Magnesium interlayered diamond coating on silicon

Diamond thin films have been deposited using hot filament chemical vapour deposition technique on manually scratched p-Si(1 0 0) substrate, with and without magnesium interlayer. In spite of magnesium melting point being lower (T_m = 649 °C) than the growth temperature of the substrate (T_s  750 °C) used in these experiments, it was found that high quality diamond films could be grown on Mg covered substrate. A liquid substrate is probably generated during the diamond film growth. Raman spectroscopy analysis exhibited only the triply degenerate, zone centre optical phonon peak at 1333 cm⁻¹ indicating that nearly stress free crystallites were present. Broadening of the Raman peak (11.76 cm⁻¹) indicates that some small crystallites also are present. Scanning electron and atomic force microscopy accompanied by X-ray diffraction analysis where used to compare the details of diamond film growth directly on scratched Si(1 0 0) and Mg interlayered scratched Si(1 0 0) substrates.     

Laser-assisted machining of compacted graphite iron

Compacted graphite iron (CGI) is a material currently under study for the new generation of engines, including blocks, cylinder liners, and cylinder heads. Its unique graphite structure yields desirable high strength, but makes it difficult to machine, thus resulting in a machining cost. Laser-assisted machining (LAM) is adopted to improve its machinability and hence machining economics. The machinability of CGI is studied by varying depth of cut, feed, and material removal temperature and then evaluating resultant cutting forces, specific cutting energy, surface roughness, and tool wear. At a material removal temperature of 400 °C and a feed of 0.150 mm/rev at a cutting speed of 1.7 m/s, it is shown that tool life is 60% greater than conventional conditions at a feed of 0.100 mm/rev. Surface roughness is improved 5% as compared to conventional machining at a feed of 0.150 mm/rev. CGI microstructure evaluated post machining by sectioning and polishing shows no change. An economic analysis shows that LAM can offer an approximately 20% cost savings for the machining of an engine cylinder liner.     

A noncontact NDE method using a laser generated focused-Lamb wave with enhanced defect-detection ability and spatial resolution

The laser generation method of a focused Lamb wave is expected to have high defect-detection abilities and spatial resolution, with the added advantage of noncontact testing. In this method, the laser beam is illuminated on the surface of an object through an arrayed arc slit. The energy of the generated Lamb wave is then concentrated at a focus of an arc. This focusing effect improves the NDE (nondestructive evaluation) performance, which is dependent on the geometries of an arrayed arc slit. In this paper, the relationships between the parameters determining the slit geometry and the focusing effect of the generated Lamb wave was investigated using a parametric study, and appropriate values of the parameters were obtained to maximize the focusing ability. In order to validate the performance of this method, an NDE system was constructed and experiments were performed to detect through-hole defects in a plate. The results showed that the proposed system could clearly detect defects as small as 0.3 mm in diameter, while the conventional line array method failed to detect defects smaller than 1 mm in diameter. Moreover, this method showed possible detection of defects much smaller than 0.3 mm, and great improvements in the spatial resolution as compared with the line array method.     

Effect of carbide additions on grain growth in TiC−Ni cermets

The growth of carbide particles in TiC-XC-2 vol.% Ni and TiC-XC-30 vol.% Ni alloys, where X=Zr, Cr, W, Ta and Mo, was fitted to an equation of the form d³-d_o ³=Kt. The grain growth behavior during liquid phase sintering at 1673K decreased markedly with the addition of Mo₂C or WC, changed little for TaC, and increased with the addition of ZrC or Cr₃C₂. The grain contiguity decreased with increasing Ni content in the TiC−Mo₂C−Ni alloy and was greater in the alloys with smaller growth rate constant. Consequently, the effect of carbide addition on the grain growth of 2 vol.% Ni alloys was found to be similar to that of 30 vol.% Ni alloys. The grain growth mechanism could be explained by the effect of contiguous carbide grain boundaries in restricting the overall grain growth, as well as the area of the solid/liquid interfaces in the alloy by the usual solution/reprecipitation model.     

Corrosion and oxidation of alloys of the Mg-Y-Zr-REM system

The corrosion resistance of an alloy of the Mg-Y-Zr-REM system obtained by sand casting and subjected to different modes of heat treatment is studied with the use of potentiodynamic polarization, immersion tests, scanning electron microscope, and Auger electron spectroscope. The microstructure of the alloy is described.     

Functional mesoporous carbon built from the 1,10-phenanthroline building block: A new class of catalyst support

A simple synthesis of a high surface area catalyst support composed of a nanoporous carbon architecture built from a 1,10-phenanthroline precursor is described.     

Characterization of polyurethane foam prepared by using starch as polyol

Polyurethane foams were prepared using starch as a main component of polyols and their structural, mechanical, and absorbing properties for organic solvents were investigated. Fourier transform infrared spectra showed that urethane linkage was formed by the reactions between ? NCO of diisocyanates and ? OH of polyols. When polyurethane foams were prepared at high molar ratio of ? NCO/? OH, the unreacted ? NCO groups were detected. Also, urea linkage was formed by the reaction between diisocyanate and water, which was used as the foaming agent. The micrographs showed that the polyurethane foams had closed‐cell structure, of which the cell size increased with ? NCO/? OH molar ratio. The density of polyurethane foams increased with molecular weight of polyethylene glycol. The compressive moduli of polyurethane foams increased with ? NCO/? OH molar ratio. Polyurethane foams prepared using toluene‐2,4‐diisocyanate as diisocyanate had the highest modulus, while those prepared using hexamethylene diisocyanate had the lowest modulus. In case of the absorbency for the organic solvents, the polyurethane foams prepared at ? NCO/? OH molar ratio of 0.8 had the maximum absorbency. Among several organic solvents, the absorbency for dimethyl sulfoxide was the highest, while the absorbency for tetrahydrofuran was the lowest. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1544–1553, 2007     

pH‐sensitive swelling and release behaviors of anionic hydrogels for intelligent drug delivery system

The pH‐sensitive swelling and release behaviors of the anionic P(MAA‐co‐EGMA) hydrogels were investigated as a biological on–off switch for the design of an intelligent drug delivery system triggered by external pH changes. There was a drastic change of the equilibrium weight swelling ratio of P(MAA‐co‐EGMA) hydrogels at a pH of around 5, which is the pK_a of poly (methacrylic acid) (PMAA). At a pH below 5, the hydrogels were in a relatively collapsed state but at a pH higher than 5, the hydrogels swelled to a high degree. When the molecular weight of the pendent poly(ethylene glycol) (PEG) of the P(MAA‐co‐EGMA) increased, the swelling ratio decreased at a pH higher than 5. The pK_a values of the P(MAA‐co‐EGMA) hydrogels moved to a higher pH range as the pendent PEG molecular weight increased. When the feed concentration of the crosslinker of the hydrogel increased the swelling ratio of the P(MAA‐co‐EGMA) hydrogels decreased at a pH higher than 5. In release experiments using Rhodamine B (Rh‐B) as a model solute, the P(MAA‐co‐EGMA) hydrogels showed a pH‐sensitive release behavior. At low pH (pH 4.0) a small amount of Rh‐B was released while at high pH (pH 6.0) a relatively large amount of Rh‐B was released from the hydrogels. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007