Electrical and thermal properties of γ‐irradiated nitrile rubber/rice husk ash composites

The effects of both the rice husk ash (RHA) loading and fumed silica (FS) loading on the structure, thermal stability, and electrical properties of acrylonitrile–butadiene rubber (NBR) composites were studied. The filler loading were chosen to be 5 and 20 phr for RHA and 5 and 30 phr for silica. Also, the effect of the γ‐irradiation dose (25 kGy) on these parameters was investigated. The structure and thermal stability were studied with X‐ray diffraction and thermogravimetric analysis techniques. Furthermore, some electrical parameters, such as the direct‐current electrical conductivity (σ_dc), activation energy (E_a), dielectric constant (?′), and dielectric loss (?″), were determined. The incorporation of both RHA and FS resulted in improved thermal stability after γ irradiation at 25 kGy. The loading of FS on NBR was shown to decrease σ_dc, ?′, and ?″ and increase E_a. On the other hand, the loading of RHA showed the opposite trend. Finally, γ irradiation of NBR composites filled with both fillers decreased the values of σ_dc, ?′, and ?″ for all the samples, which followed the trend for the unirradiated composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

One‐pot synthesis of a few nanocomposites with poly(N‐vinylcarbazole) and CdS,Ag, Pd50–Ag50, and Pt50–Ru50 nanoparticles with γ irradiation

The one‐pot synthesis of nanocomposites of a conductive poly(N‐vinylcarbazole) (PVK) with CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles was performed with γ irradiation in a tetrahydrofuran–water mixture (3/1 vol %). For comparison, the CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles were also prepared with γ irradiation with polyvinylpyrrolidone as a stabilizer. Ultraviolet–visible spectroscopy, transmission electron microscopy, X‐ray diffraction analysis, and photoluminescence spectroscopy were used for the characterization of CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles and nanocomposites of PVK with CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles. The absorption spectrum of the CdS‐nanoparticle‐based composite revealed a quantum confinement effect. The emission spectrum of the composite with CdS nanoparticles and PVK indicated the block effect of PVK for surface recombination. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1809–1815, 2006     

Improvement of compatibility of poly(ethylene terephthalate) and poly(ethylene octene) blends by γ‐irradiation

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene octene) (POE) were prepared by melt blending with various amounts of trimethylolpropane triacylate (TMPTA). The mechanical properties, phase morphologies, and gel fractions at various absorbed doses of γ‐irradiation have been investigated. It was found that the toughness of blends was enhanced effectively after irradiation as well as the tensile properties. The elongation at break for all studied PET/POE blends (POE being up to 15 wt %) with 2 wt % TMPTA reached 250–400% at most absorbed doses of γ‐irradiation, approximately 50–80 times of those of untreated PET/POE blends. The impact strength of PET/POE (85/15 wt/wt) blends with 2 wt % TMPTA irradiated with as little as 30 kGy absorbed dose exceeded 17 kJ/m², being approximately 3.4 times of those of untreated blends. The improvement of the mechanical properties was supported by the morphology changes. Scanning electron microscope images of fracture surfaces showed a smaller dispersed phase and more indistinct inter‐phase boundaries in the irradiated blends. This indicates increased compatibility of PET and POE in the PET/POE blends. The changes of the morphologies and the enhancement of the mechanical properties were ascribed to the enhanced inter‐phase boundaries by the formation of complex graft structures confirmed by the results of the gelation extraction and Fourier Transform Infrared analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Properties of biodegradable hydrogels prepared by γ irradiation of microbial poly(ϵ-lysine) aqueous solutions

Poly(?-lysine) (PL) hydrogels have been prepared by means of γ irradiation of PL produced by Streptomyces albulus in aqueous solutions. When the dosage of γ irradiation was 70 kGy or more and the concentration of PL in water was 1–7 wt %, transparent hydrogels (opaque hydrogels for 1–3 wt % PL concentration) could be produced. In the case of 70 kGy of γ irradiation and 5 wt % PL concentration, the specific water content (wt of absorbed water/wt of dry hydrogel) of the PL hydrogel was approximately 160. Specific water contents of PL hydrogels decreased markedly with an increase in the dosage of γ irradiation. The specific water contents were increased with an increase in PL concentration in the irradiated solution. This result indicates the presence of a radical scavenger in the PL solution. Swelling equilibria of PL hydrogels were measured in water or in aqueous solutions of various pHs or concentrations of NaCl, Na₂SO₄, and CaCl₂. Under acid conditions, the PL hydrogel swelled due to the ionic repulsion of the protonated amino groups in the PL molecules. The degree of deswelling in electrolyte solution was smaller than that of other ionic hydrogels [poly(γ-glutamic acid), poly(acrylic acid) etc.]. In addition, the enzymatic degradations of PL hydrogel were studied at 40°C and pH 7.0 in an aqueous solution of the neutral protease [Protease A (Amano)] produced from Aspergillus oryzae. The rate of enzymatic degradation of the respective PL hydrogels was much faster than the rate of simple hydrolytic degradation. The rate of enzymatic degradation decreased with the increase in γ-irradiation dose during preparation of the PL hydrogel. © 1995 John Wiley & Sons, Inc.     

Thermal decomposition behavior of γ‐irradiated poly(vinyl acetate)/poly(methyl methacrylate) miscible blends

Miscible polymer blends based on various ratios of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were prepared in film form by the solution casting technique using benzene as a common solvent. The thermal decomposition behavior of these blends and their individual homopolymers before and after γ‐irradiation at various doses (50–250 kGy) was investigated. The thermogravimetric analysis technique was utilized to determine the temperatures at which the maximum value of the rate of reaction (T_max) occurs and the kinetic parameters of the thermal decomposition. The rate of reaction curves of the individual homopolymers or their blends before or after γ‐ irradiation displayed similar trends in which the T_max corresponding to all polymers was found to exist in the same position but with different values. These findings and the visual observations of the blend solutions and the transparency of the films gave support to the complete miscibility of these blends. Three transitions were observed along the reaction rate versus temperature curves; the first was around 100–200°C with no defined T_max, which may arise from the evaporation of the solvent. The second T_max was in the 340–380°C range, which depended on the polymer blend and the γ‐irradiation condition. A third transition was seen in the rate of reaction curves only for pure PVAc and its blends with PMMA with ratios up to 50%, regardless of γ‐ irradiation. We concluded that γ‐irradiation improved the thermal stability of PVAc/PMMA blends, even though the PMMA polymer was degradable by γ irradiation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1773–1780, 2006     

A comparative study of the lattice structure,optical band gap,electrical conductivity and polarization at different stages of the heat treatment of chemical routed Al(OH)3

Aluminium hydroxide (Al(OH)₃) was prepared by chemical reaction of the Al(NO₃)₃ in alkaline medium. The as-prepared powder was heated in the temperature range 250 °C to 1250 °C for studying the structural phase transformation at different stages of the heat treatment. The synchrotron x-ray diffraction patterns confirmed a structural transformation of Al(OH)₃ through different (Boehmite, γ, θ, δ, and α) polymorphic phases of Al₂O₃ on increasing the heat treatment temperature. The samples in Boehmite (γ-AlOOH) and α- Al₂O₃ phases showed Raman active modes, whereas the intermediate (meta-stable) multi-phased structure showed weak Raman active peaks. The analysis of UV–visible spectra of the samples indicated two optical band gap energy values in the high energy range 4.50–4.73 eV and low energy range 3.06–3.84 eV. The voltage dependence of current, capacitance and electrical polarization were recorded to study electrical properties in heat treated samples. The capacitance value, derived from the polarization, showed a usual increasing trend on decreasing the measurement frequency (inverse of the time) of driving electric voltage. The measured electrical polarization in the samples was found to be highly correlated to their electrical conductivity and the results are helpful to understand the role of electrical conductivity on exhibiting the apparently ferroelectric properties in high conductive and low polarizable dielectric oxides.     

Tensile properties of polypropylene flame-retardant composites

The polypropylene (PP) flame-retardant composites filled with aluminum hydroxide (Al(OH)₃), magnesium hydroxide (Mg(OH)₂), zinc borate (ZB), nanometer calcium carbonate (nano-CaCO₃), and polyolefin elastomer (POE) were prepared using a twin-screw extruder, and the tensile properties were measured at room temperature by means of an electronic universal test machine (Model CMT4104) in this paper, to identify the influence of the flame-retardant content on the tensile properties. The results showed that the tensile strength decreased roughly nonlinearly while the tensile elongation at break decreased nonlinearly with increasing the flame-retardant weight fraction. The Young’s modulus and the tensile fracture strength increased nonlinearly with an addition of the flame-retardant weight fraction. The tensile ductility of PP/Al(OH)₃/Mg(OH)₂/ZB/Nano-CaCO₃/POE composite was the best in the three kinds of the composite systems. Moreover, good agreement was showed between the predictions and the measurements of the tensile strength.     

Structure Property Relationship in BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–NiO X8R System

A novel BaTiO₃–Na_0.5Bi_0.5TiO₃–Nb₂O₅–NiO (BT‐NBT‐Nb‐Ni) system that meets the X8R specification (?55°C–150°C, ΔC/C≤±15%) of multilayer ceramic capacitors (MLCCs) was fabricated, with a maximum dielectric constant of 2350 at room temperature (25°C). Core–shell microstructure was observed by transmission electron microscopy (TEM), accounting for the good dielectric temperature stability. The role of Ni on the formation of core–shell structure and phase structure, and the subsequent relationship between structure and dielectric/ionic conduction properties were investigated. It was observed that the addition of Ni could adjust the ratio of core/shell, and significantly reduces the dielectric loss over the studied temperature range. A new Ba₁₁(Ni, Ti)₂₈O_66+x phase with a 10‐layer close‐packed structure was identified by X‐ray diffraction (XRD), serving as a source of oxygen vacancies for ionic conduction in addition to Ba(Ni,Ti)O₃. Furthermore, the impedance spectroscopy measurements demonstrated the remarkable impact of these Ni‐induced oxygen vacancies on both the grain and grain‐boundary conductivities.     

Synthesis and Thermal,Structural, Dielectric,Magnetic and Magnetoelectric Studies of BiFeO3‐MgFe2O4 Nanocomposites

Spinel–perovskite magnetoelectric (ME) nanocomposites xMgFe₂O₄–(1?x)BiFeO₃, x = 0.1, 0.2, 0.3, and 0.4 were synthesized by sol‐gel method and characterized by differential thermal analysis, X‐ray diffraction analysis, dielectric and magnetic measurements. The samples were calcined at various temperatures and then the effect of annealing temperature on structural and magnetic properties was studied. From transmission electron microscopy, the average crystal size was found to be 30–50 nm. The magnetic behavior is found to be dependent on annealing temperature and magnesium ferrite content. The dielectric behavior with frequency and temperature has been modified with the induction of magnesium ferrite. The relative change of dielectric constant with magnetic field was observed in the nanocomposites. This relative change of magnetic field‐induced dielectric constant can also be expressed by Δε ~ γM² (where γ is magnetoelectric coupling coefficient).     

Dielectric properties of SrTiO3/POE flexible composites for microwave applications

Composites fabricated with SrTiO₃ ceramic filler dispersed inside a thermoplastic polyolefin elastomer (POE) polymer matrix, with excellent dielectric properties and good flexibility, have been studied in this paper. The relative permittivity of SrTiO₃/POE composites blended with different volume fraction of ceramic filler was investigated as a function of temperature and frequency. The results indicated that with the increase of ceramic filler, both the relative permittivity and the dissipation factor of composites increased. Good frequency stability within a wide range was observed in all the samples. The theoretical dielectric constant obtained from the effective medium theory of Bruggeman's model is in good agreement with the experimental data. For the composites containing 40 vol.% SrTiO_3, the dielectric constant and the loss tangent were 11.0 and 0.01 at 900 MHz, respectively, while the mechanical test results showed good flexibility on the final quality of the composites with the elongation of 90%. This indicates that the ST/POE composites have the promising characteristics for potential applications in the flexible dielectric waveguide and related flexible microwave devices.     

Ferroelectric and magnetic properties in (1−x)BiFeO3–x(0.5CaTiO3–0.5SmFeO3) ceramics

Multiferroic ceramics were prepared and characterized in (1?x)BiFeO₃–x(0.5CaTiO₃–0.5SmFeO₃) system by a standard solid‐state reaction process. The structure evolution was investigated by X‐ray diffraction and Raman spectrum analyses. The refinement results confirmed the different phase assemblages with varying amounts of polar rhombohedral R3c and nonpolar orthorhombic Pbnm as a function of the substitution content. In the compositions range of 0.2≤x≤0.5, polar R3c and nonpolar Pbnm coexisted, which was referred to polar‐to‐nonpolar morphotropic phase boundary (MPB). According to the dielectric and DSC analysis results, the ceramics with x≤0.2 changed to diffused ferroelectric, and the ferroelectric properties were enhanced significantly. Two dielectric relaxations were detected in the temperature range of 200‐300 K and 500‐700 K, respectively. The high‐temperature dielectric relaxation was attributed to the grain‐boundary effects. While the low temperature dielectric relaxation obtained in the samples with x=0.3‐0.5 was related to the charge transfer between Fe²⁺ and Fe³⁺. The magnetic hysteresis loops measured at different temperature indicated the enhanced magnetic properties in the present ceramics, which could be attributed to the suppressed cycloidal spin magnetic structure by Ti ions. In addition, the rare‐earth Sm spin moments might also affect the magnetic properties at relatively lower temperature.     

Dynamic mechanical properties and morphology of high‐density polyethylene/CaCO3 blends with and without an impact modifier

Dynamic mechanical analysis and differential scanning calorimetry were used to investigate the relaxations and crystallization of high‐density polyethylene (HDPE) reinforced with calcium carbonate (CaCO₃) particles and an elastomer. Five series of blends were designed and manufactured, including one series of binary blends composed of HDPE and amino acid treated CaCO₃ and four series of ternary blends composed of HDPE, treated or untreated CaCO₃, and a polyolefin elastomer [poly(ethylene‐co‐octene) (POE)] grafted with maleic anhydride. The analysis of the tan δ diagrams indicated that the ternary blends exhibited phase separation. The modulus increased significantly with the CaCO₃ content, and the glass‐transition temperature of POE was the leading parameter that controlled the mechanical properties of the ternary blends. The dynamic mechanical properties and crystallization of the blends were controlled by the synergistic effect of CaCO₃ and maleic anhydride grafted POE, which was favored by the core–shell structure of the inclusions. The treatment of the CaCO₃ filler had little influence on the mechanical properties and morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3907–3914, 2007     

Mechanical properties and fracture morphology of Al(OH)3/polypropylene composites modified by PP grafting with acrylic acid

Al(OH)₃/polypropylene (PP) composites modified by polypropylene grafted with acrylic acid (FPP) were prepared by melt extrusion. Effect of PP grafting with acrylic acid on mechanical properties and fracture morphology of Al(OH)₃/polypropylene composites were investigated. Although incorporation of Al(OH)₃ reduced the mechanical properties of PP, addition of FPP increased the mechanical properties of Al(OH)₃/PP composites. It is suggested that addition of FPP improve the dispersion of Al(OH)₃ and the interfacial interaction between filler and matrix. Mechanical properties of Al(OH)₃/FPP/PP composites depend on the grafting rate and the content of FPP. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2617–2623, 2001     

Property transitions in high‐density polyethylene/maleated poly(ethylene–octene)/calcium carbonate ternary composites

Ternary composites of high‐density polyethylene (HDPE)/maleated poly(ethylene–octene) (POE‐g)/calcium carbonate (CaCO₃) were prepared by the melt extrusion process. Crystallization behavior investigation and mechanical properties study showed that there existed a transition in both crystallization temperature (T_c) and impact strength of ternary composites. These transitions were attributed to the development of morphology, with variation of concentration of POE‐g in ternary composites. The strength of interfacial adhesion also influenced the property transitions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3361–3366, 2006     

Uniform Coating of BaTiO3–Dy2O3–SiO2 Compound Nano Layer on Ni Particles for MLCC Electrode

Uniform coating of nanometer‐scale BaTiO₃–Dy₂O₃–SiO₂ layers on spherical Ni particles are achieved by controlled hydrolysis of tetrabutyl titanate (TBT), hydrothermal reaction with Ba(OH)₂, and co‐precipitation of tetraethylorthosilicate (TEOS) and Dy(NO₃)₃. The composition of the coating layer is similar to rare earth oxide‐silica–doped BaTiO₃, which is the main component of dielectric layer for base metal electrode (BME) multilayer ceramic capacitors (MLCCs). After coating, the shrinkage onset temperature of Ni particles is significantly increased. After sintered to pellets, the electrode has good electrical conductivity. This electrode material has good compatibility with rare earth oxide and silica‐doped BaTiO₃ dielectric materials, and could serve as promising candidate for application in the next generation BME‐MLCCs.     

π-conjugated soluble nickel–polyyne copolymer: Synthesis and third-order optical nonlinearity

By means of homogeneous stepwise condensation method, both the Ni–polyyne copolymers with PPh₃ and PBu₃ ligands, and modified π-conjugated nickel-containing copolymers have been synthesized and confirmed by infrared (IR) analysis. The Ni–polyyne copolymers obtained are yellow powder having a M _w of about 1 ∼ 2 × 10⁴ and a molecular weight distribution (MWD) of less than 3, and they are soluble in tetrahydrofuran (THF), CHCl₃, and toluene. Their third-order nonlinear optical properties have been investigated by a degenerate four-wave mixing (DFWM) technique. The effect of the nature of the ligands attached to the nickel atoms, the structure, and the length of π-conjugation between the 2 metal centers in the main chain on the hyperpolarizability γ of the Ni–polyyne polymers have been discussed. The maximum susceptibility χ⁽³⁾ and hyperpolarizability γ of the Ni–polyyne polymers reach 5.17 × 10⁻¹² and 2.30 × 10⁻³⁰ esu, respectively. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1165–1172, 1998     

Bi(Zn2/3Nb1/3)O3–(K0.5Na0.5)NbO3 High‐Temperature Lead‐FreeFerroelectric Ceramics with Low Capacitance Variation in a Broad Temperature Usage Range

The xBi(Zn_2/3Nb_1/3)O₃–(1?x)(K_0.5Na_0.5)NbO₃ (abbreviated as xBZN–(1?x)KNN) ceramics have been synthesized using the conventional solid‐state sintering method. The phase structure, dielectric properties and “relaxorlike” behavior of the ceramics were investigated. The 0.03BZN–0.97KNN ceramics show a broad and stable permittivity maximum near 2000 and lower dielectric loss (≤5%) at a broad temperature usage range (100°C–400°C) and the capacitance variation (ΔC/C_150°C) is maintained smaller than ±15%. The 0.03BZN–0.97KNN ceramics only possess the diffuse phase transition and no frequency dispersion of dielectric permittivity, which indicates that 0.03BZN–0.97KNN ceramics is a high temperature “relaxorlike” ferroelectric ceramics. These results indicate that 0.03BZN–0.97KNN ceramics are excellent promising candidates for preparing high‐temperature multilayer ceramics capacitors.     

Sol–Gel Synthesis and Characterization of Na0.5Bi0.5TiO3–NaTaO3Thin Films

Thin films with the composition 70 mol% Na_0.5Bi_0.5TiO₃ + 30 mol% NaTaO₃ were prepared by sol–gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low‐ (kHz–MHz) and microwave‐frequency (15 GHz) ranges were investigated. In the low‐frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature‐stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between ?25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO₂/TiO₂/Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.     

Ultra‐Wide Temperature Stable Dielectrics Based on Bi0.5Na0.5TiO3–NaNbO3 System

The microstructure, phase structure, ferroelectric, and dielectric properties of (1?x)Bi_0.5Na_0.5TiO₃‐xNaNbO₃ [(1?x)BNT‐xNN] ceramics conventionally sintered in the temperature range of 1080°C–1120°C were investigated as a candidate for capacitor dielectrics with wide temperature stability. Perovskite phase with no secondary impurity was observed by XRD measurement. With increasing NN content, (1?x)BNT‐xNN was found to gradually transform from ferroelectric (x = 0–0.05) to relaxor (x = 0.10–0.20) and then to paraelectric state (x = 0.25–0.35) at room temperature, indicated by P–I–E loops analysis, associated with greatly enhanced dielectric temperature stability. For the samples with x = 0.25–0.35, the temperature coefficient of capacitance (TCC) was found <11% in an ultra‐wide temperature range of ?60°C–400°C with moderate dielectric constant and low dielectric loss, promising for temperature stable capacitor applications.     

Ein effektives Verfahren zur Herstellung von 1α,25-Dihydroxy-cholecalciferol (Calcitriol) aus 1α3β,25-Trihydroxy-cholesta-5,7-dien (Procalcitriol)

An Effective Procedure for the Synthesis of 1α,25-Dihydroxy-cholecalciferol (Calcitriol) Starting with 1α,3β, 25-Trihydroxy-cholesta-5,7-diene (Pro-Calcitriol) In order to develop an effective synthesis of the important vitamin D metabolite 1α,25-(OH)₂-cholecalciferol (calcitriol) 5a starting with pro-calcitriol 1a the influence of reaction temperature and degree of turnover of 1a to the compositions of the photoproducts at irradiation in a 500 ml photoreactor were investigated. The combination of the highly photostable filter solution consisting of 2,7-dimethyl-3,6-diaza-cyclohepta-1,6-diene-tetrafluoroborate and biphenyl in ethanol realizes the double wavelength irradiation in the range of 290 to 300 nm and > 330 nm resulting in a highly amount of the desired pre-calcitriol 2a . The reversible photoisomers of pre-calcitriol 2a 1α,25-(OH)₂-lumisterol₃ 4a and 1α,25-(OH)₂-tachysterol₃ 3a were isolated from an irradiation mixture in pure form by means of an appropriate combination of flash-chromatography, MPLC and preparative HPLC, respectively. The isomers 2a, 3a and 4a were characterized chromatographically and spectroscopically. Photoisomerization of 1a at −45 °C using the filter solution mentioned above and recycling all reversible photoisomers resulted in highly pure 5a after thermally induced isomerization of 2a isolated from the irradiation mixture by means of flash-chromatography on Ag⁺- impregnated silica with a yield of 68%.