- 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)
Currently, the utilization efficiency of energy still remains at a low level, although the depletion of fossil fuel is appoaching. Therefore, it is of great significance to develop new materials and technologies for energy-saving and environment protection. Phase-change materials (PCM), which can absorb or release heat through inversible phase change, are very promising in the fields of heat storage and thermal management. In this paper, the characteristics and classification of PCM were introduced briefly in the first section, and then the application and development status of PCM were reviewed and analyzed detailedly. In the third part, the main problems of PCM were pointed out, and the related research work and recent research progress were analyzed and discussed. Finally, it was pointed out that optimizing material properties through new functional composite technology, designing new material system, expanding new application fields are the main development directions of phase change energy storage materials.
Hyperbranched polymers (HBPs) are a new kind of polymers used as modifiers of epoxy resins to increase their strength and toughness without affecting the processability. The influence of some HBPs on the physical properties and thermal resistance of epoxy resin was summarized in this paper, including four parts:hyperbranched polyether as an epoxy modifier, hyperbranched polyamide/polyimide/polyethyleneimine as an epoxy modifier, hyperbranched polysiloxanes as an epoxy modifier and other hyperbranched polymers as an epoxy modifier. Then the drawback of hyperbranched polymers used as modifiers of epoxy resins was revealed. In addition, more and more fascinating materials and devices based on hyperbranched polymers will be successfully developed and fabricated in the future. The main limitation of the HBPs in the field of epoxy resin modification is that the synthesis steps of most HBPs are cumbersome. Thus, in the future, with the advent of simpler, greener synthetic methods, HBPs will be more widely used in other emerging fields and modified resins.
Polymer derived ceramics (PDCs) process has been one of the predominant fabrication technologies for ceramic materials. As a desirable raw material for the preparation of ceramics with high performance-to-cost ratio, polysiloxane (PSO) derived SiOC ceramics have been well developed. The SiOC ceramics derived from hetero element-modified PSO are the research hotspot of PDCs technology in recent years because the thermal stability can be enhanced and the functional properties can be expanded by the incorporation of hetero element. In this paper, microstructure of SiOC ceramics was introduced first, and then the current status of hetero element-modified PSO derived SiOC ceramics was reviewed from the viewpoints of improving thermal stability and expanding functional properties, respectively. In subsequent study, two key problems which should be paid much attention are to elucidate the operation mechanism of hetero element based on the evolution of atom local chemical environment and to enhance the application of modified SiOC ceramics.
The preparation of porous ceramics by freezing casting has received increasing attention in recent years because of the advantages of green economy, controllable pore structure and excellent material properties. Based on the brief introduction to the principle of freezing casting process, the pore forming mechanism and conditions of freezing casting process were elaborated. The effect of liquid medium and freezing conditions on pore structure of porous ceramics was discussed in details. The material system of porous ceramics prepared by freezing casting and the typical technological conditions were summarized. Finally, it was pointed out that the research directions of freeze casting in the future are the effective control of pore structure and the preparation of new functionalized porous ceramics.
The "octahedral structure model" is introduced for three-dimensional reticulated porous materials, as well as the mathematical relations of their basic physical and mechanical properties. On this basis, the verification works about some performance relations, including the conductivity and tension, etc, are reviewed in this paper. A number of issues were discussed with the emphases on the practicality of these mathematical and physical relations, the rationality of the correction coefficients, the significant influence on the calculation results, and the allowable stress and the plastic index value of the corresponding dense body were also analyzed in details. According to this mathematical and physical relationship, the performance indexes such as the electrical resistivity of porous products can be calculated by the easily measurable basic parameters like the porosity. The experimental results prove this way feasible. Therefore, this method can be superior to the finite element and other complex computational methods.
The effects of surfactant structure and concentration on the preparation of high concent-ration graphene aqueous dispersion by HPH-LPE were systematically studied by UV-Vis spectra, TEM and laser granularity analyser. Three different types of surfactants were used:anionic, cationic and non-ionic. It is found that long hydrophobic segment, double bond and benzene ring structure is the key structure that can promote the performance of the surfactant and the optimum concentration of the surfactant is slightly higher than critical micelle concentration (CCMC).In the test range, Tween80 presents the best performance. The optimum concentration is 0.012mmol·L-1, and the obtained graphene aqueous dispersion concentration is 564.3mg·L-1. However, it seems no significant effect on the graphene quality of surfactant structure and concentration.
Cu hollow microspheres were synthesized by thermal decomposition of Cu(Ⅱ) formate-octylamine complexes in molten paraffin using oleyl amine (OA) as the surfactant. The synthesized products were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal constant analyzer, UV-Vis-NIR and photo-thermal conversion test device. The relevant synthesis mechanism of Cu hollow microspheres was analyzed. The results show that Cu hollow microspheres can be obtained under the conditions of reaction temperature at 110℃, reaction time at 3h and amount of OA at 0.005mol, the average diameter and wall thickness of Cu hollow microspheres are about 380nm and 70nm, respectively. The formation mechanism of Cu hollow microspheres is that the primary Cu nanocrystals driven by minimizing the interface energy may aggregate around the gas-liquid interface between liquid paraffin and bubbles. The thermal conductivity and photo-thermal conversion performance of Cu hollow microspheres suspension are better than those of solid Cu.
Porous polycaprolactone (PCL) bone scaffolds were prepared by selective laser sintering and chitosan/hydroxyapatite(CS/HA) suspension was prepared by in situ synthesis. The CS/HA was attached to the surface of the PCL scaffold by vacuum immersion, low speed centrifugation and freezing gel, to improve the biocompatibility and cell proliferation activity of the PCL scaffolds. The phase and porous structure of the composite scaffolds were observed by X ray diffraction (XRD) and scanning electron microscopy (SEM). The compressive strength and Young's modulus of the scaffolds were measured, the water contact angles on the surface of the scaffolds were measured and the biological properties of the composite scaffolds were studied by in vitro cell experiments. The experimental results show that hydroxyapatite (HA) is prepared by in situ synthesis, and CS/HA gel adhered well to the surface of PCL bone scaffold. The hydrophilicity of the surface of the PCL scaffold is improved by CS/HA, and the biocompatibility and cell proliferation activity of them are greatly enhanced.
According to the material research that human articular cartilage is expected to be repaired after injury, a new artificial cartilage-like material was prepared by thermal polymerization in this experiment. Under water bath insulation and initiator conditions, hydroxyethyl methacrylate(CH2＝CCH3COOCH2CH2OH, HEMA) and medical glycerol(C3H8O3) were polymerized into a new gel. And the surface morphology was compared with that of porcine cartilage, and the mechanical properties such as compressive strength and elasticity were tested. By analyzing and characterizing with FTIR spectra, the host of gel is still PHEMA, and glycerol exists in gel phase. The hardness of gel decreases with the increase of glycerol ratio, while the surface roughness of gel increases. When the mass ratio of HEMA to glycerol is 1:1-1:3, the hardness of the gel is close to that of pig cartilage, and the surface is smooth under the conditions of 1:1 and 1:2. Gels of four mass ratios have good compressive strength and elasticity. When the mass ratio is 1:1, the compressive properties and comprehensive properties are the best. The experimental results indicate that PHEMA and glycerol gel polymers have good mechanical properties as artificial cartilage materials, they may provide further investigation for clinical trials.
Using flower-like ZnO@carbon sphere (ZnO@C) as precursor, Ag3PO4/ZnO@carbon sphere (Ag3PO4/ZnO@C) ternary composites were synthesized via an in-situ precipitation method, Ag3PO4 nanoparticles were deposited on the surface of the ZnO@C. The samples were characterized by XRD, SEM, Raman, UV-Vis DRS and transient photocurrent responses. The visible light photocatalytic performance of samples was also investigated. The results show that the photocatalytic performance of Ag3PO4 can be improved by combining with ZnO@C. Among the samples, AP-Z-5(5%(mass fraction) ZnO@C and Ag3PO4) shows the best photocatalytic performance. It can nearly completely degrade methylene blue (MB) after 20min illumination in the presence of 5mg/L Fe(NO3)3, and remain 86% degradation rate after 4 cycles. Additionally, AP-Z-5 can degrade MB very well even in the mixed contaminant solution including Cr(Ⅵ) and MB.
The moisture absorption properties of carbon fiber reinforced plastics (CFRP) laminates treated with three kinds of hygrothermal environments (relative humidity 85% RH, temperature 25, 70, 85℃ respectively) were investigated by accelerated moisture absorption method. Tensile, compressive and shear tests were carried out to study the effect of hygrothermal conditions on the mechanical behavior of CFRP laminates. Meanwhile, the damage mechanism of CFRP laminates in hygrothermal environment was analyzed by scanning electron microscopy and infrared spectroscopy. Finally, a formula which could predict the mechanical properties of CFRP laminates in hygrothermal environments was proposed by least square method. The results show that the moisture absorption characteristics of CFRP laminates in preliminary stage accords with Fick's law well. At the same humidity, the CFRP's moisture absorption speeds, the moisture saturation contents and times are increased with the increment of the environmental temperature. The mechanical properties of CFRP laminates in 90°tensile test and shear test are decreased most obviously. Water molecules are associated with epoxy resin through hydrogen bonds after the treatment in hygrothermal environment, however, there is no chemical structure change in the components of the CFRP laminate. The formula of mechanical performance degradation under different hygrothermal conditions is basically consistent with the experimental results.
PTFE/Al/MoO3 composites with different PTFE concentrations were prepared by mold pressing and sintering. The materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), in addition, the properties of the composites under quasi-static compression and dynamic impact were also studied. The results indicate that, the strength of PTFE/Al/MoO3 composites is increased first and then decreased with the increase of PTFE, reaches the maximum of 80MPa when the volume fraction of PTFE is 70%. Meanwhile, these specimens can ignite under quasi-static compression conditions, with a huge explosion and bright flames, while no ignition phenomenon was observed in the other specimens under the same conditions. Under the dynamic impact conditions, all of the PTFE/Al/MoO3 composites can ignite, but with the increase of PTFE, the degree of intensity is decreased gradually. The reaction products are AlF3, Al2O3, Mo and C, indicating that the redox reactions of Al and PTFE, Al and MoO3have both been triggered. Under the dual influence of material strength and composition, the energy required for ignition of PTFE/Al/MoO3 composites tends to drop first and then increase with the increase of PTFE.
Degradable polylactide (PLA) nanofibers can be prepared by solvent free melt electrospinning technology which is promising, challenging and green. The nanofiber membrane prepared by this method have high porosities and strong adsorption capacities, and thus are useful for treating the environmental pollution efficiently. The organic montmorillonite(OMMT) was introduced into PLA, and the PLA/OMMT nanofiber membrane were prepared at 260℃ by using a self-made melt differential electrospinning device. The effect of OMMT content of PLA nanofiber membrane on the morphology, the oil absorption property, the air filtration performance and the degradability was investigated, and the optimum OMMT content was obtained. The research shows that the thermal stability of PLA is increased and the crystallinity of PLA is decreased significantly after adding OMMT. When the OMMT content is 2%, the diameter of the fiber reaches 450nm. The oil absorption rate of the nanofiber membrane is 133.5g/g which is 4-5 times higher than that of commercially available PP non-wovens, and the oil holding rate is 84.2g/g. Moreover, the nanofiber membrane has good reuse performance. The air filtration efficiency of the nanofiber membrane for dust particles(≥0.3μm) is 99.31%, reaching the European standard H11 filtration class. The degradation of PLA/OMMT nanofiber membrane is improved comparing with the pure PLA, which reduces the second pollution and accords with the requirements of industrial green environmental protection.
AlCoCrCuFe high-entropy alloy was fabricated by melting-casting method. The phase structure, microstructure and friction and wear property for this alloy without and with CeO2 doping were investigated by XRD, SEM, EDS, microhardness tester and friction-wear tester, respectively. The results show that AlCoCrCuFe alloy has BCC+FCC dual phase structure. 1%(mass fraction)CeO2 addition improves the diffraction peak of AlCoCrCuFe alloy. The microstructure of two above alloys is typical dendrite structure. The interdendrite region is mainly Cu-rich and Ce-rich area, and the dendrite microstructure is layered grid structure of spinodal decomposition. After CeO2 adding, the microhardness increases from 441.5HV to 475.3HV, and the friction coefficient and the mass loss rate decrease from 0.55 and 1.44% to 0.4 and 1.28%, respectively.
The low cycle fatigue (LCF) property and low cycle dwell fatigue (LCDF) property of bimodal structure and lamellar structure for Ti60 titanium alloy under high peak stress were studied by means of optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The results show that microstructure has little effect on LCF property, while significantly influences LCDF property. The dwell fatigue sensitivity of bimodal structure is higher than that of lamellar structure. Under dwell loading condition, the fatigue life decreases remarkably. The fatigue life decreases with the increase of the peak stress, while the dwell fatigue sensitivity increases. Within the same cycle, plastic strain accumulation of LCDF is greater than that of LCF, and the plastic strain accumulation of bimodal structure is more than that of lamellar structure. The LCF crack initiates at the specimen surface with single source, while LCDF crack originates inside of specimen with multiple sources. There are quasi-cleavage facets on the fracture surface. The density of facets for bimodal structure is higher than that of lamellar structure.
Critical damage value of material was obtained by physical experiment combined with a finite element software. True stress-strain curve of Ti600 alloy was studied by high temperature tensile test at 1010℃ and 0.001s-1. A simplified Normalized Cockcroft & Latham ductile fracture criterion was used, in which ε and σ were substituted by ε1 and σUTS, respectively. The critical damage value of Ti600 alloy on the above experimental condition was calculated and then was embedded in a finite element software to verify its accuracy by analysing high temperature tensile process. The result shows that the critical damage value of Ti600 alloy at 1010℃ and 0.001s-1 equals 0.643. By the finite element analysis, the crack initiation and propagation are predicted well and computational variety law of minimum cross sectional area is basically agreed with the experimental law. Hence, the critical damage value of Ti600 alloy obtained by combining a Normalized Cockcroft & Latham ductile fracture criterion with a finite element software is fairly precise.
Based on the Clyne-Davies model, the hot tearing susceptibility (CSC) of MgZn9YxZr0.5(x=1, 2, 4, 6, mass fraction/%) was predicted. The microstructure and morphology of hot tearing regions of the alloys were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the curves of solidification shrinkage stress with temperature (or time) of MgZn9YxZr0.5 alloys based on the "T" type hot tearing permanent-mold were collected. The results demonstrate that the predicted values of CSC are consistent with that of measured values of crack volume. The hot tearing susceptibility of the alloys from high to low is:MgZn9Y1Zr0.5>MgZn9Y6Zr0.5>MgZn9Y2Zr0.5>MgZn9Y4Zr0.5; the dendrite coherency temperature and the initial temperature of hot tearing decrease with the Y content increasing when w(Y) is not more than 4%.When w(Y) is 6%, the dendrite coherency temperature and the initial temperature of hot tearing increase. With the increase of Y content, the change of precipitation phase type, content and the dendrite tendency of α-Mg in the solidification process of MgZn9YxZr0.5 alloys is considered as the main micro-mechanism that affects crack initiation, propagation and hot tearing in grain boundary.
The rotational bending fatigue life and fatigue crack initiation mechanism of Cr4Mo4V bearing steel were studied by means of rotating bending fatigue test at room temperature. The rotational bending fatigue test was carried out on a PQ1-6 rotary bending fatigue test machine. The fatigue limit and S-N curve were measured by the up-down method. The fracture of the fatigue specimen was observed by SEM, and the crack initiation source type and crack propagation behavior were analyzed. The effect of defect size on fatigue life was analyzed by the ratio σ'/σw, defect of the nominal stress amplitude at the location of the defect to the measured ultimate fatigue strength of the defect. The results show that the safety fatigue limit of Cr4Mo4V bearing steel is 1019MPa, and the S-N curve data of Cr4Mo4V bearing steel shows a downward trend and a large dispersion. Fracture observation shows that there are five types of initiation, namely surface defects leading to initiation, near-surface carbides leading to initiation, near-surface non-metallic inclusions leading to initiation, internal non-metallic inclusions leading to initiation and internal carbides initiation. Internal crack fractures have fish-eye features. When the fatigue life exceeds 107 cycles, a granular bright area (GBF) is observed in the vicinity around the internal initiation source carbides. The fatigue fracture was observed with broken carbides, and the broken carbide increased the crack growth rate. Carbides cracking can occur in the bearing steel Cr4Mo4V under the action of cyclic stresses. These fractured carbides attract the crack tip leading to faster growth rate. Influence of carbide size on the near surface initiation can be quantitatively analyzed by using the critical volume density of carbides. The values of σ'/σw, defect are higher than 1 and the larger the σ'/σw, defect, the shorter the fatigue life is.
NiCr-30%Cr3C2(mass fraction) ceramic-metallic coatings were sprayed with two types of bond layer (electro-deposited Ni+HVOF NiCr bond layer and electro-deposited Ni bond layer) by HVOF. The coating with Ni bond layer was vacuum annealed at different temperatures (800, 850℃ and 900℃). Phase, microstructure and mechanical properties under different loads of coatings were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), electron-tensile tester, ball-on-disk (BOD) and step profiler. The results show that the adhesion strength of the coat-ing with Ni bond layer reaches 64MPa and is improved obviously after annealing. The wear resistance of the coating with Ni bond layer is superior to that with Ni-NiCr bond layer and improved signific-antly under 20N loading, while the wear resistance of the two coatings is with no much difference and the wear resistance of the coating with Ni bond layer is decreased after annealing under 5N loading.
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