Dense Oxide Film Research Articles

The aluminum current collector with honeycomb-like surface and thick Al2O3 film increased durability and enhanced safety for lithium-ion batteries

Durability and safety are main factors contributing to the market requirement of lithium-ion batteries (LIBs) in practical applications. The improvement of current collector has been proven as an effective approach to enhance comprehensive performance of LIBs. To achieve a sufficient electrical contact between the current collector and active materials, honeycomb-like surface of aluminum current collector is etched by direct current in sulfuric acid and phosphoric acid mixed solution. At the same time, a dense anodic aluminum oxide film is formed on the surface of aluminum current collector, which can protect LIBs from corrosion and thermal runaway. Experimental results show that the adhesion between the active material and aluminum current collector was improved by 23% after anodization. The corrosion resistance of alumina foil was promoted significantly in ethyl methyl carbonate and ethylene carbonate electrolyte with LiPF6. The corrosion current peak reduces to 0.022 mA/cm2 from 0.267 mA/cm2 after surface treatment. The capacity retention rate of the LiCoO2 electrode with an oxidation-treated aluminum current collector is 6.3% higher than with untreated aluminum foil at 5C after 500 cycles. What’s more, the nail penetration demonstrates that the aluminum current collector we prepared can reduce the temperature of the full batteries surface when the nail pierced, which improved the safety performance of LIBs.

High performance novel flexible perovskite solar cell based on a low-cost-processed ZnO:Co electron transport layer

In this work, high quality uniform and dense nanostructured cobalt-doped zinc oxide (ZnO:Co) films were used as electron-transport layers in CH3NH3PbI3-based planar heterojunction perovskite solar cells (PSCs) on a flexible conductive substrate. Highly photo catalytically active ZnO:Co films were prepared by a low cost hydrothermal process using the aqueous solution of zinc nitrate hexahydrate, hexamethylenete-tramine and cobalt (II) nitrate hexahydrate. ZnO:Co films were deposited on indium tin oxide (ITO) covered polyethylene terephthalate (PET) flexible substrates. The growth was controlled by maintaining the autoclave temperature at 150 °C for 4 h. The CH3NH3PbI3 layer was deposited on the ZnO:Co films by spin coating. Spiro-OMeTAD was employed as a hole-transporting material. The structural, morphology and optical properties of the grown ZnO nanostructures were characterized by X-ray diffraction (XRD), field-emission scanning electron microcopy (FESEM), energy-dispersive X-ray spectrometry (EDX), ultraviolet-visible (UV-Vis) and photoelectrochemical propriety. XRD spectra showed that both ZnO and ZnO:Co nanorods had a hexagonal wurtzite structure with a strong preferred orientation along the (002) plane. The surface morphology of films was studied by FESEM and showed that both the pure and Co-doped ZnO films had hexagonal shaped nanorods. In the steady state, the ZnO electrode gave a photocurrent density of about 1.5 mA/cm2. However, the Co-doped ZnO electrode showed a photocurrent density of about 6 mA/cm2, which is 4-fold higher than that of the ZnO electrode. Based on the above synthesized Co-doped ZnO films, the photovoltaic performance of PSCs was studied. The Co-doped ZnO layers had a significant impact on the photovoltaic conversion efficiency (PCE) of the PSCs. The latter was attributed to an efficient charge separation and transport due to the better coverage of perovskite on the nanostructured Co-doped ZnO films. As a result, the measured PCE under standard solar conditions (A M 1.5G, 100 mW/cm2) reached 7%. SCAPS-1D simulation was also performed to analyze the effect of the co-doped ZnO thin film on the corresponding solar cell performances.

Electrolytic in‐process dressing grinding performance of a multi‐layer brazed coarse‐grained diamond wheel using an electrolyte containing carbon microspheres

AbstractAn electrolyte containing carbon microspheres (CMSs) was prepared for electrolytic dressing of a multi‐layer brazed coarse‐grained diamond wheel. And the influence of CMSs on the electrolytic in‐process dressing grinding performance of Si3N4 ceramics with the brazed wheel was investigated. The results indicate that the CMSs can increase the electrolytic capacity of the electrolyte, which increases the thickness of the oxide film formed on the brazed wheel surface, and the worn diamond grit can easily fall off from the bonding matrix. In addition, the CMSs were adsorbed and distributed on the film, which effectively improves its densification and adhesion strength. This thicker and denser oxide film can improve the polishing effect of the brazed wheel. Thus, a better machined surface quality and less subsurface damage of the Si3N4 ceramics can be obtained by the multi‐layer brazed coarse‐grained diamond wheel with electrolyte containing CMSs.

A strong and ductile medium-entropy alloy resists hydrogen embrittlement and corrosion

Strong and ductile materials that have high resistance to corrosion and hydrogen embrittlement are rare and yet essential for realizing safety-critical energy infrastructures, hydrogen-based industries, and transportation solutions. Here we report how we reconcile these constraints in the form of a strong and ductile CoNiV medium-entropy alloy with face-centered cubic structure. It shows high resistance to hydrogen embrittlement at ambient temperature at a strain rate of 10−4 s−1, due to its low hydrogen diffusivity and the deformation twinning that impedes crack propagation. Moreover, a dense oxide film formed on the alloy’s surface reduces the hydrogen uptake rate, and provides high corrosion resistance in dilute sulfuric acid with a corrosion current density below 7 μA cm−2. The combination of load carrying capacity and resistance to harsh environmental conditions may qualify this multi-component alloy as a potential candidate material for sustainable and safe infrastructures and devices.

Steam oxidation behavior of Y-bearing cladding tube with aluminizing coating

A kind of Y-bearing ferritic/martensitic fuel cladding tube with qualified dimensions, acceptable mechanical properties as well as good flattening and flaring performance was manufactured recently by our group. In this paper, to improve and further evaluate its oxidation resistance, the cladding tube was aluminized firstly and then subjected to high temperature steam oxidation at 1200 °C for 8 h. The results indicated that aluminizing coating with gradient content of Al was prepared on the tube successfully. And the matrix microstructure was transformed from tempered martensite into ferrite during aluminizing. Weight gains after high temperature steam oxidation were 72.7 and 1.48 mg cm−2 for the bare and aluminized tubes, respectively. The latter one exhibited better oxidation resistance due to the generated dense aluminum oxide film. Meanwhile, Kirkendall pores were formed near oxidation surface and should be eliminated for the real application of the aluminized tube in the future.

Oxide Coated Nano-Porous Ag Thin Film for Chemical Sensing By Gas Flow Sputtering

A completely non-destructive analytical method is one of the great advantages of Raman spectroscopy. However, low efficiency of Raman signals should be improved to be widely used for detecting less than ppm of chemicals. Surface enhanced Raman scattering (SERS), which is a valuable technique for detecting the target substance very sensitively, is a method of amplifying Raman signals by the plasmon coupling effect at the gap between the nanoparticles. For this reason, materials and the nano-structure such as particle size, shape, gap and density were major factors for determining the performance of the SERS substrate.In this study, gas flow sputtering (GFS) was used for fabricating SERS substrates. The nano-porous structure was observed using scanning electron microscope (SEM) and crystal structures were also analyzed by X-ray diffraction (XRD). The density of the nano-porous structure was calculated using the thickness of the film and the mass difference before and after deposition.Silver (Ag) was widely studied as SERS substrate, due to excellent SERS effect and lower price than that of other noble metals. However, Ag has a significant degradation in SERS effect with time which appears to be a problem caused by oxidation of the Ag surface. Owing to this problem, fabricating a highly reproducible SERS substrate is a challenging issue and many researchers are conducting study.To solve this problem, Ag dense film and oxide film were sequentially deposited. Then, Ag nano-porous thin film was deposited on the oxide film to form a dielectric nano-gap between Ag dense film and Ag nano-porous thin film. Also, to protect from oxidation, Ag nano-porous thin film was coated with a thin oxide film using in-situ co-sputtering. The structure of nano-porous thin film was controlled by varying the sputtering power, time, process pressure.As a result, rhodamine 6G of less than 0.5 uM was successfully detected and it showed much improved Raman signal compared with single Ag nano-porous thin film. In addition, the aging problem, which was the most important issue, also reduced noticeably.

Aggregate ceramic films produced at room temperature by press forming

AbstractRecently, the demand for flexible or stretchable Internet‐of‐things devices has increased with the rise in popularity of wearables. Also, research is progressing for the development of oxide‐based all‐solid‐state lithium‐ion batteries, which are expected to have improved safety and performance compared with current batteries. Room‐temperature processes for the production of oxide films would facilitate the development of such novel devices. Press forming is a simple room‐temperature process; however, conventional press forming cannot produce highly dense green compacts. Here, we developed a new press forming‐based, room‐temperature process, the mega‐press forming (MF) method, that produces highly dense aggregate oxide films at a pressure below 1 GPa, which is lower than that at which oxide particles fracture, by taking advantage of the differences in cohesive force between microsized and nanosized particles. We used our novel process to produce highly dense lead zirconate titanate aggregate films on aluminum foil at room temperature, and found that when impregnated with silicone oil, these films exhibited low leakage current density and saturated polarization hysteresis properties. Furthermore, we were able to produce films with a porosity of only 6%, which is much lower than that of films produced by conventional press forming (20%). Thus, the MF method will be useful for the development of novel functional composite ceramics that are difficult to fabricate using high‐temperature processes.

5-Methyl-1H-Benzotriazole as an Effective Corrosion Inhibitor for Ultra-Precision Chemical Mechanical Polishing of Bearing Steel

5-methyl-1H-benzotriazole was used as an effective corrosion inhibitor in acidic H2O2-based slurries for ultra-precision chemical mechanical polishing (CMP) of a high carbon chromium GCr15 bearing steel (AISI 52100). The CMP performance of GCr15 steel and the corresponding corrosion inhibition mechanism of 5-methyl-BTA were thoroughly investigated. The CMP results reveal that, compared with 1,2,4-triazole, 1,2,3-triazole and BTA, 5-methyl-BTA achieves the best corrosion inhibition performance, and the surface roughness Ra of GCr15 steel greatly improves, which can be attributed to the triazole and hydrophobic methyl functional groups. In synergy with H2O2, 5-methyl-BTA can be both chemically and physically adsorbed on the GCr15 steel surface in acidic medium. Specifically, the chemical adsorption mainly occurs by chemical reactions between 5-methyl-BTA and iron of GCr15 steel to form a surface complex. In the presence of 1.0 wt% H2O2 and 20 mM 5-methyl-BTA, the sparse corrosion inhibition film formed by 5-methyl-BTA together with the dense oxide film constitutes a complete passivation film, eventually resulting in the nanoscale planarization. The results can provide a guide for the selection of appropriate nitrogen-containing corrosion inhibitors for bearing steels CMP.

Improved Redox Cycling Durability in Alternative Ni Alloy-Based SOFC Anodes

Repeated reduction and oxidation of metallic nickel in the anodes of solid oxide fuel cell (SOFC) causes volume changes and agglomeration. This disrupts the electron conducting network, resulting in deterioration of the electrochemical performance. It is therefore desirable to develop more robust anodes with high redox stability. Here, new cermet anodes are developed, based on nickel alloyed with Co, Fe, and/or Cr. The stable phases of these different alloys are calculated for oxidizing and reducing conditions, and their electrochemical characteristics are evaluated. Whilst alloying causes a slight decrease in power generation efficiency, the Ni-alloy based anodes have significantly improved redox cycle durability. Microstructural observation reveals that alloying results in the formation of a dense oxide film on the surface of the catalyst particle (e.g. Co-oxide or a complex Fe–Ni–Cr oxide). These oxide layers help suppress oxidation of the underlying nickel catalyst particles, preventing oxidation-induced volume changes/agglomeration, and thereby preserving the electron conducting pathways. As such, the use of these alternative Ni-alloy based cermets significantly improves the redox stability of SOFC anodes.

Tribological properties of nano/ultrafine-grained FeCoCrNiMnAlx high-entropy alloys over a wide range of temperatures

Previous studies have shown that high-entropy alloys (HEAs) have good wear resistance, especially at elevated temperatures. However, for nano/ultrafine-grained bulk HEAs, there is a lack of understanding of the friction and wear properties. In this work, nano/ultrafine-grained FeCoCrNiMnAlx HEAs were produced by powder metallurgy, and the effects of Al addition and temperature on the friction and wear properties of the alloys were studied. The addition of Al led to grain refinement, body-centered cubic (BCC) phase precipitation and an increased hardness, which significantly improved the wear resistance of the alloys at various temperatures. At elevated temperatures, such as 800 °C, the alloys (especially the Al-containing alloys) exhibited outstanding wear resistance, which was mainly attributed to the formation of the continuous and dense oxide film on the worn surface due to the nano-/ultrafine-grained structure. Additionally, the Al-containing alloys also showed good antifriction properties at 800 °C.

Microstructure and corrosion behavior of as-homogenized Mg-xLi-3Al-2Zn-0.2Zr alloys (x = 5, 8, 11 wt%)

The microstructure and corrosion behavior of as-homogenized Mg-xLi-3Al-2Zn-0.2Zr alloys (x = 5, 8, 11 wt%) were investigated. As the Li content increases from 5 wt% to 11 wt%, the alloys undergo a phase transition from α-Mg single-phase to α-Mg + β-Li dual-phase and then to β-Li single-phase. All alloys contain AlLi phase, filamentous AlLi phase exists in α-Mg matrix in eutectic form while round-like AlLi phase exists in β-Li matrix in granular form. The corrosion of as-homogenized LAZ532–0.2Zr and LAZ1132–0.2Zr alloys is mainly filiform corrosion and pitting corrosion, while that of as-homogenized LAZ832–0.2Zr alloy is mainly galvanic corrosion. As-homogenized LAZ832–0.2Zr alloy exhibits the best corrosion resistance attributed to the finer filamentous AlLi phase in α-Mg matrix, the smaller round-like AlLi particles distributed in β-Li matrix and along the α-Mg/β-Li interface, and the denser oxide film containing a small amount of Li2CO3.

Dry Wear Behavior of Cladded NiCoCrAlY Coating on Cast Iron at Elevated Temperatures

To improve the service life of valve retainer in the engine exhaust system, the NiCoCrAlY alloy coating was fabricated on compacted graphite cast iron by laser cladding. Microstructure and high-temperature wear resistance of the coating were studied. The coating exhibits a refined dendritic structure. The M23C6 nano-precipitates with rod-shape are embedded the γ(Fe, Ni) solid solution dendrites, and the M7C3 nano-precipitates are distributed in the inter-dendrite region. The average nano-hardness of the coating and the substrate are measured as 4.08 GPa and 3.96 GPa, respectively. The wear morphologies and coefficient of friction variation reveal that the friction layer formed at 25°C and 600°C is a mechanical mixing layer and a composite layer, respectively. The coating possesses excellent wear resistance at 600°C due to the formation of a dense oxide film. The main component of the oxide film is identified as Fe2O3, Fe3O4, Al2O3, CrO2, CrO3 and Cr2O3.

Influence of aluminium addition on oxidation resistance of Ta-W alloy

ABSTRACT Alloys with composition of Ta-10 wt.% W and Ta-10 wt.% W-6 wt.% Al, respectively, were prepared by the hot-press sintering process. The oxidation behaviour at 900°C and 1000°C was studied. The oxidation weight gain curves of the Ta–10%W alloy followed the linear law and the final oxidation product was Ta2O5 solid solution. Meanwhile, due to the addition of Al, the oxidation weight gain curves of the Ta–10%W–6%Al alloy followed the parabolic law. The final oxidation products at 900°C formed a dense outer layer Al2O3 and an inner layer. However, after being oxidised at 1000°C, the oxidation products included Al2O3, AlTaO4 and Ta22W4O67. Since the dense Al2O3 oxide film was consumed by the generation of AlTaO4, the inward diffusion of oxygen cannot be prevented. The oxidation resistance degraded at 1000°C. The addition of Al significantly improved the oxidation resistance of the Ta-W-based alloy system.

Investigation of the Electrochemical Kinetics of Aluminum Deposition from Ionic Liquids

The electrochemical deposition of a number of reactive metals such as Al, Ta and Nb from ionic liquids (ILs) generated high interest during the last decades. Their deposition from aqueous solutions is not possible since these metals have a rather negative Nernst potential. Non-aqueous media have a broader electrochemical window (> 3 V) and offer new possibilities for industrial applications by electrochemical plating of highly reactive metals. Due to its excellent properties such as high conductivity and the formation of a dense oxide film, the possible applications of aluminum range from electronics and optics all the way to coatings for corrosion protection and decorative purposes. The negative standard potential of aluminum (-1.66 V vs. SHE) led to the development of non-aqueous electrolytes used in industrial processes (e.g. SIGAL process), which are often based on highly flammable and/or volatile chemicals, leading to high costs and risks for the operator. ILs are non-flammable, have a high solubility for metal salts and there is no hydrogen embrittlement due to their aprotic nature. Furthermore, continuously decreasing prices for ILs make them more interesting for industrial processes. Aluminum was one of the first metals electrochemically deposited from ILs. There are a lot of reports about the pure metal and its alloys. However, there are some basic knowledge gaps about the electrochemical kinetics of the aluminum deposition from ILs. This paper will discuss recent results from the authors’ lab on the electrochemical kinetics of the deposition of aluminium from 1-ethyl-3-methyl-imidazolium based ILs. A number of high and low amplitude step experiments completed by cyclic voltammetry and conductivity measurements were employed to shed light on the diffusion, nucleation and charge transfer mechanism of the aluminium deposition.

Comparative Study on the Oxidation Behavior of Austenitic and Ferritic Heat-Resistant Stainless Steels at High Temperatures

A comparative study of the high-temperature oxidation behavior and mechanism of 0Cr25Ni20 austenitic heat-resistant stainless steel (AHSS) and 0Cr18AlSi ferritic heat-resistant stainless steel (FHSS) at 800°C, 900°C, and 1000°C in air up to 140 h was performed using isothermal oxidation tests. The oxidation kinetics of 0Cr25Ni20 AHSS and 0Cr18AlSi FHSS followed the parabolic law. The oxide films on 0Cr25Ni20 AHSS were composed of continuous and dense Cr2O3, MnCr2O4, and a small amount of NiMn2O4, whereas silicon exhibited internal oxidation and deteriorated the adhesion between the oxide film and substrate. Nickel-free 0Cr18AlSi FHSS exhibited good oxidation resistance at 800°C and 900°C due to dense, continuous, and well-adhered multicomponent oxide films containing Al2O3, Cr2O3, MnCr2O4, and a small amount of MnFe2O4. The oxidation resistance of 0Cr18AlSi FHSS declined at 1000°C, mainly due to the formation of nonprotective Fe2O3 and severe internal oxidation of aluminum.

Preparation and properties of PAN-based carbon fiber-reinforced SiCO aerogel composites

Abstract To overcome the brittleness issue of SiCO aerogels, the polyacrylonitrile-based (PAN) carbon fiber was impregnated with SiCO sol to obtain carbon fiber-reinforced SiCO aerogel composites (C/SiCO). SiCO sol was prepared through an acid-alkaline two-step catalysis by using methyltrimethoxysilane (MTMS) and dimethyldiethoxysilane (DMDES) as precursors. C/SiCO-1, C/SiCO-2 and C/SiCO-3 were obtained after repeated impregnation of the SiCO sol and gelating, aging, supercritical drying and pyrolyzing one to three times. SEM images show that the SiCO aerogel fills the pores between the carbon fibers, and the nanoporous structure of the SiCO aerogel can effectively improve the thermal insulation of the composites. As the times of impregnation of the SiCO sol increased, the mechanical properties and oxidation resistance of C/SiCO have been improved significantly. The bending strength of C/SiCO-3 was 32.52 MPa, and the compressive strength (25%e) was 51.98 MPa. After heating at 1600 °C, the linear shrinkage in the thickness direction of C/SiCO-1 was 20.72%, while that of C/SiCO-3 was only 1.85%. A dense SiO2 molten oxide film formed on the surface of C/SiCO at high temperature, and its extremely low oxygen permeability effectively protected the inside of the composites.

Iron Powder Third Body Contribution to Friction Performance of Copper-Matrix Friction Composites

Iron third body contribution to friction performance of copper-matrix friction composites was explored by adding prefabricated iron powder into the friction surface. Friction tests were carried out under a sliding speed (V) range of 1.57–23.55 m/s and contact pressures (P) of 0.25–0.51 MPa by a pin-on-disc tribometer. These showed that an iron third body increased the friction coefficient when P • V <2 75, and the average friction coefficient increment was 0.04 (7.29%). The reason was that iron third bodies played the role of abrasives, promoting an engaging force between the friction couple. When P • V > 275, the average friction coefficient decrement was 0.04 (8.59%). This was because of oxidation of the iron third body, such that a smooth and dense oxide film was formed on the surface, assisting in a friction coefficient reduction.

Influence of thermal shock behavior on microstructure and mechanical properties of IN718 superalloy

The influence of thermal shock behavior between 960 °C and room temperature on microstructure and tensile properties of IN718 alloy after three heat treatments was investigated in this paper. The experiments show that protective and dense oxide films with the composition of Cr2O3, Ti0.95Nb0.95O4 and (Cr, Fe)2O3 are formed on the surface of alloys. The average oxide films increased with the thermal shock cycle. The thermal shock behavior changed the distribution and quantities of δ phases, which have significantly reduced the strength and increased the elongation of IN718 alloy. The decrease of strength was mainly determined by the dissolution of strengthening phase and grain coarsening. High standard treatment alloy shows the best thermal shock resistance since the strength decreased smallest after thermal shock.

Studies on as-cast microstructure and oxidation behavior of the Fe[sbnd]Cr[sbnd]B[sbnd]Al alloys at 1073 K

Based on the FeCrB alloy, the Fe12Cr1.5BxAl (x = 0, 2, 4, 6 and 8 wt%) alloys were designed by adding Al. The as-cast microstructure and cyclic oxidation behavior have been investigated extensively in this study. The results reveal that the as-cast microstructure of FeCrB alloy consists of martensite (bcc), retained austenite (orthorhombic) and M2(B,C)-bct, M7(C,B)3-hcp, M23(C,B)6-complex fcc boron-carbides, gradually changing to α-(Fe,Al,Cr) solid solution (bcc), M2(B,C)-bct, M7(C,B)3-hcp, M23(C,B)6-complex fcc boron-carbides and Fe3Al intermetallic compound with the increasing of Al contents. The oxidation kinetics of all alloy samples follow a parabolic oxidation kinetic law. The oxidation rate constant kp in Al-free FeCrB alloy is nearly four times of that in FeCrB8Al alloy. The additions of Al refine the grains and make the distribution of elements more uniform, which results in forming a continuous and dense oxide film containing Al2O3 oxide with excellent fluidity and thermal stability, remarkably enhancing the high temperature oxidation resistance of FeCrBAl alloy.

The general corrosion behavior of ENiCrFe-7 weld overlay cladding material in deoxygenated high-temperature and high-pressure water

ABSTRACT The general corrosion behavior of Alloy ENiCrFe-7 in deoxygenated high-temperature and high-pressure water was investigated. The results showed that the precipitates of Alloy ENiCrFe-7 included niobium carbide and Al-Ti-O compounds, and the weight gain increased fast firstly before 2250 h, then the weight gain slowed down. There were obvious large particles spread on denser oxide film after 3000 h exposure. Ni was present at a single chemical metallic Ni state, Fen+ content of the outer layer was close to 60%, which was much higher than that of the matrix. The oxide film consisted of an inner layer and an outer layer, the inner layer was mainly composed of Cr2O3 and the outer layer was mainly composed of Fe3O4 and FeCr2O4. Finally, it is found that the preferential corrosion location of pitting was niobium carbide precipitates by in same site observation, while Al-Ti-O compounds was not dissolved in deoxygenated high-temperature and high-pressure water for 1500 h exposure. The size and number of the pitting was not significantly changed with increasing exposure time.