• Volume 29, Issue 5

October 2006,   pages  421-546

• Growth and study of barium oxalate single crystals in agar gel

Barium oxalate was grown in agar gel at ambient temperature. The effect of various parameters like gel concentration, gel setting time and concentration of the reactants on the growth of these crystals was studied. Prismatic platy shaped spherulites and dendrites were obtained. The grown crystals were characterized by X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis. An attempt is made to explain the spherulitic growth mechanism.

• Growth mechanism of NaClO3 and NaBrO3 crystals from aqueous solutions

A study of growth rates of NaClO3 and NaBrO3 has been carried out using a small growth cell by in situ observation. Normal growth rates of {100} faces of NaClO3 and {111} faces of NaBrO3 along $\langle 110 \rangle$ direction are measured under relatively high supersaturation ranging from 3–8%. In the initial stages of growth, {100}, {110} and {111} faces develop in NaClO3 and gradually all the faces are replaced by the {100} faces only. In the case of NaBrO3, mostly {111} faces develop with occasional occurrence of small {100} faces at the intersection of {111} faces. The growth mechanisms are investigated from growth rate vs supersaturation plots and from the observations of surface features. In the present supersaturation range, the growth mechanism appears to be due to two-dimensional growth mechanism.

• Photocatalytic degradation of rhodamine B dye using hydrothermally synthesized ZnO

The sunlight mediated photocatalytic degradation of rhodamine B (RB) dye was studied using hydrothermally prepared ZnO (𝑇 = 150°C and 𝑃 ∼ 20–30 bars). Zinc chloride was used as the starting material along with sodium hydroxide as a solvent in the hydrothermal synthesis of ZnO. Different durations were tried to obtain pure ZnO phase, which was later confirmed through powder X-ray diffraction. The photocatalytic behaviour of the prepared ZnO was tested through the degradation of RB. The disappearance of organic molecules follows first-order kinetics. The effect of various parameters such as initial dye concentration, catalyst loading, pH of the medium, temperature of the dye solution, on the photo degradation of RB were investigated. The thermodynamic parameters of the photodegradation of RB, like energy of activation, enthalpy of activation, entropy of activation and free energy of activation revealed the efficiency of the process. An actual textile effluent containing RB as a major constituent along with other dyes and dyeing auxiliaries was treated using hydrothermally synthesized ZnO and the reduction in the chemical oxygen demand (COD) of the treated effluent revealed a complete destruction of the organic molecules along with colour removal.

• Tungstophosphoric acid supported onto hydrous zirconia: Physicochemical characterization and esterification of 1° and 2° alcohol

The Keggin type heteropolyacid, 12-tungstophosphoric acid (PW), was supported onto hydrous zirconia (Z) by impregnation method and designated as ZH3. The ZH3 was calcinated at 300°C and 500°C and designated as ZH33 and ZH35, respectively. The resulting materials were characterized by FTIR, diffuse reflectance spectroscopy (DRS), XRD, surface area measurement (BET method) and particle size distribution. The surface morphology was studied by scanning electron microscopy. The acidity of all materials was evaluated by carrying out chemisorption of ammonia and esterification of 1° alcohol (𝑛-butanol) with different acids like formic acid, acetic acid and propionic acid and 2° alcohol (cyclohexanol, iso-butanol) with acetic acid. Above studies show the high dispersion of HPA in a non-crystalline form on the support as well as uniform distribution of particles of ZH3 which contains 30% 12-tungstophosphoric acid. It also shows that when ZH3 was calcinated at 500°C, it possesses highest acidity for both chemisorption of NH3 as well as esterification reactions.

• Rheology and structure of aqueous bentonite–polyvinyl alcohol dispersions

The influence of polymer on flow behaviour of Balikesir, Turkey bentonite dispersions (2%, w/w) was studied for non-ionic polymer, polyvinyl alcohol (PVA). In a range of 3.3 × 10-6 – 3.3 × 105 mol/l, PVA was added to the bentonite dispersions in different concentrations and its behaviour was observed on rheology parameters. Thixotropy was detected by a hysteresis loop of the flow curves. The data were interpreted taking into account the interactions of colloidal clay particles, bentonitic clay concentrations, structure, and concentrations of added PVA. The particle size analysis was explained by surface orientation of PVA to the clay particles dispersed in aqueous solution. Zeta potential determination also emphasized that PVA molecules got attached on the face and edge surface of clay particles. The morphology of bentonite dispersions was analysed by scanning electron micrograph (SEM). FTIR studies carried out in parallel to rheology studies showed that hydrogen bonds were formed between surface of the clay, and absorbed PVA molecules and adsorbed water. The presence of PVA did not prevent extensive swelling of bentonite.

• Crystallization of 𝑀-type hexagonal ferrites from mechanically activated mixtures of barium carbonate and goethite

𝑀-type hexagonal ferrite precursor was prepared by a soft mechanochemical treatment of BaCO3 and 𝛼-FeOOH mixtures. The effect of milling on its structure and thermal behaviour was examined by XRD, SEM and FTIR. Well crystallized 𝑀-type hexagonal ferrite was formed from just 1 h milled precursors at 800°C. The beneficial effect of milling was explained in terms of increased homogeneity with simultaneous hetero bridging bond formation between powder constituents.

• Formation of oxygen complexes in controlled atmosphere at surface of doped glassy carbon

The effects of boron and phosphorus incorporation in phenolic resin precursor to the oxidation resistance of glassy carbon have been studied. In order to reveal the nature and composition of the oxygen complexes formed at the surface of doped glassy carbon, under controlled atmosphere, the surface of the samples was cleaned under vacuum up to 1273 K. Specific functional groups, subsequently formed under dry CO2 or O2 atmosphere on the surface of boron-doped and phosphorus-doped glassy carbon samples, were examined using the temperature-programmed desorption method combined with mass spectrometric analysis. Characterization of surface properties of undoped and doped samples has shown that in the presence of either boron or phosphorus heteroatoms, a lower amount of oxygen complexes formed after CO2 exposure, while, typically, higher amount of oxygen complexes formed after O2 exposure. It has been concluded that the surface of undoped glassy carbon has a greater affinity towards CO2, while in the presence of either boron or phosphorus heteroatoms, the glassy carbon surface affinity becomes greater towards O2, under experimental conditions.

• Synthesis and characterization of gelatin based polyester urethane scaffold

For tissue engineering purpose two gelatin based polyester urethane scaffolds of different compositions were prepared from lactic acid, polyethylene glycol 400 (PEG 400) and characterized by FTIR, XRD for their mechanical and morphological properties using SEM and optical microscopic analyses. Degradation and swelling studies of gelatin based polyester urethane scaffolds in phosphate buffer saline (PBS) were performed. Human keratinocyte cells were cultured within these scaffolds, which showed good cell adherence and proliferation.

• Morphology, crystallization and dynamic mechanical properties of PA66/nano-SiO2 composites

This article addresses the effect of nano-SiO2 on the morphology, crystallization and dynamic mechanical properties of polyamide 66. The influence of nano-SiO2 on the tensile fracture morphology of the nanocomposites was studied by scanning electron microscopy (SEM), which suggested that the nanocomposites revealed an extensive plastic stretch of the matrix polymer. The crystallization behaviour of polyamide 66 and its nanocomposites were studied by differential scanning calorimetry (DSC). DSC nonisothermal curves showed an increase in the crystallization temperature along with increasing degree of crystallinity. Dynamic mechanical properties (DMA) indicated significant improvement in the storage modulus and loss modulus compared with neat polyamide 66. The tan ä peak signifying the glass-transition temperature of nanocomposites shifted to higher temperature.

• Characteristics of electrocodeposited Ni–Co–SiC composite coating

Electrodeposited composites are gaining importance for their advantages including low cost, ease and simplicity of operation to tailor made coatings for tribological applications. Generally, composites containing carbides (like SiC) are preferred for high wear resistance along with increased hardness, improved corrosion resistance, and high temperature oxidation resistance as compared to alloy and pure metal electroplating. In the present work, electrolytic codeposition technique was adopted in the deposition of Ni–Co–SiC composite coating on mild steel substrate, using nickel alloyed with cobalt as the binder phase with SiC as dispersed particles. To improve the properties of coating further, Cr plating was also performed. Since the particle size and volume percent variation of dispersoid have great importance in codeposition, so the effect of these two variables on the process of codeposition and properties was observed. Morphological studies of Ni–Co–SiC coating were carried out with scanning electron microscopy and X-ray diffraction analysis to correlate the mechanical and corrosion behaviour of the coating.

• Effect of condensation product of glycyl–glycine and furfural on electrodeposition of zinc from sulphate bath

Zinc electrodeposition from sulphate bath was carried out in presence of condensation product formed between glycyl–glycine (GGL) and furfural (FFL). The bath constituents were optimized through Hull cell experiments. Operating parameters such as pH, temperature and current density were also optimized. Current efficiency and throwing power were measured. Polarization study revealed shift of potential towards negative direction in the presence of addition agents. Corrosion resistance test revealed good protection of base metal by zinc coating obtained from developed electrolyte. SEM photomicrographs showed fine-grained deposit in the presence of condensation product. IR spectrum of the deposit showed inclusion of condensation product in the deposit during plating. The consumption of brightener in the lab scale was 7 mLL-1 for 1000 amp-h.

• Optimizing growth conditions for electroless deposition of Au films on Si(111) substrates

Electroless deposition of Au films on Si(111) substrates from fluorinated-aurate plating solutions has been carried out at varying concentrations, deposition durations as well as bath temperatures, and the resulting films were characterized by X-ray diffraction, optical profilometry, atomic force microscopy and scanning electron microscopy. Depositions carried out with dilute plating solutions (&lt; 0.1 mM) at 28°C for 30 min produce epitaxial films exhibiting a prominent Au(111) peak in the diffraction patterns, while higher concentrations or temperatures, or longer durations yield polycrystalline films. In both epitaxial and polycrystalline growth regimes, the film thickness increases linearly with time, however, in the latter case, at a rate an order of magnitude higher. Interestingly, the surface roughness measured using atomic force microscopy shows a similar trend. On subjecting to annealing at 250°C, the roughness of the film decreases gradually. Addition of poly (vinylpyrrolidone) to the plating solution is shown to produce a X-ray amorphous film with nanoparticulates capped with the polymer as evidenced by the core-level photoelectron spectrum. Nanoindentation using AFM has shown the hardness of the films to be much higher (∼ 2.19 GPa) than the bulk value.

• Morphology, surface topography and optical studies on electron beam evaporated MgO thin films

Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol–gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or have mesh like morphology. The bar regions are believed to be of magnesium hydroxide formed due to absorption of moisture. Their AFM images exhibit columnar/pyramidal/truncated cone structure, providing support to the 3D Stranski–Krastanov model for film growth. Further, they are shown to have high transmittance (∼90%) in the wavelength range 400–600 nm, but absorb radiation below 350 nm substantially giving signature of a band transition.

• Influence of bismuth on properties and microstructures of Sr0.5Ba0.5–𝑥Bi𝑥 TiO3 thin films

The influence of bismuth (Bi) on the dielectric and ferroelectric properties of Sr0.5Ba0.5–𝑥Bi𝑥 TiO3 (BST, 0 &lt; 𝑥 &lt; 0.030 mol) thin films was studied. The results showed that the dielectric constant (𝜀r) and dielectric loss (tan 𝛿) decreased, and temperature, 𝑇m, for maximum and 𝜀r (Curie temperature), moved to lower temperature with increasing Bi content. The 𝑃r, 𝑃s and 𝐸c were 0.22 𝜇C/cm2, 0.32 𝜇C/cm2 and 60 kV/cm, respectively for Sr0.5Ba0.485Bi0.015TiO3 thin films measured at 100 Hz, 20 V. The microstructure of BST thin films was studied by XRD and TEM. Tetragonal perovskite grains existed in BST thin films, but the grain size decreased with increasing doping ratio in BST. The characteristic absorption band for octahedron [TiO2] (471.65 cm-1) was shifted to lower wave number.

• Structural, optical and electrical properties of chemically deposited nonstoichiometric copper indium diselenide films

Thin films of copper indium diselenide (CIS) were prepared by chemical bath deposition technique onto glass substrate at temperature, 60°C. The studies on composition, morphology, optical absorption, electrical conductivity and structure of the films were carried out and discussed. Characterization included X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDAX) and absorption spectroscopy. The results are discussed and interpreted.

• Structural and electrochemical behaviour of sputtered vanadium oxide films: oxygen non-stoichiometry and lithium ion sequestration

Structural and electrochemical aspects of vanadium oxide films recently reported from ICMCB/ENSCPB have been examined using appropriate structural models. It is shown that amorphous films are nonstoichiometric as a result of pre-deposition decomposition of V2O5. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of V2O5 and V2O4 regions. Lithium intercalation into these regions is considered to occur sequentially and determined by differences in group electronegativities. Open circuit voltages (OCV) have been calculated for various stoichiometric levels of lithiation using available thermodynamic data with approximate corrections. Sequestration of lithium observed in experiments is shown to be an interfacial phenomenon. X-ray photoelectron spectroscopic observation of the formation of V3+ even when V5+ has not been completely reduced to V4+ is shown to be entirely consistent with the proposed structural model and a consequence of initial oxygen nonstoichiometry. Based on the structural data available on V2O5 and its lithiated products, it is argued that the geometry of VO𝑛 polyhedron changes from square pyramid to trigonal bipyramid to octahedron with increase of lithiation. A molecular orbital based energy band diagram is presented which suggests that lithiated vanadium oxides, Li𝑥 V2O5, become metallic for high values of 𝑥.

• # Bulletin of Materials Science

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

Posted on July 25, 2019