Modulation of electromagnetic wave absorption by carbon shell thickness in carbon encapsulated magnetite nanospindles–poly(vinylidene fluoride) composites

A series of Fe₃O₄/C core–shell nanospindles with different shell thickness have been synthesized by a wet chemical method and subsequent high-temperature carbonization. The thickness of carbon shell can be well adjusted from 9 to 32 nm by changing the addition amounts of resorcinol and formaldehyde precursors during the coating process. Structure and morphology characterizations reveal that the carbon shell is amorphous structure and uniformly encapsulates on porous Fe₃O₄ nanospindles. For the first time, a flexible Fe₃O₄/C/poly(vinylidene fluoride) (PVDF) composite absorber was prepared by embedding the core–shell Fe₃O₄/C nanospindles in PVDF matrix. The electromagnetic properties of the composite show strong dependence on the carbon-shell thickness. The impedance matching for electromagnetic absorption is improved by the synergy effect between Fe₃O₄ nanospindles and encapsulated carbon shell. The Fe₃O₄/C/PVDF composite with thick carbon shell exhibits strong electromagnetic wave absorbing ability with thin absorber thickness. The minimum reflection loss for the absorber with thickness of 2.1 mm can reach −38.8 dB.     

聚吡咯/无机纳米粒子复合材料的制备及其电磁屏蔽性能研究进展

综述了聚吡咯（PPy）包覆无机纳米粒子复合材料的主要制备方法及其在电磁屏蔽领域的研究进展,重点讨论了金属单质、氧/碳/氮化物以及碳系材料这三大类无机纳米粒子与PPy复合构成的核壳结构材料的电磁屏蔽性能及相关屏蔽机理。结果表明,核壳结构能够集PPy和无机纳米粒子各自的优势于一体,并发挥二者的协同效应,该方法是制备新型电磁屏蔽材料的一种有效途径。     

Enhanced electromagnetic interference shielding performance of geopolymer nanocomposites by incorporating carbon nanotubes with controllable silica shell

The development of construction materials with exceptional electromagnetic interference (EMI) shielding performance is urgently needed to restrict the admittance of electromagnetic (EM) radiation. In this work, silica (SiO₂)-coated carbon nanotubes (S-CNT) with different shell thicknesses (～7, ～10, and ～15 nm) were prepared by a sol-gel method. The effect of SiO₂ shell thickness on the EMI shielding performance of the resulting geopolymer nanocomposites was studied. The coated SiO₂ shell effectively facilitated the dispersion of CNT in the geopolymer matrix due to the chemical reaction between SiO₂ and the geopolymer. The dispersability of modified CNT could be further improved by increasing the thickness of the SiO₂ shell. However, electron delocalization was hindered by the insulating SiO₂ shell. The conductive nature of CNT was restored during geopolymerization when the SiO₂ shell was thin. A high EMI shielding effectiveness (SE) of 24.2 dB was achieved for the geopolymer nanocomposite containing 5 vol% S-CNT with a thin SiO₂ shell. The value achieved was more competitive than reported composites for construction when the sample thickness and filler content were considered.     

探究新型固体吸附剂——巯基花生壳

以花生壳为原料,用硫代乙醇酸和乙酸酐改性花生壳做固体吸附剂,并探讨了巯基花生壳在不同吸附条件下,定量吸附水中的Ag(Ⅰ),用原子吸收光度法分别测定其含量的方法。在温度为25℃时,1.5 g巯基花生壳吸附做振荡吸附1.5小时可以达到最佳效率(可吸附约260.46μg/g Ag);或室温下,1.5 g巯基花生壳在pH为4.0的银溶液中做振荡吸附1.5小时可达到最佳效率。     

壳核结构SiC/C纤维的制备与吸波性能的研究

采用活性碳纤维转换法制备了壳核结构SiC/C纤维,采用拉曼光谱、SEM、XRD以及热重分析等测试方法对比研究了生成SiC的厚度对壳核结构SiC/C纤维样品的热重及吸波性能的影响。结果表明:包裹SiC壳层后样品吸波性能得到提高,样品厚度为3.0 mm时,保温4 h样品的最小反射损耗在8.24 GHz处达到-17.22 dB,低于-10 dB(90%的电磁波被吸收)的频宽在2.0 mm处达到4.8 GHz(11.12~15.92 GHz);保温3 h样品的最小反射损耗在8.23 GHz处达到-14.45 dB,低于-10 dB(90%的电磁波被吸收)的频宽在2.0 mm处达到4.56 GHz(10.88~15.44 GHz);且随着SiC含量的升高,试样微波吸收性能有所增强;制备的壳核结构SiC/C纤维样品起始氧化温度提高了150 ℃以上,并且最终残余质量在50%左右,即包裹SiC纤维后样品的抗氧化能力大大提高。     

Cytotoxicity of InP/ZnS quantum dots related to reactive oxygen species generation

Indium phosphide (InP) quantum dots (QDs) have emerged as a presumably less hazardous alternative to cadmium-based particles, but their cytotoxicity has not been well examined. Although their constituent elements are of very low toxicity to cells in culture, they nonetheless exhibit phototoxicity related to generation of reactive oxygen species by excited electrons and/or holes interacting with water and molecular oxygen. Using spin-trap electron paramagnetic resonance (EPR) spectroscopy and reporter assays, we find a considerable amount of superoxide and a small amount of hydroxyl radical formed under visible illumination of biocompatible InP QDs with a single ZnS shell, comparable to what is seen with CdTe. A double thickness shell reduces the reactive oxygen species concentration approximately two-fold. Survival assays in five cell lines correspondingly indicate a distinct reduction in toxicity with the double-shell InP QDs. Toxicity varies significantly across cell lines according to the efficiency of uptake, being overall significantly less than what is seen with CdTe or CdSe/ZnS. This indicates that InP QDs are a useful alternative to cadmium-containing QDs, while remaining capable of electron-transfer processes that may be undesirable or which may be exploited for photosensitization applications.     

Scale-up and design of a continuous microwave treatment system for the processing of oil-contaminated drill cuttings

A continuous microwave treatment system has been developed for the remediation of contaminated drill cuttings at pilot scale. Using the mechanisms of oil removal as a basis, a design was produced using electromagnetic simulations to find the optimum microwave applicator geometry which yielded the most favourable power density distribution. Bulk materials handling and process engineering principles were systematically integrated with the electromagnetic design to produce a system capable of treating 500 kg/h of material. The effects of the key design parameters are simulated, and a number of the simulations are verified with experimental data. It is shown that the environmental discharge threshold of 1% oil can be achieved in continuous operation, and the sensitivity of the system to changing feedstock properties is also highlighted. The parity between the simulations and experimental results in this paper highlights the necessity of electromagnetic modelling in the design and scale-up microwave processing equipment.     

Multiscale design of high‐voltage multilayer energy‐storage ceramic capacitors

Multilayer energy‐storage ceramic capacitors (MLESCCs) are studied by multiscale simulation methods. Electric field distribution of a selected area in a MLESCC is simulated at a macroscopic scale to analyze the effect of margin length on the breakdown strength of MLESCC using a finite element method. Phase field model is introduced to analyze the dielectric breakdown mechanism of MLESCC at a mesoscopic scale. The microstructure of selected area is generated through voronoi tessellation random construction routine containing core‐shell‐structured dielectric materials. The effects of margin length, shell permittivity, and shell volume fraction on the breakdown strength of MLESCC are respectively studied. Results indicate that the breakdown strength of MLESCC can be enhanced by adopting larger margin lengths, or by increasing the shell permittivity or volume fraction.     

Influence of a graphite shell on the thermal and electromagnetic characteristics of FeNi nanoparticles

Graphite-coated FeNi alloy nanoparticles have been prepared by a modified arc-discharge method in an alcohol atmosphere and have been characterized by means of X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, Raman spectroscopy, thermal gravimetric analysis and scanning differential thermal analysis. The results show that the nanoparticles have a core/shell structure, with FeNi alloy as core and graphite layers as shell. Compared with FeNi nanoparticles with an oxide shell, the graphite shell restricts the growth of the FeNi nanoparticles, which leads to lower saturation magnetization and higher natural-resonance frequency. Due to the enhancement of the thermal stability by the graphite shell and its oxidation protection, the graphite-coated FeNi nanoparticles are stable in air below 240 °C. The electromagnetic characteristics of the graphite-coated FeNi nanoparticles have been studied in the 2-18 GHz range. The graphite shell dramatically improves the magnetic/dielectric loss and the attenuation constant in the 9-18 GHz range through the enhancement of the electrical resistivity and the protection of the FeNi cores, leading to enhanced microwave-absorption properties in this range.     

Flow,Solidification, and Solute Transport in a Continuous Casting Mold with Electromagnetic Brake

A three‐dimensional mathematical model is developed to study coupled turbulent flow, heat, solute transport, and solidification in a slab continuous caster with electromagnetic brake. Based on the analogy analysis, all the governing equations can be expressed as a general differential equation and be solved by a general numerical method. Numerical results show that a small corner‐vortex appears near the free surface due to the interaction between the moving solidified shell and the upward flow. Influenced by the fluid flow, the temperature and solute distribution can also be divided into the upper and lower recirculation zones but the distribution of carbon concentration is opposite to that of temperature. The three‐dimensional magnetic field can effectively damp the local flow and affect heat and solute transfer in the mold.     

Fabrication of core–shell microspheres using alginate and chitosan–polycaprolactone for controlled release of vascular endothelial growth factor

Alginate microspheres loaded with vascular endothelial growth factor (VEGF) were prepared via an emulsification method using calcium chloride as a crosslinker. The microspheres with encapsulation efficiency of about 80% were coated by chitosan–polycaprolactone (CH–PCL) with various PCL percentages changing from around 15 to 42 wt.% to fabricate core–shell alginate/CH–PCL microspheres with an average size of around 40 μm. It was found that the CH–PCL coating layer on the core–shell microspheres could have a sandwich-like structure. The PCL content in the CH–PCLs and the concentration of CH–PCL solutions in preparing the microsphere functioned as two key factors to regulate the release profiles of the microspheres. Some selected alginate/CH–PCL microspheres were further crosslinked using genipin as a crosslinker, and the amount of genipin was found to be another impactful factor to mediate the release patterns of the microspheres. In vitro release measurements revealed that VEGF-release from these core–shell microspheres was controlled either by Fickian diffusion or non-Fickian transport that involves both diffusion and swelling. Some optimized core–shell microspheres were capable of maintaining sustained VEGF-release in an approximately linear manner over a period of time longer than 4 weeks and did not involve a significant initial burst.     

Elastomeric films from structured latexes

A model structured latex that is capable of forming a self-curable elastomeric film under mild temperature conditions was developed. In this model latex system, a small amount of dimethyl meta-isopropenyl benzyl isocyanate (TMI®) was copolymerized with n-butyl acrylate (BA) onto poly(butadiene-co-styrene) [(P(Bd-S)] seed latex particles. In the final stage of the film formation process, the latex particles coalesce with each other, and interdiffusion of PBA-based polymer chains in the shell layers of adjacent structured particles occurs. At this stage, the isocyanate groups in the P(BA-TMI) shell layer would begin to crosslink by either a moisture-cure reaction via trace amounts of water remaining in the latex film or by a post-added crosslinker that contains amine groups. Improved elastomeric properties of the latex film are expected from this kind of “interphase” crosslinking structure. However, latex films prepared from the model P(Bd-S)/P(BA-TMI) core/shell latexes were cracked and brittle, which was explained by the formation of a highly crosslinked/grafted core/shell interphase zone. Saturation of the residual double bonds in the P(Bd-S) seed latex particles by hydrogenation was found to be an effective way to reduce the development of the interphase zone and the degree of crosslinking during the second-stage polymerization. An elastomeric film with good mechanical and anti-aging properties was formed from this hydrogenated-P(Bd-S)/P(BA-TMI) structured latex. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1143–1152, 1997     

Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La0.6Sr0.4MnO3 Nanoparticles

The intrinsically core/shell structured La_0.6Sr_0.4MnO₃nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of −41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than −10 dB is obtained in the 5.5–11.3 GHz range for absorber thicknesses of 1.5–2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La_0.6Sr_0.4MnO₃nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials.     

不设阳极保护不锈钢管壳式浓硫酸冷却器的应用

介绍了已使用8年多的不设阳极保护不锈钢管壳式浓硫酸冷却器的技术参数、使用工况和使用效果,认为Edmestom SX管壳式浓硫酸冷却器的耐腐蚀性能优越,可在ω(H2SO4)=97．5％-99．0％的范围内长期稳定工作,换热能力的富裕量较大,经济效益和社会效益显著。由于现场不具备综合利用低温位热量的条件,故未能充分展示其优越性能。     

The experimental and theoretical study on the spatial-temporal distribution of electromagnetic radiation from JO-8 explosions.

The detonating fuse in the multistage warhead will be subjected to strong electromagnetic interference, derived from electromagnetic radiation generated by explosion of the shaped charge warhead, which may cause premature detonation or misfire. In order to explore the possible electromagnetic environment surrounded the detonating fuse, the spatial-temporal distribution of electromagnetic radiation after the explosion of JO-8 explosive was investigated in this paper. The electromagnetic radiation signal was collected and its frequency coverage was analyzed in the far-field area by the field blast test. Moreover, based on electromagnetic theory, a theoretical model of electromagnetic radiation generated by the explosion of JO-8 explosive was established, and the spatial-temporal distribution of the electric field intensity was illustrated in detail for several typical positions after the explosion. The better agreement between experimental and theoretical results indicates that the proposed theoretical model and computational method are reasonable. On this basis, the distributions of electric field intensity for different positions and various explosive weights were predicted respectively by using distance and explosive weight as variables. This study is expected to provide a reference for the research on the electromagnetic radiation for explosive explosion and anti-explosive electromagnetic interference.     

Dividing wall column—A breakthrough towards sustainable distilling

Dividing wall column (DWC) is a single shell, fully thermally coupled distillation column capable of separating mixtures of three or more components into high purity products. Compared to conventional columns-in-series and/or in-parallel configurations a DWC requires much less energy, capital and space. This makes DWC to something that corresponds with the present day idea of sustainable process technology. Based on published papers and patent literature this paper aims to give a complete overview of the work done so far on the research and implementation of DWCs, from early ideas on thermal coupling of distillation columns to practical issues that needed to be solved for their successful implementation. Approaches to short-cut and rigorous simulation, optimization, and control are highlighted, with particular focus on column internals and dimensioning, which is only conceptually considered in academic publications. A survey of relevant patents is included providing information on equipment innovations and application areas of industrial interest. Finally authors look at what is needed on research and engineering side to enable maximization of potential gains by building DWCs for obtaining four or even more products containing two or more partition walls in parallel, which is something not yet attempted in industrial practice.     

γ射线辐射法制备石墨/镍复合材料及其电磁性能

为提高鳞片状石墨在电磁波吸收方面的应用性能,采用γ辐射一步法制备了鳞片状石墨/镍复合材料。实验在常温常压下进行,将鳞片状石墨置于镍盐溶液内,控制溶液的镍盐浓度,再加入氧化性自由基清除剂并将该混合溶液置于钴60辐照室辐照,获得了纳米金属镍包覆在鳞片状石墨表面的复合材料。通过XRD、SEM对复合材料进行了结构和形貌的表征,复合材料为核壳结构、由纯纳米镍与石墨构成,同时提出了γ辐射法合成该复合材料的复合机理,并且研究了复合材料在2～18GHz频段的电磁性能。     

Preparation of core–shell nanoparticle‐based hindered amine stabilizer and its application in polyoxymethylene

Core–shell nanoparticles chemically functionalized by hindered amine stabilizer (HAS), poly(BA‐MMA‐co‐PMPA) (PBMP), were prepared by two‐stage emulsion polymerization from butyl acrylate, methyl methacrylate, and 1,2,2,6,6‐pentamethylpiperidin‐4‐yl acrylate. The incorporation of HAS into the particles was confirmed by nuclear magnetic resonance (¹H‐NMR) and the core–shell microstructure of PBMP particles was revealed by transmission electron microscopy. Furthermore, PBMP capable of one‐step toughening and photostabilizing, was melt‐blended with polyoxymethylene (POM), and its dispersion in POM was investigated by scanning electron microscope. The results showed that the core–shell nanoparticles could be well dispersed in POM matrix, indicating its good compatibility with POM. The UV resistance and impact resistance of POM were obviously improved by the HAS‐functional core–shell nanoparticles simultaneously. In addition, the core–shell nanoparticles could confer excellent protection to the surface of POM from UV‐light damage, regardless of the adverse effects on the thermal‐oxidative stability of POM, as investigated by thermogravimetry analysis under aerobic condition. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012