HA/β-TCP plasma sprayed coatings on Ti substrate for biomedical applications

The present work focuses on the fabrication of βTCP (β-tricalcium phosphate) and HA/βTCP (hydroxyapatite/β-tricalcium phosphate) composite coatings by plasma spraying. The starting powders were produced via solid-state method using 2 wt% MgO to stabilize βTCP phase. The synthesized powders were preliminarily granulated to be used by the plasma spray process. Coatings obtained on titanium substrates are uniform and well adherent but due to the high temperature and cooling rate typical for plasma spraying process, βTCP phase is almost totally transformed into the α allotrope. Thermal treatment at 800 °C allows the reconversion of the phase αTCP→ βTCP. It is therefore possible to produce coatings with tuneable dissolution properties by selecting the proper initial powder mixture and the specific thermal treatment.     

Wave-oriented signal processing of dispersive time-domainscattering data

Phase-space data processing is receiving increased attention because or its potential for furnishing new discriminants relating to classification and identification of targets and other scattering environments. Primary emphasis has been on time-frequency processing because of its impact on transient, especially wideband, short-pulse excitations. Here, we investigate the windowed Fourier transform, the wavelet transform, and model based superresolution algorithms within the context of a fully quantified and calibrated test problem investigated by us previously: two-dimensional (2-D) short-pulse plane wave scattering by a finite periodic array of perfectly conducting coplanar flat strips. Because the forward problem has been fully calibrated and parametrized, some quantitative measures can be assigned with respect to the tradeoffs of these time-frequency algorithms, yielding tentative performance assessments of the tested processing algorithms     

The lost-wax casting of icons, utensils, bells, and other items in South India

Indian artisans and craftsmen have long been masters at extracting and shaping metals and alloys, as proven by archaeological finds from the 2nd—3rd millennia B.C. For example, two well-known artifacts, castings of the dancing girl of Mohenjo Daro and the Mother Goddess of Adichanallur, Tamilnadu, depict a high degree of metallurgical knowledge. Those castings were formed by the lost wax process, which later was modified and became known as investment casting. In various parts of India, this age-old casting process is still being practiced, without any major modifications. This paper discusses details of the process used by the Indian artisans of Swamimalai, Tamilnadu, and Mannar, Kerala, South India in shaping copper-base alloys into icons and utensils, bells, and lamps.     

The effect of mischmetal addition on the structure and mechanical properties of a cast Al-7Si-0.3Mg alloy containing excess iron (up to 0.6 Pct)

The effect of Fe content (0.2 to 0.6 pct) on the microstructure and mechanical properties of a cast Al-7Si-0.3Mg (LM 25/356) alloy has been investigated. Further, 1 pct mischmetal (MM) additions (a mixture of rare-earth (RE) elements) were made to these alloys, and their mechanical properties at room and at elevated temperatures (up to 200 °C) were evaluated. A structure-property correlation on this alloy was attempted using optical microstructure analysis, fractographs, X-ray diffraction, energy-dispersive analysis of X-rays (EDX), and quantitative metallography by image analysis. An increase in Fe content increased the volume percentage of Fe-bearing intermetallic compounds (β and π phases), contributing to the loweryield strength (YS), ultimate tensile strength (UTS), percentage elongation, and higher hardness. An addition of 1 pct MM to the alloys containing 0.2 and 0.6 pct Fe was found to refine the microstructure; modify the eutectic silicon and La, Ce, and Nd present in the MM; form different intermetallic compounds with Al, Si, Fe, and Mg; and improve the mechanical properties of the alloys both at room and elevated temperatures.     

Immobilization of papain on crosslinked polymer supports: Role of the macromolecular matrix on enzymic activity

Papain was immobilized on polymer supports with spacer arms of varying nature and length. As the length of the spacer arm increased, there was a marked increase in the extent of enzyme immobilization and activity of immobilized enzymes. When a long, flexible and hydrophilic polyethylene glycol spacer was introduced between the polystyrene backbone and the functional group used for immobilization, the extent of coupling and enzyme activity increased. Dependence of enzyme activity on the nature and extent of crosslinking and on the nature of the polymeric backbone was investigated. Hydrophilic polyacrylamide-based supports were found to be more efficient supports for immobilization compared to hydrophobic polystyrene-based supports.     

Kinetics and mechanism of oligomerization of cardanol using acid catalysts

The kinetics and mechanism of oligomerization of cardanol over acid catalysts were studied. GPC results showed the formation of a mixture of oligomers such as dimer, trimer, tetramer, etc. IR spectra of the products of oligomerization showed a decrease in the intensity of the double bond absorption band at 1630 cm^?1 and the disappearance of terminal vinyl bands at 895 cm^?1 and 907 cm^?1. ¹H NMR spectra showed drastic changes in the unsaturated proton resonance signals at 5.5δ with respect to saturated protons at 0.2–2.5δ. The ratio of resonance integrals of unsaturated to saturated protons decreased from 1 : 6.5 to 1 : 20 after oligomerization. GPC studies showed that the rate of formation of the dimer, trimer, tetramer, etc. follow an identical path and that the individual oligomers are formed in the same weight percentage at any time during the reaction. A kinetic scheme is proposed to explain this phenomenon. Kinetic studies showed that the oligomerization reaction follows first order kinetics with respect to the monomer concentration and the rate constant is K = 6.6 × 10^?5s^?1. A probable mechanism for the oligomerization of cardanol is proposed.     

Semiflexible random thermotropic copolymers from 8‐(3‐hydroxy phenyl) octanoic acid and 3‐chloro‐4‐hydroxy benzoic acid/3,5‐dibromo‐4‐hydroxy benzoic acid

Two series of semiflexible random thermotropic copolymers containing 8‐(3‐hydroxy phenyl) octanoic acid (HPOA) with either 3‐chloro‐4‐hydroxy benzoic acid or 3,5‐dibromo‐4‐hydroxy benzoic acid were prepared by melt polycondensation techniques. The copolyesters were characterized with Fourier transform infrared spectroscopy, dilute solution viscometry, hot‐stage polarized light microscopy, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction. Studies revealed that the amount of HPOA as a disruptor incorporated into the backbone of substituted 4‐hydroxy benzoic acids had a detrimental effect on the liquid‐crystalline behavior. Mesophase‐transition temperatures were observed between 210 and 250°C, and the optical textures were of typical nematic phases. The degree of crystallinity decreased with an increase in the HPOA content. The thermal stability of the copolymers was in the range of 310–370°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Structure and properties of some vegetable fibres

The stress-strain curves for pineapple leaf fibre have been analysed. Ultimate tensile strength (UTS), initial modulus (YM), average modulus (AM) and elongation of fibres have been calculated as functions of fibre diameter test length and test speed. UTS, YM, and elongation lie in the range of 362 to 748 MN m^–2, 25 to 36 GN m^–2, and 2.0 to 2.8%, respectively for fibres of diameters ranging from 45 to 205m. UTS Was found to decrease with increasing test lengths in the range 15 to 65 mm. Various mechanical parameters show marginal changes with change in speed of testing in the range of 1 to 50 mm min^–1. The above results are explained on the basis of structural variables of the fibre. Scanning electron microscope studies of the fibres reveal that the failure of the fibres is mainly due to large defect content of the fibre bo1h along the fibre and through the cross-section, The crack is always initiated by the defective cells and further aggravated by the weak bonding material between the cells.