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a talk by
Director of the Vatican Observatory, Rome
About this talk
Why did we go to the Moon? Why does the Vatican support an astronomical observatory? These questions mask a deeper question: why do individuals choose to spend their lives in pursuit of pure knowledge? The motivation behind our choices, both as individuals and as a society, controls the sorts of science that gets done. It determines the kinds of answers that are found to be satisfying. And ultimately, it affects the way in which we think of ourselves.
About the speaker
Guy Consolmagno, SJ is a brother in the Roman Catholic Society of Jesus (the Jesuits), working since 1993 as an astronomer and meteorite specialist at the Specola Vaticana (Vatican Observatory), located in the Papal summer gardens outside Rome. Since 2014 he has been president of the Vatican Observatory Foundation, which supports the work of the Observatory and especially its 1.8 meter Vatican Advanced Technology Telescope (VATT) in Arizona. In September of 2015 he was named Director of the Vatican Observatory by Pope Francis.
Consolmagno's research explores connections between meteorites, asteroids, and the evolution of small solar system bodies. Along with more than 200 scientific publications, he is the author of a number of popular books, including: Turn Left at Orion (with Dan Davis), and most recently, Would You Baptize an Extraterrestrial? (with Fr. Paul Mueller, S.J.). He also has hosted science programs for BBC Radio 4, has been interviewed in numerous documentary films, and writes a monthly science column for the British Catholic magazine, The Tablet.
A native of Detroit, MI, Consolmagno earned two degrees from MIT and a doctorate in planetary sciences from the University of Arizona, was a postdoctoral research fellow at Harvard and MIT, served in the US Peace Corps (Kenya), and taught university physics at Lafayette College before entering the Jesuits in 1989. He has served as chair of the American Astronomical Society’s Division for Planetary Sciences (AAS/DPS) and on the planetary surfaces nomenclature committee of the International Astronomical Union (IAU). Asteroid “4597 Consolmagno” was named in recognition of his work. In 2014 he won the Carl Sagan Med al for public outreach by the AAS/DPS.
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Recently, severe plastic deformation (SPD), which encompasses mechanical alloying in liquid nitrogen (cryomilling) and high-pressure torsion, has emerged as a successful strategy for the synthesis of nanostructured alloys and composites. Results from various groups around the world reveal considerable improvements in the physical performance of a variety of SPD processed metals and alloys. While increases in strength of several 100% are commonly documented, ductility, however, appears to scale inversely with strength in these materials; this behavior has been attributed to limited dislocation activity at these length scales. This challenge has been addressed via the introduction of additional size scales that facilitate plasticity during deformation. The concept of a bimodal microstructure has recently been extended into the realm of metal composites with tri-modal microstructural characteristics, to accomplish ultra-high strength values. In this lecture, published data of cryomilled alloys and composites are reviewed and discussed with particular emphasis on the following topics: recent findings in the area of cryomilled materials; primary consolidation and secondary processing methods; microstructural evolution from nanostructured powders to bulk materials during consolidation; and mechanical behavior of consolidated materials. The deformation behavior and the underlying mechanisms of cryomilled materials are discussed in an effort to shed light into the fundamental behavior of ultrafine grained and nanostructured materials.
BIO:
Enrique J. Lavernia returned as dean to the College of Engineering on January 1, 2011 after serving as provost and executive vice chancellor of the University of California, Davis, from January 2009–December 2010. He joined the campus in 2002 as dean of the College of Engineering, where he was also promoted to Distinguished Professor in 2007. Prior to his arrival to Davis in 2002, Lavernia served as Chair and Chancellor’s Professor in the Department of Chemical Engineering and Materials Science at UC Irvine. He was named the 1998 Biochemical and Biochemical Engineering Materials Science “Science Teacher of the Year” at UCI. Elected to the National Academy of Engineering in 2013, Lavernia is also a fellow of the American Association for the Advancement of Science (2000); a fellow of the American Society of Mechanical Engineers (2006); and fellow of ASM International (1998).
Dean Lavernia is a Fellow of the American Association for the Advancement of Science, the American Society of Mechanical Engineers, the ASM International, and the Alexander von Humboldt Foundation. Named Presidential Young Investigator by the National Science Foundation, Lavernia also received a Young Investigator Award from the Office of Naval Research. In 2011 he received the Hispanic Engineer National Achievement Award (HEENAC) and the Society for the Advancement of Chicanos and Native Americans in Science (SACNAS) Distinguished Scientist Award. Dean Lavernia is also the recipient of the 2013 Edward DeMille Campbell Memorial Lectureship, and the 2013 ASM International Gold Medal Award.
Dean Lavernia’s research interests include synthesis of structural materials and metal matrix composites with particular emphasis on processing fundamentals; thermal spray processing of nano-structured materials; spray atomization and deposition of structural materials; solidification processing of metal matrix composites; synthesis and behavior of nano-crystalline materials; and mathematical modeling of advanced materials and processes. He has published 400 journal and 200 conference publications on topics ranging from nano-materials to aluminum alloys.
Dean Lavernia earned his B.S. with Honors in Solid Mechanics from Brown University in 1982, his M.S. in Metallurgy from the Massachusetts Institute of Technology (M.I.T.) in 1984, and his Ph.D. in Materials Engineering from M.I.T. in 1986.
]]>Enrique J. Lavernia, Distinguished Professor
Department of Chemical Engineering and Materials Science
University of California, One Shields Ave., Davis, CA 95616, USA
Email Leslie Bayor (leslie.bayor@mse.gatech.edu) for reservation information. Participants will receive free football tickets to the 3:30 pm, Tech vs Middle Tennessee State Game.
]]>SUMMARY: Photovoltaic (PV) cells with a three dimensional (3D) morphology are anexciting new research thrust with promise to create cheaper, more efficientsolar cells. This work introduces a new type of 3D PV device based onvertically aligned carbon nanotube (CNT) arrays. These arrays are paired withthe thin film heterojunction, CdTe/CdS, to form a complete 3D PV device(3DCNTPV).
The main benefit of the 3DCNTPV cell is the ability to utilizemultiple photon interactions with the solar cell surface. This threedimensionality allows photons to interact multiple times with the photoactivematerial, which increases the absorption and the overall power output over whatis possible with a two dimensiona (2D) morphology. To quantify the increasedpower output arising from these multiple photon interactions, a new absorptionefficiency term, h3D, is introduced. Thetheoretical basis behind this new term and how it relates to the absorptionefficiency of a planar cell, h2D, is derived. This theory is validated by monte carlosimulations.
A series of 3DCNTPV prototype cells was developed. Marriageof a complicated 3D structure with production methods traditionally used forplanar CdTe solar cell is challenging. This work examines the problemsassociated with manufacturing these types of cells and systematically altersproduction methods and architecture of the semiconductor layers and electrodesto increase the short circuit current (Isc), eliminate parasiticshunts, and increase the open circuit voltage (Voc). Originalprototype cells suffered from very low power output. Isc and Voc inlater cells was increased by an order of magnitude and300%, respectively. Output power of the 3DCNTPV cells wasmeasured at varying incident angles of light and these cells show anincrease in the normalized power output compared to similar planar cells whenthe solar flux is at off-normal angles. Experimental power output vs. zenithangle of the 3DCNTPV cells shows very good agreement with the theory proposedin this work.
]]>To alleviate these concerns, an alternate infill mustmatch safety and performance while alleviating environmental and healthconcerns associated with GCRI. Plus, acandidate could come from other sources of benign waste streams, such asrecycled PET from drink bottles to non-salvaged components of post-consumercarpet (both broadloom and selected tiles), to remain economical. In addition, the infill's properties such theshape and size could be optimized by statistical modeling to reduce the amountof required material while maintaining performance and safety levels in thefilled turf.
This proposal outlines two topics of the dissertationresearch. First, compare thecomposition, bulk properties and impact performance of several waste materialstreams to the properties of GCRI. Second, determine important infill properties by modeling to optimizethe infill itself and possibly use polymer particles with controlled size,shape, and other factors. Ideally thiswork will define specifications for raw material that leads to idealperformance of the final product. Ultimately, the selected infill candidate will replace GCRI withoutincreased cost, reduced performance or impaired impact safety while remainingbeneficial to health and environment.
]]>Summary: We have used a molecular modeling of both random andblocky sequence hydrogel networks of poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl
methacrylate) (P(VP-co-HEMA)) with a composition ofVP:HEMA = 37:13 to investigate the effect of the monomeric sequence and thewater content on the equilibrium structures and the mechanical and transportproperties by full-atomistic molecular dynamics (MD) simulations. The degree of randomness of the monomersequence for the random and the blocky copolymers, were 1.170 and 0.104,respectively, and the degree of polymerization was fixed at 50. The equilibrated density of the hydrogel wasfound to be larger for the random sequence than for the blocky sequence at lowwater contents (< 40 wt %), but this density difference decreased withincreasing water content. The paircorrelation function analysis shows that VP is more hydrophilic than HEMA andthat the random sequence hydrogel is solvated more than the blocky sequencehydrogel at low water content, which disappears with increasing water content.
Correspondingly, the water structure is more disrupted bythe random sequence hydrogel at low water content but eventually develops theexpected bulk-water-like structure with increasing water content. From mechanical deformation simulations, thestress-strain analysis showed that the VP is found to relax more efficiently,especially in the blocky sequence, so that the blocky sequence hydrogel showsless stress levels compared to the random sequence hydrogel. As the water content increases, the stresslevel becomes identical for both sequences. The elastic moduli of the hydrogels calculated from the constant strainenergy minimization show the same trend with the stress-strain analysis. Ascorbic acid and D-glucose were used tostudy the effect of the monomeric sequence on the diffusion of small guestmolecules within the hydrogels. Byanalyzing the pair correlation functions, it was found that the guest moleculehas greater accessibility to the VP units than to the HEMA units with bothmonomeric sequences due to its higher hydrophilicity compared to the HEMAunits. The monomeric sequence effect onthe P(VP-co-HEMA) hydrogel is clearly observed with 20 wt % water content, butthe monomeric sequence effect is significantly reduced with 40 wt % watercontent and disappears with 80 wt % water content. This is because the hydrophilic guestmolecules are more likely to be associated with water molecules than with thepolymer network at the high water content. By analyzing the mean square displacement, the displacement of the guestmolecules and the inner surface area, it is also found that the guest moleculeis confined in the system at 20 wt % water content, resulting in highlyanomalous subdiffusion. Therefore, thediffusion of the guest molecules is directly affected by their interaction withthe monomer units, the monomeric sequence and the geometrical confinement inthe hydrogel at a low water content, but the monomeric sequence effect and therestriction on the diffusion of the guest molecule are significantly decreasedwith increasing the water content.
We also investigated the de-swelling mechanisms of thesurface-grafted
poly(N-isopropylacrylamide) (P(NIPAAm)) brushescontaining 1300 water molecules at 275 K, 290 K, 320 K, 345 K, and 370 K. We clearly observed the de-swelling of thewater molecules for P(NIPAAm) above the lower critical solution temperature(LCST) (~305 K). Below the LCST, we didnot observe the de-swelling of water molecules. Using the upper critical solution temperature (UCST) systems(poly(acrylamide) brushes) for comparison purposes, we did not observe thede-swelling of water molecules at a given range of temperatures. By analyzing the pair correlation functionsand the coordination numbers, the de-swelling of the water molecules occurreddistinctly around the isopropyl group of the P(NIPAAm) brush above the LCSTbecause C(NIPAAm) does not offer sufficient interaction with the watermolecules via the hydrogen bonding type of secondary interaction. We also found that the contribution of the
N(NIPAAm)-O(water) pair is quite small because of thesteric hindrance of the isopropyl group. By analyzing the change in the hydrogen bonds, the hydrogen bondsbetween polar groups and water molecules in the P(NIPAAm) brushes weaken withincreasing temperature, which leads to the de-swelling of the water moleculesout of the brushes above the LCST. Belowthe LCST, the change in the hydrogen bonds is not significant. Again, the contribution of theNH(NIPAAm)-water pairs is insignificant; the total number of hydrogen bonds is~20, indicating that the interaction between the NH group and the watermolecules is not significant due to steric hindrances. Lastly, we observed that the total surfacearea of the
P(NIPAAm) brushes that is accessible to water moleculesis decreased by collapsing the brushes followed by the de-swelling of watermolecules above the LCST.
]]>SUMMARY:
Withexcellent electrical, thermal and mechanical properties as well as largespecific surface area, graphene has been applied in next-generationnano-electronics, gas sensors, transparent electrical conductors, thermallyconductive materials, and superior energy capacitors etc. Convenient andproductive preparation of graphene is thereby especially important and stronglydesired for its manifold applications.
Chemicallydeveloped functionalized graphene from graphene oxide (GO) has significantlyhigh productivity and low cost, however, toxic chemical reduction agents (e.g.hydrazine hydrate) and raised temperature (400-1100°C) are usually necessary inGO reduction yet not preferred in current technologies. Here, microwaves (MW)are applied to reduce the amount of graphene oxide (GO) at a relatively lowtemperature (~165oC). Experimental results indicate that resurgenceof interconnected graphene-like domains contributes to a low sheet resistancewith a high optical transparency after MW reduction, indicating the very highefficiency of MW in GO’s reduction.
Moreover,graphene is usually recumbent on solid substrates, while vertically alignedgraphene architecture on solid substrate is rarely available and less studied.For TIMs, electrodes of ultracapacitors, etc, efficient heatdissipation and electrical conductance in normal direction of solid surfaces isstrongly desired. In addition, large-volume heat dissipation requires a jointcontribution of a large number of graphene sheets. Graphene sheets must be alignedin a large scale array in order to meet the requirements for TIM application.Here, thermally conductive fuctionalized multilayer graphene sheets (fMGs) areefficiently aligned in a large scale by vacuum filtration method at roomtemperature, as evidenced by SEM images and polarized Raman spectroscopy. Aremarkably strong anisotropy in properties of aligned fMGs is observed.Moreover, VA-fMG TIMs are prepared by constructing a three-dimensionalvertically aligned functionalized multilayer graphene architecture betweencontact Silicon/Silicon surfaces with pure Indium as a metallic medium.Compared with their counterpart from recumbent A-fMGs, VA-fMG TIMs havesignificantly higher equivalent thermal conductivity and lower contact thermalresistance.
Electricaland thermal conductivities of polymer composite are also greatly interestedhere. Previous researches indicated that filler loading, morphology of fillers,and chemical bonding across filler/polymer interfaces have significantinfluence on electrical/thermal conductivity of polymer composite. Therefore,the research also pays substantial attention to these issues. First, electricalresistivity of CPCs is highly sensitive on volume or weight ratio (fillerloading) of conductive fillers in polymer matrix, especially when fillerloading is close to percolation threshold (pc). Thermaloxidation aging usually can cause a significant weight loss of polymer matrixin a CPC system, resulting in a filler loading change which can be exhibited bya prompt alteration in electrical resistivity of CPCs. Here, the phenomena areapplied as approach for in-situ monitoring thermal oxidation statusof polymeric materials is developed based on an electrical sensors based onconductive polymeric composites (CPCs). The study developed a model forelectrical resistivity of sensors from the CPCs as a function of aging time atconstant aging temperature, which is in a good agreement with aBoltzmann-Sigmoidal equation. Based on the finding, the sensors show theircapability of in-situ in-situ monitor andestimate aging status of polymeric components by a fast and convenientelectrical resistance measurement.
Second,interfacial issues related to these thermal conductive fillers are systemicallystudied. On the one hand, the study focuses on relationship between morphologyof h-BN particles and thermal conductivity of their epoxy composites. It isfound that spherical-agglomeration of h-BN particles can significantly enhancethermal conductivity of epoxy resin, compared with dispersed h-BN plates, bysubstantially reducing specific interfacial area between h-BN and epoxy resin.On the other hand, surface of high thermal conductive fillers such as SiCparticles and MWNTs are successfully functionalized, which makes their surface reactivewith bisphenol A diglycidyl ether and able to form chemical bonding betweenfillers and epoxy resin. By this means, thermal conductivity of polymercomposites is found to be significantly enhanced compared with control samples,indicating the interfacial chemical bonding across interface between thermalconductive fillers and polymer matrix can promote heat dissipation in polymericcomposites. The finding can benefit a development of high thermal conductivepolymer composites by interfacial chemical bonding enhancement to meet thedemanding requirements in current fine pitch and Cu/low k technology.
]]>Abstract: Traditional vapor phase deposition techniques of PZToffer poor conformality over three-dimensional surfaces due to their reactanttransport mechanisms. As an alternative, sol-gel synthesis may provide newprocess possibilities to overcome this hurdle but the film quality is usuallyinferior. The first part of this study is dedicated to the characterization ofthe electric properties and yield of PZT thin film prepared by the sol-gelprocess. Several conducting materials that can be coated on three-dimensionalsurfaces have been evaluated as electrodes, and the possibility to form aconformal coating over a three-dimensional surface by solution coatingtechniques has been demonstrated.
ZnO and GaN micro/nanowires are promising piezoelectricmaterials for energy harvesting and piezotronic device applications. The second part of this study is focused onZnO and GaN micro/nanowires grown by physical vapor deposition techniques. Themorphology and chemical compositions are revealed by electron microscopy.Utilizing the as-grown ZnO nanowires, single nanowire based photocell isfabricated, and its performance is studied in terms of its response time,repeatability, excitation position and polarization dependence upon He-CdUV-laser illumination. Employing the as-grown GaN nanowires, single nanowirebased strain sensor is demonstrated, and its behavior is discussed in terms ofthe polar axis orientation of the nanowire and the Schottky contacts.
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Summary:
Since their discovery in 1985, fullerenes have been widely studied due to the unique chemical, electronic, and photophysical properties offered by the fullerene cage; research has led to fullerene application in numerous technological areas, including well publicized use in organic photovoltaic devices (OPVs), artificial photosynthesis, supramolecular assemblies, and potential use in quantum computing. This thesis research was largely motivated by the potential quantum computing applications for fullerenes encapsulating spin-active atoms. The overall goal of this research was to achieve alignment of endohedral fullerene dimers defined as covalently linked pairs of fullerene cages where each fullerene cage encapsulates a spin-active atom; however, the research discussed herein encompasses both monomer and dimer C60 behavior.
Devices where quantum effects dominate have a variety of potential uses in both classical and quantum computation, addressing issues with both decreasing size and increasing complexity. Buckminster fullerenes are ideal cages for spin-active atoms used for quantum computing such as atomic nitrogen (14N@C60, 15N@C60) as the carbon cage provides almost total isolation of atomic properties as well as the ability for arrangement of spins with respect to one another. However, large aligned arrays of endohedral fullerenes are required to successfully achieve quantum computation. Self-assembled molecular networks are ideal for developing large because the spacing and geometry are typically well-defined by non-covalent interactions. Three self-assembly approaches will be discussed in depth here including (1) block copolymer templates as guides for fullerene alignment; (2) Langmuir-Blodgett (LB) deposition of monolayers and multilayers; and (3) surface-directed assembly of fullerene monolayers.
Abstract: Building fuel efficient automobiles is increasingly important due to the rising cost of energy. One way to improve fuel efficiency is to reduce the overall automobile weight. Weight reductions using steel components are desirable because of easy integration into existing manufacturing systems. Designing components with Advanced High Strength Steels (AHSS) has allowed for material reductions, while maintaining strength requirements. Two Advanced High Strength steel microstructures investigated in this research utilize different strengthening mechanisms to obtain a desired tensile strength grade of 590MPa. One steel, HR590, utilizes precipitation strengthening to refine the grain size and harden the steel. The other steel, HR590DP, utilizes a dual phase microstructure consisting of martensite constituents in a ferrite matrix. The steels are processed to have the same tensile strength grade, but exhibit different fatigue behavior. The central objective of this research is to characterize and compare the fatigue behavior of these two steels. The results show the dual phase steel work hardens at a low fatigue life. The precipitation strengthened microstructure shows hardening at low strain amplitudes, softening at intermediate strain amplitudes and little to no effect at high strain amplitudes. These different fatigue responses are characterized and quantified in this research. Additionally, observations showing the fracture surfaces and the bulk microstructure are analyzed.
]]>Summary: In this research, atomistic simulations are employed toinvestigate defect nucleation and free volume of grain boundaries andnanocrystalline materials. Nanocrystalline materials are of particular interestdue to their improved mechanical properties and alternative strainaccommodation processes at the nanoscale. These processes, or deformationmechanisms, within nanocrystalline materials are strongly dictated by thelarger volume fraction of grain boundaries and interfaces due to smalleraverage grain sizes. The behavior of grain boundaries within nanocrystallinematerials is still largely unknown. One reason is that experimentalinvestigation at this scale is often difficult, time consuming, expensive, orimpossible with current resources. Atomistic simulations have shown thepotential to probe fundamental behavior at these length scales and providevital insight into material mechanisms. Therefore, we utilize atomisticsimulations to explore structure-property relationships of face-centered-cubic(fcc) grain boundaries, and investigate the deformation of nanocrystallinecopper as a function of average grain size.
Molecular statics employing an embedded atom methodpotential are utilized in this research to construct fcc bicrystalline grainboundary structures.
The boundaries are then deformed at 10K under uniaxialtension and simple shear at a constant strain rate to elucidate the influenceof interfacial structure on inelastic deformation. An algorithm is alsopresented to compute interfacial free volume in the bicrystalline structuresand quantitatively track its evolution with imposed strain. Representativenon-equilibrium grain boundaries are instantiated using excess free volume as ameasure of the degree of non-equilibrium state, and then deformed to explorethe influence of structure on deformation response. It is shown that excessfree volume alters interfacial atomic processes critical for dislocationnucleation and grain boundary sliding, resulting in lower grain boundarystrength.
Volume-averaged kinematic metrics are formulated fromcontinuum mechanics theory and applied to the results of atomistic simulationsto provide new insight into atomic deformation and rotation fields. Inelasticdeformation mechanisms common to nanocrystalline metals, such as heterogeneousdislocation nucleation, grain boundary sliding, and grain boundary migrationare analyzed with the proposed metrics using bicrystalline grain boundaries.The results indicate that unique deformation fields are associated with eachmechanism and a sense of the deformation history of the atomic fields areprovided through the utilization of neighbor lists from the referenceconfiguration. Other metrics use current configuration quantities to displaythe fronts of propagating dislocation networks.
The kinematic metrics are also leveraged to explore thetensile deformation of nanocrystalline copper at 10K. The distribution ofdifferent strain accommodation mechanisms is estimated and we are able topartition the role of competing mechanisms in the the overall strain of thenanocrystalline structure as a function of grain size. Grain boundaries areobserved to be influential in smaller grained structures, while dislocationglide is more influential as grain size increases. Under compression, however,the resolved compressive normal stress on interfaces hinders grain boundaryplasticity, leading to a tension-compression asymmetry in the strength ofnanocrystalline copper. The mechanisms responsible for the asymmetry are probedwith atomistic simulations and the volume-averaged metrics. Finally, theutility of the metrics in capturing non-local nanoscale deformation behaviorand their potential to inform higher-scaled models is discussed.
]]>Abstract: Thescience of metallurgy has a history almost as long as human civilizationitself. A great variety of metals and metallic alloys at different stages havebecome the very cornerstone on which our society is based, since the inceptionof this ancient yet vibrant discipline.
However,computational metallurgical mechanics remains elusive largely owing to thedisconnect between the modern computational approaches and the complexity ofmost metallurgical topics. Just tapping into one of the most discussedmetallurgical phenomena, decarburization, the work presented in this thesissummarizes the research conducted on quantifying the progression ofdecarburization and its impact on the mechanical properties of steel samples.
Thetopics researched in this work serve, but are not limited to, the production ofhollow metal proppants used for underground oil and natural gas reserveextraction, including calculating the progression and the impact ofdecarburization that occurs during the heat processing of steel in atime-dependent fashion and modeling the deformation behavior of a maragingsteel hollow sphere. Then the decarburization model is modified to relate theoverall mechanical properties of the impact-resistantMg/Al/maraging-steel-hollow-sphere composite material to its microstructure.
Asmuch as 95% by weight of all metal produced worldwide is steel. In order toobtain higher strength and eliminate residual stress, steel is heated to hightemperatures to allow for homogenization followed by heat treating at a varietyof temperatures and times to enhance the overall mechanical properties.However, decarburization, commonly known as the loss of carbon to theenvironment due to its reaction with the atmosphere, will occur andresult in considerable strength loss. To avoid potential dangers such asreduced static and fatigue properties, the mechanical property variations mustbe determined with respect to the heat treatment temperature and time. Thiswork also outlines the procedures used to quantify the effects of processingtemperature on the microstructure. These effects include average particle size,particle volume fraction, void and porosity. Once completed, the deformationbehavior of the maraging steel hollow spheres is investigated in the subsequentwork to visualize the stress environment in which the proppants would function.To further the effort, the hollow maraging steel spheres are cast into Mg/Alalloy matrix and the properties of the resulted impact-resistant compositematerial are simulated loosely based on the microstructure model establishedfor the decarburization process.
Modelingmakes it economically practical to assess the targeted materials' overallproperties, behaviors and the mechanical responses in conjunction with stressenvironment, material dimensions (sphere size, sphere wall thickness, etc.)among other variables, before a structure is built. Additionally, more advancedmodeling can enable the quantitative descriptions of more complex metallurgicalphenomena such as the effects of impurity elements, geometric changes of thesecond-phase particles, and deformation under complex loading situations.
]]>Specifically, the proposed research will utilize in situ thermogravimetric analysis of a
spectrum of compositions of ZrB2 and HfB2-based compounds with additives of SiC, TaSi2,
and TaB2. The former is known to produce a protective silicate glass layer (up to ~ 1500 deg.C), and the latter have been shown by some to confer oxidation resistance at higher temperatures.
A labratory balance mounted on a lifting table beneath a furnace with Zircothal heating
elements able to reach 2000 deg.C is used to perform the oxidation studies.
In addition to the oxidation studies, characterization of the materials' ability to dissipate
excess heat will be performed. The thermal expansion of the samples will be determined with
a graphite differential dilatometer, the thermal diffusivity is determined by the laser flash
method, and these values will be used to calculate the thermal conductivity. As the materials
will be expected to not only conduct heat but radiate it away also, the spectral emittance of each sample will be determined using a spectral radiometer.
This research will contribute to the understanding and modeling suitability of a class
of materials expected to find use in the next generation of supersonic aircraft and reusable
spacecraft. In addition, it will contribute to the science of UHTC materials and offer new
understanding as to the mechanics of oxidation resistance at high temperatures.
Title: Oxidation Resistance, Electrical and Thermal Conductivity, and Spectral Emittance of Fully Dense HfB2 and ZrB2 with SiC, TaSi2, and TaB2 Additives
]]>Date: Tuesday, April 5, 2011
Time: 11am to 1pm
Location: MRDC Plaza
*If it rains, we will be inside the Love building on the 1st and 2nd floorAtriums
You must have a meal ticket in order to gain entrance at the picnic,as we will have a registration table upon entering the designated area for ouroutdoor lunch together.
See either:
Abstract: The demand forclean, secure, and renewable energy has stimulated great interest in fuelcells. Among all types of fuel cells, solid oxide fuel cells (SOFCs) offergreat promise for the most efficient and cost-effective utilization of a widevariety of fuels such as hydrocarbons, coal gas and gasified biomass. Thecritical technical barrier to fuel flexibility is the vulnerability of thestate-of-the-art Ni-YSZ (yttria-stabilized-zirconia) anode materials to cokingand sulfur poisoning. In addition, the high operating temperatures of SOFCs,stemming from the low ionic conductivity of the electrolyte materials and thepoor performance of the cathode materials at lower temperatures, increase costsand reduce the system operation life. Therefore, the main objective of theresearch is to develop new electrolyte and electrode materials with highelectrical conductivity and electrocatalytic activity at low temperatures andto gain fundamental understanding of the interrelationships between latticestructure, local atomic environment, bulk transport, surface property andelectrocatalytic activity.
Four researchthrusts will be detailed in this presentation. First, a new electrolyte wasshown to have the highest ionic conductivity below 750oC of allknown electrolyte materials for SOFCs applications. Synchrotron-based X-raydiffraction and Extended X-ray Absorption Fine Structure (EXAFS) were employedto investigate the lattice structure and local atomic environment. Second, whenused in combination with Ni as a composite anode, it was shown to provideexcellent tolerance to carbon buildup (coking) and deactivation (poisoning) bycontaminants commonly encountered in readily available fuels. The mechanismresponsible for the enhanced electrocatalytic activity was unraveled byanalyzing the anode surfaces using Raman spectroscopy and Scanning AugerNanoprobe. Third, a simple, cheap surface modification of state-of-the-artNi-YSZ anode was developed that could be more readily adopted in the latestfuel cell systems, demonstrating direct utilization of hydrocarbons, CO andgasified carbon fuels. Advanced electron microscopy and spectroscopy, Ramanspectroscopy and Density functional theory (DFT) calculations were used tounderstand the anodic reactions occurring on nano-islands and nanostructuredmetal/oxide interface. Last, a new composite cathode with simultaneous transportof proton, oxygen vacancies and electronic defects was developed forlow-temperature SOFCs based on oxide proton conductors.
In conclusion,this report represents a critical step toward an economically feasible fuelcell for utilization of a wide variety of readily available fuels as well as aunique mechanistic investigation of structure-property relationship andsurface- and interfaces-involved chemical and electrochemical reactions.
]]>ThesisTitle: New Materials for Intermediate-temperature Solid Oxide Fuel Cells to be Poweredby Carbon- and Sulfur- Containing Fuels
]]>Summary:
Aptamers aresingle-stranded oligonucleotide sequences that exhibit high affinity and highspecificity binding for nonnucleotide targets.
Using a procedure called "systematic evolution ofligands by exponential enrichment" (SELEX), aptamers can be identifiedfrom combinatorial libraries consisting of ~ 1012-1015 random sequences. Thisin vitro selection procedure has led to the discovery of aptamers for a varietyof targets including but not limited to ions, small macromolecules, and wholecells. Due to their small molecular weight, ease of processing, and long-termstability, aptamers are now increasingly explored as potential alternatives toantibodies as high affinity ligands. These characteristics highlight thepotential impact of aptamers in areas such as biosensing, diagnostics, andtherapeutics.
Goldnanoparticles have been widely studied for various diagnostic, imaging andtherapeutic applications due to their shape and size-dependent opticalproperties. Tight control over the size distribution and shape of goldnanoparticles using conventional solution precipitation approaches, however, ischallenging. In addition, subsequentassembly of nanoparticles into well-organized spatial patterns on substratescan pose additional challenges. The overall goal of the proposed research is toidentify aptamer sequences from a random library that bind both to goldnanoparticles and to gold ions. Ifsuccessful, this approach to aptamer screening will potentially allow for thesimultaneous precipitation and patterning of homogeneous, spherical goldnanoparticles.
]]>Summary:Lithium-ion (Li-ion) battery technologyis of particular interest due to its high energy and power characteristics thatare adaptable to meet the needs of existing and emerging applications rangingfrom electronics to transportation to electrical grid stability. High capacitybulk materials (silicon, germanium), explored to advance beyond the currentindustry standard (graphite) anode, pose a critical challenge to long batterylifetimes due to large volume changes of the host material as a result of Liinsertion/extraction. Without sufficient mechanical robustness of silicon- orgermanium- based anodes and without free space available in the electrode forvolume expansion, the significant stresses generated during cell operationcommonly lead to rapid capacity losses and mechanical degradation of the anode.
Anodescomprised of nanomaterials have been investigated as alternatives to bulkmaterials since their constrained dimensions may provide increasedelectrochemical activity and improved mechanical stability. Several typesof nanocomposites materials were found to offer good electrochemicalperformance but the lack of fundamental understanding of structure-propertyrelationship in these composites limit further developments of high capacityanode technology.
The proposed research considers twoanode architectures which can be generally described as a carbon substrate(graphene or vertically aligned carbon nanotubes) coated with combinations ofLi ion reactive layers (silicon, germanium, carbon). The anodes are similar incomposition but differ in microstructure. These differences allow for furtherexamination of the relationship between material structure, materialproperties, and anode performance. This research has already demonstratedthat highly structured and tunable composite anodes can be created throughvapor deposition techniques with stable performance and specific capacitybeyond state-of-the art graphite achieved. Further investigation of themechanisms that may lead to degradation of these systems are currently beingexplored to further enhance the anode stability.
]]>Shape preservingsilica magnesiothermic reduction makes use of gas-silica displacement chemistryto convert intricately shaped, hierarchically ordered, three-dimensional silicastructures into porous silicon replicas while maintaining complex features ofthe starting silica template down to ~15 nm. This technique has been usedto convert a number of starting silica templates into porous silicon replicasincluding diatom frustules, inverse opals, nanospheres, micropatternedstructures, etc., which exhibit enhanced surface area and porosity due to thenature of the silicon conversion chemistry.
Despite theprogress made in applying silica magnesiothermic reduction to a wide range ofsilica templates, understanding of the mechanisms enabling shape preservationis still poor. In particular, large compressive stresses (~2-5 GPa) areevolved in the products of silica magnesiothermic reduction due to largechanges in molar volume upon reaction (~20-60% depending upon silicapolymorph/crystallinity). Despite these stresses, geometric distortionbetween the silica templates and porous silicon replicas is only verymodest. This implies that a stress relaxation mechanism operatesconcurrently with the reaction, which enables the process to be shapepreserving. This investigation hopes to gain a better understanding ofthe nature of this stress relaxation mechanism. Silica wafers will bemagnesiothermically treated to produce thin product films on the surface whichwill be characterized using XRD (sin2ψ method)to quantify the compressive stress evolved in these product films. Annealingtreatments at the reaction temperature will then be applied to induce stressrelief in the product films. Microstructural changes in the product filmswill then be characterized to discern correlations between the microstructuralevolution of the product films and the rate of stress relief during annealing,revealing the nature of the stress relaxation mechanism operating during silicamagnesiothermic reduction. It is hoped that this work will provide abetter understanding of the silica magnesiothermic reduction process which canbe used to attain better replication of starting silica templates as thecomplexity of these templates increases.
]]>Title: Study of theStress Relaxation Mechanisms Enabling Shape Preserving Silica MagnesiothermicReduction
]]>Twelve speakers from around the world will participate inthe 2011 Materials and Sciences Engineering Symposium from on Feb. 24 in theGrand Ballroom Salon of the Georgia Tech Hotel and Conference Center. Theevent will kick off at 8 a.m. with a welcome from Georgia Tech PresidentG.P."Bud" Peterson on "the future for sustainability." The12 speakers, who will discuss their particular sub-material area ofexpertise, will be followed by a discussion and complimentary banquet. Seelinks below for agenda and more information.
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Abstract:
Quantitative relationships among processing parameters, microstructure,and material properties are of considerable interest in the context ofdevelopment of robust processing routes that optimize the required materialproperties. As a result, the scientific literature contains a large number ofexperimental and theoretical studies on microstructure-propertiesrelationships. Fracture sensitive mechanical properties such as ductility,ultimate tensile strength, fatigue life, and fracture toughness depend on theaverage microstructural parameters as well as the distributions ofmicrostructural parameters and their extrema.Development of quantitativerelationships between such material properties and microstructuraldistributions and extrema has received considerably less attention,particularly in the wrought metals and alloys. Accordingly, an importantobjective of this research is to perform a systematic investigation in thisdirection.
Thedependence of the fracture-sensitive mechanical properties on themicrostructural distributions and extrema often leads to substantialvariability in these properties: a set of specimens having the same averagechemistry, the same average processing history, and the same averagemicrostructural parameters such as volume fractions of different constituentscan exhibit substantially different material properties. The presentresearch (i) is concerned with highstrength (~ 1000 MPa) high martensite (>50%) dual phase steel where themartensite is a topologically continuous phase (matrix) containing a dispersionof islands of ferrite, and (ii) focuses on understanding the microstructural origins of the variability infracture sensitive mechanical properties, in particular variability in the roomtemperature uniaxial tensile ductility. The research involves quantitativemicrostructure characterization using stereology and digital image processingand quantitative fractography using scanning electron microscopy (SEM) andfracture profilometry. The analysis of the quantitative fractographic andmicrostructural data obtained in this research leads to useful guidelines forreducing the variability in the tensile ductility of the dual phase steel underinvestigation.
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In this research,first, a comprehensive understanding of the fundamental molecular mechanismswill be pursued by characterizing the membrane materials using moleculardynamics (MD). MD investigates the polymer materials at the atomic level, withthe aim to obtain an understanding of the molecular level reasons for thethermodynamic properties and transport mechanisms of these membranes. Anunderstanding of how the structure and size of the clusters affect theirstability and their dissolution mechanism is sought for the catalysts bystudying their quantum mechanical properties. The appropriate tool for this isdensity functional theory (DFT). Using the understanding obtained for themembrane and catalyst, an MD model of the three phase interface region will bedeveloped to understand how the various materials interact and affect eachother.
]]>Ultra-high temperature (i.e., > 2500°C)engineering applications present continued materials challenges. Refractorymetal/ceramic composites have great potential to satisfy the demands of extremeenvironments (e.g., the environment experienced in solid rocket motors uponignition), though general scalable processing techniques to fabricate complexshaped parts are lacking. The work embodied in this dissertation advancesscientific knowledge in the development of processing techniques to formcomplex, near net-shape, near net-dimension, near fully-dense refractorymetal/ceramic composites with controlled phase contents and microstructures.
Three research thrusts will be detailed in this presentation. First, theutilization of rapid prototyping techniques, such as computer numericalcontrolled machining and three dimensional printing, for the fabrication ofporous tungsten carbide preforms and their application with the DisplaciveCompensation of Porosity process (a solid-volume-increasing reactiveinfiltration technique) to produce tungsten/zirconium carbide-bearingcomposites is demonstrated. Second, carbon substrates and preforms have beenreactively converted to porous metal/metal carbide replicas via a novelgas-solid displacement reaction. Lastly, a reaction-based process forsynthesizing refractory metal/ceramic micro/nanocomposites will be discussed.These novel reaction processing techniques combined have the potential toproduce micro/nanostructured refractory metal/ceramic composite materials withtailorable microstructures for ultra-high temperature applications.
]]>Wednesday, December 8th, 2010 - 11 AM
]]>Abstract:
Boron carbide(B4C) is a non-oxide ceramic in the same class of nonmetallic hard materials assilicon carbide and diamond. The high hardness, high elastic modulus and lowdensity of B4C make it a nearly ideal material for personnel and vehiculararmor. B4C plates formed via hot-pressing are currently issued to U.S. soldiersand have exhibited excellent performance; however, hot-pressed articles containinherent processing defects and are limited to simple geometries such aslow-curvature plates.
Recent advances in the pressureless sintering of B4C haveproduced
theoretically- dense and complex-shape articles that alsoexhibit superior ballistic performance.
However, the cost of this material is currently high dueto the powder shape, size, and size distribution that are required, whichlimits the economic feasibility of producing such a product. Additionally, thelow fracture toughness of pure boron carbide may have resulted in historicallylower transition velocities (the projectile velocity range at which armorbegins to fail) than competing silicon carbide ceramics in high-velocitylong-rod tungsten penetrator tests. Lower fracture toughness also limitsmulti-hit pro- tection capability. Consequently, these requirements motivatedresearch into methods for improving the densification and fracture toughness ofinexpensive boron carbide composites that could result in the development of asuperior armor material that would also be cost-competitive with otherhigh-performance ceramics.
The primaryobjective of this research was to study the effect of titanium and car- bonadditives on the sintering and mechanical properties of inexpensive B4Cpowders.
The boron carbide powder examined in this study was asub-micron (0.6 μm median particle size) boron carbide powder produced by H.C.Starck GmbH via a jet milling process. A carbon source in the form of phenolicresin, and titanium additives in the form of 32 nm and 0.9 μm TiO2 powders wereselected. Parametric studies of sinter- ing behavior were performed viahigh-temperature dilatometry in order to measure the in-situ sample contractionand thereby measure the influence of the additives and their amounts on theoverall densification rate. Additionally, broad composition andsintering/post-HIPing studies followed by characterization and mechanicaltesting elucidated the effects of these additives on sample densification,microstructure de- velopment, and mechanical properties such as Vickershardness and microindentation fracture toughness.
Based upon thisresearch, a process has been developed for the sintering of boron carbide thatyielded end products with high relative densities (i.e., 100%, or theo- reticaldensity), microstructures with a fine (2-3
μm) grain size, and high Vickers microindentationhardness values. In addition to possessing these improved physical properties,the costs of producing this material were substantially lower (by a factor of 5or
more) than recently patented work on the pressurelesssintering and post- HIPing of phase-pure boron carbide powder. This recentlypatented work developed out of our laboratory utilized an optimized powderdistribution and yielded samples with high relative densities and high hardnessvalues.
The current work employed the use of titanium and carbonadditives in specific ratios to activate the sintering of boron carbide powderpossessing an approximately mono-modal particle size distri- bution. Uponheating to high temperatures, these additives produced fine-scale TiB2 andgraphite inclusions that served to hinder grain growth and substantiallyimprove overall sintered and post-HIPed densities when added in sufficientconcentrations.
The fine boron carbide grain size manifested as a resultof these second phase inclu- sions caused a substantial increase in hardness;the highest hardness specimen yielded a hardness value (2884.5 kg/mm^2)approaching that of phase-pure and theoretically- dense boron carbide (2939 kg/mm^2).
Additionally, the same high-hardness composi- tionexhibited a noticeably higher fracture toughness (3.04 MPa·m^1/2) compared tophase-pure boron carbide (2.42 MPa·m^1/2), representing a 25.6% improvement. Apotential consequence of this study would be the development of a superiorarmor material that is sufficiently affordable, allowing it to be incorporatedinto the general soldier's armor chassis.
]]>Synergistic Methods for the Production of High-Strengthand Low-Cost Boron Carbide
]]>Abstract: It is proposed tostudy the fragmentation and behavior of certain structural energetic materialsand how these processes contribute to their reactivity. The constitutiveproperties of aluminum based intermetallic forming systems will be studied toquantify the physics of the deformation and fragmentation processes and thesubsequent effect on reaction initiation.
Particular emphasis will be placed on the influence ofmicrostructure morphology and composition.
The proposed research will utilize a variety of experimentsincluding Hopkinson Bar impact and explosive fragmentation to understand theconstitutive and fragmentation behavior of various material systems. Theseexperiments will be utilized to inform and confirm a series of mesoscalesimulations that will directly investigate the impact of microstructuremorphology and composition on the formation of fragments and the reactivity ofthese systems.
The constitutive and fragmentation behavior is the key tothe application of structural energetic materials to safer and more effectivemunitions.
Using structural energetic materials will permit thecreation of more efficient and safer munitions.
]]>Hosted by:
Anselm and Carol Griffin & Bob and Sheila Snyder
Date: December 12th, 2010
Time: 11:30am - 3:30pm
Location: Hotel Midtown - 125 10th Street NE, Atlanta, GA -- MAP --
RSVP: http://www.mse.gatech.edu/news-and-events/2010-MSE-Chair-holiday-brunch-rsvp
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Abstract:
Small form-factor packages with high integration density aredriving the innovations in chip-to-package interconnections. Metallurgicalinterconnections have evolved from the conventional eutectic and lead-freesolders to fine pitch copper pillars with lead-free solder cap. However,scaling down the bump pitch below 50-80µm and increasing the interconnectdensity with this approach creates a challenge in terms of accurate solder masklithography and joint reliability with low stand-off heights. Going beyond thestate of the art flip-chip interconnection technology to achieve ultra-finebump pitch and high reliability requires a fundamentally- different approachtowards highly functional and integrated systems. This research demonstrates alow-profile copper-to-copper interconnect material and process approach withless than 20µm total height using adhesive bonding at lower temperature thanother state-of-the-art methods. The research focuses on: (1) exploring a novelsolution for ultra-fine pitch (< 30µm) interconnections, (2) advancedmaterials and assembly process for copper-to-copper interconnections, and (3)design, fabrication and characterization of test vehicles for reliability andfailure analysis of the interconnection.
This research represents the first demonstration ofultra-fine pitch Cu-to-Cu interconnection below 200°C using non-conductive film(NCF) as an adhesive to achieve bonding between silicon die and organicsubstrate. The fabrication process optimization and characterization of copperbumps, NCF and build-up substrate was performed as a part of the study. Thetest vehicles were studied for mechanical reliability performance underunbiased highly accelerated stress test (U-HAST), high temperature storage(HTS) and thermal shock test (TST). This robust interconnect scheme was alsoshown to perform well with different die sizes, die thicknesses and withembedded dies. A simple and reliable, low-cost and low-temperature direct Cu-Cubonding was demonstrated offering a potential solution for future flip chippackages as well as with chip-last embedded active devices in organicsubstrates.
]]>Time: 1:30 PM, Tuesday 8th November
Location: MaRC 351
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ABSTRACT
The process of gel spinning has been employed- because ofits utility in producing high strength, high modulus fibers of poly(vinylalcohol), PVA. Researchers have embeddedsingle walled carbon nanotubes (SWNTs) into the matrix of gel-spun PVA fibersfor the two-fold purpose of templating molecular chain extension and forbearing mechanical stress. Thedispersion and exfoliation of embedded SWNTs can influence the efficacy of loadtransfer. Molecular interactions betweencarbon nanotubes (CNTs), the matrix polymer, and the dispersing solvent areknown to influence interfacial adhesion and the distribution of CNTs throughoutthe polymer composite.
The structure-property relationships of stage-drawn PVAand SWNT composite fibers are described herein. The mechanical properties, thermal behaviors, and microstructures ofgel-spun fibers were characterized at several stages of heat drawing. Evidence of the molecular chain extension ofPVA has been supported by thermal analysis and IR spectroscopy. Structural deviations from the idealizedmicrostructure include lamellar crystals, solvated polymer, and themisalignment of polymer microphases and SWNTs.
Uniaxially aligned SWNTs were found to influence thealigning of electron donating and withdrawing moieties of PVA and DMSO. The aligning of PVA’s functional groups hasbeen attributed to non-covalent bonding, i.e. electronic field effects betweenSWNTs and PVA’s hydroxyl and carbonyl moieties. The sulfoxide moieties of DMSO imbibed in SWNT composite fiberspreferentially aligned normal to the fibers axis, however no preferentialorientation was observed among unfilled PVA fibers. Nearly 40 % of imbibed DMSO is influenced bythe orientation of embedded SWNTs.
Literature has reported ageing to have a positive affecton the drawability of PVA gels. Theageing of PVA/CNT gels in being carried out in the current study. The structure and properties of PVA/CNT fibersprocessed with varying gelation histories are under investigation.
]]>Date & Time: Thursday, November 18, 2010 at 9:00 AM
Location: MRDC I 4401
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Abstract
In this dissertation work, a constanttemperature embossing process was developed and investigated. By softening andcrystallizing a supercooled polymer at the same temperature, the embossing andsolidification stages can be carried out isothermally without thermal cycling.The new process was demonstrated for replicating rectangular trenches withdifferent aspect ratio for two different polymers PET and PEEK.The rawmaterials were characterized for their thermal and rheological properties todetermine the processing parameters. The polymers were also characterized by amodified tensile testing apparatus to determine the tensile properties of thefilm during embossing. The processing parameters including embossingtemperature, embossing pressure and embossing time were varied based on thematerial properties and optimized. A semi-empirical model was established tocorrelate the crystallizing kinetics of the materials to the change inrheological properties during embossing. The model was used as a tool topredict the rheological properties of the polymer at conditions whereexperimental determination is difficult.Finally, embossing simulations with thesemi-empirical rheological model were conducted to study the unique processdynamics of constant-temperature embossing and verify some experimentalfindings. Different cases of constant-temperature embossing involving low tohigh rates of crystallization were simulated and compared with the conventionalembossing process. Based on the experimental and simulation results, processingstrategies for constant-temperature embossing were devised.
]]>Abstract
This talk will provide an overview of our recent developments in bio-inspired nanomaterials for tissue regenerationand sensing. Bio-responsive nanomaterials are of growing importance with potential applications including drugdelivery, diagnostics and tissue engineering. Our recent simple conceptually novel approaches to real-timemonitoring of protease, lipase and kinase enzyme action using modular peptide functionalized NPs will bepresented.
The highly interdisciplinary field of Tissue Engineering (TE) can also benefi t from advances in the design ofbio-responsive nanomaterials. TE involves the development of artificial scaffold structures on which new cells areencouraged to grow. The ability to control topography and chemistry at the nanoscale offers exciting possibilitiesfor stimulating growth of new tissue through the development of novel nanostructured scaffolds that mimic thenanostructure of the tissues in the body. Recent developments in this context will be discussed.
About Dr. Stevens
Professor Molly Stevens is Research Director for Biomedical Material Sciences in the Institute of Biomedical Engineering atImperial College London. She joined Imperial in 2004 from Postdoctoral training with Professor Robert Langer at MIT. Shegraduated from Bath University with a first-class honours degree in Pharmaceutical Sciences and was awarded a PhD inbiophysical investigations from the University of Nottingham (2000).
Abstract:
A disagreeable side effect of longer lifespans is the failure of one part of the body — the knees, for example — before the body as a whole is ready to surrender. The search for replacement body parts has fuelled the highly interdisciplinary field of tissue engineering and regenerative medicine. In view of the challenges in this field, one must consider that the human embryo in its first eight weeks of life undergoes an extraordinary transformation from a single cell to a 3-cm-long fetus with a beating heart, gut, nervous system, and limbs with fingers and toes. This progression involves massive growth, physical folds and twists, and myriad cellular and molecular events of breathtaking complexity; yet it is the ultimate goal of this field of tissue engineering to recreate some of these processes in microcosm, to replace and regenerate lost tissue. At last the field has entered a period of fruition, and seems set to realize its potential to treat a multitude of debilitating and deadly conditions such as myocardial infarction, spinal injury, osteoarthritis, osteoporosis, diabetes, liver cirrhosis and retinopathy.
This talk will outline progresses in the field and how we are developing new bioactive materials that can be implanted into the body and provide the right environmental cues that promote tissue regeneration of large volumes of highly organized tissue such as bone. Controlling the properties of these polymer and inorganic materials right down at the nanoscale is crucial for the optimal tissue regeneration as will be discussed.
About Dr. Stevens
Professor Molly Stevens is Research Director for Biomedical Material Sciences in the Institute of Biomedical Engineering at Imperial College London. She joined Imperial in 2004 from Postdoctoral training with Professor Robert Langer at MIT. She graduated from Bath University with a first-class honours degree in Pharmaceutical Sciences and was awarded a PhD in biophysical investigations from the University of Nottingham (2000).
Abstract:
System integration and miniaturization demands aredriving integrated thin film capacitor technologies with ultra-high capacitancedensities for power supply integrity and efficient power management. Theemerging need for voltage conversion and noise-free power supply in bioelectronics and portable consumer productsrequire ultra high-density capacitance of above 100 μF/cm2 with BDV 16-32 V,independent capacitor array terminals and non-polar dielectrics. The aim ofthis research,therefore, is to explore a new silicon- compatible thin filmnanoelectrode capacitor technology that can meet all these demands. Thenanoelectrode capacitor paradigm has two unique advances. The first advance isto achieve ultra-high surface area thin film electrodes by sintering metallicparticles directly on a silicon substrate at CMOS- compatible temperatures. Thesecond advance of this study is to conformally- deposit medium permittivitydielectrics over such particulate nanoelectrodes using Atomic Layer Deposition(ALD) process.
Thin film copper particle nanoelectrode with open-porousstructure was achieved by choosing a suitable phosphate-ester dispersant,solvent and a sacrificial polymer for partial sintering of copper particles toprovide a continuous high surface area electrode. Capacitors with conformal ALDalumina as the dielectric and Polyethylene dioxythiophene (PEDT) as the topelectrode showed 30X enhancement in capacitance density for a 20-30 microncopper particulate bottom electrode and 150X enhancement of capacitance densityfor a 75 micron electrode. These samples were tested for their mechanical andelectrical properties by using characterization techniques such as SEM, EDS,I-V and C-V plots. A capacitance densityof 30 μF/cm2 was demonstrated using thisapproach with BDVs of above 30 V.
The technology is extensible to much higher capacitancedensities with better porosity control, reduction in particle size and higherpermittivity dielectrics.
]]>Time: 1:15 PM, Tuesday 9th November --Location: MaRC 351
Thesis Title: High-density capacitor array fabrication onsilicon substrates
]]>Abstract:
Oxide nanowire arrays are playing an important role inenergy sciences nowadays, including energy harvesting, energy storage, andpower management. By utilizing a wet chemical growth method, we demonstratedthe capabilities of synthesizing density controlled vertical ZnO nanowirearrays on a general substrate, optimizing the aspect ratio of the vertical ZnOnanowire arrays guided by a statistical method, epitaxially growing patternedvertical ZnO nanowire arrays on inorganic substrates, epitaxially growingpatterned horizontal ZnO nanowire arrays on non-polar ZnO substrates, and thelift-off of the horizontal ZnO nanowire arrays onto general flexiblesubstrates. In addition, single crystalline
PbZrxTi1-xO3 (PZT) nanowire arrays were epitaxially grownon conductive and nonconductive substrates by hydrothermal decomposition.
Beyond that, based on the as-synthesized ZnO nanowirearrays, we demonstrated multilayered three dimensionally integrated directcurrent and alternating current nanogenerators. By integrating a ZnO nanowirebased nanogenerator with a ZnO nanowire based nanosensor, we demonstratedsolely ZnO nanowire based self-powered nanosystems. Also, utilizing acommercial full-wave bridge rectifier, we rectified the alternating outputcharges of the nanogenerator based on PZT nanowire arrays, and the rectifiedcharges were stored into capacitors, which were later discharged to light up alaser diode (LD). In addition, blue/near-ultraviolet (UV) light emitting diodes(LED) composed of ordered ZnO nanowire arrays on p-GaN wafers were presented.
]]>Host: Edwards, Washington
]]>Abstract:
Today, ethanol, as well as other biofuels, has beenincreasingly gaining popularity as a major alternative liquid fuel to replaceconventional gasoline for road transportation. One of the key challenges forthe future use of bioethanol is to increase its availability in the market viaan efficient and economic way. However, one major concern in using the existinggas-pipelines to transport fuel-grade ethanol or blended fuel is the potentialcorrosion and stress corrosion cracking (SCC) susceptibility of carbon steelpipelines in these environments. In this talk, both phenomenological andmechanistic investigations have been carried out in order to address thepossible degradation phenomena of X-65 pipeline carbon steel in simulatedfuel-grade ethanol (SFGE). Firstly, the susceptibilities of stress corrosioncracking of this steel in SFGE were studied. Ethanol chemistry of SFGE wasshown to have great impact on the stress corrosion crack initiation/propagationand the corrosion mode transition. Inclusions in the steel can increase localplastic strain and act as crack initiation sites. Secondly, the anodic behaviorof carbon steel electrode was investigated in detail under different ethanolchemistry conditions. General corrosion and pitting susceptibility underunstressed condition were found to be sensitive to the ethanol chemistry.
Low tendency to passivate and the sensitivity to ethanolchemistry are the major reasons which drive corrosion process in this system.Oxygen plays a critical role in controlling the passivity of carbon steel in ethanol.
Thirdly, the detailed study was carried out to understandthe SCC mechanism of carbon steel in SFGE. A film related anodic dissolutionprocess was identified to be a major driving force during the crackpropagation. Fourthly, more detailed electrochemical impedance spectroscopy(EIS) studies using phase angle analysis and transmission line simulationreveal a clearer physical picture of the stress corrosion cracking process inthis environment. Fifthly, the cathodic reactions of carbon steel in SFGE werealso investigated to understand the oxygen and hydrogen reactions. Hydrogenuptake into the pipeline steel and the conditions of the fractures related tohydrogen embrittlement were identified and studied.
]]>CHARACTERIZATION OF OPEN CELLED METALLIC FOAM
Abstract:
Open cell metal foams are a type of engineered materialcan be characterized by high porosity, high strength to weight ratio, tortuousflow paths and high surface area to volume ratio. It is the structure thatgives the metal foams the characteristics that make them well suited for manyapplication including heat exchangers. In this work, the structure of opencelled metal foams is quantitatively characterized using an image analysisbased method in order to predict the evaporative heat transfer of the metalfoam using the fluid permeability. Several image processing algorithms weredeveloped to quantitatively characterize the porosity, surface area per unitvolume and the tortousity of metal foams from digital images of the crosssections of the material, and an expression was used to calculate the fluidpermeability. An algorithm was developed to partion the pore space in thedigital images so that individual cells within the structure could also be quantitativelycharacterized. Tools were also developedto predict the structure of open celled foam processed using the sacrificialtemplate method by digitally constructing microstructures based the particlepacking of the sacrificial templating material.
]]>To celebrate the exciting mergerof MSE and PFE under the School of Materials Science and Engineering, we’d liketo invite you to our Fall Social on Thurs., September 2 from
11 am – 1 pm in the Burdell Plaza,outside of the J. Erskine Love Building. After a brief welcome and mergerannouncements, students will enjoy lunch and the opportunity to meet and minglewith their classmates. Representatives from our student organizationswill be on hand to recruit new members.
We are setting up an RSVP systemand will email you shortly with instructions. Participants will need toRSVP!! Upon arriving at the Social, those who have signed up will receivetickets, redeemable for meals and door prizes. In the event of inclementweather, the Social will be held on the second, and third floor atriums of theLove Building.
We look forward to officiallywelcoming you back to campus and to joining our degree programs into thelargest and most diverse, nationally ranked MSE School in the country.
In order to allow for adequatefood planning, all attendees MUST RSVP by Monday, August 30. Onthe day of the social, you will be issued a ticket, redeemable for lunch andfor door prizes. If you will join us, please let us know via this website:
https://www2.mse.gatech.edu/fall_social/rsvp.asp
]]>Hosts: Nelson & Calhoun
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