Understanding the Reaction Mechanism of Nanocomposite Thermites

Nanocomposite energetics are a relatively new class of materials that combine nanoscale fuels and oxidizers to allow for the rapid release of large amounts of energy. In thermite systems (metal fuel with metal oxide oxidizer), the use of nanomaterials has been illustrated to increase reactivity by multiple orders of magnitude as a result of the higher specific surface area and smaller diffusion length scales. However, the highly dynamic and nanoscale processes intrinsic to these materials, as well as heating rate dependencies, have limited our understanding of the underlying processes that control reaction and propagation. For my dissertation, I have employed a variety of experimental approaches that have allowed me to probe these processes at heating rates representative of free combustion with the goal of understanding the fundamental mechanisms. Dynamic transmission electron microscopy (DTEM) was used to study the in situ morphological change that occurs in nanocomposite thermite materials subjected to rapid (10^11 K/s) heating. Aluminum nanoparticle (Al-NP) aggregates were found to lose their nanostructure through coalescence in as little as 10 ns, which is much faster than any other timescale of combustion. Further study of nanoscale reaction with CuO determined that a condensed phase interfacial reaction could occur within 0.5-5 µs in a manner consistent with bulk reaction, which supports that this mechanism plays a dominant role in the overall reaction process. Ta nanocomposites were also studied to determine if a high melting point (3280 K) affects the loss of nanostructure and rate of reaction. The condensed phase reaction pathway was further explored using reactive multilayers sputter deposited onto thin Pt wires to allow for temperature jump (T-Jump) heating at rates of ~5x10^5 K/s. High speed video and a time of flight mass spectrometry (TOFMS) were used to observe ignition temperature and speciation as a function of bilayer thickness. The ignition process was modeled and a low activation energy for effective diffusivity was determined. T-Jump TOFMS along with constant volume combustion cell studies were also used to determine the effect of gas release in nanoparticle systems by comparing the reaction properties of CuO and Cu2O.

CONSTRAINTS ON THE LITHOSPHERIC STRUCTURE OF MID OCEAN RIDGES FROM OCEANIC CORE COMPLEX MORPHOLOGY

The Mid-oceanic ridge system is a feature unique to Earth. It is one of the fundamental components of plate tectonics and reflects interior processes of mantle convection within the Earth. The thermal structure beneath the mid-ocean ridges has been the subject of several modeling studies. It is expected that the elastic thickness of the lithosphere is larger near the transform faults that bound mid-ocean ridge segments. Oceanic core complexes (OCCs), which are generally thought to result from long-lived fault slip and elastic flexure, have a shape that is sensitive to elastic thickness. By modeling the shape of OCCs emplaced along a ridge segment, it is possible to constraint elastic thickness and therefore the thermal structure of the plate and how it varies along-axis. This thesis builds upon previous studies that utilize thin plate flexure to reproduce the shape of OCCs. I compare OCC shape to a suite of models in which elastic thickness, fault dip, fault heave, crustal thickness, and axial infill are systematically varied. Using a grid search, I constrain the parameters that best reproduce the bathymetry and/or the slope of ten candidate OCCs identified along the 12°—15°N segment of the Mid-Atlantic Ridge. The lithospheric elastic thicknesses that explains these OCCs is thinner than previous investigators suggested and the fault planes dip more shallowly in the subsurface, although at an angle compatible with Anderson’s theory of faulting. No relationships between model parameters and an oceanic core complexes location within a segment are identified with the exception that the OCCs located less than 20km from a transform fault have slightly larger elastic thickness than OCCs in the middle of the ridge segment.

Interorganizational Innovation: The Role of Suppliers in Enhancing Buyer Innovation

This dissertation explores the effect of innovative knowledge transfer across supply chain partners. My research seeks to understand the manner by which a firm is able to benefit from the innovative capabilities of its supply chain partners and utilize the external knowledge they hold to increase its own levels of innovation. Specifically, I make use of patent data as a proxy for firm-level innovation and develop both independent and dependent variables from the data contained within the patent filings. I further examine the means by which key dyadic and portfolio supply chain relationship characteristics moderate the relationship between supplier innovation and buyer innovation. I investigate factors such as the degree of transactional reciprocity between the buyer and supplier, the similarity of the firms’ knowledge bases, and specific chain characteristics (e.g., geographic propinquity) to provide greater understanding of the means by which the transfer of innovative knowledge across firms in a supply chain can be enhanced or inhibited. This dissertation spans three essays to provide insights into the role that supply chain relationships play in affecting a focal firm’s level of innovation. While innovation has been at the core of a wide body of research, very little empirical work exists that considers the role of vertical buyer-supplier relationships on a firm’s ability to develop new and novel innovations. I begin by considering the fundamental unit of analysis within a supply chain, the buyer-supplier dyad. After developing initial insights based on the interactions between singular buyers and suppliers, essay two extends the analysis to consider the full spectrum of a buyer’s supply base by aggregating the individual buyer-supplier dyad level data into firm-supply network level data. Through this broader level of analysis, I am able to examine how the relational characteristics between a buyer firm and its supply base affect its ability to leverage the full portfolio of its suppliers’ innovative knowledge. Finally, in essay three I further extend the analysis to explore the means by which a buyer firm can use its suppliers to enhance its ability to access distant knowledge held by other organizations that the buyer is only connected to indirectly through its suppliers.