bluuebunny/crossref_metadata_2025 huggingface dataset:
High Activity Dual Colloid Ammonia Synthesis Catalysts
Authors: Vanderspurt Thomas Henry , Richard Michael A.
Published: March 2011

A new synthesis technique produces a family of iron and iron alloy catalysts with a micro-morphology uniquely suited for ammonia synthesis catalysts.
Characterization of Supported Metal Oxides by Laser Raman Spectroscopy: Supported Vanadium Oxide on Al2O3 and TiO2
Authors: Wachs Israel E. , Hardcastle Franklin D. , Chan Shirley S.
Published: March 2011

The interaction of supported vanadium oxide with Al2O3 and TiO2 substrates is examined with Raman spectroscopy. The Raman spectra of the supported vanadium oxide reveal that the strong interaction of the vanadium oxide with the Al2O3 and TiO2 supports results in the formation of an atomically dispersed surface vanadium oxide phase as well as supported crystalline V2O5. The relative concentrations of the atomically dispersed surface vanadium oxide and crystalline V2O5 depend on the vanadium oxide loading and the surface area of the oxide support.
Mdiecuiar Die Catmalysis: Hexane Ackmzation Over Pt/KL
Authors: Thuster Samjel J. , Steger Jwhn J.
Published: March 2011

It is proposed that the high aromatization selectivity of Pt supported in zeolite L is caused by the ability of the channels to collimate the flux of hexane molecules, leading to end-on adsorption at the Pt surface.
The Effect of Sodium Catalyst Dispersion on the Carbon Dioxide Gasification Rate
Authors: Li Jian , Adriaan R. P. , Heiningen Van
Published: March 2011

The CO2 gasification rate of black liquor char (b1c) is studied in a thermogravimetric analysis set-up at temperatures between 600 to 800° C. B1c is prepared via fast pyrolysis of the dry solids in spent liquor of the kraft wood pulping process. B1c gasification by CO2 is well described by Langmuir-Hinshelwood type kinetics. The gasification rate of blc is one order of magnitude larger than a high surface area activated carbon impregnated with 12% Na2CO3. Also, the gasification rate of b1c remains high at sodium-carbon ratios where the rate of Na2CO3 impregnated chars would be strongly reduced. With SEM-EDS mapping and line scans it is shown that the unique gasification properties of b1c are caused by a very fine distribution of sodium in the carbon structure.
Energetics of Adsorbed Dimers VIA Self-Consistent Scattering Theory
Authors: Feibelman Peter J.
Published: March 2011

A new approach to the surface electronic structure problem, based on a self-consistent scattering theory of point defects, permits 1st-principles calculations for an isolated cluster of adatoms and defects on an otherwise perfect infinite crystalline surface. A first numerical application of the method explains important observations concerning the interaction and diffusion of adatom dimers on Field Ion Microscope tips. Further studies will shed light on questions such as: What impurity species migrate to what kind of surface defects? What is the contribution of substrate atom positional relaxation to adsorption and diffusion barrier energies?
Wipp Site Studies: Secondary Selenite Veins in the Rustler Formation and Dewey Lake Red Beds
Authors: Brookins D. G. , Lambert S. J.
Published: March 2011

Defense-generated transuranic (TRU) waste will be stored at WIPP in the bedded halite of the Salado Formation (Permian), which is overlain by the impure Permian evaporites of the Rustler Formation and the Dewey Lake Red Beds. Both the Rustler and Dewey Lake contain abundant to less common secondary selenite veins of uncertain origin, and dissolution zones occur in the Rustler. The Rustler Formation also contains two dolomite aquifers, the Magenta and Culebra members. The purpose of this study is to determine whether vein selenite is locally derived, or has been introduced in moving groundwater solutions. We have used Sr isotopic studies and REE, U and other trace element data to address the problem. The Sr isotopic data show that neither the Salado nor Rustler anhydrites have exchanged with secondary sources of Sr, and this is supported by the REE and U data. Further, selenite veins from the Rustler possess Sr isotopic compositions identical to the Rustler, indicating local origin, and this is also supported by the U and REE data. Selenite veins from the Dewey Lake Red Beds possess Sr isotopic compositions closer to surface caliche deposits, and may contain near-surface derived Sr. U and REE data show more scatter and evidence for extrinsic sources than the vein/host-rock pairs from the Rustler. Sr isotopic compositions of the Magenta and Culebra indicate that the Magenta has undergone less water/rock interaction than the Culebra. Collectively, the data argue for more possible surface or near-surface water/rock interactions in the Dewey Lake Red Beds than in the Rustler Formation; such interactions in the Salado Formation have been minimal.
The Role Of Chemical Reaction In Waste-Form Performance
Authors: Chambré P. L. , Kang C. H. , Lee W. W.-L. , Pigford T. H.
Published: March 2011

The dissolution rate of waste solids in a geologic repository is a complex function of waste form geometry, chemical reaction rate, exterior flow field, and chemical environment. We present here an analysis to determine the steady-state mass transfer rate, over the entire range of flow conditions relevant to geologic disposal of nuclear waste. The equations for steady-state mass transfer with a chemical-reaction-rate boundary condition are solved by three different mathematical techniques which supplement each other. This theory is illustrated with laboratory leach data for borosilicate-glass and a spherical spent-fuel waste form under typical repository conditions. For borosilicate glass waste in the temperature range of 57°C to 250°C, dissolution rate in a repository is determined for a wide range of chemical reaction rates and for Peclet numbers from zero to well over 100, far beyond any Peclet values expected in a repository. Spent-fuel dissolution in a repository is also investigated, based on the limited leach data now available.
Simulation of Effects of Redox and Precipitation on Diffusion of Uranium Solution Species in Backfill
Authors: Carnahan C. L.
Published: March 2011

This investigation addresses the problem of prediction of the rate of migration of redox-sensitive solution species within packing and backfill materials under conditions of variable oxidation potential. Effects of changes of oxidation potential and precipitation of stable uranium compounds during diffusion of uranium from a region of high oxidation potential into a region of low oxidation potential were simulated numerically. Questions of particular interest addressed in the investigation were the existence of a moving “redox front” and the influence of precipitation-dissolution processes on uranium migration. The simulations showed that no expanding redox fronts existed at any simulated time up to 3.2×105 years (1013 s). In simulations where precipitation of stable solids was not allowed, variations of oxidation potential did not affect total uranium concentrations in solution. Concentration profiles could be predicted simply by diffusion of the (constant) source concentrations. In simulations where precipitation of stable solids was allowed, uraninite and calcium uranate accumulated at the source-transport domain interface, while coffinite penetrated further into the transport domain. Total uranium concentrations in regions of precipitation were determined by solubilities of the precipitated solids, and were six to seven orders of magnitude lower than those in the simulations without precipitation, throughout the domain of transport.
The Solubility and Sorption of Lead-210 and Carbon-14 in a Near-Field Environment
Authors: Bayliss S. , Ewart F. T. , Howse R. M. , Smith-Briggs J. L. , Thomason H. P. , Willmott H. A.
Published: March 2011

This paper reports the results of some recent experimental studies of the solubility and sorption behaviour of lead-210 and carbon-14 under cementitious near-field conditions.

These studies have shown that under these conditions carbon-14 will have a maximum solubility limit of 10−4 M and that the distribution ratio, RD, will increase with increasing carbon-14 concentrations from 10−9 to 10−7 M. Not all of the carbon in the cement is available for exchange with carbon in the pore water. Differences in values of RD are observed between the two cement grout types studied, SRPC and OPC/BFS. Lead has been shown to have a maximum solubility limit of about 10−3 M at high pH. Good agreement is obtained between these measurements and thermodynamic modelling using the PHREEQE code. No differences were observed between lead solubilities under reducing or oxidising conditions at high pH values using the same phase separation techniques. Lead is particularly sensitive to the phase separation techniques employed. A factor of up to 250 difference is observed between 25000 and 30000 molecular weight cut-off filters. The values of RD for lead increase with decreasing lead concentrations and the values of RD for 10−3 M solutions are observed to be 500 mlg−1 for SRPC and 1300 mlg−1 for OPC/BFS.
High-Level Waste Dissolution and Secondary Mineral(S) Formation and Dissolution
Authors: Zavoshy S. J.
Published: March 2011

A mathematical model of waste dissolution that includes the formation of secondary solid precipitate(s) explicitly is formulated. For a static type of experiment, the model indicates that the concentration of the highly soluble species compared to the concentration of the main component of the matrix is equal to their corresponding density in the matrix (i.e., congruent release). For low solubility nuclides, the solubility limit of precipitate(s) may be exceeded (depending on the waste composition) and a supersaturated solution is temporarily achieved. From the model, the concentration of radionuclides and mass flux at the waste form surface in a geologic repository is obtained. Numerical results (Sr-90) indicate that the liquid-surface concentration rises very rapidly after dissolution starts. In the first week, the solubility limit of Sr precipitate(s) is exceeded and Sr solid precipitate(s) will be formed. Subsequently the concentration decreases and becomes almost equal to the solubility limit and remains so for up to 1 year. It decreases later due to radioactive decay. After the first week, the surface concentration and surface mass flux are independent of the retardation coefficient throughout the leaching process. The mass transfer rate is determined by the matrix dissolution rate and not by the solubility of the precipitate.
Effects of Radiation on the Oxidation Potential of Salt Brine
Authors: Gray W. J.
Published: March 2011

Two different types of experiments have shown that alpha and gamma radiation each increase the redox potential of salt brines. Other experiments have shown that the decrease in potential indicated by platinum electrodes in irradiated brines is due to the response of the electrodes to the hydrogen generated from the resulting water decomposition. Platinum electrodes indicated no change in redox potential of solutions containing equimolar concentrations of K3Fe(CN)5 and K4Fe(CN)5 when they were gamma irradiated in quartz containers; when stainless steel containers were used, the solutions reacted with the stainless steel but gamma radiation had no significant effect on that reaction or the solution composition. A gamma radiation dose rate of 2.4 × 104 rad/h measurably increased the uniform corrosion rate of mild steel in salt brines at 75°C, but at 150°C the increased thermal corrosion rate obscured any effect of even higher gamma radiation dose rates.
The Effect of Waste Package Components on Radionuclides Released from Spent Fuel Under Hydrothermal Conditions
Authors: Rawson Shirley A. , Neal William L. , Burnell James R.
Published: March 2011

The Basalt Waste Isolation Project has conducted a series of hydrothermal experiments to characterize waste/barrier/rock interactions as a part of its study of the Columbia River basalts as a potential medium for a nuclear waste repository. Hydrothermal tests of 3–15 months duration were performed with light water reactor spent fuel and simulated groundwater, in combination with candidate container materials (low-carbon steel or copper) and/or basalt, in order to evaluate the effect of waste package materials on spent fuel radionuclide release behavior. Solutions were filtered through 400 and 1.8 nm filters to distinguish colloidal from dissolved species. In all experiments, 14C, 129I, and 137Cs occurred only as dissolved species, whereas the actinides occurred in 400 nm filtrates primarily as spent fuel particles. Actinide concentrations in 1.8 nm filtrates were below detection in steel-bearing experiments. In the system spent fuel + copper, apparent time-invariant concentrations of 14C and 137Cs were obtained, but in the spent fuel + steel system, the concentrations of 14C and 137Cs increased gradually throughout the experiments. In experiments containing basalt or steel + basalt, 137Cs concentrations decreased with time. In tests with copper + basalt, 14C and 129I concentrations attained time-invariant values and 137Cs concentrations decreased. Concentrations for the actinides and fission products measured in these experiments were below those calculated from Federal regulations governing radionuclide release.
Summary of Results From the Series 2 and Series 3 NNWSI Bare Fuel Dissolution Tests
Authors: Wilson C. N.
Published: March 2011

The Nevada Nuclear Waste Storage Investigations (NNWSI) Project is studying dissolution and radionuclide release behavior of spent nuclear fuel in Nevada Test Site groundwater. Specimens prepared from pressurized water reactor (PWR) fuel rod segments were tested for multiple cycles in J-13 well water. The Series 2 tests were run in unsealed silica vessels under ambient hot cell air (25°C) for five cycles for a total of 34 months. The Series 3 tests were run in sealed stainless steel vessels at 25°C and 85°C for three cycles for a total of 15 months. Selected summary results from Series 2 and Series 3 tests with bare fuel specimens are reported.

Actinide concentrations tended to saturate and then often decreased during test cycles. Uranium concentrations in later test cycles ranged from 1 to 2 μg/ml in the Series 2 Tests versus about 0.1 to 0.4 μg/ml in Series 3 with the lowest concentrations occurring in the 85°C tests. Formation of a calciumuranium-silicate phase identified as uranophane in the 85°C Series 3 Tests is thought to have limited uranium concentration in these tests. Americium-241, Pu-239 and Pu-240 activities measured in filtered solution decreased to less than 1 pCi/ml in the 85°C tests. Preferential release of fission products Cs, I, Sr and Tc, and activation product C-14, was indicated relative to the actinides. Tc-99 and Cs-137 activities measured in solution after Cycle 1 increased linearly with time, with the rate of increase greater at 85°C than at 25°C. Continuous preferential release of soluble fission products is thought to result primarily from the dissolution of fine particles of fission product phases concentrated on grain boundaries.
Pourbaix Diagram for The Prediction of Waste Glass Durability in Geologic Environments
Authors: Jantzen Carol M.
Published: March 2011

Dissolution of nuclear waste glass occurs by corrosion mechanisms similar to those of metallurgical and mineralogic systems albeit on different time scales. The effects of imposed pH and oxidation potential (Eh) conditions existing in natural environments on metals and minerals have been quantatively and phenomenologically described in compendiums of Pourbaix (pH-potential) diagrams. Construction of Pourbaix diagrams to quantify the response of nuclear waste glasses to repository specific pH and Eh conditions is demonstrated. The expected long-term effects of groundwater contact on the durability of nuclear waste glasses can then be unified.
Chemical Corrosion of Cogema Glass R7T7 in High Saline Brines
Authors: Lutze Werner , Müller R. , Montserrat W.
Published: March 2011

In the Federal Republic of Germany, the salt dome formation at Gorleben has been selected as a possible site for final disposal of HLW. The waste form will be borosilicate glass, e. g. the French Cogema glass R7T7. The corrosion of this glass has been investigated in three reference salt brines (brine 1: high Mg, brine 2: Ca and Mg, and brine 3: high Na) at three different temperatures, 110°, 150°, and 190°C and three S/V ratios, 10, 100, and 1000m−1. Results are presented for brine 1 and are compared qualitatively with those obtained for the other brines. As in deionized water and pure NaCl, the corrosion rate decreases when silica saturation is approached, but the reaction does not cease. The data after silica saturation were used to calculate upper limiting, i. e. time-independent corrosion rates. The long-term data indicate that a transport process through the growing surface layer may become rate controlling, and that the rate may further decrease after silica saturation.
Chemical Corrosion of Lead-Iron Phosphate Glass
Authors: Lutze Werner , Schubert P.
Published: March 2011

This study provides experimental data on the corrosion of lead-iron phosphate (LIP) glass (6.4 wt% LWR waste loading) and the first comparison with the dissolution kinetics of borosilicate (BS) nuclear waste glass (all experiments at 90°C). Based on previous experiments the hypothesis was made that the alteration phenomena and the corrosion mechanism are analogous to what is known for BS glasses. The corrosion rate was found to be constant, 0.06gm−2d−1, at high flow rates (MCC 5 type test), based on total mass loss and on ion conductivity measurements in the leachate. In an MCC 1 type experiment, doped glasses (32p, 210Pb and 137Cs, respectively) were corroded and the release of activity into solution monitored. The release rates were 0.05gm−2 d−1 in the beginning, but decreased drastically when the solution became saturated with respect to Pb(OH)2 and Pb3 (PO4)2. Glass corrosion continued at a low rate as indicated by Cs activity measurements. The higher chemical durability of the LIP glass vs. BS glasses in DI water is a result of a smaller initial corrosion rate (10 to 10O×) and the fact that the saturation concentration is lower for LIP glass, i. e. it takes less dissolved glass (10 to 50×) to reach saturation than in the case of BS glass.
Corrosion of Lead and Lead Alloys in Simulated Repository Environments
Authors: Goodwin Frank E. , Guenther Richard J.
Published: March 2011

A series of corrosion tests were sponsored by the International Lead Zinc Research Organization, Inc. and conducted by Battelle Northwest to obtain information regarding the suitability of lead for applications in the containment of high-level nuclear waste. Two grades of unalloyed lead and two lead alloys were exposed to basalt, salt, and tuff simulated repository environments for times up to 1 year and temperatures from 55 to 200°C. Information was obtained on the corrosion rates, corrosion products, and concentration of lead in the test liquids under these conditions, which were intended to simulate the anticipated environments in candidate U.S. nuclear waste repositories. Leachates from the 12-month tests were analyzed in order to prepare synthetic leachates that were used to conduct scoping evaluations of the transport of lead in basalt and tuff environments.
Rapid Particle Size Analysis of Fly Ash with a Commercial Laser Diffraction Instrument
Authors: Diamond Sidney
Published: March 2011

Particle size distributions of a suite of fly ashes previously analyzed by aclassical sedimentary proced ure have been redetermined using a commercial laser-based particle size measurement system. For most of the fly ashes the concordance between the two sets of data was unexpectedly close, considering the different physical principles involved in the two types of measurement. Laser diffraction instruments (“laser sizers”) appear to have the potential for extremely rapid and accurate size distribution measurement for fly ashes to be used in commercial applications. Such determinations, easily carried out on a routine basis, could serve as important elements in future specifications for acceptance and quality assurance programs.
Sulphate Durability of Plain and Fly Ash Mortars
Authors: Day R. L. , Ward M. A.
Published: March 2011

Sulphate expansion and strength tests were performed on mortars containing equal proportions of Type 10 (ASTM Type I) Portland cement and fly ash as the cementitious material. Two intermediate-Ca subbituminous ashes, one high-Ca subbituminous ash and one bituminous ash were tested. Control mortars manufactured with Types 10 and Type 50 (Type V ASTM) cements and one mortar containing 50% replacement of cement with limestone powder were also examined. The period and temperature of curing prior to sulphate exposure and the concentration and pH of the attacking solutions were other test parameters. Results indicate that the two intermediate-Ca subbituminous ashes from Alberta Canada, combined with Type 10 cement produce mortars that show excellent long-term strength, acceptable short term strength, and are highly resistant to attack by aggressive sulphate solutions. In some cases durability of these mortars was better than the control mortar made with Type 50 cement. On the other hand, mortar made using the high-Ca ash showed very high susceptibility to sulphate attack; at the same time, mortars made with this ash showed good strength development. Qualitative x-ray diffraction analysis indicates the presence of more lime, magnesium and iron bearing crystalline compounds in the high-Ca ash than in the Alberta ashes. These appear to be responsible for the poor performance in sulphate environments.
Low Cement/High Fly Ash Concretes: Their Properties and Response to Chemical Admixtures
Authors: Dodson V. H.
Published: March 2011

In practice, the amount of fly ash added to portland cement concrete varies depending upon the desired end properties of the concrete. Generally, when a given portland cement concrete is redesigned to include fly ash, between 10 and 50% of the cement is replaced by a volume of fly ash equal to that of the cement. Sometimes as much as twice the volume of the cement replaced, although 45.4 kg (100 lbs) of cement will only produce enough calcium hydroxide during its reaction with water to react with about 9 kg (20 lbs) of a typical fly ash. The combination of large amounts of certain fly ashes with small amounts of portland cement in concrete has been found to produce surprisingly high compressive strengths, which cannot be accounted for by the conventional “pozzolanic reaction”. Ratios of cement to fly ash as high as 1:15 by weight can produce compressive strengths of 20.7 MPa (3,000 psi) at I day and over 41.4 MPa (6,000 psi) at 28 days. Methods of identifying these “hyperactive” fly ashes along with some of the startling results, with and without chemical admixtures are described.
Hydration Characteristics and Morphological Features of Concretes from Structures in Australia, England and the United States
Authors: Baweja Daksh , Roper Harold , Cabrera Jose G. , Cook David J.
Published: March 2011

Scanning electron microscope studies were carried out on concretes obtained from structures in Australia, England and the United States as part of an assessment of their durability performances. The ages of the structures ranged from nine to thirty years. All structures contained fly ash concretes in some sections, and, in a few cases, direct comparison between these concretes and ordinary portland cement (OPC) concretes was possible. Water: cement ratios of the concretes varied from 0.44 to 0.90. The sources of fly ash were identified in each case. The structures chosen had a range of use classifications encompassing building, hydraulic structures, bridge structures, towers and foundations. Deterioration effects of concretes in some structures were more common than in others. Based on observations, conclusions were drawn on the morphological features and hydration characteristics of the concretes.
The Permeability of Chloride Ions in Fly Ash-Cement Pastes, Mortars and Concrete
Authors: Malek R. I. A. , Roy D. M.
Published: March 2011

Fly ash-cement pastes are known to develop fine pore structures that may retard the transport of ionic species. The rapid chloride permeability technique for studying the Cl- ion diffusion in hydrated fly ash/cement pastes, mortars and concrete was used. The technique applies an electrical potential across a cylindrical sample and measures the charge passed in a certain period of time. The results obtained on pastes and mortars cured for 28 days were reported previously and contrasted with those of neat cement pastes and mortars. The present paper reports more extensive studies made to examine the chloride permeabilities of pastes and mortars cured for up to 90 days. In addition, the effect of variable fly ash contents was examined. Concrete samples were included in the test scheme and the data were compared with pastes and mortars. Two important factors controlling the test results are discussed: first the mix design and curing conditions; second the experimental conditions during Cl- permeability measurements. In the second factor, the amount and rate of heat build up and the chloride ion concentrations are compared with the current passed. In addition, measuring current versus resistivity are critically discussed in terms of the voltage-current varistic characteristics of cement matrices.
On the Glass in Coal Fly Ashes: Recent Advances
Authors: Hemmings R. T. , Berry E. E.
Published: March 2011

Recent advances in the characterization of the glassy aluminosilicate phases in coal fly ashes are reviewed and discussed in terms of the development of new models describing their mechanism of formation, composition, structural relationships and chemical reactivity. Characterization techniques such as electron microscopy, x-ray diffraction, infrared and Raman spectroscopy, nuclear magnetic resonance and Mössbauer spectroscopies, thermal analysis, acid dissolution, silanation, and density fractionation have been used as experimental probes, and reveal a range of information relating to the glass phases from the macro, through the micro, to the nano-structural levels. Complex inter- and intra-particle heterogeneity in ash is observable not only in bulk chemical and mineralogical analyses but also at the molecular level in the constituent glasses. Remarkable relationships between ash particle size, density and glass composition have been observed and lead to a new proposed mechanism for ash morphogenesis based on temperature-viscosity effects in the mineral precursor melts in the boiler flame. A glass-ceramic model for fly ash particle structure is proposed and discussed in terms of phase relations in the CaO–SiO2–Al2O3 and FeO–Fe2O3–A12O3–SiO2 systems, modification of the aluminosilicate glasses by alkali and alkaline earth metal cations, and microheterogeneity involving glass devitrification and phase separation.
The effect of Bond Characteristics Between Steel Slag fine Aggregate and Cement Paste on Mechanical Properties of Concrete and Mortar
Authors: Yuji Wang
Published: March 2011

The ordinary fine aggregate in concrete has been replaced by ground and sieved steel slag fine aggregate, treated and exposed to air for three months. Compared with concrete made from natural sand, properties such as compressive strength, flexural strength, elastic modulus, permeability and abrasion resistance are considerably improved. The improvement increases with a decrease in w/c ratio, an increase in curing time and an increase in the replacement weight of sand. These results are due to the fact that the steel slag contains some active minerals such as C3S, C2S, C4AF, etc., and shows favorable surface physical characteristics that improve the bond between steel slag particles and cement paste. The results of XRD, SEM and EPM microhardness showed that there are heavier concentration of ions, with finer crystals and a lower degree of CH orientation at the interfacial zone between steel slag particles and cement paste. The study also found small cementitious and fibrous C-S-H crystals growing from the fine aggregate, which are linked with hydrated products from cement paste making the bond and structural characteristic more favorable with cement. The steel slag fine aggregate is an active mineral similar to cement. The bond between the aggregate and cement paste is strengthened both physically and chemically.
Submicroscopic Structure and Characteristics of Intermediate-Calcium Fly Ashes
Authors: Dudas M. J. , Warren C. J.
Published: March 2011

The surface and near surface characteristics of alkaline fly ash particles were studied to evaluate the heterogeneous chemistry and structure of ash in order to provide data and understanding of the dissolution behavior of elemental constituents. Fly ash was subjected to a range of chemical weathering intensities in laboratory column experiments. Weathered ash from columns were then analyzed for surface morphology and chemical compositional change. Determinations included chemical characterization by instrumental neutron activation analyses, surface analysis by SEM-EDXA of whole and fractured particles, surface glass analysis by selective dissolution, and mineralogy by powder x-ray diffraction. These data were used to develop a physical model of fly ash particles that describes the heterogeneous distribution of elements on or in a reactive glass hull and in matrix glass and mullite. The model is discussed in terms of elemental partitioning and its application to the mechanistic approach advocated for prediction of leachate composition.
Fixation of Leachable Elements in Composite Waste Forms from North Dakota Lignite Coal Conversion Ash
Authors: Hasseti D. J. , Hassett D. F.
Published: March 2011

Composite waste forms prepared using solid and liquid waste streams from an integrated coal gasification facility at Beulah, North Dakota, were evaluated for the potential leachability of select trace elements using batch tests. Cylinders were fabricated from seven blends of the solid components using liquid waste incinerator blowdown, multi-effect evaporator concentrate, or tap water. Individual waste forms and composites were leached using the same protocols. Both long term and short term leaching tests were used to evaluate these composite waste forms.Comparisons of measured concentrations of elements with values calculated from data on individual components were used to determine any change in leachability that may have occurred. These changes were expressed as a fixation factor, which is a term derived by dividing the calculated leachability by the measured concentrations from the actual leaching tests. Results from these experiments indicated that leachability of some elements could be lowered by the mixing of various solid and liquid waste streams. Ettringite formation is one possible mechanism responsible for fixation of several of the elements.
Bulk Composition of the Glassy Phase in Some Commercial PFA's
Authors: Qian J. C. , Glasser F. P.
Published: March 2011

The bulk chemistries of five Class F and one Class C pulverized fuel ash (PFA) are compared with the chemical compositions of the glass phase therein, the latter having been determined by analytical electron microscopy. Relative to the bulk, the glasses of Class F ashes concentrate Al2O3 and alkalis but reject Fe2O3. The glass phase is notably inhomogeneous on a micrometer scale; for example, large local variations occur in its Al2O3/SiO2 ratios. The Class C ash contained amorphous material with lower average Al2O3 contents than in Class F, but the extent of compositional homogeneities were greater.
Microstructure and Chemical Variation in Class F Fly Ash Glass
Authors: Qian J. C. , Lachowski E. E. , Glasser F. P.
Published: March 2011

Fly ash consists of mixtures of crystalline substances in a glassy matrix. This matrix is itself inhomogeneous. The combustion process gives rise to compositional fluctuations typically on a micrometer scale; these fluctuations are preserved in the glass and are gradational. However, high-resolution transmission electron microscopy of Class F ash also reveals the existence of interfaces on a nanometer scale. These arise as a consequence of phase separation. Textures and interfaces typical of spinodal decomposition and possibility also suggestive of classical immiscibility have been observed. It is believed that the occurrence of phase separation resulting in nanometer-scale inhomogeneities will be a feature common to most Class F glasses. The consequences of this complex microstructure to reactivity are not as yet known, but some speculations are presented.
Speciation in Size and Density Fractionated Fly Ash III. The influence of HCL Leaching on the Glassy Constituents of a High-Ca Fly Ash
Authors: Berry E. E. , Hemmings R. T. , Cornelius B. J.
Published: March 2011

Ash density fractions, separated from a high-Ca fly ash, were leached with 6M HCl at 105°C. The density fractions (<0.79 and >2.85 g.cm−3) selected for leaching have been shown in previous work to consist largely of two different glass types, designated Glass I and Glass II. It was shown that both Glass I and Glass II are leachable to yield solutions containing Al and modifier cations. Acid attack on Glass I appears to involve hydrolysis of Si–O–Al (silalane) bridges along with ion exchange at available non-bridging oxygen sites. Attack on Glass II is more extensive, with both silalane and siloxane bridges being hydrolysed, and ion-exchange occurring at non-bridging oxygens. The products of leaching are aluminosilicates. In the case of Glass I, these remain as pseudomorphic, hollow spheres; whereas, for Glass II, substantial reprecipitation of silica (alumina) gel was found.
The Internal Structure of a Low-Calcium Fly Ash
Authors: Kilgour Carol I. , Diamond Sidney
Published: March 2011

A low calcium fly ash, rich in iron oxide, was subjected to shaking in 1% HF for up to 20 hours, and measurements were made at intervals of the following parameters: total weight loss, composition of the dissolved material, x-ray peak intensities of crystalline components and residual glass, and internal structures present within the fly ash spheres as revealed by the progressive dissolution treatments. The same fly ash was subjected to similar but longer-term treatment with simulated cement pore solution (potassium and sodium hydroxide). The compositions of the magnetically separated fraction and the non-magnetic residue were also separately determined. As a result of these studies, it was suggested that: (a) the time at which all of the potassium is dissolved might be used as an indicator of the completion of glass dissolution; (b) the position of the x-ray band for residual (more resistant ) glass shifts to higher 2Θ angle before the glass is completely dissolved; (c) in this fly ash, as determined by chemical analysis, all of the iron is in the magnetically-separable fraction, a feature that permitted estimation of the overall glass composition; and (d) this fly ash contains certain poorly understood components including silica-rich spheres, small spheres yielding EDXA signals only for iron, and “patches” of silica and alumina bearing material not of mullite composition, but all of which are highly resistant to HF dissolution.
Characterization of North American Lignite Fly Ashes I. Chemical Variation
Authors: Stevenson Robert J. , Collier James C. , Crashell John J. , Quandt Larry R.
Published: March 2011

The chemical variation of central North American lignite fly ash can be compared using the major and minor oxide analyses and the distribution pattern of the inter-grain chemistries of the individual fly ash particles. AAS and electron microprobe chemical analysis of nineteen fly ashes have been used to illustrate the variations in bulk sample and individual grain chemistry. This information documents the chemical variability of the lignite fly ashes by geographic region. There is a direct relationship between grains rich in SiO2 and Al2O3 and in the Na2O content of the grains in lignite derived fly ashes. There is also a direct relationship between grains rich in CaP and the MgO and SO3 content of the grains in lignite derived fly ashes.
Cross-Sectioning Magnetic Thin Films for Tem
Authors: Ho H.-M. , Thomas G. , Schooley C. N. , Gau J.-S.
Published: March 2011

Oblique incidence magnetic thin films are considered to be the most appropriate recording media for the next generation of video tape applications. In order to study the microstructure of such thin films, a specimen preparation technique employing ultramicrotomy has been developed. Because oblique incidence thin films have a porous structure and poor adhesion to the substrate, the problem of splitting of the thin films from the substrate is severe. This problem is reduced considerably by the following exercises: 1. using an acrylic embedding resin e.g. LR White (London Resin Co.), 2. thorough degreasing with solvents, 3. using a 55° diamond knife, and 4. trimming the block with a microtome before actual sectioning. The details of this preparation technique and some results obtained with this technique are presented.
Dimpling of Cadmium Telluride Samples for Transmission Electron Microscopy
Authors: Lee Michael E. , Neijs E. O. de , Letsoalo A. M.
Published: March 2011

A technique for preparing thin sections in CdTe samples for transmission electron microscopy by a method of mechanical dimpling combined with chemical etching has been investigated. The dimpling rates and surface morphologies of dimpled (100) CdTe samples as a function of pressure, abrasive size and viscosity are presented. This technique produces dimpled samples of well controlled geometries and surface morphologies and offers the advantage of a high dimpling rate and the precise determination of the dimple position. The disadvantage of this technique is that a final application of chemical etching or atom milling is still required to produce electron thin sections.
Preparation of Thin-Foil TEM Specimens from Sub-Millimeter Particulate
Authors: Kelly Thomas F. , Libera Matthew R. , Sande John B. Vander
Published: March 2011

The particulate produced by many of the methods of rapid solidification, such as atomized powder, is of order 50 microns in diameter and is thus much too small to form the 3mm diameter disc conventionally used for thin-foil microscopy. 50 microns is, however, much too thick for direct TEM study on a support film and grid. A technique is described in detail that produces a composite wafer where atomized metal powder is sandwiched between two layers of electroplated nickel. This wafer is about 25 mm in diameter and about 250 microns thick. 3mm diameter TEM discs can be punched from the wafer and thinned by combinations of grinding, dimpling, jet-polishing, and ion milling. Depending on the composition and structure of the powder under study, the composite nature of the wafer can sometimes promote undesirable galvanic effects during jet polishing and differential thinning rates during ionmilling. Typical results are presented and discussion of the benefits and shortcomings of this technique is made. The method should be applicable to a variety of materials and geometries.
Specimen Cage Modification for Tem in-Situ Shearing
Authors: Meike Annemarie
Published: March 2011

In-situ strain experiments with the electron microscope have contributed substantially to our understanding of deformation in metals and ceramics. However, physical characteristics of rock-forming minerals limit the direct application of experimental procedures developed for metals. The minerals muscovite (KAl2(Si3Al)O10(OH,F)2) and biotite (K(Mg0.6–1.8 Fe2.4–1.2) (Si3Al)O10 (OH,F)2) are chosen to develop techniques for preliminary deformation experiments. The present communication describes modifications of sample preparation techniques for micas. The standard tensile straining configuration is altered to a simple shear geometry by means of an intermediary specimen cage to allow the use of a more favorable sample orientation. The extension of the shearing geometry to the in-situ deformation of other rock-forming minerals is discussed.
Preparation of in Situ Cu-Nb Composite Sheet and Wire for Tem Analysis
Authors: Trybus C. L. , Laabs F. C. , Pelton A. R. , Spitzig V. A.
Published: March 2011

Cu-Nb in situ composites attain anomolous increases in strength upon mechanical deformation. The unique filamentary microstructures that evolve during processing (cold rolling and/or wire drawing) are the source of the strengthening. Results from transmission electron microscopy characterization studies have played a key role in the understanding of the relationships between structure and properties. However, the fabrication of reliable TEM samples has been extremely challenging for the following reasons: (1) traditional electrochemical techniques are not suitable for the two-phase microstructure, (2) preparation of longitudinal and transverse sections of fine (∼150 μm diameter wires) and thin (∼60 μm thick) sheet is tedious, and (3) it is necessary to avoid excessive heat (< 30°C) during sample preparation to preserve the metastable structural arrangements. This paper will review the procedures used to prepare TEM specimens from bulk wire and sheet samples as well as from extracted Nb filaments. Proper techniques for plating, mounting, sectioning, polishing, and ion-thinning will be discussed.
A Rapid Specimen Preparation Technique For Cross-Section Tem Investigation Of Semiconductors and Metals
Authors: Vanhellemont J. , Bender H. , Rossou L.
Published: March 2011

A simple and rapid specimen preparation technique for the cross section TEM investigation of layered structures is discussed. Its wide applicability is illustrated for the investigation of processed silicon, compound semiconductors, silicon on quartz and also for metal/metal oxide interfaces.
Preparation of Liquids and Colloidal Dispersions for Tem: Cryo-Sem Studies of Bare-Film and Freeze-Fracture Specimens
Authors: Bellare J. R. , Sheehan J. G. , Davis H. T. , Scriven L. E.
Published: March 2011

Liquid and colloidal microstructures can be imaged at high resolution with cryo-TEM and cryo-SEM by fast-freezing with a Controlled Environment Vitrification System. Frozen bare-films can be directly imaged by TEM, while films sandwiched between metal plates can be frozen, fractured, and directly imaged with cryo-SEM or indirectly imaged by TEM after replication. We describe sample preparation techniques and report cryo-SEM studies of particle distributions and fracture patterns in such specimens.
A Technique for Preparing Transmission Electron Microscope Specimens Using Cleavage
Authors: Boone T. , Nakahara S.
Published: March 2011

A technique for observing both plan view and cross sections of a specimen directly in a transmission electron microscope (TEM) without relying on a tedious thinning operation was developed. This technique involves cleaving a specimen perpendicular to the plane, so that the thin (electron transparent) section of the cleaved edge can be directly imaged by TEM. The only limitations of this technique are that a specimen must be readily criacked or cleaved and that, since the transparent region is often bounded by a 90° corner, the extent of electron transparent region is somewhat localized. Nevertheless, the technique has the advantages of the ease of specimen preparation, and the absence of contamination or damage introduced in other conventional thinning methods. The geometry of the cleaved specimen is also suitable for reflection electron microscopy.
Properties of Patterned Gallium Arsenide on Silicon
Authors: Matyi R.J. , Shichijo H. , Kim T.S. , Tsai H.L.
Published: March 2011

The growth of GaAs on Si by MBE through openings in an oxide or nitride represents a convenient means for achieving monolithic GaAs/Si integration. We have examined a number of the materials growth and processing issues that must be resolved in order to achieve this goal. Some of the specific areas that have been investigated are (a) the effect of trench etching on the morphology of the patterned GaAs; (b) the dependence of patterned feature size on Hall mobility in both as-grown and postgrowth annealed samples; (c) the effect of annealing on the defect structure in the transition region from single crystal GaAs to polycrystalline growth; (d) the dependence of GaAs MESFET performance on proximity to the polycrystal transition; and (e) the performance of Si MOS devices following the GaAs MBE growth. Specific growth and processing issues concerning the integration of GaAs and Si device functions have also been examined.
Defect Reduction in Mocvd Grown Si/GaAs
Authors: Al-Jassim M.M. , Nishioka Takashi , Itoh Yoshio , Yamamoto Akio , Yamaguchi Masafumi
Published: March 2011

The effectiveness of thermal annealing and strained layer superlattices (SLS's) in defect reduction in Si/GaAs structures was studied. The GaAs layers were grown on (100) Si substrates by low pressure MOCVD. They were evaluated by TEM, HREM, EBIC and PL. As-grown layers contained dislocation densities in the 108-109 cm−2 range, depending on the layer thickness. Post-growth and in situ annealing were performed on a wide variety of these structures. TEM examination showed that in situ annealing was more effective as it resulted in confining a large portion of the threading dislocations to the interface region. Furthermore, the interaction of threading dislocations to form closed loops was evident. Additionally, the effect of GaAs/GaInAs and GaInAs/GaAsP SLS's on dislocation bending was investigated. The former SLS, although not lattice matched to GaAs, proved more effective.
Growth and Characterization of Multilayered Structure of GaAs/Epi-Si/SiO2 /Si Composite
Authors: Yang C.S. , Yue A. S.
Published: March 2011

The monolithic integration of GaAs and Si devices is highly attractive for very high speed LSI and optoelectronic integrated circuits. To accomplish this, the epitaxial growth of GaAs films on Si substrates has been successfully realized. However, in the GaAs/Si structure, the conductive nature of the silicon substrate results in a severe transmission line loss [1,2]. To help solve this problem, we suggest to grow GaAs film on SOI (silicon on insulator) substrate for microwave device application. This GaAs/SOI structure will have low transmission line loss and excellent radiation hardness. In this paper, we present some cross-section SEM and TEM data and discuss the transmission line loss and radiation hardness of this multilayered structure.
MBE Growth of GaAs on an Exactly (001)-Oriented Si Substrate and Selective Epitaxial Growth for Fabrication of Modulation-Doped Fet's
Authors: Noge H. , Kano H. , Hashimoto M. , Igarashi I.
Published: March 2011

GaAs layers free of antiphase domains (APD's) have been grown by molecular beam epitaxy (MBE) on nominally (001)-oriented Si substrates. This is achieved by preheating the substrates at 950 °C over 60 min or at 1000 °C over 5 min in an ultrahigh vacuum. The maximum Hall mobility at 293 K is 5300 cm2 /Vs for the APD-free GaAs layer doped with Si at a concentration of 2×1016 cm−3 . Selective epitaxial growth of GaAs has been carried out on a Si substrate pattrened with SiO2, which was formed by wet O2 oxidation. By choosing an appropriate thickness of the SiO2 layer, the warpage of wafers can be reduced to zero. While single-crystalline GaAs is grown on Si-exposed areas, highly-resistive (ρ ≧ 105 Ωcm) poly-crystalline GaAs is deposited on SiO2 . This technique has been successfully applied for the device isolation of modulation-doped FET's (MODFET's, HEMT's, etc.) on Si without mesa-etching. The transconductance of the MODFET with a 3 µm-long gate reaches 88 mS/mm at 293 K.