Search

Ultrasound assistance was applied to friction stir transient liquid phase spot welding (FSTLPSW) to attain a high-quality dissimilar copper-aluminum joint in this study. Different ultrasound-assisted times were selected for comparing with the conventional condition without ultrasound. The interfacial microstructure evolution of conventional joint was analyzed combined with the measured temperature cycle. The ultrasound assistance improved the joint quality by regulating the interfacial microstructure. Cavitation erosion, broken IMC particles and thicker eutectic layer appeared in ultrasound-assisted joint. The highest tensile shear strength of 7.38 kN was obtained under the ultrasound-assisted time of 60 s which was 43.1 % higher than that of the conventional joint. The fracture location transferred from IMC layers to eutectic layer under the ultrasound assistance.

Decorating semi-conducting metal oxide with noble metal has been recognized as a viable approach to improve the sensitivity of gas sensor. However, conventional method which relys on noble metal nanoparticles is confronted with drawback of significantly increased cost. To maximize the atom efficiency and reduce the cost for practical industrial application, designing sensor material with noble metal isolated single atom sites (ISAS) doping is a desired option. Here, we report an atomically dispersed platinum on one-dimensional arranged porous γ-Fe2O3 nanoparticle composites as highly efficient ethanol gas sensor. The optimized sample (Pt1-Fe2O3-ox) exhibited a high response (Ra/Rg = 102.4) and good selectivity to ethanol gas. It is demonstrated only the Pt single atom sites with high valance can effectively promote the adsorption capacity to ethanol and consequently enhance the sensitivity of sensing process by changing the electrical structure of Fe2O3 support. This work indicates the single atom sites could play a vital role in improving the performance of conventional metal oxides gas sensors and pave way for the exploration of ISAS-enhanced gas sensor for other volatile organic compounds (VOCs).

The artificial intelligence technique is utilized to improve evaluation of thermally induced solid-state reaction kinetics. A general regression neural network (GRNN) model was applied to directly determine the kinetic triplets, i.e., activation energy, pre-exponential factor, and mechanism model. The effect of number of heating rate on prediction performance of the GRNN model was assessed based on the estimation indictors. The obtained kinetic triplets based on the triple heating rates were considered to be accepted. The prediction ability of the GRNN model was very robust at more than three heating rates. The relative errors for kinetic parameters derived from five heating rates were within ± 4%, and the cognition rates for mechanism models were up to 99.6%. The developed GRNN model was successfully applied in the high-temperature synthesis of Li4Ti5O12/C composites. It is expected that the model also could be extended to estimate the kinetics of other solid-state reactions.

Grouting is an important method to reinforce fractured rock mass in underground engineering. To improve the grouting reinforcement effect of fractured rock mass, the theory of self-stress grouting reinforcement was put forward for the first time, and the self-stress grouting material was developed. The swelling stress of self-stress grouting material was tested by self-developed testing device to analyze the relationship between swelling stress and expansive agent content. Then, with cement, bentonite, silica fume, FZ expansive agent, accelerator, water reducer and water as raw materials, the effects of bentonite-cement ratio, silica fume content, accelerator content and water reducer content on the fluidity, initial setting time, uniaxial compressive strength at 3 days and 28 days of grouts were investigated by orthogonal test. Finally, the optimum proportion of the cement-based self-stress composite grouting material was applied to reinforce crushed coal blocks and the surrounding rocks of mine roadway, respectively. The results shown the optimum expansive agent content of the grout was 10%, corresponding swelling stress of 0.82 MPa. The proportion of the cement-based self-stress composite grouting material was bentonite-cement ratio of 1, FZ expansive agent content of 10%, silica fume content of 6%, accelerator content of 2.9%, and retarder content of 2.5%. The uniaxial compressive strength of the crushed coal blocks after reinforcement was 12.1 MPa, which was greater than the strength of the original coal. The cement-based self-stress composite grouting material had significant effect on the reinforcement of the surrounding rocks of mine roadway.

A series of concrete mixes with metakaolin (MK) content ranging from 0 to 30% and water/cementitious materials (W/CM) ratio varying from 0.30 to 0.50 were produced for performance testing. The results showed that adding MK up to 20% as ordinary Portland cement (OPC) replacement best improved the 28-day and 70-day cube strengths, whereas adding MK up to 30% as OPC replacement always increased the cohesiveness and decreased the sorptivity, but impaired the workability. Moreover, the cement equivalent factor (CEF), i.e. the equivalent mass of OPC per mass of MK added, for each performance attribute, including workability and cohesiveness, was evaluated. Whilst the actual CEF of MK was generally higher at a higher W/CM ratio and lower at a higher MK content, overall, the average CEFs were found to be 1.98, 2.17, 3.83, 1.93, 2.12, and 4.70 for slump, flow, cohesiveness, 28-day cube strength, 70-day cube strength, and sorptivity coefficient, respectively. These CEF values indicated that the MK is a highly effective cementitious material for improving the cohesiveness, strength, and durability. Moreover, it has been demonstrated that the CEFs for workability and cohesiveness are useful parameters in aiding the mix design of MK concrete., This research was funded by National Natural Science Foundation of China (grant number 51678161), Research Project of Guangdong Provincial Education Department of China (grant number 2018GXJK197), Guangdong Provincial Education Department Educational Reformation Project (grant number 595 in year 2018), Research Centre of Green Building Materials and Modular Integrated Construction Technology of Guangdong Province of China (grant number ZCZX201803), Featured and Innovative Project for Colleges and Universities of Guangdong Province (grant number 2017KTSCX061) and Pearl River S&T Nova Program of Guangzhou City (grant number 201906010064)

α-V2O5 (001) thin films were fabricated by reactive magnetron sputtering. The effects of the deposition temperature as well as the oxygen flux on the crystal structure, surface morphology and terahertz property were studied. The formation of vanadyl oxygen defect leads to a transient charge distribution that forms THz radiating dipoles in α-V2O5(001) surface. THz properties are closely related with the thermally reduced surface of α-V2O5 (001) films. Dynamics of the formation of surface oxygen vacancies accompanied with VO6 octahedral distortion is the key to understand the THz luminescence from the thermally reduced surface of V2O5.

In situ synchrotron x-ray imaging and diffraction are used to investigate deformation of a rolled magnesium alloy under uniaxial compression at room and elevated temperatures along two different directions. The loading axis (LA) is either perpendicular or parallel to the normal direction, and these two cases are referred to as LA ⊥ 〈 c 〉 and LA ∥ 〈 c 〉 loading, respectively. Multiscale measurements including stress–strain curves (macroscale), strain fields (mesoscale), and diffraction patterns (microscale) are obtained simultaneously. Due to initial texture, { 10 1 ¯ 2 } extension twinning is predominant in the LA ⊥ 〈 c 〉 loading, while dislocation motion prevails in the LA ∥ 〈 c 〉 loading. With increasing temperature, fewer { 10 1 ¯ 2 } extension twins are activated in the LA ⊥ 〈 c 〉 samples, giving rise to reduced strain homogenization, while pyramidal 〈 c + a 〉 slip becomes readily activated, leading to more homogeneous deformation for the LA ∥ 〈 c 〉 loading. The difference in the strain hardening rates is attributed to that in strain field homogenization for these two loading directions.

Heteroatom-doped Fe-NC catalyst has emerged as one of the most promising candidates to replace noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). However, delicate controls over their structure parameters to optimize the catalytic efficiency and molecular-level understandings of the catalytic mechanism are still challenging. Herein, a novel pyrrole-thiophene copolymer pyrolysis strategy to synthesize Fe-isolated single atoms on sulfur and nitrogen-codoped carbon (Fe-ISA/SNC) with controllable S, N doping is rationally designed. The catalytic efficiency of Fe-ISA/SNC shows a volcano-type curve with the increase of sulfur doping. The optimized Fe-ISA/SNC exhibits a half-wave potential of 0.896 V (vs reversible hydrogen electrode (RHE)), which is more positive than those of Fe-isolated single atoms on nitrogen codoped carbon (Fe-ISA/NC, 0.839 V), commercial Pt/C (0.841 V), and most reported nonprecious metal catalysts. Fe-ISA/SNC is methanol tolerable and shows negligible activity decay in alkaline condition during 15 000 voltage cycles. X-ray absorption fine structure analysis and density functional theory calculations reveal that the incorporated sulfur engineers the charges on N atoms surrounding the Fe reactive center. The enriched charge facilitates the rate-limiting reductive release of OH* and therefore improved the overall ORR efficiency.

High temperature wear properties of titanium carbide (TiC) composite coatings fabricated by laser cladding with titanium powder and varied percentages of carbon nano-tube (CNT) powders on titanium substrates have been tested by pin-on-disk wear under dry sliding conditions. The results reveal that TiC composite coatings fabricated with proper addition of CNT give promising high temperature wear resistance which is ten times higher than that of the titanium substrate. The high temperature wear behavior and friction coefficient of the titanium substrate and the composite coatings were investigated. It was found that the wear behavior of the dominant wear mechanism of the TiC composite coatings is adhesive wear and oxidation, whereas the Ti substrate exhibits abrasive wear, adhesive wear, serious plastic deformation, and oxidation at high temperature. The improvement of the wear resistance is believed to be attributed to the reinforcement phase of TiC which can also provide high hardness according to the microstructure observation of the composite coatings by SEM, EDX and microhardness measurements.

The as yet unresolved microstructure of the periodic layers formed in the reactive diffusion system Mg/SiO(2) was clarified by using high-resolution field-emission SEM. The periodic layered structure actually consists of the single-phase layer of Mg(2)Si and the two-phase layer of (Mg(2)Si + MgO) alternated within the reaction zone. According to the experimental observations and in line with the diffusion-induced stresses model, the mechanism controlling this phenomenon could be attributed to the stresses induced by the difference in interface growth rates of Mg(2)Si and MgO phases within the layer. When the elastic deformation of the slow-growing aggregated-MgO phase reaches its elastic maximum, it will be split off from the reaction front by the neighboring Mg(2)Si phase and a new periodic layer forms. The computer simulation results are coinciding well with the experimental data. (C) 2009 Elsevier Ltd. All rights reserved.

The influences of ultrasonic field to polishing performance of Polishing Based on Coupling Vibration of Liquid (PCVL) are analyzed here. The simulation results shows that sound field in the original polishing device is rather uneven due to the existence of standing wave. To obtain better polishing performance, the experimental equipment was modified. Uniformity of the sound field was improved by preventing standing wave, thus a better surface quality could be achieved. Furthermore, a higher machining efficiency could be also obtained because sound intensity was strengthened at the same time. From the results serials of experiments, the improvements made by modified equipment are clearly shown.

In this study, the thermomechanical behavior of shape memory alloy (SMA) that is connected in series with a viscoelastic solid is studied. The viscoelastic materials are simplified to two-element spring–dashpot models: Maxwell model and Kelvin model. The constitutive equation of SMA depicted by Brinson's model is coupled with the governing equation of viscoelastic solid to predict the stress history in SMA. It is found that the viscosity coefficient η and modulus E in viscoelastic solids have significant effects on the stress response of SMA.