Microstructural development in aluminide diffusion coatings on nickel-base superalloy single crystals

An investigation has been made of the microstructural stability of aluminide diffusion coatings during post-coating thermal exposure. This study has employed edge-on transmission electron microscopy to examine high-activity pack aluminised single crystals of a gamma prime strengthened nickel-base superalloy. The influence of exposure temperature, duration and atmosphere as well as the initial coating thickness has been assessed. Two major processes have been found to contribute to microstructural changes in the coating. These are, firstly, the transformation of the coating matrix (β-phase, nominally NiAl) to other Ni-Al based phases, especially γ' (nominally Ni3(Al, Ti)) and, secondly, the precipitation of chromium containing phases. The work has enabled the roles of three processes contributing to γ formation, namely: oxidation of the coating surface, interdiffusion with the substrate and ageing of the coating, to be understood. In addition, the factors leading to the formation of a sequence of chromium-containing phases have been identified.

Modelling short crack growth behaviour in nickel-base superalloys

This paper provides a description of the features and mechanisms of facetted short crack growth in Ni-base superalloys, and briefly reviews existing short crack growth models in terms of their application to Ni-base alloys. The concept of “soft barriers” is introduced to produce a new two-phase model for local microstructural effects on short crack growth in Waspaloy. This is derived from detailed observations of crack growth through individual grains. The model differs from all previous approaches in highlighting the importance of crack path perturbations within grains. Potential applications of the model in alloy development are discussed.

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.

The effects of foam rolling on muscular co-activation around the knee joint

The major objectives of this thesis were to determine if foam rolling had any effect on antagonist muscle activation and whether those changes would alter muscular co-activation patterns. The results from this thesis along with current literature will help clinicians to develop adequate exercise prescription for rehabilitative and pre-activity purposes. The existing literature has shown that foam rolling or roller massagers can increase range of motion (ROM), improve performance, and alter pain perception, however little research exists regarding changes in muscle activation following foam rolling. This study developed a reliable method for measuring muscle activation around the knee joint and using that method found that foam rolling the quadriceps can impair hamstrings muscle activation likely due to greater levels of perceived pain when rolling the quadriceps.

Spacetime foam induced collective bundling of intense fields

This research is supported by the Carnegie Trust for the Universities of Scotland (TO) and by the EPSRC GG-Top Project and the Cruickshank Trust (CW).

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.

Assessing charge contribution from thermally treated Ni foam as current collectors for Li-ion batteries

In this report we have investigated the use of Ni foam substrates as anode current collectors for Li-ion batteries. As the majority of reports in the literature focus on hydrothermal formation of materials on Ni foam followed by a high temperature anneal/oxidation step, we probed the fundamental electrochemical responses of as received Ni foam substrates and those subjected to heating at 100°C, 300°C and 450°C. Through cyclic voltammetry and galvanostatic testing, it is shown that the as received and 100°C annealed Ni foam show negligible electrochemical activity. However, Ni foams heated to higher temperature showed substantial electrochemical contributions which may lead to inflated capacities and incorrect interpretations of CV responses for samples subjected to high temperature anneals. XRD, XPS and SEM analyses clearly illustrate that the formation of electrochemically active NiO nanoparticles on the surface of the foam is responsible for this behavior. To further investigate the contribution of the oxidized Ni foam to the overall electrochemical response, we formed Co3O4 nanoflowers directly on Ni foam at 450°C and showed that the resulting electrochemical response was dominated by NiO after the first 10 charge/discharge cycles. This report highlights the importance of assessing current collector activity for active materials grown on transition metal foam current collectors for Li-ion applications.

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 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.

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.

The Effect of Foam Core Density on the Flexural and Axial Behaviour of Sandwich Panels of Varying Slenderness with Natural Flax-FRP and Glass-FRP Composite Skins

This study investigates the effect of foam core density and skin type on the behaviour of sandwich panels as structural beams tested in four-point bending and axially compressed columns of varying slenderness and skin thickness. Bio-composite unidirectional flax fibre-reinforced polymer (FFRP) is compared to conventional glass-FRP (GFRP) as the skin material used in conjunction with three polyisocyanurate (PIR) foam cores with densities of 32, 64 and 96 kg/m3. Eighteen 1000 mm long flexural specimens were fabricated and tested to failure comparing the effects of foam core density between three-layer FFRP skinned and single-layer GFRP skinned panels. A total of 132 columns with slenderness ratios (kLe/r) ranging from 22 to 62 were fabricated with single-layer GFRP skins, and one-, three-, and five-layer FFRP skins for each of the three foam core densities. The columns were tested to failure in concentric axial compression using pinned-end conditions to compare the effects of each material type and panel height. All specimens had a foam core cross-section of 100x50 mm with 100 mm wide skins of equal thickness. In both flexural and axial loading, panels with skins comprised of three FFRP layers showed equivalent strength to those with a single GFRP layer for all slenderness ratios and core densities examined. Doubling the core density from 32 to 64 kg/m3 and tripling the density to 96 kg/m3 led to flexural strength increases of 82 and 213%, respectively. Both FFRP and GFRP columns showed a similar variety of failure modes related to slenderness. Low slenderness of 22-25 failed largely due to localized single skin buckling, while those with high slenderness of 51-61 failed primarily by global buckling followed by secondary skin buckling. Columns with intermediate slenderness experienced both localized and global failure modes. High density foam cores more commonly exhibited core shear failure. Doubling the core density of the columns resulted in peak axial load increases, across all slenderness ratios, of 73, 56, 72 and 71% for skins with one, three and five FFRP layers, and one GFRP layer, respectively. Tripling the core density resulted in respective peak load increases of 116, 130, 176 and 170%.

Effects of lycopene on the induction of foam cell formation by modified LDL.

The effect of lycopene on macrophage foam cell formation induced by modified low-density lipoprotein (LDL) was studied. Human monocyte-derived macrophages (HMDM) were incubated with lycopene in the presence or absence of native LDL (nLDL) or LDL modified by oxidation (oxLDL), aggregation (aggLDL), or acetylation (acLDL). The cholesterol content, lipid synthesis, scavenger receptor activity, and the secretion of inflammatory [interleukin (IL)-1β and tumor necrosis factor (TNF)-α] and anti-inflammatory (IL-10) cytokines was determined. Lycopene was found to decrease the synthesis of cholesterol ester in incubations without LDL or with oxLDL while triacylglycerol synthesis was reduced in the presence of oxLDL and aggLDL. Scavenger receptor activity as assessed by the uptake of acLDL was decreased by ∼30% by lycopene. In addition, lycopene inhibited IL-10 secretion by up to 74% regardless of the presence of nLDL or aggLDL but did not affect IL-1β or TNF-α release. Lycopene also reduced the relative abundance of mRNA transcripts for scavenger receptor A (SR-A) in THP-1 macrophages treated with aggLDL. These findings suggest that lycopene may reduce macrophage foam cell formation induced by modified LDL by decreasing lipid synthesis and downregulating the activity and expression of SR-A. However, these effects are accompanied by impaired secretion of the anti-inflammatory cytokine IL-10, suggesting that lycopene may also exert a concomitant proinflammatory effect.

The induction of macrophages foam cell formation by chylomicron remnants

The accumulation of foam cells in the artery wall causes fatty streaks, the first lesions in atherosclerosis. LDL (low-density lipoprotein) plays a major role in foam cell formation, although prior oxidation of the particles is required. Recent studies, however, have provided considerable evidence to indicate that CMRs (chylomicron remnants), which carry dietary lipids in the blood, induce foam cell formation without oxidation. We have shown that CMRs are taken up by macrophages and induce accumulation of both triacylglycerol and cholesterol, and that the rate of uptake and amount of lipid accumulated is influenced by the type of dietary fat in the particles. Furthermore, oxidation of CMRs, in striking contrast with LDL, inhibits, rather than enhances, their uptake and induction of lipid accumulation. In addition, the lipid accumulated after exposure of macrophages to CMRs is resistant to efflux, and this may be due to its sequestration in lysosomes. These findings demonstrate that CMRs induce pro-atherogenic changes in macrophages, and that their effects may be modulated by dietary factors including oxidized fats, lipophilic antioxidants and the type of fat present.