Greatly enhanced corrosion/wear resistances of epoxy coating for Mg alloy through a synergistic effect between functionalized graphene and insulated blocking layer

The poor corrosion and wear resistances of Mg alloys seriously limit their potential applications in various industries.The conventional epoxy coating easily forms many intrinsic defects during the solidification process,which cannot provide sufficient protection.In the current study,we design a double-layer epoxy composite coating on Mg alloy with enhanced anti-corrosion/wear properties,via the spin-assisted assembly technique.The outer layer is functionalized graphene(FG)in waterborne epoxy resin(WEP)and the inner layer is Ce-based conversion(Ce)film.The FG sheets can be homogeneously dispersed within the epoxy matrix to fill the intrinsic defects and improve the barrier capability.The Ce film connects the outer layer with the substrate,showing the transition effect.The corrosion rate of Ce/WEP/FG composite coating is 2131 times lower than that of bare Mg alloy,and the wear rate is decreased by~90%.The improved corrosion resistance is attributed to the labyrinth effect(hindering the penetration of corrosive medium)and the obstruction of galvanic coupling behavior.The synergistic effect derived from the FG sheet and blocking layer exhibits great potential in realizing the improvement of multi-functional integration,which will open up a new avenue for the development of novel composite protection coatings of Mg alloys.

Spin-polarized pairing induced by the magnetic field in the Bernal bilayer graphene

Recent experimental findings have demonstrated the occurrence of superconductivity in Bernal bilayer graphene when induced by a magnetic field.In this study,we conduct a theoretical investigation of the potential pairing symmetry within this superconducting system.By developing a theoretical model,we primarily calculate the free energy of the system with p+ip-wave parallel spin pairing,p+ip-wave anti-parallel spin pairing and d+i d-wave pairing symmetry.Our results confirm that the magnetic field is indeed essential for generating the superconductivity.We discover that the p+ip-wave parallel spin pairing leads to a lower free energy for the system.The numerical calculations of the energy band structure,zero-energy spectral function and density of states for each of the three pairing symmetries under consideration show a strong consistency with the free energy results.

Effect of external magnetic field on the instability of THz plasma waves in nanoscale graphene field-effect transistors

The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.

MG@ZIF7-MIP的制备及对水环境中双酚A的电化学传感检测

为了解决常规双酚A检测分析方法无选择性、需要标准样品、预处理过程复杂等缺陷,以磁性石墨烯(MG)为基底、ZnO作为Zn源在MG表面原位生长ZIF-7,合成了高效导电复合膜MG@ZIF-7;选择MG@ZIF-7为载体、内分泌干扰物双酚A(BPA)为模板分子、丙烯酰为功能单体、二乙烯基苯为交联剂,采用表面分子印迹技术成功制备了分子印迹杂化膜(MG@ZIF7-MIP),并通过TEM、XRD、XPS、FT-IR等测试手段对其进行了分析表征;构建了以MG@ZIF7-MIP修饰电极为工作电极的分子印迹电化学传感器,对水环境中内分泌干扰物BPA进行选择性检测。结果表明:MG@ZIF7-MIP修饰电极对BPA的线性响应范围为0.001~0.100μmol/L(R=0.9763),响应平衡时间为4 min,检测限为9.84 ng/L(S/N=3),建立了一种快速响应、实用性强、高灵敏检测双酚A的分析方法。

微弧氧化后Mg-8Li合金表面MgLiAlY-LDHs@GO膜层的生长及耐蚀性能

目的提高Mg-8Li合金的耐蚀性能。方法首先在Mg-8Li合金表面制备微弧氧化膜(MAO),然后使用原位水热法在微弧氧化膜表面原位生长掺杂氧化石墨烯(GO)的四元(MgLiAlY)层状双羟基金属氧化物(LDHs)智能自修复膜层。采用SEM、XRD、FT-IR、EDS、ICP等手段研究MgLiAlY-LDHs@GO膜层的形貌、结构以及成分。通过EIS、Tafel以及浸泡试验等研究膜层的耐蚀性能,分析膜层的腐蚀行为,阐释其耐蚀机理。结果GO的掺杂可以促使LDHs纳米片生长得更加致密,主体层板中具有缓蚀作用的Y3+可以提高涂层的耐蚀性,四元LDHs的生长所需要的Mg^(2+)、Li^(+)、Al^(3+)等离子来源于镁锂合金基体以及微弧氧化膜的溶解,其中Li+也可以促进LDHs纳米片生长得更为均匀细密。膜层的腐蚀电流密度为6.03×10^(–7)A/cm^(2),比MAO膜层降低了1个数量级,提高了镁锂合金的耐蚀性能。结论GO的负载使LDHs的耐蚀性能和膜层稳定性均有一定程度的提升,引入稀土元素Y会改变LDHs的骨架,造成晶格畸变,使得LDHs微观形貌呈现褶皱状,剩下部分以Y(OH)3形式存在于涂层表面,可进一步提高膜层的耐蚀性能和稳定性。

GaFeO_(3)∶Mg晶体的生长及磁学性能研究

本文利用光学浮区法生长出了直径为7 mm的铁电单晶Mg_(x)Ga_(1-x)FeO_(3)(x=0.02、0.05、0.07和0.10),研究了Mg^(2+)对GaFeO_(3)(GFO)晶体饱和磁化强度和磁性转变温度的作用。通过XRD测试了晶体的结构和物相,结果显示,所有制备的晶体样品对应标准晶体卡库GFO(PDF#76-1005)的衍射特征,无其他杂相出现。XRD精修结果表明,该晶体结构为正交结构,空间群为Pna 2_(1),晶格常数和晶胞体积随着Mg^(2+)掺杂量的增加,呈现先增加后减小的趋势。通过综合物性测量系统研究了晶体的磁性能,结果表明,磁性转变温度和饱和磁化强度随着Mg^(2+)掺杂量的增加,同样呈现先增加后减小的趋势。当Mg^(2+)掺杂量x=0.07时,磁性转变温度和饱和磁化强度达到最大,分别为187.82 K、8.75 emu/g,达到了掺杂改性的目的。

Efficient degradation of dye pollutants in wastewater via photocatalysis using a magnetic zinc oxide/graphene/iron oxide-based catalyst

In this paper, we present a proof-of-concept study of the enhancement of photocatalytic activity via a combined strategy of fabricating a visible-light responsive ternary heterostructure and improving overall photostability by incorporating magnetic zinc oxide/graphene/iron oxide (ZGF). A solvothermal approach was used to synthesize the catalyst. X-ray diffraction (XRD), scanning electron microscopic, energy dispersive X-ray, transmission electron microscopic, vibrating sample magnetometric, and ultraviolet–visible diffuse reflectance spectroscopic techniques were used to characterize the synthesized samples. The obtained optimal Zn(NO_(3))_(2) concentration, temperature, and heating duration were 0.10 mol/L, 600℃, and 1 h, respectively. The XRD pattern revealed the presence of peaks corresponding to zinc oxide, graphene, and iron oxide, indicating that the ZGF catalyst was effectively synthesized. Furthermore, when the developed ZGF was used for methylene blue dye degradation, the optimum irradiation time, dye concentration, catalyst dosage, irradiation intensity, and solution pH were 90 min, 10 mg/L, 0.03 g/L, 100 W, and 8.0, respectively. Therefore, the synthesized ZGF system could be used as a catalyst to degrade dyes in wastewater samples. This hybrid nanocomposite consisting of zinc oxide, graphene, and iron oxide could also be used as an effective photocatalytic degrader for various dye pollutants.

行波磁场对Cu-Ni-Si-Mg合金组织和性能的影响

研究了在凝固过程中行波磁场对Cu-Ni-Si-Mg合金组织和性能的影响。结果表明,随着磁场电流强度的增加,在晶粒细化的同时,合金的组织形貌逐渐向等轴晶转变,树枝晶在磁场的作用下尺寸不断减小。磁场电流为90 A时晶粒细化效果最好,铸锭几乎全部由细小的等轴晶组成,晶粒尺寸降至(0.5±0.19) mm,相比于未加行波磁场的合金,晶粒细化了约94%。采用透射电子显微镜对显微组织进行观察,并对衍射花样进行标定,发现晶界处的析出相为δ-Ni2Si。在磁场电流为60 A的条件下,合金的拉伸性能最好,与未施加磁场的样品相比,屈服强度提高了41.8%,抗拉强度提高了12.9%,但合金的硬度不受行波磁场影响。本文通过行波磁场细化晶粒,为提高时效强化型铜合金的强度提供了一种可规模化生产的技术。

Bimodal growth of Fe islands on graphene

Magnetic metals deposited on graphene hold the key to applications in spintronics. Here, we present the results of Fe islands grown on graphene/Si C(0001) by molecular beam epitaxy, which are investigated by scanning tunneling microscopy. The two types of islands distinguished by flat or round tops are revealed, indicating bimodal growth of Fe. The atomic structures on the top surfaces of flat islands are also clearly resolved. Our results may improve the understanding of the mechanisms of metals deposited on graphene and pave the way for future spintronic applications of Fe/graphene systems.

晶界扩散Mg对钕铁硼磁体磁性能及微观组织的影响

烧结Nd-Fe-B磁体在风力发电、电动汽车等环保节能新能源产业中扮演着重要角色,因此研究制备高矫顽力及高磁能积的钕铁硼永磁材料是目前迫切需要解决的重要问题。本研究基于磁控溅射沉积非稀土元素Mg薄膜,再经过热处理使其扩散进入磁体内部,通过设定不同的扩散温度和时间,得到最佳扩散工艺参数,磁体矫顽力最大值达到17.12 kOe,增幅达到3.86 kOe,综合磁性能较为良好。通过对比分析实验前后磁体的磁性能和微观组织,Mg元素扩散过程中,低熔合金与富Nd相结合形成低熔液相,润湿性良好的低熔液相促进富Nd相流动,形成连续平滑的细晶界。这种方法可提高材料性能,适用于制备、表面改性和界面工程等领域。

Enhanced resonance frequency in Co2FeAl thin film with different thicknesses grown on flexible graphene substrate

The flexible materials exhibit more favorable properties than most rigid substrates in flexibility,weight saving,mechanical reliability,and excellent environmental toughness.Particularly,flexible graphene film with unique mechanical properties was extensively explored in high frequency devices.Herein,we report the characteristics of structure and magnetic properties at high frequency of Co2FeAl thin film with different thicknesses grown on flexible graphene substrate at room temperature.The exciting finding for the columnar structure of Co2FeAl thin film lays the foundation for excellent high frequency property of Co2FeAl/flexible graphene structure.In-plane magnetic anisotropy field varying with increasing thickness of Co2FeAl thin film can be obtained by measurement of ferromagnetic resonance,which can be ascribed to the enhancement of crystallinity and the increase of grain size.Meanwhile,the resonance frequency which can be achieved by the measurement of vector network analyzer with the microstrip method increases with increasing thickness of Co2FeAl thin film.Moreover,in our case with graphene film,the resonance magnetic field is quite stable though folded for twenty cycles,which demonstrates that good flexibility of graphene film and the stability of high frequency magnetic property of Co2FeAl thin film grown on flexible graphene substrate.These results are promising for the design of microwave devices and wireless communication equipment.

Superconducting joints using reacted multifilament MgB_(2)wires:A technology toward cryogen-free MRI magnets

The development of superconducting joining technology for reacted magnesium diboride(MgB_(2))conductors remains a critical challenge for the advancement of cryogen-free MgB_(2)-based magnets for magnetic resonance imaging(MRI).Herein,the fabrication of superconducting joints using reacted carbon-doped multifilament MgB_(2)wires for MRI magnets is reported.To achieve successful superconducting joints,the powder-in-mold method was employed,which involved tuning the filament protection mechanism,the powder compaction pressure,and the heat treatment condition.The fabricated joints demonstrated clear superconducting-to-normal transitions in self-field,with effective magnetic field screening up to 0.5 T at 20 K.To evaluate the interface between one of the MgB_(2)filaments and the MgB_(2)bulk within the joint,serial sectioning was conducted for the first time in this type of superconducting joint.The serial sectioning revealed space formation at the interface,potentially caused by the volume shrinkage associated with the MgB_(2)formation or the combined effect of the volume shrinkage and the different thermal expansion coefficients of the MgB_(2)bulk,the filament,the mold,and the sealing material.These findings are expected to be pivotal in developing MgB_(2)superconducting joining technology for MRI magnet applications through interface engineering.

磁性Fe_(3)O_(4)/Mg-藻渣生物炭复合材料活化过硫酸盐处理甲基橙染料废水的应用

目的:探究不同条件下磁性Fe_(3)O_(4)/Mg-藻渣生物炭复合材料活化过硫酸氢钾对甲基橙染料废水的处理能力。方法:通过甲基橙溶液模拟染料废水,研究不同试验条件下(初始pH、甲基橙初始浓度、复合材料投加量、过硫酸氢钾投加量)磁性Fe_(3)O_(4)/Mg-藻渣生物炭复合材料活化过硫酸氢钾处理甲基橙染料废水的效果。结果:酸性条件下甲基橙染料废水降解速率随pH增大而减小,碱性环境下随pH增大而增大;甲基橙染料废水的去除效果与甲基橙初始浓度呈反比,与过硫酸氢钾的投加量呈正比;一定条件下增加复合材料投加量能提升对甲基橙的去除效果。结论:磁性藻渣生物炭复合材料活化过硫酸氢钾氧化甲基橙染料废水具有优异的性能,可作为一种高效的去除方法应用于染料废水处理领域。

Magnetic and microwave absorbing properties of M-type barium ferrite/graphene oxide composite microwave absorber

In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autocombustion method. X-ray diffraction （XRD）, a scanning electronic microscopy （ SEM ）, a physical properties measurement system （PPMS-9）, and a vector network analyzer were used to analyze their structure, surface morphology, magnetic and absorbing properties, respectively. The results show that the absorbing band of the composite absorbing material is widened and the absorbing strength is increased compared with the pure M-type barium ferrite. The sample with the content of doped graphene oxide of 3% has the minimum reflectivity at 10 to 18 GHz frequencies. Hence, the doped graphene oxide effectively improves the absorbing properties of M-type barium ferrite.

Magnetic Fe_3O_4-Reduced Graphene Oxide Nanocomposites-Based Electrochemical Biosensing

An electrochemical biosensing platform was developed based on glucose oxidase(GOx)/Fe3O4-reduced graphene oxide(Fe3O4-RGO) nanosheets loaded on the magnetic glassy carbon electrode(MGCE).With the advantages of the magnetism, conductivity and biocompatibility of the Fe3O4-RGO nanosheets, the nanocomposites could be facilely adhered to the electrode surface by magnetically controllable assembling and beneficial to achieve the direct redox reactions and electrocatalytic behaviors of GOx immobilized into the nanocomposites. The biosensor exhibited good electrocatalytic activity, high sensitivity and stability. The current response is linear over glucose concentration ranging from 0.05 to 1.5 m M with a low detection limit of0.15 μM. Meanwhile, validation of the applicability of the biosensor was carried out by determining glucose in serum samples. The proposed protocol is simple, inexpensive and convenient, which shows great potential in biosensing application.

Broadband absorption of graphene from magnetic dipole resonances in hybrid nanostructure

As emerging new material, graphene has inspired great research interest. However, most of the studies focused on how to improve the absorption efficiency of graphene, but payed little attention on broadening absorption bandwidth while ensuring high absorption efficiency. In this work, we proposed a hybrid nanostructure, which not only can improve absorption efficiency but also can increase absorption bandwidth. The proposed hybrid nanostructure consists of a monolayer graphene sandwiched between three Ag gratings with different widths and a SiO2 spacer on a Ag substrate, these three gratings and substrate can excite three independent magnetic dipole resonances. In our calculations, we numerically demonstrate the proposed hybrid structure can achieve graphene absorption bandwidth of 0.311 μm in near-infrared region with absorption exceeding 30%. We also studied absorption peaks dependence on gratings widths and SiO2 spacer thickness, and explained the results using physical mechanism. Our research can provide a theoretical guidance for future device preparation.

Novel Visible Light Driven Magnetically Separable Graphene/BiOBr Composite Photocatalysts with Enhanced Photocatalytic Activity

Novel visible light magnetically separable graphene-based BiOBr composite photocatalysts were prepared for the first time. The structures, morphologies and optical properties were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and ultravioletvisible spectroscopy, respectively. The photocatalytic activity of the resulting samples was evaluated by degradation of tetracycline under visible light irradiation. An appropriate amount of introduced graphene can significantly enhance the photocatalytic activities. The enhanced activities were mainly attributed to the enhanced light absorption and the interfacial transfer of electrons. The corresponding photocatalytic mechanism was proposed based on the results.

Aggregation of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite

In this work we report that when ferromagnetic metals （Fe, Co and Ni） are thermMly evaporated onto n-layer graphenes and graphite, a metal nanowire and adjacent nanogaps can be found along the edges regardless of its zigzag or armchair structure. Similar features can also be observed for paramagnetic metals, such as Mn, Al and Pd. Meanwhile, metal nanowires and adjacent nanogaps cannot be found for diamagnetic metals （Au and Ag）. An external magnetic field during the evaporation of metals can make these unique features disappear for ferromagnetic and paramagnetic metal; and the morphologies of diamagnetic metal do not change after the application of an external magnetic field. We discuss the possible reasons for these novel and interesting results, which include possible one-dimensional ferromagnets along the edge and edge-related binding energy.

Reduced Graphene Oxide Coupled Magnetic CuFe2O4-TiO2 Nanoparticles with Enhanced Photocatalytic Activity for Methylene Blue Degradation

CuFe_2O_4-TiO_2/graphene nanocomposites have been prepared via a one-step hydrothermal method,and the as-prepared CuFe_2O_4-TiO_2/graphene was characterized by X-ray powder diffraction,Raman spectroscopy,scanning electron microscopy and transmission electron microscopy.The transmission electron microscopy demonstrated that CuFe_2O_4-TiO_2 nanoparticles were successfully dispersed on the graphene sheets.Photocatalytic activity of nanocomposites was evaluated in terms of degradation of methylene blue（MB） dye solution under visible light radiation.Results showed that the photocatalytic efficiency of CuFe_2O_4-TiO_2/graphene nanocomposites was higher than its individual pure oxides（CuFe_2O_4 or TiO_2） and TiO_2/graphene.The enhancing photocatalytic activity performance of the CuFe_2O_4-TiO_2/graphene nanocomposites may attributed to the mutual effect between the Cu Fe_2O_4,Ti O_2 nanoparticles and the graphene sheets.Moreover,Cu Fe_2O_4 nanoparticles have excellent magnetic property,which makes the CuFe_2O_4-TiO_2/graphene heteroarchitecture magnetically recyclable in a suspension system.

Simulation of electromagnetic-flow fields in Mg melt under pulsed magnetic field

The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260？？ under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and then it is substituted into the magnetic field model.The fluid flow model was solved with the acquired electromagnetic force.The effects of pulse voltage frequency on the current wave and on the distribution of magnetic and flow fields were numerically studied.The pulsed magnetic field increases melt convection,which stirs and fractures the dendritic arms into pieces.These broken pieces are transported into the bulk liquid by the liquid flow and act as nuclei to enhance grain refinement.The Joule heat effect produced by the electric current also participates in the microstructural refinement.