A conducting composite based on poly(N‐vinylcarbazole)–formalin resin and acetylene black

A poly(N‐vinylcarbazole) (PNVC)–formalin (FO) resin (PNVC‐FO) was prepared via copolycondensation between N‐vinylcarbazole (NVC) and FO in the presence of dry HCl gas in toluene medium at 110°C. A highly conducting composite of PNVC‐FO resin with nanodimensional acetylene black (AB) was prepared by carrying out the polycondensation reaction in presence of a suspension of acetylene black (AB) in toluene. The inclusion of PNVC in the PNVC‐FO‐AB composite was confirmed by FT‐IR analysis. Scanning electron microscopic analyses of PNVC‐FO resin and PNVC‐FO‐AB composite revealed formation of spherical particles and aggregates of irregular shapes respectively. Thermogravimetric analyses revealed the overall stability order as: AB > PNVC‐FO‐AB composite > PNVC‐FO resin > PNVC homopolymer. In sharp contrast to PNVC and PNVC‐FO resin, which were both nonconducting (10^?12 to 10^?16 S/cm), the conductivity of the composites reached values between 0.75 S/cm and 6.54 S/cm corresponding to AB loading of 28–49 wt % respectively. Temperature versus conductivity studies revealed an initial increase in conductivity upto 200°C and current–voltage characteristics of the PNVC‐FO‐AB composite showed a linear trend consistent with Ohmic behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3837–3843, 2007     

A conducting nanocomposite of acetylene black with preformed poly‐N‐vinylcarbazole crosslinked by anhydrous FeCl3

A conducting nanocomposite of crosslinked poly‐N‐vinylcarbazole (CLPNVC) with nanodimensional acetylene black (AB) was prepared by oxidative crosslinking of preformed PNVC through pendant carbazole moieties in presence of anhydrous FeCl₃ as an oxidant and AB suspension in CHCl₃ medium at 65°C. The incorporation of CLPNVC moieties in the CLPNVC‐AB composite was endorsed by Fourier transform infrared analysis. Scanning electron microscopic analysis showed formation of lumpy aggregates with average sizes in the 130–330 nm ranges. The thermal stability of the CLPNVC‐AB composite was appreciably higher than that of the PNVC‐AB composite. The direct current conductivities of the composites were significantly enhanced relative to that of the PNVC homopolymer (10^?12–10^?16 S/cm) and varied in the range of 10^?4–10^?2 S/cm depending on the amount of AB loading in the CLPNVC‐AB composite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 819–824, 2006     

Conducting composites of polythiophene and polyfuran with acetylene black

Conducting composites of polythiophene (PTP) and polyfuran (PF) with acetylene black (AB) were prepared via chemical oxidative polymerization of thiophene and furan in a suspension of AB in CHCl₃ at room temperature using anhydrous FeCl₃ as the oxidant. Formation of PTP and PF and their subsequent incorporation in PTP–AB and PF–AB composite systems were confirmed by FTIR analysis. Scanning electron microscope analysis showed the presence of compact clusters of particles in both composites. Transmission electron micrographs of PTP–AB and PF–AB composites showed formation of globular polymer encapsulated AB particles with average diameters of the order of ～100 nm in both systems. Thermogravimetric analysis revealed that the overall thermal stability varied in the order: AB > PTP–AB > PTP and AB > PF–AB > PF. DC conductivity values for the PTP–AB and PF–AB composites were of the order of 10^?2 and 10^?3 S cm^?1, respectively. Copyright © 2004 Society of Chemical Industry     

Synthesis and electrochemical properties of α-LiVOPO4 as cathode material for lithium-ion batteries

Triclinic α-LiVOPO₄ with excellent electrochemical properties is prepared, using δ-VOPO₄, LiNO_3, and a highly conductive carbon material (acetylene black) as raw materials, by a two-step method, for the first time. Transmission electron microscopy reveals that the synthesized nanoscale α-LiVOPO₄ is approximately 50–100?nm in size, and its surface is covered by 1.68?nm thick acetylene black, which not only improves the ionic conductivity of the material, but prevents material-size growth at high temperature, and particle agglomeration. In addition, the initial discharge capacity of α-LiVOPO₄ sintered at 600?°C over 10?h is the highest, reaching 111.7?mAh?g^?1 at 0.05?°C. The capacity retention rate is 95.1%, which is 106.3?mAh?g^?1 after 50 cycles.     

Thermal and mechanical properties of the precursor polymers: Comparison of their properties with poly(amic acid)

The DSC thermograms of P-PHA show a large endothermic peak at 450–550°C. As the annealing temperature increases from 250°C to 400°C, the endothermic peaks become smaller and then disappear for samples annealed above 450°C. As observed for P-PHA, the endothermic enthalpy of PHA and PAA became smaller with an increasing annealing temperature. The cyclization onset temperature (T₁) of the three precursors increases linearly with an increasing annealing temperature at a constant annealing time (30 min). Otherwise, the initial decomposition onset temperature (T₂) was shown to be constant. T₂ of P-PHA, PHA, and PAA were observed in the temperature ranges of 601–603°C, 576–577°C, and 532–534°C, respectively. These TGA results confirm that all of the samples are thermally stable. Increasing the annealing temperature of the three precursor polymers significantly increases the tensile properties of the films. The tensile properties of all annealed precursors were much higher than those of the unannealed films. In contrast, the initial modulus of PAA is improved only slightly when compared with the other two polymers regardless of the heat treatment. The biaxial stresses in the PHA and PAA films were investigated by holographic interferometry. The stresses in the films were 6.85–7.61 MPa for PHA and 27.01–27.70 MPa for PAA.     

Hydrothermal synthesis of LiMn2O4/C composite as a cathode for rechargeable lithium-ion battery with excellent rate capability

A spinel LiMn₂O₄/C composite was synthesized by hydrothermally treating a precursor of manganese oxide/carbon (MO/C) composite in 0.1 M LiOH solution at 180 °C for 24 h, where the precursor was prepared by reducing potassium permanganate with acetylene black (AB). The AB in the precursor serves as the reducing agent to synthesize the LiMn₂O₄ during the hydrothermal process; the excess of AB remains in the hydrothermal product, forming the LiMn₂O₄/C composite, where the remaining AB helps to improve the electronic conductivity of the composite. The contact between LiMn₂O₄ and C in our composite is better than that in the physically mixed LiMn₂O₄/C material. The electrochemical performance of the LiMn₂O₄/C composite was investigated; the material delivered a high capacity of 83 mAh g⁻¹ and remained 92% of its initial capacity after 200 cycles at a current density of 2 A g⁻¹, indicating its excellent rate capability as well as good cyclic performance.     

Effect of doping polyacrylic acid with some dopants as studied by different techniques

The molecular weight of polyacrylic acid (PAA) was determined by a viscometric method using NaNO₃ as solvent at 30°C. The specific electric conductivities (σ) of PAA as well as PAA doped with carbon black (CB), chromium oxide (Cr₂O₃), and cupferron with different concentrations (from 0.25 to 1 wt %) were measured at a temperature range 360–400 K. IR spectra of some polymers were determined and it was shown that when PAA was doped with 0.5 wt % CB, a C? O? C band appeared at 775–875 cm^?1. The positron annihilation lifetime (PAL) spectra in PAA doped with the above‐mentioned dopants were measured as a function of their concentrations. It was observed that the short lifetime intensity I₁ decreased, whereas the intermediate lifetime intensity I₂, which is related to the conductivity of the material, increased with increasing the wt % of Cr₂O₃ and cupferron as well as at low concentrations of CB. These results are discussed in terms of the conducting island model. It was found that there were distinct positive relationships between σ and I₂. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 877–883, 2002; DOI 10.1002/app.10381     

Effect of structural change of pitch on the thermal conductivity of epoxy‐based composites filled with heat‐treated pitch

Petroleum‐based pitches were used as filler materials to study the effects of heat‐treatment‐induced changes in pitch structure on the thermal conductivity of epoxy‐based composites. The heat treatment was performed in two steps: the first involved heating the pitch to 250 °C in order to remove the low‐molecular‐weight compounds from the pitch, and the second involved heating the pitch to either 430 or 450 °C. There was no significant difference in the curing behavior of the diglycidyl ether of bisphenol A (DGEBA)/pitch composites, regardless of the heat‐treatment temperature. However, the thermal conductivity of the DGEBA/pitch composites improved with increasing heat‐treatment temperature, and the epoxy composite prepared with pitch heat‐treated at 430 °C exhibited the maximum thermal conductivity. This can be attributed to structural changes in the pitch, such as the distance between adjacent planes (d‐spacing), crystallite height (L_c) and crystallite width (L_a). Although L_c of the pitch increased with increasing heat‐treatment temperature, the d‐spacings and L_a decreased. These results suggest that the heat treatment of the pitch led to a well‐stacked crystalline structure. However, compared with the pitch heat‐treated at 430 °C, that heat‐treated at 450 °C exhibited lower thermal conductivity in the DGEBA/pitch composite because of the low L_a, resulting in the loss of basal carbon as a consequence of in situ gasification, and pyrolysis of the low‐molecular‐weight compounds in the pitch. © 2013 Society of Chemical Industry     

Process induced alignment of carbon nanotube decreases longitudinal thermal conductivity of Al2O3 based porous composites

Alumina (Al₂O₃) based porous composites, reinforced with zirconia (ZrO₂), 3 and 8 mol% Y₂O₃ stabilized ZrO₂ (YSZ) and 4 wt% carbon nanotube (CNT) are processed via spark plasma sintering. The normalized linear shrinkage during sintering process of Al₂O₃-based composite shows minimum value (19.2–20.4%) for CNT reinforced composites at the temperature between 1650 °C and 575 °C. Further, the combined effect of porosity, phase-content and its crystallite size in sintered Al₂O₃-based porous composite have elicited lowest thermal conductivity of 1.2 Wm⁻¹K⁻¹ (Al₂O₃-8YSZ composite) at 900 °C. Despite high thermal conductivity of CNT (∼3000 Wm⁻¹K⁻¹), only a marginal thermal conductivity increase (∼1.4 times) to 7.3–13.4 Wm⁻¹K⁻¹ was observed for CNT reinforced composite along the longitudinal direction at 25 °C. The conventional models overestimated the thermal conductivity of CNT reinforced composites by up to ∼6.7 times, which include the crystallite size, porosity, and interfacial thermal resistance of Al₂O₃, YSZ and, CNT. But, incorporation of a new process induced CNT-alignment factor, the estimated thermal conductivity (of <6.6 Wm⁻¹K⁻¹) closely matched with the experimental values. Moreover, the high thermal conductivity (<76.1 Wm⁻¹K⁻¹) of the CNT reinforced porous composites along transverse direction confirms the process induced alignment of CNT in the spark plasma sintered composites.     

Effect of LaB6 addition on compressive creep behavior with simultaneous oxide scale growth of spark plasma sintered ZrB2-SiC composites

A study has been carried out to examine the effect of LaB₆ addition on the compressive creep behavior of ZrB₂-SiC composites at 1300–1400°C under stresses between 47 and 78 MPa in laboratory air. The ZrB₂-20 vol% SiC composites containing LaB₆ (10% in ZSBCL-10 and 14% in ZSBCL-14) besides 5.6% B₄C and 4.8% C as additives were prepared by spark plasma sintering at 1600°C. Due to cleaner interfaces and superior oxidation resistance, the ZSBCL-14 composite has exhibited a lower steady-state creep rate at 1300°C than the ZSBCL-10. The obtained stress exponent (n ∼ 2 ± 0.1) along with cracking at ZrB₂ grain boundaries and ZrB₂-SiC interfaces are considered evidence of grain boundary sliding during creep of the ZSBCL-10 composite. However, the values of n ∼ 1 and apparent activation energy ∼700 kJ/mol obtained for the ZSBCL-14 composite at 1300–1400°C suggest that ZrB₂ grain boundary diffusion is the rate-limiting mechanism of creep. The thickness of the damaged outer layer containing cracks scales with temperature and applied stress, indicating their role in facilitating the ingress of oxygen causing oxide scale growth. Decreasing oxidation-induced defect density with depth to a limit of ∼280 μm, indicates the predominance of creep-based deformation and damage at the inner core of samples.     

Enhanced ion transport in polymer–ionic liquid electrolytes containing ionic liquid-functionalized nanostructured carbon materials

An effective chemical strategy for the synthesis of polymer–ionic liquid (IL) electrolytes with ion-conducting channels, physically modulated by variously dimensioned IL-functionalized carbon materials (IL-FCMs) including carbon black (CB), multi-walled carbon nanotubes (MWCNT) and reduced graphene oxide sheets (RGO) is reported, enabling a fundamental understanding of the relationship between carbon structures and ion transport behavior. The risk of electrical shorts is eliminated by the presence of IL groups on the surfaces of CMs and only minimal amounts of the IL-FCMs (⩽1.0 wt.%) in the polymer/IL composite electrolytes (e.g., polymer matrix filled with 1.0 wt.% IL-FCMs has a conductivity of ∼10⁻⁷ S cm⁻¹ at 100 °C). Increase in ion transport within the reorganized ion channels of the composite polymer electrolytes (CPEs) is confirmed by the enhanced ionic conductivity and low activation energy for through-plane and in-plane ionic conduction at different temperature (40–160 °C). Maximum improvement in the ionic conductivity (150–300% at 100 °C) can be achieved by optimizing the carbon structure and the loading ratio, which leads to highly ionic conductive polymer/IL composite electrolytes for practical applications.     

Studies on sublimation of disperse dye out of dyed polymers. I. Rate of sublimation and amorphous transition points of poly(ethylene terephthalate)

Four samples of poly(ethylene terephthalate) film of various crystallinities and orientation were dyed with p-nitroaniline and disperse dyes. When these films were heated under a 2–3 × 10^?3 mm Hg vacuum at a specified temperature T, the dye sublimed out of the dyed specimen. The amount (M_t/M_∞) of sublimed dye is in linear proportion to the square root of the sublimation time, t^½, where M_t and M_∞ are the amounts of dye sublimed for times t and t = ∞. The diffusion coefficient D, calculated from the slope of the above plot, is independent of the dye concentration of the film. When log D is plotted against 1/T°K over the temperature range 320–520°K, the relation is composed of two to four intersecting lines with the slope decreasing with elevation of temperature and with the breaks at about 89°–98°, 122°–135°, 155° and 175°–176°C. These breaks are the amorphous transitions: the first is the glass transition temperature T_g, the second and the fourth are the amorphous transitions corresponding to the crystalline transition points, i.e., the cold crystallization temperature and the smectic–triclinic transition temperature. With some exceptions, these amorphous transitions are found also by dilatometry and electrical conductivity measurements. The apparent activation energy for diffusion decreases from about 100 kcal/mole for the glass state to 22–24 kcal/mole for the region above 180°C. The activation energy for each region changes slightly with the size of dye molecule and the crystallinity and orientation of the film.     

Preparation of nanostructured porous carbon composite fibers from ferrum alginate fibers

Nano‐microstructured porous carbon composite fibers (Fe₂O₃@C/FeO@C/Fe@C) were synthesized by the thermal decomposition of ferrum alginate fibers. The ferrum alginate fiber precursors were prepared by wet spinning, and calcined at 300–1000°C in high purity nitrogen. The resulting composite fibers consist of carbon coated Fe₂O₃/FeO/Fe nanoparticles and porous carbon fibers. All the prepared nanostructures were investigated using thermal gravimetry, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscope (TEM), and nitrogen adsorption–desorption isotherm. The results show that there are five stages in the decomposition process of the ferrum alginate fibers. Transitions between the five stages are affected by the decomposition temperature. XRD results show that maghemite (Fe₂O₃), wüstite (FeO), martensite (Fe) nanoparticles were formed at 300–500°C, 600–700°C, 800–1000°C, respectively. Scanning electron microscopy and TEM results indicate that the composite fibers consist of nanoparticles and porous carbon. The diameter of the nanosized particles increased from 100 to 500 nm with increasing reaction temperature. The nitrogen adsorption–desorption results also show that the composite fibers have a micro‐ and mesoporous structure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Yttrium incorporation in Cr2AlC: On the metastable phase formation and decomposition of (Cr,Y)2AlC MAX phase thin films

Herein we report on the synthesis of a metastable (Cr,Y)₂AlC MAX phase solid solution by co-sputtering from a composite Cr–Al–C and elemental Y target, at room temperature, followed by annealing. However, direct high-temperature synthesis resulted in multiphase films, as evidenced by X-ray diffraction analyses, room-temperature depositions, followed by annealing to 760°C led to the formation of phase pure (Cr,Y)₂AlC by diffusion. Higher annealing temperatures caused a decomposition of the metastable phase into Cr₂AlC, Y₅Al₃, and Cr-carbides. In contrast to pure Cr₂AlC, the Y-containing phase crystallizes directly in the MAX phase structure instead of first forming a disordered solid solution. Furthermore, the crystallization temperature was shown to be Y-content dependent and was increased by ∼200°C for 5 at.% Y compared to Cr₂AlC. Calculations predicting the metastable phase formation of (Cr,Y)₂AlC and its decomposition are in excellent agreement with the experimental findings.     

Thermal,stability, morphological,and conductivity characteristics of polypyrrole prepared in aqueous medium

The aqueous polymerization of pyrrole with varying FeCl₃/Py mol ratio produces black insoluble powders. IR characterization reveals the shifting of the N? H stretching band to higher frequency with increasing FeCl₃ amount in the feed composition due to lowering of intermolecular H-bonding. SEM shows a spongy texture of the polymer. TGA indicates the initial decomposition temperatures (180°–237°C) to be somewhat dependent on the FeCl₃/Py feed ratio. DSC suggests the glass-transition temperature to be in the range 160–170°C for the polymers prepared with various feed compositions. The conductivity is also dependent on the FeCl₃/Py feed composition and levels off at a value of ～3 ohm^?1cm^?1. © 1994 John Wiley & Sons, Inc.     

Microstructure and Microfabrication Considerations for Self‐Supported On‐Chip Ultra‐Thin Micro‐Solid Oxide Fuel Cell Membranes

La_0.6Sr_0.4Co_0.8Fe_0.2O_{3 – δ} (LSCF) has been sputtered on bare Si and Si₃N₄ and yttria‐stabilised zirconia (YSZ) thin films to investigate annealing temperature‐ and thickness‐dependent microstructure and functional properties, as well as their implications for designing failure‐resistant micro‐solid oxide fuel cell (μSOFC) membranes. The LSCF thin films crystallise in the 400–450 °C range; however, after annealing in the 600–700 °C range, cracks are observed. The formation of cracks is also thickness‐dependent. High electrical conductivity, ∼520 Scm^–1 at 600 °C, and low activation energy, ∼0.13 eV, in the 400–600 °C range, are still maintained for LSCF films as thin as 27 nm. Based on these studies, a strong correlation between microstructure and electrical conductivity has been observed and an annealing temperature‐thickness design space that is complementary to temperature‐stress design space has been proposed for designing reliable membranes using sputtered LSCF thin films. Microfabrication approaches that maintain the highest possible surface and interface quality of heterostructured membranes have been carefully examined. By taking advantage of the microstructure, microfabrication and geometrical structural considerations, we were able to successfully fabricate large‐area, self‐supported membranes. These results are also relevant to conventional or grid‐supported SOFC membranes using ultrathin nanocrystalline cathodes and μSOFCs using cathode thin films other than LSCF.     

Microwave sintering of IR-transparent Y2O3–MgO composite ceramics

A method for preparation of dense Y₂O₃–MgO composite ceramics by the microwave sintering was developed. The initial powders were obtained by glycine-nitrate self-propagating high-temperature synthesis (SHS) with different oxidant-to-fuel ratio. Density and IR-transmission of microwave sintered Y₂O₃–MgO ceramics increase with respect to dispersity of the SHS-powders and reach its maximum values for the powder prepared in a 20% fuel excess. The sintering behavior of Y₂O₃–MgO compacts was investigated by optical dilatometry and measuring an electric conductivity upon heating. Significant microwave radiation power surges at temperatures of 900–1000 °C, caused by the decomposition of magnesium carbonate, have been found. As a result of matching the conditions for the synthesis of powders and sintering modes, a transmission of composite ceramics of 78% at a wavelength of 6 μm was achieved at a maximum processing temperature of 1500 °C.     

High temperature dielectric properties of calcium zirconate

The electrical properties of dense, high purity CaZrO₃ discs, sintered at 1380°C with and without added ZrO₂, were investigated up to 950°C. Dielectric constant, loss tangent, and electrical conductivity were measured from 25 to 725°C, and the real and imaginary impedances were measured between 800 and 950°C by impedance spectroscopy techniques. Dielectric constant increased by 8% above 300°C and loss tangent increased from .1% at 25°C to ∼2% above 300°C. Activation energy of electrical conductivity determined between 300°C and 950°C by alternative current (AC) and direct current (DC) measurements. These results indicate that CaZrO₃ could be a useful dielectric material for capacitor applications up to 500°C. A reported decrease in conductivity due to addition of excess ZrO₂ into stoichiometric CaZrO₃ could not be confirmed.     

Effect of thermal aging on electrical conductivity of the 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid‐doped polyaniline fiber

The thermal characteristics of inherently conductive polyaniline (PANi) fiber have been studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Fibers show five major weight losses at ∼100°C, 165°C, 215°C, 315°C, and 465°C, which are associated with the removal of moisture, residual solvent, decompositions of the sulfonic acid and degradation of PANi fiber, respectively. The 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSA) that dopes the PANi (in fiber form) performs two‐stage decompositions. The conductivity of the drawn fibers aged at 50°C, 100°C, 150°C, and 190°C under vacuum for various periods of time decreases, particularly at temperatures higher than 100°C. The reduction in conductivity of the fiber aged at temperatures lower than 100°C is mainly due to the evaporation of the residual solvent (15–20% in the as‐spun fiber). Further decrease in conductivity of the fiber aged at temperatures higher than 100°C is caused by the decomposition of the dopant AMPSA. The temperature‐dependent conductivity of the fiber was measured at 15 K (−258.5°C) to 295 K (21.5°C). The conductivity of both aged and un‐aged fibers is all temperature activated, however, the conductivity of the un‐aged fibers is higher than that of the aged fibers. Although a negative temperature coefficient was observed in the temperature range from 240 K (–24.5°C) to 270 K (–3.5°C) for the un‐aged fibers, it was disappeared when the fibers were thermal aged at 100°C for 24 h in vacuum oven. These results indicate that the residual solvent trapped inside the fiber enhanced the electrical conductivity of the fibers and its “metallic” electrical conductivity at temperatures ∼263 K (–10°C). © 2001 John Wiley & Sons, Inc. † J Appl Polym Sci 79: 2503–2508, 2001     

Layered YSZ/SCSZ/YSZ Electrolytes for Intermediate Temperature SOFC Part I: Design and Manufacturing

(Sc₂O₃)_0.1(CeO₂)_0.01(ZrO₂)_0.89 (SCSZ) ceramic electrolyte has superior ionic conductivity in the intermediate temperature range (700–800 °C), but it does not exhibit good phase and chemical stability in comparison with 8 mol% Y₂O₃–ZrO₂ (YSZ). To maintain high ionic conductivity and improve the stability in the whole electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed. Because of a mismatch of coefficients of thermal expansion and Young's moduli of SCSZ and YSZ phases, upon cooling of the electrolytes after sintering, thermal residual stresses will arise, leading to a possible strengthening of the layered composite and, therefore, an increase in the reliability of the electrolyte. Laminated electrolytes with three, four, and six layers design were manufactured using tape‐casting, lamination, and sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at ∼30 μm, the thickness of the SCSZ inner layer varied from ∼30 μm for a Y–SC–Y three‐layered electrolyte, ∼60 μm for a Y–2SC–Y four‐layered electrolyte, and ∼120 μm for a Y–4SC–Y six‐layered electrolyte. The microstructure, crystal structure, impurities present, and the density of the sintered electrolytes were characterized by scanning and transmission electron microscopy, X‐ray and neutron diffraction, secondary ion mass spectroscopy, and water immersion techniques.