Matching Items (3)
Description
In material science, microstructure plays a key role in determining properties, which further determine utility of the material. However, effectively measuring microstructure evolution in real time remains an challenge. To date, a wide range of advanced experimental techniques have been developed and applied to characterize material microstructure and structural evolution on different length and time scales. Most of these methods can only resolve 2D structural features within a narrow range of length scale and for a single or a series of snapshots. The currently available 3D microstructure characterization techniques are usually destructive and require slicing and polishing the samples each time a picture is taken. Simulation methods, on the other hand, are cheap, sample-free and versatile without the special necessity of taking care of the physical limitations, such as extreme temperature or pressure, which are prominent
issues for experimental methods. Yet the majority of simulation methods are limited to specific circumstances, for example, first principle computation can only handle several thousands of atoms, molecular dynamics can only efficiently simulate a few seconds of evolution of a system with several millions particles, and finite element method can only be used in continuous medium, etc. Such limitations make these individual methods far from satisfaction to simulate macroscopic processes that a material sample undergoes up to experimental level accuracy. Therefore, it is highly desirable to develop a framework that integrate different simulation schemes from various scales
to model complicated microstructure evolution and corresponding properties. Guided by such an objective, we have made our efforts towards incorporating a collection of simulation methods, including finite element method (FEM), cellular automata (CA), kinetic Monte Carlo (kMC), stochastic reconstruction method, Discrete Element Method (DEM), etc, to generate an integrated computational material engineering platform (ICMEP), which could enable us to effectively model microstructure evolution and use the simulated microstructure to do subsequent performance analysis. In this thesis, we will introduce some cases of building coupled modeling schemes and present
the preliminary results in solid-state sintering. For example, we use coupled DEM and kinetic Monte Carlo method to simulate solid state sintering, and use coupled FEM and cellular automata method to model microstrucutre evolution during selective laser sintering of titanium alloy. Current results indicate that joining models from different length and time scales is fruitful in terms of understanding and describing microstructure evolution of a macroscopic physical process from various perspectives.
issues for experimental methods. Yet the majority of simulation methods are limited to specific circumstances, for example, first principle computation can only handle several thousands of atoms, molecular dynamics can only efficiently simulate a few seconds of evolution of a system with several millions particles, and finite element method can only be used in continuous medium, etc. Such limitations make these individual methods far from satisfaction to simulate macroscopic processes that a material sample undergoes up to experimental level accuracy. Therefore, it is highly desirable to develop a framework that integrate different simulation schemes from various scales
to model complicated microstructure evolution and corresponding properties. Guided by such an objective, we have made our efforts towards incorporating a collection of simulation methods, including finite element method (FEM), cellular automata (CA), kinetic Monte Carlo (kMC), stochastic reconstruction method, Discrete Element Method (DEM), etc, to generate an integrated computational material engineering platform (ICMEP), which could enable us to effectively model microstructure evolution and use the simulated microstructure to do subsequent performance analysis. In this thesis, we will introduce some cases of building coupled modeling schemes and present
the preliminary results in solid-state sintering. For example, we use coupled DEM and kinetic Monte Carlo method to simulate solid state sintering, and use coupled FEM and cellular automata method to model microstrucutre evolution during selective laser sintering of titanium alloy. Current results indicate that joining models from different length and time scales is fruitful in terms of understanding and describing microstructure evolution of a macroscopic physical process from various perspectives.
ContributorsChen, Shaohua (Author) / Jiao, Yang (Thesis advisor) / Wang, Qinghua (Committee member) / Emady, Heather (Committee member) / Gel, Aytekin (Committee member) / Arizona State University (Publisher)
Created2018
Description
As selenium and chromium are toxic even at low levels, it is very necessary to remove them from drinking water with proper ways. In this work, titanium dioxide based photocatalysts were mainly investigated in detail for their photoreduction ability towards selenate and chromate in aqueous environment. Firstly, photoreduction ability of layered double hydroxide (LDH) nanosheets with commercial TiO2 particle hybrid materials was investigated towards selenate or chromate. The results showed that commercial LDH/TiO2 (P90) composite, homemade LDH nanosheets/TiO2 (P90) composite and also in situ LDH/TiO2 (P25) composite all did not indicate significant improvement on photoreduction performance towards selenate or chromate. Secondly, TiO2 nanosheets material was synthesized with TiS2 as precursor via hydrothermal treatment. Morphology of TiO2 nanosheets were characterized by SEM, AFM and TEM. Photodegradation of MB (methylene blue) with TiO2 nanosheets was performed. In the future, first approach is to synthesize visible-light driven LDH photocatalyst NiFe-LDH nanosheets with TiO2 nanosheets hybrid material for selenate removal. Second approach is to use anion intercalation/insertion via electrochemical process to remove anions in drinking water.
ContributorsJing, Hangkun (Author) / Chan, Candace K. (Thesis advisor) / Sieradzki, Karl (Committee member) / Wang, Qinghua (Committee member) / Arizona State University (Publisher)
Created2018
Description
This dissertation describes the synthesis and study of porous nanocarbon and further treatment by introducing nitrogen and oxygen groups on nanocarbon, which can be used as electrodes for energy storage (supercapacitor). Electron microscopy is used to make nanoscale characterization. ZnO nanowires are used as the template of the porous nanocarbon, and nitrogen doping and oxidation treatment can help further increase the capacitive performance of the nanocarbon.
The first part of this thesis focuses on the synthesis of ZnO nanowires. Uniform ZnO nanowires with ~30 nm in width are produced at 1100℃ in a tube furnace with flowing gases (N2: 500 sccm; O2: 15 sccm). The temperature control is one of the most important parameters for making thin and ultra-long ZnO nanowires.
The second part of the thesis is about the synthesis of nanocarbons. Ultrapure ethanol is used as the carbon source to make carbonaceous deposition on ZnO nanowires. The thickness of the nanocarbons can be controlled by reaction temperature and reaction time. When the reaction time was controlled around 1h, the carbonaceous materials coating the ZnO nanowires become very thin. Then by flowing (1000 sccm) hydrogen at 750℃ through the reaction tube the ZnO nanowires are removed due to reduction and evaporation. Electrochemical evaluation of the produced nanocarbons shows that the nanocarbons possess very high specific surface area (>1400 m2/g) and a capacitance as high as 180 F/g at 10A/g in 6M KOH).
The third part of the thesis is the treatment of the as-synthesized nanocarbons to further increase capacitance. NH3 was used as the nitrogen source to react with nanocarbons at 700℃ to incorporate nitrogen group. Nitric acid (HNO3) is used as the oxidant to introduce oxygen groups. After proper nitrogen doping, the nitrogen doped nanocarbons can show high specific capacitance of 260 F/g at 1A/g in 6M KOH. After further oxidation treatment, the capacitance of the oxidized N-doped nanocarbons increased to 320 F/g at 1A/g in 6M KOH.
The first part of this thesis focuses on the synthesis of ZnO nanowires. Uniform ZnO nanowires with ~30 nm in width are produced at 1100℃ in a tube furnace with flowing gases (N2: 500 sccm; O2: 15 sccm). The temperature control is one of the most important parameters for making thin and ultra-long ZnO nanowires.
The second part of the thesis is about the synthesis of nanocarbons. Ultrapure ethanol is used as the carbon source to make carbonaceous deposition on ZnO nanowires. The thickness of the nanocarbons can be controlled by reaction temperature and reaction time. When the reaction time was controlled around 1h, the carbonaceous materials coating the ZnO nanowires become very thin. Then by flowing (1000 sccm) hydrogen at 750℃ through the reaction tube the ZnO nanowires are removed due to reduction and evaporation. Electrochemical evaluation of the produced nanocarbons shows that the nanocarbons possess very high specific surface area (>1400 m2/g) and a capacitance as high as 180 F/g at 10A/g in 6M KOH).
The third part of the thesis is the treatment of the as-synthesized nanocarbons to further increase capacitance. NH3 was used as the nitrogen source to react with nanocarbons at 700℃ to incorporate nitrogen group. Nitric acid (HNO3) is used as the oxidant to introduce oxygen groups. After proper nitrogen doping, the nitrogen doped nanocarbons can show high specific capacitance of 260 F/g at 1A/g in 6M KOH. After further oxidation treatment, the capacitance of the oxidized N-doped nanocarbons increased to 320 F/g at 1A/g in 6M KOH.
ContributorsZhang, Yizhi (Author) / Liu, Jingyue (Thesis advisor) / Wang, Qinghua (Committee member) / Deng, Shuguang (Committee member) / Arizona State University (Publisher)
Created2020