查看更多>>摘要：Trimethylamine (TMA), which mainly emanates from decaying fish, is an important freshness indicator of seafood. In this work, a TiO_2-NiFe_2O_4 heterojunction was successfully synthesized for TMA detection using a simple and efficient hydrothermal method. The materials were characterized using X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. The TiO_2-NiFe_2O_4-based sensor exhibited the largest response (12) to 10 ppm of TMA at 307 °C The response was further improved under white-light irradiation, increasing from 2.5 to 4.5 as the TMA concentration approached 3 ppm. The enhanced gas-sensing performance of the TiO_2-NiFe_2O_4 sensor under light irradiation was then explored by density functional theory (DFT) with an optical carrier. We believe that the developed strategy improves the gas-sensing ability for TMA detection and can potentially be used in gas sensors.
查看更多>>摘要：Additive manufacturing has been vastly applied to fabricate various structures of nickel-titanium (NiTi) shape memory alloys due to its flexibility to create complex structures with minimal defects. However, the microstructure heterogeneity and secondary phase formation are two main problems that impede the further application of NiTi alloys. Although post-heat treatment is usually adopted to improve or manipulate NiTi alloy properties, it cannot realize the spatial control of thermal and/or mechanical properties of NiTi alloys. To overcome the limitations of uniform post-heat treatment, this study proposes an in-situ heat treatment strategy that is integrated into the directed energy deposition of NiTi alloys. The proposed method will potentially lead to new manufacturing capabilities to achieve location-dependent performance or property manipulation. The influences of in-situ heat treatment on the thermal and mechanical properties of printed NiTi structures were investigated. The investigations were carried out in terms of thermal cycling, microstructure evolution, and mechanical properties by 3D finite element simulations and experimental characterizations. A low-power laser beam was adopted to localize the in-situ heat treatment only to the current printed layer, facilitating a reverse peritectic reaction and a transient high solution treatment successively. The proposed in-situ heat treatment on the specimen results in a more obvious phase transformation peak in the differential scanning calorimetry curves, about 50-70% volume reduction for the Ti_2Ni phase, and approximately 35 HV reduction on microhardness.
查看更多>>摘要：Secondary hot-working on dual phase titanium alloys are essential for microstructural modification to tailor mechanical properties, which is typically challenging due to a narrow available processing window, especially during industrial scale manufacturing. Poor workability, strain induced porosity and adiabatic temperature rise in α+β phase region (i.e., sub-transus) are some of the main challenges faced. Cyclic thermal treatment (CTT) is an emerging technology showing potentials for microstructure modification (i.e., globularisation) in Ti-6A1-4V with significantly reduced mechanical work in the α+β region. This study summarises the results of CTT investigations conducted on a wrought Ti-6A1-4V alloy subjected to various thermo-mechanical conditions to develop different initial microstructures. Samples with uniform strain distributions were extracted from pre-forged samples and subsequently subjected to CTT using both conventional electric furnace (i.e., for slow heating and cooling rates), and induction heating (i.e., for faster heating and cooling rates). CTT of the samples forged at sub-transus temperature in conventional furnace led to maximum (i.e. -100%) globularisation and significant coarsening of a grains, resulting in an equiaxed bimodal microstructure. On the other hand, CTT with induction heating method has resulted in a maximum of 80% globularisation fraction in samples forged to 60% reduction, and -35% globularisation fraction in those forged to 20% reduction. The globularisation mechanisms during CTT of the sub-transus forged samples was dominated by the boundary splitting and thermal grooving. A Johnson-Mehl-Avarmi-Kolmogorov (JMAK) based model has been developed to predict the evolution of globularisation and grain growth during CTT. The developed JMAK model was then successfully incorporated into DEFORM~R software as post-processing user subroutines. The predicted microstructure evolution by Finite Element (FE) simulations shown a good convergence towards the experimentally measured data following CTT.
查看更多>>摘要：A photostable Ag_3PO_4/BCN type-II p-n heterojunction has been demonstrated by loading nano Ag_3PO_4 on B-doped g-C_3N_4 nanosheet (BCN). The photocatalysts were successfully characterized by various physico-chemical techniques and their photocatalytic activities were tested towards the water oxidation reaction to produce oxygen and Cr (VI) reduction under visible light. The HRTEM confirms Ag_3PO_4 with a particle size of 15 nm has been deposited on BCN to construct a p-n heterojunction. The BCNS-50 absorbs more visible light in the solar spectrum as compared to other catalyst, demonstrating the ability to generate 587 umol h~(-1)g~(-1) O_2 and reduces 98% of 20 ppm Cr (VI) solution in 1 h. The lower PL intensity as well as lower arc value in case of BCNS-50 suggests the maximum e-h separation and lower charge transfer resistance across the semiconductor/electrolyte interface. The BCN sheet provides a compact heterojunction where the oxidation peak of Ag_3PO_4 decreases gradually and disappear in case of BCNS-50 suggesting the enhance stability of Ag_3PO_4 in the heterojunction. BCNS-50 could able to produce -139 and 3087.5 uA photocurrent both in cathodic and anodic direction which is approximately 7 and 2.4 folds higher as compared to nano Ag_3PO_4. The generation of photocurrent in both cathodic and anodic direction confirms the formation of p-n heterojunction which further supported by Mott-Schottky analysis. Furthermore the construction of the p-n heterojunction is verified via Mott-Schottky study. DFT calculation explains the contribution of various atomic orbital of Ag_3PO_4 and BCN towards the formation of hybrid orbital in the heterojunction and the path for charge derealization between them. This work may provide a limelight and alternative pathway for enhanced photocatalytic performance on construction of the p-n heterojunction in a simple way.
查看更多>>摘要：The understanding of the fracture mechanism of amorphous alloys (AAs) is of importance for their engineering applications as advanced structural materials. In this study, a series of micro-tensions of Cu_(45)Zr_(45)Co_(10) AA microwires were conducted under different strain rates ranging from 5 x 10~(-5)s~(-1) to 1 x 10~(-2)s~(-1). It is found that all microwires fracture by shear cracking, but the shear fracture strengths exhibit pronounced rate-dependent uncertainties. Based on both lognormal and Weibull statistical analyses, the studied AA microwires reveal a positive rate-sensitivity of fracture strengths. However, increasing strain rates incurs the decrease in the fracture reliability. We demonstrate that the fracture reliability of AA microwires is dominated by a square root singularity of the characteristic lengths of shear offset on fracture surfaces, which satisfies linear elastic fracture mechanics.
查看更多>>摘要：A hybrid-material of titanium-oxide quantum dots (QDs) anchored on graphene nanoribbons (TiO_2@GNRs) was prepared by a simple hydrolysis strategy followed by heat-treatment. The GNRs can effectively accelerate the charge transference in the TiO_2@GNRs. And the TiO_2 QDs of ~5 nm can be thoroughly lithiatied/ sodiated in electrically confined space of GNRs. Motivated by its unique structure, the electrochemical charge/discharge behaviors of the TiO_2@GNRs serving as anodes for Li/Na-ion batteries (LIBs/SIBs) were evaluated. Reversible charge capacities of 320.8 mAh g~(-1) for LIBs and 101.6 mAh;g~(-1) for SIDs were demonstrated over 100 cycles at a rate of 0.5 A g~(-1), respectively. And Li and Na storage capacities of 209.0 and 42.2 mAh g~(-1) were retained at 8.0 A g~(-1) respectively. The desirable charge capacities, stable cyclic ability, and excellent rate performance of TiO_2@GNRs can be ascribed to the ultra-small TiO_2 size benefiting for full insertion/extraction of alkali ions and shortening their transfer pathway as well as enhanced electronic and ionic conductivity of the overall electrodes and interfacial confinement of GNRs for maintaining the electrode integrity.
查看更多>>摘要：Supercritical hydrothermal synthesis is a promising technology to produce nano-ZrO_2 due to its simple craft, short reaction time and low cost. In this paper, nano-ZrO_2 particles with an average particle size of 5.66-35.43 nm were successfully prepared by supercritical hydrothermal method. Meanwhile, the influences of reaction temperature, pressure, time, precursor concentration and pH value on the particle size distributions and surface topographies of nano-ZrO_2 were investigated under different conditions. Reaction time and precursor concentration were strong influencing factors of particle sizes and distributions. The reaction mechanisms of different crystal forms were controlled by pH value of the precursor. Under acidic conditions, soluble [Zr4(OH)_8(H_2O)_(16)]~(8+) was produced due to the hydrolysis of precursors, and the appearance of abundant monoclinic nucleus was triggered subsequent condensation of [Zr_4(OH)_8(H_2O)_(16)]~(8+). In-situ crystallization dominated the crystallization process and the tetragonal phase was formed by the rearrangement of the precursor structures. The intermediate product Zr(OH)_3NO_3 was detected under high pH conditions.
查看更多>>摘要：Ultra-fine Ta_4HfC_5 and TaHfC_2 powders were prepared through the pyrolysis of a precursor synthesised by using a facile one-pot reaction. HfCl_4, TaCl_5, and phenolic resins were used as the sources of hafnium (Hf), tantalum (Ta), and carbon (C), respectively. The as-synthesised precursors were further utilised to prepare Ta_4HfC_5- and TaHfC_2-modified carbon/carbon (C/C-Ta_4HfC_5 and C/C-TaHfC_2) composites through precursor infiltration and pyrolysis. The transformation of Ta_4HfC_5 and TaHfC_2 precursors into ultra-fine ceramic powders and anti-ablation performance of the C/C-Ta_4HfC_5 and C/C-TaHfC_2 composites were investigated. The carbothermal reduction of Ta_2O_5 and Hf_6Ta_2O_(17) and the solid solution reaction between HfC and TaC occur successively during the pyrolysis of Ta_4HfC_5 precursors. HfC and TaC undergo a sufficient solid solution reaction at 1800 °C to form the Ta_4HfC_5 solid solution with a particle size of 200-300 nm. The pyrolysis products of TaHfC_2 precursors acquired at 1400-1600 °C are composed of TaC, HfC and TaHfC_2. High-temperature pyrolysis promotes the solid solution reaction between TaC and HfC. The TaHfC_2 solid solution with a particle size of 100-150 nm is formed at 1800 °C. The introduction of TaHfC_2 and Ta_4HfC_5 solid solutions into the C/C composite substantially enhances their anti-ablation performance. The linear ablation rates of C/C-Ta_4HfC_5 and C/C-TaHfC_2 are 11.04 and 16.97 um/s, respectively, which are considerably lower than that of the C/C composite. The good anti-ablation performance of the C/C-Ta_4HfC_5 and C/C-TaHfC_2 composites can be attributed to the formation of the Ta_2O_5 and Hf_6Ta_2O_(17).
查看更多>>摘要：A novel organic-inorganic hybrid compound based on iron fluoride, formulated as (H_2Piper)_4 [(FeF_6)_2FeF_5(H_20)(H_20)4] (Piper = Piperazine), C1, has been synthesized through hydrothermal method and characterized by X-ray single-crystal diffraction, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and dielectric measurements. Single-crystal X-ray study demonstrated that C1 crystallizes in P 1 space group with lattice parameters: a =12.5535(5) A, b =12.8715(4) A, c =22.2774(8) A, a = 92.321(3)°, p = 95.957 (3)°, y = 91.946(3)°, V = 3574.6 A~3 and Z= 4. In the molecular arrangement, [FeF_6]`(3-) and [FeF_5(H_20)]~(2-) anions are connected to [H_2Piper]~(2+) cations and free water molecules through hydrogen bonds (O-H-F and N-H--F) generating 3D network. Thermal analysis (DSC and TG) of C1 confirmed the presence of two phase transitions as well as the temperature of the decomposition of the hybrid material. The complex impedance of C1 was investigated in the temperature range 410-530 K and in the frequency range 200-2.106 Hz. Additionally, an electrical equivalent circuit was reported to explain the impedance results. The variation of the dc and ac conductivity corroborated two phase transitions of the title compound. Furthermore, the frequency dependence of alternative current (ac) conductivity was interpreted in terms of Jonscher's law. The alternative current (ac) electrical conduction in C1 material was accounted for in terms of two processes that can be assigned to the hopping transport mechanism (CBH and NSPT model). The temperature dependences of dielectric permittivity indicated a relaxation process and highlighted the good protonic conduction of this material.
查看更多>>摘要：Annealing at different temperatures was applied to a hot-rolled Ti-15Nb-5Zr-4Sn-1Fe (wt%) alloy to obtain α+β dual-phase structure with varying a phase fraction. The evolutions of a + p dual-phase structure, mechanical properties, and deformation mechanisms were systematically investigated. With increasing a phase from 5.5% to 33.7%, the stability of the retained p matrix was gradually enhanced and the p domain size was decreased. The deformation mechanisms changed from stress-induced p to a' martensitic transformation to stress-induced p to a" martensitic transformation, mechanical twinning of the p matrix, and finally dislocation slip accompanied with increasing a phase. Accordingly, Young's modulus decreased monotonously attributed to gradually suppressed athermal a phase, while the yield strength first decreased slightly owing to the change of stress-induced martensite from a' to a", and then increased rapidly when the long-range stress-induced martensite was suppressed. A good combination of low Young's modulus, high strength, and high ductility was obtained in a microstructure composed of ultrafine grained α+β dual-phase showing dislocation dominated plastic deformation. This study possibly serves as a templet to guide the development of ultrafine grained α+β dual-phase structured metastable p-Ti alloy for biomedical application.
NSTL
Elsevier