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      20 May 2021, Volume 49 Issue 5 Previous Issue    Next Issue
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    Review
    High-fracture-toughness ternary layered ceramics: from the MAX to MAB phases
    Yue-lei BAI, Hang YIN, Guang-ping SONG, Xiao-dong HE, Xin-xin QI, Jin GAO, Bing-bing HAO, Jin-ze ZHANG
    2021, 49 (5): 1-23.   DOI: 10.11868/j.issn.1001-4381.2020.001171
    Abstract ( 850 ( PDF (33188KB)( 286 Citation

    The MAX phase of the ternary layered compound and the recently attracted attention of the MAB phase have become the research hotspots in the field of structural ceramics for more than 20 years because of their common characteristics of ceramics and metals. The high damage tolerance and high fracture toughness are different from the essential characteristics of traditional ceramics. The overall development of MAX phase and the latest research progress of MAB phase were briefly reviewed in this article, focusing on the analysis of the effect of multi-scale layered structure on macro-mechanical behavior and its internal mechanism. Based on the results of first-principles calculations, the bond stiffness model was established and the quantitative characterization of chemical bond strength was realized, and more importantly, it was clarified that "sufficiently" weak interlayer bonding is the root cause for the extraordinary mechanical properties of ternary layered ceramics. The magnetocaloric effect (MCE) of Fe2AlB2 near room temperature shows the good application prospects of MAB phase compounds in the functional field. After more than 20 years of continuous research, the structure and performance of MAX-phase compounds have gradually become clear. At present, application research for specific scenarios is vigorously carried out all over the world. However, the current knowledge of MAB phase compounds is still very limited. Therefore, synthesizing and characterizing the structure, mechanical properties, physical properties, and service behaviour of existing MAB phase compounds are the important tasks at this stage. First-principles numerical simulation based on density functional theory (DFT) can play an important role, just as in understanding the extraordinary properties of MAX phase compounds and discovering new compounds.

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    Research progress in degradation behavior of biodegradable medical Mg-based alloys in vivo and in vitro
    Ya-qiang TIAN, Guan-zhang ZHAO, Yun LIU, Yuan ZHANG, Xiao-ping ZHENG, Lian-sheng CHEN
    2021, 49 (5): 24-37.   DOI: 10.11868/j.issn.1001-4381.2020.000338
    Abstract ( 465 ( PDF (20773KB)( 163 Citation

    As a new generation of medical degradable biomaterials, magnesium alloys were known as "revolutionary medical metal materials" due to their good biocompatibility, unique degradability and excellent mechanical transmission. However, the corrosion resistance of magnesium alloys is poor and there are phenomena such as rapid and uneven degradation.The research progress in improving the degradation properties of magnesium alloys was introduced from four aspects: microalloying, heat treatment process, plastic deformation and surface modification. The degradation rate and degradation modes of medical magnesium alloys in vivo and in vitro under different processing methods were compared. The influence of microstructure evolution and film characteristics of magnesium alloys under different processing conditions on the destruction mechanism of the Cl- for the film layer and the three-dimensional degradation morphology were revealed.The correlation data analysis model between different process conditions and corrosion degradation rate of magnesium alloys in simulated solution was established.Finally, it was pointed out that the focus of future research in this field is to analyse the main action mechanism of microstructure on magnesium alloys degradation properties from multiple perspectives and to build a prediction model of microstructure on magnesium alloys degradation life.

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    Auxetic metamaterials and structures
    Yu-kui GAO
    2021, 49 (5): 38-47.   DOI: 10.11868/j.issn.1001-4381.2019.000391
    Abstract ( 473 ( PDF (8602KB)( 601 Citation

    Auxetic metamaterials and structures have excellent mechanical properties such as shear resistance, impact resistance, fracture resistance, energy absorption and vibration isolation, permeability variability, synclastic curvature in bending, etc. Auxetic metamaterials have broad application prospects in the fields of aerospace, navigation, mechanical automation, biomedicine, national defense and military and textile industry. Based on the deformation mechanism of auxetic metamaterials and structure, the physical models of re-entrant mechanism, rotating rigid mechanism, chiral/antichiral mechanism, fibril/nodule mechanism, miura-folded mechanism, buckling-induced mechanism, helical auxetic yarn structure were reviewed. These models can be widely applied in various engineering applications such as light laminated plates, fluid transportation and yarn to improve their properties. Finally, prospects to the upcoming challenges and progress trends of auxetic metamaterials and structures are made.It is pointed out that the application of negative Poisson's ratio effect can help compensate the change of volume and area under the deformation of uniaxial loading. Then the shock resistance of turbine blade, antenna and car suction box can be improved. As a result, this review can provide benefits for the development of auxetic metamaterials.

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    Friction performance of hydrotalcite as lubrication oil (grease) additive and its influence factors
    Gui-jin LI, Zhong-lun ZHANG, Zhi-min BAI
    2021, 49 (5): 48-55.   DOI: 10.11868/j.issn.1001-4381.2020.000416
    Abstract ( 355 ( PDF (2383KB)( 124 Citation

    Hydrotalcite applied in mechanical friction system exhibits good friction and wear resistance. Friction performance of hydrotalcite as lubrication oil (grease) additive and its influence factors were summarized systematically in this paper. The mechanism and regulation of preparation methods, cation radius, the ratio of divalent and trivalent cations, the type of inorganic anions between layers, the intercalation of organic anions, crystallinity on the friction reduction and antiwear properties were analyzed comparatively. The basic principle and control directions of the structural composition design of hydrotalcite lubrication materials were clarified. Based on the research status, it was suggested that the industrial test verification of hydrotalcite, the evaluation of the influence of hydrotalcite on the quality of lubricating oil (grease), and the basic research about the interaction between hydrotalcite and the friction surface should be strengthened.

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    Research status and application of phase change humidity storage composite materials
    Hao ZHANG, Jun-jie ZANG, Hai-li LI, Zhi-fang ZONG
    2021, 49 (5): 56-65.   DOI: 10.11868/j.issn.1001-4381.2020.000792
    Abstract ( 295 ( PDF (5793KB)( 115 Citation

    Currently, the utilization efficiency of energy still remains at low level, although the depletion of fossil fuel is approaching. Therefore, while vigorously developing new energy, it is of great significance to develop new materials with "passive self-adjustment ability". Phase change humidity storage composite materials is a kind of composite material with phase change and temperature controlling property and humidity storage and humidity controlling property, which are very promising in the field of building wall material. In this paper, the action principle of phase change humidity storage composite materials, packaging technique of phase change material, classification and selection of humidity-controlling material were introduced briefly in the first section. And then the application of phase change humidity storage composite materials in building wall material were reviewed and analyzed in detail. In the third part, characteristics of double-shell phase change micro-nano capsules, polyfatty acid/SiO2 phase change and humidity storage composite materials and decanoic acid-palmitic acid @ Ce-La/TiO2 composites were pointed out. Main problems and research status of phase change humidity storage composite materials were pointed. Finally, it was pointed out the optimized durability of phase change humidity storage composite materials, developing multi-functional phase change humidity storage composite materials are the main development directions of phase change humidity storage composite materials.

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    Research Article
    Microstructure and properties of 3D printed agarose and sodium alginate composite hydrogel
    Gui-ping TANG, Qian YAN, Jie LIU, Bo SONG, Shi-feng WEN, Yu-sheng SHI
    2021, 49 (5): 66-74.   DOI: 10.11868/j.issn.1001-4381.2020.000011
    Abstract ( 351 ( PDF (12688KB)( 183 Citation

    The biological scaffolds of tissue engineering are required to have good biocompatibility, matched mechanical properties, as well as morphology and microstructure for cell growth and reproduction. Although a large number of biomaterials have been developed to prepare tissue-engineering scaffolds, the forming problems and poor mechanical properties of the scaffolds still seriously limit the development of tissue engineering. The sodium alginate was used as raw material, and its mechanical properties were enhanced by agarose. The structure and morphology of sodium alginate/agarose composite hydrogels with different ratios were studied, the mechanical properties were tested. In addition, the composite hydrogel scaffold was formed by direct ink writing, and the size of the microscopic pores in composite hydrogels were designed and observed. The results show that the composite hydrogels with different ratios have little difference in water content, all around 90%. Apart from the pure agarose gel and the composite gel with a volume ratio of 1:2, the surface and cross section of the composite gel in other ratios are relatively rough. Agarose can enhance the composite gel to a certain extent, and the composite gel with the volume ratio of sodium alginate to agarose of 2:1 has the highest compression modulus, which can reach 0.353 MPa. The decomposition of calcium carbonate created submicron pores in the composite hydrogel, therefore the prepared composite hydrogel has rough surface and micro-pores, which is conducive for cell growth and reproduction.

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    Preparation of W18O49/C-TiO2 direct Z-scheme photocatalyst and photocatalytic water splitting for H2 production
    Kun ZHANG, Yu-rong YANG, Fei-yang CHEN, Qi QI, Chun-guang ZHANG, Fan GAO
    2021, 49 (5): 75-81.   DOI: 10.11868/j.issn.1001-4381.2020.000692
    Abstract ( 255 ( PDF (10764KB)( 131 Citation

    W18O49/C-TiO2 direct Z-scheme photocatalyst was prepared by a simple hydrothermal method. The structure, morphology, transport properties of photogenerated carriers and energy band structure were characterized by XRD, SEM, TEM, HRTEM, PL and other measurements. Under simulated sunlight illumination, the photocatalytic water splitting performance for hydrogen (H2) production and quantum efficiency were studied without adding any sacrificial agent. The results show that the construction of W18O49/C-TiO2 direct Z-scheme photocatalyst can significantly improve light absorption, accelerate the separation and transport of photogenerated carriers, and enable more photogenerated electrons participate in the photocatalytic reduction reaction, so the sample possesses high efficient photocatalytic activity. The photocatalytic H2 production tests show that under simulated sunlight illumination, the W18O49/C-TiO2 direct Z-scheme heterojunction can achieve H2 production rate of 209 μmol·h-1·g-1 without adding any sacrificial agents. It also exhibits strong photocatalytic stability; the H2 production remains unchanged during the 24 h cycle test.

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    Preparation and electromagnetic interference shielding performance of epoxy composites modified with three-dimensional graphene aerogels
    Yu CHEN, Dai-jun ZHANG, Jun LI, Jia-xuan WEN, Xiang-bao CHEN
    2021, 49 (5): 82-88.   DOI: 10.11868/j.issn.1001-4381.2020.000509
    Abstract ( 381 ( PDF (6686KB)( 215 Citation

    Graphene aerogels/epoxy composites were prepared by vacuum-impregnated process with graphene aerogels as the functional filler and epoxy resin as polymer matrix. The changes in chemical structure of graphene aerogels during the preparation process and carbonization treatment were investigated by FT-IR, XPS and XRD. The results show that GO@PAA aerogel is prepared by the physical interaction between graphene oxide (GO) and polyamide acid (PAA). PAA will be transformed to polyimide by imidization and graphene oxide is partially reduced during the 300 ℃ thermal treatment. With the carbonation temperature increases, reduction degree of graphene sheets and the carbonation degree of polyimide are increased gradually. Meanwhile, SEM images and OM images show that graphene aerogels can also maintain the good three-dimensional network structure after carbonation treatment and vacuum impregnation. On this basis, graphene aerogels, which serve as the functional filler, taking advantage of the good three-dimensional network structure, can improve the corresponding composites with good electrical property and electromagnetic interference shielding performance. With only 6.23%(mass fraction) graphene aerogels (G@C-1100), the corresponding composites exhibit high electrical conductivity of 252 S·m-1 and an excellent electromagnetic interference shielding effectiveness of 70 dB.

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    Preparation and photodynamic performance of electrospinning CA/PpIX porous fibrous membrane
    Hui-ying SHEN, Zi-hao LYU, Su-yu ZHUANG, Xiu-ming CAO, Qing-qing WANG
    2021, 49 (5): 89-97.   DOI: 10.11868/j.issn.1001-4381.2020.000495
    Abstract ( 332 ( PDF (11674KB)( 164 Citation

    To address the problem of drug-resistant bacterial infections, a photodynamic broad-spectrum antibacterial cellulose acetate/protoporphyrin (CA/PpIX) porous microfibre membrane was prepared by electrospinning. The surface morphology of the fibrous membrane was observed by scanning electron microscope (SEM) and the distribution of PpIX on CA membrane was observed by laser confocal scanning microscope (CLSM). The change of the basic chemical structure of membrane before and after loading PpIX was analyzed by Fourier infrared spectroscopy (FT-IR) and Raman spectrometer. Through the DPBF substrate oxidation experiment and the antibacterial ability against S. aureus and E. coli, the photodynamic performance of the material was explored, and the gradient experiment of inorganic salt solution (KI, NaNO2, MgCl2) was designed to explore the effect of its interaction with 1O2 on the antibacterial performance. The results show that the loading of PpIX does not change the basic morphology of the fibrous membrane, but it gives the membrane good substrate oxidation and antibacterial properties (illumination 30 min, the antibacterial efficiency against S. aureus achieves 99.537%). KI, MgCl2and NaNO2solutions all have certain enhancement effects on photodynamic antibacterial mediated by CA/PpIX, among which KI solution has the most obvious enhancement effect. The interaction between the inorganic salt KI and 1O2 produces more free radicals, which can significantly potentiate the photodynamic antibacterial effect. The 100 mmol/L KI solution can potentiate the antibacterial efficiency of the composite fibrous membrane against S. aureus and E. coli to 99.9999%.

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    Effect of applying pressure during carbonization process on structure and properties of carbon paper for gas diffusion layer
    Tao FANG, Li CHEN, Bo-bo LIAN, Jian HU, Hai-long LI
    2021, 49 (5): 98-105.   DOI: 10.11868/j.issn.1001-4381.2020.000629
    Abstract ( 381 ( PDF (10786KB)( 271 Citation

    Carbon paper is one of the most commonly used materials for the gas diffusion layer of proton exchange membrane fuel cell, and its performance is the premise to ensure the stable operation of the cell. In order to improve the structure and properties of carbon paper and make it better meet the performance requirements of fuel cell, this study was conducted to press different amounts of graphite plates in the carbonization process to control the applied pressure and analyze the microstructure evolution and mechanism of carbon paper under different pressure. In addition, the effects of applied pressure on the in-plane resistivity, pore size distribution, surface roughness and mechanical properties of carbon paper were also studied. The results show that applying pressure helps to restrain the cracking of resin carbon, reduce the generation of cracks and improve graphitization degree of carbon paper to a certain extent. Furthermore, with the increase of applied pressure, the surface roughness of carbon paper is reduced gradually, while the average and maximum apertures also decrease. When the applied pressure reaches 3600 Pa, compared with the samples without pressure, the in-plane resistivity of carbon paper decreases from 17.15 mΩ·cm to 12.79 mΩ·cm, the tensile strength and flexural strength are improved by 150% and 82.9% respectively.

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    Coprecipitation synthesis and properties of color tunable and upconversion luminescence in Tb3+ and Yb3+ co-doped Y(PO3)3 materials
    Hui-ling LI, Lan-ping LI, Qi-liang RAO, Ling ZHANG, Xue-yu CHEN, Man-qi GU, Jin-yu YANG
    2021, 49 (5): 106-113.   DOI: 10.11868/j.issn.1001-4381.2019.001062
    Abstract ( 252 ( PDF (4971KB)( 138 Citation

    Tb3+ and Yb3+ co-doped Y(PO3)3 upconversion luminescence phosphors were prepared by coprecipitation method. The structure and optical properties of the as-synthesized Y(PO3)3: Tb3+, Yb3+ samples were investigated by XRD, SEM, FI-IR and upconversion luminescence spectrophotometer (UPL), respectively. XRD results show that the as-synthesized samples are Tb3+ and Yb3+ co-doped Y(PO3)3 crystals with monoclinic structure (space group P21/c). UPL results display that the obtained Tb3+ and Yb3+ co-doped Y(PO3)3 samples emit the Tb3+ characteristic upconversion blue-green luminescence under 980 nm excitation. The doping content of Tb3+ ions affects the upconversion luminescence properties of the as-prepared Y(PO3)3: x Tb3+, 20%(mole fraction, the same below) Yb3+ samples. When the doping amount of Tb3+ is 2%-10%, the 5D47F6 emission peak of the Y(PO3)3: x Tb3+, 20% Yb3+ samples splits into two emission peaks centered at 481 nm and 491 nm. The dominant upconversion peak is located at 547 nm for the Y(PO3)3: x Tb3+, 20% Yb3+ samples when the Tb3+ doping content is 10%-20%. The concentration quenching can be observed when the doping amount of Tb3+ is over 20%. The doping ratio of Tb3+ to Yb3+ and the excitation power density also exhibit effect on the upconversion luminescence properties of the prepared samples. The upconversion blue-green emission color of the as prepared Tb3+ and Yb3+ co-doped Y(PO3)3 samples can be tuned by changing the doping amount ratio of Tb3+ to Yb3+.The upconversion luminescence mechanism of Y(PO3)3: Tb3+, Yb3+ samples was also discussed. The 5D37FJ (J=6, 5, 4) and 5D47FJ (J=6, 5, 4, 3) upconversion luminescence are attributed to a three- and two-photon absorption mechanisms, respectively.

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    Effect of thermo-oxidative aging on mechanical properties and tribological behaviors of acrylonitrile-butadiene rubber
    Bo LI, Sheng-xin LI, Zhi-nan ZHANG, Jian ZHANG, Guang-yao XIONG, Ming-xue SHEN
    2021, 49 (5): 114-121.   DOI: 10.11868/j.issn.1001-4381.2020.000426
    Abstract ( 346 ( PDF (16496KB)( 142 Citation

    Acrylonitrile-butadiene rubber (NBR) was conducted with accelerated aging under the thermo-oxidative environment, a test on the tribological performance of aged NBR was carried out using UMT-3 tribo-tester. Based on an aging test at the various aging time and different aging temperatures. The static tensile tester, SEM, EDS, and 3D optical profilometer were used to investigate the changes of rubber mechanical properties and tribological properties with aging temperature and time before and after aging. The performance degradation of the NBR after thermo-oxidative aging, the microscopic morphology of the worn surface, and the evolution of the wear mechanism were discussed. Results demonstrate that the aging temperature and aging time have a substantial influence on the mechanical properties of the rubber. The elongation at break and fracture stress are gradually decreased with the extension of aging time. With an increase in the aging temperature, a small increase in temperature will cause a significant decrease in mechanical properties. Shore hardness of the rubber is more sensitive to the aging temperature changes. With the increasing temperature, the growth rate of shore hardness is changed from low to first fast and then slow. The evolution trends of rubber aging are dividing into three areas: A, B, and C because of different aging degrees, and there are different damage mechanisms between various areas. The wear mechanism gradually changes from adhesive wear to abrasive wear, or fatigue and abrasive wear exist together.

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    Process investigation on ultrasonic vibration enhanced friction stir welding of 2195 aluminum-lithium alloy
    Lei SHI, Xiang DAI, Chuan-song WU, Li FU
    2021, 49 (5): 122-129.   DOI: 10.11868/j.issn.1001-4381.2020.000735
    Abstract ( 314 ( PDF (16375KB)( 129 Citation

    A novel ultrasonic vibration enhanced friction stir welding (UVeFSW) process was employed to join the rolled 2195 aluminium-lithium alloy of 4 mm thickness. The effects of superimposing ultrasonic on the macro metallograph, microhardness and tensile properties of welded joints were compared and analyzed. The effect of process parameters on the weld formation and joint mechanical properties of aluminium-lithium alloy by ultrasonic vibration enhanced friction stir welding was investigated. The results show that under the same process parameters superimposing ultrasonic energy in friction stir welding can improve the formability of 2195 aluminium-lithium alloy and enhance the plastic material flow in the weld nugget zone, which can reduce or even eliminate the void defect in the conventional friction stir welding joint. The microhardness at the top and middle of the nugget zone increases due to the ultrasonic effect, while the bottom of the weld does not change much. The fracture surfaces of the joints show a ductile fracture mode, and the elongation of the joints increases after ultrasonic vibration energy is applied, and the fracture dimples are more fine and uniform. Under the welding parameters studied the maximum tensile strength and elongation of the joint are 282.8 MPa and 11.5%, respectively. Under the conditions with rotational speed of 600 r/min and welding rate of 225 mm/min, the application of ultrasound can improve the tensile strength and the elongation of the joint by 17.5 MPa and 3.7% respectively.

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    Effect of intermediate thermomechanical treatment on microstructure and properties of 2A97 Al-Li alloy
    Juan YU, Zheng LU, Yuan LU, Yan-cai XIONG, Guo-ai LI, Zhao-hui FENG, Shi-jia HAO
    2021, 49 (5): 130-136.   DOI: 10.11868/j.issn.1001-4381.2019.000198
    Abstract ( 295 ( PDF (19547KB)( 137 Citation

    Effect of intermediate thermomechanical treatment on tensile properties at short-transverse direction, intergranular corrosion, macrostructure and microstructure of 2A97 Al-Li alloy thin plate were studied by tensile testing, intergranular corrosion, EBSD and TEM.The results show that with the increase of compression deformation, the strength and elongation of the alloy increase first and then decrease slightly. When compression deformation is 20%, the grain size of recrystallization is fine and the uniformly dispersed δ' can be found in the grains, δ' phase located in the grain boundary is discontinuously distributed, the tensile property is the best, and the elongation rate is obviously improved; when the compression deformation is 25%, the intergranular corrosion resistance of the alloy is the best. The tensile and corrosion properties of the alloy are jointly affected by the interaction of grain morphology and precipitated phase.

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    Effect of supersonic fine particle bombardment on microstructure and fatigue properties of TC11 titanium alloy
    Yong-li WU, Yi XIONG, Zheng-ge CHEN, Xiao-qin ZHA, Yun YUE, Yu-liang LIU, Jin-min ZHANG, Feng-zhang REN
    2021, 49 (5): 137-143.   DOI: 10.11868/j.issn.1001-4381.2020.000435
    Abstract ( 233 ( PDF (23103KB)( 104 Citation

    The high cycle fatigue behavior of TC11 titanium alloy with lamellar structure before and after surface nanocrystallization was studied by supersonic fine particle bombardment (SFPB).The microstructure of the high cycle fatigue fracture and its vicinity were compared and analyzed by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD).The results show that there are 30-50 μm thick nanolayers on the surface of titanium alloy after SFPB treatment, and the size of nanocrystalline is about 5-15 nm.The fatigue performance is improved obviously and the fatigue life is increased about 8-10 times under the same stress level, the fatigue striation width becomes narrow, and the multiple of fatigue life increases gradually with the decrease of loading level.The fatigue fracture surface before and after SFPB treatment consists of the fatigue source zone, the crack propagation zone and the instantaneous fracture zone, but the fatigue source after SFPB treatment moves from the surface layer before treatment to the subsurface.After fatigue loading, the surface microstructure of SFPB treated specimens is still in nanometer scale, but there are a lot of deformation twins, dislocation tangles and a small amount of deformation-induced martensite in the subsurface microstructure.

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    Oxidation behavior of SiC/SiC composites in air at high temperature
    Zhi-liang HONG, Qiao-jun ZHANG, Kai-yuan LI, Hong-bao GUO, Cheng-yu ZHANG, Yong-sheng LIU
    2021, 49 (5): 144-150.   DOI: 10.11868/j.issn.1001-4381.2020.001169
    Abstract ( 299 ( PDF (14706KB)( 436 Citation

    As one of important candidates for advanced aerocraft engine hot components, SiC/SiC composites would undergo oxidative and corrosive damage when subjected to high temperature combustion environment. Oxidation behavior of SiC/SiC composites at 1100-1300 ℃ in air was investigated in the present work, to clarify the oxidative and corrosive behavior of the composites. The oxidation kinetics curves were obtained. The morphology and composition evolution of the oxidized materials were analyzed by SEM, XPS and XRD. The results show that the oxidation kinetics of SiC/SiC composites at 1100-1300 ℃ follow the parabolic law and the oxides on the surface mainly consist of silica. Slight oxidation occurs at 1100 ℃. The oxidation rate increases with increasing temperature. The oxidation process is mainly concentrated in the BN interface phase and the pores of the matrix. The bending strength of the composite decreases with the oxidation extent.

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    Effect of silica sol addition on sintering properties of porous alumina ceramics
    Hong-yu LIN, Xiao-hong LI, Lu CHEN, Bo YANG, Sen YAO, Xiao-zhou ZENG, An-lin LI, Yang LI
    2021, 49 (5): 151-156.   DOI: 10.11868/j.issn.1001-4381.2019.000971
    Abstract ( 351 ( PDF (6010KB)( 134 Citation

    Porous alumina ceramics were prepared by using calcined α-Al2O3 as raw material, nano silica sol as high temperature binder and carboxymethy cellulose as molding binder with processes of mixing, aging, molding and sintering.The effect of silica sol addition on sintering properties was investigated by test method of SEM and XRD. The linear shrinkage, volume density, porosity and flexural strength were also tested.The results show that the quartz silicon dioxide which is pyrolysed product from silica sol could bond the alumina particles together to form porous ceramics and improve the mechanical properties.The essence of silica sol bonding is physical bonding.The silicon dioxide in the sol begins to react with alumina to form mullite when the sintering temperature reaches 1500 ℃, and the porous ceramics tend to be compact with excellence mechanical properties.The flexural strength is about (105.5±8.0) MPa.The content of mullite phase increases with sintering temperature.However, with much higher content of mullite generation, the porosity increases and the mechanical performance degrades.The porous alumina ceramics with excellence performance can be obtained when the sintering temperature is between 1400 ℃ and 1500 ℃.

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    Preparation and mechanical properties of ZrO2/Al2O3 porous ceramics
    Hao-ran JIANG, Shuo LIN, Kang-fei ZHANG, Hai-yan WANG, Jia-qi WANG, Xiu-lan HE
    2021, 49 (5): 157-162.   DOI: 10.11868/j.issn.1001-4381.2019.001040
    Abstract ( 208 ( PDF (9535KB)( 127 Citation

    ZrO2/Al2O3porous ceramics were prepared by gel-foaming technique. The rheological property of slurry, the effect of solid content on the microstructure and mechanical property of the porous green bodies and the relationship between the MgO sintering additive content with the compressive strength and porosity of porous ceramics were investigated. The results show when the dispersant content is 0.4%(mass fraction), ball milling time is 4 h and the pH value is 4, the low viscosity is conductive to gelcasting. The porosity of green body reduces with the increase of solid content. The excessive solid content makes the slurry hard to flow, and the big pores and cracks form during gelcasting process, then the compressive strength of green body decreases. The mechanical properties of porous ceramics are improved with the phase transformation and micro-crack toughening induced by the ZrO2. The densification of pore supports increases, the porosity reduces and compressive strength increases with the increase of sintering additive content. The highest compressive strength is 30 MPa. The porous ceramics with appropriate porosity and high compressive strength can be prepared by introducing suitable contents of ZrO2 and sintering additive.

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    Composition and properties of methyl silicate/silicate composite coatings
    Shuang-hong ZHANG, Bo YANG, Wei ZHAI, Shuang LI, Gang KONG
    2021, 49 (5): 163-170.   DOI: 10.11868/j.issn.1001-4381.2019.000850
    Abstract ( 371 ( PDF (5334KB)( 138 Citation

    Methyl silicate/silicate composite coatings were prepared using a two-step method. The morphology, chemical composition, hydrophobicity and corrosion resistance of the coatings were investigated by scanning electron microscope (SEM) with energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FT-IR), contact angle tests, neutral salt spray (NSS) tests and potentiodynamic polarization curve, respectively, and were compared with those of single silicate coating and methyl silicate coating. The corrosion mechanism of methyl silicate/silicate composite coatings were analysed by electrochemical impedance spectroscopy (EIS) as well as equivalent circuit. The results show that the compositions of methyl silicate/silicate composite coatings outer layer are the almost same as the compositions of single methyl silicate coating, different from single methyl silicate coating with lots of cracks on surface, the composite coatings are uniform and smooth with no crack, and the adhesion is good. Single silicate coating is hydrophilic. Compared with single silicate coating, methyl silicate/silicate composite coating is hydrophobic, corrosion inhibition of cathodic process is obviously enhanced, and polarization impedance of the composite coating is 5 times more than that of the single silicate coating, total impedance values of composite coatings are more than 100 kΩ·cm2, corrosion current density of composite coatings is reduced by 60%.

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    Electrodeposition of completely amorphous Ni-B alloy coatings
    Xi-zheng HAN, Jing-yin FEI, Li-na ZHAO, Bao-qiang YAN, Jun WANG
    2021, 49 (5): 171-177.   DOI: 10.11868/j.issn.1001-4381.2020.000412
    Abstract ( 256 ( PDF (22049KB)( 122 Citation

    In order to solve the problem that it is difficult to prepare highly amorphous Ni-B alloy coating, the control variable method was used to explore the influence law of bath composition on the amorphous process of Ni-B alloy coating, and the electrodeposition method was used to prepare high-B amorphous Ni-B composite coating. X-ray diffraction (XRD) was used to characterize the phase structure of the sedimentary layer, and field emission scanning electron microscopy (FESEM) and energy spectrum analysis (EDS) were used to investigate the microscopic morphology and element distribution composition of the sedimentary layer. The results show that the sedimentary layer can be changed from crystalline state to amorphous state by controlling the composition of solution. The resulting sediments are highly amorphous. This system can be electrodeposited to obtain amorphous Ni-B alloy sediments with a complete, close and meticulous surface, and almost no metal crystal diffraction peak. The content of B in the sediments can be increased to 10.21%(mass fraction).

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