• Volume 28, Issue 5

August 2005,   pages  383-513

• Preparation of microstructured hydroxyapatite microspheres using oil in water emulsions

Hydroxyapatite (HAP) microspheres with peculiar spheres-in-sphere morphology were prepared by using oil-in-water emulsions and solvent evaporation technique. Ethylene vinyl acetate co-polymer (EVA) was used as the binder material. Preparation of HAP/EVA microspheres was followed by the thermal debinding and sintering at 1150°C for 3 h to obtain HAP microspheres. Each microsphere of 100–1000 𝜇m was in turn composed of spherical hydroxyapatite granules of 2–15 𝜇m size which were obtained by spray drying the precipitated HAP. The parameters such as percentage of initial HAP loading, type of stabilizer, concentration of stabilizer, stirring speed and temperature of microsphere preparation were varied to study their effect on the particle size and geometry of the microspheres obtained. It was observed that these parameters do have an effect on the size and shape of the microspheres obtained, which in turn will affect the sintered HAP microstructure. Of the three stabilizers used viz. polyoxyethylene(20) sorbitan monopalmitate (Tween-40), sodium laurate and polyvinyl alcohol (PVA), only PVA with a concentration not less than 0.1 wt% showed controlled stabilization of HAP granules resulting in spherical microspheres of required size. Morphologically better spherical microspheres were obtained at 20°C. Increasing the stirring speed produced smaller microspheres. Smaller microspheres having size &lt; 50 𝜇m were obtained at a stirring speed of 1500 ± 50 rpm. A gradual decrease in pore size was observed in the sintered microspheres with increase in HAP loading.

• Preparation of ultrafine LiTaO3 powders by citrate gel method

A gel was formed when a aqueous solution of Li(NO3), TaF5 and citric acid in stoichiometric ratio was heated in a water bath. This gel on decomposition at 700°C produced fine crystallites of ternary oxide, LiTaO3 (LT). The phase contents and lattice parameters were studied by powder X-ray diffraction (XRD). Particle size and morphology were studied by transmission electron spectroscopy (TEM).

• Structure and coercivity of nanocrystalline Fe–Si–B–Nb–Cu alloys

Crystallization behaviour and magnetic properties of melt-spun Fe–Si–B–Nb–Cu alloys have been investigated. It is found that the primary phase changes from 𝛼-Fe(Si) to Fe3Si (DO3) on increasing the Si content. The coercivity of the alloys containing the Fe3Si phase is significantly lower as compared to the alloy containing 𝛼-Fe(Si) phase. A heat treatment temperature–time–coercivity map has been obtained for optimization of the coercivity.

• Influence of alloying and secondary annealing on anneal hardening effect at sintered copper alloys

This paper reports results of investigation carried out on sintered copper alloys (Cu, 8 at%; Zn, Ni, Al and Cu–Au with 4 at%Au). The alloys were subjected to cold rolling (30, 50 and 70%) and annealed isochronally up to recrystallization temperature. Changes in hardness and electrical conductivity were followed in order to investigate the anneal hardening effect. This effect was observed after secondary annealing also. Au and Al have been found to be more effective in inducing anneal hardening effect.

• Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

Single crystals of the lamellar compound, ZrSe3, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe3 were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe3 single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.

• Crystal growth and reflectivity studies of Zn1–𝑥Mn𝑥Te crystals

Single crystals of Zn1–𝑥Mn𝑥Te were prepared by vertical Bridgman crystal growth method for different concentrations of Mn. Chemical analysis and reflectivity studies were carried out for compositional and band structure properties. Microscopic variation in composition between starting and end compounds was observed from EDAX analysis. Linear dependence of fundamental absorption edge (𝐸0) as a function of Mn concentration (𝑥) was expressed in terms of a straight line fit and a shift in 𝐸0 towards higher energy was observed in reflectivity spectra of Zn1–𝑥Mn𝑥Te.

• D.C. electrical conductivity measurements on ADP single crystals added with simple organic compounds

Pure and impurity added (with urea and thiourea) ADP single crystals were grown by the free evaporation method. D.C. electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 40–150°C by the conventional two-probe method. Activation energies were also determined. The present study indicates that the conductivity increases with the increase in impurity concentration and temperature.

• Magnetoelectric effect in metal–PZT laminates

Magnetoelectric (ME) composites are two-phase composites consisting of piezoelectric and piezomagnetic materials as the participating constituents. These magnetoelectric composites when placed under external magnetic field, show electrical polarization (magnetoelectric output). The ME coupling is mediated by mechanical stress. In the present study, we have synthesized Ni/PZT/Ni and Fe/PZT/Fe layered composites for studying their ME output by dynamic magnetoelectric set up in which both d.c. and a.c. magnetic fields can be varied. The ME output obtained in these composites are higher than those obtained in 40% Ni0.97Co0.03Mn0.01 Fe1.9O4 + 60% BaTi1.02O3.04. The results with varying d.c. and a.c. magnetic fields are presented.

• Preparation and characterization of polymer composites based on charge-transfer complex of phenothiazine–iodine in polystyrene

Polymer composites based on charge-transfer complex of phenothiazine and iodine with polystyrene have been prepared in different weight ratios and characterized by FTIR, XRD, mechanical, microstructure and electrical properties (d.c. as well as a.c.). These composites show semiconducting behaviour as the conductivity increases with increasing temperature. Low percolation threshold (10% wt CTC) has been found indicating that processable conducting polymers with improved mechanical properties can be prepared by this method.

• Structural and electrical measurements of CdZnSe composite

The 𝐼–𝑉 characterization and the electrical resistivity of selenium rich Se85Cd15–𝑥Zn𝑥 (𝑥 = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be polycrystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements of 𝐼–𝑉 characteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 × 108𝛺 m and minimum 7.3 × 105𝛺 m and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.

• Ultra low and negative expansion glass–ceramic materials produced from pyrophyllite and blast furnace slag

Ultra low and negative expansion glass–ceramic materials have been obtained from pyrophyllite and blast furnace slag. The batch composition was modified with the addition of lithium carbonate, hydrated alumina, boric acid and nucleating agent (titania). The batch was melted at 1400°C followed by casting in the form of bars and annealed at 510°C for 4 h. The annealed specimens were subjected to heat treatment at predetermined temperatures selected from DTA study of the parent glass. Thermal expansion measurement and X-ray diffraction analysis revealed that the specimen nucleated at 545°C for 4 h and crystallized at 720°C for 2 h which resulted in negative coefficient of thermal expansion [(–) 9 to (–) 2 × 10$^{-7}/{}^\circ$C] over the temperature range (30–600°C) due to the formation of 𝛽-eucryptite while other heating schedule showed the formation of spodumene and lithium aluminium silicates. The samples showed excellent flexural strength value and varied in the range 120–200 MPa depending upon the phases present.

• Effect of titania on fired characteristics of triaxial porcelain

Titania was progressively added in the range 3–9 wt% into a triaxial porcelain body consisting of clay, quartz and feldspar. The composed bodies were heated at five different temperatures in the range 1200–1400°C and their fired properties as well as phases evolved were studied. The results revealed that beyond 1300°C, formation of more liquid phases caused bloating in samples which led to generation of pores. This effect is more pronounced in TiO2 containing samples. In the present system, 1300°C appeared to be the optimum temperature at which porosity was almost negligible and strength was maximum (45 MPa), particularly in presence of TiO2. From the results of XRD studies, it was revealed that quartz content primarily decreased with increase in TiO2 content due to excess glass formation and its subsequent dissolution. Mullite content increased with increase in TiO2 content. No significant effect was observed beyond 6 wt% addition. Microstructure primarily showed the presence of quartz grain and cluster of smaller sized primary mullite crystals in both the samples without and with TiO2. Very few secondary mullite crystals were also observed. SEM picture of sample containing 9 wt% TiO2 showed some grain boundary crack due to cooling stress generated in the glassy phase. The drastic reduction of residual strength after 8 cycles of heating at 800°C and cooling particularly in TiO2 containing samples suggests controlled heat treatment of the vitrified samples necessary to promote secondary crystallization process for the enhancement of strength. Attempts have also been made to correlate the constitutional parameters with the properties.

• Characterization and microstructure of porous lead zirconate titanate ceramics

Porous lead zirconate titanate (PZT) ceramics are widely used because of their low acoustic impedance, high figure of merit and high hydrostatic sensitivity. In the present work, porous PZT ceramics were fabricated by incorporating polyethylene oxide (PEO) as pore-forming agent. Both PZT powder and PEO were mixed with a binder at different ratios and compaction was carried out. The samples were slowly heated to remove the pore-forming agent and binder without cracks, followed by controlled sintering and electrode forming. Samples were poled using corona poling technique. The ferroelectric properties and microstructure of the prepared ceramics were characterized. The correlation of porosity with microstructure and ferroelectric properties were discussed.

• Effect of phase separation on the fracture toughness of SiO2–B2O3–Na2O glass

Fracture toughness of glass is usually poor, due to the absence of grain boundaries and discontinuities. The compositions of the glass studied are in the phase separated region of SiO2–B2O3–Na2O system. The interface between the glass in glass separation enhances the fracture toughness. The increase in the connectivity of phase separated regions causes increase of fracture toughness from 0.98 through 1.43 to 1.54 MPam1/2.

• Optical absorption and fluorescence properties of Er3+ in sodium borate glass

Spectroscopic properties of Er3+ ions in sodium borate glass have been studied. The indirect and direct optical band gaps (𝐸opt) and energy level parameters (Racah (𝐸1, 𝐸2 and 𝐸3), spin-orbit (𝜉4f) and configurational interaction (𝛼)) are evaluated. Spectral intensities for various absorption bands of Er3+ doped sodium borate glass are calculated. Using Judd–Ofelt intensity parameters (𝛺2, 𝛺4, 𝛺6), radiative transition probabilities (𝐴), branching ratios (𝛽) and integrated absorption cross sections (𝛴 ) are reported for certain transitions. The radiative lifetimes (𝜏R) for different excited states are estimated. From the fluorescence spectra, the emission cross section (𝜎p) for the transition, ${}^{4}I_{13/2} \rightarrow {}^{4}I_{15/2}$ is reported.

• Correlation between ionic conductivity and fluidity of polymer gel electrolytes containing NH4CF3SO3

Nonaqueous polymer gel electrolytes containing ammonium triflate (NH4CF3SO3) and dimethylacetamide (DMA) with polymethylmethacrylate (PMMA) as the gelling polymer have been synthesized which show high value of conductivity (∼ 10-2 S/cm) at 25°C. The conductivity of polymer gel electrolytes containing different concentrations of NH4CF3SO3 shows a small decrease with the addition of PMMA and this has been correlated with the variation of fluidity of these gel electrolytes. The small decrease in conductivity with PMMA addition shows that polymer plays the role of stiffener and this is supported by FTIR results which also indicates the absence of any active interaction between polymer and NH4CF3SO3 in these gel electrolytes.

• High-energy heavy ion testing of VLSI devices for single event upsets and latch up

Several very large scale integrated (VLSI) devices which are not available in radiation hardened version are still required to be used in spacecraft systems. Thus these components need to be tested for highenergy heavy ion irradiation to find out their tolerance and suitability in specific space applications. This paper describes the high-energy heavy ion radiation testing of VLSI devices for single event upset (SEU) and single event latch up (SEL). The experimental set up employed to produce low flux of heavy ions viz. silicon (Si), and silver (Ag), for studying single event effects (SEE) is briefly described. The heavy ion testing of a few VLSI devices is performed in the general purpose scattering chamber of the Pelletron facility, available at Nuclear Science Centre, New Delhi. The test results with respect to SEU and SEL are discussed.

• Synthesis of MoO3 and its polyvinyl alcohol nanostructured film

The synthesis of ultrafine MoO3 through a self-propagating combustion route employing polyethylene glycol as fuel is reported. The precursor molybdenum oxalate is employed in this study for the conversion of the precursor to ultrafine MoO3 particles. The solvent casting method is adopted for the synthesis of MoO3 dispersed polyvinyl alcohol nanostructured film (MoO3–PVA). These synthesized MoO3 and their composite samples are characterized for their structure, morphology, bonding and thermal behaviour by XRD, SEM, IR and DSC techniques, respectively. The distribution of MoO3 in polyvinyl alcohol gives a crystalline polymer, a compact structure and an increase in glass transition temperature.

• Photocurrent enhancement of d.c. sputtered copper oxide thin films

Copper oxide (CuO) thin films with photocurrent as high as 25 𝜇Α/cm2 were deposited on conductive glass substrates using d.c. reactive sputtering. This was the highest reported photocurrent for sputtered 𝑝-type copper oxide measured in the electrolyte KI. The photocurrent drastically increased up to 25 𝜇Α/cm2 as the sputtering pressure and the substrate temperature were increased up to 8.5 mbar and 192°C, respectively. All the synthesized films contained single phase of CuO in this range of pressure and substrate temperature. Variation of the photocurrent, photovoltage, structure and absorbance with deposition conditions were studied in detail.

• Studies on preparation and characterization of indium doped zinc oxide films by chemical spray deposition

The preparation of indium doped zinc oxide films is discussed. Variation of structural, electrical and optical properties of the films with zinc acetate concentration and indium concentration in the solution are investigated. XRD studies have shown a change in preferential orientation from (002) to (101) crystal plane with increase in indium dopant concentration. Films deposited at optimum conditions have a low resistivity of 1.33 × 10-4 𝛺m with 94% transmittance at 550 nm. SEM studies have shown smooth polycrystalline morphology of the films. Figure of merit is evaluated from electrical resistivity and transmittance data.

• A new condensation product for zinc plating from non-cyanide alkaline bath

Zinc electroplating from non-cyanide alkaline solution is carried out in the presence of condensation product formed between DL-alanine (DLA) and glutaraldehyde. The bath constituents and bath variables are optimized through standard Hull cell experiments. The current efficiency and the throwing power are measured. High shift of potential towards more cathodic direction was observed in presence of addition agents. Corrosion resistance test reveals good protection of base metal by zinc coating obtained from the developed electrolyte. SEM photomicrographs show fine-grained deposit in the presence of condensation product. IR spectrum of the scraped deposit shows the inclusion of the condensation product in the deposit during plating. The consumption of brightener in the lab-scale is 6 mLL-1 for 1000 amp-hour.

• Silver nanoparticles of variable morphology synthesized in aqueous foams as novel templates

In this paper, we describe the synthesis of silver nanocrystals within aqueous foams as a template. More specifically, we show that aqueous Ag+ ions may be electrostatically complexed with the anionic surfactants aerosol OT (sodium bis-2-ethylhexyl-sulfosuccinate, (AOT) and sodium dodecyl sulphate (SDS)) in a highly stable liquid foam. After drainage of the foam, the silver ions are reduced in situ by introducing sodium borohydride into the foam by capillary flow. This leads to the formation of silver nanoparticles of spherical, tape- and sheet-like morphology in the foam. The structure of the foam is extremely complex and presents reaction sites of different spatial extent. The differences in foam reaction–site geometry are believed to be responsible for the morphology variation in the silver nanoparticles observed. The silver nanoparticles are observed to be extremely stable in solution suggesting that the AOT or SDS molecules stabilize them. This approach appears promising for application in large-scale synthesis of nanoparticles and may be readily extended to other chemical compositions.

• A convenient thermal decomposition-co-reduction synthesis of nanocrystalline tungsten disilicide

Nanocrystalline WSi2 was synthesized by a thermal decomposition-co-reduction route via the reaction of anhydrous tungsten hexachloride and sodium fluorosilicate with metallic potassium in an autoclave at 650°C. X-ray powder diffraction pattern indicated that it was tetragonal WSi2. Transmission electron microscope image showed that it consisted of particles with an average diameter of about 50 nm. TGA and DTA indicated that it had good thermal stability below 600°C in air.

• Bulletin of Materials Science

Volume 43, 2020
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• Editorial Note on Continuous Article Publication

Posted on July 25, 2019