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Description
Membranes are a key part of pervaporation processes, which is generally a more
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.
ContributorsYin, Huidan (Author) / Lind, Mary Laura (Thesis advisor) / Mu, Bin (Committee member) / Nielsen, David (Committee member) / Seo, Don (Committee member) / Lin, Jerry (Committee member) / Arizona State University (Publisher)
Created2017
Description
The stability of nanocrystalline microstructural features allows structural materials to be synthesized and tested in ways that have heretofore been pursued only on a limited basis, especially under dynamic loading combined with temperature effects. Thus, a recently developed, stable nanocrystalline alloy is analyzed here for quasi-static (<100 s-1) and dynamic loading (103 to 104 s-1) under uniaxial compression and tension at multiple temperatures ranging from 298-1073 K. After mechanical tests, microstructures are analyzed and possible deformation mechanisms are proposed. Following this, strain and strain rate history effects on mechanical behavior are analyzed using a combination of quasi-static and dynamic strain rate Bauschinger testing. The stable nanocrystalline material is found to exhibit limited flow stress increase with increasing strain rate as compared to that of both pure, coarse grained and nanocrystalline Cu. Further, the material microstructural features, which includes Ta nano-dispersions, is seen to pin dislocation at quasi-static strain rates, but the deformation becomes dominated by twin nucleation at high strain rates. These twins are pinned from further growth past nucleation by the Ta nano-dispersions. Testing of thermal and load history effects on the mechanical behavior reveals that when thermal energy is increased beyond 200 °C, an upturn in flow stress is present at strain rates below 104 s-1. However, in this study, this simple assumption, established 50-years ago, is shown to break-down when the average grain size and microstructural length-scale is decreased and stabilized below 100nm. This divergent strain-rate behavior is attributed to a unique microstructure that alters slip-processes and their interactions with phonons; thus enabling materials response with a constant flow-stress even at extreme conditions. Hence, the present study provides a pathway for designing and synthesizing a new-level of tough and high-energy absorbing materials.
ContributorsTurnage, Scott Andrew (Author) / Solanki, Kiran N (Thesis advisor) / Rajagopalan, Jagannathan (Committee member) / Peralta, Pedro (Committee member) / Darling, Kristopher A (Committee member) / Mignolet, Marc (Committee member) / Arizona State University (Publisher)
Created2017
Description
Hg1-xCdxTe (MCT) has historically been the primary material used for infrared detectors. Recently, alternative substrates for MCT growth such as Si, as well as alternative infrared materials such as Hg1-xCdxSe, have been explored. This dissertation involves characterization of Hg-based infrared materials for third generation infrared detectors using a wide range of transmission electron microscopy (TEM) techniques.
A microstructural study on HgCdTe/CdTe heterostructures grown by MBE on Si (211) substrates showed a thin ZnTe layer grown between CdTe and Si to mediate the large lattice mismatch of 19.5%. Observations showed large dislocation densities at the CdTe/ZnTe/Si (211) interfaces, which dropped off rapidly away from the interface. Growth of a thin HgTe buffer layer between HgCdTe and CdTe layers seemed to improve the HgCdTe layer quality by blocking some defects.
A second study investigated the correlation of etch pits and dislocations in as-grown and thermal-cycle-annealed (TCA) HgCdTe (211) films. For as-grown samples, pits with triangular and fish-eye shapes were associated with Frank partial and perfect dislocations, respectively. Skew pits were determined to have a more complex nature. TCA reduced the etch-pit density by 72%. Although TCA processing eliminated the fish-eye pits, dislocations reappeared in shorter segments in the TCA samples. Large pits were observed in both as-grown and TCA samples, but the nature of any defects associated with these pits in the as-grown samples is unclear.
Microstructural studies of HgCdSe revealed large dislocation density at ZnTe/Si(211) interfaces, which dropped off markedly with ZnTe thickness. Atomic-resolution STEM images showed that the large lattice mismatch at the ZnTe/Si interface was accommodated through {111}-type stacking faults. A detailed analysis showed that the stacking faults were inclined at angles of 19.5 and 90 degrees at both ZnTe/Si and HgCdSe/ZnTe interfaces. These stacking faults were associated with Shockley and Frank partial dislocations, respectively. Initial attempts to delineate individual dislocations by chemical etching revealed that while the etchants successfully attacked defective areas, many defects in close proximity to the pits were unaffected.
A microstructural study on HgCdTe/CdTe heterostructures grown by MBE on Si (211) substrates showed a thin ZnTe layer grown between CdTe and Si to mediate the large lattice mismatch of 19.5%. Observations showed large dislocation densities at the CdTe/ZnTe/Si (211) interfaces, which dropped off rapidly away from the interface. Growth of a thin HgTe buffer layer between HgCdTe and CdTe layers seemed to improve the HgCdTe layer quality by blocking some defects.
A second study investigated the correlation of etch pits and dislocations in as-grown and thermal-cycle-annealed (TCA) HgCdTe (211) films. For as-grown samples, pits with triangular and fish-eye shapes were associated with Frank partial and perfect dislocations, respectively. Skew pits were determined to have a more complex nature. TCA reduced the etch-pit density by 72%. Although TCA processing eliminated the fish-eye pits, dislocations reappeared in shorter segments in the TCA samples. Large pits were observed in both as-grown and TCA samples, but the nature of any defects associated with these pits in the as-grown samples is unclear.
Microstructural studies of HgCdSe revealed large dislocation density at ZnTe/Si(211) interfaces, which dropped off markedly with ZnTe thickness. Atomic-resolution STEM images showed that the large lattice mismatch at the ZnTe/Si interface was accommodated through {111}-type stacking faults. A detailed analysis showed that the stacking faults were inclined at angles of 19.5 and 90 degrees at both ZnTe/Si and HgCdSe/ZnTe interfaces. These stacking faults were associated with Shockley and Frank partial dislocations, respectively. Initial attempts to delineate individual dislocations by chemical etching revealed that while the etchants successfully attacked defective areas, many defects in close proximity to the pits were unaffected.
ContributorsVaghayenegar, Majid (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Committee member) / Crozier, Peter A. (Committee member) / Bertoni, Mariana I. (Committee member) / Arizona State University (Publisher)
Created2017
Description
Facilities Management (FM) around the globe at different companies in different industries are often forced to make difficult decisions on whether or not to transition a workplace environment and how to decide what factors of a workplace environment can benefit or hinder a company's productivity. The data and research presented within this paper are targeted at aiding and educating FM in determining what factors to consider in a workplace transition to an open-seating design and validate the importance of recognizing how these factors impact the productivity of the individual and the organization. Data contained in this paper was gathered through two different survey samples: 1) a semiconductor company that transitioned its employees from cubicles and offices to an open-seating environment; and 2) a general study open to professionals and their experiences and opinions on workplace environments. This data was used to validate or disprove the views on open-seating workspace held by the FM industry today. Data on the topic of how employees react to being transitioned to open-seating environments and looking at the breakdown of the results between engineers and non-engineers is examined within this research. Also covered within the research is data on transitions to other seating environments outside of open-seating concepts to evaluate and compare transition types. Lastly, data was gathered and discussed on the amount of time needed to adapt after a transition and what environment types were linked to being the most productive. This research provides insight on workplace environments and transitions and how they have an impact on productivity and can be used in the decision process when considering transitioning environments.
ContributorsThalin, William (Author) / Sullivan, Kenneth (Thesis advisor) / Smithwick, Jake (Committee member) / Stone, Brian (Committee member) / Arizona State University (Publisher)
Created2017
Description
This research explores some of the issues, challenges and dilemmas of existing research found in the construction workforce, it starts with past research that can be found on the current problems in the industry and how it has developed. It covers the distinguishing factors that influence a construction company's success and how it has affected depending on the characteristics of the company. It was to examine the effectiveness of the recruitment and selection practices of entrants in the construction industry workforce and pathways to improve those practices.
ContributorsHatfield, Whitney (Author) / Ariaratnam, Samuel (Thesis advisor) / Chasey, Allan (Committee member) / Bearup, Wylie (Committee member) / Arizona State University (Publisher)
Created2017
Description
Fully distributed wireless sensor networks (WSNs) without fusion center have advantages such as scalability in network size and energy efficiency in communications. Each sensor shares its data only with neighbors and then achieves global consensus quantities by in-network processing. This dissertation considers robust distributed parameter estimation methods, seeking global consensus on parameters of adaptive learning algorithms and statistical quantities.
Diffusion adaptation strategy with nonlinear transmission is proposed. The nonlinearity was motivated by the necessity for bounded transmit power, as sensors need to iteratively communicate each other energy-efficiently. Despite the nonlinearity, it is shown that the algorithm performs close to the linear case with the added advantage of power savings. This dissertation also discusses convergence properties of the algorithm in the mean and the mean-square sense.
Often, average is used to measure central tendency of sensed data over a network. When there are outliers in the data, however, average can be highly biased. Alternative choices of robust metrics against outliers are median, mode, and trimmed mean. Quantiles generalize the median, and they also can be used for trimmed mean. Consensus-based distributed quantile estimation algorithm is proposed and applied for finding trimmed-mean, median, maximum or minimum values, and identification of outliers through simulation. It is shown that the estimated quantities are asymptotically unbiased and converges toward the sample quantile in the mean-square sense. Step-size sequences with proper decay rates are also discussed for convergence analysis.
Another measure of central tendency is a mode which represents the most probable value and also be robust to outliers and other contaminations in data. The proposed distributed mode estimation algorithm achieves a global mode by recursively shifting conditional mean of the measurement data until it converges to stationary points of estimated density function. It is also possible to estimate the mode by utilizing grid vector as well as kernel density estimator. The densities are estimated at each grid point, while the points are updated until they converge to a global mode.
Diffusion adaptation strategy with nonlinear transmission is proposed. The nonlinearity was motivated by the necessity for bounded transmit power, as sensors need to iteratively communicate each other energy-efficiently. Despite the nonlinearity, it is shown that the algorithm performs close to the linear case with the added advantage of power savings. This dissertation also discusses convergence properties of the algorithm in the mean and the mean-square sense.
Often, average is used to measure central tendency of sensed data over a network. When there are outliers in the data, however, average can be highly biased. Alternative choices of robust metrics against outliers are median, mode, and trimmed mean. Quantiles generalize the median, and they also can be used for trimmed mean. Consensus-based distributed quantile estimation algorithm is proposed and applied for finding trimmed-mean, median, maximum or minimum values, and identification of outliers through simulation. It is shown that the estimated quantities are asymptotically unbiased and converges toward the sample quantile in the mean-square sense. Step-size sequences with proper decay rates are also discussed for convergence analysis.
Another measure of central tendency is a mode which represents the most probable value and also be robust to outliers and other contaminations in data. The proposed distributed mode estimation algorithm achieves a global mode by recursively shifting conditional mean of the measurement data until it converges to stationary points of estimated density function. It is also possible to estimate the mode by utilizing grid vector as well as kernel density estimator. The densities are estimated at each grid point, while the points are updated until they converge to a global mode.
ContributorsLee, Jongmin (Electrical engineer) (Author) / Tepedelenlioğlu, Cihan (Thesis advisor) / Spanias, Andreas (Thesis advisor) / Tsakalis, Konstantinos (Committee member) / Reisslein, Martin (Committee member) / Arizona State University (Publisher)
Created2017
Description
This dissertation treats a number of related problems in control and data analysis of complex networks.
First, in existing linear controllability frameworks, the ability to steer a network from any initiate state toward any desired state is measured by the minimum number of driver nodes. However, the associated optimal control energy can become unbearably large, preventing actual control from being realized. Here I develop a physical controllability framework and propose strategies to turn physically uncontrollable networks into physically controllable ones. I also discover that although full control can be guaranteed by the prevailing structural controllability theory, it is necessary to balance the number of driver nodes and control energy to achieve actual control, and my work provides a framework to address this issue.
Second, in spite of recent progresses in linear controllability, controlling nonlinear dynamical networks remains an outstanding problem. Here I develop an experimentally feasible control framework for nonlinear dynamical networks that exhibit multistability. The control objective is to apply parameter perturbation to drive the system from one attractor to another. I introduce the concept of attractor network and formulate a quantifiable framework: a network is more controllable if the attractor network is more strongly connected. I test the control framework using examples from various models and demonstrate the beneficial role of noise in facilitating control.
Third, I analyze large data sets from a diverse online social networking (OSN) systems and find that the growth dynamics of meme popularity exhibit characteristically different behaviors: linear, “S”-shape and exponential growths. Inspired by cell population growth model in microbial ecology, I construct a base growth model for meme popularity in OSNs. Then I incorporate human interest dynamics into the base model and propose a hybrid model which contains a small number of free parameters. The model successfully predicts the various distinct meme growth dynamics.
At last, I propose a nonlinear dynamics model to characterize the controlling of WNT signaling pathway in the differentiation of neural progenitor cells. The model is able to predict experiment results and shed light on the understanding of WNT regulation mechanisms.
First, in existing linear controllability frameworks, the ability to steer a network from any initiate state toward any desired state is measured by the minimum number of driver nodes. However, the associated optimal control energy can become unbearably large, preventing actual control from being realized. Here I develop a physical controllability framework and propose strategies to turn physically uncontrollable networks into physically controllable ones. I also discover that although full control can be guaranteed by the prevailing structural controllability theory, it is necessary to balance the number of driver nodes and control energy to achieve actual control, and my work provides a framework to address this issue.
Second, in spite of recent progresses in linear controllability, controlling nonlinear dynamical networks remains an outstanding problem. Here I develop an experimentally feasible control framework for nonlinear dynamical networks that exhibit multistability. The control objective is to apply parameter perturbation to drive the system from one attractor to another. I introduce the concept of attractor network and formulate a quantifiable framework: a network is more controllable if the attractor network is more strongly connected. I test the control framework using examples from various models and demonstrate the beneficial role of noise in facilitating control.
Third, I analyze large data sets from a diverse online social networking (OSN) systems and find that the growth dynamics of meme popularity exhibit characteristically different behaviors: linear, “S”-shape and exponential growths. Inspired by cell population growth model in microbial ecology, I construct a base growth model for meme popularity in OSNs. Then I incorporate human interest dynamics into the base model and propose a hybrid model which contains a small number of free parameters. The model successfully predicts the various distinct meme growth dynamics.
At last, I propose a nonlinear dynamics model to characterize the controlling of WNT signaling pathway in the differentiation of neural progenitor cells. The model is able to predict experiment results and shed light on the understanding of WNT regulation mechanisms.
ContributorsWang, Lezhi (Author) / Lai, Ying-Cheng (Thesis advisor) / Wang, Xiao (Thesis advisor) / Papandreoou-Suppappola, Antonia (Committee member) / Brafman, David (Committee member) / Arizona State University (Publisher)
Created2017
Description
Total dose sensing systems (or radiation detection systems) have many applications,
ranging from survey monitors used to supervise the generated radioactive waste at
nuclear power plants to personal dosimeters which measure the radiation dose
accumulated in individuals. This dissertation work will present two different types of
novel devices developed at Arizona State University for total dose sensing applications.
The first detector technology is a mechanically flexible metal-chalcogenide glass (ChG)
based system which is fabricated on low cost substrates and are intended as disposable
total dose sensors. Compared to existing commercial technologies, these thin film
radiation sensors are simpler in form and function, and cheaper to produce and operate.
The sensors measure dose through resistance change and are suitable for applications
such as reactor dosimetry, radiation chemistry, and clinical dosimetry. They are ideal for
wearable devices due to the lightweight construction, inherent robustness to resist
breaking when mechanically stressed, and ability to attach to non-flat objects. Moreover,
their performance can be easily controlled by tuning design variables and changing
incorporated materials. The second detector technology is a wireless dosimeter intended
for remote total dose sensing. They are based on a capacitively loaded folded patch
antenna resonating in the range of 3 GHz to 8 GHz for which the load capacitance varies
as a function of total dose. The dosimeter does not need power to operate thus enabling
its use and implementation in the field without requiring a battery for its read-out. As a
result, the dosimeter is suitable for applications such as unattended detection systems
destined for covert monitoring of merchandise crossing borders, where nuclear material
tracking is a concern. The sensitive element can be any device exhibiting a known
variation of capacitance with total ionizing dose. The sensitivity of the dosimeter is
related to the capacitance variation of the radiation sensitive device as well as the high
frequency system used for reading. Both technologies come with the advantage that they
are easy to manufacture with reasonably low cost and sensing can be readily read-out.
ranging from survey monitors used to supervise the generated radioactive waste at
nuclear power plants to personal dosimeters which measure the radiation dose
accumulated in individuals. This dissertation work will present two different types of
novel devices developed at Arizona State University for total dose sensing applications.
The first detector technology is a mechanically flexible metal-chalcogenide glass (ChG)
based system which is fabricated on low cost substrates and are intended as disposable
total dose sensors. Compared to existing commercial technologies, these thin film
radiation sensors are simpler in form and function, and cheaper to produce and operate.
The sensors measure dose through resistance change and are suitable for applications
such as reactor dosimetry, radiation chemistry, and clinical dosimetry. They are ideal for
wearable devices due to the lightweight construction, inherent robustness to resist
breaking when mechanically stressed, and ability to attach to non-flat objects. Moreover,
their performance can be easily controlled by tuning design variables and changing
incorporated materials. The second detector technology is a wireless dosimeter intended
for remote total dose sensing. They are based on a capacitively loaded folded patch
antenna resonating in the range of 3 GHz to 8 GHz for which the load capacitance varies
as a function of total dose. The dosimeter does not need power to operate thus enabling
its use and implementation in the field without requiring a battery for its read-out. As a
result, the dosimeter is suitable for applications such as unattended detection systems
destined for covert monitoring of merchandise crossing borders, where nuclear material
tracking is a concern. The sensitive element can be any device exhibiting a known
variation of capacitance with total ionizing dose. The sensitivity of the dosimeter is
related to the capacitance variation of the radiation sensitive device as well as the high
frequency system used for reading. Both technologies come with the advantage that they
are easy to manufacture with reasonably low cost and sensing can be readily read-out.
ContributorsMahmud, Adnan, Ph.D (Author) / Barnaby, Hugh J. (Thesis advisor) / Kozicki, Michael N (Committee member) / Gonzalez-Velo, Yago (Committee member) / Goryll, Michael (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2017
Description
Alloying in semiconductors has enabled many civilian technologies in optoelectronic, photonic fields and more. While the phenomenon of alloying is well established in traditional bulk semiconductors, owing to vastly available ternary phase diagrams, the ability to alloy in 2D systems are less clear. Recently anisotropic materials such as ReS2 and TiS3 have been extensively studied due to their direct-gap semiconductor and high mobility behaviors. This work is a report on alloys of ReS2 & ReSe2 and TiS3 &TiSe3.
Alloying selenium into ReS2 in the creation of ReS2xSe2-x, tunes the band gap and changes its vibrational spectrum. Depositing this alloy using bottom up approach has resulted in the loss of crystallinity. This loss of crystallinity was evidenced by grain boundaries and point defect shown by TEM images.
Also, in the creation of TiS3xSe3-x, by alloying Se into TiS3, a fixed ratio of 8% selenium deposit into TiS3 host matrix is observed. This is despite the vastly differing precursor amounts and growth temperatures, as evinced by detailed TEM, EDAX, TEM diffraction, and Raman spectroscopy measurements. This unusual behavior contrasts with other well-known layered material systems such as MoSSe, WMoS2 where continuous alloying can be attained. Cluster expansion theory calculations suggest that only limited composition (x) can be achieved. Considering the fact that TiSe3 vdW crystals have not been synthesized in the past, these alloying rejections can be attributed to energetic instability in the ternary phase diagrams estimated by calculations performed. Overall findings highlight potential means and challenges in achieving stable alloying in promising direct gap and high carrier mobility TiS3 materials.
Alloying selenium into ReS2 in the creation of ReS2xSe2-x, tunes the band gap and changes its vibrational spectrum. Depositing this alloy using bottom up approach has resulted in the loss of crystallinity. This loss of crystallinity was evidenced by grain boundaries and point defect shown by TEM images.
Also, in the creation of TiS3xSe3-x, by alloying Se into TiS3, a fixed ratio of 8% selenium deposit into TiS3 host matrix is observed. This is despite the vastly differing precursor amounts and growth temperatures, as evinced by detailed TEM, EDAX, TEM diffraction, and Raman spectroscopy measurements. This unusual behavior contrasts with other well-known layered material systems such as MoSSe, WMoS2 where continuous alloying can be attained. Cluster expansion theory calculations suggest that only limited composition (x) can be achieved. Considering the fact that TiSe3 vdW crystals have not been synthesized in the past, these alloying rejections can be attributed to energetic instability in the ternary phase diagrams estimated by calculations performed. Overall findings highlight potential means and challenges in achieving stable alloying in promising direct gap and high carrier mobility TiS3 materials.
ContributorsAgarwal, Ashutosh (Author) / Tongay, Sefaattin (Thesis advisor) / Green, Matthew (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2018
Description
Asphalt concrete is the most recycled material in the United States and its reclamation allows the positive reuse of the constituent aggregates and asphalt binder, contributing to the long-term sustainability of the transportation infrastructure; decreasing costs, and the total energy and greenhouse emissions embodied into new materials and infrastructure. Although the national trends in Reclaimed Asphalt Pavements (RAP) usage are encouraging, the environmental conditions in Phoenix, Arizona are extreme and needs further consideration.
The objective of this research study was to evaluate the viability of using RAP in future pavement maintenance and rehabilitation projects for the City. Agencies in the State of Arizona have been slow adopting the use of RAP as a regular practice. While the potential benefits are great, there is some concern on the impact to long-term pavement performance.
RAP millings were sampled from the city’s stockpiles; processed RAP and virgin materials were provided by a local plant. Two asphalt binders were used: PG 70-10 and PG 64-16. RAP variability was evaluated by aggregate gradations; extracted and recovered binder was tested for properties and grading.
A mixture design procedure based on the City’s specifications was defined to establish trial blends. RAP incorporation was based on national and local practices. Four different RAP contents were studied 10%, 15%, 25%, and 25% content with a softer binder, in addition to a control mix (0% RAP).
Performance tests included: dynamic modulus to evaluate stiffness; Flow Number, to assess susceptibility for permanent deformation (rutting); and Tensile Strength Ratio as a measure of susceptibility to moisture damage.
Binder testing showed very stiff recovered asphalts and variable contents with a reasonable variability on aggregate gradations. Performance test results showed slightly higher modulus as RAP content increases, showing a slight improvement related to rutting as well. For moisture damage potential, all mixtures performed well showing improvement for RAP mixtures in most cases.
Statistical analysis showed that 0%, 10%, 15% and 25% with softer binder do not present significant statistical difference among mixtures, indicating that moderate RAP contents are feasible to use within the City paving operations and will not affect greatly nor negatively the pavement performance.
ContributorsARREDONDO, GONZALO ZELADA (Author) / Kaloush, Kamil (Thesis advisor) / Mamlouk, Michael (Committee member) / Stempihar, Jeffrey (Committee member) / Arizona State University (Publisher)
Created2018