- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
Hemicellulose-based hydrogels are three-dimensional networks formed by crosslinking hydrophilic polymers with tunable swelling behavior, acceptable biocompatibility and mechanical properties, and have received much attention in the field of soft materials especially in hemicellulose-based materials.Herein, recent advances and developments in hemicellulose-based hydrogels were reviewed.The preparation methods, mechanism of their gelation process, and the performance of the hemicellulose-based hydrogels were presented from both chemical and physical cross-linking approaches, while the differences in various initiation systems such as light, enzyme, microwave irradiation and glow discharge electrolysis plasma in chemical cross-linking were compared.The latest applications of hemicellulose-based hydrogels in drug-controlled release, wound dressing, water purification, 3D printing dispersions, etc, were introduced, respectively.Finally, the challenges in the development of hemicellulose-based hydrogels were summarized briefly and future prospect was also given, which provides a reference for the synthesis of new hemicellulose-based hydrogels.
Precious metal nanoclusters have unique electronic structure and fluorescent properties, and can be used as fluorescent probes in a wide range of applications such as biomarkers and ion detection. This paper reviews the preparation methods of thiol-protected silver clusters, including bottom-up and top-down methods, focusing on optimizing the reduction process of the reaction, selecting excellent thiol ligands, changing the pH values of the system, and strictly controlling. The research status of the preparation of thiol-protected silver clusters was introduced in terms of etching time and reaction temperature during the reaction, and ideas and suggestions for further research were provided. At the same time, based on the excellent fluorescence properties of thiol-protected silver clusters, the research progress in the detection of small molecules such as Cu2+, Hg2+, I- and cysteine was introduced. Finally, it was pointed out that the fluorescence quantum yield and safety of metal nanoclusters are improved, and the reaction mechanism of metal nanoclusters with heavy metal ions and biomacromolecules is studied in depth, and the synthesis methods of high purity and diversity alloy clusters or transition metal nanoclusters are explored. The preparation of fluorescent sensing materials for the realization of highly efficient thiol-protected silver clusters is a hot trend in future research.
The metal surface anti-corrosion technology has always been the focus of attention in the field of industrial engineering. With the advancement of science and technology and the consideration of environmental protection, its green environmental protection requirements have gradually become one of the important indicators of the current metal surface anti-corrosion technology. In this paper, in order to study the research progress of green anti-corrosion coating technology on metal surface in recent years, based on a large number of domestic and foreign literatures, the classification, characteristics and application of membrane technology and anti-corrosion mechanism of three typical new technologies in metal surface anti-corrosion coating, i.e. self-assembled monolayers(SAMs) technology, corrosion inhibitor and molecular sieve membrane technology were reviewed. At the same time, other feasible green anti-corrosion coating technologies such as coating additives and graphene coatings and the developing trend of self-assembled monolayers, corrosion inhibitor and molecular sieve membrane technology in system construction, process optimization and composite coating design and etc are pointed out.
The spherical SiO2 was used as raw material to prepare the first-level and second-level microstructure surface by layer-by-layer assembly method. The surface morphology, hydrophobic properties were characterized by SEM and contact angle measurement instrument and then the effect of the low surface energy modifications, different size, different level on the hydrophobic properties was studied, and the hydrophobic stability under different conditions were studied. The results show that the film is changed from hydrophilic to hydrophobic after modification; before modification, hydrophobic performance of second-level microstructure with the mixture of 2 μm and 20 nm SiO2 is higher than 2 μm or 20 nm microstructure in the first level and it is the same after modification, whose contact angle and rolling angle of second-level microstructure is 161.3° and 3.2°, respectively. The second-level microstructure surface can still maintain good hydrophobic performance after experiencing 240℃ high temperature and 200 h ultraviolet irradiation.
Fe-Bi24O31Cl10 photocatalytic materials were prepared by modified solution combustion method using bismuth nitrate, citric acid, ammonium chloride and ferric nitrate as raw materials. The influence of Fe3+ doping on its photocatalytic performance was evaluated by degrading rhodamine B in visible light.XRD, XPS, UV-vis, SEM, HTEM and FT-IR were used to study the effects of different Fe3+ doping amount on the phase, elemental valence, optical absorption performance, microscopic morphology and particle distribution, crystal surface spacing and chemical structure composition of Bi24O31Cl10.The results show that doped Fe3+ does not change the phase and morphology of Bi24O31Cl10, but its sheet size is obviously smaller, its thickness is thinner, its optical absorption property is enhanced, and the photoelectron hole recombination ratio is decreased. Compared with pure Bi24O31Cl10, Fe3+ doping can significantly improve the photocatalytic activity of Bi24O31Cl10.The photocatalytic activity of Bi24O31Cl10 is the highest when the doping amount of Fe3+ is 0.5% (mole fraction), and the decolorization rate of RhB is 75% when exposed to visible light for 50 min, which is 44% higher than that of pure Bi24O31Cl10.
The quaternary alloys La0.8-xCexMg0.2Ni3.8 (x=0, 0.1, 0.3, 0.5) were prepared by induction melting, and the effects of partial substitution of Ce for La on the phase structure and electrochemical performances of super lattice La4MgNi19 negative materials were investigated. Results show that La4MgNi19 alloys contain LaNi5 phase, (La, Mg)2Ni7(3R-Ce2Ni7 and 2H-Gd2Co7) phase, (La, Mg)5Ni19 (3R-Ce5Co19) phase. The 2H-Pr5Co19 type phase appears while (La, Mg)2Ni7 phase disappears, after partial substitution of Ce for La. The increase of Ce element substitution has led to an obvious increase of the abundance of A5B19 phase and decrease of AB5 phase accordingly. Ce contributes to the formation of A5B19 phase, especially 2H-Pr5Co19 type phase. With the increase of Ce content from 0 to 0.5, the maximum discharge capacity of alloy electroded increases firstly and then decreased. The x=0.1 alloy exhibits a maximum discharge capacity of 380.36 mAh/g. It is also found that this substitution has caused a significant increase in the activation number, the cyclic stability, high-rate discharge ability. The well performance demonstrates that it is the hydrogen diffusion in the alloy that controls the high rate discharge.
Mn3O4 for supercapacitors was prepared by hydrothermal method at different reaction temperature and certain reaction time. Y doped and composite graphene were realized. The morph-ology, structure and electrochemical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical workstation. The standard PDF cards 89-4837 are identical and the single phase Mn3O4 belongs to tetragonal system. The space group is I41/amd (No. 141). The prepared Mn3O4 is rod like particle. The specific capacitance of Y-Mn3O4 and Y-Mn3O4/graphene composites can reach 89 F·g-1 and 267 F·g-1 when Y content is 5%. The cyclic voltammetry curves of Y-Mn3O4/graphene composites are rectangular, indicating that Y doped and graphene loading synergistically improve the electrochemical performance of Mn3O4.
Ag-TiO2 photocatalysts with different doping concentration were prepared by sol-gel method using tetrabutyl titanate and silver nitrate as raw materials. The crystal structure, surface morphology, chemical composition, optical properties of the samples were characterized by XRD, SEM, XPS, DRS and PL, respectively. The photocatalytic activity of xAg-TiO2(x=1%, 2%, 4%, 6%, atom fraction) under UV light and simulated sunlight was evaluated by the degradation of Rhodamine B by using mercury lamp and xenon lamp as the light source, respectively. The results indicate that the photocatalytic activity of TiO2 under UV light and simulated sunlight enhances as the recombination rate of photogenerated electron-hole decreases and the absorption of simulated sunlight increases by Ag doping. 1%Ag-TiO2 exhibits the best photocatalytic activity. The degradation rates of Rhodamine B are 91% under UV light and 89% under simulated sunlight, which are 1.18 and 1.24 times higher than that of pure TiO2. The reaction rate constants are 0.01257 min-1 and 0.01150 min-1, which are 1.49 and 1.74 times higher than that of pure TiO2.
The CoSiB/Pd multilayers with MgO/Pd underlayer were deposited by magnetron sputtering technique on the glass substrate. The effect of MgO underlayer's thickness t on perpendicular magnetic anisotropy of CoSiB/Pd multilayer was studied, and the thermal stability of multilayers with MgO/Pd underlayer was analyzed. The results show that the performance of PMA of samples improves due to the introduction of the MgO in the bottom layer through the analysis of anomalous Hall effect of samples, when the thickness t of MgO is 3.5 nm, the squareness of the sample is the best. The hysteresis loops of the best sample MgO(3.5 nm)/Pd(3 nm)/[CoSiB(0.5 nm)/Pd(0.8 nm)]2/Ta(2 nm) is tested, and the effective magnetic anisotropy constant(Keff) of the sample reaches 2.0×105 J/m3. The thermal stability analysis shows that the Keff reaches the maximum value 2.6×105 J/m3 at the annealing temperature of 200℃; the sample can still maintain good PMA performance, when the annealing temperature reaches 400℃.
Carbon/aramid fiber hybrid multi-layered biaxial weft knitted fabric was prepared in term of intraply hybridization. The mechanical properties and effect of hybrid ratio on mechanical properties were studied. Through uniaxial tension and three-point bending experiments, the tensile and bending properties and effect of hybrid ratio on mechanical properties were obtained. The results show that the tensile properties of composites are improved by adding aramid fibers according to a certain hybrid ratio, which shows a positive hybrid effect. Due to the addition of aramid fibers with good elongation, the tensile fracture elongation of the composites obviously increases, and the failure modes of the composites appear complete brittle fracture mode (C12 material failure mode) and "broom" fiber fracture mode (C8A4, C6A6 material failure mode). Besides, the fracture toughness of carbon fiber reinforced composites is effectively improved by adding aramid fibers at a certain hybrid ratio. The flexural strength and modulus of carbon/aramid hybrid MBWK fabric reinforced composites decrease with the increasing of hybrid ratio. With aramid content changing from 42% (volume fraction, the same below)(C6A6) to 59.2% (C4A8), the decreasing ratio of the bending strength and bending modulus are high. The bending deflection of 0° samples with a hybrid ratio of 59.2% (C4A8) is the highest, the value is 7.49 mm, which is much higher than that of pure aramid fiber or carbon fiber reinforced composites. The bending deflection of all 90° samples is higher than that of pure aramid fiber or pure carbon fiber reinforced composites, which shows the positive hybrid effects.
A cylindrical representative volume element model of polymer nano-composites reinforced by carbon nanotubes under a fixed tension stress was developed. The stress distribution in each layer of carbon nanotubes was numerically studied through developing a shear lag model. Finite element analysis was adopted to validate the results obtained by shear lag analysis. The effects of layer numbers, aspect ratio, content of carbon nanotubes and three kinds of matrix materials of epoxy resin, nylon and polymethyl methacrylate on the stress distribution in each layer of carbon nanotubes were analyzed. The results show that the stress distribution in graphene sheets of carbon nanotubes is significant influenced by layer numbers and the aspect ratio of carbon nanotubes under a fixed tension stress. The saturation stress of carbon nanotubes is decreased with the increase of the layer numbers and the value correlated with the number of layers. Single-walled carbon nanotubes are observed to perform the best utilization of its properties. It is found that the effective length is increased with the increase of the aspect ratio of carbon nanotubes. Significant increase of the saturation stress and decrease of the effective length of carbon nanotubes are observed respectively with the decrease of the content of carbon nanotubes. It is also indicated that different polymer matrix materials play little effect on the stress distribution in carbon nanotubes.
Melt blending method dominated by normal stress for polymer-based composite was realized via a self-developed vane mixer. Effects of mixing sequences and mixing time on the microstructure, rheological properties, thermal properties and tensile strength of PA6/HDPE/CNTs ternary blend were experimentally investigated. SEM results show that the normal stress flow field can realize the uniform dispersion of PA6 and CNTs in a short time. Compared with the other two mixing sequences, the blend of the mixing sequence that HDPE and CNTs are firstly mixed to form the masterbatch, and then the masterbatch is mixed with PA6 (HDPE/CNTs+PA6) has the smallest PA6 particle size; DSC results show that Xc is significantly affected by the mixing sequence; mechanical properties show that the better tensile strength is obtained when the mixing sequence is HDPE/CNTs+PA6 and proper mixing time can further improve the tensile strength of the blend.The results aforementioned indicate that the normal stress flow field provides enough energy for the CNTs to overcome the energy barrier of the HDPE/PA6 two-phase interface and migrate into the PA6 phase, which proves that the normal stress flow field has higher dispersion efficiency.
For the purpose of electromagnetic requirement without reflective layer, the absorbing properties of sandwich structures were calculated. According to the calculated results, different kinds of absorbing foams were prepared and the electromagnetic properties of foams were characterized. The radar cross section (RCS) of wave absorbing foam sandwich structures was also investigated. The calculated results show that sandwich structure has the optimized broadband absorbing property, when dielectric constant is 2.3-2.7 and dielectric loss is 0.24-0.26. There is obvious change law for the dielectric constant of foam with carbon black absorber. The electromagnetic property of PMI foam is close to that of the optimized absorbing foam through calculation. The sandwich structure of wave absorbing PMI foam with 8%(mass fraction) carbon black absorber has the optimized broadband stealth performance, which is corresponding to the calculated result. The sandwich structure can achieve electromagnetic wave stealth through wave transmitting in low frequency band and wave absorbing in high frequency band.
Amino acids modified hydroxyapatite (AA/HAP) composites were synthesized in the presence of different concentrations of serine (Ser), aspartic acid (Asp) and glutamic acid (Glu). The composites were characterized by Fourier transform infrared spectrometer, X-ray diffractometer (XRD) and transmission electron microscope (TEM), and were evaluated in the in vitro remineralization of acid-etched bovine enamel. The results show that amino acids (AA)can interfere with the growth of HAP crystal plane, resulting in the increase of the solubility and decrease of the ordered structure of the HAP crystals. XRD patterns and TEM analysis show that AA has a significant inhibitory effect on the [100] crystalline direction of HAP.Meanwhile, the HAP composites modified by AA have refined crystalline size when compared with the HAP without AA. The cytotoxicity of the materials was evaluated by CCK-8 assay and the results show that the relative cell activity of AA/HAP composites is better than the HAP. Field emission scanning electron microscope images show that the HAP without amino acids and the HAP modified with two different concentrations of amino acids both can repair the surface lesions of bovine enamel. While only the AA/HAP synthesized in the presence of 10 mmol·L-1 Ser, Asp and Glu generates a dense remineralization layer with a thickness of approximately 22 μm in the subsurface restoration, and obtains the best surface microhardness recovering.
The thermal compression experiment of TB17 titanium alloy in the β phase region was carried out by Gleeble-3800 hot compression simulator. The dynamic recrystallization behavior and transformation mechanism in the β phase region of the TB17 titanium alloy were studied. The results show that the dynamic recovery (DRV) and dynamic recrystallization (DRX) occur in the β-phase region during deformation process of the TB17 titanium alloy. There are two dynamic recrystallization nucleation sites at different strain rates. At low strain rate, it mainly nucleates inside the grains, and at high strain rate, it is near the grain boundary. According to EBSD and TEM analyses, the main mechanism happened at low strain rate is continuous dynamic recrystallization (CDRX) which mainly is controlled by sub-grain rotation. Discontinuous dynamic recrystallization (DDRX) occurs at high strain rates, the main form of deformation is grain boundary shear accompanied by sub-grain rotation. Although the two dynamic recrystallizations are transformed in different ways, the essence is to form new dynamic recrystallized grains through the propagation, slip and cell structure evolution of dislocations.
To study the dynamic recrystallization and texture evolution of GH4169 alloy during the cross wedge rolling processing, the microstructure, crystal orientation and texture in the surface and core of the GH4169 alloy with the area reduction of 30% and 50% were analyzed by the metallographic microscope (OM) and electron backscatter diffraction (EBSD), respectively.The results show that the crystal orientation gradually tends to be random with the occurrence of dynamic recrystallization during the cross wedge rolling process of GH4169 alloy. There are more high-angle grain boundaries in the rolled surface than those in the core. No evident change of the texture intensity in the rolled surface can be observed, while the core texture intensity increases obviously. The textures have rotated after the cross wedge rolling and the previous types of {001}〈1${\rm{\bar 1}}$0〉, {111}〈1${\rm{\bar 1}}$0〉, {111}〈0${\rm{\bar 1}}$1〉 change to the types of {001}〈0${\rm{\bar 1}}$0〉, {112}〈1${\rm{\bar 1}}$0〉, {110}〈1${\rm{\bar 1}}$1〉, {110}〈1${\rm{\bar 1}}$2〉. The dynamic recrystallization and texture evolution of GH4169 alloy are dominated by the special deformation characteristics of the cross wedge rolling.
Microporosity in the body and platform of the three different compositions complex nickel-based single crystal castings solidified by high rate solidification (HRS) process was investigated by the X-ray tomography (XRT). The results show that the solidification range and the dendrite tortuosity have a strong effect on the formation of microporosity. In the body of the casting, the arrangement mode of dendrites among three different compositions castings is the same. Due to the largest solidification range of the first generation single crystal SX1, its porosity volume fraction is the largest. The difference of solidification range in the second generation single crystal SX2 and the third generation single crystal SX3 is not obvious, thus, their porosity volume fraction is mostly influenced by the eutectic volume fraction. With the increase of single crystal generation, the level of refractory elements will be increased, also the eutectic fraction of the body increases. Therefore, the size of interdendritic zone in the final solidification stage is increased, and the pressure drop in liquid phase is reduced, leading to the decrease of porosity volume fraction. The porosity in the platform is mostly decided by the dendrite tortuosity compared with that in the body. In the platform of the first generation single crystal SX1, there is no obvious difference in the dendrite tortuosity, thus, the volume fraction of porosity is similar to that in the body. Due to the larger dendrite tortuosity in the second generation single crystal SX2 and the third generation single crystal SX3, the corresponding porosity volume fraction is increased.
S32750 duplex stainless steel samples with different initial microstructures obtained by solid solution heat treatment (SHT) were cold rolled with the thickness reduction of 80% and subsequently annealed at 1050℃. The distribution of phase boundary and grain boundary character for the as-processed samples was investigated by SEM-EBSD and XRD techniques. Furthermore, the effect of microstructure on mechanical properties and intergranular corrosion resistance was analyzed by means of tensile testing, nano-indentation and double loop electrochemical potential reactivation (DL-EPR) method. The results show that the fine-grained microstructure with the areal ratio of α to γ about 1, the highest fraction of phase boundaries out of the total interfaces (grain boundaries +phase boundaries), and the least grain clustering within the respective α and γ phases was obtained in the sample previously treated by high temperature SHT and subsequent cold rolling and annealing. As a result, the sample exhibits excellent mechanical properties. After the cold-rolled and annealed samples are sensitized at 750℃ for 4 h, the σ phase precipitates readily along the α grain boundary. The sample previously treated by high temperature SHT and subsequent cold rolling and annealing also possess better intergranular corrosion resistance due to the relatively small amount of α grain boundary and high population of phase boundaries meeting K-S orientation relationship between α and γ. Therefore, the strength and intergranular corrosion resistance might be improved simultaneously by controlling and designing interface character distribution via appropriate thermal mechanical treatment in duplex stainless steel.
Two-stage aging behavior of pulse variable polarity plasma arc welding(PVPPAW)joint of 7075 aluminum alloy with thickness of 10 mm was studied by mechanical properties, electrical conductivity test and TEM analysis, and the reasonable two-stage aging process was determined. Results show that the tensile strength of 7075 aluminum alloy PVPPAW joints increases first and then decreases with the increase of second-step aging temperature and time. After second-step aging with 160℃/12 h, the tensile strength of joint is 545.1 MPa, which increases by 37% than as-weld. And the conductivity is 27.9%IACS, the resistance to stress corrosion is improved than as-weld. The main strengthening phases of the weld center are η' phase and η phase. The precipitated phases of grain interior and grain boundary grow up and become coarsened gradually, and the precipitated free zone in the grain boundary becomes wider with the increase of the second-step aging temperature and time.
TC4 titanium alloy bulk specimens were prepared by laser deposition manufacturing.The effect of annealing treatment on mechanical properties, microstructure of LDMed TC4 titanium alloy was studied by optical microstructure (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD).The experimental results show that the microstructure is basketweave structure after α+β two-phase region annealing treatment and is transformed to Widmanstatten structure after β phase region annealing treatment.The mechanical properties still show significant anisotropy after annealing:Z-direction samples exhibit low strength and high plasticity, while XY-direction samples show high strength and low plasticity.The samples have a greatly decrease in strength and plasticity after β phase region annealing treatment.The annealing temperature has obvious influence on the anisotropy of the samples. The tensile properties of XY-direction samples are evidently scattered.Both direction samples exhibit ductile fracture after α+β two-phase region annealing treatment. The strength and plasticity of the samples decrease greatly after β single phase region annealing treatment, and the XY-direction samples are brittle fracture.
The wear resistance of TC4 titanium alloy was improved by plasma nitriding and the optimum nitriding temperature was investigated. TC4 titanium alloy was nitrided at 650, 700, 750, 800, 850℃ and 900℃ with LDM1-100 plasma nitriding equipment respectively, the temperature holding time is 10 h for each nitriding treatment. The microstructure, surface morphology, surface roughness, phase structure and hardness of nitrided samples at different temperatures were characterized by optical microscope, scanning electron microscope, white light three-dimensional topography instrument and microhardness tester. The tribological properties of TC4 titanium alloy after plasma nitriding were tested by CETR UMT-3 multifunctional friction and wear tester. The results show that the surface microhardness and roughness of TC4 titanium alloy increase with the increase of temperature. After nitriding at 900℃, the surface microhardness of TC4 titanium alloy reaches 1318HV0.05, which is about 4 times as high as that of the substrate (360HV0.05). The increase of hardness is due to the formation of hard nitride phases (TiN and Ti2N phases) on the surface of nitrided sample and the nitride content increases with the increase of nitriding temperature. The load-carrying capacity of nitrided samples at 800℃ and 900℃ is significantly higher than that of nitriding samples at low temperatures (below 750℃). Compared with the original TC4 sample, the wear volume of the nitrided sample significantly reduces. When nitriding temperature is 850℃, the wear volume of the nitrided sample is 1.2% (1 N), 3.0% (3 N) and 62.2% (5 N) of that of the untreated sample, and the improvement of wear resistance of the sample is the most obvious.
|
Founded in 1956 (monthly) ISSN 1001-4381 CN 11-1800/TB Sponsored by AECC Beijing Institute of Aeronautical Materials |
