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      20 September 2022, Volume 50 Issue 9 Previous Issue    Next Issue
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    Research progress in low-temperature discharge performance of Ni-rich ternary lithium-ion batteries
    Fujuan HAN, Zenghua CHANG, Jinling ZHAO, Rennian WANG, Haiyang DING, Shigang LU
    2022, 50 (9): 1-17.   DOI: 10.11868/j.issn.1001-4381.2021.000485
    Abstract ( 173 ( PDF (1271KB)( 148 Citation

    With the rapid development of the new energy automotive industry, consumers' requirements for the range of electric vehicles have been increasing. The Ni-rich ternary lithium-ion battery has become the most promising power battery in electric vehicles due to its high specific energy, but the battery system still faces the problem of poor performance at low temperature.The research progress on low temperature performance of Ni-rich ternary power battery in recent years was summarized in this review. The influence factors on the low temperature performance of Ni-rich ternary power battery were summarized emphatically. On the one hand, the effects of low temperature performance from thermodynamics were analyzed, including the structural change of the Ni-rich ternary cathode materials and graphite anode materials, electrolytic phase transformation and solvation structure changes, and glass transition of binder. On the other hand, rate controlling step in the low temperature discharge process in the Ni-rich ternary lithium-ion battery was summed up. According to this, main modification measures of low-temperature performance in Ni-rich ternary power battery were summarized. Low temperature electrolyte was designed by optimizing solvents, improving lithium salts and applying new additives. In order to improve the low temperature performance of electrode materials, three methods were mainly employed: substitution, surface modification and smaller material particle size. The remaining shortcomings of the research on low-temperature performance of the battery were summarized, and the research on the low temperature thermodynamic characteristics of batteries is not clear enough. In addition, the research methods for the low temperature kinetic process of batteries are single, and the influence of the reaction sequence in batteries is insufficiently understood.

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    Research progress in nitrogen-doped electrically conductive silicon carbide ceramics
    Jianguo YANG, Weijian SHEN, Huaxin LI, Yanming HE, Chuanyang LYU, Wenjian ZHENG, Yinghe MA, Lianfeng WEI
    2022, 50 (9): 18-31.   DOI: 10.11868/j.issn.1001-4381.2021.001052
    Abstract ( 111 ( PDF (973KB)( 110 Citation

    The electrically conductive silicon carbide (SiC) ceramics that can be machined by electrical discharge machining, can not only overcome the highlight shortcomings of traditional high resistivity-grade SiC ceramics in machinability, but also maintain its other excellent properties. It has outstanding advantages to replace traditional high resistivity-grade SiC ceramics in the field of structural ceramics. In this paper, the nitrogen doping principle of electrically conductive SiC ceramics was illustrated, and then the powder sintering methods, sintering additives, thermoelectric and mechanical properties were summarized. Meanwhile, in order to provide guidance for the control of electrical properties, the electrical properties-related factors were discussed. In the end, the main challenges of nitrogen-doped electrically conductive SiC ceramics were pointed out, and the future interests were suggested to focus on the development of new sintering technology and additive, as well as clarifying the control mechanism of electrical properties, thereby establishing the technical foundation for fabrication of high-performance conductive SiC ceramics with controllable electrical resistivity.

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    Influence of pre-transition elements on structures and properties in Fe-Ni based alloy design
    Xiaolong CHEN, Wensheng LI, Ming LOU, Kai XU, Leilei CHEN, Keke CHANG
    2022, 50 (9): 32-42.   DOI: 10.11868/j.issn.1001-4381.2021.001061
    Abstract ( 71 ( PDF (881KB)( 103 Citation

    Fe-Ni based alloys have been widely used in nuclear and aerospace industries due to their excellent high temperature strength, preferable combination of hardness and toughness, outstanding corrosion and oxidation resistance. However, with the accelerated development of modern industry, the service environment becomes more severe, thus the traditional Fe-Ni based alloys may hardly meet the requirements of future engineering applications. In this paper, the effects of the addition of pre-transition group elements on the phase structure and properties of Fe-Ni alloys were reviewed. Based on the basic theory of thermodynamics of phase diagram and phase transition, the focus is on the effects of addition of pre-transition group elements (RE, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, etc.) on the phase structure of the alloy; the relationship between the composition-structure-service properties of Fe-Ni-based alloys were further discussed; and it was pointed out that the current research work on element modified Fe-Ni based alloys tends to focus on the synergistic effect of multiple alloys on Fe-Ni based alloys, and lacks the research on adding a single element and the corresponding thermal and kinetic data support. On this basis, the mechanism of action of different elements was explored; the corresponding thermal and kinetic databases were established to optimize the simulation and calculation solutions of alloys in the oxidation process.

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    Research Article
    Preparation of graphene-carboxymethyl cellulose composite aerogel and evaluation of oil absorption performance
    Linlin ZHANG, Xuelin GU, Xiaoxiao XIANG, Huie LIU, Shuang CHEN
    2022, 50 (9): 43-51.   DOI: 10.11868/j.issn.1001-4381.2021.000479
    Abstract ( 85 ( PDF (1026KB)( 93 Citation

    With graphite oxide (GO) as the main raw material, combining with carboxymethyl cellulose (CMC), hydrothermal reduction combined ice template method was used to prepare graphene/carboxymethyl cellulose composite aerogel (HGA/CMC), through drying under the environmental pressure and hydrophobic modification. The HGA/CMC was characterized through SEM, FT-IR, XPS and microcomputer controlled electronic universal testing machine, which proves the successful combination between GO and CMC and the effective hydrophobic modification. HGA/CMC can absorb pure oil because of its abundant pore structure, the adsorption capacity of oil is 70.28-172.78 g·g-1, and the higher the oil density is, the greater the oil mass can be adsorbed by aerogel per unit mass. Furthermore, HGA/CMC shows good selective adsorption capacity for floating oil on water, heavy oil on water bottom and emulsified oil in water. HGA/CMC can be recycled by mechanical extrusion, and its adsorption capacity loss is only 15% after 10 times of extrusion regeneration. It is an oily wastewater treatment material with application potential.

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    Effect of carbon carrier pretreatment on oxygen reduction performance of Co-N/C non-platinum catalyst for fuel cell
    Xiaohui SUN, Shuhong LIU, Lu LU, Jicheng SHI, Hongfeng XU
    2022, 50 (9): 52-58.   DOI: 10.11868/j.issn.1001-4381.2021.001081
    Abstract ( 97 ( PDF (919KB)( 102 Citation

    Cobalt (Co) based oxygen reduction catalysts have become one of the important choices to replace platinum based oxygen reduction catalysts because of their low price, high reserves and easy availability. ECP600 JD was pretreated with nitric acid, mixed with cobalt acetate tetrahydrate, and then pyrolyzed at 800 ℃ in ammonia atmosphere to prepare Co-N/C oxygen reduction catalyst. The infrared spectrum test, alkali neutralization titration and specific surface area measurement show that the number of oxygen-containing functional groups on the surface of ECP600 JD increases, the pore size of ECP600 JD remains unchanged, but the proportion of mesopores increases after nitric acid acidification pretreatment. XRD and TEM tests show that Co5.47N is formed from ECP600 JD and cobalt acetate tetrahydrate after ammonia heat treatment, the Co-N/C catalyst is dispersed evenly without agglomeration. Electrochemical tests show that after pretreatment, the electrocatalytic performance of the prepared Co-N/C catalyst for oxygen reduction reaction (ORR) is better. Under alkaline conditions, the current density reaches 4.2 times that before pretreatment, and belongs to four electron transfer in catalytic kinetics.

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    Preparation of core@dual-shell BT@TiO2@PDA nanoparticles and dielectric properties of BT@TiO2@PDA/PI composite films
    Jingyuan TANG, Yiting LONG, Xu HUANG, Linyu PU
    2022, 50 (9): 59-69.   DOI: 10.11868/j.issn.1001-4381.2021.000673
    Abstract ( 63 ( PDF (1375KB)( 80 Citation

    To improve the interface compatibility, dielectric properties and energy storage density of polyimide(PI)-based composite materials, the core@dual-shell nanoparticles, BT@TiO2@PDA were obtained via facile solution method using the dopamine to coat on the BT@TiO2 nanoparticles, which is barium titanate (BT) coated with amorphous-TiO2, hydrolyzed from tetra-n-butyl titanate (TBT). A series of modified BaTiO3/PI (BT@TiO2@PDA/PI) composites with different contents of BT@TiO2@PDA were prepared through a solution casting film formation method. The results show that the dispersion of nanofillers in the polymer matrix and the interface compatibility between them can be improved by utilizing core@dual-shell nano-structured BaTiO3. The permittivity κ of BT@TiO2@PDA/PI composite films with 40%(mass fraction) filler loading increase to 8.8 (1 kHz), which is about 2.7 times higher than that of pristine polyimide, 1.4 times higher than that of pristine BaTiO3/PI composite films. Temperature-dependent and frequency-dependent dielectric performance tests confirm that BT@TiO2@PDA/PI composites possess good temperature and frequency stability. In the frequency range of 100 kHz, the dielectric loss of the composites is less than 0.010; when the filler loadings are under 40%, the permittivity of the composites decreases by less than 0.6 (1 kHz) from 25 ℃ to 160 ℃.

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    Preparation of carbon-chlorine co-doped mesoporous g-C3N4 by bubble template method and photocatalytic performance
    Yuan LIU, Hua ZHAO, Huipeng LI, Tianfeng CAI, Yucheng WANG
    2022, 50 (9): 70-77.   DOI: 10.11868/j.issn.1001-4381.2021.000810
    Abstract ( 57 ( PDF (1065KB)( 81 Citation

    A carbon-chlorine co-doped mesoporous g-C3N4(C-Cl-CN) photocatalyst with a high specific surface area was prepared from melamine, glucose and ammonium chloride and its performance for photocatalytic degradation of rhodamine B(RhB) was investigated. The crystal structure, chemical composition and micro-morphology of the catalysts were characterized by X-ray diffraction pattern(XRD), X-ray photoelectron spectroscope(XPS), scanning electron microscope(SEM), UV-Vis diffuse reflection spectra(UV-Vis DRS) and photoluminescence(PL). The results show that C-Cl-CN has a high specific surface area(108.7 m2/g) and the rate constant of RhB degradation is 0.02290 min-1, which is 9.4 times higher than that of pure g-C3N4, and has excellent catalytic stability. Glucose and ammonium chloride act as double-bubble templates and elemental dopants in the polymerization process, which enhance the specific surface area of the catalyst on the one hand and reduce the energy bandgap, on the other hand, significantly enhance the light absorption performance of the catalyst.

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    Preparation and characterization of intercalated calcium-based montmorillonite nanocompounds with organophosphorus flame retardants
    Jianyu QIN, Hanpeng ZHAO, Jinyu YAO, Wenchao ZHANG, Rongjie YANG
    2022, 50 (9): 78-88.   DOI: 10.11868/j.issn.1001-4381.2021.000148
    Abstract ( 41 ( PDF (1178KB)( 77 Citation

    Three organophosphorus flame retardants (9, 10-dihydro-9-oxa-10-phosphophenanthrene-10-oxa (DOPO), triphenyl phosphate (TPP) and pentaerythritol phosphate (PEPA)) were intercalated into the layer of calcium-based montmorillonite (CaMMT) by a simple, direct and solvent-free method, and three organophosphorus flame retardant montmorillonite nanocompounds (DOPO-CaMMT, TPP-CaMMT and PEPA-CaMMT) were prepared. X-ray diffraction (XRD) shows that the three phosphorus-containing small molecules are successfully intercalated into the layer of CaMMT. It was verified by transmission electron microscope (TEM) that the interlayer spacing of CaMMT in the three nanocompounds shows different degrees of increase. The change of thermal stability of the nanocompounds was characterized by thermogravimetric analysis (TGA). The formation mechanism of the three nanocompounds was studied. The results show that TPP and PEPA are intercalated into CaMMT in one step, while DOPO is intercalated into CaMMT in two steps with a larger interlayer spacing. The nanocompounds formed by the intercalation of three organophosphorus flame retardants into CaMMT layer are expected to achieve better dispersion of CaMMT in polymer and synergistic flame retardant effect of phosphorus and silicon.

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    Synthesis of 2D Ce-MOFs nanosheets and visiblelight-mediated decarboxylation performance
    Sijun LI, Lanxing SHAO, Li FENG, Hu CHENG, Jinliang ZHUANG
    2022, 50 (9): 89-96.   DOI: 10.11868/j.issn.1001-4381.2022.000161
    Abstract ( 60 ( PDF (917KB)( 81 Citation

    Two-dimensional Ce-MOFs nanosheets were successfully constructed by using ceric ammonium nitrate as metal salt and 1, 3, 5-tris(4-carboxyphenyl)benzene (H3BTB) as organic ligand, together with the use of acetic acid as modulator.Acetic acid modulator shows significant effects on the morphology and crystallinity of Ce-MOFs. Ce-MOFs microspheres synthesized without acetic acid as modulator (named Ce-BTB-H0) are composed of highly cross-linked small nanosheets with low crystallinity and surface areas. On the contrary, Ce-MOFs synthesized with acetic acid (named Ce-BTB-H60) consist of dispersed nanosheets, and show improved crystallinity and higher surface areas than that of Ce-BTB-H0. Using blue LED as light source and oxygen as oxidant, two-dimensional Ce-MOFs nanosheets enable decarboxylation oxygenation of a variety of substituted phenylacetic acid to their corresponding benzaldehydes and benzyl alcoholsunder irradiation of blue LED in oxygen atmosphere at room temperature.Moreover, Ce-BTB-H60nanosheets show better photocatalytic performance due to their higher crystallinity, larger specific surface area and improved dispersity than that of Ce-BTB-H0.

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    Thermodynamic performance of 2NaBH4+MgH2 hydrogen storage system improved by transition metal fluoride
    Senliang XI, Xiaojun WANG, Tonghuan ZHANG, Zongying HAN, Meng GAO, Shixue ZHOU, Hao YU
    2022, 50 (9): 97-104.   DOI: 10.11868/j.issn.1001-4381.2020.000986
    Abstract ( 45 ( PDF (1197KB)( 70 Citation

    The 2NaBH4+MgH2 and 2NaBH4+MgH2+0.1MFx (M=Ni, Ti, Zr;x=2, 3, 4) hydrogen storage composites were prepared by ball milling. The morphology, element distribution, and crystal structure of the composites were detected by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. In addition, the hydrogen release thermodynamic properties of the materials were tested by differential scanning calorimetry (DSC) and temperature-programmed desorption (TPD). The results show that the peak temperature of the first hydrogen release process for 2NaBH4+MgH2 is decreased by 8.9, 35.7 ℃ and 54.5 ℃ by the addition of NiF2, TiF3 and ZrF4, respectively. In addition, the NaMgF3 phase that appeared during the hydrogen release process changes the reaction path of the first hydrogen release process, and catalyzes the second hydrogen release process of 2NaBH4+MgH2, which reduces the peak temperature of the second dehydrogenation process by 18.0 ℃, 31.1 ℃ and 34.1 ℃, respectively. The quantity ratio of hydrogen release for 2NaBH4+MgH2 reaches 91.7%, 91.9% and 98.7% by the addition of NiF2, TiF3 and ZrF4, respectively. In these three catalysts, ZrF4 shows the best catalytic effect on the entire hydrogen release process of 2NaBH4+MgH2. Therefore, 2NaBH4+MgH2+0.1ZrF4can be used as a potential application system of fuel cell hydrogen supply system.

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    Effect of powder metallurgy preparation process on properties of TiC reinforced high chromium cast iron matrix composites
    Jiahao XU, Xuanguo WANG, Zhenhua YAO
    2022, 50 (9): 105-112.   DOI: 10.11868/j.issn.1001-4381.2020.001167
    Abstract ( 59 ( PDF (1406KB)( 108 Citation

    TiC reinforced high chromium cast iron(HCCI) matrix composites were prepared by high energy ball milling and vacuum sintering.Scanning electron microscope (SEM) and differential scanning calorimetry (DSC) were employed to analyze the powder at different time of ball milling.The effect of sintering temperature on microstructures, hardness and densities of high chromium iron-based composites was explored.The wear resistance of the composites and high chromium cast iron under the same process was compared.The results show that the size of powder particles tends to be stable, the powder activity increases and the sintering property is improved after 12 h of ball milling.TiC in sintered samples is uniformly distributed in the matrix.The grains in the composites grow gradually, the hardness and densities of the composites continuously increase with the increase of sintering temperature.After sintering for 2 h under the condition of supersolidus liquid phase sintering at 1280 ℃, the relative density of composites is 94.17%, the hardness is 49.2HRC and the bending strength is 980 MPa. In the pin and disc wear test, the wear resistance of the composites is 1.52 times than that of the single high chromium cast iron materials, and the wear mechanism is abrasive wear and slight oxidation wear.

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    Effect of carbon fiber tow structure on ablative properties of carbon fiber/phenolic composites
    Guoqiang KONG, Zhenhe AN, Huazhen WEI, Ying LI, Meng SHAO, Qiubing YU, Xiaojun JI, Juying LI, Kang WANG
    2022, 50 (9): 113-119.   DOI: 10.11868/j.issn.1001-4381.2021.000701
    Abstract ( 53 ( PDF (805KB)( 100 Citation

    Carbon fiber reinforced carbon/phenolic composites were prepared by using phenolic resin as matrix, plain carbon cloth and short carbon fiber as reinforcing agent. The ablation resistance of the composite was studied by oxygen/acetylene ablation test. The bending property of the composite was characterized by electronic tensile testing machine. The ablation surface of the composite was observed by scanning electron microscope. The ablation performance of the composite was verified by solid rocket motor. The results show that the mass ablation rate of oxyacetylene in carbon/phenolic composites prepared with these two structural forms of carbon fibers as reinforcements has a positive correlation with the size of carbon fiber tow. The smaller the carbon fiber tow, the lower the mass ablation rate of carbon fiber. When the carbon fiber reinforcer is in the single filament state, the oxyacetylene mass ablation rate of the composite is the lowest, which is 0.046 g/s, and the influence of carbon fiber type and specification on the mass ablation rate of oxyacetylene becomes smaller. The experimental results of solid rocket motor show that the ablation erosion resistance of carbon fiber/phenolic composites in monofilament state is obviously better than that of bundle carbon fiber/phenolic composites.

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    Microwave absorbing properties of carbonyl iron room temperature vulcanized silicone rubber composites
    Yujie MI, Mingming SONG, Cunrui ZHANG, Guien ZHANG, Yuexiang WANG, Zhimin CHANG
    2022, 50 (9): 120-126.   DOI: 10.11868/j.issn.1001-4381.2021.000554
    Abstract ( 49 ( PDF (897KB)( 103 Citation

    In order to prepare a high-bandwidth absorbing material with both mechanical properties and electromagnetic absorption properties, a nano-particle modification and physical blending method were used to design and prepare a carbonyl iron room temperature vulcanized silicone rubber composite material based on polydimethylsiloxane. The mechanical properties and wave absorbing properties of the composite material were systematically analyzed. The results show that when the mass fraction of white carbon black is 3%, the composite material has the best comprehensive mechanical properties and is convenient for material processing; the composite material is a magnetic loss type wave absorbing material, and the attenuation constant of the material is positively correlated with the carbonyl iron content and frequency. According to simulation calculations, the absorption peak of electromagnetic waves gradually shifts to low frequency as the thickness of the composite material and the content of carbonyl iron are increased at 2-18 GHz. When the thickness of the composite material is 1.5 mm and the mass fraction of carbonyl iron is 75%, the effective absorption bandwidth of the absorbing material can reach 9.07 GHz, accounting for 56.68% of the target bandwidth. In practical applications, the formula can be optimized and the thickness of the material can be controlled according to the needs of the application scenario to achieve the best absorbing effect.

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    Research Article
    Effect of Ru on microstructure evolution of the fourth generation nickel-based single crystal superalloy DD22 during long-term aging
    Yunsong ZHAO, Zhao YANG, Ruizhi CHEN, Jian ZHANG, Yushi LUO, Lirong LIU
    2022, 50 (9): 127-136.   DOI: 10.11868/j.issn.1001-4381.2022.000105
    Abstract ( 61 ( PDF (1378KB)( 102 Citation

    The morphological evolution of γ′ phase, the precipitation of TCP phases and the evolution of the interfacial dislocation networks in DD22 nickel-based single crystal superalloys with different Ru contents (3% and 5%, mass fraction) were investigated by transmission electron microscopy and field emission scanning electron microscopy during long-term aging at 1130 ℃. The results show that γ′ phase of 5Ru alloy are smaller in size and more regular in shape than that of 3Ru alloy. The mismatch of γ/γ′ phases is larger in 5Ru alloy, and the high content of Ru causes the reverse distribution of elements such as Re and Mo. During long-term aging at 1130 ℃, the coarsening rate, dissolution rate and rafting rate of γ′ phase in 5Ru alloy are lower than those of 3Ru alloy. There is still no TCP phase precipitation in 5Ru alloy after long-term aging for 1000 h, while a small amount of TCP phase is precipitated in 3Ru alloy after long-term aging for 50 h. With the prolongation of long-term aging time, the number and size of TCP phases both increase. Compared with 3Ru alloy, the interfacial dislocation networks of 5Ru alloy are denser and more regular after long-term aging for 1000 h. Above all, the reverse distribution of elements and low diffusion coefficient of Ru make 5Ru alloy exhibit higher microstructural stability than 3Ru alloy.

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    High temperature oxidation behavior of 310S heat-resistant steel
    Qian MENG, Dongyang LI, Jiangren YANG, Tianzeng LIU
    2022, 50 (9): 137-149.   DOI: 10.11868/j.issn.1001-4381.2021.001254
    Abstract ( 67 ( PDF (1858KB)( 78 Citation

    The oxidation kinetics and film structure of two kinds of 310S heat-resistant steels (1# and 2#) with different grain sizes and composition at 800-1100 ℃ were studied by static oxidation discontinuous mass gain method. The differences of oxidation properties between the two steels were compared, and the growth mechanism of oxide film and the reasons for the differences were clarified. The results show that the oxide film is composed of Si-rich oxide layer and Cr-rich oxide layer and the oxidation rate of sample 1# is lower at 800-900 ℃; Cr-Mn oxide layer is added to the oxide film at 1000 ℃ and is transformed into Cr-Mn-Fe oxide layer at 1100 ℃, and their oxidation rates are similar; on the whole, the oxide film of sample 2# is denser, smoother, more adherent and more protective at all temperatures. Particularly, the spinel layer and the chromium oxide layer of the two are greatly different in the form at 1100 ℃, and the form of the oxide film of sample 2# is more conducive to long-term oxidation resistance. In general, the oxidation resistance of sample 2# is better than that of sample 1#. The smaller average grain size and more uniform grain of sample 2# improve the diffusion flux of preferred oxidation elements and reduce the uneven growth of oxide film, resulting in the differences of oxidation properties between the two.

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    Corrosion behavior of heat-resistant stainless steel in high temperature molten glass
    Haiding LIU, Denghua CHEN, Qubo HE, Fei GUO, Dongzhe WANG, Yanlong MA
    2022, 50 (9): 150-158.   DOI: 10.11868/j.issn.1001-4381.2021.000878
    Abstract ( 64 ( PDF (1597KB)( 90 Citation

    The development of the nuclear industry and nuclear energy have prompted studies focusing on disposal of nuclear waste in a green and safe way. The use of metal containers to fill glass solidified nuclear waste and then landfill is currently the dominant way in waste disposal. However, the high temperature corrosion caused by the high temperature molten glass on the surface of the metal container becomes an important factor accelerating the failure of the container. Therefore, an in-depth understanding of the corrosion behavior of metals in high temperature molten glass is necessary to ensure the safety of disposal of nuclear waste.The S30815 heat-resistant stainless steel was selected as the research object, and the corrosion morphology, composition and phase structure of the S30815 heat-resistant stainless steel kept in 1100 ℃ molten glass for different time were deeply analyzed. The results show that the molten glass corrodes inward along the grain boundary into the matrix and molten glass gradually replaces the steel by occupying the grain boundary and further penetrates the grains to form corrosion pits. Cr and Si elements in the heat-resistant stainless steel diffuse into the molten glass during corrosion, resulting in a decrease of content at the surface, and finally promote the transformation of metal surface from austenite to martensite. The corrosion of heat-resistant stainless steel by molten glass is alkaline dissolution. A continuous and stable oxide film cannot be formed on the surface, which means the corrosion will continue with the extension of holding time.

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    Effect of Gd on microstructure and corrosion behavior of Mg-xGd-1Er-1Zn-0.6Zr alloys
    Xiongfei LIU, Wenbo DU, Junjian FU, Yunfeng WANG, Shubo LI, Xunming ZHU, Zhaohui WANG
    2022, 50 (9): 159-168.   DOI: 10.11868/j.issn.1001-4381.2020.001140
    Abstract ( 60 ( PDF (1235KB)( 78 Citation

    The Mg-xGd-1Er-1Zn-0.6Zr alloys with Gd contents of 7%(mass fraction), 9% and 11% were prepared by gravity casting method.The microstructure of the alloys was studied by means of optical microscope, scanning electron microscope and X-ray diffractometer.The corrosion behavior of the alloys were evaluated by means of open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy measurements in 3.5%NaCl solution.The results show that when Gd content increases from 7% to 11%, the peak time of open circuit potential decreases from 1609 s to 851 s, the charge transfer resistance decreases from 588.50 Ω to 31.9 Ω, the corrosion current density increases from 2.21×10-5 A/cm2 to 3.97×10-5 A/cm2, indicating that the corrosion resistance of the alloys decreases with the increase of Gd content.It is attributed to the combined operation of the micro-galvanic corrosion effect as well as corrosion barrier effect of second phase.When the Gd content increases from 7% to 11%, the volume fraction of (Mg, Zn)3(Gd, Er) phase increases from 1.9% to 5.2%, and changes from discontinuous distribution to semi-continuous distribution along grain boundaries, the volume fraction of the lamellar-shape LPSO phase increases from 11.7% to 26.7% and penetrates into grains.The increase in the volume fraction of the (Mg, Zn)3(Gd, Er) phase and the lamellar-shape LPSO phase results in the decrease of corrosion resistance, however, a large number of fine lamellar-shape LPSO phases is able to prevent the corrosion from spreading and slow down the growth of corrosion rate of the alloy with 11%Gd content in 8-24 h.

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    Microstructure and mechanical property of full Cu3Sn solder joints during high-temperature aging
    Yangyang ZHU, Xiaoyan LI, Weidong ZHANG, Hu ZHANG, Xi HE
    2022, 50 (9): 169-176.   DOI: 10.11868/j.issn.1001-4381.2021.000977
    Abstract ( 51 ( PDF (1075KB)( 95 Citation

    620 ℃ thermal aging was carried out on full Cu3Sn solder joints for various duration, the microstructure evolution of solder joints were investigated. The mechanical properties of solder joints after aging were characterized by nano indentation test and shear test. The results show that, during the thermal aging, the Cu20Sn6 is first precipitated in planar along Cu/Cu3Sn interface, it grows continuously until the complete consumption of Cu3Sn. Subsequently, Cu20Sn6 transforms to two-phase layer, which consists of Cu20Sn6 and Cu13.7Sn. As the aging time increases, Cu13.7Sn is precipitated in waves at the Cu/two-phase layer interface by consuming the two-phase layer and grows continuously until it occupies the entire interface area. Meanwhile, there is growth in the number and size of voids in the middle of the solder joint, which eventually coalesces into microcracks. The hardness of Cu20Sn6, Cu3Sn and Cu13.7Sn phases are 9.62, 7.15, 4.67 GPa, and the elasticity modulus are 146.5, 134.0, 133.2 GPa, respectively.With the increase of aging time, the shear strength of solder joints increases first and then decreases, and remains more than 20.1 MPa within 120 min. The fracture morphology and fracture path also change.

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