Showing papers in "Journal of Wuhan University of Technology-materials Science Edition in 2019"

Morphological, Mechanical and Thermal Properties of Poly(lactic acid) (PLA)/Cellulose Nanofibrils (CNF) Composites Nanofiber for Tissue Engineering

Abstract: Composite nanofiber membranes based on biodegradable poly(lactic acid) (PLA) and cellulose nanofibrils (CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young’s moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.

Wear Properties of Plasma Transferred Arc Fe-based Coatings Reinforced by Spherical WC Particles

Abstract: Fe-based coatings reinforced by spherical WC particles were produced on the 304 stainless steel by plasma transferred arc (PTA) to enhance the surface wear properties. Three different Fe/WC composite powder mixtures containing 0wt%, 30wt%, and 60wt% of WC were investigated. The microstructure and phase composition of the Fe/WC composite PTA coatings were evaluated systemically by using scanning electron microscope (SEM) and X-ray diffraction (XRD). The wear properties of the three fabricated PTA coatings were investigated on a BRUKER UMT TriboLab. The morphologies of the worn tracks and wear debris were characterized by using SEM and 3D non-contract profiler. The experimental results reveal that the microhardness on the cross-section and the wear resistance of the fabricated coatings increase dramatically with the increasing adding WC contents. The coating containing 60wt% of WC possesses excellent wear resistance validated by the lower coefficients of friction (COF), narrower and shallower wear tracks and smaller wear rate. In the pure Fe-based coating, the main wear mechanism is the combination of adhesion and oxidative wear. Adhesive and two-body abrasive wear are predominated in the coating containing 30wt% of WC, whereas threebody abrasion wear mechanism is predominated in the coating containing 60wt% of WC.

Evaluation on Self-healing Mechanism and Hydrophobic Performance of Asphalt Modified by Siloxane and Polyurethane

Abstract: In order to inhibit and remove the thin ice and extend the lifetime of the damaged bridge, the self-healing mechanism and hydrophobic performance of asphalt modified by siloxane and polyurethane (ASP) were studied by dynamic shear rheology (DSR), fluorescence microscope (FM), atomic force microscope (AFM), the fracture-healing-re-fracture test and molecular simulations. The experimental results indicated that the self-healing capability of ASP increased with increasing heating time and temperature. Furthermore, the addition of siloxane could improve the reaction energy barrier and complex modulus, and it is believed that the self-healing is a viscosity driven process, consisting of two parts namely crack closure and properties recovery. Contact angle of ASP increased with the increasing siloxane content and it deduced that the siloxane could improve the hydrophobic performance of ASP and the ASP molecule model could simulate well the self-healing mechanism and hydrophobic performance of ASP.

Physiological Effects of MgO and ZnO Nanoparticles on the Citrus maxima

Abstract: Toxicity of MgO and ZnO nanoparticles at concentrations of 250, 500 or 1 000 mg/L for Citrus maxima seedlings was investigated to evaluate the potentiality of their use as nano-fertilizers. Uptake and translocation of metal oxide nanoparticles and lipid peroxidation were measured and compared with those of plants exposed to the highest equivalent concentrations of Mg2+ and Zn2+. MgO nanoparticles were translocated from roots to shoots, while translocation of ZnO nanoparticles was low. Exposure to Mg2+ and MgO at all concentrations entailed severe toxicity and strong oxidative stress. ZnO nanoparticles showed only mild toxicity, while Zn2+ caused leaf vein chlorosis and strong oxidative stress to plant shoots. In conclusion, the toxicity of MgO nanoparticles to the plant resulted from the dissolved Mg2+ concentration, while that of ZnO nanoparticles was not correlated with the dissolved Zn2+ concentration. Our findings are significant for development and application of MgO and ZnO nanoparticles as nano-fertilizers in agriculture.

Effects of N Doping on the Microstructures and Optical Properties of TiO2

Abstract: TiO2 nanopowders with different nitrogen (N) dopant concentrations were first synthesized by sol-gel method. XRD, TEM, HRTEM, XPS, UV-vis DRS were used to characterize the effects of N doping on the microstructures and optical properties of TiO2. The results indicated that the prepared TiO2 only contained anatase phase with a slight distortion, and the N doping improved the dispersity of TiO2. The N doping leaded to more defects in TiO2, capturing the charge carriers and inhibiting the combination of electrons and holes. Also, the N-doped TiO2 was composed of Ti, O and N. Further, N was doped into the TiO2 lattice by substituting for O, forming the oxidized nitrogen in the form of Ti–N–O or Ti–O–N bond, and Ti was present in the form of Ti4+ in TiO2. Finally, the absorbance of N-doped TiO2 was obviously improved in both UV and visible light region. Optical absorption edges of N-doped TiO2 samples showed obvious red shift, which expanded spectral absorption range of TiO2 and improved the utilization efficiency of visible light. It is concluded that N element was successfully doped into TiO2 crystal lattice, and the N dopant concentration of 3.0% was designed to modify TiO2.

Fabrication and Characterization of One Interpenetrating Network Hydrogel Based on Sodium Alginate and Polyvinyl Alcohol

Abstract: One interpenetrating network hydrogel based on sodium alginate (SA) and polyvinyl alcohol (PVA) was synthesized by combining the raw materials of PVA and SA with the double physical crosslinking methods of freezing thawing and Ca2+ crosslinking. The PVA-SA composite hydrogel have been characterized by scanning electron microscopy for surface morphology, infrared spectroscopy for investigating the chemical interactions between PVA and SA, X-ray diffraction for studying the PVA-SA composite structure property and thermal gravimetric for understanding the PVA-SA composite thermal stability. The swelling behavior and the degradation rate of the PVA-SA composite hydrogel were studied in simulated gastrointestinal fluid. Using bovine serum albumin (BSA) and salicylic acid as the model drugs, the release behavior of the PVA-SA composite hydrogel on macromolecular protein drugs and small molecule drug were evaluated. The results showed that the water absorption and degradation ability of the PVA-SA composite hydrogel was much better compared to the pure SA hydrogel or pure PVA hydrogel. The hydrogel exhibited remarkable pH sensitivity and the network was stable in the simulated intestinal fluid for more than 24 h. With the advantages such as mild preparation conditions, simple method, less reagent and none severe reaction, the PVA-SA composite hydrogel is expected to be a new prosperous facile sustained drug delivery carrier.

Self-Healing Concrete with Crystalline Admixture—A Review

Abstract: The scope of the present paper is to understand the effects of crystalline admixture on the self-healing capacity of the cementitious composites. Previous studies were examined and a conclusion was drawn to the effect that different additives to crystalline admixture tend to improve self-healing of concrete for larger cracks. It is recommended that initial treatment with chemical admixture can stimulate and heal further cracks and it has the better repeatability trend in mixing with the concretes and mechanical recovery is possible even under repetitive preloading. Effective self- healing with chemical admixtures even under open-air exposure, leads to study the importance of a service ability design parameter including the maximum allowable crack width by repeatability analysis as a function of the exposure with the concept of sealable crack width.

The Influence of Atmospheric Pressure on Air Content and Pore Structure of Air-entrained Concrete

Abstract: To study the effect of atmospheric pressure on the properties of fresh and hardened air-entrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus (Lhasa, 61 kPa) and the plains (Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure (LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure (NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores (pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.

Characterization of Metal Oxide-modified Walnut-shell Activated Carbon and Its Application for Phosphine Adsorption: Equilibrium, Regeneration, and Mechanism Studies

Abstract: We prepared a kind of metal oxide-modified walnut-shell activated carbon (MWAC) by KOH chemical activation method and used for PH3 adsorption removal. Meanwhile, the PH3 adsorption equilibrium was investigated experimentally and fitted by the Toth equation, and the isosteric heat of PH3 adsorption was calculated by the Clausius-Clapeyron Equation. The exhausted MWAC was regenerated by water washing and air drying. Moreover, the properties of five different samples were characterized by N2 adsorption isotherm, SEM/EDS, XPS, and FTIR. The results showed that the maximum PH3 equilibrium adsorption capacity was 595.56 mg/g. The MWAC had an energetically heterogeneous surface due to values of isosteric heat of adsorption ranging from 43 to 90 kJ/mol. The regeneration method provided an effective way for both adsorption species recycling and exhausted carbon regeneration. The high removal efficiency and big equilibrium adsorption capacity for PH3 adsorption on the MWAC were related to its large surface area and high oxidation activity in PH3 adsorption-oxidation to H3PO4 and P2O5. Furthermore, a possible PH3 adsorption mechanism was proposed.

Effects of Polypropylene Fibers on the Physical and Mechanical Properties of Recycled Aggregate Concrete

Abstract: The viability of using polypropylene fibers (PPF) in concrete was largely studied. Yet, few of the existing research studies investigated the effects of PPF on the properties of concrete containing recycled concrete aggregate (RCA). Mixes with different RCA replacement ratios and different PPF content were designed and tested. The test results showed that the addition of PPF did not change significantly the compressive strength and the density of the concrete, but slightly decreased its modulus of elasticity and Poisson’s ratio. The drop in the splitting tensile strength and the flexural strength due to RCA inclusions was to a large extent compensated by the PPF addition. The water absorption decreased and the percent voids increased with increased PPF addition. Correlations between the RCA content, the PPF content and the properties of concrete were studied. Useful regression models were proposed to predict the properties of concrete in relevant ranges of RCA and PPF content.

Isolation and Characterization of Acid-soluble Collagen and Pepsin-soluble Collagen from the Skin of Hybrid Sturgeon

Abstract: By using the wastes fish skin of sturgeon processed as a raw material, a macromolecule biomaterial of collagen was extracted. Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were successfully isolated from the skin of hybrid sturgeon with two extraction methods. The yields of ASC and PSC based on the wet weight of skin were 5.73 ± 0.11% and 10.26 ± 0.39%, respectively. The denaturation and melting points of ASC (26.83 °C and 110.49 °C) and PSC (26.54 °C and 102.99 °C) were assessed by Circular dichroism (CD) and Differential scanning calorimetry (DSC). ASC and PSC appeared to be dense sheet-like film linked by random-coiled filaments under scanning electron microscopy (SEM). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared spectroscopy (FTIR) confirmed that both the ASC and PSC were Type I collagen and maintained a complete triple helix structure. These results indicated that both ASC and PSC possessed good biological activity and could be widely used in medical biomaterials and other fields.

Effect of Sintering Time on Structure and Properties in CuO-doping KNN-LS-BF Piezoelectric Ceramics

Abstract: The 0.6mol% CuO-doping 0.996(0.95Na0.5K0.5NbO3-0.05LiSbO3)-0.004FeBiO3 (KNN-LSBF-CuO) piezoelectric ceramics were synthesized by a solid-state reaction technique, and the structure and piezoelectric properties dependence of sintering time in KNN-LS-BF-CuO ceramics were studied. It is found that all the samples sintered for various time are perovskite structure mixed with orthorhombic symmetry phase and tetragonal phase, but the sintering time has significant influences on the crystalline and properties. When the sintering time increases from 2 hours to 6 hours, the grain of KNN-LS-BF-CuO ceramics becomes more homogeneous and more tight-arrangement. The experimental results reveal that the longer sintering time than 4 hours is beneficial for improving partial properties, such as d33, tgδ, and Qm, but is adverse to er and kp, the KNNLS-BF-CuO ceramics with optimum properties can be synthesized for 6 hours at 1 060 °C.

Preparation of Two-dimensional Ti2CTx by Molten Fluorinated Salt Method

Abstract: We prepared a two-dimensional transition metal carbide Ti2CTx by treatment of Ti2AlC in molten fluoride salt. Two fluorinated salt systems were used to etch Al from Ti2AlC powder precursor under the argon atmosphere, and then the resulting MXene was delaminated with TBAOH to produce few-layered nanosheets of Ti2CTx. The reaction was undergone at different temperatures to study the effect of temperature. The results show that the optimal reaction temperature is 600 °C in LiF-NaF-KF system, and 850 °C in NaFKF system. The molten salt treated products are delaminated and quasi-2D MXene sheets can be obtained. The thickness of the MXene sheets prepared from the binary molten salt system is smaller than that of the ternary molten salt system.

Preparation of Hierarchically Interconnected Porous Banana Peel Activated Carbon for Methylene Blue Adsorption

Abstract: Hierarchically interconnected porous activated carbon have high specific surface areas, large numbers of dye adsorption sites, and interconnected pores for dye molecule diffusion and transportation. We prepared hierarchically interconnected porous banana peel activated carbons (BPACs) via a green method involving hydrothermal pretreatment and KOH activation, and systematically tested its methylene blue (MB) adsorption capacity. SEM showed that the BPACs had an interconnected porous structure and high-porosity surface. The Brunauer-Emmett-Teller surface area was 601.21 m2/g, the adsorption average pore diameter was 2.11 nm, and the total pore volume was 0.32 cm3/g. The MB adsorption capacity increased with increasing temperature, initial MB concentration, and pH value; it decreased with increasing adsorbent dosage. The adsorption isotherms and kinetic results for MB adsorption on BPACs were best described by the Langmuir adsorption and pseudo-second-order kinetic models, respectively. BPACs have a well-developed hierarchically interconnected porous structure, which increase the MB adsorption capacity and removal efficiency. Systematic MB adsorption tests show that BPAC is a highly efficient and easily available adsorbent.

Design of Eco-friendly Ultra-high Performance Concrete with Supplementary Cementitious Materials and Coarse Aggregate

Abstract: Aiming to investigate the mix design of eco-friendly UHPC with supplementary cementitious materials and coarser aggregates, we comprehensively studied the workability, microstructure, porosity, compressive strength, flexural strength, and Young’s modulus of UHPC. Relationship between compressive strength and Young’s modulus was obtained eventually. It is found that the compressive strength, flexural strength, and Young’s modulus of UHPC increase by 19.01%, 10.81%, and 5.99%, respectively, when 40wt% cement is replaced with supplementary cementitious materials. The relationship between compressive strength and Young’s modulus of UHPC is an exponential form.

Effect of Nano Silica on Hydration and Microstructure Characteristics of Cement High Volume Fly Ash System Under Steam Curing

Abstract: The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition of NS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.

Synergistic Corrosion Inhibition Effect of Molybdate and Phosphate Ions for Anodic Oxidation Film Formed on 2024 Aluminum Alloy

Abstract: In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. We investigated the influences of two inorganic corrosion inhibitors (ammonium dihydrogen phosphate and sodium molybdate) on the corrosion resistance of anodic oxidation films on 2024 aluminum alloy, and studied the synergistic effect of two corrosion inhibitors. The corrosion resistance of anodic oxidation film in 3.5wt% NaCl solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. Results show that, after adding the single ammonium dihydrogen phosphate or sodium molybdate of 0.01 M to oxalic acid electrolyte, inhibition efficiencies of the anodized samples are 10% and 47%, respectively. However, in the presence of two inhibitors with the same concentration of 0.01 M, inhibition efficiency can be as high as 92%. Therefore, we observed the significantly synergistic corrosion inhibition effect of molybdate and phosphate ions for anodic oxidation film formed on 2024 aluminum alloy.

Two Dimension C3N4/MoS2 Nanocomposites with Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

Abstract: MoS2-decorated C3N4 (C3N4/MoS2) nanosheets hybrid photocatalysts were prepared by a simple sonication-impregnation method. Face-to-face lamellar heterojunctions were well established between two dimension (2D) C3N4 and MoS2 nanosheets. The effects of MoS2 content on the light absorption, charge transfer and photocatalytic activity of the hybrid samples were investigated. Characterization results show that MoS2 nanosheets are well anchored on the face of C3N4 nanosheets and the composites have well dispersed layered morphology. After loading with MoS2, the light absorption of composites was much improved, especially in visible-light region. The photocatalytic activities of C3N4/MoS2 samples were evaluated based on the H2 evolution under visible light irradiation (λ > 400 nm). When the loading amount of MoS2 was increased to 5 wt%, the highest H2 evolution rate (274 μmol·g-1·h-1) was obtained. Compared with samples obtained from direct impregnation method, sonication pretreatment is favorable for the formation of 2D layered heterojuctions and thus improve the photocatalytic activity. Slightly deactivation of C3N4/MoS2 composites could be observed when recycled due to the mild photocorrosion of MoS2. Based on the band alignments of C3N4 and MoS2, a possible photocatalytic mechanism was discussed, where MoS2 could efficiently promote the separation of the photogenerated carriers of C3N4.

Isothermal Adsorption Characteristics and Kinetics of Cr Ions onto Ettringite

Abstract: The isothermal absorption properties and kinetic model of Cr (VI) and Cr (III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the adsorption of chromium ions with different valence states. The results show that the adsorption of Cr(III) onto ettringite at 20 °C agrees with Langmuir’s isothermal model. The ion binding stability was significantly greater than that of Cr (VI). While the adsorption of Cr(VI) onto ettringite agrees with Freundlich’s isothermal model, the D-R model fits the adsorption isotherms of two types of valence Cr (R2> O.994). It can be concluded that the adsorption of Cr (III) onto ettringite is mainly by chemical adsorption and that the adsorption of Cr (VI) onto ettringite is mainly by physical adsorption. Dynamic model fitting and model parameter analyses show that the adsorption of Cr (III) onto ettringite agrees with the pseudo second order kinetics model given by Lagergren. The formation of chemical bonds is the main factor causing the fast adsorption. Cr (VI) adsorption is mainly dominated by liquid film diffusion, and the adsorption rate is much slower than that of Cr (III) adsorption.

Luminescent BODIPY-based Porous Organic Polymer for CO 2 Adsorption

Abstract: Luminescent porous materials have shown various applications such as electronic devices, gas adsorption, energy materials and photocatalysis. Consequently, we designed and prepared a new type borondipyrromethene (BODIPY) based porous organic polymer (POP) by using Sonogashira coupling reaction. This POP-1 exhibits high thermal stability with moderate surface area. In addition, POP-1 is highly emissive in a solid state. Due to enrichment of different kinds of heteroatoms in the skeleton of the porous polymer, POP-1 selectively captures carbon dioxide (CO2) with relative high adsorption selectivity of CO2/N2.

Effect of Hygrothermal Cycle Aging on the Mechanical Behavior of Single-lap Adhesive Bonded Joints

Abstract: The aging behavior of single lap joints (SLJ) in hygrothermal cycles was investigated and compared by using a shearing strength test, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG/DTG), energy dispersive spectrometry (EDS) and scanning electronic microscopy (SEM). The temperature/relative humidity was set at 80 ℃/95% and–40 ℃/30% for 20 cycles, 40 cycles, and 60 cycles (one cycle was 12 hours), respectively. The experimental results show that hygrothermal aging significantly decreases the failure strength of adhesive joints. However, the failure displacement increases as the number of aging cycles increases. In addition, hygrothermal aging changes the failure mode of the adhesive joints from a cohesive fracture in un-aged adhesive layers to an interfacial failure of aged adhesive joints.

Effect of Spherical Particle Size on the Electrochemical Properties of Lithium Iron Phosphate

Abstract: The effect of spherical particle size on the surface morphology, electrochemical property and processability of lithium iron phosphate was systematically studied. Spherical lithium iron phosphate with different particle size distributions controlled with ball time of precursor slurry was prepared by spray drying method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), charge and discharge measurements and EIS. The electrochemical performances of the sample materials were measured by coin cells and 14500 batteries. XRD shows that the spherical lithium iron phosphate with different particle sizes all have good crystal structure due to the perfect mixing of the raw materials and rapid drying. The lithium iron phosphate microsphere with different particle sizes self-assembled with submicron primary particles has a core-shell structure. The longer ball time the precursors are, the smaller the active material particles are prepared. The electrode material with 6 h ball time of precursor slurry has the best physical properties and the processability. The composite has a uniform particle size and higher tap density of 1.46 g/cm3, which delivers a discharge capacity of 167.6 mAh/g at a discharge rate of 0.5 C. The results were confirmed by the 14 500 mA·h cylindrical batteries, which delivers a discharge capacity of 579 mAh at 0.5 C. And low-temperature performance with capacity of 458.5 mA h at −20 °C under a discharge rate of 0.5 C is the 79.2% of the same discharge rate at 25 °C. Otherwise, the 14500 batteries also exhibit excellent cycling performance and the capacity maintains 93% after 2 000 cycles.

Laser Cladding Fe-Al-Cr Coating with Enhanced Mechanical Properties

Abstract: Dense Fe-Al-Cr coatings with approximately 50 μm in thickness are successfully prepared on the 1045 carbon steel substrates via a laser cladding process. Proper Cr content (5 at% Cr) will lead to decrease in the melting point, and improves the viscosity of the liquid and the nucleation rate of the molten pool, leading to refining grains of the solidification structure. As a result, the Fe-29Al-5Cr laser cladding layer exhibits the best hardness, plasticity properties, and wear resistance at 400 °C. Excessive Cr for the Fe-29Al-7.5Cr coating leads to the formation of Cr2Al in the grain boundaries and thermal vacancies during the solidification process, resulting in inferior mechanical properties and poor tribological behavior.

Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Abstract: Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.

Excellent Electrochemical Performances of Intrinsic Polyaniline Nanofibers Fabricated by Electrochemical Deposition

Abstract: A simple route to synthesize the polyaniline (PANI) nanofibers with diameter about 150 nm was reported. In this strategy, the PANI nanofibers were fabricated by electrochemical deposition by using two-electrode configuration in 0.01 M aniline and 0.01 M H2SO4 electrolytes. The as-prepared materials were characterized by scanning electron microscopy (SEM), infrared spectroscopy (FTIR), Raman spectroscopy and thermogravimetric analysis (TGA). The electrochemical properties of the PANI nanofibers electrode as supercapacitor materials were investigated. The PANI nanofibers electrode showed high capacitance of 485 F·g-1 at 0.1 A·g-1, and the decrease in the specific capacitance is about 3.5% in 1 000 cycles. The results indicate that the PANI nanofibers electrode shows high stability and retains its electrochemical capacitance property over 1 000 cycles, suggesting PANI nanofibers have promising applications in high-performance supercapacitors.

Mechanical Properties of Micro-regions in Cement-based Material based on the PeakForce QNM Mode of AFM

Abstract: In this paper, the cement paste and the mortar were tested using the PF-QNM technique. It is shown that the PF-QNM technique is very powerful to characterize the mechanical properties of micro- and nanostructures in the cement-based materials. It does not have strict requirements for test environment and it does not damage the surface of the material. High-resolution images can be obtained very easily, and they can be analyzed statistically. The test results show that PF-QNM analysis can test not only the mechanical properties of the cement paste, but also investigate the interfacial regions in the cement-based material, including the variation in the mechanical properties of interface regions and the extension of the interfacial regions. During the test, care must be taken to choose the size of test area; indeed, a test area too small is not representative but too large leads to lack of stability. The recommended side is a square with a length of in the range 10–30 μm.

Synthesis of Cr2AlC from Elemental Powders with Modified Pressureless Spark Plasma Sintering

Abstract: We introduced a modified pressureless sintering strategy by SPS with a new T-shape die and tapered punches, which helps the evaporation of melted Al and reduces the sample sticking with the inner wall of the die. Thus, the die breaking risk in the sintering process or the de-molding process is avoided at all. At a low temperature and short holding time, a high purity of Cr2AlC was obtained in this SPS process from the optimization of different molar ratios of raw materials. Simultaneously, the high porosity of the as-obtained sample was also a distinguishing feature worth noticing. The reaction mechanism for this process was also discussed in detail. This study presented a new venue for future development of high purity “MAX” materials and others related materials by a modified pressureless sintering strategy.

Properties of Alkali-activated Yellow River Sediment-slag Composite Material

Abstract: In order to consume the Yellow River sediment as much as possible and improve the longterm stability of the Yellow River, Yellow River sediment was utilized as the main raw material to produce a composite material. Ca(OH)2 was used as alkali-activator to activate the active SiO2 and Al2O3 compositions in Yellow River sediment. 10 wt% slag was added into the mixture to further improve the strength of the composites. The effect of activity rate of the Yellow River sediment and dosage of Ca(OH)2 on the compressive strength of the Yellow River sediment-slag composite material at different curing ages was researched. XRD, SEM/ EDS, light microscope and FTIR were used to further explore the products and the microstructure of the composite material. Results showed that the active ratio of sediment had a great influence on the compressive strength of specimen. In addition, the compressive strength of specimen increased with the increase of Ca(OH)2 dosage and curing age. When the dosage of Ca(OH)2 was more than 5 wt% as well as the curing age reached 90 days, the compressive strength of the composite material could meet the engineering requirement. In the alkali-activated process, the main product was hydrated calcium silicate (C-S-H) gel, which filled up the gaps among the sediment particles and decreased the porosity of the specimen. Moreover, the CaCO3 produced by the carbonization of the C-S-H gel and excess Ca(OH)2 also played a role on the strength.

Creep Model of High-Strength High-Performance Concrete Under Cyclic Loading

Abstract: Concrete creep under both static and cyclic loading conditions was investigated. Four groups of high-strength high-performance concrete (HSHPC) prism specimens were fabricated, and three of these specimens were loaded periodically by the MTS Landmark Fatigue Testing Machine System. Creep characteristics and creep coefficients of HSHPC under static loading and cyclic loading, respectively, were obtained and compared. The experimental results show that the creep strains under cyclic loading with a mean stress of 0.4 fcp and an amplitude of 0.2 fcp increase significantly compared with the creep strains under static loading, and the maximum value was 1.2–2.3 times at early stages. In addition, the creep coefficient increases nonlinearly with the number of cyclic loading repetitions. The influence coefficient for cyclic loading γcyc=1.088×(N/N0)0.078 was introduced based on the previous HSHPC creep model, and then the modified creep model under cyclic loading was established. Finally, the residual method, the CEB coefficient of variation method and the B3 coefficient of variation method were applied to evaluate the modified creep model. The statistical results demonstrate that the modified creep model agrees well with the experimental measurements. Hence, it has important theoretical and practical values for accurately predicting the deflection of concrete bridges under cyclic traffic loading.

Oxygen Evolution Efficiency and Chlorine Evolution Efficiency for Electrocatalytic Properties of MnO2-based Electrodes in Seawater

Abstract: To improve both oxygen evolution efficiency and stability at high temperatures, Mn, Mn+Mo, Mn+Mo+V, and Mn+Fe+V oxide electrodes were prepared on a Ti substrate, with an intermediate layer of IrO2, by an anodic deposition method. The crystal structure, surface morphology, pore size distribution, specific surface area, and voltammetric charge were then characterized for each electrode. The results demonstrated that for Mn-O electrodes, the preferential orientation of the (100) crystal plane and the mesopore structure played negative roles in the oxygen evolution reaction. On the basis of the electrocatalytic properties of MnO2- based electrodes in seawater, the outer surface voltammetric charge at a scan rate of 500 mV·s−1 was shown to effectively indicate whether oxygen evolution reactions were preferred over chlorine evolution reactions. The Mn-O electrode exhibited oxygen evolution efficiency of only 47.27%, whereas the Mn+Mo, Mn+Mo+V and Mn+Fe+V oxide electrodes displayed oxygen evolution efficiency of nearly 100%. This means that adding Mo, V, and Fe elements to the electrode can improve its crystal structure and morphology as well as further enhancing its oxygen evolution efficiency.