Thermodynamic analysis and sustainability improvement of nanoparticles synthesis processes with application to titanium dioxide
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Increasing world population, dwindling resources, and the degradation of natural ecosystems make thermodynamics and sustainability improvement of manufacturing processes a prominent goal for the engineering community for the foreseeable future. Although nanomanufacturing is expected to generate major economic impacts estimated in the billions of dollars, little is known about the energy consumption, potential environmental health and safety risks associated with public exposure of nanoparticles synthesis processes. The overarching objective of this research is to present a complete thermodynamic (including energy consumption and exergy losses) analysis and sustainability improvement for the nanoparticles synthesis processes. Firstly, the introductions of sustainable manufacturing, industrial ecology, energy consumption and nanotechnology are introduced briefly in Chapter 1. Then problem statement, research objective and contribution are clearly stated. Secondly, the literature review on data collection (top-down and bottom-up), thermodynamic model, mechanical model, finite element analysis and manufacturing processes are summarized in Chapter 2. Thirdly, the energy consumption and exergy losses general model for nanoparticles synthesis processes (divided into two main processes: precursor transport and chemical reaction) based on thermodynamics and kinetics is created in Chapter 3, which includes all the assumptions, boundaries, conditions and equations of model. Both first law and second law of thermodynamics were used for energy consumption and exergy losses of nanoparticles synthesis processes which are considered as steady state, steady flow open system. A simplified exergy model was also created for nanoparticles synthesis process. A two dimensional kinetic differential equations describing the conservation of mass, momentum and energy with appropriate boundary conditions was modeled for precursor transport process (convection and diffusion). The NPs chemical reaction process was modeled by thermodynamic model. Fourthly, the created model was applied to titanium dioxide nanoparticles (TiO2 NPs) synthesis processes. Background, crystal structure and route of TiO2 NPs are introduced in first section. Then the experimental setup, calculation and analysis for electrochemical annodization process (including five main processes: formation of oxide layer, chemical diffusion, physical diffusion, infiltration and crystallization) of TiO2 NPs are placed in detail. Based on results from experimental data and discussions, the energy consumption and exergy losses for the specific electrochemical annodization process are clearly demonstrated and the identification of sustainability improvement potential is also given. The thermodynamic model about size dependence of nanoparticles on electrical voltage is also discussed and validated by both experimental data and literature data. Fifthly, conclusion is given that the created model is validated by the electrochemical annodization process of TiO2 NPs and can also be applied to other nanoparticles synthesis processes, which is really essential and fundamental for sustainability development and life cycle assessment of manufacturing process. Future work is indicated in the end.