Kinetics and mechanism of the K2CrO4?NaAsO2 redox‐initiated aqueous polymerization of acrylonitrile

The kinetics and mechanism of acrylonitrile polymerization initiated by a redox pair [potassium chromate (K₂CrO₄) and sodium arsenite (NaAsO₂)] were studied. The overall rate of polymerization was proportional to √[K₂CrO₄] × [NaAsO₂], and the energy of activation was approximately 10.5 kJ/mol. Polyacrylonitrile was recovered as a coagulum in the medium. The formation of polyacrylonitrile was confirmed with Fourier transform infrared and ¹H‐NMR analyses. Scanning electron microscopy analysis of the polymer revealed the formation of aggregates of polymer particles (3–67 nm). Thermogravimetric studies indicated 50% weight loss at 400°C, and dynamic thermal analysis scan studies revealed an exothermic peak at 507°C due to massive oxidative thermal degradation of the polyacrylonitrile backbone. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 276–280, 2005     

Novel Supramolecular Square Grid-Like Structure: Synthesis and Characterization of [(Me3Sn)2CrO4]

Reactions of K₂Cr₂O₇ and K₂CrO₄ with Me₃SnCl yielded [(Me₃Sn)₂CrO₄] (1) and [(Me₃Sn)₂CrO₄?(Me₃SnOH)] (2), respectively, which were characterized by elemental analysis, ¹H-NMR spectroscopy, and an X-ray diffraction study. Compound 1 shows a novel square grid-like structure consisting of CrO₄ ^2? and Me₃Sn⁺ ions, whereas 2 exhibits a three-dimensional structure composed of CrO₄ ^2?, Me₃Sn⁺, and [(Me₃Sn)₂SnOH]⁺ ions.     

Composite screen‐printed thick films for high dielectric constant devices: Bi4Ti3O12–CaCu3Ti4O12 films

In this paper, we did a study of the effect of the presence of BIT (Bi₄Ti₃O₁₂) in the dielectric and optical properties of the CaCu₃Ti₄O₁₂ (CCTO) thick films. The films were prepared by the solid sate procedure. Mechanical alloying followed by the solid state procedure has been used successfully to produce powders of CaCu₃Ti₄O₁₂ (CCTO) and BIT (Bi₄Ti₃O₁₂) to be used in the composites. We also look at the effect of the grain size of the BIT and CCTO in the final properties of the composite film. The samples were studied using X‐Ray diffraction, scanning electron microscopy (SEM), Raman and infrared spectroscopy. We also did a study of the dielectric function (K) and dielectric loss (D) of the films. The role played by the grain size of CCTO and BIT in the dielectric constant and structural properties of the films are discussed. These measurements confirm the potential use of such materials for small high dielectric planar devices. These films are also attractive for capacitor applications and certainly for microelectronics, microwave devices (mobile phones for example), where the miniaturization of the devices is crucial. POLYM. COMPOS., 28:771–777, 2007. © 2007 Society of Plastics Engineers     

Magnetic anisotropy of (100)- and (110)-oriented epitaxial CrO2 films grown on SnO2- the effects of strain and interface

The crystal structures and magnetic properties of CrO₂ films of different orientations and thicknesses grown on SnO₂ were investigated and compared with those on TiO₂. Results reveal that large anisotropic strains were found in (100) films, but only small strains existed in (110) films. The magnetic anisotropies of CrO₂ (110) films on SnO₂ and TiO₂ were found to be similar. As for CrO₂ (100) films, magnetic anisotropies were quite different-at the same thickness, the magnetic anisotropy of the film on SnO₂ substrate was higher than that on TiO₂. However, the easy axes of the films were found to be always along c axis even at very small thickness, and no easy axis switching was observed. First-principle calculations reveal that magnetic anisotropy energy is not only concerned with anisotropic strain but also with the substrate. The competition between the anisotropic preference of interface and the effect of strains may be one important factor for determining the actual easy axis direction. The combined effects of strain and interface may also be one reason for the magnetic anisotropic difference between CrO₂ (100) films on SnO₂ and TiO₂.     

Effect of ethylene carbonate on properties of PVP-CsAlO2-LiClO4 solid polymer electrolytes

ABSTRACT

Solid polymer electrolytes (SPEs) have been widely studied due to its extensive applications in high energy rechargeable batteries, supercapacitors, fuel cells, photoelectrochemical and electrochromic displays. Herein, SPEs based on polyvinyl pyrrolidone (PVP) doped with cesium aluminate (CsAlO₂) nanoparticles (NPs), lithium perchlorate (LiClO₄) as an electrolyte and varying amounts viz., 2, 4, 6 and 8 wt.% of ethylene carbonate (EC) as plasticizer have been fabricated by solution intercalation technique. The structural features of PVP-CsAlO₂-LiClO₄-EC SPEs have been studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The morphology of PVP-CsAlO₂-LiClO₄-EC SPEs has been examined by scanning electron microscopy (SEM). The thermal properties of the SPEs were characterized by the thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC) techniques. The TGA and DSC results revealed that a significant reduction in thermal stability and glass transition temperature (T_g) of PVP with an increase in EC content in SPE films. The optoelectrical properties of PVP-CsAlO₂-LiClO₄-EC SPE films have been evaluated using UV–visible spectroscopy. The band gap energy (E_g) was found to decrease with an increase in EC content, exhibiting a minimum of 4.23 eV for PVP-8 wt.% CsAlO₂-15 wt.% LiClO₄-8 wt.% EC. This could be ascribed to the formation of localized states and increased degree of disorder in the PVP-CsAlO₂-LiClO₄ SPE films. The integrated plasticizers increase the values of refractive index (RI), optical conductivity, and dielectric constants of PVP-CsAlO₂-LiClO₄ SPE films. The AC conductivity of the SPEs has been evaluated at room temperature using digital LCR meter in the frequency range 100 Hz – 5 MHz. The conductivity strongly depends on CsAlO₂ NPs and EC plasticizer content in SPEs.     

Development and Study of Solid Polymer Electrolyte Based on Polyvinyl Alcohol: Mg(ClO4)2

Magnesium ion-conducting solid polymer electrolytes consisting of polyvinyl alcohol with magnesium perchlorate (Mg(ClO₄)₂) as electrolytic salt have been developed and their experimental investigations are reported. The solid polymer electrolytes have been prepared by well-known solution casting method using double-distilled water as a solvent. The highest room temperature conductivity of the order of 10^?4 S cm^?1 was obtained for the solid polymer electrolyte with the composition 80?mol% polyvinyl alcohol:20?mol% Mg(ClO₄)₂. The pattern of the temperature-dependent conductivity shows Arrhenius behavior. The Fourier transform infrared spectroscopy analysis confirms the complex formation of the polymer with the salt. The X-ray diffraction results reveal that the crystalline phase of polymer host has completely changed on the addition of dopant. Differential scanning calorimetry studies show a decrease in melting temperature of the polyvinyl alcohol with the increasing dopant concentration. The real part of dielectric permittivity shows a strong dispersion at lower frequencies, which implies the space charge effects arising from the electrodes. The loss tangent spectrum reveals that the jumping probability per unit time decreases with the increasing salt concentration. The total ionic transference number measured has been found to be in the range of 0.92–0.94 for all the polymer electrolyte systems. The result reveals that the conducting species are predominantly ions. The solid polymer electrolyte with highest conductivity showed an electrochemical stability of 2?V. The results obtained by cyclic voltammetry on stainless steel/solid polymer electrolyte/stainless steel, Mg/solid polymer electrolyte/Mg symmetrical cells show evidence for reversibility.     

The optical properties of PVA/TiO2 composite nanofibers

The electrospun nanofibers emerge several advantages because of extremely high specific surface area and small pore size. This work studies the effect of PVA nanofibers diameter and nano‐sized TiO₂ on optical properties as reflectivity of light and color of a nanostructure assembly consisting polyvinyl alcohol and titanium dioxide (PVA/TiO₂) composite nanofibers prepared by electrospinning technique. The PVA/TiO₂ composite spinning solution was prepared through incorporation of TiO₂ nanoparticles as inorganic optical filler in polyvinyl alcohol (PVA) solution as an organic substrate using the ultrasonication method. The morphological and optical properties of collected composites nanofibers were highlighted using scanning electron microscopy (SEM) and reflective spectrophotometer (RS). The reflectance spectra indicated the less reflectance and lightness of composite with higher nanofiber diameter. Also, the reflectance and lightness of nanofibers decreased with increasing nano‐TiO₂ concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Novel Supramolecular Square Grid-Like Structure: Synthesis and Characterization of [(Me3Sn)2CrO4]

Reactions of K₂Cr₂O₇ and K₂CrO₄ with Me₃SnCl yielded [(Me₃Sn)₂CrO₄] (1) and [(Me₃Sn)₂CrO₄(Me₃SnOH)] (2), respectively, which were characterized by elemental analysis, ¹H-NMR spectroscopy, and an X-ray diffraction study. Compound 1 shows a novel square grid-like structure consisting of CrO₄ ^2– and Me₃Sn⁺ ions, whereas 2 exhibits a three-dimensional structure composed of CrO₄ ^2–, Me₃Sn⁺, and [(Me₃Sn)₂SnOH]⁺ ions.     

Planar model system for olefin polymerization: the Phillips CrO x /SiO2 catalyst

A planar CrO _x /SiO₂/Si(100) model for the Phillips ethylene polymerization catalyst has been prepared by spincoat impregnation from an aqueous solution of CrO₃. The model catalyst polymerizes ethylene from the gas phase at 160°C with a constant activity and forms a 400 nm thick layer of polyethylene in 1 h. The superior definition of the polymer films produced on this catalyst and the control over the distribution of active sites on its flat surface make this model catalyst an ideal substrate for kinetic studies on catalytic polymerization and for morphologic studies of the polymer product by scanning force microscopy. At extremely low catalyst loading we observe isolated polymer islands formed on single chromium sites. The work also opens attractive opportunities for future studies of nascent morphology of catalytically formed polymers. This revised version was published online in June 2006 with corrections to the Cover Date.     

Freestanding Ag2S/CuS PVA films with improved dielectric properties for organic electronics

The prime goal of this work is to synthesize free‐standing polyvinyl alcohol (PVA) films doped with Ag₂S, CuS, Ag₂S/CuS alloy, and Ag₂S/CuS nanocomposites through the sol–gel route. The dependence of Ag₂S content in the PVA nanocomposite films on both the real and imaginary parts of the complex permittivity and loss tangent values was examined. An enhanced dielectric constant was achieved with minimum dielectric loss due to the insulating silica layer. By changing the Ag₂S content in Ag₂S/CuS PVA films, the AC conductivity is improved with pure Ag₂S nanoparticles exhibiting highest values of the order of 10^?6?10^?9 S/cm. The Cole–Cole parameters were calculated and the semicircles observed in the plots indicate a single relaxation process. The results suggest that these composite films are potential materials for embedded capacitor applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43568.     

Temperature dependent dielectric properties of self‐standing and flexible poly(vinylidene fluoride) films infused with Er3+ doped GeO2 and SiO2 nanoparticles

The synthesis of Er³⁺@GeO₂ and Er³⁺@SiO₂ nanoparticle impregnated self‐standing poly(vinylidene fluoride) films by a facile solution casting technique has been reported. The prepared films were thoroughly characterized using X‐ray diffraction technique, field emission scanning electron microscopy, and transmission electron microscopy. The optical properties were evaluated using UV–Vis spectroscopy. Detailed study on the temperature dependent dielectric properties of the composite films with different Er³⁺ content were also investigated to establish the electrical properties of the same, which revealed the presence of different relaxation processes, namely, and ρ. Due to the smaller size, Er³⁺@SiO₂ was found to disperse better in the PVDF matrix than Er³⁺@GeO₂, which resulted in higher dielectric constant of the former at 300 K. At higher temperature (403 K), the behavior was reversed due to the formation of larger sized low mobility complexes. An investigation on ac conductivity proved the conduction mechanism for neat as well as composite PVDF films to follow the Correlated Barrier Hopping model. The loading of Er³⁺@GeO₂ and Er³⁺@SiO₂ nanoparticles in the PVDF matrix significantly enhances the dielectric properties without losing the flexibility of the composite films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44016.     

High dielectric permittivity and percolative behavior of polyvinyl alcohol/potassium dihydrogen phosphate composites

A new kind of anhydrous, transparent, and flexible potassium dihydrogen phosphate (KH₂PO₄ or KDP)/polyvinyl alcohol (PVA) composite in the form of film (0.10 mm) has been prepared by solution casting technique. KDP is well dispersed in the polymer matrix as observed from the microstructural studies. Frequency and temperature dependent dielectric properties of the composites have been studied with varying KDP concentrations. The PVA/KDP composite films exhibited extraordinarily high relative permittivity ε′ ∼ 430 (80 times higher compared with pure PVA and even higher than KDP) near the percolation threshold (ϕ_C = 2.5 wt % KDP) with low dielectric losses (∼ 0.15) at 1 kHz and room temperature. Such flexible, low loss and high dielectric permittivity material has enormous importance for application in devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and electrical properties of nitrile‐containing polyimide/BaTiO3 composite films

Polyimide composite films were prepared by mixing the BaTiO₃ particles into poly(amic acid) solution followed by film casting and thermal imidization under controlled temperature conditions. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(4‐aminophenoxy)benzonitrile, using N‐methyl‐2‐pyrrolidone as solvent. The surface of BaTiO₃ particles was modified by treating with an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to characterize the structure and properties of the composites. The influence of BaTiO₃ content on the composite film properties was evidenced. The films exhibited good thermal stability having the initial decomposition temperature above 520°C. They had stable dielectric properties over large intervals of temperature and frequency. The dielectric constant and the dielectric loss increased with the increase of BaTiO₃ content. The dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions γ and β. At higher temperature an α‐relaxation that corresponds to the glass transition and a conductivity process were evidenced. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Investigation on inhibition of CrO4 2− and MoO4 2− ions on carbon steel pitting corrosion by electrochemical noise analysis

The inhibition effect of chromate (CrO₄ ^2–) and molybdate (MoO₄ ^2–) anions on the pitting corrosion of 16Mn carbon steel in 0.1 M NaCl containing bicarbonate solution was studied based on electrochemical noise analysis (ENA) and the potentiodynamic polarization method. The experimental results indicated that, once the pits occur on the surface of the carbon steel after 4–6 h of immersion, increasing the concentration of CrO₄ ^2– and MoO₄ ^2– ions accelerate the repassivation process, and attenuate the duration and the nucleation rate of metastable pits. Further analysis demonstrated that noise resistance R _n might not be suitable for the evaluation of the inhibition efficiency of CrO₄ ^2– and MoO₄ ^2– anions on pitting corrosion in the present system. However, the transient charge q _pit, which is an integral of all current transients during a certain period, can characterize the inhibition performance on pitting corrosion. A new definition of inhibition efficiency based on q _pit is given.     

Thermal and morphological studies on γ‐Fe2O3 polystyrene composites and the affect of additives

γ‐Fe₂O₃polystyrene (PS) composite films were prepared by a gel‐casting technique to obtain monodisperse composite films. To understand the effect of additives on the prepared composite films, additives such as rice husk ash and thiourea were made to disperse into the PS matrix. The as‐prepared γ‐Fe₂O₃ PS composite films, along with their additives, were subjected to characterization and study by X‐ray diffraction, scanning electron microscopy, thermal, IR, and dielectric measurement techniques. These studies showed monodisperse and chemically homogenous composite films with an increase in thermal behavior. An interesting self‐assembly of rod‐like nanoparticles of γ‐Fe₂O₃ particles into the polymer matrix, which formed spherical packets, was observed for the γ‐Fe₂O₃PS composite film. The electrical behavior of these films was interesting, as some showed conduction whereas others showed an increase in dielectric behavior. This nature was explained by the dielectric measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 778–788, 2004     

The tunability in (Ba,Sr)TiO3–Mg2TiO4 system

(Ba, Sr)TiO₃–Mg₂TiO₄ composite ceramics were fabricated via solid-state reaction method. X-ray diffraction, scanning electron microscopy and Raman spectroscopy were used to characterize the phase compositions and microstructures. The dielectric characteristics and tunability of composite ceramics were investigated. Depending on the tunability, the composition of (Ba, Sr)TiO₃–Mg₂TiO₄ can be divided into three regions: initial decreasing region, unusual increasing region and final decreasing region. This unusual increased tunability is due to electric field redistribution caused by composite effect, that is proved by the simulation result. Moreover, the change of Curie temperature also has a great impact on the tunability in this region.     

Development of Multiferroism in PVDF with CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles

Thin films of some polymer-ceramic nanomultiferroic composites (in 0–3 connectivity) of compositions (1-x) PVDF-xCoFe₂O₄ (x?=?0.05, 0.1, 0.5) have been fabricated through a solution casting route. Based on X-ray diffraction pattern and data, basic crystal structure and unit cell parameters were obtained. The surface morphology of the materials was studied using a scanning electron microscopy (SEM) technique. Structural investigation confirms the presence of a polymeric electro-active β-phase of matrix (PVDF) and nano filler spinel phase of the incorporated nano-ceramics. The observed SEM micrographs confirm that the nanoparticles are well distributed in the PVDF matrix without any agglomeration with a lesser spherulitic microstructure. The flexible nano-composites fabricated with polymer (PVDF) and CoFe₂O₄ provide high permittivity (relative dielectric constant) and low loss tangent. An impedance spectroscopy (IS) technique was employed to study the effect of grain and grain boundary in the resistive properties of the composite materials in terms of electric circuit. The study of AC conductivity as a function of frequency follows Jonscher’s power law. The improved conductivity and dielectric, magnetic, and measured first-order magnetoelectric coefficients suggest some promising applications in the embedded capacitors as well as in multifunctional devices.     

High-temperature stability and leaching kinetics of the hexavalent chromium compound,chrome-hauyne (Ca4Al6CrO16)

Cr-refractories usually contain Cr(III) compounds that can convert into carcinogenic Cr(VI) compounds such as CaCrO₄ and Ca₄Al₆CrO₁₆ under alkaline and oxygen-rich conditions. Literature provides insight into the characteristics, thermal stability, and aqueous solubility of CaCrO₄, while there is hardly any data available on Ca₄Al₆CrO₁₆. The present paper comprehensively studied high-temperature stability and leaching kinetics and other characteristics of Ca₄Al₆CrO₁₆ by using high-temperature XRD, TG-DSC, XPS, Raman, and TRGS 613. XPS confirmed that chromium in Ca₄Al₆CrO₁₆ is present in the +6 oxidation state. Ca₄Al₆CrO₁₆ is thermally stable up to 1500 °C in the air but decomposes in nitrogen above 1258 °C to form the Cr³⁺-containing phases CaCr₂O₄ and Ca₆Al₄Cr₂O₁₅. The Ksp of Ca₄Al₆CrO₁₆ in deionized water is 1.0381 × 10⁻²², 4.5723 × 10⁻²¹ and 2.3489 × 10⁻²⁰ at 12, 25, and 40 °C, respectively. The leaching process of Ca₄Al₆CrO₁₆ is chemical reaction controlled, with an apparent activation energy of 58.78 kJ/mol.     

Ru-Promoted CrO x /Al2O3 Catalyst for the Low-Temperature Oxidative Decomposition of Trichloroethylene in Air

A series of Ru-promoted CrO _x /Al₂O₃ as catalysts for the low-temperature oxidative decomposition of trichloroethylene (TCE) were characterized and evaluated in comparison with an unpromoted CrO _x /Al₂O₃ catalyst. Catalyst characterization was conducted by surface area measurement, X-ray diffraction and X-ray photoelectron spectroscopy. Catalyst performance in the TCE decomposition reaction was evaluated with respect to the initial catalytic activity, the rate of catalyst deactivation, and the product concentrations of CO and Cl₂ under dry or wet air conditions. The presence of a small amount of Ru, as much as 0.4 wt% in a CrO _x /Al₂O₃ catalyst, brought about several beneficial effects on the catalytic reaction performance. As compared with the unpromoted CrO _x /Al₂O₃, this Ru-promoted CrO _x /Al₂O₃ catalyst showed enhanced catalytic activity (249 versus 264 °C in terms of temperature at which 50% of TCE conversion occurred), a reduced concentration of CO (180 versus 325 ppm) in the product, and a decreased propensity to deactivation. Performance improvements of the Ru-promoted CrO _x /Al₂O₃ catalyst were thought to originate from its enhanced oxidation activity due to the coexisting highly-dispersed Ru oxides rendering less active Cr(III) to more active Cr(VI), and facilitating the process of supplying activated oxygen for the reaction system.     

Synthesis of La2NiO4 via a PVA-based route

Single-phase La₂NiO₄ has been prepared using polyvinyl alcohol (PVA) as a complexing agent. Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to characterize precursor and derived oxide powders. The particle size and morphologies of La₂NiO₄ crystallites were characterized by field emission scanning electron microscope (FSEM). The effect of the mol ratios of metal ion to hydroxyl groups in polyvinyl alcohol on the formation of La₂NiO₄ was investigated. XRD analysis showed that single-phase and well-crystallized La₂NiO₄ was obtained from precursor with M/OH = 1:3 at 900 °C. The La₂NiO₄ ceramics sintered at 1300 °C for 4 h exhibits an electrical conductivity of 42.5 Ω⁻¹ cm⁻¹ at room temperature.