• Volume 34, Issue 1

February 2011,   pages  1-181

• Synthesis, characterization and gas sensing performance of SnO2 thin films prepared by spray pyrolysis

In this work, SnO2 thin films were deposited onto alumina substrates at 350°C by spray pyrolysis technique. The films were studied after annealing in air at temperatures 550°C, 750°C and 950°C for 30 min. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption spectroscopy technique. The grain size was observed to increase with the increase in annealing temperature. Absorbance spectra were taken to examine the optical properties and bandgap energy was observed to decrease with the increase in annealing temperature. These films were tested in various gases at different operating temperatures ranging from 50–450°C. The film showed maximum sensitivity to H2S gas. The H2S sensing properties of the SnO2 films were investigated with different annealing temperatures and H2S gas concentrations. It was found that the annealing temperature significantly affects the sensitivity of the SnO2 to the H2S. The sensitivity was found to be maximum for the film annealed at temperature 950°C at an operating temperature of 100°C. The quick response and fast recovery are the main features of this film. The effect of annealing temperature on the optical, structural, morphological and gas sensing properties of the films were studied and discussed.

• Thermodynamic modeling to analyse composition of carbonaceous coatings of MnO and other oxides of manganese grown by MOCVD

Equilibrium thermodynamic analysis has been applied to the low-pressure MOCVD process using manganese acetylacetonate as the precursor. CVD phase stability diagrams” have been constructed separately for the processes carried out in argon and oxygen ambient, depicting the compositions of the resulting films as functions of CVD parameters. For the process conduced in argon ambient, the analysis predicts the simultaneous deposition of MnO and elemental carbon in 1:3 molar proportion, over a range of temperatures. The analysis predicts also that, if CVD is carried out in oxygen ambient, even a very low flow of oxygen leads to the complete absence of carbon in the film deposited oxygen, with greater oxygen flow resulting in the simultaneous deposition of two different manganese oxides under certain conditions. The results of thermodynamic modeling have been verified quantitatively for lowpressure CVD conducted in argon ambient. Indeed, the large excess of carbon in the deposit is found to constitute a MnO/C nanocomposite, the associated cauliflower-like morphology making it a promising candidate for electrode material in supercapacitors. CVD carried out in oxygen flow, under specific conditions, leads to the deposition of more than one manganese oxide, as expected from thermodynamic analysis (and forming an oxide–oxide nanocomposite). These results together demonstrate that thermodynamic analysis of the MOCVD process can be employed to synthesize thin films in a predictive manner, thus avoiding the inefficient trial-and-error method usually associated with MOCVD process development. The prospect of developing thin films of novel compositions and characteristics in a predictive manner, through the appropriate choice of CVD precursors and process conditions, emerges from the present work.

• Effect of temperature and time on solvothermal synthesis of tetragonal BaTiO3

Tetragonal BaTiO3 nanoparticles are synthesized via solvothermal route in an ethanol water mixture. Ba(OH)2.8H2O is used as Ba precursor and TiO2 (P25 Degussa ∼25 nm, 30% anatase, 70% rutile) is used as Ti precursor in the Ba : Ti molar ratio 2 : 1. Effect of temperature and time study on solvothermal synthesis of BaTiO3 revealed that a moderate reaction temperature i.e. 185°C and longer reaction time favour tetragonal phase stabilization. Dissolution–precipitation appears to be the transformation mechanism for the crystallization of BaTiO3 from particulate TiO2 precursor.

• Aqueous colloids of graphene oxide nanosheets by exfoliation of graphite oxide without ultrasonication

Aqueous colloids of graphene oxide nanosheets were produced from exfoliation of graphite oxide using a magnetic stirrer and heat treatment in the absence of ultrasonication. Laser particle measurements showed that the particle size distribution of graphite oxide dispersed in de-ionized water was significantly influenced by treatment time indicating an increasing exfoliation level of graphite oxide. Atomic force microscopy (AFM) confirmed that single-layer graphene oxide nanosheets with a thickness of ∼1 nm were obtained after 72 h of magnetic stirring and heat treatment. These findings provide a new methodology for preparation of single-layer graphene oxide nanosheet colloids.

• Chitosan–silver oxide nanocomposite film: Preparation and antimicrobial activity

The chitosan–silver oxide encapsulated nanocomposite film was prepared by solution casting method. The prepared film was characterized by FTIR, scanning electron microscopy (SEM), thermal studies, and UV-Vis spectroscopy. The elemental composition of the film was studied by energy dispersive X-ray analysis (EDAX). The antibacterial activity of the composite film against pathogenic bacteria viz. Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa was measured by agar diffusion method. Our observations suggest that chitosan as biomaterial based nanocomposite film containing silver oxide has an excellent antibacterial ability for food packaging applications.

• Facile synthesis of poly(𝑝-phenylenediamine)/MWCNT nanocomposites and characterization for investigation of structural effects of carbon nanotubes

Poly(𝑝-phenylenediamine) (P𝑝PD)/carboxylic acid-functionalized multiwalled carbon nanotubes (𝑐-MWCNTs) nanocomposites were prepared by chemical oxidative polymerization using potassium persulfate (K2S2O8) as an oxidant. Field-emission scanning electron microscopy (FE–SEM) and field-emission transmission electron microscopy (FE–TEM) showed that a tubular layer of P𝑝PD was coated on the surface of carbon nanotubes with a thickness of 10–20 nm. FT–IR analysis provided an evidence for the formation of nanocomposites. The thermal stability of nanocomposites was improved by addition of 𝑐-MWCNTs as confirmed by thermogravimetric analysis (TGA). XRD spectra showed that the crystalline nature of P𝑝PD was not affected much by the addition of 𝑐-MWCNTs. As the content of 𝑐-MWCNTs was increased, the electrical conductivity of the nanocomposites increased due to the interaction between polymer and nanotubes that enhances electron delocalization.

• Dynamic characteristics of multi-walled carbon nanotubes under a transverse magnetic field

This paper reports the results of an investigation into the effect of transverse magnetic fields on dynamic characteristics of multi-walled carbon nanotubes (MWNTs). Couple dynamic equations of MWNTs subjected to a transverse magnetic field are derived and solved by considering the Lorentz magnetic forces induced by a transverse magnetic field exerted on MWCNTs. Results show that the transverse magnetic field exerted on MWNTs makes the lowest frequency of the MWNTs nonlinearly decrease and the highest frequency, changeless. When the strength of applied transverse magnetic fields is larger than a given value the two walls of MWNTs appear in the radial and axial coaxial vibration phenomena.

• Dielectric relaxation behaviour of Sr2SbMnO6 ceramics fabricated from nanocrystalline powders prepared by molten salt synthesis

Double perovskite polycrystalline single phase and dense Sr2SbMnO6 (SSM) ceramics, fabricated using the nanocrystalline powders synthesized by molten salt method, exhibited high dielectric constant with low dielectric loss as compared to that of SSM ceramics obtained from the powders prepared by solid-state synthesis method. The dielectric data obtained over a wide frequency (100 Hz–1 MHz) and temperature (190 K–300 K) ranges exhibited distinct relaxations owing to both the grain and grain boundary. The dielectric dispersion was modeled using the Cole–Cole equation consisting of two separate relaxation terms corresponding to the grain and grain boundary. The grain and grain boundary relaxations observed in the Nyquist plots (𝑍' and 𝑍) were modeled by an equivalent circuit consisting of two parallel RC circuits connected in series with each other. A careful analysis of both the impedance (𝑍'' vs𝜔) and modulus (𝑀'' vs𝜔) behaviour corroborated the conclusions drawn fromthe dielectric data.

• Effect of gamma radiation on electrical and optical properties of (TeO2)0.9 (In2O3)0.1 thin films

We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO2)0.9 (In2O3)0.1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 𝜇Gy/𝜇A/cm2. These values are far superior to any presently available real-time gamma radiation dosimeter.

• Small angles X-ray diffraction and Mössbauer characterization of annealed Tb/Fe multilayer

The effect of thermal annealing on the structure and magnetic properties of crystalline Tb/Fe multilayers has been studied using conversion electron Mössbauer spectrometry and small-angle X-ray diffraction. The growth of Tb–Fe amorphous alloy from the interface is observed with increasing annealing temperature. After annealing at 873 K, a clear total mixing of the multilayers by interdiffusion has been evidenced. The results are compared with the effect of ion irradiation in the same system.

• Microwave absorbing properties of activated carbon fibre polymer composites

Microwave absorption of composites containing activated carbon fibres (ACFs) was investigated. The results show that the absorptivity greatly depends on increasing ACF content in the absorbing layer, first increasing and then decreasing. When the content is 0.76 wt.%, the bandwidth below −10dB is 12.2 GHz. Comparing the absorption characteristics of the ACF composite with one containing unactivated fibres, it is found that carbon fibre activation increases the absorption of the composite.

• Effect of ion beam irradiation on metal particle doped polymer composites

Polymethyl methacrylate (PMMA) was prepared by solution polymerization method. Different concentrations (10, 20 and 40%) of Ni powder were dispersed in PMMA and the composite films were prepared by casting method. These films were irradiated with 120 MeV Ni$^{10+}$ ions at a fluence of 5 × 1012 ions/cm2. Electrical, structural and chemical properties of the composites were studied by means of an LCR meter, X-ray diffraction, FTIR spectroscopy and SEM/AFM, respectively. The results showed that the conductivity increases with metal concentration and also with ion beam irradiation. This reveals that ion beam irradiation promotes the metal/polymer bonding and converts polymeric structure into hydrogen depleted carbon network. It was observed from XRD analysis that percentage crystallinity and crystalline size decrease upon irradiation. This might be attributed to rupture of some polymeric bonds, which is also corroborated with FTIR spectroscopic analysis. Ion beam tempts graphitization of polymeric material by emission of hydrogen and/or other volatile gases. Surface morphology of the pristine and irradiated films was studied by atomic force microscopy (AFM)/scanning electron microscopy (SEM). Result showed that the surface roughness increases after ion beam irradiation.

• Structure refinement of polycrystalline orthorhombic yttrium substituted calcium titanate: Ca1−𝑥Y𝑥TiO3+𝛿 (𝑥 = 0.1–0.3)

The perovskite ceramic phases with composition Ca1−𝑥Y𝑥TiO3+𝛿 (where 𝑥 = 0.1, 0.2 and 0.3; hereafter CYT-10, CYT-20 and CYT-30) have been synthesized by solid state reaction at 1050°C. The structure refinement using general structure analysis system (GSAS) software converges to satisfactory profile indicators such as Rietveld parameters: Rp, Rwp, RF2 and goodness of fit. The title phases crystallize at room temperature in the space group 𝑃𝑏𝑛𝑚 (#62) with 𝑎 = 5.3741(4) Å, 𝑏 = 5.4300(4) Å, 𝑐 = 7.6229(5) Å and 𝑍 = 4. Major interatomic distances, bond angles and structure factors have been calculated from the step analysis data of the compound. The crystal morphology has been examined by scanning electron microscopy. Energy dispersive X-ray (EDX) analysis of the specimens show that yttrium enters into the structural framework of CaTiO3. The particle size of the ceramic phases along major reflection planes ranges between 12 and 40 nm. The polyhedral (CaO8 and TiO6) distortions and valence calculations from bond strength data are also reported.

• Polycarboxylate derivative of 𝛼-amino acid as growth modifier of sulphide minerals

Construction of modified inorganic mineral with controlled mineralization analogues of those produced by nature is now of current interest for understanding the mechanism of the in vivo biomineralization processes, as well as looking for fresh industrial and technological applications. Low-molecular-weight chiral polycarboxylate ligands derived fromnaturally occurring 𝐿-\alpha-amino acids have been used asmodel systems to study the effect of small organic matrix on crystal growth modification. The sulphide minerals are characterized by PXRD, FT–IR and SEM. Furthermore, the optical properties of these minerals have been characterized by UV-Vis and photoluminescence (PL) spectra.

• Transient charging and discharging current study in pure PVF and PVF/PVDF fluoro polyblends for application in microelectronics

The transient current were analysed by considering the effect of variation of forming time, temperature, field and composition of blend specimens. Measurements indicated that transient charging and discharging currents exhibited thermally activated character but did not show mirror image behaviour at different temperatures and field values. The log 𝐼–log 𝑡 plots were found to follow the Curie–Von Schweidler law with the value of decay constant 𝑛’ lying in the range of 0.029–2.9456. These observed characteristics also indicated that the transient charging in PVF:PVDF fluoro polyblends occur partly due to orientation of dipoles but predominantly due to trapped space charges and hopping of charge carriers amongst localized states. The modification in transient behaviour on blending PVDF with PVF have been explained on the basis of plasticization effect which increases free volume and molecular mobility and 𝑇g modification in the trap structure.

• Performance of waterborne acrylic surface coatings on wood impregnated with Cu-ethanolamine preservatives

Two waterborne acrylic coatings were applied on spruce wood, impregnated with two copperethanolamine containing preservatives (CuE and CuEQ), one of them (CuEQ) containing a boron compound, octanoic acid and a quaternary ammonium compound as additives. Lower contact angles and deeper penetration of both coating types were observed on CuEQ treated, compared to untreated or CuE-treated wood. Improved adhesion of coatings on CuEQ impregnated wood was exhibited as well. In general, characteristics of surface finishes on copper-ethanolamine treated wood were comparable to untreated wood. It was also shown that copper leaching from the preserved wood was significantly reduced by application of the surface finishes.

• Effect of low level substitution of Sr–Ba on transport and magnetic behaviour of La0.67Ca0.33MnO3

In this paper we report the investigation of transition metal oxide compound, La0.67Ca0.25Sr0.04Ba0.04MnO3 (LCSBMO), along with La0.67Ca0.33MnO3 (LCMO), synthesized by sol–gel route under identical conditions. The effect of simultaneous low level substitution of large size ions such as Sr2+ and Ba2+ for Ca2+ ions on the electronic transport and magnetic susceptibility properties are analysed and compared apart from microstructure and lattice parameters. The temperature dependent electrical transport of the polycrystalline pellets of LCSBMO and LCMO when obeying the well studied law, ρ = ρ0 + ρ2 𝑇2 for 𝑇 &lt; 𝑇MI, is observed to differ by more than 50% from the values of ρ0 and ρ2, with the former compound showing enhanced electrical conductivity than the latter. Similarly in fitting the adiabatic small polaron model for resistivity data of both the samples for 𝑇 &gt; 𝑇MI, the polaron activation energy is found to differ by about 11%. In addition, the temperature dependent a.c. magnetic susceptibility study of the compounds shows a shift of about 6% in the paramagnetic to ferromagnetic transition temperature (285 K for LCSBMO and 270 K for LCMO).

• Influence of lead oxide addition on LnTiTaO6 (Ln = Ce, Pr and Nd) microwave ceramics

The effect of PbO addition on the structural, processing and microwave dielectric properties of LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are reported. Conventional solid state ceramic route was used for the preparation of samples. Phase pure LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are prepared at a calcination temperature of 1300°C. The samples are sintered at optimized temperatures. Addition of PbO reduces the sintering temperature. The crystal structure of the materials was analysed using X-ray diffraction techniques and the surface morphology of the sintered samples was analysed using scanning electron microscopy. The dielectric constant at microwave frequency range decreases for higher PbO addition for all the samples but the quality factor improves on small PbO addition. The thermal stability of resonant frequency was also improved with PbO addition on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems suitable for practical applications.

• Effect of temperature on polarization reversal of strontium-doped lead zirconate titanate (PSZT) ceramics

The effect of temperature on polarization reversal of strontium-doped lead zirconate titanate ceramics was studied. The piezoelectric properties viz. dielectric constant and piezoelectric coupling coefficient, were used for polarization reversal characteristic. These properties and apparent coercive field weremeasured during polarization reversal at different temperatures. Results indicated that at higher temperature apparent coercive field decreased. Polarization reversal and further polarization reversal was quite asymmetric. After polarization reversal, dielectric constant was found to increase at all temperatures while piezoelectric coupling coefficient increased above the temperature of polarization. The trend shown by dielectric constant indicates that at 25°C, 1.5 kV/mm field can be applied safely to this material without much compromising the properties. D.c. field of 3.0 kV/mm and 100°C temperature can be predicted as poling parameters from their effect on kp. Apparent coercive field has shown non-linear relationship with temperature. It was of exponential decay type.

• Dielectric response of PLZT ceramics 𝑥/57/43 across ferroelectric– paraelectric phase transition

The dielectric properties of lead lanthanum zirconate titanate (PLZT) ceramics [Pb(Zr0.57Ti0.43)O3 +𝑥 at% of La, 𝑥 = 3, 5, 6, 10 and 12] have been measured in the frequency range 1 Hz–1 MHz using the vector impedance spectroscopy (VIS) at different temperatures. All the compositions show both non-dispersive and dispersive dielectric responses in different temperature regions. The non-dispersive region obeys the universal dielectric response. A low frequency (&lt; 1 kHz) relaxation phenomenon with a high value of distribution parameter ℎ’ (∼0.4 to 0.6) has been observed in all the compositions around the temperature corresponding to themaximum dielectric constant (𝑇m). The activation energies as calculated from the relaxation and d.c. conduction processes are comparable. The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content.

• Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0.0–5.0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al2O3–5B2O3) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure andmicrochemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (𝜀r), quality factor (𝑄 × 𝑓) and temperature coefficient of resonant frequency (𝜏f) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B2O3 and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600°C with optimum density (∼ 4 g/cm3) as compared with pure alumina powders recycled from Al dross (3.55 g/cm3 sintered at 1700°C).

The sintered ceramic bodies show different ranges for the dielectric properties. Dielectric constant exists between 24 and 29, quality factor (𝑄 × 𝑓) is ranging between 15,236 and 22,020 GHz with a slight increase than those recorded with commercial alumina (10,000 – 20,000 GHz) and temperature coefficient of resonant frequency (𝜏f) in the –69 to –83 ppm/°C range. The addition of SrO up to 5 wt% leads to a maximum (𝜀r) value (29) due to relatively higher ionic polarizability of Sr2+ than that of the Al3+ and B3+ ions. On the other hand, changing chemical and phase composition with the formation of platelets of Sr-hexaluminate phase (SrAl12O19) results in maximizing value of (𝑄 × 𝑓) up to 22,020 GHz at ≈ 8 GHz and large negative charge of (𝜏f) to –83 ppm/°C.

• Structure and electric transport properties of LnSr2FeTiO7 (Ln = La, Nd and Gd)

Three new phases with compositions, LaSr2FeTiO7, NdSr2FeTiO7 and GdSr2FeTiO7, were prepared by the traditional ceramic method. Lazy–Pulverix analysis of the X-ray diffraction data suggests that the phases crystallize in the RP-type (𝑛 = 2) structure in the space group, 𝐼4/𝑚𝑚𝑚. The cell dimensions along the 𝑐-axis decrease with decrease in size of the rare earth ions. Electrical resistivity, as a function of temperature, shows that the materials are insulators and the resistivity decreases with decrease in the size of the rare earth ion, which is attributed to increase in the three-dimensional character.

• Plasma nitriding of AISI 52100 ball bearing steel and effect of heat treatment on nitrided layer

In this paper an effort has been made to plasma nitride the ball bearing steel AISI 52100. The difficulty with this specific steel is that its tempering temperature (∼170–200°C) is much lower than the standard processing temperature (∼460–580°C) needed for the plasma nitriding treatment. To understand the mechanism, effect of heat treatment on the nitrided layer steel is investigated. Experiments are performed on three different types of ball bearing races i.e. annealed, quenched and quench-tempered samples. Different gas compositions and process temperatures are maintained while nitriding these samples. In the quenched and quench-tempered samples, the surface hardness has decreased after plasma nitriding process. Plasma nitriding of annealed sample with argon and nitrogen gas mixture gives higher hardness in comparison to the hydrogen–nitrogen gas mixture. It is reported that the later heat treatment of the plasma nitrided annealed sample has shown improvement in the hardness of this steel. X-ray diffraction analysis shows that the dominant phases in the plasma nitrided annealed sample are 𝜀 (Fe2−3N) and 𝛾 (Fe4N), whereas in the plasma nitrided annealed sample with later heat treatment only 𝛼-Fe peak occurs.

• Characterization on strength and toughness of welded joint for Q550 steel

Q550 high strength steel was welded using gas shielded arc welding and three different welding wires without pre- or post-heat treatments. The paper investigates the influence of welding wire on the microstructure, tensile strength and impact toughness of Q550 steel weld joints. Results showed that the microstructure of the weld metal of joints produced using ER50-6 wire was a mixture of acicular ferrite and grain boundary ferrite including pro-eutectoid ferrite and ferrite side plate. Acicular ferrite was mainly obtained in the weld metal of the joints produced using MK.G60-1 wire. Pro-eutectoid ferrite was present along the boundary of prior austenite. Crack initiation occurred easily at pro-eutectoid ferrite when the joint was subjected to tensile. Tensile strength and impact toughness were promoted with increasing acicular ferrite. Tensile strength of the joint fabricated using MK.G60-1 wire was close to that of base metal. And tensile samples fractured at location of the fusion zone, which had lower toughness and thus became the weak region in the joint. Impact absorbing energy was the highest in the heat affected zone. Fibrous region in fracture surfaces of impact specimens was characterized as transgranular fracture with the mechanism of micro-void coalescence. Acicular ferrite microstructure region corresponded to relatively large dimples while boundary ferrite microstructure corresponded to small dimples.

• An investigation of X-ray and radio isotope energy absorption of heavyweight concretes containing barite

This study investigated the X-ray and radioisotope energy absorption capacity of heavyweight concrete containing barite aggregate. Concrete plates were prepared using differing amounts of barite aggregate instead of normal aggregate. Density–thickness–energy variations of these concretes for 85 keV, 118 keV, 164 keV, 662 keV and 1250 keV ray energies were recorded. It was observed that the concretes with greater barite content had a higher density and energy absorption capacity.

• Preparation and characterization of a novel bone graft composite containing bone ash and egg shell powder

Egg shells which were hitherto discarded as wastes were collected, purified and powdered into a particle size in the range of 5–50 𝜇m. A composite bone graft material in cylindrical form was prepared using egg shell powder (ESP), bone ash (BA) and gelatin. These bone grafts were characterized for their FT–IR, TGA, XRD, SEM and mechanical properties. The mechanical studies indicate that the composite having a stoichiometric ratio of BA (3 g) and ESP (7 g) has shown better mechanical properties. X-ray diffraction (XRD) data indicated the crystallographic nature of BA is akin to hydroxyapatite (HA) and both BA and ESP did not lose their crystalline nature when bone grafts were prepared. This revealed that ESP may be used as a component in bone graft utilizing the solid waste from the poultry industry.

• # Bulletin of Materials Science

Volume 43, 2020
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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019