has a potential effect in minimising surface oxidation and improving electrochemial performance of the material.

Enhanced field-effect mobility (>250 cm2/V·s) in GaN MOSFETs with deposited gate oxides via mist CVD

We report an enhanced field-effect mobility (>250 cm2·V−1·s−1) in GaN MOSFETs. High mobility was achieved by reducing the oxidation of the GaN surface, which was a major factor affecting channel mobility in GaN MOSFETs. Among various gate oxide deposition methods, mist CVD using O3 suppressed GaN surface oxidation. The best field-effect mobility was observed using mist CVD-deposited gate oxides, achieving a peak mobility of 266 cm2·V−1·s−1 with a high threshold voltage of 4.8 V.

The effect of surface states accumulation on photo-electrochemical performances of Bi24Fe2O39 grown by supersonic beams

Holes accumulation on the surface of bismuth ferrite oxides (BFO) photoanodes for photoelectrochemical (PEC) water splitting (WS) is one of the major issues limiting the overall cell efficiency. However, among the various BFO crystal structures, no evidence of this mechanism has been reported for Bi24Fe2O39, a scarcely investigated phase. Herein we characterize the morphological, structural and PEC properties of 100 nm thick nanogranular films of a Bi24Fe2O39 single phase synthesized by supersonic cluster beam deposition. The films were tested as photoanodes for the WS reaction in KOH and Na2SO4 + Na2SO3 electrolytes. The PEC data provide direct evidence of holes accumulation on the surface of the material with increasing applied biases. The interesting performances of this material at low biases suggest a possible use as photocatalyst under visible light irradiation.

Correlating gas permeability and morphology of bio-based polyether-block-amide copolymer membranes by IR nanospectroscopy

Correlating gas permeability and morphology of bio-based polyether-block-amide copolymer membranes by IR nanospectroscopy

Unveiling the orientation growth mechanism and solar-blind response performance of β-Ga2O3 (100) film on SiC substrate with AlN buffer layer

Optimizing the orientation of β-Ga2O3 has emerged as an effective strategy to design high-performance β-Ga2O3 device, but the orientation growth mechanism and approach have not been revealed yet. Herein, by employing AlN buffer layer, the highly preferred orientation of β-Ga2O3 (100) film rather than (-201) film is realized on 4H-SiC substrate at low sputtering power and temperature. Because β-Ga2O3 (100) film exhibits a slower growth speed than (-201) film, the former possesses the higher dangling bond density and the lower nucleation energy, and a large conversion barrier exists between these two orientations. Moreover, the AlN buffer layer can suppress the surface oxidation of the 4H-SiC substrate and eliminate the strain of β-Ga2O3 (100) film, which further reduces the nucleation energy and enlarges the conversion barrier. Meanwhile, the AlN buffer layer can increase the oxygen vacancy formation energy and decrease the oxygen vacancy concentration of β-Ga2O3 (100) film. Consequently, the solar-blind photodetector based on the oriented film exhibits the outstanding detectivity of 1.22 × 1012 Jones and photo-to-dark current ratio of 1.11 × 105, which are the highest among the reported β-Ga2O3 solar-blind photodetector on the SiC substrate. Our results offer in-depth insights into the preferred orientation growth mechanism, and provide an effective way to design high-quality β-Ga2O3 (100) orientation film and high-performance solar-blind photodetector.

Corrosion behavior of Cr/RE alloyed rebar in carbonated simulated concrete pore solutions with chloride ions

Corrosion behavior of Cr/RE alloyed rebar in carbonated simulated concrete pore solutions with chloride ions

Effects of low-molecular-weight organic acids on the transformation and phosphate retention of iron (hydr)oxides

The retention and mobilization of phosphate in soils are closely associated with the adsorption of iron (hydr)oxides and root exudation of low-molecular-weight organic acids (LMWOAs). This study investigated the role of LMWOAs in phosphate mobilization under incubation and field conditions. LMWOAs-mediated iron (hydr)oxide transformation and phosphate adsorption experiments revealed that the presence of LMWOAs decreased the phosphate adsorption capacity of iron (hydr)oxides by up to ~74 % due to the competition effect, while LMWOAs-induced iron mineral transformation resulted in an approximately six-fold increase in phosphate retention by decreasing the crystallinity and increasing the surface reactivity. Root simulation in rhizobox experiments demonstrated that LMWOAs can alter the contents of different extractable phosphate species and iron components, leading to 10 % ~ 30 % decreases in available phosphate in the near root region of two tested soils. Field experiments showed that crop covering between mango tree rows promoted the exudation of LMWOAs from mango roots. In addition, crop covering increased the contents of total phosphate and available phosphate by 9.08 % ~ 61.20 % and 34.33 % ~ 147.33 % in the rhizosphere soils of mango trees, respectively. These findings bridge the microscale and field scale to understand the delicate LMWOAs-mediated balance between the retention and mobilization of phosphate on iron (hydr)oxide surface, thereby providing important implications for mitigating the low utilization efficiency of phosphate in iron-rich soils.

Capillarity interaction of NiTi melt with crucible oxides

The interaction of nitinol melt with Al2O3, ZrO2, BeO and Y2O3 oxides used as crucible materials has been studied. Capillary interaction has been monitored directly using the method of sessile drop with video and thermal imaging in 10-3torr vacuum at 1350 °C. Nitinol melt drops have been formed in a high-density graphite dispenseror directly on the substrate surface. The contact angleson the surface of polished oxides have been obtained. The contact angles established within 30 sec increase in the sequence Al2O3, ZrO2, BeO and Y2O3 from 30° to 70°. The corrosion resistance of the oxides has been studied for cross-sections using scanning electron microscopy with energy dispersion analysis. The phase composition at the ceramic/melt boundary has been studied using transmission electron microscopy. Thermodynamic analysis of melt chemical interaction with oxides has been conducted within equilibrium concentration calculation.

A potential-controlled electrochromic visual biosensor based on distance readout for zearalenone detection

In this work, a potential-controlled electrochromic visual biosensor was developed for detecting zearalenone (ZEN) using a distance readout strategy. The sensor chip includes a square detection area and a folded signal output area created with laser etching technology. The detection area is modified with graphene oxide and ZEN aptamer, while Prussian blue (PB) is electrodeposited onto the signal output channel. When an appropriate voltage is applied, PB in the signal output area is reduced to colorless Prussian white (PW). The target ZEN molecules have the capability to release aptamers from graphene oxide (GO) surface in the detection area, resulting in a subsequent change in the potential of the visual signal output channel. This change determines the length of the channel that changes from blue to colorless, with the color change distance being proportional to the ZEN concentration. Using this distance readout strategy, ZEN detection within the range of 1 ng/mL to 300 ng/mL was achieved, with a detection limit of 0.29 ng/mL.

Low-loss α-tantalum coplanar waveguide resonators on silicon wafers: fabrication, characterization and surface modification

The performance of state-of-the-art superconducting quantum devices is currently limited by microwave dielectric loss at different interfaces. α-tantalum is a superconductor that has proven effective in reducing dielectric loss and improving device performance due to its thin low-loss oxide. Here, we demonstrate the fabrication of high-quality factor α-tantalum coplanar-waveguide resonators directly on pristine 300 mm silicon wafers over a variety of metal deposition conditions and perform a comprehensive material and electrical characterization study. Additionally, we apply a surface treatment based on hydrofluoric acid that allows us to modify different resonators surfaces, leading to a reduction in two-level system loss in the devices by a factor of three. This loss reduction can be entirely attributed to the removal of surface oxides. Our study indicates that large scale manufacturing of low-loss superconducting circuits should indeed be feasible and suggests a viable avenue to materials-driven advancements in superconducting circuit performance.