archives@tulane.edu / Reactive Cavitation Erosion (RCE), a new materials processing technique for the production of functionalized nanomaterials in which acoustic cavitation erosion is performed in a reactive medium, is described herein. Background material on acoustic cavitation erosion in the form of a literature review is presented. The effects of fluid properties and ambient pressure on the bubble dynamics at the high acoustic pressures commensurate with RCE are studied. The solutions to the Rayleigh-Plesset equation (RPE) and Keller-Miksis equation (KME) are compared. It is shown that to a first approximation, the RPE and KME give similar results. Analyses of the RPE solutions for real-world fluids reveal that many fluids result in cavitation intensity comparable to or greater than that of water. The groundwork for future modelling of RCE was established through the development of the Hemispherical Pit Model (HPM). The HPM is based upon a simple geometrical model of the volume loss process and contains parameters that may be more directly related to material properties and experimental parameters. Formation of functionalized clinoatacamite nanoparticles is achieved through Reactive Cavitation Erosion of copper discs in a 1 M guanidine hydrochloride solution. From analyses, the mechanism for formation of the clinoatacamite proceeded from ablation of metallic copper from the disc surface followed by subsequent reactions in solution. / 1 / Jeremy William Wright

Historically, coatings were processed from natural oils, fats, and resins; the first well-known and widely used being lacquer [Meir-Westhues, 2007]. In the 20th century, synthetic resins were developed to achieve coatings with improved properties. Of these coating compositions, polyurethanes (PURs) were one of the most prevalent. Polyurethanes became possible in 1937 when Otto Bayer developed the diisocyanate polyaddition process [Randall et al, 2002]. Since that time, literally thousands of PUR compositions have been used commercially. The primary application of interest in this study is that of coatings for wood substrates. It is well-known among materials researchers that there can be a number of differences between microwave and conventional materials treatment techniques [Clark et al, 1996], including enhanced reaction rates, lowered processing temperatures for some products, and selective interactions in composite systems. The primary goals of this research were to determine (1) whether microwave energy affected the cure rate in a water-based, aliphatic PUR, and (2) if there was an effect of microwave frequency on the cure rate. The primary tool for determining extent of cure in the PUR samples was Fourier transform infrared spectroscopy (FTIR). Using this characterization method, the changes in intensities of four bonds specific to the PUR composition were followed. It was determined that, in the particular PUR composition studied, microwave energy had an effect on the cure rate when compared with conventional heating, and that there was a frequency effect on the cure rate. Additionally, a deeper understanding of the use of FTIR spectroscopy techniques for studying cure kinetics was developed. / Master of Science

A scalable spray processing technique was used to fabricate carbon nanotube (CNT)-based film electrodes and solid-state supercapacitors. The sprayed CNT-based electrodes comprised a randomly interconnected meso-porous network with a high electrical conductivity. Layer-by-layer (LbL) deposition of functionalised and oppositely charged single-wall carbon nanotubes (SWNTs) increased the electrode density and improved charging and discharging kinetics when compared with carboxylic functionalised only SWNT electrodes. The capacitance was further increased to 151 F g-1 at 2 mV s-1 and 120 F g-1 at 100 mV s-1 after vacuum and H2 heat treatments that removed the functional groups, and resulted in a hybrid microstructure of SWNTs and multi-layer graphene sheets from unzipped SWNTs. Flexible solid-state supercapacitors were fabricated by directly spraying multi-wall carbon nanotube (MWNT)-based aqueous suspensions onto both sides of a Nafion membrane and dried. A single cell with MWNT-only electrodes had a capacitance of 57 F g-1 per electrode at 2 mV s-1 and 44 F g-1 at 150 mV s-1. Cells with MWNT/ionomer electrodes showed a higher H+ mobility and a lower charge transfer resistance, and the capacitance increased to 145 F g-1 at 2 mV s-1 and 91 F g-1 at 150 mV s-1. Finally, MWNT/TiO2 nanoparticle/ionomer hybrid electrodes were used in the same solid-state supercapacitor configuration and provided a capacitance of 484 F g-1 per electrode at 5 mV s-1 and 322 F g-1 at 100 mV s-1. A qualitative model of the charge storage mechanism was developed, where TiO2 promoted H+ ions via redox reactions that fed protons into the proton-conducting ionomer coating over the MWNTs (in which the TiO2 was embedded), while electrons were readily conducted through the MWNT scaffold. This solid-state supercapacitor provided both attractive energy (31.8 Wh kg-1) and power (14.9 kW kg-1) densities, where such high energy density is difficult to achieve for MWNTs alone and such high power density is difficult for metal oxides alone, especially in the solid state.

This thesis describes the processing and characterisation of Al-70Si alloys manufactured by gas atomised spray forming at Sandvik-Osprey (Neath, UK) and Oxford University using a newly commissioned spray forming pilot-plant facility. Spray formed Al-70Si (CE7) provides an attractive balance of thermophysical properties making it suitable for thermal management applications. Microstructural characterisation of CE7 was conducted using optical microscopy, image analysis, electron probe micro analysis (EPMA) and electron backscatter diffraction (EBSD). Microscopy revealed an interpenetrating network microstructure consisting of fine, randomly oriented polycrystalline primary Si interpenetrated by large, α-Al grains devoid of eutectic Si. Mechanical testing and thermal cycling simulated a service environment and revealed for the first time crack initiation, growth and blunting mechanisms, the effect of intermetallic phases on the bulk mechanical properties, and anisotropy effects resulting from macrosegregation of Al during solidification. A relationship between the inter-phase interface length and the fracture toughness has been proposed and methods of interface length refinement have been investigated, including chill casting and spray forming. Spray formed CE7 modified with separate additions of B, P, P+Ce and Sr have been microstructurally and mechanically characterised and compared with binary CE7. While alloy additions were effective in refining primary and eutectic Si in chill cast alloys, spray formed alloys showed little change in interface length. Particle injection of Si-Al powder was effective in refining the scale of the spray formed microstructure, and improving mechanical properties. The deleterious effect of intermetallic phases on bulk mechanical properties has been demonstrated and highlighted the importance of melt cleanliness and materials control during manufacturing.

Three classes of Al-matrix composite were manufactured to combine dissimilar metals and incorporate structural hierarchy, in an attempt to develop unusual combinations of mechanical properties. The first class combined a brittle, nano-quasicrystalline forming Al-3Fe-2Cr-2Ti phase with a ductile Al-4Cu phase into a layered structure using low pressure plasma spraying (LPPS). By using a substrate with multi-scale topological features, an ultra-thick (>2mm) deposit was successfully sprayed, which was subsequently consolidated by hot rolling to reduce residual porosity. The microstructure comprised a 'brick-wall' structure consisting of a convoluted arrangement of inter-leaved discreet droplet splats. Structure-property relationships were studied for four volume fractions of ductile additions and in-situ electron microscopy of beams subjected to 3-point bending suggested the ductile additions were providing additional toughening to the composite by a crack-bridging mechanism. The second class of composite investigated highly deformed microstructures of Al with 20vol% additions of either Sn or Ti. Nano-scale fibrous structures of the minority additions were achieved via an accumulative extrusion method, where extruded rod was abraded, degreased, bundled and re-extruded. This process was repeated to create refined microstructures while retaining a large material section. Fracture properties were studied in three point bending and crack growth monitored using Digital Image Correlation (DIC) to produce strain fields of the deforming beam surface. Modest changes were observed in mechanical properties with weak interfaces between poorly bonded extruded rods dominating fracture behaviour. Whiskers formed on polished surfaces of extruded Al-20vol%Sn and were monitored in real time by electron microscopy. Growth rates of up to 2.8nm/s were measured, which exceeds re- ported values in the literature on electroplated coatings by at least one order of magnitude. This may provide a convenient new means of studying whisker formation and calls into question current growth models. The third class of composite combined heavily rolled sheets of Al-20vol%Sn and Al-20vol%Ti with glass fibre/epoxy sheets to produce a laminate with multi-scale architecture. This laminate was designed as a proof-of-concept hierarchical material with structures ranging from the near millimetre scale of the metal-polymer layers, to the micro-sized glass fibre reinforcement of the epoxy and the nano-scale filamentary/lamellar microstructure of the highly deformed metal sheets. Fracture of such laminates was investigated in 3-point bending with continuous optical monitoring.

In this thesis, nanosecond pulsed lasers are used as the tools to generate microstructures on metal and glass. The applications of these structures are described too. The production of micro structures is demonstrated using diode-pumped solid state (DPSS) Nd:YVO4 lasers operating at wavelengths of 532nm or 1064 nm. The laser fluence and scanning speed are important parameters to control the results. The first part of thesis is on the laser generation of microstructures on metal surfaces. Copper (Cu) and titanium (Ti) have been studied. According to the reflectivity of metals, Cu is processed by a 532nm laser and Ti is processed by a 1064nm laser. It is shown that the periods of surface microstructures are highly dependent on the hatch distance (overlapping distance between laser scanning). Only if the laser fluence is greater than a threshold, may the microstructures on metals be induced. The thresholds are measured by the diameters of ablated areas at different fluence. Laser generated surface microstructures have been applied to modify the reflectivity of a Cu sample. It was found that laser induced surface microstructures on Copper can decrease the surface reflectivity by almost 97% between 250 nm and 700 nm. To find the mechanism of how to form microstructure on metal surface with laser, laser ablation and heating models have been studied. The 1D ablated numerical model is calculated in Matlab. The pressure of metal vapour is an important parameter, as it pushes the melted metal out of surface to form microstructures after re-solidification. The second part of thesis is on glass welding with microstructures on glass surfaces. The soda-lime glasses containing silver nanoparticles (from the company Codixx) have been studied and welded with Schott B270 glass. Compared with other techniques for welding glass, lasers offer the advantage of a relatively simple and flexible technique for joining the local area underneath the cover glass. Most of the laser energy is deposited in the Ag nanoparticle layer because of the large absorption coefficient at 532 nm. Expanded microstructures generated by the laser are applied to fill the gap between the glass surfaces. This is attributed to the formation of bubbles in the Ag nanoparticle layer after laser processing. The welded samples have the joint strength of 4.9 MPa and have great potential for industrial applications. A 3D analytical model is used to estimate the temperature of the glass after the laser pulse. The increase in temperature is about 129 °C. To induce the bubble in glass, many laser pulses are necessary. This is very different from the results for the metals.

According to the International Energy Agency, the global Electric Vehicle (EV) sales are experiencing approximately 24% annual growth and the total market could reach 4 million in 2020 and 21.5 million by 2030. However, the mass production of lithium-ion batteries (LIBs) to power EV creates concerns over environmental impacts and the long-term sustainability of critical elements for producing the major battery components. Although much investment has been made, it is still imperative to develop an effective LIB production and recycling process. This dissertation demonstrates a green and sustainable paradigm for LIBs where the batteries are manufactured and direct recycled to form a closed loop. The water-based cathode electrode delivers comparable cycle life and rate performance to the ones from the conventional organic solvent-based process. The direct recycling process has the advantages to regenerate the cathode material from electrode instead of decomposing into elements. Utilization of a water-soluble binder enables separating the cathode compound from spent electrodes using water, which is then successfully regenerated to deliver comparable electrochemical performance to the pristine one. When scaled up, the degraded cathode material can be directly regenerated by an optimized relithiation thermal synthesis (RTS) method to resynthesize the homogeneous cathode powder of high quality. The key factors and sintering procedures are studied to ensure the performance of the product. The pilot scale test successfully scales up to Kg-level with recycled output materials delivering good electrochemical performance. To automate the direct recycling process and improve the efficiency, machine learning and sensors are utilized in a novel battery disassembly platform. It can classify different batteries based on their types and sizes. The processing temperature is instantly monitored using thermal imager, and the prediction model is trained to give the prediction for measures taken by a closed loop control system. Furthermore, the image recognition is employed for quality control after the cutting process and the defect can be mitigated to ensure effective dismantling of End-of-life (EOL) batteries. The integration of machine learning techniques makes the elaborate dismantling process safer and more efficient. / Doctor of Philosophy / According to the International Energy Agency, the global Electric Vehicle (EV) sales are experiencing approximately 24% annual growth and the total market could reach 4 million in 2020 and 21.5 million by 2030. However, the mass production of lithium-ion batteries (LIBs) to power EV creates concerns over environmental impacts and the long-term sustainability of critical elements for producing the major battery components. In this work, a green and sustainable manufacturing and recycling paradigm for LIBs is ushered and scaled up to pilot-scale test. Compared with the electrodes produced by conventional organic solvent-based process, the water-based electrodes can deliver comparable battery performance, meanwhile reduce the cost as well as the pollution to environment. The spent batteries are successfully regenerated to form the closed loop system with minimal external toxic solvent used. At pilot-scale, Kg-level battery material can be directly regenerated to deliver high-quality cathode powder. It provides the guidance of design parameters for large-scale battery recycling in industry. To automate the direct recycling process and improve the efficiency, machine learning and sensors are utilized in a novel battery disassembly platform. The integration of machine learning techniques makes the elaborate dismantling process safer and more efficient.

No / This study presents the data elements to develop a new processing route to transform elastomeric waste residue (particulates) into acoustic and thermal insulation materials that can compete with commercial products. The approach is to bind these grain and fibre particulates with a foaming polyurethane or a similar polymer, the chemistry of which can be manipulated to control the structure stiffness and the evolution of the foaming gas into open or closed cells. Here the study uses two examples of such residues, tyre and carpet shreds both composed of fibres trapping grains of either rubber or PVC. Compounds were made from these systems with different PU binders and the structural properties (density, porosity, air flow resistivity, tortuosity and stiffness) and performance properties (sound absorption, sound transmission, impact sound insulation and thermal conductivity) were measured as a function of binder loading and chemistry. The data obtained show clearly that performance can be tailored by tailoring structural properties resulting with materials that match or even outperform commercial products. The data set obtained here can be usefully exploited with available acoustic and thermal insulation materials model to take the approach further and extended to other waste systems.

Particulate reinforced Al alloy composites (AlMCs) are recognized as important structural materials due to their lightweight, high modulus and strength and high wear resistance. In order to understand the effect of matrix, reinforcement and secondary processing techniques on the microstructure development and mechanical properties of AlMCs produced by powder metallurgy routes, Al alloy composites reinforced with three types of reinforcements by different secondary processing techniques have been produced and examined. Fabrication of Al or 6061Al alloy based composites reinforced with nano-sized SiC particles (~500nm), micro-sized (<25µm) quasicrystalline alloy particles (hereinafter referred to as “NQX”) and micro-sized Nb particles (~130µm) has been carried out by powder metallurgy routes followed by extrusion or cold rolling. After extrusion, a homogeneous distribution of secondary particles has been obtained with rare interfacial reaction products. The 6061Al/SiC composites exhibit superior mechanical properties than either monolithic alloys or composites reinforced with micro-sized particles with retained ductility while the 6061Al/NQX and 6061Al/Nb composites show limited improvement in tensile strength mainly due to their reinforcement size and poor interfacial bonding. After cold rolling, the evolution in microstructure, texture and strength has been analysed. A typical near β fibre texture with highest intensities near Copper and Brass orientations has been developed for 6061Al/NQX and 6061Al/Nb composites. For 6061Al/SiC composites, a randomized texture with very small grains has achieved due to the presence of the non-deformable SiC particles. Mechanical property tests including microhardness, three-point bending tests and tensile tests have been carried out on cold rolled samples and the results exhibit some level of improvement when compared with as-extruded samples due to work hardening. Finally, the work moves on to the general discussion based on the previous result chapters. The microstructural development related to reinforcement, matrix and interfacial areas during extrusion and cold rolling has been summarised and the correlation between microstructure and mechanical properties has been discussed. The thesis provides a thorough understanding of AlMCs produced by powder metallurgy routes in terms of matrix, reinforcement and processing techniques. It can provide reference to the future development of AlMCs for high strength applications.

This project addressed two main problems pertaining to Al₂O₃-FeAl2O4 nanocomposites developed via solid state precipitation: the mechanisms for precipitation in ceramic solid solution via reduction reaction, and the mechanisms for the improved mechanical properties and wear resistance of the developed Al2O3-FeAl2O4 nanocomposites. A model was proposed for precipitation in ceramic solid solutions via reduction reactions (the PRCS model). The thermodynamics of reduction reactions during aging treatments under various atmospheres were calculated and discussed relative to the second phase precipitate formation. Attempts were made to measure the corresponding diffusion kinetics using a new theory developed here based on volume fraction profiles of second phase particles in the aged samples. It was found that the measured apparent oxygen vacancy diffusivities conform well to the oxygen vacancy grain boundary diffusion coefficients reported in the literature, and the measured apparent matrix diffusivity conforms well to the Fe3+ ion matrix diffusion coefficients reported in literature. Based on the thermodynamics calculations, diffusion kinetics and some essential mechanisms that were discussed, the PRCS model was proposed. This has two aspects: macroscopic and microscopic. The macroscopic aspect of PRCS model was mainly used to explain the general aspects of microstructure and the distribution of intergranualar second phase particles. The microscopic aspect of the PRCS model was mainly used to explain the precipitation of intragranualar nanoparticles. The mechanical properties, thermal residual stress and wear resistance of selected Al2O3-FeAl2O4 nanocomposites were measured. The results revealed that the Al2O3-FeAl2O4 possessed improved fracture toughness (by around 46%), flexural strength (by around 30%) and abrasive wear resistance (by a factor of around 5) with respect to monolithic alumina. Several mechanisms were proposed to explain the improvements in both mechanical properties and wear resistance. Compressive residual stress was found in the surface layer of Al2O3-FeAl2O4 nanocomposites due to the thermal expansion coefficient mismatch between surface layer and bulk parts. Such residual stress was also interpreted as the main reason for the improvements in both mechanical properties and wear resistance.