Characterisation of bauxite and seawater neutralised bauxite residue using XRD and vibrational spectroscopic techniques

Bauxite refinery residues are derived from the Bayer process by the digestion of crushed bauxite in concentrated caustic at elevated temperatures. Chemically, it comprises, in varying amounts (depending upon the composition of the starting bauxite), oxides of iron and titanium, residual alumina, sodalite, silica, and minor quantities of other metal oxides. Bauxite residues are being neutralised by seawater in recent years to reduce the alkalinity in bauxite residue, through the precipitation of hydrotalcite-like compounds and some other Mg, Ca, and Al hydroxide and carbonate minerals. A combination of X-ray diffraction (XRD) and vibrational spectroscopy techniques, including mid-infrared (IR), Raman, near-infrared (NIR), and UV–Visible, have been used to characterise bauxite residue and seawater neutralised bauxite residue. The ferric (Fe³⁺) ions within bauxite residue can be identified by their characteristic NIR bands, where ferric ions produce two strong absorption bands at 25,000 and 14,300 cm⁻¹. The presence of adsorbed carbonate and hydroxide anions can be identified at around 5,200 and 7,000 cm⁻¹, respectively, attributed to the 2nd overtone of the 1st fundamental overtones observed in the mid-IR spectra. The complex bands in the Raman and mid-IR spectra around 3,500 cm⁻¹ are assigned to the OH-stretching vibrations of the various oxides present in bauxite residue, and water. The combination of carbonate and hydroxyl units and their fundamental overtones give rise to many of the features of the NIR spectra.     

Nanoscale films of organic dyes for broadband environmental sensing

Two types of suitably substituted organic dye molecules namely copper phthalocyanine and Rose Bengal were electrostatically self-assembled on gold-coated glass substrates, the gold surface being modified with poly(allylaminehydrochloridethe). The surface plasmon resonance technique was employed to investigate the sensing properties of organic dyes on exposure to three different volatile organic compounds. The films using phthalocyanine molecules were considered to be an optimal material because of its fast response and full recovery. This behaviour is attributed to the film surface morphology, molecular orientation in the film architecture, and sizes and dipole moments of vapours.     

Polymerization of olefins through heterogeneous catalysis. IX. Experimental study of propylene polymerization over a high activity MgCl2-supported Ti catalyst

Results from an experimental study of propylene polymerization in heptane diluent over a high activity Mg-supported Ti catalyst are presented. The study provides an examination of the effect of operating conditions on polymerization rate, product melt index, and powder bulk density. Among the findings are that product bulk density decreases with increasing operating temperature and decreasing operating pressure while prepolymerization increases the bulk density. The results support the hypothesis that polymer morphology is closely linked to mass transfer limitations within the growing polymer particle during the early stages of polymerization.     

Impaired sensorineural function after allergen-induced mediator release

We tested the hypothesis that allergen-induced mediator release augments the magnitude of isocapnic dry gas hyperpnea-induced bronchoconstriction in sensitized guinea pigs. Male Hartley guinea pigs were sensitized by spontaneous inhalation of ovalbumin (OA) aerosol on days 0 and 7 of the study. On day 14, sensitized animals again breathed OA aerosol and were prospectively divided into a group that exhibited labored breathing (LB), presumably reflecting OA-induced inflammatory mediator release, and a group that did not exhibit LB at this time. Control guinea pigs breathed saline aerosol on days 0, 7, and 14. Bronchoalveolar lavage on day 17 disclosed relative eosinophilia in OA+LB, but not in OA-LB, animals. On day 17, the bronchoconstrictor responses to increasing intravenous (i.v.) doses of acetylcholine (ACh), substance P (SP), neurokinin A (NKA), and capsaicin, as well as dry gas hyperpnea, were measured in vivo in animals from each group. Control and OA-LB guinea pigs exhibited similar responses, but OA+LB animals demonstrated augmented bronchoconstriction induced by i.v. administration of ACh, SP, or NKA. However, despite their augmented responsiveness to these exogenous constrictor agonists, OA+LB animals displayed no greater bronchoconstriction after dry gas hyperpnea or i.v. capsaicin administration. It is known that both dry gas hyperpnea and i.v. capsaicin cause bronchoconstriction in guinea pigs by releasing endogenous tachykinins from airway sensory C-fibers. Thus, our results suggest that allergen-induced mediator release impairs endogenous tachykinin release from airway sensory C-fibers in guinea pigs.     

Correlation between fixed positive charge and hot-electron immunityfor nitridized oxides

Nitrogen in the gate oxide of a 3.3-V, 0.4-μm CMOS technology was modulated in a variety of ways, including treatments with N₂ O, NO, oxidation at elevated pressure, and post-oxidation annealing. A direct correlation was observed between the fixed positive charge and the hot-electron immunity, regardless of the means by which the nitrogen was incorporated, or subsequently annealed. The implication is that one benefit and one drawback of nitrided-oxide gate oxides are inextricably linked, with significant effects on the transistor design