Engineering

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Now showing 1 - 3 of 3
  • (2006) Bandyopadhyay, Srikanta; Zeng, Qinghua; Berndt, Christopher C.; Rizkalla, Sami; Gowripalan, N.; Matisons, Janis
    Conference Paper
    The topics of ACUN-5 will cover all aspects of the science and technology of composite materials, from materials fabrication, processing, manufacture, structural and property characterisation, theoretical analysis, modelling and simulation, materials design to a variety of applications, such as aerospace, automotive, infrastructure, packaging, ship-building, and recreational products. ACUN-5 will bring together the latest research and developments of the complete range of composite materials, including biocomposites, medical-composites, functional and smart composites, gradient and layered composites, nanocomposites, structural composites and mimicking natural materials. The reinforcements will range from nano-, micro-, meso- to macro-scale in polymer, metal, ceramic and cementitious matrices.

  • (2022) Zhou, Jinling
    Thesis
    Over the past two decades, Bismuth ferrite (BiFeO3, BFO) thin films have attracted significant attention on account of their attractive multifunctional properties, ranging from room-temperature multiferroicity to robust high Curie temperature (Tc), large switchable spontaneous polarization (Ps) and enhanced electromechanical response, and ability to generate photovoltaic current etc. In particular, the past decade has seen huge efforts devoted to engineering the phase structure of BFO films to achieve a morphotropic phase boundary -(MPB)-like materials system with excellent ferroelectric properties and high electromechanical response. In this thesis, strain engineering and site engineering are applied to tailor the phase composition of epitaxial BFO films through a chemical solution deposition (CSD) method. The compressive epitaxial strain provided by the lattice misfit between the film and the lanthanum aluminate (LaAlO3, LAO) substrate can stabilize a tetragonal-like (T’) phase. The chemical pressure produced by the A-site substitution of smaller Sm element can induce a ferroelectric rhombohedral (R) to paraelectric orthorhombic (O) phase transition. The coexistence of these diverse polymorphs of BFO is expected to generate an MPB effect, where a maximum electromechanical property usually reports. The thesis first employs the misfit strain engineering (BFO films grown on LAO substrates) to tune the phase fraction in mixed-phase (rhombohedral-like (R’)-T’ coexistence) BFO films by altering the synthesis parameters via the CSD method. It shows that the T’-phase fraction ranging from 10% to 35% is achieved by decreasing the spin-coated layers from four to one layer. In a two-layer configuration, the T’-phase fraction is further found that can be varied from 8% to 38% by changing the precursor concentration and heating treatment parameters. The mixed-phase BFO films show a typical polydomain structure with a polarization-orientation dependent conduction behavior whereby poled-up (polarization pointing away from the lower electrode) domains have higher conductivity. An optimized film with a T’-phase fraction of ~ 28% shows the lowest leakage current of <0.1 A/cm2 up to field strengths of 500 kV/cm. Upon increasing electric field, the mixed-phase film shows an interface-limited Schottky emission to bulk-limited space-charge-limited-conduction (SCLC) mechanism predominate leakage current transition. The thesis then applies site engineering (A-site substitution with Sm) to tailor the phase structure of BFO films deposited on strontium titanate (SrTiO3, STO, the lattice parameter is similar to that of BFO) substrates. The role of the Sm on the precursor gelation chemistry is first studied. It is found that the electronegativity of the cation species in metal nitrates affects the reaction rate of the hydrolysis reaction and esterification reaction. The structural investigation of the crystalline films shows that the phase transition occurs at x = 0.10 with paraelectric O phase and antipolar phase appearance. The domain contrast of as-grown BFO/BSFO (BSFO: Bi1-xSmxFeO3) films reduces gradually with the increase of the Sm composition. More importantly, Sm introduction greatly improves the ferroelectric properties of BFO films. At an Sm ratio of 0.14, a fully developed polarization hysteresis loop is achieved. When the Sm ratio is increased to 0.15, an electric-field-induced distorted double hysteresis loop is observed. Then strain engineering and site engineering are combined to construct a complex phase configuration in BSFO films. A structural evolution from T’-R’ to T’-R’-O, and then to T’-O phases is demonstrated with the increase of the Sm ratio. The synergetic effects of misfit strain and chemical pressure drive the phase transition composition to a higher value of 0.14 compared to that of strain-free BSFO/LSMO//STO (LSMO: La0.67Sr0.33MnO3) films at 0.10. Likewise, Sm doping in the A-site leads to the decrease of the piezoresponse force microscopy (PFM) amplitude. While an enhanced domain switching behavior is attained at MPB. The ferroelectric properties show a transition from a single ferroelectric square-shaped to a slightly distorted double hysteresis loop with the Sm3+ doping content increasing from 0.14 to 0.16. The investigation of the resistive switching behavior shows an interesting transition of the current flow under the external bias from “high resistance state (HRS)-> low resistance state (LRS)->HRS->LRS” to “HRS->LRS->LRS->HRS”. This thesis provides a comprehensive understanding of the effects of epitaxial strain or/and chemical pressure on the phase composition of BFO films and their multifunctional properties. The appealing physical properties induced by the structure evolution promote the seeking of novel phase structure of perovskite oxides in thin-film form.

  • (2023) Siddika, Ayesha
    Thesis
    Over 750,000 vehicles in Australia reach the end of their lifespan yearly, leading to the disposal of 22,500 tonnes of waste glass (WG) from their windshields and windows. These materials are usually sent to landfills due to their complex structure and costly recycling process. However, this thesis proposes an alternative by utilising WG as the primary raw material for producing sustainable Low-CO2 foamed composites (FC). The FCs, particularly glass foam and alkali-activated foamed composites (AFCs) are increasingly used in insulation, water treatment, and energy sectors, replacing conventional materials that are flammable, energy-intensive, and expensive. Since glass foam manufacturing is energy-intensive and non-eco-friendly due to its involvement with different chemicals and high-temperature melting-annealing (1400℃), researchers tried to develop alternative methods such as powder sintering and gel casting. These methods enable the sintering of glass foam mixtures at lower temperatures (700-1000℃), aiming to reduce energy consumption, reduce emissions from materials and create a sustainable manufacturing process. Uniformly distributed, finely sized, and homogeneous pores play a crucial role in the properties and application of FC. However, the powder sintering method, which relies on stabilising chemicals to enhance pore characteristics, emits CO2; and faces limitations in industrial applicability due to the need for pelletisation of dry glass powder for achieving uniform particle contact. On the other hand, gel-casting is recognised as an eco-friendly method but requires a lengthy gelation process at elevated temperatures, which is energy-inefficient. Additionally, the controlling parameters that influence foaming, reactivity, and fresh properties of the mix, and their correlation with pore formation and distribution in the final FCs, are not well understood. Hence, this thesis aims to develop sustainable and eco-friendly methods to enhance the pore characteristics of glass foam and AFCs, addressing these challenges and knowledge gaps. The main objectives include comprehensive investigations into the parameters controlling activation, foaming, and fresh and final properties of glass foam and AFCs, fostering a thorough understanding and bridging existing knowledge gaps. In this thesis, a curing-sintering method is proposed to eliminate the use of a chemical stabilising agent and the associated emissions from the materials during sintering. The method involves a process wherein glass powder, fly ash additive, and calcium carbonate foaming agent were mixed with water and cured in sealed plastic wraps. After the curing process, the samples were sintered at 800℃. During curing, physical interlocking, filler effects of the particles and the alkalinity of the glass and calcium carbonate aid in forming weak bonds along the particle surfaces. These weak bonds ensure uniform contact and stability among the particles, eliminating the need for pelletisation. Moreover, this stabilisation process helps maintain pore stability during sintering and achieve homogenous pore size distribution. Additionally, it contributed to reducing the leaching of metals from the glass foam. It is noteworthy that during sintering, regardless of the energy source perspective, the decomposition of calcium carbonate resulted in CO2 emissions detected in the gas analysis test. This thesis presents a novel combined mechanical and chemical foaming technique to completely eliminate emissions from materials during foaming, reduce energy consumption during gelation, and enhance pore characteristics in glass foams. The process involves rapid alkali-activation of precursors, followed by controlled foaming and subsequent hardening. The resulting glass foams were then sintered at temperatures ranging from 700°C to 800°C. The low-speed mechanical foaming applies minimal shearing stress to the activated paste, while surfactants reduce surface tension, preventing pore coalescence. Additionally, chemical foaming using low-concentration hydrogen peroxide minimises anisotropic pore formation. As a result, the desired pore distribution was achieved without the need for lengthy gelation. The correlation between controlling parameters, reactivity in the mix, foaming, and their impact on the final properties of FC was investigated through chemical, rheological, microstructural, and mechanical characterisations at different stages of the process. The activated mix underwent percolation and partial dissolution of precursor particles. During the hardening process, inter-particle gel interactions, cross-linking of the gels, and rigidification of the network occur sequentially and concurrently with foaming caused by hydrogen peroxide decomposition. The formation and cross-linking of the gels contribute to the structural build-up of the system, ensuring pore stability in fresh FC. By promoting the early-age reactivity of the precursor mix, the pore structure in these foams can be controlled. Key parameters for controlling reactivity include water-to-binder ratio, rapid-setting binder (slag), activator, and curing conditions. Through optimised mix design and controlled parameters in the combined foaming method, sustainable AFCs can be developed at ambient conditions using a high volume of WG as the primary raw material, without requiring sintering. It is anticipated that the findings of this research will contribute to a comprehensive understanding of the control of process parameters and pore structure in glass foam and alkali-activated foamed materials using sustainable and environmentally friendly approaches. Ultimately, this study presents a commercially viable and more eco-friendly method for recycling waste glasses from vehicle windows and windshields, transforming them into low-CO2 foamed composites for use in various industries.