242 Matching Results

Search Results

Advanced search parameters have been applied.

Hydraulic Activity in Synthetic and Commercial Slags

Description: Slag, by itself, shows very little hydraulic activity. However, hydration is greatly accelerated by incorporation of the slag with Portland cement. This phenomenon is due to the activating role of calcium hydroxide released from the hydration of Portland cement. This study was aimed at finding other activators that will increase hydration in both synthetic and commercial slags. The effects of chemical composition and the aggregation state of the slag on the hydration process were also investigated. For the synthetic slags, the aggregation state was altered by different quenching techniques. The chemical composition was varied by synthesizing a series of slags. The degree of hydration was studied by developing a thermogravimetric analysis technique and the glass content was determined using microscopy. Minerals were determined using powder x-ray diffraction analysis.
Date: May 1982
Creator: Saad, Bahruddin bin
Partner: UNT Libraries

Calcium Silicates: Glass Content and Hydration Behavior

Description: Pure, MgO doped and B2C3 doped monocalcium, dicalcium, and tricalcium silicates were prepared with different glass contents. Characterization of the anhydrous materials was carried out using optical microscopy, infrared absorption spectroscopy, and X-ray powder diffraction. The hydration of these compounds was studied as a function of the glass contents. The hydration studies were conducted at 25°C. Water/solid ratios of 0.5, 1, 10, and 16 were used for the various experiments. The hydration behavior was monitored through calorimetry, conductometry, pH measurements, morphological developments by scanning electron microscopy, phase development by X-ray powder diffraction, and percent combined water by thermogravimetry. A highly sensitive ten cell pseudo-adiabatic microcalorimeter was designed and constructed for early hydration studies. Conductometry was found to be of great utility in monitoring the hydration of monocalcium silicate and the borate doped dicalcium silicates.
Date: August 1987
Creator: Zgambo, Thomas P. (Thomas Patrick)
Partner: UNT Libraries

Directed synthesis of crystalline plutonium (III) and (IV) oxalates: accessing redox-controlled separations in acidic solutions

Description: Both binary and ternary solid complexes of Pu(III) and Pu(IV) oxalates have been previously reported in the literature. However, uncertainties regarding the coordination chemistry and the extent of hydration of some compounds remain mainly because of the absence of any crystallographic characterization. Single crystals of hydrated oxalates of Pu(III), Pu{sub 2}(C{sub 2}O{sub 4}){sub 3}(H{sub 2}O){sub 6}{center_dot}3H{sub 2}O (I) and Pu(IV), KPu(C{sub 2}O{sub 4}){sub 2}(OH){center_dot}2.5H{sub 2}O (II), were synthesized under moderate hydrothermal conditions and characterized by single crystal X-ray diffraction studies. Compounds I and II are the first plutonium(III) or (IV) oxalate compounds to be structurally characterized via single crystal X-ray diffraction studies. Crystallographic data for I: monoclinic, space group P21/c, a = 11.246(3) A, b = 9.610(3) A, c = 10.315(3) A, Z = 4 and II: monoclinic, space group C2/c, a = 23.234(14) A, b = 7.502(4) A, c = 13.029(7) A, Z = 8.
Date: January 1, 2009
Creator: Runde, Wolfgang; Brodnax, Lia F; Goff, George S; Bean, Amanda C & Scott, Brian L
Partner: UNT Libraries Government Documents Department

ACS Symposium Support

Description: The funds from this DOE grant were used to help cover the travel costs of five students and postdoctoral fellows who attended a symposium on 'Hydration: From Clusters to Aqueous Solutions' held at the Fall 2007 American Chemical Society Meeting in Boston, MA, August 19-23. The Symposium was sponsored by the Physical Chemistry Division, ACS. The technical program for the meeting is available at http://phys-acs.org/fall2007.html.
Date: February 20, 2010
Creator: Jordan, Kenneth D.
Partner: UNT Libraries Government Documents Department

Structure of water adsorbed on a mica surface

Description: Monte Carlo simulations of hydration water on the mica (001) surface under ambient conditions revealed water molecules bound closely to the ditrigonal cavities in the surface, with a lateral distribution of approximately one per cavity, and water molecules interposed between K{sup +} counter ions in a layer situated about 2.5 {angstrom} from a surface O along a direction normal to the (001) plane. The calculated water O density profile was in quantitative agreement with recent X-ray reflectivity measurements indicating strong lateral ordering of the hydration water but liquid-like disorder otherwise.
Date: January 29, 2002
Creator: Park, Sung-Ho & Sposito, Garrison
Partner: UNT Libraries Government Documents Department

[Energies of organic compounds]

Description: The enthalpy of reduction of lactones to the corresponding diols has been determined, allowing the enthaipies of formation of the lactones to be determined. Results of this study agree well with data obtained for enthalpies of hydrolysis of the lactones. We have begun the measurement of the enthalpies of reduction of norbornanones, and we have shown that it is possible to determine the difference in energy between the exo and endo forms of the product alcohols by measuring the equilibrium constant as a function of temperature. The study of the enthalpies of hydration of carbonyl compounds has continued, and the enthalpies of hydrolysis of the corresponding ketals is being determined. The study of the enthalpies of hydration of alkenes is nearly completed, and the rearrangement reactions which were uncovered are being investigated.
Date: December 31, 1991
Creator: Wiberg, K.B.
Partner: UNT Libraries Government Documents Department

Novel Polyoxometalate Containing Membranes for PEM Fuel Cells

Description: Current proton exchange membrane (PEM) technologies are inadequate to address the projected needs for fuel cell performance above 80 ºC. Continuing research into traditional ion carriers in novel membrane materials offers the promise of marginal improvement, representing only an evolutionary increase in performance. This conclusion is supported by the role of water in conduction. Thus, the key to better PEMs is not to eliminate water, but to change the role of water by developing ion carriers that will bind water more tightly than traditional sulfur or phosphorus based carriers resulting in materials that will conduct at higher temperatures. This change entails having a carrier structure that interacts more intimately with water and by increasing the ion carrier anionic charge to result in more tightly held inner shell protonated waters of hydration. Both of these factors synergistically act to maintain a critical water concentration at the carrier necessary for conduction. In this work, polyoxometalate (POM) clusters were selected to serve as these different proton carriers.
Date: March 1, 2009
Creator: Harrup, Mason K.; Stewart, Frederick F.; Luther, Thomas A & Trowbridge, Tammy
Partner: UNT Libraries Government Documents Department

Quantized ionic conductance in nanopores

Description: Ionic transport in nanopores is a fundamentally and technologically important problem in view of its ubiquitous occurrence in biological processes and its impact on DNA sequencing applications. Using microscopic calculations, we show that ion transport may exhibit strong non-liDearities as a function of the pore radius reminiscent of the conductance quantization steps as a function of the transverse cross section of quantum point contacts. In the present case, however, conductance steps originate from the break up of the hydration layers that form around ions in aqueous solution. Once in the pore, the water molecules form wavelike structures due to multiple scattering at the surface of the pore walls and interference with the radial waves around the ion. We discuss these effects as well as the conditions under which the step-like features in the ionic conductance should be experimentally observable.
Date: January 1, 2009
Creator: Zwolak, Michael; Lagerqvist, Johan & Di Ventra, Massimilliano
Partner: UNT Libraries Government Documents Department

Hydration and mobility of HO-(aq)

Description: The hydroxide anion plays an essential role in many chemical and biochemical reactions. But questions of its hydration state and transport in water are currently controversial. Here we address this situation using the quasi-chemical theory of solutions. The simplest such approach suggests that HO [H20]3- is the most probable species at infinite dilution in aqueous solution under standard conditions, followed by the HO . [H20]2- and HO . [HzO]- forms which are close together in stablity. HO . [H20]4- is less stable, in contrast to recent proposals that the latter structure is the most stable hydration species in solution. Ab initio molecular dynamics results presented here support the dominance of the tri-hydrated form, but that the population distribution is broad and sensitive to solution conditions. On the basis of these results, the mobility of hydroxide can be simply that of a proton hole. This contrasts with recent proposals invoking the interconversion of a stable 'trap' structure HO . [H20]4- to HO . [H20]3- as the rate determining step in the transport process.
Date: October 31, 2002
Creator: Asthagiri, D. (Dilipkumar); Pratt, Lawrence Riley; Kress, J. D. (Joel D.) & Gomez, M. A. (Maria A.)
Partner: UNT Libraries Government Documents Department

Kinetic Isotopic Fractionation During Diffusion of Ionic Speciesin Water

Description: Experiments specifically designed to measure the ratio of the diffusivities of ions dissolved in water were used to determine D{sub Li}/D{sub K}, D{sub 7{sub Li}}/D{sub 6{sub Li}}, D{sub 25{sub Mg}}/D{sub 24{sub Mg}}, D{sub 26{sub Mg}}/D{sub 25{sub Mg}}, and D{sub 37{sub Cl}}/D{sub 35{sub Cl}}. The measured ratio of the diffusion coefficients for Li and K in water (D{sub Li}/D{sub K} = 0.6) is in good agreement with published data, providing evidence that the experimental design being used resolves the relative mobility of ions with adequate precision to also be used for determining the fractionation of isotopes by diffusion in water. In the case of Li we found measurable isotopic fractionation associated with the diffusion of dissolved LiCl (D{sub 7{sub Li}}/D{sub 6{sub Li}} = 0.99772 {+-} 0.00026). This difference in the diffusion coefficient of {sup 7}Li compared to {sup 6}Li is significantly less than reported in an earlier study, a difference we attribute to the fact that in the earlier study Li diffused through a membrane separating the water reservoirs. Our experiments involving Mg diffusing in water found no measurable isotopic fractionation (D{sub 25{sub Mg}}/D{sub 24{sub Mg}} = 1.00003 {+-} 0.00006). Cl isotopes were fractionated during diffusion in water (D{sub 37{sub Cl}}/D{sub 35{sub Cl}} = 0.99857 {+-} 0.00080) whether or not the co-diffuser (Li or Mg) was isotopically fractionated. The isotopic fractionation associated with the diffusion of ions in water is much smaller than values we found previously for the isotopic fractionation of Li and Ca isotopes by diffusion in molten silicate liquids. A major distinction between water and silicate liquids is that water, being a polar liquid, surrounds dissolved ions with hydration shells, which very likely play an important but still poorly understood role in reducing isotopic fractionation associated with diffusion.
Date: June 9, 2005
Creator: Richter, Frank M.; Mendybaev, Ruslan A.; Christensen, John; Hutcheon, Ian D.; Williams, Ross W.; Sturchio, Neil C. et al.
Partner: UNT Libraries Government Documents Department

Characterizing the nano and micro structure of concrete to improve its durability

Description: New and advanced methodologies have been developed to characterize the nano and microstructure of cement paste and concrete exposed to aggressive environments. High resolution full-field soft X-ray imaging in the water window is providing new insight on the nano scale of the cement hydration process, which leads to a nano-optimization of cement-based systems. Hard X-ray microtomography images on ice inside cement paste and cracking caused by the alkali-silica reaction (ASR) enables three-dimensional structural identification. The potential of neutron diffraction to determine reactive aggregates by measuring their residual strains and preferred orientation is studied. Results of experiments using these tools will be shown on this paper.
Date: October 22, 2008
Creator: Monteiro, P. J. M.; Kirchheim, A. P.; Chae, S.; Fischer, P.; MacDowell, A. A.; Schaible, E. et al.
Partner: UNT Libraries Government Documents Department

Zinc surface complexes on birnessite: A density functional theory study

Description: Biogeochemical cycling of zinc is strongly influenced by sorption on birnessite minerals (layer-type MnO2), which are found in diverse terrestrial and aquatic environments. Zinc has been observed to form both tetrahedral (Zn{sup IV}) and octahedral (Zn{sup VI}) triple-corner-sharing surface complexes (TCS) at Mn(IV) vacancy sites in hexagonal birnessite. The octahedral complex is expected to be similar to that of Zn in the Mn oxide mineral, chalcophanite (ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O), but the reason for the occurrence of the four-coordinate Zn surface species remains unclear. We address this issue computationally using spin-polarized Density Functional Theory (DFT) to examine the Zn{sub IV}-TCS and Zn{sup VI}-TCS species. Structural parameters obtained by DFT geometry optimization were in excellent agreement with available experimental data on Zn-birnessites. Total energy, magnetic moments, and electron-overlap populations obtained by DFT for isolated Zn{sup IV}-TCS revealed that this species is stable in birnessite without a need for Mn(III) substitution in the octahedral sheet and that it is more effective in reducing undersaturation of surface O at a Mn vacancy than is Zn{sub VI}-TCS. Comparison between geometry-optimized ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O (chalcophanite) and the hypothetical monohydrate mineral, ZnMn{sub 3}O{sub 7} {center_dot} H{sub 2}O, which contains only tetrahedral Zn, showed that the hydration state of Zn significantly affects birnessite structural stability. Finally, our study also revealed that, relative to their positions in an ideal vacancy-free MnO{sub 2}, Mn nearest to Zn in a TCS surface complex move toward the vacancy by 0.08-0.11 {angstrom}, while surface O bordering the vacancy move away from it by 0.16-0.21 {angstrom}, in agreement with recent X-ray absorption spectroscopic analyses.
Date: January 5, 2009
Creator: Kwon, Kideok D.; Refson, Keith & Sposito, Garrison
Partner: UNT Libraries Government Documents Department

Establishment of Vapor Hydration Test (VHT) Capabilities at the Savannah River Technology Center

Description: This report summarizes the procedure of conducting a Vapor Hydration Test and the results of initial testing at the SRTC in order to illustrate that the Westinghouse Savannah River Company now has the capabilities to perform these durability tests.
Date: March 10, 2003
Creator: Lorier, T. H.
Partner: UNT Libraries Government Documents Department

Theories of hydrophobic effects and the description of free volume in complex liquids

Description: Recent progress on molecular theories of hydration of nonpolar solutes in liquid aqueous solution has lead to new ways to thinking about the old issue of free volume in liquids. This article surveys the principal new results with particular attention to the context of general issues of packing in liquids.
Date: December 1998
Creator: Pratt, L. R.; Garde, S. & Hummer, G.
Partner: UNT Libraries Government Documents Department

Competitive ion kinetics in direct mass spectrometric organic speciation. 1993 Progress report

Description: The following joint projects are either in progress, or have been completed. (1) Southern Illinois University, Prof. S. Scheiner--Combined experimental-theoretical study of the thermochemistry of protonation, complexation, and hydration of di- and polyfunctional ethers. (2) Eastern illinois University, Prof. C. Deakyne--Essentially the same framework as above. The focus here was to determine whether C or N lone pair electrons were more effective in forming ionic hydrogen bonds. (3) Virginia Commonwealth University-Prof. S. El-Shall--The author put the wrap on a joint thermochemical (NIST) and beam expansion study (VCU) which probed structures and stabilities of methanol clusters incorporating either CH{sub 3}CN or (CH{sub 3}){sub 3}N. MeCN and TMA were chosen because of their widely differing proton affinities (PA`s) and the fact that they form single H-bonds (i.e., complex intraclusters involving multiple bonding are unlikely). (4) University of Maryland-Baltimore County-Prof. J. Liebman and the Phillips Laboratory Supercomputer Center, Kirtland Air Force Base, NM-A. Fant--One of the most perplexing problems among physical organic chemists has involved the site of protonation of a class of molecules referred to as quinones and, in particular, the symmetric member, para-benzoquinone, C{sub 6}H{sub 4} (=O{sub 2}), designated below as PBQ. Possible protonation sites either the ring or carbonyl function.
Date: December 31, 1993
Creator: Sieck, L.W.
Partner: UNT Libraries Government Documents Department

Hydrogen speciation in hydrated layers on nuclear waste glass

Description: The hydration of an outer layer on nuclear waste glasses is known to occur during leaching, but the actual speciation of hydrogen (as water or hydroxyl groups) in these layers has not been determined. As part of the Nevada Nuclear Waste Storage Investigations Project, we have used infrared spectroscopy to determine hydrogen speciations in three nuclear waste glass compositions (SRL-131 & 165, and PNL 76-68), which were leached at 90{sup 0}C (all glasses) or hydrated in a vapor-saturated atmosphere at 202{sup 0}C (SRL-131 only). Hydroxyl groups were found in the surface layers of all the glasses. Molecular water was found in the surface of SRL-131 and PNL 76-68 glasses that had been leached for several months in deionized water, and in the vapor-hydrated sample. The water/hydroxyl ratio increases with increasing reaction time; molecular water makes up most of the hydrogen in the thick reaction layers on vapor-phase hydrated glass while only hydroxyl occurs in the least reacted samples. Using the known molar absorptivities of water and hydroxyl in silica-rich glass the vapor-phase layer contained 4.8 moles/liter of molecular water, and 0.6 moles water in the form hydroxyl. A 15 {mu}m layer on SRL-131 glass formed by leaching at 90{sup 0}C contained a total of 4.9 moles/liter of water, 2/3 of which was as hydroxyl. The unreacted bulk glass contains about 0.018 moles/liter water, all as hydroxyl. The amount of hydrogen added to the SRL-131 glass was about 70% of the original Na + Li content, not the 300% that would result from alkali=hydronium ion interdiffusion. If all the hydrogen is then assumed to be added as the result of alkali-H{sup +} interdiffusion, the molecular water observed may have formed from condensation of the original hydroxyl groups.
Date: January 15, 1987
Creator: Aines, R. D.; Weed, H. C. & Bates, J. K.
Partner: UNT Libraries Government Documents Department

Scientific legacy of Robert L. Platzman. preliminary report.

Description: One of the founders of radiation physics and chemistry, Platzman (1918--73) taught us elements of our current understanding such as the hydrated electron, the basic theory of the yield of ions and other initial product species, and the importance of the oscillator-strength spectrum. In addition to all this seen in the literature, he left many unpublished materials, some of which contain stimulating thoughts and valuable ideas for experimental and theoretical work in the twenty-first century.
Date: June 28, 2000
Creator: Inokuti, M.
Partner: UNT Libraries Government Documents Department

[Energies of organic compounds]

Description: The first part of our study of the enthalpy of reduction of carbonyl compounds has been completed and includes four aldehydes, acetone, a series of cyclic ketones and ethyl acetate. Results suggest that some of the literature data for these compounds are significantly in error. Equilibrium constants have been measured for the reaction of carbonyl compounds with water to give hydrates as well as with methanol to give either hemiacetals or acetals. They cover a wide range, and studies are underway to determine the reasons for the differences. Studies of the enthalpies of hydration of some alkenes which yield tertiary alcohols have been completed, as well as a study of the hydrolysis of lactones. The ``gauche effect`` has been studied, and has been shown to result from the formation of bent bonds when atoms of much different electronegativity are joined.
Date: July 1, 1995
Partner: UNT Libraries Government Documents Department

Polymer Electrolyte Fuel Cells Membrane Hydration by Direct Liquid Water Contact

Description: An effective means of providing direct liquid hydration of the membrane tends to improve performance particularly of cells with thicker membranes or at elevated temperatures. Supplying the water to the membrane from the anode flow-field through the anode backing via wicks would appear to have advantages over delivering the water through the thickness of the membrane with regards to the uniformity and stability of the supply and the use of off-the-shelf membranes or MEAs. In addition to improving cell performance, an important contribution of direct liquid hydration approaches may be that the overall fuel cell system becomes simpler and more effective. The next steps in the evolution of this approach are a demonstration of the effectiveness of this technique with larger active area cells as well as the implementation of an internal flow-field water reservoir (to eliminate the injection method). Scale-up to larger cell sizes and the use of separate water channels within the anode flow-field is described.
Date: November 1, 1998
Creator: Wilson, M.S.; Zawodzinski, C. & Gottesfeld, S.
Partner: UNT Libraries Government Documents Department

Gallium Zeolites for Light Paraffin Aromatization

Description: The primary original goal of this project was to investigate the active state of gallium-containing MFI catalysts for light paraffin aromatization, in particular the state of gallium in the active material. Our original hypothesis was that the most active and selective materials were those which contained gallium zeolitic cations, and that previously reported conditions for the activation of gallium-containing catalysts served to create these active centers. We believed that in high silica materials such as MFI, ion-exchange is most effectively accomplished with metals in their 1+ oxidation state, both because of the sparsity of the anionic ion-exchange sites associated with the zeolite, and because the large hydration shells associated with aqueous 3+ cations hinder transport. Metals such as Ga which commonly exist in higher oxidation states need to be reduced to promote ion-exchange and this is the reason that reduction of gallium-containing catalysts for light paraffin aromatization often yields a dramatic enhancement in catalytic activity. We have effectively combined reduction with ion-exchange and we term this combined process ''reductive solid-state ion-exchange''. Our hypothesis has largely been proven true, and a number of the papers we have published directly address this hypothesis.
Date: February 10, 1999
Creator: Price, G.L. & Dooley, K.M.
Partner: UNT Libraries Government Documents Department

Structure of the (1014) Surfaces of Calcite, Dolomite, and Magnesite under Wet and Dry Conditions

Description: Atomistic computer simulation methods have been employed to model the structure of the (10{bar 1}4) surfaces of calcite, dolomite and magnesite. The authors calculations show that under vacuum conditions, calcite undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the calcite surface is stabilized and the amount of relaxation is substantially reduced. In contrast, the dolomite and magnesite surfaces are destabilized by hydration as indicated by a significant increase in the surface energies relative to the dry surface.
Date: June 12, 2000
Partner: UNT Libraries Government Documents Department

Energies of organic compounds

Description: The studies included hydrolysis of ketals, hydration of alkenes, barrier to rotation about C-O bonds in esters and acids, hydrolysis of lactones, reduction of ketones, non-bonded interactions, and enthalpies of vaporization of ketones, ketals, and other compounds.
Date: July 1, 1995
Creator: Wiberg, K.B.
Partner: UNT Libraries Government Documents Department

Outer Sphere Adsorption of Pb(II)EDTA on Goethite

Description: FTIR and EXAFS spectroscopic measurements were performed on Pb(II)EDTA adsorbed on goethite as functions of pH (4-6), Pb(II)EDTA concentration (0.11 {micro}M - 72 {micro}M), and ionic strength (16 {micro}M - 0.5M). FTIR measurements show no evidence for carboxylate-Fe(III) bonding or protonation of EDTA at Pb:EDTA = 1:1. Both FTIR and EXAFS measurements suggest that EDTA acts as a hexadentate ligand, with all four of its carboxylate and both amine groups bonded to Pb(II). No evidence was observed for inner-sphere Pb(II)-goethite bonding at Pb:EDTA = 1:1. Hence, the adsorbed complexes should have composition Pb(II)EDTA{sup 2{minus}}. Since substantial uptake of PbEDTA(II){sup 2{minus}} occurred in the samples, we infer that Pb(II)EDTA{sup 2{minus}} adsorbed as outer-sphere complexes and/or as complexes that lose part of their solvation shells and hydrogen bond directly to goethite surface sites. We propose the term ''hydration-sphere'' for the latter type of complexes because they should occupy space in the primary hydration spheres of goethite surface functional groups, and to distinguish this mode of sorption from common structural definitions of inner- and outer-sphere complexes. The similarity of Pb(II) uptake isotherms to those of other divalent metal ions complexed by EDTA suggests that they too adsorb by these mechanisms. The lack of evidence for inner-sphere EDTA-Fe(III) bonding suggests that previously proposed metal-ligand - promoted dissolution mechanisms should be modified, specifically to account for the presence of outer-sphere precursor species.
Date: July 16, 1999
Creator: Bargar, John R
Partner: UNT Libraries Government Documents Department