Electromagnetic wave absorption properties of multi-walled carbon nanotubes decorated with La-doped BaTiO3 nanocrystals synthesized by a solvothermal method

Ba_1−xLa_xTiO₃/multi-walled carbon nanotube (MWCNT) nanocomposites with different concentrations of La³⁺ doping, were synthesized by a solvothermal process. The prepared nanocomposites had a hybrid microstructure in which Ba_1−xLa_xTiO₃ nanocrystals with diameter of 10–30 nm were firmly immobilized on the MWCNTs sidewalls. Electromagnetic (EM) wave absorption properties of La-doped BaTiO₃/MWCNT nanocomposites were investigated in the 7.5–18 GHz frequency range for an absorber thickness of 1 mm. The reflection loss (RL) calculated from the EM parameters of the samples, moved to low frequencies with increasing La³⁺ doping. The widest absorption bandwidth, with the lowest frequency range, was observed in a nanocomposite doped with 1.5 at% La³⁺. An RL exceeding −5 dB for this sample was obtained in the frequencies ranging from 9.6 to 16.3 GHz, with the optimal RL of −17.4 dB at 10.9 GHz, due to enhanced interfacial polarization resulting in developed ε^″r${{\epsilon }^{″}}_{\text{r}}$. In addition, the RL for the sample shifted to the low frequency region and the peaks became sharper in the 2–18 GHz frequency range with increasing absorber thickness. For BaTiO₃/MWCNT nanocomposites, La³⁺ doping can greatly improve the EM wave absorbing ability in a thin absorber thickness and the donor-doped nanocomposites show promise for application in EM wave shielding materials with broad absorption bandwidths.     

One-step synthesis,electromagnetic and microwave absorbing properties of α-FeOOH/polypyrrole nanocomposites

One-step synthesis of α-FeOOH/polypyrrole (PPy) nanocomposites is reported for the first time via a facile one-step chemical method in the presence of OH⁻, Fe²⁺, Fe³⁺ and pyrrole monomer. α-FeOOH nanorods are in situ formed in PPy matrix and the content of α-FeOOH nanorods increases with decreasing the molar ratio of pyrrole to Fe²⁺ ([Py]/[Fe²⁺] ratio). The electromagnetic and microwave absorbing properties of the nanocomposites are investigated as a function of the [Py]/[Fe²⁺] ratio. The results show that the PPy nanocomposites exhibit good conductivity (up to 16.10 S/cm) and antiferromagnetic behavior. The reflection loss evaluation based on the absorbing wall theory at the thickness of 2 mm shows that the nanocomposite at [Py]/[Fe²⁺] = 1.0 exhibits the best microwave absorbing property in the 2–18 GHz. And the corresponding reflection frequency range under −10 dB and −5 dB is 4.2 GHz and 5.8 GHz, respectively.     

Preparation of polybenzoxazine-functionalized Fe3O4 nanoparticles through in situ Diels–Alder polymerization for high performance magnetic polybenzoxazine/Fe3O4 nanocomposites

Hybrids and nanocomposites of polymer and magnetic Fe₃O₄ nanoparticles have been utilized as magnetically-responsive materials and magnetically-directed nanoparticles. In this work, we prepare polymer-functionalized Fe₃O₄ nanoparticles through in situ Diels–Alder polymerization using maleimide-functionalized Fe₃O₄ nanoparticle as a precursor. Polybenzoxazine-functionalized Fe₃O₄ nanoparticles (MNP-PBz) have been obtained and characterized with Fourier Transform Infrared, X ray photoelectron, and Raman spectroscopies. The high saturation magnetization value of 51.9 emu g⁻¹ of the MNP-PBz nanoparticles demonstrates its superparamagnetism. Moreover, MNP-FBz has been utilized as a nanofiller for preparation of cured PBz/MNP-PBz nanocomposites, which contain various MNP-PBz contents of 67, 50, 33, and 17 wt.%. The sample of PBz/MNP-PBz-67 shows a storage modulus of 8.0 GPa, a saturation magnetization value of 37.6 emu g⁻¹, and a glass transition temperature above 380 °C. As a result, the PBz/MNP-PBz nanocomposites could be classified as magnetically-responsive high performance materials.     

Influence of SiO2 fillers on microwave absorption properties of carbonyl iron/carbon black double-layer coatings

Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO₂ was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18 GHz. With increasing SiO₂ content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18 GHz. When the coating with the optimized SiO₂ and CI weight concentration (SiO₂:CI:ER) of 2:5:1, the optimal RL got to −17.3 dB and the effective absorption band (RL better than −4 dB) reached 5.7 GHz. In comparison, the minimum RL value was only −5.9 dB and the bandwidth (RL better than −4 dB) was just 4.1 GHz for the SiO₂-free composite coating.     

Yttria-stabilized zirconia-based composites with adaptive thermal conductivity

Thermal conductivity trends in a “chameleon coating” thin film were characterized with a time-domain thermoreflectance (TDTR) technique. A yttria-stabilized zirconia (YSZ)-based nanocomposite material containing ∼21 vol.% silver (Ag) was employed for this study. The thermal conductivity (k) of the as-deposited composite film was measured with TDTR and found to have a value of 7.4 ± 1.4 W m⁻¹ K⁻¹. The film was then annealed at 500 °C for 1 h to stimulate Ag flow from within the composite to the surface via diffusion. The Ag that coalesced on the surface during annealing was removed to expose the underlying porous YSZ matrix, and the sample was reexamined with the TDTR technique. The thermal conductivity of the porous nanocomposite YSZ material was then measured to be 1.6 ± 0.2 W m⁻¹ K⁻¹, which is significantly lower than a fully dense control sample of pure nanocrystalline YSZ (2.0 ± 0.1 W m⁻¹ K⁻¹). The annealed film displayed a 20% reduction in thermal conductivity as compared to the control sample and a 4–5-fold reduction in thermal conductivity as compared to the as-deposited material. The experiments demonstrate temperature triggering of a composite material, resulting in self-modifying thermal conductivity and diffusion-controlled porosity. These aspects can be used to enhance or restrict thermal transport (i.e., a thermal switch). The applicability of the TDTR technique to measurements of thin, nanoporous film materials is also demonstrated.     

Experimental design in the electrodeposition process of porous composite Ni–P + TiO2 coatings

In this paper, an environmentally friendly electroplating process of the composite Ni–P + TiO₂ coatings was developed. Such coatings were prepared by in situ codeposition of Ni–P with TiO₂ powder (anatase) on a polycrystalline copper substrate from the nickel-plating bath in which titanium dioxide particles were held in suspension. The codeposition was carried out under galvanostatic conditions on a rotating disc electrode. To optimize the production conditions of the Ni–P coatings modified with TiO₂ by the method of mathematical statistics, the Hartley's polyselective quasi D optimum plan of experiments was used. The relationship between the percentage content in the electrodeposited composite Ni–P + TiO₂ coatings (z) and the electrodeposition parameters like cathodic current density (j_dep), bath temperature (T) as well as content of TiO₂ powder suspended in the galvanic bath (c), has been described by the adequate cubic polynomial equation and illustrated graphically. Based on the Hartley's plan it can be stated that the maximal TiO₂ content of 28.7 at.% in the Ni–P + TiO₂ coating can be obtained for the following optimal parameters of the electrodeposition process: j_dep = 0.05 A cm⁻², c = 99 g dm⁻³ and T = 40 °C. The chemical and physical characteristics of the coating obtained under such optimum conditions, have been presented. The deposit exhibits the presence of TiO₂ particles embedded into the amorphous Ni–P matrix. It has been ascertained that embedding of TiO₂ powder to the amorphous Ni–P matrix leads to the production of deposits with large surface area. Such electrochemical codeposition method may be a good alternative in the field of porous composite coatings used in gas evolution.     

Enhanced microwave absorption of ZnO-coated planar anisotropy carbonyl-iron particles in quasimicrowave frequency band

For the aim of thin electromagnetic wave absorbers used in quasimicrowave frequency band, planar anisotropy carbonyl-iron (PACI) particles coated with ZnO nanoshells were prepared by ball milling technique and chemical precipitation method. Compared with the as-milled PACI/paraffin composite, lower dielectric constant was obtained for the composite containing PACI at ZnO particles, and hence a dramatic enhancement of reflection loss (RL) was obtained. The minimum RL of PACI at ZnO composite reaches −31.93 dB at 1.96 GHz with the matching thickness of 2.5 mm. Furthermore, the absorbing property is further improved after the PACI at ZnO composite was rotationally oriented in an external magnetic field. The minimum RL of the oriented PACI at ZnO composite reaches −40.06 dB and the matching thickness reduces to 2.2 mm with a slight variation of matching frequency. The PACI at ZnO core-shell particles exhibit great potential in application of the thin absorber in the 1–4 GHz frequency range.     

Fabrication and properties of titanium–hydroxyapatite nanocomposites

Titanium–hydroxyapatite nanocomposites with different HA contents (3, 10, 20 vol%) were produced by the combination of mechanical alloying (MA) and powder metallurgical process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vickers microhardness as high as 1030 and 1500 HV_0.2, which is more than 4–6 times higher than that of a conventional microcrystalline titanium. Titanium nanocomposite with 10 vol% of HA was more corrosion resistant (i_C = 1.19 × 10⁻⁷ A cm⁻², E_C = −0.41 V vs. SCE) than microcrystalline titanium (i_C = 1.31 × 10⁻⁵ A cm⁻², E_C = −0.36 V vs. SCE). Additionally, the electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. Mechanical alloying and powder metallurgy process for the fabrication of titanium–ceramic nanocomposites with a unique microstructure are developed.     

Effects of GeO2 on the thermal stability and optical properties of Er/Yb-codoped oxyfluoride tellurite glasses

The aim of this article was to study the influence of GeO₂ on the thermal stability and optical properties of Er³⁺/Yb³⁺ codoped (70 − x)TeO₂–xGeO₂–PbF₂–BaF₂ (TGEYx) glasses prepared by using a melting method. The properties of Er³⁺/Yb³⁺ codoped glasses were investigated by using differential scanning calorimetry, upconversion luminescence, Raman and optical absorption spectra. The results indicated that TGEY35 glass with the germanate–tellurite mixed network showed the best thermal stability and poor crystallization tendency. With increasing the GeO₂ content, the maximum phonon energy of oxyfluoride tellurite glass network increased, while the phonon density decreased. The upconversion emission intensities enhanced obviously based on the decreasing phonon density of glass hosts, while the increasing red emission (657 nm) with the increase of GeO₂ concentration was attributed to the relative larger maximum phonon energy which matching the energy gap between the pertinent ⁴S_3/2 and ⁴F_9/2 levels.     

Effect of α-Fe2O3 addition on the morphological,optical and decolorization properties of ZnO nanostructures

Visible light sensitive photocatalysts of Fe₂O₃/ZnO nanocomposites were prepared by a simple solid-state reaction method, using zinc acetate, α-Fe₂O₃ and sodium hydroxide at room temperature. The products were characterized by scanning electron microscopy, powder X-ray diffraction, N₂ adsorption–desorption measurement, UV–vis absorption, and photoluminescence spectroscopy and used for photodecolorization of Congo red. The characterization results showed that the morphology, crystallite size, BET surface area and optical absorption of the samples varied significantly with the Fe³⁺ to Zn²⁺ ratios. The nanocomposites show two absorption edges at ultraviolet and visible region. The optical band gap values of these nanocomposites were calculated to be about 3.98–3.81 eV and 2.88–2.98 eV, which show a red shift from that of pure ZnO. These red shifts are related to the formation of Fe s-levels below the conductive band edge of ZnO and effectively extend the absorption edge into the visible region. The growth mechanisms of the samples are proposed. These nanocomposites showed high decolorization ability in visible light with wavelength up to about 400 nm. Among the samples, Fe₂O₃/ZnO nanoflower (molar ratio of Fe³⁺ to Zn²⁺ is 1:100) exhibited higher decolorization efficiency than the other nanocomposites. It could be considered as a promising photocatalyst for dyes treatment.     

Electrochemical performance of CuO nanocrystal film fabricated by room temperature sputtering

To develop high performance anode materials for thin film batteries, copper oxide (CuO) film is fabricated at room temperature by reactive radio frequency magnetron sputtering. Morphological characterization shows that the CuO film consists of compacted CuO columnar grains of 20 nm in diameter and 200 nm in thickness. The measurement of lithium storage capacity and cyclability of the CuO film show that the first charge capacity of the film is 585 mAh g⁻¹ with an efficiency of 68.3% at a current density of 200 mA g⁻¹. After the 50th cycle, the capacity retention remains as high as 97.4%. The nanostructured CuO film also shows a good rate capability even being cycled at 3000 mA g⁻¹ (5 C), demonstrating that the CuO film can be a promising material as an anode for high performance thin film batteries, especially for thin film battery with amorphous electrolyte.     

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential () = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v=20 mV s−1). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 × 10⁻⁴ to 4.0 × 10⁻³ mol L⁻¹ for the determination of nitrite, with a detection limit of 2.1 × 10⁻⁴ mol L⁻¹ and the amperometric sensitivity of 8.04 mA/mol L⁻¹.     

Synthesis and microwave absorption enhancement of Fe-doped NiO@SiO2@graphene nanocomposites

Fe-doped NiO@SiO₂@graphene nanocomposites have been successfully fabricated for the first time, in which Fe-doped NiO nanoparticles are about 3 nm in diameter. In order to measure their electromagnetic properties, Fe-doped NiO@SiO₂@graphene (25 wt%) wax composites were then prepared. The experimental results show that Fe-doped NiO@SiO₂@graphene nanocomposites exhibit significantly enhanced microwave absorption performance in terms of both the maximum reflection loss value and the absorption bandwidth in comparison with NiO@SiO₂@graphene. The maximum reflection loss of Fe-doped NiO@SiO₂@graphene nanocomposites can reach −51.2 dB at 8.6 GHz with a thickness of 4 mm, and the absorption bandwidth with the reflection loss below −10 dB is 4 GHz (from 7 to 11 GHz). Therefore, this kind of nanocomposites may have the potential as high-efficient absorbers for microwave absorption applications.     

Magnetic and microwave absorption properties of polymer composites with amorphous Fe-B/Ni-Zn ferrite nanoparticles

In this study, polymer composites containing amorphous Fe-B submicrometer particles and Ni-Zn ferrite nanoparticles were fabricated. A polymer composite of mixed particles showed high permeability of μ^′r=13.7 at 0.5 GHz and μ^″r=8.3 at 1.2 GHz. In addition, this composite exhibited good microwave absorption properties (R.L. < −20 dB) in the frequency range of 0.65-1.12 GHz for absorber thickness of 2.38-4.06 mm. It is concluded that this polymer composite can be used for fabricating microwave absorbers in the UHF range, and would result in thinner microwave absorbers than any other microwave absorbers reported thus far.     

Sol–gel synthesis of Cr substituted Li0.5Fe2.5O4: Cation distribution,structural and magnetic properties

Li_0.5Cr_xFe_2.5−xO₄ powders with fine sized particles were successfully synthesized by sol–gel auto combustion, using lithium nitrate, ferric nitrate, chromium nitrate, and citric acid as the starting materials. The process takes only a few minutes to obtain as-prepared Cr-substituted lithium ferrite powders. The resultant powders were annealed at 600 °C for 4 h and investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM). Lattice parameter, bulk density and particle size are found to decrease with increasing Cr concentration, whereas X-ray density and porosity showed an increasing trend with the Cr content. Cation distribution indicates that the chromium ion occupy octahedral B-site. The magnetic moments calculated from Neel's molecular field model are in agreement in the experiment result, which indicates that the saturation magnetization decreases linearly from 37.36 to 4.27 emu/g with increasing Cr³⁺ content. However, coercivity, it increases with the Cr³⁺ substitution.     

Investigation on passivity of titanium under steady-state conditions in acidic solutions

The passivity of titanium was studied using potentiostatic polarization combined with Mott–Schottky analysis in acidic solutions. The oxide layer was characterized as an n-type semiconducting, oxygen deficient oxide (TiO_{1.993–1.996}) with a donor density in the range of 10¹⁹–10²⁰ cm⁻³ depending on electrode potential and electrolyte pH. The calculated thickness for the inner oxide layer was in the range of 1–4 nm, increasing linearly with applied potential and exponentially with electrolyte pH. The potential- and pH-dependence of the inner oxide thickness was interpreted by a modified point defect model for the migration-controlled oxide growth, in which the rate-determining step in the passive film growth processes was assumed to be the donor lattice migration.     

Synthesis and characterization of titanium-45S5 Bioglass nanocomposites

Titanium-45S5 Bioglass nanocomposites were synthesized by the combination of mechanical alloying and powder metallurgy process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vicker’s microhardness as high as 770 HV_0.2 for Ti-20 wt.% 45S5 Bioglass, which is more than three times higher than that of a conventional microcrystalline titanium (225 HV_0.2). Additionally, titanium-10 wt.% of 45S5 Bioglass nanocomposites (i_c = 1.20 × 10⁻⁷ A/cm², E_c = −0.42 V vs. SCE) were more corrosion resistant than microcrystalline titanium (i_c = 2.27 × 10⁻⁶ A/cm², E_c = −0.36 V vs. SCE). In vitro biocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the disks of the materials and cell growth was examined. The morphology of the cell cultures obtained on Ti-10 wt.% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. Mechanical alloying and powder metallurgy process for the fabrication of titanium-45S5 Bioglass nanocomposites with a unique microstructure, higher hardness, lower Young’s modulus and better corrosion resistance, in comparison to microcrystalline titanium, were developed. On the other hand, Ti-10 wt.% 45S5 Bioglass composites posses higher fracture toughness compared to 45S5 Bioglass. The proper modification of chemical composition and microstructure of Ti-bioceramic nanocomposites can expand the use of titanium in the biomedical fields.     

Deposition and characterization of BN/Si(0 0 1) using tris(dimethylamino)borane

Boron nitride thin films could be deposited on Si(0 0 1) by chemical vapor deposition (CVD) at atmospheric pressure using a single source precursor. IR absorption spectra of films deposited between 750 and 1000°C using B[N(CH₃)₂]₃ (tris(dimethylamino)borane, TDMAB) as the boron and nitrogen source showed a peak absorption at ∼1360 cm⁻¹ characteristic of the in-plane vibrational mode seen in h-BN. It was noted that the mode at 800 cm⁻¹ is very weak. The observed growth rate varied exponentially with temperature in the range 850-900°C. Ellipsometry measurements were used to investigate the thickness and optical constant of the films. The refractive index, slightly lower than the bulk material, is close to 1.65-1.7 depending on the surface morphology of the films. The surface morphology of thin layers has been observed by atomic force microscopy with an increase of the surface roughness from 0.3 to 3.5 nm as the growth temperature increases from 800 to 950°C.     

Preparation of SrTi0.1Fe0.9O3−δ and its photocatalysis activity for degradation of methyl orange in water

Magnetic perovskite-type SrTi_0.1Fe_0.9O_3−δ was synthesized by stearic acid gel combustion method. The obtained powders were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM) and UV-Visible absorption spectrum techniques. Mean valence of Fe ion and the concentration of oxygen vacancies in SrTi_0.1Fe_0.9O_3−δ were measured by iodometric method. The magnetic properties of the SrTi_0.1Fe_0.9O_3−δ were measured, and the SrTi_0.1Fe_0.9O_3−δ was also evaluated for its photocatalytic activity towards the degradation of methyl orange (MO) under the sunlight irradiation. The experimental results show that the SrTi_0.1Fe_0.9O_3−δ is the photocatalyst possessing of magnetic property and visible-light activity, i.e., bifunctional photocatalyst. The SrTi_0.1Fe_0.9O_3−δ is applicable to the magnetic separation process and also shows excellent photocatalytic activity for the degradation of MO. The optimal conditions for photocatalytic degradation were methyl orange concentration of 20 mg L⁻¹ at pH 6.0 with the SrTi_0.1Fe_0.9O_3−δ concentration of 7.29 mg L⁻¹ for 3 h. In addition, the SrTi_0.1Fe_0.9O₃ is reusable and maintain relatively high activity. This study could point out a potential way to develop new and more active magnetic perovskite-type photocatalysts.     

Crystal structure and ionic conductivity of ruthenium diphosphate ARu2(P2O7)2, A=Li, Na, and Ag, with a tunnel structure

Crystal structure and ionic conductivity of ruthenium diphosphates, ARu₂(P₂O₇)₂ A=Li, Na, and Ag, were investigated. The structure of the Ag compound was determined by single crystal X-ray diffraction techniques. It crystallized in the triclinic space group P−1 with a=4.759(2) Å, b=6.843(2) Å, c=8.063(1) Å, α=90.44(2)°, β=92.80(2)°, γ=104.88(2)°, V=253.4(1) Å³. The host structure of it was composed of RuO₆ and P₂O₇ groups and formed tunnels running along the a-axis, in which Ag⁺ ions were situated. The ionic conductivities have been measured on pellets of the polycrystalline powders. The Li and Ag compounds showed the conductivities of 1.0×10⁻⁴ and 3.5×10⁻⁵ S cm⁻¹ at 150 °C, respectively. Magnetic susceptibility measurement of the Ag compound showed that it did not obey the Curie-Weiss law and the effective magnetic moment decreased as temperature decreased due to the large spin-orbital coupling effect of Ru⁴⁺ ions.