Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

Fabrication and characteristics of composite containing HCl-doped polyaniline and Ni nanoparticles

HCl-doped polyaniline powder (HCl-PANI) was synthesized using a polymerization procedure and then Ni nanoparticles were deposited on the HCl-PANI at room temperature by direct current magnetron sputtering. After this process the HCl-PANI–Ni composite was obtained. Ni nanoparticle size ranges from 5 nm to 20 nm in the composite. HCl-PANI structure is not influenced by the Ni nanoparticles. The composite pellet exhibits room temperature ferromagnetism and a conductivity of about 0.66 S/cm. A temperature dependence of the conductivity from 160 K to 290 K reveals that a carrier transport mechanism in the composite is three-dimensional variable range hopping. Thermogravimetric analysis reveals that a weight loss of the HCl-PANI–Ni composite is larger than that of the HCl-PANI for the same heating temperature. The weight loss difference between the composite and the HCl-PANI increases with increasing the temperature.     

Microstructural characterization of high-silicon iron alloys produced by spray forming and co-injection of Si particles

Fe–Si alloys are widely used for magnetic applications. However, it is very difficult to process Fe–Si with a silicon content exceeding 3.5 wt.%Si (upper limit for products commercially available by the I/M route) due to the alloy's low ductility, which is attributed mainly to the formation of B2 and DO3 ordered phases that embrittle the material. To overcome this obstacle, the main focus of this work was to produce thin sheets of Fe–5 wt.%Si alloy in two steps: (1) as a Fe–3.5%Si + 3%Si_p (Si particles) composite, using spray forming, and (2) rolling and heat treating (HT) the composite to dissolve the silicon and homogenize its content throughout the thickness of the sheet. To this end, 3 wt.%Si_p were co-injected into the main stream of the Fe–3.5 wt.%Si spray, followed by hot-rolling of the billet at 850 °C to obtain 0.45 mm gauge thin sheets. The final material was heat-treated at 780/510 °C for 8 h or at 1250 °C for 1 h and then air cooled. The grain orientation was analyzed by EBSD and the distribution of iron, silicon and impurities was identified by X-ray dot mapping. The heat treatment caused diffusion and dissolution of the silicon particles and grain growth. However, the final silicon content was strongly dependent on the atmosphere of the heat treatment furnace. In the absence of oxygen, the silicon content reached 4.9 wt.% distributed homogeneously throughout the thickness of the composite. In the presence of oxygen, the silicon diffused to the surface and only 3.5 wt.% remained in the matrix.     

Electrospinning of carbon nanofiber supported Fe/Co/Ni ternary alloy nanoparticles

Polyacrylonitrile (PAN)-based carbon nanofiber supported Fe/Co/Ni ternary alloy nanoparticles were prepared by using the electrospinning technique for potential fuel cell applications. The solution was prepared by adding pre-solved catalytic precursor into PAN/DMF solution. The effect of PAN and catalyst precursor concentration on solution properties (viscosity and conductivity) and heat stabilization temperature has been investigated. Electrospun nanofibers were characterized by field emission scanning electron microscope, transmission electron microscope, energy dispersive spectrometer and X-ray diffractometer. It has been found that ternary nanoparticle size is in the range of 5–115 nm (average: 20 nm) and is a crystal alloy of Fe, Co and Ni. Also, TEM results demonstrate that in some regions metal nanoparticles tend to agglomerate into larger particles mainly due to the non-uniform distribution of nanoparticles in as-spun condition. PAN-derived carbon nanofiber mean diameter was measured as 200 nm by varying from 40 nm to 420 nm.     

The reduction of silver nitrate to metallic silver inside polyaniline nanotubes and on oligoaniline microspheres

Polyaniline (PANI) reduces silver nitrate to metallic silver. Composites based on conducting polymer and silver have been prepared with equimolar proportions of reactants. Polyaniline bases having different morphologies – granular or nanotubular – and oligoaniline microspheres have been left to react with silver nitrate in acidic, neutral, and alkaline media. The content of silver, typically 20–30 wt.%, was determined by thermogravimetric analysis. Clusters of 40–80 nm silver particles are produced in the granular form of PANI. The formation of silver inside PANI nanotubes has been observed. With oligoaniline microspheres, silver was produced on their surface, and on PANI agglomerates accompanying them. The highest conductivity, 943 S cm^?1, was found with silver reduced by nanotubular PANI base in 0.1 M nitric acid at 17.3 wt.% silver content. The standard granular PANI, used as a reference material, yielded a composite having a much lower conductivity of 8.3 × 10^?5 S cm^?1 at 24.3 wt.% Ag. There is no simple correlation between the conductivity and silver content. Infrared and Raman spectroscopies have been used to study the changes in the molecular structure of the PANI bases of various morphologies before and after reaction with silver nitrate.     

Conducting behaviors of PPy/ITO composites synthesized by polymerization

Conducting composites core layers of indium tin oxide (ITO) particles embedded in polypyrrole (PPy) were prepared by polymerization. The morphology, molecular structure and electrical property of the composites were characterized by X-ray diffraction, Fourier transform infrared, scanning electron microscope, thermogravimetric analysis and conductivity measurement methods. The results indicated the ITO combined with PPy by chemical bond energy not the physical combine. Electrical conductivity measurements on the samples pressed into pellets showed that the maximum conductivity attained 13.97 ± 0.05 S/cm for PPy/ITO composites, at ITO particle doping concentration of 50 wt%. The highest conductivity of PPy/ITO crossing-rod composites was 11.00 ± 0.05 S/cm, of which the content of ITO crossing-rod was 15 wt%. The PPy/ITO composites showed a higher conductivity by comparing with that of neat PPy.     

The formation and evolution of oxide particles in oxide-dispersion-strengthened ferritic steels during processing

The fabrication of oxide-dispersion-strengthened (ODS) steels is a multi-stage process involving powder ball milling, degassing and consolidation by hot isostatic pressing. Y is introduced by mechanical alloying (MA) with either Y₂O₃ or Fe₂Y so a high density of Y–Ti–O-based oxide nanoparticles is formed. The evolution of ～2 nm oxide nanoparticles and larger >5 nm grain boundary oxides has been studied at each step of the processing. The nanoparticle dispersions produced in material MA with Fe₂Y were comparable to those produced by alloying with Y₂O₃. Hence the majority of oxygen which forms the nanoparticles must be incorporated from the atmosphere during MA, rather than being introduced via the alloying additions. During mechanical alloying, a high density of subnanometer particles are formed (2.5 ± 0.5 × 10²⁴ m^?3). The oxygen content of the nanoparticles decreases slightly on annealing, and then the composition of the nanoparticles remains constant throughout subsequent processing stages. The nanoparticle size increases during processing up to ～2 nm radius, while the number density decreases to 4 ± 0.5 × 10²³ m^?3. Grain boundary oxides (>5 nm) have a Ti–Cr–O-rich shell, and contain no Y before consolidation, but have similar core composition to the matrix nanoparticles after consolidation. The formation of the larger grain boundary oxides is shown to take place during the degassing and consolidation stages, and this occurs at the expense of the nanoparticles in the matrix. This work provides a mechanistic understanding of the importance of controlling the oxygen content in the powder during MA, and the resulting impact on the formation of the ODS microstructure.     

Conductivity changes of dodecylbezensulfonic acid-doped polyaniline during pressure loading/unloading

Conductivity changes of polyaniline (PANi) doped with alkylbenzenesulfonic acid were investigated during pressure loading/unloading. PANi was chemically synthesized with ethylbenzenesulfonic acid (EBSA), octylbezenesulfonic acid (OBSA), and dodecylbenzenesulfonic acid (DBSA). Pellets were made for the comparison of chain length effects of PANi doped with alkylbenzenesulfonic acid on the conductivity change during pellet compression and expansion. PANi doped with DBSA exhibited the highest response to the pressure change. Relative amounts of DBSA to aniline (ANi) were adjusted to find out the optimal composition. It was revealed that the relative compositions of DBSA to PANi of pellets are similar (S/N ratio = 0.29–0.35) irrespective of feed ratios, but the conductivity change of pellets upon pressure loading/unloading becomes greater as the increase of relative amounts of DBSA to ANi in synthetic media. The variations of the conductivity change during repeated pressure loading/unloading were also compared. PANi pellets prepared from a solution containing [DBSA]/[ANi] = 2/1 retained more than 80% of the initial conductivity change value after 2000 cycles.     

Maghemite polymer nanocomposites with modulated magnetic properties

A method is presented for the production of maghemite polymer nanocomposites with modulated magnetic properties. Magnetic nanocomposites prepared using this method show regular variation in the magnetic blocking temperature from 2 K to 300 K, and variation in the saturation magnetization from 0 to 50 emu g⁻¹ (Fe₂O₃). The method is based on the in situ formation of maghemite nanoparticles in nitrogen-base polymer matrixes. The particle size can be varied regularly from 1.5 nm to 16 nm by changing the ratio of iron loading in the polymer and/or the Fe(II)/Fe(III) ratios. The particles are isolated and uniformly distributed within the matrix. The materials were characterized by electron microscopy, electron energy loss spectroscopy, Mössbauer spectroscopy, infrared spectroscopy, small angle X-ray scattering, wide angle X-ray scattering and magnetic measurements. The nanocomposites obtained are useful model material for the study of the magnetic behavior of magnetic nanoparticles, as well as for use in many industrial and biomedical applications.     

Comments on the “Reply to comments on the paper ‘On the nature of inhibition performance of imidazole on iron surface’” by J.O. Mendes and A.B. Rocha

Two DFT-GGA studies reported almost an order of magnitude different adsorption energies of imidazole on Fe (1 0 0), −0.7 vs. −5.9 eV, which inevitably leads to conclusion that one of them is wrong. But which? In their Reply to my Comments, Mendes and Rocha explained that the difference emerges due to different treatment of magnetization, which should be constrained to bulk value. In these Comments, it is rigorously demonstrated that different treatments of magnetization lead to similar adsorption energies (−0.75 ± 0.1 eV) and that magnetization should be treated self-consistently. The issue is therefore firmly settled.     

Mechanical and tribological properties of electrically conductive SiC based cermets

Three different types of SiC based cermets with various content (30, 40, 50 wt.%) of electrically conductive TiNbC phase have been fabricated by hot-pressing without sintering additives. The effect of TiNbC content on the basic mechanical, electrical and tribological properties of SiC-TiNbC cermets was investigated. Tribological properties have been characterized by the ball-on-disc method at the ambient temperature and dry wear conditions with air humidity 35–40% at the load of 5–30 N, sliding distance of 500 m, with the static partner made from SiC. Corresponding wear rate was calculated and wear mechanisms were identified. Resulting materials were relatively hard, with increasing amount of TiNbC the hardness increased from 19.8 ± 1 GPa for 30 wt.% of TiNbC up to 25.4 ± 0.9 GPa at 50 wt.% of TiNbC. The fracture toughness values were independent on TiNbC phase and varied between 2.7 and 2.9 MPa.m^1/2. Similarly, Young's modulus increased from 354 GPa to 435 GPa. It was found that electrical conductivity of SiC cermets was rapidly improved with increased fraction of metallic phases and was three orders of magnitude higher at 30 wt.% TiNbC addition and around four order of magnitude higher at 50 wt.% of TiNbC metallic phase comparing to conventional semiconductive SiC ceramics with electrical conductivity ~ 10 Sm^− 1. Coefficient of friction (between 0.3 and 0.5) and wear resistance (10^− 6–10^− 7 mm³/Nm) were comparable with the wear resistant SiC materials.     

One-pot synthesis of magnetic and mesoporous bioactive glass composites and their sustained drug release property

A novel kind of magnetic and mesoporous bioactive glass (MMBG) composite with Fe₃O₄ nanoparticles confined and dispersed in ordered mesoporous glass matrices has been prepared by a one-pot synthesis route of simultaneous evaporation-induced self-assembly of Ca, P, Si and Fe sources and subsequent reduction in an H₂ atmosphere. The MMBG composites exhibit the type IV isotherm curve with a well-defined step P/P₀ between 0.4 and 0.8. Ibuprofen storage and release experiments with these composites show adjustable loading amounts from 199 to 420 mg g⁻¹ and a sustained drug release property. A superparamagnetic behavior was identified and the saturation magnetization of the bioactive glass composites was found to increase at increased loading amounts of Fe species. The magnetic and mesoporous bioactive glass composites are believed to be potentially applicable for selectively targeted drug delivery and hyperthermia treatment of bone tumors.     

Effect of vacuum annealing on characteristics of the HCl-doped polyaniline pellets

Powders of HCl-doped polyanilines were prepared by using a solution polymerization process and then were pressed to the polyaniline pellets. The pellets were annealed in vacuum at 140, 200 and 260 °C for times up to 120 min, respectively. Electrical property and micromorphology of the pellets were studied by using a four-point probe technique and a scanning electron microscopy. The conductivity of the pellets decreases sharply when the annealing time reaches 30 min and then decreases gradually with further increasing annealing time. When the pellets are annealed under the conditions of 200 °C/120 min, 260 °C/90 min and 260 °C/120 min, the resistance of the pellets could not be measured by the four-point probe technique and the pellets show an insulating characteristic. The breakdown voltage increases with increasing annealing temperature and time. The maximum breakdown voltage is about 875 V/cm. The degradation of the conductivity is mainly attributed to the loss of chlorine in the polyaniline pellets. The micromorphology of the pellets becomes heterogeneous with thermal aging.     

Effect of Ni content on the compression properties and abrasive wear behavior of the (TiB2–TiCxNy)/Ni composites

The (TiB₂–TiC_xN_y)/Ni composites were fabricated by the method of combustion synthesis and hot press consolidation in a Ni–Ti–B₄C–BN system. The effect of Ni content on the microstructure, hardness, compression properties and abrasive wear behavior of the composites has been investigated. The results indicate that with the increase in Ni content from 30 wt.% to 60 wt.%, the average size of the ceramic particles TiB₂ and TiC_xN_y decreases from 5 μm to ≤ 1 μm, while the hardness and the abrasive wear resistance of the composites decrease. The composite with the Ni content of 30 wt.% Ni possesses the highest hardness (1560.8 Hv) and the best abrasive wear resistance. On another hand, with the increase in the Ni content, the compression strength increases firstly, and then decreases. The composite with 50 wt.% Ni possesses the highest compression strength (3.3 GPa). The hardness and fracture strain of the composite with 50 wt.% Ni are 1251.2 Hv and 3.9%, respectively.     

High performance tungsten synthesized by microwave sintering method

The W–Ni alloys with varying amount of Ni (0.1, 0.25, 0.5 and 1.0 wt.%) were microwave sintered at 1450 °C for different holding time 5, 15 and 30 min, and their microstructure, grain size, relative density, thermal conductivity, and Vickers microhardness were characterized. Comparing to the addition of Fe and Cr, the Ni addition can greatly improve the relative density and maintain the high thermal conductivity of W at the same time. It was shown that the addition of 1.0 wt.% Ni into W and microwave sintering at 1450 °C for 5 min would be the best conditions to obtain W–Ni alloys with a relative density close to 100% and an average grain size as small as 15 μm. The Vickers microhardness and thermal conductivity of the sintered W–Ni samples range from 370 to 440 and from 90 to 130 W/m K, respectively.     

Fabrication and absorbing property of microwave absorbers based on BaAl2Fe10O19 and poly(o-toluidine)

BaFe₁₀Al₂O₁₉/poly(o-toluidine) (BFA/POT) composite were synthesized by in situ polymerization of o-toluidine in the presence of BaFe₁₀Al₂O₁₉ particles. The structure, composition and morphology of the obtained samples were characterized by using XRD, FT-IR, UV–vis spectroscopy, SEM, and TEM techniques. Their electrical conductivity, magnetic property and microwave absorbing property were measured by the four-probe meter, the vibrating sample magnetometer and the vector network analyzer, respectively. The results indicated that BFA particles were coated effectively by POT polymer chains and some interaction between POT chains and BFA particles were existed in the composite. The conductivity and saturation magnetization of BFA/POT composite were smaller than those of pure polymer and pure BFA, respectively. The constitution and film thickness of absorbent had a great effect on its microwave absorbing property. The microwave absorbing properties of the BFA/POT composite were better than those of pure BFA and POT. When optimizing the mass rate of BFA to OT up to 0.3, the composite with the thickness of 2 mm had the minimum reflection loss of ?29.16 dB at approximately 14.06 GHz, and the maximum available bandwidth of 9.3 GHz, respectively. The results are shown that these composite could be used as advancing absorption and shielding materials due to their favorable microwave absorbing properties.     

Thermal properties of W–Cu composites manufactured by copper infiltration into tungsten fiber matrix

W–Cu composites were produced by the technique of copper infiltration into tungsten fiber preforms (CITFP) under vacuum circumstance. Fibrous structure preforms with various volume fraction of tungsten fiber were fabricated by the process of mold pressing and sintering. The molten copper was infiltrated into the open pores of the preforms under vacuum at 1473 K to 1573 K for 1 h to produce W–Cu composites with compositions of 10–30 wt.% copper balanced with tungsten. The microstructure, relative densities, and thermal properties of the composites were investigated and measured. The relative as-sintered density was enhanced with the increase of the sintering temperature. The thermal conductivity of the W–Cu30 composite with 28.2 wt.% Cu was 241 W/(m · K) at 298 K, 10% higher than that of the W–Cu alloy with similar copper content produced by conventional powder metallurgy process. The thermal expansion of the composites was decreased with the increase of tungsten content, keeping the same tendency as the prediction by the rule of weighted average of volume ratio of compositions.     

Synthesis,characterization and magnetic properties of polyaniline-magnetite nanocomposites

In this work we report a new and straightforward method to prepare the polyaniline-magnetite nanocomposite PANI-Fe₃O₄. The method utilizes Fe₃O₄ nanoparticles as the oxidizing agent assisted by UV light to synthesize PANI-Fe₃O₄ magnetic nanocomposite. FTIR and XRD analyses confirm that polyaniline has been obtained in the emeraldine salt form and that the mean diameter of the Fe₃O₄ nanoparticles before synthesis was of the order of 25 nm; for the PANI-Fe₃O₄ nanocomposite in HCl after 4 h of reaction, the mean diameters were of the order of 11 nm. Also, feroxyhite was detected as a secondary phase for the nanocomposite. The dc conductivity results for the pure magnetite were about 2.4 × 10^?6 S cm^?1, while the nanocomposites were of the order of 10^?5 S cm^?1, confirming the increase in conductivity with the increasing amount of PANI. The magnetic measurements showed ferromagnetic behavior for the nanoparticles, with high-saturated magnetization (M_S = 74.30 emu g^?1) and a coercive force of 93.40 Oe. In addition, it was observed that the saturated magnetization for the nanocomposite strongly depends on the reaction time under UV irradiation.     

High-field magnetization and specific heat of UCu2T3Al7 alloys where T = Cr,Mn and Fe(II)

The UCu₂T₃Al₇ alloys, where T = Cr, Mn and Fe, crystallize in the ThMn₁₂-type tetragonal structure. Earlier investigation of magnetic and electrical properties revealed their complex magnetic behavior except of the Cr compound, which is paramagnetic, whereas their electrical resistivity is weakly temperature dependent. At present we report on the magnetization measurements at 4.2 and 77 K in the steady magnetic field up to 14 T and in the pulsed field up to 34 T with a pulse duration of 10 ms at T = 4.2 K. These experiments confirmed paramagnetism of the Cr alloy and showed lack of saturation for the compounds of the Mn and Fe with the “saturation” magnetic moment amounting to 3.1 and 5.0 μ_B/f.u., respectively. In turn, the specific heat was measured in the temperature range 1.2–70 K in magnetic field μ₀H = 0 and 7 K using a home-made and fully automatic calorimeter. The investigation of the specific heat at temperature 2–300 K has been done using Quantum Design PPMS machine. The magnetic field does not in principle influence the obtained results, whereas the coefficient of the electronic specific heat, γ is strongly enhanced and amounts to 410, 330 and 150 mJ mol^?1 K^?2 for the Cr, Mn and Fe compounds, respectively.     

A DSC analysis of thermodynamic properties and solidification characteristics for binary Cu–Sn alloys

The liquidus temperatures and enthalpies of fusion for Cu–Sn alloys are systematically measured across the whole composition range by differential scanning calorimetry (DSC). The liquidus slope vs. Sn content is derived on the basis of the measured results. The measured enthalpy of fusion is related to the Sn content by polynomial functions, which exhibit one maximum value at 55 wt.% Sn and two minimum values around 28.9 wt.% Sn and 90 wt.% Sn, respectively. The undercoolability of those liquid alloys solidifying with primary α (Cu) solid solution phase is stronger and can be further enhanced by increasing the cooling rate. However, other alloys with the preferential nucleation of intermetallic compounds display smaller undercoolings and are not influenced by cooling rate. Microstructural observations reveal that peritectic reactions can rarely be completed. With the increase in undercooling, the primary α (Cu) dendrites are refined in the peritectic Cu–22 wt.% Sn alloy. For the hyperperitectic Cu–70 wt.% Sn alloy, typical peritectic cells are formed in which the peritectic η(Cu₆Sn₅) phase has wrapped the primary ε(Cu₃Sn) phase. The DSC curves of metatectic-type Cu–Sn alloys indicate that the metatectic transformation γ → ε + L upon cooling is an exothermic event, and a large undercooling of 70 K is required to initiate this transformation in metatectic Cu–42.5 wt.% Sn alloy. The metatectic microstructures are characterized by (ε + η) composite structures. The η phase is mainly distributed at the grain boundaries of the coarse ε phase, but are also dispersed as small particles inside ε grains. The volume fraction of the η phase increases with the Sn content.