Polymer-induced generation and characterization of electrophoretic properties of hollow TiOX nanospheres for electronic paper

Hollow TiO_X nanospheres have been successfully prepared using hollow core–double shell latex particles (poly(styrene-co-methyl methacrylate-co-butyl acrylate-co-methacrylic acid) (abbreviated in poly(St-co-MMA-co-BA-co-MAA)) as template, which involves the deposition of inorganic coating on the surface of hollow core–shell latex particles and subsequent removal of the latex by calcinations in air or ammonia gas. Ti(OBu)₄ was used as precursor for the preparation of hollow TiO_X nanospheres. TEM of white hollow core–double shell polymers particles with an aperture of approximately 225 nm displays the perfect characteristic hollow nanospheres structure of primary core–double shell particles. The formation of TiO_X was confirmed by XRD analysis and hollow structure of the particles was revealed by transmission electron microscopy (TEM). When the calcined temperature was at 800 °C, hollow TiO₂ nanospheres were arranged regularly with the diameter range of 130–170 nm. The electrophoretic properties were characterized by JS94J micro-electrophoresis apparatus. The electrophoretic mobility of white TiO₂ and black TiO hollow spheres in tetrachloroethylene were 1.09 × 10⁻⁵ and 3.12 × 10⁻⁵ cm²/V s, and the zeta potentials were 7.10 and 20.24 mV, respectively. The results show that white TiO₂ particles and black TiO hollow nanoparticles are suitable as electrophoretic particles and possess the application potential in the future electrophoretic display.     

Uniform TiO2–PANI composite capsules and hollow spheres

Here we demonstrated a simple and reliable method to prepare single or multiple core/shell structured capsules and then demonstrate how to produce single or multiple-layer hollow spheres. Those capsules or hollow spheres could be made of organic and/or inorganic functional materials depending on the experimental design. Core–shell composite capsules consisting of TiO₂–polyaniline (PANI) shell and polystyrene (PS) core were prepared by using core–shell structured sulfonated-PS spheres as templates. Aniline was polymerized in the shell of sulfonated-PS spheres. Since the PANI was in situ doped by sulfonic acid, the as-synthesized composite capsules had good conductivity. After PS cores were dissolved in solvent, hollow TiO₂–PANI spheres formed, which could be further calcined to produce mesoporous hollow TiO₂ spheres. The cavity size of the hollow spheres was uniform, at approximately 170 nm in diameter and with a shell thickness of 30 nm. The cavity size and the shell thickness can be synchronously controlled by adjusting the sulfonation reaction time of PS spheres. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray powder scattering were employed to characterize these as-prepared spheres.     

Thin films of silica particles covered with lanthanide substituted Keggin polyoxometalates and their optical properties

In this paper, the chemical grafting method has been adopted to prepare hybrid core–shell particles by covering the surfaces of monodisperse uniform silica with lanthanides–polyoxometalates Ka (EuXWO₃₉)₂ (X = Si, B, a = 13 or 15) shells, respectively. The thin films of core/shell polyoxometalates/silica particles were successfully fabricated by standard spin-coating method. The hybrid core–shell particles and thin films were characterized by IR, UV–vis spectra, scanning electron microscopy and luminescent spectra, respectively. The hybrid core–shell particles show the strong luminescence which could be seen by naked eyes. The excitation spectrum of thin film of polyoxometalate/silica particles show the ligand to metal charge transfer band, which could be not seen in the excitation spectrum of lanthanides–polyoxometalate. The ratios of the electronic dipole ⁵D₀ → ⁷F₂ transitions to the magnetic dipole ⁵D₀ → ⁷F₁ ones in the emission spectra of thin films have changed, which indicated the various symmetry of sites occupied by Eu³⁺ ions in thin films.     

Improvement of optical properties of nanocrystalline Fe-doped ZnO powders through precipitation method from citrate-modified zinc nitrate solution

Nanocrystalline Zn_1−xFe_xO (where x = 0, 0.01 and 0.02) powders were successfully synthesized by a precipitation method from citrate-modified zinc nitrate solution. X-ray powder diffraction, Fourier transformed infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy were used to study the structural properties. The optical properties were determined by UV–vis spectrophotometer and luminescent spectrometer. In this study, the optical band gap of nanocrystalline ZnO powder increased from 3.170 eV to 3.214 eV when the Fe concentration in the solution was increased up to 2 mol. %.     

Microwave synthesis and characterization of Zn-doped nickel ferrite nanoparticles

Microwave assisted combustion method was used to synthesize nanocrystalline Zn_xNi_1−xFe₂O₄ from a stoichiometric mixture of corresponding metal nitrates and urea powders. The structural, chemical and magnetic properties of Ni–Zn ferrite was determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM) and DC conductivity measurements. Results showed that the material was spinel structure with a high purity with an estimated crystallite size of 20 nm by X-ray line profile fitting. TEM analysis showed necked near-spherical particles with an average size of 20 nm, reflecting highly crystalline nature of these nanoparticles. Magnetic properties showed anomalities as the Zn doping level increased. This has been explained and attributed to the relative positions of Ni, Zn, and Fe ions in the crystal lattice.     

磁场热处理对磁性吸波材料微波吸收特性的影响

采用高能球磨及热处理方法制备Nd11.76Fe82.36B5.88和Nd11.76Fe77.36Cr5B5.88粉体,借助X射线衍射仪和矢量网络分析研究磁场热处理对粉体组织结构和微波吸收特性的影响。结果发现:在热处理过程中,加入磁场可以促进Nd11.76Fe82.36B5.88粉体各铁磁性相和非铁磁性相的晶粒长大,使Nd11.76Fe82.36B5.88粉体反射率的最小值从普通热处理粉体的-14 dB降低到-24.3 dB,Nd11.76Fe77.36Cr5B5.88粉体的反射率最小值从普通热处理粉体的-30.5 dB降低到-48 dB;磁场热处理使Nd11.76Fe82.36B5.88和Nd11.76Fe77.36Cr5B5.88粉体的吸波带变窄,且在微波损耗过程中,磁损耗作用增大,而介电损耗作用减弱。     

Microwave properties of powders produced by high-energy milling of iron with paraffin

The structural and phase composition and magnetostatic and microwave properties of powders produced by simultaneous milling of carbonyl iron and paraffin taken in volume ratios ranging from 10 : 90 to 80 : 20 have been studied. It has been shown that the shape of the powder particles depends substantially on the amount of Fe in the mixture. At an Fe content of 30 vol %, the particles acquire a platelet shape; at an Fe content of more than 40 vol %, the agglomeration of the particles is observed. At an Fe content above 30 vol %, the Fe₃C phase is formed in the particles, which leads to an increase in the coercive force and a decrease in the specific saturation magnetization of the powder. The frequency dependences of the microwave magnetic and dielectric permeabilities of the composite materials containing the prepared powders have been measured, and the frequency dependences of the intrinsic magnetic permeability of these powders have been determined. It has been shown that the static magnitude of the intrinsic magnetic permeability reaches a maximum in powders containing 30 vol % Fe in the initial mixture.     

Study of the structure and magnetic properties of Co nanoparticles in the matrix of highly porous amorphous carbon

This paper presents the results of investigations into the structure and the magnetic properties of powders consisting of Co nanoparticles in the matrix of a high-porous amorphous carbon material. An analysis of X-ray diffraction and nuclear magnetic resonance spectra revealed the presence of hcp and fcc phases of cobalt in the particles of the powder and demonstrated the existence of a highly defective state, which could be related to a high concentration of defects of the “displaced-plane” type. The magnetometric measurements showed that the powder particles were in the ferromagnetic state and were characterized by a high field of the local magnetic anisotropy.     

Magnetic properties of nanocrystalline Ni3Fe compacts prepared by spark plasma sintering

Nanocrystalline Ni₃Fe compacts were successfully prepared by spark plasma sintering starting from wet mechanically alloyed powders. The influences of the sintering conditions: sintering temperature, sintering time and particle size on the compact magnetic properties are investigated. It is found that high sintering temperature, increased sintering duration and larger particle size leads to compacts with improved soft magnetic properties. A contamination with carbon of the compacts during the sintering processes has been found to reduce their magnetic properties. It is found that a heat treatment at the temperature of 450 °C during 4 h, in hydrogen atmosphere, leads to an improvement of the compact coercivity and of the maximum relative permeability of the compact to up to 600% and 50% respectively. Spark plasma sintering can consequently be considered as promising compaction technique for processing Ni₃Fe nanocrystalline powder in particular and nanocrystalline soft magnetic alloys in general.     

Effect of composition and milling parameters on the critical ball milling of Ti–Si–B powders

The absence of brittle phases and elevated temperature during ball milling of a powder mixture containing a large amount of ductile component can contribute to reach an excessive agglomeration denoting a critical ball milling (CBM) behavior. This work reports in the effect of composition and milling parameters on the CBM behavior of Ti–Si–B powders. High-purity elemental Ti–Si–B powder mixtures were processed in a planetary ball mill in order to prepare the Ti₆Si₂B compound and two-phase Ti + Ti₆Si₂B alloys. TiH₂ chips instead of titanium powder were used as a starting material. To avoid elevated temperature in the vials during ball milling of Ti–Si–B powders the process was interrupted after each 10 min followed by air-cooling. Following, the milled powders were hot-pressed at 900 °C for 1 h. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Short milling times followed by air-cooling contributed to obtain a large amount of powders higher than 75% in the vials. Only Ti and TiH₂ peaks were observed in XRD patterns of Ti–Si–B and TiH₂–Si–B, respectively, suggesting that extended solid solutions were achieved. The large amount of Ti₆Si₂B and Ti + Ti₆Si₂B structures were formed during hot pressing from the mechanically alloyed Ti–Si–B and TiH₂–Si–B powders.     

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr₂N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.     

机械合金化制备Fe-10%Ni合金研究

采用纯Fe粉和Ni粉利用高能卧式搅拌球磨机制备了Fe-10%Ni(质量分数,下同)合金,利用X射线衍射(XRD)、扫描电子显微镜(SEM)、差热分析(DTA)研究了球磨粉末的相组成、形貌和热稳定性,并对其热压烧结的块材进行了组织分析与性能测试。结果表明,在球磨机转速400 r/min,球料比20:1条件下,球磨8 h后,Ni原子完全固溶在Fe原子晶格中,形成体心立方结构Fe(Ni)过饱和固溶体,延长时间到16 h,球磨粉末颗粒尺寸更均匀细小,但仍为体心立方Fe(Ni)固溶体。对球磨16 h的合金粉末在500~800℃进行退火处理,发现粉末结构稳定,仍为体心立方Fe(Ni)固溶体。对球磨16 h的合金粉末进行热压烧结,发现950℃下烧结块材中出现少量fcc结构的Fe(Ni)固溶体相,而继续在970℃复烧后则完全转变为面心立方结构的Fe(Ni),但950℃热压烧结块材的强度和延伸率高于970℃复烧的块材,原因在于无压复烧块材中产生氧化物和孔洞。     

Reinforcement of Al–Fe–Ni alloys with the in situ formation of composite materials

One of the most effective methods for the improvement of the mechanical properties of metals is their reinforcement with non-metallic materials. In the present work powder of K₂TiF₆ and KBF₄ was added in an Al–Fe–Ni alloy while the alloy was in liquid form at 1060 °C with a 5 wt.% mixture of powders and with simultaneous stirring for 30 min. The liquid was squeeze-casted at 150 bar. The as-cast specimens were examined with electron microscopy and X-ray diffraction. SEM analysis revealed that the as-formed material is composed by needle-like crystallites along with a dentritic form and an interdendritic phase. The composition of the needle-like crystallites may presumably be expressed by the formula (Fe-Ni)Al₃. The rest of the matrix consists of almost pure Al grown dentritically, while the interdendritic phase contains Fe and Ni dissolved in Al. EDS analysis also proved the existence of spots with high Ti concentration, which probably refer to the Ti–B compounds. Finally TEM verified the presence of nanocrystals in the matrix.     

Structural and magnetic properties of Fe50Co50 system

The Fe₅₀Co₅₀ alloys were prepared by mechanical alloying of the Fe and Co powders using a high-energy ball mill. The Fe₅₀Co₅₀ system was also obtained as a thin film by the pulsed laser deposition method. Both powder and thin film samples were characterized by X-ray diffraction and Mössbauer spectroscopy. The formation of the bcc-FeCo solid solution was investigated as a function of milling time. Both Fe₅₀Co₅₀ systems reveal similar magnetic hyperfine fields of about 35 T. Typically, the powders have random spin orientation, while the thin film shows an out-of-plane magnetic texture.     

Preparation and characterization of carbonyl iron soft magnetic composites with magnesioferrite insulating coating layer

Spherical carbonyl iron (Fe) powders were coated with magnesioferrite (MgFe₂O₄) insulating coating layer and then mixed with epoxy-modified silicone resin (ESR). Soft magnetic composites (SMCs) were fabricated by compaction of the coated powders and annealing treatment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the MgFe₂O₄ layer was coated on the surface of the iron powders. The magnetic properties of SMCs were determined using a vibrating sample magnetometer and an auto testing system for magnetic materials. The results showed that the SMCs prepared at 800 MPa and 550 °C exhibited a significant core loss of 167.5 W/kg at 100 kHz and 50 mT.     

Ball milled Ni–Ti powder deposited by cold spraying

A 50Ni–50Ti powder was produced by solid state synthesis via mechanical alloying from elemental Ti and Ni powders. The product was characterized using X-ray diffraction, scanning electron microscopy and optical microscopy.Cold spraying makes possible to deposit the coating of temperature sensitive materials, such as nanostructured material, without any significant change in the microstructure of feedstock. The preliminary results of this work showed that the ball milled Ni–Ti coating can be deposited by cold spraying. The coating presents a multilayer structure consisting of the alternate flattened Ni and Ti particles.     

Phase transformation and exchange bias effects in mechanically alloyed Fe/magnetite powders

Nanostructured powders processed by ball milling of a mixture of Fe and Fe₃O₄ at room temperature are shown to undergo an incomplete redox reaction with formation of FeO during the milling process. This reaction is favored by the high energy introduced during the mechano-alloying process. Concurrent effects of milling such as grain refinement down to the nanometre scale lead at the end of the milling processes to a mixed multiphase powder of nanograins, with Fe and Fe oxide grains inter-dispersed. We show that in the as-milled Fe/Fe₃O₄ powder, during milling process, wüstite (FeO) is formed as a consequence of the redox reaction. Moreover, with increasing temperature, the system undergoes an inverse phase transformation towards the initial Fe and Fe₃O₄ phases until about 450 °C. Above this temperature the reduction reaction Fe + Fe₃O₄ = 4FeO is reinitiated, resulting in sharp decrease of Fe and Fe₃O₄ content from about 550 °C and almost complete disappearance of these phases at about 900 °C. This transformation was investigated via an energy-dispersive in situ X-ray diffraction experiment using the synchrotron radiation. This study allows direct collection of X-ray patterns after few minutes exposure, at selected temperatures, ranging between 20 °C and 1000 °C. The structural and magnetic characterizations of the nanograin powders, as-milled and annealed at several temperatures, are studied using XRD, SEM and magnetic measurements. Such ferromagnetic-antiferromagnetic composites are extensively studied as they exhibit exchange bias effect, with a large impact in technological applications. The magnetic behaviour and intrinsic mechanisms leading to the occurrence of exchange bias effects are discussed and related to the samples microstructural features. A significant exchange bias effect, related to FeO content, is observed for as-milled sample, the effect being less pronounced upon annealing the nanograin powder.     

A study on mechanochemical behavior of B2O3–Al system to produce alumina-based nanocomposite

One possible route for producing the fine and homogenous distribution of hard particles in composite microstructure is the mechanochemical processing in which high-energy ball milling promotes the reaction in a mixture of reactive powders. In this study mechanochemical reaction of B₂O₃ and Al powder during ball milling was studied. The phase transformation and microstructure of powder particles during ball milling were investigated by X-ray diffractometry and scanning electron microscopy. The results showed that during ball milling the B₂O₃–Al reacted with a combustion mode producing Al₂O₃–AlB₁₂ nanocomposite. The crystallite size of Al₂O₃ and AlB₁₂ was 40 and 25 nm, respectively. This structure appeared to be stable upon annealing.     

Influence of aluminum oxides on abrasive wear resistance of Fe–50 at.% Al intermetallic sinters

This paper presents the influences of processing parameters on the tribological properties of Fe–50 at.% Al intermetallics obtained by sintering in the presence of liquid phase elemental Fe and Al powders. The wear resistance of FeAl under dry sliding against C45QT steel under ambient conditions was studied in a pin-on-disc contact configuration. Although processing parameters such as sintering temperature and homogenization time had an effect on the wear resistance of FeAl intermetallics, the particle size of Al₂O₃ oxides derived from oxidized aluminum and iron powders and formed during sintering had the greatest influence.     

Magnetic and structural studies of mechanically alloyed (Fe50Co50)62Nb8B30 powder mixtures

Amorphous (Fe₅₀Co₅₀)₆₂Nb₈B₃₀ powder mixture was prepared by mechanical alloying from elemental Fe, Co, B and Nb powders in a planetary ball mill under argon atmosphere. Structural, thermal and magnetic properties were performed on the milled powders by means of X-ray diffraction, differential scanning calorimetry and magnetic measurements. The amorphous state is reached after 125 h of milling. The excess enthalpy due to the high density of defects is released at temperature below 300 °C. Crystallisation and growth of crystal domains are the dominating processes at high temperatures. The saturation magnetisation decreases rapidly during the first 25 h of milling to about 15.24 A m²/kg and remains nearly constant on further milling. Coercivity, H_c, value of about 160 Oe is obtained after 125 h of milling.