Passive Oxide Layer Research Articles

Growth of gallium cerium oxide passivation layer on 4H-Silicon carbide substrate and its metal-oxide-semiconductor characteristics

Gallium cerium oxide (GaxCeyOz) passivation layer was successfully grown on 4H-silicon carbide (SiC) through postdeposition annealing at 800 °C in nitrogen-oxygen-nitrogen (N2–O2–N2) ambient. The gracing incident X-ray diffraction and ultraviolet–visible spectrophotometer measurements have confirmed the successful incorporation of Ga3+ cation into the CeO2 lattice to form the ternary GaxCeyOz passivation layer. In addition, the thicknesses of GaxCeyOz passivation layer and silicon dioxide (SiO2) interfacial layer (IL) were determined using field-emission scanning electron microscopy and X-ray reflectivity characterizations. A high dielectric constant (k) value of 24.11 was attained for the investigated Al/GaxCeyOz/4H–SiC/Al metal-oxide-semiconductor (MOS) structure attributable to the nitrogen ions accumulating at the interface that have retarded the growth of SiO2 IL. Besides, the effective oxide charge, slow trap density, interface trap density, interface state density, as well as leakage current density-electric field characteristic of the investigated GaxCeyOz passivation layer on 4H–SiC substrate was presented in this work.

SURFACE MODIFICATION AND SURFACE COMPOSITES DEVELOPMENT TECHNIQUES FOR BIOCOMPATIBLE AND BIODEGRADABLE ALLOYS

The degradation control of implants has now become a most critical factor for investigation. The rapid degradation or uncontrolled degradation of metals causes allergic reaction and implants failure. The biocompatibility and biodegradability of biometals are essential properties for the development of bioimplants. The biodegradation is the chemical reaction of implants metal with the surrounding body fluids. The gradual dilution of metal oxide with the body fluid is considered as a degradation. Magnesium, zinc, and iron metals are biodegradable metals. The biodegradability of as-cast metals is not capable of fulfilling the need of patients, therefore, degradation of implants is required to be in control. Many more research articles have been published on improvement of corrosion resistive implant surface by coating, passivation oxide layer, plasma spraying, electropolishing, blasting, chemical etching, laser treatment, heat treatment, severe plastic deformation (SPD), alloying, and development of surface composites. This paper critically reviewed the surface modification and surface composite fabrication techniques to improve the biodegradability, biocompatibility, and strength of implants.

Modulation of GaAs nanowire growth by pre-treatment of Si substrate using a Ga focused ion beam

We reveal a novel phenomenon observed after self-catalytic growth of GaAs nanowires (NWs) on Si(111) substrates treated with a Ga focused ion beam (FIB). Depending on the ion dose, NW arrays with various geometrical parameters can be obtained. A minor treatment of the substrate enables a slight increase in the surface density of NWs relative to an unmodified substrate area. As the ion dose is increased up to ∼0.1 pC μm−2, the growth of GaAs NWs and nanocrystals is suppressed. However, a further increase in the ion dose stimulates the crystal growth leading to the formation of extremely thin NWs (39 ± 5 nm) with a remarkably high surface density of up to 15 μm−2. Resting upon an analysis of the surface structure before and after stages of ion-beam treatment, ultra-high vacuum annealing and NW growth, we propose a mechanism underlying the phenomenon observed. We assume that the chemical interaction between embedded Ga ions and a native Si oxide layer leads either to the enhancement of the passivation properties of the oxide layer within FIB-modified areas (at low and middle ion doses), or to the etching of the passivating oxide layer by excess Ga atoms, resulting in the formation of pores (at high ion doses). Due to this behavior, local fabrication of GaAs NW arrays with a diverse range of characteristics can be implemented on the same substrate. This approach opens a new way for self-catalytic growth of GaAs NWs.

Bespoke Energetic Zeolite Imidazolate Frameworks-8 (ZIF-8)/Ammonium Perchlorate Nanocomposite: A Novel Reactive Catalyzed High Energy Dense Material with Superior Decomposition Kinetics

Aluminum is the universal fuel for solid propellants; however, its passive oxide layer could impede the full exploitation of its enthalpy. Meanwhile, common catalyst could not contribute to combustion enthalpy. This study shaded light on the multifunctional energetic metal-organic frameworks ZIF-8 with combustion enthalpy 21 KJ/g as high energy dense material as well as a novel catalyst for solid propellants. As-prepared ZIF-8 particles exhibited a highly crystalline structure with an average particle size of 40 nm. The performance of ZIF-8 as high-energy dense material was assessed to aluminum particles via integration into ammonium perchlorate (APC). ZIF-8/APC and Al/APC composites were prepared via the solvent–nonsolvent method; the decomposition enthalpy was investigated via DSC. ZIF-8 offered an increase in APC total decomposition enthalpy by 98.4%, to 39.11% for Al. ZIF-8 exhibited a superior catalytic behavior by lowering the APC high-temperature decomposition peak (HTD) by 81.48 °C compared to 70.3 °C for Al. The decomposition kinetics of ZIF-8/AP nanocomposite was investigated via Kissinger’s formula. The ZIF-8 offered a remarkable reduction in APC apparent activation energy at low-temperature decomposition peak and HTD peaks by peak by 16.5% and 30%, respectively. The superior catalytic performance of ZIF-8 was attributed to Zn+2 electron deficient centers with the exclusive formation of ZnO nanoparticles during combustion. ZIF-8 with gaseous decomposition products could boost specific impulses.

Probing the Corrosion Rates of Novel Titanium Substrates in a Simulated PEM Fuel Cell Environment

Metallic bipolar plates are often used in proton exchange membrane fuel cells (PEMFCs) due to their facile manufacturing process, high electrical and thermal conductivity, and mechanical strength. [1] Titanium is particularly popular due to its corrosion-resistive properties which come from a naturally occurring passive oxide layer on its surface. However, the naturally occurring passive film cannot fully withstand the acidic environment of an operating PEMFC. And inherently, without this protective layer; corrosion will inevitably occur. [2] Thicker oxide layers can be formed on the surface by exposing the titanium to elevated temperatures in the presence of oxygenIn this study, the corrosion resistance of commercially pure titanium with thermally grown oxidation layers and titanium directly coated with a commercial sub-oxide coating was investigated. The corrosion resistance of the various samples was examined with potentiostatic and potentiodynamic tests in sulfuric acid solution at various temperatures to simulate PEMFC conditions. The samples were also subjected to a novel accelerated stress test to evaluate long term durability under fuel cell vehicle startup and shutdown conditions.

Formulation and testing of a high-tin borosilicate nuclear waste glass for in-can melting

Borosilicate waste glasses were successfully developed to immobilize two high-level waste raffinate streams via an in-can melter process with an Inconel 601 canister at 1050 °C. Measured viscosity and crystallinity thermal profiles were within the targeted processing constraints for the in-can melter process. Measured chemical durability of the glass by ASTM C1285–21 (Method A), ranged from normalized loss of boron, NL(B) = 1.44 – 2.65 g·m−2, and NL(B) decreased with increased waste loading, accompanied by increased SnO2 crystallinity. Measured corrosion of the in-can melter canister by a glass melt showed that Inconel 601 performed well at 1100 °C for up to 500 hr. Resistance polarization measurements versus time revealed that Inconel 601 corrosion rates in (and by) glass melts decreased from an initial rate of 63 mm·y−1 down to 10.2 mm·y−1 after 137 h with increased duration, which was attributed to formation of an oxide passivation layer (mainly Cr2O3) at the alloy-glass interface.

Deposition current density-induced grain boundary engineering of electrodeposited cobalt coatings for enhanced electrochemical stability

ABSTRACT Cobalt coatings were electrodeposited at different deposition current densities (10 mA·cm−2, 20 mA·cm−2, 30 mA·cm−2, 40 mA·cm−2, 60 mA·cm−2) over mild steel substrate. The coating deposited at 30 mA·cm−2 showed the highest corrosion resistance (Rp = 7515Ω·cm2) due to a higher fraction of Low energy grain boundary constitution (i.e. coincidence site lattices (CSLs) and low angle grain boundaries (LAGB)) and exhibited higher fraction of stabler Co3O4 passive oxide layer. The coatings electrodeposited at 60 mAcm−2 exhibited lower corrosion resistance (Rp = 1304 Ω·cm2) due to a higher fraction of high-angle grain boundaries and a higher fraction of relatively lesser stable Co(OH)2.

Enhanced performances of a-IGZO TFTs with oxide passivation layers fabricated by hollow cathode assisted PLD

Pulsed laser deposition (PLD) and two-step thermal annealing are combined to fabricate MgO, TiO2, Y2O3, Al2O3, ZrO2 and HfO2 passivation layers on a-IGZO TFTs. The influences of the passivation layers on the electrical properties are investigated. It is found that conventional PLD is sufficient to deposit high-quality Y2O3 and ZrO2 passivation layers, but hollow cathode assisted PLD (HC-PLD) should be employed to solve the oxygen deficiency in MgO, TiO2, Al2O3, and HfO2 thin films by oxygen plasma. Furthermore, two-step annealing is adopted to improve the performances of the devices: Firstly, a-IGZO thin films are pre-annealed to enhance the carrier mobility. Secondly, the passivation layers are deposited on a-IGZO and the whole structures are post-annealed to endow the good on-off performance. The sharp a-IGZO/passivation interfaces remain after thermal annealing. The Hall mobility is mainly restricted by the scattering of metal ions at the a-IGZO/passivation interface. TiO2 passivated devices exhibit the highest Hall mobility of 16.7 cm2V−1s−1, owing to the smaller cation charge. The threshold voltage stability under positive gate bias is dependent on the metal-oxygen bond strength in the passivation layers. ZrO2 passivated devices have the lowest threshold voltage shift, beneficial from the strong Zr-O bonds. The subthreshold performance and the stability under illumination are determined by the oxygen vacancies at a-IGZO/passivation interfaces and ZrO2 passivated devices exhibit the lowest subthreshold swing and the best illumination stability.

Investigation of the regeneration of the passive surface oxide layer of TiAl6V4 alloy printed by WAAM technology using different electrochemical test methods

AbstractThe kinetics of oxide layer formation on surface of Ti6Al4V alloy samples is a very important property especially if their application as medical implants is planned. Damaged protective surface layer usually heals in ambient condition however; during the self‐healing process toxic species can get into the surrounding living tissue. In our experiment the kinetics of the healing process proceeding at 3D printed alloy surface has been studied using electrochemical methods, among them scanning electrochemical microscopy. More than 40 min. time period was found long enough for total healing.

A comprehensive review on synergistic and individual effects of erosion–corrosion in ferrous piping materials

Abstract The degradation of materials due to erosion–corrosion occurs on the components that handle particle-laden corrosive slurry. The combined attack of mechanical erosion and corrosion shows increased material loss than the individual action of erosion and corrosion. The synergy accelerates material removal by eroding the corroded surface layer and corroding the surface due to the elimination of the passivating oxide layer by erosion. The synergism of erosion–corrosion is found to be more complex. Further, the coupled effect of mechanical erosion and electrochemical corrosion and the factors influencing erosion–corrosion still needs to be fully investigated. This review aims to provide a general and detailed summary of the interaction between erosion and corrosion of materials for the applications of pump impellers, pipelines for desalination, and oil and gas transportation. Importance is also given to the factors influencing erosion–corrosion, such as erodent particle properties (hardness, size, and shape), slurry properties (particle concentration, pH value, temperature), and flow characteristics (impingement angle, velocity). The various erosion models and the most used apparatus have also been reviewed.

Understanding the enhanced corrosion performance of two novel Ti-based biomedical high entropy alloys

The microstructure and corrosion behavior of two novel biomedical high entropy alloys (HEA)s, namely Hf27Nb12Ta10Ti23Zr28 and Hf30Nb14Ta10Ti28Zr18 that were previously designed utilizing machine learning, were investigated in depth. The microstructure of the alloys was determined to be dendritic, with some elemental segregations governed by the solidification kinetics occurring during the arc-melting process. Static immersion experiments were carried out in artificial saliva (AS) and simulated body fluid (SBF) to investigate the ion release behavior of the HEAs and reveal the dissolution kinetics of the passive film forming on the surface. The composition of the corresponding surface oxide layers was examined using X-ray photoelectron spectroscopy, which provided detailed insight into the stability of passive oxide layers and sub-oxide formation. Potentiodynamic polarization experiments performed in AS and SBF at 37 ºC demonstrated that both HEAs exhibit superior corrosion behavior as compared to the CoCrMo alloy, one of the conventional metallic implant materials of choice.

Synthesis of Co(OH)F@Al nanobelt array on various substrates for pyro-MEMS

Metastable intermolecular composites (MICs) composed by solid fuel and oxidizer can undergo violent redox reaction with release of huge amount of energy. Integration of MIC with microelectromechanical-system (MEMS) is of particular interest to meet the demand of miniaturization in modern pyrotechnic devices. Meanwhile, fluorine-containing oxidizers are favored in MIC owing to their potential to fluorinate the oxide passivation layer in common elemental fuels. Herein, Co(OH)F was employed for the first time as a novel fluorine-containing oxidizer in Al-based MIC. Vertically aligned Co(OH)F@Al nanobelt arrays (NAs) with tunable morphology were successfully fabricated on a variety of substrates (Si, glass, Ni, Cu, Ti) via a facile hydrothermal synthesis followed by electron beam evaporation. The whole fabrication process is highly compatible with modern MEMS technology. The thermal behavior of pure Co(OH)F and Co(OH)F@Al composites was comprehensively investigated by TG-DSC and a series of ex-situ and in-situ characterization. It was found that, Co(OH)F@Al composites achieved main exothermal reaction before melting of Al regardless of morphology and equivalence ratio. This feature is attributed to the etching of Al2O3 shell by HF released from Co(OH)F which is termed as pre-ignition reaction. To elucidate the effect of micro-structure on the actual specific heat release, we proposed a phenomenological model which can be a reference for future micro-structure design of MIC.

Fabrication of sub-5 nm uniform zirconium oxide films on corrugated copper substrates by a scalable polymer brush assisted deposition method

We demonstrate a polymer brush assisted approach for the fabrication of continuous zirconium oxide (ZrO2) films over large areas with high uniformity (pin-hole free) on copper (Cu) substrates. This approach involves the use of a thiol-terminated polymethyl methacrylate brush (PMMA-SH) as the template layer for the selective infiltration of zirconium oxynitrate (ZrN2O7). The preparation of a highly uniform covalently grafted polymer monolayer on the Cu substrate is the critical factor in fabricating a metal oxide film of uniform thickness across the surface. Infiltration is reliant on the chemical interactions between the polymer functional group and the metal precursor. A following reductive H2 plasma treatment process results in ZrO2 film formation whilst the surface Cu2O passive oxide layer was reduced to a Cu/Cu2O interface. Fundamental analysis of the infiltration process and the resulting ZrO2 film was determined by XPS, and GA-FTIR. Results derived from these techniques confirm the inclusion of the ZrN2O7 into the polymer films. Cross-sectional transmission electron microscopy and energy dispersive X-ray mapping analysis corroborate the formation of ZrO2 layer at Cu substrate. We believe that this quick and facile methodology to prepare ZrO2 films is potentially scalable to other high-κ dielectric materials of high interest in microelectronic applications.

Corrosion Behavior and Bio-Functions of the Ultrafine-Grained Ti6Al4V-5Cu Alloy with a Dual-Phase Honeycomb Shell Structure in Simulated Body Fluid.

Titanium alloys are widely used in biomedical applications. However, cases of implant failure due to fatigue fracture and bacterial infection are common. In addition, implants are susceptible to metal ions (Al, V) released by long-term exposure to human body fluids, which causes neuropathy, mental disorders, and other diseases. Thus, development of novel materials to achieve long-term safety of implants is currently a research hotspot. Recently, our research group has developed an ultrafine-grained Ti6Al4V-5Cu alloy with a unique "dual-phase honeycomb shell" (DPHS) structure, which possesses high fatigue strength and stability. This study further affirmed its higher corrosion behavior, antibacterial properties, and cytocompatibility compared to the coarse-grained Ti6Al4V and Ti6Al4V-5Cu alloys. The ultrafine-grained structure of Ti6Al4V-5Cu having DPHS increased the proportion of phases (Cu-rich phases, β-phase, and Ti2Cu intermetallic phase) with a lower surface potential. It was observed that the developed microstructure was conducive to a stable configuration of the oxide (passive) layer on the alloy surface. In addition, the low-phase interfacial energies of the ultrafine-grained structure with DPHS even facilitated the improvement of the denseness of the protective passive film and eventually enhanced the corrosion behavior. Besides, the fine-Cu-rich phases and the micro-galvanic couples formed between them and the matrix significantly increased the contact frequency of bacteria, thus increasing the contact sterilization efficiency of the ultrafine-grained Ti6Al4V-5Cu alloy. These results showed that the new ultrafine-grained Ti6Al4V-5Cu alloy has excellent corrosion resistance and biological functions for clinical application.

Corrosion of a spark plasma sintered Fe-Cr-Mo-B-C alloy in 3.5% NaCl solution

In this study, the corrosion behavior of a Fe-Cr-Mo-B-C alloy, fabricated by spark plasma sintering of an amorphous alloy powder, in 3.5% NaCl solution was analyzed. Electrochemical impedance spectroscopy and potentiodynamic polarization are techniques which were used for electrochemical performance estimation of samples and the results were further compared with conventional alloys: 1080 carbon steel and 304 stainless steel. Corrosion surface products were characterized through Scanning electron microscopy, Energy dispersive x-ray spectroscopy and X-ray photoelectron spectroscopy. Specimens sintered at 800℃ (S1-800) had achieved 94% densification approximately while the sample sintered at 900℃ (S2-900), had densified more which was 98% approximately. S2-900 had better corrosion resistance than S1-800 while in comparison to conventional alloys; it was inferior to 304 stainless steel. It was concluded that the increase in density of sintered samples favoured the formation of more uniform surface products and enhanced the formation of the passive chromium oxide (Cr2O3) layer.

Transition metal nanoparticles composite Al(OH)3 catalysts for hydrogen generation of Al/H2O system

BackgroundEnhanced reaction of Al and water through catalysts is an excellent method for hydrogen generation. The generation of hydrogen is closely connected to the activity of catalysts. MethodsThis work prepares a highly active metal-composite aluminum hydroxide (MCAH) catalyst by a simple co-precipitation method. The metallic nanoparticles are Ni, Co, and Ag. The MCAH catalyst exhibits a robust catalytic effect and significantly promotes the reaction of Al and water by decreasing the induction time. Characterization using powder X-ray diffraction, field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) adsorption analysis show that the metallic nanoparticles are attached to the surface of aluminum hydroxide, increasing the catalytic activity, which is considered to be assistant to the generation of hydrogen. Significant findingsThe high catalytic activity could be due to the high specific surface area (such as Ni-Al(OH)3 for 144.1 m2/g) and stability. Furthermore, the dissociation of water molecules on the surface of the catalyst and the micro galvanic interaction between the metals and the Al(OH)3 could promote the hydration of the passive oxide layer on the surface of Al particles. Therefore, accelerate hydrogen generation.

Exotic Inverse Kinetic Isotopic Effect in the Thermal Decomposition of Levitated Aluminum Iodate Hexahydrate Particles

Aluminum iodate hexahydrate ([Al(H2O)6](IO3)3(HIO3)2; AIH) represents a novel, oxidizing material for energetic applications. Recently, AIH was synthesized to replace the aluminum oxide passivation layer of aluminum nanoenergetic materials (ALNEM). The design of reactive coatings for ALNEM-doped hydrocarbon fuels in propulsion systems requires fundamental insights of the elementary steps of the decomposition of AIH. Here, through the levitation of single AIH particles in an ultrasonic field, we reveal a three-stage decomposition mechanism initiated by loss of water (H2O) accompanied by an unconventional inverse isotopic effect and ultimate breakdown of AIH into gaseous elements (iodine and oxygen). Hence, AIH coating on aluminum nanoparticles replacing the oxide layer would provide a critical supply of oxygen in direct contact with the metal surface thus enhancing reactivity and reducing ignition delays, further eliminating decades-old obstacles of passivation layers on nanoenergetic materials. These findings demonstrate the potential of AIH to aid in the development of next-generation propulsion systems.

Capture-reduction mechanism for promoting Cr(VI) removal by sulfidated microscale zerovalent iron/sulfur-doped graphene-like biochar composite

The application of microscale zerovalent iron (mZVI) in the removal of Cr(VI) from water is plagued with the readily formation of oxide passivation layer. In this study, we propose a “capture-reduction” mechanism to enhance the Cr(VI) removal performance of mZVI under anaerobic condition through dual modification, i.e., sulfidation and construction of composite with sulfur-doped graphene like biochar (SGB). The S-mZVI/SGB has a Cr(VI) removal capacity of 70.2 mg·g− 1 at circumneutral pH, which is 56 times of that of mZVI. The 1,10-phenanthroline shielding experiments indicate that the contribution of Fe(II) to Cr(VI) removal is only 17.6%. Density-theory-functional (DFT) calculation results indicate that sulfur doping could significantly promote the adsorption of Cr(VI) on SGB nanosheets. The mechanism study confirmed the “capture-reduction” Cr(VI) removal mechanism, whereby the SGB nanosheets capture Cr(VI) ions and receive electrons from Fe0 to reduce Cr(VI) to Cr(III). Considering its advantages such as low cost and easy preparation, the S-mZVI/SGB composite is a promising green material for the removal of Cr(VI) from water.Graphical

Ti-15Zr and Ti-15Zr-5Mo Biomaterials Alloys: An Analysis of Corrosion and Tribocorrosion Behavior in Phosphate-Buffered Saline Solution.

It is crucial for clinical needs to develop novel titanium alloys feasible for long-term use as orthopedic and dental prostheses to prevent adverse implications and further expensive procedures. The primary purpose of this research was to investigate the corrosion and tribocorrosion behavior in the phosphate buffered saline (PBS) of two recently developed titanium alloys, Ti-15Zr and Ti-15Zr-5Mo (wt.%) and compare them with the commercially pure titanium grade 4 (CP-Ti G4). Density, XRF, XRD, OM, SEM, and Vickers microhardness analyses were conducted to give details about the phase composition and the mechanical properties. Additionally, electrochemical impedance spectroscopy was used to supplement the corrosion studies, while confocal microscopy and SEM imaging of the wear track were used to evaluate the tribocorrosion mechanisms. As a result, the Ti-15Zr (α + α' phase) and Ti-15Zr-5Mo (α″ + β phase) samples exhibited advantageous properties compared to CP-Ti G4 in the electrochemical and tribocorrosion tests. Moreover, a better recovery capacity of the passive oxide layer was observed in the studied alloys. These results open new horizons for biomedical applications of Ti-Zr-Mo alloys, such as dental and orthopedical prostheses.

Exploring Electrical Conductivity of Thiolated Micro‐ and Nanoparticles of Gallium

Nano‐/microparticles of gallium (Ga), as a low‐melting‐point metal, are extensively used in the fields of soft electronics and sensors to provide thermal and electrical conductivity. However, a passivating oxide layer can be formed on the surface of Ga nano‐/microparticles during the synthesis process. This oxide layer is removed by a secondary sintering step, especially mechanical sintering, which is generally not a controllable process, and compromises the integrity of the system. Herein, thiol molecules, 1‐butanethiol, thiophenol, and 4‐mercaptopyridine, that can functionalize the surface of Ga via sonication to reduce the oxidation of Ga surface are used. The resulting particles exhibit electrical conductivity based on metal–molecule junctions without the requirement for a sintering step. In particular, 4‐mercaptopyridine functionalized, thiolated Ga particles exhibit higher electrical conductivity compared to the other three thiolated Ga systems as the organic material conjugation provides conductive pathways for the mix. Subsequently, using these particle systems, soft devices are developed that can be used for gas, exhalation, and flex sensing. This study provides insights into the possibility of creating combinations of organic molecules with liquid metal‐based nano‐/microparticles to generate electrically conductive mixes and the prospects of fabricating multifunctional sensors.