bluuebunny/crossref_metadata_2025 huggingface dataset:
Modifying Nafion with Nanostructured Inorganic Oxides for Proton Exchange Membrane Fuel Cells
Authors: Daiko Yusuke , Klein Lisa C. , Nogami Masayuki
Published: April 2011

Nafion, a perfluorosulfonate ionomer, was modified to increase its thermal stability and reduce its methanol permeability. Hybrid membranes of TiO2·SiO2/Nafion and TiO2·SiO2·P2O5/Nafion™ were prepared using an infiltration sol-gel method. Si(OC2H5)4and Ti(OC4H9)4were infiltrated into dry NafionTMmembranes, followed by hydrolysis and condensation reactions in first HCl and then NH4OH solutions. The level of inorganic content was controlled by the infiltration time, incorporating up to 50 wt%. Solvent uptake, swelling, water content and proton conductivity were measured at room temperature. Hybrid membranes of TiO2·SiO2/Nafion with ∼30 wt% of infiltrated oxides showed a significantly lower methanol uptake of ∼20wt% and a swelling ratio of 1.15, as compared to those of unmodified NafionTMmembrane, ∼60wt% for methanol uptake and 1.8 for swelling ratio. Proton conductivities for TiO2·SiO2/Nafion hybrid membranes decreased with increasing infiltrated oxides. However, infiltrated membranes treated in phosphoric acid solutions to increase the number of P-OH groups showed a six-fold increase in proton conductivity.
Hybrid Proton-Carrier Polymer Composites for High-Temperature FCPEM Applications
Authors: Pern F. J. , Turner J. A. , Herring A. M.
Published: April 2011

Hybrid proton-carrier polymer composites were fabricated in an effort to develop high-performance high-temperature proton exchange membranes (PEMs) for fuel cell applications in the 100°–200°C range. The solution-cast hybrid membranes comprise a polymer host and a SiO2-based proton-carrier composite that was synthesized via sol gel approach using a functional silane and tetraethoxysilane (TEOS) in acidic conditions. The primary H+-carrying component was either a heteropoly silicotungstic acid (STA) or a sulfonic acid (SFA) that was thermooxidatively converted from a mercapto (-SH) group. The embedding level of STA on the silane-modified SiO2 sol gel composites was strongly affected by the presence and the functional group of the silane. Ion exchange capacity (IEC) of the water-washed, SiO2-based STA and SFA proton-carrier composite powders is in the range of 1.8–3.5 mmol/g, two to three times higher than that for Nafion 117 (0.9 meq/mol). A glycidylmethacrylate-type copolymer, PEMAGMA, which is stable up to ∼225°C, was able to produce mechanically robust and flexible hybrid membranes. Upon curing, the PEMAGMA composite membranes showed a ∼75% gel under the present formulation and retained the "free" STA effectively with slight loss when extracted in an 85°C water. The W12-STA-containing PEMAGMA membranes followed the weight loss trends of water from STA and the SiO2-based sol gel composite, showing a 10 wt% loss at 150°C and a 15 wt% loss at 225°C. Fuel cell performance tests of the preliminary films gave a Voc in the 0.85–0.93 V range, but a low current density of <4 mA/cm2. The resistive characteristics were attributed to inhomogeneous distribution of the sol gel nanoparticles in the PEMAGMA matrix, a result of phase separation and particulate agglomeration during film forming.
Degradation Behavior of Novel Poly(α-hydroxy acid)-Derived Polyesters
Authors: Sy Jay , Xu Xiaojun , Lipski Anna Marie , Stevens Molly , Shastri V. Prasad
Published: April 2011

Due to their bioresorbable characteristics biodegradable polyesters are attractive materials for sutures, fracture fixation devices, and drug delivery systems. These polymers degrade primarily through a bulk erosion mechanism. In many instances including drug delivery and fabrication of orthopaedic devices, surface erosion is desired as it confers linearity with respect to degradation and changes in modulus. We hypothesized that surface erosion could be achieved in poly(αΏ-hydroxy acids) by tuning the lipophilicity of the system and hence the water uptake. Toward this end, we used a modular design strategy to manipulate the hydrophilic-lipophilic balance (HLB) of a polymer chain at various stages by judicious choice of building blocks. Using this novel synthetic strategy we have synthesized a library of degradable polyesters derived from poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) that exhibit surface erosion behavior. Surface erosion was further verified by ultrastructure analysis of degraded polymer pellets and thin films by Scanning Electron Microscopy and tapping mode Atomic Force Microscopy respectively.
Collagen-Inspired Nano-fibrous Poly(L-lactic acid) Scaffolds for Bone Tissue Engineering Created from Reverse Solid Freeform Fabrication
Authors: Chen Victor J. , Smith Laura A. , Ma Peter X.
Published: April 2011

Reverse solid freeform (SFF) fabrication was used to create highly-controlled macroporous structures in nano-fibrous poly (L-lactic acid) (PLLA) scaffolds. By using a computer-aided design (CAD) program to create a negative template for the scaffold, the three-dimensional (3-D) mold was created on a 3-D printer using a wax. After the template was printed, a solution of PLLA in tetrahydrofuran (THF) was cast into the mold, and was subsequently phase separated at -70°C which gives the nano-fibrous morphology. This resulted in a 3-D nano-fibrous scaffold with a uniform fiber mesh throughout the entire matrix, and greatly increased the surface area within the scaffold. Fiber diameters in these scaffolds were 50-500 nm, similar to type I collagen, and the densities of the fiber meshes can be altered by changing the polymer concentration. To examine the scaffold's potential for tissue regeneration, MC3T3-E1 osteoblasts were seeded and cultured on the scaffolds. Results show that the osteoblasts attached and proliferated on the scaffolds. After 6 weeks in culture, bone-like tissue was evident within the nano-fibrous scaffolds. By having the ability to control the macroporous architecture, interconnectivity, orientation, and external shape of the scaffold, as well as the nanometer-scaled fibrous features in the pore walls, this SFF fabrication/phase separation technique has great potential to design and create ideal scaffolds for bone tissue engineering.
Fabrication of Super Water-Repellent Surfaces by Nanosphere Lithography
Authors: Shiu Jau-Ye , Kuo Chun-Wen , Chen Peilin , Mou Chung-Yuan
Published: April 2011

: Inspired by the water-repellent behavior of the micro- and nano-structured plant surfaces, superhydrophobic materials, with a water contact larger than 150° superhydrophobic surfaces using a combination of nanosphere lithography and plasma etching. It has been found that the water contact angle on these surfaces can be systematically tuned from 132° to 168° by trimming the diameters of polystyrene nanospheres using oxygen plasma. The water contact angles measured on these surfaces can be modeled by the Cassie's formulation without any adjustable parameter.
Relationship Between Dip-Coating Fabrication Parameters and the Elastic Properties of Rubber Latex Prosthesis
Authors: Neves-Junior W.F.P. , Santos T. C. dos , Ferreira M. , Mulato M. , Coutinho-Netto J.
Published: April 2011

In the present work we are mainly interested in the use of the natural latex extract from the Hevea brasiliensis for medical applications. This presentation focuses on the influence of the fabrication parameters on the final elastic properties of the tubes obtained by dip-coating. The elastic properties of the prosthesis were investigated using tension-deformation experiments. The influence of important fabrication parameters were studied, such as: dip-coating velocity, final prosthesis thickness (which was varied as a function of the number of baths), and thermal treatment. Single and cycled tension-deformation experiments were performed with closed and opened samples considering longitudinal and axial directions. A model is proposed for the anisotropy of the elastic behavior, which involves the sulfur bonds between polymeric chains.
Self-Assembling Microspheres from Charged Functional Polyelectrolytes and Small-Molecule Counterions
Authors: Mckenna Brandon , Birkedal Henrik , Bartl Michael H. , Deming Timothy J. , Stucky Galen D.
Published: April 2011

Micrometer-sized spheres have been found to assemble from homopolymer electrolytes and small, multivalent counterions in water. In contrast to previous efforts, these vesicles do not use preformed templates, do not require block copolymers, and do not necessarily employ nanoparticles. We have investigated the requirements for vesicle formation with regards to both components of the assembly. Self-assembly occurs with a variety of poly-amino acids and counterions, all of which require a minimum number of charged groups to promote non-covalent crosslinking. We show how the assembly process is controlled by pH and how, in consequence, the pKa's of the reactants can be used to reliably predict sphere formation. By varying the nature of the small counterions, we have determined the requirements for assemblies. The assemblies have been further investigated using confocal microscopy and fluorescent labeling of the different components.
Effects of Surface Texturing on Cell Adhesion for Artificial Joints
Authors: Shi B. , Fairchild A. , Kleine Z. , Kuhn T. , Liang H.
Published: April 2011

One of the major issues of joint implants is their loss (detachment) and subsequent failure after a limited number of years in application. Understanding and improving cell adhesion to implanting materials to extend lifespan, lubrication, and self-regeneration properties are therefore substantially important. In this research, we investigate effects of surface properties, such as wettabilty and texture on cell culture for the purpose of biotribological applications. Materials used are polyurethane, polyvinyl alcohol, and glass. Surface analysis indicates that surface structures have profound impact on cells growth.
Adsorption of Amelogenin Nanopheres onto Charged Surfaces, A Model for Tooth Enamel Matrix Re-construction
Authors: J. Moradian-Oldak , C. Gergely , N. Bouropoulos , F.J.G. Cuisinier
Published: April 2011

Amelogenins are hydrophobic proteins that constitute more than 90% of the secretory stage enamel matrix. The assembly of amelogenin into nanospheres has been postulated to be a key factor in controlling the structural organization of the enamel extracellular matrix framework, which provides the scaffolding for the elongated and oriented growth of enamel apatite crystals. To get insight into the structure and function of amelogenin in controlling the process of crystal growth we have utilized two different approaches to investigate adsorption of amelogenin nanospheres onto charged surfaces: A) analysis of adsorption of amelogenin onto hydroxyapatite crystals by means of Langmuir Model for protein adsorption. B) analysis of amelogenin mono or multi-layer formation by sequential adsorption process onto auto-assembled polyelctrolytes films. Our data indicate that amelogenin nanospheres adsorb onto the surface of apatite crystals as binding units with defined adsorption sites. We found that amelogenin nanospheres are negatively charged and a monolayer of these nanospheres adsorbed in an irreversible way on positively ending polyelectrolyte multilayers most likely through electrostatic interactions.
Effects of Surface Roughness and Maximum Load on the Mechanical Properties of Cancellous Bone Measured by Nanoindentation
Authors: Donnelly Eve , Baker Shefford P. , Boskey Adele L. , Meulen Marjolein C. H. van der
Published: April 2011

Nanoindentation was used to assess the mechanical properties of lamellar and interlamellar tissue in dehydrated rabbit cancellous bone. The effects of surface roughness and maximum nanoindentation load on the measured mechanical properties were examined in two samples of differing surface roughness using maximum loads ranging from 250-3000 μN. As the ratio of indentation depth to surface roughness decreased below approximately 3:1, the variability in material properties increased substantially. At low loads, the indentation modulus of the lamellar bone was approximately 20% greater than that of the interlamellar bone, while at high loads the measured properties of both layers converged to an intermediate value. Relatively shallow indentations made on smooth surfaces revealed significant differences in the properties of lamellar and interlamellar bone that are consistent with microstructural observations of lamellar bone as more mineralized than interlamellar bone.
Regular, low density cellular structures - rapid prototyping, numerical simulation, mechanical testing
Authors: Stampfl J. , Seyr M.M. , Luxner M.H. , Pettermann H.E. , Woesz A. , Fratzl P.
Published: April 2011

Cellular solids form the basis of many biological and engineering structures. Most models use the relative density and the mechanical properties of the bulk material as the main parameter for the prediction of the mechanical properties of such structures. In this work the influence of the architecture of periodic cellular solids on the mechanical properties is investigated numerically and experimentally.

Using computer aided design, structures with 8x8x8 base cells are designed and fabricated. The physical prototypes which are tested experimentally are made from thermosetting and thermoplastic polymers by employing Rapid Prototyping (RP) techniques. Various RP techniques are compared regarding their suitability for the fabrication of cellular materials.

For numerical simulation of the cellular structures, linear Finite Element analysis is employed. Three-dimensional models are set up using higher order beam elements. In a first step, the structure is treated as an infinite medium and homogenization via a 'periodic micro-field approach' is used. The entire elastic tensors for different relative densities are evaluated, from which the directional dependencies of the Young's moduli are derived. In a second step, simulations of finite structures are performed for direct comparison with experiments. Samples consisting of several basic cells are modeled which leads to a better correspondence to the experimental setup. Finite structures of different numbers of cells are modeled to study the influence of the sample size.

The experimental and numerical results correspond very well and form a consistent picture of the problem. The multi-disciplinary approach leads to a comprehensive view of effects which govern the mechanical behaviour of the investigated cellular structures.
Corrosion of Copper Nuclear Waste Containers In Aqueous Sulphide Solutions
Authors: Smith J. , Qin Z. , Shoesmitha D.W. , King F. , Werme L.
Published: April 2011

Electrochemical and surface analytical techniques are being used to determine the mechanismand kinetics of Cu corrosion in the presence of sulphide, with the primary goal of developing a mixed potential model for Cu corrosion under disposal conditions. Corrosion potential (Ecorr) measurements indicate the formation of copper sulphide films is rapid leading to rate control by the cathodic reduction of water. Impedance spectroscopy suggests the anodic charge transfer process is rapid leading to film growth limited by diffusive transport. Experiments are underway to determine the current-potential relationships necessary in the development of a mixed potential model.
Reexamining the Dissolution of Spent Fuel: A Comparison of Different Methods for Calculating Rates
Authors: Hanson Brady D. , Stout Ray B.
Published: April 2011

Dissolution rates for spent fuel have typically been reported in terms of a rate normalized to the surface area of the specimen. Recent evidence has shown that neither the geometric surface area nor that measured with BET accurately predicts the effective surface area of spent fuel. Dissolution rates calculated from results obtained by flowthrough tests were reexamined comparing the cumulative releases and surface area normalized rates. While initial surface area is important for comparison of different rates, it appears that normalizing to the surface area introduces unnecessary uncertainty compared to using cumulative or fractional release rates. Discrepancies in past data analyses are mitigated using this alternative method.
Risk-Based Evaluation of Long-Term Safety for a Yucca Mountain Repository Using the IMARC TSPA Code
Authors: Kessler John , Apted Michael , Kozak Matthew , Zhou Wei
Published: April 2011

The Electric Power Research Institute (EPRI) has conducted independent total system performance assessments (TSPAs) of the proposed Yucca Mountain spent fuel and high-level radioactive waste repository for 15 years. EPRI uses its TSPA code, IMARC, currently in its eighth version. The major results of the IMARC-8 analyses are presented in this paper. In all of the situations evaluated by EPRI using IMARC-8, the results for the reference repository concept for Yucca Mountain are well within the regulatory criteria established in the applicable regulations, 10 CFR 63 and 40 CFR 197. Further analyses indicate that at least two of the repository barriers must fail to function as anticipated for dose risks to rise as much as one millirem per year (1/15th of the regulatory limit).
Self-Irradiation of Monazite Ceramics: Contrasting Behavior of PuPO4 and (La,Pu)PO4 Doped with Pu-238
Authors: Burakov Boris E. , Yagovkina Maria A. , Garbuzov Vladimir M. , Kitsay Alexander A. , Zirlin Vladimir A.
Published: April 2011

To investigate the behavior of monazite during accelerated radiation damage, which simulates effects of long term storage, 238Pu-doped polycrystalline samples of (La,Pu)PO4 and PuPO4 were synthesized for the first time ever and studied using powder X-ray diffraction (XRD) analysis and optical microscopy. The starting precursor materials were obtained by precipitation of La and (or) Pu from their aqueous nitrate solutions followed by calcination in air at 700°C for 1 hour, cold pressing, and sintering in air at 1200-1250°C for 2 hours. The 238Pu contents in ceramic samples measured using gamma spectrometry were (in wt.% el.): 8.1 for (La,Pu)PO4 and 7.2 for PuPO4. The (La,Pu)PO4 monazite remained crystalline at ambient temperature up to a cumulative dose of 1.19 × 1025 alpha decays/m3. In contrast, the PuPO4 monazite became nearly completely amorphous at a relatively low dose of 4.2 × 1024 alpha decays/m3. Swelling and crack formation due to the alpha decay damage was observed in the PuPO4 ceramic. Also, under self-irradiation this sample completely changed color from initial deep blue to black. The (La,Pu)PO4 monazite was characterized by a similar change in color from initial light blue to gray, however, no swelling or crack formation have so far been observed. The results of this study allow us to conclude that the radiation damage behavior of monazite strictly depends on the chemical composition. The justification of monazite-based ceramics as actinide waste forms requires additional investigation.
A Novel Equation for Prediction of Intrinsic Sorption Constants of Metal Cations at Mineral-Water Interfaces
Authors: Xu Huifang , Wang Yifeng
Published: April 2011

The sorption of radionuclides onto mineral-water interfaces is an important mechanism of radionuclide retardation in subsurface environments. Although a large body of data on metal sorption has been accumulated, the interaction of radionuclides at the mineral-water interface is still not well quantified. In this paper, we establish a linear free energy relationship that can correlate intrinsic metal sorption constants to the known thermodynamic properties of metal cations and mineral phases. This relationship can be used to predict the intrinsic sorption constants of metal cations adsorption on various mineral-water interfaces. Based on a surface complexation model, an adsorption constant of a cation Mn+ onto a mineral surface can be represented by the sum of “intrinsic” and coulombic terms, that is logKads, Mn+ = logKint, Mn+ - (nF/2.303RT)0. To construct our linear free energy relationship, we further decompose an intrinsic sorption constant into the solvation contribution, which characterizes the work to be done to move a cation from one dielectric medium (solution) to another (interface), and the chemical contribution, which characterizes the chemical bonding abilities of cations to mineral surface sites. The overall intrinsic sorption constant can be calculated by the equation of:

2.303RTlogKint, Mn+ = -ΩMn+ (1/εk) - a* δG0n, Mn+ - b* - β*rMn+ + δG0f, Mn+, or

2.303 RT logKint, Mn+ = -ΩMn+ (1/εk) + a* δG0s, Mn+ + (1 - a*)δG0f, Mn+ - b* - β* rMn+,

where, ΩMn+ is interfacial Born solvation coefficient of cation M, εk is the dielectric constant of a mineral; δG0n, Mn+, δG0s, Mn+ and δG0f, Mn+ are the non-solvation energy, solvation energy and the Gibbs free energy formation of a cation, respectively; rMn+ is the ionic radius of a cation; and a*, β*, and b* are constants, which can be determined by fitting the equation to the existing experimental data. We have applied the equation to the sorption of divalent cations on oxide, hydroxide, and silicate minerals. In particular, based on additivity of molecular polarizabilities, we have used the equation to calculate the intrinsic sorption constants of divalent metals and radionuclides on interstratified clay minerals that are commonly found in the nature or are proposed as backfills for nuclear waste geologic repositories. The discrepancies between calculated and measured values are generally within 0.8 log unit.
Study of Ni(II) sorption on chlorite - a fracture filling mineral in granites
Authors: Gustafsson Å. , Molera M. , Puigdomenech I.
Published: April 2011

Chlorite is an Fe(II)-containing phyllosilicate which is often present as a fracture filling mineral in e.g. granitic rocks. It may therefore be significant in influencing redox conditions and sorption processes in granitic groundwaters. The sorption properties of chlorite may therefore be important when modelling the migration of radionuclides under reducing conditions around nuclear waste repositories or in sites contaminated by mining waste.

The sorption behaviour of Ni(II) onto a natural chlorite (Karlsborg, Sweden) was investigated using a batch technique. The effects of three different background electrolyte concentrations (0.01 M, 0.1 M and 0.5 M NaClO4), different pH values (ranging from 4 to 11) and different Ni(II) concentrations (10−6 and 10−8 M) were studied under anoxic conditions in a glove-box. Ni(II) solutions were spiked with 63Ni and β-Liquid scintillation counting (LSC) was used to determine the concentration of nickel in the bulk solution, allowing the calculation of solid-water distribution coefficients for the metal ion.

The results of the sorption experiments show strong pH dependence at pH > 5, but the sorption is independent of ionic strength. The maximum adsorption is found in the pH range between 7 and 11 with Kd values ≍103 cm3/g. A diffuse double layer model has been used to describe the experimental results.
Product consistency test of fully radioactive high-sodium content borosilicate glass K-26
Authors: Ojovan N.V. , Startceva I.V. , Barinov A.S. , Ojovan M.I. , Bacon D.H. , McGrail B.P. , Vienna J.D.
Published: April 2011

Chemical durability of fully radioactive, high-sodium borosilicate glass K-26 was evaluated using the product consistency test PCT-A. Examination revealed normalised leaching rates as high as 5.93•10−2, 4.05•10−2 and 2.93•10−2 g/m2•day for sodium, boron and silicon respectively. Data on chemical durability of glass K-26 are consistent with similar composition glasses. These are of particular interest for performance assessment models.
Aqueous Dissolution of Pyrochlore and Zirconolite in F--bearing Solutions
Authors: Zhang Zhaoming , Li Huijun , Vance Eric R. , McLeod Terry , Scales Nicholas
Published: April 2011

We have studied the aqueous durability of pyrochlore-structured yttrium-titanate (Y2Ti2O7) and Nd/Al-bearing zirconolite [(Ca0.8Nd0.2)Zr(Ti1.8Al0.2)O7] in both neutral and acidic solutions, with and without the presence of 0.001 M of NaF. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to characterize the composition, structure and morphology of the pyrochlore (Y2Ti2O7) and zirconolite surfaces, both before and after static dissolution testing at 90 and 150°C for four weeks. The leachates were also analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to estimate the individual elemental releases. The results show that the presence of F- ions only has a significant effect in acidic media on the dissolution behavior of pyrochlore and zirconolite. This detrimental effect is more pronounced for pyrochlore than zirconolite; the Y2Ti2O7 surface was replaced completely by alteration products after dissolution testing at 150°C for 4 weeks in acidic media with 0.001 M fluoride ions.
Rapid Method for ICP-MS Analysos of Plutonium in Sediment Samples
Authors: Greis Christina , Düker Anders , Pettersson Håkan , Karlsson Stefan , Allard Bert
Published: April 2011

A rapid and reliable method for quantification of transuranium elements in environmental samples is required from the aspect of emergency preparedness. Determination of these elements in e.g. sediment samples includes three steps: sample dissolution, chemical separation and measurement. Different acids were used for leaching of plutonium, americium and neptunium from contaminated sediment (during heating or microwave digestion). Chemical separation was performed by co-precipitation (with Fe(OH)3 or NdF3), by anion exchange or by liquid-liquid extraction (with tributylphosphate, trioctylamine and thenoyl trifluoroacetone, respectively). The following radioisotopes were quantified by quadrupole ICP-MS equipped with an ultrasonic nebulizer (USN): 237Np, 239Pu, 240Pu, 241Pu, 242Pu and 241Am. Data are only given for 239Pu and 240Pu in this paper. Plutonium was also measured by alpha spectrometry in some samples, as well as 137Cs and 241Am by gamma spectrometry. The agreement between concentrations of plutonium obtained by ICP-MS and alpha spectrometry was good, which demonstrates that a simple and rapid procedure for analysis of plutonium by quadrupole ICP-MS is feasible.
Separation of 137Cs from Acidic Nuclear Waste Simulant via an Engineered Inorganic Ion Exchanger
Authors: Tranter T.J. , Vereshchagina T.A. , Anshits A.G. , Fomenko E. , Aloy A.S. , Sapozhnikova N.V.
Published: April 2011

An engineered ion exchange material has been prepared for the specific purpose of removing radioactive cesium from acidic waste. Separating the fission product 137Cs from the bulk of the nuclear waste stream is often advantageous because, after typical cooling times, this isotope is usually the primary source of gamma radiation dose. The engineered ion exchanger was prepared using ammonium molybdophosphate impregnated into hollow glass crystalline microspheres. The microspheres or cenospheres, are refractory compounds of silica and alumina that are derived from the fly ash produced in coal combustion. This paper describes equilibrium experiments that were conducted with the engineered ion exchanger and a simulated acidic waste solution. These tests indicate that the new material has a high capacity and selectivity for cesium in these matrices.
Dissolution Rate of Colloidal Silica in Highly Alkaline Solution
Authors: Chida Taiji , Niibori Yuichi , Tochiyama Osamu , Mimura Hitoshi , Tanaka Koichi
Published: April 2011

For the performance assessment of the radioactive waste repository, it is important to clarify the dynamic behavior of silica (silicic acid and hydrous or unhydrous silicon dioxides). The behavior of silica would be complicated when cement is used for the construction of the repository, since silica takes various forms due to polymerization, precipitation and dissolution with change of pH or temperature. In order to know the fundamental kinetic property of silica, this study has examined the dissolution rate of colloidal-silica.

In the experiment, the concentration of silica in a soluble form was determined by the silicomolybdenum-yellow method. In this study, soluble-silica was defined as silica reacting with molybdate reagent and coloring yellow, and colloidal-silica was defined as silica in liquid phase except for soluble-silica. Colloidal-silica was obtained through the polymerization process, where the pH value of silica solution was brought down from over 10 by HNO3 solution. This study examined dissolution rate of colloidal-silica again by setting to 10 or 13 in pH-value and 288 K, 298 K or 313 K in temperature. In the experimental results, the dissolution reaction of colloidal-silica proceeded linearly with time, when the dissolution of colloidal silica was not restricted by the solubility of silica. To estimate the dissolution rate, we assumed df /dt = k*, where f is the soluble-silica fraction defined as the amount of soluble-silica divided by the silica amount introduced into the sample solution, t the time (s) and k* the rate constant (s-1). The activation energy for the dissolution of the colloidal-silica at pH 13 was estimated to be approximately 80 kJ·mol-1which was similar to that for amorphous silica (solid phase) at pH 13. This suggests the same reaction mechanism for the dissolution of colloidal-silica and amorphous silica in highly alkaline solution.
Evidence for Neptunium Incorporation into Uranium (VI) Phases
Authors: Buck Edgar C. , Hanson Brady D. , Friese Judah I. , Douglas Matt , McNamara Bruce K.
Published: April 2011

This paper examines the ability of electron energy-loss spectroscopy (EELS) combined with transmission electron microscopy (TEM) to detect both low concentrations of Np in a U matrix and to provide evidence for incorporation of Np in U(VI) phases. The case for U(VI) secondary minerals acting as solubility-controlling phases for Np in repository performance assessment models has not been fully established. Direct evidence for incorporation, rather than sorption, continues to be difficult to obtain. Detection of Np with TEM-EELS is hampered by the occurrence of a plural (multiple) scattering event from the more abundant U atoms (U-M5 + U- O4,5), that results in severe overlap on the Np-M5 edge at ∼3665 eV. By examining the energy âgap' between the Np-M5 and Np-M4 edges (184 eV), a method for observing Np independently of the plural scattering event has been established. Clear evidence of Np incorporation into synthetic studtite {(UO2)(O2)(H2O)2](H2O)2} and uranophane {Ca(UO2)2(SiO3OH)2(H2O)5} has been found with TEM-EELS. The EELS technique continues to remain an important tool for examining the potential for transuranic behavior in nuclear waste materials.
Effect of External Gamma Irradiation on Dissolution of the UO2 Matrix
Authors: Jégou C. , Muzeau B. , Broudic V. , Peuget S. , Poulesquen A. , Roudil D.
Published: April 2011

Leaching experiments were done on UO2 pellets doped with alpha-emitters (238/239Pu, 1500 - year batch), in the presence of an external gamma irradiation source (A60Co = 260 Ci, γ dose rate = 650 Gy h−1). The effects of α and γ radiation and the nature of the cover gas (air or Ar + 4% H2) on water radiolysis, and on oxidizing dissolution of the UO2 matrix, are quantified and discussed. The cover gas clearly has a major role in the effect of γ radiolysis. The dissolution rate in an aerated medium is 83 mg m−2 d−1 compared with only 6 mg m−2 d−1 in Ar + 4% H2. The rate drop is accompanied by a reduction of about four orders of magnitude in the hydrogen peroxide concentrations in the homogeneous solution. The UO2 alteration rate under gamma radiation in Ar + 4% H2 is comparable to the rate obtained in the presence of alpha radiolysis alone for the doped UO2 pellets with the highest alpha activities (4.75 × 108 Bq/g UO2, 15 - year batch).
Radiolytic Corrosion of238Pu-doped UO2Pellets in 5 M NaCl Solution
Authors: Kelm M. , Bohnert E.
Published: April 2011

Deaerated 5 M NaCl solution is alpha-irradiated up to 700 days in the presence of UO2pellets. Experiments are conducted with238Pu-doped pellets in pure brine and with undoped UO2pellets in a238Pu containing brine. The long-lived radiolysis products H2, O2and ClO3-are formed in all cases proportional to the dose applied on the solution and with yields corresponding to 200, 80 and 7 nMol/(L*Gy).

The U concentrations increase with time but do not exceed about 10−4Mol/L thus indicating Uranium to be solubility limited. Moreover, the rinse solutions of the vessels at the end of the experiments contain up to one order of magnitude more U than found in the solutions. The total amounts of mobilized U deviate by less than a factor 10 from each other regardless of the large ratio of surface dose rates (ratio up to 2300) or mean dose rates (ratio up to 100), applied while the reference experiment (UO2pellet in pure brine) yields only some 10−7Mol/L U which is over 3 orders of magnitude lower than observed in experiments with radiation present.

The simulation of the radiation chemical processes using a kinetic reaction model can reasonably reproduce the findings of the experiments with respect to the formation of H2and O2and give the order of magnitude for the concentrations of chlorine species and of oxidized UO2.
Valencies of Mn impurities in ZnO
Authors: Petit L. , Schulthess T. C. , Svane A. , Temmerman W.M. , Szotek Z.
Published: April 2011

We use the self-interaction corrected (SIC) local spin-density (LSD) approximation to investigate the groundstate valency configuration of Mn impurities in p-type ZnO. In Zn1−xMnxO, we find the localized Mn2+ configuration to be preferred energetically. When codoping Zn1−xMnxO with N, we find that four d-states stay localized at the Mn site, while the remaining d-electron charge transfers into the hole states at the top of the valence bands. If the Mn concentration [Mn] is equal to the N concentration [N], this results in a scenario without carriers to mediate long range order. If on the other hand [N] is larger than [Mn], the N impurity band is not entirely filled, and carrier mediated ferromagnetism becomes theoretically possible.
Spin-orbit coupling and magnetic spin states in cylindrical quantum dots
Authors: Destefani C. F. , Ulloa Sergio E. , Marques G. E.
Published: April 2011

We make a detailed analysis of each possible spin-orbit coupling of zincblende narrow-gap cylindrical quantum dots built in a two-dimensional electron gas. These couplings are related to both bulk (Dresselhaus) and structure (Rashba) inversion asymmetries. We study the competition between electron-electron and spin-orbit interactions on electronic properties of 2-electron quantum dots.
Selective Voltage-Controlled Hole Spin in Non-Magnetic Resonant Tunneling Diodes
Authors: Bittencourt A. C. R. , Marques G. E. , Gobato Y. Galvão , Vercik A. , Camps I. , Brasil M. J. S. P
Published: April 2011

We report theoretical and experimental observation of photoexcitated hole spin selection in GaAs/GaAlAs n-i-n in resonant tunneling diodes. When subjected to magnetic and electric parallel fields, the spin splitted hole levels leads to several peak structure in the transmissivity. These experimental results are interpreted as an evidence of tunneling transport through spin polarized hole levels of non-magnetic diodes.
Terahertz measurements of the Photoactive Protein Bacteriorhodopsin mutant D96N: M and P states
Authors: Chen J.-Y. , Knab J. R. , Cerne J. , Hillebrecht J. R. , Birge R. R. , Markelz A. G.
Published: April 2011

We use terahertz (THz) spectroscopy as a biomaterials characterization tool. Previously we have shown a strong contrast between the THz dielectric response for wild type (WT) and D96N mutant of bacteriorhodopsin. In those studies we observed a large increase in the THz absorbance of WT with excitation to thermally captured photo-intermediates whereas no such increase in absorbance was observed for the mutant D96N. These results suggest that the THz response is sensitive to structural changes and relative flexibility of biomolecules. However the photo-intermediate populations of the WT and D96N samples were not equivalent in those measurements. While the WT samples had relaxed (bR), M and P state intermediates present, the D96N samples had only bR and M states. Here we present terahertz absorbance measurements of D96N as a function of M and P state populations at room temperature. The THz response is constant for intermediate states populations up to 23% M state and up to 30% P state. These results verify that there is a fundamental difference in the conformational dynamics as measured by THz dielectric response for a single residue mutation.
Fast Simulation Protocol for Protein Structural Transitions: Modeling of the Relationship of Structure and Function
Authors: Setty Arun K. , Zuckerman D. M.
Published: April 2011

An approach is developed to study the dynamics of protein conformational transitions in depth. A computational (Monte Carlo) approach based on a united residue model is used. Unbiased transitions between the Apo and Holo conformations/states of calmodulin are observed at the rate of 1 per day per processor. A series of models of increasing complexity is studied, accounting for hydrophobic interactions and calcium binding. Details of the transitional region and structural information about intermediate states are obtained. Statistically converged ensembles of transitions are obtained in a reasonable real time period.
Teaching Corporate Culture – an Engineer's Survival Guide
Authors: Savage Richard N.
Published: April 2011

The transition from new engineering graduate to successful member of corporate America is a difficult journey. Often the skills required are not part of a student's traditional undergraduate education. At Cal Poly, we have integrated a new course into our existing Senior Project curriculum which enables students to develop the professional skills necessary to become an effective member of any corporation. Key skills such as communication, problem solving and project management are practiced through active learning techniques. These as well as other topics studied are required for ABET certification.

The new course investigates the mission and values that are at the foundation of any corporation's culture. It challenges students to evaluate their own personal leadership potential. Organization structures along with the roles and responsibilities of Engineering, Marketing, Sales, Operations, Finance and Executive management are studied along with the interdisciplinary nature of engineering and technology. The rigors and metrics of a typical product development methodology are explored along with the concepts of program management and the protection of intellectual property. Business models are studied which enable students to evaluate the impact engineering can have on a company's financial success. Moreover, the students learn that they are members of a global community with environmental and social responsibilities. The impact of technology on society can be profound and students are challenged to consider difficult ethical issues as well as exciting career opportunities.
Flame spray synthesis of tin oxide nanoparticles for gas sensing
Authors: Sahm Thorsten , Mädler Lutz , Gurlo Alexander , Barsan Nicolae , Pratsinis Sotiris E. , Weimar Udo
Published: April 2011

Tin oxide nanoparticles for gas sensing application have been synthesized with an aerosol method. The particles were manufactured with the versatile Flame spray Pyrolysis (FSP) method producing highly crystalline powders with closely controlled a primary particle and crystallite size of 10 nm and 17 nm. The single crystalline particles were only slightly aggregated and directly used for thick film sensor deposition by drop coating and screen printing.The flame made SnO2 nanoparticles showed high and rapidresponse to reducing gases such as propanal and CO.
Room Temperature Hydrogen Gas Sensitivity of Nanocrystalline-Doped Tin Oxide Sensor Incorporated into MEMS Device
Authors: Shukla Satyajit , Agrawal Rajnikant , Ludwig Lawrence , Cho Hyoung , Seal Sudipta
Published: April 2011

Nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin film sensor has been sol-gel dip-coated on a microelectromechanical systems (MEMS) device. The micro-sensor device is successfully utilized to sense ppm level H2 at room temperature with high sensitivity. The chamber pressure has no pronounce effect on the room temperature H2 sensitivity.
In2O3 nanowire mat devices as high performance NO2 gas sensors
Authors: Zhang Daihua , Liu Zuqin , Zhou Chongwu
Published: April 2011

A high sensitive and reliable In2O3 nanowire mat devices are fabricated. Detection of NO2 gas down to ppb levels was achieved. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. Furthermore, this simple device shows certain selectivity to NO2 with other common chemicals such as NH3, O2, CO and H2 around.
Themodynamic and Kinetic Principles for Electrochemical Gas Sensors Based on Solid Ionic Conductors
Authors: Tsagarakis Evangelos D. , Weppner Werner
Published: April 2011

Several concepts can be applied for gas detection using solid ionic conductors. The fundamental characteristics and the essential variables for proper design of electrochemical cells are analyzed in terms of the sensing principle applied. The principal properties for materials as components of electrochemical devices are being illustrated. Employment of dynamic method allows implementation of the Fourier coefficients to generate a complex plane plot representation. This can be particularly useful for extracting information regarding the selectivity of an electrochemical cell to multiple gas species. Moreover, modeling the system response upon a periodical perturbation can be beneficial on understanding the individual processes and optimizing the overall performance.
Rational Synthesis and Optimization of Multifunctional Solid-State Gas Sensors
Authors: Schwank Johannes , Korotcenkov Ghenadii
Published: April 2011

A new approach is discussed for the rational synthesis and development of optimized multifunctional solid-state gas sensors. Multifunctionality—the incorporation of multiple types of reactivities into a material, such as acid and/or base functionalities, oxidation and/or reduction functionalities, etc.—isa requirement in many gas sensing applications. The front end of many gas sensors contains catalytic layers, so that optimization of catalysts and optimization of gas sensors can be carried out in a synergistic fashion.

Multifunctionality presents unique challenges to rational catalyst and sensor systems development because the overall performance of the material is a convolution of the performance of the various subcomponents, and optimization of these individual subcomponents in isolation does not necessarily lead to optimal, or even acceptable, overall performance. A major obstacle to dealing with these difficulties is the inherent complexity of heterogeneous systems prepared by traditional approaches, which makes it difficult to unambiguously identify the compositions and morphologies of the local active sites and their interactions. Further complicating the problem is the requirement to function in environments that can vary on both short and long time scales. A key to understanding, controlling, and optimizing these materials is the ability to produce and study well-defined sensor materials with well-defined composition and morphology, with the flexibility to vary the composition easily without jeopardizing the structural uniformity.

The development of new or improved materials for gas sensor applications requires a search for novel and innovative approaches to the nano-scale design of these materials. The use of the technology of surface modification by successive ionic layer deposition (SILD) method is such an innovative approach that will be discussed in this paper.
Surface Plasma Treatment and Sensibilization of Tin Dioxide Films for Enhancement of Gas Sensitivity and Selectivity
Authors: Dmitriev Serghei V. , Brinzari Vladimir I. , Korotcenkov Ghenadii S.
Published: April 2011

Results of investigation aimed at the improvement of gas sensitive characteristics of tin dioxide thin film's based gas sensors through their treatment in high frequent (HF) oxygen plasma and sensibilization by means of doping are presented.

Tin dioxide thin films were deposited from alcohol solutions of SnCl45H2O by means of chemical spray pyrolysis method on alumina substrate at the temperatures in the range from 400 to 500°C. The thickness of films was varied in the range 20–100 nm.

Surface treatment of obtained tin dioxide layers was carried out in pure oxygen plasma at room temperature and 3-4 times increase of the resistance and gas sensitivity was obtained at that. These parameters' changing is discussed from the point of view of thin film's stoichiometry alteration, for control of which there were used IR and SIMS measurements. Obtained results are compared with results of the film's high temperature (∼600oC) thermal annealing on air.

To increase thin film's gas sensitivity and selectivity the doping with Pd and Cu was applied. Doping was carried out also through chemical spray pyrolysis method from the solutions of corresponding compounds of Pd and Cu. Such modification of SnO2 surface hasallowed to increasing sensitivity to H2 up to 5.103 rel. units (high selectivity) at the simultaneous shift of sensitivity maximum from 350 to 150°C. Doping with Cu has allowed to increasing 4-5 times sensitivity and selectivity toward CH4 and C3H8 gases in air and reducing operating temperatures from 500–520°C to 350–370°C.

It is concluded that combination of HF oxygen plasma tin dioxide film' treatment and its surface sensibilization is an effective way to considerably improvement of gas sensitive and selective characteristics of tin dioxide based thin film gas sensors (TFGS).
Fe2O3:SnO2 Nanostructured System as Semiconductor Gas Sensor Material
Authors: Arbiol J. , Morante J. R. , Rumyantseva M. , Kovalenko V. , Gaskov A.
Published: April 2011

In the present work, we report a detailed study based on transmission electron microscopy of the microstructure and composition of the Fe2O3: SnO2 nanometrical binary system obtained by sol-gel. We studied a set of samples based in a pure Fe2O3 material where we added SnO 2 from 0 to 50% Sn-Fe nominal content. The structure of our composites will change from pure a-Fe2O3 to the well-known cassiterite SnO 2 structure for high Sn content. Distortions on the structural parameters will be attributed to the presence Sn4+ ions on the α-Fe2O3 structure and Fe3+ ions on the SnO2 cassiterite structure.
Formation of Porous Silicon Layers on Insulating Substrate for Microbridge – Type Sensor Applications
Authors: Andrushin Sergey Ya. , Balagurov Leonid A. , Bayliss Sue C. , Liberova Galina V. , Petrova Elena A. , Unal Bayram , Yarkin Dmitrii G.
Published: April 2011

Formation processes of porous silicon on insulating substrate were studied. It was demonstrated that both electrochemical and chemical formation methods allow to transform heavily doped p-type polycrystalline silicon into homogeneous porous silicon. Porous silicon was successfully used as sacrificial layer in the fabrication process of microbridge structures.