Effect of Bismuth substitution on the enhancement of thermoelectric power factor of nanostructured BixCo3-xO4

Bismuth Cobalt Oxide (Bi_xCo_3-xO₄) nanoparticles with different compositions (x?=?0, 0.025, 0.05, 0.1, 0.2) were prepared by chemical precipitation method. The structural, morphological and thermal properties of the prepared samples were studied by XRD, SEM, FTIR and TG&DTA analysis. X-ray diffraction analysis shows that pure phase of Cobalt oxide was formed till x?≤?0.05 and while increasing the Bi concentration (0.05?≤ x?≤?0.2) mixed phases of Co₃O₄, Co₂O₃, CoO and separate phase of Bi₂O₃ were formed. The diffraction peaks were reasonably shifted due to substitution of Bi²⁺ ions. XPS analysis conforms the presence of mixed valance states of Co and presence of Bi with their binding states in the samples. The electrical resistivity and Seebeck coefficient were measured for Bi_xCo_3-xO₄ (0?≤ x?≤?0.2) at different temperatures. It was observed that the electrical resistivity decrease till x?≤?0.05 due to the substitution of Bi ions in Cobalt lattice and increases at higher x values (0.05?≤ x?≤?0.2) due to the formation of Bi₂O₃ phase. The Bi substitution has considerably reduced the electrical resistivity by one order when completely dissolved in the cobalt oxide lattice at lower x values. The Seebeck coefficient value gradually increased for all samples of Bi_xCo_3-xO₄ (0?≤ x?≤?0.2). The power factor was calculated from electrical resistivity and Seebeck coefficient and the maximum power factor of 0.025 µWm^?1K^?2 was obtained for Bi_0.2Co_2.8O₄ sample at 530?K. The experimental results revealed that the Bi substitution have promising effect on the thermoelectric properties of nanostructured Bi_xCo_3-xO₄ (0?≤ x?≤?0.2).     

Nanoflakes to nanorods and nanospheres transition of selenious acid doped polyaniline

Morphology transition of selenious acid doped polyaniline from nanoflakes to nanorods and nanospheres was explored by changing the selenious acid-aniline (dopant-monomer) mole ratio in the aniline polymerization. The transition of polyaniline nanospheres to nanorods occurred when the dopant-monomer mole ratio was between 1 and 0.5. The formation of polyaniline nanorods was dominant when the dopant-monomer mole ratio is 0.5. At mole ratio 0.5, nanorods were obtained with the diameter at around 150 nm. At mole ratio 1, both the nanorods and nanospheres were formed and formation of the nanosphere is favored when the mole ratio is more than 1. When the mole ratio was low (0.125-0.03), polyaniline showed flakes like morphology. The morphology transition was studied by scanning electron microscopy and the molecular structure was confirmed by X-ray diffraction, FTIR and UV-vis spectroscopy. A simple and practical route to synthesize polyaniline nanostructures was demonstrated using selenious acid as effective dopant. The mechanism governing the formation of the polyaniline nanostructures is discussed.     

Influence of triethylamine on the anodic dissolution characteristics of Ni,Cu and their alloys in non-aqueous solvents containing fluoride media: voltammetric and surface morphologic study

Multisweep cyclic voltammetric (CV) responses of nickel, copper, Monel and nickel–copper alloy had been extensively studied and compared in different non-aqueous solvents, such as acetonitrile (AN), propylene carbonate (PC) and sulpholane-containing anhydrous hydrogen fluoride (AHF) medium in the absence and the presence of triethylamine (Et₃N). The quantity of dissolution and surface morphological transformation on the electrodes as a result of anodic polarisation were investigated by means of atomic absorption spectroscopy and scanning electron microscopy (SEM), respectively. The CV study indicates that Ni, Cu and their alloys are highly unstable in AN/AHF medium. Surface morphology of Ni after polarisation in this medium reveals the generation of number of pits, whereas the evolution of small crystallites of CuF₂ is noted on the polarised alloy material, as evidenced by SEM pictures. The dissolution characteristics decrease significantly in PC/AHF medium and become low in sulpholane-containing fluoride medium on the four electrodes. The relative solubility of metal fluoride film in the three solvents increases in the order: sulpholane < PC < AN. The voltammograms suggest that addition of Et₃N (0.5 M) to AN- and PC-containing AHF medium helps both in maintaining uniform dissolution and generating compact fluoride film on the electrode surface. The addition of Et₃N to AHF/sulpholane medium shows only little influence in improving the electrocatalytic oxidation process.     

Study of plasma- and detonation gun-sprayed alumina coatings using taguchi experimental design

Atmospheric plasma spraying (APS) is a most versatile thermal spray method for depositing alumina (Al₂O₃) coatings, and detonation gun (D-gun) spraying is an alternative thermal spray technology for depositing such coatings with extremely good wear characteristics. The present study is aimed at comparing the characteristics of Al₂O₃ coatings deposited using the above techniques by using Taguchi experimental design. Alumina coating experiments were conducted using a Taguchi fractional-factorial (L₈) design parametric study to optimize the spray process parameters for both APS and D-gun. The Taguchi design evaluated the effect of four APS and D-gun spray variables on the measured coating attributes. The coating qualities evaluated were surface roughness, porosity, microhardness, abrasion, and sliding wear. The results show that the coating quality is directly related to the corresponding coating microstructure, which is significantly influenced by the spray parameters employed. Though it is evident that the D-gun-sprayed coatings consistently exhibit dense and uniform microstructure, higher hardness, and superior tribological performance, the attainment of suitable plasma-sprayed coatings can be improved by employing the Taguchi analysis.     

Machining Parameters Optimisation for Turning Cylindrical Stock into a Continuous Finished Profile Using Genetic Algorithm (GA) and Simulated Annealing (SA)

The economics of machining have been of interest to many researchers. Many researchers have dealt with the optimisation of machining parameters for turning operations with constant diameters only. All CNC machines produce finished components from bar stock. Finished profiles consist of straight turning, facing, taper and circular machining. This research concentrates on optimising the machining parameters for turning cylindrical stock into continuous finished profiles. Arriving at a finished profile from a cylindrical stock is done in two stages, rough machining and finish machining. Rough machining consists of multiple passes and finish machining consists of single-pass contouring after the stock is removed in rough machining. The machining parameters in multipass turning are depth of cut, cutting speed and feed. The machining performance is measured by the production cost. In this paper the optimal machining parameters for continuous profile machining are determined with respect to the minimum production cost, subject to a set of practical con-straints. The constraints considered in this problem are cutting force, power constraint and tool tip temperature. Due to high complexity of this machining optimisation problem, a simulated annealing (SA) and genetic algorithm (GA) are applied to resolve the problem. The results obtained from GA and SA are compared. ID="A2"Correspondance and offprint requests to: Dr P. Asokan, Department of Production Engineering, Regional Engineering College, Tiruchirap–palli–620 015, Tamil Nadu, India. E-mail: asokan@rect.ernet.in