0-3 magnetic nanocomposites via EPD: Current status for power component fabrication and future directions

Inductors and transformers (here referred to as power components) for modern AC/DC switching power supplies require magnetic materials that have high power density and efficiency at high frequencies, with high magnetic saturation, low coercivity, and multi-micrometer thicknesses to increase magnetic energy storage and power handling. Rather than using a single-phase magnetic material in a polymer-based composite, a composite formed from two magnetic phases (such as a 0-3 nanocomposite) can simultaneously achieve all of the listed requirements and benefit from contributions by both the zero- and three-dimensional phases to the magnetic properties. The fabrication of 0-3 magnetic nanocomposites for power component applications requires a method to deposit magnetic nanoparticles into thick, physically stable yet porous films, and a subsequent method for infiltrating the magnetic nanoparticle film with another magnetic material. Here, the deposition of magnetic nanoparticles into micron-thick films using electrophoretic deposition (EPD) is discussed. This is described along with a new method, to improve upon traditional EPD methods by increasing film–substrate interactions with chelating agents, therefore increasing film stability. Next, the use of electro-infiltration for fully incorporating a secondary magnetic material within the nanoparticle film is presented, showing the cumulative fabrication process with the addition of a multilayered nanocomposite fabrication technique for increasing overall nanocomposite thickness. The subsequent cross-sectional and magnetic characterization of the fabricated 0-3 nanocomposites is also shown. Finally, future directions for 0-3 magnetic nanocomposites are offered, with emphasis on potential materials synthesis techniques and on translating knowledge beyond power component applications.     

Synthesis and Magnetic Characterization of Metal-filled Double-sided Porous Silicon Samples

A magnetic semiconductor/metal nanocomposite with a nanostructured silicon wafer as base material and incorporated metallic nanostructures (Ni, Co, NiCo) is fabricated in two electrochemical steps. First, the silicon template is anodized in an HF-electrolyte to obtain a porous structure with oriented pores grown perpendicular to the surface. This etching procedure is carried out either in forming a sample with a single porous layer on one side or in producing a double-sided specimen with a porous layer on each side. Second, this matrix is used for deposition of transition metals as Ni, Co or an alloy of these. The achieved hybrid material with incorporated Ni- and Co-nanostructures within one sample is investigated magnetically. The obtained results are compared with the ones gained from samples containing a single metal.     

Electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes: FFT-impedance spectroscopy of the growth process and magnetic properties

The electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes has been investigated by fast Fourier transform-impedance spectroscopy (FFT-IS) in the frequency range from 75 Hz to 18.5 kHz. The impedance data could be fitted very well using an electric circuit equivalent model with a series resistance connected in series to a simple resistor-capacitor (RC) element and a Maxwell element. Based on the impedance data, the Co deposition in ultra-high aspect ratio InP membranes can be divided into two different Co deposition processes. The corresponding share of each process on the overall Co deposition can be determined directly from the transfer resistances of the two processes. The impedance data clearly show the beneficial impact of boric acid on the Co deposition and also indicate a diffusion limitation of boric acid in ultra-high aspect ratio InP membranes. The grown Co nanowires are polycrystalline with a very small grain size. They show a narrow hysteresis loop with a preferential orientation of the easy magnetization direction along the long nanowire axis due to the arising shape anisotropy of the Co nanowires.     

Self‐assembled polymer nanocomposites and their networks

Synthetic modifications to block‐copolymer structure‐directing agents lead to polymerizable macromers suitable for templating the growth of mesoporous silica particles, which can subsequently react in situ to form extended nanocomposites and nanocomposite networks. Suitably functionalized triblock polymers can preserve the structure‐directing capabilities of the triblock polymer for templating ordered mesoporous silica particle growth and also generate a reactive matrix for subsequent polymer network formation via the reactive end groups. The final self‐assembled products are polymer nanocomposites or novel crosslinked nanocomposite networks whose organic/inorganic composition ratios can vary systematically. The novel self‐assembly route described here should be generally applicable to the synthesis of intimately mixed nanocomposites and nanocomposite networks, starting from a wide variety of block polymeric template/macromer/ordered silica systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41111.     

Formation of different calcium phosphate phases on the surface of porous Al2O3-ZrO2 nanocomposites

Biomimetic deposition of calcium phosphates onto Al₂O₃-ZrO₂ nanocomposites provides greater surface bioactivity, leading to the formation of biomaterials that can potentially replace and restore bone tissues. This study is aimed at evaluating the formation of different calcium phosphate phases using biomimetic coating on chemically treated and untreated surfaces of porous Al₂O₃-ZrO₂ (5 vol%) nanocomposites at different incubation times. To this end, the porous materials fabricated by gelcasting were calcined, sintered, chemically treated or left untreated, and biomimetically coated during a period of 14–21 days. The results indicated high porosity of the nanocomposite surfaces as well as high pore interconnectivity, which favours osseointegration. Additionally, it was observed that chemical treatment may influence the amount of calcium phosphates formed on the nanocomposite surfaces as well as the minimum incubation time, favouring the formation of a particular calcium phosphate phase over the nanocomposite surface.     

Study on dispersion and intercalation of organoclay in PP and PP‐g‐MA matrices

Understanding the complex mechanism of dispersion and intercalation of the clay tactoids can allow us to control the final morphology, homogeneity, and the macroscopic properties of clay nanocomposites. The objective of this work is a multiscale study of the dispersion state of PP/organoclay and PP‐g‐MA/organoclay composite. The microscopic investigation, WAXS diffractograms, rheological analysis, and mechanical properties were used to characterize the dispersion of organoclay in PP and PP‐g‐MA matrices during melt blending in two different shear rates. The morphological results show a system of aggregating intercalated clay particles which disperse by increasing mixing time with a strain‐controlled process and a very quick intercalation process in early mixing times for PP‐g‐MA/organoclay nanocomposite, while PP/organoclay samples only form microcomposites. The relative network modulus of these intercalated particles as a function of mixing time was obtained; and the tensile modulus of nanocomposite samples were compared with Halpin‐Tsai model prediction. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Modeling of isochronal complex magnetic susceptibility of polymer–magnetic nanocomposites using fractional calculus

In this work, we report on the application of fractional calculus to the modeling of the isochronal behavior of complex magnetic susceptibility obtained from polymer–magnetic nanocomposites composed of cobalt‐ferrite nanoparticles embedded into a chitosan matrix. From the isochronal measurements of real and imaginary parts of the complex magnetic susceptibility and temperature‐dependent static measurements, performed at different applied dc‐fields, it was observed that the spins' response is mainly leaded by three contributions, which are attributed to the intrinsic magnetic anisotropy of the particles, the surface‐to‐core spins exchange within particles and to the dipole‐dipole interactions among particles. Accounting these contributions, the proposed magnetic model was capable to describe, in very precise way, the experimental behavior of both, real and imaginary, parts of the complex magnetic susceptibility, at temperatures below to that related to the transition of the polymer–magnetic nanocomposite into the superparamagnetic regime. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Cobalt/graphene oxide nanocomposites: Electro-synthesis,structural, magnetic,and electrical properties

In this research, different samples of cobalt/graphene oxide nanocomposites were successfully synthesized electrochemically by applying different voltages. Their structure, magnetization and electrical properties were studied using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), atomic force microscope (AFM), fourier transformation infrared (FT-IR), vibrating sample magnetometer (VSM), two point probe electrical conductivity meter, galvanostat/potentiostat, and universal testing machine. The results of structural characterization confirmed the formation of cobalt/graphene oxide nanocomposites. The FESEM images showed the porous flower-like structure of particles deposited on the graphene oxide sheets. The AFM images clearly showed the surface roughness and the dispersion of nanoparticles on graphene oxide sheets. Room-temperature magnetization values range from 18 emu g^?1 to 167 emu g^?1, depending on the applied voltage. In order to study the electrical properties of the nanocomposites, the volumetric resistivity and volumetric conductivity under different pressures and the current-voltage characteristic curves were measured. Based on the results, the nanocomposites synthesized by applying 8 V and 23 V show ohmic behavior and have the highest volumetric conductivity. The volumetric conductivity increases with increasing the pressure. The nanocomposite prepared by applying 23 V presents good structural, magnetic, and electrical properties.     

Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers

In this study, the fabrication of magnetic multilayers with a controlled value of the in-plane uniaxial magnetic anisotropy field in the range of 12 to 72 kA/m was achieved. This fabrication was accomplished by the deposition of bilayers consisting of an obliquely deposited (54°) 8-nm-thick anisotropic Co layer and a second isotropic Co layer that was deposited at a normal incidence over the first layer. By changing the thickness value of this second Co layer (X) by modifying the deposition time, the value of the anisotropy field of the sample could be controlled. For each sample, the thickness of each bilayer did not exceed the value of the exchange correlation length calculated for these Co bilayers. To increase the volume of the magnetic films without further modification of their magnetic properties, a Ta spacer layer was deposited between successive Co bilayers at 54° to prevent direct exchange coupling between consecutive Co bilayers. This step was accomplished through the deposition of multilayered films consisting of several (Co_{8 nm-54°}/Co_{X nm-0°}/Ta_{6 nm-54°}) trilayers.     

Environmental water remediation using covalently functionalized zerovalent iron nanocomposites with 2-pyridinecarboxaldehyde via 3-aminopropyltrimethoxysilane and ethylenediamine

The adsorption technology involving nano zerovalent iron (NZVI) has been widely employed to remediate polluted water based on a number of economic aspects. However, this technology is facing a high challenge in the removal process of pollutants due to hydrolysis and stability characteristics of zerovalent iron. Therefore, this study is aimed to demonstrate a method for encapsulation and functionalization of NZVI nanoparticles with 3-aminopropyltrimethoxysilane (NH₂) and 2-pyridinecarboxaldehyde (PY), respectively to produce the target nanocomposite (NZVI-NH₂-PY). Zerovalent iron nanoparticles are also aimed to functionalize with ethylenediamine (ED) and 2-pyridine carboxaldehyde to produce NZVI-ED-PY nanocomposite. The TEM images showed that the sizes of NZVI-NH₂-PY and NZVI-ED-PY nanocomposites are in the range 3.33–4.35 and 5.42–10.36 nm, respectively. More characterization evidences were concluded by thermal gravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The two novel magnetic nanocomposites have been used for removal of Co(II), Zn(II), Pb(II), Cd(II), Hg(II), Cu(II) beside radioactive isotopes (⁶⁵Zn and ⁶⁰Co) from water. NZVI-NH₂-PY nanocomposite was more selective toward Hg(II), Pb(II) and Cd(II), while NZVI-ED-PY was more selective toward Z(II), Co(II) and Co(II). Different kinetic models were applied and the investigated metal ions were characterized to undergo the pseudo-second order using both NZVI-NH₂-PY and NZVI-ED-PY nanocomposites.     

Electrical properties of polycarbonate/expanded graphite nanocomposites

In present study, polymer matrix nanocomposites based on polycarbonate as matrix and expanded graphite (EG) as reinforcement were fabricated using a simple solution method followed by hot pressing. Scanning electron microscopy revealed almost uniform dispersion and three dimensional networks of EG particles in the matrix. The dc and ac electrical conductivities of the nanocomposites increased with increasing EG content in the matrix. The electrical percolation threshold was observed between 1 and 2 wt % EG. The improvement in the conductivity of 10 wt % nanocomposite was found more than 13 orders of magnitude higher than that of pure matrix. The dielectric constant (at 1 MHz) of the nanocomposite containing 10 wt % EG was increased to about 137. The significant increase in electrical conductivity, dielectric constant, and dissipation factor for the nanocomposites might be good for the applications in antistatic/electromagnetic interference shielding applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47274.     

ELASTODYNAMIC RESPONSE OF VIBRATIONS IN A MAGNETO-MICROPOLAR POROUS MEDIUM POSSESSING CUBIC SYMMETRY

The present investigation is concerned with the propagation of plane waves in a micropolar porous half-space possessing cubic symmetry in contact with vacuum under the influence of constant magnetic field. After deriving the frequency equations, the behavior of curves for phase velocity, attenuation coefficient, and specific loss is depicted graphically to study the effects of magnetism and anisotropy on the propagation of waves in a micropolar porous half-space possessing cubic symmetry. The path of surface particles is also obtained for the propagation of Rayleigh waves. Some special cases of interest are also deduced from the present investigation.     

Gelation performance of poly(ethylene imine) crosslinking polymer–layered silicate nanocomposite gel system for potential water‐shutoff use in high‐temperature reservoirs

Polymer gels have been widely used for water shutoff in mature oil fields. In this paper, polyacrylamide (PAM)–montmorillonite (MMT) nanocomposites (NC) were prepared through in situ intercalative polymerization. Fourier transform infrared spectroscopy and X‐ray diffraction were conducted to characterize the prepared PAM/MMT nanocomposites. The gelation performance of poly(ethylene imine) (PEI) crosslinking PAM/MMT nanocomposite gel system (NC/PEI gel system) was systematically investigated by bottle testing and viscosity measurement methods. The results showed that the gelation performance of the NC/PEI gel system was greatly affected by the total dissolved solids, PAM/MMT nanocomposite concentration, and PEI concentration. The NC/PEI gel system exhibited much better thermal stability and gelation performance than the PAM/PEI gel system at the same conditions. The gelation performance after flowing through porous media of the NC/PEI gel system before injection and that of the subsequently injected gel system was different. The gel strength decreased and the gelation time was delayed after the gel system before injection was flowed through porous media. However, the gel strength of the subsequently injected gel system did not decrease, and only the gelation time was delayed after flowing through porous media. This study suggests that the NC/PEI gel system can be used as a potential water‐shutoff agent in high‐temperature reservoirs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44243.     

以石墨烯为核树状大分子包覆Co纳米复合材料制备及其吸附性能研究

通过化学还原法制备了以石墨烯为核树状大分子包覆Co纳米复合材料。利用FTIR、TG、XRD和TEM对所制备产物进行了结构表征。考察了不同p H、吸附时间和温度条件下,制备的以石墨烯为核第三代数树状大分子纳米复合材料(G3.0-PAMAM/Co)对刚果红吸附效果的影响。结果表明,G3.0-PAMAM/Co对刚果红是强有力的磁性吸附剂;对刚果红的吸附动力学能符合Lagergren准二级吸附模型,主要为化学吸附;吸附热力学能符合Langmuir等温吸附模型,最大吸附量可达161.49 mg/g。     

Synthesis and characterization of magnetite (Fe3O4)—Polyvinyl alcohol‐based nanocomposites and study of superparamagnetism

The aim of this investigation was to design iron oxide containing nanocomposites which could display superparamagnetic behavior and thus find application in biomedical and allied fields. To achieve the proposed objectives methyl methacrylate was polymerized by a redox system comprising of metabisulphite and persulphate in the immediate presence of a crosslinker, N,N′‐methylene bis acrylamide and a preformed polymer, i.e., polyvinyl alcohol. Into the prepared polymer matrix nanosized magnetite (Fe₃O₄) particles were evenly dispersed by in situ precipitation of Fe²⁺/Fe³⁺ ions. The nanocomposite materials were characterized by techniques like FTIR, SEM, TEM, XRD, and DSC. The magnetic behavior of nanocomposites and bulk magnetite particles was studied under varying applied magnetic fields and their superparamagnetic property was examined. The iron‐oxide polymer nanocomposites were also studied for microhardness. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Fabrication and magnetic properties of cobalt-dispersed-alumina composites

High-density cobalt-dispersed-alumina (Co/Al₂O₃) composites were successfully prepared by hot-pressing of alumina-cobalt composite powders with fine cobalt 30 nm in diameter. The nanocomposite powders were prepared by co-deposited processing of Al³⁺and Co²⁺, followed by calcination and selective reduction. The phase composition of Co/Al₂O₃ composites were -Al₂O₃, fcc-Co and a little amount of hcp-Co. Microstructural investigations revealed that submicron-sized cobalt particles were dispersed homogeneously at alumina grain boundaries, forming intergranular composites. Meanwhile growth and coalescence of cobalt particles occurred with increasing Co-content. The ferromagnetic properties of the composites were measured, because of the magnetic dispersions, which indicated a functional value of Co/Al₂O₃ composites. The effects of grain size and the residual stresses on magnetic properties for Co/Al₂O₃ system were discussed in detail.     

Porous carbon-silica composites and carbon materials from rice husk: Production technology, texture, and dispersity

A method based on carbonization in a fluidized-bed catalytic reactor is suggested for utilization of rice husks, which are hard-to-recycle waste from paddy production. The bottom ash resulting from carbonization at 465–600°C is a carbon-silica nanocomposite (C/SiO₂) with a SiO₂ content of 58.7–81.8 wt % and a specific surface area of S _BET = 152–232 m²/g. Leaching of SiO₂ with hydrofluoric acid yields porous carbon materials with a specific surface area of 165–494 m²/g and a SiO₂ content of <1%. These materials have been characterized by small-angle X-ray scattering (SAXS), transmission electron microscopy, and X-ray diffraction. Particle size data for SiO₂ in the carbon-silica nanocomposite have been obtained for the first time. As the carbonization temperature is raised from 465 to 600°C, the average particle size of silica increases from 5.5 to 8.1 nm. Development of the SAXS procedure for determining the size of silica particles in the carbon matrix would provide a promising tool for knowingly designing porous carbon materials with preset properties. The carbonization of rice husks in a fluidized catalyst bed is among the most promising methods of their conversion into C/SiO₂ nanocomposites and porous carbon materials with the use of template synthesis approaches.     

Polyethylene Nanocomposites with Ni,Co, and Fe Carbon-Based Magnetic Fillers

In the present study, the effect of Ni, Co, and Fe carbon-based magnetic fillers (Ni-C, Co-C, and Fe-C) was investigated on the magnetic, mechanical, thermal, and morphological properties of polyethylene nanocomposites. The in situ polymerization technique was used to prepare nanocomposites of polyethylene from the ethylene monomer introducing small amounts of filler ranging from 1 to 2 wt.%. The metal-carbonized fillers were obtained by pyrolysis of wood sawdust activated by Ni, Co, or Fe salts. X-ray diffraction showed that the fillers were of nanometric size. Thermogravimetric analysis was executed to investigate the thermal strength of the materials as well as to calculate the metal content in the carbon-based fillers. The onset degradation temperature showed an enhancement of 17°C, whereas the maximum degradation temperatures increased 4°C with the introduction of the filler. Differential scanning calorimetry indicated an improvement of 3°C in crystallization temperature, whereas the melting temperature remained unchanged compared to neat polyethylene. The filler was shown to increase the modulus of elasticity of the nanocomposites. The addition of 1.0 wt.% of the metal-carbonized material in the diamagnetic polymer matrix resulted in a thermoplastic nanocomposite with ferromagnetic behavior. POLYM. ENG. SCI., 60:988–995, 2020. © 2020 Society of Plastics Engineers     

溶胶–凝胶法制备碳纳米管-In_2O_3纳米复合材料及其气敏性

以碳纳米管（carbon nanotubes,CNT）为模板,在超声波辅助条件下,利用溶胶–凝胶法合成CNT–In2O3纳米复合粉体,用该复合粉体制备CNT–In2O3气敏元件。借助X射线衍射、透射电子显微镜、傅立叶变换红外光谱仪和能量色散谱仪对产物进行表征,研究了CNT–In2O3气敏元件的气敏性。结果表明：CNT–In2O3纳米复合粉体是一种由In2O3纳米颗粒均匀包裹在直径约为20～30nm的碳纳米管上的纳米复合材料。CNT–In2O3气敏元件在低温对NO2有较高的灵敏度,该元件对NO2的灵敏度高于纯In2O。当CNT和InC13·4H2O的摩尔比为3：10时,CNT–In2O3气敏元件对NO2的灵敏度最大,且灵敏度随NO2浓度的增大而增大。该气敏元件在200℃时对NO2的响应时间为10s,恢复时间为70s。     

Polyimide/substituted polyaniline–copolymer–nanoclay composite thin films with high damping abilities

Polyimide (PI)/poly(N‐ethyl aniline‐co‐aniline‐2‐sulfonic acid)–clay (SPNEAC) nanocomposite films containing water‐soluble SPNEAC were successfully synthesized. Atomic force microscopy studies showed a homogeneous distribution of coated clay particles in the PI matrix. The particle sizes varied between about 50 nm and about 220 nm in height and 6–7 μm in length in the nanocomposite containing 5 wt % SPNEAC. Average surface roughnesses of 0.253 and 34.9 nm were obtained for neat PI and the 5 wt % SPNEAC–PI nanocomposite, respectively. Dynamic mechanical spectrometry was used to study the viscoelastic transitions and their temperatures. The dynamic mechanical spectrometry results show a decreasing glass‐transition temperature of the nanocomposites with increasing SPNEAC weight fraction. The area under the α‐transition peak, which is associated with damping and impact energy, increased with increasing SPNEAC weight fraction. The impact energy of the nanocomposites was estimated with a viscoelastic model. It increased with increasing SPNEAC weight fraction, and a maximum value of 84.9 mJ was obtained. The viscoelastic model was based on the area under the α‐transition peak, rubbery plateau modulus, and sample volume. A 5 wt % addition of SPNEAC improved the impact energy of neat PI films by 300%. Scanning electron micrographs of the nanocomposite films showed a less compact cross‐sectional morphology. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013