Effects of microstructure on long and short crack growth in nickel base superalloys

The use of engineering materials in critical applications necessitates the accurate prediction of component lifetime for inspection and renewal purposes. In fatigue limited situations, it is necessary to be able to predict the growth rates of cracks from initiation at a defect through to final fracture. To this end, fatigue crack growth data are presented for different microstructures of typical nickel base superalloys used in gas turbine engines. Crack growth behaviour throughout the life history of the crack, i.e. from the short crack through to the long crack propagation regime, is described for each microstructural condition and discussed in terms of current theories of fatigue crack propagation.

Effect of Surfactants on the Structure and Morphology of Magnesium Borate Hydroxide Nanowhiskers Synthesized by Hydrothermal Route

Magnesium borate hydroxide (MBH) nanowhiskers were synthesized using a one step hydrothermal process with different surfactants. The effect surfactants have on the structure and morphology of the MBH nanowhiskers has been investigated. The X-ray diffraction profile confirms that the as-synthesized material is of single phase, monoclinic MgBO2(OH). The variations in the size and shape of the different MBH nanowhiskers have been discussed based on the surface morphology analysis. The annealing of MBH nanowhiskers at 500 °C for 4 h has significant effect on the crystal structure and surface morphology. The UV–vis absorption spectra of the MBH nanowhiskers synthesized with and without surfactants show enhanced absorption in the low-wavelength region, and their optical band gaps were estimated from the optical band edge plots. The photoluminescence spectra of the MBH nanowhiskers produced with and without surfactants show broad emission band with the peak maximum at around 400 nm, which confirms the dominant contribution from the surface defect states.

Indényles greffés d'un bras moléculaire fonctionnalisé comme ligands hémilabiles de nouveaux catalyseurs de nickel(II)

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Résistance à la fracture de boîtiers en céramique soumis à une contrainte de torque par le biais d'un fil en torsion, en acier ou en nickel-titane

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Supercapattery based on binder-free Co3 (PO4)2·8H2O multilayer nano/microflakes on nickel foam

A binder-free cobalt phosphate hydrate (Co3(PO4)2·8H2O) multilayer nano/microflake structure is synthesized on nickel foam (NF) via a facile hydrothermal process. Four different concentrations (2.5, 5, 10, and 20 mM) of Co2+ and PO4–3 were used to obtain different mass loading of cobalt phosphate on the nickel foam. The Co3(PO4)2·8H2O modified NF electrode (2.5 mM) shows a maximum specific capacity of 868.3 C g–1 (capacitance of 1578.7 F g–1) at a current density of 5 mA cm–2 and remains as high as 566.3 C g–1 (1029.5 F g–1) at 50 mA cm–2 in 1 M NaOH. A supercapattery assembled using Co3(PO4)2·8H2O/NF as the positive electrode and activated carbon/NF as the negative electrode delivers a gravimetric capacitance of 111.2 F g–1 (volumetric capacitance of 4.44 F cm–3). Furthermore, the device offers a high specific energy of 29.29 Wh kg–1 (energy density of 1.17 mWh cm–3) and a specific power of 4687 W kg–1 (power density of 187.5 mW cm–3).

Indényles greffés d'un bras moléculaire fonctionnalisé comme ligands hémilabiles de nouveaux catalyseurs de nickel(II)

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Résistance à la fracture de boîtiers en céramique soumis à une contrainte de torque par le biais d'un fil en torsion, en acier ou en nickel-titane

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

(Table 1) Determined and theoretical chemical composition of thaumasite of ODP Hole 135-841B

Hole 841B was drilled in the forearc region of the Lau Basin at a water depth of 4810 m. The hole penetrated a roughly 500-m-thick series of Miocene volcanic sediments with a number of basaltic to andesitic units (sills?) varying in thickness between 7 cm and 17 m. The volcanics are slightly to moderately altered and contain analcite, chabazite, natrolite-thompsonite, heulandite (?), prehnite, and quartz as secondary phases. In addition, thaumasite [Ca3Si(OH)6 * 12H2O](SO4)(CO3) was identified in the altered sequence. Sulfur isotope data of two thaumasite separates (+23.5 per mil and +21.1 per mil d34S) indicate a seawater origin of the sulfate sulfur. It is suggested that thaumasite is a product of low-temperature (<60 °C), seawater-derived CaCl2-rich fluids that were almost identical in composition to those presently circulating in the sub-seafloor.

(Table 3) Reduced inorganic sulphur, d34S and nickel content of ODP Leg 165 sites

Leg 165 of the Ocean Drilling Program afforded a unique opportunity to investigate organic and inorganic geochemistry across a wide gradient of sediment compositions and corresponding chemical pathways. The solid fractions at Sites 998, 999, 1000, and 1001 reveal varying proportions of reactive carbonate species, a labile volcanic ash fraction occurring in discrete layers and as a dispersed component, and detrital fluxes that derive from continental weathering. The relative proportions and reactivities of these end-members strongly dictate the character of the diagenetic profiles observed during the pore-water work of Leg 165. In addition, alteration of the well-characterized basaltic basement at Site 1001 has provided a strong signal that is reflected in many of the dissolved components. The relative effects of basement alteration and diagenesis within the sediment column are discussed in terms of downcore relationships for dissolved calcium and magnesium. With the exception of Site 1002 in the Cariaco Basin, the sediments encountered during Leg 165 were uniformly deficient in organic carbon (typically <0.1 wt%). Consequently, rates of organic oxidation were generally low and dominated by suboxic pathways with subordinate levels of bacterial sulfate reduction and methanogenesis. The low rates of organic remineralization are supported by modeled rates of sulfate reduction. Site 1000 provided an exception to the generally low levels of microbially mediated redox cycling. At this site the sediment is slightly more enriched in organic phases, and externally derived thermogenic hydrocarbons appear to aid in driving enhanced levels of redox diagenesis at great depths below the seafloor. The entrapment of these volatiles corresponds with a permeability seal defined by a pronounced Miocene minimum in calcium carbonate concentration recognized throughout the basin and with a dramatic downcore increase in the magnitude of limestone lithification. The latter has been tentatively linked to increases in alkalinity associated with microbial oxidation of organic matter and gaseous hydrocarbons. Recognition and quantification of previously unconstrained large volumes and frequencies of Eocene and Miocene silicic volcanic ash within the Caribbean Basin is one of the major findings of Leg 165. High frequencies of volcanic ash layers manifest as varied but often dominant controls on pore-water chemistry. Sulfur isotope results are presented that speak to secondary metal and sulfur enrichments observed in ash layers sampled during Leg 165. Ultimately, a better mechanistic understanding of these processes and the extent to which they have varied spatially and temporally may bear on the global mass balances for a range of major and minor dissolved components of seawater.

(Table 2, page 72) Chemical compositin of the two nodule types used in this investigation

Two Pacific Ocean manganese nodules, one from the ocean basin and one from a sea-mount, were examined in transmission electron microscopes at 100 and 650 kV. Of the many specimens examined, ten electron diffraction crystal spot patterns were identified. Sodium birnessite was observed six times and todorokite, Giavanoli's synthetic birnessite, hydrohausmanite and -Fe2O3 one time each. Ferric hydroxide was synthesized in the laboratory and shown to be the same as the primary iron mineral observed in the manganese nodules. The ferric hydroxide had a particle size range from 30 to 450 ?. Manganese oxide particles were frequently embedded in a mass of smaller ferric hydroxide particles.

The syntheses and characterization of nickel complexes; investigation of Ni(dppp)2 and [NiX(dppp)n]x, potentially catalytically active nickel(0)/(I) species for cross-coupling reactions

This thesis describes an investigation in which we compare Ni(0), Ni(I) and Ni(II) complexes containing 1,3-bis(diphenylphosphino)propane (dppp) as a phosphine ligand for their abilities to effect three types of cross-coupling reactions: Buchwald-Hartwig Amination, Heck-Mizoroki, and Suzuki-Miyaura cross-coupling reactions with different types of substrates. The Ni(0) complex Ni(dppp)2 is known and we have synthesized it via a new procedure involving zinc reduction of the known NiCl2(dppp) in the presence of an excess of dppp. The Ni(0) complex was characterized by NMR spectroscopy and X-ray crystallography. Since Ni(I) complexes of dppp seem unknown, we have synthesized what at this stage appear to be NiXdpppn/[NiX(dppp)n]x (X = Cl, Br, I; n = 1,2, x = 1, 2) by comproportionation of molar equivalents of Ni(dppp)2 and NiX2dppp, X= Cl, Br, I.