Synthesis,characterization, and electrical properties of polypyrrole–bimetallic oxide composites

In this study, polypyrrole (PPy) and its bimetallic oxide composites (PPy–V₂O₅–MnO₂) were synthesized via a modified chemical oxidation polymerization method in the aqueous medium with FeCl₃·6H₂O as an oxidant. The synthesized materials were characterized with various analytical techniques to investigate their structural, crystallographic, thermal, morphological, optical, and electrical properties. The Fourier transform infrared study confirmed the successful synthesis of the materials, whereas the X-ray diffraction analyses showed the amorphous and crystalline natures of the PPy and PPy–V₂O₅–MnO₂ composites, respectively. The bimetallic oxide content improved the thermal stability of the composites, as ratified by thermal analysis. The synthesized PPy had a globular and spongy nature, whereas the composites were mixtures of short and long rod-shaped particles. The bimetallic oxide blend enhanced the doping, surface area and semiconducting nature of composites, and lower electrical resistance compared with those of the PPy. The resistance of the synthesized materials depended on the V₂O₅–MnO₂ blend content in the composites and the temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47680.     

Structure and thermal properties of heat treated plasma sprayed ceria–yttria co-stabilized zirconia coatings

Thick plasma sprayed thermal barrier coatings are suitable for thermal and hot corrosion protection of metal components in land-based turbine and diesel engines. In this work, ceria–yttria co-stabilized zirconia coatings were deposited by atmospheric plasma spraying in a mixture of non-transformable tetragonal t′ and cubic c zirconia phases. Free-standing coatings were isothermally annealed at 1315 °C for different times and their crystal structure was studied by XRD. No phase decomposition occurred. Columnar grains grew in the molten splats with increasing annealing time according to a preferential direction and, after 50 h of heat treatment, they were partially replaced by equiaxed grains. Both in-plane and out-of-plane thermal expansion coefficients (CTEs) were measured from coating expansion during heating. The CTE was slightly sensitive to thermal exposure in out-of-plane direction, whereas it kept almost constant in plane direction. The specific heat capacity Cp of annealed coatings, measured by differential scanning calorimetry (DSC), decreased in comparison with as-sprayed coating, due to high-temperature sintering.     

Physical characteristics and sintering behavior of ultrafine zirconia–ceria powders

Ultrafine zirconia–12 mol% ceria powders have been prepared by the coprecipitation technique. The azeotropic distillation with n-butanol has been carried out to ensure complete elimination of the residual water in the precipitate. This procedure has proved to be quite effective in preventing the formation of agglomerates, which are responsible for inhomogeneities in the sintered microstructure, and for non-densification at low temperatures. The crystallization of the solid solution occurs at 430 °C as determined by thermal analyses. The specific surface of the calcined powder is 127.9 m² g⁻¹ and the pore size distribution exhibits only a maximum at approximately 9 nm. Total shrinkage of the compacted powder reached 30% at 1200 °C. Sintered specimens show six bands characteristics of the tetragonal phase in the Raman spectrum. Specimens with apparent densities >95% of the theoretical density and average grain size of 230–400 nm were obtained after sintering at 1200 °C.     

Synthesis and structural,morphological, compositional,optical and electrical properties of DBSA-doped PPy–WO3 nanocomposites

Synthesis of DBSA-doped PPy–WO₃ (organic–inorganic) nanocomposites, using a novel approach, has been proposed, and further envisaged for their structural, compositional, morphological, optical and electrical properties. DBSA-doped PPy–WO₃ nanocomposites demonstrate superior above mentioned properties than their counterparts i.e. either PPy or WO₃. The XRD spectra of nanocomposites supported to conclude that both i.e. PPy and DBSA have no impact on the crystallinity of WO₃ nanoparticles. The chemical structure of DBSA-doped PPy–WO₃ nanocomposites have been elucidated using FTIR spectra. The morphologies and surface roughnesses of the DBSA-doped PPy–WO₃ nanocomposites were confirmed using scanning electron microscope and atomic force microscope images, respectively. Interconnected type morphology and 13 nm average surface roughness were confirmed for DBSA doped PPy–WO₃ hybrid nanocomposites. The EDX and XPS analyses evidence that, the formation of DBSA doped PPy–WO₃ hybrid nanocomposites without any elemental impurities. The absorption peak of DBSA-doped PPy–WO₃ nanocomposites shift towards the lower wavelength side as compared to the PPy–WO₃ (50%) hybrid nanocomposites. Anionically charged sulfonate group which is supposed to stabilize doped state of the DBSA-PPy–WO₃ nanocomposites, may be responsible for this shift. The dc electrical conductivity of DBSA-doped PPy–WO₃ nanocomposites increases as the content of DBSA is increased from 10 to 50% this could be accounted for by the generation of conduction path through the PPy–WO₃ nanocomposites as DBSA has anionic surfactant nature by preventing an agglomeration of functional material.     

Synthesis and properties of electrical conductive and antibacterial siloxane-modified carbon fiber–silver–acrylate nanocomposites

First, silanized carbon fiber (SCF) was synthesized, then silanized carbon fiber–silver (SCF-S) was obtained. Finally, silanized carbon fiber–silver–acrylate (SCF-S-A) electrical conductive and antibacterial composites were prepared. The structures of CF, SCF, SCF-S, and SCF-S-A were characterized by X-ray photoelectron spectroscopy, FTIR, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV spectra. The electrical conductive and antibacterial properties of SCF-S-A nanocomposites were studied. The results showed that electrical conductive and antibacterial activity properties of SCF-S-A nanocomposites were improved. When the content of SCF-S was 50%, the conductivity of SCF-S-A nanocomposites was maximum. The SCF-S-A nanocomposites will have promising application in high-performance electrical conductive and antibacterial materials.     

Processing and characterisation of fine crystalline ceria gadolinia–yttria stabilized zirconia powders

For low temperature SOFCs the yttria stabilized zirconia (YSZ)-coated ceria is a promising candidate for replacing YSZ-electrolyte. An important requirement for the co-firing feasibility of such a configuration is the densification of ceria at low temperatures (<1400°C). Fine crystalline gadolinia doped ceria (CGO)-powder readily sinterable at 1250°C was synthesized by co-precipitation with oxalic acid of 0·05 M and crystallization in methanol at 200°C for 6 h. The fabrication and characterisation of solid solution phases with a graded composition (CGO)_x(YSZ)_1−x, to be used as an interlayer between YSZ and CGO, in order to avoid delamination, were also studied and discussed. CGO_xYSZ_1−x powders, prepared by the glycine combustion method, required higher sintering temperatures (1500°C) to densify, while they showed significantly lower ionic conductivity than YSZ and CGO, attributed to the large lattice deformation and scattering of oxygen ions.     

Effect of sintering temperature electrical properties of ZNR doped with Pr–Co–Cr–La

The microstructure, electrical properties, and dielectric characteristics of the ZNR (zinc oxide-based nonlinear resistors), which are composed of zinc oxide-based ceramics doped with Pr–Co–Cr–La, were investigated at different sintering temperatures (1240, 1245, 1250, 1255, 1260, and 1300 °C). The increase of sintering temperature led to more densified ceramics, whereas it decreased the nonlinear properties and breakdown voltage. The highest nonlinearity was obtained from 1240 °C, with 79.3 in nonlinear coefficient and 0.3 μA in leakage current. As the sintering temperature increased, the donor density increased from 0.90 × 10¹⁸ to 2.59 × 10¹⁸/cm³, and the barrier height decreased from 1.90 to 0.67 eV, and the dielectric dissipation factor increased from 0.0874 to 0.2839.     

Synthesis,microstructure and electrical conductivity of carbon nanotube–alumina nanocomposites

Carbon nanotube–alumina (CNT–Al₂O₃) nanocomposites have been synthesized by direct growth of carbon nanotubes on alumina by chemical vapor deposition (CVD) and the as-grown nanocomposites were densified by spark plasma sintering (SPS). Surface morphology analysis shows that the CNTs and CNT bundles are very well distributed between the matrix grains creating a web of CNTs as a consequence of their in situ synthesis. Even after the SPS treatment, the CNTs in the composite material are still intact. Experimental result shows that the electrical conductivity of the composites increases with the CNT content and falls in the range of the conductivity of semiconductors. The nanocomposite with highest CNT content has electrical conductivity of 3336 S/m at near room temperature, which is about 13 orders of magnitude increase over that of pure alumina.     

Synthesis of monodisperse nanocrystalline 8 mol-% yttria doped ceria powder by oleate complex route

Abstract

Preparation of monodisperse nanocrystalline yttria doped ceria powder by the oleate complex route has been reported. Y(III) and Ce(III) oleate complexes have been prepared by the reaction between YCl₃, Ce(NO₃)₃ and sodium oleate at the interface of hexane rich and water rich conjugate layers of water-ethanol-hexane ternary liquid system. Cubic yttria doped ceria crystallises when the waxy solid containing Y(III) oleate and Ce(III) oleate complexes was heat treated at 400°C. The powder after planetary ball milling contains monodisperse near spherical particles of 0·2?μm. These particles contain monodisperse nanocrystallites of size <10?nm. The yttria doped ceria powder pellets were sintered to >98% theoretical density at 1450°C. The sintered ceramic showed an ionic conductivity of 0·0623?S?cm^?1 at 800°C and activation energy of 1·0?eV.     

Synthesis,structural and electrical properties of Bi1−xDyxFeO3 multiferroic ceramics

Polycrystalline ceramic samples of dysprosium (Dy³⁺) doped bismuth ferrite of general formula Bi_1?xDy_xFeO₃ (x=0.00, 0.01, 0.05 and 0.1) have been prepared by standard solid state reaction method. Powder X-ray diffraction (XRD) analysis reveals that all the samples crystallize in the rhombohedral structure with noncentrosymmetric R3c space group. The refined lattice parameters decrease with the increase of Dy concentration within the same structure symmetry. The bond lengths among atoms for all the compounds were calculated by the Rietveld analysis. The frequency and temperature dependent dielectric constants (real and imaginary parts) have been measured. The real part of dielectric constant reveals that the Neel temperature decreases with the increase of Dy-substitution down to ～200 °C for 10% substitution to the Bi site.     

Mechanical and thermal properties of silicon carbide ceramics with yttria–scandia–magnesia

Two different SiC ceramics with a new additive composition (1.87 wt% Y₂O₃–Sc₂O₃–MgO) were developed as matrix materials for fully ceramic microencapsulated fuels. The mechanical and thermal properties of the newly developed SiC ceramics with the new additive system were investigated. Powder mixtures prepared from the additives were sintered at 1850 °C under an applied pressure of 30 MPa for 2 h in an argon or nitrogen atmosphere. We observed that both samples could be sintered to ≥99.9% of the theoretical density. The SiC ceramic sintered in argon exhibited higher toughness and thermal conductivity and lower flexural strength than the sample sintered in nitrogen. The flexural strength, fracture toughness, Vickers hardness, and thermal conductivity values of the SiC ceramics sintered in nitrogen were 1077 ± 46 MPa, 4.3 ± 0.3 MPa·m^1/2, 25.4 ± 1.2 GPa, and 99 Wm⁻¹ K⁻¹ at room temperature, respectively.     

Morphological,structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.     

Synthesis,processing and properties of TaC–TaB2–C ceramics

Multi-phase ceramics in the TaC–TaB₂–C system were prepared from TaC and B₄C mixtures by reactive pressureless sintering at 1700–1900 °C. The pressureless densification was promoted by the use of nano-TaC and by the presence of active carbon in the reaction products. The presence of TaB₂ inhibited grain growth of TaC and increased the hardness compared to pure TaC. If a coarse TaC powder was used, the compositions did not densify. In contrast, pure nano-TaC was pressureless sintered at 1800 °C by the addition of 2 wt.% carbon introduced as carbon black or graphite. The introduction of carbon black resulted in fully dense TaC ceramics at temperatures as low as 1500 °C. The grain size of nominally pure TaC ceramics was a strong function of carbon stoichiometry. Enhanced grain size in sub-stoichiometric TaC, compared to stoichiometric TaC, was observed. Additional work is necessary to optimize processing parameters and evaluate the properties of ceramics in the TaC–TaB₂–C system.     

Spark plasma sintering and hot pressing of ZTA-NbC materials – A comparison of mechanical and electrical properties

Zirconia toughened alumina can be made electrically conductive and thus electric discharge machinable by addition of a percolating dispersion of niobium carbide. In order to boost the productivity of the sintering process spark plasma sintering was tested at identical temperature and pressure but shorter dwell than in hot pressing. SPS sintering parameters for ZTA-NbC are developed and spark plasma sintered ceramics are compared to the hot pressed benchmark.During SPS a percolating NbC backbone of niobium carbide grains is formed which enhances electrical conductivity but impedes densification. Identical strength at however higher sintering temperature is achieved by SPS but the fracture resistance and hardness were always superior in hot pressed samples. The monoclinic content of zirconia grains in as fired SPS samples is higher despite smaller average grain size and the transformation toughening effect is less pronounced. SPS promises economic benefits due to shorter dwell and cooling cycles.     

Microstructure and electrical properties of ZnO–Bi2O3-based varistor ceramics by different sintering processes

The effect of sintering processes, such as open sintering, sintering inside a closed crucible, and sintering within a powder bed, on the microstructure and V–I characteristics of ZnO–Bi₂O₃-based varistor ceramics was investigated at sintering temperatures in the range 1000–1200 °C. The results from the experiments showed that the microstructure and electrical properties of the samples varied according to the sintering method and temperature. Optimal values for the electrical characteristics of the varistor ceramics by different sintering processes were obtained when the sintering was conducted at 1100 °C. At the same sintering temperature, the different processes affected the properties differently. At 1000 °C, the samples sintered within a powdered bed showed better electrical properties than those subjected to the other two processes, while at 1100 or 1200 °C, the samples sintered in an open crucible exhibited the best electrical properties.     

Synthesis,microstructure, and mechanical properties of WC–TiC–Co ceramic composites

A ceramic composite constituting the formula 78 wt% WC–16 wt% TiC–6 wt% Co denoted as the 78WC–16TiC–6Co ceramic composite was fabricated using a powder metallurgy process, by utilising commercially available WC and Co powders, and laboratory produced TiC powders. TiC powders were produced from machining chips of Grade 4 Titanium. Five different procedures were followed for the manufacturing process by altering the amount of the binding agent (stearic acid) and/or compacting pressure and/or sintering regime (temperature and time) and/or mixing process (dry mixing and mechanical alloying). Characterisation investigations conducted on the sintered samples revealed that stearic acid as the binding agent resulted in the decrease of the relative density while mechanical alloying (MA) induced finer microstructures. The 78WC–16TiC–6Co composites manufactured from commercially available and laboratory produced TiC powders using similar process procedures (including MA) exhibited similar characteristics in terms of relative density, hardness, and wear performance.     

Synthesis,characterization and controlled release properties of zinc–aluminium-beta-naphthoxyacetate nanocomposite

An organic–inorganic nanohybrid nanocomposite was synthesized by co-precipitation method using beta-naphthoxyacetate (BNOA) as guest anion and zinc–aluminium layered double hydroxide (Zn–Al-LDH) as the inorganic host. A well-ordered nanohybrid nanocomposite was formed when the concentration of BNOA was 0.08 M and the molar ratio of Zn to Al, R = 2. Basal spacing of layered double hydroxide containing nitrate ions expanded from 8.9 to 19.5 Å in resulting of Zn–Al-BNOA nanocomposite was obtained indicates that beta-naphthoxyacetate was successfully intercalated into interlayer spaces of layered double hydroxide. It was also found out the BET surface area increased from 1.13 to 42.79 m² g^?1 for Zn–Al-LDH and Zn–Al-BNOA nanocomposite, respectively. The BJH average pore diameter of the synthesized nanocomposite is 199 Å which shows mesoporous-type of material. CHNS analysis shows the Zn–Al-BNOA nanocomposite material contains 36.2 % (w/w) of BNOA calculated based on the percentage of carbon in the sample. Release of BNOA from the lamella of Zn–Al-BNOA was controlled by the zeroth and first order kinetics at the beginning of the deintercalation process up to 200 min and controlled by pseudo-second order kinetics for the whole process. This study suggests that layered double hydroxide can be used as a carrier for organic acid herbicide controlled release formulation of BNOA.     

Synthesis,characterization, optical and electrical properties of thermally stable polyazomethines derived from 4,4′-oxydianiline

Three soluble, thermally stable azomethine polymers were synthesized by the oxidative polycondensation of azomethine bisphenols using NaOCl as an oxidant in aqueous alkaline medium. The azomethine bisphenol monomers, 4,4′-oxybis[N-(2-hydroxy-3-methoxybenzilidine)aniline], 4,4′-oxybis[N-(2-hydroxy-5-bromobenzilidine)aniline] and 4,4′-oxybis[N-(2-hydroxynaphthalidine) aniline] were synthesized by the condensation of 4,4′-oxydianiline with three aromatic aldehydes. The structures of the monomers and polymers were confirmed by Fourier Transform infrared spectroscopy, UV–visible, ¹H-NMR and ¹³C-NMR spectroscopic techniques. Morphology of the synthesized polymers was characterized using scanning electron microscope. The thermal stability of the polymers is evidenced by high carbines residue obtained in TGA. Fluorescence spectra showed that the emission maxima centred in the region 420–460 nm for all the compounds with large stokes shift values (?λ_ST). Electrical conductivity of iodine-doped polymers was measured by four-point probe technique. The synthesized polymers have shown good electrical conductivity on iodine doping, and it increases with the increase in iodine vapour contact time. The self-extinguishing property of the synthesized polymers was studied by the calculation of the limiting oxygen index values with van Krevelen’s equation.     

Effects of washing and calcination–milling on ionic release and surface properties of yttria stabilized zirconia

Crystallographic features, physical properties and ionic release from yttria stabilized zirconia (YSZ) in suspension were studied by means of XRD, TEM, light-scattering particle size, BET, ICP and zeta potential analysis. It was found that Zr, Y, Na, and to a lesser extent Ca, Hf and Pd leach from 8 mol% YSZ powder. The impurities present increase the zeta potential of suspensions made from as-received YSZ. A trace amount of tetragonal phase observed in 8 mol% YSZ persists following washing and calcination–milling. Dislocations and crystallographic defects together with fractured crystals which form during milling of the calcined powder should lead to the formation of more broken bonds; as a result the surface of the particles can support higher surface charge density. Washing and calcination–milling lead to a shift of the isoelectric point of 8 mol% YSZ from pH 8.4 to pH 6.3 and 6.8, respectively. Due to higher chemical stability and previously shown positive impacts on microstructure and performance of fuel cells, use of calcined YSZ can be more advantageous than as received powder.