The preparation and gas sensitivity study of polypyrrole/zinc oxide

Polypyrrole (PPy) was prepared by chemical oxidation polymerization, analyzed by FT-IR, elemental analysis and HRTEM, and studied for gas sensitivity. It suggested that PPy had sensitivity to NH₃, H₂S and NO_x, and showed irreversibility to NO_x gas. The organic–inorganic hybrid materials PPy/ZnO with different PPy weight percents were prepared by mechanical mixing, and the sensitivity study of the materials to toxic gases NH₃, H₂S, NO_x was carried out at different operating temperatures 30, 60, and 90 °C. It was found that PPy/ZnO materials (PPy(1%)/ZnO, PPy(3%)/ZnO, PPy(5%)/ZnO, PPy(10%)/ZnO, PPy(20%)/ZnO) had better selectivity and reversibility to NO_x than pure PPy, and much lower working temperature than the reported working temperature of ZnO (about 350–450 °C). Their sensitivity increased with the increasing concentration of NO_x at particular working temperature, and among them PPy(10%)/ZnO had the maximum sensitivity to NO_x in the same condition. They showed no response to 1000, 1500, 2000 ppm NH₃ or H₂S. The response mechanism of PPy/ZnO materials to NO_x was discussed.     

Structural and magnetic properties of UFe6Ga6

UFe₆Ga₆ polycrystalline samples were prepared by arc-melting, and single crystals were grown by the Czochralski method. This compound crystallizes in the orthorhombic ScFe₆Ga₆-type structure (space group Immm, a=5.0560(4), b=8.5484(7) and c=8.6914(7) Å), an ordered variant of the ThMn₁₂-type structure. A ferromagnetic-type transition at T_C=530(5) K is seen in the magnetization and A.C.-susceptibility measurements, and no other magnetic anomaly is observed down to 5 K. Single crystal magnetization measurements along the three different crystallographic axes indicated a as the easy direction, with a spontaneous magnetization M_S=12.3 μ_B/f.u. at 5 K. The analysis of the ⁵⁷Fe Mössbauer spectroscopy data indicated magnetic hyperfine fields, B_hf, significantly lower on 4f sites than on 8k sites, in agreement with the trend already observed on UFe_xAl_12−x, where the average B_hf were found to increase with the iron–iron interatomic distances.     

The influence of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture

We examine the effects of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-additive concentration, molecular weight, and specimen elongation on the temperature-dependent electronic transport properties of polyaniline films prepared with AMPSA in the presence of a great excess of a formic and dichloroacetic acid (DCAA) solvent mixture. The AMPSA-additive dependent resistivity and thermopower are reported for free-standing PANI:AMPSA_x (M_w=200,000 g mol⁻¹) films (x=0.1–0.5) in the temperature range from 2 to 325 K. The low-temperature data indicate that these samples are just on the insulating side of a disorder-induced metal–insulator (M–I) transition (dρ/dT<0), and that thermal motion at elevated temperatures is sufficient to produce a metallic state (dρ/dT>0) at room temperature. Transport occurs via variable-range hopping (VRH) for temperatures below 200 K, with hopping parameters that are a strong function of x; increased AMPSA concentration decreases the resistivity and moves the samples towards the M–I phase boundary. There is a minimum in the resistivity for all samples at a temperature T_min that is also doping dependent. Stretch orientation of PANI:AMPSA_0.5 films, prepared with higher molecular weight PANI (M_w=300,000 g mol⁻¹), along the resistivity measurement direction decreases the room-temperature resistivity at the expense of a more insulating low-temperature state. The T_min values of both stretched and unstretched PANI:AMPSA_0.5 films are pushed below 200 K, which reflects reduced disorder in film processed with higher molecular weight polyaniline. These results reflect an evolution in the underlying inhomogeneous mesoscopic disorder present in doped conducting polymers.     

Effect of Fe additions on microstructure and mechanical properties of a multi-component Nb–16Si–22Ti–2Hf–2Al–2Cr alloy at room and high temperatures

The phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe alloys (where x = 1, 2, 4, 6 at.%, hereafter referred to as 1Fe, 2Fe, 4Fe and 6Fe alloys, respectively) prepared by arc-melting were investigated. It was observed that the nominal Fe content affected the solidification path of the multi-component alloy. The as-cast 1Fe alloy primarily consisted of a dendritic-like Nb_SS phase and (α+γ)-Nb₅Si₃ silicide, and the as-cast 2Fe and 4Fe alloys primarily consisted of an Nb_SS phase, (α+γ)-Nb₅Si₃ silicide and (Fe + Ti)-rich region. In addition to the Nb_SS phase, a multi-component Nb₄FeSi silicide was present in the as-cast 6Fe alloy. When heat-treated at 1350 °C for 100 h, the 1Fe and 6Fe alloys almost exhibited the same microstructures as the corresponding as-cast samples; for the 2Fe and 4Fe alloys, the (Fe + Ti)-rich region decomposed, and Nb₄FeSi silicide formed. The fracture toughness of the as-cast and heat-treated Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe samples monolithically decreased with the nominal Fe contents. It is interesting that at room temperature, the strength of the heat-treated samples was improved by the Fe additions, whereas at 1250 °C and above, the strength decreased, suggesting the weakening role of the Nb₄FeSi silicide on the high-temperature strength. As the nominal Fe content increased from 1 at.% to 6 at.%, for example, the 0.2% yield strength increased from 1675 MPa to 1820 MPa at room temperature; also, the strength decreased from 183 MPa to 78 MPa at 1350 °C.     

Crystal structures of the compounds formed in DyCo2–DyGa2 pseudo-binary system at 773 K

DyCo_2?xGa_x alloys with x from 0 to 2 were prepared by arc melting and investigated by X-ray powder diffraction. Six ternary compounds with different Ga contents x, DyCo₂, DyCo_1.33Ga_0.67, DyCoGa, DyCo_0.67–0.35Ga_1.33–1.65, DyCo_0.25–0.15Ga_1.75–1.85, and DyGa₂, were formed in the system. The crystal structures of these compounds were determined by Rietveld refinement method with TOPAS V3.0 software. The Rietveld refinements reveal that DyCo_1.33Ga_0.67 crystallized in the MgZn₂-type structure (P6₃/mmc) with a = 5.414(1) and c = 8.452(1) Å, DyCoGa in the Co₂Si-type structure (Pnma) with a = 7.052(1), b = 4.393(1) and c = 6.958(1) Å, DyCo_0.5Ga_1.5 in the GdPdSi-type structure (Imma) with a = 4.341(1), b = 7.007(1) and c = 7.551(1) Å, and DyCo_0.2Ga_1.8 in the AlB₂-type structure (P6/mmm) with a = 4.339(1) and c = 3.634(1) Å. The relationships between these structures were discussed.     

Electrodeposited conducting polymer–magnetic metal composite films

Electrically conducting polypyrrole (PPy)–iron group (Ni, Co, Fe and their alloys) composite films have been electrodeposited at cathodic process to give “tailored” soft and hard magnetism. The composites of the PPy doped with dodecylsulfate (DS) (PPy–DS) with NiFe alloy showed soft magnetism with coercivity H_C,∥ <9 Oe, while the PPy–DS with CoMnP alloy showed hard magnetism with H_{C, ∥}>1085 Oe. These results indicate that composites of conducting polymer–magnetic metals can be easily fabricated by electrodeposition.     

Spin-glass-like behaviour in the ternary U3Fe4+xAl12−x uranium–iron aluminide

The U₃Fe_4+xAl_12?x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd₃Ru₄Al₁₂-type structure (e.g. P6₃/mmc), with room temperature parameters a = 8.7516(3) Å and c = 9.2653(4) Å for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagomé net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, T_f = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel–Fulcher law is followed with values typical for a spin-glass. ⁵⁷Fe Mössbauer data show that there is no freezing of the iron magnetic moments directions below T_f, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.     

Phase equilibria in the system Au–Cu–Si and structural characterization of the new compound Au5±xCu2±xSi

The ternary Au–Cu–Si system was investigated by means of powder X-ray diffraction (XRD) for phase identification, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) for microstructures and chemical compositions, light optical microscopy (LOM), and differential thermal analysis (DTA) for the determination of thermal effects. Three isothermal sections were constructed at 250 °C, 400 °C and 650 °C. A new ternary compound τ, Au_5±xCu_2±xSi, was identified and its crystal structure was determined by means of single crystal X-ray diffraction. It adopts a new crystal structure type in space group Pnma, Pearson symbol oP32 and shows a composition range between Au_5.6Cu_1.4Si and Au_4.4Cu_2.6Si at 250 °C. Lattice parameters were found to vary between a = 9.64–9.50 Å, b = 7.61–7.64 Å and c = 6.90–6.89 Å from the Au-rich to the Au-poor composition limit. Three vertical sections, at 10 and 30 at.% Si and at 10 at.% Cu, were constructed based on DTA data and four invariant ternary phase reactions were identified. A partial ternary reaction scheme (Scheil diagram) and a partial liquidus projection are given.     

Microstructural evolution and mechanical properties of an Nb–16Si in-situ composite with Fe additions prepared by arc-melting

This paper deals with phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–xFe in-situ composites (where x = 2, 4, 6 at.%, referred as to 2Fe, 4Fe and 6Fe alloys, hereafter) prepared by arc-melting. It is found that with additions of Fe, Nb₄FeSi silicide arises and microstructures of as-cast samples are consisted of dendritic-like Nb_SS phase, Nb₃Si block, and Nb₄FeSi matrix in the 2Fe and 4Fe alloys, and of the dendritic-like Nb_SS phase and Nb₄FeSi matrix in the 6Fe alloy. When heat-treated at 1350 °C for 100 h, part of the Nb₃Si phase decomposes in the 2Fe and 4Fe alloys, and the 6Fe alloy shows no change in microstructure as compared with the as-cast one. The Nb₄FeSi silicide is found to be brittle, its fracture toughness and elastic modulus are first obtained, having values about 1.22 MPa m^1/2, and 310 GPa, respectively. The fracture toughness of the bulk as-cast and heat-treated Nb–16Si–xFe samples are changed slightly by the Fe additions, which is in a range of 9.03–10.19 MPa m^1/2. It is interesting that at room temperature, strength is improved by the Fe additions, whereas at 1250 °C and 1350 °C the strength decreases. As the Fe content increased from 2 at.% to 6 at.%, for example, the 0.2% yield strength increases from 1410 MPa to 1580 MPa at room temperature, decreases from 479 MPa to 385 MPa at 1250 °C.     

Crystal structures of PrAlxGe2−x compounds

The PrAl_xGe_2−x cross-section of the Pr–Al–Ge system at 1073 K was studied. The homogeneity ranges of two ternary praseodymium alumogermanides, PrAl_1.55–1.48Ge_0.45–0.52 and PrAl_1.42–0.98Ge_0.58–1.02, were determined and their crystal structures refined from X-ray single-crystal diffraction data. The former has a hexagonal structure of the AlB₂ type (hP3, P6/mmm, a=4.3223(3), c=4.2585(4) Å for x=1.476(2)) and the latter a tetragonal structure of the LaPtSi type (tI12, I4₁md, a=4.2534(5), c=14.641(2) Å for x=1). For both structures, the Al–Ge interatomic distances are close to the sum of the covalent radii, whereas the Pr–Al(Ge) distances agree well with the sum of the metallic radii. The solubility of Ge in the cubic Laves phase PrAl₂ was found to be less than 2 at.%, that of Al in off-stoichiometric PrGe_2−x less than 8 at.%. Al(Ge)-centered R₆ trigonal prisms constitute a common geometrical feature of the structures of the germanides RGe_2−x and alumogermanides RAl_xGe_2−x formed by the light rare-earth elements. Substitution of Ge for Al, or replacement of a large rare-earth element by a smaller one, leads to a reduction of the prism volume.     

Microstructure and martensitic transformation behavior of Ni56-xMn25FexGa19 shape memory alloys简

Microstructure, martensitic transformation behavior, mechanical and shape memory properties of Ni56-x Mn25 Fex Ga19(x = 0, 2, 4, 6, 8) shape memory alloys were investigated using optical microscopy(OM), X-ray diffraction analysis(XRD), differential scanning calorimeter(DSC), and compressive test. It is found that these alloys are composed of single non-modulated martensite phase with tetragonal structure at room temperature, which means substituting Fe for Ni in Ni56 Mn25 Ga19 alloy has no effect on phase structure. These alloys all exhibit a thermoelastic martensitic transformation between the cubic parent phase and the tetragonal martensite phase. With the increase of Fe content, the martensitic transformation peak temperature(Mp) decreases from 356 °C for x = 0 to 20 °C for x = 8, which is contributed to the depressed electron concentration and tetragonality of martensite. Fe addition remarkably reduces the transformation hysteresis of Ni–Mn–Ga alloys. Substituting Fe for Ni in Ni56 Mn25 Ga19 alloy can decrease the strength of the alloys and almost has no influence on the ductility and shape memory property.     

Metastable alloy bulk bodies in the Fe–W system prepared by mechanical alloying and shock compression

Bulk bodies of metastable alloys including supersaturated solid solutions and amorphous phases in the iron (Fe)–tungsten (W) system were prepared by mechanical alloying (MA) and shock compression. The X-ray diffraction patterns of the W solid solutions were obtained for the MA-treated powders in the Fe_xW_100−x system with Fe content of x≤30 mol%, and that of Fe solid solution was obtained with an Fe content of x=90 mol%. For the mixed powders with Fe content of 40≤x≤70 mol%, the peaks of Fe completely disappeared, and the amorphous halo-like patterns were observed around the (110) peak of W solid solution. For the mixed powder with an Fe content of 80 mol%, an X-ray diffraction pattern of a two-phase mixture of Fe and W solid solutions was obtained. For the MA-treated powders, the lattice parameters of W solid solutions were smaller than that of pure W, and those of Fe solid solutions were larger than that of pure Fe. No large crack could be observed in shock-consolidated bulk bodies, and the cross sections of the bulk bodies showed a metallic gloss. The X-ray diffraction patterns of shock-consolidated bulk bodies formed in a specific low pressure range did not change significantly from those of the MA-treated powders, which indicated that the metastable phases were successfully consolidated by shock compression without decomposition or recrystallization. Above a driving shock pressure of 40.1 GPa in capsule for the 30:70 mol% Fe–W system and that of 30.5 GPa for the 50:50 mol% Fe–W system, the X-ray diffraction patterns of the recovered bulk bodies showed the appearance of the peaks of Fe₇W₆ intermetallic compound and the peaks of Fe. The recovered specimens of the metastable solid solution phases in the 80:20 mol% Fe–W system did not recrystallize or decompose up to a driving shock pressure of 39.5 GPa. It was confirmed by the Electron Probe Micro Analysis (EPMA) that Fe and W dispersed well at the submicron level in the shock-consolidated bulk bodies. The Vickers hardnesses of the bulk bodies were much higher than those of pure Fe and pure W polycrystals.     

Phase Equilibria in the Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–InSb System

The phase diagram of the (Sb₂Te₃)_100?x –InSb _x system was determined based on x-ray diffraction (XRD) analysis, differential thermal analysis (DTA), and microhardness and density measurements. An intermediate compound with composition Sb₂Te₃·2InSb was formed as a result of syntectic reaction, melting incongruently at 553 °C. This compound has tetragonal lattice with unit cell parameters of a = 4.3937 Å, b = 4.2035 Å, c = 3.5433 Å, α = 93.354°, and β = γ = 90°. Sb₂Te₃·(2 + δ)InSb (?1 ≤ δ ≤ +1) and (Sb₂Te₃)_100?x (InSb) _x (90 ≤ x ≤ 100) solid solutions exist in the investigated system, based on the intermediate compound Sb₂Te₃·2InSb and on InSb, respectively. Also, two invariant equilibria exist in the system, with eutectic point coordinates at compositions of x = 60 and x ≈ 85 mol% InSb and eutectic temperatures of T _E = 541 and T _E ≈ 501 °C, respectively.     

Effects of La substitution on microstructure and hydrogen storage properties of Ti–Fe–Mn-based alloy prepared through melt spinning

The as-spun Ti_1–xLa_xFe_0.8Mn_0.2 (x=0, 0.01, 0.03, 0.06, 0.09, molar fraction) alloys were prepared by melt spinning. The effects of La substitution for Ti on the microstructure, hydrogen storage kinetics and thermodynamics of TiFe-type Ti–Fe–Mn-based alloy were investigated. The as-spun alloys hold the TiFe single phase, which transforms to TiFeH_0.06, TiFeH, and TiFeH₂ hydrides after hydrogenation. La substitution promotes the formation of micro-defects (such as dislocations and grain boundaries) in the alloys, thus facilitating hydrogen diffusion. In addition, the hydrogen storage kinetics properties are improved after introducing La element. With the rise of La content, the hydrogen storage capacity decreases firstly and then increases, but the absolute value of hydriding enthalpy change (|ΔH|) increases firstly and then reduces. When x=0.01, the maximum value of |ΔH| is obtained to be (25.23±0.50) kJ/mol for hydriding, and the alloy has the maximum hydrogen absorption capacity of (1.80±0.04) wt.% under the conditions of 323 K and 3 MPa.     

Effect of Single and Double Sintering on Microstructure and Magnetic Properties of Gd-Substituted Ni-Cd Ferrites

Two different groups, I and II, which are fired one and two times, respectively, from Ni-Cd ferrites of chemical formula Ni_0.7Cd_0.3Gd _x Fe_2?x O₄ (x = 0 to x = 0.1 with step = 0.025) have been prepared by conventional ceramic method. The effect of Gd-substitution on the microstructure and magnetic properties of the two groups has been studied. X-ray patterns indicated the presence of a minor secondary phase with the spinel phase at Gd-concentrations with x = 0.075 and 0.1. SEM and VSM are used to investigate the microstructure and to measure the magnetization of the samples at room temperature, respectively. The initial permeability is measured as a function of temperature and Curie temperature is determined. It was found that there are considerable differences in the microstructure and the magnetic properties of the two groups. Although the Gd-substitution decreased the values of both saturation magnetization M _s and initial permeability μ_i, the value of Curie temperature T _C has been improved. Moreover, the double sintering process improved the magnetization and densification of samples.     

New equilibrium phase in the Fe–Ge system obtained by mechanical alloying

A new equilibrium phase has been found in the Fe–Ge system. It has the composition Fe₂Ge₃, and decomposes at about 580°C due to a peritectoid reaction, giving FeGe (cubic modification) and FeGe₂. The phase forms by a eutectoid reaction from FeGe₂ at about 530°C; however, this transformation is kinetically inhibited. The Fe₂Ge₃ compound is likely to have a tetragonal lattice, structure type of Ru₂Sn₃, a=5.59 Å, c=8.92 Å.     

Synthesis and characterization of bismuth alkaline titanate powders

In this work, samples of bismuth alkaline titanate, (K_0.5Na_0.5)_(2?x/2)Bi_(x/6)TiO₃, (x = 0.05–0.75) have been prepared by conventional ceramic technique and molten salts. Metal oxides or carbonates powders were used as starting raw materials. The crystalline phase of the synthesized powders was identified by the X-ray diffraction (XRD) and particle morphology was characterized by scanning electron microscopy (SEM). Solid state reaction method was unsuccessful to obtain pellets. From XRD results, a rhombohedral structure was detected and the parameter lattice were estimated to be a = 5.5478 Å and α = 59.48°. These parameters were used to refine the structure by Rietveld analysis. SEM results showed several morphologies. Apparently, bismuth is promoting the grain growth whose sizes vary from 30 nm to 180 nm It is expected that these materials can be utilized in practical applications as substitutes for lead zirconatetitanate (PZT)-based ceramics.     

Magnetic properties of polyaniline doped with FeCl3

Magnetic properties of polyaniline (PANI) doped with FeCl₃ were investigated as a function of temperature and magnetic field. The temperature dependence of the magnetic susceptibility (χ) of PANI doped with FeCl₃ exhibits dominant paramagnetic component (well described by Curie–Weiss law with a negative Curie–Weiss temperature Θ) accompanied by a small temperature-independent paramagnetic contribution. Magnetization measured as the function of magnetic field shows smaller saturation effect than expected for non-interacting iron ions. These two observations suggest weak antiferromagnetic (AF) interactions between Fe ions.     

Anomalous magnetism and electron paramagnetic resonance spectroscopy of the ZrNi1−xCrxSn solid solution

The static magnetic properties and electron paramagnetic resonance (EPR) spectra of ZrNi_1−xCr_xSn solid solution (0<x≤0.4) have been investigated in the temperature range 140–300 K. Materials were prepared by arc-melting of the pure metals. It was found that ferromagnetic ordering occurs in the samples with small chromium concentration. EPR spectra of the materials with x=0.05, 0.1, 0.2 consist of three absorption lines. The I and II lines are characterised by g=1.99±0.01, ΔH_pp=(120±5) G type and g=1.980±0.001, peak-to-peak width ΔH_pp=(10±1) G, respectively. They have been attributed to Cr³⁺ ions in Ni-sites of the lattice coupled by magnetic dipolar interaction (type I) and to exchange coupled Cr³⁺ pairs or clusters of more than two Cr³⁺ ions (type II). The third line detected in the samples with x=0.3, 0.4 characterised by g_eff=2.0003±0.0001 and ΔH_pp=(3.0±0.5) G has been interpreted as conduction electron spin resonance (CESR).     

Conductive fibers from enzymatically synthesized polyaniline

Conducting polyaniline (PANI) fibers have been spun from a water-soluble form of PANI which was enzymatically synthesized. The enzyme, horseradish peroxidase (HRP) was used to polymerize aniline in the presence of sulfonated polystyrene (SPS) to directly form a water-soluble, conducting, PANI/SPS complex which combines moderate electrical conductivity with appreciable processability. The PANI/SPS complex was spun into fibers from aqueous solution using a dry-spinning technique. Thermal studies which included thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and DMA show that the complex has very good thermal stability and a T_g at 150°C. Mechanical properties of the fibers show a tenacity of 0.34 cN/dtex for the as-spun fibers with an increase to 0.56 cN/dtex after thermal stretch alignment. Wide angle X-Ray diffraction shows the presence of two weak peaks at d values of 4.16 Å and 2.95 Å for the drawn fibers, while no crystalline reflections were observed for cast films. The drawn fibers also show an order of magnitude improvement in conductivity. These results show that some degree of fiber orientation and crystallinity may be induced during processing.