bluuebunny/crossref_metadata_2025 huggingface dataset:
Description and Classification of Uranium Oxide Hydrate Sheet Topologies
Authors: Miller M. L. , Finch R. J. , Burns P. C. , Ewing R. C.
Published: April 2011

The uranyl oxide hydrates (UOH) are important corrosion products of uraninite and UO 2 in spent nuclear fuel under oxidizing conditions. However, the systematics of the crystal chemistry, thermodynamic parameters, and solubilities of this mineral group are poorly understood. With the exception of the synthetic UO2 (OH)2 polymorphs, all UOH crystal structures are based on sheets of edge-sharing 5- and 4-coordinated uranyl dipyramids. This structural similarity suggests that it is possible to develop a model by which to estimate the thermodynamic behavior of UOHs from data on structural endmember phases. Toward this end, a method of quantitatively describing all known UOH sheets has been developed. Only four structural unit chains are required to construct the uranyl oxide hydrate sheets (as well as the structurally similar U3O8 sheets). The H-chain is restricted to α-UO2 (OH)2 and is made up of hexagonally coordinated uranyl ions sharing opposing edges. The “arrowhead” chain composed of pentagonal dipyramids sharing edges and alternating with trigonal vacancies is present in all other UOH sheets. These arrowhead chains are directed and can occur in both an ↑ and ⇓ “sense” within a single sheet. The P-chain consists of edge-sharing pentagonal dipyramids forming a zigzag chain. The P-chain is flanked on both sides by arrowhead chains of the same “sense”. The remaining structural unit is a discontinuous “chain” of rhombic dipyramids. This “R-chain” is produced when nested adjacent ⇑ and ⇓arrowhead chains are translated by a diagonal shift. This “chain” occurs in sheets which contain only 4-coordinate uranyl ion and those containing both 4- and 5-coordinate uranyl ions.
Sulfur Polymer Cement as a Low-Level Waste Glass Matrix Encapsulant, Part I: Thermal Processing
Authors: Sliva Paul , Peng Y. Benjamin , Bunnell L. Roy , Peeler David K. , Feng Xiangdong , Martin Paul , Turner Paul J.
Published: April 2011

Sulfur polymer cement (SPC) is a candidate material to encapsulate low-level waste (LLW) glass. Molten SPC will be poured into a LLW glass cullet-filled canister, surrounding the glass to act as an additional barrier to groundwater intrusion. This paper covers the first part of a study performed at Pacific Northwest National Laboratory concerned with the fundamental aspects of embedding LLW glass in SPC. Part one is a study of the SPC itself. Variations in SPC properties are discussed, especially in relation to long-term stability and controlling crystallization in a cooling canister.
Vitrifiable Concrete for Disposal of Spent Nuclear Fuel Reprocessing Waste AT I.N.E.L.
Authors: Gougar M. L. D. , Siemer D. D. , Scheetz B. E.
Published: April 2011

A cement capable of being Hot Isostatically Pressed (HIP 'ed) into a glass-ceramic has been proposed for use as the waste form for SNF reprocessing wastes at the Idaho National Engineering Laboratories. Such an “intermediate” cement, with a composition based on that of common glasses, has been designed and tested. The cement formulations included mixed I.N.E.L. wastes, blast furnace slag, reactive silica, alumina, and I.N.E.L. soil or vermiculite, which was activated with potassium or sodium hydroxide. Modified FUETAP processing was performed and the cement was subsequently characterized. Results of compressive strength testing ranged from 1452 psi to 4163 psi, exceeding the NRC-suggested standard of >500 psi. Total dissolved solids concentrations in waste form leachates were calculated from a static leach test in which leachate conductivity was measured. Effective diffusivities for radioisotopes Cs and Sr were calculated from leachate analysis data. Diffusivity values were on the order of 10-15 to 10-10 cm2/sec, which compare favorably with diffusivities in other materials.
Pore Solution Chemistry of Simulated Low Level Liquid Waste Incorporated Cement Grouts
Authors: Sahu Sadananda , Diamond Sidney
Published: April 2011

Expressed pore solutions from simulated low level liquid waste cement grouts cured at room temperature, 50°C and 90°C for various duration were analyzed by standard chemical methods and ion chromatography. The solid portions of the grouts were formulated with portland cement, fly ash, slag, and attapulgite clay in the ratios of 3:3:3:1. Two different solutions simulating off-gas condensates expected from vitrification of Hanford low level tank wastes were made. One is highly alkaline and contains the species Na+, PO43-, NO2-, NO3- and OH-. The other is carbonated and contains the species Na+, PO43-, NO2- NO3- and CO32- In both cases phosphate rapidly disappeared from the pore solution, leaving behind sodium in the form of hydroxide. The carbonates were also removed from the pore solution to form calcium carbonate and possibly calcium monocarboaluminate. These reactions resulted in the increase of hydroxide ion concentration in the early period. Subsequently there was a significant reduction OH- and Na+ ion concentrations. In contrast high concentration of NO2- and NO3- were retained in the pore solution indefinitely.
Immobilization Index of Liquid LLW in Cementitious Grouts
Authors: Sahu Sadananda , Diamond Sidney
Published: April 2011

The ability of grouts formulated from mixtures of cementitious materials and attapulgite clay to immobilize various chemical species in the projected off-gas waste stream from vitrification of Hanford low level tank wastes was studied. Three different solid blends were evaluated, with cement :fly ash : slag clay weight ratios of 3:3:3:1, 3:0:6:1, and 0:0:9:1. The blended solids were mixed with a simulated low level liquid waste solution containing Na+, NO2-, NO3-, PO43- and OH- ions, in the proportion of 1 liter of solution to 1 kg of solid blend, and were cured either at 22°C (room temperature), 50°C or 90°C. Pore solutions were expressed at various ages and were analyzed to determine the reductions in concentrations of the individual ionic species. The results were expressed in the form of immobilization index (I) calculated for each species. The immobilization indices for Na+ (I Na+ ) and for OH- (IOH-)were similar in each case, and were found to be highest when only slag and clay was present (blend 0:0:9:1). The immobilization index for phosphate, , was 1 in all cases, i.e. phosphate was completely removed from solution. On the other hand removal of NO2- and NO3- ions was generally ineffective.
Influence of the Titanium Dioxide Addition in Matrix Formulation on the Radwaste-Mortar Matrix Characteristics
Authors: Perić Aleksandar D.
Published: April 2011

The rutile form of titanium dioxide (TiO2) was added to mortar matrix preparations with the objective to improve the mechanical and physico-chemical characteristics of the radwaste-mortar matrix mixtures, in particular the leach-rate of the immobilized radionuclide. The final solidified radwaste form was made with high water-to-cement ratio (0.36) for easy leaching of the immobilized radionuclide, 37Cs. TiO2was added to the mortar formulation, replacing the appropriate amount of cement, in the amounts of 1,2,5,8 and 10 weight percents of total cement weight. In the highly basic environment of the mortar (pH ≅ 12), the titanium will form a HTiO-type membrane, which is semi-permeable and selective for the cations like Cs+ in the pH range above 5.5. Only the rutile form of TiO2was observed in the prospected radwastemortar mixture samples, using X-ray Fluorescence Spectrometry. Nevertheless, 137Cs leach-rate for the matrix formulations prepared with TiO2 was notably lower than the normally prepared (TiO2 free) samples. Furthermore, the mechanical strength of the samples prepared with TiO2 was higher than that of the TiO 2-free samples, and the correlation between the mechanical strength and TiO2 content appears to be exponential over the composition range explored here. Improvement of the physico-chemical properties of the titanium prepared formulations, is a topic of further investigations.
Electronic Structure Calculations of Calcium Silicate Hydrates
Authors: Sterne P. A. , Meike A.
Published: April 2011

Many phases in the calcium-silicate-hydrate system can develop in cement exposed over long periods of time to temperatures above 25°C. As a consequence, chemical reactions involving these phases can affect the relative humidity and water chemistry of a radioactive waste repository that contains significant amounts of cement. In order to predict and simulate these chemical reactions, we are developing an internally consistent database of crystalline Ca-Si-hydrate structures. The results of first principles electronic structure calculations on two such phases, wollastonite (CaSiO3) and xonotlite (Ca6Si6O17(OH)2), are reported here. The calculated ground state properties are in very good agreement with experiment, providing equilibrium lattice parameters within about 1–1.4% of the experimentally reported values. The roles of the different types of oxygen atoms, which are fundamental to understanding the energetics of crystalline Ca-Si-hydrates are briefly discussed in terms of their electronic state densities. The good agreement with experiment for the lattice parameters and the consistency of the electronic density of states features for the two structures demonstrate the applicability of these electronic structure methods in calculating the fundamental properties of these phases.
A Procedure to Evaluate the Potential for Microbially Influenced Degradation of Cement-Solidified Low-Level Radioactive Waste Forms
Authors: Rogers R. D. , Hamilton M. A. , Veeh R. H. , Mcconnell J. W.
Published: April 2011

Because of its apparent structural integrity, cement has been widely used in the United States as a binder to solidify Class B and C low-level radioactive waste (LLW). However, the resulting cement preparations are susceptible to failure due to the actions of stress and environment. An environmentally mediated process that could affect cement stability is the action of naturally occurring microorganisms. The U.S. Nuclear Regulatory Commission (NRC), recognizing this eventuality, stated in their Technical Position on Waste Form, Revision 1, that the effects of microbial action on waste form integrity must be addressed. This paper provides recent results from a program that examined the effects of microbially influenced degradation (MID) on cement-solidified LLW. Data are provided which were obtained during the development of an evaluation method using acid-producing bacteria. Results presented here are from work with one type of these bacteria, the sulfur-oxidizingThiobacillus. Commercially prepared, cement-solidified, low-level radioactive waste form samples made from power reactor wastes were evaluated using a new biodegradation test developed for the NRC. Testing demonstrated that MID has the potential to severely compromise the structural integrity and nuclide retentiveness of ion-exchange resin and evaporator-bottoms wastes that have been solidified with cement. It was found that the waste form specimens physically deteriorated after 60 days of exposure to the thiobacilli. Also, the data show that significant amounts of Cs-137, Cs-134, Co-60, C-14, Tc-99, and Sr-90 contained in the waste forms were leached in the presence ofThiobacillus.
Modelling the Long-Term Chemical Evolution of Cement-Groundwater Systems
Authors: Neall F. B.
Published: April 2011

The importance of the large volumes of cement and concrete in the planned Swiss L/ILW repository in influencing the chemical environment of the repository and the sorption behaviour of the radionuclides has lead to an interest the long-term evolution of cement-groundwater systems for safety assessment purposes.

A model is presented which simulates the leaching of a column hydrated cement/concrete with fresh groundwater, using a sequential mixing tank approach. The chemical model includes the incongruent dissolution of the CSH-gel phase and reaction of three other cement phases which make up over 90 wt. % of the hydrated cement paste. The model takes account of porosity changes due to dissolution and precipitation. Different concrete compositions can be included in the column in order to represent, for example, a section through a repository cavern. The model can be run as a 1-D flow-through system or as a quasi-1-D system in which flow in any segment is proportional to porosity. Although the model does not include the sophisticated transport models of currently available coupled codes, it does allow the possibility of assessing the duration of high pH conditions within the repository and the influence of different concrete/cement types or different waste type/loading as a first stage to determining long-term transport of radionuclides from the near field.
Excess Pu Disposition in Zirconolite-Rich Synroc Containing Nepheline
Authors: Vance E. R. , Hart K. P. , Day R. A. , Begg B. D. , Angel P. J. , Loi E. , Weir J. , Oversby V. M.
Published: April 2011

A titanate Synroc ceramic for the immobilization of Pu-bearing waste was designed to consist of 70 wt% zirconolite (CaZrTi2O7) + 15 wt% nepheline (NaAlSiO4) + 15 wt% rutile (TiO2). It contained 10 wt% of Pu plus 6 wt% of Gd as a neutron poison. The material was made by our standard sol-gel route, using a mixture of alkoxides and nitrates, followed by stirdrying and calcination. It was fabricated by hot-pressing at 1150–1250°C/20 MPa for 2 hours in a collapsible metal bellows. Though zirconolite was the majority phase, ∼20 wt% of perovskite also formed. Some of the Na, intended for nepheline, partitioned into the titanate phases. 84-day differential total leach rates of Pu were in the order of 10−5 g/m2/d at 90 and 200°C. Companion ceramics using molar substitution of Ce for Pu confirmed the idea that Ce is a good simulant of Pu from a solid state chemical view, but that there are limitations in terms of leach rate parallels.
Models and Strategies for Blending Nuclear Wastes to Minimize Immobilized Waste Volume
Authors: Hoza M.
Published: April 2011

Hanford tank waste will be separated into high-level and low-level portions; each portion will then be vitrified to produce a stable glass form for disposal. Because of the wide variability in the tank waste compositions, blending is being considered as a way to reduce the number of distinct compositions that must be vitrified and to minimize the resultant volume of vitrified waste.

This paper discusses several approaches to blending and models developed to formulate blends for each approach. The models produce optimized blends which minimize the volume of glass required such that all composition and property constraints on the glass are satisfied. The paper will discuss several blending strategies, and will provide the results of calculations comparing the approaches and strategies. Finally, an overall strategy for retrieving, blending, and vitrifying Hanford tank waste will be briefly discussed.

Results of the calculations for high-level waste show that an effective blending strategy can greatly reduce the volume of glass required to immobilize the waste.
Selective Extraction of Cs and Co from Liquid Radioactive Waste
Authors: Karlin Y. V. , Prozorov L. B. , Chuikov V. Y. , Kropotov V. N.
Published: April 2011

This paper demonstrates that selective sorbents (in particular, ferri-ferrocyanide nickel) can be regenerated electrochemically. It is shown that the degree of sorbent regeneration and the ion permselectivity of the process depends on the electric current density, the apparatus design and the scheme of the extraction process.
Effect of Microbial Action on the Corrosion Potential of Austenitic Alloy Containers for High-Level Nuclear Waste
Authors: Angell P. , Dunn D. S. , Cragnolino G. A.
Published: April 2011

The safe disposal of high-level nuclear waste (HLW) entails the ability to ensure the integrity of waste containers for prolonged time periods. It is generally accepted that under certain conditions, microbial action may change local benign environments to those in which localized corrosion can be actively promoted. The use of repassivation potential (Erp) in relation to the value of the corrosion potential (Ecorr) has been proposed as a means of assessing the propensity of a metallic material to localized corrosion. Microbial activity is known to influence Ecorr however, the precise mechanism is unresolved. Shewanella putrefaciens, a bacteria with many of the characteristics of sulfate-reducing bacteria (SRB), are being grown under controlled conditions on 316L stainless steel (SS) surfaces to understand the relationship between Ecorr and metabolic activity. It has been observed that the growth of the bacteria under aerobic conditions, without the production of metabolic sulfide, leads to only minor variation in Ecorr. These changes possibly correlate to the periods of active bacterial growth.
Modelling the Consumption of Oxygen by Container Corrosion and Reaction with Fe(II)
Authors: Kolář M. , King F.
Published: April 2011

A model is described that predicts the rate of O2 consumption in a sealed nuclear fuel waste disposal vault as a result of container corrosion, reaction with biotite and the oxidation of organics and other oxidizable impurities in the clay. The most important reactions leading to the consumption of O2 for Cu containers in a conceptual Canadian disposal vault are container corrosion, the oxidation of dissolved Cu(I) and the oxidation of organics and other impurities in the clay. Consumption of O2 by the oxidation of dissolved Fe(II) from biotite is significant in backfill materials containing crushed granite and in the rock itself. The O2 initially trapped in the disposal vault is predicted to be consumed in between 50 and 670 a.
A Numerical Model for the Corrosion of Copper Nuclear Fuel Waste Containers
Authors: King F. , Kolář M.
Published: April 2011

A model is presented for the prediction of the long-term corrosion behaviour of Cu nuclear fuel waste containers. The model is based on a kinetic description of the processes involved in the uniform corrosion of Cu in a conceptual Canadian disposal vault. The 1-dimensional, multilayer model accounts for mass-transport, electrochemical and chemical processes and predicts the spatial and temporal variations of the concentrations of various dissolved, precipitated and adsorbed species, as well as the time dependence of the corrosion rate and the corrosion potential (ECORR). The variation of [O2], [Cu(II)] and ECORR with time can also be used to predict the maximum period over which localized corrosion processes, such as pitting or stress corrosion, may occur. Predictions from the model suggest that 25-mm-thick Cu containers will not fail due to uniform corrosion or pitting in periods <106 a.
Effects of Anionic Species on the Polarization Behavior of Copper for Waste Package Material in Artificial Ground Water
Authors: Imai Hachiro , Fukuda Takanori , Akashi Masatsune
Published: April 2011

The effects of HCO3, Cl, and SO42- on copper as a candidate material for overpacking for geological disposal of high level radioactive wastes are studied at 303 K in dissolved oxygen(DO)- controlled, ground-water simulating aqueous solutions by using a cyclic polarization curve method.

Two types of polarization curve were determined: Type A in which free corrosion proceeds in the active dissolution mode, and Type P in which passivation takes place in a potential domain characterized by a potential that corresponds to Eb, the potential at which the passivated film is broken. Polarization dependence on DO was also determined: when only HCO3 is present, a Type A curve results for DO < 0.5 ppm when HCO3 = 10 – 300 ppm, transiting to a Type P curve when HCO3 > 3,000 ppm; when DO < 15ppm, however, a Type P results for HCO3 ≤ 10 ppm; when either Cl− or SO42- coexists with HCO3, HCO3 promotes passivation while Cl- and SO42- promote active dissolution, the influence of Cl− being greater than that of HO42- if HCO3 content is constant. The presence of either CI or SO42 over 100 ppm makes the curve Type A irrespective of DO, both species shifting Eb toward the less noble direction.

The constant potential test shows that the passivated film of copper is easily broken if Cl− is present.
Neptunium(V) Sorption Behavior on Clinoptilolite, Quartz and Montmorillonite
Authors: Bertetti F. P. , Pabalan R. T. , Turner D. R. , Almendarez M. G.
Published: April 2011

Performance assessment models have identified237Np as a radionuclide of concern in meeting release limits established for the geologic disposal of high-level nuclear waste at the proposed repository at Yucca Mountain, Nevada. In this study, quartz, clinoptilolite, and montmorillonite, which are minerals representative of phases that occur both in the rock matrix and as fracture coatings at Yucca Mountain, were reacted with237Np-bearing solutions to characterize the sorption behavior of Np(V) on these minerals.

Batch experiments were conducted over a wide range of conditions in which pH of solution, surface loading, sorbent surface area, initial concentration of Np(V), and partial pressure of CO2were varied. Initial Np(V) concentrations were between 1 × 10-7and 1- 10-6M in electrolyte solutions of 0.1 or 0.01 M NaNO3. The oxidation state of Np in solution was verified with NIR spectroscopy and by solvent extraction. Prior to the start of experiments, minerals were pretreated to eliminate impurities, and the clinoptilolite and montmorillonite were converted to Na-form by ion exchange with NaCI solutions.

Results indicate that, for all three minerals, Np(V) sorption begins at pH values coincident with the start of hydrolysis in solution (-7). For solutions undersaturated with respect to atmospheric CO2, sorption increases continuously with increasing pH. Under equilibrium with atmospheric CO2, Np(V) sorption is important in the pH range (7–9.5) where NpO2(OH)°(aq) is significant, whereas sorption is inhibited at higher pH where neptunyl carbonate complexes are the predominant species.
SNL-1, a Highly Selective Inorganic Crystalline Ion Exchange Material for Sr2+ in Acidic Solutions
Authors: Nenoff T. M. , Thoma S. G. , Miller J. E. , Trudell D. E.
Published: April 2011

A new inorganic ion exchange material, called SNL-1, has been prepared at Sandia National Laboratories. Developmental samples of SNL-1 have been determined to have high selectivity for the adsorption of Sr from highly acidic solutions (1 M HNO3). This paper presents results obtained for the material in batch ion exchange tests conducted at various solution pH values and in the presence of a number of competing cations. Results from a continuous flow column ion exchange experiment are also presented.
Applications of in Situ Cosmogenic Nuclides in the Geologic Site Characterization of Yucca Mountain, Nevada
Authors: Gosse J. C. , Harrington C. D. , Whitney J. W.
Published: April 2011

The gradual buildup of rare isotopes from interactions between cosmic rays and atoms in an exposed rock provides a new method of directly determining the exposure age of rock surfaces. The cosmogenic nuclide method can also provide constraints on erosion rates and the length of time surface exposure was interrupted by burial. Numerous successful applications of the technique have been imperative to the complete surface geologic characterization of Yucca Mountain, Nevada, a potential high level nuclear waste repository. The 10Be exposure age of Black Cone lava, within a ten mile radius of the proposed repository site, is 840 ± 210 kyr (in agreement with previous K/Ar dates of 1.0 ± 0.1 Ma). Rates of erosion of the tuff bedrock (< 0.4 cm/kyr from 7 10Be measurements) and of hillslope colluvium (∼ 0.5 cm/kyr from 10Be dates on boulder deposits) preclude denudation of the mountain as a concern. Neotectonic concerns (rate of slip and timing of last significant movement along faults) are also being addressed with in situ 14C and 10Be measurements on scarp surfaces and on fault-dissected landforms where no surficial expression of the fault is preserved.
The Yucca Mountain Standard: Proposals for Leniency
Authors: Pigford T. H.
Published: April 2011

The proposed geologic repository at Yucca Mountain, Nevada, for spent nuclear fuel and other highly radioactive waste needs an official standard to protect the public from release of radioactivity. Standards proposed by the U.S. Congress, the nuclear industry (NEI), the Electric Power Research Institute (EPRI), the Department of Energy (DOE), and the TYMS Committee of the National Research Council (NRC) are reviewed. Each of these proposals would introduce a degree of leniency not heretofore experienced in radiation protection. No adequate scientific justification is presented. Some scientifically invalid proposals are said to be justified on the grounds of policy. Most leading industrial nations are designing geologic repositories to meet the traditional criteria for safety and for protecting public health, including quantitative calculations of doses for the periods when significant doses can occur, rather than stopping calculations at 10,000 years as many in the U.S. would have us do. There is no evidence that they are seriously seeking more lenient standards for public health protection. The U.S. has the resources and skills to protect future people from our waste with the same care that we now protect the public from radiation. We should assert our will to do so. The Yucca Mountain project will be seriously damaged if it is directed to depart from the traditional conservative criteria for determining safety and protection of public health, criteria that are adopted in other countries working on geologic disposal.
ElectroluminesCence Behavior in Polymer Blend of Two Luminescent Polymers
Authors: Zyung Taehyoung , kim Jang-Joo , kang In-Nam , hwang Do-Hoon , Shim Hongku
Published: April 2011

We report the electroluminescence behaviour of the devices made with the polymer blend of two emissible polymers, poly(2-methoxy,5-(2′ethyl-hexoxy)-1,4-phenylene vinylene)(MEHPPV) and poly[ 1,3-propanedioxy- 1,4-phenylene- 1,2-ethenylene-(2,5-bis(trimethylsilyl)- 1,4- phenylene)-l,2-ethenylene-l,4-phenylene](B-polymer) luminescing at 580 nm and 480 nm respectively. The quantum efficiency increases with the composition ratio of B-polymer by two order of magnitude of that of MEH-PPV. Luminescence behaviour of the blend system was explained by hole blocking, exciton transfer behavior of the matrix polymer (B-polymer) and efficient confinement of the injected carriers in MEH-PPV.
Synthesis And Properties Of Crosslinkable Phenylacetylene Donor-Acceptor Molecules
Authors: Spilman G. E. , Jiang T. , Lu Q. , Martin D. C.
Published: April 2011

Based on our previous work using benzocyclobutene (BCB) moieties in extended-chain polymers [1], it was thought that the construction of unsymmetrical molecules around the BCB unit might result in thermally crosslinkable NLO-active materials. The feasibility of incorporating such a functional system in donor-acceptor molecules without disrupting processability is discussed and demonstrated. The synthesis, processing, and characterization of these molecules was investigated by thermogravimetry, differential scanning calorimetry, and optical microscopy using a specially designed hot stage which makes it possible to apply an inplane electric field at elevated temperatures. The ability to rapidly and irreversibly crosslink bulk films without the generation of volatile byproducts provides a novel method for sustaining poled optical properties by locking in the desired orientation. The anisotropy of the electrically poled melt and sustained birefringence after BCB crosslinking and cooling demonstrates the achievement of molecular alignment in these new materials.
The Quest For Molecule-Based Magnets
Authors: Miller Joel S. , Epstein Arthur J.
Published: April 2011

In the past decade a new class of magnets possessing spins on organic species have been discovered and studied. These magnets can be fabricated at room temperature and may enable useful devices and/or processes. Herein we discuss several of the mechanisms that can enable the stabilization of magnetic ordering and also provide examples of molecule-based magnets.
Conducting Polymers with Molecular Recognition Elements:Design of Highly Sensitive Sensory Aterials
Authors: Swager Timothy M. , Marsella Michael J. , Zhou Qin , Newland Robert J.
Published: April 2011

A number of approaches to the design and synthesis of conducting polymer-based sensory materials are presented. To elicit a selective sensory response synthetic receptors have been integrated into the polymers such that binding of an analyte produces electronic, electrostatic, and/or structural perturbations. A key element is the use of assemblies of many receptors which are “wired in series” by a conjugated polymeric structure. It is demonstrated that this configuration produces an inherent sensitivity gain over single isolated receptor-based sensory molecules.
Anti-Corrosion Studies of Novel Conductive Polymer Coatings on Aluminum Alloys
Authors: Racicot R. J. , Clark R. L. , Liu H-B , Yang S. C. , Alias M. N. , Brown R.
Published: April 2011

We report the corrosion protection properties of a novel conductive polymer coating on aluminum alloys. The conductive polymer coating is a double strand molecular complex of polyaniline and a polyelectrolyte. The double strand polyaniline offers advantages in stability and processability over other forms of conductive polymers. The coated aluminum alloys (AA7075- T6) were evaluated for corrosion protection in an aggressive salt environment of.5N NaCl solutions using cyclic polarization and electrochemical impedance spectroscopy. Corrosion current densities were calculated for uncoated alloy samples and alloys coated with the conductive and non-conductive derivative of the double strand polymer. The conductive form of the double strand polyaniline coating shows a two order of magnitude lowering of the corrosion current over the uncoated samples and a one order magnitude lowering over the non-conductive form of the polymer coated samples. The shape of the cyclic polarization data closely resembles results of sulfuric acid anodized aluminum. This data indicates that the conductive state of the polymer is required for improved corrosion protection and an anodized type protection is occurring.
Models of Electron-Hole Screening and Exciton Binding in Conjugated Polymers
Authors: Yaron David , Moore Eric , Gherman Benjamin
Published: April 2011

The use of semi-empirical quantum chemistry to calculate the exciton binding energy of conjugated polymers is discussed. Both the Pariser-Parr-Pople (PPP) model with Ohno parameterization and the models present in the MOPAC program overestimate the exciton binding energy relative to that observed in solid-state materials. Inclusion of Coulomb screening from adjacent chains may correct this overestimation. The solvation energy of a point charge in polyacetylene is calculated as 0.9eV, using Hartree-Fock theory to describe the polarization induced in the solvent chains. It is argued that including screening by modifying the electron-electron interaction energy of the PPP model introduces physically unreasonable side effects and is not consistent with the 0.9eV solvation energy of a point charge. Electron-hole screening models are then discussed along with the need to consider the relative time scales of the electron-hole motion and the dielectric response.
Conductivity Tailoring Of Melt-Processible Polyaniline In Polyolefin Blends By Using Viscosity Ratio
Authors: Tanner J. O. , Ikkala O. T. , Laakso J. , Passiniemi P.
Published: April 2011

Polyaniline (PANI) is a semi-rigid polymer which does not melt and has only limited solubility. Protonation to yield electrical conductivity generally renders a polyelectrolyte which is still less processible. Even selection of the dopant to be bulky or “functionalized” does not render PANI-complex to become melt-processible unless additional additives are used. Neste Oy (Finland) in cooperation with Uniax (U.S.A.) has identified several proprietary additives to allow melt-processibility. We show that in this way PANI-complex starts rheologically to behave in many respects like a conventional polymer. For example, in blends of PANI-complex with polypropylene, their viscosity ratio can be used to render either the PANI-complex or PP continuous, completely analogically to the “classical” polymer blends.
Elastomeric Conductive Ipn From Polyaniline And Fullerene-Based Networks
Authors: Wang Lee Y. , Chiang Long Y. , Kuo C. S. , Lin J. G. , Huang C. Y.
Published: April 2011

Polyhydroxylated fullerenes were utilized as an efficient hyper cross-linking agent in the synthesis of polyurethane networks. The resultant elastomers exhibited greatly enhanced thermal stability in comparison with those of the corresponding linear polyurethane and analogous elastomers, which were cross-linked by 1,1,1- tris(hydroxymethyl)ethane. A synthetic method leading to the preparation of a thin layer of conductive polyaniline/polyurethane IPN at the near surface of a fullerenol- based elastomeric substrate was demonstrated, using aqueous ammonium persulfate as an oxidizing agent in the presence of HCI. This new material exhibits a conductivity of 2.0 S/cm at ambient temperatures with the retention of most bulk properties of the parent elastomer, such as elongation and tensile strength at break.
Electrical Properties of Ion Implanted and Chemically Doped Polyaniline Films
Authors: Aleshin Andrej N. , Mironkov Nikita B. , Suvorov Alexander V. , Conklint Jeanine A. , Su Timothy M , Kaner Richard B.
Published: April 2011

The electronic transport mechanism for ion implanted and chemically doped polyanilinefilms was investigated through temperature dependent dc conductivity measurements over thetemperature range 1.8 – 300K. Chemically synthesized emeraldine base polyaniline free-standingfilms (∼40 µm thick) were irradiated by Ar ions at an energy of 90 keV and doses ranging from 1 ×1014 to 3 × 1017 cm-2 to an estimated thickness of 100 nm. Chemical modification of Polyanilinefilms consisted of doping with 1.0 M H2SO4.

Ion implantation and chemical doping were found to considerably increase the roomtemperature dc conductivity of polyaniline films reaching values up to 800 S cm-1and 8 S cm-1, respectively. Both ion irradiated and chemically doped polyaniline films exhibit p-type conduction.An increase in the irradiation dose increases the stability of the conducting layer compared tochemical doping. In both cases the samples are on the insulator side of the metal-insulatortransition, where cr(T) exhibits a common temperature dependent characteristic of the variablerange hopping (VRH) transport mechanism:σ(T) = σ (0) exp[ - (To / T)m ] (1)where m = 0.5 and To = 103 to 104K. The influence of electron-electron Coulomb the low temperature VRH of ion implanted and chemically doped polyanilCinoeu floilmmbs iisn tperreascetniotend
Synthesis of A 1,1′-Binaphthyl Based Main Chain Chiral Conjugated Polymer
Authors: Hu Qiao-Sheng , Vitharana Dilrukshi , Pu Lin
Published: April 2011

The synthesis and characterization of a 1,1′-binaphthyl based main chain chiral conjugated polymer, R-9, is described. The polymer is prepared from the palladium-catalyzed Suzuki coupling of an optically active binaphthyl molecule, (R)-2,2′-dihexyloxy-1,1′-binaphthyl-6,6′- diboronic acid, R-4 with 1,4-bis(p-bromostyryl)benzene (E:Z = 1:1.2), 8. The Suzuki coupling of 8 with 6-neopentyloxynaphthyl-2-boronic acid, 1 1, leads to the formation of a conjugated molecule 10. The structure of this molecule represents the repeat unit of R-9. The electronic absorption spectrum of 10 demonstrates that the degree of conjugation in the chiral conjugated polymer is almost the same as that of its repeat unit.
Structure-Electronic Properties Relationships in Conducting Polymers: CP-MAS NMR and MM Analysis
Authors: Bradamante S. , Berlin A. , Canavesi A. , Zotti G.
Published: April 2011

The anodic oxidative polymerization of alkyl functionalized 4H-cyclopenta[2, 1-b:3,4-b']- dithiophene (CPDT) followed by undoping provides soluble and processable materials. We used CP MAS and high resolution NMR to analyze the monomers and polymers with the aim of correlating their structural features and conductivity. T1 relaxation values in solution and solid state were compared. Information about the preferred conformations of the polymers (backbone, distances, torsional angles) was deduced using the Molecular Modeling approach. The conclusions were derived by combining the indications obtained from both the spectroscopic and computational methods.
Electroluminescence with Laddertype Poly(paraphenylenes)
Authors: Tasch S. , Niko A. , Leising G. , Scherf U.
Published: April 2011

We present the optical and electronic properties of a new laddertype poly(paraphenylene) (LPPP), the m-LPPP, having the highest intramolecular order and highest environmental stability in the familiy of the LPPPs up to now. The m-LPPP is an excellent candidate for the usage as an active layer in electroluminescence (EL) devices, due to its well defined structure and high purity, as the spectral behaviour of the absorption coefficient cc confirms. cx is very low (αmin <12 cm−1) in the subgap region with a steep onset to the interband transition leading to welir"resolved vibrationally split maxima (αmax ≈ 1.1×105 cm−1). Moreover, the high quantum efficiency of fluorescence (up to 30 % in films) makes the m-LPPP a promising material for high efficiency-EL devices.

The polymer-light emitting diodes (PLEDs), which were fabricated in air stable sandwich structures ITO/m-LPPP/Al, are characterized by high quantum efficiencies up to 4% and cwoperation lifetimes around 170 h. The PLEDs produced homogeneous bright light in the blue and blue-yellow spectral range, with the dominant emission maximum located at 461 nm. The onset field significantly depends on the thickness of the m-LPPP layers (Emin ≈ 0.5 MV/cm; Emax ≈ 2.6 MV/cm) due to ordering effects in the cast polymer. In the blue-green spectral range, the shape of the EL spectra and hence the emission colour can be controlled, by varying the applied electric field.
Solid State Structure and Photoluminescence properties of poly(2,5-dialkoxy-p-phenyleneethynylene)s
Authors: Weder Christoph , Wagner Michael J. , Wrighton Mark S.
Published: April 2011

In an effort to better understand the relationship between molecular structure and photophysical properties, we have prepared and investigated a series of novel poly(2,5-dialkoxy-p-phenyleneethynylene)s. Wide angle X-ray diffraction measurements show that the supramolecular structure can be easily and significantly influenced by the nature of substituents covalently linked to the rigid-rod polymer main chains. Polymers which have sterically hindered side chains are essentially amorphous, while those with only linear side chains can form lamellar structures with a significant degree of long-range order. High photoluminescence quantum yields, up to 0.86 in solution and 0.36 in the solid state, have been measured. While the solution quantum yields are independent of the functionalization, solid state quantum efficiencies were found to be related to the degree of long-range order in the samples. In samples with a high degree of long-range order, the close proximity of the coplanar oriented polymer backbones is assumed to lead to the formation of eximer complexes which provide non emissive decay channels and, hence, result in comparable low photoluminescence quantum yields. In samples that adopt only a small extent of long-range order, the rigid-rod conjugated polymer backbones behave as if they were ‘dissolved’ in a hydrocarbon solvent and consequently high quantum efficiencies are obtained. Preliminary results indicate the suitability of these polymers as the emitting layer in electroluminescent devices.
Excited-State Intramolecular Proton Transfer in Polymers
Authors: Tarkka Richard M. , Jenekhe Samson A.
Published: April 2011

Excited state intramolecular proton transfer (ESIPT) has been demonstrated in new intramoleculary hydrogen bonded (IHB) polymers of interest as photostabilizers, triplet quenchers, photochromic materials, laser dyes and electroluminescent materials. The new IHB polymers containing the 2-(2-hydroxyphenyl)benzoxazole moiety in the main chain were used to explore the effects of polymer structure, extended conjugation and competition with excimer formation on the ESIPT process. It was found that polymer structure, and particularly extent of conjugation, affects an IHB polymer's ability to exhibit ESIPT.
BaTiO3 Thin Films for Electro-optic and Non-linear Optical Applications
Authors: Block B. A. , Wessels B. W.
Published: April 2011

Er-doped BaTiO3 thin films have been investigated as a candidate for an optically active waveguide medium. Epitaxial layers were prepared by metal-organic chemical vapor deposition at low pressure. The properties of the characteristic Er3+ luminescence transition at 0.8 eV have been investigated for epitaxial Er doped BaTiO3 thin films for various Er concentrations. The photoluminescent intensity was found to increase by a factor greater than 500 when the doping level was increased from 1 × 1020 cm−3 to 2.2 × 1021cm−3, indicating that concentration quenching was not significant at the highest doping levels. A complex emission spectra was observed and was attributed to the multi-site substitution of Er in BaTiO3. Transient decay measurements revealed a 7 ms radiative lifetime for the 0.80 eV transition that was independent of concentration.
Dielectric Behavior of CVD (Ba,Sr)TiO3 thin Films on Pt/Si
Authors: Streiffer S.K. , Basceri C. , Kingon A.I. , Lipa S. , Bilodeau S. , Carl R. , Van Buskirk P.C.
Published: April 2011

We have investigated the dielectric behavior of polycrystalline (Ba,Sr)TiO3 thin films deposited by liquid-source metalorganic chemical vapor deposition. The time-domain polarization current, the frequency dependence of the permittivity, and the dielectric loss for these CVD films are all described by a single set of parameters via the phenomenology of Curie - von Schweidler behavior. No change in the general form of the permittivity is found out to 1.5 GHz, suggesting that this description of the response is valid into the frequency range of interest for many applications. Low-frequency dispersion is found to be controllable, leading to films with very low dissipation factors and almost frequency-independent dielectric response. Finally, a non-zero intercept of the inverse of capacitance versus film thickness suggests the existence of a series interfacial capacitance, arising from either microstructural inhomogeneity or energy barriers to carrier transport at the film-electrode interfaces.
MOCVD OF SnO2 on Silicon Microhotplate Arrays for use un Gas Sensing Applications
Authors: Dimeo F. , Semancik S. , Cavicchi R.E. , Suehle J.S. , Chaparala P. , Tea N.H.
Published: April 2011

The quantitative detection of gas concentrations in mixed atmospheres is becoming increasingly important in manufacturing processing, environmental monitoring, and medical diagnostics. Several conductive oxides, such as SnO2, ZnO, and TiO2, are well known to exhibit changes in resistivity when exposed to various gases at temperatures ranging from 200–500°C. Current discrete devices based on resistive changes such as the Taguchi sensor, however, suffer from certain performance problems, including poor gas detection specificity. Integrated arrays of sensors, fabricated using planar technology, offer a promising solution to these problems, as well as other benefits such as low power consumption and low cost.

In this paper, we report the results of using Metalorganic Chemical Vapor Deposition (MOCVD) to fabricate thin films of SnO2 on microhotplate arrays. The studied arrays contain 4 micromachined, suspended elements, each having an integrated resistive heater that produces a rapid thermal rise time ∼3 msec. By separately heating individual elements, we can take advantage of the thermally selective nature of the MOCVD process to limit deposition to these areas, resulting in a maskless deposition process. In addition, these array elements have surface electrical contacts that permit the measurement of the resistance of the thin films during deposition, as well as when they are operated in a gas sensing mode. In situ growth measurements will be reported.
Study of Microstructure and Gas Sensing Properties of tin Oxide thin Films Prepared by Metal Organic Chemical Vapor Deposition
Authors: Lee Sang Woo , Liu Donihang , Tsai Ping P. , Chen Haydn
Published: April 2011

Tin oxide (SnO2) thin films were deposited on polycrystalline alumina (A12O3) substrates using metal organic chemical vapor deposition (MOCVD) technique at the growth temperature of 600°C. X-ray diffraction, scanning electron microscopy, and Auger electron spectroscopy were applied for the microstructure characterization of the films. The films were subjected to sensing tests under 1% H2 environment by monitoring changes in the electrical resistance of the films at elevated temperatures. There is a trend to exhibit sensor temperature characteristic in the deposited thin films which show a local maximum in the electrical resistance curve as a function of ambient temperature. The local maximum occurred at a relatively higher temperature than found in bulk sintered ceramics.
Silicon Nitride Tools Coated With Tic Or Tin Composite Diamond Structures
Authors: Fan W.D. , Jagannadham K. , Narayan J.
Published: April 2011

Composite diamond coatings on Si3N4 substrates have been developed to minimize stresses/strains and improve wear and adhesion properties. The coatings consist of a first layer of discontinuous diamond crystallites which are anchored to the Si3N4 substrate by a second interposing layer of TiC or TiN film. A top third layer of continuous diamond film is grown epitaxially on the first layer. The diamond films and TiC or TiN films were deposited using hot filament chemical vapor deposition and laser physical vapor deposition, respectively. The TiC and TiN films were examined by X-ray diffraction. The diamond films were characterized by scanning electron microscopy and Raman spectroscopy. Adhesion of the diamond coatings was investigated using overlap polishing with diamond paste, wear against Al-12.5%Si alloy, and pull-test. The results show that after introducing an interposing layer of TiC or TiN, adhesion of diamond coatings on Si3N4 substrates is improved significantly. After polishing test against diamond paste for 4 hours, only 30% of diamond was retained with single diamond coating while 80% of diamond was found with TiN composite diamond coating. The mechanism of improvement of adhesion is discussed.
Characterization Of Amorphous Carbon Films Based On Carbon, Nitrogen, and hydrogen*.
Authors: Efstathiadis H. , Akkerman Z. , Smith F. W.
Published: April 2011

A series of amorphous hydrogenated carbon-nitrogen alloy films (a-CxNyHz) has been prepared via plasma-enhanced chemical vapor deposition from mixtures of nitrogen and acetylene. It is found that as the ratio R=N2/C2H2 is increased from zero to 100, the nitrogen incorporation into the films is increasing while the deposition rate is decreasing for 0<R<10 and is saturating at a value of about 1.0 A/sec for 10<R<100. The absorption associated with the N-H stretching mode increases while that of the C-H stretching mode decreases with increase of R. The optical constants and the energy gaps of these films have also been determined. A free energy model previously developed for the prediction of the bonding in amorphous a-CxHyalloys is extended and applied here to a-CxNyHz. Predictions are presented for the bonding of tetrahedral C(sp3), trigonal C(sp2), linear C(sp1), pyramidal N(sp 3), trigonal N(sp 2), and linear N(sp1) atoms in the alloy, and the bonding of H to these atoms.