Combustion synthesis of CuFe2O4

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe₂O₄, one of the important ferrites, is envisaged for substituting the carbon anode in Hall-Heroult cells. A single step combustion process has been used for the synthesis of CuFe₂O₄ powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C.     

Erosive-corrosive wear of aluminum alloy composites: Influence of slurry composition and speed

The Erosion-corrosion behavior of a SiC particle reinforced Al-Si alloy has been studied in two different environments, namely saline and acidic, to simulate sea water and mining atmospheres, respectively. These studies were performed at different sand concentrations (20-40 wt%) and varying rotational speeds (700-900 rpm). It is noted from the present study that the composite exhibited better wear resistance than the alloy in marine and acidic atmospheres irrespective of sand content and speed. It is also noted that the wear rates increased with increasing sand content and speed irrespective of material due to increase in the severity of erosive/abrasive attacks. However, the wear rates decreased at higher speeds (e.g., 1100 rpm) due to increased intercollisions and rebounding and also the decrease in the mobility of the erodant particles. It is observed that erosion is the dominant mode of material removal in these two media. Corrosive attack was more predominant in the acidic media than in the NaCl media at lower sand concentrations (0-20 wt%). However, at higher sand concentrations (30-40 wt%) corrosive attack was more severe in the NaCl medium. Scanning electron microscopic (SEM) observation shows that Al/Si interfaces act as predominant sites for corrosion attack rather than the Al/SiC interfaces. Formation and removal of the passive layer, preferential attack at the Al/Si interfaces, fragmentation and wear of SiC particles were observed as mechanisms of material removal in marine and acidic media. SEM studies of the eroded-corroded surfaces indicated that an increase in the sand content of the slurry and in the rotational speed of the slurry increased resulted in greater damage to the SiC particles and matrix, resulting in an increase in wear rates.     

Comparison of various organic stabilizers as capping agents for CdS nanoparticles synthesis

Results of the studies on the preparation and characterization of CdS nanoparticles capped with various organic stabilizers are presented in this article. Solutions of Cadmium acetate and Sodium sulphide were taken as the precursors. CdS nanoparticles were synthesized in an aqueous medium with Mercaptopropionic acid (MPA) as the stabilizer and non-aqueous methods were used for the synthesis of Polyvinyl Pyrrolidone (PVP) and thiophenol-capped CdS nanoparticles. The synthesized CdS nanoparticles were characterized by the optical absorption and X-ray diffraction (XRD) studies. Particle sizes estimated from the band gap values using Effective Mass Approximation (EMA) agreed fairly well with those calculated from the XRD using Scherrer formula. The quantity and the concentration of the stabilizers needed for effective capping of the CdS nanoparticles were different in the three cases considered. Stability of the synthesized CdS nanoparticles was studied at different intervals of time for 10 days. A change in particle size was observed at lower stabilizer concentrations for the first few days. But at higher stabilizer concentrations there was no change in particle size with time.     

Characterization of poly(indole‐5‐carboxylic acid) in aqueous rechargeable cells

Self-doped poly(indole-5-carboxylic acid) (P5CO₂H) is electrodeposited from acetonitrile containing 0.1M LiClO₄ as electrolyte and characterized by UV–vis, IR, cyclic voltammetry, and scanning electron microscopy techniques. The polymer is evaluated as a cathode active material together with a Zn anode in rechargeable cells containing 1M ZnSO₄ at pH 5. The cell shows an open circuit voltage of 1.36 V and a specific capacity of 67 Ah kg⁻¹. The ac impedance study shows a predominant diffusion mechanism. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 917–922, 2005     

Characteristics of aqueous polycarbazole batteries

The characteristics of electrochemically prepared polycarbazole (PCARB) as the cathode active material for secondary batteries are studied in aqueous electrolytes. The cell of the type Zn/Zn(ClO₄)₂/PCARB has a specific capacity of 30 Ah/kg and an energy density of 46 Wh/kg. The coulombic efficiency is about 80–90% and is dependent on the thickness of PCARB films. Cole‐Cole plots for PCARB electrodes by impedance measurements have been obtained at different oxidation potentials as a function of doping. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 145–150, 1999     

Photoluminescence study of PVP capped CdS nanoparticles embedded in PVA matrix

Photoluminescence properties of polyvinyl pyrrolidone (PVP) capped cadmium sulphide (CdS) nanoparticles embedded in polyvinyl alcohol matrix (PVA) are reported. The PVP-CdS nanoparticles are prepared by non-aqueous method wherein cadmium nitrate is used as the cadmium source and hydrogen sulphide as the sulphur source. The synthesized nanoparticles are dispersed in polyvinyl alcohol (PVA) matrix and cast as self-standing flexible (PVP-CdS)-PVA films. The nanocomposites are characterized by optical absorption spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. XRD and TEM studies show the formation of cubic CdS particles with average size ∼3-5 nm. Thermal studies, carried out to observe the changes in PVA matrix due to the incorporation of PVP-CdS nanoparticles show strong interaction between the polymer matrix and nanoparticles. The photoluminescence emission spectra of the nanocomposites show two peaks, at 502 and 636 nm, which are attributed to the band edge and surface defects respectively, of CdS nanoparticles. Effective surface capping with optimum concentration of polyvinyl pyrrolidone leads to the quenching of surface defect-related emission.     

Dithiocarbamates as a Sensitive Electroanalytical Reagent: Determination of Chromium by Catalytic Hydrogen Wave at DME in Water Systems and Vegetables

Simple, sensitive catalytic hydrogen polarographic method was developed for the determination of chromium (VI) with ammonium piperidine dithiocarbamate (Amm Pip-DTC) and ammonium morpholine dithiocarbamate (Amm Mor-DTC) in various water systems and vegetables. The method was based on the catalytic hydrogen wave of Amm Pip-DTC-Cr(VI) and Amm Mor-DTC-Cr(VI) complexes in the presence of NH₄Cl–NH₄OH medium at pH 7.5 and 9.6 and produce a catalytic hydrogen waves at −1.59 and −1.65 V Vs SCE, respectively. Various optimum parameters such as effect of pH, NH₄Cl–NH₄OH, Pip-DTC, metal ion concentrations and excipient effect on peak height were investigated to enhance the sensitivity, selectivity, and detection limits of the present method and compared in terms of Students t test and variance ratio f test with differential pulse polarography (DPP) method. The proposed method was applied for the determination of chromium (VI) in various water system and vegetables and the results obtained were in good agreement with DPP.     

Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 × 10⁻² Ω cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide.     

Rectifying properties of poly(N-methylaniline)

The electrical properties of various metal (Al/In/Sb/Sn)/poly(N-methylaniline)/gold Schottky diodes are described. The temperature-dependent dark current (J)–voltage (V ) characteristics indicate that the junctions formed with Al/In possess better rectifying properties with Schottky emission. In the case of junctions formed with Sb/Sn, Poole–Frenkel emission appears to be the dominant mechanism. The junction parameters of ideality factor, reverse saturation current, and barrier potential have been evaluated and compared with the reported values for Schottky barriers based on polyaniline and a few of its substituted derivatives. The capacitance (C)–voltage (V ) data obtained at different frequencies have been used to evaluate the carrier concentration, mobility, depletion width, contact potential, and work function of the polymer.