• Volume 29, Issue 3

June 2006,   pages  201-337

• ac MH loop measurements on Mn doped YBa2Cu3O7–𝛿 superconductors

Isothermal ac MH (magnetization-field) loops for varying field amplitudes were recorded at 77 K on YBa2(Cu1–𝑥Mn𝑥)3O7–𝛿 with 𝑥 = 0, 0.010, 0.015, 0.020, 0.025, 0.035 and 0.050, YBa2(Cu0.075Fe0.025)3O7–𝛿, YBa2(Cu0.075Ni0.025)3O7–𝛿 and YBa2(Cu0.075Zn0.025)3O7–𝛿 samples up to a maximum field amplitude of 80 Oe. Flat band susceptibility, ac losses and flux profiles were deduced from the ac MH loops. The undoped sample exhibited a minimum weak link ac loss and the 5.0% doped sample showed maximum weak link ac loss. Ni and Fe doped samples showed higher granular losses. 𝐽cg estimated from the flux profiles decreases monotonically with increasing concentrations of Mn up to 2.5%.

• On the study of phase formation and critical current density in superconducting MgB2

Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1 : 2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (𝑇C) and critical current density (𝐽C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2 : 2 ratio, at temperatures around 790°C. Critical current density has been found to vary systematically with processing temperature.

• Powder XRD studies on 𝑛-C28H58 : 𝑛-C𝑥H2𝑥+2 (𝑥 = 10, 12, 14, 16, 18) hydrocarbon mixtures: Phase strength analysis

Powder XRD investigations were made on mixtures of title compounds and strength of monoclinic, orthorhombic and super-lattice phases were evaluated. Interpretations were made in terms of the influence of tunnel-like defects (TLIDs) and a linear relationship was noticed between the strength of orthorhombic phase and 〈$\ell$TLID 〉.

• A coprecipitation technique to prepare Sr0.5Ba0.5Nb2O6

An aqueous mixture of ammonium oxalate and ammonium hydroxide was used to coprecipitate barium and strontium ions as oxalates and niobium ions as hydroxide under basic conditions. This precursor on calcining at 750°C yielded Sr0.5Ba0.5Nb2O6 phase. This is a much lower temperature than that prepared by traditional solid state method (1000°C) as reported for the formation of Sr0.5Ba0.5Nb2O6 (SBN). Transmission electron microscopic (TEM) investigations revealed that the average particle size was 80 nm for the calcined powders. The room temperature dielectric constant at 1 kHz was found to be 1100. The ferroelectric hysteresis loop parameters of these samples were also studied.

• Synthesis and characterization of porous polyurethaneurea membranes for pervaporative separation of 4-nitrophenol from aqueous solution

Hydroxyterminated polybutadiene (HTPB) based porous polyurethaneurea (PUU) membranes were prepared. The porosity was developed by incorporation of lithium chloride into polymer matrix with subsequent leaching of the same in hot water. Scanning electron microscopic analysis of the prepared membrane surfaces was performed. The pervaporation performance of the synthesized membrane was studied with aqueous 4-nitrophenol solution as feed. The effects of various parameters on 4-nitrophenol separation factor and total as well as 4-nitrophenol flux were studied. Polyurethaneurea membrane was found to permeate 4-nitrophenol selectively with high separation factors for the organic component. Pore size and number of pores on the surface of the membrane were calculated from SEM image of the membranes. Effects of pore size and porosity on pervaporation flux were also investigated.

• External stimuli response on a novel chitosan hydrogel crosslinked with formaldehyde

Keeping in mind the significance of hydrogels as an external stimuli sensitive super absorbing material, some transparent covalent hydrogels of chitosan were prepared by crosslinking with varying amounts of formaldehyde solution used as crosslinking agent. The characteristics of hydrogels were investigated by Fourier transform infrared (FT–IR) spectroscopy and swelling experiments. The effect of crosslinking agent on water absorbency has been investigated. The hydrogels exhibited a relatively higher swelling ratio in the range of 2066–3306% and equilibrium water content (EWC) in the range of 95.38–97.06% at pH 7 and 35°C temperature. The influence of external stimuli such as pH, temperature, and ionic strength of the swelling media on equilibrium swelling properties has been observed. Hydrogels showed a typical pH and temperature responsive behaviour such as low pH and high temperature has maximum swelling while high pH and low temperature show minimum swelling. An increase in the ionic strength of swelling media caused a continuous decrease in the swelling of hydrogels at both acidic and basic pH.

• Synthesis, X-ray structure and N–H…O interactions in 1,3-diphenyl-urea

The synthesis, X-ray structure and role of intermolecular interactions have been studied in case of 1,3-diphenyl-urea, owing to its medicinal importance. The compound crystallizes in orthorhombic crystal system (space group, 𝑃𝑛𝑎21) with unit cell parameters, 𝑎 = 9.118(3), 𝑏 = 10.558(2), 𝑐 = 11.780(3) Å and 𝑍 = 4. The structure has been solved by direct methods and refined to a final 𝑅-value of 0.0316. The oxygen atom of the carbonyl group is responsible for the existence of two N–H…O intermolecular interactions.

• Abrasive wear behaviour of bio-active glass ceramics containing apatite

In this study, abrasive wear behaviour of bio-active glass ceramic materials produced with two different processes is studied. Hot pressing process and conventional casting and controlled crystallization process were used to produce bio-active ceramics. Fracture toughness of studied material was calculated by fracture toughness equations using experimental hardness results of the bio-active glass ceramic material. Two fracture toughness equations in the literature were used to identify the wear behaviour of studied ceramics. Wear resistance results that identified with both of the equations were similar. The results showed that the abrasive wear resistance of the bio-active glass ceramics produced with hot pressing process was found to be higher than that of the ceramics produced by conventional casting and controlled crystallization process.

• Synthesis of an organic–inorganic hybrid material by solid state intercalation of 2-mercaptopyridine into Na-, Al(III)- and Co(II)-montmorillonite

The preparation of an organic–inorganic hybrid material by solid state intercalation of 2-merca-ptopyridine (2Mpy) into Na-, Co(II)- and Al(III)-montmorillonite has been studied using a variety of techniques. The extension of 𝑑001 from XRD proves that the intercalation of 2-mercaptopyridine into Na-, Co(II)- and Al(III)-mont occurs at ambient temperature in 5 mn. When the intercalated samples were heated at different temperatures, we found that the 𝑑001 gave different values. For instance, for intercalated Al(III)- and Co(II)-, 𝑑001 remained unchanged for a temperature under 500°C. However, for intercalated Na-mont, it shifted to 14 Å for a temperature of 300°C, the washing of different samples with a methanol solution shifted the 𝑑001 of intercalated Na-mont to 14 Å. However, for intercalated Al(III) and Co(II), it did not change. This proves that in the case of Na-mont, the molecules of 2-mercaptopyridine interact with the clay through hydrogen bindings and physical interactions. However, for Al(III) and Co(II), it forms coordination linking and physical interaction. 13C NMR and FTIR spectroscopy have been employed for the characterization of the intercalation compounds. Tautomeric equilibrium between thiol and thione species of 2-mercaptopyridine must be taken into account to explain the arrangement of molecular aggregates and their particular orientation in the interlayer space. The isotherm of adsorption–desorption of nitrogen and topographic AFM images prove that intercalation of 2Mpy is accompanied by a total blockage of clay porosity and an increase in roughness.

• Transport through track etched polymeric blend membrane

Polymer blends of polycarbonate (PC) and polysulphone (PSF) having thickness, 27 𝜇m, are prepared by solution cast method. The transport properties of pores in a blend membrane are examined. The pores were produced in this membrane by a track etching technique. For this purpose, a thin polymer membrane was penetrated by a single heavy ion of Ni7+ of 100 MeV, followed by preferential chemical etching of the ion track. Ion permeation measurements show that pores in polymeric membrane are charged or neutralized, which depends upon the variation in concentration of the solvent. The 𝑉–𝐼 curve at concentration, N/10, shows that the pores are negatively charged, whereas at concentration, N/20, the linear nature of 𝑉–𝐼 curve indicates that the pores approach towards neutralized state and on further concentration, N/40, the pores become fully neutralized, consequently the rectifier behaviour of pores has been omitted.

The gas permeability of hydrogen and carbon dioxide of this membrane was measured with increasing etching time. The permeability was measured from both the sides. Permeability at the front was larger than the permeability at the back which shows asymmetric behaviour of membranes.

• Discrimination of surface tracking patterns of gamma irradiated polymers using fractals

The purpose of this paper is to evaluate the radiation resistance of gamma irradiated ethylene propylene diene monomer (EPDM) and to identify the pattern discriminating abilities of the surface tracking patterns. Simple objects can be described by the ideal shape primitives such as cubes, cones and cylinders. But most of the natural objects are so complex that cannot be described in terms of simple primitives. Fractals have been very successfully used to address the problem of modeling and to provide a description of naturally occurring phenomena and shapes, wherein conventional and existing mathematical models were found to be inadequate. The geometrical patterns of dielectric breakdown like electrical trees, surface discharges, and lightning are known to be of fractal in nature. These fractal patterns can be analysed numerically using fractal dimensions and lacunarity. Surface tracking occurring in HV insulation systems is a very complex phenomenon and more so are the shapes of tracking patterns. It has been fairly well established that the shapes and the underlying parameters causing tracking have a 1 : 1 correspondence and therefore, methods to describe and quantify these patterns must be explored. This paper reports preliminary results of such a study wherein 2-𝑑 tracking patterns of gamma irradiated ethylene propylene diene monomer were analysed and found to possess fairly reasonable pattern discriminating abilities. This approach appears promising and further research is essential before any long-term predictions can be made.

• Low cycle fatigue behaviour of Ti–6Al–5Zr–0.5Mo–0.25Si alloy at room temperature

Low cycle fatigue (LCF) behaviour of the near 𝛼 titanium alloy, Ti–6Al–5Zr–0.5Mo–0.25Si (LT26A), was investigated in the (𝛼 + 𝛽) as well as 𝛽 treated conditions at room temperature. LCF tests were carried out under total strain controlled mode in the range of 𝛥 𝜀t/2: from ± 0.60% to ± 1.40%. The alloy shows cyclic softening in both the conditions. Also it exhibits dual slope Coffin–Manson (C–M) relationship in both the treated conditions.

• Electrical discharge machining studies on reactive sintered FeAl

Electrical discharge machining (EDM) studies on reactive sintered FeAl were carried out with different process parameters. The metal removal rate and tool removal rate were found to increase with the applied pulse on-time. The surface roughness of machined surface also changed with the applied pulse on-time. XRD analysis of machined surface of sintered FeAl showed the formation of Fe3C phase during the EDM process. The debris analysis was used to identify the material removal mechanism occurring during the EDM of sintered FeAl.

• Effect of microalloying on aging of a Cu-bearing HSLA-100 (GPT) steel

Investigations were carried out on aging of a HSLA-100 steel containing Cu as the major alloying element and Nb, Ti and V as microalloying elements. The aging process after varying amounts of cold deformation was followed by hardness measurements and microstructural changes were studied using light and electron microscopy. Presence of Ti activates the formation of (Nb, Ti)C precipitates and completely suppresses the precipitation of Cu. Even a solution treatment at 1100° C is not sufficient to completely dissolve Nb and Ti in the matrix and undissolved (Nb, Ti)C precipitates were observed in oil quenched state. Strain induced aging at 400°C causes simultaneous coarsening of existing precipitates and nucleation of fresh carbides, which results in multi-stage hardening in this steel. Strong precipitate-dislocation interactions cause retardation in recrystallization of deformation structure leading to retention of high hardness levels even on prolonged aging.

• Characterization of zinc–nickel alloy electrodeposits obtained from sulphamate bath containing substituted aldehydes

Zinc alloy offers superior sacrificial protection to steel as the alloy dissolves more slowly than pure zinc. The degree of protection and the rate of dissolution depend on the alloying metal and its composition. Zinc-nickel alloy may also serve as at less toxic substitute for cadmium. In this paper the physico-chemical characterization of zinc-nickel electrodeposits obtained from sulphamate bath containing substituted aldehydes was carried out using hardness testing, X-ray diffraction, and corrosion resistance measurements. The corrosion behaviour of these samples in a 3.5% NaCl solution was examined. The decrease in 𝐼corr and high charge transfer resistance indicated the improved corrosion resistance of these deposits.

• Mössbauer studies on an AISI 1137 type steel

An AISI 1137 type medium carbon steel was studied by means of scanning electron microscopy and Mössbauer spectroscopy. This steel in as received state at room temperature was ferritic. Different heat treatments on related steel exhibited different microstructures such as pearlite and bainite. Also magnetism of these product phases was determined as 32.7 T and 32.6 T relatively where ferromagnetism of ferritic phase in as received state was 33.05 T. Mössbauer parameters such as isomer shifts and % volumes were also determined before and after transformations.

• Growth and characterization of gel grown pure and mixed iron–manganese levo-tartrate crystals

Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation, we have grown pure and mixed iron (II)–manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing the content of manganese in the crystals. The crystals were characterized by FTIR spectroscopy, powder XRD, TGA, VSM and dielectric study. Crystal structures of different mixed crystals were studied. From TGA it was observed that on heating the hydrated crystals became anhydrous and then converted into oxides. Paramagnetic nature of the crystals was revealed from VSM study. The variation of the dielectric constant with frequency was studied. The results are discussed.

• Anisotropic properties of aligned SWNT modified poly (methyl methacrylate) nanocomposites

The poly (methyl methacrylate) (PMMA)/single-walled carbon nanotube (SWNT) composites with good uniformity, dispersion and alignment of SWNT were fabricated in an improved figuration process. The semidried mixture was stretched along one direction at a drawing ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The transmission electron microscopic (TEM) observation demonstrated that SWNT in the PMMA/SWNT composite tends to align in the stretching direction owing to a torque exerting on it in the stretching process. The electrical and mechanical properties of PMMA/SWNT composite were studied as a function of SWNT orientation and concentration. The aligned SWNT modified PMMA/SWNT composite presented highly anisotropic properties. The experimental results showed that the electrical conductivity and mechanical properties of composite rise with the increase of SWNT concentration, and that composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The thermogravimetric analysis (TGA) revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.

• Optical, structural and electrical properties of Mn doped tin oxide thin films

Mn doped SnO𝑥 thin films have been fabricated by extended annealing of Mn/SnO2 bilayers at 200°C in air for 110 h. The dopant concentration was varied by controlling the thickness of the metal layer. The overall thickness of the film was 115 nm with dopant concentration between 0 and 30 wt% of Mn. The films exhibit nanocrystalline size (10–20 nm) and presence of both SnO and SnO2. The highest transmission observed in the films was 75% and the band gap varied between 2.7 and 3.4 eV. Significantly, it was observed that at a dopant concentration of ∼ 4 wt% the transmission in the films reached a minimum accompanied by a decrease in the optical band gap. At the same value of dopant concentration the resistivity also reached a peak. This behaviour appears to be a consequence of valence fluctuation in Sn between the 2+ and 4+ states. The transparent conductivity behaviour fits into a model that attributes it to the presence of Sn interstitials rather than oxygen vacancies alone in the presence of Sn2+.

• Surface characterization of sol–gel derived indium tin oxide films on glass

Indium tin oxide (ITO) films containing different In : Sn atomic ratios, viz. 90 : 10, 70 : 30, 50 : 50, 30 : 70, were deposited on two types of glass substrates by sol–gel spinning technique. XPS analysis of the films was done under as-received and after-sputtering conditions. The narrow spectra obtained for the Na1𝑠, In3𝑑, Sn3𝑑 and O1𝑠 have been discussed. Oxygen was found to exist in three chemical environments in as-received samples due to the existence of

1. environmental hydroxyl (–OH) group,

2. crystalline ITO and

3. amorphous ITO; but it was in two chemical environments, (ii) and (iii), after surface cleaning by sputtering.

The presence of both tin metal and tin oxides was confirmed by the peak analysis of Sn3𝑑. The In : Sn atomic ratio taken in the precursor sols did not change considerably in the case of developed films of low Sn content, but considerable change was observed in the films having high Sn content.

• Influence of Zn doping on electrical and optical properties of multilayered tin oxide thin films

In this study, the electrical and optical properties of Zn doped tin oxide films prepared using sol–gel spin coating process have been investigated. The SnO2 : Zn multi-coating films were deposited at optimum deposition conditions using a hydroalcoholic solution consisting of stannous chloride and zinc chloride. Films with Zn doping levels from 0–10 wt% in solution are developed. The results of electrical measurements indicate that the sheet resistance of the deposited films increases with increasing Zn doping concentration and several superimposed coatings are necessary to reach expected low sheet resistance. Films with three coatings show minimum sheet resistance of 1.479 k𝛺/ in the case of undoped SnO2 and 77 k𝛺/ for 5 wt% Zn doped SnO2 when coated on glass substrate. In the case of single layer SnO2 film, absorption edge is 3.57 eV and when doped with Zn absorption edge shifts towards lower energies (longer wavelengths). The absorption edge lies in the range of 3.489–3.557 eV depending upon the Zn doping concentration. The direct and indirect transitions and their dependence on dopant concentration and number of coatings are presented.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019