• Volume 39, Issue 3

June 2016,   pages  603-912

• Stability field diagrams for Ln–O–Cl systems

Isothermal stability field diagrams for Ln−O−Cl systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) are developed by taking partial pressures of volatile components oxygen and chlorine as variables. Thermodynamic properties of all the oxides and trichlorides (LnCl$_3$) are available in the literature. However, data for oxychlorides (LnOCl) and dichlorides (LnCl$_2$) are limited. Based on systematic trends in stability of these compounds across the lanthanide series, missing data are estimated to construct the diagrams for 13 Ln−O−Cl systems at 1000 K. All the lanthanide elements form stable LnCl$_3$ and LnOCl. Dichlorides of Nd, Sm, Eu, Dy, Tm and Yb are stable. For systems in which dichlorides are unstable (Ln = La, Ce, Pr, Gd, Tb, Ho, Er), the LnOCl is in equilibrium with the metal (Ln) and the stability field of LnOCl is sandwiched between those of oxides and trichlorides. Stability field diagrams of lanthanide systems forming stable LnCl$_2$ are of two kinds: in the first kind (Ln = Nd,Dy) the stability fields of Ln and LnOCl are in contact and the stability field of LnOCl separates the fields of chlorides and oxides. In diagrams of the second kind (Ln = Sm, Eu, Tm, Yb) there is a direct equilibrium between the oxides and dichlorides at low partial pressures of oxygen and chlorine. There is no contact between the stability fields of Ln and LnOCl; the stability field of LnOCl intervenes between the oxide and chloride phases only at higher partial pressures.

• Effect of crosslinker on the swelling and adsorption properties of cationic superabsorbent

In the present study, superabsorbents (SAPs) of cationicmonomer [2-(methacryloyloxy) ethyl] trimethylammonium chloride have been prepared by free radical solution polymerization with different crosslinkers. They were subjected to repeated cycles of swelling and de-swelling in deionized water and NaCl solution. The conductivity of the swelling medium was measured and related to the swelling/de-swelling characteristics of the SAPs. The swelling capacity was also determined in saline solution. The swelling and de-swelling processes were described by first-order kinetics. The SAPs exhibited varied swelling capacity for crosslinkers of the same functionality as well as different functionality. The SAPs were used to adsorb the dye Orange G at different initial concentrations of the dye. The equilibrium adsorption data followed the Langmuir adsorption isotherms. The SAPs were also used to adsorb three other dyes, namely, Congo red, Amido black and Alizarin cyanine green. They exhibited different adsorption capacities for different dyes. The adsorption phenomenon was found to follow first-order kinetics.

• Structural studies of Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$ $+$ Ag superconducting system

We have studied for the first time the effect of Ag addition (0–15 wt%) to the superconducting system, Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$, on its crystal structure and local structural features, using synchrotron X-ray diffraction(SXRD) and Raman spectroscopy, respectively. SXRD and subsequent Rietveld refinement studies on powders of Nd$_{1.85}$Ce$_{0.15}$CuO$_4$ $+$ Ag system indicate a small but significant change in lattice parameter upon Ag addition, showing evidence for possible incorporation of Ag to the extent of $\sim$1 wt%. Raman spectroscopic studies indicate that the parent structure of Nd$_{1.85}$Ce$_{0.15}CuO$_{4}$remains unaffected with no major local structural changes on doping with silver. However, all Raman modes show minor phonon hardening upon Ag addition, which is consistent with the unit cell volume reduction as is observed in XRD. A systematic bleaching out of the apical oxygen defect mode was also observed with increased Ag addition. Polarized Raman measurements helped to identify the asymmetric nature of the B1g Raman mode. X-ray diffraction studies on pellets of Nd$_{1.85}$Ce$_{0.15}CuO$_4$ $+$ Ag system further indicate a randomization of preferred orientation upon Ag addition. The superconductivity of the Nd$_{1.85}$Ce$_{0.15}$CuO$_4$ $+$ Ag system has been well characterized for all the compositions studied.

• Structural modification of tantalum crystal induced by nitrogen ion implantation

This paper investigates the effect of nitrogen ion implantation on tantalum surface structure. In this experiment, nitrogen ions which had an energy of 30 keV and doses of $1 \times 10^{17}$ to $10 \times 10^{17}$ ions cm$^{−2}$ were used. X-ray diffraction analysis (XRD) was applied for both the metallic Ta substrate and the study of new structures that have been created through the nitrogen ion implantation. Atomic force microscopy (AFM) was also used tocheck the roughness variations prior to and also after the implantation phase. The experimental results show the formation of hexagonal tantalum nitride (TaN$_{0.43}$) in addition to the fact that by increasing the ion dose, the nitrogen atoms occupy more interstitial spaces in the target crystal. The nitride phase also seen for $3\times 10^{17}$ and $5\times 10^{17}$ ions cm$^{−2}$, while it disappeared for higher dose of $7\times 10^{17}$ and $1\times 10^{18}$ ions cm$^{−2}$. The FWHM of the dominant peak of tantalum nitride suggest the growth of the crystallite’s size, which is in agreement with the AFM results ofthe grains.

• Synthesis and electrical field-assisted sintering behaviour of yttria-stabilized tetragonal ZrO$_2$ nanopowders by polyacrylamide gel method

The tetragonal ZrO$_2$ nanopowders stabilized with 3 mol% Y$_2$O$_3$ (3YSZ) were synthesized using a polyacrylamide gel method. The mean particle size of the 3YSZ nanopowders was found to decrease with increasing molecular ratio of monomer to the precursor salt. The 3YSZ nanopowders with mean particle size of 12 nm can be densified in 1 h at 800$^{\circ}$C, by the application of a d.c. electrical field. Under a constant d.c. electrical field, the current density through the specimen of 3YSZ rose rapidly when the temperature increased to a certain value. In the sintering process, the current density was restricted when the sharp increase occurred. By limiting current density to different values for one hour, it was found that current density was the most important factor in electrical field assisted sintering process. The grain size of 3YSZ bulk increased with the enhanced current density. The stable stageof electrical field-assisted sintering process can be explained by Joule heating. Corresponding real temperature of specimens is estimated by applying black body radiation theory.

• Synthesis and characterization of core–shell magnetic molecularly imprinted polymer nanoparticles for selective extraction of tizanidine in human plasma

In this study, simple, effective and general processes were used for the synthesis of a new nanomolecularly imprinted polymers (MIPs) layer on magnetic Fe3O4 nanoparticles (NPs) with uniform core–shell structure by combining surface imprinting and nanotechniques. The first step for the synthesis of magnetic NPs was co-precipitation of Fe$^{2+}$ and Fe$^{3+}$ in an ammonia solution. Then, an SiO$_2$ shell was coated on the magnetic core with the Stöber method. Subsequently, the C$=$C groups were grafted onto the silica-modified Fe$_3$O$_4$ surface by 3-(trimethoxysilyl) propyl methacrylate. Finally, MIPs films were formed on the surface of Fe$_3$O$_4$@SiO$_2$ by the copolymerization of C$=$C end groups with methacrylic acid (functional monomer), ethylene glycol dimethacrylate (crosslinker),2,2-azobisisobutyronitrile (initiator) and tizanidine (template molecule). The products were characterized using techniques that included Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), UV spectrophotometry, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Measurement of tizanidine through use of the core–shell magnetic molecularly imprinted polymers nanoparticles (MMIPs-NPs) in human plasma samples compared to the paracetamol showed that the synthesized nanosized MMIP for tizanidine has acted selectively.

• Synthesis of 1-D ZnO nanorods and polypyrrole/1-D ZnO nanocomposites for photocatalysis and gas sensor applications

1-D ZnO nanorods and PPy/1-D ZnO nanocomposites were prepared by the surfactant-assisted precipitation and in situ polymerization method, respectively. The synthesized nanorods and nanocomposites were characterized by UV–Vis spectrophotometer, Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), which gave the evidence of 1-D ZnO nanorods, polymerization of pyrrole monomer and strong interaction between PPy and 1-D ZnO nanorods, respectively. Photocatalytic activity of 1-D ZnO nanorods was conducted by $3^3$ level full-factorial design to evaluate the effect of three independent process variables viz., dye concentration (crystal violet), catalyst concentration (1-D ZnO nanorods) and the reaction time on the preferred response: photodegradation efficiency (%). The PPy/1-D ZnO nanocompositeswere used for the sensing of NH$_3$, LPG, CO$_2$ and H$_2$S gases, respectively, at room temperature. It was observed that PPy/1-D ZnO nanocomposites with different 1-D ZnO nanorod weight ratios (15 and 25%) had better selectivity and sensitivity towards NH3 at room temperature.

• Synthesis of polyaniline/ZrO$_2$ nanocomposites and their performance in AC conductivity and electrochemical supercapacitance

Polyaniline/zirconium oxide (PANI/ZrO$_2$) nanocomposites have been synthesized by incorporating ZrO$_2$ nanoparticles into the PANI matrix via liquid–liquid interfacial polymerization method. The composite formationand structural changes in PANI/ZrO$_2$ nanocomposites were investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). PXRD pattern of PANI/ZrO$_2$ nanocomposites exhibited sharp and well-defined peaks of monoclinic phase of ZrO$_2$ in PANI matrix. SEMimages of the composites showed that ZrO$_2$ nanoparticles were dispersed in the PANI matrix. The FT-IR analysis revealed thatthere was strong interaction between PANI and ZrO$_2$. AC conductivity and dielectric properties of the nanocomposites were studied in the frequency range, 50–10$^6$ Hz. AC conductivity of the nanocomposites obeyed the power lawindicating the universal behaviour of disordered media. The nanocomposites showed high dielectric constant in the order of 10$^4$, which could be related to dielectric relaxation phenomenon. Further, the materials were checked fortheir supercapacitance performance by using cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Among the synthesized nanocomposites, PANI/ZrO2-25 wt.% showed a higherspecific capacitance of 341 F g$^{-1}$ at 2 m Vs$^{-1}$ and good cyclic stability with capacitance retention of about 88% even after 500 charge–discharge cycles.

• Synthesis and optical properties of SiO$_2$–Al$_2$O$_3$–MgO–K$_2$CO$_3$–CaO–MgF$_2$–La$_2$O$_3$ glasses

A series of five glass compositions were prepared by using the conventional melt quenching technique in the system SiO$_2$–Al$_2$O$_3$–MgO–K$_2$CO$_3$–CaO–MgF$_2$–La$_2$O$_3$ with different contents of SiO$_2$, MgO, K$_2$CO$_3$, MgF$_2$ and La$_2$O$_3$. The effects on the optical and physical properties of these glasses due to the addition of La$_2$O$_3$ as well as variation of the various oxides have been investigated. X-ray diffraction analysis is used to confirm the amorphous nature of the prepared glasses. Structures of glasses were studied by using UV–Vis and Fourier transforms infrared spectroscopy. The drilling test was also performed on their glass ceramic samples to confirm the machinability.

• Design of multi-layer anti-reflection coating for terrestrial solar panel glass

To date, there is no ideal anti-reflection (AR) coating available on solar glass which can effectively transmit the incident light within the visible wavelength range. However, there is a need to develop multifunctional coatingwith superior anti-reflection properties and self-cleaning ability meant to be used for solar glass panels. In spite of self-cleaning ability of materials like TiO2 and ZnO, these coatings on glass substrate have tendency to reduce lighttransmission due to their high refractive indices than glass. Thus, to infuse the anti-reflective property, a low refractive index, SiO$_2$ layer needs to be used in conjunction with TiO$_2$ and ZnO layers. In such case, the optimization ofindividual layer thickness is crucial to achieve maximum transmittance of the visible light. In the present study, we propose an omni-directional anti-reflection coating design for the visible spectral wavelength range of 400–700 nm,where the maximum intensity of light is converted into electrical energy. Herein, we employ the quarter wavelength criteria using SiO$_2$, TiO$_2$ and ZnO to design the coating composed of single, double and triple layers. The thicknessof individual layers was optimized for maximum light transmittance using essential Mcleod simulation software to produce destructive interference between reflected waves and constructive interference between transmitted waves.

• Co-based soft magnetic bulk glassy alloys optimized for glass-forming ability and plasticity

Co-based bulk glassy alloys (BGAs) have become more and more important because of their nearly zero magnetostriction and high giant magneto-impedance effect. Here, we report the improvement of glass-formingability (GFA), soft-magnetic properties and plasticity by a small addition of Mo atoms in CoFeBSiNbMo BGAs.(Co$_{0.6}$Fe$_{0.4}$)$_{69}$B$_{20.8}$Si$_{5.2}$Nb$_{5−x}$Mo$_{x}$ ferromagnetic BGA cylindrical glassy rods were fabricated successfully with adiameter of 5 mm by conventional copper mould casting method. It reveals that the substitution of a small amount of Mo for Nb makes the composition to approach a eutectic point and effectively enhances the GFA of alloy. Inaddition to high GFA and superhigh strength, the compressive test shows that the Mo addition can improve the plasticity for the obtained BGAs. The combination of high GFA, excellent soft-magnetic properties and good plasticitydemonstrated in our alloys is promising for the future applications as functional materials.

• Structural investigation of V$_2$O$_5$–P$_2$O$_5$–K$_2$O glass system with antibacterial potential

The $x$V$_2$O($1 − x$)[0.8 P$_2$O$_5$·0.2K$_2$O] glass system with $0 \lt x \lt 50$ mol% was prepared and the structural changes induced in these glasses by increasing the vanadium oxide content were investigated by IR and ESR spectroscopies. The dual behaviour role of V$_2$O$_5$ oxide, as network modifier (for $x\lt 10$ mol%) and the network former ($x\gt 20$ mol%), as a consequence of phosphate network depolymerization and P–O–V and V–O–V linkages appearance was also highlighted. The antibacterial effect of the glasses with $x \lt 20$ mol% V$_2$O$_5$ content was tested by optical density (OD) measurements. A linear correlation between the amount of vanadium and the antibacterial effect was evidenced.

• Wear behaviour of Zr-based in situ bulk metallic glass matrix composites

Zr-based bulk metallic glass (BMG) and its in situ BMG matrix composites with diameter of 3 mm were fabricated by conventional Cu-mould casting method and the dry sliding wear behaviour of the BMG and composites was investigated. Compared to the pure BMG, the composites exhibited a markedly improved wear resistance from 10 to 48% due to the existence of various volume fractions of the ductile $\beta$-Zr dendritic phase embedded in the glassy matrix. The composites showed lower friction coefficient and wear rate than the pure BMG. Meanwhile, the surface wearing of the composite with a proper amount of $\beta$-Zr dendrites was less severe compared to that of the pure BMG. The worn surface of the composite was covered with mild grooves and some fine wear debris, which exhibited the characteristic of a mild abrasive wear. The improvement of the wear resistance of the composite with the proper amount of $\beta$-Zr crystalline phase is attributed to the fact that the $\beta$-Zr crystalline phase distributed in the amorphous matrix has some effective load bearing, plastic deformation and work hardening ability to decrease strain accumulation and the release of strain energy in the glassy matrix, restrict the expanding of shear bands and cracks, and occur plastic deformation homogeneously.

• Green fluorescence of terbium ions in lithium fluoroborate glasses for fibre lasers and display devices

In this paper, for the first time, the visible fluorescence properties, resonance energy transfer mechanism responsible for non-radiative decay rates of ${}^5$D$_4$ $\to$ ${}^7$F$_5$ transition and also quenching of fluorescence intensity of the ${}^5$D$_3$ $\to$ ${}^7$F$_5$ transition of various concentrations of Tb$^{3+}$ ions in LBZLFB glasses are reported. Optical absorption, fluorescence spectra and quantum efficiencies are measured and analysed. Green fluorescence related to ${}^5$D$_4$ $\to$ ${}^7$F$_5$ (548 nm) transition is registered under excitation of 378 nm of Tb$^{3+}$ ions. Based on excitation and fluorescence measurements, several spectroscopic parameters for Tb$^{3+}$ ions are examined as a function of concentration by Judd–Ofelt theory to judge the suitability of studied glasses for display devices and fibre lasers.

• Effect of transition metal elements on the structural and optical properties of ZnO nanoparticles

Undoped and transition metal (TM)-doped ZnO nanoparticles (Zn$_{0.98}$X$_{0.02}$O-NPs, X= Mn, Cr, Co and Fe) were synthesized from a metal nitrate precursor and gelatin by a sol–gel method. The compounds were synthesized at calcination temperatures of 550$^{\circ}$C for 6 h. The synthesized undoped/doped ZnO-NPs were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). XRD results indicated that the sample products were crystalline with a hexagonal wurtzite phase. SEM images showed the ZnO-NPs nearly spherical shapes and a non-uniform shape for doped ZnO-NPs. The crystalline development in the ZnO-NPs was investigated by X-ray peak broadening. The size–strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain of the undoped and doped ZnO-NPs. The obtained results showed that strain ofthe NPs plays an important role in peak broadening; moreover, the mean crystalline size of the undoped and doped ZnO-NPs estimated from the SEM and the SSP method was highly inter-correlated. Finally, optical properties ofthe samples were studied by a UV–Vis spectrometer.

• Magnetic force microscopy and simulation studies on Co$_{50}$Fe$_{50}$ elliptical nanomagnets

We studied the magnetization reversal mechanism of single-layered Co50Fe50 nanomagnets by measuring the magnetization reversal and using the micromagnetic simulations. The magnetization reversal strongly depends on the thickness of the nanomagnets. In the remanent state, the magnetic force microscopy studies and the simulation data showed the formation of single and vortex states depending on the thickness of nanomagnets.

• Effects of calcium impurity on phase relationship, ionic conductivity and microstructure of Na$^{+}$-$\beta/beta"$-alumina solid electrolyte

Ca-doped Na$^{+}$-$\beta/beta"$-alumina was synthesized using a solid-state reaction. The changes in the properties of Na$^{+}$-$\beta/beta"$-alumina resulting from the presence of Ca impurity were studied. Ca (0–5 wt%) was added to the respective samples, which were then sintered. The specimens were characterized using X-ray diffraction, scanningelectron microscopy, densimetry and impedance analysis. In the sintered specimens, the $\beta"$-alumina phase fraction decreased as Ca content increased, whereas the relative sintered density increased. The surface morphology of Cadoped Na$^{+}$-$\beta/beta"$-alumina specimens showed a Ca-rich layer, which was the main cause of increase in the specificresistance.

• Effects of Nb doping on the microstructure, ferroelectric and piezoelectric properties of 0.7BiFeO$_3$–0.3BaTiO$_3$ lead-free ceramics

Donor-doped lead-free Bi$_{0.7}$Ba$_{0.3}$(Fe$_{0.7}$Ti$_{0.3}$)$_{1−x}$Nb$_{0.66x}$O$_{3}$ + 1 mol% MnO$_2$ ceramics were prepared by a conventional oxide-mixed method and the effects of Nb-doping on microstructure, piezoelectric and ferroelectricproperties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure with rhombohedral symmetry. The grain growth of the ceramics is inhibited after the addition of Nb doping. High electricinsulation ($R = 10^9–10^{10}$ $\Omega$·cm) and the poor piezoelectric performance and weak ferroelectricity are observed after the addition of Nb$_2$O$_5$ in the ceramics. Different from the donor effect of Pb-based perovskite ceramics, the introduction of Nb into 0.7BiFeO$_3$–0.3BaTiO$_3$ degrades the piezoelectricity and ferroelectricity of the ceramics. The Bi$_{0.7}$Ba$_{0.3}$(Fe$_{0.7}$Ti$_{0.3}$)$_{1−x}$Nb$_{0.66}$xO$_3$ + 1 mol% MnO2 ceramic with $x = 0$ exhibits the optimum piezoelectric properties with $d_{33} = 133$ pN C$^{−1}$ and $k_p = 0.29$ and high Curie temperature ($T_C = 603^{\circ}$C).

• Structure and properties of (1−x)[(K$_{0.5}$Na$_{0.5}$)NbO$_3$–LiSbO$_3$]– xBiFe$_{0.8}$Co$_{0.2}$O$_3$ lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics $(1−x)$[0.95(K$_{0.5}$Na$_{0.5}$)NbO$_3$–0.05LiSbO$_3$]–$x$BiFe$_{0.8}$Co$_{0.2}$O$_{3}$(KNN–LS–$x$BFC) were prepared by a conventional sintering technique. The effect of BFC content on the structure, piezoelectricand electrical properties of KNN–LS ceramics was investigated. The results reveal that the BFC is effective in promoting the sinterability and the electrical properties of the ceramics sintering at low temperature of 1030$^{\circ}$C. Theceramics show a single perovskite structure, in which the tetragonal phase decreases while the orthorhombic phase increases with the increase of $x$. The more the BFC content is, the smaller and homogeneous grains were formed.With the increase of $x$, the $d_{33}$ and the $k_p$ increase to a maximum value and then slightly decrease, but the $Q_m$ increases continuously. As BFC content increases, the Curie temperature $T_c$ and remnant polarization $P_r$ decrease, but the diffusivity of phase transition in KNN–LS ceramics will intensify and the coercive field $E_c$ fluctuate between 1.16 and 1.51 kV mm$^{−1}$. The samples with $x =0.004$ exhibit optimum electrical properties at room temperature ($d_{33} = 268 pC$ N$^{−1}$, $k_p =52$%, $\epsilon_r = 1366$, $\tan \delta =2.11$%, $T_c = 325^{\circ}$C, $P_r = 20.4$ $\mu$C cm$^{−2}$, $E_c =1.16$ kV mm$^{−1}$).

• Synergism in anticorrosive paints

The present work depicts synergism anticorrosive behaviour between zinc hypophosphite and zinc phosphate in a commercial pigment mixture. Also, the performance of anticorrosive paints was evaluated. Synergism anticorrosive behaviour was evaluated by corrosion potential and linear polarization measurements in pigment suspensions. The protective layer obtained with this pigment mixture was investigated by scanning electron microscopy (SEM). Then, the anticorrosive properties of the pigment were assessed by incorporating it into alkyd and epoxy paints which were evaluated by salt spray test and electrochemical noise technique. The morphology and the nature of the protective layer grown under the paint film were also studied by SEM. Experimental results showed that improved anticorrosion protection is achieved in paints with reduced zinc phosphate contents as a consequence of the synergistic interaction between zinc hypophosphite and the other components of the pigment mixture. The electrochemical noise technique proved to be adequate to monitor corrosion in painted panels and is able to detectcorrosion under the paint film from very early stages. This paper identified the need to study synergism between anticorrosive pigments to try to reduce the phosphate content in anticorrosive paints.

• Fabrication of graphene–TiO$_2$ nanocomposite with improved photocatalytic degradation for acid orange 7 dye under solar light irradiation

In this study, photodegradation of the non-biodegradable azo dye acid orange 7 (AO7) was selected as modal target in aqueous solution using graphene–TiO$_2$ (GR–TiO$_2$) hybrid nanocomposite, was well investigatedand elucidated. The crystal phase, special surface area, microscopic analysis of the GR–TiO$_2$ and also, chemical state of the photocatalysts were studied by powdered X-ray diffraction (PXRD), Raman spectrum, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution scanning electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Brunauere Emmette Teller (BET) method andphotoluminescence spectroscopy (PL). During photocatalysis, the GR–TiO$_2$ nanocomposite improved photocatalytic performance compared with that of pure TiO$_2$ towards AO7 organic azo-dye degradation. The reusability test ofphotocatalytic activity was also examined. A conceivable reaction mechanism was suggested and nattered on the basis of tentative effects. Therefore, the GR–TiO$_2$ nanomaterial can be widely used as a photocatalyst for treatingthe organic dye contaminant in the field of environmental protection.

• Influence of nanometric silicon carbide on phenolic resin composites properties

This paper presents a preliminary study on obtaining and characterization of phenolic resin-based composites modified with nanometric silicon carbide. The nanocomposites were prepared by incorporating nanometric silicon carbide (nSiC) into phenolic resin at 0.5, 1 and 2 wt% contents using ultrasonication to ensure uniform dispersion of the nanopowder, followed by heat curing of the phenolic-based materials at controlled temperature profile up to 120$^{\circ}$C. The obtained nanocomposites were characterized by FTIR spectroscopy and scanning electron microscopy analysis and evaluated in terms of mechanical, tribological and thermal stability under load. The results highlight the positive effect of the nanometric silicon carbide addition in phenolic resin on mechanical, thermo-mechanical and tribological performance, improving their strength, stiffness and abrasive properties. The best results were obtained for 1 wt% nSiC, proving that this value is the optimum nanometric silicon carbide content. The results indicate that these materials could be effectively used to obtain ablative or carbon–carbon composites in future studies.

• Effect of europium content on physical properties of In$_2$O$_3$ thin films for sensitivity and optoelectronic applications

In$_2$O$_3$:Eu thin films were successfully grown by spray pyrolysis. XRD studies showed that the films had In$_2$O$_3$ cubic structure with (004) preferential orientation and best crystal properties at 1.5% Eu doping level. Theoptical band gap energy decreased with Eu content around 4.1 eV. Urbach energy was of the order of 278 meV, it decreased with Eu content which indicates a decrease in the defects by doping. The dispersion of the refractive index was discussed. Raman spectroscopy showed the band positions corresponding to In$_2$O$_3$ cubic phase with a small shift related to europium incorporation within In$_2$O$_3$ matrix. PL measurements showed a large band which was located at 410 nm and related to the band-to-band transitions and other bands related to impurity levels. Finally, theelectric conductivity was investigated depending on the effect of temperature. Activation energy was found to range from 45 to 60 meV for films which were prepared with 1%Eu content.

• Influence of heat treatment on the structural, morphological and optical properties of DC magnetron sputtered Ti$_{x}$Si$_{1−x}$O$_2$ films

Ti$_x$Si$_{1−x}$O$_2$ thin films were formed onto unheated p-silicon and quartz substrates by sputtering composite target of Ti80Si20 using reactive DC magnetron sputtering method. The as-deposited films were annealed in oxygenatmosphere at different temperatures in the range 400–900$^{\circ}$C. X-ray photoelectron spectroscopic indicated that the as-deposited films formed at oxygen flow rate of 8 sccm were of Ti$_{0.7}$Si$_{0.3}$O$_2$. X-ray diffraction studies revealed that the as-deposited films were amorphous. The films annealed at 800$^{\circ}$C were exhibited broad (101) peak which indicated the growth of nanocrystalline with anatase phase of TiO$_2$. The crystallite size of the films increased from 9 to 12 nm with increase of annealing temperature from 800 to 900$^{\circ}$C, respectively, due to increase in crystallinity and decrease in defect density. XPS spectra of annealed films showed the characteristic core level binding energies of the constituent Ti$_{0.7}$Si$_{0.3}$O$_2$. Optical band gap decreased from 4.08 to 3.95 eV and the refractive index decreased from 2.11 to 2.08 in the as-deposited and the films annealed at 900$^{\circ}$C due to decrease in the lattice strain and dislocation density.

• Bis-methyl imidazolium methylidene bis(trifluoromethanesulfonyl)imide, crystal structure, thermal and dielectric studies

A new geminal di-cationic ionic liquid (IL) containing a central cationic unit methylidene capped by a basic functionality (imidazole) is synthesized. The compound was characterized by means of ${}^1$H, ${}^13$C, ${}^19$F NMR, IR and Raman spectroscopies and its crystal structure is confirmed by single crystal X-ray diffraction method. The X-ray studies on ([M(CH$_2$)IM$^{2+}$][2NTf$^−_2$ ]) show that it crystallizes in monoclinic system with space group:P 21/c. Thermal properties were investigated in the temperature range from 0 to 400$^{\circ}$C by using differential thermal (DTA) and thermogravimetric (TGA) analyses. The frequency-dependent electrical data are discussed using complexdielectric permittivity in the frequency range of ($10^{−2}–10^6$ Hz) and in the temperature range of $−50–20^{\circ}$C. The outstanding dielectric and thermal properties make this IL as promising candidate for electrochemical devices.

• Oxygen evolution reaction of Ti/IrO$_2$–SnO$_2$ electrode: a study by cyclic voltammetry, Tafel lines, EIS and SEM

The electrochemical characteristics towards oxygen evolution reaction of thermally prepared Ti/IrO$_2$–SnO$_2$ electrodes were examined. Two electrodes prepared with two different IrO$_2$ compositions were analysed in Na$_2$SO$_4$ electrolyte. Cyclic voltammetry, steady state polarization curves, impedance spectroscopy and open circuit potential were performed to investigate the performance and stability of these electrocatalysts. It has foundthat the surface electrochemistry of Ti/IrO$_2$–SnO$_2$ anodes are governed by the Ir(III)/Ir(IV) couple. The impedance spectroscopy investigation permitted to propose an equivalent circuit to describe the modifications occurred in differentpotentials during oxygen evolution reaction. The same equivalent circuit was found to describe both electrodes. Moreover, the double layer capacitance and microstructure analysis reflected that the inner surface makes a largecontribution to the electrochemically active surface area of Ti/IrO$_2$–SnO$_2$ anodes. It was found that the stability and the electrocatalytic activity mainly depend on changes in the IrO$_2$ composition of the electrode and its morphology during oxygen evolution reaction.

• Curcumin loaded in bovine serum albumin–chitosan derived nanoparticles for targeted drug delivery

The main aim of this study is to prepare biocompatible polymeric nanoparticles for targeted delivery of curcumin to human colorectal adenocarcinoma (DLD-1) cells. Curcumin has an ability to block proliferation ofcancer cells by suppressing the nuclear transcription factor NF-KB hence, it is chosen as drug in the current study. To avoid its low bio-availability, high dosage and poor aqueous solubility, curcumin nanoparticles are prepared and loaded in naturally available biopolymers like chitosan and bovine serum albumin (BSA) by nanoprecipitation method at pH 6.3. The prepared nanoformulation was then characterized for surface morphology, particle size, polydispersity index, FT-IR spectra, UV–Visible spectrometer, confocal microscopy and in vitro cytotoxicity studies. Results showed that sizes of the prepared nanoparticles were ranged between 181 and 363 nm and curcumin-loaded particles were selectively targeting colorectal carcinoma cells effectively when concentration gets increased. So this study proved that BSA–chitosan based nanoparticles can be used as an efficient vehicle for effective curcumin delivery in treatment of cancer cells.

• Bactericidal paper trays doped with silver nanoparticles for egg storing applications

In this study, a cost-effective way to deposit the silver nanoparticles (AgNPs) on paper egg trays was developed, which proved suitable for prolonged storage of table eggs for house-hold use without deterioration of egg quality. Silver nanoparticles were synthesized based on chemical reduction approach and mixed with gelatin–chitosan mixer used as a colloidal stabilizer as well as fixing agent. AgNPs-doped paper egg trays were characterized by TEM, SEM, FTIR, EDX and XRD. AgNPs containing egg trays were tested for its bactericidal effect against commonly found bacteria on egg shells, E. coli, S. aureus, Streptococcus spp and Salmonella spp. Storing of eggs in the AgNPs-deposited paper egg trays improved the shelf-life of the eggs by more than 14 days compared to controls (eggs stored in conventional trays). In conclusion, the developed paper trays possessed strong antimicrobial activity and it could be an effective storage material for eggs.

• Ab initio calculations of fundamental properties of SrTe$_{1−x}$O$_x$ alloys

Structural, electronic, optical and thermodynamic properties of the SrTe$_{1−x}$O$_x$ alloys ($0 ≤ x ≤ 1$) in rock-salt phase are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory. The exchange-correlation potential for structural properties was calculated by the standard local density approximation (LDA) and GGA (PBE) and the new form of GGA (WC) which is an improved form of the most popular Perdew–Burke–Ernzerhof (PBE), while for electronic properties, in addition to LDA, GGA corrections; Engel–Vosko GGA (EV-GGA) and modified Becke–Johnson (mBJ) schemes were also applied. The results show that the use of GGA (WC) in our calculations is more appropriate than GGA and LDA and gives a good description of structural properties such as lattice parameters and bulk modulus. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows almost nonlinear dependence on the composition. In addition to FP-LAPW method, the composition dependence of the refractive index and the dielectric constant was studied by different models. On the other hand, the thermodynamic stability of this alloy was investigated by calculating the excess enthalpy of mixing $\Delta H_m$ as well as the phase diagram.

• Investigation of fibre orientation using SEM micrograph and prediction of mechanical properties through micromechanical modelling

The present study concerns the fabrication of short sisal fibre-reinforced polypropylene (PP/SF) composites by melt mixing with different fibre length (3, 6 and 10 mm) comprising of 70% of matrix PP and 30% of SFs followed by injection moulding. The PP/MA-g-PP/SF composites were prepared with the ratio of 65:5:30 with the optimized fibre length of 6 mm at different mould temperatures (25, 45 and 65$^{\circ}$C) in a similar fashion. This work also further extended to study the effect of fibre orientation of the composites by numerical calculation of secondorder orientation tensor. To evaluate the fibre orientations PP/MA-g-PP/SF composites at different mould temperatures,scanning electron microscope micrographs were used to estimate the accurate principal directions and two-dimensional fibre orientation distributions through centre coordinates of the elliptical fibre images. Finally, a mathematical model of modified rule of mixture was adopted to compare the predicted tensile strength and modulus with the experimental findings.

• Analysis of fibre waviness effect through homogenization approach for the prediction of effective thermal conductivities of FRP composite using finite element method

In this study, homogenization approach is proposed to analyse the fibre waviness in predicting the effective thermal conductivities of composite. Composites that have wavy fibre were analysed by finite element method toestablish equivalence between micro- and macro-mechanics principles, thereby, it is possible to minimize the computational efforts required to solve the problem through only micro-mechanics approach. In the present work, the influence of crest offset, wavy-span on the thermal conductivities of composite for different volume fractions and thermal conductivity mismatch ratios were also studied. It is observed that the homogenization results are in good agreement with minimal % error from those obtained through pure micro-mechanics approach at the cost of low computational facilities and less processing time for converged solutions.

• Ni–Fe–Al$_2$O$_3$ electrodeposited nanocomposite coating with functionally graded microstructure

In this study, a Ni–Fe–Al$_2$O$_3$ nanocomposite coating was deposited on the substrate of low-carbon steel by electrodeposition from a sulphate-based bath. The effects of frequency and duty cycle were investigated to producethe functionally graded (FG) coating. For this purpose, first, the coatings with duty cycle-decreased method (DDM) were deposited in eight steps from 88 to 11%. At the second step, frequency-increased method (FIM) was utilized from 50 to 6400 Hz during eight steps. Assessing of coatings was carried out by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), potentiodynamic test, Vickers microhardness test and wear test.Microstructure evaluations gained by SEM and EDS demonstrated that the continuous alterations of duty cycle contribute for manufacturing of FG coatings, so that the maximum particle fraction was in the free surface of the coating and its amount was gradually decreased to the interface. These investigations showed that FIM had no effect on production of graded structure. Corrosion and wear tests indicated high corrosion and wear resistance of DDM coatings in comparison to FIM coatings. Investigating the best coatings obtained from both above methods exhibited 50 and 20% reduction in corrosion current density and wear rate, respectively, for DDM specimen in comparison to FIM sample.

• Adsorption of hexavalent chromium by graphite–chitosan binary composite

Graphite chitosan binary (GCB) composite was prepared for hexavalent chromium adsorption from studied water. GCB was characterized by TGA, FTIR, SEM and X-ray diffraction techniques.Wide porous sorptive surface of 3.89 m$^2$ g$^{−1}$ and absorptive functionalities of GCB was due to 20% (w/w) graphite support on chitosan evidenced from FTIR and SEM that impart maximum adsorption at pH 4, agitation with 200 rpm for 180 min. Adsorption studies revealed intraparticle diffusion models and best-fitted kinetics was pseudo 2nd order one. A wellfitted Langmuir isotherm model suggested monolayer adsorption with an adsorption capacity ($q_m$) of 105.6 mg g$^{−1}$ and $R^2 = 0.945$. Sorption mechanisms based on metal ionic interactions, intrusion/diffusion and chemisorptions onto composite. This graphite chitosan binary composite improve sorbent capacity for Cr(VI).

• Adsorption and reduction: combined effect of polyaniline emeraldine salt for removal of Cr(VI) from aqueous medium

In this study, we have reported the removal of Cr(VI) ions by polyaniline (PANI) particles from aqueous medium. PANI in its emeraldine salt (ES) form can interact with Cr(VI), which is present as HCrO$^{−}_4$ in two ways. The adsorption of HCrO$^{−}_4$ ions due to the electrostatic interaction between partially positively charged PANI backbone and Cr(VI) anions causes the major portion of Cr(VI) removal and a small portion of Cr(VI) is reduced to Cr(III) by PANI (ES). The adsorption follows Langmuir adsorption isotherm and second-order kinetic model. It is observed that the removal of Cr(VI) is negligibly effected by the presence of other anions in the aqueous medium. The adsorption capacity of PANI (ES) is found to be 123 mg g$^{−1}$, which is very high compared to activated carbonbased materials. The adsorbed anions can be desorbed by converting PANI emeraldine salt (ES) to PANI emeraldinebase (EB). The EB form of PANI can be converted into ES form by treating with acid, which can be reused as adsorbent. It is important to note that the PANI (ES) is oxidized by HCrO$^{−}_4$ ions which decrease the hydrophilicity of thesurface of PANI particles. This causes the decrease in adsorption capacity of recycled PANI.

• Room temperature deposition of amorphous p-type CuFeO$_2$ and fabrication of CuFeO$_2$/n-Si heterojunction by RF sputtering method

Transparent conducting amorphous p-type CuFeO$_2$ (CFO) thin film was prepared by radio-frequency (RF) magnetron sputtering method at room temperature using polycrystalline CuFeO$_2$ target. Amorphous structureof as-deposited film was confirmed by XRD. XPS analysis convinced that the chemical state of Cu$^{+}$ and Fe$^{3+}$ in the film, and the chemical composition of the thin films is close to the stoichiometry of CuFeO$^2$. Surface morphology of the film was analysed by SEM studies. p-type nature and concentration of carriers was investigated by Hall effect measurement. The p–n heterojunction in the structure of Al/n-Si/p-CuFeO$_2$/Al showed good rectifying behaviour with a forward and reverse currents ratio of 555 at 2 V. The turn-on voltage and reverse leakage current values were found to be 0.9 V and 4 $\mu$A at $−$2 V. Further, the conduction mechanism of forward bias voltage was controlled by thermionic emission (TE) and trap-space charge limited current (TCLC) mechanisms.

• Influence of SMA reinforcement on the impact resistance of GFRP composite laminates under different temperatures

Plain glass fibre-reinforced polymeric (GFRP) laminates and GFRP reinforced with randomly oriented short strips of shape memory alloy (SMA) were prepared by hand lay-up method. The SMA strip reinforcement was placed at 0.75 $\times$ thickness of the laminate with weight fractions of 2, 4 and 6%. The specimens were exposed to drop weight impact test and the experiments were conducted at a constant impact velocity of 2.80 m s$^{−1}$ with different test temperatures such as 303, 333 and 363 K. The impact damage area was evaluated using lighting technique and fracture response was analysed using scanning electron microscopic (SEM) images. Absorption of impact energyand damage area due to low velocity impact were calculated. It was observed that with the higher temperature, the SMA/GFRP laminates exhibit marginally-enhanced damage resistance compared to the plain GFRP laminates. Also, addition of SMA reinforcement was not contributing much to the impact resistance at higher temperature.

• Ni(II) decorated nano silicoaluminophosphate molecular sieves-modified carbon paste electrode as an electrocatalyst for electrooxidation of methanol

In this work, we reported amethod for the synthesis of nanosized silicoaluminophosphate (SAPO) molecular sieves that are important members of zeolites family. The synthesized SAPO was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) as well as infrared (IR) techniques. Then, the modified carbon paste electrode was prepared by nano SAPO molecular sieves and nickel (II) ion incorporated at this electrode. The electrochemical behaviour of the modified electrode (Ni-SAPO/CPE) towards the oxidation of methanol was investigated by cyclic voltammetry and hronoamperometry methods. It has been found that the oxidation current is extremely increased by using Ni-SAPO/CPE compared to the unmodified Ni-CPE, it seems that Ni$^{2+}$ inclusion into nano SAPO channels provides the active sites for catalysis of methanol oxidation. The effect of some parameters such as scan rate of potential, concentration of methanol, amount of SAPO was investigated on the oxidation of methanol at the surface of modified electrode. The values of electron transfer coefficient, charge-transfer rate constant and electrode surface coverage for the Ni(II)/Ni(III) couple in the surface of Ni-SAPO/CPE were found to be 0.555, 0.022 s$^{−1}$ and 5.995 $\times$ 10$^{−6}$ mol cm$^{−2}$, respectively. Also, the diffusion coefficient and the mean value of catalytic rate constant for methanol and redox sites of modified electrode were obtained to be $1.16\times 10^{−5}$ cm$^2$ s$^{−1}$ and $4.62\times 10^4$ cm$^3$ mol$^{−1} s$^{−1}\$, respectively. The good catalytic activity, high sensitivity, good selectivity and stability and easy in preparation rendered the Ni-SAPO/CPE to be a capable electrode for electrocatalytic oxidation of methanol.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019