A magnetic susceptibility study of emeraldine base polyaniline

Paramagnetic spins are found even in carefully synthesized samples of emeraldine base polyaniline. We report here magnetic susceptibility data up to a temperature of 475 K on a number of emeraldine base samples that were synthesized at different oxidant to monomer ratios. All the samples, although electrically insulating, show the presence of Pauli-like susceptibility. A simple albeit physically realistic model involving spin-pairs is shown to lead to such a dependence on temperature. The analysis of the data indicates that polarons in emeraldine base are created in pairs and that the intra-pair interactions encompass a broad distribution of antiferromagnetic exchange couplings.     

Physicochemical and catalytic properties of palladium deposited on polyaniline-coated silica gel

The chemical incorporation of palladium into polyaniline (PANI) deposited onto the silica gel microparticles (15-μm in diameter) was studied. The as-prepared silica particles coated with PANI–hydrochloride (AC) were treated with aqueous ammonia solution (0.1 M) to transform polyaniline to its base (BA) form. Both AC and BA samples were reacted with PdCl₂ solutions (2.3×10⁻³ M) strongly differing in the concentration of HCl (0.1 M HCl, series K; 6.6×10⁻⁴ M HCl, series Z). Two series of samples with 0.43–2.14 wt.% Pd were obtained. Fourier-transform infra red (FTIR), UV-Vis, X-ray photoelectron spectroscopies (XPS) and scanning electron microscopy have been used to examine the nature of processes involved upon insertion of Pd and to characterize palladium species in the final samples. Very similar palladium species were found in the polymer matrix independently of the acidity of PdCl₂ solutions and the extent of PANI protonation (AC and BA samples). Pd²⁺ was the only form if no more than 0.86% Pd was introduced. Incorporation of higher content of palladium resulted in the partial reduction (14.6–28.7%) of Pd²⁺ to Pd⁰. The presence of Pd²⁺ species in the form of complexes in which besides Cl⁻ ligands also nitrogen groups of PANI participated has been postulated. The catalytic properties of Pd/PANI-SiO₂ have been studied in the liquid-phase hydrogenation of 2-ethylanthraquinone (EAQ) at 60 °C under 1 atm of hydrogen. Very low activity of the as-prepared catalysts significantly increased due to reduction of the samples with NaH₂PO₂ and subsequently with dihydrogen. The specific activities of reduced series K and Z samples were comparable and the maximum activity exhibited catalysts with 1–1.5% Pd.     

Synthesis and characterization of poly (aniline-co-acrylonitrile) using organic benzoyl peroxide by inverted emulsion method

An inverted emulsion process was adopted to synthesize conducting copolymers of aniline and acrylonitrile using benzoyl peroxide (BPO) as a novel oxidizing agent. The influence of polyacrylonitrile (PAN) ratio on the properties of conducting copolymers is reported. The chemical structures of the copolymers were characterized spectroscopically by UV-Vis, FT-IR, FT-Raman and EPR. The solubility of polyaniline (PAni) and PAni–PAN copolymers in dimethyl sulphoxide (DMSO) was confirmed by electronic absorption spectra. The conductivity of these copolymers lie in the range (1.26–4.20)×10⁻² S/cm. TGA thermogram of copolymers showed multi-step thermal degradation behaviour. X-ray scattering studies reflected that the copolymers are semicrystalline and showed two crystalline peaks at 17 and 25 (2θ).     

Controllable fabrication of tube-in-tubes using anodic aluminum oxide templates

We have developed a method to fabricate tube-in-tubes that are relatively long and made in all the pores of porous anodic aluminum oxide (AAO) nano-templates. Relatively a very small amount of Co was deposited in the pores of AAO templates prepared without doing a voltage drop at the end of anodization, and then etched in NaOH solution. This caused the carbon nanotubes (CNTs) to grow out from all the pores, and larger diameter carbon nanotubes were also made on the inner surface of all the pores, by forming tube-in-tubes. We were able to control the gap between the inner surface of the larger tubes and the outer surface of the smaller ones of tube-in-tubes in some range by changing the etching time in NaOH solution. Tube-in-tubes that are relatively long and controlled the gap could be used as a storage, particularly for hydrogen gas.     

Magnetic structure of the HoPdSn compound

A polycrystalline sample of the HoPdSn compound was prepared and studied by powder neutron diffraction. This compound crystallizes in the orthorhombic TiNiSi-type structure (space group Pnma). The Ho atoms occupy the 4c position. Below T_N=3.7 K, the Ho moments equal to 6.0(1) μ_B form a magnetic structure described by the propagation vector k=(1/3,1/2,1/3) and are parallel to the a-axis.     

An evaluation of switching criteria for ferroelectrics under stress and electric field

The multi-axial responses of barium titanate (BaTiO₃) and hard lead zirconate titanate (PZT-4D) are measured for stress and electric field loadings, and are compared to the response of soft lead zirconate titanate (PZT-5H) taken from a previous study. First, poled ferroelectric specimens are subjected to an electric field at an angle to the original poling direction. Second, unpoled ferroelectric specimens are loaded by a uniaxial compressive stress and a parallel, proportional electric field. The switching surfaces of BaTiO₃ and PZT-4D are constructed from the experimental measurements, and compared with existing data for PZT-5H. The measured responses are then used to evaluate the accuracy of existing micromechanical and phenomenological models of ferroelectric switching.     

Effect of nitrogen and carbon on electron exchange and shape memory in a Fe–Mn–Si base shape memory alloy

The influence of carbon and nitrogen on the electronic properties and shape memory in Fe₆₂Mn₁₆Si₁₀Cr₉Ni₄ (at.%) alloy was studied by means of conduction electron spin resonance (CESR) and dilatometry. It was shown that carbon causes localization of electrons at the atomic sites and clustering of substitutional atoms, whereas nitrogen leads to an increased concentration of free electrons at the Fermi surface and assists in a more homogeneous distribution of substitutional solutes. A larger recovered strain is found in the nitrogen-doped alloy in comparison with the carbon one. The role of carbon- and nitrogen-caused change in the electronic properties, short range atomic order and strengthening on the shape memory effect is discussed.     

Effect of adding Pd nanoparticles to dimercaptan-polyaniline cathodes for lithium polymer battery

The electrochemical properties of 2,5-dimercapto-1,3,4-thiadiazole (DMcT)—polyaniline (PAn) composite films containing Pd nanoparticles (average diameter: 28 nm) were investigated. Compared to DMcT–PAn composite film, the DMcT–PAn composite film containing Pd nanoparticles showed enhanced redox current and discharge capacity. The enhanced activity is attributed to the nanosize dispersion of the Pd catalyst particles within the DMcT–PAn matrix. UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) results confirmed the interactions between DMcT and Pd nanoparticles. We have obtained the positive effect of Pd nanoparticles addition on the redox activity of the DMcT–PAn composite.     

Magnetic study of Ti-substituted NiFe2O4 ferrite

The Ni_1+xTi_xFe_2−2xO₄ (0 ≤ x ≤ 0.1) ferrite systems prepared by a semi-chemical route, have been studied by electron paramagnetic resonance (EPR) at X-band, Mössbauer spectroscopy and magnetization measurements at various temperatures. EPR spectra of these samples comprise generally a broad and asymmetric EPR signal. The variation of g_eff and peak-to-peak line width ΔH_pp, with Ti concentration and temperature are attributed to the variation of dipole–dipole interaction and the superexchange interaction. Mössbauer spectra comprise two sets of sextet attributed to Fe³⁺ at two distinct sites-A and -B. Ti⁴⁺ ions are concluded to occupy the octahedral B-sites. Magnetic moment is found to decrease with the increase of Ti⁴⁺ concentration. The effective magnetic field H_eff at the A-sites also follows a similar trend. The reason is attributed to the canted structure of spins in the Ti-doped samples. An anomalous behavior at x = 0.015 is observed in the properties studied here and some sort of phase change is believed to occur at 473 K in these ferrites.     

Effect of shear heating during injection molding on the morphology of PC/LCP blends

Fiber relaxation of liquid crystalline polymer (LCP) in the mold during injection molding was investigated. A blend of LCP and polycarbonate was used. The LCP used, namely LC5000, is a thermotropic LCP consisting of 80% and 20% of hydroxybenzoic acid and ethylene terephthalate, respectively. The filling of the mold and the temperature profile of the melt in the mold, after the mold has been completely filled, were computed using the finite element/finite difference method (FE/FDM). The morphology of the fibers was greatly influenced by the temperature of the different layers in the sample. This was confirmed by scanning electron microscopy (SEM) examination of the injection-molded specimen. When shear heating caused the temperature of the melt to increase above 280 °C, relaxation of the fibers was rapid. This resulted in a final morphology where the LCP existed in short fibers or ellipsoids. It was concluded that the high shear rate, which is needed for fiber deformation, must be accompanied by fast cooling to minimize the effects of shear heating, so that the fibers formed could be retained.     

Spin-Relaxation of NiO Encapsulated Gd203 Core-Shell Nanoparticles

Nickel oxide encapsulated gadolinium oxide （Gd203~IiO） core-shell nanoparticles （Nps） has been synthesized by polyol method and analyzed by transmission electron microscopy. The particle size is found to vary from 25 to 35 nm. Raman spectra show the gadolinium oxide core material peaks are found to be diminished by the mass effect of the NiO shell material. The dynamics of the magnetic moment has been studied with the help of temperature dependent electron paramagnetic resonance （EPR） spectroscopy. Peak-to-peak line width （AHpp） value of the EPR spectra increases with decreasing temperature. Temperature dependence of line width shows the dominance of spin-lattice relaxation in these systems, and it can be used as T~ contrast agent. Spin number estimated from EPR studies increases with the decrease of the temperature. The interfacial exchange coupling between the core and shell region is found to be existing at very low temperatures as determined by EPR studies in this non-magnetic/antiferromagnetic （NM/AFM） core/shell nanosystem. The effects of the temperature on the magnetic properties of the Gd203/NiO core/shell NPs and the underlying mechanism have been discussed.     

Internal inversion of thin-walled tubes using a die: experimental and theoretical investigation

The design of sound double-walled tubular parts by external inversion using a die is presently well established. Major parameters are identified, the influence of lubrication is sufficiently well understood and the typical modes of deformation that may occur during the forming process are fully characterized. In contrast to external inversion, there are almost no published works that comprehensively cover the conception of double-walled tubular parts by internal inversion using a die.This paper draws from fundamental research on the internal inversion of thin-walled tubes using a die to the establishment of formability diagrams in terms of the major process parameters. Fundamental research is based on a comprehensive theoretical and experimental investigation of a wide range of subjects, such as: development of plastic instability modes (local buckling), thickening of the tube-wall and occurrence of wrinkling phenomena at the free curved end of the inwardly inverted tubes. The influence of the frictional conditions prevailing at the contact interface between the tube and the die is also examined. The theoretical investigation is supported by numerical predictions based on the finite element flow formulation and the overall methodology is assessed by means of experimental tests on industrial Al6060 Aluminium alloy tubes (annealed and naturally aged) under laboratory-controlled conditions.     

Properties of copolymer of 2,2′:5′,2″-terthiophene-5,5″-dicarboxylic acid and polyethylene oxide

A new type of alternating regular copolymer of 2,2′:5′,2″-terthiophene-5,5″-dicarboxylic acid (TDCA) with polyethylene oxide (PEO) was synthesized. The product was characterized by NMR, UV-Vis and fluorescence spectra, EPR spectroscopy, X-ray diffraction (XRD) and DSC measurements. Copolymer is dissolved in dimethylformamide (DMFA) and dimethylsulfoxide (DMSO). Using TEM, it was ascertained that due to a different chemical structure of polymeric sub-units the separated phases in the solid state are formed on a sub-nanometer level.     

Boron content dependence of crystallization, glass forming ability and magnetic properties in amorphous Fe-Zr-B-Nb alloys

The glass forming ability (GFA) was investigated in Fe_91−xZr₅B_xNb₄ alloys with B contents of 0–36 at.%. The GFA changes with B content, and fully amorphous alloys were prepared by melt spinning for B contents between 5 and 30 at.%. The amorphous alloys crystallize with a primary crystallization mode in the low B content range of 5≤x≤20 at.%, but in the eutectic mode in the high B content range of 20<x<30 at.%. A single new metastable Fe-Zr-B-Nb cubic phase with a lattice constant of 1.0704 nm, a saturation magnetization of 137 emu/g and a coercivity of 7.3 Oe at room temperature is formed when crystallizing in a polymorphous mode at x=30 at.%. The glass transition temperature (T_g), crystallization temperature (T_x), Curie temperature (T_c) and saturation magnetizations (M_s) of the amorphous alloys increase with increasing B content, but the coercivity (H_c) decreases. As the B content exceeds 20 at.%, not only increase the T_g, T_x and GFA sharply, due to the change of crystallization mode, but also the concentration dependence of the T_c and M_s changes. It is concluded that the amorphous alloys have better GFA, thermal stability and soft magnetic properties for the high B contents of 25–30 at.% than for the low B contents of 5–20 at.%.     

Crystal structure and magnetic properties of ZnV2O4

We present structural and magnetic data on ZnV₂O₄ single crystals. Single crystal X-ray diffraction shows the measured crystals to be of very high quality, especially with respect to atomic order. The measured magnetic susceptibility resembles to that of a spin glass system, surprising for a translational invariant structure. The results are discussed in the framework of disorder in a magnetically frustrated lattice.     

Comments on “An alternative physical explanation of the Hall–Petch relation”

Bata and Pereloma describe a physical model that proposes to explain the Hall–Petch relationship. The model is based on an averaging process for the work required to emit a dislocation from a tilt boundary. The purpose of the present comment is to examine several assumptions at the heart of the proposed model. Consideration is first directed at the fundamental premise that application of an average stress is sufficient to induce emission of a straight dislocation from a boundary, even though that stress is far below the stress required to overcome the highest energy barrier. The averaging process is also shown to emphasize the weak long-range interaction of the emitted dislocation with the original boundary, the consequences of which are considered.     

An active method of monitoring tool wear states by impact diagnostic excitation

This paper presents an active method of monitoring tool wear states by using impact diagnostic excitation in the machining process. Because the dynamic characteristics of tool vibration in machining process will change with the tool wear development, the damping ratio, which is one of the important dynamic characteristics of tool vibration, will be used for monitoring the tool wear states in machining. In order to obtain the damping ratio, impact diagnostic excitation was applied to the tool in the feed direction and the signals of the tool vibration were measured for some flank wears under different cutting conditions. The signals were analyzed through FFT analyzer and computer, and then the damping ratio of the tool vibration in the feed direction was calculated. The experimental results have shown that the damping ratio measured by impact excitation increases linearly with tool wear development and the increment of the damping ratio is different for each cutting condition, but the damping ratio can be uniquely determined through the flank worn area. To explain the reason for increase with tool wear development, the damping mechanism on the flank worn land was also discussed. The results of the discussions and numerous cutting experiments have indicated that the presented active method could be used for effectively monitoring the tool wear states in machining.     

dc-Magnetic susceptibility and EPR studies of vapour phase grown Cd1−xCoxTe crystals

Cd_1−xCo_xTe crystals (x = 0.001, 0.003, 0.005, 0.007 and 0.009) were grown by vapour phase technique. The grown diluted magnetic semiconducting (DMS) crystals were subjected to magnetization and dc-magnetic susceptibilities at room temperature. EPR spectra were recorded at 20 K for samples of all compositions. EPR spectra exhibited a broad resonance band around g  5.43. All the studies indicated the paramagnetic nature of the samples.     

TEM study of superstructure in a perovskite lead lanthanum zirconate stannate titanate ceramic

The superstructure of an antiferroelectric Pb_0.97La_0.02(Zr_0.66Sn_0.25Ti_0.09)O₃ phase, whose composition is near the morphotropic-phase boundary, was characterized. Systematic selected-area diffraction revealed that there were two kinds of superlattice reflections in the pseudocubic reciprocal lattice, i.e. superlattice reflections (h, k, l all odd), and one-dimensional incommensurate superlattice reflections, where g denotes the vectors of fundamental or superlattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of . Based on the rhombohedral reciprocal lattice, the reflections were no longer superlattice but fundamental reflections, and the reciprocal vector of the one-dimensional incommensurate reflections was re-expressed as

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, where h, k, l are integers and (−h + k + l) = 3n. In the light of the average structure and the reflection condition, the superspace Bravais class of the phase with one-dimensional incommensurate structure was determined to be in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed.