Post-annealing Heat Treatment Research Articles

Excellent Bifunctional Oxygen Evolution and Reduction Electrocatalysts (5A1/5)Co2O4 and Their Tunability.

Hastening the progress of rechargeable metal-air batteries and hydrogen fuel cells necessitates the advancement of economically feasible, earth-abundant, inexpensive, and efficient electrocatalysts facilitating both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a recently reported family of nano (5A1/5)Co2O4 (A = combinations of transition metals, Mg, Mn, Fe, Ni, Cu, and Zn) compositionally complex oxides (CCOs) [Wang et al., Chemistry of Materials, 2023,35 (17), 7283-7291.] are studied as bifunctional OER and ORR electrocatalysts. Among the different low-temperature soft-templating samples, those subjected to 600 °C postannealing heat treatment exhibit superior performance in alkaline media. One specific composition (Mn0.2Fe0.2Ni0.2Cu0.2Zn0.2)Co2O4 exhibited an exceptional overpotential (260 mV at 10 mA cm-2) for the OER, a favorable Tafel slope of 68 mV dec-1, excellent onset potential (0.9 V) for the ORR, and lower than 6% H2O2 yields over a potential range of 0.2 to 0.8 V vs the reversible hydrogen electrode. Furthermore, this catalyst displayed stability over a 22 h chronoamperometry measurement, as confirmed by X-ray photoelectron spectroscopy analysis. Considering the outstanding performance, the low cost and scalability of the synthesis method, and the demonstrated tunability through chemical substitutions and processing variables, CCO ACo2O4 spinel oxides are highly promising candidates for future sustainable electrocatalytic applications.

Pulsed laser deposition grown non-stoichiometry transferred ZnGa2O4 films for deep-ultraviolet applications

It is generally known that Zn volatilization would result in a serious degradation in film quality and device performance during a non-stoichiometric ZnGa2O4 target ablation. This work highlights the effect of various substrate temperatures and partial oxygen pressures on the microstructural and optoelectronic properties of stoichiometric ZnGa2O4 films. First-principle studies have been performed to calculate the formation energy per atom of pure Ga2O3, ZnGa2O4, and ZnO to understand the mechanism of preparing ZnGa2O4 by pulsed laser deposition, revealing the stability of Ga2O3 > ZnGa2O4 > ZnO under various growth parameters. Sufficient oxygen partial pressure should be introduced to deposit a large amount of ZnO, and then the Ga:Zn ratio can be adjusted to the most suitable 2:1 by controlling the substrate temperature and post-annealing heat treatment. The X-ray diffraction analysis revealed the high crystalline nature of stoichiometric ZnGa2O4 film. The average transmittance of above 80% and wide energy gap of 5.18 eV revealed the potential of stoichiometric ZnGa2O4 film in deep-ultraviolet photodetectors. This stoichiometric ZnGa2O4 film exhibited the photo/dark current ratio of 3.63 × 104 and high responsivity of 1.97 A/W at the bias of 5 V under the illumination wavelength of 220 nm for deep-ultraviolet applications.

Simultaneously minimizing residual stress and enhancing strength of selective laser melted nano-TiB2 decorated Al alloy via post-uphill quenching and ageing

Selective laser melting (SLM) of aluminium alloys is of research interest to produce customized or complex-shaped metal components for functional or structural applications. In order to palliate the undesirable residual stress developed in the SLM process, traditional post-annealing heat treatment has been widely used to lower residual stress in selective laser melted (SLMed) Al alloys. However, the traditional post-annealing method usually leads to a decrease in strength which is another concern for applications. In this study, we developed and validated a new strategy combining post-uphill quenching and subsequent ageing to simultaneously minimise residual stress and increase the strength of SLMed nano-TiB2 decorated Al alloy parts. The results show that the high as-built residual stress was partly counteracted by the newly-produced residual stress in the opposite direction during the uphill quenching stage and synergistically reduced by dislocation recovery during the ageing stage. The microstructural features of grains and cell structures remain unchanged after the treatment. While substantial new nano-Si particles with dot-like or needle-like morphology precipitate inside the cells. The tensile strength was improved mainly due to effective precipitation strengthening by dispersed nanosized Si precipitates. The proposed strategy is expected to be useful in other materials and components fabricated by SLM in which residual stress is also unwanted.

Modeling and Experimental Studies on Adsorption and Photocatalytic Performance of Nitrogen-Doped TiO2 Prepared via the Sol–Gel Method

Nitrogen-doped TiO2 has a great potential as a photocatalyst under visible light irradiation with applications in the removal of air and water pollutants, and the treatment of bacterial contaminations. In this study, nitrogen-doped TiO2 nanoparticles were synthesized via the sol–gel method and a post-annealing heat treatment approach. The effects of annealing treatment on the photocatalyst crystalline size and degree of crystallinity were analyzed. Methylene blue dye was used as the model water contaminant for the evaluation of the photoactivity of the synthesized nitrogen-doped TiO2 nanoparticles. The degradation of methylene blue was attributed to three mechanisms, i.e., adsorption, photocatalysis, and direct light photolysis. A kinetic model was developed to distinguish the impact of these three different mechanisms on the removal of contaminants. Adsorption and photocatalysis are heterogeneous processes for removing water organic contaminants. The characterization analysis demonstrates that they are relevant to the microstructures and surface chemical compositions of nitrogen-doped TiO2 photocatalysts. The processing–structure–performance relationship helped to determine the optimal processing parameters for nitrogen-doped TiO2 photocatalyst to achieve the best performance. While we used methylene blue as the model contaminant, the generalized quantitative model framework developed in this study can be extended to other types of contaminants after proper calibration.

Influence of the spark-plasma texturing conditions on the intragranular features of Bi-2223 ceramic samples

The influence of the spark-plasma texturing (SPT) conditions on the intragranular superconducting properties of $$\hbox {Bi}_{1.65}\hbox {Pb}_{0.35}\hbox {Sr}_2\hbox {Ca}_2\hbox {Cu}_3\hbox {O}_{10+\delta }$$ (Bi-2223) samples has been investigated. Also, the SPT samples were subjected to a post-annealing heat treatments (PAHT) in different times. Intragranular superconducting features, extracted from magnetoresistance measurements, $$\rho (T,H)$$ , in applied magnetic fields up to 9 T, were studied by analyzing the temperature dependence of the in-plane upper critical field, $$H^{ab}_\text{c2}(T)$$ , and the magnetic field dependence of the pinning energy at zero temperature, U(0, H). The results indicated that, before and after the PAHT, values of the $$H^{ab}_\text{c2}(0)$$ , obtained by using the Werthamer–Helfand–Hohenberg formula, increased $$\sim 21 \%$$ , i.e., from 115.8 to 140.2 T. We have also found that the effective intragranular pinning energy at zero applied magnetic field, $$U_0 = U(0,0)$$ , also increased over approximately three times, from 0.28 to 0.98 eV. These results strong strongly indicate that the SPT process is responsible for inducing deoxygenation at the intragranular level of ceramic samples, a feature presumably occurring near of the end of planar defects.

Experimental and numerical investigations of low cycle fatigue behavior of cryorolled AA 5754

The objective of the present work is to study the influence of cryogenic forming on low cycle fatigue (LCF) properties of Al-Mg (AA 5754) alloy. AA 5754 is rolled at liquid nitrogen temperature (cryorolling) for maximum of 40% thickness reduction. Post-annealing heat treatment (PAHT) at 250oC for 2 hours is adopted to enhance the mechanical and fatigue properties of the cryorolled alloy. A series of uniaxial strain controlled LCF tests are executed at three different strain amplitudes from 0.4% to 0.6% for cryorolled (CR) and annealed cryorolled (ACR) AA 5754 alloy. PAHT significantly improves the tensile strength as well as ductility of CR alloys. LCF tests reveal that cryorolled alloys show mild hardening in the initial cycles followed by noticeable cyclic softening at all strain amplitudes. In contrast, only cyclic hardening behavior is depicted by ACR specimens at all strain amplitudes. The extended finite element method (XFEM) has been utilized to simulate the tensile behavior of the specimen. Finite Element Method (FEM) coupled with Chaboche kinematic hardening cyclic plasticity model is used for simulating hysteresis loop obtained during LCF test. The present study exhibits good match between simulations and experimental results.

Thermal Chemically Deposited Zno Nanostructures: Influence of Post-Deposition Annealing Temperature on Ph Sensor Performance

Zinc oxide (ZnO) nanostructures were synthesized via thermal chemical deposition (TCVD) method and applied as the sensing membrane of an extended-gate field effect transistor (EGFET) pH sensor. The ZnO nanostructures undergone a post-deposition heat treatment with the temperature ranging from 200-500 °C for 15 min in air ambient. The influence of the post-deposition heat treatment on the physical and pH sensing characteristics was investigated. The FESEM images showed that the surface morphology of the samples were dependent on post-annealing treatment. The as-deposited sample showed the biggest grain size and non-uniformed structures. Applying the post-annealing heat treatment caused the surface morphology to become denser and uniform. The most ideal temperature for the heat treatment for EGFET pH sensor application was found at 300 °C resulting in a pH sensitivity of 48.2 mV/pH with 0.9646 linearity.

Improved magnetic properties of Zn-substituted strontium W-type hexaferrites

The Zn2+ substitution for the Fe2+ site was found to be effective for the improvement of the saturation magnetization (Ms) of strontium W-type hexaferrite (SrFe18O27). For this study, polycrystalline SrFe18O27 with various Zn-substituents of SrZnxFe(2-x)Fe16O27 (SrZnxFe(2-x)W, 0.0 ≤ x ≤ 1.5) were sintered at high temperatures in a reduced oxygen atmosphere of 10−3 atm. While pure SrZnxFe(2-x)W-type solid solutions (0.0 ≤ x ≤ 1.0) could be obtained, the second phase of ZnFe2O4 was obtained from the sample of x = 1.5, and the second phases of Sr2Zn2Fe12O22 and ZnFe2O4 was obtained from the sample of x = 2.0. With increasing x up to 1.0, Ms values were monotonously increased and the highest Ms value of 87.7 emu/g was obtainable from the sample of x = 1.0 sintered at 1250 °C. In addition, post-annealing heat treatments of samples for oxygenation at 300 °C in pure oxygen gas revealed that oxygen non-stoichiometry increased with increasing the sintering temperature, leading to the increase in Ms, unit cell volume, and electrical conductivity.

Highly dense and textured superconducting (Bi,Pb)2Sr2Ca2Cu3O10+δ ceramic samples processed by spark-plasma texturing

Consolidated powders of the superconducting cuprate Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) by the spark-plasma texturing (SPT), spark-plasma sintering (SPS), and the traditional solid-state reaction method were investigated by several techniques and their features compared. The results show that SPT samples exhibit a higher degree of texture, as inferred by a Lotgering factor of ∼0.73 along the [00l] direction and a relative density of 96% of the theoretical value. From magnetic hysteresis loops M vs. H at 5K, the intragranular critical current densities along two applied magnetic field orientations, Jc0c and Jc0ab, relative to the compacting pressure direction, were determined. The anisotropy factor, γJ=Jc0ab/Jc0c, yielded an estimate of ∼2 in the SPS sample and ∼19 for samples obtained via the SPT method. In the latter samples, Jc0c at 5K is close to 1.3×108A/cm2, a value higher than others found for the same compound. The temperature dependence of the electrical resistivity, ρ(T), analyzed within the framework of a current conduction model for granular superconductors, supports the higher degree of texture of SPT samples and indicates changes in the oxygen content when samples are subjected to a post-annealing heat treatment. All the results reveal the promising capabilities of the SPT method for improving volume density, texture, and grain boundary connectivity of superconducting Bi-2223 materials.

Spark Plasma Sintering of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ Superconducting Samples: Evaluation of Microstructure and Mechanical Properties

Powders of single-phase Bi1.65Pb0.35 Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by the spark plasma sintering (SPS) method at 750 ∘C. The SPS samples exhibited very high density, but are oxygen deficient, as inferred from magnetization, M(T), data. Therefore, the samples were then subjected to a post-annealing heat treatment in air, at 750 ∘C for 5 min. From the combined data of X-ray diffraction, microstructures observed by SEM, and Vickers microhardness measurements, we have found that SPS post-annealed samples showed the presence of an extra phase. According to the EDS analysis and X-ray diffraction results, the extra was identified as an infinite layer compound with general formula Ca1−x Sr x CuO2. Irrespective of the presence of this additional phase, the superconducting properties of post-annealed SPS samples are optimized when they are heat treated in air, at 750 ∘C for just 5 min. We have also observed a decrease in the Vickers as well as different indentation features in post-annelaed samples when compared with SPS ones. The occurrence of a decohesion of grains has been also observed, a feature similar to that found previously in the same material. On the other hand, a pile up formation occurred throughout the indentation in the sample, in which the annealing was carried out. 3-D profilometer characterizations confirmed these results, which are close related to the occurrence of the extra phase Ca1−x Sr x CuO2.

10 to 25-fold increase in the transport superconducting critical current density of spark-plasma sintered Bi-2223 superconductors

Pre-reacted powders of (Bi-Pb)2Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at two different temperatures TD: 750 and 830 °C. The results indicate the occurrence of grains with core-shell morphology, where the shell is oxygen deficient. A post-annealing heat treatment (PAHT), performed in air, at 750 °C, and for a brief time interval, is responsible for a 10 to 25-fold increase in the transport superconducting current density at 77 K. The role of the oxygen-deficient shell, before and after the PAHT, was investigated by means of magnetic and transport measurements. We argue that the PAHT is two folds: (i) it is responsible for the decrease of the width of the oxygen-deficient shell, then increasing the oxygen content along the grain boundaries; (ii) it promotes the formation of conduction current paths along the grain boundaries of the SPS material.

Effect of grain size on nanomechanical property Ni80Fe20 thin film

The purpose of this paper is to describe the results of this study into the structure and nanomechanical properties of Ni80Fe20 thin film. The films were sputtered onto glass substrates with thicknesses of 500 Å, 1000 Å, and 1500 Å, respectively. These three thicknesses were tested both at room temperature (RT) and with a post-annealing heat treatment temperature of 250 °C for 1 h. The plane-view microstructure was observed under a high-resolution transmission electron microscope (HRTEM) to determine grain distribution. The selected area diffraction (SAD) pattern was obtained with the HRTEM to investigate NiFe microstructures. Electron diffraction patterns demonstrated that NiFe thin film has a face-centered cubic (FCC) structure and strong NiFe (111) crystallization. Annealing treatment increased the grain size distribution of the thin film. The grain size is increased at the thicker thickness of NiFe thin film. Nano-indentation was used to measure hardness and Young's modulus; based on these results and the grain size, the decline of hardness can be reasonably inferred from an enlarged grain size, which is consistent with the Hall–Petch effect. However, the rising Young's modulus measurement can be reasonably associated with the effect of the sputtered adhesion of NiFe thin film.

The effect of processing routes on the structure and properties of magnesium–TiNi composites

TiNi particulate-reinforced magnesium matrix composites were fabricated by rotary hot swaging and post-annealing heat treatment. The magnesium matrix of the processed composites was observed to contain elongated grains comprised of equiaxed recrystallised grains. Each elongated grain was surrounded by thin, non-continuous magnesium oxide layers composed of nanometric magnesium oxide particles. The TiNi reinforcement particles preserved their starting spherical shape during processing and testing. However, the hot deformation and annealing heat treatment changed the underlying room temperature microstructures and transformation behaviours of the reinforcements. In contrast to the majority of the ceramic reinforcements, the ductility of the composites was not significantly degraded by the addition of TiNi reinforcements; conversely, an approximately 25% enhancement was recorded in the elongation values for the Mg–5vol% TiNi alloy. While the yield strengths of the composites changed linearly with increasing reinforcement content, the highest compression peak strength value was obtained with the addition of 5vol% TiNi, beyond which the strength was slightly decreased. During mechanical testing, the TiNi particles debonded due to insufficient bonding between the matrix and reinforcement, and fracture resulted largely within the oxide layers present in the interfacial region and the magnesium oxide film in the magnesium grain boundaries.

Electrochemical performance of spinel LiMn 2O 4 cathode materials made by flame-assisted spray technology

Spinel lithium manganese oxide LiMn 2O 4 powders were synthesized by a flame-assisted spray technology (FAST) with a precursor solution consisting of stoichiometric amounts of LiNO 3 and Mn(NO 3) 2·4H 2O dissolved in methanol. The as-synthesized LiMn 2O 4 particles were non-agglomerated, and nanocrystalline. A small amount of Mn 3O 4was detected in the as-synthesized powder due to the decomposition of spinel LiMn 2O 4 at the high flame temperature. The impurity phase was removed with a post-annealing heat-treatment wherein the grain size of the annealed powder was 33 nm. The charge/discharge curves of both powders matched the characteristic plateaus of spinel LiMn 2O 4 at 3 V and 4 V vs. Li. However, the annealed powder showed a higher initial discharge capacity of 115 mAh g −1 at 4 V. The test cell with annealed powder showed good rate capability between a voltage of 3.0 and 4.3 V and a first cycle coulombic efficiency of 96%. The low coulombic efficiency from capacity fading may be due to oxygen defects in the annealed powder. The results suggest that FAST holds potential for rapid production of uniform cathode materials with low-cost nitrate precursors and minimal energy input.

Growth and Structural Characterizations of Nanostructured Chromium-Zirconium-Nitride Thin Films for Tribological Applications

Nanostructured Cr-Zr-N thin films were grown on Si(100) substrates in a mixture of Ar and N2 plasma. The nitrogen partial pressure was varied to produce and control the stoichiometric forms obtained. All the Cr-Zr-N films exhibited a nanostructure with an average grain size of less than 10 nm, as determined by X-ray diffractogram analysis, and were formed in the solid-solution. As the contents of nitrogen in the film increased, it lead to changes in the crystal texture and competitive growth. The maximum root mean square roughness was 7.87 nm at a 20% nitrogen partial pressure and the roughness tended to decrease as the grain size decreased. The nano-indentation showed that the films grown at a 20% nitrogen partial pressure and annealed at 700 � C had the highest reduced modulus and hardness at 349.2 and 35.1 GPa, respectively. The mechanical properties of films can be improved by a post-annealing heat treatment. With respect to the electrical properties of these films, the sheet resistance, which is related to the defect level, tended to increase as the nitrogen partial pressure increased. [doi:10.2320/matertrans.M2010140]

The structural, magnetic and nanomechanical properties of hexagonal Co thin films

Ferromagnetic (FM) Co thin film can provide a free and/or pinned layer in the magnetic tunnel junction (MTJ). Because the mechanical and microstructure properties of Co are crucial to device performance in read head, gauge sensor, and magnetoresistance random access memory (MRAM) applications, it is worthwhile to study the strength and durability of the device. However, few researchers have studied these properties at room temperature (RT) and in heat-annealing environments. In this work, Co thin films were sputtered onto the glass substrates with the thickness ( t f) varied from 100 Å to 500 Å under different conditions: (a) the substrate temperature ( T s) kept at RT and (b) T s = RT and post-annealing heat treatments. The hardness and Young's modulus of the Co thin films were obtained from nanoindentation tests. To observe the grain distribution, we observed the plane-view microstructure with high-resolution transmission electron microscopy (HRTEM). From the electron diffraction pattern, we found that the Co thin film had a hexagonal (HCP) structure. Based on the nanoindentation results, the mechanical properties of Co thin films are an interesting issue in the magnetic industry applications.

Magnetic properties of Co-ferrite thin films prepared by PLD with in situ heating and post-annealing

Co-ferrite thin films on (1 0 0) SiO 2 substrates were deposited using pulsed laser deposition with in situ heating and post-annealing heat treatments. The structure and magnetic properties of the films were analyzed by X-ray diffractionmetry, atomic force microscopy, transmission electron microscopy, Raman spectroscopy and alternating gradient force magnetometry. High perpendicular coercivity around 8.9 kOe has been obtained in the film with in situ substrate heating at 700 °C. High coercivity of Co-ferrite thin film was found to be related to nanocystalline grain size, large lattice strain, surface roughness and preferential texture structure.

Magnetic and structural properties of MnAl/Ag granular thin films with L10 structure

Abstract MnAl/Ag granular thin films with the L1 0 structure have been prepared by sputtering MnAl/Ag peusdo-multilayer precursors at a temperature around 200 °C. The effects of the bilayer thicknesses and post-annealing heat treatment on the particle structure, microstructure and magnetic properties were investigated.

Extrinsic conductivity in ferroelectric PZT film capacitors made by laser ablation deposition

Electrical properties of ferroelectric lead–zirconate–titanate (PZT) thin-film devices are affected by the composition and structure of the PZT film itself and also by the electrode material and the interface between the electrode and ceramics. In this paper we consider capacitor structures with platinum thin-film electrodes (Pt/PZT/Pt/substrate) which typically have very high dc resistivity, but suffer from the polarization fatigue due to the high stress and oxygen vacancy build-up in the interface between the electrode and ceramic thin film. Both platinum electrodes and Nd-modified PZT (PNZT) thin films were fabricated by the pulsed laser-ablation deposition and post-annealing heat treatments. The behaviour of the conductivity in the PNZT thin-film capacitors was studied as a function of temperature and electric field. Low-field resistivities of the order of 1012 Ωcm were measured for the films at room temperature. Some differences were found in the current–voltage characteristics between capacitor structures made on MgO(100) and oxidized silicon(100) substrates, respectively. Assuming the Poole–Frenkel emission mechanism for the conduction, the activation energies of conduction were obtained to be between 0.15 and 0.18 eV.

CO2 laser annealing of plasma-deposited high-T c superconducting thick films

Recent advances in the fabrication of high-T c superconducting thick films demand processing techniques which can eliminate film/substrate interdifiusion that occurs during subsequent post-annealing heat treatment after the film is deposited, thereby limiting the application of the thick films for devices. The present study evaluates laser annealing techniques for plasma-deposited Y-Ba-Cu-O thick films using a high-energy CO2 laser (10.6Μm) in a continuous wave mode. The results are compared with those obtained by conventional furnace annealing techniques necessary for post-heat treatment of as-deposited superconducting thick films. The high-T c superconducting phase is recovered by cationic diffusion during subsequent post-annealing heat treatment. Crystallographic phases and microstructural characterization have been performed using XRD, SEM, and EPMA analytical techniques. The significance of the technology lies in the elimination of film/substrate interdiffusion problems, thereby resulting in high-quality superconducting thick films. The technology will significantly reduce the post-annealing times usually required by conventional furnace annealing techniques.