Matching Items (19)
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- All Subjects: chemical engineering
- All Subjects: Materials Science
- Genre: Masters Thesis
- Creators: Emady, Heather
Description
Topological insulators with conducting surface states yet insulating bulk states have generated a lot of interest amongst the physics community due to their varied characteristics and possible applications. Doped topological insulators have presented newer physical states of matter where topological order co&ndashexists; with other physical properties (like magnetic order). The electronic states of these materials are very intriguing and pose problems and the possible solutions to understanding their unique behaviors. In this work, we use Electron Energy Loss Spectroscopy (EELS) – an analytical TEM tool to study both core&ndashlevel; and valence&ndashlevel; excitations in Bi2Se3 and Cu(doped)Bi2Se3 topological insulators. We use this technique to retrieve information on the valence, bonding nature, co-ordination and lattice site occupancy of the undoped and the doped systems. Using the reference materials Cu(I)Se and Cu(II)Se we try to compare and understand the nature of doping that copper assumes in the lattice. And lastly we utilize the state of the art monochromated Nion UltraSTEM 100 to study electronic/vibrational excitations at a record energy resolution from sub-nm regions in the sample.
ContributorsSubramanian, Ganesh (Author) / Spence, John (Thesis advisor) / Jiang, Nan (Committee member) / Chen, Tingyong (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2013
Description
Lithium-ion and lithium-metal batteries represent a predominant energy storage solution with the potential to address the impending global energy crisis arising from limited non-renewable resources. However, these batteries face significant safety challenges that hinder their commercialization. The conventional polymeric separators and electrolytes have poor thermal stability and fireproof properties making them prone to thermal runaway that causes fire hazards and explosions when the battery is subjected to extreme operating conditions. To address this issue, various materials have been investigated for their use as separators. However, polymeric, and pure inorganic material-based separators have a trade-off between safety and electrochemical performance. This is where zeolites emerge as a promising solution, offering favorable thermal and electrochemical characteristics. The zeolites are coated onto the cathode as a separator using the scalable blade coating method. These separators are non-flammable with high thermal stability and electrolyte wettability. Furthermore, the presence of intracrystalline pores helps in homogenizing the Li-ion flux at anode resulting in improved electrochemical performance. This research delves into the preparation of zeolite separators using a commercial zeolite and lab-scale zeolite to study their safety and electrochemical performance in lithium-ion batteries. At low C-rates, both zeolites exhibited excellent capacity retention and capacity density displaying their potential to advance high-performance safe lithium-ion batteries. The commercial zeolite has demonstrated remarkable capacity retention and good performance in terms of charge and discharge cycles, as well as stability. This makes it a valuable resource for the scaling up of electrode-coated separator technology.
Furthermore, the previous study demonstrated the superior electrochemical performance of plate silicalite separator (also a lab-made zeolite) with both lithium-ion and lithium-metal batteries. However, the process of scaling up and achieving precise control over plate silicalite particle size, and morphology using the existing synthesis procedure has proven challenging. Thus, the modification of process conditions is studied to enhance control over particle size, aspect ratio, and yield to facilitate a more efficient scaling-up process. Incorporation of stirring during the crystallization phase enhanced yield and uniformity of particle size. Also, the increase in temperature and time of crystallization enlarged the particles but did not show any significant improvement in the aspect ratio of the particles.
ContributorsNalam, Ramasai Dharani Harika (Author) / Lin, Jerry (Thesis advisor) / Emady, Heather (Committee member) / Seo, S. Eileen (Committee member) / Arizona State University (Publisher)
Created2023
Description
Electrospun fibrous membranes have gained increasing interest in membrane filtration applications due to their high surface area and porosity. To develop a high-performance water filtration membrane a novel zwitterionic functionalized zwitterionic Polysulfone was Electrospun to bead free fibers on Polysulfone membranes. The SBAES25 was successfully Electrospun on Polysulfone membrane and thermal pressed at above Tg to improve the properties of membrane. The aim of this work is to study Electrospun zwitterionic Polysulfone nanofiber membrane with different characterization methods. The electrospinning method was studied using different polymer concentrations and electrospinning conditions. Scanning Electron Microscopy was used to study the porosity and diameter size of the fiber. TGA-ASSAY method was used to study the difference in water uptake ratio of Polysulfone membrane with and without the Electrospun fiber. A goniometer was used to test the water contact angle of the membrane. Tensile tests were performed to study the improvements in mechanical properties.
ContributorsErravelly, Nitheesh Kumar (Author) / Green, Matthew (Thesis advisor) / Emady, Heather (Committee member) / Seo, Eileen S (Committee member) / Arizona State University (Publisher)
Created2023
Description
Lithium nickel manganese cobalt oxides (NMCs) are layered oxide cathode materials which are becoming increasingly popular as the demand for lithium-ion batteries increases. Lithium-ion batteries are used to power modern vehicles and for other battery applications. To better understand the structure and energetics of NMCs, various molar ratios of these compounds were synthesized via a sol-gel method and characterized with powder X-ray diffraction profile fitting. Lattice constants for the nickel, manganese, and cobalt solid solutions were determined. High temperature oxide melt solution calorimetry was used to determine the enthalpies of formation and mixing. All but Li2MnO3 had the same space group as LiCoO2 (R-3m). The lattice constants approximately followed a linear fit with cobalt mole fraction (R2average= 0.973) for the cobalt series. As the molar ratio of cobalt increased the lattice constants decreased. The nickel series was less linear (R2average=0.733) and had an opposite lattice constant trend to cobalt. The manganese series possessed a roughly linear trend when excluding the outlier Li2MnO3 (R2average=0.282). The formation enthalpy of the cobalt series becomes more negative as more cobalt is added. A second order polynomial fit could be used to model the enthalpies of mixing for the series. NMC2.5,2.5,5 exhibited the most stable energetics. A third order polynomial fit could be used to model the enthalpy of mixing for the nickel and manganese series with NMC811 and NMC181 exhibiting the most stable energetics.
ContributorsKanitz, William James (Author) / Navrotsky, Alexandra (Thesis advisor) / Chan, Candace (Committee member) / Xu, Hongwu (Committee member) / Arizona State University (Publisher)
Created2023
Description
The purpose of this study was to comprehend the global warming potential (GWP), cost variability, and competitiveness of steel with rising carbon taxes. Aluminum, glass fiber composite, and carbon fiber composite were chosen as competing materials. In order to compare the aforementioned factors, the GWP of several processes to produce steel, aluminum, and fiber composites was examined. Cost analyses of various methods were also carried out to determine their viability. Energy consumption data for each of the paths under consideration were taken from the literature for the study. To get the consistent GWP for traditional and decarbonized scenarios, the required energy is multiplied with corresponding energy source (natural gas or electricity). Even after accounting for the carbon tax and the weight-reduction factor, the results show that steel still has the lowest production costs, followed by aluminum, while fiber composites remain the most costly. EAF- steel and secondary aluminum has least GWP followed by H2-DRI (Hydrogen- Direct Reduced Iron)steel and NG-DRI (Natural Gas- Direct Reduced Iron) steel with carbon capture and storage (CCS). The state of art technology for glass fiber reinforced composite also emits less carbon dioxide but the cost of production is still high. Carbon fiber reinforced composite emits most carbon dioxide and is least economical.
ContributorsRajulwar, Vaishnavi Vijay (Author) / Seetharaman, Sridhar (Thesis advisor) / Emady, Heather (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2023
Description
Adsorption is fundamentally known to be a non-isothermal process; in which temperature increase is largely significant, causing fairly appreciable impacts on the processkinetics. For porous adsorbent particles like metal organic frameworks (MOFs), silica
gel, and zeolite, the resultant relative heat generated is partly distributed within the
particle, and the rest is transferred to the surrounding ambient fluid (air).
For large step changes in adsorbed phase concentration and fast adsorption rates,
especially, the isothermality of adsorption (as in some studies) is an inadequate assumption and inspires rather erroneous diffusivities of porous adsorbents. Isothermal models, in consequence, are insufficient for studying adsorption in porous adsorbents. Non-isothermal models can satisfactorily and exhaustively describe adsorption
in porous adsorbents. However, in many of the analyses done using the models, the
thermal conductivity of the adsorbent is assumed to be infinite; thus, particle temperature is taken to be fairly uniform during the process—a trend not observed for
carbon dioxide (CO2) adsorption on MOFs.
A new and detailed analysis of CO2 adsorption in a single microporous MOF-5
particle, assuming a finite effective thermal conductivity along with comprehensive
parametric studies for the models, is presented herein. A significant average temperature increase of 5K was calculated using the new model, compared to the 0.7K
obtained using the Stremming model. A corresponding increase in diffusivity from
8.17 x 10-13 to 1.72 x 10-11 m2/s was observed, indicating the limitations of both
isothermal models and models that assume constant diffusivity.
ContributorsNkuutu, John (Author) / Lin, Jerry (Thesis advisor) / Emady, Heather (Committee member) / Deng, Shuguang (Committee member) / Arizona State University (Publisher)
Created2023
Description
This study presents an evaluation of the predicted flow behavior and the minimum outlet diameter in a computationally simulated hopper. The flow pattern in hoppers was simulated to test three size fractions, three moisture levels of microcrystalline cellulose (MCC), and two hopper wall angles in Multiphase Flow with Interphase eXchanges (MFiX). Predictions from MFiX were then compared to current literature. As expected, the smaller size fractions with lower water content were closer to ideal funnel flow than their larger counterparts. The predicted minimum outlet diameter in simulations showed good agreement with close to ideal flowability. These findings illustrate the connection between lab flowability experiments and computational simulations. Lastly, three fluidized bed simulations were also created in MFiX with zeolite 13X to analyze the pressure and velocity within the bed. The application of flowability simulations can improve the transport of solids in processing equipment used during the production of powders.
ContributorsBuchanan, Lidija (Author) / Emady, Heather (Thesis advisor) / Muhich, Christopher (Committee member) / Deng, Shuguang (Committee member) / Arizona State University (Publisher)
Created2023
Description
Granulation is a process within particle technology where a liquid binding agent is added to a powder bed to create larger granules to modify bulk properties for easier processing. Three sets of experiments were conducted to screen for which factors had the greatest effect on granule formation, size distribution, and morphological properties when wet granulating microcrystalline cellulose and water. Previous experiments had identified the different growth regimes within wet granulation, as well as the granule formation mechanisms in single-drop granulation experiments, but little research has been conducted to determine how results extracted from single drop experiments could be used to better understand the first principles that drive high shear granulation. The experiment found that under a liquid solid ratio of 110%, the granule growth rate was linear as opposed to the induction growth regime experienced at higher liquid solid ratios. L/S ratios less than 100% led to a bimodal distribution comprised of large distributions of ungranulated powder and large irregular granules. Insufficient water hampered the growth of granules due to lack of enough water bridges to connect the granules and powder, while the large molecules continued to agglomerate with particles as they rotated around the mixer. The nozzle end was augmented so that drop size as well as drop height could be adjusted and compared to single-drop granulation experiments in proceeding investigations. As individual factors, neither augmentation had significant contributions to granule size, but preliminary screens identified that interaction between increasing L/S ratio and decreasing drop size could lead to narrower distributions of particles as well as greater circularity. Preliminary screening also identified that decreasing the drop height of the nozzle could increase the rate of particle growth during the 110% L/S trials without changing the growth mechanisms, indicating a way to alter the rate of steady-state particle growth. This paper screens for which factors are most pertinent to associating single-drop and wet granulation in order to develop granulation models that can ascertain information from single-drop granulations and predict the shape and size distribution of any wet granulation, without the need to run costly wet granulation experiments.
ContributorsLay, Michael (Author) / Emady, Heather (Thesis advisor) / Muhich, Christopher (Committee member) / Holloway, Julianne (Committee member) / Arizona State University (Publisher)
Created2019
Description
Rotary drums are commonly used for their high heat and mass transfer rates in the manufacture of cement, pharmaceuticals, food, and other particulate products. These processes are difficult to model because the particulate behavior is governed by the process conditions such as particle size, particle size distribution, shape, composition, and operating parameters, such as fill level and rotation rate. More research on heat transfer in rotary drums will increase operating efficiency, leading to significant energy savings on a global scale.
This research utilizes infrared imaging to investigate the effects of fill level and rotation rate on the particle bed hydrodynamics and the average wall-particle heat transfer coefficient. 3 mm silica beads and a stainless steel rotary drum with a diameter of 6 in and a length of 3 in were used at fill levels of 10 %, 17.5 %, and 25 %, and rotation rates of 2 rpm, 6 rpm, and 10 rpm. Two full factorial designs of experiments were completed to understand the effects of these factors in the presence of conduction only (Case 1) and conduction with forced convection (Case 2). Particle-particle friction caused the particle bed to stagnate at elevated temperatures in Case 1, while the inlet air velocity in Case 2 dominated the particle friction effects to maintain the flow profile. The maximum heat transfer coefficient was achieved at a high rotation rate and low fill level in Case 1, and at a high rotation rate and high fill level in Case 2. Heat losses from the system were dominated by natural convection between the hot air in the drum and the external surroundings.
This research utilizes infrared imaging to investigate the effects of fill level and rotation rate on the particle bed hydrodynamics and the average wall-particle heat transfer coefficient. 3 mm silica beads and a stainless steel rotary drum with a diameter of 6 in and a length of 3 in were used at fill levels of 10 %, 17.5 %, and 25 %, and rotation rates of 2 rpm, 6 rpm, and 10 rpm. Two full factorial designs of experiments were completed to understand the effects of these factors in the presence of conduction only (Case 1) and conduction with forced convection (Case 2). Particle-particle friction caused the particle bed to stagnate at elevated temperatures in Case 1, while the inlet air velocity in Case 2 dominated the particle friction effects to maintain the flow profile. The maximum heat transfer coefficient was achieved at a high rotation rate and low fill level in Case 1, and at a high rotation rate and high fill level in Case 2. Heat losses from the system were dominated by natural convection between the hot air in the drum and the external surroundings.
ContributorsBoepple, Brandon (Author) / Emady, Heather (Thesis advisor) / Muhich, Christopher (Committee member) / Holloway, Julianne (Committee member) / Arizona State University (Publisher)
Created2019
Description
While the solution diffusion model and pore flow model dominate pervaporation transport mechanism modeling, a new model combining the solution diffusion and viscous flow models is validated using membranes with large scale defects exceeding 2 nm in diameter. A range of membranes was characterized using scanning electron microscopy and x-ray diffraction (XRD) to determine quality and phase characteristics. MFI zeolite membranes of He/SF6 pure gas permeation ideal selectivities of 25, 15, and 3 for good, medium, and poor quality membranes were subjected to liquid pervaporations with a 5% ethanol in water feed, by weight. Feed pressure was increased from 1 to 5 atm, to validate existence of viscous flow in the defects. Component molar flux is modeled using the solution diffusion model and the viscous flow model, via J_i=F_i (γ_i x_i P_i^sat )+(ρ )/M_W ∅/μ_ij x_i P_h. A negative coefficient of thermal expansion is observed as permeances drop as a function of temperature in all three membranes, where ϕ=((ϵr_p^2)/τ∆x). Experimental parameter ϕ increased as a function of temperature, and increased with decreasing membrane quality. This further proves that zeolitic pores are shrinking in one direction, and pulling intercrystalline voids larger, increasing the (ϵ/τ) ratio. Permiabilities of the bad, medium, and good quality membrane also decreased over time for both ethanol and water, meaning that fundamental membrane characteristics changed as a function of temperature. To conclude, the model reasonably fits empirical data reasonably well.
ContributorsWilliams, Suzanne Jean (Author) / Lin, Jerry Y.S. (Thesis advisor) / Emady, Heather (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2016