Annealing Treatment In Air Research Articles

Transmittance enhancement and unique optical absorption of Yb2Hf2O7 ceramics via air annealing

Highly transparent Yb2Hf2O7 (YbHO) transparent ceramics hold promise as radiation shielding windows and luminescent host materials, and vacuum sintering is an effective way to fabricate highly dense YbHO ceramics. However, some F+ and F defect centers and some Yb2+ ions will be generated during vacuum sintering of YbHO transparent ceramics, resulting in low transparency. In response to this problem, air annealing treatment at different temperatures was adopted to eliminate defect centers of vacuum sintered YbHO ceramics and oxidize Yb2+ to Yb3+ in this work. YbHO ceramic with high in-line transmittance of 76 % at 750 nm was obtained via air annealing at 1300 °C for 4 h, which is extremely close to its limit of 79 %. Additionally, a unique optical absorption phenomenon was observed after annealing in the YbHO ceramic. The synergy effect of YbHf2++Ov+YbHf3+ in these ceramics generated from air-annealing process were proposed for the relevant reaction mechanisms involving serious optical absorption. This work is expected to provide guidance for the development of high-performance Yb-doped transparent ceramics for gamma-shielding windows and host materials.

Stable and Highly Active Single Atom Configurations for Photocatalytic H2 Generation.

The employment of single atoms (SAs), especially Pt SAs, as co-catalysts in photocatalytic H2 generation has gained significant attention due to their exceptional efficiency. However, a major challenge in their application is the light-induced agglomeration of these SAs into less active nanosized particles under photocatalytic conditions. This study addresses the stability and reactivity of Pt SAs on TiO2 surfaces by investigating various post-deposition annealing treatments in air, Ar, and Ar-H2 environments at different temperatures. It is described that annealing in an Ar-H2 atmosphere optimally stabilizes SA configurations, forming stable 2D rafts of assembled SAs ≈0.5-1nm in diameter. These rafts not only resist light-induced agglomeration but also exhibit significantly enhanced H2 production efficiency. The findings reveal a promising approach to maintaining the high reactivity of Pt SAs while overcoming the critical challenge of their stability under photocatalytic conditions.

Defect assisted self‐reduction and post annealing of Mn ions activated garnet transparent ceramics

AbstractTransition‐metal Mn2+ ion‐doped transparent ceramics (TCs) are promising color‐convertors to improve color rendition for solid‐state lighting. However, the stabilization of Mn2+ remains a challenge owing to the changeable atmosphere in the specific preparation of TC. In this work, the variations of valence states of Mn ions in typical garnet lattice host (YAG and LuAG) throughout the TC fabrication were demonstrated. By combined first principles calculation and experimental investigation, an enhanced self‐reduction of Mn ions was clarified in LuAG host, which was originated from the higher concentration of oxygen vacancy defects. Moreover, the air annealing treatment could significantly weaken and enhance the absorption of Mn2+ and Mn3+ respectively, degrading the orange–red emission peaking at 594 nm. On account of the oxidation of Mn2+ ions, a photoluminescence spectra redshift of 9 nm was observed with increasing air annealing temperature and oxygen content, owing to strengthened crystal field strength surrounding Mn2+ ions. Finally, a high color rendering index of 74.5 of resultant white laser diodes device structured by single‐phase LuAG:Ce,Mn TCs was obtained based on an efficient energy transfer process from Ce3+ to Mn2+. This study will deepen the understanding of the crystal defects inside TCs on luminescence properties, as well as inspiring more exploration on defect control to develop high performance ceramic color‐convertor.

Effects of RF magnetron sputtering power on the structure and nanohardness of high-entropy alloys (TiVCrNbSiTaBY)N hard coatings

High-entropy alloys (TiVCrNbSiTaBY)N hard coatings were deposited on silicon wafers and stainless steel plates using radio-frequency (RF) magnetron sputtering. The effects of RF power on the elemental composition, morphology, structure and nanohardness of coatings are evaluated. The coatings exhibit smooth surface with low roughness less than 1 nm. Higher RF power introduces more silicon into coatings and densifies the columnar structure. The coatings present nanocomposite structure of face-centered cubic phase and amorphous Si3N4. With increasing RF power, the content of amorphous phase rises and crystal grains are refined. The changes in structure lead to a tendency for nanohardness and elastic modulus of coatings to first increase and then decrease. The coating grown at 800 W has the highest nanohardness and highest elastic modulus of ∼38.1 GPa and ∼451.2 GPa, respectively. The strengthening mechanism is explained by the nanocrystal-TiN/amorphous-Si3N4 model. The annealing treatment in air demonstrates that the coating exhibits excellent oxidation resistance at 800 °C.

Tungsten doped indium oxide (IWO) transparent electrode used in air-annealed perovskite solar cells

The common transparent electrode materials used in perovskite solar cells (PSCs), for example, the tin-doped indium oxide (ITO), usually have low carrier mobility and low transmittance in the near-infrared region which limits the short circuit current density (JSC). Accordingly, it is urgent to seek a novel transparent conductive material with high mobility and high transmittance. In this work, the tungsten doped indium oxide (IWO) film, composed of 0.5 wt% WO3 and 99.5 wt% In2O3, is employed in PSCs to act as the transparent electrode. The IWO-based PSCs exhibit superior performance as compared with the ITO-based counterparts mainly due to the excellent opto-electrical properties of IWO, such as high carrier mobility and infrared transmittance, fine surface morphology, etc. The performance of devices is further optimized by air-annealing treatment of the absorber layer. Air-annealing improves the crystallinity, decreases the defect states, and as a result, inhibits the non-radiative recombination. In summary, we fabricated the champion device based on IWO with the JSC of 26.2 mA/cm2 and its power conversion efficiency achieves 23.64%, the maximum record of IWO-based PSCs.

Ti-doped Fe2O3 photoanodes on three-dimensional titanium microfiber felt substrate for photoelectrochemical oxygen evolution reaction

The macroporous structure of conductive substrates with large surface areas is crucial for fabricating semiconductor electrodes that offer better photoelectrochemical (PEC) performance in the water-splitting reaction. In this study, three-dimensional (3D) titanium microfiber felt (Ti felt) was used as a conductive substrate to prepare a Ti-doped Fe2O3 photoanode via a hydrothermal method with a two-step annealing treatment in air and argon atmospheres. Compared to conventional two-dimensional (2D) substrates, such as fluorine-doped tin oxide (FTO)-coated glass and Ti sheets, the loading amount of Fe2O3 on Ti felt was 2–5 times higher for a similar substrate geometric area. The thickness of Fe2O3 on the Ti felt (∼0.6 µm) was less than that on the 2D substrates. Ti-doped Fe2O3 on Ti felt (Ti-felt/Ti-Fe2O3) exhibits a higher photocurrent density than FTO/Ti-Fe2O3 and Ti-sheet/Ti-Fe2O3. Mott–Schottky analysis shows that the donor density of Ti-felt/Ti-Fe2O3 (8.58 × 1021 cm−3) was more than 10 times higher than that of FTO/Ti-Fe2O3 and Ti-sheet/Ti-Fe2O3. Analyses of the incident photon-to-current conversion efficiency (IPCE) and Faradaic efficiency indicated that Ti-felt/Ti-Fe2O3 showed higher PEC activity for the oxygen evolution reaction (OER) than FTO/Ti-Fe2O3. The enhanced PEC activity is ascribed to the higher donor density and moderate thickness of the Ti-doped Fe2O3 layer, which contribute to a short electron transport distance. Furthermore, the high loading of Fe2O3 on the Ti-felt substrate increased the photoabsorption in the UV and visible light regions and the photocurrent response at wavelengths near the band edge, even at low light intensities. This study provides new insights for preparing hematite photoanodes with higher PEC activity for the OER using a 3D porous substrate, rather than conventional 2D substrates.

Chemical Dopant-Free Controlled MoTe2/MoSe2 Heterostructure toward a Self-Driven Photodetector and Complementary Logic Circuits.

Two-dimensional (2D) van der Waals heterostructures based on transition metal dichalcogenides are expected to be unique building blocks for next-generation nanoscale electronics and optoelectronics. The ability to control the properties of 2D heterostructures is the key for practical applications. Here, we report a simple way to fabricate a high-performance self-driven photodetector based on the MoTe2/MoSe2 p-n heterojunction, in which the hole-dominated transport polarity of MoTe2 is easily achieved via a straightforward thermal annealing treatment in air without any chemical dopants or special gases needed. A high photoresponsivity of 0.72 A W-1, an external quantum efficiency up to 41.3%, a detectivity of 7 × 1011 Jones, and a response speed of 120 μs are obtained at zero bias voltage. Additionally, this doping method is also utilized to realize a complementary inverter with a voltage gain of 24. By configuring 2D p-MoTe2 and n-MoSe2 on demand, logic functions of NAND and NOR gates are also accomplished successfully. These results present a significant potential toward future larger-scale heterogeneously integrated 2D electronics and optoelectronics.

Lightweight chitosan-derived carbon/rGO aerogels loaded with hollow Co1-xNixO nanocubes for superior electromagnetic wave absorption and heat insulation

Designing lightweight electromagnetic (EMW) absorption materials with an ultra-broad effective absorption bandwidth (EAB), strong reflection loss (RL), and low filling level remains a challenging. In this study, an anisotropic chitosan-derived carbon/reduced graphene oxide (rGO) aerogel loaded with hollow ZIF-67 nanocubes (CG3) was constructed via unidirectional freeze-drying, heat treatment, and in situ ZIF-67 growth, followed by chemical etching. The interconnected oriented cell walls, hollow ZIF-67 nanocubes, and heterogeneous carbon/rGO interfaces enhanced EMW absorption as a result perfect impedance matching, multiple scattering, and strong dielectric polarizations. Thus, an outstanding EMW absorption performance with an ultra-broad EAB of 9.5 GHz and a minimal RL (RLmin) of −53.3 dB was achieved for the CG3 aerogel with an ultra-low filling ratio (5.5 wt%). Further, to integrate strong EMW absorption and heat insulation abilities, the hollow ZIF-67 nanocubes loaded on the carbon/rGO aerogel were converted into hollow Co1-xNixO nanocubes (CG4) via a cation exchange reaction and annealing treatment in air. Owing to the oriented pore structure, the CG4 aerogel exhibited obviously anisotropic EMW absorption and heat insulation. When the CG4 aerogel was cut along the longitudinal section parallel to the direction of ice crystal growth (CG4-L), a tubelike porous structure was revealed, and this endowed the aerogel with the highest EMW absorption (EAB = 8.7 GHz, RLmin = -52.3 dB) and thermal insulation (thermal conductivity = 0.057 W m−1 K−1) performance because of the extended EMW transmission and thermal transfer pathways. Thus, this work offers an important design strategy for obtaining high-performance thermally insulating, EMW-absorbing composites.

Assembly of high-performance hybrid supercapacitors using FeCo2O4 microflowers as battery-type cathode materials

In this work, FeCo2O4 microflowers (MFs) and microparticles (MPs) were respectively prepared at different temperatures via a wet chemical method, along with a post annealing treatment in air. These MFs and MPs exhibited huge specific surface area and a large number of mesopores. Several electrochemical tests were conducted in a three-electrode configuration. The FeCo2O4 MFs delivered a specific capacity of 301.3C g−1, higher than 253.9C g−1 for FeCo2O4 MPs. A hybrid supercapacitor (HSC) device was assembled with FeCo2O4 as cathode and activated carbon (AC) as anode to investigate the practical applications in electrochemical energy storage. The FeCo2O4 MFs//AC HSC delivered a capacity of 107.2C g−1 at 1 A g−1 and an energy density (Ed) of 25.7 W h kg−1 at 862.6 W kg−1, respectively, while the FeCo2O4 MPs//AC HSC showed an Ed of 23.8 W h kg−1 at the power density (Pd) of 878.9 W kg−1. The two HSCs showed little capacity decay after 3000 cycles at 6 A g−1. The capacity of FeCo2O4 MFs and the obtained Ed of HSC were in a high status among those of transition metal oxides (TMOs)-based electrodes reported earlier. The current synthetic strategy can be used as a reference to the synthesis of other similar electrochemical materials for HSC electrodes.

Atomic Layer Grown Zinc–Tin Oxide as an Alternative Buffer Layer for Cu2ZnSnS4-Based Thin Film Solar Cells: Influence of Absorber Surface Treatment on Buffer Layer Growth

Zn1-x Sn x O y (ZTO) deposited by atomic layer deposition has shown promising results as a buffer layer material for kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. Increased performance was observed when a ZTO buffer layer was used as compared to the traditional CdS buffer, and the performance was further increased after an air annealing treatment of the absorber. In this work, we study how CZTS absorber surface treatments may influence the chemical and electronic properties at the ZTO/CZTS interface and the reactions that may occur at the absorber surface prior to atomic layer deposition of the buffer layer. For this, we have used a combination of microscopy and synchrotron-based spectroscopies with variable information depths (X-ray photoelectron spectroscopy, high-energy X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy), allowing for an in-depth analysis of the CZTS near-surface regions and bulk material properties. No significant ZTO buffer thickness variation is observed for the differently treated CZTS absorbers, and no differences are observed when comparing the bulk properties of the samples. However, the formation of SnO x and compositional changes observed toward the CZTS surface upon an air annealing treatment may be linked to the modified buffer layer growth. Further, the results indicate that the initial N2 annealing step integrated in the buffer layer growth by atomic layer deposition, which removes Na-CO x species from the CZTS surface, may be useful for the ZTO/CZTS device performance.

Tailoring the chemical heterogeneity of Mn-modified 0.75BiFeO3-0.25BaTiO3 ceramics for piezoelectric sensor applications

The Mn-modified 0.75BiFeO3-0.25BaTiO3 (75BFBTMn) piezoelectric ceramic possesses a high depolarization temperature of 500 °C and a large piezoelectric coefficient of 110 pC/N, showing the potential for high temperature piezoelectric sensors. However, 75BFBTMn ceramic usually suffers dielectric degradation and abrupt drop of piezoelectric coefficient in the range of 300 °C to 500 °C. Combined the high-energy synchrotron X-ray diffraction analysis with Backscatter-SEM results, it is demonstrated that the electrical thermal instability is owing to the existence of chemical inhomogeneity. The Air-annealing treatment is able to decrease the volume fraction of pseudo-cubic phase and the lattice distortion, removes the chemical inhomogeneity in the grain and free Bi2O3 at grain boundary, and then eliminates dielectric anomalies and piezoelectric degradation with temperature. These results indicate that air-annealing is a simple but effective method to eliminate the chemical inhomogeneity in 75BFBTMn ceramics, thereby improving the property thermal stability for high temperature piezoelectric sensor applications.

Boosted charge transfer and photocatalytic CO2 reduction over sulfur-doped C3N4 porous nanosheets with embedded SnS2-SnO2 nanojunctions

Two-dimensional porous nanosheet heterostructure materials, which combine the advantages of both architecture and components, are expected to feature a significant photocatalytic performance toward CO2 conversion into useful fuels. Herein, we provide a facile strategy for fabricating sulfur-doped C3N4 porous nanosheets with embedded SnO2-SnS2 nanojunctions (S-C3N4/SnO2-SnS2) via liquid impregnation-pyrolysis and subsequent sulfidation treatment using a layered supramolecular structure as the precursor of C3N4. A hexagonal layered supramolecular structure was first prepared as the precursor of C3N4. Then Sn4+ ions were intercalated into the supramolecular interlayers through the liquid impregnation method. The subsequent annealing treatment in air simultaneously realized the fabrication and efficient exfoliation of layered C3N4 porous nanosheets. Moreover, SnO2 nanoparticles were formed and embedded in situ in the porous C3N4 nanosheets. In the following sulfidation process under a nitrogen atmosphere, sulfur powder can react with SnO2 nanoparticles to form SnO2-SnS2 nanojunctions. As expected, the exfoliation of sulfur-doped C3N4 porous nanosheets and ternary heterostructure construction could be simultaneously achieved in this work. Sulfur-doped C3N4 porous nanosheets with embedded SnO2-SnS2 nanojunctions featured abundant active sites, enhanced visible light absorption, and efficient interfacial charge transfer. As expected, the optimized S-C3N4/SnO2-SnS2 achieved a much higher gas-phase photocatalytic CO2 reduction performance with high yields of CO (21.68 μmolg−1 h−1) and CH4 (22.09 μmolg−1 h−1) compared with the control C3N4, C3N4/SnO2, and S-C3N4/SnS2 photocatalysts. The selectivity of CH4 reached 80.30%. Such a promising synthetic strategy can be expected to inspire the design of other robust C3N4-based porous nanosheet heterostructures for a broad range of applications.

Solvent-Free Synthesized Monolithic Ultraporous Aluminas for Highly Efficient Removal of Remazol Brilliant Blue R: Equilibrium, Kinetic, and Thermodynamic Studies.

In this study, ultraporous aluminas (UPA) were synthesized as new effective adsorbents for Remazol Brilliant Blue R (RBBR) removal from aqueous solutions. The UPA monoliths were grown via facile oxidation process, followed by isochronous annealing treatment in air at different temperatures, through which γ, θ, and α phase polycrystalline fibrous grains of UPA can be accordingly obtained. The experimental factors that affect the material adsorption performances including initial pH, contact time, and temperature were comprehensively studied by batch experiments. The RBBR adsorption isotherms of UPA(γ) and UPA(θ) powders were found almost identical, while UPA(α) powders showed low effectiveness. To obtain the desirable mechanical stability of the UPA monolith with considerable RBBR adsorption capacity, UPA(θ) powders were further studied. The UPA(θ) powders exhibited maximum RBBR adsorption at pH 2 due to the positively charged surface under acidic conditions. Compared with the Lagergren pseudo-first-order model, the pseudo-second-order model was found to explain the adsorption kinetics better. Despite the film diffusion dominating the adsorption process, the contributions of the intraparticle diffusion and chemical reactions were also found significant. The adsorption equilibrium data at different temperatures were fitted by the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherm models. The Langmuir model was found the most effective in the description of equilibrium data, and the maximum RBBR adsorption capacity retained by UPA(θ) powders was 122.55 mg·g−1 at 295 K. Thermodynamic parameters (ΔG0, ΔH0, and ΔS0) indicated the adsorption process was spontaneous and exothermic in nature.

Co3 O4 Polyhedron@MnO2 Nanotube Composite as Anode for High-Performance Lithium-Ion Batteries.

In this work, a novel lollipop nanostructure of Co3 O4 @MnO2 composite is prepared as anode material in lithium-ion batteries (LIBs). Cobalt metal-organic framework (ZIF-67) is grown on the open end of MnO2 nanotubes via a self-assembly process. The obtained ZIF-67@MnO2 is then converted to Co3 O4 @MnO2 by a simple annealing treatment in air. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction characterizations indicate that the prepared Co3 O4 @MnO2 takes a lollipop nanostructure with a stick of ≈100nm in diameter, consisting of MnO2 nanotube, and a head part of ≈1µm, consisting of Co3 O4 nanoparticles. The charge-discharge tests illustrate that this unique novel configuration endows the resulting Co3 O4 @MnO2 with excellent electrochemical performances, delivering a capacity of 1080mAh g-1 at 300mA g-1 after 160 cycles, and 696mAh g-1 at 1 A g-1 after 210 cycles, compared with 404mAh g-1 and 590 for pure Co3 O4 polyhedrons and pure MnO2 nanotubes at 300mA g-1 after 160 cycles, respectively. The lollipop configuration consisting of porous Co3 O4 polyhedron and MnO2 nanotube shows excellent structural stability and facilitates lithium insertion/extraction, leading to excellent cyclic stability and rate capacity of Co3 O4 @MnO2 -based LIBs.

Fe3C nanocrystals encapsulated in N-doped carbon nanofibers as high-efficient microwave absorbers with superior oxidation/corrosion resistance

In addition to the demand of thin, lightweight, broadband and high-efficient characteristics, exploring microwave absorbents with superior resistance to oxidation and corrosion is urgently need for practical applications. Herein, carbon nanofibers embedded by α-Fe2O3, Fe or Fe3C nanocrystals are prepared through electrospinning technique followed by carbonization in different atmospheres. The one-dimensional structures can intertwine into three-dimensional conductive network, which is favored for energy dissipation. The Fe3C/N-doped carbon nanofibers show boosting microwave absorption properties compared to the bare carbon, α-Fe2O3/C and Fe/C nanofibers. The Fe3C/N-doped carbon nanofibers show an optimal reflection loss of −57.9 dB at 5.8 GHz with a thickness of 4.1 mm. Meanwhile, a reflection loss of −54.5 dB can be achieved at 17.8 GHz, when the absorber thickness is only 1.5 mm. The superior microwave absorption properties are attributed to the dipole polarization, interfacial polarization and ferromagnetic resonance, induced by the synergistic effect of Fe3C nanocrystals and carbon nanofibers. Moreover, acid-soaking and air-annealing treatments reveal that the Fe3C/N-doped carbon nanofibers show remarkable corrosion and oxidation resistance. This work suggests that encapsulating magnetic nanocrystals in dielectric carbon-based materials is an efficient strategy to construct high-efficient lightweight microwave absorbents with oxidation/corrosion resistance.

Cation ratio and oxygen defects for engineering the magnetic transition of monodisperse nonstoichiometric zinc ferrite nanoparticles

Monodisperse nonstoichiometric zinc ferrite nanoparticles with a tunable size of 4.1–32.2 nm are fabricated via thermal decomposition. An extrinsic impurity phase of the ZnO component is present in the zinc ferrite nanoparticles with a size of <10 nm, but this phase can be eliminated after the air annealing treatment. The atom ratio of Zn/Fe and concentration of oxygen vacancies decrease as the particle size of zinc ferrite increases, causing magnetic transition from superparamagnetism to ferromagnetism. The X-ray magnetic circular dichroism spectra reveal that the spin magnetic moments of Fe3+ are reduced, and the orbital magnetic moments are frozen with the increasing atom ratio of Zn/Fe. Therefore, saturation magnetization decreases. The saturation magnetizations of all the zinc ferrite nanoparticles decrease after the air annealing treatment, suggesting that oxygen vacancies considerably influence the magnetic properties. The air annealing treatment can minimize the number of oxygen defects, which trigger some of the Fe3+-OV-Fe3+ ferrimagnetic couplings to transfer into the Fe3+-O2−-Fe3+ antiferromagnetic couplings. This work provides new insights regarding the magnetic performance of spinel ferrites by tuning the stoichiometric ratio and oxygen defects.

Enhancing the Néel temperature in 3d/5d R2NiIrO6 (R=La, Pr and Nd) double perovskites by reducing the R3+ ionic radii

Double perovskites containing Ir4+ were synthesised by a citrate technique, followed by an annealing treatment in air at 1100 °C. The crystal structure of the three compounds, with formula R2NiIrO6 (R= La, Pr and Nd), were determined using a combined refinement against neutron powder diffraction (NPD) and synchrotron x-ray powder diffraction (SXRPD) data sets. At room temperature, all the samples were indexed in the space group P21/n and the monoclinic symmetry remains in the 300 to 1273 K temperature range. Magnetization measurements suggest competitive antiferromagnetic and ferromagnetic interactions, with an unexpected increment of the ordering temperature (TN) along the series. The magnetic structures of all the samples were defined with the propagation vector k = 0; the Ni2+ and Ir4+ moment arrangement, different for each compound, shows a strong dependence on the nature of the rare-earth ion.

Oxygen-doped hollow, porous NiCoP nanocages derived from Ni-Co prussian blue analogs for oxygen evolution.

An oxygen-doped, hollow, porous NiCoP nanocage (O-NiCoP Cages) electrocatalyst was synthesized derived from Ni-Co Prussian blue analogs. O-NiCoP Cages exhibited an overpotential of 310 mV at 10 mA cm-2 and a Tafel slope of 84 mV dec-1, significantly higher than that of undoped NiCoP nanocages, and also better than that of RuO2 and several reported phosphide electrocatalysts. This work provides a new strategy for the design of highly efficient oxygen evolution reaction (OER) electrocatalysts based on hollow, nanostructured and heteroatom-doped metal phosphides.

Enhanced water oxidation activity of 3D porous carbon by incorporation of heterogeneous Ni/NiO nanoparticles

Considering the expensive and rare property of noble-metal based materials, great efforts are made to synthesize high-activity, economical and electrochemically stable catalyst for oxygen evolution reaction (OER) in harsh alkaline. Heterogeneous materials coupled by transition metal and carbon exhibit high capability for OER in recent years. Here, three-dimensional (3D) porous carbon coupled with Ni and NiO hybrid nanoparticles (Ni-Cx-y, x and y are annealing temperature and time, respectively) is synthesized via high temperature pyrolysis and air annealing treatment. Redox reaction between carbon atoms and nickel ions during synthesis could achieve a high-level graphitization, which greatly enhances the corrosion resistance of catalyst in alkaline solution. The overpotential at 10 mA cm−2 and Tafel slope of Ni-C500-20 achieve 353 mV and 97 mV dec–1, respectively. Increased defects and intrinsic activity induced by air annealing process and synergistic effect between carbon, Ni and NiO give rise to the enhanced OER performance of as-prepared catalyst, as confirmed by in-situ Raman spectra. The catalyst conforms to sustainable and economic development concept, being a potential material for OER.

Study on friction behavior of SiC-B4C composite ceramics after annealing

PurposeThis study aims to investigate the friction behavior of SiC-B4C composite ceramics treated by annealing in air sliding against SiC balls.Design/methodology/approachThe dry sliding tests were performed with a ball-on-disk tribometer in ambient air condition. Analysis of friction coefficient, phase compositions of the surfaces, morphologies of worn surfaces of disks and wear scars of balls and surface profiles of wear tracks for disks were carried out using Raman spectroscope, microscope and surface profilometer.FindingsThe results show that a self-lubricating layer with the main composition of H3BO3 was successfully fabricated on the surface of SiC-B4C composite ceramics by the annealing treatment in air. When the mass fraction of SiC is more than that of B4C, SiC-B4C composite ceramics show higher friction coefficients, the values of which are 0.38 for 80 Wt.%SiC-20 Wt.%B4C and 0.72 for 60 Wt.%SiC-40 Wt.%B4C, respectively. SiC-B4C composite ceramics show lower friction coefficients when the mass fraction of B4C is more than that of SiC. The low friction coefficients of 40 Wt.%SiC-60 Wt.% B4C composite ceramics (0.16) and 20 Wt.%SiC-80 Wt.% B4C composite ceramics (0.20) are attributed to the formation of a sufficient amount of H3BO3 layer, rather than the layer of silicon oxides.Originality/valueThis study will help to understand the friction behavior of SiC-B4C composite ceramics with different ratios of SiC to B4C treated by annealing in air.