Codeposition of nanocrystalline aluminides on a copper substrate

The present study concerns codeposition of nanocrystalline aluminide particles (NbAl₃ and Cu₉Al₄) along with electrodeposition of Cu on a Cu substrate. It is shown that the success of codeposition primarily depends on the selection of an appropriate electrolyte. Following codeposition under an optimum deposition condition, the microstructure, phase identity and composition of the deposit layer have been studied. In addition, microhardness and electrical resistivity of the deposit have been determined. A suitable correlation of the microstructure and composition of the deposit with its properties suggests that codeposition of NbAl₃ is more effective in enhancing the hardness. However, codeposition beyond a limit adversely affects the electrical conductivity. The optimum conditions for codeposition to enhance hardness without adversely affecting conductivity have been determined. Finally, it is predicted codeposition could be a suitable technique for developing a surface composite microstructure with uniform distribution of nanocrystalline aluminide particles.     

Dispersion polymerization of aniline using hydroxypropylcellulose as stabilizer: role of rate of polymerization

Hydroxypropylcellulose (HPC) has been used as a steric stabilizer for preparing polyaniline dispersions using the route of oxidative dispersion polymerization of aniline. Using strongly acidic conditions (1 mol l^?1 HCl), low temperature of about 2 °C and a concentration of aniline as low as 0.5%, ammonium peroxodisulfate at 1.25% and hydroxypropylcellulose concentrations at 0.5–1 g d l^?1, unstable dispersions were obtained not only in water but also in aqueous alcohols (ethanol and methanol) up to at least 70 vol% alcohol. In contrast, dispersions that remained stable for at least 72 h were obtained when the alcohol concentration of the medium was as high as about 80 vol%. Kinetic studies of the polymerization systems suggested that success in the latter case was due to a lowering of the rate of polymerization. Transmission electron microscopy studies showed that dispersion particles prepared in 80 vol% alcohol media are spherical in shape and their diameter decreases with increasing stabilizer concentration. However, a change of morphology from spherical to aggregated needle‐shaped was observed when the rate was increased by increasing the aniline concentration from 0.5% to 0.75% g d l^?1 in the above recipe. The aggregated particles were found to be broken down to spherical nanoparticles when the as‐prepared dispersions were sonicated for about 30 min. The sonicated dispersion on drying showed the presence of fractal clusters of polyaniline particles in the dried film. The fractal dimension was determined to be 1.77 which agreed well with the theoretical value determined by computer simulation based on a diffusion limited cluster–cluster aggregation model in three dimensions. © 2001 Society of Chemical Industry     

Exploring the simultaneous effect of nano‐silica reinforcement and electron‐beam irradiation on a model LDPE/EVA‐based TPE system

BACKGROUND: The technical properties of polyolefinic thermoplastic elastomer (TPE) systems can be modified significantly using fillers like nano‐silica. Controlled irradiation can potentially be an effective way of tailoring the technical properties of such nano‐silica‐filled TPE systems. RESULTS: The effect of controlled electron‐beam irradiation on the properties of a pristine silica nanoparticle‐filled model low‐density polyethylene/ethylene–(vinyl acetate) (LDPE/EVA) TPE system is explored in this paper. The morphology of such a filled system was investigated using scanning electron microscopy (SEM) and field‐emission SEM. The dispersion of silica particles was analysed using transmission electron microscopy which clearly indicates that at low loading a fine dispersion of silica occurs in the polymer matrix. Swelling studies and Fourier transform infrared analyses indicate the occurrence of a favourable EVA–silica interaction. On the whole, it is observed that electron‐beam irradiation induces a high degree of reinforcement in all the silica‐filled samples through interfacial crosslinking as well as controlled crosslinking in the two polymer phases. In a few samples the processing characteristics are remarkably preserved following concurrent nano‐silica reinforcement and irradiation, while the technical properties of TPE systems, including set, solvent swelling and mechanical properties, are improved. However, the improvement in properties is a strong function of sequence of addition of filler in the LDPE/EVA blends. CONCLUSION: The green technique studied can be potentially extended for the improvement of the technical properties of conventional TPE systems. Copyright © 2009 Society of Chemical Industry     

Influence of martensite morphology on the work-hardening behavior of high strength ferrite–martensite dual-phase steel

This study concerns influence of martensite morphology on the work-hardening behavior of high-strength ferrite–martensite dual-phase (DP) steel. A low-carbon microalloyed steel was subjected to intermediate quenching (IQ), step quenching (SQ), and intercritical annealing (IA) to develop different martensite morphologies, i.e., fine and fibrous, blocky and banded, and island types, respectively. Analyses of work-hardening behavior of the DP microstructures by differential Crussard–Jaoul technique have demonstrated three stages of work-hardening for IQ and IA samples, whereas the SQ sample revealed only two stages. Similar analyses by modified Crussard–Jaoul technique showed only two stages of work-hardening for all the samples. Among different treatments, IQ route has yielded the best combination of strength and ductility due to its superior work-hardening behavior. The influence of martensite morphology on nucleation and growth of microvoids/microcracks has been correlated with the observed tensile ductility.     

Sulphated polysaccharides from Indian samples of Enteromorpha compressa (Ulvales,Chlorophyta): Isolation and structural features

Heteroglycan and xyloglucan rich fractions were extracted from Indian samples of Enteromorpha compressa in 25% yield by sequential extractions with water and alkali. This heteroglycan is sulfated and has an apparent molecular mass of 55 kDa. Chemical structural analysis of this polysaccharide revealed a branched structure having 1,4- and 1,2,4-linked rhamnose 3-sulphate, 1,4-linked glucose, 1,3- and 1,6- linked galactose, 1,4- and terminally linked glucuronic acid and 1,4-linked xylose partially sulfated on O-2. Chemical and spectroscopic analysis showed that the 4-M KOH extracted hemicellulosic fraction contained an unusual β-(1,4)-linked linear xyloglucan. Enzyme hydrolysis and analysis of the resulting fragments by matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) showed that this linear polymer contained partially sulfated Glc₃Xyl₂ or Glc₄Xyl₂ as oligomeric building subunits.     

Grafting. III. Copolymerization of methyl methacrylate and methacrylic acid

The method of graft copolymerization of methyl methacrylate on halogen-containing polymer has been utilized for grafting of methyl methacrylate–methacrylic acid monomer pair onto poly(vinyl chloride) and chlorinated rubber. Substantial grafting could be obtained by using the method reported earlier. However, the compositions of the grafted chains are found to deviate appreciably from the compositions calculated from r₁ and r₂ values reported in literature. The reactivity ratios for this pair of monomers have been therefore evaluated using azobisisobutyronitrile and n-butane thiol–dimethyl sulfoxide as initiators. The anomalies of the grafted chain compositions have been discussed and an explanation presented on preferential solvation.     

A comparison between isoparametric Lagrangian elements in 2D BEM

A comparison between a family of isoparametric C°-continucus elements in the context of two-dimensional elastostatics using the direct boundary element method is presented. The elements studied use Lagrangian shape functions of orders quadratic, cubic and quartic. The relative efficiencies of these elements from the viewpoint of accuracy of solution as well as cost effectiveness are examined through certain selected problems. It emerges from the present study that the quartic element is more reliable in accuracy than the lower members of the family without being necessarily more expensive.     

Diffraction of shear waves by a rigid strip in a medium of monoclinic type

Summary The paper discusses the two dimensional problem of diffraction of shear waves by a rigid strip in an infinite medium of monoclinic type. This problem is reduced to a system of dual integral equations of which the solution provides the diffracted field. The method of steepest descent has been used in the determination of the diffracted fields at a large distance from the strip. Diffraction pattern for displacement and stress field have been computed and the effect of anisotropy is distinctly marked.With 6 Figures     

On self-adaptive features in real-parameter evolutionary algorithms

Due to the flexibility in adapting to different fitness landscapes, self-adaptive evolutionary algorithms (SA-EAs) have been gaining popularity in the recent past. In this paper, we postulate the properties that SA-EA operators should have for successful applications in real-valued search spaces. Specifically, population mean and variance of a number of SA-EA operators such as various real-parameter crossover operators and self-adaptive evolution strategies are calculated for this purpose. Simulation results are shown to verify the theoretical calculations. The postulations and population variance calculations explain why self-adaptive genetic algorithms and evolution strategies have shown similar performance in the past and also suggest appropriate strategy parameter values, which must be chosen while applying and comparing different SA-EAs