Effect of electron beam irradiation and degree of boric acid loading on the properties of styrene-butadiene rubber

Synthetic and totally amorphous styrene-butadiene rubber (SBR) has been loaded with varying contents of boric acid. Vulcanization of prepared composites as well as of unloaded rubber has been induced by ionizing radiation of accelerated electron beam of varying doses up to 250 kGy. Evaluation of prepared composite subjected to this range of irradiation has been followed up through the measurement of mechanical, physical, electrical and thermal properties of vulcanized composites. Mechanical properties, namely tensile strength (TS) and Young’s modulus were found to increase, whereas elongation at break (E_b) and permanent set (PS) were found to decrease with the increase in degree of boric acid loading as well as irradiation dose. On the other hand, physical properties, namely the gel content, have increased whereas the swelling number has decreased. Moreover, increase in the decomposition temperature has been attained. Also, limited increase in electrical conductivity has taken place. Data obtained indicate enhancement in thermal as well as in physico-mechanical properties of prepared composites. Moreover, 60 phr of boric acid has attained good mechanical properties.     

Mullite–zirconia–zircon composites: Properties and thermal shock resistance

In the refractory field mullite and zirconia are the basis of materials used in the glass industry or when high chemical stability and corrosion resistance are necessary. In this work various mullite–zirconia/zircon compositions were investigated to improve the thermal shock (TS) resistance of dense composites produced by slip casting and sintering at 1600 °C. Zircon (SiZrO₄) acts as bonding phase and its thermal decomposition adds zirconia and silica to the material. Resultant composites were characterized by density and dilatometric measurements, XRD and SEM techniques. TS behavior was tested by quenching in water with quenching temperature differentials ΔT from 400 to 1200 °C. The degree of damage after the TS was experimentally evaluated through the variation of the elastic modulus E which is measured by the excitation technique. The severity of the TS test and the effect of the number of thermal cycles on E for each ΔT employed were determined.The tested materials retained their original mechanical properties for temperatures below a critical temperature ΔT_c near 600 °C. Materials quenched from ΔT of 1000 °C showed as much as 30% reduction in E indicating the important microstructure damage. The TS resistance improved with increasing zircon addition to 35 wt% in agreement with the behavior predicted from R parameter for crack initiation.     

Novel gamma irradiated agarose-gelatin-hydroxyapatite nanocomposite scaffolds for skin tissue regeneration

Agarose-gelatin-hydroxyapatite composites prepared by freeze-drying technique were gamma irradiated with various doses (25 kGy, 50 kGy and 100 kGy). X-ray Diffraction (XRD) analysis revealed the pure phase of HAp and the intensity of prominent planes of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) were found to decrease on irradiation. Fourier Transform Infrared spectra (FTIR) showed functional groups of HAp and polymer composites, and higher disorder of the polymer matrix on irradiation. In addition, gamma irradiation led to a drastic reduction in the wettability (62%) and the compressive modulus (76%) of the scaffolds. There was significant enhancement (113%) in pore size of the scaffolds at higher fluence (100 kGy). The swelling and the dissolution studies of the gamma irradiated scaffolds showed that it had an appreciable change in the scaffold's mechanical and biological properties viz., compressive modulus, cell proliferation, hemolysis etc. The irradiated biomaterials exhibited enhanced hemocompatibility, antimicrobial activity and cell viability. The above results clearly reveal that the gamma irradiation is a suitable tool to tailor the multifunctional properties of the composites and could be used for various biomedical applications.     

A study of the thermal and mechanical properties of electron beam irradiated HDPE/EPDM blends in the presence of triallyl cyanurate

The enhancing effects of cross-linking by the addition of 1, 3, and 5 wt% of triallyl cyanurate (TAC) to blends containing 80 wt% of high-density polyethylene (HDPE) and 20 wt% of ethylene–propylene diene monomer (EPDM) during electron beam irradiation were investigated. More specifically, the thermal and mechanical properties were studied as a function of the electron beam irradiation dose and an amount of the cross-linking agent, such as triallyl cyanurate (TAC). The results showed that the values of the gel content, thermal stability, tensile properties, impact strength, and rheology increased with increasing irradiation dose up to 150 kGy. For higher doses, the values decreased. Addition of the cross-linking agent to the HDPE/EPDM blends showed an enhanced cross-linking effect of various properties during electron beam irradiation. The addition of 3 wt% of TAC led to the highest thermal and mechanical properties. An irradiation dose of 150 kGy with the addition of 3 wt% TAC was the optimal condition to obtain blends with the best properties.     

Dielectric tunable properties of high dielectric breakdown Ba0.5Sr0.5TiO3–Zn2P2O7 composite ceramics

Dielectric properties of Ba_0.5Sr_0.5TiO₃–xZn₂P₂O₇ (x = 1, 3, 5, 10, 15 wt%) composite ceramics, which were prepared by solid-state reaction process, were intensively investigated. The results showed that the Curie temperature (T_c) of composites gradually shifted to lower temperature (?140 °C) with increasing the content of Zn₂P₂O₇, and the dielectric constant were tuned effectively from 2020 to 107, while maintaining a relatively high tunability. Zn₂P₂O₇ additions remarkably inhibited the grain growth of Ba_0.5Sr_0.5TiO₃ phases, and improved the breakdown strength of samples up to 385 kV/cm. The sample with x = 10 wt% exhibited good dielectric properties (?_r = 290, tg δ = 0.0006, T = 20.5%, BDS = 297 kV/cm). Meanwhile Zn₂P₂O₇ addition also made the T_c far away from the room temperature, which reduced the sensitivity of the dielectric constant to temperature change and simultaneously improved the stability of materials.     

Thermoluminescence response of 120 MeV Ag9+ and γ-ray exposed LiMgBO3:Dy3+ nanophosphors for dosimetry

Thermoluminescence(TL) response of LiMgBO₃:Dy³⁺ nanophosphor synthesized by combustion method was examined using γ-ray and 120 MeV Ag⁹⁺ swift heavy ion (SHI) irradiation. The LiMgBO₃:Dy³⁺ samples were exposed to 0.01 kGy −5 kGy γ-rays while for the different fluences the samples were irradiated with 120 MeV Ag⁹⁺ SHI over the range 1×10¹¹ ions cm⁻² to 1×10¹³ ions cm⁻². The prominent TL glow curve peaks appeared at 396 K and 390 K for the γ-ray and 120 MeV Ag⁹⁺ SHI irradiated samples. The glow curves for the SHI iradiated samples were more complex than those of the γ-ray exposed samples. The effect of different heating rates on the TL response was also determined. The trapping parameters (i.e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen's formulae. The TL response curve against γ-ray exposure illustrated a good linear response upto 3 kGy and after that the response was sublinear. For the 120 MeV Ag⁹⁺ ion irradiated samples, the material exhibited a sublinear dependence against ion irradiation for the studied fluence. The good TL response against γ-ray irradiation suggested that the material can be explored for a possible application in dosimetry.     

Short polyethylene terephthalate fiber (PET) reinforced NBR rubber composites

Acrylonitrile-butadiene rubber (NBR) has been reinforced with different content of PET up to 25 phr. Vulcanization of prepared composites as will as the unreinforced ones have been induced by ionizing radiation of accelerated electron beam of varying dose up to 150 kGy. Evaluations of the vulcanized composites have been followed up through the measurement of mechanical, physical and thermal properties. Also, scanning electron microscope (SEM) was performed. Mechanical properties, namely tensile strength (TS) and hardness were found to increase with the increase of irradiation dose as well as the increase in the content of PET up to 25 phr. Also, elongation at break (ε _b) was found to decrease with the increase of irradiation dose; however, the decrease in ε_b is not consistence with the increase in fibers loading. Young’s modulus (E) and tensile modulus at 25% elongation (E25) were found to increase with the increase of irradiation dose and fiber loading up to 20 phr. Also, the volume fraction of swollen rubber increases as irradiation dose and/or fiber content increased; it was more influenced by irradiation rather than fiber loading. Anisotropic swelling increased with irradiation and fiber loading up to 20 phr. SEM photomicrograph showed that irradiation causes adhesion between PET fiber and NBR where less pulling out and less pitting on the surface were observed. The thermal properties of the composite irradiated at 100 kGy reveal that the activation energy (E _a) increases up to 10 phr fiber content. When the composite that contains 10 phr fiber irradiated at doses higher than100 kGy, Ea decreased.     

Physicochemical properties of Ni-loaded yttrium stabilized zirconia nanotubes for solid oxide fuel cells

Yttrium-stabilized zirconia nanotubes (YSZNTs) were prepared using a conventional hydrothermal method, and their characteristics were compared with those of yttrium-stabilized zirconia nanoparticles (YSZNPs) synthesized in this study and with those of commercial YSZNPs (CYSZNPs). YSZNTs had widths and lengths of 20–30 nm and 100–700 nm respectively. The electrical conductivity of NiO (60.0 wt%)-loaded YSZNTs (40.0 wt%) was higher than those of NiO/YSZNPs and NiO/CYSZNPs at the same NiO loading. The zeta-potentials of YSZNTs in aqueous solution, determined by electrophoretic light scattering (ELS), indicated high positive surface charges at lower pH values, which is known to be related to surface stability, but negative values at high pH. The results of cyclic voltammetry (CV) and H₂-temperature-programmed reduction (H₂-TPR) confirmed that NiO(60.0 wt%)/YSZNTs (E_red = −0.445 mV) were more reduced than NiO/YSZNPs (E_red = −0.517 mV) and NiO/CYSZNPs (E_red = −0.516 mV).     

Electron beam irradiation of polycarbonate reinforced acrylonitrile butadiene rubber

The effects of electron beam irradiation and polycarbonate (PC) concentration on the properties of acrylonitrile butadiene rubber (NBR) were investigated. The electron beam irradiation doses were from 25 to 150 kGy, whereas the PC contents were from 10 to 30 phr. It was found that the mechanical properties of NBR such as tensile strength (TS), hardness and tear strength (Ts) were remarkably improved by the incorporation of PC, while elongation at break (E_b) and thermal properties were decreased. However, the improvement in TS of NBR/PC blends was strongly dependant on PC content, in which maximum improvements need higher doses. On the other hand, the maximum value of Ts for all the blend ratios was at 25 kGy, whereas the hardness increases with increasing irradiation dose. Moreover, it was observed that the fuel resistance of NBR/PC was higher than NBR and decreases by increasing the content of PC.     

Aluminum titanate based ceramics from aluminum sludge waste

This work aims at obtaining aluminum titanate-based ceramics (Al₂TiO₅: AT) composites from industrial wastes. Al-sludge waste and rutile ore were used as rich sources of alumina and titania instead of pure materials. Sludge-(0–40 wt%) rutile mixtures were mixed, formed and fired at 1350 °C for various times. Phase composition, microstructure, densification, mechanical and thermal behaviors of the obtained AT composites have been investigated. Complete conversion of the starting materials to AT with bulk density of 3.199 g/cm³, compressive strength and modulus of rupture of 326.425 MPa and 30.84 MPa, respectively and very low CTE (−0.927*10⁻⁶ K⁻¹) were achieved by firing the sludge-(30 wt%) rutile at 1350 °C for 4 h. These results suggest that the obtained AT-ceramics from Al-sludge waste-rutile ore are a promising and an ecofriendly route.     

High performance Aurivillius-type bismuth titanate niobate (Bi3TiNbO9) piezoelectric ceramics for high temperature applications

This paper reports the significant improved piezoelectric properties of high temperature bismuth titanate niobate (Bi₃TiNbO₉, BTN) polycrystalline ceramics. The piezoelectric performance of BTN ceramics is significantly enhanced by cerium modifications. The dielectric measurements indicate that the Curie temperature T_c gradually decreases over the temperature range of 907–889 °C with cerium contents increasing up to 0.7 wt%. The BTN-5Ce (BTN+0.5 wt% CeO₂) exhibits optimized piezoelectric properties with a piezoelectric constant d₃₃ of 16 pC/N, which is five times the value of unmodified BTN (d₃₃~3 pC/N), while BTN-5Ce maintains a high Curie temperature T_c of 894 °C. The temperature-dependent electrical impedance and electromechanical coupling factors (k_p, and k_t) reveal that the BTN-5Ce exhibits thermally stable electromechanical coupling characteristics up to 500 °C but significantly deteriorates at 600 °C due to high conductivity at a higher temperature. The thermally stable electromechanical properties in combination with the ceramics׳ high electrical resistivity (10⁶ Ω cm at 500 °C) and high Curie temperature (~900 °C) demonstrate that cerium-modified BTN ceramics are good materials for high temperature sensing applications.     

Dielectric properties of barium titanate–molybdenum composite

The barium titanate–molybdenum composites were prepared through solid state reaction method in argon atmosphere. The microstructure, resistivity, and dielectric properties of the composites were investigated. XRD results indicated that chemical reactions between barium titanate (BaTiO₃:BT) and molybdenum (Mo) have taken place during sintering, resulting in the formation of BaMoO₄ (BM) and BaTi₂O₅ (BT₂). The resistivity decreased with the increasing amount of Mo in the composites. The composites (when x = 5 and 20 wt.%) showed lower dielectric constant than pure BaTiO₃, especially, the dielectric constant (when x = 20 wt.%) reached a minimum value (<10⁴), while composites (when x = 10 and 15 wt.%) showed rather high dielectric constant at temperatures range from 25 °C to 160 °C. The dielectric constant of the composite gradually decreased with increase in frequency at the room temperature. The dielectric constant of composite (when x = 5 wt.%) comes up to 10⁴, and the T_c (Curie temperature) of the composite was relatively higher than that of BT (120 °C).     

Frequency scaling of ac hopping transport in amorphous carbon nitride

The dynamics of hopping transport in amorphous carbon nitride is investigated in both Ohmic and non-linear regimes. Dc current and ac admittance were measured in a wide range of temperatures (90 K < T < 300 K), electric fields (F < 2 × 10⁵ V cm^− 1) and frequencies (10² < f < 10⁶ Hz).The dc Ohmic conductivity is described by a Mott law, i.e. a linear ln(σ_OHMIC) vs T^− 1/4 dependence. The scaling of field-enhanced conductivity as ln(σ / σ_OHMIC) = ϕ[F^S / T] with S ≈ 2/3, observed for F > 3 × 10⁴ V cm^− 1 over 5 decades in σ(T,F), is explained by band tail hopping transport; the filling rate, Γ_F(E_DL), of empty states at the transport energy is obtained with a “filling rate” method which incorporates an exponential distribution of localized states, with a non-equilibrium band tail occupation probability f(E) parametrized by an electronic temperature T_EFF (F).As the ac frequency and temperature increase, the increase in conductance G is accurately described by Dyre's model for hopping transport within a random spatial distribution of energy barriers. This model predicts a universal dependence of the complex ac conductivity of the form σ_ac = σ(0)[iωτ / ln(1 + iωτ)], where σ(0) is the zero frequency ac conductivity and τ(T,F) is a characteristic relaxation time. We find that the inverse characteristic time 1 / τ can also be described by a Mott law. It is compatible with the filling rate Γ_F(E_DL) at the transport energy, which governs the dc conductivity; this rate increases with increasing dc field, as more empty states become available in the band tail for hopping transitions. This “universal” scaling law for the ac conductance provides a scaling parameter K(T,F) = τ(T,F) σ(T,F,ω = 0) / ɛ which is found to decrease with increasing electric field from 5 to 0.5, depending weakly on temperature. Our band tail hopping model predicts a high-field value of K(T,F) smaller than the Ohmic value, under the condition (eFγ^− 1 / E°) ≤ (kT / E°)^1/4, where γ^− 1 is the localization radius and E° the disorder energy of the band tail distribution.     

Fabrication of continuously porous SiC–Si3N4 composite using SiC powder by extrusion process

Large amounts of waste SiC sludge containing small amounts of Si and organic lubricant were produced during the wire cutting process of single crystal silicon ingots. Waste SiC sludge was purified by washing it with organic solvent and purified SiC powder was used to fabricate the continuously porous SiC–Si₃N₄ composites, using an extrusion process, in which carbon, 6 wt% Y₂O₃ + 2 wt% Al₂O₃ and ethylene vinyl acetate were added as a pore-forming agent, sintering additives and binder, respectively. In the burning-out process, the binder and carbon were fully removed and continuously porous SiC–Si₃N₄ composites were successfully fabricated. The green bodies containing waste SiC, Si powder and sintering additives were nitrided at 1400 °C in a flowing N₂ + 10% H₂ gas mixture. The continuously porous composites contained SiC, α-Si₃N₄, β-Si₃N₄ and few Fe phases. The pore size of the second passed and third passed SiC–Si₃N₄ composites was 260 μm and 35 μm in diameter, respectively. The values of bending strength and hardness in the second passed and third passed samples were 62.97 MPa, 388 Hv and 77.82 MPa, 423 Hv, respectively.     

Influence of SiO2 on electrical properties of the highly nonlinear ZnO-Bi2O3-MnO2 varistors

The ZnO-Bi₂O₃-MnO₂-xSiO₂ (ZBMS) varistor was prepared at a low sintering temperature of 880 °C via the conventional solid state method. The phase transformation, microstructure, and electrical properties of the ZBMS varistor were studied as a function of doping amount of SiO₂. It is showed that the growth of ZnO grain is restrained by the introducing of SiO₂; and the grain size decreases from 4.68 μm to 2.98 μm. The breakdown voltage E_1mA exhibits a simultaneous variation from 608.11 V/mm to 1232.88 V/mm. It is also revealed that SiO₂ has a significant effect on the Schottky barrier structure. As a result, the highest barrier height φ_b of 5.34 eV is attained at a composition of x = 2.0 wt%, which contributes to the highest nonlinear coefficient α of 73.68. Moreover, all the samples show low leakage current of I_L < 0.1 μA.     

Synthesis of bimetallic PtPd nanocubes on graphene with N,N-dimethylformamide and their direct use for methanol electrocatalytic oxidation

Bimetallic PtPd nanocubes supported on graphene nanosheets (PtPdNCs/GNs) were prepared by a rapid, one-pot and surfactant-free method, in which N,N-dimethylformamide (DMF) was used as a bi-functional solvent for the reduction of both metal precursors and graphene oxide (GO) and for the surface confining growth of PtPdNCs. The morphology, structure and composition of the thus-prepared PtPdNCs/GNs were characterized by transmission electron microscopy (TEM), high resolution TEM, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Because no surfactant or halide ions were involved in the proposed synthesis, the prepared PtPdNCs/GNs were directly modified onto a glassy carbon electrode and showed high electrocatalytic activity for methanol oxidation in cyclic voltammetry without any pretreatments. Moreover, with the synergetic effects of Pt and Pd and the enhanced electron transfer by graphene, the PtPdNCs/GNs composites exhibited higher electrocatalytic activity (j_p = 0.48 A mg⁻¹) and better tolerance to carbon monoxide poisoning (I_f/I_b = 1.27) compared with PtPd nanoparticles supported on carbon black (PtPdNPs/C) (j_p = 0.28 A mg⁻¹; I_f/I_b = 1.01) and PtNPs/GNs (j_p = 0.33 A mg⁻¹; I_f/I_b = 0.95). This approach demonstrates that the use of DMF as a solvent with heating is really useful for reducing GO and metal precursors concurrently for preparing clean metal–graphene composites.     

The solid state structure of polycarbonate blends with lead phthalocyanine

The physical properties of polycarbonate blends containing the nonlinear optical dye lead tetracumylphenoxy phthalocyanine were characterized. Blends with up to 20 wt% dye were prepared and characterized in terms of density, refractive index, glass transition temperature, loss modulus, subambient relaxation behavior, and free volume hole size from positron annihilation lifetime spectroscopy. The dye strongly affected the physical properties of the blend. The initial 0.1 wt% dye produced a dramatic increase in the density. A similar trend in the refractive index was accounted for by the change in density using a relationship between density and refractive index derived from the Lorentz–Lorenz equation. Increasing the dye content to 8 wt% led to a large reduction in the glass transition temperature. An increase in E′ and a decrease in the subambient γ-relaxation intensity accompanied the large decrease in T_g. This behavior fit the conventional concept of antiplasticization, which has been described for other low molecular weight diluents in PC. Recognizing that the dye was present as a mixture of monomer, dimer and higher aggregates, it was shown that the monomer form was responsible for the antiplasticization. In the glass, dimer and higher aggregates were viewed as nanoparticle fillers. It was confirmed that the antiplasticization effect was due to a reduction in excess hole free volume of the polymer.     

Influence of molecular weight of polydimethylsiloxane precursors and crosslinking content on degree of ethanol swelling of crosslinked networks

Using PDMS (polydimethylsiloxane) as a basic polymeric matrix to the preparation of ethanol-permselective pervaporation membranes is a vibrant field of research. In this paper, a detailed study of the effects of the molecular weight of PDMS precursors and the content of the TEOS (tetraethyl orthosilicate) crosslinker on the degree of swelling in ethanol and ethanol contact angle is reported. Five PDMS precursors with molecular weights of 26.6 K, 35.5 K, 50.2 K, 71.7 K, and 110.4 K, and five crosslinking contents (1 wt%, 2 wt%, 5 wt%, 10 wt%, and 15 wt%) were chosen to prepare twenty-five PDMS networks. Considering only the maximum tensile strength of the networks, the optimum molecular weight of the precursor was found to be 35.5 K and the optimum crosslinker content was 5 wt%. The average Young’s modulus of the PDMS network prepared under these conditions reached 0.63 MPa after using toluene to extract the network. Some uncrosslinked precursors always occur in the networks, and have some influence on the molecular weight of the precursors and the crosslinker content that is used. It was found that the content of the uncrosslinked precursors has direct effect on the contact angle of ethanol sessile drops at the surface of the extracted PDMS networks, and higher extraction corresponded to a smaller ethanol contact angle. A combined parameter (S), defined as the quotient of the extraction amount (A_E) and the tensile elastic modulus (E_Y), gives a good linear relationship with the increase in weight of networks swelled in ethanol. This means that the degree of equilibrium swelling of the networks is simultaneously strongly influenced by the tensile modulus and the content of the uncrosslinked precursors.     

Influence of processing on fracture toughness of Si3N4 + graphene platelet composites

Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPL) and two processing routes; hot isostatic pressing (HIP) and gas pressure sintering (GPS). The influence of the processing route and graphene platelets’ addition on the fracture toughness has been investigated. The matrix of the composites prepared by GPS consists of Si₃N₄ grains with smaller diameter in comparison to the composites prepared by HIP. The indentation fracture toughness of the composites was in the range 6.1–9.9 MPa m^0.5, which is significantly higher compared to the monolithic silicon nitride 6.5 and 6.3 MPa m^0.5. The highest value of K_IC was 9.9 MPa m^0.5 in the case of composite reinforced by the smallest multilayer graphene nanosheets, prepared by HIP. The composites prepared by GPS exhibit lower fracture toughness, from 6.1 to 8.5 MPa m^0.5. The toughening mechanisms were similar in all composites in the form of crack deflection, crack branching and crack bridging.     

Electrical and mechanical characterization by instrumented indentation technique of La0.85Sr0.15Ga0.8Mg0.2O3−δ electrolyte for SOFCs

La_0.85Sr_0.15Ga_0.8Mg_0.2O_3?δ pellets obtained by the polymeric organic complex solution method, isostatic pressing and sintering at 1350 °C have been electrical and mechanically studied. Electrical measurements evidenced reasonable ionic conductivities (0.01 S cm^?1 at 800 °C), which were comparable to those reported for the La_1?xSr_xGa_1?yMg_yO_3?δ prepared by other synthesis methods. On the other hand, the mechanical properties (elastic modulus, E and hardness, H) have been determined at micro/nanometric scale using the instrumented indentation technique. While E did not vary significantly with the increasing indentation depth (h), H values strongly decreased with the indentation depth up to 500 nm. For h > 500 nm, both mechanical properties remained almost constant, thus obtaining E = 271 ± 6 GPa and H = 13.2 ± 0.4 GPa. Finally, the residual imprints and fracture mechanisms have been observed by atomic force microscopy (AFM).