Publications

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We report on the novel room temperature method of synthesizing advanced nuclear fuels; a method that virtually eliminates any volatility of components. This process uses radiolysis to form stable nanoparticle (NP) nuclear transuranic (TRU) fuel surrogates and in-situ heated stage TEM to sinter the NPs. The radiolysis is performed at Sandia's Gamma Irradiation Facility (GIF) 60Co source (3 x 10{sup 6} rad/hr). Using this method, sufficient quantities of fuels for research purposes can be produced for accelerated advanced nuclear fuel development. We are focused on both metallic and oxide alloy nanoparticles of varying compositions, in particular d-U, d-U/La alloys and d-UO2 NPs. We present detailed descriptions of the synthesis procedures, the characterization of the NPs, the sintering of the NPs, and their stability with temperature. We have employed UV-vis, HRTEM, HAADF-STEM imaging, single particle EDX and EFTEM mapping characterization techniques to confirm the composition and alloying of these NPs.

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Reprocessing nuclear fuel releases gaseous radio-iodine containing compounds which must be captured and stored for prolonged periods. Ag-loaded mordenites are the leading candidate for scavenging both organic and inorganic radioiodine containing compounds directly from reprocessing off gases. Alternately, the principal off-gas contaminant, I2, and I-containing acids HI, HIO3, etc. may be scavenged using caustic soda solutions, which are then treated with bismuth to put the iodine into an insoluble form. Our program is focused on using state-of-the-art materials science technologies to develop materials with high loadings of iodine, plus high long-term mechanical and thermal stability. In particular, we present results from research into two materials areas: (1) zeolite-based separations and glass encapsulation, and (2) in-situ precipitation of Bi-I-O waste forms. Ag-loaded mordenite is either commercially available or can be prepared via a simple Ag+ ion exchange process. Research using an Ag+-loaded Mordenite zeolite (MOR, LZM-5 supplied by UOP Corp.) has revealed that I2 is scavenged in one of three forms, as micron-sized AgI particles, as molecular (AgI)x clusters in the zeolite pores and as elemental I2 vapor. It was found that only a portion of the sorbed iodine is retained after heating at 95o C for three months. Furthermore, we show that even when the Ag-MOR is saturated with I2 vapor only roughly half of the silver reacted to form stable AgI compounds. However, the Iodine can be further retained if the AgI-MOR is then encapsulated into a low temperature glass binder. Follow-on studies are now focused on the sorption and waste form development of Iodine from more complex streams including organo-iodine compounds (CH3I). Bismuth-Iodate layered phases have been prepared from caustic waste stream simulant solutions. They serve as a low cost alternative to ceramics waste forms. Novel compounds have been synthesized and solubility studies have been completed using competing groundwater anions (HCO3-, Cl- and SO42-). Distinct variations in solubility were found that related to the structures of the materials.

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Inelastic neutron scattering, density functional theory, ab initio molecular dynamics, and classical molecular dynamics were used to examine the behavior of nanoconfined water in palygorskite and sepiolite. These complementary methods provide a strong basis to illustrate and correlate the significant differences observed in the spectroscopic signatures of water in two unique clay minerals. Distortions of silicate tetrahedra in the smaller-pore palygorskite exhibit a limited number of hydrogen bonds having relatively short bond lengths. In contrast, without the distorted silicate tetrahedra, an increased number of hydrogen bonds are observed in the larger-pore sepiolite with corresponding longer bond distances. Because there is more hydrogen bonding at the pore interface in sepiolite than in palygorskite, we expect librational modes to have higher overall frequencies (i.e., more restricted rotational motions); experimental neutron scattering data clearly illustrates this shift in spectroscopic signatures. Distortions of the silicate tetrahedra in these minerals effectively disrupts hydrogen bonding patterns at the silicate-water interface, and this has a greater impact on the dynamical behavior of nanoconfined water than the actual size of the pore or the presence of coordinatively-unsaturated magnesium edge sites.

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Inelastic neutron scattering, density functional theory, ab initio molecular dynamics, and classical molecular dynamics were used to examine the behavior of nanoconfined water in palygorskite and sepiolite. These complementary methods provide a strong basis to illustrate and correlate the significant differences observed in the spectroscopic signatures of water in two unique clay minerals. Distortions of silicate tetrahedra in the smaller-pore palygorskite exhibit a limited number of hydrogen bonds having relatively short bond lengths. However, without the distorted silicate tetrahedra, an increased number of hydrogen bonds are observed in the larger-pore sepiolite with corresponding longer bond distances. Because there is more hydrogen bonding at the pore interface in sepiolite than in palygorskite, we expect librational modes to have higher overall frequencies (i.e., more restricted rotational motions); experimental neutron scattering data clearly illustrates this shift in spectroscopic signatures. It follows that distortions of the silicate tetrahedra in these minerals effectively disrupt hydrogen-bonding patterns at the silicate?water interface, and this has a greater impact on the dynamical behavior of nanoconfined water than the actual size of the pore or the presence of coordinatively unsaturated magnesium edge sites.

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This one-year exploratory LDRD aims to provide fundamental understanding of the mechanism of CO2 scrubbing platforms that will reduce green house gas emission and mitigate the effect of climate change. The project builds on the team members expertise developed in previous LDRD projects to study the capture or preferential retention of CO2 in nanoporous membranes and on metal oxide surfaces. We apply Density Functional Theory and ab initio molecular dynamics techniques to model the binding of CO2 on MgO and CaO (100) surfaces and inside water-filled, amine group functionalized silica nanopores. The results elucidate the mechanisms of CO2 trapping and clarify some confusion in the literature. Our work identifies key future calculations that will have the greatest impact on CO2 capture technologies, and provides guidance to science-based design of platforms that can separate the green house gas CO2 from power plant exhaust or even from the atmosphere. Experimentally, we modify commercial MFI zeolite membranes and find that they preferentially transmit H2 over CO2 by a factor of 34. Since zeolite has potential catalytic capability to crack hydrocarbons into CO2 and H2, this finding paves the way for zeolite membranes that can convert biofuel into H2 and separate the products all in one step.

A molecular-scale interpretation of interfacial processes is often downplayed in the analysis of traditional water treatment methods. However, such an approach is critical for the development of enhanced performance in traditional desalination and water treatments. Water confined between surfaces, within channels, or in pores is ubiquitous in technology and nature. Its physical and chemical properties in such environments are unpredictably different from bulk water. As a result, advances in water desalination and purification methods may be accomplished through an improved analysis of water behavior in these challenging environments using state-of-the-art microscopy, spectroscopy, experimental, and computational methods.

The water dynamics in a series of Sandia octahedral molecular sieves (SOMS) were investigated using high speed 1H magic angle spinning (MAS) NMR spectroscopy. For these materials both the 20% Ti-substituted material, Na 2Nb1.6Ti0.4(OH)0.4O 5.6·H2O and the 0% exchanged end member, Na 2Nb2O6·H2O were studied. By combining direct one dimensional (1D) MAS NMR experiments with double quantum (DQ) filtered MAS NMR experiments different water environments within the materials were identified based on differences in mobility. Two dimensional (2D) DQ correlation experiments were used to extract the DQ spinning sideband patterns allowing the residual 1H-1H homonuclear dipolar coupling to be measured. From these DQ experiments the effective order parameters for the different water environments were calculated. The water environments in the two different SOMS compositions investigated revealed very large differences in the water mobility. © 2007 Materials Research Society.

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In this study the separation capabilities of silicalite and the titanosilicate molecular sieve ETS-10 for binary mixtures of hydrogen/methane and hydrogen/carbon dioxide were evaluated by equilibrium molecular simulation techniques. This is the first molecular simulation study that presents mixture adsorption isotherms of these components in silicalite and ETS-10, and determines selectivities based on the simulation results. Grand Canonical Monte Carlo (GCMC) simulations were carried out for pure components and binary mixtures for hydrogen/carbon dioxide and hydrogen/methane at 298 K to determine pure and mixture adsorption isotherms. The pure and mixture adsorption isotherms were calculated up to pressures of approximately 2000 bar. The results of this study indicate that the separation of hydrogen from methane or from carbon dioxide in silicalite would be successful, since hydrogen in a 50% bulk mixture does not adsorb unless the pressure is very high, on the order of 500 bar. In contrast, in ETS-10, hydrogen in a 50% bulk mixture adsorbs at a pressure near 10 bar. Simulations of adsorption in ETS-10 show at low, intermediate and high pressures a higher selectivity for the separation of carbon dioxide from hydrogen than the separation of methane from hydrogen. Simulations of adsorption in silicalite show a higher selectivity for the separation of carbon dioxide from hydrogen than the methane/hydrogen separation at high pressures only. Analysis of isosteric heat of adsorption information indicates that silicalite is energetically homogeneous with the adsorbates. In contrast, ETS-10 has energetic heterogeneity, as shown by the decrease of the heat of adsorption with increasing loading. © 2006 Elsevier B.V. All rights reserved.

MFI zeolite membranes have been synthesized on tubular α-alumina substrates to investigate the separation of p-xylene (PX) from m-xylene (MX) and o-xylene (OX) in binary, ternary, and simulated multicomponent mixtures in wide ranges of feed pressure and operating temperature. The results demonstrate that separation of PX from MX and OX through the MFI membranes relies primarily on shape-selectivity when the xylene sorption level in the zeolite is sufficiently low. For an eight-component mixture containing hydrogen, methane, benzene, toluene, ethylbenzene, PX, MX, and OX, a PX/(MX + OX) selectivity of 7.71 with a PX flux of 6.8 × 10-6 mol/(m2 s) was obtained at 250 °C and atmospheric feed pressure. The addition of a small quantity of nonane to the multicomponent mixture caused drastic decreases in the fluxes of aromatic components and the PX separation factor because of the preferential adsorption of nonane in the zeolite channels. The nanoscale intercrystalline pores also caused serious decline in the PX separation factor. A new method of online membrane modification by carbonization of 1,3,5-triisopropylbenzene in the feed stream was found to be effective for reducing the intercrystalline pores and improving the PX separation. © 2006 Elsevier B.V. All rights reserved.

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Alkylation reactions of benzene with propylene using heterogeneous catalysts H+-β zeolite, MCM-22, and ZSM-5 were studied for their affinity for cumene production. This work focused on the gas-phase reaction using different crystalline catalysts at several temperatures and amounts of reactants using both batch and continuous fixed-bed reactors. The properties of baseline commercial H+ -β catalysts versus versions modified with Ga, La, and Pt were studied. Quantitative analysis of product mixture was performed by gas chromatography. For the batch reactor, β-zeolite produced the highest cumene yield and selectivity of 72% and 92%, respectively, at 225°C. At this temperature, a benzene:propylene dilution of 7:1 molar ratio was the optimum. For the continuous system, cumene production is favored at lower space velocities, higher benzene-to-propylene ratio, and temperatures close to 225°C. Ga modification of the H+-β zeolite significantly enhanced cumene yield in the continuous fixed-bed reactor at 225°C, from 27% of the unmodified β-zeolite to 36% for the Ga-modified one. The life span of modified β-catalysts was studied in the fixed-bed reactor for the first eight hours of reaction. Copyright © Taylor & Francis Group, LLC.

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Materials in the La{sub 0.1}Sr{sub 0.9}Co{sub 1-y}MnyO{sub 3-{delta}} (LSCM) family are potentially useful as ceramic membranes for high-temperature oxygen separations. A series of LSCM samples was synthesized by solid state methods and characterized by powder X-ray diffraction, thermogravimetric analysis, and four-probe conductivity. The materials were indexed in the cubic Pm-3m space group. TGA data implied that LSCM can reversibly absorb and desorb oxygen versus temperature and partial oxygen pressure, while powder diffraction data showed that the material maintained the cubic perovskite structure. Preliminary four-probe conductivity measurements signify p-type semiconducting behavior.

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The conclusions of this paper are: (1) Adsorption/desorption on bulk unmodified zeolites showed isoprene adsorbed by zeolite-L and n-pentane adsorbed by zeolite-Y and ZSM-5; (2) Bulk carbonization is used to passivate zeolite activity toward organic adsorption/decomposition; (3) Based on the bulk modified zeolite separation results, we have determined that the MFI type has the most potential for isoprene enrichment; (4) Modified MFI type membrane are jointly made by Sandia and the Univ. of Colorado. Separation experiments are performed by Goodyear Chemical; (5) Isoprene/n-pentane separations have been demonstrated by using both zeolite membranes and modified bulk zeolites at various temperatures on the Goodyear Pilot-scale unit; and (6) Target zeolite membrane separations values of 6.7% isoprene enrichment have been established by economic analysis calculations by Burns & McDonnell.

We have synthesized defect-free aluminosilicate and silicalite zeolite thin films supported on commercially available alpha and gamma alumina disk substrates. We have also built a permeation unit that can test both pure and mixed gases from room temperature to 250 C. Results indicate fluxes on the order of 10{sup -6} to 10{sup -7} mole/(m{sup 2}Pa sec) and excellent separation values for H{sub 2} or CO{sub 2}. For the Al/Si membrane: H{sub 2}/N{sub 2} {ge} 61, H{sub 2}/CO{sub 2} {ge} 80, H{sub 2}/CH{sub 4} = 7, CH{sub 4}/CO{sub 2} {ge} 11; for the TPA/Si membrane: H{sub 2}/N{sub 2} {ge} 61, H{sub 2}/CO{sub 2} {ge} 80, H{sub 2}/CH{sub 4} = 7, CH{sub 4}/CO{sub 2} {ge} 11. Our data show that we can use the adsorption ability plus the effective pore diameter of the zeolite to 'tune' the selectivity of the membrane. Another avenue of research is into bulk novel molecular sieve materials, with the goal of 'tuning' pore sizes to molecular sieving needs. A novel crystalline 12-ring microporous gallophosphate material is described.

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A series of amorphous silicate materials with the general formula Na{sub x+2y}M{sub x}{sup 3+}Si{sub 1-x}O{sub 2+y}(M{sup 3+} = Al, Mn, Fe, Y) were studied. Samples were synthesized by a precipitation reaction at room temperature. The results indicate that the ion-exchange capacity (IEC) decreases as follows: Al > Fe > Mn > Y. Additionally, the IEC increases with increasing aluminum concentration. Structural studies show that the relative amount of octahedrally coordinated aluminum increases with increasing Al content, as does the total amount of AlO{sub 4} species increases. The data suggest that the IEC value of these amorphous aluminosilicates is dependent on the tetrahedrally coordinated aluminum. Regeneration of the Al-silicate with acetic acid does not decrease the IEC significantly.

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An environmentally friendly method and materials study for desalinating inland brackish waters (i.e., coal bed methane produced waters) using a set of ion-exchange materials is presented. This desalination process effectively removes anions and cations in separate steps with minimal caustic waste generation. The anion-exchange material, hydrotalcite (HTC), exhibits an ion-exchange capacity (IEC) of {approx} 3 mequiv g{sup -1}. The cation-exchange material, an amorphous aluminosilicate permutite-like material, (Na{sub x+2y}Al{sub x}Si{sub 1-x}O{sub 2+y}), has an IEC of {approx}2.5 mequiv g{sup -1}. These ion-exchange materials were studied and optimized because of their specific ion-exchange capacity for the ions of interest and their ability to function in the temperature and pH regions necessary for cost and energy effectiveness. Room temperature, minimum pressure column studies (once-pass through) on simulant brackish water (total dissolved solids (TDS) = 2222 ppm) resulted in water containing TDS = 25 ppm. A second once-pass through column study on actual produced water (TDS = {approx}11,000) with a high carbonate concentration used an additional lime softening step and resulted in a decreased TDS of 600 ppm.

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The enthalpies of formation of hydrotalcite-like phases containing Mg and Al and intercalated with NO{sub 3}{sup -}, Cl{sup -}, I{sup -}, ReO{sub 4}{sup -}, or CO{sub 3}{sup 2-} were determined using high-temperature oxide melt and room-temperature acid solution calorimetry. The relative stability of phases bearing the various anions was gauged by comparing the enthalpy of formation from the single-cation components ({Delta}{sub f}H{sup scc}). Trends relating {Delta}{sub f}H{sup scc} to the nature of intercalating anions (halides, NO{sub 3}{sup -}, and CO{sub 3}{sup 2-}) show small stabilization from the mechanical mixtures of single-cation components. The aim of this study was to relate the enthalpy of formation to the nature of interlayer bonding in hydrotalcite-like compounds (HTLCs) bearing various anions, to uncover trends in the relative aqueous solubilities of these phases. The entropy of formation of these compounds was estimated using an approximation based on third-law entropy measurements for the compound Mg{sub 0.74}Al{sub 0.26}(OH){sub 2}(CO{sub 3}){sub 0.13} {center_dot} 0.39H{sub 2}O which were performed in a previous study. This approximation for the third-law entropy was combined with the enthalpy data from our calorimetric measurements performed in this work in order to calculate the standard-state free energy of formation for the HTLCs. The solubility products for the compounds investigated in this study were calculated from these free energies of formation and were used in geochemical calculations. The results of these calculations support our previous hypothesis that carbonate-intercalated HTLCs are less soluble than phases bearing other anions such as nitrates and halides. We suspect that the solubilities of HTLCs bearing anions other than carbonate may correspond to the solubilities of single-cation phases bearing the same anions.

Efficient and environmentally sound methods of producing hydrogen are of great importance to the US as it progresses toward the H2 economy. Current studies are investigating the use of high temperature systems driven by nuclear and/or solar energy to drive thermochemical cycles for H2 production. These processes are advantageous since they do not produce greenhouse gas emissions that are a result of hydrogen production from electrolysis or hydrocarbon reformation. Double-substituted perovskites, A1-xSrxCo1-yBy O3-δ (A = Y, La; B = Fe, Ni, Cr, Mn) were synthesized for use as ceramic high-temperature oxygen separation membranes. The materials have promising oxygen sorption properties and were structurally robust under varying temperatures and atmospheres. Post-TGA powder diffraction patterns revealed no structural changes after the temperature and gas treatments, demonstrating the robustness of the material. The most promising material was the La0.1Sr0.9Co1-xMnx O3-δ perovskite. The oxygen sorption properties increased with increasing Mn doping.

The need for fresh water has increased exponentially during the last several decades due to the continuous growth of human population and industrial and agricultural activities. Yet existing resources are limited often because of their high salinity. This unfavorable situation requires the development of new, long-term strategies and alternative technologies for desalination of saline waters presently not being used to supply the population growth occurring in arid regions. We have developed a novel environmentally friendly method for desalinating inland brackish waters. This process can be applied to either brackish ground water or produced waters (i.e., coal-bed methane or oil and gas produced waters). Using a set of ion exchange and sorption materials, our process effectively removes anions and cations in separate steps. The ion exchange materials were chosen because of their specific selectivity for ions of interest, and for their ability to work in the temperature and pH regions necessary for cost and energy effectiveness. For anion exchange, we have focused on hydrotalcite (HTC), a layered hydroxide similar to clay in structure. For cation exchange, we have developed an amorphous silica material that has enhanced cation (in particular Na{sup +}) selectivity. In the case of produced waters with high concentrations of Ca{sup 2+}, a lime softening step is included.

Conclusions of this paper are: (1) Adsorption/desorption on bulk unmodified zeolites showed isoprene adsorbed by zeolite-L and n-pentane adsorbed by zeolite-Y and ZSM-5; (2) Bulk carbonization is used to passivate zeolite activity toward organic adsorption/decomposition; (3) Based on the bulk modified zeolite separation results, we have determined that the MFI type has the most potential for isoprene enrichment; (4) Modified MFI type membranes are jointly made by Sandia and the Univ. of Colorado. Separation experiments are performed by Goodyear Chemical; (5) Isoprene/n-pentane separations have been demonstrated by using both zeolite membranes and modified bulk zeolites at various temperatures on the Goodyear Pilot-scale unit; and (6) Target zeolite membrane separations values of 6.7% isoprene enrichment have been established by economic analysis calculations by Burns & McDonnell.

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This project will attempt to develop a new family of inorganic crystalline porous materials under IMF that will lead to improvement of energy efficiency and productivity via improved separations. Initially this project will be focused on materials for the separation of linear from branched hydrocarbons. However, it is anticipated that the results will provide the basis of knowledge to enable this technology to be applied toward additional hydrocarbon and chemical separations. Industrial involvement from Goodyear and Burns & McDonnell provides needed direction for solving real industrial problems, which will find application throughout the US chemical and petroleum industries.

A family of microporous phases with compositions Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-x}(OH){sub x} {center_dot} H{sub 2}O (0 {le} x {le} 0.4) transform to Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-0.5x} perovskites upon heating. In this study, we have measured the enthalpies of formation of the microporous phases and their corresponding perovskites from the constituent oxides and from the elements by drop solution calorimetry in 3Na{sub 2}O {center_dot} 4MoO{sub 3} solvent at 974 K. As Ti/Nb increases, the enthalpies of formation for the microporous phases become less exothermic up to x = {approx}0.2 but then more exothermic thereafter. In contrast, the formation enthalpies for the corresponding perovskites become less exothermic across the series. The energetic disparity between the two series can be attributed to their different mechanisms of ionic substitutions: Nb{sup 5+} + O{sup 2-} {yields} Ti{sup 4+} + OH{sup -} for the microporous phases and Nb{sup 5+} {yields} Ti{sup 4+} + 0.5 V{sub O}** for the perovskites. From the calorimetric data for the two series, the enthalpies of the dehydration reaction, Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-x}(OH){sub x} {center_dot} H{sub 2}O {yields} Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-0.5X} + H{sub 2}O, have been derived, and their implications for phase stability at the synthesis conditions are discussed.

There is a great need for robust, defect-free, highly selective molecular sieve (zeolite) thin film membranes for light gas molecule separations in hydrogen fuel production from CH{sub 4} or H{sub 2}O sources. In particular, we are interested in (1) separating and isolating H{sub 2} from H{sub 2}O and CH{sub 4}, CO, CO{sub 2}, O{sub 2}, N{sub 2} gases; (2) water management in PEMs and (3) as a replacement for expensive Pt catalysts needed for PEMs. Current hydrogen separation membranes are based on Pd alloys or on chemically and mechanically unstable organic polymer membranes. The use of molecular sieves brings a stable (chemically and mechanically stable) inorganic matrix to the membrane [1-3]. The crystalline frameworks have 'tunable' pores that are capable of size exclusion separations. The frameworks are made of inorganic oxides (e.g., silicates, aluminosilicates, and phosphates) that bring different charge and electrostatic attraction forces to the separation media. The resultant materials have high separation abilities plus inherent thermal stability over 600 C and chemical stability. Furthermore, the crystallographically defined (<1 {angstrom} deviation) pore sizes and shapes allow for size exclusion of very similarly sized molecules. In contrast, organic polymer membranes are successful based on diffusion separations, not size exclusion. We envision the impact of positive results from this project in the near term with hydrocarbon fuels, and long term with biomass fuels. There is a great need for robust, defect-free, highly selective molecular sieve (zeolite) thin film membranes for light gas molecule separations in hydrogen fuel production from CH{sub 4} or H{sub 2}O sources. They contain an inherent chemical, thermal and mechanical stability not found in conventional membrane materials. Our goal is to utilize those zeolitic qualities in membranes for the separation of light gases, and to eventually partner with industry to commercialize the membranes. To date, we have successfully: (1) Demonstrated (through synthesis, characterization and permeation testing) both the ability to synthesize defect-free zeolitic membranes and use them as size selective gas separation membranes; these include aluminosilicates and silicates; (2) Built and operated our in-house light gas permeation unit; we have amended it to enable testing of H{sub 2}S gases, mixed gases and at high temperatures. We are initiating further modification by designing and building an upgraded unit that will allow for temperatures up to 500 C, steady-state vs. pressure driven permeation, and mixed gas resolution through GC/MS analysis; (3) Have shown in preliminary experiments high selectivity for H{sub 2} from binary and industrially-relevant mixed gas streams under low operating pressures of 16 psig; (4) Synthesized membranes on commercially available oxide and composite disks (this is in addition to successes we have in synthesizing zeolitic membranes to tubular supports [9]); and (5) Signed a non-disclosure agreement with industrial partner G. E. Dolbear & Associates, Inc., and have ongoing agreements with Pall Corporation for in-kind support supplies and interest in scale-up for commercialization.

A new family of framework titanosilicates, A{sub 2}TiSi{sub 6}O{sub 15} (A=K, Rb, Cs) (space group Cc), has recently been synthesized using the hydrothermal method. This group of phases can potentially be utilized for storage of radioactive elements, particularly {sup 137}Cs, due to its high stability under electron radiation and chemical leaching. Here, we report the syntheses and structures of two intermediate members in the series: KRbTiSi{sub 6}O{sub 15} and RbCsTiSi{sub 6}O{sub 15}. Rietveld analysis of powder synchrotron X-ray diffraction data reveals that they adopt the same framework topology as the end-members, with no apparent Rb/K or Rb/Cs ordering. To study energetics of the solid solution series, high-temperature drop-solution calorimetry using molten 2PbO {center_dot} B{sub 2}O{sub 3} as the solvent at 975 K has been performed for the end-members and intermediate phases. As the size of the alkali cation increases, the measured enthalpies of formation from the constituent oxides and from the elements ({Delta}H{sub f,el}) become more exothermic, suggesting that this framework structure favors the cation in the sequence Cs{sup +}, Rb{sup +}, and K{sup +}. This trend is consistent with the higher melting temperatures of A{sub 2}TiSi{sub 6}O{sub 15} phases with increase in the alkali cation size.

The synthesis, characterization, and separations capability of defect-free, thin-film zeolite membranes were presented. The one-micron thick sodium-aluminosilicate films of Silicalite-1 and ZSM-5 were synthesized by hydrothermal methods on either disk- or tube-supports. Techniques for growing membranes on both Al2O3 substrates as well as oxide-coated stainless steel substrates were presented. The resulting defect-free zeolite films had high flux rates at room temperature (∼ 10-7 mole/Pa-sec-sq m) and showed selective separations (3-7) between pure gases of H2 and CH4, O2, N2, CO2, CO, SF6. Results from mixed gas studies showed similar flux rates as pure gases with enhanced selectivity (15-50) for H2. The selectivity through both Silicalite-1 and ZSM-5 membranes was compared and contrasted for several gas mixtures. Data comparisons for defect-free and "defect-filled" membranes were also discussed. Under operation, the flow through these membranes quickly reached its maximum value and was stable over long periods of time. Results from experiments at high temperatures, ≤ 300°C, were compared with the data obtained at room temperature. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA, 8/22-26/2004).

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Alkylation reactions of benzene with propylene using zeolites were studied for their affinity for cumene production. The current process for the production of cumene involves heating corrosive acid catalysts, cooling, transporting, and distillation. This study focused on the reaction of products in a static one-pot vessel using non-corrosive zeolite catalysts, working towards a more efficient one-step process with a potentially large energy savings. A series of experiments were conducted to find the best reaction conditions yielding the highest production of cumene. The experiments looked at cumene formation amounts in two different reaction vessels that had different physical traits. Different zeolites, temperatures, mixing speeds, and amounts of reactants were also investigated to find their affects on the amount of cumene produced. Quantitative analysis of product mixture was performed by gas chromatography. Mass spectroscopy was also utilized to observe the gas phase components during the alkylation process.

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As a participating national lab in the inter-institutional effort to resolve performance issues of the non-elutable ion exchange technology for Cs extraction, they have carried out a series of characterization studies of UOP IONSIV{reg_sign} IE-911 and its component parts. IE-911 is a bound form (zirconium hydroxide-binder) of crystalline silicotitanate (CST) ion exchanger. The crystalline silicotitanate removes Cs from solutions by selective ion exchange. The performance issues of primary concern are: (1) excessive Nb leaching and subsequent precipitation of column-plugging Nb-oxide material, and (2) precipitation of aluminosilicate on IE-911 pellet surfaces, which may be initiated by dissolution of Si from the IE-911, thus creating a supersaturated solution with respect to silica. In this work, they have identified and characterized Si- and Nb-oxide based impurity phases in IE-911, which are the most likely sources of leachable Si and Nb, respectively. Furthermore, they have determined the criteria and mechanism for removal from IE-911 of the Nb-based impurity phase that is responsible for the Nb-oxide column plugging incidents.

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The synthesis, structure and some properties of C{sub 2}H{sub 7}N{sub 4}O {center_dot} ZnPO{sub 4} (guanylurea zinc phosphate) are reported. The cationic template was prepared in situ by partial hydrolysis of the neutral 2-cyanoguanidine starting material. The resulting structure contains a new, unprotonated, zincophosphate layer topology as well as unusual N-H-O template-to-template hydrogen bonds which help to stabilize a ''double sandwich'' of templating cations between the inorganic sheets. Crystal data: C{sub 2}H{sub 7}N{sub 4}O {center_dot} ZnPO{sub 4}, M{sub r} = 229.44, monoclinic, P2{sub 1}/c, a = 13.6453 (9) {angstrom}, b = 5.0716 (3) {angstrom}, c = 10.6005 (7) {angstrom}, {beta} = 95.918 (2){sup 0}, V = 729.7 (1) {angstrom}{sup 3}, R(F) = 0.034, wR(F) = 0.034.

Exploratory hydrothermal synthesis in the system Cs2O-SiO2-TiO2 has produced a new polymorph of Cs2TiSi6O15 (SNL-A), whose structure was determined using a combination of experimental and theoretical techniques (29Si and 133Cs NMR, X-ray powder diffraction, and density functional theory). SNL-A crystallizes in the monoclinic space group Cc with unit cell parameters a = 12.998(2) Å, b = 7.5014(3) Å, c = 15.156(3) Å, and β = 105.80(3)°. The SNL-A framework is an unbranched drier single-layer silicate with silicon tetrahedra and titanium octahedra that are linked in 3-, 5-, 6-, 7-, and 8-membered rings in three dimensions. SNL-A is distinctive from a previously reported C2/c polymorph of Cs2TiSi6O15 by orientation of the Si2O52- layers and by different ring geometries. Similarities and differences between the two structures are discussed. Other characterizations of SNL-A include TGA-DTA, Cs/Si/Ti elemental analyses, and SEM/EDS. Furthermore, the chemical and radiation durability of SNL-A was studied in interest of ceramic waste form applications. These studies show that SNL-A is durable in both radioactive and rigorous chemical environments. Finally, calculated cohesive energies of the two Cs2TiSi6O15 polymorphs suggest that the Cc SNL-A phase (synthesized at 200 °C) is energetically more favorable than the C2/c polymorph (synthesized at 1050 °C).

The solution-mediated synthesis and single crystal structure of (CN{sub 3}H{sub 6}){sub 2} {center_dot} Zn(HPO{sub 3}){sub 2} are reported. This phase is built up from a three-dimensional framework of vertex-linked ZnO{sub 4} and HPO{sub 3} building units encapsulating the extra-framework guanidinium cations. The structure is stabilized by template-to-framework hydrogen bonding. The inorganic framework shows a surprising similarity to those of some known zinc phosphates. Crystal data: (CN{sub 3}H{sub 6}){sub 2} {center_dot} Zn(HPO{sub 3}){sub 2}, AI,= 345.50, orthorhombic, space group Fdd2 (No. 43), a = 15.2109 (6) {angstrom}, b = 11.7281 (5) {angstrom}, c = 14.1821 (6) {angstrom}, V = 2530.0 (4){angstrom}{sup 3}, Z = 8, T = 298 (2)K, R(F) = 0.020, wR(F) = 0.025.

Abstract not provided.

The syntheses, crystal structures and some properties of {alpha}- and {beta}-ZnHPO{sub 3}{center_dot}N{sub 4}C{sub 2}H{sub 4} are reported. These two polymorphs are the first organically-templated hydrogen phosphites. They are built up from vertex-sharing HPO{sub 3} pseudo pyramids and ZnO{sub 3}N tetrahedra, where the Zn-N bond represents a direct link between zinc and the neutral 2-cyanoguanidine template. {alpha}-ZnHPO{sub 3}{center_dot}N{sub 4}C{sub 2}H{sub 4} is built up from infinite layers of vertex-sharing ZnO{sub 3}N and HPO{sub 3} groups forming 4-rings and 8-rings. {beta}-ZnHPO{sub 3}{center_dot}N{sub 4}C{sub 2}H{sub 4} has strong one-dimensional character, with the polyhedral building units forming 4-ring ladders. Similarities and differences to related zinc phosphates are discussed. Crystal data: {alpha}-ZnHPO{sub 3}{center_dot}N{sub 4}C{sub 2}H{sub 4}, M{sub r} = 229.44, monoclinic, P2{sub 1}/c, a = 9.7718 (5) {angstrom}, b = 8.2503 (4) {angstrom}, c = 9.2491 (5) {angstrom}, {beta} = 104.146 (1){sup 0}, V = 723.1 (1) {angstrom}{sup 3}, R(F) = 2.33%, wR(F) = 2.52%. {beta}-ZnHPO{sub 3}{center_dot}N{sub 4}C{sub 2}H{sub 4}, M{sub r} = 229.44, monoclinic, C2/c, a = 14.5092 (9) {angstrom}, b = 10.5464 (6) {angstrom}, c = 10.3342 (6) {angstrom}, {beta} = 114.290 (1){sup 0}, V = 1441.4 (3) {angstrom}{sup 3}, R(F) = 3.01%, wR(F) = 3.40%.

The structure of Na{sub 16}Nb{sub 12.8}Ti{sub 3.2}O{sub 44.8}(OH){sub 3.2} {center_dot} 8H{sub 2}O, a member of a new family of Sandia Octahedral Molecular Sieves (SOMS) having a Nb/Na/M{sup IV} (M= Ti, Zr) oxide framework and exchangeable Na and water in open channels, was determined from Synchrotron X-ray data. The SOMS phases are isostructural with variable M{sup IV}:Nb(1:50--1:4) ratios. The SOMS are extremely selective for sorption of divalent cations, particularly Sr{sup 2+}. The ion-exchanged SOMS undergo direct thermal conversion to a perovskite-type phase, indicating this is a promising new method for removal and sequestration of radioactive Sr-90 from mixed nuclear wastes.

A study of zeolite crystallization from sol-gel precursors using the vapor phase transport synthesis method has been performed. Zeolites (ZSM-5, ZSM-48, Zeolite P, and Sodalite) were crystallized by contacting vapor phase organic or organic-water mixtures with dried sodium silicate and dried sodium alumino-silicate gels. For each precursor gel, a ternary phase system of vapor phase organic reactant molecules was explored. The vapor phase reactant mixtures ranged from pure ethylene diamene, triethylamine, or water, to an equimolar mixture of each. In addition, a series of gels with varied physical and chemical properties were crystallized using the same vapor phase solvent mixture for each gel. The precursor gels and the crystalline products were analyzed via Scanning Electron Microscopy, Electron Dispersive Spectroscopy, X-ray mapping, X-ray powder diffraction, nitrogen surface area, Fourier Transform Infrared Spectroscopy, and thermal analyses. The product phase and purity as a function of the solvent mixture, precursor gel structure, and precursor gel chemistry is discussed.

An astonishing variety of inorganic networks templated by organic species have been reported over the last 10 years. A great deal of attention has been paid to the structure-directing role of the organic species, and the structural effect of variously coordinated cations, for example distorted octahedral vanadium and pyramidal tin. Less exploratory work has been carried out on the anionic part of the inorganic network, and most groups reported so far (phosphate, germanate, etc.) invariably adopt tetrahedral coordination. The possibilities of incorporating the pyramidal [HP0{sub 3}]{sup 2{minus}} hydrogen phosphite group into extended structures templated by inorganic, alkaline earth cations was explored a few years ago. In this paper the authors report the synthesis, crystal structure, and some properties of (CN{sub 3}H{sub 6}){sub 4}{center_dot}Zn{sub 3}(SeO{sub 3}){sub 5}, the first organically-templated phase to contain the pyramidal selenite [SeO{sub 3}]{sup 2{minus}} anion.

A number of Hanford tanks have leaked high level radioactive wastes (HLW) into the surrounding unconsolidated sediments. The disequilibrium between atmospheric C0{sub 2} or silica-rich soils and the highly caustic (pH > 13) fluids is a driving force for numerous reactions. Hazardous dissolved components such as {sup 133}Cs, {sup 79}Se, {sup 99}Tc may be adsorbed or sequestered by alteration phases, or released in the vadose zone for further transport by surface water. Additionally, it is likely that precipitation and alteration reactions will change the soil permeability and consequently the fluid flow path in the sediments. In order to ascertain the location and mobility/immobility of the radionuclides from leaked solutions within the vadose zone, the authors are currently studying the chemical reactions between: (1) tank simulant solutions and Hanford soil fill minerals; and (2) tank simulant solutions and C0{sub 2}. The authors are investigating soil-solution reactions at: (1) elevated temperatures (60--200 C) to simulate reactions which occur immediately adjacent a radiogenically heated tank; and (2) ambient temperature (25 C) to simulate reactions which take place further from the tanks. The authors studies show that reactions at elevated temperature result in dissolution of silicate minerals and precipitation of zeolitic phases. At 25 C, silicate dissolution is not significant except where smectite clays are involved. However, at this temperature CO{sub 2} uptake by the solution results in precipitation of Al(OH){sub 3} (bayerite). In these studies, radionuclide analogues (Cs, Se and Re--for Tc) were partially removed from the test solutions both during high-temperature fluid-soil interactions and during room temperature bayerite precipitation. Altered soils would permanently retain a fraction of the Cs but essentially all of the Se and Re would be released once the plume was past and normal groundwater came in contact with the contaminated soil. Bayerite, however, will retain significant amounts of all three radionuclides.

Ongoing hydrothermal Cs-Ti-Si-O-H2O phase investigations has produced several new ternary phases including a novel microporous Cs-silicotitanate molecular sieve, SNL-B with the approximate formula of Cs3TiSi3O9.5 · 3H2O SNL-B is only the second molecular sieve, Cs-silicotitanate phase reported to have been synthesized by hydrothermal methods. Crystallites are very small (0.1 x 2 μm2) with a blade-like morphology. SNL-B is confirmed to be a three-dimensional molecular sieve by a variety of characterization techniques (N2 adsorption, ion exchange, water adsorption/desorption, solid state cross polarization-magic angle spinning nuclear magnetic resonance). SNL-B is able to desorb and adsorb water from its pores while retaining its crystal structure and exchanges Cs cations readily. Additional techniques were used to describe fundamental properties (powder X-ray diffraction, FTIR, 29Si and 133Cs MAS NMR, DTA, SEM/EDS, ion selectivity, and radiation stability). The phase relationships of metastable SNL-B to other hydrothermally synthesized Cs-Ti-Si-O-H2O phases are discussed, particularly its relationship to a Cs-silicotitanate analogue of pharmacosiderite, and a novel condensed phase, a polymorph of Cs2TiSi6O15 (SNL-A). (C) 2000 Elsevier Science B.V. All rights reserved. Ongoing hydrothermal Cs-Ti-Si-O-H2O phase investigations has produced several new ternary phases including a novel microporous Cs-silicotitanate molecular sieve, SNL-B with the approximate formula of Cs3TiSi3O9.5·3H2O. SNL-B is only the second molecular sieve, Cs-silicotitanate phase reported to have been synthesized by hydrothermal methods. Crystallites are very small (0.1×2 μm2) with a blade-like morphology. SNL-B is confirmed to be a three-dimensional molecular sieve by a variety of characterization techniques (N2 adsorption, ion exchange, water adsorption/desorption, solid state cross polarization-magic angle spinning nuclear magnetic resonance). SNL-B is able to desorb and adsorb water from its pores while retaining its crystal structure and exchanges Cs cations readily. Additional techniques were used to describe fundamental properties (powder X-ray diffraction, FTIR, 29Si and 133Cs MAS NMR, DTA, SEM/EDS, ion selectivity, and radiation stability). The phase relationships of metastable SNL-B to other hydrothermally synthesized Cs-Ti-Si-O-H2O phases are discussed, particularly its relationship to a Cs-silicotitanate analogue of pharmacosiderite, and a novel condensed phase, a polymorph of Cs2TiSi6O15 (SNL-A).