bluuebunny/crossref_metadata_2025_split huggingface dataset:
Imaging Of Hierarchically Structured Materials
Authors: Sarikaya Mehmet , Aksay Ilhan A. 
Published: March 2011

AbstractWe describe techniques used to characterize hierarchically structured synthetic and biological materials. These techniques decipher the structures through the dimensional spectrum from the molecular and atomic scales (10.−10m) to the macro scales (10−3m) where the overall shape of the material emerges. Techniques used to image surfaces and internal structures can be categorized according to their wavelength and thus spatial resolution as light, x-ray, and electron microscopy. We also discuss newly emerging microscopy techniques that image surfaces at the atomic level without a focusing lens, such as scanning tunneling and atomic force microscopies, with the aid of field ion microscope and scanned probe microscopes. Transmission electron microscopy (TEM), a unique tool for multipurpose imaging, provides structural information through direct imaging, diffraction, and spectroscopic analysis. We illustrate the major TEM techniques used to analyze structural hierarchy with examples of synthetic and biological materials. We also describe light optical microscopy and scanning probe microscopy techniques, which cover the opposite ranges of the dimensional spectrum at the micrometer and subangstrom levels.
Hierarchical Structures that Arise from Self-Assembling Systems
Authors: Marzio Edmund A. Di 
Published: March 2011

AbstractA working definition of the term hierarchy that is consistent with past usage is that a hierarchy is an assemblage of assemblages. Self-assembling systems are essential to those hierarchical structures that contain structure on micro and nano distance scales since these tiny structures being so large in number can not be manipulated individually as is possible for larger structures. It is shown how self-assembling structures are nothing more than materials that have undergone a structure inducing phase transition. The induced structures can be either equilibrium structures (example lamellar block copolymers) or kinetic patterns (example snowflakes). Polymer systems provide a rich source of phase transitions. There are at least ten classes of polymer phase transitions. [1] helixrandom coil [2) polymerization or one-dimensional crystallization [3] adsorption [4] collapse transition [5] coilfstretch transition [6] liquidliquid transitions [7] crystallization [8] liquid crystals-plastic crystals [9] glass-amorphous and sol-gel transitions [10] soaps-membranes-micellesvesicles-block copolymers. These phase transitions can interact with each other creating an even richer overlay of self-assembled systems. We discuss three aspects of the building of Hierarchical structures from selfassembling systems.
Hierarchical Cellular Materials
Authors: Gibson L. J. , Ashby M. F. 
Published: March 2011

AbstractCellular materials are made up of an interconnecting network of strut- or plate-like members. Natural cellular materials include wood, cancellous bone, cork, palm and leaves. Engineering cellular materials are either in the form of honeycombs, with two-dimensional, prismatic cells, or foams with three-dimensional, polyhedral cells. Natural cellular materials usually have multiple phases at multiple scales while engineering cellular materials use a single phase at a single scale.In this paper, the efficiencies of various natural cellular materials are estimated by analyzing their behavior at various microstructural scales. The results of the analysis suggest microstructural design of hierarchically structured engineering cellular materials.
Biomimetic Mineralization of an Aligned, Self-Assembled Collagenous Matrix.
Authors: Christiansen David , Silver Frederick H. 
Published: March 2011

AbstractAn in-vitro method of mineralizing an aligned, self-assembled collagenous matrix is presented. Reconstituted collagen fibers were mineralized by exposure to saturated solutions of calcium and phosphate of varying pH in a double diffusion chamber for seven days at room temperature. Microscopic investigation of the mineral precipitate within the fibers indicate the formation of hydroxyapatite crystals with features comparable to mineral observed in bone and avian tendon. Mechanical test results indicate that tensile strength and tangent modulus increase after mineralization in comparison to unmineralized control fibers. These results suggest that mineralization of collagen fiber in-vitro may parallel some of the events seen in mineralization of bone and turkey tendon. In addition, mineralized collagen fibers may be useful in the design of composites for the replacement or augmentation of hard tissue
Hierarchical and Modulable Hydrophobic Folding and Self-assembly in Elastic Protein-based Polymers: Implications for Signal Transduction
Authors: Urry D. W. , Luan C.-H. , Peng S. O. , Parker T. M. , Gowda D. C. 
Published: March 2011

AbstractWhen the hydrophobic (apolar) and polar moieties of elastomeric polypeptides are properly balanced, the polypeptides are soluble in water at lower temperatures but undergo folding and assembly transitions to increased order on raising the temperature. The temperatures, Tt, and heats, ΔHt, of these inverse temperature transitions are determined by differential scanning calorimetry for a series of elastomeric polypentapeptides: poly(VPAVG), poly(IPAVG), poly(VPGVG), poly(IPGVG), poly[0.5(VPGVG),0.5(IPGVG)] and poly[0.82(IPGVG),0.18(IPGEG)] where V = Val, P = Pro, A = Ala, G = Gly, I = lle and E = Glu.On increasing the hydrophobicity as when replacing V(Val) by I(lle) which is the addition of one CH2moiety per pentamer, the temperature of the transition is lowered by 15 to 20°C and the heat of the transition is increased by more than one kcal/mole, for the above examples, by more than a factor of two.When differential scanning calorimetry thermograms are obtained on mixtures of poly(VPAVG) plus poly(IPAVG) or of poly(VPGVG) plus poly(IPGVG), it is found that the polypentapeptides self-separate, i.e., they de-mix, even though in the latter case the conformations have been shown to be essentially identical before and after their respective transitions.When the polymer, poly[0.82(IPGVG),0.18(IPGEG)], is studied as a function of pH, increasing the degree of ionization is found to increase the temperature and to decrease the heat of the transition such that, with the correct balance of I with the variable E(GluCOO−), the values of Ttand ΔHtcan be made to approach those of poly(VPGVG). Acid-base titration studies indicate that less than one Glu(COO−) in 200 residues can raise the value of Ttby 25°C and decrease ΔHtby 90%.These and additional data are interpreted to mean that there exists an hierarchical hydrophobic folding, that the hierarchical hydrophobic folding can be modulated by changing the degree of ionization or by changes in a number of intensive variables, that changes in these intensive variables can be used to drive folding/unfolding-assembly/disassembly transitions under isothermal conditions, and that these unfolding/folding and disassembly/assembly transitions can be used to achieve signal transduction. This is called the ΔTtmechanism of free energy (signal) transduction.
Polymer Liquid Crystals and Their Blends: A Hierarchy of Structures
Authors: Brostow Witold , Hess Michael 
Published: March 2011

AbstractHierarchical structures are possible in polymer liquid crystals (PLCs) since each molecule contains at least two kinds of building blocks that are not homeomorphic to each other. We discuss some examples of molecular structures and phase structures of monomer liquid crystals (MLCs) and PLCs: smectic phases formed by interdigitated MLC molecules; PLC molecule classification based on increasing complexity – and its consequences on properties of the materials; and formation and phase structures of LC-rich islands in PLCs and in PLC blends. Some rules pertaining to hierarchical structures are formulated. The knowledge of hierarchies is neccessary – but not sufficient – for intelligent procesing of PLCs and their blends and for achieving properties defined in advance. Computer modelling represents another important element of building materials to order.
Si Nanostructure Fabrication by Ga+ FIB Selective Doping and Anisotropic Etching
Authors: Steckl A. J. , Mogul H. C. , Mogren S. 
Published: March 2011

ABSTRACTA novel fabrication technique involving the use of focused ion beam (FIB) selective implantation to fabricate nanostructures on crystalline Si substrates in conjunction with anisotropic etching is described. Using this maskless & resistless approach, Si nanostructures were fabricated by FIB implantation of Ga+ at doses from 1015 to 1016/cm 2. Wet etching in KOH/IPA does not attack the implanted region, while it removes the underlying Si anisotropically, with a very low etch rate on the {111} planes. The result is a cantilever-like structure whose thickness is dependent on the implantation energy and dose. Pre-etching rapid thermal annealing at 600°C for 30 sec does not prevent structure fabrication and post-etching RTA does not affect the shape of the structures.
Reversible Luminescence Quenching of Porous Si by Solvents
Authors: Lauerhaas Jeffrey M. , Credo Grace M. , Heinrich Julie L. , Sailor Michael J. 
Published: March 2011

ABSTRACTInteraction of the solvents tetrahydrofuran, diethyl ether, methylene chloride, toluene, o-xylene, benzene, and methanol with luminescent porous n- Si (PS) results in reversible quenching of the luminescence associated with this material. The degree of quenching ranges from 99% – 50%, and scales with solvent dipole moment. Reaction with gaseous Cl2, Br2, or I2 results in irreversible quenching, associated with a surface reaction that removes Si-H bonds. Total luminescence quenching is observed on treatment of a PS wafer with a solution of the electron donor ferrocene in toluene, suggesting that charge transfer quenching may also be operative in this material. Luminescence is partially recovered by rinsing the PS in pure toluene. The data show that photoluminescence of PS is highly sensitive to surface adsorbates, suggesting that carrier trapping is easily induced in this material.
Microstructural Characterization of Photoluminescent Porous Silicon
Authors: Macaulay J. M. , Ross F. M. , Searson P. C. , Sputz S. K. , People R. , Friedersdorf L. E. 
Published: March 2011

ABSTRACTWe have used electron microscopy to examine the microstructure of porous silicon films over a wide range of doping levels, and photoluminescence spectroscopy to study their optical properties. We discuss the impact of our experimental results on models from the literature which were proposed to explain visible luminescence from porous silicon.
Effect of Surface Finish on Nuclear Glass Dissolution Rate
Authors: Dussossoy J.L. , Dubois C. , Vernaz E. , Chambaudet A. 
Published: March 2011

ABSTRACTThe influence of the surface finish on nuclear glass dissolution was investigated. Seven different surface finishes were tested: a specimen as cut, three specimens polished with 220, 600 and 4000 mesh SiC paper and one with 1 μm diamond powder, a flame-polished specimen and a thermal rupture specimen.The initial glass corrosion rates were measured after 7 and 28 days of Soxhlet leaching at 100°C. The surface finish of each glass coupon was also assessed by three-dimensional analysis before and after leaching for 28 days. Leaching solution analyses showed that the mean apparent leach rate for the first 7 days was highly dependent on the surface finish: the measured rates ranged from 3.8·g.m-2d-1 for the as-cut specimen to 1.3 g·m-2d-1 for the flamepolished specimen. The differences in the leach rates diminished considerably after 28 days of leaching: the mean rate measured between 7 and 28 days for the as-cut and polished specimens was identical (1.7 g·m-2d-1), but was still lower for the remaining two specimens. Three-dimensional surface analysis showed that leaching revealed surface defects (superficial microcracks) produced by cutting or polishing. These effects were less perceptible on the flame-polished or thermally ruptured specimens. The actual surface area of the cut and polished specimens exceeded the apparent geometrical area.In another experiment, the leach rates measured for as-cut specimens and flamepolished specimens were measured over periods of five months or more using a thermogravity balance placed above the Soxhlet device. The experiment confirmed the existence of an initial period during which the dissolution rate for the as-cut specimen was much higher than the mean corrosion rate.
Materials Interface Interactions Test (MIIT); in-Situ Testing of Simulated Hlw Forms in Salt- Performance of Srs Simulated Waste Glass After up to 5 Years of Burial at the Waste Isolation Pilot Plant (WIPP)
Authors: Wicks G.G. , Lodding A.R. , Macedo P.B. , Clark D.E. 
Published: March 2011

ABSTRACTThe first field tests conducted in the United States involving burial of simulated high-level waste [HLW] forms and package components, were started in July of 1986. The program, called the Materials Interface Interactions Test or MIIT, is the largest cooperative field-testing venture in the international waste management community. Included in the study are over 900 waste form samples comprising 15 different systems supplied by 7 countries. Also included are approximately 300 potential canister or overpack metal samples along with more than 500 geologic and backfill specimens. There are almost 2000 relevant interactions that characterize this effort which is being conducted in the bedded salt site at the Waste Isolation Pilot Plant (WIPP), near Carlsbad, New Mexico. The MIIT program represents a joint endeavor managed by Sandia National Laboratories in Albuquerque, N.M., and Savannah River Laboratory in Aiken, S.C. and sponsored by the U.S. Department of Energy. Also involved in MIIT are participants from various laboratories and universities in France, Germany, Belgium, Canada, Japan, Sweden, the United Kingdom, and the United States. In July of 1991, the experimental portion of the 5-yr. MIIT program was completed. Although only about 5% of all MIIT samples have been assessed thus far, there are already interesting findings that have emerged. The present paper will discuss results obtained for SRS 165/TDS waste glass after burial of 6 mo., 1 yr. and 2 yrs., along with initial analyses of 5 yr. samples.
Time-Dependence of Volatilization of 137Cs and 106Ru Over High-Level Waste Glass in a Canister
Authors: Kamizono Hiroshi , Muraoka Susumu 
Published: March 2011

ABSTRACTVolatility of 137Cs and 106Ru at 600ºC over high-level waste glass in a canister is numerically analyzed. The time-dependence of normalized concentrations of each radionuclide is traced by a differential equation based on a simple model consisting of competitive forward and backward steps. It is assumed that, as time proceeds, a surface layer forms on the glass and serves as a protective barrier against volatilization. It is found that the forward rate of volatilization for 137Cs is about 140 times greater than that of 106Ru at 600ºC. The effects of the glass surface area and plenum volume on the concentration excursion inside the canister are closely estimated by the differential equation.
Structures and Stabilities of Trivalent and Tetravalent Rare Earth Ions in Sevenfold Andeightfold Coordination in Fluorite-Related Complex Oxides
Authors: Morss Lester R. 
Published: March 2011

ABSTRACTThis paper reports the preparation and characterization of a series of oxides containing3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M4+/M3+ reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic-size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M3+ and M4+ lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxies. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi2O7-x and CaMZr2O7-x. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi2O7 is a pyrochlore, a = 10.142(4) Å with Ce4+ much more easily reducible than in the perovskite BaCeO3. By contrast, a preparation with the stoichiometry “CaPrTi2O7-x” is a two-phase mixture of perovskite CaTiO3 and a presumably Pr3+-rich pyrochlore Pr2Ti2O7(?). CaTbTi2O7-x appears to be a Tb3+ pyrochlore, a = 10.149(2) Å. CaCeZr2O7 is a pyrochlore, a = 10.524(1) sÅ. A preparation of “CaPrZr2O7-x” also appeared to yield a two-phase mixture, perovskite CaZrO3 and pyrochlore Pr2Zr2O7. In this paper, the structures, f-element ion sites, and M(IV)- MM1I stability trends in the CaMTi2O7-x and CaMZr2O7-x oxides are compared with the structural and stability trends in the perovskites BaMO3 which have M4+ ions in sixfold (tilted octahedra) coordination.
Enthalpies of Formation of Rare Earth and Actinide(III) Hydroxides; their Acid-Base Relationships and Estimation of their Thermodynamic Properties
Authors: Morss Lester R. , Williams Clayton W. 
Published: March 2011

ABSTRACTThis paper reviews the literature on rare earth(III) and actinide(III) hydroxide thermodynamics, in particular the determination of their enthalpies of formation at 25 ºC. The hydroxide unit-cell volumes, lanthanide/actinide ion sizes, and solid-solution stability trends have been correlated with a generalized acid-base strength model for oxides to estimate properties for heterogeneous equilibria that are relevant to nuclear waste modeling and to characterization of potential actinide environmental interactions. Enthalpies of formation and solubility-product constants of actinide(III) hydroxidesare estimated
SIMULATING THE BEHAVIOUR OF FISSION PRODUCTS IN UO2
Authors: Grimes Robin W. 
Published: March 2011

ABSTRACTFission products in nuclear fuels exhibit a significant variation in solubility and stability. To understand better the reasons for this variation, the Mott-Littleton simulation technique has been used to calculate solution energies of the fission products Br, Kr, Rb, Sr, Y, Zr, Te, I, Xe, Cs, Ba, La and Ce. Nonstoichiometry and variable charge state are important components of the model.
The Critical Condition for the Initiation of Localized Corrosion of Mild Steels in Contact with Bentonite Used For Nuclear Waste Package
Authors: Nakayama Guen , Akashi Masatsune 
Published: March 2011

ABSTRACTIt has been established that the mild steels which undergo the general corrosion in the acidic to neutral environments, attain the passivity status in alkaline environments, thereby becoming liable to the localized corrosion, such as pitting corrosion and crevice corrosion. Now, for the case of using bentonite as a buffer to stand between the hostrock and the geological disposal packages of high level nuclear waste, localized corrosion behaviors of mild steel as a candidate for such a package has been studied quantitatively for environments where the the otherwise neutral ground water would be turned slightly alkaline with pH = 9.5 - 10.0.In view of the lack of quantitative data on the passivity-to-localized corrosion of mild steel in natural water environments of weak alkalinity, the present authors have previously determined an empirical E-pH diagram for mild steel with a 20 °C, 1 m mol/L [HC03-], 10 ppm [CI -] solution simulating the natural water environment concerned; it has been shown that the general corrosion-to-passivity transition condition was determined to be pHd =9.4, and the mild steel was shown to be liable to localized corrosion over a large portion of the passivity domain. The present paper discusses behaviors, mechanisms, and critical conditions for initiation of localized corrosion in mild steel placed in bentonitesuspending natural water environment, in terms of the critical potentials for pitting (Vc), and crevice corrosion (ER,CREV). Bentonite was addid to the solution in varying amounts to give bentonite-to-solution ratios up to 0.1, while the pHvalue was adjusted appropriately with sodium carbonate, always keeping the bentonite particles in suspension.It is demonstrated that bentonite particles suspended in water will deposit upon the steel on receipt of Fe2 + ions, thereby promoting pitting corrosion by preventing repassivation and promoting crevice corrosion by acting as an effective crevice, once the environment conditions become favorable for localized corrosion.We conclude therefore that disposal package made of mild steel and placed in an underground water environment with bentonite as buffer will be liable to localized corrosion.
Alteration of Natural Uranyl Oxide Hydrates in Si-Rich Groundwaters: Implications For Uranium Solubility
Authors: Finch R.J. , Ewing R.C. 
Published: March 2011

ABSTRACTThe uranyl oxide hydrates are common initial corrosion products of uraninite (nominally U02+x) during weathering. In the presence of dissolved silica these early-formed phases alter to uranyl silicates (most commonly soddyite, U2SiO8-2H2O, and uranophane, CaU2Si2O11·6H2O). Uraninite, however, usually contains radiogenic Pb, and the earlyformed Pb-poor uranyl oxide hydrates alter incongruously to uranyl silicates plus Pb-enriched uranyl oxide hydrates such as curite. Similar to dissolved silica, radiogenic Pb may also serve to limit the mobility of U in nature by fixing U in solid phases. Curite may also play an important role in the formation of uranyl phosphates, which are significantly less soluble than the uranyl silicates, and control U solubility in many groundwaters associated with altered U ore.
Uranium Redistribution and Fixation During Chlorite Weathering at Koongarra, Australia
Authors: Murakami Takashi , Isobe Hiroshi , Nagano Tetsushi , Nakashima Satoru 
Published: March 2011

ABSTRACTThe chemical forms of iron minerals and uranyl species have been examined non-destructively by visible microspectroscopy and electron microprobe analysis in order to obtain a better understanding of uranium redistribution and fixation mechanisms. The uranyl species are associated with sub-micron sized iron minerals, such as hematite (Fe2O3), goethite (FeOOH), and ferrihydrite (Fe4-5(OH,O)12). Additionally, some uranium is fixed to goethite in weathered chlorite grains. Sub-micron sized saleeite, Mg(UO2)2(PO4)2. 1OH2O, is the most probable uranyl phase associated with the iron minerals. This suggests that the uranium fixation in the vicinity of the Koongarra uranium ore deposits is the result of the coprecipitation and sorption of microcrystals of saleeite on to the iron minerals released during weathering of chlorite.
The Long-Term Dissolution Behaviour of the Pamela Borosilicate Glass SM527 - Application of SA/V as Accelerating Parameter
Authors: Lemmens K. , Iseghem P. Van 
Published: March 2011

ABSTRACTThe Al2O3 rich borosilicate glass SM527 was submitted to corrosion tests with glass surface area to solution volume ratios ranging from 10 to 10000 m-1. This latter condition would correspond with a 1000 fold acceleration relative to the reference MCCI condition. Powdered glass was used to reach SANV ratios of 500 m-1 and more. The leaching solutions were either distilled water or referred to Boom clay disposal conditions. The results based on the boron concentration in solution revealed a relatively linear dependence on SA/V.t0.5 in the pure solutions, on the longer term (DW and clay water). Diffusion is suggested to be the process governing the glass dissolution, although other processes should not be excluded. In a clay / clay water mixture (slurry), long term dissolution seems to be limited by saturation. Short term data for boron are largest in the clay slurry, but with time the boron concentrations converge to similar values in the three media considered. The use of SA/V as an accelerating factor is promising, but certainly requires additional research.