An alternative approach in ceramic shell investment casting of AZ91D magnesium alloy: In situ melting technique

In this research, the possibility of ceramic shell investment casting of a magnesium alloy using in situ melting technique was explored. AZ91D granules were charged into shell investment mould and in situ melted under various processing parameters including heating temperature, flux application, shell mould thickness and permeability. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques were used to characterise the cast samples. Thermal analysis was employed to further investigate the effect of mould thickness on the solidification behaviour of the metal. It was found that mixing flux with the granules not only reduced the temperature at which melting can be achieved, but it also contributed to produce castings with acceptable surface quality. The use of thinner mould provided higher solidification rate, which is believed to favour in situ melting of the granules. It enabled melting of the granules at 650 °C, which in turn helped to suppress the mould–metal reaction and produce castings with good surface quality. Shell mould permeability showed no influence on suppressing the mould–metal reaction at 650 °C.     

In Vitro Release Studies of Flurbiprofen from Different Topical Formulations

ABSTRACT

The release profiles of flurbiprofen (F) from different gel and ointment formulations were studied in order to evaluate factors governing the release process. Carbopol 934P (CAB), poloxamer 407 (POL), and eudragit S100 (EUD) gel bases were used, while emulsion (EML) and polyethylene glycol (PEG) ointments were employed. The release studies were conducted using membraneless diffusion cells and lipophilic receptor medium, isopropyl myristate (IPM). The effects of gelling agent concentrations and the initial drug load on drug release were determined. Hydrogels were observed to give higher amounts of drug release than hydrophobic EUD gel and ointments, despite the lower bulk viscosity of these bases. Flurbiprofen release from CAB gels was 3.06–1.56-fold higher than from other formulations. Over a 4-hr period, the amount of F released was 492.8 and 316.0 µg/cm² from 2% CAB and 25% POL gels, while it was 213.05, 168.61, and 160.9 µg/cm² from EML, 40% EUD, and PEG bases, respectively. The diffusivity of F in the gel bases was an inverse function of the polymer concentrations over the range of 1–3% CAB, 20–30% POL, and 35–45% EUD gels. Drug release was increased from the bases as the initial F concentration increased over the range 0.25–1.0%, while the diffusion coefficient observed an inverse relationship. The CAB and POL gels could be the vehicles of choice for the rapid release and onset of F after topical application.     

Effect of Ni7+ Ion Irradiation on Structure and Ammonia Sensing Properties of Thermally Oxidized Zinc and Indium Films

ZnO and In2O3 films were prepared by thermal oxidation of vacuum deposited zinc and indium films, respectively onto the glass substrate at 30 C. The fabricated films have been irradiated with 100-MeV Ni7+ ions at different fluences ranging from 5×1011 to 5×1013 ions/cm2. The structural and gas sensing properties of pristine and irradiated films have been discussed. X-ray diffraction (XRD) pattern of pristine and irradiated films reveal that the films are polycrystalline in nature and crystallinity increases after irradiation. In this study, highly porous In2O3 nanorods evolved when being irradiated at a fluence of 5×1013 ions/cm2 while ZnO film shows decrease in number of nanowires. The ammonia sensing performance of the Ni7+ irradiated In2O3 films shows an improvement as compared to its pristine counterpart.     

Ultra-fine Al–Si hypereutectic alloy fabricated by direct metal deposition

Ultra-fine Al–Si hypereutectic alloy with <10 μm primary Si phase was fabricated by direct metal deposition (DMD). The microstructure and microhardness of the hypereutectic alloys manufactured under different scanning speeds and laser powers during DMD were investigated. Compared with the conventional modified hypereutectic alloy whose primary Si phase is around 40 μm, the primary Si particle obtained by DMD has a much smaller size of about 5–10 μm. With increased scanning speed and laser power, the volume fraction and size of the primary Si increase. The unique hypoeutectic microstructure can be found around the primary Si phase in the hypereutectic alloy. With increased scanning speed, the size of eutectic Si grain decreases and the microhardness of deposition increase. However, the size of eutectic Si reaches the minimum value at a certain power level, and the microhardness of deposition reaches the maximum value at 850 W laser powers. The mircohardness of the deposited hypereutectic alloy is approximately 2.5 times of that of the raw eutectic alloy.     

Iodide substitution in lithium borohydride, LiBH4-LiI

The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH₄-LiI. The structural chemistry and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance infrared spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is observed as formation of two solid solutions of Li(BH₄)_1−xI_x, which merge into one upon heating. The solid solutions have hexagonal structures (space group P6₃mc) similar to the structures of h-LiBH₄ and β-LiI. The solid solutions have iodide contents in the range ∼0-62 mol% and are stable from below room temperature to the melting point at 330 °C. Thus the stability of the solid solutions is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH₄ and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid solution Li(BH₄)_1−xI_x, measured by the Sieverts method, are improved as compared to those of LiBH₄. After four cycles of hydrogen release and uptake the Li(BH₄)_1−xI_x solid solution maintains 68% of the calculated hydrogen storage capacity in contrast to LiBH₄, which maintains only 25% of the storage capacity after two cycles under identical conditions.     

Alumina powder assisted carbon nanotubes reinforced Mg matrix composites

Mg matrix composites reinforced by carbon nanotubes (CNTs)-Al₂O₃ mixture, which was synthesized by in situ growing CNTs over Al₂O₃ particles through chemical vapor deposition (CVD) using Ni catalyst, were fabricated by means of powder metallurgy process, followed by hot-extrusion. By controlling synthesis conditions, the as-grown CNTs over Al₂O₃ particles possessed high degree of graphitization, ideal morphology, higher purity and homogeneous dispersion. Due to the ‘vehicle’ carrying effect of micrometer-level A₂O₃, CNTs were easy to be homogeneously dispersed in Mg matrix under moderate ball milling. Meanwhile, Al₂O₃ particles as catalyst carriers, together with CNTs, play the roles of synergistic reinforcements in Mg matrix. Consequently, the Mg matrix composites reinforced by CNTs-Al₂O₃ mixture exhibited remarkable mechanical properties.     

Plastic coupled instabilities of I-shaped steel beams

The paper presents the case of plastic instability of I-shaped beams where the rotation capacity is a very important characteristic in order to assure the required ductility in plastic or seismic design. The failure of such beams can be due to the local plastic plate buckling of compression flange and local plate buckling of the web in flexural compression, produced in-plane or out-of-plane. In the same time the failure can occurs by coupling of these two local buckling modes. In order to study the plastic buckling of beams and to determine the available rotation capacity which is required by the plastic or seismic design, the collapse plastic mechanism theory was developed and a specialized computer program DUCTROT-M was elaborated. The parametrical analysis reveals the paramount importance of the web to thickness ratio and furthermore the sensitivity in out-of-plane buckling of the European hot-rolled sections.