Symposium Organizers
Christian Mailhiot Lawrence Livermore National Laboratory
Premkumar B. Saganti Prairie View A&M University
Daryush Ila Alabama A&M University
II1: Theory & Modeling (High Performance Simulation)
Session Chairs
Christian Mailhiot
Premkumar Saganti
Thursday PM, April 20, 2006
Room 2022 (Moscone West)
9:00 AM - **II1.1
Radiation Shielding Analysis for Various Materials in the Extreme Jovian Environment.
William Atwell 1
1 NASA Systems, The Boeing Company, Houston, Texas, United States
Show AbstractEarlier particle experiments in the 1970s on Pioneer-10 and -11 and Voyager-1 and -2 provided Jupiter flyby particle data, which were used by Divine and Garrett to develop the first Jupiter trapped radiation environment model. This model was used to establish a baseline radiation effects design limit for the Galileo onboard electronics. Recently, Garrett et al. have developed an updated Galileo Interim Radiation Environment (GIRE) model based on Galileo electron data. In this paper, the GIRE model was utilized to generate particle spectra as a function of Rj (Rj = radius of Jupiter = ~71,400 km). Using these spectra and a high-energy particle transport code, radiation exposures and dose effects for a variety of shielding materials and thicknesses are presented. In addition, Jun, et al., have developed a heavy ion trapped particle model based on the heavy ions of C, O, and S from the Galileo Heavy Ion Counter (HIC) experiment in the radial range from 2.5Rj to greater than 30Rj, and a discussion of these data is presented.
9:30 AM - II1.2
Dynamical Fracture Instabilities Due to Local Hyperelasticity at Crack Tips.
Markus Buehler 1 , Huajian Gao 2
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Max Planck Institute for Metals Research, Stuttgart Germany
Show Abstract9:45 AM - II1.3
Relationship Between Energy Profile and Structural Modification in Polyethyleneterphthalate Irradiated by Heavy MeV Ions.
Virendra Singh 1 , Amita Chandra 1 2 , T Singh 1 , Alok Srivastava 1
1 Chemistry, Panjab University Chandigarh, Chandigarh India, 2 Physics & Astrophysics, University of Delhi, New Delhi India
Show Abstract10:00 AM - II1.4
Molecular Modeling of High-Temperature Oxidation-Resistant Nanocoatings on Ni-Cr-Fe Alloys.
Haiying Zhang 1 , Susan Kerber 2 , Hugo Lopez 1
1 Materials Department, University of Wisconsin - Milwaukee, Milwaukee, Wisconsin, United States, 2 , Material Interface, Inc., Sussex, Wisconsin, United States
Show Abstract10:15 AM - II1.5
Atomistic Studies of Plastic Deformation and Dissipation in Crystalline HMX.
Eugenio Jaramillo 1 , Thomas Sewell 1 , Alejandro Strachan 2
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Purdue University, West Lafayette, Indiana, United States
Show AbstractWe are using large scale molecular dynamics simulations of crystalline octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) to better understand the dominant fundamental mechanisms of inelastic deformation and other dissipative processes in anisotropic organic molecular crystals. A fully flexible force field (Smith, G. D. and Bharadwaj, R. K.; J. Phys. Chem. B 1999, 103, 3570) used in numerous preceding studies is used without modification in the present work. Our results, based on the results of simulations containing 25,000-250,000 molecules, indicate a large degree of directional anisotropy in response to compression, for both quasi-static and shock loading. Plastic deformation is observed for some loading directions whereas solid-solid phase transitions are observed for others. The emphasis of the present talk will be identifying and characterizing detailed molecular mechanisms and rate dependencies in those cases for which dislocation-induced plasticity occurs.
10:45 AM - II1.7
Modeling of Serviceable Fracture Conditions of the Fuel Elements of High-temperature Gas Reactors (HTGR).
Anatoly Lanin 1 , Ivan Fedik 1
1 Agency on Atomic Energy, Research institute "LUCH", Podolsk, Moscow, Russian Federation
Show AbstractEffect of thermal elastic and residual stresses on function ability of fuel elements without coating from ZrC+UC, NbC +UC is analyzed on the basis of fracture mechanics. The fuel elements are maintained over the range temperatures up to 3300 K, at an intensive heat rate 20-40 KW/CM<2>, dynamic loads and the neutron flux 10<15> - 10<16> C<-1>CM<-2>. Simultaneous origination of thermal stresses owing to the temperature difference on cross-section of the fuel element and residual stresses of two modes: due to the non-uniform radiation swelling and due to a relaxation of the thermal elastic stresses has been revealed by calculations and modeling experiments. These stresses effect on the fracture peculiarities depending on a temperature level of the fuel element, densities of a heat flow and a radiation dose on different sections of the fuel assembly.Modeling experiments are carried out with use of electron-beam and induction installations. The level of residual stresses is measured by X-ray sin2 ψ method on the model and irradiated specimens. Engineering industry of nuclear technology. Editor E. O. Adamov , "Engineering industry", 2005, chapter 6.2.4" Nuclear rocket engines , pp .521-538. Lanin A.G., Deryavko I.I.. Influence of residual stresses on thermal stress resistance of refractory ceramics // J. Eur. Ceram.Sos.V.20, 2000, pp. 209-213Derjavko I.I., Egorov V.S., Lanin A.G., etc. X-Ray examination of the residual macrostresses in the the carbide rod fuel elements.. Bulletin of Scientific Nuclear Center, Kazakhstan « the Nuclear physics and a radiative Physical science» ;Issue, 2001, pp.. 95-98
11:30 AM - II1.8
Kinetics of the Nucleation and Growth of Helium Bubbles in bcc Iron and Ferritic Steels.
Chaitanya Deo 1 , Srinivasan Srivilliputhur 1 , Michael Baskes 1 , Stuart Maloy 1 , Michael James 2 , Maria Okuniewski 3 , James Stubbins 3
1 MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 D-5, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Department of Nuclear Engineering, University of Illinois, Urbana Champaign, Champaign, Illinois, United States
Show AbstractLarge quantities of helium and hydrogen are produced due to spallation and transmutation in structural materials in fusion and accelerator driven reactors.The effect of He on the accumulation of defects and defect clusters and the influence of the resulting microstructure on physical and mechanical properties has been the focus of a large number of experimental and modeling studies over the past twenty years. The present work is aimed at quantifying these effects in ways that were not possible in earlier studies. This is accomplished through systematic and coordinated computational modeling and experiments. The modeling approach employs both molecular dynamics and kinetic Monte Carlo simulations to study the dynamic evolution of He and defect clusters in bcc iron and ferritic steels over relevant time scales. We study the mechanisms by which helium atoms migrate and interact with other defects and investigate the effect of these mechanisms on the nucleation of embryonic gas bubbles. The long time evolution of the extrinsic gas atoms and their accumulation at vacancies is studied using a kinetic Monte Carlo algorithm that is parameterized by the migration energies of the point defect entities. The migration of gas atoms, clustering with vacancies and gas-gas clustering as well as dissociation of gas atoms from clusters are mechanisms that are considered in the model. First order reaction kinetics are observed when gas clusters with vacancies. If gas-gas clustering is allowed, mixed order diffusion limited kinetics are observed. When dissociation of gas from clusters is allowed, gas-vacancy clusters survive to steady state while gas-gas clusters dissolve. The simulations yield cluster size distributions and reaction rate constants that can be used to quantify microstructural evolution of the irradiated metal.
11:45 AM - II1.9
Ion Beam Shaping of Nanometals: Process Modeling and Atomistic Simulations of Extreme Conditions
Karl-Heinz Heinig 1 , Arjen Vredenberg 2 , Toulemonde Marcel 3 , Kai Nordlund 4
1 Inst. of ion beam physics and materials research, Research Center Rossendorf, DRESDEN Germany, 2 Debye Institute, Utrecht University, UTRECHT Netherlands, 3 , Laboratoire CIRIL-GANIL, CAEN France, 4 Accelerator Laboratory, University of Helsinki, HELSINKI Finland
Show AbstractRecently, a novel type of ion-beam induced deformation of metal nano-objects has been found. Under heavy ion irradiation, Au nanospheres in a silica matrix first elongate into rods. At higher fluences they combine into nanowires that continue to grow during irradiation. Such anisotropically shaped metal nanoparticles may have great potential in a wide range of fields. For example, nanorods exhibit a split plasmon resonance, with one of the bands shifting into the infrared. Arrays of such particles have a great potential as nanophotonic guides in the (infra)red, an important telecom wavelength regime, but outside the range of plasmon resonances of spherical metal particles.Here, we present a model and atomistic computer simulations of this ion beam shaping. The experimental lower threshold for ion beam shaping of 6 keV/nm ion energy deposition along the ion track coincides with the theoretically required energy for melting of SiO_2 in the ion track of a few nanometer diameter. Heating occurs on a timescale of a few tens of fs. Thus, temperature gradients of several billion Kelvin per cm can be reached. The Au nanosphere experiences such an extreme environment if it is touched by an ion track. These extreme conditions are similar to femtosecond laser processing of Au layers [1] wherefrozen nanojets have been observed. Laser-induced nanojet formation and ion beam shaping have obviously the same driving force: Based on atomistic simulations we prove that thermocapillarity drives material of a Au nanosphere, which is touched by an ion track, from the hot equator to the colder pole regions.(Thermocapillarity is the driving force for the well-known Marangoni effect). Additionally, the transiently extreme high temperature in the molten SiO_2 ion track dissolves Au, which diffuses fast and precipitates during cooling into tiny Au clusters. Superposition of tracks leads to a highly anisotropic “track diffusion” transport of Au from short nanorods to longer ones, which can be considered as a special case of Ostwald ripening.[1] F. Korte, J. Koch, and B.N. Chichkov, Appl. Phys. A 79, 879–881 (2004)
12:00 PM - II1.10
Experimental and ab-initio Investigations of a New Hard Material : osmium diboride.
Mohamed Hebbache 1 , Dragana Zivkovic 2 , L. Stuparevic 2 , Mabrouk Zemzemi 1
1 Materiaux et Phenomenes Quantiques, University of Paris 7, Paris France, 2 Department of Metallurgy, University of Belgrade, Bor
Show AbstractSuperhard materials have many industrial applications wherever resistance to abrasion and wear are important. The synthesis of new superhard materials is one of the great challenges to scientists. Up to date, light atoms like carbon, boron and nitrogen are considered as the best candidates to form superhard materials. Recently, it has been found that osmium, which is the haviest elemental crystal, is less compressible than diamond [1]. Low compressibility materials are often superhard. Consequently, there is an increased interest in this transition metal and its compounds. Several experimental and theoretical works have been recently devoted to osmium. For instance, it has been predicted that osmium could undergo phase transitions at very high pressures [2-3]. As for numerous transition metal carbides, nitrides and borides, it is expected that binary compounds of osmium with light elements could also be superhard. To our best knowledge, osmium nitride does not exist in crystalline form while osmium carbide OsC is either metastable or has a narrow temperature-stability range [4]. On contrary, osmium borides exist [5-7]. Nothing is known about their physical properties. The main reason for such data lack is that very high temperatures, larger than 1800 °C, are required to synthesize these materials. Moreover, osmium still has bad press, due to the formation of the tetroxide OsO_4 which boils at 130 °C and which is extremely toxic. We recently overcame these difficulties and confirmed the existence of two hexagonal phases, OsB_1.1, Os_2B_3 and an orthorhombic phase, OsB_2 [8]. Our microhardness measurements show that the synthesized OsB_2 is extremely hard [8] (see also Ref.[9]). In addition, first-principles calculations have been conducted to investigate its physical properties [10]. It is shown that OsB_2 is also a low compressibility material. OsB_2 can be used in applications like hard coating.References :[1] H. Cynn, J. E. Klepeis, C. S. Yoo and D. A. Young, Phys. Rev. Lett. 88, 135701 (2002). [2] F. Occelli, D. L. Farber, J. Badro, C. M. Aracne, D. M. David and M. Hanfland, Phy. Rev. Lett. 93, 095502 (2004).[3] M. Hebbache and M. Zemzemi, Phys. Rev. B 70, 224107 (2004).[4] C. P. Kempter, J. Chem. Phys. 41, 1515 (1964).[5] J. H. Buddery and A. J. E. Welch, Nature (London) 167, 362 (1951). [6] B. Aronsson, E. Stenberg and J. Aselius, Nature (London) 195, 377 (1962); B. Aronsson, Acta Chem. Scand. 17, 2036 (1963).[7] R. B., Jr., Roof and C. P. Kempter, J. Chem. Phys. 37, 1473 (1962).[8] L. Stuparevic and D. Zivkovic, J. Therm. Analys. Calor. 76, 975 (2004).[9] R. B. Kaner, J. J. Gilman and S. H. Tolbert, Science 308, 1268 (2005) and references therein.[10] M. Hebbache, L. Stuparevic and D. Zivkovic (submitted).
12:15 PM - **II1.11
Radiation Risk Mitigation with Material Shielding Strategies for Deep-Space Human Explorations.
Francis Cucinotta 1
1 Space & Life Sciences Directorate, NASA - Johnson Space Center, Houston, Texas, United States
Show AbstractUnavailable at time of submission.
II2: Synthesis & Growth
Session Chairs
Daryush ILA
Robert Zimmerman
Thursday PM, April 20, 2006
Room 2022 (Moscone West)
2:30 PM - II2.1
Evidence for a Structural Transition to the Superprotonic Phase of CsH2PO4 Under High Pressure.
Cristian Botez 1 , Russell Chianelli 2 , Jianzhong Zhang 3 , Jiang Qian 3 , Juraj Majzlan 4 , Cristian Pantea 5
1 Physics, University of Texas - El Paso, El Paso, Texas, United States, 2 Chemistry, University of Texas - El Paso, El Paso, Texas, United States, 3 Los Alamos Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Institute of Mineralogy, Petrology and Geochemistry, University of Freiburg, Freiburg Germany, 5 Materials Science and Technology - National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIt was recently demonstrated that the fully-hydrogen-bonded solid acid CsH2PO4 can function as a fuel cell electrolyte, based on its considerable proton conductivity enhancement upon heating (superprotonic behavior)[1]. Despite the considerable interest generated by these findings, the structural details and the micro-dynamics responsible for the superprotonic behavior of CsH2PO4 and other phosphate-based solid acids are not fully understood. In fact, the mere nature of the superpotonic phase of CsH2PO4 is still under debate. Some authors indicate a polymorphic phase transition [2], while others associate the superprotonic behavior to chemical changes such as water loss and polymerization [3]. Here we present results from synchrotron X-ray diffraction experiments aimed at getting more insight into the structural aspects of the superprotonic phase of this material. The main experimental challenge in the study of the high-temperature behavior of CsH2PO4 is to prevent its chemical decomposition, which, under ambient conditions, occurs at 227 °C, slightly below the superprotonic transition temperature of 232 °C. Decomposition can be avoided by either 1) keeping the sample under a H2O-saturated atmosphere, or 2) subjecting the sample to a pressure of 1.0±0.2 GPa. We used the latter approach in our experiments. CsH2PO4 monocrystals were grown by slow evaporation from an aqueous solution prepared by mixing stoichiometric amounts of H3PO4 and Cs2CO3. Crystals were subsequently ground to a fine powder. X-ray diffraction data were collected on the high-pressure X17B2 beamline at the National Synchrotron Light Source, Brookhaven National Laboratory. The sample was initially compressed at room temperature to 1.02 GPa, followed by heating in steps of 20-30 °C up to the a temperature of 375 °C. At each temperature step powder diffraction data corresponding to a 1-6Å d-spacing range were collected. Our data show that a cubic phase (a=4.88Å) appears in the 255°C-275°C temperature range upon heating under pressure (1.0±0.2 GPa). A 1000-fold increase in the proton conductivity (indicating the transition to the superprotonic phase) was previously observed under the same non-ambient conditions [2]. Moreover, optical microscopy work indicated a cubic symmetry for the high-temperature phase of CsH2PO4 [4] and laboratory X-ray diffraction studies, carried out on samples contained in H2O-saturated atmosphere, reported a cubic cell parameter of a=4.96Å (at T>235 °C) [5], in excellent agreement with our findings. Therefore, our results represent strong evidence that the superprotonic behavior in CsH2PO4 is associated with a monoclinic⇒cubic polymorphic structural transition and is not due to chemical modifications.[1] D.A. Boysen et al., Science, 303(5654), 2004;[2] D.A. Boysen et al.,Chem. Matter., 15(727),2003;[3] J.-H. Park, Phys. Rev. B,69(054104),2004;[4]A.I. Baranov et al., Ferroelectrics, 100(135),1989;[5] A. Preisinger et al., J. Chem Phys.,166-169(511), 1994
2:45 PM - II2.2
Time Resolved Dynamics of Femtosecond Laser Ablation of Si (100) with Thin Thermal Oxide Layers (20 – 1200 nm).
Joel McDonald 1 4 , Vanita Mistry 3 , Katherine Ray 3 , John Nees 4 , Steven Yalisove 2 4
1 Applied Physics, University of Michigan, Ann Arbor, Michigan, United States, 4 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan, United States, 3 School of Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractFemtosecond (fs) laser ablation of Si(100) with thermally grown oxide films was studied with pump/probe imaging and spectroscopy techniques in order to understand the role of film thickness on ablation dynamics. A pump/probe imaging technique was used in which an image was made of a delayed probe pulse reflected from the area of a sample irradiated with a pump pulse. By changing the delay between the pump and probe pulses, images were obtained of the surface reflectivity of the laser affected region as a function of time. The images showed an interference phenomenon known as Newton’s Rings, the temporal evolution of which provided a range for the expansion rate of the ablated material. An absolute value for the expansion rate was not obtained from this experiment as the analysis required knowledge of the refractive index of the material ablated from the silicon surface, which was unknown. A dual-pulse laser induced breakdown spectroscopy (LIBS) experiment was then performed to more accurately determine the velocity of the ablated material. With LIBS, the light emitted by an ablation event is collected and used to determine the chemical content of the ablated material. In this experiment, a low energy primary laser pulse was directed at normal incidence onto a sample surface, resulting in ablation of material that did not produce light emission sufficient for elemental detection of Si at the characteristic wavelength of 390 nm in the measured LIBS spectrum. A second high-energy laser pulse was directed parallel to and at a fixed distance above the sample surface exposed to the primary pulse. With proper delay between the primary and secondary pulses, the secondary pulse encountered and subsequently interacted strongly with the material ablated from the sample by the primary pulse. This produced light emission sufficient for detection of Si. The velocity of the ejected material was then determined by the onset of signal at the characteristic wavelength of Si at a given delay and the distance of the secondary pulse from the sample surface. The values of the velocity determined from the dual pulse LIBS experiment were used to back calculate the refractive index of the ablated material using the information obtained from the pump-probe imaging experiment discussed above. Time-lapse movies of the collected images showing the dynamics of material ablation produced by fs laser pulses will be shown. The expansion rate or velocity, and refractive index of the ablated material as a function of thermal oxide film thickness will be presented. Molecular dynamics and hydrodynamics simulations of the experiments described above will also be discussed in order to enhance understanding of the observed phenomenon. The techniques for determining expansion rates of material as a result of fs laser ablation may be applied to a variety of materials and used to understand the uniquely intense interaction of fs laser pulses with materials.
3:00 PM - II2.3
Spatially Resolved MicroDiffraction Analysis of the Plastic Deformation in the Shock Recovered Al Single Crystal
Rozaliya Barabash 1 , G. Ice 1 , W. Liu 1 , J. Belak 2 , G. Campbell 2 , M. Kumar 2 , H. Lorenzana 2 , J. Wark 3
1 Metals and Ceramics Div., Oak Ridge National Laboratory, Oak Ridge TN, Tennessee, United States, 2 University of California, Lawrence Livermore National Laboratory, Livermore, California, United States, 3 Department of Physics, Clarendon Laboratory, University of Oxford, Oxford United Kingdom
Show AbstractStrong shock waves result in the transition from elastic to plastic compression. As a result of dislocation motion and the strong interaction between dislocations and elastic waves, an initially random dislocation distribution becomes unstable and forms a correlated dislocation arrangement into dislocation walls. Some fraction of the dislocations may remain randomly distributed, and the rest form various correlated groupings and more organised disclination arrangements. Regions with geometrically necessary dislocations may form causing local lattice curvature. A spatially resolved diffraction method with a sub micrometer-diameter beam and 3D differential aperture technique is applied to quantitatively characterize both the parameters of dislocation structure and strain gradients in the shock recovered samples of Al (123) single crystal. We describes how geometrically necessary dislocations and effective strain gradient alter white beam Laue patterns. We show how to quantitatively determine the orientation and density of geometrically necessary dislocations in the shock recovered samples of Al being initially oriented for single slip. The microbeam-Laue diffraction reveals several distinct zones located at different depths under the shock front. Pronounced streaking of Laue images are observed in the zones close to the front and back surface of the after shock (123) Al single crystal. They indicate the formation of geometrically necessary dislocations being consistent with a single slip mode in the near surface regions. In the depth of the Al single crystal the portion of geometrically necessary dislocations in the dislocation ensemble reduces, and in the same time the portion of statistically stored dislocations increases. An intensive void formation is observed in the region close to the center of the samples, which is accompanied by a peculiar complicated shape of the Laue diffraction images. To get a better understanding of the reasons for such a shape of the Laue image the 3D depth resolved measurements were performed. These measurements showed that in the central region an alternating local lattice rotations take place. This is due to the inhomogeneous plastic deformation surrounding each void. The density and organization of dislocations is presented as a function of depth under the shock front as well as comparison to SEM on the same samples.
3:15 PM - II2.4
Elucidation of Nucleation and Growth Mechanisms in Solid-Solid Phase Transitions
Stefano Leoni 1 , Dirk Zahn 1
1 , Max Planck Institute for Chemical Physics of Solids, Dresden Germany
Show Abstract3:30 PM - II2.5
Synthesis and Evaluation of Nanocrystalline Ceramic Scintillators.
Joshua Kuntz 1 , Nerine Cherepy 1 , Stephen Payne 1 , Thomas Tillotson 1 , Joe Satcher 1
1 Chemistry and Materials Science, Lawrence Livermore National Lab, Livermore, California, United States
Show AbstractThe need to detect and identify radiation sources for the prevention of nuclear proliferation has been a driving force to develop new scintillator materials for use in radiation detection equipment. This study focuses on the production of transparent ceramic scintillators for gamma ray detection. Nanoparticles of garnet and cubic oxide ceramics have been produced with dopants of various lanthanide series ions. Production methods include precipitation and sol-gel routes to synthesize the nanocrystalline powders. The materials have been evaluated for their relative light yields. Ongoing efforts include processing and consolidation of the powders with the goal of producing bulk transparent ceramic scintillators. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
3:45 PM - II2.6
Synthesis of Dielectric Films by Microwave Assisted CVD.
Nicholas Ndiege 1 2 , Vaidyanathan Subramanian 2 , Rich Masel 2 1 3 , Mark Shannon 3 2 1
1 Materials Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Chemical and biomolecular engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractDeposition of dielectric films has received unprecedented interest in the past decade due to significant advances made primarily in the microelectronic industry. SiO2 as a dielectric barrier in microelectronic applications has reached its possible limits prompting the need for high k dielectrics (typically transition metal oxides) as a substitute. Another field with a pressing demand for high k dielectric films is in the synthesis of photonic bandgap materials for microscale refractory insulation coatings. The stumbling block in achieving these materials is the formation of transition metal silicide interfaces, low film growth rates and deformation of thick (>1μm) films i.e. cracking, buckling and even catastrophic delamination. In this study, we report use of microwave assisted chemical vapor deposition of Ta2O5 films on silicon at atmospheric conditions. Films generated are dense and stable with thicknesses varying from 1μm to 30 μm. Characterization of the resulting films was done using XRD, SEM, XPS, AES and profilometry techniques.
II3: Sensors, Devices & MEMS
Session Chairs
Satilmis Budak
Claudiu Muntele
Thursday PM, April 20, 2006
Room 2022 (Moscone West)
4:30 PM - II3.1
A Novel Mechanical Method to Measure Shear Strength in Specimens Under Pressure.
Juan Escobedo 1 , David Field 1 , David Lassila 2 , Mary Leblanc 2
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 MMED, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractA new experimental apparatus has been developed for performing shear tests on specimens held under moderately high hydrostatic pressures (on the order of 4 GPa). This testing procedure experimentally determines the pressure-dependent shear strength of thin foil specimens. Initial experiments on polycrystalline Ta were performed under pressures ranging from 1 to 4 GPa. It has been observed that both yielding and hardening behavior are sensitive to the imposed pressure. Tests on both single crystal and polycrystalline Mo specimens have been performed. The results from the single crystal will allow one to study the effect of pressure on the dislocation mobility for specific slip systems. The results obtained from different orientations of the single crystals are compared versus the results of the tests using polycrystalline foils. The differences in behavior allow the study of effects of the grain microstructure on the pressure-dependent mechanical response.
4:45 PM - II3.2
Device for in situ Electronic Characterization of MEMS Applicable to Conducting Structural Materials.
David Garmire 1 , Hyuck Choo 1 , Richard Muller 1 , Sanjay Govindjee 1 , James Demmel 1
1 BSAC, UC Berkeley, Berkeley, California, United States
Show AbstractWe have developed a CMOS-compatible, compact device and a simple procedure for measuring three important characteristics of planar-processed MEMS structures: in-plane over- or under-cut, Young’s Modulus, and comb-drive forces. This device enables localized continuous monitoring of stiffness and actuation forces of MEMS systems during operation in harsh environments. Accurately determining these few properties also enables the determination of many other important properties [1] [2]. This device is suitable for recalibrating systems during changing environmental conditions as well as process characterization.Because these three properties can vary significantly between process runs and even in a single run across an individual wafer, we must make the test structure relatively small and readily placed near to working MEMS structures. Our test device fits into a 1.5 mm by 1.5 mm area including bond pads.To demonstrate the device, we fabricate a cantilevered structure with several comb-drives on each side of the shuttle in an SOI (silicon on insulator) process. We introduce a complementary comb structure, similar to an engineering Vernier scale, except that in our complementary comb structure, the ends of a fixed set of comb teeth are spaced equilaterally from the ends of a mating moving set of comb teeth that translates parallel to the fixed comb. The capacitance between the fixed and moving combs in the measuring-comb structure varies as the moving-comb fingers are successively positioned in-and-out of alignment; it is at a maximum when the fingers are in registration and a minimum when the fingers of one comb align with spaces in the other. The maxima and minima are typically detectable even for very small signals and spacings. Furthermore, spacings between the maxima and minima are not affected by variations in structural cut rates. We use a differential amplifier in a charge integrator circuit to measure the capacitance. This circuit is capable of measuring very small capacitive differences [3]. By equating the cantilever motion from the actuation of two separate comb-drives and also measuring the change in capacitance on the comb-drive actuators, we are able to measure the desired quantities. We measure over-cut as 0.16±0.05 microns compared with an optical measurement of 0.1±0.1 microns, the comb-drive fringing field factor as 1.39±0.06, and the Young’s Modulus as 156±4GPa. We are manufacturing the device in silicon carbide and silicon germanium processes and will make further characterizations.[1] J. V. Clark, D. Garmire, M. Last, and J. Demmel, Nanotech 2004, March 7-11 2004, Vol. 1, pp. 402-405.[2] J. V. Clark, Electro Micro-Metrology. Ph.D. Thesis, University of California - Berkeley, 2005.[3] B. E. Boser, "RF Analog-to-Digital Converters; Sensor and Actuator Interfaces; Low-Noise Oscillators, PLLs and Synthesizers," R.J. van de Plassche, J. H. Huijsing, and W. M. C. Sansen (eds.), Kluwer Academic Publishers, November 1997.
5:00 PM - II3.3
Surface Characterization of Silicon Carbide Following Shallow Implantation of Platinum Ions for High Temperature Hydrogen Sensing Applications.
Claudiu Muntele 1 , Sergey Sarkisov 1 , Iulia Muntele 1 , Daryush Ila 1
1 Physics, Alabama A&M University, Normal, Alabama, United States
Show AbstractSilicon carbide is a promising wide-bandgap semiconductor intended for use in fabrication of high temperature, high power, and fast switching microelectronics components running without cooling. For hydrogen sensing applications, silicon carbide is generally used in conjunction with either palladium or platinum, both of them being good catalysts for hydrogen. When such a coating is applied on the exposed surface of SiC, the chemical reaction between the catalyst and hydrogen produces a detectable change in the surface chemical potential. Our past work dealt with both palladium coated SiC and palladium implanted SiC sensors. In this work we are investigating the effects of temperature on the structure of devices built using very shallow platinum ion implantation into semi-insulating silicon carbide, and tungsten layer deposition for electrical contacts. Since the sensors are supposed to work at 800 °C, we used various annealing steps up to this temperature level. We used atomic force microscopy (AFM) for monitoring the silicon carbide surface morphology before and after implantation, Rutherford Backscattering Spectrometry (RBS) for measuring the amount and depth profile of the platinum and tungsten distribution, and optical measurements (optical absorption spectrometry – OAS and Raman) to determine the irradiation defects evolution of the SiC crystalline lattice.Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NAG8-1933 from NASA, and by National Science Foundation under Grant No. EPS-0447675.
5:15 PM - II3.4
SiC Based Neutron Flux Monitors in Very High Temperature Nuclear Reactors
Weiqi Luo 1 , Wolfgang Windl 1 , Behrooz Khorsandi 2 , Thomas Blue 2
1 Materials Science & Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Nuclear Engineering, The Ohio State University, Columbus, Ohio, United States
Show AbstractThe Gas Turbine-Modular Helium Reactor (GT-MHR) and Very-High-Temperature Reactor (VHTR) are next-generation high-temperature reactor types that operate at temperatures in the range up to 850 °C and 1000 °C, respectively. In order to monitor the neutron flux in this environment, a new type of diode neutron detector is currently under development based on the hexagonal 4H polytype of silicon carbide (SiC). 4H-SiC has some outstanding properties such as a high electronic band gap and remarkable radiation hardness, making it an appropriate candidate material for high-temperature and high-fluence detector diodes. An important problem in this context is the long-time reliability of the diodes with respect to the continuous irradiation and high temperatures in next-gemeration reactors. In this paper, we discuss a computational methodology to study the accumulation of damage as a function of temperature and its influence on the electrical properties of the diode, using kinetic-Monte Carlo and binary collision approximation (BCA) based codes in conjunction with atomic-level electronic-structure based modeling of the charge transport based on the Landauer formulation. Specifically, we use the MCNP5 code to determine the fraction of neutrons which pass the SiC detector and hit Si or C “primary knock-on atoms” (PKAs). From the MCNP5 output, we use the neutron characteristics before and after each collision to determine the PKA energy and direction cosines, using conservation of energy and neutron characteristics. These data are then used as input for the MARLOWE code to estimate the number and types of C- and Si-defects in the resulting damage cascade. Since all these codes assume very low temperatures in the sample, we simulate the annealing effects of temperature using kinetic-lattice Monte Carlo modeling based on kinetic parameters from ab initio calculations, where experimental values are unavailable. Continuous operation at finite temperature can be modeled by combining the above codes. We will also discuss how the modeling results in combination with the appropriate experimentation at the OSU Reactor Facility help with design questions such as finding the most appropriate positions for the detectors in the reactor or the need for temperature shielding.
5:30 PM - II3.5
A Biocompatible Coating for CMUT.
Matthew Beasley 1 , Xuefeng Zhuang 1 , Amin Nikoozadeh 1 , Butrus Khuri-Yakub 1 , Beth Pruitt 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractBiocompatible coatings were researched for use with capacitive micromachined ultrasonic transducers (CMUTs) that enables transcutaneous and in vivo medical imaging at high frequency. To use CMUTs inside the conductive and corrosive environment of a living animal, a biocompatible material must coat the device and provide electrical isolation to the active areas of each element. Ideally, the coating would match acoustically to the silicon membrane and surrounding medium to eliminate unwanted reflections that otherwise show up as image artifacts. Parylene and polydimethylsiloxane (PDMS) were selected for this study based on these determining factors, along with their chemical inertness, process compatibility and thermal and mechanical stability. The behavior of the CMUT was analytically predicted using the theory of plates. The flexural rigidity was found through the governing equation based on Young’s modulus, Poisson’s ratio, and plate thickness. The equivalent flexural rigidity of the composite plate was determined to account for the coating. The equivalent silicon thickness was calculated and combined with standard algorithms for suspended membranes to predict resonance. Analytical and finite element modeling was used to estimate DC deflection of coated and uncoated membranes of varying thicknesses. A variety of different CMUT arrays were used, including ring and linear arrays. The dimensions of the elements were varied between arrays to give a range of center frequencies from 5 to 30 MHz. The parylene and PDMS coatings were applied after the ultrasound transducers were fabricated.The characteristics of coated and uncoated transducers were compared side by side. Membrane collapse voltage and resonant frequency in air were measured using a network analyzer. The average resonant frequency for parylene coated CMUTs decreased by 6.5% with a 1.2% standard deviation. The PDMS coating reduced the average resonant frequency by 24.2% with a 10.1% standard deviation. The resonance in air was significantly dampened by PDMS, but not by parylene. A 10% increase in collapse voltage was observed for the devices with parylene. A larger variation was seen with PDMS coated devices, with increases ranging from 5-12%. The membrane peak displacements and acoustic crosstalk were measured using a laser vibrometer. The peak membrane displacement in air decreased by 18% and 7% with the parylene and PDMS devices, respectively. In air, no reduction in element-to-element crosstalk was seen in either of the coated devices. Parylene degradation was tested by submerging devices in tap water. With a pulse input, the devices remained electrically isolated for 48 hours. Under continuous activation, the devices remained isolated for 3 hours. The CMUT with parylene coating was able to detect an echo signal from a plane reflector in a water tank. Results showed parylene provided a biocompatible interface for CMUTs without adversely affecting performance.
5:45 PM - II3.6
Optical Properties of Shocked GaP: Experimental Results and Theoretical Modeling.
Paulius Grivickas 1 , Matthew McCluskey 1 , Yogendra Gupta 1
1 Institute for Shock Physics and Department of Physics, Washington State University, Pullman, Washington, United States
Show AbstractIII-V compound semiconductors and their alloys are key components in optoelectronic devices ranging from lasers to solar cells. Relating the strains in these layered devices to the optical properties is an important scientific and practical need. Shock-wave compression, due to the uniaxial strain conditions that are generated, is well suited to address this need. In this work, we examined optical transmission and photoluminescence changes of sulfur-doped GaP in time-resolved, shock loading experiments. Longitudinal stresses in the range 2.5 – 5 GPa were applied along the [100], [110] and [111] crystallographic axes of the zincblende crystals. To achieve high resolution absorption and luminescence spectra, the sample target was cooled using liquid nitrogen. Under shock compression, the absorption edge of GaP exhibited a strain- and orientation-dependant red shift and broadening. These effects were strongest for compression along the [100] direction and smallest for the [110] direction. The results were modeled with indirect transition theory, assuming several absorption components of different optical strength. Our fitting procedure yielded the nonlinear shifts and splitting of the intrinsic band gap of GaP along the examined crystallographic axes. The results were confirmed by photoluminescence measurements that monitored the peak shifts of sulfur-bound excitons. From our shock-compression experiments, we derived a consistent set of optical deformation potentials, which deviate substantially from those obtained by conventional uniaxial stress measurements. Potential reasons for this discrepancy will be discussed.
II4: Poster Session: Materials in Extreme Environments
Session Chairs
Daryush ILA
Christian Mailhiot
Premkumar Saganti
Friday AM, April 21, 2006
Salons 8-15 (Marriott)
9:00 PM - II4.1
Boron-Doped Diamond Schottky Diodes for Temperature Sensing.
Jonghoo Park 1 , Zhenqiang Ma 1 , James Blanchard 1
1 Electrical and computer Engineering, University of Wisconsin-madison, Madison, Wisconsin, United States
Show Abstract9:00 PM - II4.10
Effect of MeV Si Ion Bombardment on Thermoelectric Characteristics of Sequentially Deposited SiO2/AuxSiO2(1-x) Nanolayers.
S. Budak 1 , B. Zheng 1 , C. Muntele 1 , Z. Xiao 2 , I. Muntele 1 , B. Chhay 1 , R.L. Zimmerman 1 , L.R. Holland 1 , D. ILA 1
1 Center for Irradiation of Materials, Alabama A.&M. University, NORMAL, Alabama, United States, 2 Electrical Engineering, Alabama A.M.University, Normal, Alabama, United States
Show Abstract9:00 PM - II4.11
Synthesis and Characteristics of Aromatic Poly (thio-ethers)For Extreme Environments
Dillip Mohanty 1 , Mathew Yonkey 1 , Chirstopher Crouse 2
1 Chemistry, Central Michigan University, M t. Pleasant, Michigan, United States, 2 Chemistry, Rice University, Huston, Texas, United States
Show AbstractIn contrast to widely used aliphatic poly (sulfides) or poly (thio-ethers), as sealants, aromatic poly (thio-ethers) have found limited applications, because, they are not readily available. In addition, they are not as economical as their aliphatic counterparts. Nevertheless, they can fill a niche in the market - under extreme environments. For example, some applications require exceptionally high thermal stability for a short duration ( ~ 350 degree Celsius for 30 seconds), consistent resistance to all organic solvents under ambient conditions. Furthermore, in the molten state the prepared materials should not undergo undesirable cross-linking reactions. This will enable it to flow into cracks where it can act as sealant. The most demanding of these requirements is that they should be able to expand and contract under inclement weather conditions to keep the cracks filled at all times. While, these needs appear to be impossible to achieve with a single family of materials, we have been successful in reaching most of these goals with modified aromatic poly (thio-ethers). The preparation and characteristics of this family of thermoplastics and post-modifications to satisfy these requirements will be discussed in detail.
9:00 PM - II4.12
Improvement on Thermoelectric Characteristics of Layered Nanostructure by Ion Beam Bombardment.
Bangke Zheng 1
1 Center for Irradiation of Materials, Alabama A&M University, Normal, Alabama, United States
Show Abstract9:00 PM - II4.13
Transport Properties of doped Al – Si framework Clathrates
Cathie Condron 1 , Susan Kauzlarich 1
1 Chemistry, UC Davis, Davis, California, United States
Show AbstractA good thermoelectric material requires the combination of high electrical conductivity (σ), low thermal conductivity (κ), and high thermopower or Seebeck coefficient (S), ultimately resulting in a high figure of merit (zT = σ S2/κ T, where T is temperature). Thus far Al – Si framework clathrate compounds have shown metallic electrical conductivity, resulting in a low Seebeck coefficient. However, by systematically decreasing the electrical conductivity to that of a semimetal or semiconductor, the thermoelectric performance of Al – Si framework clathrates may be improved. Single crystals of Ba8(B,Al)xSi46-x were prepared utilizing the molten flux growth method. Single crystal x-ray diffraction studies confirm Ba8(B,Al)xSi46-x adopts the clathrate (I) structure type, space group Pn-3m, with lattice parameters decreasing with increasing B content. Resistivity has been measured and increases with increasing B content. The electrical transport properties and thermal stability of these B doped clathrates will be presented and discussed.
9:00 PM - II4.15
Morphological Characterization and in vitro Biocompatibility of a Porous Jickel–titanium Alloy.
Oleg Prymak 1 , Denise Bogdanski 2 , Manfred Koeller 2 , Stefan A. Esenwein 2 , Gert Muhr 2 , Felix Beckmann 3 , Tilman Donath 3 , Michel Assad 4 , Matthias Epple 1
1 Institute for Inorganic Chemistry, University of Duisburg-Essen, Essen Germany, 2 Department of Surgery, BG Kliniken Bergmannsheil, Bochum Germany, 3 GKSS-Research Center Geesthacht, Institute for Materials Research, Geesthacht Germany, 4 Centre for Bone and Periodontal Research, McGill University, Montreal, Quebec, Canada
Show Abstract9:00 PM - II4.16
Fatigue Resistance and Nickel Release of Coated and Uncoated NiTi Orthodontic Wires.
Oleg Prymak 1 , Thorsten Peitsch 1 , Arndt Klocke 2 , Baerbel Kahl-Nieke 2 , Matthias Epple 1
1 Institute for Inorganic Chemistry, University of Duisburg-Essen, Essen Germany, 2 Department of Orthodontics, University Hospital Hamburg-Eppendorf, Hamburg Germany
Show Abstract9:00 PM - II4.17
High Temperature Characterization of RF Sputtered Silicon Carbon Nitride Thin Films
Arun Vijayakumar 1 , Ravi Todi 1 2 , Kalpathy Sundaram 1 2 , Kevin Coffey 2
1 School of Electrical Engineering and Computer Science, University of Central Florida, Orlando, Florida, United States, 2 Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida, United States
Show AbstractSilicon carbon nitride is considered a promising candidate for application in extreme environments due to its favorable chemical and mechanical properties. Thin films of amorphous silicon carbon nitride (α-SiCxNy) were deposited in an r.f magnetron sputtering system using a powder pressed SiC target. The N2/Ar gas flow ratio was varied during sputtering in order to obtain films with varying composition. We studied the properties of SiCN thin films under high temperature conditions. Electrical characteristics of the films were measured under various high temperature conditions. Surface analytical techniques such as XPS and optical profilometry were used to study the composition and surface roughness of the deposited films and correlated with the electrical measurements. Based on our measured electrical characteristics and film composition studies, we attempt to explain some of the behavioral aspects of the sputtered SiCN thin films under high temperature conditions and discuss the possible implications to their applicability in extreme harsh environment conditions.
9:00 PM - II4.18
Sol-gel Synthesis of Thick Ta2O5 Films for Photonic Band gap Materials.
Nicholas Ndiege 1 2 , Tabitha Wilhoite 1 , Vaidyanathan Subramanian 2 , Rich Masel 2 1 3 , Mark Shannon 3
1 Materials Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractAdvances in microelectromechanical systems has generated an ever growing demand for novel insulating material applicable to high temperature systems. Photonic bandgap materials are appealing for such applications, specifically Ta2O5 due to its high index of refraction, refractory nature and negligible absorbance in the infrared region. The challenge faced in the realization of such materials is the synthesis of crack free Ta2O5 films whose thickness is in the order of a quarter wavelength of the incident infrared radiation.This work seeks to investigate the effect of addition of polyvinyl pyrollidone (PVP) as a binder material in the sol gel synthesis of thick, uniform and crack free Ta2O5 films. Incorporation of PVP into the sol precursor has enabled uniform and crack free films with thicknesses of up to 2.4 microns to be realized. Chemical probing of the precursor was conducted via TGA, FTIR, and NMR analysis of the sol to elucidate the processes behind this film formation. The calcined oxide films were characterized via SEM, XRD and XPS.
9:00 PM - II4.19
Damage Effects of Ionizing Radiation in Polymer Film Electrets.
Marco Parada 1 , Renato Minamisawa 1 , Adelaide de Almeida 1 , Iulia Muntele 2 , Daryush ILA 2
1 Departamento de Fisica e Matematica - FFCLRP, Universidade de Sao Paulo, Ribeirao Preto Brazil, 2 Physics-Center for Irradiation of Materials, Alabama A&M University, Normal, Alabama, United States
Show AbstractDosimeters produced with electret materials are able to detect γ- and X-rays, α, β, electrons and other charged particles and, with appropriate converters, fast and slow neutrons. To produce and use an electret dosimeter the polymer must be charged in a system able to inject an initial charge into the electret material. After charging it can be exposed to ionizing radiation and the remaining charge density can be read, with the help of an appropriate device, for radiation dosimetry estimations. In this work we have charged and exposed PFA (Tetrafluoroethylene-per-fluoromethoxyethylene) and FEP (Tetrafluoroethylene-hexa-fluoropropylene) polymer films to several MeV proton fluences and to several radiation absorbed doses using 60Co-gamma and X-Rays sources. In order to determine damage that can compromise the use of these materials as dosimeters, the virgin, charged and exposed films were analysed with Optical Absorption Photospectrometry (OAP), Fourier Transform Infrared (FTIR) and micro-RAMAN spectroscopy. The analysis results are shown to demonstrate the damage caused by the expositions to the cited radiations sources in the polymers.
9:00 PM - II4.2
Femtosecond Laser Irradiation of Thin Foils – Thermal and Mechanical Shock Assessment at the Micron and Sub-micron Scale.
Yoosuf Picard 1 2 , Kristin Tebo 1 2 , Tresa Pollock 1 , Steven Yalisove 1 2
1 Materials Science & Engineering, University of Michigan--Ann Arbor, Ann Arbor, Michigan, United States, 2 Center for Ultrafast Optical Science, University of Michigan--Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractThe interaction between femtosecond laser pulses and material surfaces is complex and extremely dynamic. Conditions far from equilibrium are present at the laser irradiated surface, characaterized by high temperatures and pressures. Recent studies using transmission electron microscopy (TEM) have provided direct evidence of limited heating and mechanical damage induced by femtosecond lasers. Critical to any understanding of high intensity femtosecond laser-material interaction is an assessment of the thermal profile induced by ultrafast irradiation and the high strain rates expected from the ensuing shock. We have conducted TEM studies of femtosecond laser irradiated, pre-thinned foils for different materials systems. Freestanding foils of a two-phase Ni-based single crystal alloy, single crystal silicon, and an amorphous silicon/polycrystalline cobalt film were irradiated with single femtosecond laser pulses below and above the threshold fluence necessary to remove material. Pointwise structural and chemical characterization indicates steep thermal gradients within, and adjacent to the vicinity of the laser irradiated region. In addition, dislocation analysis suggests high strain rate loading generated by ultrashort pulses.
9:00 PM - II4.20
A Mother-daughter Mechanism for Mode I Dominated Cracks: Supersonic Crack Motion Along Interfaces of Dissimilar Materials.
Markus Buehler 1 , Huajian Gao 2
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Max Planck Institute for Metals Research, Stuttgart Germany
Show Abstract9:00 PM - II4.21
Effect of Pressure on Electronic Structure of Pb1-xSnxTe Alloys Doped with Gallium.
Evgeny Skipetrov 1 , Alexander Golubev 2 , Nikolay Dmitriev 1 , Vasily Slyn'ko 3
1 Faculty of Physics, M.V.Lomonosov Moscow State University, Moscow Russian Federation, 2 Faculty of Material Sciences, M.V.Lomonosov Moscow State University, Moscow Russian Federation, 3 , Institute of Material Science Problems, Chernovtsy Ukraine
Show Abstract9:00 PM - II4.23
Photochemical Processing of Solid Carbon Dioxide and Carbon Dioxide Mixtures.
T. Dillingham 1 , David Cornelison 1 , Joe Dinius 1
1 Physics and Astronomy, Northern Arizona University, Flagstaff, Arizona, United States
Show AbstractThe investigation of the photochemical processes that can occur in solids like carbon dioxide and carbon dioxide mixtures have important applications in atmospheric physics, astrophysics, and planetary astronomy. In this investigation, carbon dioxide ices and ice mixtures are grown at various temperatures using a closed-cycle helium cryostat. The ices are irradiated with x-rays for periods of up to six hours. The chemical changes that occur during this processing are monitored using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. A quadrupole mass spectrometer was also used to study the gas phase species evolving from the ice surface during photoprocessing. The XPS, FTIR and mass spectrometer results are presented and correlated. It is noted that significant differences are observed, particularly for the time dependence of the evolution of the gas phase molecules, between ices grown at 77 K as compared to those grown at 20 K and at intermediate temperatures.*Supported by the NAU Intramural Grants Program and the NASA Space Grant Program.
9:00 PM - II4.3
Surface Modification of Glassy Polymeric Carbon by Glow Discharge.
Volha Abidzina 1 , I.V. Tereshko 1 , R. L. Zimmerman 2 , I. Muntele 2 , C. Muntele 2 , B. Chhay 2 , D. Ila 2 , I. Elkin 3
1 , Belarusian-Russian University, Mogilev Belarus, 2 , Center for Irradiation of Materials, Alabama A&M University, Normal, Alabama, United States, 3 , Research and Production Enterprise KAMA VT, Mogilev Belarus
Show AbstractGlassy polymeric carbon (GPC), which is made from cured phenolic resins, has a high chemical inertness that has resulted in the material being used as high temperature and radiation field coating, as high temperature heat-exchangers as well as biomaterial in medicine, such as in the manufacture of heart valves. The GPC wares are produced in house at various shape and size at pyrolysis temperatures between 200C to 3000C. The FTIR results indicates that the aromatics structures start forming graphite like tangled ribbons at about 530C and the trapped pores are most available at about 700C pyrolysis temperature. These tangled ribbons are most visible by TEM at temperatures above 1000C heat treatment. In this work we will present the results of our study on the effects of low-energy ions produced by glow-discharge with both partially and fully cured phenolic resins and compare them with our previous results obtained from MeV ion bombardment of GPC. These effects enhance the erosion resistance and corrosion resistance properties of GPC. The chemical changes on this partially cured and fully cured resin are studied using FTIR, micro-Raman spectroscopy and Rutherford Backscattering Spectrometry (RBS). The surface roughness was measured using optical microscopy and atomic force microscopy (AFM). The increased porosity was monitored by introducing lithium from a molten LiCl salt into the GPC and using the (p, α) nuclear reaction analysis (NRA) to measure the increased concentration of Li in the treated GPC. The NRA results were correlated with increased pore availability.Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NAG8-1933 from NASA, and by National Science Foundation under Grant No. EPS-0447675.
9:00 PM - II4.4
Nanostructural Evolution of Au on Silica Surfaces Exposed to Low Energy Ions*
Volha Abidzina 1 , I.V. Tereshko 1 , R. L. Zimmerman 2 , S. Budak 2 , B. Zheng 2 , C. Muntele 2 , D. Ila 2 , I. Elkin 3
1 , Belarusian-Russian University, Mogilev Belarus, 2 , Center for Irradiation of Materials, Alabama A&M University, Normal, Alabama, United States, 3 , Research and Production Enterprise KAMA VT, Mogilev Belarus
Show AbstractInclusion of metal ions in photorefractive materials followed by thermal annealing leads to an increase in optical absorption. We have used both glow discharge as well as thermal annealing to change the optical properties of suprasil. We used the effects of the low energy ions to induce the nucleation of nanoscale crystals on and near surface of silica nano-layer containing low concentrations of Au. To proceed with this investigation, samples were produced using the co-deposition of a thin films consisting of Au plus silica on a suprasil substrate. We used thermal annealing as well as glow discharge and then observed and studied the formation of nano-layer of nanoscale Au crystals in silica film. We will present our results on the formation of nanoscale gold crystals on and near surface of silica due to exposure to low energy ions.*Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NAG8-1933 from NASA, and by National Science Foundation under Grant No. EPS-0447675.
9:00 PM - II4.5
Void Distributions in Temperature Cycled TATB-based High Explosives
Trevor Willey 1 , J. Handly 1 3 , T. van Buuren 1 , B. Weeks 2 , J. Lee 1 , J. Illavsky 4 , G. Overturf 1 , J. Kinney 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , BWXT Pantex, Amarillo, Texas, United States, 2 Dept. of Chemical Engineering, Texas Tech University, Lubbock, Texas, United States, 4 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractCollapse of small voids roughly 100 nm to 1 micron in size create so called hot-spots within an energetic material during detonation. These hot spots are ignition sites that grow in temperature, size, and pressure and sustain the reaction. Properties of the detonation depend on these hot-spots, and thus the distribution, number, and size of the voids within the material.We are investigating polymer blended systems containing the insensitive explosive triamino-trinitrobenzene (TATB). The volume of these explosives increases in a non-reversible manner when exposed to cycled temperatures. Such expansion could cause changes in void distributions of interest. Furthermore, several mechanisms for this non-reversible growth have been proposed and investigated modeling techniques, but none of the mechanisms have been experimentally verified.Ultra-small Angle X-ray Scattering (USAXS) is used to investigate these void distributions in both freshly pressed specimens, and samples that have undergone thermal cycling between -60 C and 74 C. The technique is able to quantify void size distributions from about 2 nm to 2 microns. Differences in the small-angle scattering occur and show voids that are on average larger and more plentiful after thermal cycling, and give insight into the mechanism for the expansion. These results are useful in predicting the detonation physics of the explosives.
9:00 PM - II4.6
Study of the Effects of Various Nanopowders in the Properties of the GPC.
Bopha Chhay 1 , I. Muntele 1 , R. Zimmerman 1 , C. Muntele 1 , D. Ila 1
1 Physics, Alabama A&M University, Normal, Alabama, United States
Show AbstractWe have introduced various nanopowders in the precursor of glassy polymeric carbon (GPC) and studied its electrical, thermal, and mechanical properties as well as its chemical structure. In general the GPC ware produced at AAMU are used for making crucible, heat-exchangers, and for prosthesis devices because of its biocompatibility. GPC wares at AAMU are synthesized from a phenolic resin solution from Georgia Pacific in a pyrolyser system at temperatures between 100 °C all the way to 2800 °C. The heat treatment includes several stages: gelling, curing, postcuring, precarbonization and carbonization. The fabrication of GPC is complicated because of the high production rate of gaseous products in critical temperatures ranges where out-diffusion is relatively slow. Special cares should be taken in the temperature programming to avoid misshapen porous and kilning faults in the GPC end result. In this work we have introduced SiC, CNT as well as sapphire nanopowders to the precursor and studied the properties of the final product at various pyrolysis temperatures. We will present our results in this meeting.
9:00 PM - II4.8
Study of Mechanical and Electrical Properties of Glassy Polymeric Carbon.
Iulia Muntele 1 , Robert Zimmerman 1 , Lawrence Holland 1 , Claudiu Muntele 1 , Bopha Chhay 1 , Daryush ILA 1
1 Physics, Alabama A&M University-Center for Irradiation of Materials, Normal, Alabama, United States
Show AbstractGlossy Polymeric Carbon (GPC) is obtained by a molding technique, in various shapes, from a phenolic resin precursor. The heat treatment of the precursor is achieved in three stages up to 1000 oC. Electrical and mechanical properties of the resulting GPC coupons are tested. Similar GPC materials produced in our laboratory displayed large strain to failure ratio, small thermal expansion coefficient and low density. Like all carbon forms, is attacked by oxygen, especially atomic oxygen. Nevertheless the kinetics for reaction with atmospheric oxygen is very slow. GPC is completely resistant to all acids and bases, and is biocompatible. GPC is a unique material, which can withstand high temperature and corrosive environments, with applications in nuclear reactors and space industry.
9:00 PM - II4.9
Shielding Materials for High-Energy Radiation on Lunar and Martian Surfaces
Richard Kiefer 1 , Amanda Boone 1 , Mi Lim 1 , Sheila Thibeault 2
1 Chemistry, College of William and Mary, Williamsburg, Virginia, United States, 2 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States
Show AbstractMicro-composites of polyethylene or polypropylene with simulated lunar regolith have been fabricated as possible materials for habitat construction on the Moon or Mars. Long-term missions will require habitats to protect humans and electronic equipment from the effects of high-energy radiation from galactic cosmic rays (GCR) and solar particle events (SPE). Shielding from this radiation is best accomplished by using materials composed of elements with small atomic numbers. Though obviously impractical, the best shield would be liquid hydrogen. Polyethylene and polypropylene have the highest hydrogen content of any polymer and thus can provide both shielding and structural integrity when combined with material from the extra-terrestrial surface (regolith). We have used polyethylene and polypropylene powders in various mass percents and thoroughly mixed them with simulated regolith powder. The mixtures were then heated in a microwave oven to form the micro-composites. The resulting materials were characterized by thermomechanical analysis (TMA), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA).
Symposium Organizers
Christian Mailhiot Lawrence Livermore National Laboratory
Premkumar B. Saganti Prairie View A&M University
Daryush Ila Alabama A&M University
II5: Environmental Effects (Temperature, Radiation, Corrosion, Erosion, Pressure)
Session Chairs
Premkumar Saganti
Robert Zimmerman
Friday AM, April 21, 2006
Room 2022 (Moscone West)
9:00 AM - **II5.1
Effects of the Radiation Environment on Nanostructured Materials
Richard Wilkins 1
1 Center for Applied Radiation Research, Prairie View A&M University, Prairie View, Texas, United States
Show AbstractMaterials using nanotechnology and materials for nanotechnology hold promise for the creation of new, lightweight and radiation resistant materials for space exploration. The potential applications of these materials are in the areas of structural materials, radiation shielding materials and electronic devices. In addition to the natural radiation environment encountered in space, these materials may also be subject to the radiation environment associated with a nuclear reactor, if this type of power is used on a future space mission. This talk will review recent experimental data on nano-composites and nano-structured electronic devices in radiation environments relevant to the space environment and/or nuclear power environment. The experiments are designed to evaluate the materials for applications in exploration class space missions.
9:30 AM - II5.2
Metallurgical and Corrosion Studies of Modified T91 Grade steel
Pankaj Kumar 1 , Debajyoti Maitra 1 , Ajit Roy 1
1 Mechanical Engineering, University of Nevada Las Vegas, Las Vegas, NV, Nevada, United States
Show AbstractThe modified 9 chromium- 1 molybdenum steel (9Cr-1Mo) containing niobium (Nb) and vanadium (V), also known as T91 grade steel, has been recommended as a target structural material for transmutation of spent nuclear fuels. In view of the beneficial effect of silicon (Si) observed in previous investigations the T91 grade steel has been modified through additions of Si content ranging between 0.5 and 2 weight percent. The tensile properties of these modified alloys have been evaluated at temperatures ranging between ambient and 550°C. The evaluation of the susceptibility of these materials to stress corrosion cracking (SCC) in the presence of molten metals are planned to be performed. Meanwhile, the susceptibility to SCC in an acidic environment is currently being evaluated. This paper will be aimed at presenting the results of both tensile and corrosion testing involving T91 grade steel containing variable Si content. Further, the fractographic evaluations by scanning electron microscopy will be attempted.
9:45 AM - II5.3
A Novel Method For The Diffusion Of Boron In 60-80 Micron Size Natural Diamond Type II/A Powder.
Adrian Mendez 1 , Mark Prelas 1 , Tushar Ghosh 1 , Michael Glasscock 1
1 Nuclear Enginneering, University of Missouri-Columbia, Columbia, Missouri, United States
Show AbstractThe purpose of this paper is to report the experimental results of boron doping on 60-80 micron size diamond particles using field enhanced diffusion with optical activation (FEDOA) [1-4]. Diamond is a wide band gap material with unique combinations of optical, thermal, mechanical and electronic properties that can be useful for a number of applications including optoelectronic applications and micro sensor technology. The incorporation of boron into diamond has been proven to change its electrical properties and convert the diamond from insulator to a p-type semiconductor [3]. A promising technique for incorporation of impurities into diamond is FEDOA. FEDOA drives impurities into single crystalline diamond material has been studied using this method[5-7]. A combination of thermal diffusion with bias, thermal ionization and optical ionization is combined in one setup. A modified version of FEDOA was implemented for the diffusion of Boron in natural Diamond type II/a powder of size 60-80 microns (Figure 1). The diamond powder was obtained from Microdiamant with 99.9% purity. The boron powder used in the experiment was amorphous, 325 mesh 90%(Assay), Mg (5%) nominal obtained from AESAR. A mixture of 3:1 Boron-Diamond mixture was used. A heating element and a diamond-boron powder holder were designed and incorporated in the FEDOA system. Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) are used to study the diamond-doped morphology and identify impurities. Boron and Hydrogen concentration results in the doped samples are studied using Prompt Gamma Neutron Activation Analysis (PGNAA) at the University of Missouri Research Reactor (MURR). The experimental results show that the samples were effectively doped with boron. It was also found that samples with high boron concentration exhibit high conductivity.
10:00 AM - II5.4
Oxidation of Fe-2.3Cr, Fe-8.6Cr, and Fe-20.1Cr-31.7Ni Alloys Between 600 and 1000oC.
Maduri Pasala 1 , Shailendra Varma 1 , Aditya Putrevu 1
1 Metallurgy & Materials Engineering, University of Texas at El Paso, El Paso, Texas, United States
Show AbstractFerrous alloys containing 2.3 (low Cr), 8.6 (Medium Cr), and 20.1% (with 31.7%Ni, high Cr/Ni) Cr have been subjected to oxidation in air in a range of temperatures from 600 to 1000oC for a period of 3 weeks. Oxidation curves in the form of weight gain per unit area (W) versus exposure time (t) have been used to determine the activation energy for each alloy. The equation, W = K.t1/2 (K is a constant to be determined experimentally), describing the oxidation kinetics can incorporate the temperature effect in the constant K with the help of an Arrhenius type of equation. Observed activation energy values have been related to the Cr concentration in the alloys. Spalling is the main feature for low Cr alloy while oxides of various elements form the main constituents of the scale in the medium and high Cr/Ni alloys. The oxides have been identified in x-ray diffraction, AES, XPS, EDS in SEM, and SEM. Sputtering the alloys has been used to monitor the nature of oxides as a function of depth. The changes in microstructures complimenting the optical microscopic observations related to oxidation have been followed by TEM.
10:15 AM - II5.5
Ge Oxidation by Hyperthermal Atomic Oxygen.
Maja Kisa 1 , Ross Harder 2 , Timothy Minton 3 , Ian Robinson 2 , Judith Yang 1
1 Materials Science and Engineering Department, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Physics Department, University of Illinois, Urbana Champaign, Illinois, United States, 3 Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, United States
Show AbstractAtomic oxygen is the most hazardous species in the low Earth orbit (LEO) environment and can lead to oxidation and erosion of spacecraft surfaces. Due to the 7.8 km s-1 velocity of the orbiting spacecraft and the density of atomic oxygen at LEO altitudes, atomic oxygen impacts the ram surfaces of spacecraft with fluxes on the order of 1015 cm-2 s-1 and with collision energies equivalent to 4.5 eV of translational energy. The goal of this work is to gain a fundamental understanding of Si and Ge oxidation by atomic oxygen at hyperthermal collision energies. Thin Ge and SiOx layers are often used as coatings to protect polymers that are exposed to the extreme environmental conditions present in LEO. Ge coatings are also used to lower the solar cells operating temperature and to prevent the build - up of electrostatic charges. The microstructure of the Si and Ge oxide layers formed by energetic atomic oxygen was compared to the microstructure of the oxide formed by molecular oxygen oxidation. A laser detonation source, capable of producing hyperthermal atomic oxygen at nominal translational energies near 5 eV, was used to expose the sample surfaces. After exposure, the oxidized samples were removed from the vacuum system and analyzed by atomic force microscopy (AFM), synchrotron X-ray diffraction (XRD), and transmission electron microscopy (TEM). We previously reported that amorphous silica formed by 5 eV atomic oxygen on a surface held at 220oC was nearly twice as thick, more ordered (similar to a quartz structure), and more homogeneous in composition, than the oxide formed by molecular oxygen [1]. Initial results on Ge are similar to Si. In comparison with the oxide layer formed by molecular oxygen exposure, the GeOx formed by atomic oxygen exposure showed increased surface roughness, increased crystallinity, and increased oxide thickness that, surprisingly, did not depend on temperature. Previous investigations at low kinetic energies of atomic oxygen suggested that the oxide thickness on Si depends on the kinetic energy of oxygen. Hence, the microstructure of the oxide film formed on Ge by atomic oxygen will be studied as a function of atomic-oxygen translational energy, in order to determine the link between translational energy and the detailed nature of the oxide film that is formed.1M. Kisa, T. K. Minton, and J. C. Yang, “Structural Comparisons of SiOx and Si/SiOx Formed by the Exposure of Silicon (100) to Molecular Oxygen and to Hyperthermal Atomic Oxygen” J.Appl. Phys., 97, 2005, 023520.
10:30 AM - II5.6
The Corrosion Behavior of Nickel-base Austenitic Alloys for Nuclear Hydrogen Generation
Ajit Roy 1 , Rama Koripelli 2 , Anand Venkatesh 2 , Joydeep Pal 2
1 Mechanical Engineering, UNLV, Las Vegas, Nevada, United States, 2 Mechanical Engineering, UNLV, Las Vegas, Nevada, United States
Show Abstract10:45 AM - II5.7
High Intensity, Ultrafast Laser Ignition of Reactive Multilayer Systems
Yoosuf Picard 1 4 , David Adams 2 , Jeremy Palmer 2 , Thomas Friedmann 3 , Steven Yalisove 1 4
1 Materials Science & Engineering, University of Michigan--Ann Arbor, Ann Arbor, Michigan, United States, 4 Center for Ultrafast Optical Science, University of Michigan--Ann Arbor, Ann Arbor, Michigan, United States, 2 Advanced Manufacturing Processes Lab, Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 Integrated Materials Research Lab, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe will demonstrate the first use of high intensity femtosecond lasers to ignite highly energetic reactive metal multilayers. Reactive multilayers have been recently explored as a new approach to combustion synthesis (CS) of materials and as localized heating sources. These multilayer systems are composed of nanometer thick, alternating layers of metals with large enthalpies of formation capable of generating a self-propagating reaction through the entire film. The method of igniting these systems can be thermal, mechanical, or electrical. Recent work has shown that common reactive multilayer systems (Ni/Al) can be machined, without ignition, using ultrafast lasers. The underlying reasons for this are not well understood. It has been postulated that a critical thermal mass must exist before the reaction will be self-propagating. To address these issues we performed a set of experiments focused on better understanding the relationship between the pulse intensity, the number of multilayers, the thickness of individual layers, thermal conductivity of the metals, the final capping layer, and the self-propagating ignition threshold for different material systems. Results will be presented that show femtosecond laser ignition thresholds as a function of layer thickness. These results will be compared to similar experiments where we were successful at initiating a self-propagating reaction using nanosecond laser pulses. We will discuss the mechanisms underlying these results, especially the role of thermal energy and the concomitant shock that is driven by the extreme thermal gradients in the material.
11:30 AM - II5.8
Solar Effects on Tensile and Optical Properties of Hubble Space Telescope Silver-Teflon Insulation.
Kim de Groh 1 , Joyce Dever 1 , Aaron Snyder 1 , Sharon Kaminski 2 , Catherine McCarthy 2 , Allison Rapoport 2 , Rochelle Rucker 2
1 , NASA Glenn Research Center, Cleveland, Ohio, United States, 2 , Hathaway Brown School, Shaker Heights, Ohio, United States
Show Abstract11:45 AM - II5.9
Characterization of Structural Change of Indium-Tin-Oxide Films Due to Exposure to Hyperthermal Atomic Oxygen.
Long Li 1 , Ross Harder 2 , Ian Robinson 2 , Sharon Miller 3 , Bruce Banks 3 , Judith Yang 1
1 Materials Science and Engineering Department, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 , NASA Glenn Research Center, Cleveland, Ohio, United States
Show Abstract12:00 PM - II5.10
Study on Corrosion Inhibition of Mild Steel by the Mixture of Calcium Nitrate and Ammonium Nitrate in Simulated Concrete pore Solution Using Cyclic Polarization Technique.
Yashar Mirabolfathi 1
1 , university, Tehran Iran (the Islamic Republic of)
Show Abstract12:15 PM - II5.11
Impact Response OF High-Temperature Uranium Phases.
Eugene Zaretsky 1 , Benny Herrmann 2 , Dov Shvarts 2
1 Mechanical Engineering, Ben Gurion University of the Negev, Beer Sheva Israel, 2 , Negev Nuclear Research Center, Beer Sheva Israel
Show Abstract12:30 PM - **II5.12
Extreme Conditions of the Nuclear Reactor Environments and Understanding the Material Conduciveness.
Lawrence Pinsky 1
1 , University of Houston, Houston, Texas, United States
Show AbstractUnavailable at time of submission.
II6: In Situ Diagnostics (Applications & Effects)
Session Chairs
Christian Mailhiot
Claudiu Muntele
Friday PM, April 21, 2006
Room 2022 (Moscone West)
2:30 PM - **II6.1
First Principles Studies of RDX Crystals Under Compression.
Jennifer Ciezak 1 , Samuel Trevino 1
1 , ARL/NIST, Gaithersburg, Maryland, United States
Show AbstractThe energetic materials community largely relies on crystalline density, obtained from theoretical calculations, to predict the performance and sensitivity of potential explosives. This approach often saves millions of dollars and years of synthetic research which would be required to bring a potential explosive to production capacity. However, densities predicted using current theoretical methods often have an undesirable error of up to 4%, that is thought to arise from the neglect of non-overlapping electron densities in current functionals. The error in the calculated density has been proposed to decrease as the system evolves under pressure. Experimental high pressure x-ray diffraction and spectroscopic data of RDX will be presented in comparison to theoretical simulations to obtain a measure of the accuracy of the theoretical methods at various pressures.
3:00 PM - II6.2
Dynamic-Diamond Anvil Cell (d-DAC); New Technology to Study Kinetics across Phase Transformations.
Geun Woo Lee 1 , William Evans 1 , Choong-Shik Yoo 1
1 Physics, Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract3:15 PM - II6.3
Rapid Undercooling and Refreeze in Laser-shock-melted Bi(Zn).
Alan Jankowski 1 , Jeffrey Colvin 1 , Bryan Reed 1 , Mukul Kumar 1
1 , UC-LLNL, Livermore, California, United States
Show Abstract4:00 PM - **II6.4
Simulation of Shock-induced Melting of Ni Using Molecular-Dynamics Coupled to a Two-temperature Model.
L. Koci 2 , Eduardo Bringa 1 , D. Ivanov 3 , J. Hawreliak 1 , A. Higginbotham 6 , J. McNaney 1 , L. Zhigilei 4 , A.B. Belonoshko 5 , B.A. Remington 1 , R. Ahuja 2
2 , Uppsala University, Uppsala Sweden, 1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , National Centre for Laser Applications, Galway Ireland, 6 , University of Oxford, Oxford United Kingdom, 4 , University of Virginia, Charlottesville, Virginia, United States, 5 , The Royal Institute of Technology, Stockholm Sweden
Show AbstractUsing non-equilibrium molecular-dynamics (MD) simulations we study shock-induced melting for embedded atom method (EAM) Ni. Dynamic melting is probed by pair correlation functions, and we find a melting lattice temperature of Tmelt=6400+-300 K, for a melting pressure of Pmelt=275 +- 10 GPa. However, when a combined MD+TTM (two temperature model) approach is used to include electronic heat conduction and electron phonon coupling, Pmelt and Tmelt change. For a given pressure, the temperature behind the shock decreases due to electronic heat diffusion into the cold, pre-shocked material. This cooling of the material behind the shock increases slightly the melting pressure, as compared to simulations without electronic heat conduction and electron-phonon coupling. The decrease in the temperature behind the shock front is enhanced if the electron phonon coupling is artificially made larger. We also explore the feasibility of using X-ray diffraction to detect melting.
4:30 PM - II6.5
Compression Testing and Microstructure of Heat-treatable Aluminum Periodic Cellular Metal.
B. Bouwhuis 1 , G. Hibbard 1
1 Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada
Show AbstractPeriodic cellular metals (PCMs) can offer higher specific strengths and stiffnesses than conventional (i.e. stochastic) metallic foams. This study examines the effects of PCM microstructure and loading conditions on the mechanical performance.PCM cores with 95% open porosity were constructed from perforated 6061 aluminium alloy sheets using a perforation-stretching method. This method places planar, periodically-perforated sheet metal in an alternating-pin jig. The pins apply force out-of-plane, plastically deforming the sheet metal into a truss-like array of struts (i.e. metal supports) and nodal peaks (i.e. strut intersections). Micro-hardness profiles were taken in the PCM struts to investigate microstructural evolution during fabrication and after heat treatment.Truss cores were tested in two limiting uniaxial compression conditions. In the first, the PCM cores are placed between smooth compression platens where the nodes are laterally free and compressive forces are resisted through PCM node-bending (i.e. free compression). In the second, the PCM cores were placed between plates where the nodes are laterally confined and compressive forces are resisted through PCM beam-buckling (i.e. confined compression). Compression response was analyzed in terms of peak compressive strength, elastic modulus, and energy density absorbed upon densification; response values were used to illustrate the effect of compression test conditions. In addition, PCM cores were tested in the age-hardened state and annealed state to determine microstructural effects on compressive response.Analysis of PCM response in free- and confined-compression conditions indicates a greater force resistance in beam-buckling over node-bending resistance mechanisms. The compressive strength, elastic modulus, and energy density of heat-treatable AA6061 PCMs are be found to respond: 1) over a wide range of value, dependent on the microstructure; 2) over a wide range of value, dependent on the PCM compression conditions; and 3) equally, if not more repeatable and with higher compressive strength-to-weight ratio than conventional metal foams.
4:45 PM - **II6.6
Effects of Extreme Radiation Environment on Composite Materials.
J. Zhou 1
1 Dept. of Mechanical Eng., NASA-CARR, Prairie View A & M University, Prairie View, Texas, United States
Show AbstractNot available at time of submission.