Host: Tim Mueller
I will make the somewhat bold claim that over the past 10 years, a new computational task has been defined and solved: this is the analytic fitting of the Born-Oppenheimer potential energy surface as a function of nuclear coordinates under the assumption of medium-range interactions, out to 5-10 Å. The resulting potentials are reactive, many-body, reach accuracies of a few meV/atom, with costs that are on the order of 1-10 ms/atom. This leaves the following challenges for ML potentials: treatment of long range interactions in a nontrivial way, e.g. consistency of treatment of open and periodic boundary conditions, environment dependent multipolar description, excited states (adiabatic surfaces), magnetism. We also still need a “shakedown” of the details among various approaches (neural networks, kernels, polynomials), and more standard protocols of putting together the training data. Tradeoffs between system- (or even project-) specific datasets and potentials vs. more general potentials will be ongoing. Further afield, another interesting question is what part of this technology can be reused to fit analytic surrogate models of *electronic* functions and functionals, such as reduced Hamiltonians, Green’s Functions, density matrices etc, not to mention many body wave functions. There have been forays in this direction already.
Meeting ID: 982 0915 3548
Host: Tim Weihs
In-Vivo Performance of Bioabsorbable BioMg 250 Implants
Abstract: The invention and alloy design principles of a bioabsorbable Mg alloy implant will be described. The alloy was designed to utilize addition elements odd in atomic size and electronegativity from the Mg atom, yet osteo-productive and as nutrients to the body. This alloy performed well in early toxicity and in vitro corrosion testing. Subsequent in vivo campaigns in rabbit femur and canine mandible models will be described. Micro CT and histology evaluations of these experiments will be presented, confirming promise in comparison to commercial Titanium and Polymer implants.
Bio: Dr. Decker is co-founder and Chief Technology Officer of Thixomat and NanoMAG. He is co-inventor of BioMg 250. Earlier in his career, he developed Ni Base Superalloys and the highest strength steel alloys, Maraging Steels. In Thixomat, he led the international commercialization of Thixomolding to 550 machines in 13 countries. He serves as Adjunct Professor of Materials Science and Engineering at The University of Michigan and on the Board of Managers of QuesTek International, a leader in ICME. Ray is a member of the National Academy of Engineering.
University of Virginia
Host: Todd Hufnagel
Operando synchrotron x-ray studies of metal additive manufacturing
Metal additive manufacturing (AM) refers to a group of disruptive technologies that build metallic three-dimensional objects by adding feedstock materials layer-wise based on computer models. AM not only unleashes the design freedom of engineers by allowing the build of geometrically complex parts but also opens up tremendous opportunities for material scientists to synthesize and process novel materials with phases and microstructures far-from-equilibrium. While AM holds the promise to completely revolutionize the industry, building defect-free metal products with precise control of material microstructures and part performance remains challenging. Indeed, substantial fundamental issues exist in metal AM which need to be addressed before the technology can reach its full potential.
At the Advanced Photon Source (APS), we have been applying operando high-speed x-ray imaging and diffraction techniques to probe a variety of metal AM processes. The superior penetration power of high-energy x-rays and the extremely high fluxes afforded by the 3rd-generation synchrotron facility allow the characterization of dynamic structural evolution in bulk metallic materials with unprecedented spatial and temporal resolutions. Many highly transient phenomena that take place during the energy-matter interaction in metal AM processes were investigated, and the mechanisms responsible for different types of defects were identified.
In the presentation, I will give a brief overview of the operando synchrotron x-ray studies of various metal AM processes (i.g. laser powder bed fusion, directed energy deposition, and binder jetting), performed at the APS in the last few years. The new insights into metal AM gained from these operando synchrotron experiments will be highlighted. Furthermore, I will elucidate how the direct observations enabled by x-ray imaging helped us understand the mechanisms of defect formation and elimination, calibrate and validate numerical models, and improve the build reliability and repeatability.
Host: Jim Spicer
The feasibility of an interstellar mission hinges on the ability to achieve a high escape velocity. 20 AU/yr would be required to reach 500 AU approximately 25 years after launch. Such speeds may be possible by performing a powered gravity assist around the Sun. We propose unconventional approach that simultaneously addresses the need for high specific impulse and close proximity to the Sun–convert the heat of the Sun into usable thrust by passing a propellant through the heat shield. Factoring in both improvements, the escape velocity is predicted to more than double relative to a conventional heat shield with a hydrazine kick stage.
To demonstrate that this technology is compatible with state-of-the-art heat shields, we designed and fabricated a 20 x 20 cm prototype on an additive manufacturing process. It was coated with a yttria-stabilized zirconia coating that can survive 2863 K (versus 2345 K for alumina). The system was tested in a custom-built outdoor test facility. At an illumination equivalent to 20 Suns, the white coating remained below 130°C. Helium propellant flowing at a rate of 1.2 g/s further reduced the temperature to 66°C. A specific impulse on the order of 200 s at 243°C was consistent with expectations. Agreement between experiment and model implies that predictions at higher temperatures hold true and that the coating could survive a perihelion of 2.5 solar radii with a hydrogen flow rate of 15 g/m2-s.
Host: Howard Katz
Adapting Electrochemical Sensing to Population-Scale Monitoring of SARS-CoV-2 Infection Spread
SARS-CoV-2 has infected over 22 million people globally, leading to ~800 thousand deaths in just ten months. However, significant uncertainty continues regarding the prevalence of asymptomatic and mild cases of COVID-19, the disease caused by SARS-CoV-2, as well as the magnitude, effectiveness, and duration of antibody responses. Gaining a better understanding of population immunity is critical to improving predictive models of infection spread and safely reopening economies worldwide. However, to fill knowledge gaps in these areas requires population-scale testing using low-cost, non-invasive, and highly specific and sensitive assays that can be deployed broadly and serially to characterize antibody responses to SARS-CoV-2. Benchmark detection approaches are based on sandwich immunoassays relying on optical readouts of fluorescence emission or color change to report antibody levels. These technologies can be costly, often require centralized facilities with trained personnel, and are, therefore, not amenable to at-home testing. More affordable technologies, such as lateral flow assays, can be inaccurate or prone to user misinterpretation. Motivated to circumvent such barriers, the Arroyo, Spangler and Ha labs have undertaken a journey to develop an at-home electrochemical assay. This presentation reports the results of our initial, 3-month effort to produce a portable immunoassay.
Host: Jonah Erlebacher
Conventional approaches to materials manufacturing have often relied on processing within a temperature range that results in liquid phase formation of some of the constituents. These methods are often limited by the equilibrium phase formation states available from the melt. In this work we will present findings on a recently-developed processing approach that enables complex, unique microstructural evolution (often to pervasively metastable states) while remaining in the solid phase state. Specifically, the SHear Assisted Processing and Extrusion (ShAPE) method will be highlighted via a number of vignettes from various classes of structural materials. Novel microstructural pathways, textural formation and mechanical properties will be discussed. These results point to the ability to design and engineering novel materials with unprecedented properties and performance.
Bio: Suveen Mathaudhu is currently the Chair of UC Riverside’s Materials Science and Engineering Program, and he studies the underpinning mechanisms that will make metallic materials and composites lighter and stronger. His research interests encompass all aspects of the fundamental processing-microstructure-property-performance relationships in metallic and composite materials. Mathaudhu is a Fellow of ASM International, the 2015 AAES Norm Augustine Award winner for Outstanding Achievement in Engineering Communication, and a 2019 NSF PECASE Awardee. He is active in several technical societies, and also an expert on the science of superheroes as depicted in comic books and their associated movies. Mathaudhu received his BS from Walla Walla University and PhD from Texas A&M University, both in Mechanical Engineering.
Host: Tim Mueller
The development of sustainable energy systems puts renewed focus on catalytic
processes for energy conversion. We will need to find new catalysts for a number of
processes if we are to successfully synthesize fuels and chemicals from solar or wind
electricity. Insight into the way the catalysts work at the molecular level may prove
essential to speed up the discovery process. The lecture will outline a theory of
heterogeneous catalysis that allows a detailed understanding of elementary chemical
processes at transition metal surfaces and singles out the most important parameters
determining catalytic activity and selectivity. The insight can be used to define catalyst
design rules and examples of their use will be given.
Host: Mingwei Chen
Two-dimensional materials (2DM) are atomically thin materials with extraordinary mechanical, electrical, and chemical properties that make them promising for next generation technologies in sensing (e.g. internet of things), flexible and transparent electronics and optoelectronics (e.g. biological interfaces), energy conversion (e.g. selective catalysis), and membrane technology (e.g. DNA sequencing). The realization of new technologies based on 2DM requires both fundamental research on the materials science of 2DM, as well as research that aims to bridge the gap between materials science and the engineering of real devices and systems. In this talk, I will describe my recent work on understanding the fundamental physics of strain, defects, and interfaces in 2DM and leveraging that understanding to control material behavior. First, I will discuss my work on controlling the mechanical state of 2DM at the nanometer-scale using atomic force microscope (AFM)-based techniques that I developed.[1-2] The extreme mechanical flexibility of 2DM is one of their most exciting attributes, but this flexibility can lead to the unwanted formation of bubbles or wrinkles (similar to a film of plastic wrap) which obscure observations of 2DM intrinsic properties. I addressed this ubiquitous problem by using an AFM to controllably manipulate 2DM layers in order to create flat and homogeneous 2DM interfaces, which enables precise characterization of 2DM intrinsic properties. In addition to removing unwanted mechanical perturbations, I invented a novel and general approach for encoding strain into 2DM with nanometer-scale precision. Using this technique, I was able to write strain gradients into a 2DM semiconductor, resulting in deterministic placement of quantum emitters. Quantum emitters are a promising technology for realizing secure quantum communications and 2DM provide potential advantages over alternative materials. Next, I will discuss my work on directly correlating nanometer-scale material defects with properties that govern optoelectronic and electronic device behavior, such as light emission and electrical conductivity. Using techniques that I developed, we were able to demonstrate a pronounced inverse relationship between photoluminescence intensity and defect density. I will also present a model that agrees well with the data and provides a guideline for further optimization of material and device behavior. Finally, I will discuss our recent investigations of the interfaces between 2DM layers, with a particular focus on the relative twist angle between layers. I will present experimental evidence of atomic reconstruction at the interface between semiconducting 2DM layers, which has significant implications for the behavior of 2DM heterostructure devices.
Host: Todd Hufnagel
Abstract: Advanced materials are broadly defined as innovative materials that have atypical sizes, microstructures, and responses. These atypical characteristics enable major, previously impossible technological breakthroughs, yet many advanced materials owe their desirable properties to complex underlying micromechanics including twinning, detwinning, and martensitic phase transformations. Establishing the relationships between these local micromechanics and macroscopic material behavior is critical to accelerating the implementation of advanced materials. Toward these goals, we utilize modern 3D X-ray diffraction techniques that offer the capability to measure the deformation and microstructure evolution inside bulk materials, in situ, and across nine orders of magnitude in length scales (nm to mm). Quantities of measure include the 3D microstructure “map” and spatially-resolved crystallographic orientation, elastic strain tensor, and phase fraction. These techniques can be used to simultaneously measure local microstructure events and the consequent macroscopic response, resulting in a tool uniquely suited for linking local micromechanics to material behavior. These capabilities will be illustrated using a number of research examples involving twinning and phase-transforming materials, using nickel-titanium shape memory alloys as a model material system. Ongoing and future work will also be discussed, including the development of a first-of-its kind laboratory scale instrument to conduct 3D X-ray diffraction experiments in-house.
Host: Jim Spicer
Carbon and graphite materials play a significant role in various nuclear energy reactor designs for generation of clean energy and in nuclear applications for space exploration. This presentation will introduce the unique properties of carbon and graphite materials that are essential for these applications and will outline several current research activities within the Carbon and Composites Group at ORNL. Emphasis will be given to the graphite-molten salt interaction studies as part of the Molten Salt Reactor Campaign. A brief overview of the various opportunities for students to become involved with research projects at ORNL will be presented.
Nidia C. Gallego is the Group Leader of the Carbon Materials Technology Group within the Materials Science and Technology Division at the Oak Ridge National Laboratory (ORNL). Her research interests include: thermal physical properties of carbon materials; development and characterization of porous carbon materials for gas separation and energy storage applications, low-cost carbon fibers; high-performance carbon fibers and graphite foams for thermal management applications; and the effects of neutron damage on the structure and properties of carbon materials; Dr. Gallego is the author of over 50 publications on the subject of high-performance carbon fibers, graphite foams for thermal management, nanoporous carbons for hydrogen storage, and effect of neutron damage on graphite foams. She is an active member of the American Carbon Society and has served on the Advisory Board since July 2010. She has organized several workshops on behalf of the American Carbon Society, and served on the organizing and technical committees of the International Carbon Conferences. In 2009 she received the Outstanding Mentor Award from the US DOE Office of Science. In 2011 Dr. Gallego was a recipient of a Fulbright Scholar Grant that allow her to be a visiting scholar for two months at the Universidad del Valle in Colombia. She is a member of the team that received the 2012 UT-Battelle Engineering Research & Development Award. She is an active member of the Hispanic Latino American Committee and the Committee for Women at ORNL.