bluuebunny/crossref_metadata_2025 huggingface dataset:
Results From Simulated Contact-Handled Transuranic Waste Experiments at the Waste Isolation Pilot Plant
Authors: Molecke Martin A. , Rob Sorensen N. , Krumhansl James L.
Published: March 2011

We conducted in situ experiments with simulated, i.e., nonradioactive, contact-handled trans-uranic (CH TRU) waste drums at the Waste Isolation Pilot Plant (WIPP) facility for a period of about four years. We performed these tests in two rooms in rock salt, at WIPP, with drums surrounded by crushed salt or 70 wt. % salt/30 wt. % bentonite clay backfills, or partially submerged in a NaCl brine pool. Air and brine temperatures were maintained at ~40°C. These full-scale (210-L drum) experiments provided in situ data on: backfill material moisture-sorption and physical properties in the presence of brine; waste container corrosion adequacy; and, migration of chemical tracers (nonradioactive actinide and fission product simulants) in the near-field vicinity, all as a function of time. Individual drums, backfill, and brine samples were removed periodically for laboratory evaluations. Waste container testing in the presence of brine and brine-moistened backfill materials served as a severe overtest of long-term conditions that could be anticipated in an actual salt waste repository. We also obtained relevant operational-test emplacement and retrieval experience. All test results are intended to support both the acceptance of actual TRU wastes at the WIPP and performance assessment data needs. We provide an overview and technical data summary focusing on the WIPP CH TRU environmental overtests involving ] 74 waste drums in the presence of backfill materials and the brine pool, with posttest laboratory materials analyses of backfill sorbed-moisture content, CH TRU drum corrosion, tracer migration, and associated test observations.
Formation of Vivianite During Microbiologically Influenced Corrosion of Steels
Authors: McNeil Michael , McKay Jennifer
Published: March 2011

Exposure of carbon and HY-80 high strength low alloy (HSLA) steels to anaerobic Postgate cultures containing sulfate reducing bacteria leads to production of mackinawite, Fe9S8, and vivianite, Fe3(PO4)2.8H2O, with minor amounts of other minerals, the vivianite being sometimes accompanied by siderite, FeCO3. The vivianite and mackinawite persist on exposure to air or oxygenated water. Green rust is a significant alteration product on some steels. The implications of these findings are discussed in light of present and possible future nuclear waste containers.
The Sorption of Niobium, Tin, Iodine and Chlorine onto Nirex Reference Vault Backfill
Authors: Baker S. , McCrohon R. , Oliver P. , Pilkington N.J.
Published: March 2011

UK Nirex Ltd is proposing to develop a deep underground repository for the disposal of solid low- and intermediate-level radioactive wastes in the UK, and is currently investigating Sellafield in Cumbria as a possible site. The Nirex Safety Assessment Research Programme (NSARP) comprises scientific research to support the post-closure performance assessment of the repository. One of the investigations carried out by AEA Technology under the NSARP is the study of the sorption of radionuclides onto the backfill. Sorption is one of the key parameters determining the rate of release of radionuclides from the repository. The radionuclides present in the waste include 94Nb, 126Sn, 129I and 36Cl. This paper reports the measurement of the sorption of niobium, tin, iodine and chlorine onto the Nirex reference vault backfill at 20±5°C by the batch sorption method. The temperature dependence of tin sorption was investigated by carrying out additional experiments at 77±5°C. Experiments on niobium solubility and sorption were carried out under saline conditions to reflect the nature of the groundwater at Sellafield. Sorption coefficients (Rd) for niobium are within the range measured in other work, whereas for tin the results are a factor of ten lower than literature values. For iodine and chlorine, the results are consistent with the literature; they also show an increase in Rd with decreasing initial inventory. The Rd values for niobium and tin are significantly higher than those for chlorine and iodine.
Effects of Nonequilibrium Adsorption on Nuclide Transport in a Porous Rock
Authors: Teng Shi-Ping , Lee Ching-Hor
Published: March 2011

An analytical solution covering the entire range of adsorption properties of rock has been derived for the migration of radiionuclide in a porous rock matrix. The analysis takes into account the advective transport, hydrodynamic dispersion, adsorption between solid phase and liquid phase, and the radioactive decay. For adsorption of nuclide within the rock, the effects of no adsorption, linear nonequilibrium adsorption, and linear equilibrium adsorption are integrated into a generic transient analytical solution. The results indicate that the assumption of equilibrium adsorption can result in underestimation of the concentration profile in the early stages of migration. However, both the equilibrium and nonequilibrium profiles eventually approach the same value. It is also noted that for the case of nonequilibrium adsorption, plateaus appear in the concentration profile of the breakthrough curves. The effects of different adsorption rates are also analyzed.
Preliminary Analysis of Potential Chemical Environments Inside Failed Waste Containers at the Proposed Yucca Mountain Repository
Authors: Colten-Bradley Virginia , Walton John C.
Published: March 2011

Prediction of radionuclide release rates for high-level waste requires estimates of the rates of waste form alteration and formation of secondary minerals inside the failed canister. Unsaturated repository sites may promote development of a variety of chemical environments related to two phase (liquid/ vapor) transport and temperature gradients caused by radiogenic decay. A mass balance (shell balance) approach is used to estimate the effects of dripping water, evaporation, and condensation on the waste canister and the presence of saline water inside the failed waste canister. The simplified calculations predict large variability of water chemistry over spatial scales of a few centimeters. The effects of the predicted aqueous chemistry on waste form alteration, secondary mineral formation, and radionuclide solubility are examined.
Preliminary Results for the Experimental Evaluation of a Radwaste Repository Near-Field Model
Authors: Kang C. H. , Lee J. O. , Hahn P. S. , Park H. H.
Published: March 2011

A series of experiments for a simplified system has been performed to evaluate a near-field model of radioactive waste repository developed by the University of California, Berkeley. In the experiments, iodine as nonsorbing species and cesium as sorbing species were employed. This paper presents the initial 200-day results of these experiments. Good agreement is found between the model and the experimental results. The results of this work will give basic ideas on the design of the near field of a repository.
Introduced Materials and Colloid Formation: a Report on the Current State of Knowledge
Authors: Meike A. , Wittwer C.
Published: March 2011

This paper reviews potential sources of colloids and enhanced adsorption of radionuclides that may stem from materials introduced into a repository setting. Three major sources of colloids are examined: metals, cements, and organics. The sensitivity of colloids to chemical species, pH, time, temperature, radiolysis, redox state, gradients of the aforementioned variables, and microbial activity is shown. We consider these influences on colloid formation and sorption with respect to introduced materials. We also discuss areas that have not been addressed but may have consequences in a repository setting.
A Preliminary Investigation of the Applicability of Surface Complexation Modeling to the Understanding of Transportation Cask Weeping
Authors: Granstaff Victoria E. , Chambers William B. , Doughty Daniel H.
Published: March 2011

A new application for surface complexation modeling is described. These models, which describe chemical equilibria among aqueous and adsorbed species, have typically been used for predicting groundwater transport of contaminants by modeling the natural adsorbents as various metal oxides. Our experiments suggest that this type of modeling can also explain stainless steel surface contamination and decontamination mechanisms.

Stainless steel transportation casks, when submerged in a spent fuel storage pool at nuclear power stations, can become contaminated with radionuclides such as 137Cs, 134Cs, and 60Co. Subsequent release or desorption of these contaminants under varying environmental conditions occasionally results in the phenomenon known as “cask weeping.” We have postulated that contaminants in the storage pool adsorb onto the hydrous metal oxide surface of the passivated stainless steel and are subsequently released (by conversion from a fixed to a removable form) during transportation, due to varying environmental factors, such as humidity, road salt, dirt, and acid rain. It is well known that 304 stainless steel has a chromium enriched passive surface layer; thus its adsorption behavior should be similar to that of a mixed chromium / iron oxide.

To help us interpret our studies of reversible binding of dissolved metals on stainless steel surfaces, we have studied the adsorption of Co+2 on Cr2O3. The data are interpreted using electrostatic surface complexation models. The FITEQL computer program was used to obtain the model binding constants and site densities from the experimental data. The MINTEQA2 computer speciation model was used, with the fitted constants, in an attempt to validate this approach.
Intrusion of Seawater into a Porous Fracture zone a Coupled Geohydrochemical Modelling Exercise
Authors: Pirhonen Veijo O.
Published: March 2011

A coupled geochemical transport program PHREEQM2D has been tested in order to examine intrusion of seawater into fracture zones which can be connected to tunnels, such as nuclear-waste repositories on the sea shores. The code consists of a flow and transport program HST2D and a chemical equilibrium program PHREEQE. It uses a mixing cell approach, where chemistry and transport are solved separately. Ion exchange is calculated by means of a simple surface complexation model.

In the present artificial exercise, replacement of groundwater by seawater in a connecting porous fracture zone was modelled without comparing the results to observed data. Dilution, mixing, ion exchange, and dissolution/precipitation reactions were examined.

The results of modeling showed that the sulphate front of seawater moved some distance towards the tunnel during the simulations. The characteristic solutes of dilute groundwater were assumed to enter the tunnel in a short period of time. Amounts of sulphates decreased due to dilution and mixing. The chemical contents of waters were also affected by dissolution, precipitation, and ion exchange. Calcite dissolved and oxyhydroxides precipitated in oxidizing water. The strongest exchangeable ions in water, Ca and Na, were retarded due to ion exchange in the mixing zones. This caused an increase in dissolution of calcite in the mixing zones. Calcite would, however, start to precipitate in the mixing zone when the ion exchange capacity of rock would be consumed.

Some important factors, such as retardation on oxide surfaces (adsorption models) and microbial activity (organic complexation models) have not been tested in the present exercise. Otherwise, the PHREEQM2D showed its applicability to modelling of chemical equilibrium, dilution, mixing, ion exchange, and elution/precipitation in discrete porous zones in transient conditions. It could be used to model temperature-enchanced, coupled geohyd-Γochemical, processes in porous zones consisting of densely fractured or crushed crystalline rock.
Further Development and Studies of Gas Methods in Matrix Diffusion
Authors: Hartikainen Kari , Väätäinen K. , Hautojärvi A. , Timonen J.
Published: March 2011

The present status of the recently introduced gas method equipment for migration studies of fractured and porous media is briefly reviewed together with advances in the experimental techniques. The conditions under which matrix diffusion can be observed in both gas flow and water flow experiments are discussed in some detail. Results for a gas flow experiment are shown, and explained with a numerical model which incorporates the effects of hydrodynamic dispersion and matrix diffusion. The necessary parameters for a corresponding water flow experiment are also briefly discussed.
Experimental Investigation of Hydrous Pyrolysis of Diesel Fuel and the Effect of Pyrolysis Products on Performance of the Candidate Nuclear Waste Repository at Yucca Mountain
Authors: Jackson Kenneth J. , Carroll Susan A.
Published: March 2011

It is thought that a significant amount of diesel fuel and other hydrocarbon-rich phases may remain inside the candidate nuclear waste repository at Yucca Mountain after construction and subsequent emplacement of radioactive waste. Although the proposed repository horizon is above the water table, the remnant hydrocarbon phases may react with hydrothermal solutions generated by high temperature conditions that will prevail for a period of time in the repository. The preliminary experimental results of this study show that diesel fuel hydrous pyrolysis is minimal at 200°C and 70 bars. The composition of the diesel fuel remained constant throughout the experiment and the concentration of carboxylic acids in the aqueous phases was only slightly above the detection limit (1–2 ppm) of the analytical technique.
An Approach to Analysis of High Level waste Container Performance in an Unsaturated Repository Environment
Authors: Walton John C. , Sridhar Narasi , Cragnolino Gustavo , Torng Tony , Nair Prasad
Published: March 2011

One of the requirements for the performance of waste packages prescribed in 10CFR 60.113 is that the high level waste must be “substantially completely” contained for a minimum period of 300 to 1000 years. During this period, the radiation and thermal conditions in the engineered barrier system and the near-field environment are dominated by fission product decay. In the present U.S design of the engineered barrier system, the outer container plays a dominant role in maintaining radionuclide containment. A quantitative methodology for analyzing the performance of the container is described in this paper. This methodology enables prediction of the evolution of the waste package environment in terms of temperature fields, stability of liquid water on the container surface, and concentration of aggressive ions such as chloride. The initiation and propagation of localized corrosion is determined by the corrosion potential of the container material and critical potentials for localized corrosion. The coiTOsion potential is estimated from the kinetics of the anodic and cathodic reactions including oxygen diffusion through scale layers formed on the container surface. The methodology described is applicable to a wide range of metals, alloys and environmental conditions.
An Accelerated Electrochemical MIC Test for Stainless Alloys
Authors: Gendron T.S. , Cleland R.D.
Published: March 2011

Previous work in our laboratory and elsewhere has suggested that MIC of stainless steels and nickel-base alloys occurs in locally anaerobic regions that support the growth of sulfate reducing bacteria (SRB). The cathodic reaction is provided by oxygen reduction at remote sites. Such a coupling between anode and cathode is difficult to reproduce in the laboratory, but can be simulated indirectly using a double electrochemical cell, as in previous work. A more realistic simulation using a single aerated electrochemical cell has now been developed, in which a second organism (P.aeruginosa)is used to provide an anoxic habitat for SRB growth and possibly a source of organic carbon, within a layer of silt. A bare alloy electrode is used as the oxygen cathode. Tests of this kind using rigorous microbiological procedures have generated pitting corrosion of several alloys in low chloride media simulating freshwater heat exchanger conditions. Similar test procedures are applicable to other environments of interest to this symposium.
The Advantages of a Salt/Bentonite Backfill for Waste Isolation Pilot Plant Disposal Rooms
Authors: Butcher B.M.
Published: March 2011

This paper concludes that a 70 wt% salt/30 wt% bentonite mixture is preferable to pure crushed salt as backfill for disposal rooms in the Waste Isolation Pilot Plant. The performance of two backfill materials is examined with regard to various selection criteria related to compliance with the transuranic radioactive waste standard 40 CFR 191, Subpart B, such as the need for low liquid permeability after closure, chemical stability, strength, ease of emplacement, and sorption potential for brine and radionuclides. Both salt and salt/bentonite are expected to consolidate to a final state of permeability ≤ 10-18 m2, which is adequate for satisfying government regulations for nuclear repositories. The real advantage of the salt/bentonite backfill depends, therefore, on bentonite’s potential for sorbing brine and radionuclides. Estimates of the impact of these properties on backfill performance are presented.
An Experimental study of Granitic Water-Saponitic Bentonite Interaction under Hydrothermal Conditions
Authors: Garralon Antonio , Cuevas Jaime , Leguey Santiago
Published: March 2011

The interaction of a saponitic clay from the Madrid Basin with synthetic groundwater (GW) simulating those from granitic areas is investigated. The experiments performed explore the reaction of clay with GW (1:3 solid to water ratio) at 45, 60 and 90°C. Water extracted from the clay slurries has been analyzed and water of this composition synthesized again to run a new reaction with the original clay (salt concentration process). The clay product of the first reaction was reacted again with GW (leaching process). These reactions were repeated in successive equilibrating steps.

Multicationic selectivity coefficients have been calculated. K > Ca > Mg > Na is the order of preference for adsorption by the clay. The selectivity of Ca is highly enhanced in both processes, the clay acting as a true complexing agent for Ca, as calcite controls the carbonate equilibrium. A clear dependence of the exchange constants on temperature with the range explored was not detected. The GW composition evolves from Ca,Na-HCO3 to Na,Mg-HCO3 (leaching) and NaCl (concentration), the solutions being buffered at pH 8.0. Mechanical properties, clay mineralogy and bulk adsorption properties remained virtually unchanged in the successive one month experiments although a slight decrease in BET specific surface area indicated some sepiolite dissolution at 90°C.
Diffusion of Uranium in Compacted Bentonite in the Presence of Carbon Steel
Authors: Idemitsu K. , Furuya H. , Tachi Y. , Inagaki Y.
Published: March 2011

In a high-level waste repository, a carbon steel overpack will be corroded by consuming oxygen trapped in the repository after closure. This will create a reducing environment in the vicinity of repository. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as uranium.

The apparent diffusivities of uranium were measured in compacted bentonite (Kunigel VI®, Japan) in contact with carbon steel under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusivities of uranium were 3.5 × 10-14 to 1.1 × 10-13 m2/s under reducing conditions and 9.0 × 10-13 to 1.4 × 10-12 m2/s under oxidizing conditions. There was no significant effect of dry density (1.6 to 1.8 g/cm3) and silica sand (0 or 40%) on the apparent diffusivities.

Since the bentonite pore water would be buffered at a pH between 8 and 9, uranium in the bentonite pore water would probably exist as a neutral hydroxide complex under reducing conditions and as an anioníc carbonate or hydroxide complex under oxidizing conditions. The anion exclusion theory cannot explain the difference of diffusivities between the two conditions. The uranium concentrations in bentonite under oxidizing conditions were one order of magnitude higher than those under the reducing conditions. The uranium concentration in the bentonite pore water under the reducing condition is estimated to be two orders of magnitude lower than that under the oxidizing conditions under the assumption of diffusion in porous media.
Estimation of Static Fatigue Behavior of Ceramic Materials as Candidate Overpack Materials
Authors: Obata Masamichi , Honda Akira , Ishikawa Hirohisa , Mano Tadashi
Published: March 2011

Static fatigue behavior is one of the important factors for life prediciton of ceramic materials. In this study, SCG (slow crack growth) parameters were measured under atmosphere conditions, and the static fatigue behavior of alumina, PSZ (partially stabilized zirconia), and titanium oxide was examined.

According to the results of the evaluatin of the static fatigue behavior, the destruction probability after 1,000 years would be less than 1/40,000 when tensile stresses occurring in the material were less than 79.4, 241.3, 8.0 MPa for alumina, PSZ, and titanium oxide, respectively. However titanium oxide could not be used because of the wall thickness that would be needed to accomplish this stress. The life prediction method includes only tht effect of preexisting flaws so the method to estimate the effect of localized corrosion is required for the future examination of the application of ceramic materials.
Corrosion of Synthesized Glasses and Glazes as Analogs for Nuclear Waste Glass Degradation
Authors: Vandiver Pamela B.
Published: March 2011

Synthesized glasses provide an opportunity to study natural corrosion processes which are intermediate in time span between geological examples of natural glasses, such as obsidians and tektites, and relatively short term laboratory tests lasting a few hours to several decades. Like natural glasses, the synthesized glasses are sufficiently abundant that laboratory studies can be conducted to study the processes, mechanisms and rates of corrosion. In addition, synthesized glasses can usually be tracked to particular archaeological find sites with known dates of production and often burial.
Potential Resources from Coal Fly Ash
Authors: Watson J. S.
Published: March 2011

Recent studies at Oak Ridge National Laboratory (ORNL) and elsewhere have identified various chemical processes for recovering useful materials, such as alumina and iron oxides, from coal combustion fly ash. Based on certain assumptions, each of these processes can yield useful products at economical prices. Most processes leave a residual solid waste with a volume only slightly less than that of the original waste. This residue may not present a serious hazard, but its volume alone makes disposal difficult for utilities with limited land available for disposal sites. Characteristics of some of the residues are being studied to determine possible beneficial uses or applications of these by-products.
Characterization of a Lignite Ash from the Metc Gasifier I. Mineralogy
Authors: McCarthy Gregory J. , Keller Lindsay P. , Stevenson Robert J. , Galbreath Kevin C. , Steinwand Aaron L.
Published: March 2011

Utilization or disposal of gasification ash requires detailed characterization of its chemistry and phase formation (mineralogy). A North Dakota lignite ash produced in the Morgantown Energy Technology Center (METC) gasifier has been studied in detail by x-ray diffraction and electron microprobe analysis. The ash was coarse (84% of grains larger than 1.0 mm) but a typical grain was composed of a dozen or more crystalline phases with dimensions on the micrometer scale as well as less abundant glass phases. Hard centimeter-size clinkers suggested partial melting followed by crystallization. Silicates (dicalcium silicates (C2S), merwinite, Ca-Na-silicate (CNS), quartz), aluminosilicates (melilite, nepheline, carnegieite), oxides (ferrite spinels, periclase, hematite), calcite and minor zeolites comprised the dominant mineralogy. Microprobe analyses were obtained for large numbers of grains of the C2S phases, CNS, merwinite, melilite, ferrite spinels and calcite. The remaining phases had crystal sizes too small for analysis. A model is proposed for the genesis of this ash based on the inorganic constituents of lignite and the gasifier operating conditions.
Characterization of a Lignite Ash from the METC Gasifier III. Correlations of Leaching Behavior and Mineralogy
Authors: Hassett D. J. , McCarthy G. J. , Henke K. R. , Korynta E. D.
Published: March 2011

Lignite gasification ash from the Morgantown Energy Technology Center (METC) gasifier was subiected to two short-term leaching treatments. The cnncentrations of regulated elements in the EPA EP procedure leachate from the bulk METC ash did not exceed the “EP Trigger Limits.” A modification of this procedure that uses a basic synthetic groundwater instead of the acid EP extractant was also performed on the bulk ash and its eleven size fractions. Water equilibria modeling was used to explain the concentrations of major elements in solution. Corcentrations of minor and trace elements in solution after leaching with synthetic groundwater were also below “EP Trigger Limits.”
Investigation of Leachability of Subbituminous Fly Ash Enhanced Road Base Materials
Authors: Garcez Ivan , Tittlebaum Marty E.
Published: March 2011

Enormous amounts of coal fly ash produced by the utilities industry create a significant disposal problem. The abundance of fly ash along with its self-hardening properties led the Louisiana Department of Transportation and Development (LA DOTD) to use fly ash as a soil stabilizer for road bases. However, the LA DOTD is primarily concerned with the strength of the material and has not studied its leaching characteristics. In this study, a total of three samples, a 30 percent subbituminous fly ash/soil mixture, subbituminous fly ash, and soil, were leached following the EPA multiple extraction procedure and analyzed by Inductively Coupled Argon Plasma Spectrometry (ICAP). Results indicate that little change in leachate quality of subbituminous fly ash was caused by the soil stabilization process. The insignificant change is attributed to the low cation exchange capacity of the soil. ICAP analysis revealed that levels of toxic metals in the leachates are well within RCRA standards.
Characterization of Fly Ash and its Reactions in Concrete
Authors: Roy Della M. , Luke Karen , Diamond Sidney
Published: March 2011

Fly ashes are currently being produced that are much more widely different from each other in composition and other characteristics than had been previously experienced, owing to the widespread use of low rank subbituminous and lignitic coals. The current ASTM classifications into Class F and Class C pozzolan categories are not adequate to describe all their important properties. Current characterization methods are reviewed, including physical characterization by particle size distribution, shape, apparent specific gravity, content of hollow grains and of residual coal fragments, etc., chemical procedures of various kinds, and SEM, EDXA, XRD, and other methods for the determination of mineralogical content and glass character. Etching and chemical dissolution procedures are particularly important. The state of these various methods, current results of their use in rly ash characterizations, and the relations of these to reactivity and performance of fly ashes in cement and concrete are discussed.
Scanning Electron Microscopy and X-Ray Diffraction Analysis of Various Size Fractions of Fly Ash
Authors: Joshi R. C. , Natt G. S. , Day R. L. , Tilleman D. D.
Published: March 2011

X-ray diffraction and scanning electron microscopic analyses have been performed on the various Western Canadial fly ash fractions and on mixtures of cement and fly ash fractions. The ash mineralogy of hydrated and unhydrated fly ash samples was examined by x-ray diffraction. Results from a study of the morphology of ash particles etched in dilute hydrofluoric acid are also included. Scanning electron microscopy indicates that most of the reactive portion of the ash is on the particle surface. Also, as the fly ash particle size increases, the amount of crystalline SiO2 increases but the quantity of calcium containing compounds decreases. Crys~alline SiO2 (the majority of which is present in the +75 μm fraction) does not take part in self-hardening reactions but does appear to take part in pozzolanic reactions.
Technical Note on the Determination of Free Lime (CaO) in Fly Ash
Authors: Schlorholtz Scott , Demirel Turgut
Published: March 2011

Many fly ashes contain free lime (CaO) and periclase (MgO) [1,2]. These two compounds, when present in excessive amounts, are known to cause soundness problems in portland cement [3,4]. Recent work [5] has indicated that the autoclave expansion of portland cement-fly ash pastes is related to the concentration of CaO and MgO in a given paste, free lime typically being more detrimental than periclase. The purpose of this technical note is to briefly discuss two methods that are currently available for determining the free lime content of fly ash, and to suggest a supplement to the autoclave test (described in ASTM C 151). The major drawback of the autoclave test is that it requires approximately two days to complete and therefore it would be helpful to have a quick chemical test that could be used to indicate the soundness properties of a given fly ash.
Characterization of Crystalline Phases in Fly Ash by Microfocus Raman Spectroscopy
Authors: Scheetz Barry E. , White William B.
Published: March 2011

The laser Raman microprobe was used to interrogate individual fly ash particles as small as 1 μm diameter and record “fingerprint” Raman spectra from both crystalline and non-crystalline components.of the fly ash. When compared to reference patterns of known crystalline phases, the Raman spectra can be used to identify crystalline phases and can give some structural information on other phases. Furthermore, because this method characterizes fly ash particles on an individual basis, correlations to both color and morphology of the particles can be made.
Characterization of Catalyzed Devitrification in Quenched Fly Ash Melts
Authors: Risbud Subhash H.
Published: March 2011

Coal combustion produces enormous quantities of residual ash often called bottom ash or fly ash. The fly ash component contains lightweight cenospheres giving the ash a fluffy character. Fly ash is captured in the coal combustion process by air pollution control devices as the gases exit the stack. Fly ash compositions are usually highly siliceous consisting mainly of the oxides of silica, alumina, calcia, and iron oxides; minor constituents such as MgO, alkali oxides, TiO2 etc. are also almost invariably present in quantities of ≈0.5 to 3 wt%. Two important aspects of crystallization of fly ash melts and glasses relate to the prevention of boiler slagging [1] and, from a waste utilization point of view, to the development of new products using fly ash as a raw material[2–4]. Ash devitrification on cooling of the melt results in friable material that does not stick to boiler walls as easily as glassy slag [5]. From another standpoint, crystallization of glassy ash slag to a fine grained equiaxed microstructure is considered a desirable glass-ceramic body for thermomechanical reasons [6].
Retardation Effects in the Hydration of Cement-Fly Ash Pastes
Authors: Grutzeck Michael W. , Fajun Wei , Roy Della M.
Published: March 2011

The hydration of high-calcium and low-calcium fly ash-cementmixtures was investigated to determine the effect of fly ash upon the hydration of a Type I portland cement, and to determine the associated mechanisms of hydration. When blended with portland cement, both fly ashes retarded the early hydration process, the high-Ca more so than the low-Ca. Analyses of solution compositions and calorimetric (heat of hydration) measurements were made. The retardation and hydration effects are discussed in terms of solution composition data and solid phase characterization. The hydration effects were interpreted and compared with the results of previous work.
Reaction Products in Fly Ash Concrete
Authors: Baker Mark D. , Laguros Joakim G.
Published: March 2011

The setting and strength gaining process of PC concrete containing Class C high lime fly ash were related to the reaction products identified using XRD and SEM. Four fly ash concrete mixes (20, 30, 40, and 50 percent replacement of cement by fly ash) and similar paste mixes were compared to control mixes for curing periods up to one year. Setting time and early compressive strength were adversely affected by the addition of fly ash. Beyond one week all of the fly ash concrete mixes gained strength at a faster rate than the corresponding control mixes. XRD studies suggest that the retardation mechanism may be associated with the high levels of ettringite formed early in the hydration process and its conversion to monosulfoaluminate. A decrease in the level of calcium hydroxide, typical of pozzolanic activity, was not in evidence. SEM micrographs of fly ash spheres in concrete at the various stages of hydration reveal an intricate crystal framework. A simple heat of hydration test is presented which helps explain the strength gains observed.
Autoclave Expansion of Portland Cement-Fly Ash Pastes
Authors: Schlorholtz Scott , Demirel Turgut
Published: March 2011

The influence of the chemical composition of fly ash on the autoclave expansion of portland cement-fly ash pastes has been studied. The autoclave expansion tests were performed as described in ASTM C 151–81. Several of the cement-fly ash pastes tested exhibited severe expansive behavior. Free lime (CaO) was the only single variable that correlated well with the expansion observed in the autoclave tests. A multivariable model was generated in which lime, magnesium oxide, and tricalcium aluminate were the significant variables. The autoclave expansion of portland cement-fly ash pastes appears to be quite sensitive to the amount of free lime present in a given mixture.
Characterization of the Ni/NiO, Interface Region in Oxidized High Purity Nickel by Transmission Electron Microscopy
Authors: Sawhill Howard T. , Hobbs Linn W.
Published: March 2011

Ni/NiO interface structures were investigated using TEM, and the observed structures were compared with current heterophase interface models. Relative magnitudes of Ni/NiO interfacial energies were obtained from measurements of dihedral angles at triple grain junctions between Ni and NiO grains. Extra reflections in diffraction patterns from oxide grains adjacent to the Ni/NiO interface were compared with kinematical structure factor calculations for several proposed structures.
Interface Study of Mo/GaAs
Authors: Ling Peiching , Chang Jyh-Kao , Lin Min-Shyong , Lou Jen-Chung
Published: March 2011

The electrical characteristics and the microstructure of Mo/GaAs Schottky diodes fabricated by electron-beam evaporation have been studied. The barrier height, ideality factor, deep trapping levels and intermetallic compounds of these annealed or unannealed Mo/GaAs Schottky diodes are obtained by using the I-V, C-V, Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM) analyses. An obvious interdiffusion at Mo/GaAs interface is observed in Mo/GaAs Schottky diodes annealed above 500°C for 10 min. DLTS results show that there are two electron traps [Ec-(0.52±0.02)'eV and Ec-(0.86±0.02) eV] and one hole trap [Ev+(0.92±0.02) eV] are demonstrated for 300°C, 400°C post-annealed Mo/GaAs diodes. TEM results also indicate that the disappearance of these deep trapping levels may correlated to the formation of intermetallic compounds GaMo3 and MoAs2 existed in Mo/GaAs diodes post-annealed above 500°C. It is believed that the metal-semiconductor interdiffusion and the intermetallic compounds play the major roles for the thermal degradation of Mo/GaAs Schottky diodes.
Defects in Platinum Silicide Formation
Authors: Warburton Michael J.
Published: March 2011

Four types of cause related defects in the formation of platinum silicide were examined by scanning Auger Microscopy (SAM). These are: “Dark Platinum”, a dark rough patch on the platinum silicide, “Aqua Regia Attack”, the apparent etch of the platinum silicide by the aqua regia used to remove pure Pt metal, “Spot Defects”, holes in the Pt-Si layer and Ti-W strip defects, the apparent defects left in the Pt-Si by the stripping of a Ti-W overlayer. Elemental Auger maps show that silicide formation was prevented, in the first three cases, by remaining oxide from a masking step. The fourth case was caused by a layer of titanium oxide overlying the Pt-Si.
Auger Electron Analysis of Oxides Grown on a Dilute Zirconium/Nickel Alloy
Authors: Ploc R. A. , Davidson R. D. , Roy J. A.
Published: March 2011

Auger electron analysis of oxides grown at 573 K in dried oxygen on the matrix and on precipitates in a 0.5 wt% Ni in zirconium alloy, is part of a larger program to study the effect of second phase particles on the oxidation and hydriding behaviour of Zircaloy-2. The alloy consisted of a zirconium matrix containing randomly distributed Zr2Ni precipitates of up to 10 μM in diameter. Oxidation simultaneously proceeded about the whole periphery of the precipitate and after approximately 50 days exposure was completely oxidized and of nearly uniform composition. The chemical structure of the oxides grown on the matrix and on the free and internal surfaces of the precipitate were determined as a function of depth in the oxide film.
Surface Segregation of Ni-Cr Alloy
Authors: Chen N. Q. , Zhang Q. J. , Hua Z. Y.
Published: March 2011

The surface segregation of a Ni-Cr alloy used for commerciel heating elements hps been examined with a scanning Auger Microprobe (SAM) and other electron spectroscopy. A variety of sample surfaces prepared by different ways, including fracturing, mechanical polishing, electrochemical polishing, annealing, oxidation and their combinptions were investigated.

Results showed that on the surface treated with mechanical polishing followed by oxidation, a continuous, hichly chromium-enriched layer would be formed in a few minutes. Three factors, i.e., mechanical polishing, oxygen environment and temperature, have been found all necessary to make this Cr enrichment happen rapidly.

Taking the advantage of high spatial resolution of AMH, other experimentol facts have been obtained by comparing SFM image and Auger map. First, the Cr segregated at the area where abrading trace (about few micrometers in width) existed. Second, during the oxidation process at early stage Cr war enriched at the arrin boundaries and soreaded laterally.

These results indicate that Cr as diffusing thru the crain boundaries to the surface and the process of mechanical nolishing played, the role for increasing a large number ofcrain boundaries. The chemical driving force of oxygenalso promotes the diffusion unto at a relatively low temperature so is to complet- the orocess in a short period.
The Effect of Oxygen on Diffusion and Compounding at Ni-GaAs(100) Interfaces
Authors: Solomon J. S. , Thomas D. R. , Smith S. R.
Published: March 2011

The effects of the presence of surface oxides and oxygen incorporated in deposited Ni films on intermixing and compounding at Ni/GaAs(100) interfaces was investigated with Auger sputter profile analysis. The Ni/GaAs structures were heated in vacuum with a high intensity incoherent lamp. Chemical changes and compound distributions were extracted from profile data by factor analysis of the Auger peaks. Diffusion coefficients for Ni at different temperatures were obtained from profile concentration gradients. The results showed that Ni diffusion was faster and activation energy lower for clean versus oxide covered GaAs substrates. Without the presence of oxygen, Ni2 GaAs readily formed at 300°C while with oxygen, the formation of Ni-Ga and Ni-As compounds prevailed over the formation of a distinct Ni2 GaAs layer.
SIMS, SAM and RBS Study of High Dose Oxygen Implantation into Silicon
Authors: Lau W. M. , Ratnam P. , Salama C. A. T.
Published: March 2011

Secondary Ion Mass Spectrometry, Scanning Auger Microscopy, and Rutherford Backscattering Spectroscopy have been used to study a buried oxide structure on silicon formed by high dose implantation. All these surface analytical techniques give useful information about the oxygen distribution in the buried oxide structure. The difficulties in these techniques have also been assessed.
Cation Solute Segregation to Surfaces of MgO and α-Al2O3
Authors: McCune Robert C.
Published: March 2011

Low energy ion scattering spectroscopy (LEIS) and Auger electron spectroscopy (AES) were used to measure the extent of impurity cation solute segregation to MgO (100) and various surfaces of single and polycrystalline Al2O3, following equilibration anneals at temperatures above 1000°C in ulfra-high vacuum. Systems studied include Ca/MgO, Ni/MgO, Ca/A12O3 and Y/Al2O3. Calcium segregation to MgO (100) is reversible and exhibits monofayer adsorption behavior with an enthalpy of segregation of approximately -55 kJ/mole with maximum occupation of surface cation sites approaching 40%. Nickel segregation to MgO(100) is masked by a preferential segregation of calcium. Calcium segregation to A12O3 surfaces has been found to be transient with a maximum surface cation site occupation of less than 10% as determined by LEIS and estimated enthalpy of segregation in the range -go to -190 kJ/mole. Yttrium segregation to surfaces of a polycrystalline Al2O3 compact was limited by competing calcium segregation at temperatures be ow 1600°C. An estimated enthalpy of segregation for yttrium to A12O3 surfaces was in the range -23 to -43 kJ/mole, with maximum cation surface site occupation of about 15%. Practical limitations to free surface measurements of solute segregation in these materials are discussed.
Secondary Ion Mass Spectroscopy of Ceramics
Authors: Taylor Jenifer A.T. , Johnson Paul F. , Amarakoon Vasantha R.W.
Published: March 2011

Application of SIMS to ceramics is a complicated but rewarding technique for characterization. The variable composition, hardness and insulating nature of these materials render spectra interpretation complex. Basic data reduction procedures from graphical data collection are presented along with spectra from SIMS applied to a glass frit, magnesium sialon, silicon and PTCR barium titanate.
Sims Analysis of Pure and Hydrated Cements
Authors: Naegele Erich , Schneider Ulrich
Published: March 2011

SIMS-measurements permit a direct determination of the hydration depth of cement particles from the depth profiles of various elements. Furthermore, surfactants containing an aromatic ring system can be analysed qualitatively and quantitatively using the SIMS-intensities of characteristic aromatic fragments. In addition, a new model for the evaluation of SIMS-spectra of oxidic materials is proposed.
Application of Sims Depth Profiling to Ceramic Materials
Authors: Taylor Jenifer A.T. , Johnson Paul F. , Amarakoon Vasantha R.W.
Published: March 2011

Depth profiling is becoming a common method of determining composition gradients for those research facilities that have access to SIMS. The problems with this procedure are briefly discussed but well referenced for those interested in using the technique. Spectra for application of depth profiling to a tantalum pentoxide layer on tantalum, silicon implanted in silica, preferential sputtering of niobium and surface treated lithium alumina silicate glass are presented.
Titaniun Silicide Formation on Heavily Doped Arsenic-Implanted Silicon
Authors: Dowben S. L. , Marsh D. W. , Smith G. A. , Lewis N. , Chow T. P. , Katz W.
Published: March 2011

Every new generation of metal/oxide/semiconductor (MOS) technology has achieved higher densities and switching speeds. In order to match these characteristics of MOS circuits, a metallization which has a low resistivity, has electrical and chemical stability, can withstand high-temperature processing and can be manufactured relatively easily and reliably is needed. These requirements make the refractory metals a suitable if not ideal choice [1,2]. However, there has been some question as to the reliability of processing during silicide formation when using refractory metals. When the metallization is used to form self-aligned silicide structures over heavily doped source and drain regions, it is crucial to understand the subsequent behavior of the dopant during the processing period. Whereas others have studied different aspects of dopant redistribution [3–8], we report in this paper a systematic study of the electrical, structural, and elemental properties of titanium silicide formation on arsenic implanted silicon as a function of implanted dose and processing temperature.
Properties of Single-Crystal Silicon Films on Amorphous SiO2on Single-Crystal Cubic Zirconia Substrates
Authors: Golecki I. , Maddox R. L. , Glass H. L. , Lin A. L. , Manasevit H. M.
Published: March 2011

A new approach to achieving a large-area silicon-on-insulator technology without pre-patterning is described. (100) Si films are first grown epitaxially on (100) yttria-stabilized cubic zirconia (YSZ) substrates by the pyrolysis of SiH4. The Si side of the /interface is then oxidized in pyrogenic steam (at 925 °C) or dry oxygen (at 1100°C) to form the structure /amorphous SiO2/. The oxidation occurs by the rapid diffusion of oxidants through the 0.42 mm thick YSZ substrate; e.g., a 0.3 μm SiO2layer is obtained in 6 h in steam. The samples are analyzed by Rutherford backscattering and channeling spectrometry, X-ray diffraction, infra-red reflectance, Auger electron spectroscopy and sheet resistance measurements. In addition to forming the preferred Si/SiO2interface, the back-side oxidation eliminates the most defective part of the Si film.
Materials Characterization with Intense Positron Beams
Authors: Rosenberg I. J. , Howell R. H. , Fluss M. J. , Meyer P.
Published: March 2011

We have developed an apparatus that provides a high flux, low energy, monoenergetic positron beam to investigate various processes which occur when a positron beam impinges on a metal surface, including annihilation at the surface, trapping in vacancies, and the emission of both fast and thermally desorbed positronium. We report here the first angular correlation of annihilation gamma-rays measurements and positronium time of flight experiments at a material surface. We applied a simple free electron model which explains the general trend of the data but differences due to the surface specific properties and the deviation from a free electron metal are evident.
Effects of Ambient Gas on the Out-Diffusion of Nickel and Copper through Thin Gold Films
Authors: Lewis R. K. , Ray S. K. , Seshan K.
Published: March 2011

The low temperature (300–400°C) out-diffusion of an underlying metal through a thin film overlayer of another metal has been studied in ambients of N2 and forming gas. Surface oxidation of this out-diffused metal can interfere with the attachment of terminating components used in semiconductor devices. AES depth profile analysis has shown that the out-diffusion of Ni through Au is suppressed in a forming gas ambient. It has also been shown that the extent of this out diffusion can be modified considerably by the presence of Cu.