Assessing the suitability of fly ash geopolymers for high temperature applications

Geopolymers are an inorganic polymer synthesised from the dissolution and polycondensation of aluminosilicates in alkaline solutions under hydrothermal condition, yielding an amorphous, three-dimensional polymeric framework (Davidovits, 1991). They are a broad class of binding material with applications that range from conventional concrete to high tech, light weight composites for use in aviation. Geopolymers have also shown promise for use in high temperature applications, such as fire proof coatings, structural concrete in fire prone areas and thermal insulation for refractory type applications, due to their intrinsic thermal stability (Barbosa and MacKenzie, 2003a).This thesis reports on an investigation into the thermal performance of geopolymers synthesised from a range of fly ashes in order to assess their suitability for use in high temperature applications. Five fly ashes from Australian power stations with contrasting chemical properties were used in the study. Geopolymers were synthesised from each of the fly ashes using sodium silicate or sodium aluminate solutions in order to achieve a set range of Si:Al compositional ratios. Thermal analysis was conducted up to 1000 °C using a constant heat rate as well as a heating regime that simulated the conditions during a fire.The fly ashes were characterised in terms of elemental composition, phase composition, particle size, density and morphology prior to being used to synthesise geopolymers. It was determined that only a portion of each of the fly ashes was available for geopolymerisation and that the reactive Si:Al ratio (amorphous Si:Al ratio) varied greatly between the fly ashes. Collie and Port Augusta fly ashes had relatively low reactive Si:Al ratios (1.15 and 1.84, respectively) whereas Eraring, Tarong and Bayswater fly ashes had high Si:Al ratios (4.98, 8.84 and 7.49, respectively). All of the fly ashes had a predominantly spherical morphology, characteristic of fly ashes, though only the Collie and Port Augusta fly ashes had a significant portion of sub 5 μm particles.The thermo-physical, mechanical and micro-structural properties of the geopolymers made from each of the fly ashes are presented and the effect of the source fly ash characteristics on the hardened product is discussed. The results varied greatly with fly ash source and the most influential fly ash characteristic was the reactive Si:Al ratio. Fly ashes with a high reactive Si:Al ratio (≥5) were sodium aluminate activated and produced geopolymers with low to moderate as-cured compressive strengths but exhibited excellent dimensional stability during heating and greater compressive strengths after heating. Fly ashes with a low reactive Si:Al ratio (<2) were sodium silicate activated and produced geopolymers with high as-cured compressive strengths but exhibited poor dimensional stability during heating and greatly reduced compressive strengths after heating. All samples exhibited strength improving microstructural changes such as improved inter-particle bonding due to sintering after firing. However, the instability of non geopolymer phases during high temperature exposure led to strength losses in some samples depending on the type and composition of the activating solution.Geopolymers from three of the fly ashes were assessed for their performance upon exposure to a simulated fire. Solid and low density foamed variants (ρ ≈ 0.9 g cm-3, k ≈ 0.3 W m-1K-1) of the mixes were used for fire testing. Fire ratings of between 60 and 90 minutes for a sample thickness of 50 mm were achieved. The solid geopolymers exhibited better fire ratings than the low density geopolymers due to their higher water content (as they contained more of the hydrated geopolymer phase). Microstructural analysis of the fire tested samples indicated that the geopolymers were not significantly damaged by dehydration and the fire exposed side exhibited analogous changes to the samples that were gradually heated to 1000 °C.The results in this thesis indicate that fly ash geopolymers have great potential for utilisation in high temperature applications provided they are synthesised from a source material with suitable physical and compositional characteristics

The use of imaging systems to monitor shoreline dynamics

The development of imaging systems is nowadays established as one of the most powerful and reliable tools for monitoring beach morphodynamics. Two different techniques for shoreline detection are presented here and, in one case, applied to the study of beach width oscillations on a sandy beach (Pauanui Beach, New Zealand). Results indicate that images can provide datasets whose length and sample interval are accurate enough to resolve inter-annual and seasonal oscillations, and long-term trends. Similarly, imaging systems can be extremely useful in determining the statistics of rip current occurrence. Further improvements in accuracy and reliability are expected with the recent introduction of digital systems

A low-metallicity massive contact binary undergoing slow Case A mass transfer: A detailed spectroscopic and orbital analysis of SSN 7 in NGC 346 in the SMC

Most massive stars are believed to be born in close binary systems where they can exchange mass, which impacts the evolution of both binary components. Their evolution is of great interest in the search for the progenitors of gravitational waves. However, there are unknowns in the physics of mass transfer as observational examples are rare, especially at low metallicity. Nearby low-metallicity environments are particularly interesting hunting grounds for interacting systems as they act as the closest proxy for the early universe where we can resolve individual stars. Using multi-epoch spectroscopic data, we complete a consistent spectral and orbital analysis of the early-type massive binary SSN 7 hosting a ON If$^\ast$+O5.5 V((f)) star. Using these detailed results, we constrain an evolutionary scenario that can help us to understand binary evolution in low metallicity. We were able to derive reliable radial velocities of the two components from the multi-epoch data, which were used to constrain the orbital parameters. The spectroscopic data covers the UV, optical, and near-IR, allowing a consistent analysis with the stellar atmosphere code, PoWR. Given the stellar and orbital parameters, we interpreted the results using binary evolutionary models. The two stars in the system have comparable luminosities of ${\log (L_1/L_{\odot}) = 5.75}$ and ${\log (L_2/L_{\odot}) = 5.78}$ for the primary and secondary, respectively, but have different temperatures (${T_1=43.6\,\mathrm{kK}}$ and ${T_2=38.7\,\mathrm{kK}}$). The primary ($32\,M_{\odot}$) is less massive than the secondary ($55\,M_{\odot}$), suggesting mass exchange. The mass estimates are confirmed by the orbital analysis. The revisited orbital period is $3\,\mathrm{d}$. Our evolutionary models also predict mass exchange. Currently, the system is a contact binary undergoing a slow Case A phase, making it the most massive [Abridged]Comment: 20 page

Magnetic Flux Braiding: Force-Free Equilibria and Current Sheets

We use a numerical nonlinear multigrid magnetic relaxation technique to investigate the generation of current sheets in three-dimensional magnetic flux braiding experiments. We are able to catalogue the relaxed nonlinear force-free equilibria resulting from the application of deformations to an initially undisturbed region of plasma containing a uniform, vertical magnetic field. The deformations are manifested by imposing motions on the bounding planes to which the magnetic field is anchored. Once imposed the new distribution of magnetic footpoints are then taken to be fixed, so that the rest of the plasma must then relax to a new equilibrium configuration. For the class of footpoint motions we have examined, we find that singular and nonsingular equilibria can be generated. By singular we mean that within the limits imposed by numerical resolution we find that there is no convergence to a well-defined equilibrium as the number of grid points in the numerical domain is increased. These singular equilibria contain current "sheets" of ever-increasing current intensity and decreasing width; they occur when the footpoint motions exceed a certain threshold, and must include both twist and shear to be effective. On the basis of these results we contend that flux braiding will indeed result in significant current generation. We discuss the implications of our results for coronal heating.Comment: 13 pages, 12 figure

On Berenstein-Douglas-Seiberg Duality

I review the proposal of Berenstein-Douglas for a completely general definition of Seiberg duality. To give evidence for their conjecture I present the first example of a physical dual pair and explicitly check that it satisfies the requirements. Then I explicitly show that a pair of toric dual quivers is also dual according to their proposal. All these computations go beyond tilting modules, and really work in the derived category. I introduce all necessary mathematics where needed.Comment: 22 pages, LaTe

The homotopy theory of dg-categories and derived Morita theory

The main purpose of this work is the study of the homotopy theory of dg-categories up to quasi-equivalences. Our main result provides a natural description of the mapping spaces between two dg-categories $C$ and $D$ in terms of the nerve of a certain category of $(C,D)$-bimodules. We also prove that the homotopy category $Ho(dg-Cat)$ is cartesian closed (i.e. possesses internal Hom's relative to the tensor product). We use these two results in order to prove a derived version of Morita theory, describing the morphisms between dg-categories of modules over two dg-categories $C$ and $D$ as the dg-category of $(C,D)$-bi-modules. Finally, we give three applications of our results. The first one expresses Hochschild cohomology as endomorphisms of the identity functor, as well as higher homotopy groups of the \emph{classifying space of dg-categories} (i.e. the nerve of the category of dg-categories and quasi-equivalences between them). The second application is the existence of a good theory of localization for dg-categories, defined in terms of a natural universal property. Our last application states that the dg-category of (continuous) morphisms between the dg-categories of quasi-coherent (resp. perfect) complexes on two schemes (resp. smooth and proper schemes) is quasi-equivalent to the dg-category of quasi-coherent complexes (resp. perfect) on their product.Comment: 50 pages. Few mistakes corrected, and some references added. Thm. 8.15 is new. Minor corrections. Final version, to appear in Inventione

Lack of involvement of lipocortin 1 in dexamethasone suppression of IL-1 release

The annexin lipocortin 1 is reported to mediate some anti-inflammatory effects of glucocorticoids, but the mechanisms of this mediation are incompletely understood. The involvement of lipocortin 1 in glucocorticoid inhibition of monocyte interleukin 1β (IL-1β) release has been investigated. Treatment of peripheral blood monocytes with 2 μg/ml lipopolysaccharide potently increased IL–1β release (p = 0.001) and dexamethasone (10−7 M) significantly reduced both resting and stimulated IL-1β release (p = 0.009). A neutralizing monoclonal antibody to lipocortin 1 (0.5–50.0 μg/ml) was unable to inhibit this effect and recombinant lipocortin 1 (2 × 10−6 M) and 188aa lipocortin 1 fragment (10−8−10−6 M) had no effect. It is concluded that lipocortin 1 is not involved in the inhibition of monocyte IL-1β release by glucocorticoids

Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain

No abstract available