• Volume 40, Issue 4

August 2017,   pages  615-876

• Tailoring of optical and electrical properties of PMMA by incorporation of Ag nanoparticles

Silver–poly(methyl methacrylate) (Ag–PMMA) nanocomposite films were prepared via ex situ chemical routeby employing sodium borohydride (NaBH$_4$) as a reducing agent. In this study, PVP-stabilized Ag nanoparticles were prepared and mixed with PMMA solution. Optical and structural characterizations of resulting nanocomposite films were performedusing UV–visible spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Characteristicsurface plasmon resonance (SPR) peak of Ag nanoparticles was observed at about 3.04 eV (408 nm) in absorptionspectra of Ag–PMMA nanocomposite films. TEM micrograph revealed that the spherical Ag nanoparticles with an averagediameter of $5.4\pm 2.5$ nm are embedded in PMMA. In Raman spectra, besides shifting of vibrational bands, enhancementin intensity of Raman signal with incorporation of Ag nanoparticles was observed. Current ($I$)–voltage ($V$) measurementsrevealed that conductivity of PMMA increased with increasing concentration of Ag nanoparticles. Analysis of $I-V$ datafurther disclosed that at voltage $\lt$2 V, ohmic conduction mechanism is the dominant mechanism, while at voltage $\gt$2 VPoole–Frenkel is the dominant conduction mechanism. Urbach’s energy, the measure of disorder, increased from 0.40 eVfor PMMA to 1.11 eV for Ag–PMMA nanocomposite films containing 0.039 wt% of Ag nanoparticles.

• Strain-induced structural, magnetic and ferroelectric properties of heterostructure BST–NZFO nanocomposite thin film at room temperature

Heterostructure Ba$_{0.7}$Sr$_{0.3}$TiO$_3$–Ni$_{0.8}$Zn$_{0.2}$Fe$_2$O$_4$ composite thin films grown on Pt–TiO$_2$–SiO$_2$–Si substrate were prepared by chemical solution process, where Ba$_{0.7}$Sr$_{0.3}$TiO$_3$ layer grew as top/bottom while Ni$_{0.8}$Zn${0.2}$Fe$_2$O$_4$ layer grew as bottom/top. Structural characterization by X-ray diffraction and atomic force microscopy showed the similar crystal structure, different lattice parameters, large lattice strain and small grain size in heterostructures, whatever their deposition sequences. Such heterostructures present simultaneously ferromagnetic and ferroelectric responses at room temperature. Inparticular, an exceptionally large saturation magnetization was observed in one heterostructures film. The growth sequencesof Ba$_{0.7}$Sr$_{0.3}$TiO$_3$ and Ni$_{0.8}$Zn$_{0.2}$Fe$_2$O$_4$ layers on the substrate remarkably affect the magnetic properties of the compositethin films at room temperature.

• Influence of preparation procedure and ferric oxide nanoparticles addition on transport properties of homogeneous cation-exchange SPPO/SPVC membrane

Homogeneous cation-exchange membranes were prepared through evaporation and phase inversion methodsusing sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) and sulfonated polyvinylchloride as binders. The effectof polymers blend’s ratio and preparation method on structure and electrochemical properties of the prepared membraneswere evaluated. The microstructures of the membranes were investigated by scanning electron microscopy (SEM) andthe sulfonation of polyvinylchloride was confirmed by elemental analyses. Moreover, the membranes performance wasevaluated by ion-exchange capacity (IEC), fixed ion concentration, membrane potential, transport number, permselectivity,areal resistance, ionic permeability, flux of ions, current efficiency, membrane oxidative stability, mechanical properties andwater content tests. The results indicated that IEC and water content were affected by the SPPO content and microstructuresof the membranes. The results showed increased efficiency and suitable electrochemical properties for membranes preparedby the evaporation method in comparison with others. Also, Fe$_2$O$_3$ nanoparticles were synthesized at room temperature by a simple sonochemical reaction between ferric chloride and NaOH. The results revealed that the addition of different amounts of Fe$_2$O$_3$ nanoparticles to the polymeric matrix could affect the hydrophilicity and transport properties of ion-exchange membranes.

• Fabrication of chitosan microparticles loaded in chitosan and poly(vinyl alcohol) scaffolds for tissue engineering application

In recent decades, the use of microparticle-mediated drug delivery is widely applied in the field of biomedicalapplication. Here, we report the new dressing material with ciprofloxacin-loaded chitosan microparticle (CMP) impregnatedin chitosan (CH) and poly(vinyl alcohol) (PVA) scaffold for effective delivery of drug in a sustained manner to thewound site.Moreover, the peculiar physiochemical and structural properties of the CH–CMP scaffold has proved better tensile strengthand excellent swelling to achieve 82% of drug release. In vitro biocompatibility was done for both scaffold using NIH 3T3 fibroblasts and human keratinocytes (HaCaT) cell lines. In vitro fluorescent activity showed distinct biocompatibility withgood cell adhesion and proliferation. However, the CH–CMP scaffold showed best result to act as promising biomaterial in effective drug delivery in tissue engineering.

• Ionic conductivity and diffusion coefficient of barium-chloride-based polymer electrolyte with poly(vinyl alcohol)–poly(4-styrenesulphonic acid) polymer complex

A composite polymer electrolyte comprising poly(vinyl alcohol)–poly(4-styrenesulphonic acid) with bariumchloride dihydrate (BaCl$_2$·2H$_2$O) salt complex has been synthesized following the usual solution casting. The ionic conductivity of polymer electrolyte was analysed by impedance spectroscopy. The highest room temperature (at 30$^{\circ}$C) conductivity evaluated was 9.38 $\times$ 10$^{−6}$ S cm$^{−1}$ for 20 wt% loading of BaCl$_2$ in the polymer electrolyte. This has been referred to as the optimum conducting composition. The temperature-dependent ionic conductivity of the polymer electrolyte exhibits the Arrhenius relationship, which represents the hopping of ions in polymer composites. Cation and anion diffusion coefficients are evaluated using the Trukhan model. The transference number and enhanced conductivity imply that the charge transportation is due to ions. Therefore this polymer electrolyte can be further studied for the development of electrochemical device applications.

• Gas sensing behaviour of cerium oxide and magnesium aluminate composites

Composites of cerium oxide (CeO$_2$) and magnesium aluminate (MgAl$_2$O$_4$) were prepared by the moltensalt synthesis (MSS) method at 1130 K. The composite samples were named as MA, MAC0.07 and MAC0.14 (at CeO$_2$:0, 0.07 and 0.14 g in MgAl$_2$O$_4$, respectively) and these were characterized by X-ray diffraction and energy-dispersiveX-ray analyses. It is seen that the microstructure of the composite samples are quite similar except for a small increasein particle size. The energy-dispersive X-ray analyses provide the presence of concentration of Ce, Mg, Al and O in thecomposite. Scanning electron microscope, coupled with energy-dispersive X-ray analysis (SEM-EDAX) was used to identifythe morphology, microstructure and elemental composition of the prepared samples. The decomposition and dissociationreactions of the precursors were determined using differential thermal and thermogravimetric analysis (TGA). A lone pairof the electron state was identified from the electro paramagnetic resonance spectrum. An optical energy band gap of 3.3 eV was calculated from the UV–Vis absorbance spectra. The gas response to changes in oxygen (O$_2$), carbon monoxide (CO) (at 0.5, 1.0 and 1.5 bar) and ethanol (at 50 and 100 ppm) was quantitatively analysed in all the samples at differentoperating temperatures (300-500 K). The magnitude of the temperature varied linearly regardless of the gas pressure insidethe chamber, by increasing the supply in the heating pad, mounted below the sensor sample. The composite samples indicatea good response to different gases with detection of the smallest change in gas pressure.

• In situ synthesis and properties of self-reinforced Si$_3$N$_4$–SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$ (La$_2$O$_3$) glass–ceramic composites

In-situ-grown $\beta$-Si$_3$N$_4$-reinforced SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$ (La$_2$O$_3$) self-reinforced glass–ceramic composites were obtained without any $\beta$-Si$_3$N$_4$ seed crystal. These composites with different compositions were prepared in a nitrogenatmosphere for comparison of phase transformation and mechanical properties. The results showed that SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$ (La$_2$O$_3$) glass can effectively promote $\alpha$- to $\beta$-Si$_3$N$_4$ phase transformation. The crystallized Y$_2$Si$_2$O$_7$–La$_{4.67}$Si$_3$O$_{13}$ phaseswith a high melting point significantly benefited the high-temperature mechanical properties of the composites. TheSi$_3$N$_4$–SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$(La$_2$O$_3$) glass–ceramic composites exhibit excellent mechanical properties compared with unreinforcedglass–ceramic matrix, which is undoubtedly attributed to the elongated $\beta$-Si$_3$N$_4$ grains. These glass–ceramic Si$_3$N$_4$ composites with excellent comprehensive properties might be a promising material for high-temperature applications.

• Ex situ synthesis of G/$\alpha$-Fe$_2$O$_3$ nanocomposite and its catalytic effect on the thermal decomposition of ammonium perchlorate

$\alpha$-Fe$_2$O$_3$ nanoparticles were prepared by a facile hydrothermal method using ferric chloride hexahydrate(FeCl$_3$·6H$_2$O) as a precursor. Graphene oxide (GO) was synthesized using a modified Hummers method and graphenenanosheets (G) were successfully obtained by thermal reduction of GO. G/$\alpha$-Fe$_2$O$_3$ nanocomposite was prepared using ex situ synthesis in the presence of $\alpha$-Fe$_2$O$_3$ nanoparticles and GO solution. The characterization of the as-prepared materialswas performed using X-ray diffraction analyses and Fourier transform infrared spectroscopy; their morphology wasinvestigated by scanning electron microscopy and transmission electron microscopy; the specific surface area (SBET) wasdetermined by nitrogen adsorption; their catalytic activity on the thermal decomposition of ammonium perchlorate (AP) wasinvestigated by differential thermal analysis (DTA). The results of DTA indicated that the obtained nanomaterials contributein ameliorating the thermal decomposition of AP; specifically, the high decomposition temperature of AP decreases from432 to 380$^{\circ}$C. A significant decrease in the activation energy was also achieved in the presence of these nanomaterials, and the mixture of ammonium perchlorate with G/$\alpha$-Fe$_2$O$_3$ showed the lowest value (from 129 to 80.33 kJ mol$^{−1}$).

• Biofilms from micro/nanocellulose of NaBH$_4$-modified kraft pulp

Industrial applications of microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) have been inuse for some time; however, there is a need to improve the production steps and at the same time to obtain better qualityproducts. NFC and MFC were generated from NaBH$_4$-modified kraft pulp, produced from a red gum tree plant (Eucalyptuscamaldulensis). The generated NFC and MFC were characterized by high-performance liquid chromatography, Fouriertransform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and ${}^{13}$C-nuclear magnetic resonance (NMR).Morphological and viscoelastic properties were investigated by scanning electron microscopy and rheometry, respectively.The storage moduli of biofilms produced from NFC and MFC were investigated by dynamic mechanical thermal analysis(DMTA). Both exhibited mostly identical FTIR spectra. When the spectra were compared with those of NaBH4-modifiedkraft pulp, minor shifts were observed due to crystallinity. In NMR spectra, disordered cellulose structures were observedfor both NFC and MFC, and these findings were also confirmed by differential scanning calorimetry. Rheology studiesrevealed that the lowest viscosity was observed with MFC. TGA results showed that NFC degraded earlier compared withNaBH$_4$-modified kraft pulp. DMTA exhibited that NFC films had about six times higher storage modulus compared withMFC.

• Synthesis and characterization of BaNiO$_3$ using a solid-state thermal decomposition method and the preparation of its stable aqueous suspension

In the present study, the preparation of BaNiO$_3$ nano-oxide is reported via simple solid-state thermal decompositionof [Ba(en)$_4$][Ni(H$_2$O)$_2$(NCS)$_4$] precursor complex for the first time. As-prepared nano-oxide was coated by citricacid to form a stable aqueous magnetic suspension. The precursor complex was characterized by conductivity measurements,ultra violet–visible spectroscopy, elemental analysis and Fourier transform infrared spectroscopy. The composition of theperovskite was confirmed by energy-dispersive X-ray spectroscopy analysis and the hexagonal structure was supported bypowder X-ray diffraction. In addition, monotonous morphology of the nano-oxide was illustrated by field-emission scanningelectron microscopy. Superparamagneticity of the nanoparticles were detected using a vibrating sample magnetometer.Finally, the hydrodynamic size as well as the zeta potential of the pristine and surface-treated BaNiO$_3$ nano-oxide weremeasured in deionized water via a dynamic light scattering analyzer and they were compared. Results show the excellentstability of the surface-modified magnetic oxide compared to the pristine.

• Novel composites of $\beta$-SiAlON and radome manufacturing technology developed at ARCI, Hyderabad, for hypervelocity vehicles

Keeping the importance of developing suitable radome (a word derived from radar $+$ dome) materials and near-net shape consolidation technique for manufacturing radomes suitable for hypersonic ($\gt$mach 5) radar-guided missilesin India, the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, hasinitiated an in-house R&D programme and successfully developed a complete process know-how for manufacturing defectfreeprototype $\beta$-SiAlON-based radome structures with all the desired properties. As a part of this R&D programme, totalsix separate sub-projects mentioned below were undertaken and executed: (i) identification of the best composition out of$\beta$-Si$^{6−z}$Al$_z$O$_z$N$_{8−z}$ ($0 ≤ z ≤ 4.1$) solid solution, which possesses a right combination of properties required for radome applications, (ii) designing of an AlN-free precursor mixture for consolidating $\beta$-Si$_4$Al$_2$O$_2$N$_6$ ceramics by following aqueous colloidal processing routes, (iii) development of a process for passivating water-sensitive AlN powder against hydrolysis, (iv) development of aqueous gelcasting (GC) and hydrolysis-assisted solidification (HAS) powder processing routes for consolidating dense $\beta$-SiAlON ceramics using highly solids loaded ($\gt$50 vol%) aqueous slurries, (v) development ofan hydrolysis-induced aqueous gelcasting (GCHAS) process, a novel near-net-shape consolidation technique, to produceradomes with very high-production yields and (vi) development of an economic route for synthesizing the low-dielectricconstant and high strength novel $\beta$-SiAlON-SiO$_2$ ceramic composites. In this paper, (i) the basis for choosing $\beta$-SiAlON based ceramics for hypervelocity radome applications, and (ii) the various bottle-neck problems faced, while executing this entire R&D work and the way they were overcome have been critically analysed and discussed systematically, while citing all the relevant and important references.

• A novel microbond bundle pullout technique to evaluate the interfacial properties of fibre-reinforced plastic composites

The interfacial properties of the fibre composite systems decide the overall usability of a composite in simpleand complex shapes, as they are the deciding factors in determination of the mechanical properties, structural propertiesand above all a complete understanding of the reliability of composite systems. In the present investigation, the interfacialproperties of carbon fibre/epoxy composites viz., matrix shrinkage pressure, interfacial frictional stress, interfacial shear stress and coefficient of friction were evaluated through a novel microbond bundle pullout test. This test is different from the single fibre pull out, fibre fragmentation or the fibre push in test. Based on some of the physical principles involving the single fibre microbond pullout test, like the contact angle of the microbond matrix drop with the fibre surface, the surface tension/energy of the two surfaces before and after adhesion and the interfacial fibre/matrix chemistry, this is simple to perform and statistically averaged mesomechanical test is also easy to evaluate and is shown to be a test method thatenables a conservative prediction of the laminate level or macromechanical shear properties of fibre composite systems.This test demonstrates the validity of the mesomechanical tests that are more relevant to the macromechanical tests thanthe micromechanical tests. Fractography carried out to corroborate the observed mechanical properties with the fracturefeatures is also reported. The general advantages of the mesomechanical interfacial tests over those based on micromechanical assumptions is also discussed along with some common limitations.

• A new nanostructured material based on fluorophosphate incorporated into a zinc–aluminium layered double hydroxide by ion exchange

Layered double hydroxides (LDHs), also called anionic clays, consist of cationic brucite-like layers and exchangeable interlayer anions. These hydrotalcite-like compounds, with Zn and Al in the layers and chloride in the interlayer space, were prepared following the coprecipitation method at constant pH. The effect of pH, aging time and anion concentration on the intercalation of fluorophosphate (PO$_3$F$_2$−, FP) in the [Zn–Al] LDH was investigated. The best crystalline material, with high exchange extent, was obtained by carrying out the exchange at 25◦C in a 0.03 M FP solution at pH 7 with at least 42 h of aging time. A mechanism for the FP intercalation was confirmed by X-ray diffraction, infrared spectroscopy and thermogravimetry (TG) analyses (TG and DTG curves).

• Characterization of hexadecyltrimethylammonium-organoclay and its individual components by thermal techniques

The properties of the materials determine their potential applications. The aim of this article is to study the properties of the organoclays using simple and rapid technologies. Organoclays with different surfactant loadings (SL) were synthesized using an Argentine bentonite with a high content of montmorillonite (Bent) and hexadecyltrimethylammonium bromide as cationic surfactant. The samples were characterized using thermal techniques. The results revealed that the hydrophilicity of the organoclays decreases with increasing SL until the SL reaches 0.8 times the cation exchange capacity of the clay; and remains constant at a higher surfactant load. The stability of organoclays was inversely proportional to the SL of each sample. The layers showed a stabilization of approximately 40$^{\circ}$C for their structural transformation temperature, caused by the presence of the surfactant. In addition, at a SL $\lt$1.0 the surfactant presented a ‘liquid-like’ structure in the interlayer space, whereas at a SL $\gt$1.0 the structure was ‘solid-like’.

• Characterization of BaTiO$_3$ piezoelectric perovskite material for multilayer actuators

In this study, we present the results of the manufacturing of BaTiO$_3$ powder, which is meant for use in stacked-diskmultilayer actuator production. The solid-state technique was used for powder preparation. The properties of bariumtitanate material, at each stage of its fabrication (powder, granulate, sintered material), influencing on its application forthe stacked-disk multilayer actuator were determined. Particularly, the four parameters of BaTiO$_3$ sinter affecting on theusability properties of actuators, not found before in the literature, were estimated. Parameters characterizing the extent ofmaterial sintering, SEM microstructures and electric properties of the fabricated pellets are presented and discussed. Thedilatometric curve was executed using the high temperature dilatometer to determine at which temperature barium titanatepellets and beams should be sintered to receive full dense sinters. Parameters characterizing the extent of material sintering:the apparent density, the apparent porosity and the water absorbability were estimated. Finally, the problem of metal layerdeposition on barium titanate ceramics during actuator fabrication is considered.

• Investigation on effect of fibre hybridization and orientation on mechanical behaviour of natural fibre epoxy composite

Nowadays bio fibre composites play a vital role by replacing conventional materials used in automotive andaerospace industries owing to their high strength to weight ratio, biodegradability and ease of production. This paper aimsto find the effect of fibre hybridization and orientation on mechanical behaviour of composite fabricated with neem, abacafibres and epoxy resin. Here, three varieties of composites are fabricated namely, composite 1 which consists of abaca fibreand glass fibre, composite 2, which consists of neem fibre and glass fibre, whereas composite 3 consists of abaca, neem fibresand glass fibres. In all the above three varieties, fibres are arranged in three types of orientations namely, horizontal (type I),vertical (type II) and 45$^{\circ}$ inclination (type III). The result shows that composites made up of abaca and neem fibres withinclined orientation (45$^{\circ}$) have better mechanical properties when compared with other types of composites. In addition, morphological analysis is carried out using scanning electron microscope to know the fibre distribution, fibre pull out, fibre breakage and crack propagation on tested composites.

• Investigation on the bulk growth of $\alpha$-LiIO$_3$ single crystals and the influence of pH on its structural, morphological and optical characteristics

$\alpha$-LiIO$_3$ is an excellent optical material exhibiting strong nonlinear optical, piezoelectric and elasto-opticproperties. However, its practical applications are limited by the insufficient reproducibility of the mentioned propertiescaused by the strong influence of the growth conditions, and, in particular, pH of the solution from which $\alpha$-LiIO$_3$3 crystal is grown. Herein, we investigate to grow bulk size good quality crystals of $\alpha$-LiIO$_3$ based on the observed problems during its crystallization process. A systematic investigation was carried out to find the effect of pH on solubility, crystal growth, structural, surface and laser damage properties of $\alpha$-LiIO$_3$ single crystals. The structure and phase of LiIO$_3$ were confirmedby powder X-ray diffractometer analysis. The functional groups of the compound were identified using Fourier transforminfrared spectroscopy. Surface defects of the grown crystals were studied by etch patterns. The crystal grown at pH 10showed 10% optical transmission enhancement in comparison to the crystals grown at pH 2. The indirect optical bandgap ofthe crystal was reinvestigated using ultraviolet–Visible–near-infrared transmittance spectrum. The laser damage thresholdstudies of the crystals grown at pH 10 reveal the higher optical radiation stability against 532 nm laser. The second-ordernonlinear optical behaviour of $\alpha$-LiIO$_3$ crystals grown at different pH conditions have been investigated by using Kurtz andPerry powder technique with Nd:YAG laser pulses at the wavelength of 1064 nm.

• Interplay of the influence of oxygen partial pressure and rf power on the properties of rf-magnetron-sputtered AZO thin films

The complex interplay between the influence of oxygen partial pressure and that of rf power on the structural,electrical and optical properties of rf-magnetron-sputtered aluminium-doped zinc oxide, AZO, thin films is illustrated. Thedependence of film electrical resistance and interplanar spacing of film crystallites on rf power seems to be different athigher oxygen partial pressure values than at lower ones. Film preparation was performed at room temperature (withoutextra heating) and low pressure $p = 0.5$ mTorr, varying the rf power density between $P = 0.57$ and 2.83 W cm$^{−2}$ at different relative oxygen partial pressure values. An explanation of film properties has been sought in terms of changes in the chemical properties of the films due to the bombardment of the films during film formation with negative oxygen ions.

• Phase transformation kinetics and microstructure of NiTi shape memory alloy: effect of hydrostatic pressure

The effect of hydrostatic pressure on the behaviour of reverse and forward transformation temperatures andphysical properties of NiTi shape memory alloy has been investigated. The transformation temperatures and physical properties of the alloy change with applied pressure. It has been clearly seen from differential scanning calorimetry that with theincrease of applied pressure, while $A_{\rm s}$, $A_{\rm f}$ and $M_{\rm f}$ transformation temperatures decrease, Ms value increases. Moreover, it is obvious that with the increase of applied pressure, Gibbs free energy increases by 5.2883 J, while elastic energy increases by 1.4687 J. In addition, entropy of the alloys decreases by 0.2335 J (g $^{\circ}$C)$^{−1}$ with applied pressure. Additionally, it is evident from the scanning electron microscopy images of the samples that there is an obvious difference in the grain sizes of the unpressured sample and the samples on which pressure is applied, the sizes being 10–100 and 30–150 $\mu$m, respectively.

• Influence of moisture absorption on the flexural properties of composites made of epoxy resin reinforced with low-content iron particles

In this work, the effect of moisture absorption on the mechanical properties of particulate composite materials isstudied. Moisture absorption constitutes a main parameter affecting the thermomechanical behaviour of composites, since itcauses plasticization of the polymer matrix with a concurrent swelling. In the present work, the influence of water absorptionon the flexural properties of particle-reinforced composites was thoroughly investigated. It was found that during the processof moisture absorption there exists a variation of the flexural properties closely related to the degradation of the mechanicalbehaviour of the composite, as well as the percentage amount of moisture absorbed. Experiments were carried out withcomposite made of epoxy resin reinforced with low-content iron particles. The variation of ultimate stress, breaking strain,deflection, elastic modulus and Poisson ratio due to water absorption was examined.

• Experimental and mechanical analysis of cement–nanotube nanocomposites

Composites of multi-walled carbon nanotubes (MWCNTs) and cement layers were manufactured by grindingcarbon nanotubes and cement powder in a planetary ball mill. Tiny cement nanoparticles were fabricated using anethylene-glycol-assisted synthesis procedure with successive hydrolysis and condensation reactions. Cement–nanotubenanocomposites were then produced by adding functionalized nanotube powder to the colloidal cement nanoparticles suspendedin ethylene glycol (weight ratio of nanotubes to cement = 1:1). Modal analysis of five-walled carbon nanotubenanocomposites with 1–5 cement layers was performed via the finite-element method. The five-walled carbon nanotubenanocomposites with different shapes were modelled using three-dimensional elastic beams of carbon bonds, nodal carbonpoint masses and cement layer shell elements. The natural frequency, vonMises stress and strain energy of the elements werecalculated by considering the Van derWaals forces between the carbon atoms in the hexagonal lattice. In the modal analysis,the greatest variation in displacement was observed along the x-axis, and the maximum values of the total displacementappeared to be larger at the cement layers than at the MWCNTs. The cement–nanotube nanocomposites exhibited a gradualdecrease in deformation and vibration as the number of cement layers was increased.

• Effects of iron concentration and redox states on failure of boron-free E-glass fibres under applied stress in different conditions

Hydrolysis resistance of boron-free E-glass fibre with different total iron oxide (Fe$_2$O$_3$) concentrations, iron redox index and durations of fibre ageing up to 180 days at 50$^{\circ}$C with 50% relative humidity (RH) was studied. The effect ofageing on the fibre failure measured in two different test environments was examined by using two-point bending method.Based on the differences in failure strains of the fibres obtained from the two conditions as a function of ageing time, theGriffith theory of solid fracture was applied to estimate glass surface energy difference in ageing conditions. The resultsshowed that stress-assisted hydrolysis, when the fibres were under stress, could lead to about 5.18 times reduction in surfaceenergy to account for 2.30 times reduction in fibre failure strain when tested in 50% RH at room temperature.Our study showedthat the boron-free E-glass aged up to 180 days only deteriorated within 13%, independent of total Fe$_2$O$_3$ concentration andFeO/Fe$_2$O$_3$ total ratio, and stress-assisted hydrolysis played a key role during sample testing. Dynamic fatigue of the aged E-glass fibres was also investigated, showing little influence of total Fe$_2$O$_3$ concentration and FeO/Fe$_2$O$_3$ total ratio on fibre stress; corrosion susceptibility was observed.

• Study of gamma radiation shielding properties of ZnO−TeO$_2$ glasses

Mass attenuation coefficient ($\mu_{\rm m}$), half value layer (HVL) and mean free path (MFP) for xZnO−(100−$x$)TeO$_2$, where $x = 10$, 15, 20, 25, 30, 35 and 40 mol%, have been measured for 0.662, 1.173 and 1.33 MeV photons emittedfrom ${}^{137}$Cs and ${}^{60}$Co using a $3\times 3 inch NaI(Tl) detector. Some relevant parameters such as effective atomic numbers ($Z_{\rm eff}$) and electron densities ($N_{el}$) of glass samples have been also calculated in the photon energy range of 0.015–15 MeV. Moreover, gamma-ray energy absorption buildup factor (EABF) and exposure buildup factor (EBF) were estimated using a five-parameter Geometric Progression (GP) fitting approximation, for penetration depths up to 40 MFP and in the energy range 0.015–15 MeV. The measured mass attenuation coefficients were found to agree satisfactorily with the theoreticalvalues obtained through WinXcom. Effective atomic numbers ($Z_{\rm eff}$) and electron densities ($N_{el}$) were found to be the highest for 40ZnO−60TeO$_2$glass in the energy range 0.04–0.2 MeV. The 10ZnO−90TeO$_2$glass sample has lower values of gamma-ray EBFs in the intermediate energy region. The reported new data on radiation shielding characteristics of zinctellurite glasses should be beneficial from the point of proper gamma shield designs when intended to be used as radiationshields. • Silver lead borate glasses doped with europium ions for phosphors applications Europium (Eu$^{3+}$) doped silver lead borate glasses with the composition of$x$Eu$_2$O$_3$−($1 − x$)Ag$_2$O−29PbO−70B$_2$O$_3$($x = 0$, 0.1, 0.2, 0.3, 0.4 and 0.5 mol%) have been successfully prepared by conventional meltquenching method. Thermal, structural and luminescence properties have been studied using thermograms, transmittance,excitation and emission spectra. From the differential scanning calorimetry studies, the glass transition temperatures ($T_g$)have been investigated and their values are ranging from 449 to 458$^{\circ}$C. The investigation of Fourier transformer infraredspectra shows the presence of boron atoms in both BO$_3$and BO$_4$units in the glass network. In addition, it was foundthat new structural groups were present, such as boroxyl rings, pyro and dipenta-borate. Photoluminescence spectroscopywas used to examine down conversion emission under 394 nm excitation, which exhibits five emission bands centred at577, 590, 612, 650 and 697 nm corresponding to${}^5$D$_0$−${}^7$F$_0$,${}^5$D$_0$−${}^7$F$_1$,${}^5$D$_0$−${}^7$F$_2$,${}^5$D$_0$−${}^7$F$_3$and${}^5$D$_0$−${}^7$F$_40$transitions ofEu$^{3+}$ions, respectively. The Commission International de I’Eclairage France 1931 chromaticity coordinates estimatedfrom the emission spectra; it was shown that a 0.5 mol% Eu$_2$O$_3\$ doped glass is quite suitable for efficient red phosphors application.

• Preparation of ZnO nanoribbon–MWCNT composite film and its application as antimicrobial bandage, antibacterial filter and thermal IR camouflage material

A zinc oxide nanoribbon (ZnO NR)–multiwall carbon nanotube (MWCNT) composite film was prepared byfiltration technique. The film was characterized by X-ray diffraction spectroscopy, scanning electron microscopy (SEM),Raman spectroscopy, infrared (IR) spectroscopy and reflectance spectroscopy. The SEM images showed ZnO NRs trappedin the porous MWCNT network. This composite film displayed a strong antimicrobial property and porous structure, whichhas potential application as an antimicrobial bandage material. The composite film successfully removed the Escherichiacoli bacteria from water and destroyed the bacteria retained on its surface due to the antibacterial action of ZnO NRs. The absorption of thermal IR radiation by the composite film was studied by thermography, which can be useful in IR camouflageapplications.

• # Bulletin of Materials Science

Current Issue
Volume 41 | Issue 1
February 2018