Talks by Students and Others in Materials Engineering. Open to All.
Thesis Defense- Advisor: Dr. Nikolai Kalugin
Photoinduced Oxidation of
Ultrathin Gallium Selenide
The purpose of this study was to characterize one component of the unknown properties of ultrathin (2D) GaSe, the oxidation process in a humid environment. This decision was brought about when, it was realized the sensitivity of ultrathin GaSe to photoinduced oxidation. Follow-up work by other researchers showed that the rate of oxidation of ultrathin GaSe varies greatly depending on the surrounding environments humidity, but the research lacked a complete breakdown of what occurs at the chemical level. This study investigates the intermediate products that form during oxidation to better understand the chemistry of the whole oxidation process.
The first step in this research was performing Raman spectroscopy on gallium selenide in ambient room conditions. It was during these tests that the phenomenon of photooxidation in gallium selenide was first noted . This finding, that gallium selenide would oxidize during analysis with a laser in ambient room conditions, led to a new branch of research on the subject. These early findings prompted further investigation into the field of photooxidation of gallium selenide and the processes that take place during oxidation.
Our results show that a due to the humidity present a hydrated selenium dioxide (selenous acid, 2SeO2∗ H2O or H2SeO3) forms during the early stages of the oxidation process, helping to accelerate the oxidation process . Further reactions cause the decomposition of these intermediate products leading to the formation of the final oxidation products, Ga2O3, SeO2, and amorphous selenium. Raman spectra confirms both the intermediate products as well as the final oxidation products. The evidence of the hydroxide’s formation and water soluble selenous acid during the water-assisted photo-induced oxidation explains the reported increase in oxidation speed.
Thesis Defense- Advisor: Pabrita Choudhury
Ab Initio Study of A-site Excess and Oxygen Deficient Lathanum Srontium Maganite as a Bi-functional OER/ORR catalyst
Perovskite oxides, being transition metal oxides, show promise as bi-functional catalysts being able to catalyze both oxygen evolution reactions (OER) and oxygen reduction reactions (ORR). These two reactions play a crucial role in energy
storage and energy conversion devices. Thus in an effort to pursue a sustainable future, the practical characterization of bi-functional catalyst performance for perovskite catalysts is paramount. An important feature of perovskite catalyst
is their ability to be tuned, as tuning can positively affect both reactivity and stability. The eg anti-bonding orbital occupancy of the transition metal B site, in the ABO3 perovskite structure, is a well-established descriptor of OER and ORR performance for a wide range perovskite catalyst. Though it has excellent capability with describing OER and ORR catalytic activity, the eg orbital
occupancy has limited applicability due to difficulty in its determination. That
is, in some cases, the eg electron can be difficult to determine as it cannot be directly determined either by a single measurement or efficiently by computational study. Therefore, there is a need to identify an equivalent descriptor that
is easier to compute. DFT has been utilized to calculate the over-potentials (performance indicator of the catalysts) for both the OER/ORR reactions and the electronic structures for different tuning of LSM. The oxidation state and
Mn d-DOS of the active surface site for LSM are both calculated. The oxidation state and a center of measure of the DOS are correlated to overpotential. It is believed that these correlations are related to and reflect the established eg
electron trend. Additionally, the stability of LSM is investigated and correlated to a center of measure of the oxygen p-DOS.
Thesis Proposal- Advisor: John McCoy
Effect of Aging on the Syntactic Foam DGEBA/DEA/GMB
This study looked at the aging behavior of the syntactic foam of bisphenol A diglycidyl ether (DGEBA) cured with diethanolamine (DEA) and filled with glass microbubbles (GMB). Quasi-static compression tests were performed to analyze how physical properties changed in relation to strain rate, aging time, and temperature. The effect of aging on the thermal properties was also explored using a DSC. It was found that the overall strength of the material increases with aging time until an upper bound specific to strain rate had been reached. The glass transition temperature, Tg, and physical aging peak temperature, TP, increased with aging time at rates dependent on the temperature at which the material was aged.
Independent Study Defense- Advisor: Bhaskar Majumdar
This study was conducted to determine the association of cast ductile iron microstructures with mechanical properties. ASTM A536, Grade 80-55-06 ductile iron steels form nodules that contribute to the strength of the alloy. Chemistry, mold patterns, temperature of melting and pouring, and shakeout times all contribute to the formation of nodules in the microstructure. The correlation of nodularity and mechanical properties has been discussed in the literature, but these parameters have not been studied or addressed to practices at Rock Island Arsenal. Most of the castings had nodularity ratings greater than 70% and their influence on mechanical properties was not defined with certainty. Although nodularity specifications are more established and recognized in industry, percentages of pearlite in the microstructure should also be considered as affecting tensile, yield and elongation.
Thesis Defense- Advisor: Deep Choudhuri
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Dual-phase mircostructures are observed in many commercial engineering structural alloys. In these microstructures, the two phases have different crys- tal structures and are related by a crystallographic orientation relationship (OR). This OR determines the interfacial structure and has a strong influence on the me- chanical response and strength of an alloy. The research conducted focuses on ex- amining the strength of interfaces with the Kurdjumov-Sachs (KS) and Nishiyama- Wasserman (NW) OR. These interfaces are formed between face-centered-cubic (fcc) and body-centered-cubic (bcc), or fcc and bcc ordered B2 structures. Such structures are found in Ni-Fe-Al alloys, steels, roll-bonded Cu-Nb alloys , and in a new categories of alloys called high entropy alloys. A summary of litera- ture indicates that although extensive research exists on fcc/B2 structures, very little is known regarding the relative strength of KS and NW interfaces in fcc/B2 microstructures. To that end, molecular dynamic simulations were conducted using prototype fcc-Ni/B2-NiAl bicrystal configurations. Simulations using such bicrystals allowed for quantitative comparisons of the relative strength of KS and NW interfaces. Simulation results unambiguously indicate that KS interfaces are stronger then NW, and have better susceptibility to crack propagation and shear deformation. Implications of these findings have been discussed.
Keywords: Bicrystals; Nishiyama-Wasserman; Kurdjumov-Sachs ; Fracture ; Crack Propagation; Shear
PhD Dissertation Proposal- Advisor: John McCoy
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Technological advancement is often inspired by nature, promoting scientists and engineers
to continually attempt to develop new material systems based on materials found in
nature. In order to strongly bind themselves to a variety of marine surfaces, mussels
produce a strong adhesive protein that is high in dopamine chemical unit concentration.
Dopamine is rich in catechol groups at the interface, which act as adhesion promoters.
Synthetic dopamine, capable of undergoing self-polymerization under ambient conditions
and becoming polydopamine (PDA),
has been demonstrated to form controllable nanometer thickness films which are capable of promoting the adhesion between the filler and binder system in a highly loaded composite. The
improvement of mechanical properties by promoting interfacial adhesion, as well as a uniform surface film to promote our formulation efforts are of particular interest to our team. This work
includes the investigation of PDA as it pertains to our experiments on tailoring crystal-binder adhesion properties in both plastic bonded explosives and high-fidelity surrogates. Neutron
reflectometry data will be presented to demonstrate the controllable nature of PDA film growth and the film’s structure. The effects of particle size and binder selection were studied in order to baseline our experiments to determine how much of an impact these variables can have and how they impact the final composite performance.
Keywords: Polydopamine; Plastic Bonded Explosive; Interfacial Modification
Thesis Defense-Advisor Michaelann Tartis
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Cancer is the second leading cause of death in the United States, and is commonly treated by chemotherapy which often results in adverse side effects. Methods such as liposomal drug delivery were developed to reduce adverse side effects. Drawbacks of the liposomal formulation include drug leakage and liposome instability. Additionally, Topotecan and Irinotecan undergo structural changes in physiological pH (pH7) making them less biologically active. In this study, phospholipid tails were attached to the phenolic or tertiary alcohol of Topotecan and Irinotecan, chemotherapeutics of the Camptothecin family, to overcome drug leakage, liposomal instability, and structural changes. The attachment or tether results in a lipid conjugated prodrug. The tethered prodrug provides a unique method in liposome self-assembly while also providing drug protection as it passively moves through blood vessels and filtering organs. Lipid prodrugs, named 2T-Irinotecan (2T-I), 2T-Topotecan (2T-T), 2TS-Irinotecan (2TS-I), and 2TS-Topotecan (2TS-T), were synthesized using a one pot Steglich esterification reaction. Thin-layer chromatography provided the best method for purification due to reduced silica surface interactions with water. The highest yields after separation were 44% for 2T-T, 22% for 2TS-T, 42% for 2T-I, and 20% for 2TS-I. The compounds' structures were validated using Nuclear Magnetic Resonance (NMR). Chemical stability studies were then performed using NMR in dimethyl sulfoxide-d6 (DMSO), and deuterium oxide (D2O) solvents. 2T-I was the most stable compound in both solvents. 2T-T and 2T-I are stable for the first 24 hours in DMSO and D2O without significant change in the NMR. To understand the lipid prodrug interactions with the formulated lipid bilayer, Differential Scanning Calorimetry (DSC) was used to test liposome formulations. DSC was used to test 2TS-T and 2T-T liposomes. Drug saturation was identified by increasing enthalpy until a plateau or significant decrease is seen in transition enthalpy. 2TS-T in liposomes has a saturation point between 20 and 40 mole% drug loading, while 2T-T has a saturation point between 40 and 60 mole% drug loading. The liposome incorporation and structural stability results collectively demonstrate the possibility of reducing adverse and off-target side effects for Topotecan and Irinotecan. By increasing drug-loading and preventing structural changes in physiological solutions, cancer treatment methods may be improved for better patient outcomes.
Keywords: Lipid conjugated prodrug; Camptothecin; Topotecan; Irinotecan; Liposomes; Targeted drug delivery; Differential Scanning Calorimetry, Nuclear Magnetic Resonance Spectroscopy
Thesis Defense-Advisor Michaelann Tartis
Traumatic brain injury impacts millions of people each year and is linked to adverse health effects like post-traumatic stress disorder (PTSD) and even death. Cavitation is suspected to be one cause of tissue damage in blast and blunt traumatic brain injuries and is associated with the generation of damage at tissue interfaces. The use of tissue mimics, like polyacrylamide gel phantoms, allow for high-speed optical events, such as cavitation, to be captured and further analyzed through image processing. However, high-speed optical imaging requires the tissue mimic to be transparent and cannot capture cavitation events deep in brain tissue. Alternatively, ultrasound is an imaging modality that uses sound waves to image a structure and therefore does not require the object to be transparent. Ultrasound is extremely sensitive to gas bubbles, the interaction of ultrasound waves with bubbles returns a nonlinear echo signal creating high contrast regions in an image. Ultrasound also allows for imaging at greater depths than possible using a high-speed camera. This research investigated cavitation in a human head phantom by developing a two-aperture high frame rate plane-wave code for a Verasonics Vantage 64 Ultrasound System paired with high-speed imaging on a Photron FASTCAM SA-Z camera. Cavitation was confirmed using high-speed imaging. Four masses, 1,200 g, 2,000 g, 3,000 g, and 4,000 g, were dropped on the cranial phantoms from four heights, 20 cm, 40 cm, 60 cm, and 80 cm. In the optical data, cavitation bubble persistence time and pixel number, which was the approximate area of the bubble in the 2-D field of view, increased as mass and height increased. In the acoustic data, regions of interest (ROI) were tracked over time and cavitation was quantified through the change in mean pixel intensity. Additionally, a layer of Polydimethylsiloxane (PDMS) was added to the top of the cranial phantoms in some tests to mimic skin and provide estimations for the dampening effects skin may have on cavitation. No significant change in cavitation in either the optical or acoustic data was observed due to this addition. This work led to the development of a tool for simultaneously capturing cavitation optically and acoustically. This tool made it possible to capture cavitation in a 3-D printed skull and in a polyacrylamide tissue phantom during an impact test and will allow for imaging non-transparent objects like brain tissue in future drop tests and blast tube experiments. In the future, this will allow our group to use ultrasound as a stand-alone detector for cavitation deep in tissues where optical imaging cannot be used. Understanding these damage mechanisms may lead to improved designs for protective equipment, like helmets, for military personnel
Thesis Defense- Advisor: David Burleigh
The Waste Isolation Pilot Plant (WIPP) is a long-term underground storage facility for low level transuranic (TRU) waste. Nuclear waste is placed inside steel drums and stored 660 meters underground within a geologic salt formation. Naturally, the steel will corrode under these conditions. For modeling purposes the steel corrosion rates must be known in order to understand gas generation that may impact radionuclide mobility. Static, flow through, and electrochemical tests were performed in order to build an understanding of the corrosion process under WIPP conditions. Static tests were used to characterize corrosion products formed during this process. A dynamic flow through set up pumped fresh brine continuously over steel samples for several months, allowing for the corrosion process to reach steady state. Electrochemical tests provided for an easy testing method for studying the initial hours of corrosion. Each measurement technique generated useful corrosion rate related data. Interferometry measurements performed on samples corroded in the flow through set up were successful in obtaining accurate surface retreat measurements. Corrosion rate data collected in this research will be used to more effectively model gas generation and identify effects of steel corrosion on radionuclide mobility.
Thesis Defense- Advisor: Pabitra Choudhury
Perovskite oxides being transition metal oxides show promise as bi-functional catalyst
being able to catalyze both oxygen evolution reactions (OER) and oxygen reduction
reactions (ORR). These two reactions play a crucial role in energy storage and energy
conversion devices. Thus in effort to pursue a sustainable future, the practical characterization
of bi-functional catalyst
performance for perovskite catalyst is paramount. The eg antibonding orbital occupancy of the
transition metal B site, in the ABO3 perovskite structure, is a well-established descriptor of OER and ORR performance for a wide range perovskite catalyst. Though, it has excellent capability of describing OER and ORR catalytic activity, the eg orbital occupancy, has limited applicability due to difficulty in its determination. That is, in some cases, the eg electron can be difficult to
determine as it cannot be directly determined either by a single measurement or computational study alone. To combat the limited applicability of the eg electron filling, the oxygen p-band center has been used as an alternate descriptor for Co based catalyst. The pband center can be computed directly with Density Functional Theory (DFT) calculations, thereby giving credence to its practicality. On the other hand, the p-band center does not appear to be a good descriptor for some other perovskites catalyst, such as Mn based ones. The goal of this work then is to study both the Mn based (e.g. La1-xSrxMnO3-δ (LSM)) and Co based (e.g. LaCoO3 (LCO)) catalysts, to access the possibility of a new descriptor that is more generally applicable than the p-band center but also more practical to determine than the eg orbital occupancy. To this end, DFT has been utilized to calculate the over potentials (performance indicator of the catalysts) for both the OER/ORR reactions, formation energies and the
electronic structures for both the LSM and LCO structures with various surfaces.
Thesis Proposal- Advisor: Deep Choudhuri
Dual-phase microstructures are observed in many commercial structural alloys. In these microstructures, the two phases have different crystal structures and are related by a crystallographic orientation relationship (OR). This OR determines the interfacial structure and has a strong influence on the mechanical response and strength of an alloy. Therefore, the proposed research focuses on examining the strength of interfaces with Kurdjumov-sachs (KS) and Nishiyama-Wasserman (NW) OR. These interfaces are formed between face-centered-cubic (fcc) and body-centered-cubic (bcc), or fcc and bcc ordered B2 structures. Such structures are found in Ni-Fe-Al Alloys, steels, roll-bonded Cu-Nb alloys, and in a new category of alloys called high entropy alloys. A summary of literature indicates that although extensive research on fcc-B2 structures, very little is known regarding the relative strength of KS and NW interfaces in fcc/B2 microstructures. To that end, molecular dynamic simulations were preformed using prototype fcc-Ni/B2-NiAl bicrystal configurations. Simulations using such bicrystals allowed for quantitative comparisons of the relative strength of KS and NW interfaces. Preliminary results unambiguously indicate that KS interfaces are stronger then NW, and have better susceptibility to crack propagation. Implications of these finding have been discussed, and further research is proposed for developing a mechanistic understanding of those results