Oxygen Diffusion Barrier Research Articles

Tailoring growth structure and oxidation performance of CrWN glass molding coating via Pt and Ir doping

Detailed electron microscopy investigations were performed to evaluate the effects of PtIr on the growth structure and oxidation resistance of the CrWN coating. The undoped CrWN coating showed an obviously coherent growth and a rough growth texture with a roughness value of 13.80 nm. The doped PtIr atoms induced a prominent structural modification on the CrWN coating and effectively inhibited the coherent growth, leading to a smoother texture and a reduced roughness value of 4.75 nm. The CrWN coating exhibited a loose texture that permitted the internal diffusion of oxygen and degraded its oxidation resistance and roughness, but these doped PtIr atoms had high chemical inertness, which enabled them to act as oxygen diffusion barriers, consequently improving the oxidation resistance and coarsening resistance of the CrWN–PtIr coating.

Performance of reactively co-sputtered titanium chromium nitride films in artificial saliva: Corrosion protection and reduction in the release of potentially toxic elements

Having been deposited on 304 stainless steel (SS304) substrates by RF reactive co-sputtering, 1 μm-thick Ti-Cr-N films were annealed at 400 °C and 700 °C. Accordingly, nitride phases of TiN and CrN, and as a result of the lost capability as an oxygen diffusion barrier, oxide phases of Fe2O3, Cr2O3, and TiO2 formed after the annealing process at 700 °C. For short-term immersion (1 h), the corrosion testing illustrated that the film annealed at 400 °C shows greater corrosion resistance than the other films and SS304. For long-term immersion (30 days), all the films demonstrated greater corrosion resistance than SS304, with the as-deposited film delivering the best performance. It was found that protective passivation layer formation, porosity closures, and surface characteristics such as pits, trenches, grooves, cracks, and protuberances govern the corrosion behavior differences. The surface micrographs imply that pitting corrosion and superficial filiform corrosion are among the underlying mechanisms affecting the surfaces. Finally, given the concerns about the capability of SS304 to release toxic elements such as chromium, it was determined that not only can Ti-Cr-N films increase the corrosion resistance of SS304 but also they can reduce the release of chromium by almost 67% in the long-term exposure.

Microstructure and properties of ZrO2/Ni3Al-Ni3Al double-layer coating on stainless steel prepared by powder sintering one-step forming process

ZrO2/Ni3Al-Ni3Al double-layer coating on stainless steel was prepared by powder sintering one-step forming process. The surface-interface morphologies, chemical element distribution and phase compositions of the coatings before and after thermal oxidation or hot corrosion were analyzed using scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The microstructure of the coating was Ni3Al matrix with dispersed ZrO2 particles, which was pure and compacted. The Ni3Al intermediate layer compactly formed between stainless steel substrate and ZrO2/Ni3Al composite coating, with good metallurgical bonding interfaces. The ZrO2/Ni3Al-Ni3Al double-layer coating exhibited a relatively high outmost microhardness of about 500 HV, and then gradually decreased from the coating to the substrate. When thermal oxidized or hot corroded at 1050 °C, a mixed oxide layer of NiO, Al2O3 and NiAl2O4 formed on the coating surface, which effectively acted as a diffusion barrier for oxygen and corrosive substances, and thus demonstrated the good protective effect of ZrO2/Ni3Al coating.

Oxygen diffusion barrier on interfacial layer formed with remote NH3 plasma treatment

An oxidation or nitridation treatment was performed on the interfacial layer (IL) with optimal oxidation state in order to form an oxygen diffusion barrier for Ge nMOSFET . Through the analysis of X-ray photoelectron spectroscopy and electrical characterization of Ge nMOSFET, the reaction mechanism and physical model were studied in details. The fewer interface traps and lower subthreshold swing can be achieved by forming oxygen diffusion barrier in an optimal IL with remote NH 3 plasma. As compared to devices with oxidation treatments , that improvement can be attributed to the nitrogen passivation and alloy-like interface formation. The proposed oxygen diffusion barrier with remote NH 3 plasma treatment on IL is a promising technique to improve the interface properties effectively without influencing equivalent oxide thickness for high performance Ge nMOSFET. • An interfacial layer buffer formation method is proposed. • An oxygen diffusion barrier can be formed by remote plasma treatment. • A n-channel Ge transistor can be enhanced by NH 3 plasma. • Reaction mechanism about oxygen diffusion is explained by material analysis.

Effects of h-BN/SiC ratios on oxidation mechanism and kinetics of C/C-BN-SiC composites

C/C-BN-SiC composite was prepared by ceramic slurry infiltration combined with resin impregnation and carbonization, and the matrix with continuous distributed self-healing phase was obtained. In this study, the kinetic characteristics and oxidation behavior of the composites with various h-BN/SiC ratios in the temperature range of 600∼1300°C were studied by combining the isothermal oxidation test with the kinetic model. The optimal h-BN/SiC ratio balances the thermal stability and fluidity of the oxidized product, which not only has high thermal stability and low oxygen permeability to acts as an oxygen diffusion barrier but also has a certain fluidity to seal defects.

Regulating the oxidation resistance of Cu-5Ag alloy by heat treatment

Improving the oxidation resistance without sacrificing the electrical conductivity of Cu is of great importance for researchers due to its widespread application. In this study, oxidation resistance of Cu-5 wt%Ag alloy under solution treatment (ST) and aging treatment (AT) were studied systematically. It has been confirmed that AT sample demonstrates considerably higher oxidation resistance than ST sample at elevated temperatures. The aging treatment enhanced the formation of a continuous Ag network along grain boundaries, which could act as a barrier for both inward diffusion of oxygen and outward diffusion of Cu along grain boundaries during oxidation.

Microstructure and Ablation Behavior of W/ZrC/SiC Coating on C/C Composites Prepared by Reactive Melt Infiltration and Atmospheric Plasma Spraying

A W/ZrC/SiC multilayer coating is prepared on carbon/carbon (C/C) composites by reactive melt infiltration (RMI) and atmospheric plasma spray (APS). The morphology and microstructure of the coating are characterized by scanning electron microscopy coupled with energy dispersive spectrometry (SEM‐EDS), X‐ray diffraction (XRD), and focused ion beam (FIB) and transmission electron microscopy (TEM). Microstructure analysis reveals that the gradient coatings exhibit smooth surface morphology, well‐defined interfaces, uniform thickness, and a highly dense architecture. After 60 s of ablation, the linear ablation rates (LARs) and mass ablation rates (MARs) of the coated composites stand at 2.58 × 10−3 mm s−1 and 5.25 × 10−3 g s−1, respectively. In general, the reason for the great ablation resistance of W/ZrC/SiC‐coated C/C composites is the comprehensive effect of the multilayer coating. The outer W coating is used as the first barrier layer to resist most thermal shocks. Then, the molten eutectics SiO2–ZrO2 formed in the ZrC/SiC layer at service temperature can fill the pores and act as a second diffusion barrier for oxygen and heat.

Oxidation behavior of Cr-coated zirconium alloy cladding in high-temperature steam above 1200\u2009\xb0C

Dense, uniform, and well-adhered chromium (Cr) coatings were deposited on zirconium (Zr) alloy claddings by using physical vapor deposition (PVD). The Cr-coated samples were tested at 1200 oC and 1300 oC, respectively, for different exposure time in water steam environment. Microstructures and compositions of the coating/substrate system after oxidation were characterized by X-ray diffraction, scanning electronic microscopy, and energy dispersion spectrometer. The microstructural results clearly demonstrated that Cr2O3 layer has been produced on the coating surface, acting as an oxygen diffusion barrier and concomitantly reducing the oxidation rate. The experimental results on weight gains soundly supported the microstructural findings that the Cr coatings could protect the Zr substrate from high-temperature steam oxidation, even at a temperature up to 1300 oC. Finally, the oxidation kinetics was theoretically analyzed and the underlying oxidation mechanism was also clarified.

Rewritable High-Mobility Electrons in Oxide Heterostructure of Layered Perovskite/Perovskite.

Perovskite oxide SrTiO3 can be electron-doped and exhibits high mobility by introducing oxygen vacancies or dopants such as Nb or La. A reversible after-growth tuning of high mobility carriers in SrTiO3 is highly desired for the applications in high-speed electronic devices. Here, we report the observation of tunable high-mobility electrons in layered perovskite/perovskite (Srn+1TinO3n+1/SrTiO3) heterostructure. By use of Srn+1TinO3n+1 as the oxygen diffusion barrier, the oxygen vacancy concentration near the interface can be reversibly engineered by high-temperature annealing or infrared laser heating. Because of the identical elemental compositions (Sr, Ti, and O) throughout the whole heterostructure, interfacial ionic intermixing is absent, giving rise to an extremely high mobility (exceeding 55000 cm2 V-1 s-1 at 2 K) in this type of oxide heterostructure. This layered perovskite/perovskite heterostructure provides a promising platform for reconfigurable high-speed electronic devices.

The Effects of Nb Addition on the Oxidation Behavior of Ni–Fe–Cr Alloys at 800 °C

High temperature oxidation of Ni–18Fe–19Cr alloys with different Nb contents (based on the chemical composition of Alloy718) was investigated to elucidate the effect of Nb on oxidation kinetics and scale formation after exposure at 800 °C in air. The experimental results indicated that the oxidation kinetics decreased with increasing niobium content. Rapid establishment of an external Cr2O3 scale was interpreted by the formation of a continuous CrNbO4 layer at the metal-oxide interface, which acts as a diffusion barrier for inward oxygen and outward Fe and Ni diffusion and is of benefit for the establishment of an external Cr2O3 scale. The early establishment of this diffusion barrier prevented internal oxidation of chromium and reduced the growth of the outer Ni2FeO4 oxide scale. The beneficial effect of Nb could be attributed to effectively increasing the volume fraction of internal oxide precipitates, which are favorable for rapid establishment of an external Cr2O3 scale.

Density functional theory study of oxygen vacancy defect diffusion properties in λ-Ta2O5

The formation energy and diffusion properties of oxygen vacancy defects in λ-Ta2O5 were studied using first-principle calculations. The calculated formation energy of neutral oxygen vacancy defects was consistent with previous studies carried out, and the charged oxygen defects considering periodic correction were also studied. The calculations obtained showed that the formation energy of +2 charged oxygen vacancy defects was 0.83–1.16 eV. Also, the diffusion activation energy consisting of oxygen vacancy defect formation energy and diffusion barrier concurred well with the diffusion activation energy measured by experiments. A linear relationship was found between the diffusion barrier and the diffusion distance.

Microstructure of High Temperature Oxidation Resistant Hf6B10Si31C2N50 and Hf7B10Si32C2N44 Films

High-temperature oxidation resistant amorphous Hf6B10Si31C2N50 and Hf7B10Si32C2N44 films were deposited by reactive pulsed dc magnetron sputtering. To investigate the oxidation mechanism, the films were annealed up to 1500 °C in air. The evolved microstructures were studied by X-ray diffraction and transmission electron microscopy. A three-layered microstructure was developed upon exposure to high temperature. An oxidized layer formed at the top surface for both films consisting of monoclinic and/or orthorhombic m-/o-HfO2 nanoparticles embedded in an amorphous SiOx-based matrix. The as-deposited bottom layer of the films remained amorphous (Hf6B10Si31C2N50) or partially recrystallized (Hf7B10Si32C2N44) exhibiting a h-Si3N4 and HfCxN1−x distribution along with formation of t-HfO2 at its top section. The two layers were separated by a partially oxidized transition layer composed of nanocrystalline h-Si3N4 and tetragonal t-HfO2. The oxidation process initiates at the bottom/transition layer interface with oxidation of Hf-rich domains either in the amorphous structure or in HfCxN1−x nanoparticles resulting in t-HfO2 separated by Si3N4 domains. The second stage occurs at the oxidized/transition layer interface characterized by densely packed HfO2, Si3N4 and quartz SiO2 nanostructures that can act as a barrier for oxygen diffusion. The small t-HfO2 nanoparticles merge and transform into large m-/o-HfO2 while h-Si3N4 forms amorphous SiOx matrix. A similar oxidation mechanism was observed in both films despite the different microstructures developed.

Permeation improvement of LCCF hollow fiber membranes by spinning and sintering optimization

The effects of grain size and wall thickness on the oxygen transport mechanism of (La0.6Ca0.4)(Co0.8Fe0.2)O3-δ hollow fiber membranes were investigated. For this purpose, hollow fiber membranes of different geometry were prepared with different spinnerets via phase inversion spinning and subsequently sintered at different temperatures. The influence of the manufacturing conditions on the LCCF microstructure were analysed by SEM, XRD and TEM. With increasing sintering temperature, the grain size increased from 0.4 µm2 at 1070 °C to 19.5 µm2 at 1245 °C. With bigger grain sizes and lower wall thickness, the oxygen flux shows an increase up to 6.2 ml min−1 cm−2 (at 1000 °C) in a 50% CO2 atmosphere. This finding implies that the grain boundaries act as oxygen diffusion barriers.

TiAl–nHA composite coatings for sintering protection of carbon fiber and improvement of carbon fiber–hydroxyapatite composites interface

To protect carbon fiber (CF) against damage from oxidation during the sintering of CF reinforced hydroxyapatite (HA) composites and improve CF–HA interface, uniform and dense TiAl–nanohydroxyapatite (nHA) coatings were successfully fabricated on the CF surface by combining multiarc ion plating with electrochemical deposition. TiAl–nHA coated CF-reinforced HA (CF/TiAl–nHA/HA) composites were prepared via pressureless sintering. Results show that CF/TiAl–nHA/HA composites present excellent mechanical properties. The fracture toughness can be satisfied with human compact bone. The improved mechanical properties probably benefit from TiAl and nHA coatings. As an oxygen diffusion barrier, TiAl coatings can protect CF against oxidative damage caused by dehydroxylation of HA in the sintering process. The nHA coatings on TiAl-CF can reduce CF–HA interfacial gaps. This study fully utilized the CF enhancement and facilitated the use of CF/HA composites for weight–bearing bone.

Kinetics and evolution of oxide scale during various stages of isothermal oxidation at 1300 °C in spark plasma sintered ZrB2 – SiC – LaB6 composites

The kinetics and oxide scale evolution during isothermal exposure of spark-plasma sintered ZrB2-20 SiC–LaB6 (7, 10 or 14 vol%) composites at 1300 °C for 1, 8, or 24 h have been examined. Random mass change observed during the first hour stems from a non-protective scale. The variation of mass gain with time is expressed by near-parabolic rate law during 0−8 h time period, and by relations indicating slower kinetics during 8−24 h, with parabolic rate constants (kp) decreasing sharply. Microstructural examination has shown a continuously evolving layered oxide scale comprising La2Si2O7, borosilicate glass (BSG), ZrSiO4, and ZrO2, where the BSG layer growth rate scales linearly with LaB6 content during 0−8 h, but shows an opposite trend on further exposure. During both time periods (0−8 and 8−24 h), kp decreased following a linear relationship with increasing BSG layer thickness, indicating its key role as diffusion barrier for oxygen.

The first-principles calculations to explore the mechanism of oxygen diffusion on vacancy defective graphene in marine environment

Graphene can play an important role in the application of marine anticorrosion. However, the vacancy defects of graphene accelerate the diffusion of oxygen to deteriorate its corrosion resistance, especially in chlorine-containing marine environments. In present paper, the diffusion energy barriers of O on P, B or Si-doped vacancy defective graphene were calculated by the first principles simulation, it was found that B-doping in vacancy defective graphene could most effectively increase the diffusion barrier of oxygen in the whole diffusion stage. Combining Bader charge and differential charge density, the bonding properties of O, Cl and dopant atoms were analyzed systematically. Adsorption energy showed that the dopant P, Si or B atom could have a stronger effect on oxygen adsorption so that it inhibited the diffusion of oxygen for vacancy defective graphene. In particular, B-doped vacancy defective graphene with highest diffusion energy barrier could most effectively inhibit the diffusion of O, indicating that it could provide the most protection against oxidative corrosion in marine environment, such as the ocean and coastal area.

Experimental characterisation of non-encapsulated bio-based concrete with self-healing capacity

The main reason for early corrosion in Reinforced Concrete (RC) structures is crack formation within the concrete cover. Cracks can lead to leakage problems, allowing chloride, oxygen, water and other aggressive chemicals to enter into concrete and eventually causes corrosion of steel reinforcement. The paper shows some results of a novel bio concrete with biological self-healing agent, which added into the concrete mixture, autonomously and actively, inhibits the concrete cracks and potential premature reinforcement corrosion. Two compositions of concrete samples were prepared and casted – CEMI and CEMIII with 60% of Ground Granulated Blast Furnace Slag (GGBS) with and without non-encapsulated bio-product utilising iron respiring bacteria. The developed bio-mineral is capable of sealing cracks and blocking pores resulting in a delay of water-born ions in RC structures, acting as a diffusion barrier of oxygen to protect steel reinforcement's passivity towards corrosion. The fresh test results show that these concretes have the potential to be used in RC heavily reinforced and manually compacted sections with vibrations. The water absorption velocity has been significantly reduced with the inclusion of bio-agent in CEMI and CEMIII concretes samples, which was associated with pores sealing. Maximum water absorption via capillary tends to reduce at least 25% when bio-agent was introduced to concrete type CEMIII. Other results emphases the efficiency of the bio-product in CEMIII medium. The bio-agent does not decrease the compressive strength of tested concretes either for CEMI and CEM III. SEM observation shows that the crystals were well developed near the surface of the crack.

ITO:SiC Ceramic Matrix Composite Thermocouples for Engine Components

Surface temperature measurements of ceramic matrix composite (CMC) based engine components within the hot section of a gas turbine engines are needed to verify engine designs and cooling requirements. Traditional temperature sensors cannot be applied to silicon carbide (SiC) based CMC's for this purpose, since they cannot be welded or embedded in the material. For these reasons, a novel thermocouple was developed for surface temperature measurement of p-type SiC-SiC CMC's. This novel thermocouple uses the p-type SiC-SiC CMC itself as one of the thermoelements and indium-tin-oxide (ITO) as the other thermoelement. Since both thermoelements are wide bandgap semiconductors, this thermocouple has exceptional thermoelectric output. A thermoelectric output of 272 μV/°K was observed for this ITO:SiC CMC thermocouple, which is an order of magnitude larger than that of type-K thermocouples. A drift rate of 3.28 °C/h was measured for this ITO:SiC CMC thermocouple. In addition, indium tin oxynitride (ITON) protective coatings deposited via reactive sputtering enabled these thermocouples to operate at 1000 °C. The ITON coating served as an oxygen diffusion barrier to prevent oxidation at the ITO:SiC CMC junction. Nitrogen and air anneals at 550 and 1000 °C, respectively, were used to improve the high temperature stability of the ITO and ITON coatings. Performance, fabrication details, and challenges using these ITO:SiC CMC thermocouple are discussed within.

Instability of UV Photoresponse in MgZnO Thin Films and Its Improvement by MgO Capping

Herein, it is shown that the UV photoresponse characteristics of MgZnO thin films deposited by pulsed laser deposition change rapidly with time if the films are exposed to ambient air and that the response can be stabilized significantly by depositing a thin capping layer of MgO on the surface of MgZnO thin film. The decay time of photocurrent in as‐deposited MgZnO thin films increases from 1.8 to 229 s and the value of peak responsivity increases by about three orders of magnitude as the film is exposed to air for about 106 s. On application of MgO capping layer, the decay time of the photocurrent marginally increases from ≈0.2 to ≈0.4 s and the value of peak responsivity increases only by one order of magnitude over the span of 106 s, thereafter showing tendency of saturation, implying much better stability in performance. The MgO capping layer is transparent to UV, but acts as a diffusion barrier for oxygen, stabilizing the UV photoresponse.

Oxygen diffusion barriers for epitaxial thin-film heterostructures with highly conducting SrMoO3 electrodes

Transition metal perovskite oxide SrMoO3 with a Mo4+ 4d2 electronic configuration exhibits a room-temperature resistivity of 5.1 μΩcm in a single-crystal form and, therefore, is considered a prominent conducting electrode material for all-oxide microelectronic devices. Stabilization of the unfavorable Mo4+ valence state in SrMoO3 thin films necessitates reductive growth conditions that are often incompatible with a highly oxidative environment necessary to grow epitaxial heterostructures with fully oxygenated functional layers (e.g., tunable dielectric BaxSr1−xTiO3). Interestingly, only a few unit cells of the perovskite titanate capping layers SrTiO3, BaTiO3, and Ba0.5Sr0.5TiO3 act as an efficient oxygen barrier and minimize SrMoO3 oxidation into electrically insulating SrMoO4 in the broad range of the thin-film growth parameters. The Mo valence state in SrMoO3, determined by x-ray photoelectron spectroscopy, is used to analyze oxygen diffusion through the capping layers. The lowest level of oxygen diffusion is observed in Ba0.5Sr0.5TiO3. A Ba0.5Sr0.5TiO3 film with a thickness of only 6 unit cells preserves the Mo4+ oxidation state in the SrMoO3 underlayer up to the oxygen partial pressure of 8 mTorr at the temperature of 630 °C. Results, therefore, indicate that SrMoO3 films covered with atomically thin Ba0.5Sr0.5TiO3 remain conducting in an oxygen environment and can be integrated into all-oxide thin-film heterostructures with other functional materials.