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1

Structure-Directing Roles and Interactions of Fluoride and Organocations with Siliceous Zeolite Frameworks  

SciTech Connect

Interactions of fluoride anions and organocations with crystalline silicate frameworks are shown to depend subtly on the architectures of the organic species, which significantly influence the crystalline structures that result. One- and two-dimensional (2D) {sup 1}H, {sup 19}F, and {sup 29}Si nuclear magnetic resonance (NMR) spectroscopy measurements establish distinct intermolecular interactions among F{sup -} anions, imidazolium structure-directing agents (SDA{sup +}), and crystalline silicate frameworks for as-synthesized siliceous zeolites ITW and MTT. Different types and positions of hydrophobic alkyl ligands on the imidazolium SDA{sup +} species under otherwise identical zeolite synthesis compositions and conditions lead to significantly different interactions between the F{sup -} and SDA{sup +} ions and the respective silicate frameworks. For as-synthesized zeolite ITW, F{sup -} anions are established to reside in the double-four-ring (D4R) cages and interact strongly and selectively with D4R silicate framework sites, as manifested by their strong {sup 19}F{sup 29}Si dipolar couplings. By comparison, for as-synthesized zeolite MTT, F{sup -} anions reside within the 10-ring channels and interact relatively weakly with the silicate framework as ion pairs with the SDA{sup +} ions. Such differences manifest the importance of interactions between the imidazolium and F{sup -} ions, which account for their structure-directing influences on the topologies of the resulting silicate frameworks. Furthermore, 2D {sup 29}Si{l_brace}{sup 29}Si{r_brace} double-quantum NMR measurements establish {sup 29}Si-O-{sup 29}Si site connectivities within the as-synthesized zeolites ITW and MTT that, in conjunction with synchrotron X-ray diffraction analyses, establish insights on complicated order and disorder within their framework structures.

Shayib, Ramzy M.; George, Nathan C.; Seshadri, Ram; Burton, Allen W.; Zones, Stacey I.; Chmelka, Bradley F. (UCSB); (Chevron ETC)

2012-02-06

2

Crystalline Silicates in Circumstellar Dust Shells  

NASA Astrophysics Data System (ADS)

The discovery of crystalline silicates outside our own Solar System by the infrared space observatory (ISO) in both young (Waelkens et al. 1996, A&A 315, L245), and evolved stars (Waters et al. 1996, A&A 315, L361) brought new inside in the circumstellar dust formation and evolution. We will present here an extensive overview of the solid state bands found in a sample of 17 stars all with oxygen-rich dust around them. For all stars good ISO-SWS (short wavelength spectrometer 2--45 ? m) spectra were available and for 12 stars also reliable ISO-LWS (long wavelength spectrometer 43--195 ? m) spectra were taken. We could identify about 50 different spectral features, most of them clustered into one of the 7 complexes (which we defined). Most bands could be identified with crystalline silicates and crystalline water ice, however still roughly 20% remains unidentified. An important result was that the presence of strong crystalline silicates bands always correlates with the presence of a disk like structure (N.B. The presence of a disk does not necessary imply a high fraction of crystalline silicates)(Molster et al. 1999, Nature 401, 563). We found that not only the strength but also the shape of the crystalline silicate features is different for sources with and without the presence of a disk. Another surprising result of this research is that the crystalline silicates contain no measurable amount of Fe. The main minerals found, are forsterite (Mg2 SiO4) and enstatite (MgSiO3). We have calculated mean crystalline silicate spectra for both the disk and the non-disk sources. By simple model fitting we derived estimates for the (relative) mass and temperature of the amorphous silicates, forsterite and enstatite. Based on these results we drew the conclusion that the crystalline and amorphous silicate grains are two separate grain populations. This work was part of a PhD-thesis and funded by NWO.

Molster, F. J.; Waters, L. B. F. M.; Tielens, A. G. G. M.

2000-12-01

3

Transition metal-silicate analogs of zeolites  

Microsoft Academic Search

The synthesis and characterization of three transition metal (Fe3+, Ti4+ and V4+)-silicate molecular sieves are discussed. The key factors for a successful incorporation of these metal ions in the growing silicate network during gel preparation\\/hydrothermal synthesis (e.g. avoidance of insoluble\\/sparingly soluble metal hydroxides\\/oxyhydroxides (Fe3+ and Ti4+) and alkali metal ions (Ti4+and V4+\\/5+)) as well as the effects of post synthesis

Paul Ratnasamy; Rajiv Kumar

1993-01-01

4

Negative Poisson's ratios in siliceous zeolite MFI-silicalite  

NASA Astrophysics Data System (ADS)

Brillouin scattering measurements of the single-crystal elastic properties of the as-made zeolite silicalite |(C3H7)4NF|4[Si96O192]-MFI provides the first experimental evidence for on-axis negative Poisson's ratios (auxeticity) in a synthetic zeolite structure. MFI laterally contracts when compressed and laterally expands when stretched along x1 and x2 directions in the (001) plane (?12=-0.061, ?21=-0.051). The aggregate Poisson's ratio of MFI, although positive, has an anomalously low value ?=0.175(3) compared to other silicate materials. These results suggest that the template-free MFI-silicalite [Si96O192] might have potential applications as tunable sieve where molecular discriminating characteristics are adjusted by application of stress along specific axes.

Sanchez-Valle, Carmen; Lethbridge, Zoe A. D.; Sinogeikin, Stanislav V.; Williams, Jennifer J.; Walton, Richard I.; Evans, Kenneth E.; Bass, Jay D.

2008-05-01

5

Negative Poisson's ratios in siliceous zeolite MFI-silicalite.  

PubMed

Brillouin scattering measurements of the single-crystal elastic properties of the as-made zeolite silicalite mid R:(C(3)H(7))(4)NFmid R:(4)[Si(96)O(192)]-MFI provides the first experimental evidence for on-axis negative Poisson's ratios (auxeticity) in a synthetic zeolite structure. MFI laterally contracts when compressed and laterally expands when stretched along x(1) and x(2) directions in the (001) plane (nu(12)=-0.061, nu(21)=-0.051). The aggregate Poisson's ratio of MFI, although positive, has an anomalously low value nu=0.175(3) compared to other silicate materials. These results suggest that the template-free MFI-silicalite [Si(96)O(192)] might have potential applications as tunable sieve where molecular discriminating characteristics are adjusted by application of stress along specific axes. PMID:18532822

Sanchez-Valle, Carmen; Lethbridge, Zoe A D; Sinogeikin, Stanislav V; Williams, Jennifer J; Walton, Richard I; Evans, Kenneth E; Bass, Jay D

2008-05-14

6

Multipolar correlations between reactants in crystalline and semiamorphous zeolites  

SciTech Connect

The authors study the role of multipolar correlations in influencing the efficiency of reaction between a fixed target molecule and a diffusing coreactant in zeolites that exhibit both crystalline and semiamorphous structures. They focus on zeolite A and construct a geometrical model whose framework structure and attendant channel patterns have the same topology as the 26-hedral cavities of type I of this aluminosilicate. They consider reaction partners interacting via (attractiverepulsive) ion-ion, angle-averaged ion-dipole, and angle-averaged dipole-dipole potentials V(r), and by coupling the theory of finite Markov processes with a lattice version of the Debye-Smoluchowski theory of encounter-controlled reactions, they quantify the differences in the diffusion-controlled rate constant k/sub D/ for reactions taking place in crystalline regions of finite extent (rafts) versus those occurring in crystalline regions surrounded by an amorphous aluminosilicate structure. Calculations based on the model introduced in this paper suggest that much of the marked cation-exchange activity and catalytic activity of fully crystalline zeolites is already captured by semiamorphous zeolites containing raft structures having the spatial extent of those found in recent experimental work by Thomas and Bursill

Mandeville, J.B.; Golub, J.; Kozak, J.J.

1988-03-24

7

Amphiphilic organosilane-directed synthesis of crystalline zeolite with tunable mesoporosity  

Microsoft Academic Search

Zeolites are a family of crystalline aluminosilicate materials widely used as shape-selective catalysts, ion exchange materials, and adsorbents for organic compounds. In the present work, zeolites were synthesized by adding a rationally designed amphiphilic organosilane surfactant to conventional alkaline zeolite synthesis mixtures. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy

Minkee Choi; Hae Sung Cho; Rajendra Srivastava; Chithravel Venkatesan; Dae-Heung Choi; Ryong Ryoo

2006-01-01

8

Thermochemistry of amorphous and crystalline zirconium and hafnium silicates.  

NASA Astrophysics Data System (ADS)

Calorimetric investigation of amorphous and crystalline zirconium and hafnium silicates was performed as part of a research program on thermochemistry of alternative gate dielectrics. Amorphous hafnium and zirconium silicates with varying SiO2 content were synthesized by a sol-gel process. Crystalline zirconium and hafnium silicates (zircon and hafnon) were synthesized by solid state reaction at 1450 °C from amorphous gels and grown as single crystals from flux. High temperature oxide melt solution calorimetry in lead borate (2PbO.B2O3) solvent at 800 oC was used to measure drop solution enthalpies for amorphous and crystalline zirconium and hafnium silicates and corresponding oxides. Applying appropriate thermochemical cycles, formation enthalpy of crystalline ZrSiO4 (zircon) from binary oxides (baddeleite and quartz) at 298 K was calculated as -23 +/-2 kJ/mol and enthalpy difference between amorphous and crystalline zirconium silicate (vitrification enthalpy) was found to be 61 +/-3 kJ/mol. Crystallization onset temperatures of amorphous zirconium and hafnium silicates, as measured by differential scanning calorimetry (DSC), increased with silica content. The resulting crystalline phases, as characterized by X-ray diffraction (XRD), were tetragonal HfO2 and ZrO2. Critical crystallite size for tetragonal to monoclinic transformation of HfO2 in the gel was estimated as 6 +/-2 nm from XRD data Crystallization enthalpies per mole of hafnia and zirconia in gels decrease slightly together with crystallite size with increasing silica content, for example from -22 to -15 +/-1 kJ per mol of HfO2 crystallized at 740 and 1006 °C from silicates with 10 and 70 mol Applications of thermal analyses and solution calorimetry techniques together with first-principles density functional calculations to estimate interface and surface energies are discussed.

Ushakov, S.; Brown, C. E.; Navrotsky, Alexandra; Boatner, L. A.; Demkov, A. A.; Wang, C.; Nguyen, B.-Y.

2003-03-01

9

Partially Crystalline Silicate Dust in Protostellar Disks  

NASA Technical Reports Server (NTRS)

We examine the infrared emission of the Herbig Ae/Be stars and show that some possess characteristics indicative of partially crystalline grains similar to those seen in Beta Pictoris and some solar system comets.

Sitko, M. L.; Lynch, D. K.; Russell, R. W.; Hanner, M. S.; Grady, C. A.

1996-01-01

10

Application of thermodynamics to silicate crystalline solutions  

NASA Technical Reports Server (NTRS)

A review of thermodynamic relations is presented, describing Guggenheim's regular solution models, the simple mixture, the zeroth approximation, and the quasi-chemical model. The possibilities of retrieving useful thermodynamic quantities from phase equilibrium studies are discussed. Such quantities include the activity-composition relations and the free energy of mixing in crystalline solutions. Theory and results of the study of partitioning of elements in coexisting minerals are briefly reviewed. A thermodynamic study of the intercrystalline and intracrystalline ion exchange relations gives useful information on the thermodynamic behavior of the crystalline solutions involved. Such information is necessary for the solution of most petrogenic problems and for geothermometry. Thermodynamic quantities for tungstates (CaWO4-SrWO4) are calculated.

Saxena, S. K.

1972-01-01

11

Influence of silica and alumina source materials on the physicochemical characteristics of crystalline zeolite beta  

Microsoft Academic Search

The influence of different silica sources such as silica sol and fumed silica on the physochemcial characteristics of well crystalline zeolite beta was studied as a function of variation in alumina sources viz. sodium aluminate and aluminium isopropoxide. Furthermore, the effect of templating organocation source on the crystallization kinetics and characteristics of fully crystalline beta zeolite was also investigated. The

M. W. Kasture; P. S. Niphadkar; S. R. Kate; P. D. Godbole; K. R. Patil; G. M. Chaphekar; P. N. Joshi

2004-01-01

12

Aluminum coordination and active sites on aluminas, Y zeolites and pillared layered silicates  

SciTech Connect

Our work has been deployed in four directions, namely, (1) Study of the distribution of aluminum within three possible kinds of coordination shells: four-fold (IV), five-fold (V), and six-fold (VI), in aluminas and dealuminated zeolites by high-resolution solid state NMR or magic angle NMR. Besides the classical one pulse spectra, nutation spectra have been studied. (2) Study of the electron deficient sites by electron paramagnetic resonance (EPR) of probe molecules on aluminas and decationated zeolites. Electron deficient sites are considered as Lewis sites. (3) Study of the model isomerization reaction 1 butene {yields} 2 cis or trans butene on the aluminas characterized in 1 and 2. (4) Synthesis of a silicate lattice in which silicon has been partially replaced by aluminum. The chosen silicate is that of the zeolite (fibrous) sepiolite. It has been characterized as indicated in 1 and 2.

Fripiat, J.J.

1991-01-01

13

Aluminum coordination and active sites on aluminas, Y zeolites and pillared layered silicates  

SciTech Connect

This report covers the activity of the laboratory over 15 months, from June 1, 1990 until August 31, 1991. Our work has been deployed in four directions, namely, (1) Study of the distribution of aluminum within three possible kinds of coordination shells: four-fold (4), five-fold(5), and six-fold(6), in aluminas and dealuminated zeolites by high-resolution solid state NMR or MAS NMR. Besides the classical one pulse spectra, nutation spectra have been studied. (2) Study of the electron deficient sites by electron paramagnetic resonance (EPR) of probe molecules on aluminas and decationated zeolites. Electron deficient sites are considered as Lewis sites. (3) Study of the model isomerization reaction 1 butene {yields} 2 cis or trans butene on the aluminas characterized in (1) and (2). (4) Synthesis of a silicate lattice in which silicon has been partially replaced by aluminum. The chosen silicate is that of zeolitic (fibrous) sepiolite.

Fripiat, J.J.

1991-01-01

14

?-? interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets.  

PubMed

One of the challenges in material science has been to prepare macro- or mesoporous zeolite. Although examples of their synthesis exist, there is a need for a facile yet versatile approach to such hierarchical structures. Here we report a concept for designing a single quaternary ammonium head amphiphilic template with strong ordered self-assembling ability through ?-? stacking in hydrophobic side, which stabilizes the mesostructure to form single-crystalline mesostructured zeolite nanosheets. The concept is demonstrated for the formation of a new type of MFI (zeolite framework code by International Zeolite Association) nanosheets joined with a 90° rotational boundary, which results in a mesoporous zeolite with highly specific surface area even after calcination. Low binding energies for this self-assembling system are supported by a theoretical analysis. A geometrical matching between the arrangement of aromatic groups and the zeolitic framework is speculated for the formation of single-crystalline MFI nanosheets. PMID:24957696

Xu, Dongdong; Ma, Yanhang; Jing, Zhifeng; Han, Lu; Singh, Bhupendra; Feng, Ji; Shen, Xuefeng; Cao, Fenglei; Oleynikov, Peter; Sun, Huai; Terasaki, Osamu; Che, Shunai

2014-01-01

15

Topotactic conversion of ?-helix-layered silicate into AST-type zeolite through successive interlayer modifications.  

PubMed

AST-type zeolite with a plate morphology can be synthesized by topotactic conversion of a layered silicate (?-helix-layered silicate; HLS) by using N,N-dimethylpropionamide (DPA) to control the layer stacking of silicate layers and the subsequent interlayer condensation. Treatment of HLS twice with 1)?hydrochloric acid/ethanol and 2)?dimethylsulfoxide (DMSO) are needed to remove interlayer hydrated Na ions and tetramethylammonium (TMA) ions in intralayer cup-like cavities (intracavity TMA ions), both of which are introduced during the preparation of HLS. The utilization of an amide molecule is effective for the control of the stacking sequence of silicate layers. This method could be applicable to various layered silicates that cannot be topotactically converted into three-dimensional networks by simple interlayer condensation by judicious choice of amide molecules. PMID:24431158

Asakura, Yusuke; Takayama, Ryosuke; Shibue, Toshimichi; Kuroda, Kazuyuki

2014-02-10

16

Zeolites  

NASA Technical Reports Server (NTRS)

Zeolites are crystalline aluminosilicates that have complex framework structures. However, there are several features of zeolite crystals that make unequivocal structure determinations difficult. The acquisition of reliable structural information on zeolites is greatly facilitated by the availability of high-quality specimens. For structure determinations by conventional diffraction techniques, large single-crystal specimens are essential. Alternatively, structural determinations by powder profile refinement methods relax the constraints on crystal size, but still require materials with a high degree of crystalline perfection. Studies conducted at CAMMP (Center for Advanced Microgravity Materials Processing) have demonstrated that microgravity processing can produce larger crystal sizes and fewer structural defects relative to terrestrial crystal growth. Principal Investigator: Dr. Albert Sacco

1992-01-01

17

Experimental constraints on permeable gas transport in crystalline silicic magmas  

NASA Astrophysics Data System (ADS)

The gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs. Hence, clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir. Recent experimental studies have determined the gas permeabilities in crystal-free rhyolite and basalt. However, no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas. In this study, we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol% to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation. Size-controlled (100-meshed) corundum crystals were used as an analog of the phenocrysts in silicic magmas. Microstructural analyses using X-ray CT showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression, that is, an increase in the vesicularity. As long as the vesicularities of melt part in the crystal-free basis (melt vesicularity) were similar, no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities <68 vol%. The corundum showed a large contact angle with aqueous fluid as well as plagioclase and alkaline feldspar; this failed to induce the efficient heterogeneous nucleation and coalescence of bubbles on its surface. The gas permeabilities of all the run products were lower than the detection limits of the present analysis (the order of 10-16 m2) at melt vesicularities <68 vol%. These results show that silicic magmas containing 30 and 50 vol% phenocrysts with a large contact angle have low gas permeabilities until the vesicularity becomes large (at least >68 vol%). This result indicates that the permeable fluid transport through a deep volcanic conduit, which has been proposed on the basis of the observations of volcanic gases and natural products, is so slow that other processes, like shear deformation or magma convection, may be needed to explain the observations.

Okumura, Satoshi; Nakamura, Michihiko; Nakano, Tsukasa; Uesugi, Kentaro; Tsuchiyama, Akira

2012-09-01

18

Amphiphilic organosilane-directed synthesis of crystalline zeolite with tunable mesoporosity.  

PubMed

Zeolites are a family of crystalline aluminosilicate materials widely used as shape-selective catalysts, ion exchange materials, and adsorbents for organic compounds. In the present work, zeolites were synthesized by adding a rationally designed amphiphilic organosilane surfactant to conventional alkaline zeolite synthesis mixtures. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analyses show that the present method is suitable as a direct synthesis route to highly mesoporous zeolites. The mesopore diameters could be uniformly tailored, similar to ordered mesoporous silica with amorphous frameworks. The mesoporous zeolite exhibited a narrow, small-angle XRD peak, which is characteristic of the short-range correlation between mesopores, similar to disordered wormhole-like mesoporous materials. The XRD patterns and electron micrographs of the samples taken during crystallization clearly showed the evolution of the mesoporous structure concomitantly to the crystallization of zeolite frameworks. The synthesis of the crystalline aluminosilicate materials with tunable mesoporosity and strong acidity has potentially important technological implications for catalytic reactions of large molecules, whereas conventional mesoporous materials lack hydrothermal stability and acidity. PMID:16892049

Choi, Minkee; Cho, Hae Sung; Srivastava, Rajendra; Venkatesan, Chithravel; Choi, Dae-Heung; Ryoo, Ryong

2006-09-01

19

Calcium-aluminum-silicate-hydrate "cement" phases and rare Ca-zeolite association at Colle Fabbri, Central Italy  

NASA Astrophysics Data System (ADS)

Very high temperature, Ca-rich alkaline magma intruded an argillite formation at Colle Fabbri, Central Italy, producing cordierite-tridymite metamorphism in the country rocks. An intense Ba-rich sulphate-carbonate-alkaline hydrothermal plume produced a zone of mineralization several meters thick around the igneous body. Reaction of hydrothermal fluids with country rocks formed calcium-silicate-hydrate (CSH), i.e., tobermorite-afwillite-jennite; calcium-aluminum-silicate-hydrate (CASH) — "cement" phases - i.e., thaumasite, strätlingite and an ettringite-like phase and several different species of zeolites: chabazite-Ca, willhendersonite, gismon-dine, three phases bearing Ca with the same or perhaps lower symmetry of phillipsite-Ca, levyne-Ca and the Ca-rich analogue of merlinoite. In addition, apophyllite-(KF) and/or apophyllite-(KOH), Ca-Ba-carbonates, portlandite and sulphates were present. A new polymorph from the pyrrhotite group, containing three layers of sphalerite-type structure in the unit cell, is reported for the first time. Such a complex association is unique. Most of these minerals are specifically related to hydration processes of: (1) pyrometamorphic metacarbonate/metapelitic rocks (natural analogues of cement clinkers); (2) mineralization between intrusive stocks and slates; and (3) high-calcium, alkaline igneous rocks such as melilitites and foidites as well as carbonatites. The Colle Fabbri outcrop offers an opportunity to study in situ complex crystalline overgrowth and specific crystal chemistry in mineral phases formed in igneous to hydrothermal conditions.

Stoppa, F.; Scordari, F.; Mesto, E.; Sharygin, V. V.; Bortolozzi, G.

2010-06-01

20

Iron silicates, iron-modulated zeolite catalysts, and molecular models thereof.  

PubMed

Iron centres incorporated in silicate frameworks or located in their pores have been shown to possess unique catalytic properties. As compared to aluminosilicates this area of zeolite chemistry is much younger and in the first part of this review the findings made so far are summarised. Molecular model compounds may help to understand the formation, corrosion and reactivity of such materials or to even develop new ones. Hence, the subsequent parts deal with molecular iron siloxides, the number of which is still quite limited, and their behaviour also in relation to the iron-modified zeolites is outlined. At first, compounds based on an incompletely condensed cubic silsequioxane are discussed, before iron(III) complexes of more basic siloxide ligands with varying steric demands are described. Finally, recent developments based on branched polydentate siloxides are presented. PMID:24939619

Pinkert, Denise; Limberg, Christian

2014-07-21

21

Discrete Dipole Approximation Models of Crystalline Forsterite: Applications to Cometary Crystalline Silicates  

NASA Astrophysics Data System (ADS)

In cometary comae, the crystalline silicate forsterite (Mg2SiO4) is the dominant crystalline component. Within the 8 - 40 micron spectral range, the crystal shape has been demonstrated to have a measurable effect on the crystalline features’ shape and peak wavelength locations. We present discrete dipole approximation (DDA) absorption efficiencies for a variety of forsterite grain shapes to demonstrate: a) that the 10, 11, 19, 23, and 33.5 micron resonances are sensitive to grain shape; b) spectral trends are associated with variations in crystallographic axial ratios; and c) that groups of similar grain shapes (shape classes) have distinct spectral features. These computations are performed using DDSCAT v7.0 run on the NASA Advanced Supercomputing (NAS) facility Pleiades. We generate synthetic spectral energy distribution (SED) fits to the Infrared Space Observatory (ISO) SWS spectra for the coma of comet C/1995 O1 (Hale-Bopp) at a heliocentric distance of 2.8 AU. Hale-Bopp is best fit by equant grain shapes whereas rounded grain shapes fit significantly poorer than crystals with sharp edges with well-defined faces. Moreover, crystals that are not significantly elongated along a crystallographic axis fit better. By comparison with Kobatake et al. (2008) condensation experiments and Takigawa et al. (2009) evaporation experiments, our analyses suggest that the forsterite crystals in the coma of Hale-Bopp predominantly are high temperature condensates. The laboratory experiments show that grain shape and grain formation temperature, and hence disk environment, are causally linked. Specifically, the Kobatake et al. (2008) condensation experiment reveals three shape classes associated with temperature: 1) ‘Bulky’ grains (1300 K < T < 1700 K), 2) ‘Platy’ grains (1000 K < T < 1300 K), and 3) columnar/needle grains (T < 1000 K). We construct DDA grain shape analogs to these shape classes to connect grain shapes to distinguishable spectral signatures and crystal formation environments.

Lindsay, Sean; Wooden, D. H.; Woodward, C. E.; Harker, D. E.; Kelley, M. S.; Murphy, J. R.

2012-10-01

22

A SPITZER INFRARED SPECTROGRAPH DETECTION OF CRYSTALLINE SILICATES IN A PROTOSTELLAR ENVELOPE  

SciTech Connect

We present the Spitzer Space Telescope Infrared Spectrograph spectrum of the Orion A protostar HOPS-68. The mid-infrared spectrum reveals crystalline substructure at 11.1, 16.1, 18.8, 23.6, 27.9, and 33.6 {mu}m superimposed on the broad 9.7 and 18 {mu}m amorphous silicate features; the substructure is well matched by the presence of the olivine end-member forsterite (Mg{sub 2}SiO{sub 4}). Crystalline silicates are often observed as infrared emission features around the circumstellar disks of Herbig Ae/Be stars and T Tauri stars. However, this is the first unambiguous detection of crystalline silicate absorption in a cold, infalling, protostellar envelope. We estimate the crystalline mass fraction along the line of sight by first assuming that the crystalline silicates are located in a cold absorbing screen and secondly by utilizing radiative transfer models. The resulting crystalline mass fractions of 0.14 and 0.17, respectively, are significantly greater than the upper limit found in the interstellar medium ({approx}<0.02-0.05). We propose that the amorphous silicates were annealed within the hot inner disk and/or envelope regions and subsequently transported outward into the envelope by entrainment in a protostellar outflow.

Poteet, Charles A.; Megeath, S. Thomas; Fischer, William J.; Bjorkman, Jon E. [Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States); Watson, Dan M.; Remming, Ian S.; McClure, Melissa K. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Calvet, Nuria; Hartmann, Lee; Tobin, John J. [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Sargent, Benjamin A.; Muzerolle, James [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Furlan, Elise [Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 264723, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Allen, Lori E. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Ali, Babar, E-mail: charles.poteet@gmail.com [NHSC/IPAC, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States)

2011-06-01

23

[Aluminum coordination and active sites on aluminas, Y-zeolites and pillared layered silicates]. Progress report  

SciTech Connect

This report is organized in four sections. In the first the authors will outline structural features which are common to all fine grained alumina, as well as to non-framework alumina in zeolites. This section will be followed by a study of the surface vs. bulk coordination of aluminum. The third section will deal with measurement of the number of acid sites and the scaling of their strength. The fourth and last section will describe three model reactions: the isomerization of 1-butene and of 2 cis-butene; the isomerization and disproportionation of oxtho-xylene; and the transformation of trichloroethane into vinyl chloride followed by the polymerization of the vinyl chloride. The relationship between chemical activity and selectivity and what is known of the local structure of the active catalytic sites will be underlined. Other kinds of zeolites besides Y zeolite have been studied. Instead of the aluminum pillared silicates they found it more interesting to study the substitution of silicon by aluminum in a layered structure containing a permanent porosity (aluminated sepiolite).

Fripiat, J.J.

1994-02-01

24

Effects of additives and heat treatment on the pore size distribution in pelletized zeolite Y  

Microsoft Academic Search

Zeolite Y is a crystalline aluminum silicate used as an adsorbent matrix in the purification of proteins. Particle size enlargement is sometimes required and is achieved by compaction of the zeolite powder followed by heat treatment. To maintain a large surface area available for adsorption, additives are used in the pelletizing procedure. Ultrastable zeolite Y (USY) was compacted into pellets

Daniel Klint; Jan-Olov Bovin

1999-01-01

25

Aluminum coordination and active sites on aluminas, Y zeolites and pillared silicates  

SciTech Connect

Effort was continued to characterize the nature of the Al species responsible for Lewis acidity in zeolites and in aluminas by NMR. While numerous techniques have been successful for scaling the acid strength of Broensted sites, the situation is not satisfactory for the Lewis acid sites. Initial rate of dehydrochlorination of 1,1,1-trichloroethane is sensitive to strength of Lewis acid sites. N-Butene isomerization has been extended to the new aluminas obtained from nano-sized precursors. O-Xylene isomerization was carried out in a recirculation reactor on H-mordenite samples containing Lewis or Broensted acid sites; effects of H[sub 2] and NO were also investigated. Cracking of methylcyclohexane and 3-methylpentane was investigated by EPR on H-mordenite. Sepiolite, a Mg silicate with zeolitic channels, had Al substituted for Si; the negative charge is balanced by, say, VO[sup 2+]. Transformation of ethanol into butadiene on this dual-function catalyst appears to result from a Prins reaction between acetaldeyde formed on the redox sites and ethylene resulting from dehydration of ethanol on Lewis sites.

Fripiat, J.J.

1992-01-01

26

Cooked GEMS - Insights into the Hot Origins of Crystalline Silicates in Circumstellar Disks and the Cold Origins of GEMS  

NASA Technical Reports Server (NTRS)

The comparison of interstellar, circumstellar and primitive solar nebula silicates has led to a significant conundrum in the understanding of the nature of solid materials that begin the planet forming processes. Crystalline silicates are found in circumstellar regions around young stars and also evolved stars ejecting particles into the interstellar medium (ISM) but they are not seen in the interstellar medium itself, the source material for star and planet formation. Crystalline silicates are minor to major components of all known early solar system materials that have been examined as meteorites or interplanetary dust samples. The strong presence of Mg-rich crystalline silicates in Oort cloud comets and their minor presence in some Kuiper belt comets is also indicated by 11.2 m peak in approx. 10 microns "silicate" infrared feature. This evidence strongly indicates that Mg-rich crystalline silicates were abundant components of the solar nebula disk out to at least 10 AU, and present out to 30 AU.

Brownlee, D. E.; Joswiak, D. J.; Bradley, J. P.; Matrajt, G.; Wooden, D. H.

2005-01-01

27

Highly mesoporous single-crystalline zeolite beta synthesized using a nonsurfactant cationic polymer as a dual-function template.  

PubMed

Mesoporous zeolites are useful solid catalysts for conversion of bulky molecules because they offer fast mass transfer along with size and shape selectivity. We report here the successful synthesis of mesoporous aluminosilicate zeolite Beta from a commercial cationic polymer that acts as a dual-function template to generate zeolitic micropores and mesopores simultaneously. This is the first demonstration of a single nonsurfactant polymer acting as such a template. Using high-resolution electron microscopy and tomography, we discovered that the resulting material (Beta-MS) has abundant and highly interconnected mesopores. More importantly, we demonstrated using a three-dimensional electron diffraction technique that each Beta-MS particle is a single crystal, whereas most previously reported mesoporous zeolites are comprised of nanosized zeolitic grains with random orientations. The use of nonsurfactant templates is essential to gaining single-crystalline mesoporous zeolites. The single-crystalline nature endows Beta-MS with better hydrothermal stability compared with surfactant-derived mesoporous zeolite Beta. Beta-MS also exhibited remarkably higher catalytic activity than did conventional zeolite Beta in acid-catalyzed reactions involving large molecules. PMID:24450997

Zhu, Jie; Zhu, Yihan; Zhu, Liangkui; Rigutto, Marcello; van der Made, Alexander; Yang, Chengguang; Pan, Shuxiang; Wang, Liang; Zhu, Longfeng; Jin, Yinying; Sun, Qi; Wu, Qinming; Meng, Xiangju; Zhang, Daliang; Han, Yu; Li, Jixue; Chu, Yueying; Zheng, Anmin; Qiu, Shilun; Zheng, Xiaoming; Xiao, Feng-Shou

2014-02-12

28

CRYSTALLINE SILICATES IN EVOLVED STARS. I. SPITZER/INFRARED SPECTROGRAPH SPECTROSCOPY OF IRAS 16456-3542, 18354-0638, AND 23239+5754  

SciTech Connect

We report the Spitzer Infrared Spectrograph (IRS) observations of three evolved stars: IRAS 16456-3542, 18354-0638, and 23239+5754. The 9.9-37.2 {mu}m Spitzer/IRS high-resolution spectra of these three sources exhibit rich sets of enstatite-dominated crystalline silicate emission features. IRAS 16456-3542 is extremely rich in crystalline silicates, with >90% of its silicate mass in crystalline form, the highest to date ever reported for crystalline silicate sources.

Jiang, B. W.; Zhang, Ke [Department of Astronomy, Beijing Normal University, Beijing 100875 (China)] [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Li, Aigen [Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States)] [Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Lisse, C. M., E-mail: bjiang@bnu.edu.cn, E-mail: kzhang@caltech.edu, E-mail: lia@missouri.edu, E-mail: carey.lisse@jhuapl.edu [Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 (United States)

2013-03-01

29

Separation of Closely Related Systems by Molecular Sieve Zeolites  

Microsoft Academic Search

Molecular sieve zeolites are robust, thermally stable selective absorbents. They are chemically pure crystalline aluminosilicates with up to 50% of their crystal volume available for adsorption. Zeolites are widely used for industrial drying, purification, and separation, as well as catalysts and ion exchangers. They can be synthesized, on a plant scale, from silica (or sodium silicate) and sodium aluminate. The

A. Dyer

1978-01-01

30

Post-synthesis treatment gives highly stable siliceous zeolites through the isomorphous substitution of silicon for germanium in germanosilicates.  

PubMed

Germanosilicates, an important family of zeolites with increasing number of members and attractive porosities, but containing a large quantity of unstable Ge atoms in the framework, meet with great obstacles in terms of limited thermal and hydrothermal stability when it comes to practical use. A facile stabilization method thus has been developed to substitute isomorphously Ge atoms for Si atoms, giving rise to ultrastable siliceous analogues of the pristine germanosilicates. PMID:24375782

Xu, Hao; Jiang, Jin-Gang; Yang, Boting; Zhang, Lin; He, Mingyuan; Wu, Peng

2014-01-27

31

Discrete dipole approximation models of chrystalline forsterite: Applications to cometary crystalline silicates  

NASA Astrophysics Data System (ADS)

The shape, size, and composition of crystalline silicates observed in comet comae and external proto-planetary disks are indicative of the formation and evolution of the dust grains during the processes of planetary formation. In this dissertation, I present the 3 -- 40 mum absorption efficiencies( Qabs) of irregularly shaped forsterite crystals computed with the discrete dipole approximation (DDA) code DDSCAT developed by Draine and Flatau and run on the NASA Advanced Supercomputing facility Pleiades. An investigation of grain shapes ranging from spheroidal to irregular indicate that the strong spectral features from forsterite are sensitive to grain shape and are potentially degenerate with the effects of crystal solid state composition (Mg-content). The 10, 11, 18, 23, and 33.5 mum features are found to be the most crystal shape sensitive and should be avoided in determining Mg-content. The distinct spectral features for the three shape classes are connected with crystal formation environment using a condensation experiment by (Kobatake et al., 2008). The condensation experiment demonstrates that condensed forsterite crystal shapes are dependent on the condensation environmental temperature. I generate DDSCAT target analog shapes to the condensed crystal shapes. These analog shapes are represented by the three shape classes: 1) equant, 2) a, c-columns, and 3) b-shortened platelets. Each of these shape classes exhibit distinct spectral features that can be used to interpret grain shape characteristics from 8 --- 40 mum spectroscopy of astronomical objects containing crystalline silicates. Synthetic spectral energy distributions (SEDs) of the coma of Hale-Bopp at rh = 2.8 AU are generated by thermally modeling the flux contributions of 5 mineral species present in comets. The synthetic SEDs are constrained using a chi2- minimization technique. The mineral species are amorphous carbon, amorphous pyroxene, amorphous olivine, crystalline enstatite, and crystalline forsterite. Using the DDSCAT computed absorption efficiencies for a large variety of forsterite crystal shapes, which are computed for 66 grain sizes between 0.1 -- 5.0 mum, the flux contribution of irregularly shaped forsterite is computed. The forsterite flux contribution is then summed with the amorphous and crystalline enstatite contributions to generate the total synthetic SED. The DDSCAT forsterite grain shape synthetic SEDs reveal that the crystalline silicates in the coma of Hale-Bopp are irregular in shape with two distinct shape characteristics related to specific formation mechanisms: 1) equant grains with sharp ( ? 90°) angles between the faces, edges, and vertices that formed as high temperature condensates in the inner 1 -- 3 AU radial region of the Solar System's protoplanetary disk; and 2) c-shortened platelet shapes that likely formed from collisional processing of the crystals. The 8 -- 40 mum silicate spectral features of Hale-Bopp's coma are compared to the silicate spectral features of the comae of 17P/Holmes during 2007 outburst and 9P/Tempel 1 during the Deep Impact experiment to show that the silicate features with crystalline resonances are remarkably similar. The similarity in silicate spectral features suggests that the grain populations in the comae of these comets are similar in shape, size, and compositon. However, Hale-Bopp is a nearly isotropic comet (NIC) that dynamically came from the Oort cloud, and 17P and 9P are ecliptic comets (ECs) that dynamically came from the Scattered Disk. The different dynamical source regions yet similar silicate (amorphous and crystalline) grain populations suggest that ECs and NICs innately have similar grains and that the typically weaker silicate features of ECs are an effect of the surface grains becoming compacted with numerous perihelion passages. Hence, the differences in silicate between ECs and NICs are the result of grain structure and not grain composition. (Abstract shortened by UMI.)

Lindsay, Sean Stephen

32

Zeolites.  

National Technical Information Service (NTIS)

Zeolites are naturally occurring aluminosilicate minerals. They have 3- dimensional framework structures of interconnected channels and cages that contain exchangeable alkali and alkaline earth cations and adsorbed water. Like phyllosilicates, zeolites ha...

D. W. Ming J. L. Boettinger

2001-01-01

33

High Silicate Crystalline-to-Amorphous Ratios in Comets C/2001 Q4 (NEAT) and Hale-Bopp  

NASA Technical Reports Server (NTRS)

Crystalline silicates, by their apparent absence in the ISM, are dust grains that experienced high temperatures in the solar nebula. Mg-rich crystalline silicates formed either by condensation from hot nebular gases (1450 K) or by the annealing of Mg-rich amorphous silicates (approximately 1000 K) in shocks in the 5-10AU region or by radial transport into and out of the hot inner zones, e.g., T(sub d) greater than 1000K at r(sub h) less than 5AU, 10(exp -6) -10(exp -5) solar mass per year, alpha = 10(exp -4) of the early solar nebula. Mg-rich crystalline silicates are found in interplanetary dust particles (IDPs) and produce IR spectral features in many Oort cloud comets. In May 2004, we discovered strong crystalline silicate features in the dynamically new Oort cloud comet C/2001 Q4 (NEAT). Thermal emission modeling of comets Q4 and C/1995 O1 (Hale-Bopp) demonstrate that both these comets have similar, high silicate crystalline-toamorphous ratios of 2.4 and 2.1, respectively, indicating that these icy planetesimals aggregated from similar reservoirs of material or that crystalline silicates were widely distributed within the comet-forming zone. This argues for efficient annealing mechanisms and radial mixing.

Wooden, D. H.; Harker, D. E.; Wodward, C. E.

2004-01-01

34

Dust in the Wind: Crystalline Silicates, Corundum, and Periclase in PG 2112+059  

NASA Astrophysics Data System (ADS)

We have determined the mineralogical composition of dust in the broad absorption line (BAL) quasar PG 2112+059 using mid-infrared spectroscopy obtained with the Spitzer Space Telescope. From spectral fitting of the solid state features, we find evidence for Mg-rich amorphous silicates with olivine stoichiometry, as well as the first detection of corundum (Al 2O3) and periclase (MgO) in quasars. This mixed composition provides the first direct evidence for a clumpy density structure of the grain-forming region. The silicates in total encompass 56.5% +/- 1.4% of the identified dust mass, while corundum takes up 38+/-3 wt.%. Depending on the choice of continuum, a range of mass fractions is observed for periclase ranging from 2.7% +/- 1.7% in the most conservative case to 9% +/- 2% in a less-constrained continuum. In addition, we identify a feature at 11.2 ?m as the crystalline silicate forsterite, with only a minor contribution from polycyclic aromatic hydrocarbons. The 5% +/- 3% crystalline silicate fraction requires high temperatures such as those found in the immediate quasar environment in order to counteract rapid destruction from cosmic rays.

Markwick-Kemper, F.; Gallagher, S. C.; Hines, D. C.; Bouwman, J.

2007-10-01

35

Pharmacokinetic Study of Zeolite A, Sodium Aluminosilicate, Magnesium Silicate, and Aluminum Hydroxide in Dogs  

Microsoft Academic Search

Zeolite A is a synthetic zeolite which may have therapeutic utility in osteoporotic individuals because of its ability to stimulate bone formation. A study of Zeolite A (30 mg\\/kg), sodium aluminosilicate (16 mg\\/kg), magnesium trisilicate (20 mg\\/kg), and aluminum hydroxide (675 mg) was designed in beagle dogs. The purpose of this study was to compare the oral bioavailability of silicon

Eugenio A. Cefali; Joseph C. Nolan; William R. McConnell; Denise Lowe Walters

1995-01-01

36

IRAS 09425-6040: A carbon star surrounded by highly crystalline silicate dust  

NASA Astrophysics Data System (ADS)

We present infrared spectroscopy and millimeter photometry and spectroscopy of the peculiar carbon star IRAS 09425-6040. The 2-15 mu m spectrum, as well as the CO millimeter line observations are typical for a (J-type) carbon star with moderate mass-loss rate. The 15-45 mu m spectrum is dominated by strong emission bands from Mg-rich and Fe-poor crystalline silicates. IRAS 09425-6040 has the highest abundance of crystalline silicates (75 per cent) observed in any source so far. The ISO data, combined with IRAS and millimeter wavelength photometry indicate the presence of large cold grains. The observations indicate that the carbon star IRAS 09425-6040 is surrounded by a stationary, massive, highly crystalline oxygen-rich dust disk which is depleted of gas. These properties are very similar to those of the disk seen in the Red Rectangle. We propose that IRAS 09425-6040 is the evolutionary progenitor of the central binary of the Red Rectangle nebula.

Molster, F. J.; Yamamura, I.; Waters, L. B. F.; Nyman, L.-Å.; Käufl, H.-U.; de Jong, T.; Loup, C.

2001-02-01

37

On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants  

NASA Astrophysics Data System (ADS)

We investigate the occurrence of crystalline silicates in oxygen-rich evolved stars across a range of metallicities and mass-loss rates. It has been suggested that the crystalline silicate feature strength increases with increasing mass-loss rate, implying a correlation between lattice structure and wind density. To test this, we analyse Spitzer Infrared Spectrograph and Infrared Space Observatory Short Wavelength Spectrometer spectra of 217 oxygen-rich asymptotic giant branch and 98 red supergiants in the Milky Way, the Large and Small Magellanic Clouds, and Galactic globular clusters. These encompass a range of spectral morphologies from the spectrally rich which exhibit a wealth of crystalline and amorphous silicate features to 'naked' (dust-free) stars. We combine spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates and temperature. We then measure the strength of the crystalline silicate bands at 23, 28 and 33 ?m. We detect crystalline silicates in stars with dust mass-loss rates which span over 3 dex, down to rates of ˜10-9 M? yr-1. Detections of crystalline silicates are more prevalent in higher mass-loss rate objects, though the highest mass-loss rate objects do not show the 23-?m feature, possibly due to the low temperature of the forsterite grains or it may indicate that the 23-?m band is going into absorption due to high column density. Furthermore, we detect a change in the crystalline silicate mineralogy with metallicity, with enstatite seen increasingly at low metallicity.

Jones, O. C.; Kemper, F.; Sargent, B. A.; McDonald, I.; Gielen, C.; Woods, Paul M.; Sloan, G. C.; Boyer, M. L.; Zijlstra, A. A.; Clayton, G. C.; Kraemer, K. E.; Srinivasan, S.; Ruffle, P. M. E.

2012-12-01

38

Pure, single phase, high crystalline, chamfered-edge zeolite 4A synthesized from coal fly ash for use as a builder in detergents  

Microsoft Academic Search

Single phase chamfered-edge zeolite 4A samples in pure form with a high crystallinity were synthesized by applying step-change of synthesis temperature during hydrothermal treatment of coal fly ash. The calcium binding capacity of these zeolite 4A samples (prepared from coal fly ash) and the commercial detergent grade zeolite 4A were tested for usage as a detergent builder. The results show

K. S. Hui; C. Y. H. Chao

2006-01-01

39

Synthesis of zeolites using highly amphiphilic cations as organic structure-directing agents by hydrothermal treatment of a dense silicate gel.  

PubMed

Silicalite-1 and siliceous *MRE zeolite were synthesized with a series of highly amphiphilic ammonium cations as organic SDAs. The relationship between the framework type and the chain length of the amphiphilic cation is explained in terms of the intermolecular N-N distance of the elongated SDA. PMID:24343560

Moteki, Takahiko; Keoh, Sye Hoe; Okubo, Tatsuya

2014-02-01

40

Aluminum coordination and active sites on aluminas, Y zeolites and pillared layered silicates. Progress report, June 1, 1990--January 31, 1992  

SciTech Connect

Our work has been deployed in four directions, namely, (1) Study of the distribution of aluminum within three possible kinds of coordination shells: four-fold (IV), five-fold (V), and six-fold (VI), in aluminas and dealuminated zeolites by high-resolution solid state NMR or magic angle NMR. Besides the classical one pulse spectra, nutation spectra have been studied. (2) Study of the electron deficient sites by electron paramagnetic resonance (EPR) of probe molecules on aluminas and decationated zeolites. Electron deficient sites are considered as Lewis sites. (3) Study of the model isomerization reaction 1 butene {yields} 2 cis or trans butene on the aluminas characterized in 1 and 2. (4) Synthesis of a silicate lattice in which silicon has been partially replaced by aluminum. The chosen silicate is that of the zeolite (fibrous) sepiolite. It has been characterized as indicated in 1 and 2.

Fripiat, J.J.

1991-12-31

41

Aluminum coordination and active sites on aluminas, Y zeolites and pillared layered silicates. Progress report, June 1, 1990--August 31, 1991  

SciTech Connect

This report covers the activity of the laboratory over 15 months, from June 1, 1990 until August 31, 1991. Our work has been deployed in four directions, namely, (1) Study of the distribution of aluminum within three possible kinds of coordination shells: four-fold (4), five-fold(5), and six-fold(6), in aluminas and dealuminated zeolites by high-resolution solid state NMR or MAS NMR. Besides the classical one pulse spectra, nutation spectra have been studied. (2) Study of the electron deficient sites by electron paramagnetic resonance (EPR) of probe molecules on aluminas and decationated zeolites. Electron deficient sites are considered as Lewis sites. (3) Study of the model isomerization reaction 1 butene {yields} 2 cis or trans butene on the aluminas characterized in (1) and (2). (4) Synthesis of a silicate lattice in which silicon has been partially replaced by aluminum. The chosen silicate is that of zeolitic (fibrous) sepiolite.

Fripiat, J.J.

1991-12-31

42

Pharmacokinetic study of zeolite A, sodium aluminosilicate, magnesium silicate, and aluminum hydroxide in dogs.  

PubMed

Zeolite A is a synthetic zeolite which may have therapeutic utility in osteoporotic individuals because of its ability to stimulate bone formation. A study of Zeolite A (30 mg/kg), sodium aluminosilicate (16 mg/kg), magnesium trisilicate (20 mg/kg), and aluminum hydroxide (675 mg) was designed in beagle dogs. The purpose of this study was to compare the oral bioavailability of silicon and aluminum from Zeolite A, sodium aluminosilicate, magnesium trisilicate, and aluminum hydroxide in dogs. Twelve female dogs received each compound as a single dose separated by one week in a randomized, 4-way, crossover design. Plasma samples were drawn at time 0 and for 24 hours after dosing. The concentrations of silicon and aluminum were determined by graphite furnace atomic absorption. The mean plasma silicon AUC values (+/- S.D.) were 9.5 +/- 4.5, 7.7 +/- 1.6, 8.8 +/- 3.0, 6.1 +/- 1.9 mg.hr/L and the mean plasma silicon Cmax values (+/- S.D.) were 1.07 +/- 1.06, 0.67 +/- 0.27, 0.75 +/- 0.31, 0.44 +/- 0.17 mg/L for Zeolite A, sodium aluminosilicate, magnesium trisilicate, and aluminum hydroxide respectively. Although mean silicon AUC and Cmax values were elevated when compared to baseline after administration of the silicon containing compounds, only the AUC from Zeolite A reached statistical significance (p = 0.041). The mean plasma silicon Tmax values (+/- S.D.) were 7.9 +/- 6.4, 5.8 +/- 4.6, 6.9 +/- 6.3 and 8.5 +/- 3.4 hrs for Zeolite A, sodium aluminosilicate, magnesium trisilicate and aluminum Hydroxide respectively.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7784344

Cefali, E A; Nolan, J C; McConnell, W R; Walters, D L

1995-02-01

43

Zeolite materials prepared using silicate waste from template synthesis of ordered mesoporous carbon.  

PubMed

Significant amount of silica waste is generated in the preparation of porous carbon materials using template synthesis. Industrial production of such porous carbon not only creates waste chemicals, but also poses significant environmental concerns and high waste treatment cost. Recycling is proposed as the best solution for tackling such chemical wastes. In this study, etched silica waste released from template synthesis of mesoporous carbon is recycled to produce precious functional microporous zeolite materials. The solid silica template is etched out with NaOH solution to produce silica-free mesoporous carbon. The collected silica waste is recycled to generate zeolites such as LTA and MFI type silica materials. The formation of zeolites is confirmed by FT-IR, XRD, (29)Si NMR, (27)Al NMR, and SEM. This straight forward green chemistry route not only recycles the waste chemicals, but also decreases environmental pollution for better improvement of our living. PMID:23792927

Kim, Yun Kyung; Rajesh, Kizhakke Palleeri; Yu, Jong-Sung

2013-09-15

44

Crystalline Silicates in Comets: Modeling Irregularly-Shaped Forsterite Crystals and Its Implications on Condensation Conditions  

NASA Technical Reports Server (NTRS)

Crystalline silicates in comets are a product of the condensation in the hot inner regions (T > or approx. equals 1400 K [1]) of our proto-planetary disk or annealing at somewhat lower temperatures (T > or approx. equals 1000-1200 K) [2, 3, 4] in shocks coupled with disk evolutionary processes that include radial transport of crystals from their formation locations out to the cold outer regions where comet nuclei formed. The grain shape of forsterite (crystals) could be indicative of their formation pathways at high temperatures through vapor-solid condensation or at lower temperatures through vapor-liquid-solid formation and growth [5, 6, 7]. Experiments demonstrate that crystals that formed from a rapidly cooled highly supersaturated silicate vapor are characterized by bulky, platy, columnar/needle and droplet shapes for values of temperature and supersaturation, T and sigma, of 1000-1450 C and < 97, 700-1000 C and 97-161, 580-820 C and 131-230, and <500 C and > 230, respectively [7]. The experimental columnar/needle shapes, which form by vapor-liquid-solid at lower temperatures (<820 C), are extended stacks of plates, where the extension is not correlated with an axial direction: columnar/needles may be extended in the c-axis or a-axis direction, can change directions, and/or are off-kilter or a bit askew extending in a combination of the a- and c-axis direction.

Wooden, Diane H.; Lindsay, Sean S.

2011-01-01

45

Aluminum coordination and active sites on aluminas, Y zeolites and pillared silicates. Progress report, January 31, 1992--January 31, 1993  

SciTech Connect

Effort was continued to characterize the nature of the Al species responsible for Lewis acidity in zeolites and in aluminas by NMR. While numerous techniques have been successful for scaling the acid strength of Broensted sites, the situation is not satisfactory for the Lewis acid sites. Initial rate of dehydrochlorination of 1,1,1-trichloroethane is sensitive to strength of Lewis acid sites. N-Butene isomerization has been extended to the new aluminas obtained from nano-sized precursors. O-Xylene isomerization was carried out in a recirculation reactor on H-mordenite samples containing Lewis or Broensted acid sites; effects of H{sub 2} and NO were also investigated. Cracking of methylcyclohexane and 3-methylpentane was investigated by EPR on H-mordenite. Sepiolite, a Mg silicate with zeolitic channels, had Al substituted for Si; the negative charge is balanced by, say, VO{sup 2+}. Transformation of ethanol into butadiene on this dual-function catalyst appears to result from a Prins reaction between acetaldeyde formed on the redox sites and ethylene resulting from dehydration of ethanol on Lewis sites.

Fripiat, J.J.

1992-12-31

46

Discrimination of zeolites and beryllium containing silicates using portable Raman spectroscometric equipment with near-infrared excitation.  

PubMed

In this paper Raman spectra were obtained for a series of zeolites (thomsonite, stilbite, natrolite) and beryllium containing silicates (beryl, chrysoberyl, euclase, phenacite, bavenite, milarite) using a portable Raman specrometer with a 785 nm laser excitation to show the possibility to apply this setting for unambiguous detection and discrimination of these silicate minerals. Obtained spectra contain the most intense Raman bands at the same positions ±2-4 cm(-1) as reported in the literature. The use of these bands permits the unambiguous identification of these phases. Data show the possibility to discriminate individual species of similar whitish color and aspect. Measurements showed an excellent correspondence of Raman bands obtained using the portable system and a laboratory Raman microspectrometer (with the same excitation laser wavelenght). However, for several minerals of these groups (chrysoberyl, bertrandite, chiavennite) Raman spectra were not of sufficient quality to permit unambiguous identification. The reasons are discussed. Raman spectrum of chiavennite CaMnBe(2)Si(5)O(13)(OH)(2)·2(H(2)O) - a transformation product occurring together with bavenite on the surface of beryl crystals was obtained for the first time using the laboratory Raman spectrometer. PMID:22099060

Jehli?ka, J; Vandenabeele, P; Edwards, H G M

2012-02-01

47

Petrologic Constraints on Amorphous and Crystalline Magnesium Silicates: Dust Formation and Evolution in Selected Herbig Ae/Be Systems  

NASA Astrophysics Data System (ADS)

The Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory surveys provided a wealth of data on the Mg-silicate minerals (forsterite, enstatite), silica, and "amorphous silicates with olivine and pyroxene stoichiometry" around Herbig Ae/Be stars. These incredible findings do not resonate with the mainstream Earth Sciences because of (1) disconnecting "astronomical nomenclature" and the long existing mineralogical and petrologic terminology of minerals and amorphous materials, and (2) the fact that Earth scientists (formerly geologists) are bound by the "Principle of Actualism" that was put forward by James Hutton (1726-1797). This principle takes a process-oriented approach to understanding mineral and rock formation and evolution. This paper will (1) review and summarize the results of laboratory-based vapor phase condensation and thermal annealing experiments, (2) present the pathways of magnesiosilica condensates to Mg-silicate mineral (forsterite, enstatite) formation and processing, and (3) present mineralogical and petrologic implications of the properties and compositions of the infrared-observed crystalline and amorphous dust for the state of circumstellar disk evolution. That is, the IR-observation of smectite layer silicates in HD142527 suggests the break-up of asteroid-like parent bodies that had experienced aqueous alteration. We discuss the persistence of amorphous dust around some young stars and an ultrafast amorphous to crystalline dust transition in HD 163296 that leads to forsterite grains with numerous silica inclusions. These dust evolution processes to form forsterite, enstatite ± tridymite could occur due to amorphous magnesiosilica dust precursors with a serpentine- or smectite-dehydroxylate composition.

Rietmeijer, Frans J. M.; Nuth, Joseph A.

2013-07-01

48

PETROLOGIC CONSTRAINTS ON AMORPHOUS AND CRYSTALLINE MAGNESIUM SILICATES: DUST FORMATION AND EVOLUTION IN SELECTED HERBIG Ae/Be SYSTEMS  

SciTech Connect

The Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory surveys provided a wealth of data on the Mg-silicate minerals (forsterite, enstatite), silica, and ''amorphous silicates with olivine and pyroxene stoichiometry'' around Herbig Ae/Be stars. These incredible findings do not resonate with the mainstream Earth Sciences because of (1) disconnecting ''astronomical nomenclature'' and the long existing mineralogical and petrologic terminology of minerals and amorphous materials, and (2) the fact that Earth scientists (formerly geologists) are bound by the ''Principle of Actualism'' that was put forward by James Hutton (1726-1797). This principle takes a process-oriented approach to understanding mineral and rock formation and evolution. This paper will (1) review and summarize the results of laboratory-based vapor phase condensation and thermal annealing experiments, (2) present the pathways of magnesiosilica condensates to Mg-silicate mineral (forsterite, enstatite) formation and processing, and (3) present mineralogical and petrologic implications of the properties and compositions of the infrared-observed crystalline and amorphous dust for the state of circumstellar disk evolution. That is, the IR-observation of smectite layer silicates in HD142527 suggests the break-up of asteroid-like parent bodies that had experienced aqueous alteration. We discuss the persistence of amorphous dust around some young stars and an ultrafast amorphous to crystalline dust transition in HD 163296 that leads to forsterite grains with numerous silica inclusions. These dust evolution processes to form forsterite, enstatite {+-} tridymite could occur due to amorphous magnesiosilica dust precursors with a serpentine- or smectite-dehydroxylate composition.

Rietmeijer, Frans J. M. [Department of Earth and Planetary Sciences, MSC 03 2040, 1-University of New Mexico, Albuquerque, NM 87131-001 (United States); Nuth, Joseph A., E-mail: fransjmr@unm.edu [Astrochemistry Laboratory, Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2013-07-01

49

Zeolitic alteration and fracture fillings in silicic tuffs at a potential nuclear waste repository, Yucca Mountain, Nevada, USA  

SciTech Connect

This paper describes the distribution and chemistry of zeolites in tuffs and in fractures at Yucca Mountain. Samples used in this study were collected from continuously-cored exploratory drill holes. A variety of analytical techniques, including optical petrography, x-ray powder diffraction, electron microanalysis, and x-ray fluorescence, were used to characterize the distribution and chemistry of zeolites in these samples.

Broxton, D.E.; Carlos, B.A.

1986-12-31

50

Zeolite matrices for pigments  

Microsoft Academic Search

Intracrystalline voids in zeolites and other crystalline molecular sieves are suitable for accommodation and stabilization of certain chromophors. Our method of ultramarine synthesis comprises a generation of the anion radicals S3? from precursors (sodium polysulfides) introduced into zeolites. The color of the resulting ultramarine was modified by introduction of various cations into the parent zeolites. Using of polysulfides combined with

S. Kowalak; M. Wróbel; N. Gol?ebniak; A. Jankowska; B. Turkot

1999-01-01

51

Synthesis strategies in the search for hierarchical zeolites.  

PubMed

Great interest has arisen in the past years in the development of hierarchical zeolites, having at least two levels of porosities. Hierarchical zeolites show an enhanced accessibility, leading to improved catalytic activity in reactions suffering from steric and/or diffusional limitations. Moreover, the secondary porosity offers an ideal space for the deposition of additional active phases and for functionalization with organic moieties. However, the secondary surface represents a discontinuity of the crystalline framework, with a low connectivity and a high concentration of silanols. Consequently, hierarchical zeolites exhibit a less "zeolitic behaviour" than conventional ones in terms of acidity, hydrophobic/hydrophilic character, confinement effects, shape-selectivity and hydrothermal stability. Nevertheless, this secondary surface is far from being amorphous, which provides hierarchical zeolites with a set of novel features. A wide variety of innovative strategies have been developed for generating a secondary porosity in zeolites. In the present review, the different synthetic routes leading to hierarchical zeolites have been classified into five categories: removal of framework atoms, surfactant-assisted procedures, hard-templating, zeolitization of preformed solids and organosilane-based methods. Significant advances have been achieved recently in several of these alternatives. These include desilication, due to its versatility, dual templating with polyquaternary ammonium surfactants and framework reorganization by treatment with surfactant-containing basic solutions. In the last two cases, the materials so prepared show both mesoscopic ordering and zeolitic lattice planes. Likewise, interesting results have been obtained with the incorporation of different types of organosilanes into the zeolite crystallization gels, taking advantage of their high affinity for silicate and aluminosilicate species. Crystallization of organofunctionalized species favours the formation of organic-inorganic composites that, upon calcination, are transformed into hierarchical zeolites. However, in spite of this impressive progress in novel strategies for the preparation of hierarchical zeolites, significant challenges are still ahead. The overall one is the development of methods that are versatile in terms of zeolite structures and compositions, capable of tuning the secondary porosity properties, and being scaled up in a cost-effective way. Recent works have demonstrated that it is possible to scale-up easily the synthesis of hierarchical zeolites by desilication. Economic aspects may become a significant bottleneck for the commercial application of hierarchical zeolites since most of the synthesis strategies so far developed imply the use of more expensive procedures and reagents compared to conventional zeolites. Nevertheless, the use of hierarchical zeolites as efficient catalysts for the production of high value-added compounds could greatly compensate these increased manufacturing costs. PMID:23138888

Serrano, D P; Escola, J M; Pizarro, P

2013-05-01

52

Quantifying defects in zeolites and zeolite membranes  

NASA Astrophysics Data System (ADS)

Zeolites are crystalline aluminosilicates that are frequently used as catalysts to transform chemical feedstocks into more useful materials in a size- or shape-selective fashion; they are one of the earliest forms of nanotechnology. Zeolites can also be used, especially in the form of zeolite membranes (layers of zeolite on a support), to separate mixtures based on the size of the molecules. Recent advances have also created the possibility of using zeolites as alkaline catalysts, in addition to their traditional applications as acid catalysts and catalytic supports. Transport and catalysis in zeolites are greatly affected by physical and chemical defects. Such defects can be undesirable (in the case of zeolite membranes), or desirable (in the case of nitrogen-doped alkaline zeolites). Studying zeolites at the relevant length scales requires indirect experimental methods such as vapor adsorption or atomic-scale modeling such as electronic structure calculations. This dissertation explores both experimental and theoretical characterization of zeolites and zeolite membranes. Physical defects, important in membrane permeation, are studied using physical adsorption experiments and models of membrane transport. The results indicate that zeolite membranes can be modeled as a zeolite powder on top of a support---a "supported powder," so to speak---for the purposes of adsorption. Mesoporosity that might be expected based on permeation and confocal microscopy measurements is not observed. Chemical defects---substitutions of nitrogen for oxygen---are studied using quantum mechanical models that predict spectroscopic properties. These models provide a method for simulating the 29Si NMR spectra of nitrogendefected zeolites. They also demonstrate that nitrogen substitutes into the zeolite framework (not just on the surface) under the proper reaction conditions. The results of these studies will be valuable to experimentalists and theorists alike in our efforts to understand the versatile and complicated materials that are zeolites.

Hammond, Karl Daniel

53

Permeability Change of Crystalline Silicate Mineral-Packed Bed Column by Highly Alkaline Plume  

SciTech Connect

For the construction of the geological disposal system, the use of the cementitious material may change the permeability of the natural barrier around the repository. Cementitious materials may alter the pH of ground water to highly alkaline. Also, the potential permeability change of the natural barrier is one of the notable factors for performance assessments of geological disposal systems. In the high pH region, the solubility of silica is very high compared to that in the natural pH (around 8). Therefore, highly alkaline groundwater would dissolve and alter a part of rock surface. Usui et al. (2005) reported that the change of mineral pore structure due to chemical reaction is the key factor to consider the change of the permeability [5-6]. Moreover, such a change of the pore structure was considered to be the result of the spatial heterogeneity of chemical composition. Since such spatial heterogeneity exists also in the sedimentary rocks consisting of crystalline minerals such as quartz and feldspar, we need to examine natural rock, in order to obtain more reliable understanding about the change of permeability induced by highly alkaline groundwater (plume). In this study, silica sand as crystalline mineral was packed in the column, and the effect of dissolution induced by the highly alkaline plume on the permeability-change was examined. The silica sand particles mainly consist of SiO{sub 2} and include Al{sub 2}O{sub 3}, FeO, and K{sub 2}O. The volumetric flow rate and the pressure difference between the inlet and outlet of the column were measured, and the permeability was calculated. At the same time, the concentrations of elements in the fluid were measured by ICP-AES. The experimental result showed that permeability decreased gradually, although the silica sand was continuously dissolved in the column. The behavior of the permeability is considered to be the result from the rearrangement of the particles, or precipitation of secondary mineral. In the column test using the silica sand as packed mineral, the flow-path seems to be clogged by the rearrangement of the particles rather than the increase of the pore space between the particles. (authors)

Hideo Usui; Yuichi Niibori; Hitoshi Mimura [Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Aramaki Aza Aoba 6-6-01-2, Aoba-ku, Sendai, 980-8579 (Japan); Osamu Tochiyama [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577 (Japan)

2007-07-01

54

Crystalline molecular sieve synthesis using quaternary ammonium-functionalized organosiliconate  

US Patent & Trademark Office Database

This invention relates to a method for preparing crystalline silicates such as zeolites from a forming mixture containing quaternary ammonium-functionalized organosiliconate as a directing agent. The products prepared depend, inter alia, on reaction conditions such as temperature, crystallization time, and pH. More particularly, this invention relates to the use of a quaternary ammonium-functionalized organosiliconate in the preparation of ZSM-5, ZSM-48, ZSM-51 and the ZSM-48 composition thus prepared.

1993-03-16

55

The initial step of silicate versus aluminosilicate formation in zeolite synthesis: a reaction mechanism in water with a tetrapropylammonium template.  

PubMed

The initial step for silicate and aluminosilicate condensation is studied in water in the presence of a realistic tetrapropylammonium template under basic conditions. The model corresponds to the synthesis conditions of ZSM5. The free energy profile for the dimer formation ((OH)(3)Si-O-Si-(OH)(2)O(-) or [(OH)(3)Al-O-Si-(OH)(3)](-)) is calculated with ab initio molecular dynamics and thermodynamic integration. The Si-O-Si dimer formation occurs in a two-step manner with an overall free energy barrier of 75 kJ mol(-1). The first step is associated with the Si-O bond formation and results in an intermediate with a five-coordinated Si, and the second one concerns the removal of the water molecule. The template is displaced away from the Si centres upon dimer formation, and a shell of water molecules is inserted between the silicate and the template. The main effect of the template is to slow down the backward hydrolysis reaction with respect to the condensation one. The Al-O-Si dimer formation first requires the formation of a metastable precursor state by proton transfer from Si(OH)(4) to Al(OH)(4)(-) mediated by a solvent molecule. It then proceeds through a single step with an overall barrier of 70 kJ mol(-1). The model with water molecules explicitly included is then compared to a simple calculation using an implicit continuum model for the solvent. The results underline the importance of an explicit and dynamical treatment of the water solvent, which plays a key role in assisting the reaction. PMID:22297854

Trinh, Thuat T; Rozanska, Xavier; Delbecq, Françoise; Sautet, Philippe

2012-03-14

56

IRAS 15099-5856: Remarkable Mid-infrared Source with Prominent Crystalline Silicate Emission Embedded in the Supernova Remnant MSH15-52  

NASA Astrophysics Data System (ADS)

We report new mid-infrared (MIR) observations of the remarkable object IRAS 15099-5856 using the space telescopes AKARI and Spitzer, which demonstrate the presence of prominent crystalline silicate emission in this bright source. IRAS 15099-5856 has a complex morphology with a bright central compact source (IRS1) surrounded by knots, spurs, and several extended (~4') arc-like filaments. The source is seen only at >=10 ?m. The Spitzer mid-infrared spectrum of IRS1 shows prominent emission features from Mg-rich crystalline silicates, strong [Ne II] 12.81 ?m, and several other faint ionic lines. We model the MIR spectrum as thermal emission from dust and compare with the Herbig Be star HD 100546 and the luminous blue variable R71, which show very similar MIR spectra. Molecular line observations reveal two molecular clouds around the source, but no associated dense molecular cores. We suggest that IRS1 is heated by UV radiation from the adjacent O star Muzzio 10 and that its crystalline silicates most likely originated in a mass outflow from the progenitor of the supernova remnant (SNR) MSH 15-52. IRS1, which is embedded in the SNR, could have been shielded from the SN blast wave if the progenitor was in a close binary system with Muzzio 10. If MSH 15-52 is a remnant of Type Ib/c supernova (SN Ib/c), as has been previously proposed, this would confirm the binary model for SN Ib/c. IRS1 and the associated structures may be the relics of massive star death, as shaped by the supernova explosion, the pulsar wind, and the intense ionizing radiation of the embedded O star.

Koo, Bon-Chul; McKee, Christopher F.; Suh, Kyung-Won; Moon, Dae-Sik; Onaka, Takashi; Burton, Michael G.; Hiramatsu, Masaaki; Bessell, Michael S.; Gaensler, B. M.; Kim, Hyun-Jeong; Lee, Jae-Joon; Jeong, Woong-Seob; Lee, Ho-Gyu; Im, Myungshin; Tatematsu, Ken'ichi; Kohno, Kotaro; Kawabe, Ryohei; Ezawa, Hajime; Wilson, Grant; Yun, Min S.; Hughes, David H.

2011-05-01

57

Zeolite exposure and associated pneumoconiosis  

SciTech Connect

Naturally occurring zeolite minerals are aluminum silicates widespread in the earth's crust. Several of these minerals have fibrous forms and have been implicated as a possible cause of benign and malignant diseases of the lung and pleura in Turkey. This report describes a patient, living in an area of Nevada rich in zeolites, who presented with idiopathic pleural thickening and pulmonary fibrosis associated with extensive pulmonary deposition of zeolites.

Casey, K.R.; Shigeoka, J.W.; Rom, W.N.; Moatamed, F.

1985-06-01

58

A vibrational spectroscopic study of the silicate mineral analcime - Na2(Al4SiO4O12)·2H2O - A natural zeolite.  

PubMed

We have studied the mineral analcime using a combination of scanning electron microscopy with energy dispersive spectroscopy and vibrational spectroscopy. The mineral analcime Na2(Al4SiO4O12)·2H2O is a crystalline sodium silicate. Chemical analysis shows the mineral contains a range of elements including Na, Al, Fe(2+) and Si. The mineral is characterized by intense Raman bands observed at 1052, 1096 and 1125cm(-1). The infrared bands are broad; nevertheless bands may be resolved at 1006 and 1119cm(-1). These bands are assigned to SiO stretching vibrational modes. Intense Raman band at 484cm(-1) is attributed to OSiO bending modes. Raman bands observed at 2501, 3542, 3558 and 3600cm(-1) are assigned to the stretching vibrations of water. Low intensity infrared bands are noted at 3373, 3529 and 3608cm(-1). The observation of multiple water bands indicate that water is involved in the structure of analcime with differing hydrogen bond strengths. This concept is supported by the number of bands in the water bending region. Vibrational spectroscopy assists with the characterization of the mineral analcime. PMID:24983920

Frost, Ray L; López, Andrés; Theiss, Frederick L; Romano, Antônio Wilson; Scholz, Ricardo

2014-12-10

59

Cesium titanium silicate and method of making  

DOEpatents

The invention is the new material, a ternary compound of cesium, silica, and titania, together with a method of making the ternary compound, cesium titanium silicate pollucite. More specifically, the invention is Cs{sub 2}Ti{sub 2}Si{sub 4}O{sub 13} pollucite which is a new crystalline phase representing a novel class of Ti-containing zeolites. Compositions contain relatively high Cs{sub 2}O and TiO{sub 2} loadings and are durable glass and ceramic materials. The amount of TiO{sub 2} and Cs{sub 2} that can be incorporated into these glasses and crystalline ceramics far exceeds the limits set for the borosilicate high level waste glass. 10 figs.

Balmer, M.L.

1997-01-07

60

Cesium titanium silicate and method of making  

DOEpatents

The invention is the new material, a ternary compound of cesium, silica, and titania, together with a method of making the ternary compound, cesium titanium silicate pollucite. More specifically, the invention is Cs.sub.2 Ti.sub.2 Si.sub.4 O.sub.13 pollucite which is a new crystalline phase representing a novel class of Ti-containing zeolites. Compositions contain relatively high Cs.sub.2 O and TiO.sub.2 loadings and are durable glass and ceramic materials. The amount of TiO.sub.2 and Cs.sub.2 that can be incorporated into these glasses and crystalline ceramics far exceeds the limits set for the borosilicate high level waste glass.

Balmer, Mari L. (West Richland, WA)

1997-01-01

61

Characterization of zeolite L nanoclusters  

Microsoft Academic Search

Zeolite L (structure code LTL) crystals are synthesized starting from homogeneous potassium aluminosilicate solutions. Particle size and shape of the formed zeolite L are examined by high-resolution transmission electron microscopy, field emission-scanning electron microscopy, X-ray diffraction, and dynamic light scattering. The synthesis conditions reported lead to nanoclusters of aligned zeolite crystalline domains of dimensions â¼40 nm in the channel direction

Michael Tsapatsis; Mark Lovallo; Masayoshi Sadakata; Mark E. Davis

1995-01-01

62

Lack of Evidence of In-Situ Decay of Aluminum-26 in a FeO-Poor Ferromagnesian Crystalline Silicate Particle, Pyxie, from Comet Wild 2  

NASA Technical Reports Server (NTRS)

One of the important discoveries from the Stardust mission is the observation of crystalline silicate particles that resemble Ca, Al-rich inclusions (CAIs) and chondrules in carbonaceous chondrites], which suggests radial transport of high temperature solids from the inner to the outer solar nebula regions and capture by accreting cometary objects. The Al-Mg isotope analyses of CAI-like and type II chondrule-like particles revealed no excess of Mg-26 derived from in-situ decay of Al-26 (Tau)(sub 1/2) = 0.705Myr; ), suggesting late formation of these particles. However, the number of Wild 2 particles analyzed for Al-Mg isotopes is still limited (n = 3). In order to better understand the timing of the formation of Wild 2 particles and possible radial transport in the protoplanetary disk, we performed SIMS (Secondary Ion Mass Spectrometer) Al-Mg isotope analyses of plagioclase in a FeO-poor ferromagnesian Wild 2 particle, which is the most abundant type among crystalline Wild 2 particles.

Nakashima, D.; Ushikubo, T.; Weisberg, M. K.; Zolensky, M. E.; Ebel, D. S.; Kita, N. T.

2014-01-01

63

Effects of the orientation of the 23Na-29Si dipolar vector on the dipolar mediated heteronuclear solid state NMR correlation spectrum of crystalline sodium silicates.  

PubMed

Dipolar-Heteronuclear Multiple Quantum Correlation (D-HMQC) experiment based on SR4(2)(1) recoupling was shown as a very efficient probe of spatial proximities in ordered or disordered materials. As crystalline sodium silicates have been extensively studied using 1D and 2D MAS NMR experiments and DFT calculations, they have been used as candidate model systems to perform this D-HMQC experiment. In this work, we demonstrate that the combination of (29)Si and (23)Na NMR at high magnetic field and DFT calculations makes it possible to revisit the assignment of the NMR signature of the ?-Na(2)Si(2)O(5) polymorph. A D-HMQC experiment performed on this crystalline sample reveals lineshape distortions on the (23)Na powder patterns extracted from the 2D correlation. Numerical simulations showed that these distortions result from an effect of the relative orientation between the (23)Na quadrupolar tensor and the (23)Na-(29)Si dipolar vector at the origin of the magnetization transfer. PMID:22591998

Martel, Laura; Cadars, Sylvian; Véron, Emmanuel; Massiot, Dominique; Deschamps, Michaël

2012-01-01

64

Crystallization of Polymers in Confined Environments: Structural Development of Semi-crystalline Polymer-Layered Silicate Nanocomposites  

NASA Astrophysics Data System (ADS)

Over the last decade, the utility of ultrafine dispersions of inorganic nanoparticles to enhance polymer performance and function as precursors to form self-passivating / self-healing inorganic coatings on the polymer surface has been established. Before developing the fundamental structure-property relationships though, a detailed understanding of processing / morphology relationships is necessary. As with other multiphase systems exhibiting nano (1-100 nm) and meso (100-500 nm) order (such as biopolymers, block-copolymers, colloidal suspensions, liquid crystals), physical properties ranging from toughness to optical clarity are determined by morphology on various length scales which in turn arise from processing history. This is anticipated to be especially important for blends containing two or more constituents with fundamental structural features on the nanoscale, such as crystal lamellae and aluminosilicate sheets. Small-angle x-ray scattering experiments with synchrotron radiation reveal the presence of ultra-long range (20-60 nm) mesoscopic ordering of the layered silicate in molten polyamide 6-layered silicate nanocomposites. This superstructure of these semi-rigid inorganic sheets provides a confined environment to examine the crystallization of polyamide 6 with traditional bulk characterization techniques. In addition to a change lamellae organization and lamellae size, the presence of the aluminosilicate layers and extent of interfacial interactions (end-tethered v. physiadsorbed chains) substantially alters the nucleation rate, growth kinetics and Brill transition of the crystal phase as revealed by isothermal crystallization experiments monitored in-situ with synchrotron radiation. These exfoliated nanocomposites provide new opportunities to investigate confined polymer crystallization as well as provide insight into the origin of various property enhancements in these systems.

Vaia, Richard A.; Lincoln, Derek M.; Wang, Zhi-Gang; Hsiao, Benjamin S.; Krishnamoorti, Ramanan

2000-03-01

65

Crystallinity-vesicularity interrelation in silicic pyroclasts - Neutron and X-Ray Computed Tomography constraints on magma permeability  

NASA Astrophysics Data System (ADS)

The permeability of magma controls gas escape during magma ascent and thus may control eruption behaviour, varying from quiet degassing to explosive fragmentation (Mueller et al., 2008). Yet, the spatial distribution of connected vs. isolated vesicle structures in magma remains poorly constrained. Additionally, the crystal distribution may influence magma permeability: a) do fractures in crystals provide additional pathways to melt-based volatile migration? and b) do low surface-tension crystal faces catalyse bubble nucleation and growth? In felsic pyroclasts, the size, shape and interconnectivity of vesicles and phenocrysts have been quantified by 3D tomography. We applied high resolution neutron computed tomography (NCT) at 20 ?m and X-ray Computed Tomography (XCT) at 5-10 ?m resolution on large samples of 15-50 cm3 to investigate the 3D structure of vesicular (? = 0.45-0.72), silica-rich pyroclastic material from various explosive eruptions. Samples are of the 2004 vulcanian and the 1783 plinian eruption of Asama (Japan), the 1997 eruption of Soufrière Hills Volcano (Montserrat) and the June 1991 vulcanian event of Unzen (Japan). Volume reconstructions of the pore space and different crystal phases were calculated with Tomoview, our custom-made software. The reconstructed volumes showed an interrelation between vesicle and crystal distribution. Differential overlapping of crystal and vesicle subvolumes trace the crystal outlines exceptionally well. Furthermore, Tomoview detected connected pathways that frequently exploited inter-fracture space of fragmented crystals. Crystal fragmentation thus appears to provide an additional mechanism for generating pore space. The evolution of a permeable network may thus be affected by the crystal content, which ultimately biases the eruptive behaviour of silicic magma.

Wiesmaier, S.; Scheu, B.; Hess, K.-U.; Schillinger, B.; Flaws, A.; Dingwell, D. B.

2012-04-01

66

Crystallinity-vesicularity interrelation in silicic pyroclasts - Implications for permeability as inferred from Neutron and X-Ray Computed Tomography  

NASA Astrophysics Data System (ADS)

The permeability of magma controls gas escape during magma ascent and thus may trigger shifts in eruption behaviour from quiet degassing towards explosive fragmentation (Mueller et al., 2008). Yet, the spatial distribution of connected vs. isolated vesicle structures in magma remains poorly constrained. Additionally, the role of the crystal distribution can be expected to influence magma permeability: a) fractures in crystals may provide additional pathways to melt-based volatile migration, and b) low surface tension crystal faces may act as catalyst to bubble nucleation and growth. In felsic pyroclasts, the highly variable size, shape and interconnectivity of vesicles and phenocrysts results in a complex structure, best quantified by 3D tomography. We applied high resolution neutron computed tomography (NCT; 50 ?m pixel/voxel-size) to investigate the 3D structure of vesicular (? = 0.45-0.72), silica-rich pyroclastic material from various explosive eruptions. Samples are of the 2004 vulcanian and the 1783 plinian eruption of Asama (Japan), the 1997 eruption of Soufrière Hills Volcano (Montserrat) and the June 1991 vulcanian event of Unzen (Japan). For large samples (15-50 cm3), Neutron Computed Tomography provides the first non-destructive method to analyse this complex 3D structure. The NCT experiments were performed at the ANTARES beamline of the neutron source at the reactor FRM II at Technische Universität München (Germany). X-ray Computed Tomography (XCT) at 5-10 ?m resolution was performed at IMETUM (Germany) to scrutinize features of one order of magnitude smaller than NCT. Our custom-made software Tomoview permits interpolated slicing and thus a voxel-to-voxel comparison of both XCT and NCT datasets. This allows for differential datasets of hydrous versus non-hydrous phases and their relation to the fabric. Volume reconstructions of the pore space and different crystal phases were calculated with Tomoview. The reconstructed volumes showed an interrelation between vesicle and crystal distribution, as well influencing the formation of connected pathways. Furthermore, crystal fragmentation appears to provide an additional mechanism for generating pore space. The evolution of a permeable network may thus be affected by the crystal content, which ultimately biases the eruptive behaviour of silicic magma.

Wiesmaier, S.; Scheu, B.; Hess, K.; Mühlbauer, M.; Schillinger, B.; Flaws, A.; Dingwell, D. B.

2011-12-01

67

Crystalline Membranes  

NASA Technical Reports Server (NTRS)

In certain aspects, the invention features methods for forming crystalline membranes (e.g., a membrane of a framework material, such as a zeolite) by inducing secondary growth in a layer of oriented seed crystals. The rate of growth of the seed crystals in the plane of the substrate is controlled to be comparable to the rate of growth out of the plane. As a result, a crystalline membrane can form a substantially continuous layer including grains of uniform crystallographic orientation that extend through the depth of the layer.

Tsapatsis, Michael (Inventor); Lai, Zhiping (Inventor)

2008-01-01

68

Synthesis and testing of nanosized zeolite Y  

NASA Astrophysics Data System (ADS)

This work focuses on the synthesis and testing of nanosized zeolite Y. The synthesis formulations of faujasite-type structure of zeolite Y prepared in nanosized form are described. The synthetic zeolite Y is the most widely employed for the preparation of fluid catalytic cracking (FCC) catalysts. The synthesis of zeolite Y is very complicated process. The mean particle size of zeolite Y is 1800 nm. The major challenge of this work involved reducing this average particle size to less than 500 nm. The preliminary experiments were conducted to obtain the pure zeolite Y using the soluble silicates as a silica source. This was achieved by applying the experimental design approach to study the effects of many parameters. The ageing time turned out to be the most significant variable affecting product purity. Based on the preliminary results, a detailed investigation was carried out to determine the effects of silica-alumina precursor preparations on zeolite Y synthesis. Aluminosilicate precursors were prepared by gelling and precipitation of soluble silicate. The as-prepared precursors were used for the hydrothermal synthesis of zeolite Y. The procedure of the precipitation of soluble silicate yielded pure zeolite Y at the conventional synthesis conditions. The extent of purity of zeolite Y depends on the surface areas of aluminosilicate precursors. A novel approach to zeolite Y synthesis was employed for the preparation of the pure nanosized zeolite Y. This was achieved by applying the method of impregnation of precipitated silica. This novel method of impregnation for zeolite Y preparation allows eliminating the vigorous agitation step required for the preparation of a homogeneous silica solution, thereby simplifying the synthesis of zeolite Y in one single vessel. In case of the synthesis of nanosized zeolite Y, the effect of varying the organic templates on the formation of nanosized particles of zeolite Y was investigated, while all other reaction parameters were kept constant. The extent to which the nanosized zeolite Y was formed depended on the types and amount of the organic templates as well as the ageing duration. The activity testing of four FCC catalysts prepared by using CREY (Calcined Rare Earth ion-exchanged) zeolites with different particle sizes was carried out in a fluidized bench-scale batch riser simulator reactor. The starting zeolites NaY of different particle sizes were subjected to two cycles of ion exchange treatment. The particle size of the supported zeolites was varied between 150 and 1800 nm. The preparation of FCC catalysts was conducted by mixing the CREY zeolite with silica-alumina matrix and silica sol binder. Each catalyst contained 25% zeolite. The results of catalytic cracking demonstrated the significant effect of size reduction of the starting zeolite Y on catalytic performance of FCC catalyst. Keywords. Zeolite NaY, Faujasite, Nanosized particles, Nanozeolite, Nanotechnology, Synthesis, Crystallization, Seeding, Ageing, Precipitated silica, Sylopol silica, Fumed silica, Silica sol, Soluble silicates, Alumina, SAR or SiO2/Al2O3 Ratios, Sodium hydroxide, Sodium aluminate, Organic templates, TMAOH, Surfactant (CTAB), Ammonium Sulfate, BET surface area, BJH Pore Size Distribution, Zetasizer Particle Size Distribution, Powder XRD, 27Al Solid-State NMR, Catalytic Impregnation, CREY Zeolite, Silica-Alumina Matrix, Ion Exchange, FCC Catalyst, Catalytic cracking, Riser SimulatorRTM, Steaming, Zeolite HY, Utrastable Zeolite Y (USY)

Karami, Davood

69

The geopolymerisation of alumino-silicate minerals  

Microsoft Academic Search

Geopolymers are similar to zeolites in chemical composition, but they reveal an amorphous microstructure. They form by the co-polymerisation of individual alumino and silicate species, which originate from the dissolution of silicon and aluminium containing source materials at a high pH in the presence of soluble alkali metal silicates. It has been shown before that geopolymerisation can transform a wide

Hua Xu; J. S. J. Van Deventer

2000-01-01

70

Synthesis of hierarchical micro/mesoporous structures via solid-aqueous interface growth: zeolitic imidazolate framework-8 on siliceous mesocellular foams for enhanced pervaporation of water/ethanol mixtures.  

PubMed

A new hierarchical micro/mesoporous composite is synthesized via direct growth of microporous zeolitic imidazolate framework-8 (ZIF-8) on siliceous mesocellular foams (MCF). Depending on different synthetic conditions, ZIF-8 with two different particle sizes, i.e., ZIF-8 microparticles and ZIF-8 nanoparticles, were successfully formed on the external surface of amine-functionalized MCF (denoted as microZIF-8@MCF and nanoZIF-8@MCF, respectively). The synthesized hierarchical micro/mesoporous ZIF-8@MCF structures were characterized with several spectroscopic techniques including X-ray diffraction (XRD), solid-state NMR, and FT-IR and electron microscopic techniques (scanning electron microscope, SEM, and transmission electron microscopy, TEM). In addition, the pervaporation measurements of the liquid water/ethanol mixture show that nanoZIF-8@MCF/PVA (poly(vinyl alcohol) mixed-matrix membrane exhibits enhanced performance both on the permeability and separation factor. Compared to conventional routes for chemical etching, this study demonstrates a promising and simple strategy for synthesizing novel hierarchical porous composites exhibiting both advantages of mesoporous materials and microporous materials, which is expected to be useful for gas adsorption, separation, and catalysis. PMID:24625412

Sue, Yu-Chain; Wu, Jhe-Wei; Chung, Shao-En; Kang, Chao-Hsiang; Tung, Kuo-Lun; Wu, Kevin C-W; Shieh, Fa-Kuen

2014-04-01

71

Improved Catalysts for Heavy Oil Upgrading Based on Zeolite Y Nanoparticles Encapsulated Stable Nanoporous Host. Fourth Semi Annual Report.  

National Technical Information Service (NTIS)

The objectives of this project are to synthesis nanocrystals of highly acidic zeolite Y, encapsulate them within the channels of mesoporous (nanoporous) silicates or nanoporous organosilicates and evaluate the zeolite Y/Nanoporous host composites as catal...

C. Ongram, M. Mitchell

2005-01-01

72

Vapor Phase Transport Synthesis of Zeolites from Sol-Gel Precursors  

SciTech Connect

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.

THOMA,STEVEN G.; NENOFF,TINA M.

2000-07-14

73

Studies on natural STI zeolite: modification, structure, adsorption and catalysis  

Microsoft Academic Search

A natural STI zeolite discovered in China was identified as a calcium-rich and stellerite-isotype zeolite of stilbite with high crystallinity and an open pore system. Both ion exchange and dealumination can stabilize the framework of the zeolite. The structural properties of the parent and the modified STI zeolites were investigated by X-ray diffraction (XRD), thermogravimetric\\/differential thermogravimetric\\/differental thermal analysis (TG\\/DTG\\/DTA), Fourier

Jun Li; Jin Qiu; Yaojun Sun; Yingcai Long

2000-01-01

74

Cometary Silicates: Interstellar and Nebular Materials  

NASA Technical Reports Server (NTRS)

Evidence for interstellar material in comets is deduced from IR spectra, insitu measurements of Halley, and chondritic porous interplanetary dust particles (CP IDPs). IR spectra of comets reveal the spectrally active minerals: amorphous carbon, amorphous silicates, and (in some comets) crystalline silicates. Evidence suggests amorphous silicates are of interstellar origin while crystalline silicates are of nebular origin. 10 microns spectra of comets and submicron amorphous silicate spherules in CP IDPs have shapes similar to lines-of-sight through the ISM. Thermal emission models of cometary IR spectra require Fe-bearing amorphous silicates. Fe-bearing amorphous silicates may be Fe-bearing crystalline silicates formed in AGB outflows that are amorphized through He+ ion bombardment in supernova shocks in the ISM. Crystalline silicates in comets, as revealed by IR spectra, and their apparent absence in the ISM, argues for their nebular origin. The high temperatures (less than l000 K) at which crystals form or are annealed occur in the inner nebula or in nebular shocks in the 5-10 AU region. Oxygen isotope studies of CP IDPs show by mass only 1 % of the silicate crystals are of AGB origin. Together this suggests crystalline silicates in comets are probably primitive grains from the early solar nebula.

Wooden, Diane H.

2002-01-01

75

The natural hydrous sodium silicates from the northern bank of Lake Chad: occurrence, petrology and genesis  

Microsoft Academic Search

Hydrous sodium silicates sometimes associated with zeolites, form in an alkaline environment, in which there is a high concentration of dissolved silica. Such an environment existed during the Holocene in N'Guigmi interdunal depressions (Lake Chad), which led to the precipitation of various types of hydrous sodium silicates, including magadiite, kenyaite, and zeolites. Scanning electron and optical microscope observations allow several

D. Sebag; E. P Verrecchia; Seong-Joo Lee; A Durand

2001-01-01

76

Improved Catalysts for Heavy Oil Upgrading Based on Zeolite Y Nanoparticles Encapsulated Stable Nanoporous Host (Final Report, October 1, 2002-September 30, 2007).  

National Technical Information Service (NTIS)

The objective of this project is to synthesize nanocrystals of highly acidic zeolite Y nanoculsters, encapsulate them within the channels of mesoporous (nanoporous) silicates or nanoporous organosilicates, and evaluate the zeolite Y/Nanoporous host compos...

C. Ingram M. Mitchell

2007-01-01

77

Growth of zeolite crystals in the microgravity environment of space  

NASA Technical Reports Server (NTRS)

Zeolites are hydrated, crystalline aluminosilicates with alkali and alkaling earth metals substituted into cation vacancies. Typically zeolite crystals are 3 to 8 microns. Larger cyrstals are desirable. Large zeolite crystals were produced (100 to 200 microns); however, they have taken restrictively long times to grow. It was proposed if the rate of nucleation or in some other way the number of nuclei can be lowered, fewer, larger crystals will be formed. The microgravity environment of space may provide an ideal condition to achieve rapid growth of large zeolite crystals. The objective of the project is to establish if large zeolite crystals can be formed rapidly in space.

Sacco, A., Jr.; Sand, L. B.; Collette, D.; Dieselman, K.; Crowley, J.; Feitelberg, A.

1986-01-01

78

Early age hydration and pozzolanic reaction in natural zeolite blended cements: Reaction kinetics and products by in situ synchrotron X-ray powder diffraction  

SciTech Connect

The in situ early-age hydration and pozzolanic reaction in cements blended with natural zeolites were investigated by time-resolved synchrotron X-ray powder diffraction with Rietveld quantitative phase analysis. Chabazite and Na-, K-, and Ca-exchanged clinoptilolite materials were mixed with Portland cement in a 3:7 weight ratio and hydrated in situ at 40 {sup o}C. The evolution of phase contents showed that the addition of natural zeolites accelerates the onset of C{sub 3}S hydration and precipitation of CH and AFt. Kinetic analysis of the consumption of C{sub 3}S indicates that the enveloping C-S-H layer is thinner and/or less dense in the presence of alkali-exchanged clinoptilolite pozzolans. The zeolite pozzolanic activity is interpreted to depend on the zeolite exchangeable cation content and on the crystallinity. The addition of natural zeolites alters the structural evolution of the C-S-H product. Longer silicate chains and a lower C/S ratio are deduced from the evolution of the C-S-H b-cell parameter.

Snellings, R., E-mail: ruben.snellings@ees.kuleuven.b [Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Heverlee (Belgium); Mertens, G. [Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Heverlee (Belgium); Cizer, O. [Department of Civil Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 40, B-3001 Heverlee (Belgium); Elsen, J. [Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Heverlee (Belgium)

2010-12-15

79

Reclaiming silver from silver zeolite  

SciTech Connect

Silver zeolite is used to capture radioiodines from air cleaning systems in some nuclear facilities at the Idaho National Engineering Laboratory. It may become radioactively contaminated and/or poisoned by hydrocarbon vapors, which diminishes its capacity for iodine. Silver zeolite contains up to 38 wt% silver. A pyrometallurgical process was developed to reclaim the silver before disposing of the unserviceable zeolite as a radioactive waste. A flux was formulated to convert the refractory aluminosilicate zeolite structure into a low-melting fluid slag, with Na[sub 2]O added as NAOH instead of Na[sub 2]CO[sub 3] to avoid severe foaming due to CO[sub 2] evolution. A propane-fired furnace was built to smelt 45 kg charges at 1300C in a carbon-bonded silicon carbide crucible. A total of 218 kg (7000 tr oz) of silver was reclaimed from 1050 kg of unserviceable zeolite. Silver recoveries of 97% were achieved, and the radioisotopes were fixed as stable silicates in a vitreous slag that was disposed of as a low level waste. Recovered silver was refined using oxygen and cast into 100 tr oz bars assaying 99.8+% silver and showing no radioactive contamination.

Reimann, G.A.

1991-10-01

80

Reclaiming silver from silver zeolite  

SciTech Connect

Silver zeolite is used to capture radioiodines from air cleaning systems in some nuclear facilities at the Idaho National Engineering Laboratory. It may become radioactively contaminated and/or poisoned by hydrocarbon vapors, which diminishes its capacity for iodine. Silver zeolite contains up to 38 wt% silver. A pyrometallurgical process was developed to reclaim the silver before disposing of the unserviceable zeolite as a radioactive waste. A flux was formulated to convert the refractory aluminosilicate zeolite structure into a low-melting fluid slag, with Na{sub 2}O added as NAOH instead of Na{sub 2}CO{sub 3} to avoid severe foaming due to CO{sub 2} evolution. A propane-fired furnace was built to smelt 45 kg charges at 1300C in a carbon-bonded silicon carbide crucible. A total of 218 kg (7000 tr oz) of silver was reclaimed from 1050 kg of unserviceable zeolite. Silver recoveries of 97% were achieved, and the radioisotopes were fixed as stable silicates in a vitreous slag that was disposed of as a low level waste. Recovered silver was refined using oxygen and cast into 100 tr oz bars assaying 99.8+% silver and showing no radioactive contamination.

Reimann, G.A.

1991-10-01

81

A sustainable template for mesoporous zeolite synthesis.  

PubMed

A generalized synthesis of high-quality, mesoporous zeolite (e.g., MFI-type) nanocrystals is presented, based on a biomass-derived, monolithic N-doped carbonaceous template. As an example, ZSM-5 single crystals with desirable large-diameter (12-16 nm) intracrystalline mesopores are synthesized. The platform provides scope to optimize template dimensions and chemistry for the synthesis of a range of micro-/mesoporous crystalline zeolites in a cost-effective and highly flexible manner. PMID:24397534

White, Robin J; Fischer, Anna; Goebel, Caren; Thomas, Arne

2014-02-19

82

Zeolite Characterization.  

National Technical Information Service (NTIS)

The Savannah River Site isolates tritium from its process streams for eventual recycling. This is done by catalyzing the formation of tritiated water (from process streams) and then sorbing that water on a 3A zeolite (molsieve) bed. The tritium is recover...

H. L. Nigg W. D. Jacobs

2007-01-01

83

Zeolite micromembranes.  

PubMed

Free-standing silicalite-1 (Sil-1) zeolite micromembranes have been successfully fabricated onto silicon substrate. Gas permeation test using permanent gases (i.e., helium, hydrogen, argon and nitrogen) and hydrocarbons (i.e., methane and n-butane) indicates that the micromembranes have excellent permeance flux and high permselectivity. PMID:15100781

Chau, Joseph Lik Hang; Leung, Adrian Yat Lai; Yeung, King Lun

2003-05-01

84

Zeta potential measurements of zeolite Y: Application in homogeneous deposition of particle coatings  

Microsoft Academic Search

Zeolite membranes are typically grown from thin coatings of sub-?m size zeolite particles on porous supports. The particles have the function of seeds in forming a dense zeolite membrane by a secondary growth process. This study focuses on how seed layer coatings can be optimally produced, crack- and agglomerate-free, by dip coating from stable dispersions of nano-crystalline zeolite Y. Surface

Tatsiana Kuzniatsova; Yanghee Kim; Krenar Shqau; Prabir K. Dutta; Henk Verweij

2007-01-01

85

Framework-Type Determination for Zeolite Structures in the Inorganic Crystal Structure Database  

NASA Astrophysics Data System (ADS)

In this work a structural characterization of zeolite crystals is performed by identifying the framework type to which each zeolite belongs. The framework type is assigned for 1433 zeolite database entries in the FIZ/NIST Inorganic Crystal Structure Database (ICSD) populating 95 framework types. These entries correspond to both natural and synthetic zeolites. Each ICSD entry is based on published work containing crystallographic information of the zeolite crystalline structure and some physical and chemical data. Today, the Structure Commission of the International Zeolite Association recognizes crystalline materials as belonging to the ``zeolite'' family only if they possess one of the approved framework types by the organization. Such information is of fundamental importance for identifying zeolites, for reference, for zeolite standards, for supporting the discovery of new zeolites, and for crystalline substance selection based on application. Unfortunately, framework-type information is not contained in the ICSD records. The long term goal of this work is filling such gap. Although the ICSD contains an extensive collection of zeolites, inclusion of zeolites belonging to the 191 accepted framework types could substantially expand such collection. The structural determination was achieved via several structural analysis methods based on numerical-computer implementations.

Yang, Shujiang; Lach-Hab, Mohammed; Vaisman, Iosif I.; Blaisten-Barojas, Estela; Li, Xiang; Karen, Vicky L.

2010-09-01

86

Zeolitic Diagenesis of Tuffs in the Miocene Chalk Hills Formation, Western Snake River Plain, Idaho.  

National Technical Information Service (NTIS)

Zeolites are common diagenetic alteration products of silicic, vitric tuffs in Cenozoic lacustrine deposits of the western United States, especially those that were deposited in highly saline and alkaline water. Such deposits have received much attention ...

R. A. Sheppard

1991-01-01

87

Microstructural Optimization of a Zeolite Membrane for Organic Vapor Separation  

Microsoft Academic Search

A seeded growth method for the fabrication of high-permeance, high-separation-factor zeolite (siliceous ZSM-5, [Si96O192]-MFI) membranes is reported. The method consists of growing the crystals of an oriented seed layer to a well-intergrown film by avoiding events that lead to a loss of preferred orientation, such as twin overgrowths and random nucleation. Organic polycations are used as zeolite crystal shape modifiers

Zhiping Lai; Griselda Bonilla; Isabel Diaz; Jose Geraldo Nery; Khristina Sujaoti; Miguel A. Amat; Efrosini Kokkoli; Osamu Terasaki; Robert W. Thompson; Michael Tsapatsis; Dionisios G. Vlachos

2003-01-01

88

Thermodynamic modeling of natural zeolite stability  

SciTech Connect

Zeolites occur in a variety of geologic environments and are used in numerous agricultural, commercial, and environmental applications. It is desirable to understand their stability both to predict future stability and to evaluate the geochemical conditions resulting in their formation. The use of estimated thermodynamic data for measured zeolite compositions allows thermodynamic modeling of stability relationships among zeolites in different geologic environments (diagenetic, saline and alkaline lakes, acid rock hydrothermal, basic rock, deep sea sediments). This modeling shows that the relative cation abundances in both the aqueous and solid phases, the aqueous silica activity, and temperature are important factors in determining the stable zeolite species. Siliceous zeolites (e.g., clinoptilolite, mordenite, erionite) present in saline and alkaline lakes or diagenetic deposits formed at elevated silica activities. Aluminous zeolites (e.g., natrolite, mesolite/scolecite, thomsonite) formed in basic rocks in association with reduced silica activities. Likewise, phillipsite formation is favored by reduced aqueous silica activities. The presence of erionite, chabazite, and phillipsite are indicative of environments with elevated potassium concentrations. Elevated temperature, calcic water conditions, and reduced silica activity help to enhance the laumontite and wairakite stability fields. Analcime stability increases with increased temperature and aqueous Na concentration, and/or with decreased silica activity.

Chipera, S.J.; Bish, D.L.

1997-06-01

89

Zeolites: Structural Properties and Benchmarks of Feasibility  

NASA Astrophysics Data System (ADS)

Zeolites are a class of microporous materials that are immensely useful as molecular sieves and catalysts. While there exist millions of hypothetical zeolite topologies, only 206 have been recognized to exist in nature, and the question remains: What distinguishes known zeolite topologies from their hypothetical counterparts? It has been found that all 206 of the known zeolites can be represented as networks of rigid perfect tetrahedra that hinge freely at the connected corners. The range of configurations over which the corresponding geometric constraints can be met has been termed the "flexibility window". Only a small percentage of hypothetical types exhibit a flexibility window, and it is thus proposed that this simple geometric property, the existence of a flexibility window, provides a reliable benchmark for distinguishing potentially realizable hypothetical structures from their infeasible counterparts. As a first approximation of the behavior of real zeolite materials, the flexibility window provides additional useful insights into structure and composition. In this thesis, various methods for locating and exploring the flexibility window are discussed. Also examined is the assumption that the tetrahedral corners are force-free. This is a reasonable approximation in silicates for Si-O-Si angles above ˜135°. However, the approximation is poor for germanates, where Ge-O-Ge angles are constrained to the range ˜120°-145°. Lastly, a class of interesting low-density hypothetical zeolites is evaluated based on the feasibility criteria introduced.

Dawson, Colby

90

Environmental Applications of Natural Zeolitic Materials Based on Their Ion Exchange Properties  

Microsoft Academic Search

\\u000a Present and potential use of natural zeolites as cation exchangers in environmental protection is reviewed. Siliceous zeolites,\\u000a such as chabazite, clinoptilolite, mordenite and phillipsite, exhibit good selectivities for cations with low charge density,\\u000a e.g., Cs+ and NH4\\u000a +, and for cations with low hydration energy, such as Pb2+. Zeolitised tuffs, containing the mentioned zeolites, may therefore be utilised for removing

C. Colella; Piazza Ie; V. Tecchio

91

A pair distribution function analysis of zeolite beta  

SciTech Connect

We describe the structural refinement of zeolite beta using the local structure obtained with the pair distribution function (PDF) method. A high quality synchrotron and two neutron scattering datasets were obtained on two samples of siliceous zeolite beta. The two polytypes that make up zeolite beta have the same local structure; therefore refinement of the two structures was possible using the same experimental PDF. Optimized structures of polytypes A and B were used to refine the structures using the program PDFfit. Refinements using only the synchrotron or the neutron datasets gave results inconsistent with each other but a cyclic refinement with the two datasets gave a good fit to both PDFs. The results show that the PDF method is a viable technique to analyze the local structure of disordered zeolites. However, given the complexity of most zeolite frameworks, the use of both X-ray and neutron radiation and high-resolution patterns is essential to obtain reliable refinements.

Martinez-Inesta, M.M.; Peral, I.; Proffen, T.; Lobo, R.F. (Delaware); (LANL)

2010-07-20

92

Synthesis and catalytic applications of combined zeolitic/mesoporous materials  

PubMed Central

Summary In the last decade, research concerning nanoporous siliceous materials has been focused on mesoporous materials with intrinsic zeolitic features. These materials are thought to be superior, because they are able to combine (i) the enhanced diffusion and accessibility for larger molecules and viscous fluids typical of mesoporous materials with (ii) the remarkable stability, catalytic activity and selectivity of zeolites. This review gives an overview of the state of the art concerning combined zeolitic/mesoporous materials. Focus is put on the synthesis and the applications of the combined zeolitic/mesoporous materials. The different synthesis approaches and formation mechanisms leading to these materials are comprehensively discussed and compared. Moreover, Ti-containing nanoporous materials as redox catalysts are discussed to illustrate a potential implementation of combined zeolitic/mesoporous materials.

Vernimmen, Jarian; Cool, Pegie

2011-01-01

93

Zeolite A imidazolate frameworks  

Microsoft Academic Search

Faujasite (FAU) and zeolite A (LTA) are technologically important porous zeolites (aluminosilicates) because of their extensive use in petroleum cracking and water softening. Introducing organic units and transition metals into the backbone of these types of zeolite allows us to expand their pore structures, enhance their functionality and access new applications. The invention of metal-organic frameworks and zeolitic imidazolate frameworks

Hideki Hayashi; Adrien P. Côté; Hiroyasu Furukawa; Michael O'Keeffe; Omar M. Yaghi

2007-01-01

94

Solar refrigeration utilizing zeolites  

Microsoft Academic Search

Zeolites offer a unique opportunity for a solid-gas adsorption refrigeration system because of their unusual sorption properties, in particular, extremely nonlinear adsorption isotherms. The operating principle of the zeolite system and experimental results are presented. The study demonstrates a zeolite system capable of providing refrigeration and ice production with very good engineering efficiency. This system utilizes natural zeolites as the

D. I. Tchernev

1979-01-01

95

MFI zeolite nanosponges possessing uniform mesopores generated by bulk crystal seeding in the hierarchical surfactant-directed synthesis.  

PubMed

The synthesis of a mesoporous material with uniform mesopore diameters and crystalline MFI zeolite walls has been achieved, simply by seeding the multiammonium surfactant-directed synthesis with bulk zeolite crystals. The bulk seeds disappeared in the final product. As a result of seeding, the mesoporous zeolites could be generated rapidly even at high Al content. PMID:24633468

Jo, Changbum; Cho, Kanghee; Kim, Jaeheon; Ryoo, Ryong

2014-03-25

96

Database of Zeolite Structures  

NSDL National Science Digital Library

The Database of Zeolite Structures is provided by the Structure Commission of the International Zeolite Association. Links include an Atlas of Zeolite Framework Types, Collection of Simulated XRD Powder Patterns for Zeolites, Catalog of Disordered Zeolite Structures, Schemes for Building Zeolite Framework Models, and Zeolite Structure References, as well as various publications. The database can be searched or browsed, and contains several useful tools such as the "input your data" link, which allows the user to enter crystallographic data not available in the database and generate the diffraction pattern.

2000-01-01

97

Ammonium removal from wastewaters using natural New Zealand zeolites  

Microsoft Academic Search

Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially toxic to fish and other aquatic life. Zeolites, which are hydrated aluminum?silicate minerals, have an affinity for ammonium ions (NH4 ) and are, therefore, potentially useful in removing this contaminant from wastewaters. The major objectives of this study were to evaluate the capacity

M. L. Nguyen; C. C. Tanner

1998-01-01

98

Cesium incorporation and diffusion in cancrinite, sodalite, zeolite, and allophane  

Microsoft Academic Search

At the US Department of Energy’s Hanford site, high level nuclear waste has leaked from underground storage tanks. The waste consists of hyperalkaline solutions, which upon contact with the sediments, caused dissolution of silicate minerals and precipitation of new aluminosilicate minerals. Cancrinite, sodalite, LTA zeolite, and allophane have been identified as the new mineral phases in laboratory simulations. Cesium, the

Jarai Mon; Youjun Deng; Markus Flury; James B. Harsh

2005-01-01

99

Synthesis and characterization of nitrogen substituted zeolites  

NASA Astrophysics Data System (ADS)

The interest in basic solid materials, particularly for basic zeolites has considerably increased in the last two decades because of their potential use in catalysis and separation. Basic zeolites have most often been obtained by ion-exchange or impregnation with alkali metal cations or grafting of organic bases onto zeolite pore walls. Such materials often suffer from instability and/or pore blockage, because none of these approaches places basic sites directly into the zeolite framework. Recently zeolitic materials have been made with some of the bridging oxygen atoms in Si--O--Si and/or Si--O--Al linkages replaced by NH groups, i.e. by substitution of framework oxygen by nitrogen. As a result, the basic strength of the framework increases due to the lower electronegativity of nitrogen with respect to oxygen. In this study, solid base catalysts are obtained by nitrogen substitution of the faujasite type of zeolites under ammonia flow at high temperatures. The efficiency of the reaction is tested by using zeolites with different aluminum contents and extraframework cations and varying the reaction conditions such as ammonia flow rate, reaction temperature and duration. The characterization studies show that high levels of nitrogen substitution can be achieved while maintaining porosity, particularly for NaY and low-aluminum HY zeolites, without a significant loss in the crystallinity. 27Al and 29 Si MAS NMR experiments performed on the nitrogen substituted zeolites show dealumination of the framework and preferential substitution for Si--OH--Al sites at the early stages of the reaction (temperatures at 750--800 °C). No preference is seen for reactions performed at higher temperatures and longer reaction times (e.g., 850 °C and 48 h). X-ray PDF analysis performed on the modified zeolites show that the Si-N distance in the 1st shell is longer than Si-O bond distance and Si-Si/Al bond distance of the Si-O/N-Si/Al linkage decreases, as an indication of a decrease in bond angle. The basicity experiments performed on the zeolites show an increase basicity with increase of the nitrogen content.

Dogan, Fulya

100

ZEOLITES: EFFECTIVE WATER PURIFIERS  

EPA Science Inventory

Zeolites are known for their adsorption, ion exchange and catalytic properties. Various natural zeolites are used as odor and moisture adsorbents and water softeners. Due to their acidic nature, synthetic zeolites are commonly employed as solid acid catalysts in petrochemical ind...

101

Natrolite: A zeolite with negative Poisson's ratios  

NASA Astrophysics Data System (ADS)

The recently published experimental elastic constants [C. Sanchez-Valle, S. V. Sinogeikin, Z. A. Lethbridge, R. I. Walton, C. W. Smith, K. E. Evans, and J. D. Bass, J. Appl. Phys. 98, 053508 (2005)] for single crystals of the orthorhombic aluminosilicate zeolite NAT (natrolite, Na2(Al2Si3O10)2H2O, Fdd2) throw valuable light on the potential of NAT as a material which exhibits single crystalline negative Poisson's ratios (auxetic). On performing an off-axis analysis of these elastic constants we confirm that the zeolite natrolite exhibits auxetic behavior in the (001) plane. This supports our preliminary report that NAT-type zeolites exhibit auxetic behavior through a mechanism involving microscopic rotation of semi-rigid structural units.

Grima, Joseph N.; Gatt, Ruben; Zammit, Victor; Williams, Jennifer J.; Evans, Kenneth E.; Alderson, Andrew; Walton, Richard I.

2007-04-01

102

Preparation and characterization of zeolite-supported molybdenum and cobalt-molybdenum sulfide catalysts  

Microsoft Academic Search

Preparation, characterization and catalysis of zeolite-supported Mo, Co(Ni) and Co(Ni)?Mo sulfide catalysts have been reviewed in the present article. Incomplete sulfidation of Mo oxides and poor dispersion of Mo sulfides were observed for zeolite-supported Mo catalysts prepared by impregnation methods, accompanied by a considerable crystallinity loss at a high calcination temperature. A significant migration of Mo oxide species into zeolite

Yasuaki Okamoto

1997-01-01

103

Unstable-Fe-site-induced formation of mesopores in microporous zeolite Y without using organic templates.  

PubMed

A novel organic template-free strategy for generating mesoporosity in Y zeolites is reported. It is revealed that Fe(3+) functioned as unstable sites in the Fe-NaY zeolite, which promotes deferrization-dealumination, leading to enhanced formation of intra-crystalline mesopores as well as desirable interconnectivity. The mesopore-enriched zeolite exhibits a remarkable ability in conversion of the bulky substrate. PMID:24473160

Guo, Dongdong; Shen, Baojian; Qi, Guodong; Zhao, Liang; Xu, Jun; Deng, Feng; Qin, Yuchen; Guo, Qiaoxia; Ren, Shenyong; Gao, Xionghou; Qin, Song; Wang, Baojie; Zhao, Hongjuan; Liu, Honghai; Pang, Xinmei

2014-03-11

104

Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags  

SciTech Connect

Accelerated carbonation is induced in pastes and mortars produced from alkali silicate-activated granulated blast furnace slag (GBFS)-metakaolin (MK) blends, by exposure to CO{sub 2}-rich gas atmospheres. Uncarbonated specimens show compressive strengths of up to 63 MPa after 28 days of curing when GBFS is used as the sole binder, and this decreases by 40-50% upon complete carbonation. The final strength of carbonated samples is largely independent of the extent of metakaolin incorporation up to 20%. Increasing the metakaolin content of the binder leads to a reduction in mechanical strength, more rapid carbonation, and an increase in capillary sorptivity. A higher susceptibility to carbonation is identified when activation is carried out with a lower solution modulus (SiO{sub 2}/Na{sub 2}O ratio) in metakaolin-free samples, but this trend is reversed when metakaolin is added due to the formation of secondary aluminosilicate phases. High-energy synchrotron X-ray diffractometry of uncarbonated paste samples shows that the main reaction products in alkali-activated GBFS/MK blends are C-S-H gels, and aluminosilicates with a zeolitic (gismondine) structure. The main crystalline carbonation products are calcite in all samples and trona only in samples containing no metakaolin, with carbonation taking place in the C-S-H gels of all samples, and involving the free Na{sup +} present in the pore solution of the metakaolin-free samples. Samples containing metakaolin do not appear to have the same availability of Na{sup +} for carbonation, indicating that this is more effectively bound in the presence of a secondary aluminosilicate gel phase. It is clear that claims of exceptional carbonation resistance in alkali-activated binders are not universally true, but by developing a fuller mechanistic understanding of this process, it will certainly be possible to improve performance in this area.

Bernal, Susan A., E-mail: susana.bernal@gmail.co [Materials Engineering Department, Composite Materials Group, CENM, Universidad del Valle, Cali (Colombia); Mejia de Gutierrez, Ruby [Materials Engineering Department, Composite Materials Group, CENM, Universidad del Valle, Cali (Colombia); Provis, John L., E-mail: jprovis@unimelb.edu.a [Department of Chemical and Biomolecular Engineering, University of Melbourne, Victoria 3010 (Australia); Rose, Volker [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2010-06-15

105

Deactivation and coke combustion studies of nanocrystalline zeolite beta in catalytic cracking of used palm oil  

Microsoft Academic Search

Nanocrystalline zeolite beta was synthesized and its catalytic cracking activity for the production of biofuel from used palm oil was determined. The catalyst was characterized for its crystallinity, surface properties and morphology. The effect of reaction temperature on the catalytic cracking activity of nanocrystalline zeolite beta was also studied. The catalyst deactivation was monitored with the time on stream data

Niken Taufiqurrahmi; Abdul Rahman Mohamed; Subhash Bhatia

2010-01-01

106

Biological and therapeutic effects of ortho-silicic acid and some ortho-silicic acid-releasing compounds: New perspectives for therapy.  

PubMed

Silicon (Si) is the most abundant element present in the Earth's crust besides oxygen. However, the exact biological roles of silicon remain unknown. Moreover, the ortho-silicic acid (H4SiO4), as a major form of bioavailable silicon for both humans and animals, has not been given adequate attention so far. Silicon has already been associated with bone mineralization, collagen synthesis, skin, hair and nails health atherosclerosis, Alzheimer disease, immune system enhancement, and with some other disorders or pharmacological effects. Beside the ortho-silicic acid and its stabilized formulations such as choline chloride-stabilized ortho-silicic acid and sodium or potassium silicates (e.g. M2SiO3; M= Na,K), the most important sources that release ortho-silicic acid as a bioavailable form of silicon are: colloidal silicic acid (hydrated silica gel), silica gel (amorphous silicon dioxide), and zeolites. Although all these compounds are characterized by substantial water insolubility, they release small, but significant, equilibrium concentration of ortho-silicic acid (H4SiO4) in contact with water and physiological fluids. Even though certain pharmacological effects of these compounds might be attributed to specific structural characteristics that result in profound adsorption and absorption properties, they all exhibit similar pharmacological profiles readily comparable to ortho-silicic acid effects. The most unusual ortho-silicic acid-releasing agents are certain types of zeolites, a class of aluminosilicates with well described ion(cation)-exchange properties. Numerous biological activities of some types of zeolites documented so far might probably be attributable to the ortho-silicic acid-releasing property. In this review, we therefore discuss biological and potential therapeutic effects of ortho-silicic acid and ortho-silicic acid -releasing silicon compounds as its major natural sources. PMID:23298332

Jurki?, Lela Munjas; Cepanec, Ivica; Paveli?, Sandra Kraljevi?; Paveli?, Krešimir

2013-01-01

107

Zeolite membranes from kaolin  

SciTech Connect

Zeolite films are sought as components of molecular sieve membranes. Different routes used to prepare zeolite composite membranes include growing zeolite layers from gels on porous supports, depositing oriented zeolites on supports, and dispersing zeolites in polymeric membranes. In most cases, it is very difficult to control and avoid the formation of cracks and/or pinholes. The approach to membrane synthesis is based on hydrothermally converting films of layered aluminosilicates into zeolite films. The authors have demonstrated this concept by preparing zeolite A membranes on alumina supports from kaolin films. The authors have optimized the process parameters not only for desired bulk properties, but also for preparing thin (ca. 5 {micro}m), continuous zeolite A films. Scanning electron microscopy shows highly intergrown zeolite A crystals over most of the surface area of the membrane, but gas permeation experiments indicate existence of mesoporous defects and/or intercrystalline gaps. It has been demonstrated that the thickness of the final zeolite A membrane can be controlled by limiting the amount of precursor kaolin present in the membrane.

Karle, B.G. [Univ. of New Mexico, Albuquerque, NM (United States). Center for Micro-Engineered Ceramics; Brinker, C.J. [Univ. of New Mexico, Albuquerque, NM (United States). Center for Micro-Engineered Ceramics]|[Sandia National Labs., Albuquerque, NM (United States); Phillips, M.L.F. [Sandia National Labs., Albuquerque, NM (United States)

1996-07-01

108

Research on Composite Silicate Dental Cements.  

National Technical Information Service (NTIS)

An eclectic theory based on observation is presented, which postulates that the worth of a silicate dental cement is a direct function of the properties of the micro-crystalline phases formed in the matrix during setting. Electron diffraction patterns of ...

T. J. Rockett C. A. Panza

1967-01-01

109

Growth of large zeolite crystals in space  

NASA Technical Reports Server (NTRS)

Synthesis studies performed using close analogs of triethanolamine (TEA) have shown that all three hydroxyl groups and the amine group in this molecule are necessary to provide nucleation suppression. Studies using C-13 nuclear magnetic resonance (NMR) revealed that the hydroxyl ions and the amine group are involved in the formation of an aluminum complex. It was also shown that silicate species fo not interact this way with TEA in an alkaline solution. These results suggest that successful aluminum complexation leads to nucleation in zeolite-A crystallization.

Sacco, A., Jr.; Dixon, A.; Thompson, R.; Scott, G.; Ditr, J.

1988-01-01

110

Thermodynamics of rock forming crystalline solutions  

NASA Technical Reports Server (NTRS)

Analysis of phase diagrams and cation distributions within crystalline solutions as means of obtaining thermodynamic data on rock forming crystalline solutions is discussed along with some aspects of partitioning of elements in coexisting phases. Crystalline solutions, components in a silicate mineral, and chemical potentials of these components were defined. Examples were given for calculating thermodynamic mixing functions in the CaW04-SrW04, olivine-chloride solution, and orthopyroxene systems.

Saxena, S. K.

1971-01-01

111

EFFECT OF QUARTZ/MULLITE BLEND CERAMIC ADDITIVE ON IMPROVING RESISTANCE TO ACID OF SODIUM SILICATE-ACTIVATED SLAG CEMENT. CELCIUS BRINE.  

SciTech Connect

We evaluated the usefulness of manufactured quartz/mullite blend (MQMB) ceramic powder in increasing the resistance to acid of sodium silicate-activated slag (SSAS) cementitious material for geothermal wells. A 15-day exposure to 90{sup o} CO{sub 2}-laden H{sub 2}SO{sub 4} revealed that the MQMB had high potential as an acid-resistant additive for SSAS cement. Two factors, the appropriate ratio of slag/MQMB and the autoclave temperature, contributed to better performance of MQMB-modified SSAS cement in abating its acid erosion. The most effective slag/MQMB ratio in minimizing the loss in weight by acid erosion was 70/30 by weight. For autoclave temperature, the loss in weight of 100 C autoclaved cement was a less than 2%, but at 300 C it was even lower. Before exposure to acid, the cement autoclaved at 100 C was essentially amorphous; increasing the temperature to 200 C led to the formation of crystalline analcime in the zeolitic mineral family during reactions between the mullite in MQMB and the Na from sodium silicate. In addition, at 300 C, crystal of calcium silicate hydrate (1) (CSH) was generated in reactions between the quartz in MQMB and the activated slag. These two crystalline phases (CSH and analcime) were responsible for densifying the autoclaved cement, conveying improved compressive strength and minimizing water permeability. The CSH was susceptible to reactions with H{sub 2}SO{sub 4}, forming two corrosion products, bassanite and ionized monosilicic acid. However, the uptake of ionized monosilicic acid by Mg dissociated from the activated slag resulted in the formation of lizardite as magnesium silicate hydrate. On the other hand, the analcime was barely susceptible to acid if at all. Thus, the excellent acid resistance of MQMB-modified SSAS cement was due to the combined phases of lizardite and analcime.

SUGAMA, T.; BROTHERS, L.E.; VAN DE PUTTE, T.R.

2006-06-01

112

Rapid crystallization of faujasitic zeolites: mechanism and application to zeolite membrane growth on polymer supports.  

PubMed

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications. PMID:24758695

Severance, Michael; Wang, Bo; Ramasubramanian, Kartik; Zhao, Lin; Ho, W S Winston; Dutta, Prabir K

2014-06-17

113

Dispersible Exfoliated Zeolite Nanosheets and Their Application as a Selective Membrane  

NASA Astrophysics Data System (ADS)

Thin zeolite films are attractive for a wide range of applications, including molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Synthesis of thin zeolite films using high-aspect-ratio zeolite nanosheets is desirable because of the packing and processing advantages of the nanosheets over isotropic zeolite nanoparticles. Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation). We demonstrated the synthesis and structure determination of highly crystalline nanosheets of zeolite frameworks MWW and MFI. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes.

Varoon, Kumar; Zhang, Xueyi; Elyassi, Bahman; Brewer, Damien D.; Gettel, Melissa; Kumar, Sandeep; Lee, J. Alex; Maheshwari, Sudeep; Mittal, Anudha; Sung, Chun-Yi; Cococcioni, Matteo; Francis, Lorraine F.; McCormick, Alon V.; Mkhoyan, K. Andre; Tsapatsis, Michael

2011-10-01

114

Hydrocarbon cracking with yttrium exchanged zeolite y catalyst  

Microsoft Academic Search

A process is described for cracking a gas oil boiling range hydrocarbon feedstock comprising the step of contacting the feedstock in a catalytic cracking zone under catalytic cracking conditions to produce convulsion products comprising gasoline with a catalyst composition. The process comprises: a Y crystalline aluminosilicate zeolite, having the structure of faujasite and having uniform pore diameters and a silica

C. F. Lochow; D. B. Kovacs

1987-01-01

115

Synthesis of ZSM-type Zeolites from Biowaste Gasification Ashes  

Microsoft Academic Search

In Taiwan, over 800 thousand tons per year (TPY) of biowastes such as sugar cane bagasse, sugar cane leaf, rice straw, and corn leaf are produced. These biomasses are the major wastes of farms and are abundantly available. However, these biowastes cause disposal and landfill problems. The main component of these biowaste ashes is SiO2. High crystallinity (99%) zeolites ZSM-5

KUEN-SONG LIN; H. PAUL WANG; NI-BIN CHANG; C. J. G. JOU; M. C. HSIAO

2003-01-01

116

Flexibility of zeolitic imidazolate framework structures studied by neutron total scattering and the reverse Monte Carlo method  

NASA Astrophysics Data System (ADS)

The zeolitic imidazolate framework ZIF-4 undergoes an amorphization transition at about 600 K, and then transforms at about 700 K to ZIF-zni, the densest of the crystalline ZIFs. This series of long-range structural rearrangements must give a corresponding series of changes in the local structure, but these have not previously been directly investigated. Through analysis of neutron total diffraction data by reverse Monte Carlo modelling, we assess the changes in flexibility across this series, identifying the key modes of flexibility within ZIF-4 and the amorphous phase. We show that the ZnN4 tetrahedra remain relatively rigid, albeit less so than SiO4 tetrahedra in silicates. However, the extra degrees of freedom afforded by the imidazolate ligand, compared to silicate networks, vary substantially between phases, with a twisting motion out of the plane of the ligand being particularly important in the amorphous phase. Our results further demonstrate the feasibility of reverse Monte Carlo simulations for studying intermolecular interactions in solids, even in cases, such as the ZIFs, where the pair distribution function is dominated by intramolecular peaks.

Beake, E. O. R.; Dove, M. T.; Phillips, A. E.; Keen, D. A.; Tucker, M. G.; Goodwin, A. L.; Bennett, T. D.; Cheetham, A. K.

2013-10-01

117

Fly ash from a Mexican mineral coal. II. Source of W zeolite and its effectiveness in arsenic (V) adsorption.  

PubMed

Coal-fired plants in Coahuila (Mexico) produce highly reactive fly ash (MFA), which is used in a one-step process as a raw material in producing zeolite. We explored two routes in the synthesis of zeolite: (a) direct MFA zeolitization, which resulted in the formation of W zeolite with KOH and analcime with NaOH and (b) a MFA fusion route, which resulted in the formation of zeolite W or chabazite with KOH and zeolite X or P with NaOH. No residual crystalline phases were present. When LiOH was employed, ABW zeolite with quartz and mullite were obtained. For both zeolitization routes, the nature of the alkali (KOH, NaOH, LiOH), the alkali/MFA ratio (0.23-1.46), and the crystallization temperature and time (90-175 degrees C; 8-24 h) were evaluated. Additionally, the effect of temperature and time on MFA fusion was studied. W zeolite was obtained by both zeolitization methods. The direct route is preferred because it is a straightforward method using soft reaction conditions that results in a high yield of low cost zeolites with large crystal agglomerates. It was demonstrated that aluminum modified W zeolite has the ability to remove 99% of the arsenic (V) from an aqueous solution of Na(2)HAsO(4).7H(2)O originally containing 740 ppb. PMID:20537461

Medina, Adriana; Gamero, Prócoro; Almanza, José Manuel; Vargas, Alfredo; Montoya, Ascención; Vargas, Gregorio; Izquierdo, María

2010-09-15

118

Antimicrobial properties of zeolite-X and zeolite-A ion-exchanged with silver, copper, and zinc against a broad range of microorganisms.  

PubMed

Zeolites are nanoporous alumina silicates composed of silicon, aluminum, and oxygen in a framework with cations, water within pores. Their cation contents can be exchanged with monovalent or divalent ions. In the present study, the antimicrobial (antibacterial, anticandidal, and antifungal) properties of zeolite type X and A, with different Al/Si ratio, ion exchanged with Ag(+), Zn(2+), and Cu(2+) ions were investigated individually. The study presents the synthesis and manufacture of four different zeolite types characterized by scanning electron microscopy and X-ray diffraction. The ion loading capacity of the zeolites was examined and compared with the antimicrobial characteristics against a broad range of microorganisms including bacteria, yeast, and mold. It was observed that Ag(+) ion-loaded zeolites exhibited more antibacterial activity with respect to other metal ion-embedded zeolite samples. The results clearly support that various synthetic zeolites can be ion exchanged with Ag(+), Zn(2+), and Cu(2+) ions to acquire antimicrobial properties or ion-releasing characteristics to provide prolonged or stronger activity. The current study suggested that zeolite formulations could be combined with various materials used in manufacturing medical devices, surfaces, textiles, or household items where antimicrobial properties are required. PMID:24242073

Demirci, Selami; Ustao?lu, Zeynep; Y?lmazer, Gonca Alt?n; Sahin, Fikrettin; Baç, Nurcan

2014-02-01

119

First principles derived, transferable force fields for CO2 adsorption in Na-exchanged cationic zeolites.  

PubMed

The development of accurate force fields is vital for predicting adsorption in porous materials. Previously, we introduced a first principles-based transferable force field for CO2 adsorption in siliceous zeolites (Fang et al., J. Phys. Chem. C, 2012, 116, 10692). In this study, we extend our approach to CO2 adsorption in cationic zeolites which possess more complex structures. Na-exchanged zeolites are chosen for demonstrating the approach. These methods account for several structural complexities including Al distribution, cation positions and cation mobility, all of which are important for predicting adsorption. The simulation results are validated with high-resolution experimental measurements of isotherms and microcalorimetric heats of adsorption on well-characterized materials. The choice of first-principles method has a significant influence on the ability of force fields to accurately describe CO2-zeolite interactions. The PBE-D2 derived force field, which performed well for CO2 adsorption in siliceous zeolites, does not do so for Na-exchanged zeolites; the PBE-D2 method overestimates CO2 adsorption energies on multi-cation sites that are common in cationic zeolites with low Si/Al ratios. In contrast, a force field derived from the DFT/CC method performed well. Agreement was obtained between simulation and experiment not only for LTA-4A on which the force field fitting is based, but for other two common adsorbents, NaX and NaY. PMID:23807115

Fang, Hanjun; Kamakoti, Preeti; Ravikovitch, Peter I; Aronson, Matthew; Paur, Charanjit; Sholl, David S

2013-08-21

120

Reactivity and applications of layered silicates and layered double hydroxides.  

PubMed

Layered materials, such as layered sodium silicates and layered double hydroxides (LDHs), are well-known for their remarkable adsorption, intercalation and swelling properties. Their tunable interlayers offer an interesting avenue for the fabrication of pillared nanoporous materials, organic-inorganic hybrid materials and catalysts or catalyst supports. This perspective article provides a summary of the reactivity and applications of layered materials including aluminium-free layered sodium silicates (kanemite, ilerite (RUB-18 or octosilicate) and magadiite) and layered double hydroxides (LDHs). Recent developments in the use of layered sodium silicates as precursors for the preparation of various porous, functional and catalytic materials including zeolites, mesoporous materials, pillared layered silicates, organic-inorganic nanocomposites and synthesis of highly dispersed nanoparticles supported on silica are reviewed in detail. Along this perspective, we have attempted to illustrate the reactivity and transformational potential of LDHs in order to deduce the main differences and similarities between these two types of layered materials. PMID:24841986

Selvam, Thangaraj; Inayat, Alexandra; Schwieger, Wilhelm

2014-07-21

121

Kinetics of silicate exchange in alkaline aluminosilicate solutions.  

PubMed

In strongly alkaline aqueous KOH solutions containing SiIV in large excess over AlIII, the kinetics of exchange of monomeric silicate with small acyclic aluminosilicate solute species is much more rapid than with either cyclic aluminosilicates or any all-silicate anions. Selective inversion recovery 29Si NMR studies of homogeneous solutions of stoichiometric composition 3.0 mol kg-1 of SiO2, 0.1 mol kg-1 of Al2O3, and 8.0 mol kg-1 of K2O in 60-75% D2O gave rate constants of 2.0 +/- 0.2 kg mol-1 s-1 and 17 +/- 4 s-1 for the forward and reverse reactions of monomeric silicate with (HO)3AlOSiOn(OH)(3-n)(n+1)- (n = 2 or 3) at 0 degree C. These rate constants are more than 10(4)-fold faster than those extrapolated from 60 to 90 degrees C for comparable reactions of silicate anions. The greater lability of acyclic aluminate centers relative to silicate is ascribed partly to the availability of HO- groups for condensation reactions on Al and mainly to the ease of expansion of the coordination number of AlIII beyond 4. The latter attribute is diminished when AlIII is constrained to be tetrahedral in cyclic structures. With respect to the mechanism of formation of zeolites from alkaline aqueous media, it is suggested that small, labile AlOSi units add rapidly to growing zeolitic structures "on demand", whereas the more kinetically inert cage or ring structures cannot. This would explain why a silicate or aluminosilicate structure that is dominant among solute species at equilibrium in the presence of a particular cation may bear little or no geometric relation to the zeolitic framework promoted kinetically by that same cation. PMID:11197023

North, M R; Swaddle, T W

2000-06-12

122

"A Novel Synthesis of Zeolite W..."  

SciTech Connect

Zeolite W has been synthesized using organometallic silicon and aluminum precursors in two hydrothermal systems: organocation containing and organocation-free. The reaction using the organocation yielded a fully crystalline, relatively uniform crystal size product, with no organic molecules occluded in the pores. In contrast, the product obtained from an identical reaction, except for the absence of the organocation, contained amorphous as well as crystalline material and the crystalline phase showed a large diversity of both crystal size and morphology. The use of organometallic precursors, either with or without an organocation, allows for the crystallization of the MER framework at much lower 0H/Si02 and (K+ Na - Al)/Si ratios than is typical of inorganic systems. The reaction products were characterized by XRD, SEM, EDS, and thermal analyses.

Nenoff, Tina M.; Thoma, Steven G.

1999-05-07

123

Hydrothermal synthesis of ytterbium silicate nanoparticles.  

PubMed

A simple, low-cost hydrothermal method was developed to synthesize 20-nm-diameter single-crystalline ytterbium silicate (Yb(2)Si(2)O(7) and Yb(2)SiO(5)) nanoparticles at 200 degrees C. This is nearly 1000 degrees C lower than that for the typical sol-gel route to ytterbium silicate powders. Obtained powders showed very low thermal conductivity, a suitable thermal expansion coefficient, and excellent thermal/structural stability, suggesting a potential application to environmental and thermal barrier coatings. Special focus was placed on assessing the hydrothermal reaction mechanism for particle formation. PMID:20085266

Chen, Hongfei; Gao, Yanfeng; Liu, Yun; Luo, Hongjie

2010-02-15

124

Diagram of Zeolite Crystals  

NASA Technical Reports Server (NTRS)

The Center for Advanced Microgravity Materials Processing (CAMMP) in Cambridge, MA, a NASA-sponsored Commercial Space Center, is working to improve zeolite materials for storing hydrogen fuel. CAMMP is also applying zeolites to detergents, optical cables, gas and vapor detection for environmental monitoring and control, and chemical production techniques that significantly reduce by-products that are hazardous to the environment. Depicted here is one of the many here complex geometric shapes which make them highly absorbent. Zeolite experiments have also been conducted aboard the International Space Station

2003-01-01

125

Role of ammonium fluoride in crystallization process of beta zeolite  

NASA Astrophysics Data System (ADS)

The addition of Na + cations to the starting gel prepared using NH 4F significantly prolonged the crystallization time of beta zeolite. However, in the case of pure silica beta zeolite an addition of more NH 4F reduced the crystallization time by one-half. From 29Si MAS NMR measurements, the signal attributed to pentacoordinated silicon was found to be more pronounced for pure silica beta zeolite in the presence of Na + cations even in the solid phase with low crystallinity, as compared to that in the absence of Na + cations. Considering the results of theoretical calculation, because of more energetically stable state of Na +[SiO 4/2F] - species, it could be presumed that Na +[SiO 4/2F] - species might exist in pure silica beta zeolite. Furthermore, as confirmed by 19F MAS NMR measurements tetraethylammonium fluoride (TEAF) species were enclathrated intact in solid phase during the initial crystallization stage. This suggests that TEAF species are required for the formation of beta zeolite framework, in other words, as "SDA" which conditions the formation of kinetically favored phase, i.e., beta zeolite. Moreover, since part of TEA + cations is replaced by sodium cations, forming Na +[SiO 4/2F] - species, the amount of TEA +[SiO 4/2F] - species involved in either nucleation or crystal growth decreases and thus the crystallization time becomes longer.

Jon, Hery; Oumi, Yasunori; Itabashi, Keiji; Sano, Tsuneji

2007-09-01

126

Zeolites in Soil Environments.  

National Technical Information Service (NTIS)

Over the past 25 years, natural zeolites have been examined for a variety of agricultural and environmental applications because of their unique cation-exchange, adsorption, and molecular sieving properties and their abundance in near-surface, sedimentary...

D. W. Ming J. L. Boettinger

2001-01-01

127

Composite zeolite membranes  

DOEpatents

A new class of composite zeolite membranes and synthesis techniques therefor has been invented. These membranes are essentially defect-free, and exhibit large levels of transmembrane flux and of chemical and isotopic selectivity.

Nenoff, Tina M. (Albuquerque, NM); Thoma, Steven G. (Albuquerque, NM); Ashley, Carol S. (Albuquerque, NM); Reed, Scott T. (Albuquerque, NM)

2002-01-01

128

ZEOLITE CHARACTERIZATION TESTING  

SciTech Connect

The Savannah River Site isolates tritium from its process streams for eventual recycling. This is done by catalyzing the formation of tritiated water (from process streams) and then sorbing that water on a 3A zeolite (molsieve) bed. The tritium is recovered by regenerating the saturated bed into a Mg-based water cracking unit. The process described has been in use for about 15 years. Recently chloride stress corrosion cracking (SCC) was noted in the system piping. This has resulted in the need to replace the corroded piping and associated molecular sieve beds. The source of chlorine has been debated and one possible source is the zeolite itself. Since new materials are being purchased for recently fabricated beds, a more comprehensive analysis protocol for characterizing zeolite has been developed. Tests on archived samples indicate the potential for mobile chloride species to be generated in the zeolite beds.

Jacobs, W; Herbert Nigg, H

2007-09-13

129

Properties of Natural Zeolites.  

National Technical Information Service (NTIS)

Samples of the naturally occuring zeolites phillipsote, clinoptilolite, erionite, and chabazite have been surveyed for their gas adsorption, ion exchange, and other characteristics. Chabazite and erionite, which are generally more stable, also have higher...

R. A. Munson

1973-01-01

130

Zeolite A imidazolate frameworks  

NASA Astrophysics Data System (ADS)

Faujasite (FAU) and zeolite A (LTA) are technologically important porous zeolites (aluminosilicates) because of their extensive use in petroleum cracking and water softening. Introducing organic units and transition metals into the backbone of these types of zeolite allows us to expand their pore structures, enhance their functionality and access new applications. The invention of metal-organic frameworks and zeolitic imidazolate frameworks (ZIFs) has provided materials based on simple zeolite structures where only one type of cage is present. However, so far, no metal-organic analogues based on FAU or LTA topologies exist owing to the difficulty imposed by the presence of two types of large cage (super- and ?-cages for FAU, ?- and ?-cages for LTA). Here, we have identified a strategy to produce an LTA imidazolate framework in which both the link geometry and link-link interactions play a decisive structure-directing role. We describe the synthesis and crystal structures of three porous ZIFs that are expanded analogues of zeolite A; their cage walls are functionalized, and their metal ions can be changed without changing the underlying LTA topology. Hydrogen, methane, carbon dioxide and argon gas adsorption isotherms are reported and the selectivity of this material for carbon dioxide over methane is demonstrated.

Hayashi, Hideki; Côté, Adrien P.; Furukawa, Hiroyasu; O'Keeffe, Michael; Yaghi, Omar M.

2007-07-01

131

Hydraulic conductivity of compacted zeolites.  

PubMed

Hydraulic conductivities of compacted zeolites were investigated as a function of compaction water content and zeolite particle size. Initially, the compaction characteristics of zeolites were determined. The compaction test results showed that maximum dry unit weight (?(dmax)) of fine zeolite was greater than that of granular zeolites. The ?(dmax) of compacted zeolites was between 1.01 and 1.17 Mg m(-3) and optimum water content (w(opt)) was between 38% and 53%. Regardless of zeolite particle size, compacted zeolites had low ?(dmax) and high w(opt) when compared with compacted natural soils. Then, hydraulic conductivity tests were run on compacted zeolites. The hydraulic conductivity values were within the range of 2.0 × 10(-3) cm s(-1) to 1.1 × 10(-7) cm s(-1). Hydraulic conductivity of all compacted zeolites decreased almost 50 times as the water content increased. It is noteworthy that hydraulic conductivity of compacted zeolite was strongly dependent on the zeolite particle size. The hydraulic conductivity decreased almost three orders of magnitude up to 39% fine content; then, it remained almost unchanged beyond 39%. Only one report was found in the literature on the hydraulic conductivity of compacted zeolite, which is in agreement with the findings of this study. PMID:23460541

Oren, A Hakan; Ozdamar, Tu?çe

2013-06-01

132

Preparation of functionalized zeolitic frameworks  

DOEpatents

The disclosure provides zeolitic frameworks for gas separation, gas storage, catalysis and sensors. More particularly the disclosure provides zeolitic frameworks (ZIFs). The ZIF of the disclosure comprises any number of transition metals or a homogenous transition metal composition.

Yaghi, Omar M; Furukawa, Hiroyasu; Wang, Bo

2013-07-09

133

Preparation of functionalized zeolitic frameworks  

DOEpatents

The disclosure provides zeolitic frameworks for gas separation, gas storage, catalysis and sensors. More particularly the disclosure provides zeolitic frameworks (ZIFs). The ZIF of the disclosure comprises any number of transition metals or a homogenous transition metal composition.

Yaghi, Omar M; Hayashi, Hideki; Banerjee, Rahul; Park, Kyo Sung; Wang, Bo; Cote, Adrien P

2012-11-20

134

SILICATE EVOLUTION IN BROWN DWARF DISKS  

SciTech Connect

We present a compositional analysis of the 10 {mu}m silicate spectra for brown dwarf disks in the Taurus and Upper Scorpius (UppSco) star-forming regions, using archival Spitzer/Infrared Spectrograph observations. A variety in the silicate features is observed, ranging from a narrow profile with a peak at 9.8 {mu}m, to nearly flat, low-contrast features. For most objects, we find nearly equal fractions for the large-grain and crystalline mass fractions, indicating both processes to be active in these disks. The median crystalline mass fraction for the Taurus brown dwarfs is found to be 20%, a factor of {approx}2 higher than the median reported for the higher mass stars in Taurus. The large-grain mass fractions are found to increase with an increasing strength in the X-ray emission, while the opposite trend is observed for the crystalline mass fractions. A small 5% of the Taurus brown dwarfs are still found to be dominated by pristine interstellar medium-like dust, with an amorphous submicron grain mass fraction of {approx}87%. For 15% of the objects, we find a negligible large-grain mass fraction, but a >60% small amorphous silicate fraction. These may be the cases where substantial grain growth and dust sedimentation have occurred in the disks, resulting in a high fraction of amorphous submicron grains in the disk surface. Among the UppSco brown dwarfs, only usd161939 has a signal-to-noise ratio high enough to properly model its silicate spectrum. We find a 74% small amorphous grain and a {approx}26% crystalline mass fraction for this object.

Riaz, B. [Instituto de Astrofisica de Canarias, E38205 La Laguna, Tenerife (Spain)], E-mail: basmah@iac.es

2009-08-10

135

Energetic Processing of Interstellar Silicate Grains by Cosmic Rays  

SciTech Connect

While a significant fraction of silicate dust in stellar winds has a crystalline structure, in the interstellar medium nearly all of it is amorphous. One possible explanation for this observation is the amorphization of crystalline silicates by relatively 'low' energy, heavy ion cosmic rays. Here we present the results of multiple laboratory experiments showing that single-crystal synthetic forsterite (Mg{sub 2}SiO{sub 4}) amorphizes when irradiated by 10 MeV Xe{sup ++} ions at large enough fluences. Using modeling, we extrapolate these results to show that 0.1-5.0 GeV heavy ion cosmic rays can rapidly ({approx}70 Million yrs) amorphize crystalline silicate grains ejected by stars into the interstellar medium.

Bringa, E M; Kucheyev, S O; Loeffler, M J; Baragiola, R A; Tielens, A G Q M; Dai, Z R; Graham, G; Bajt, S; Bradley, J; Dukes, C A; Felter, T E; Torres, D F; van Breugel, W

2007-03-28

136

Production of biofuel from waste cooking palm oil using nanocrystalline zeolite as catalyst: Process optimization studies  

Microsoft Academic Search

The catalytic cracking of waste cooking palm oil to biofuel was studied over different types of nano-crystalline zeolite catalysts in a fixed bed reactor. The effect of reaction temperature (400–500°C), catalyst-to-oil ratio (6–14) and catalyst pore size of different nanocrystalline zeolites (0.54–0.80nm) were studied over the conversion of waste cooking palm oil, yields of Organic Liquid Product (OLP) and gasoline

Niken Taufiqurrahmi; Abdul Rahman Mohamed; Subhash Bhatia

2011-01-01

137

Crystallization of JBW, CAN, SOD and ABW type zeolite from transformation of meta-kaolin  

Microsoft Academic Search

The crystallization of low silica zeolites, including JBW, CAN, SOD and Li-ABW was investigated on the hydrothermal transformation of China meta-kaolin in alkaline medium at 473 K, and characterized with XRD, SEM and 29Si MAS NMR. The significant influence of the inorganic additives on the products formed was observed. The crystallization process of JBW zeolite with high crystallinity from the

De-Chang Lin; Xiao-Wen Xu; Feng Zuo; Ying-Cai Long

2004-01-01

138

Microwave-hydrothermal synthesis of Al-substituted tobermorite from zeolites  

Microsoft Academic Search

Here, we report the rapid synthesis of Al-substituted tobermorites from zeolites under microwave-hydrothermal (M-H) conditions. The synthesized phases were characterized by powdered XRD analysis, SEM and selective Cs exchange determination. Zeolites served as aluminosilicate sources and M-H conditions yielded highly crystalline Al-substituted tobermorites in 2h at 180°C and they showed high selectivity for Cs. For example, an Al-substituted tobermorite synthesized

Sridhar Komarneni; Jayanth S Komarneni; Bharat Newalkar; Stephen Stout

2002-01-01

139

Topotactic condensation of layer silicates with ferrierite-type layers forming porous tectosilicates.  

PubMed

Five different hydrous layer silicates (HLSs) containing fer layers (ferrierite-type layers) were obtained by hydrothermal syntheses from mixtures of silicic acid, water and tetraalkylammonium/tetraalkylphosphonium hydroxides. The organic cations had been added as structure directing agents (SDA). A characteristic feature of the structures is the presence of strong to medium strong hydrogen bonds between the terminal silanol/siloxy groups of neighbouring layers. The five-layered silicates differ chemically only with respect to the organic cations. Structurally, they differ with respect to the arrangement of the fer layers relative to each other, which is distinct for every SDA-fer-layer system. RUB-20 (containing tetramethylammonium) and RUB-40 (tetramethylphosphonium) are monoclinic with stacking sequence AAA and shift vectors between successive layers 1a0 + 0b0 + 0.19c0 and 1a0 + 0b0 + 0.24c0, respectively. RUB-36 (diethyldimethylammonium), RUB-38 (methyltriethylammonium) and RUB-48 (trimethylisopropylammonium) are orthorhombic with stacking sequence ABAB and shift vectors 0.5a0 + 0b0± 0.36c0, 0.5a0 + 0b0 + 0.5c0 and 0.5a0 + 0b0± 0.39c0, respectively. Unprecedented among the HLSs, two monoclinic materials are made up of fer layers which possess a significant amount of ordered defects within the layer. The ordered defects involve one particular Si-O-Si bridge which is, to a fraction of ca. 50%, hydrolyzed to form nests of two [triple bond, length as m-dash]Si-OH groups. When heated to 500-600 °C in air, the HLSs condense to form framework silicates. Although all layered precursors were moderately to well ordered, the resulting framework structures were of quite different crystallinity. The orthorhombic materials RUB-36, -38 and -48, general formula SDA4Si36O72(OH)4, which possess very strong hydrogen bonds (d[OO] ? 2.4 Å), transform into a fairly or well ordered CDO-type silica zeolite RUB-37. The monoclinic materials RUB-20 and -40, general formula SDA2Si18O36(OH)2OH, possessing medium strong hydrogen bonds (d[OO] ? 2.65 Å) are transformed into poorly ordered framework silicates. Some rules of thumb can be established concerning the successful zeolite synthesis via a topotactic condensation of layered precursors. Favourably, the precursor (i) possesses already a well ordered structure without defects, (ii) contains strong inter-layer hydrogen bonds and does not contain strong intra-layer hydrogen bonds and (iii) contains a suitable cation. The nature of the organic cation (size, geometry, flexibility, thermal stability) plays a key role in the formation of a microporous tectosilicate with well ordered structure. RUB-36 which meets these criteria yields a well ordered condensation product (RUB-37). PMID:24875843

Marler, B; Wang, Y; Song, J; Gies, H

2014-07-21

140

Controlling the adsorption enthalpy of CO(2) in zeolites by framework topology and composition.  

PubMed

Zeolites are often investigated as potential adsorbents for CO(2) adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra-framework cations), the CO(2) adsorption heats at low coverages vary from -20 to -60 kJ mol(-1), and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion-exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and -SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO(2) adsorption complexes are identified and discussed at the molecular level. A general model for CO(2) adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model. PMID:22887989

Grajciar, Lukáš; ?ejka, Ji?í; Zukal, Arnošt; Otero Areán, Carlos; Turnes Palomino, Gemma; Nachtigall, Petr

2012-10-01

141

The importance of zeolites in the potential high-level radioactive waste repository at Yucca Mountain, Nevada  

SciTech Connect

Zeolitic rocks play an important role in retarding the migration of radionuclides that occur in solution as simple cations (Cs, Sr, Ba). However, the interaction of zeolites with complex transuranic species in solution provides little if any advantage over other common silicate minerals. The most important consequences of zeolite occurrences near a high-level radioactive waste repository environment are likely to be their response to thermal loading and their impact on site hydrology. Partial zeolite dehydration during the early thermal pulse from the repository and rehydration as the repository slowly cools can have an important impact on the water budget of a repository in unsaturated rocks, provided that the long-term heating does not result in zeolite destabilization.

Vaniman, D.T.; Bish, D.L.

1993-07-01

142

Optical Properties of Astronomical Silicates in the Far-infrared  

NASA Technical Reports Server (NTRS)

Correct interpretation of a vast array of astronomical data relies heavily on understanding the properties of silicate dust as a function of wavelength, temperature, and crystallinity. We introduce the QPASI-T (Optical Properties of Astronomical Silicates with Infrared Techniques) project to address the need for high fidelity optical characterization data on the various forms of astronomical dust. We use two spectrometers to provide extinction data for silicate samples across a wide wavelength range (from the near infrared to the millimeter). New experiments are in development that will provide complementary information on the emissivity of our samples, allowing us to complete the optical characterization of these dust materials. In this paper, we present initial results from several materials including amorphous iron silicate, magnesium silicate and silica smokes, over a wide range of temperatures, and discuss the design and operation of our new experiments.

Rinehart, Stephen A,; Benford, Dominic J.; Dwek, Eli; Henry, Ross M.; Nuth, Joseph A., III; Silverberg, Robert f.; Wollack, Edward J.

2008-01-01

143

Silicate volcanism on Io  

NASA Technical Reports Server (NTRS)

This paper is mainly concerned with the nature of volcanic eruptions on Io, taking into account questions regarding the presence of silicates or sulfur as principal component. Attention is given to the generation of silicate magma, the viscous dissipation in the melt zone, thermal anomalies at eruption sites, and Ionian volcanism. According to the information available about Io, it appears that its volcanism and hence its surface materials are dominantly silicic. Several percent of volatile materials such as sulfur, but also including sodium- and potassium-rich materials, may also be present. The volatile materials at the surface are continually vaporized and melted as a result of the high rates of silicate volcanism.

Carr, M. H.

1986-01-01

144

Silicate volcanism on Io  

NASA Astrophysics Data System (ADS)

This paper is mainly concerned with the nature of volcanic eruptions on Io, taking into account questions regarding the presence of silicates or sulfur as principal component. Attention is given to the generation of silicate magma, the viscous dissipation in the melt zone, thermal anomalies at eruption sites, and Ionian volcanism. According to the information available about Io, it appears that its volcanism and hence its surface materials are dominantly silicic. Several percent of volatile materials such as sulfur, but also including sodium- and potassium-rich materials, may also be present. The volatile materials at the surface are continually vaporized and melted as a result of the high rates of silicate volcanism.

Carr, M. H.

1986-03-01

145

Advances in nanosized zeolites.  

PubMed

This review highlights recent developments in the synthesis of nanosized zeolites. The strategies available for their preparation (organic-template assisted, organic-template free, and alternative procedures) are discussed. Major breakthroughs achieved by the so-called zeolite crystal engineering and encompass items such as mastering and using the physicochemical properties of the precursor synthesis gel/suspension, optimizing the use of silicon and aluminium precursor sources, the rational use of organic templates and structure-directing inorganic cations, and careful adjustment of synthesis conditions (temperature, pressure, time, heating processes from conventional to microwave and sonication) are addressed. An on-going broad and deep fundamental understanding of the crystallization process, explaining the influence of all variables of this complex set of reactions, underpins an even more rational design of nanosized zeolites with exceptional properties. Finally, the advantages and limitations of these methods are addressed with particular attention to their industrial prospects and utilization in existing and advanced applications. PMID:23803972

Mintova, Svetlana; Gilson, Jean-Pierre; Valtchev, Valentin

2013-08-01

146

Adsorption of aqueous Zn(II) species on synthetic zeolites  

NASA Astrophysics Data System (ADS)

To supply a good quality drinkable water tends to become a strategic task in both developed and under development countries in the world due to the number of potential contamination sources. One of the major problems is derived from the presence of heavy toxic metals like zinc or lead resulting from industrial activities. Zeolites are known as very efficient mineral substrates for fixing aqueous ionic species through their wide range of channels present in the crystalline structure and due to their strong surface reactivity. MicroPIXE coupled with microRBS (3.05 MeV 4He + ions) have been used to quantify the incorporation of zinc within two commercial zeolites containing alkali elements (zeolite X and clinoptilolite) in the concentration range of: 0.0002-0.05 M at neutral pH. At the beginning of the interaction between zeolite and Zn(II) solution, the adsorption process exhibits a direct proportionality between the content of zinc fixed on the mineral substrate and the aqueous concentration up to 0.01 M. Beyond this point a saturation effect seems to occur, indicating the strong decrease of available adsorption sites. Sodium or potassium ions are probably exchanged with Zn(II) ions during this process. The compared behaviour of the two zeolites is then discussed in terms of kinetic effects based on ionic radius values. A co-adsorption test carried on with a 50-50% Zn(II) 0.001 M-Pb(II) 0.001 M solution shows that lead does not occupy the same sites as zinc because the content of zinc fixed on the zeolite sample exactly corresponds to the result obtained with a pure 0.001 M Zn(II) solution. All these data clearly showed that zeolite surface reactivity is greatly influenced by the mineral cage-like structure and particularly the presence of pockets, spaces and channels.

Badillo-Almaraz, Véronica; Trocellier, Patrick; Dávila-Rangel, Ignacio

2003-09-01

147

Monodispersed Ultrafine Zeolite Crystal Particles by Microwave Hydrothermal Synthesis  

SciTech Connect

Microwave hydrothermal synthesis of zeolites is reviewed. Monodispersed ultrafine crystal particles of zeolite (Silicalite-1) have been synthesized in batch reactor vessels by microwave irradiation heating of aqueous basic silicate precursor solutions with tetra propyl ammonium hydroxide as the templating molecule. The effects of major process parameters (such as synthesis temperature, microwave heating rate, volume ratio (i.e., the volume of the initial synthesis solution over the total volume of the reactor vessel), and synthesis time on the zeolite particle characteristics are studied using a computer-controlled microwave reactor system that allows real-time monitoring and control of reaction medium temperature. The changes in the morphology, size and crystal structure of the particles are investigated using scanning electron microscope, dynamic light scattering, X-ray diffraction, and BET surface analysis. We have found that the synthesis temperature, volume ratio, and heating rate play a significant role in controlling the particle size, uniformity, and morphology. Microwave processing has generated new morphologies of zeolite particles (i.e., uniform block-shaped particles that contain mixed gel-nanocrystallites and agglomerated crystal particles) that could not be made by a conventional hydrothermal process. At higher synthesis temperature and lower volume ratio, irregular block-shaped particles were produced, whereas increasing the volume ratio promoted the formation of monodispersed single-crystal particles with uniform shape. Our results clearly demonstrate that faster microwave heating is advantageous to enhance the zeolite crystallization kinetics and produces larger-size crystal particles in shorter time. In addition, zeolite crystallization mechanisms, depending on the microwave heating rate, were also discussed.

Hu, Michael Z. [ORNL; Harris, Michael Tyrone [ORNL; Khatri, Lubna [ORNL

2008-01-01

148

Synthesis, deposition and characterization of magnesium hydroxide nanostructures on zeolite 4A  

SciTech Connect

Research highlights: {yields} Reports a simple precipitation-growth method to produce nanostructures of Mg(OH){sub 2} on the surface of zeolite 4A. {yields} Able to control the growth of the nanostructures by manipulating the experimental procedure. {yields} Able to deposit Mg(OH){sub 2} onto specific sites namely bridging hydroxyl protons (SiOHAl) on the surface of zeolite 4A. -- Abstract: The precipitation and self-assembly of magnesium hydroxide Mg(OH){sub 2} nanopetals on dispersed zeolite 4A particles was investigated. Mg(OH){sub 2}/zeolite nanocomposites were produced from magnesium chloride solutions and characterized via X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared analysis (FTIR), and solid state NMR. It was determined that Mg(OH){sub 2} interacted with bridging hydroxyl protons (SiOHAl) on the zeolite surface, but not with silanol or aluminol groups. NMR analysis showed that 13% of the tetrahedral Al sites on the zeolite were converted to octahedral Al. The zeolite structure and crystallinity remained intact after treatment, and no dealumination reactions were detected. This suggests that the deposition-precipitation process at ambient conditions is a facile method for controlling Mg(OH){sub 2} nanostructures on zeolites.

Koh, Pei-Yoong; Yan, Jing; Ward, Jason; Koros, William J. [School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, GA 30332-0100 (United States)] [School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, GA 30332-0100 (United States); Teja, Amyn S., E-mail: amyn.teja@chbe.gatech.edu [School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, GA 30332-0100 (United States); Xu, Bo [School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 801 Ferst Drive NW, Atlanta, GA 30332-0295 (United States)] [School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 801 Ferst Drive NW, Atlanta, GA 30332-0295 (United States)

2011-03-15

149

CO 2 capture and MWCNTs synthesis using mesoporous silica and zeolite 13X collectively prepared from bottom ash  

Microsoft Academic Search

Ground power plant bottom ashes were alkali-fused at 600°C for 1h and silicate extraction was conducted in water at room temperature. The supernatant solution was then used to make mesoporous silicas after adding a triblock copolymer, Pluronic P123, as a template, whereas the solid precipitate was used to make zeolite 13X. This combined synthesis scheme enabled high levels of silicate

Ji-Eun Park; Han-Kyol Youn; Seung-Tae Yang; Wha-Seung Ahn

150

Shock-Enhanced Dissolution of Silicate Minerals: An Important Planetary Surface Process.  

National Technical Information Service (NTIS)

This study was undertaken to examine the effect of shock loading on rock-water interactions and on the dissolution of silicate phases. Shock-recovery experiments were carried out on oligoclase, hornblende, and labradorite. No additional crystalline phases...

M. B. Boslough R. T. Cygan

1987-01-01

151

Use of hydrogen sulfide to improve benzene production over zeolites  

Microsoft Academic Search

A process is described for producing aromatic hydrocarbons, the process comprising contacting a feedstock comprising one or more of ethylene, propane and propylene with a catalyst comprising a crystalline zeolite material having the structure of ZSM-5 or ZSM-11. The contacting takes place under sufficient aromatization conditions including a temperature of from about 100°C to about 700°C, a pressure of from

1986-01-01

152

Association of indigo with zeolites for improved color stabilization.  

PubMed

The durability of an organic color and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidizing conditions, using Raman and ultraviolet-visible (UV-Vis) spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In the absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high color stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment. PMID:20925983

Dejoie, Catherine; Martinetto, Pauline; Dooryhée, Eric; Van Elslande, Elsa; Blanc, Sylvie; Bordat, Patrice; Brown, Ross; Porcher, Florence; Anne, Michel

2010-10-01

153

Association of Indigo with Zeolites for Improved Color Stabilization  

NASA Astrophysics Data System (ADS)

The durability of an organic colour and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidising conditions, using Raman and UV-visible spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high colour stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment.

Dejoie, Catherine; Martinetto, Pauline; Dooryhée, Eric; van Elslande, Elsa; Blanc, Sylvie; Bordat, Patrice; Brown, Ross; Porcher, Florence; Anne, Michel

2010-10-01

154

Pyrolytic Synthesis of Carbon Nanotubes from Sucrose on a Mesoporous Silicate  

NASA Technical Reports Server (NTRS)

Multiwall carbon nanotubes were synthesized from sucrose by a pyrolytic technique using mesoporous MCM-41 silicate templates without transition metal catalysts. The Nanotubes were examined in the carbon/silicate composite and after dissolution of the silicate. High resolution transmission electron microscopy study of the multiwall nanotubes showed them to be 15 nm in diameter, 200 nm in length and close-ended. There was variation in crystallinity with some nanotubes showing disordered wall structures.

Abdel-Fattah, Tarek; Siochi, Mia; Crooks, Roy

2005-01-01

155

Hydrophobic zeolites for biofuel upgrading reactions at the liquid-liquid interface in water/oil emulsions.  

PubMed

HY zeolites hydrophobized by functionalization with organosilanes are much more stable in hot liquid water than the corresponding untreated zeolites. Silylation of the zeolite increases hydrophobicity without significantly reducing the density of acid sites. This hydrophobization with organosilanes makes the zeolites able to stabilize water/oil emulsions and catalyze reactions of importance in biofuel upgrading, i.e., alcohol dehydration and alkylation of m-cresol and 2-propanol in the liquid phase, at high temperatures. While at 200 °C the crystalline structure of an untreated HY zeolite collapses in a few hours in contact with a liquid medium, the functionalized hydrophobic zeolites keep their structure practically unaltered. Detailed XRD, SEM, HRTEM, and BET analyses indicate that even after reaction under severe conditions, the hydrophobic zeolites retain their crystallinity, surface area, microporosity, and acid density. It is proposed that by preferentially anchoring hydrophobic functionalities on the external surface, the direct contact of bulk liquid water and the zeolite is hindered, thus preventing the collapse of the framework during the reaction in liquid hot water. PMID:22548687

Zapata, Paula A; Faria, Jimmy; Ruiz, M Pilar; Jentoft, Rolf E; Resasco, Daniel E

2012-05-23

156

Separations Using Zeolite Membranes  

Microsoft Academic Search

This overview describes some of the main features of the use of zeolite membranes for separation applications. Four different types of separations are considered: separation of non-adsorbing compounds, of organic molecules, of permanent gases from vapors, and of water (or polar molecules) from organic (or non-polar) species. Several factors, such as the limiting pore size and pore size distribution, surface

Joaquín Coronas; Jesús Santamaría

1999-01-01

157

Diffusion in zeolites  

Microsoft Academic Search

Recent developments in the study of intracrystalline diffusion in zeolites by novel macroscopic methods and the results obtained by some of these methods are reviewed. For many systems there is a significant discrepancy between the macroscopic and microscopic (QENS, PFG NMR) diffusivity values. A possible explanation is suggested.

Douglas M. Ruthven

1995-01-01

158

Annealing of Pre-Cometary Silicate Grains in Solar Nebula Shocks  

NASA Technical Reports Server (NTRS)

Comets contain crystalline silicate grains which could only have formed at high temperatures, not generally experienced by comets. We test the hypothesis that amorphous silicates were annealed by shock waves in the solar nebula. Additional information is contained in the original extended abstract.

Harker, D. E.; Desch, S. J.

2002-01-01

159

Thermochemistry of Silicate Speciation in Aqueous Sodium Silicate Solutions: Ionization and Polymerization of Small Silicate Ion.  

National Technical Information Service (NTIS)

The thermochemistry of simple silicate oligomers in aqueous sodium silicate solutions is rationalized by a model that qualitatively predicts equilibria among monomer, dimer, and trimer silicate structures. Unlike previous models, it incorporates the influ...

J. Yang A. V. McCormick

1993-01-01

160

IMPROVED CATALYSTS FOR HEAVY OIL UPGRADING BASED ON ZEOLITE Y NANOPARTICLES ENCAPSULATED IN STABLE NANOPOROUS HOSTS  

SciTech Connect

The focus of this project is to improve the catalytic performance of zeolite Y for petroleum hydrocracking by synthesizing nanoparticles of the zeolite ({approx}20-25 nm) inside nanoporous silicate or aluminosilicate hosts. The encapsulated zeolite nanoparticles are expected to possess reduced diffusional path lengths, hence hydrocarbon substrates will diffuse in, are converted and the products quickly diffused out. This is expected to prevent over-reaction and the blocking of the zeolite pores and active sites will be minimized. In this phase of the project, procedures for the synthesis of ordered nanoporous silica, such as SBA-15, using block copolymers and nonionic surfactant were successful reproduced. Expansion of the pores sizes of the nanoporous silica using trimethylbenzene is suggested based on shift in the major X-Ray Diffraction peak in the products to lower 2 angles compared with the parent SBA-15 material. The synthesis of ordered nanoporous materials with aluminum incorporated in the predominantly silicate framework was attempted but is not yet successful, and the procedures needs will be repeated and modified as necessary. Nanoparticles of zeolite Y of particle sizes in the range 40 nm to 120 nm were synthesized in the presence of TMAOH as the particle size controlling additive.

Conrad Ingram

2003-09-03

161

'Water Splitting' by Titanium Exchanged Zeolite A.  

National Technical Information Service (NTIS)

Visually detectable and chromatographically and mass spectrally identified hydrogen gas evolves from titanium (III) exchanged zeolite A immersed in water and illuminated with visible light. Titanium(III) exchanged zeolite X and zeolite Y do not produce th...

S. M. Kuznicki E. M. Eyring

1978-01-01

162

Zeolite crystal growth in space  

NASA Technical Reports Server (NTRS)

The growth of large, uniform zeolite crystals in high yield in space can have a major impact on the chemical process industry. Large zeolite crystals will be used to improve basic understanding of adsorption and catalytic mechanisms, and to make zeolite membranes. To grow large zeolites in microgravity, it is necessary to control the nucleation event and fluid motion, and to enhance nutrient transfer. Data is presented that suggests nucleation can be controlled using chemical compounds (e.g., Triethanolamine, for zeolite A), while not adversely effecting growth rate. A three-zone furnace has been designed to perform multiple syntheses concurrently. The operating range of the furnace is 295 K to 473 K. Teflon-lined autoclaves (10 ml liquid volume) have been designed to minimize contamination, reduce wall nucleation, and control mixing of pre-gel solutions on orbit. Zeolite synthesis experiments will be performed on USML-1 in 1992.

Sacco, Albert, Jr.; Thompson, Robert W.; Dixon, Anthony G.

1991-01-01

163

Energetics and structures of fluoro- and chlorofluorocarbons in zeolites: Force field development and Monte Carlo simulations  

SciTech Connect

Canonical Monte Carlo simulations on the adsorption of a series of fluoro-, chlorofluoro-, and hydrofluorocarbons (CF{sub 4}, CF{sub 3}Cl, CF{sub 2}Cl{sub 2}, CFCl{sub 3}, CHF{sub 3}) in siliceous Y and NaY zeolites have been performed and are compared with available calorimetric data on the same host-guest systems. A new force field for fluorocarbon-type molecules in zeolites has been developed, and the (N,V,T) simulations predict adsorption heats with good accuracy. Further insights into the key features of host-guest interactions are gleaned from the relative contributions of the short-range and electrostatic interactions to the total adsorption heats and the analysis of host-guest pair functions. In siliceous Y, host-guest interactions are driven primarily by F{hor_ellipsis}O{sub zeolite} and Cl{hor_ellipsis}O{sub zeolite} van der Waals interactions, and H{hor_ellipsis}O{sub zeolite} hydrogen bonding in the case of hydrogen-containing fluorocarbons. When the fluorocarbon is adsorbed in a cation-containing zeolite, such as NaY, additional F{hor_ellipsis}Na{sub zeolite} electrostatic interactions with Na cations of the supercage are clearly revealed and control the orientation of the sorbate molecules within the supercages. In addition, (N,V,T) simulations have enabled us to compare the behavior of CHF{sub 3} with that of CHCl{sub 3}. The heats of adsorption at zero loading are very similar, but the relative contributions of the short-range and long-range interactions are inverted between the two systems, with the electrostatic term dominating in the case of the fluorocarbon.

Mellot, C.F. [Univ. de Versailles Saint-Quentin (France). Inst. Lavoisier] [Univ. de Versailles Saint-Quentin (France). Inst. Lavoisier; Cheetham, A.K. [Univ. de Versailles Saint-Quentin (France). Inst. Lavoisier] [Univ. de Versailles Saint-Quentin (France). Inst. Lavoisier; [Univ. of California, Santa Barbara (Canada). Materials Research Lab.

1999-05-13

164

SO2 REMOVAL FROM FLUE GASES USING UTILITY SYNTHESIZED ZEOLITES  

SciTech Connect

It is well known that natural and synthetic zeolites (molecular sieves) can adsorb gaseous SO{sub 2} from flue gas and do it more efficiently than lime based scrubbing materials. Unfortunately their cost ($500-$800 per ton) has deterred their use in this capacity. It is also known that zeolites are easy to synthesize from a variety of natural and man-made materials. The overall objective of the current work has been to evaluate the feasibility of having a utility synthesize its own zeolites, on-site, from fly ash and other recycled materials and then use these zeolites to adsorb SO{sub 2} from their flue gases. Work to date has shown that the efficiency of the capture process is related to the degree of crystallinity and the type of zeolite that forms in the samples. Normally, those samples cured at 150 C contained a greater proportion of zeolite and as such were more SO{sub 2} adsorptive than their low-temperature counterparts. However, in order for the project to be successful, on site synthesis must remain an option, i.e. 100 C synthesis. In light of this, the experimental focus now has two aspects. First, compositions of the starting materials are being altered by blending the current suite of fly ashes with ground glass cullet and silica fume to promote the formation and growth of well crystallized and highly adsorptive zeolites. Second, greater degrees of reaction at significantly lower temperatures are being promote by ball milling the fly ash prior to use, by the use of more concentrated caustic solutions, and by the addition of zeolite seeds to the reactants. In all cases studies will focus on the effect of structure type and degree of conversion on SO{sub 2} adsorption. Future work will concentrate on the study of the effect of weathering on the suitability of converting fly ash into zeolites. This is an especially important study, considering the acres of fly ash now in storage throughout the US.

Michael Grutzeck

1999-04-30

165

Density functional modelling of silicate and aluminosilicate dimerisation solution chemistry.  

PubMed

Common throughout sol-gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density functional theory (DFT), and are compared with: (i) existing values reported in the literature, and (ii) new and previously published DFT-derived data for similar silicate reactions at near-neutral pH. From the results it is seen that the energetics of deprotonation and dimerisation reactions depend greatly on the pH value, and these results correlate well with existing experimental values and trends. Hence, this investigation exemplifies that an accurate replication of the solution environment is crucial for obtaining useful theoretical results for species dissolved in non-ideal environments. PMID:21180742

White, Claire E; Provis, John L; Kearley, Gordon J; Riley, Daniel P; van Deventer, Jannie S J

2011-02-14

166

Synthesis of non-siliceous mesoporous oxides.  

PubMed

Mesoporous non-siliceous oxides have attracted great interest due to their unique properties and potential applications. Since the discovery of mesoporous silicates in 1990s, organic-inorganic assembly processes by using surfactants or block copolymers as soft templates have been considered as a feasible path for creating mesopores in metal oxides. However, the harsh sol-gel conditions and low thermal stabilities have limited the expansion of this method to various metal oxide species. Nanocasting, using ordered mesoporous silica or carbon as a hard template, has provided possibilities for preparing novel mesoporous materials with new structures, compositions and high thermal stabilities. This review concerns the synthesis, composition, and parameter control of mesoporous non-siliceous oxides. Four synthesis routes, i.e. soft-templating (surfactants or block copolymers as templates), hard-templating (mesoporous silicas or carbons as sacrificial templates), colloidal crystal templating (3-D ordered colloidal particles as a template), and super lattice routes, are summarized in this review. Mesoporous metal oxides with different compositions have different properties. Non-siliceous mesoporous oxides are comprehensively described, including a discussion of constituting elements, synthesis, and structures. General aspects concerning pore size control, atomic scale crystallinity, and phase control are also reviewed. PMID:23942521

Gu, Dong; Schüth, Ferdi

2014-01-01

167

Temperature dependent thermal conductivity of pure silica MEL and MFI zeolite thin films  

NASA Astrophysics Data System (ADS)

This paper reports the temperature dependent cross-plane thermal conductivity of pure silica zeolite (PSZ) MFI and MEL thin films measured using the 3? method between 30 and 315 K. PSZ MFI thin films were b-oriented, fully crystalline, and had a 33% microporosity. PSZ MEL thin films consisted of MEL nanoparticles embedded in a nonuniform and porous silica matrix. They featured porosity, relative crystallinity, and particle size ranging from 40% to 59%, 23% to 47%, and 55 to 80 nm, respectively. Despite their crystallinity, MFI films had smaller thermal conductivity than that of amorphous silica due to strong phonon scattering by micropores. In addition, the effects of increased relative crystallinity and particle size on thermal conductivity of MEL thin films were compensated by the simultaneous increase in porosity. Finally, thermal conductivity of MFI zeolite was predicted and discussed using the Callaway model based on the Debye approximation.

Fang, Jin; Huang, Yi; Lew, Christopher M.; Yan, Yushan; Pilon, Laurent

2012-03-01

168

Molecular Chemistry in a Zeolite: Genesis of a Zeolite Y-Supported Ruthenium Complex Catalyst  

SciTech Connect

Dealuminated zeolite Y was used as a crystalline support for a mononuclear ruthenium complex synthesized from cis-Ru(acac){sub 2}(C{sub 2}H{sub 4}){sub 2}. Infrared (IR) and extended X-ray absorption fine structure spectra indicated that the surface species were mononuclear ruthenium complexes, Ru(acac)(C{sub 2}H{sub 4}){sub 2}{sup 2+}, tightly bonded to the surface by two Ru-O bonds at Al{sup 3+} sites of the zeolite. The maximum loading of the anchored ruthenium complexes was one complex per two Al{sup 3+} sites; at higher loadings, some of the cis-Ru(acac){sub 2}(C{sub 2}H{sub 4}){sub 2} was physisorbed. In the presence of ethylene and H{sub 2}, the surface-bound species entered into a catalytic cycle for ethylene dimerization and operated stably. IR data showed that at the start of the catalytic reaction, the acac ligand of the Ru(acac)(C{sub 2}H{sub 4}){sub 2}{sup 2+} species was dissociated and captured by an Al{sup 3+} site. Ethylene dimerization proceeded 600 times faster with a cofeed of ethylene and H{sub 2} than without H{sub 2}. These results provide evidence of the importance of the cooperation of the Al{sup 3+} sites in the zeolite and the H{sub 2} in the feed for the genesis of the catalytically active species. The results presented here demonstrate the usefulness of dealuminated zeolite Y as a nearly uniform support that allows precise synthesis of supported catalysts and detailed elucidation of their structures.

Ogino, I.; Gates, B.C.

2009-05-22

169

Studies in colloidal silicates  

Microsoft Academic Search

Summary  The electrical conductance of the mixture obtained by the progressive addition of a sodium silicate to a ferric chloride solution\\u000a first decreases then increases and finally there is again a drop till the soda content of the silicate equals the chloride\\u000a content of the ferric chloride solutions. This shows that the free hydrochloric acid already present in the ferric chloride

K. L. Yadava; S. Ghosh

1957-01-01

170

Serpentines and related silicates  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I5? `Phyllosilicates - Part ?' of Volume 27 `Magnetic properties of non-metallic inorganic compounds based on transition elements` of Landolt-Börnstein - Group III `Condensed Matter'. It presents silicates belonging to the serpentines and related silicates, discussing their crystal structure and lattice parameters, magnetic properties, neutron diffraction data, nuclear gamma resonance (NGR) , nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) data,electrical resistivity, thermal properties, Raman and infrared spectra and optical properties.

Burzo, E.

171

Thermal processing and crystallization of amorphous Mg-Ca silicates  

NASA Astrophysics Data System (ADS)

The structural evolution of sol-gel-produced amorphous Mg(x)Ca(1-x)SiO3 silicates is investigated. Mid-IR Fourier transform infrared spectroscopy and synchrotron X-ray diffraction are used to confirm the amorphous nature of the as-prepared silicates, while subsequent in situ synchrotron X-ray powder diffraction measurements are used to study the evolution of crystalline mineral phases as a function of annealing temperature. Multiple silicate phases, including diopside, enstatite, forsterite, and SiO2, are identified, while Rietveld (i.e., structure) refinement of the diffraction data is used to quantify phase change relationships. Investigated as possible analogs for the refractory dust grain materials likely to have been present in the early solar nebula, the likely relevance of these investigations to the observed silicate compositions of chondritic meteorites and cometary bodies and the processing of their precursor materials is discussed.

Day, Sarah J.; Thompson, Stephen P.; Evans, Aneurin; Parker, Julia E.; Connor, Leigh D.; Tang, Chiu C.

2013-08-01

172

High-Silica Rock Coatings on Mars: Constraining Secondary Silicate Mineralogy and Chemical Weathering Processes on Mars  

Microsoft Academic Search

Thermal Emission Spectrometer (TES) data have been fundamental to understanding Martian surface mineralogy. These data, however, require careful modeling based on laboratory spectroscopic measurements, and modeling of some minerals for Mars has been equivocal. Due to high degrees of spectral similarity, it is difficult to distinguishing silicate glass, clay minerals, zeolites, palagonitized glass, and other secondary products such as amorphous

M. D. Kraft; J. R. Michalski; T. G. Sharp

2003-01-01

173

Effect of geological reaction time on transformation temperature in zeolitic diagenesis  

SciTech Connect

Zeolites found in the Neogene sediments in northern Japan show a vertical zonal arrangement. The zeolite zones are formed primarily by maximum temperature during burial diagenesis. The effect of geological reaction time on transformation temperature to progress in the zeolitization was studied at eight deeply drilled wells in oil-producing areas of Japan. The strata in these wells have continuously deposited under marine environments until recent time and reach geologically maximum burial depth. The geological reaction time at the upper limit of each zeolite zone was estimated from the sedimentation rate on the basis of micropaleontological datum levels and corresponds to the burial time during which the strata have subsided. The transformation temperature of zeolites was determined from the present subsurface temperature, which was obtained by the correction of bottom-hole temperature measured during a wireline log run. The transformation temperature decreases gradually with increasing geological reaction time. The transformation temperatures of silicic glass to clinoptilolite and clinoptilolite to analcime are 58 and 105/sup 0/C at 1.8 mega-annum (Ma) and 50 and 92/sup 0/C at 5 Ma. respectively. The temperature-time relation on the zeolitization in marine sediments is similar to that in thermal maturation of organic matter in sediments.

Sasaki, A.

1986-01-01

174

DFT calculations of EPR parameters for copper(II)-exchanged zeolites using cluster models.  

PubMed

The coordination environment of Cu(II) in hydrated copper-exchanged zeolites was explored through the use of density functional theory (DFT) calculations of EPR parameters. Extensive experimental EPR data are available in the literature for hydrated copper-exchanged zeolites. The copper complex in hydrated copper-exchanged zeolites was previously proposed to be [Cu(H(2)O)(5)OH](+) based on empirical trends in tetragonal model complex EPR data. In this study, calculated EPR parameters for the previously proposed copper complex, [Cu(H(2)O)(5)OH](+), were compared to model complexes in which Cu(II) was coordinated to small silicate or aluminosilicate clusters as a first approximation of the impact of the zeolitic environment on the copper complex. Interpretation of the results suggests that Cu(II) is coordinated or closely associated with framework oxygen atoms within the zeolite structure. Additionally, it is proposed that the EPR parameters are dependent on the Si/Al ratio of the parent zeolite. PMID:20000556

Ames, William M; Larsen, Sarah C

2010-01-14

175

Crystalline Beams  

NASA Astrophysics Data System (ADS)

Crystalline Beams are ordered stale of an ensemble of ions circulating in a Storage Ring with very small velocity fluctuations. They can be obtained from ordinary warm ion beams with the application of intense cooling techniques, namely electron and/or laser cooling. A phase transition occurs when sufficiently small velocity spreads are reached, freezing the particle-to-particle spacing in strings, zig-zags, and helices... The properties and feasibility of Crystalline Beams depend on the choice of the lattice of the Storage Ring. There are three issues closely related to the design of the Storage Ring, namely: the determination of Equilibrium Configurations, Confinement Conditions, and Stability Conditions. Of particular concern is the effect of the trajectory curvature and of the beam momentum spread. They both set the requirements on the amount of momentum cooling, on the focussing, and on the distribution of bending in the lattice of the Storage Ring. The practical demonstration of Crystalline Beams may create the basis for an advanced technology of particle accelerators. The limitations due to Coulomb intra-beam scattering and space-charge forces would be finally be brought under control, so that ordered beams of ions can be achieved for a variety of new applications.

Ruggiero, Alessandro G.

2000-12-01

176

Properties of zeolite Y in various forms and utilization as catalysts or supports for cerium oxide in ethanol oxidation  

Microsoft Academic Search

Zeolite Y in sodium form (NaY) was synthesized using silica source from rice husk, transformed to ammonium form (NH4Y), and calcined to convert to proton form (HY). The direct conversion of NH4Y to HY resulted in loss of the zeolite crystallinity and lower surface area. Thus, the NH4Y was further used in the preparation of cerium (Ce) catalysts. The NH4Y

Jan-Jezreel F. Saceda; Kamolwan Rintramee; Supattra Khabuanchalad; Sanchai Prayoonpokarach; Rizalinda L. de Leon; Jatuporn Wittayakun

177

Crystal Structure and Chemical Composition of a Presolar Silicate from the Queen Elizabeth Range 99177 Meteorite  

NASA Technical Reports Server (NTRS)

Mineral characterization of presolar silicate grains, the most abundant stardust phase, has provided valuable information about the formation conditions in circumstellar environments and in super-nova (SN) outflows. Spectroscopic observations of dust around evolved stars suggest a majority of amor-phous, Mg-rich olivine grains, but crystalline silicates, most of which are pyroxene, have also been observed [1]. The chemical compositions of hundreds of presolar silicates have been determined by Auger spectroscopy and reveal high Fe contents and nonstoichiometric compositions intermediate to olivine and pyroxene [2-6]. The unexpectedly high Fe contents can partly be attributed to secondary alteration on the meteorite parent bodies, as some grains have Fe isotopic anomalies from their parent stellar source [7]. Only about 35 presolar silicates have been studied for their mineral structures and chemical compositions by transmission electron microscopy (TEM). These grains display a wide range of compositions and structures, including crystalline forsterite, crystalline pyroxene, nanocrystalline grains, and a majority of amorphous nonstoichiometric grains. Most of these grains were identified in the primitive Acfer 094 meteorite. Presolar silicates from this meteorite show a wide range of Fe-contents, suggestive of secondary processing on the meteorite parent body. The CR chondrite QUE 99177 has not suffered as much alteration [8] and displays the highest presolar silicate abundance to date among carbonaceous chondrites [3, 6]. However, no mineralogical studies of presolar silicates from this meteorite have been performed. Here we examine the mineralogy of a presolar silicate from QUE 99177.

Nguyen, A. N.; Keller, L. P.; Rahman, Z.; Messenger, S.

2013-01-01

178

Porous Zeolite: A Potential Ecomaterial.  

National Technical Information Service (NTIS)

A new method of wastewater treatment of fertilizer plant by natural zeolite was set up. In this paper the natural zeolite is pretreated in high temperature to increase the capability of removing NH4+ in wastewater. The capability can be increased more tha...

D. Z. Wang Y. Jiang Z. Chen R. Fang

1994-01-01

179

Electrorheological characterization of zeolite suspensions  

Microsoft Academic Search

The rheological properties of the electrorheological (ER) fluids prepared from commercial zeolites 3A, 5A and 13X suspended in silicone oil were investigated through steady shear and oscillatory shear experiments. Dielectric spectra of the fluids were also measured to examine their possible correlation with the flow behavior of the ER fluids. Among the zeolite ER fluids investigated, the ER fluid using

M. S. Cho; H. J. Choi; I.-J. Chin; W.-S. Ahn

1999-01-01

180

Thermal behavior of natural zeolites  

SciTech Connect

Thermal behavior of natural zeolites impacts their application and identification and varies significantly from zeolite to zeolite. Zeolites evolve H{sub 2}0 upon heating, but recent data show that distinct ``types`` of water (e.g., loosely bound or tightly bound zeolitic water) do not exist. Rather water is bound primarily to extra-framework cations with a continuum of energies, giving rise to pseudocontinuous loss of water accompanied by a dynamic interaction between remaining H{sub 2}0 molecules and extra-framework cations. These interactions in the channels of zeolites give rise to dehydration dependent on the extra-framework cation, in addition to temperature and water vapor pressure. The dehydration reaction and the extra-framework cation also affect the thermal expansion/contraction. Most zeolites undergo dehydration-induced contractions that may be anisotropic, although minor thermal expansion can be seen with some zeolites. Such contractions can be partially or completely irreversible if they involve modifications of the tetrahedral framework and/or if rehydration is sluggish. Thermally induced structural modifications are also driven initially by dehydration and the concomitant contraction and migration of extra-framework cations. Contraction is accommodated by rotations of structural units and tetrahedral cation-oxygen linkages may break. Thermal reactions that involve breaking of tetrahedral cation-oxygen bonds markedly irreversible and may be kinetically limited, producing large differences between short- and long-term heating.

Bish, D.L.

1993-09-01

181

Synthesis of Foam-Shaped Nanoporous Zeolite Material: A Simple Template-Based Method  

ERIC Educational Resources Information Center

Nanoporous zeolite foam is an interesting crystalline material with an open-cell microcellular structure, similar to polyurethane foam (PUF). The aluminosilicate structure of this material has a large surface area, extended porosity, and mechanical strength. Owing to these properties, this material is suitable for industrial applications such as…

Saini, Vipin K.; Pires, Joao

2012-01-01

182

Zeolite formation from coal fly ash and its adsorption potential  

SciTech Connect

The possibility in converting coal fly ash (CFA) to zeolite was evaluated. CFA samples from the local power plant in Prachinburi province, Thailand, were collected during a 3-month time span to account for the inconsistency of the CFA quality, and it was evident that the deviation of the quality of the raw material did not have significant effects on the synthesis. The zeolite product was found to be type X. The most suitable weight ratio of sodium hydroxide (NaOH) to CFA was approximately 2.25, because this gave reasonably high zeolite yield with good cation exchange capacity (CEC). The silica (Si)-to-aluminum (Al) molar ratio of 4.06 yielded the highest crystallinity level for zeolite X at 79% with a CEC of 240 meq/100 g and a surface area of 325 m{sup 2}/g. Optimal crystallization temperature and time were 90{sup o}C and 4 hr, respectively, which gave the highest CEC of approximately 305 meq/100 g. Yields obtained from all experiments were in the range of 50-72%. 29 refs., 5 tabs., 7 figs.

Duangkamol Ruen-ngam; Doungmanee Rungsuk; Ronbanchob Apiratikul; Prasert Pavasant [Chulalongkorn University, Bangkok (Thailand). Department of Chemical Engineering

2009-10-15

183

Calibration analysis of zeolites by laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Laser induced breakdown spectroscopy was used for calibration analysis of different types of microporous crystalline aluminosilicates with exactly ordered structure — zeolites. The LIBS plasma was generated using a Q-switched Nd:YAG laser operating at the wavelength of 532 nm and providing laser pulses of 4 ns duration. Plasma emission was analysed by echelle type emission spectrometer, providing wide spectral range 200-950 nm. The spectrometer was equipped with intensified CCD camera providing rapid spectral acquisition (gating time from 5 ns). The optimum experimental conditions (time delay, gate width and laser pulse energy) have been determined for reliable use of LIBS for quantitative analysis. Samples of different molar ratios of Si/Al were used to create the calibration curves. Calibration curves for different types of zeolites (mordenite, type Y and ZSM-5) were constructed. Molar ratios of Si/Al for samples used for calibration were determined by classical wet chemical analysis and were in the range 5.3-51.8 for mordenite, 2.3-12.8 for type Y and 14-600 for ZSM-5. Zeolites with these molar ratios of Si/Al are usually used as catalysts in alkylation reactions. Laser induced breakdown spectroscopy is a suitable method for analysis of molar ratio Si/Al in zeolites, because it is simple, fast, and does not require sample preparation compared with classical wet chemical analysis which are time consuming, require difficult sample preparation and manipulation with strong acids and bases.

Hor?á?ková, M.; Grolmusová, Z.; Hor?á?ek, M.; Rakovský, J.; Hudec, P.; Veis, P.

2012-08-01

184

Parameters influencing zeolite incorporation in PDMS membranes  

Microsoft Academic Search

The incorporation of several types of zeolite in PDMS membranes is studied, by measuring the tensile strength, xylene sorption, and density of the membranes. The zeolite is shown to be involved in the cross-linking of the membrane. The interaction between the PDMS matrix and the zeolites results in reinforced membranes in the case of zeolite Y. The parameters influencing the

Ivo F. J. Vankelecom; Else Scheppers; Robin Heus; Jan B. Uytterhoeven

1994-01-01

185

Interstellar Silicate Analogs for Grain-surface Reaction Experiments: Gas-phase Condensation and Characterization of the Silicate Dust Grains  

NASA Astrophysics Data System (ADS)

Amorphous, astrophysically relevant silicates were prepared by laser ablation of siliceous targets and subsequent quenching of the evaporated atoms and clusters in a helium/oxygen gas atmosphere. The described gas-phase condensation method can be used to synthesize homogeneous and astrophysically relevant silicates with different compositions ranging from nonstoichiometric magnesium iron silicates to pyroxene- and olivine-type stoichiometry. Analytical tools have been used to characterize the morphology, composition, and spectral properties of the condensates. The nanometer-sized silicate condensates represent a new family of cosmic dust analogs that can generally be used for laboratory studies of cosmic processes related to condensation, processing, and destruction of cosmic dust in different astrophysical environments. The well-characterized silicates comprising amorphous Mg2SiO4 and Fe2SiO4, as well as the corresponding crystalline silicates forsterite and fayalite, produced by thermal annealing of the amorphous condensates, have been used as real grain surfaces for H2 formation experiments. A specifically developed ultra-high vacuum apparatus has been used for the investigation of molecule formation experiments. The results of these molecular formation experiments on differently structured Mg2SiO4 and Fe2SiO4 described in this paper will be the topic of the next paper of this series.

Sabri, T.; Gavilan, L.; Jäger, C.; Lemaire, J. L.; Vidali, G.; Mutschke, H.; Henning, T.

2014-01-01

186

Verified Syntheses of Zeolitic Materials  

NSDL National Science Digital Library

From the International Zeolitic Association comes this online version of the special issue of Microporous and Mesoporous Materials, Volume 22, Issues 4-6, featuring a "cookbook" of "recipes" for making zeolites. Zeolites, of which there are over 100 structure types, occur naturally in some cases, but usually are prepared synthetically. Few are available commercially so researchers wanting to test a zeolite in a new application often must attempt the synthesis of the base zeolite in the laboratory. This book is intended to assist in this endeavor, says the editor, Dr. Harry Robson of Louisiana State University. The recipes can be accessed by material name or structure type. A preface, introductory and explanatory notes, and safety information are provided. The recipes include information on source materials, batch preparation and crystallization instructions, product phase, and XRD characterization. The contributor's name, date of entry, and references accompany each recipe.

187

Computer simulations of the adsorption and diffusion processes of 1-butene in MCM-22 zeolite  

NASA Astrophysics Data System (ADS)

The adsorption and diffusion of 1-butene in purely siliceous MCM-22 zeolite have been studied by the grand canonical Monte Carlo and molecular dynamic simulation. The adsorption behavior of 1-butene was explored in detail from adsorption sites, interaction energies. The mass clouds show that 1-butene can be adsorbed freely in MCM-22 zeolite, and adsorbed preferentially in 10-MR (member rings) channel system with high interaction energy. The diffusion characteristic for 1-butene in two independent channel systems was investigated by using molecular dynamic simulation. The results were obtained by analysis the trajectories of diffusion and the diffusion coefficients, which shows that a large diffusion for 1-butene in both channel systems, especially in the supercage system. The adsorption and the diffusion of the hydrocarbon molecules were affected by the different sizes and structures of 10-MR and 12-MR in MCM-22 zeolite. Moreover, the positions where the molecules are expected to react were revealed.

Zhang, Guo; Zheng, Qing-Chuan; Zhang, Hong-Xing; Liu, Tao; Zhu, Yu-Jun; Fu, Hong-Gang

2009-05-01

188

Dispersion and orientation of zeolite ZSM-5 crystallites within a fluid catalytic cracking catalyst particle.  

PubMed

Confocal fluorescence microscopy was employed to selectively visualize the dispersion and orientation of zeolite ZSM-5 domains inside a single industrially applied fluid catalytic cracking (FCC) catalyst particle. Large ZSM-5 crystals served as a model system together with the acid-catalyzed fluorostyrene oligomerization reaction to study the interaction of plane-polarized light with these anisotropic zeolite crystals. The distinction between zeolite and binder material, such as alumina, silica, and clay, within an individual FCC particle was achieved by utilizing the anisotropic nature of emitted fluorescence light arising from the entrapped fluorostyrene-derived carbocations inside the zeolite channels. This characterization approach provides a non-invasive way for post-synthesis characterization of an individual FCC catalyst particle in which the size, distribution, orientation, and amount of zeolite ZSM-5 aggregates can be determined. It was found that the amount of detected fluorescence light originating from the stained ZSM-5 aggregates corresponds to about 15?wt?%. Furthermore, a statistical analysis of the emitted fluorescence light indicated that a large number of the ZSM-5 domains appeared in small sizes of about 0.015-0.25??m(2), representing single zeolite crystallites or small aggregates thereof. This observation illustrated a fairly high degree of zeolite dispersion within the FCC binder material. However, the highest amount of crystalline material was aggregated into larger domains (ca. 1-5??m(2)) with more or less similarly oriented zeolite crystallites. It is clear that this visualization approach may serve as a post-synthesis quality control on the dispersion of zeolite ZSM-5 crystallites within FCC particles. PMID:24616006

Sprung, Christoph; Weckhuysen, Bert M

2014-03-24

189

Oxygen and hydrogen isotope geochemistry of zeolites  

NASA Technical Reports Server (NTRS)

Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

Karlsson, Haraldur R.; Clayton, Robert N.

1990-01-01

190

Oxygen and hydrogen isotope geochemistry of zeolites  

NASA Astrophysics Data System (ADS)

Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

Karlsson, Haraldur R.; Clayton, Robert N.

1990-05-01

191

Steps toward interstellar silicate mineralogy. V. Thermal Evolution of Amorphous Magnesium Silicates and Silica  

NASA Astrophysics Data System (ADS)

The thermally induced amorphous-to-crystalline transition has been studied for bulk sheets and micrometre-sized particles of magnesium silicate glass (MgSiO3), nanometre-sized amorphous magnesium silicate (MgSiO3 and Mg2SiO4 smokes) and amorphous silica particles (SiO2). Silicate glass was produced by the shock-quenching of melts. Samples of nanometre-sized smoke particles have been obtained by the laser ablation technique. Both the MgSiO3 and the Mg2SiO4 smokes have been found to consist of two particle species; particles of smaller size ranging in diametre from 10 nm to about 100 nm and bigger size ranging from a few 100 nm to almost 3 micrometres in diametre. Nanometre-sized particles have been shown to be depleted in magnesium whereas the micrometre-sized particles were found to be enriched in Mg. Generally, the particles are composed of nonstoichiometric magnesium silicates with compositions varying even inside of the particles. Frequently, the particles contained internal voids that are assumed to have been formed by thermal shrinkage or outgassing of the particles' interior during cooling. Annealing at 1000 K transformed the magnesium silicate smokes into crystalline forsterite (c-Mg2SiO4), tridymite (a crystalline modification of SiO2) and amorphous silica (a-SiO2) according to the initial Mg/Si-ratio of the smoke. Crystallization took place within a few hours for the Mg2SiO4 smoke and within one day for the MgSiO3 smoke. The MgSiO3 glass evolved more slowly because crystallization started at the sample surface. It has been annealed at temperatures ranging from 1000 to 1165 K. In contrast to the smoke samples, MgSiO3 glass crystallized as orthoenstatite (MgSiO3). Only after 50 hours of annealing at 1000 K, weak indications of forsterite and tridymite formation have been found in the X-ray diffraction spectra. At a temperature of 1000 K, amorphous silica nanoparticles showed distinctly lower rates of thermal evolution compared with the magnesium silicates. At 1220 K, the timescale of crystallization of a-SiO2 into cristobalite and tridymite amounts to 4.5 h. From the experiments, crystallization parameters have been obtained: activation energy and velocity of crystal growth. The spectra shown in this study will be made publically available in the electronic database (http://www.astro.uni-jena.de).

Fabian, D.; Jäger, C.; Henning, Th.; Dorschner, J.; Mutschke, H.

2000-12-01

192

The adsorption of fatty acids from vegetable oils with zeolites and bleaching clay\\/zeolite blends  

Microsoft Academic Search

The adsorption of model fatty acids (hepatnoic, oleic), using spiked vegetable oils, was studied using different kinds of\\u000a zeolites (A-zeolite, X, Y-zeolites, mordenite), Y-zeolite exchanged with different cations (alkali, alkaline earth, transition\\u000a metal ions), and with bleaching clay\\/zeolite blends. The adsorption process was shown to be governed by the molecular sieving\\u000a properties of the zeolites involved as well as the

D. R. Taylor; C. B. Ungermann; Z. Demidowicz

1984-01-01

193

The synthesis of zeolites from fly ash and the properties of the zeolite products  

Microsoft Academic Search

Fly ash produced during the combustion of powdered coal could be converted up to 45% into zeolite. By varying the experimental conditions different types of zeolite were produced, e.g. zeolite Na-P1, zeolite K-G and zeolite ZK19. By this zeolitization process the cation exchange capacity (CEC) was raised from 0.02 to circa 2.4 meq\\/g. Anionic heavy metals were largely extracted by

G Steenbruggen; G. G Hollman

1998-01-01

194

Thermal conductivity of model zeolites: molecular dynamics simulation study  

NASA Astrophysics Data System (ADS)

The thermal conductivity of model zeolites was investigated using non-equilibrium molecular dynamics calculations. This type of calculation was found to overestimate the thermal conductivity of low-density silica polymorphs. A better reproduction of the experimental results was found for zeolites, and this was related to the lower phonon mean free path. The thermal conductivity of framework silicates was shown to be determined primarily by the vibrations of the continuous oxygen sublattice. Thus, the most drastic suppression of the heat transfer was related to alterations of the O-O distances; for example, a sixfold reduction in thermal conductivity compared to that of siliceous LTA zeolite was found for LTA-A1PO4. Framework cations were shown to affect the heat transfer by changing the vibrational modes of the structural building units of the framework and non-framework counter-cations, by disturbing the oxygen sublattice locally and acting as Rayleigh and resonant scatterers. A model assuming the heat transfer to be due only to non-dispersive acoustic phonons failed to reproduce the dependence of the thermal conductivity on the mass of the cations and the unit-cell dimension, thus suggesting a more sophisticated mechanism of heat transfer to be operative in framework materials. The effect of non-framework non-ionic species on the thermal conductivity was shown to be determined by their effect on the characteristics of the oxygen framework vibrations. Thus, repulsive interactions between the oxygen sublattice and Xe8 clusters, reducing the anisotropy and anharmonicity of the oxygen vibrations, give rise to enhanced heat transfer in LTA-SiO2 at ambient conditions.

Murashov, Vladimir V.

1999-02-01

195

21 CFR 573.260 - Calcium silicate.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Calcium silicate. 573.260 Section 573.260 Food and Drugs... Food Additive Listing § 573.260 Calcium silicate. Calcium silicate, including synthetic calcium silicate,...

2013-04-01

196

21 CFR 573.260 - Calcium silicate.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 2009-04-01 false Calcium silicate. 573.260 Section 573.260 Food and Drugs... Food Additive Listing § 573.260 Calcium silicate. Calcium silicate, including synthetic calcium silicate,...

2009-04-01

197

21 CFR 172.410 - Calcium silicate.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 2009-04-01 false Calcium silicate. 172.410 Section 172.410 Food and Drugs...CONSUMPTION Anticaking Agents § 172.410 Calcium silicate. Calcium silicate, including synthetic calcium silicate,...

2009-04-01

198

21 CFR 573.260 - Calcium silicate.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Calcium silicate. 573.260 Section 573.260 Food and Drugs... Food Additive Listing § 573.260 Calcium silicate. Calcium silicate, including synthetic calcium silicate,...

2010-04-01

199

Hydrothermal interactions of cement or mortar with zeolites or montmorillonites  

SciTech Connect

Concretes, grouts, clays and/or zeolites are candidate borehole, shaft or tunnel plugging materials for any nuclear waste repository. Interactions between these plugging materials may take place under mild hydrothermal conditions during the life of a repository. Class H cement or motar (PSU/WES mixture) was reacted with one of two montmorillonites, clinoptilolite or mordenite at 100/sup 0/ and 200/sup 0/C for different periods under a confining pressure of 30 MPa. The solid reaction products were characterized by x-ray powder diffraction and scanning electron microscopy after the hydrothermal treatments. When zeolites were in contact (not intimate mixture) with class H cement, they did not seem to alter but clinoptilolite altered to analcime, and mordenite became poorly crystalline in the presence of mortar (containing NaCl) at both 100/sup 0/ and 200/sup 0/C. When cement or mortar was intimately mixed with zeolites or montmorillonites and reacted hydrothermally, the reaction resulted in the formation of Al substituted tobermorite (11A type) in all cases (this type of reaction is expected at the interface) at both 100/sup 0/ and 200/sup 0/C. The mechanism of tobermorite formation includes the decomposition of zeolites or montmorillonites in the presence of alkaline (pH approx. = 12) cement or mortar and recrystallization to form Al substituted tobermorite. Cesium sorption measurements in 0.01N CaCl/sub 2/ on the reaction products revealed that selective Cs sorption increased in most cases, even though little or none of the original zeolites and montmorillonites remained in the products. For example, Cs sorption K/sub d/ (mL/g) increased from 80 in the untreated mortar + Ca montmorillonite mixture to 1700 in the interaction product which is Al substituted tobermorite. Thus, we discover here that Al substituted tobermorite has good selectivity for Cs.

Komarneni, S.; Roy, D.M.

1983-01-01

200

Clinoptilolite zeolitized tuff from Central Alborz Range, North Iran  

NASA Astrophysics Data System (ADS)

Zeolites are hydrated alumino-silicates of the alkaline and alkaline earth cations, principally sodium, potassium, calcium, and magnesium (Iijima 1980; Hay 1981). Zeolites occur principally in unmetamorphosed sedimentary rocks and are particularly widespread in volcani-clastic strata (Hay, 1978). Clinoptilolite is a natural zeolite of the heulandite group with the simplified formula of (Na, K)6 Si30 Al6 O72 .nH2. It is the most common natural zeolite found mainly in sedimentary rocks of volcanic origin. Alborz zone is one of the important geological divisions in Iran. This zone is restricted to Kopeh dagh zone in North & Central Iranian zone in South and is a region of active deformation within the broad Arabian-Eurasia collision zone (Allen et al. 2003). The zeolitized green tuff belt from Central Alborz which introduce here are made of volcanoclastic sequence of Karaj Formation. This belt is about 40 km long along Alborz Range and is Eocene in age. Zeolites and associated minerals of this altered vitric tuff studied. Zeolitization took place in some beds of Karaj Formations, with average range of 3 to 300 meters thickness. There are several gypsum lenses which interbed with a widespread green tuff succession in the studied area. On the basis of chemical composition these tuffs are in the range of acid to intermediate volcanic rocks. Also magmatic affinity is calc-alkaline and geological setting of the area belongs to volcanic arc granitoid. Petrographic data has shown that various shape and size of shard glass are the main component of tuffs. Based on the field studies, detail microscopy, XRD and electron microprobe analysis (EMPA), the following main minerals are determined: Clinoptilolite+montmorillonite+crystobalite. Clinoptilolite and smectite are predominant minerals in all altered samples. Concerning the Si/Al ratio of 40 point analyses of glass shards the Alborz tuff has clinoptilolite composition. Otherwise the chemical composition of altered shard glass is very similar to clinoptilolite structural formula. By using medium results of chemical data the structural formula for Firuzkuh clinoptilolite is as follow: Si 29.91 Al 6.01 Fe2+ 951 Mg2+ 0.393 Ca 0.222 Na 3.162 K 1.422 Paleogeographic conditions have provided a marginal shallow seawater environment which has been filled by volcanoclastics sequence. In Eocene the zeolitization occur as layers which are confined stratigraphically, it seems this process that took place only in preferred tuffaceous horizons which enriched by shard glass. So the term staratabound can be used for this type zeolitization. In altered tuffs there are a close relationship between clinoptiloite and montmorilonite in some deposits. Alborz range, there was an occasionally marine environment (existence of marine microfossils) with humid climate (remnants of plants in some points). Transformation process (glass zeolite + smectite) provides a further silica contribution to the system, which finally in supersaturation and decreasing pH favors the precipitation of silica in altered tuff. This may have occurred when ground water flow become to mix with saline water to lowering the pH.

Taghipour, Batoul

2010-05-01

201

Radiation damage of a glass-bonded zeolite waste form using ion irradiation.  

SciTech Connect

Glass-bonded zeolite is being considered as a candidate ceramic waste form for storing radioactive isotopes separated from spent nuclear fuel in the electrorefining process. To determine the stability of glass-bonded zeolite under irradiation, transmission electron microscope samples were irradiated using high energy helium, lead, and krypton. The major crystalline phase of the waste form, which retains alkaline and alkaline earth fission products, loses its long range order under both helium and krypton irradiation. The dose at which the long range crystalline structure is lost is about 0.4 dpa for helium and 0.1 dpa for krypton. Because the damage from lead is localized in such a small region of the sample, damage could not be recognized even at a peak damage of 50 dpa. Because the crystalline phase loses its long range structure due to irradiation, the effect on retention capacity needs to be further evaluated.

Allen, T. R.; Storey, B. G.

1997-12-05

202

Towards the rational design of efficient organic structure-directing agents for zeolite synthesis.  

PubMed

Zeolites are crystalline microporous materials with application in diverse fields, especially in catalysis. The ability to prepare zeolites with targeted physicochemical properties for a specific catalytic application is a matter of great interest, because it allows the efficiency of the entire chemical process to be increased (higher product yields, lower undesired by-products, less energy consumption, and cost savings, etc). Nevertheless, directing the zeolite crystallization towards the material with the desired framework topology, crystal size, or chemical composition is not an easy task, since several variables influence the nucleation and crystallization processes. The combination of accumulated knowledge, rationalization, and innovation has allowed the synthesis of unique zeolitic structures in the last few years. This is especially true in terms of the design of organic and inorganic structure-directing agents (SDAs). In this Minireview we will present the rationale we have followed in our studies to synthesize new zeolite structures, while putting this in perspective with the advances made by other researchers of the zeolite community. PMID:24115577

Moliner, Manuel; Rey, Fernando; Corma, Avelino

2013-12-23

203

Preliminary study of natural zeolite as catalyst for decreasing the viscosity of heavy oil  

NASA Astrophysics Data System (ADS)

Natural zeolite such as heulandite and clipnotilolite are found in abundant quantities in many regions in the world, particularly in Indonesia. The catalytic ability of natural zeolites were investigated in aquathermolysis in order to decreasing the viscosity of heavy oil. Prior to test the ability, a milling treatment of natural zeolite was carried out on variation of time 4, 6 and 8 hrs and subsequently followed by activation with a simple heating at 300°C. The physical and chemical properties of zeolites before and after of milling as well as the activation were characterized using XRD, SEM and EDS. XRD results indicated the decreasing crystallinity of the treated zeolite. SEM results showed that the particle size was from 0.5 to 2 ?m, indicating the reducing of particle size after the treatment. The catalytic test showed that the addition of natural zeolite (0.5 wt.%) on the mixed of heavy oil and water in an autoclave at temperature 200°C during 6 hrs can reduce the viscosity of heavy oil up to 65%.

Merissa, Shanti; Fitriani, Pipit; Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal

2013-09-01

204

The growth of zeolites A, X and mordenite in space  

NASA Technical Reports Server (NTRS)

Zeolites are a class of crystalline aluminosilicate materials that form the backbone of the chemical process industry worldwide. They are used primarily as adsorbents and catalysts and support to a significant extent the positive balance of trade realized by the chemical industry in the United States (around $19 billion in 1991). The magnitude of their efforts can be appreciated when one realizes that since their introduction as 'cracking catalysts' in the early 1960's, they have saved the equivalent of 60 percent of the total oil production from Alaska's North Slope. Thus the performance of zeolite catalysts can have a profound effect on the U.S. economy. It is estimated that a 1 percent increase in yield of the gasoline fraction per barrel of oil would represent a savings of 22 million barrels of crude oil per year, representing a reduction of $400 million in the United States' balance of payments. Thus any activity that results in improvement in zeolite catalyst performance is of significant scientific and industrial interest. In addition, due to their 'stability,' uniformity, and, within limits, their 'engineerable' structures, zeolites are being tested as potential adsorbents to purify gases and liquids at the parts-per-billion levels needed in today's electronic, biomedical, and biotechnology industries and for the environment. Other exotic applications, such as host materials for quantum-confined semiconductor atomic arrays, are also being investigated. Because of the importance of this class of material, extensive efforts have been made to characterize their structures and to understand their nucleation and growth mechanisms, so as to be able to custom-make zeolites for a desired application. To date, both the nucleation mechanics and chemistry (such as what are the 'key' nutrients) are, as yet, still unknown for many, if not all, systems. The problem is compounded because there is usually a 'gel' phase present that is assumed to control the degree of supersaturation, and this gel undergoes a continuous 'polymerization' type reaction during nucleation and growth. Generally, for structure characterization and diffusion studies, which are useful in evaluating zeolites for improving yield in petroleum refining as well as for many of the proposed new applications (e.g., catalytic membranes, molecular electronics, chemical sensors) large zeolites (greater than 100 to 1000 times normal size) with minimum lattice defects are desired. Presently, the lack of understanding of zeolite nucleation and growth precludes the custom design of zeolites for these or other uses. It was hypothesized that the microgravity levels achieved in an orbiting spacecraft could help to isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation, which occurs since zeolites are twice as dense as the solution from which they are formed. This was expected to promote larger crystals by allowing growing crystals a longer residence time in a high-concentration nutrient field. Thus it was hypothesized that the microgravity environment of Earth orbit would allow the growth of large, more defect-free zeolite crystals in high yield.

Sacco, Albert, Jr.; Bac, N.; Coker, E. N.; Dixon, A. G.; Warzywoda, J.; Thompson, R. W.

1994-01-01

205

Activity of zeolite-containing catalysts in the pyrolysis of low-quality gasolines  

SciTech Connect

The effect of the composition and structure of the zeolite component on the activity of zeolite-containing catalysts in the production of small olefins by the pyrolysis of low-quality gasoline. The experiments were carried out in a laboratory flow system with a fixed catalyst bed. The catalysts had a magnesium silicate carrier containing different cationic forms of y-type synthetic zeolites, chabazite, erionite, and mordenite, as well as a natural clinoptilolite zeolite obtained from the Aidag deposit in the Azerbaidzhan SSR. The hydrocarbon raw material was a low-quality Karachukhur gasoline with an octane rating of 42. The experiments were carried out in the range 550/sup 0/ to 650/sup 0/C and volumetric flow rate of the liquid raw material of from 1 to 5 h/sup -1/. The gaseous reaction products were analyzed chromatographically. The major factors affecting olefin formation in the presence of zeolite-containing catalysts are the temperature of the pyrolysis of the liquid hydrocarbons and volumetric flow rate of the raw material. 2 figures, 1 table. (DP)

Tagiev, D.B.; Sharifova, E.B.; Zeinalova, F.A.; Zul'fugarov, Z.G.; Minachev, Kh.M.

1981-02-01

206

The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust  

NASA Technical Reports Server (NTRS)

Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar abundances. The latter observation may indicate a decoupling of the silicate and sulfide components in grains that condense in stellar outflows. The amorphous silicate grains described here were not extensively affected by irradiation, sputtering, or thermal processing and may represent relatively pristine circumstellar grains. They are strong candidates for the "dirty silicates" in astronomical observations of circumstellar dust shells. The polycrystalline grains were originally amorphous silicate grains that were likely annealed in the early solar nebula but the processing was not sufficient to erase their anomalous oxygen isotopic compositions.

Keller, L. P.; Messenger, S.

2010-01-01

207

Optical Properties of Astronomical Silicates with Infrared Techniques (OPASI-T)  

NASA Technical Reports Server (NTRS)

Astronomical dust is observed in a variety of astrophysical environments and plays an important role in radiative processes and chemical evolution in the galaxy. Depending upon the environment, dust can be either carbon-rich or oxygen-rich (silicate grains). Both astronomical observations and ground-based data show that the optical properties of silicates can change dramatically with the crystallinity of the material, and recent laboratory research provides evidence that the optical properties of silicate dust vary as a function of temperature as well. Therefore, correct interpretation of a vast array of astronomical data relies on the understanding of the properties of silicate dust as functions of wavelength, temperature, and crystallinity. The OPASI-T (Optical Properties of Astronomical Silicates with Infrared Techniques) project addresses the need for high quality optical characterization of metal-enriched silicate condensates using a variety of techniques. A combination of both new and established experiments are used to measure the extinction, reflection, and emission properties of amorphous silicates across the infrared (near infrared to millimeter wavelengths), providing a comprehensive data set characterizing the optical parameters of dust samples. We present room temperature measurements and the experimental apparatus to be used to investigate and characterize additional metal-silicate materials.

Rinehart, Stephen

2010-01-01

208

Synthesis and structure determination of the hierarchical meso-microporous zeolite ITQ-43.  

PubMed

The formation of mesopores in microporous zeolites is generally performed by postsynthesis acid, basic, and steam treatments. The hierarchical pore systems thus formed allow better adsorption, diffusion, and reactivity of these materials. By combining organic and inorganic structure-directing agents and high-throughput methodologies, we were able to synthesize a zeolite with a hierarchical system of micropores and mesopores, with channel openings delimited by 28 tetrahedral atoms. Its complex crystalline structure was solved with the use of automated diffraction tomography. PMID:21868673

Jiang, Jiuxing; Jorda, Jose L; Yu, Jihong; Baumes, Laurent A; Mugnaioli, Enrico; Diaz-Cabanas, Maria J; Kolb, Ute; Corma, Avelino

2011-08-26

209

Zeolites in complex nitrogen biofertilizers  

Microsoft Academic Search

A novel technology for producing complex, ecologically safe biofertilizer, combining advantageous properties of both zeolites and nitrogen-fixing microorganisms has been developed. The resulted biofertilizer is a complex of high-activity nitrogen-fixing strain of Azotobacter chroococcum, isolated from the soil in Armenia and the local zeolite modified by the new technology considering the specific features of this microorganism. The new technology for

Anahit Chakhalyan; Gayane Avetisova; Ashot Saghiyan; Leyli Chil-Akopyan; Lusine Melkonyan; Rudolf Gevorkyan; Hakob Sargsyan; Liana Ghazarian

2008-01-01

210

IMPROVED CATALYSTS FOR HEAVY OIL UPGRADING BASED ON ZEOLITE Y NANOPARTICLES ENCAPSULATED STABLE NANOPOROUS HOST  

SciTech Connect

The objectives of this project are to synthesis nanocrystals of highly acidic zeolite Y, encapsulate them within the channels of mesoporous (nanoporous) silicates or nanoporous organosilicates and evaluate the ''zeolite Y/Nanoporous host'' composites as catalysts for the upgrading of heavy petroleum feedstocks. Our results to date are summarized as follows. The synthesis of high surface ordered nanoporous silica of expanded pore diameter of 25 nm (larger than the standard size of 8.4 nm) using trimethylbenzene as a pore size expander was accomplished. The synthesis of zeolite Y nanoparticles with median pore size of approximately 50 nm (smaller than the 80 nm typically obtained with TMAOH) using combined TMABr/TMAOH as organic additives was also accomplished. The successful synthesis of zeoliteY/Nanoporous host composite materials by sequential combination of zeolite precursors and nanoporous material precursor mixtures was implied based on results from various characterization techniques such as X-Ray diffraction, infrared spectra, thermal analysis, porosimetry data. The resulting materials showed pore sizes up to 11 nm, and infrared band at 570 cm{sup -1} suggesting the presence of both phases. Work in the immediate future will be focused on the following three areas: (1) Further characterization of all-silica and aluminosilicate mesoporous materials with expanded pore sizes up to 30 nm will continue; (2) Research efforts to reduce the average particle size of zeolite nanoparticles down to 35-30 nm will continue; (3) Further synthesis of polymer-SBA15 nanocomposites will be conducted by changing the amount and chemistry of the zeolitic precursors added; and (4) Investigation on the catalytic properties of the materials using probe catalytic reactions (such as cumene cracking), followed by catalytic testing for heavy oil conversion.

Conrad Ingram; Mark Mitchell

2005-03-21

211

Tailored crystalline microporous materials by post-synthesis modification.  

PubMed

Crystalline microporous solids are an important class of inorganic materials with uses in different areas impacting our everyday lives, namely as catalysts, adsorbents, and ion exchangers. Advancements in synthesis have been invaluable in expanding the classical aluminosilicate zeolites to new unique framework types and compositions, motivating innovative developments. However, the inexhaustible post-synthetic options to tailor zeolite properties have been and will continue to be indispensable to realize emerging and to improve conventional applications. Starting from the routine drying and template removal processes that every zeolite must experience prior to use, a wide spectrum of treatments exists to alter individual or collective characteristics of these materials for optimal performance. This review documents the toolbox of post-synthetic strategies available to tune the properties of zeolitic materials for specific functions. The categorisation is based on the scale at which the alteration is aimed at, including the atomic structure (e.g. the introduction, dislodgment, or replacement of framework atoms), the micropore level (e.g. template removal and functionalisation by inorganic and organic species), and the crystal and particle levels (e.g. the introduction of auxiliary porosity). Through examples in the recent literature, it is shown that the combination of post-synthetic methods enables rational zeolite design, extending the characteristics of these materials way beyond those imposed by the synthesis conditions. PMID:22996351

Valtchev, Valentin; Majano, Gerardo; Mintova, Svetlana; Pérez-Ramírez, Javier

2013-01-01

212

Mesoporous zeolite single crystal catalysts: Diffusion and catalysis in hierarchical zeolites  

Microsoft Academic Search

During the last years, several new routes to produce zeolites with controlled mesoporosity have appeared. Moreover, an improved catalytic performance of the resulting mesoporous zeolites over conventional zeolites has been demonstrated in several reactions. In most cases, the mesoporous zeolites exhibit higher catalytic activity, but in some cases also improved selectivity and longer catalyst lifetime has been reported. The beneficial

Claus Hviid Christensen; Kim Johannsen; Eric Törnqvist; Iver Schmidt; Henrik Topsøe; Christina Hviid Christensen

2007-01-01

213

Separation of Cesium and Strontium with Zeolites.  

National Technical Information Service (NTIS)

Basic studies of separation of cesium and strontium were made with specimens of zeolite, including the synthetic zeolites A, X and Y, synthetic mordenite, natural modernite and clinoptilolite. Ammonium chloride, which is considered to be the most suitable...

T. Kanno H. Hashimoto

1976-01-01

214

Zeolite Ammonia Removal from Catfish Pond Waters,  

National Technical Information Service (NTIS)

The research focused on developing a zeolite filtration system which will prevent toxic ammonia build-up in catfish ponds. Zeolites are ion exchangers and some natural species are capable of selectively removing ammonia from various types of water systems...

W. R. Reynolds C. W. Williford

1987-01-01

215

Mining Environmental Target Investigation: Natural Zeolites.  

National Technical Information Service (NTIS)

Information on the mining and processing of zeolites is reviewed. Composition, structure, and varieties of zeolite, including erionite (12510428), mordenite (12043742), natrolite (1318952), ferrierite (12173307), and phillipsite (12174184) are presented. ...

A. Albers

1981-01-01

216

Effect of mechanical treatment on the silicate lattice of kaolinite  

NASA Astrophysics Data System (ADS)

X-ray diffraction, differential thermal and chemical analysis have been used to investigate the effect of mechanical treatment on the crystalline lattice of kaolinite. It was established that mechanical treatment leads to amorphization of the mineral and the release of hydroxyl water, but the continuity of kaolinite's silicate lattice remains intact despite certain deformations, and the phase transformations of the mineral thus occur without any noticeable change in temperature.

Zulumyan, N. H.; Papakhchyan, L. R.; Isahakyan, A. R.; Beglaryan, H. A.; Aloyan, S. G.

2012-12-01

217

Annealing of Silicate Dust by Nebular Shocks at 10 AU  

NASA Technical Reports Server (NTRS)

Silicate dust grains in the interstellar medium are known to be mostly amorphous, yet crystalline silicate grains have been observed in many long-period comets and in protoplanetary disks. Annealing of amorphous silicate grains into crystalline grains requires temperatures greater than or approximately equal to 1000 K, but exposure of dust grains in comets to such high temperatures is apparently incompatible with the generally low temperatures experienced by comets. This has led to the proposal of models in which dust grains were thermally processed near the protoSun, then underwent considerable radial transport until they reached the gas giant planet region where the long-period comets originated. We hypothesize instead that silicate dust grains were annealed in situ, by shock waves triggered by gravitational instabilities. We assume a shock speed of 5 km/s, a plausible value for shocks driven by gravitational instabilities. We calculate the peak temperatures of pyroxene grains under conditions typical in protoplanetary disks at 5-10 AU. We show that in situ annealing of micron-sized dust grains can occur, obviating the need for large-scale radial transport.

Harker, David E.; Desch, Steven J.; DeVincenzi, D. (Technical Monitor)

2001-01-01

218

Mechanism of Microwave Heating of Zeolite A  

Microsoft Academic Search

The mechanism of microwave heating of A zeolite was studied by comparing the heating properties, cation distributions and dielectric properties of 3A, 4A and 5A zeolites. It was easy to heat hydrated 4A zeolite to a glowing (melting) temperature by microwave (2.45 GHz) radiation from room temperature but was difficult to heat the same zeolite with little hydration. When 4A

Tatsuo Ohgushi; Sridhar Komarneni; Amar S. Bhalla

2001-01-01

219

Core-shell strain structure of zeolite microcrystals.  

PubMed

Zeolites are crystalline aluminosilicate minerals featuring a network of 0.3-1.5-nm-wide pores, used in industry as catalysts for hydrocarbon interconversion, ion exchangers, molecular sieves and adsorbents. For improved applications, it is highly useful to study the distribution of internal local strains because they sensitively affect the rates of adsorption and diffusion of guest molecules within zeolites. Here, we report the observation of an unusual triangular deformation field distribution in ZSM-5 zeolites by coherent X-ray diffraction imaging, showing the presence of a strain within the crystal arising from the heterogeneous core-shell structure, which is supported by finite element model calculation and confirmed by fluorescence measurement. The shell is composed of H-ZSM-5 with intrinsic negative thermal expansion whereas the core exhibits a different thermal expansion behaviour due to the presence of organic template residues, which usually remain when the starting materials are insufficiently calcined. Engineering such strain effects could have a major impact on the design of future catalysts. PMID:23832126

Cha, Wonsuk; Jeong, Nak Cheon; Song, Sanghoon; Park, Hyun-jun; Thanh Pham, Tung Cao; Harder, Ross; Lim, Bobae; Xiong, Gang; Ahn, Docheon; McNulty, Ian; Kim, Jungho; Yoon, Kyung Byung; Robinson, Ian K; Kim, Hyunjung

2013-08-01

220

Isomerization of alkenes during drying over zeolites  

Microsoft Academic Search

We observed that zeolite 5A, a zeolite commonly used for drying, isomerized 1-butene and 1-hexene at room temperature. The activity for 1-butene isomerization on 3A, 4A, 5A and 13X zeolites at temperatures of 300 to 565 K is reported.

David T. Lynch; Sieghard E. Wanke

1994-01-01

221

Chapter 17 Hydrocarbon processing with zeolites  

Microsoft Academic Search

This chapter on hydrocarbon processing with zeolites covers both existing and new catalytic applications of zeolites in oil refining and gas conversion. By way of introduction some structural aspects related to these industries are discussed to provide some background in which to relate the current and future developments. Further, the unique opportunities and limitations of zeolites are discussed in order

I. E. Maxwell; W. H. J. Stork

2001-01-01

222

Entrapping of Cs and Sr in heat-treated zeolite matrices  

NASA Astrophysics Data System (ADS)

A solidification-stabilization procedure aiming at immobilizing Cs+ and Sr2+, two of the radioactive species more frequently present in nuclear power plant wastewaters, was successfully tested. Both cations were simultaneously exchanged by a blend of two zeolites, a phillipsite-rich tuff, selective for Cs+, and a synthetic zeolite Linde-type A, selective for Sr2+. The contaminated material was then heat treated up to 1200 °C with the result of safely immobilizing both cations, as demonstrated by leaching estimation with three different procedures. X-ray studies of the single cation-loaded zeolites or mixture of them helped to interpret the immobilization mechanism, involving cation trapping in chemically stable crystalline/amorphous matrices formed as a result of firing.

Liguori, B.; Caputo, D.; Iucolano, F.; Aprea, P.; de Gennaro, B.

2013-04-01

223

Exploring the nature of the 9-13 micron silicate emission discovered in quasars  

NASA Astrophysics Data System (ADS)

While for type-2 AGN the 9.7 micron absorption from amorphous silicates is well known, the silicate emission feature predicted for type-1 AGN has not been observed so far. Now, our low resolution IRS spectra of two ultra-luminous Palomar-Green quasars show a broad emission feature between 9 and 13 micron rest frame wavelength which contributes about 20% of the quasars total luminosity in this wavelength band. We strongly suggest that this feature is due to silicates in emission. If true, then this result is spectacular in that it provides excellent spectroscopic evidence for the torus-like distribution of dust around quasars, a crucial requirement for the AGN unified schemes. Also remarkable is the fact that the emission feature is not located at rest frame wavelength 9.7 micron typical for amorphous silicates, rather it lies red-shifted in the wavelength range of crystalline silicates. While amorphous silicates are formed in cold regions, crystalline silicates require hot environments. Furthermore, at high spectral resolution ISOSWS observations have shown that, for example in Herbig Ae-Be stars, the crystalline silicates exhibit a family of several sharp lines. At the low resolution of our IRS spectra this family of lines will be smeared out, probably resulting in the single broad feature we see in those two quasars yet observed. Resolving the family of crystalline silicate lines will provide best evidence for the silicate nature of the broad emission bump seen in our quasars. Therefore, we propose to perform high resolution IRS spectroscopy of the two bright quasars 3C249.1 (= PG 1100+772) and 3C351 (= PG 1704+608); at their redshift about z=0.3 the rest-frame 9-13 micron bump shifts to 12-18 micron, hence is ideally covered by the IRS Short-HiRes mode. These observations will establish the nature of the broad emission feature as crystalline silicates, thereby providing unique templates for dust features in luminous AGN.

Siebenmorgen, Ralf; Haas, Martin; Kruegel, Endrik; Schulz, Bernhard

2005-06-01

224

Silicate matrix for actinide wastes  

SciTech Connect

Secure immobilization of actinide wastes of complex compositions from the weapons-related program is a very real and difficult problem emerging both in Russia and the United States. Prospective materials to incorporate the wastes are ceramics and glass-ceramics consisting of durable crystalline actinide-containing phases. This paper focuses on the chemical, thermal, and radiation stabilities of two silicate-based garnet-britholite forms. The samples were produced by inductive melting in a cold crucible. Their compositions in weight percent were as follows: 27.1/29.2 CaO; 25.8/15.4 Fe{sub 2}O{sub 3}; 29.1/31.4 SiO{sub 2}; {minus}/3.0 La{sub 2}O{sub 3}; 8.0/5.0 Ce{sub 2}O{sub 3}; {minus}/8.0 Nd{sub 2}O{sub 3}; {minus}/2.0 EuO; 10.0/{minus}Gd{sub 2}O{sub 3}, and {minus}/6.0 ZrO{sub 2}. Scanning electron microscopy/energy-dispersive spectroscopy and X-ray research shows that the first sample is composed of synthetic garnet (70 vol%), britholite (15%), pyroxene-wollastonite (10%), and spinel (5%). A specific feature of the second sample is the existence of glass, which reached up to 90%. The results allow one to conclude that garnet with stoichiometry A{sub 3}{sup VIII}B{sub 2}{sup VI}(SiO{sub 4}){sub 3}, A = (Ca, Fe{sup 2+}, REE{sup 3+}), B = Fe{sup 3+}, Zr{sup 4+} and britholite {minus}(Ca{sup 2+}, REE{sup 3+}){sub 5}Is{sub 3}O{sub 12.5} have great isomorphic capacities with respect to various species of waste streams.

Smelova, T.V.; Krylova, N.V.; Yudintsev, S.V.; Nikonov, B.S.

2000-07-01

225

A new approach to evaluate natural zeolite ability to sorb lead (Pb) from aqueous solutions  

NASA Astrophysics Data System (ADS)

Lead (Pb) is a hazardous pollutant commonly found in aquatic ecosystems. Among several methods available, the addition of sorbent amendments to soils or sediments is attractive, since its application is relatively simple, while it can also be cost effective when a low cost and re-usable sorbent is used; e.g. natural zeolites. Zeolites are crystalline aluminosilicates with a three-dimensional structure composed of a set of cavities occupied by large ions and water molecules. Zeolites can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+, which are rather loosely held and can readily be exchanged for others in an aqueous solution. Natural zeolites are capable of removing cations, such as lead, from aqueous solutions by ion exchange. There is a wide variation in the cation exchange capacity (CEC) of natural zeolites because of the different nature of various zeolites cage structures, natural structural defects, adsorbed ions, and their associated gangue minerals. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, such as clays and feldspars, metals, quartz, or other zeolites as well. These impurities affect the CEC even for samples originated from the same region but from a different source. CEC of the material increases with decreasing impurity content. Potentially exchangeable ions in such impurities do not necessarily participate in ion exchange mechanism, while, in some cases, impurities may additionally block the access to active sites. For zeoliferous rocks having the same percentage of a zeolitic phase, the CEC increases with decreasing Si/Al ratio, as the more Si ions are substituted by Al ions, the more negative the valence of the matrix becomes. Sodium seems to be the most effective exchangeable ion for lead. On the contrary, it is unlikely that the potassium content of the zeolite would be substituted. A pretreatment with high concentration solutions of Na, such as 2 M NaCl, can significantly improve zeolite CEC by bringing the material to near homoionic form. pH and temperature are the critical parameters for using natural zeolites as sorbents. Zeolites should not be used in extremely acidic, neither in extremely basic pH conditions, except for very short times. The exchange of Pb, requires low solution pH, to avoid precipitation but not too low because the H+ are competitive ions for ion exchange; as a result the zeolite CEC related to Pb removal may be downgraded. If pH enters the basic range (e.g. pH>8), more aquatic complexes with lower positive valence than those prevailing in lower pH are produced; these complexes are less attracted by the negative charged zeolitic matrix. Pb uptake is favored at higher temperatures as ion exchange (including the diffusion of exchangeable ions inside the material and the medium, and vice versa) is an endothermic process. With the increase of temperature there is a decrease in hydration of all available exchangeable cations that eases the movement within the channels of the solid matrix. Additionally, the mobility of the potassium ions, present in the zeolitic material, also increases with the temperature resulting in enhanced CEC.

Drosos, Evangelos I. P.; Karapanagioti, Hrissi K.

2013-04-01

226

Smectites and related silicates  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I5a `Phyllosilicates' of Volume 27 `Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III `Condensed Matter'. It presents smectites and related silicates with regard to their crystal structures, lattice parameters, magnetic properties, neutron diffraction data, nuclear gamma resonance (NGR) data, electron spin resonance (ESR) data, nuclear magnetic resonance (NMR) data, electrical resistivities, heat capacities, dielectric properties, X-ray absorption fine-structure (XAFS) studies, infrared and Raman spectra and optical spectra.

Burzo, E.

227

Parameters influencing zeolite incorporation in PDMS membranes  

SciTech Connect

The incorporation of several types of zeolite in PDMS membranes is studied, by measuring the tensile strength, xylene sorption, and density of the membranes. The zeolite is shown to be involved in the cross-linking of the membrane. The interaction between the PDMS matrix and the zeolites results in reinforced membranes in the case of zeolite Y. The parameters influencing the dispersion of the zeolite in the membrane are investigated, as well as several aspects of the preparation method. Finally, the idea of cross-linking is applied to explain the results of water/ethanol pervaporation. 25 refs., 9 figs., 4 tabs.

Vankelecom, I.F.J.; Scheppers, E.; Heus, R.; Uytterhoeven, J.B. (Katholieke Universiteit Leuven (Belgium))

1994-11-24

228

Cesium Incorporation and Diffusion in Cancrinite, Soalite, Zeolite, and Allophane  

SciTech Connect

At the US Department of Energy?s Hanford site, high level nuclear waste has leaked from under4 ground storage tanks. The waste consists of hyperalkaline solutions, which upon contact with the 5 sediments, caused dissolution of silicate minerals and precipitation of secondary aluminosilicate minerals. Cancrinite, sodalite, LTA zeolite, and allophane have been identified as the new mineral phases 7 in laboratory simulations. Cesium, the major radionuclide in the waste solutions, may be incorporated 8 into the structural framework of the precipitates. The objectives of this study were to determine the 9 resistance of incorporated Cs to ion exchange and the mobility and diffusion coefficient of Cs in the 10 minerals. The minerals were synthesized in solutions mimicking the tank waste and were washed with 11 deionized water. Two sets of experiments were conducted to test the resistance of Cs to ion exchange. 12 In the first set, Cs was exchanged three times at 80 C by 0.5 N Na, K, or Ca. The Cs remaining in 13 minerals was quantified after acid digestion. In the second set, we studied the Cs desorption kinetics 14 by using 0.1 M Na as ion exchanger. Cesium concentration in the solution phase was measured as a 15 function of time for 23 days. Cesium incorporated in sodalite and cancrinite was far more difficult to 16 replace than that in LTA zeolite and allophane. Most of the incorporated Cs (94?99%) in LTA zeolite 17 and allophane was readily exchangeable with Na or K; less than 20% of Cs in sodalite and <55% of 2 Cs in cancrinite could be exchanged. The fraction of desorbed Cs was also affected by the exchanging 19 ions; the ion with lowest dehydration energy (K) was the most effective in replacing Cs. The results 20 of the desorption kinetics experiments showed that Cs desorbed quickly from LTA zeolite and the Cs 21 diffusion coefficient was close to that in solution; i.e., about 10?9 m2/s. Solid-state NMR analysis 22 supported the high mobility of Cs in LTA zeolite. Cesium desorption from cancrinite, sodalite, and 23 allophane, however, was slow, suggesting that Cs was trapped in cages and channels of these minerals. 24 Effective diffusion coefficients for Cs in cancrinite and sodalite were near 10?14 m2/s.

Mon, Jarai; Deng, Youjun; Flury, Markus; Harsh, James B.

2005-11-28

229

Propylene oligomerization over zeolite catalysts  

SciTech Connect

Zeolites (ZSM-5, boralites, offretite, HY, mordenite, and omega) were bonded with 20 wt% sepiolite into composite catalysts to oligomerize propylene in a fixed-bed, automated pilot unit operating at 30-50 atm under isothermal conditions. Product distributions indicate that oligomer size and structure correlates well with the zeolite pore diameter. In addition to C/sub 6/-C/sub 12/ and higher oligomers, aromatics and branched saturates are formed, indicating the presence of cracking, hydrogen and methyl transfer, isomerization, and dehydrocyclization reactions. Offretite (and HY) minimize C/sub 7/ and C/sub 8/ formation, while the boralite used has shown better oligomerization activity and product yields than either ZSM-5 or the other zeolites tested.

Hsu, J.T.; Galya, L.G.; Occelli, M.L.

1984-08-01

230

IMPROVED CATALYSTS FOR HEAVY OIL UPGRADING BASED ON ZEOLITE Y NANOPARTICLES ENCAPSULATED IN STABLE NANOPOROUS HOST  

SciTech Connect

The objectives of this project are to synthesis nanocrystals of highly acidic zeolite Y, encapsulate them within the channels of mesoporous (nanoporous) silicates or nanoporous organosilicates and evaluate the ''zeolite Y/Nanoporous host'' composites as catalysts for the upgrading of heavy petroleum feedstocks. Our results to date are summarized as follows. The synthesis of high surface ordered nanoporous silica of expanded pore diameter of 25 nm (larger than the standard size of 8.4 nm) using trimethylbenzene as a pore size expander was accomplished. The synthesis of zeolite Y nanoparticles with median pore size of approximately 50 nm (smaller than the 80 nm typically obtained with TMAOH) using combined TMABr/TMAOH as organic additives was also accomplished. The successful synthesis of zeoliteY/Nanoporous host composite materials by sequential combination of zeolite precursors and nanoporous material precursor mixtures was implied based on results from various characterization techniques such as X-Ray diffraction, infrared spectra, thermal analysis, porosimetry data. The resulting materials showed pore sizes up to 11 nm, and infrared band at 570 cm{sup -1} suggesting the presence of both phases. New results indicated that good quality highly ordered nanoporous silica host can be synthesized in the presence of zeolite Y seed precursor depending on the amount of precursor added. Preliminary research on the catalytic performance of the materials is underway. Probe acid catalyzed reactions, such as the cracking of cumene is currently being conducted. Work in the immediate future will be focused on the following three areas: (1) Further characterization of all-silica and aluminosilicate mesoporous materials with expanded pore sizes up to 30 nm will continue; (2) Research efforts to reduce the average particle size of zeolite nanoparticles down to 35-30 nm will continue; (3) Further synthesis of ZeoliteY/Nanoporous host composite catalysts of improved structural and physicochemical characteristics will be conducted by changing the amount and chemistry of the zeolitic precursors added; and (4) Investigation on the catalytic properties of the materials using probe catalytic reactions (such as cumene cracking), followed by catalytic testing for heavy oil conversion.

Conrad Ingram; Mark Mitchell

2005-03-31

231

Exfoliated zeolite sheets and block copolymers as building blocks for composite membranes  

NASA Astrophysics Data System (ADS)

Mixed matrix materials, comprising of zeolites incorporated in suitable matrix (polymeric or inorganic), are promising as future membrane materials with high permselectivity. However, they suffer from the drawback of low productivity due to increase in the membrane thickness by incorporation of micron-sized zeolites crystals as well as the low-permeability matrices employed currently. Nanocomposite membranes, consisting of thin zeolite sheets (˜2 nm) embedded in an appropriate matrix, can provide a solution to this problem. This thesis addresses some of the material challenges to make such nanocomposite membranes. A high permeability polymer was synthesized by combining the glassy polystyrene (PS) with the rubbery polydimethylsiloxane (PDMS) in a block copolymer architecture. The mechanical toughness of the material was optimized to facilitate the fabrication of thin free standing films and its gas transport properties were evaluated. The PS-PDMS-PS triblock copolymers were successfully hydrogenated for the first time to obtain the PCHE-PDMS-PCHE triblock copolymers (PCHE stands for polycyclohexylethylene). The hydrogenation reaction proceeded without any polymer chain breaking and the resultant polymer showed some interesting, rather unexpected thermodynamic properties. These polymeric materials are potentially useful as the matrix of nanocomposite membranes. Highly crystalline zeolite sheets were obtained by exfoliation of zeolite lamellae. Preservation of crystal morphology and pore structure, which presents a major challenge during the exfoliation process, was successfully addressed in this work by judicious choice of operating conditions. Lamellae were exfoliated by surfactant intercalation and subsequently melt processing with polymers, resulting in polymer nanocomposites containing thin zeolite sheets (˜2.5 nm) with well preserved pore structure. A method to obtain polymer-free exfoliated sheets was also developed to facilitate the fabrication of inorganic composite membranes. These zeolite sheets can be used as the selectivity-enhancement additive in composite membranes.

Maheshwari, Sudeep

232

Zeolitical materials for microbiological filtrations.  

PubMed

The paper presents some aspects about synthesis of new materials called zeolites which can be utilised as filters with wide application in clinical practice in microbiology and in pharmaceutical industry. The SAPO-5, SAPO-11 and SAPO-34 zeolites were synthesised by hydrothermal crystallisation and using different mixtures. The crystallisation was carried out in teflon-lined stainless steel autoclaves at 180-195 degrees C for 1-2 days, under autogenous pressure. Filtering properties of these materials are different because their pore diameters are different. PMID:12092241

Ciobanu, O; Ciobanu, G

2001-01-01

233

Observation of muonium in zeolites  

NASA Astrophysics Data System (ADS)

Muonium has been directly detected over a range of temperatures and fields by transverse field ?SR in different zeolites: 3A, 13X, USY, ZSM-5, and S-115 (a high-silica form of ZSM-5), as well as in silica gel. The polarizations determined from data at 75 and 150 G were independent of both field and temperature. The amounts of Mu seen vary from ?20% to 40%, with a large missing fraction seen in every case, which may be partly due to slow Mu formation. There is also a fast Mu relaxation rate seen in all samples. This is the first direct observation of Mu in zeolites.

Arseneau, D. J.; Fleming, D. G.; Fyfe, C. A.; Senba, M.

2003-02-01

234

Fundamentals and applications of pervaporation through zeolite membranes  

Microsoft Academic Search

Zeolite membranes have uniform, molecular-sized pores, and they separate molecules based on differences in the molecules’ adsorption and diffusion properties. Zeolite membranes are thus well suited for separating liquid-phase mixtures by pervaporation, and the first commercial application of zeolite membranes has been for dehydrating organic compounds. Because of the large number of zeolites that can be prepared, zeolite membranes have

Travis C. Bowen; Richard D. Noble; John L. Falconer

2004-01-01

235

Application of Synthetic Zeolites (molecular Sieves) to Catalysis  

Microsoft Academic Search

CONTENTS I. Introduction 904 II. General information on zeolites, and on some of their physicochemical properties 904 III. Preparation of zeolite catalysts 905 IV. Applications of zeolite catalysts 906 V. Selectivity of zeolite catalysts 911 VI. Operating mechanism of zeolite catalysts 912

Khabib M. Minachev; V. I. Garanin; Ya I. Isakov

1966-01-01

236

21 CFR 172.410 - Calcium silicate.  

Code of Federal Regulations, 2013 CFR

...Drugs 3 2013-04-01 2013-04-01 false Calcium silicate. 172.410 Section 172.410 Food...HUMAN CONSUMPTION Anticaking Agents § 172.410 Calcium silicate. Calcium silicate, including synthetic calcium...

2013-04-01

237

DIRECT LABORATORY ANALYSIS OF SILICATE STARDUST FROM RED GIANT STARS  

SciTech Connect

We performed combined focused ion beam/transmission electron microscopy studies to investigate the chemistry and structure of eight presolar silicate grains that were previously detected by NanoSIMS oxygen isotope mapping of the carbonaceous chondrite Acfer 094. The analyzed presolar silicates belong to the O isotope Groups I/II ({sup 17}O-enriched and {sup 18}O-depleted) and therefore come from 1-2.5 M{sub sun} asymptotic giant branch stars of close-to-solar or slightly lower-than-solar metallicity. Three grains are amorphous, Mg-rich, and show a variable, but more pyroxene-like composition. Most probably, these grains have formed under circumstellar low-temperature conditions below the crystallization temperature. Three grains are Fe-bearing glasses similar to the 'glass with embedded metal and sulfides' (GEMS) grains found in interplanetary dust particles. However, two of the meteorite GEMS grains from this study lack comparatively large ({approx}>20 nm) Fe-rich inclusions and have sulfur contents <1 at.%, which is different than observed for the majority of GEMS grains. These grains likely condensed under strong non-equilibrium conditions from an Si-enriched gas. One olivine is characterized by a crystalline core and an amorphous, more Fe-rich rim, which is probably the result of interstellar medium sputtering combined with Mg removal. The detection of another olivine with a relatively high Fe content (Mg no. 0.9) shows that circumstellar crystalline silicates are more Fe-rich than astrophysical models usually suggest. The overall predominance of olivine among the crystalline silicate stardust population compared to pyroxene indicates preferential formation or survival of this type of mineral. As pyroxene is indeed detected in circumstellar outflows, it remains to be seen how this result is compatible with astrophysical observations and experimental data.

Vollmer, Christian; Hoppe, Peter [Max Planck Institute for Chemistry, Particle Chemistry Dept., Joh.-J.-Becherweg 27, D-55128 Mainz (Germany); Brenker, Frank E. [Geoscience Institute/Mineralogy, Goethe-University Frankfurt, Altenhoeferallee 1, D-60438 Frankfurt (Germany); Stroud, Rhonda M. [Naval Research Laboratory, Code 6360, Washington, DC 20375 (United States)], E-mail: cvollmer@mpch-mainz.mpg.de

2009-07-20

238

Subaru/COMICS Study on Silicate Dust Processing around Young Low-Mass Stars  

NASA Astrophysics Data System (ADS)

We have obtained 8-13 ?m spectra of 30 young (1-10 Myr) low-mass pre-main-sequence stars using COMICS on the 8.2 m Subaru Telescope to examine dust evolution in protoplanetary disks. Most spectra show silicate emission features of various strengths and shapes, indicative of dust processing during the different stages of protoplanetary disk evolution. We have analyzed the observed silicate emission features using a simple model previously applied to the more massive and luminous Herbig Ae/Be systems. We determined the feature strength and shape and derived the composition and typical size of the silicate dust grains. We confirm the previously reported dependency of the silicate feature strength and shape on the grain size of the amorphous silicate dust. We examine the relation between the derived dust properties and stellar and circumstellar disk parameters, such as systemic age, luminosity of H? (LH?), disk mass, and opacity power-law index ? at radio wavelengths. A possible relation is found between silicate feature strength (grain size indicator) and the LH?, which may be an indicator of accretion activity. It implies that the turbulence induced by accretion activity may be important for grain size evolution in the disk. No clear correlation between the crystallinity and the stellar/disk parameters is found. We find that on average 5%-20% in mass of the silicate dust grains is in crystalline form, irrespective of systemic age. This latter finding supports the idea that crystalline silicate is formed at an early evolutionary phase, probably at the protostellar phase, and is remaining during the later stages. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Honda, Mitsuhiko; Kataza, Hirokazu; Okamoto, Yoshiko K.; Yamashita, Takuya; Min, Michiel; Miyata, Takashi; Sako, Shigeyuki; Fujiyoshi, Takuya; Sakon, Itsuki; Onaka, Takashi

2006-08-01

239

Nitride formation by the carbothermal reduction of a zeolite-polyacrylonitrile inclusion compound  

Microsoft Academic Search

An inclusion compound between zeolite and polyacrylonitrile has been applied as a precursor for the carbothermal reduction process. By heat treatment at 1400 to 1600° C in N2, ß-sialon was mainly obtained. The X phase, a-Si3N4, the 15R-AlN phase, AIN, and mullite also formed under certain firing conditions. On the other hand, a-Si2N4 was detected as the principal crystalline phases

Yoshiyuki Sugahara; Hiromitsu Hiraiwa; Kazuyuki Kuroda; Chuzo Kato

1988-01-01

240

UTILITY OF ZEOLITES IN HAZARDOUS METAL REMOVAL FROM WATER  

EPA Science Inventory

Zeolites are well known for their ion exchange, adsorption and acid catalysis properties. Different inorganic pollutants have been removed from water at room temperature by using synthetic zeolites. Zeolite Faujasite Y has been used to remove inorganic pollutants including arseni...

241

Synthesis, structure, and carbon dioxide capture properties of zeolitic imidazolate frameworks.  

PubMed

Zeolites are one of humanity's most important synthetic products. These aluminosilicate-based materials represent a large segment of the global economy. Indeed, the value of zeolites used in petroleum refining as catalysts and in detergents as water softeners is estimated at $350 billion per year. A major current goal in zeolite chemistry is to create a structure in which metal ions and functionalizable organic units make up an integral part of the framework. Such a structure, by virtue of the flexibility with which metal ions and organic moieties can be varied, is viewed as a key to further improving zeolite properties and accessing new applications. Recently, it was recognized that the Si-O-Si preferred angle in zeolites (145 degrees ) is coincident with that of the bridging angle in the M-Im-M fragment (where M is Zn or Co and Im is imidazolate), and therefore it should be possible to make new zeolitic imidazolate frameworks (ZIFs) with topologies based on those of tetrahedral zeolites. This idea was successful and proved to be quite fruitful; within the last 5 years over 90 new ZIF structures have been reported. The recent application of high-throughput synthesis and characterization of ZIFs has expanded this structure space significantly: it is now possible to make ZIFs with topologies previously unknown in zeolites, in addition to mimicking known structures. In this Account, we describe the general preparation of crystalline ZIFs, discussing the methods that have been developed to create and analyze the variety of materials afforded. We include a comprehensive list of all known ZIFs, including structure, topology, and pore metrics. We also examine how complexity might be introduced into new structures, highlighting how link-link interactions might be exploited to effect particular cage sizes, create polarity variations between pores, or adjust framework robustness, for example. The chemical and thermal stability of ZIFs permit many applications, such as the capture of CO(2) and its selective separation from industrially relevant gas mixtures. Currently, ZIFs are the best porous materials for the selective capture of CO(2); furthermore, they show exceptionally high capacity for CO(2) among adsorbents operating by physisorption. The stability of ZIFs has also enabled organic transformations to be carried out on the crystals, yielding covalently functionalized isoreticular structures wherein the topology, crystallinity, and porosity of the ZIF structure are maintained throughout the reaction process. These reactions, being carried out on macroscopic crystals that behave as single molecules, have enabled the realization of the chemist's dream of using "crystals as molecules", opening the way for the application of the extensive library of organic reactions to the functionalization of useful extended porous structures. PMID:19877580

Phan, Anh; Doonan, Christian J; Uribe-Romo, Fernando J; Knobler, Carolyn B; O'Keeffe, Michael; Yaghi, Omar M

2010-01-19

242

Tailored zeolites for the removal of metal oxyanions: overcoming intrinsic limitations of zeolites.  

PubMed

This review aims to present a global view of the efforts conducted to convert zeolites into efficient supports for the removal of heavy metal oxyanions. Despite lacking affinity for these species, due to inherent charge repulsion between zeolite framework and anionic species, zeolites have still received considerable attention from the scientific community, since their versatility allowed tailoring them to answer specific requirements. Different processes for the removal and recovery of toxic metals based on zeolites have been presented. These processes resort to modification of the zeolite surface to allow direct adsorption of oxyanions, or by combination with reducing agents for oxyanions that allow ion-exchange with the converted species by the zeolite itself. In order to testify zeolite versatility, as well as covering the wide array of physicochemical constraints that oxyanions offer, chromium and arsenic oxyanions were selected as model compounds for a review of treatment/remediation strategies, based on zeolite modification. PMID:24794984

Figueiredo, Hugo; Quintelas, Cristina

2014-06-15

243

Spin probes of chemistry in zeolites  

SciTech Connect

Electron spin resonance (EPR) studies in zeolites are reviewed in which radiolysis was used to ionize the zeolite lattice, create reactive intermediates, spin label reaction products and to provide a window onto chemistry and transport of adsorbates and matrix control of chemistry. The review examines reactions of radical cations and the influence of the geometry constraints inside the zeolite, explores how zeolite model systems can be used to learn about energy and charge transfer in solids and illustrates the use of radiolysis and EPR for in situ spectroscopic studies of solid-acid catalysis. The various spin probes created inside the zeolite pores report on properties of the zeolites as well as shed light on radiolytic processes.

Werst, D.W.; Trifunac, A.D.

1997-09-01

244

Phonolite-hosted zeolite deposits in the Kaiserstuhl Volcanic Complex, Germany  

NASA Astrophysics Data System (ADS)

Several subvolcanic phonolitic intrusions occur within the Miocene Kaiserstuhl Volcanic Complex (KVC) located in the central-southern segment of the Upper Rhine Graben, which is part of the European Cenozoic Rift System. Hydrothermally altered phonolitic rocks are of economic interest, due to the high (>40 wt%) zeolite content, which accounts for the remarkable zeolitic physicochemical properties of the ground rock. These properties have widespread industrial application in water softening, catalysis, remediation of soils and soil quality, wastewater treatment, and as additive in the cement industry. Currently the largest phonolite intrusion Fohberg is active in mining, located in the eastern part of the KVC. The Endhale phonolite, approximately 1.5 km to the north marks a further deposit currently under exploration. Both phonolites are hosted in Tertiary sedimentary units. The aim of this study is to carry out a new mineralogical and geochemical data a) to evaluate the manifestation of hydrothermal alteration of the Fohberg and Endhale phonolitic intrusions, and b) to constrain the physical and chemical properties of the fluids, which promoted hydrothermal replacement of primary igneous minerals. The high degree of alteration is in contrast to the only slightly altered Kirchberg phonolite in the western KVC. The alkaline intrusive bodies are characterized by the primary mineralogy: feldspathoid mineral, K-feldspar, aegirine-augite, wollastonite, and andradite, with additional REE-minerals (e.g. götzenite). Fluid-induced re-equilibration of feldspathoid minerals and wollastonite caused breakdown to a set of secondary phases. Feldspathoid minerals are totally replaced by secondary phases including various zeolite species, calcite, and barite. Wollastonite breakdown results in the formation of various zeolites, calcite, pectolite, sepiolite, and quartz. The large variability of secondary minerals indicates a heterogenic fluid composition throughout the phonolitic intrusions and through time. Zeolites formed during sub-solidus hydrothermal alteration under alkaline conditions and completely replace feldspathoid minerals in the matrix of the rock. A sequence of Ca-Na dominated zeolite species (gonnardite, thomsonite, mesolite) is followed by pure sodium endmember species (analcime, natrolite). These sequence reflects an increase in log[aNa+)/(aH+)] of the precipitating fluid. In contrast to the Fohberg phonolitc the Endhale phonolite contains analcime in addition to natrolite as pure Na zeolite species. The appearance of analcime is caused by higher silica activity during fluid rock interaction, which favors the formation of analcime over natrolite. The Fohberg phonolite is cut by fractures, which are totally or partially sealed with secondary minerals. Secondary minerals contain zeolites, followed by calcite and a variety of other silicates, carbonates, and sulphates as younger generations. Stable isotope analyses of late fracture calcite indicate the late circulation of meteoric fluids and mobilization of organic matter from surrounding sedimentary units.

Weisenberger, Tobias; Spürgin, Simon

2014-05-01

245

Interconnectivity of Fe O S liquid in polycrystalline silicate perovskite at lower mantle conditions  

Microsoft Academic Search

An important aspect of planetary core formation concerns whether interconnectivity of liquid metal can occur in crystalline silicates, which at low melt fractions requires that the dihedral angle between the two phases is <60°. [Shannon, M.C., Agee, C.B., 1998. Percolation of core melts at lower mantle conditions. Science 280, 1059 1061] previously reported that dihedral angles in mantle assemblages decrease

Hidenori Terasaki; Daniel J. Frost; David C. Rubie; Falko Langenhorst

2007-01-01

246

Synthesis of high-purity Na-A and Na-X zeolite from coal fly ash.  

PubMed

Coal fly ash (CFA) was used as a raw material for the synthesis of zeolite molecular sieve. The synthesis began with the pretreatment of CFA to remove impurities (e.g., Fe2O3, CaO, etc.) under various acid types (HCl, H2SO4, and HNO3) and acid/CFA ratios (5-25 mL(acid)/g(CFA)). High product purity (up to 97%) was achieved with HCl (20%wt), and acid/CFA ratio of 20 mL(HCl)/g(CFA). The treated CFA was then converted to zeolite by the fusion reaction under various Si/Al molar ratios (0.54-1.84). Zeolite type A was synthesized when the Si/Al molar ratios were lower than 1, whereas sodium aluminum silicate hydrate was formed when the Si/Al molar ratio were higher than 1. The highest water adsorption performance of the zeolite product, i.e., the outlet ethanol concentration of 99.9%wt and the specific adsorption capacity of 2.31 x 10(-2) g(water)/g(zeolite), was observed with the Si/Al molar ratio of 0.82. The zeolite was tested for its water adsorption capacity repeatedly 10 times without deactivation. Implications: This work evaluated the technical feasibility in the conversion of CFA to zeolite, which would help reduce the quantity of waste needed to be landfilled. This adds value to the unwanted material by converting it into something that can be further used. The synthesized products were shown to be quite stable as water adsorbent for the dehydration of ethanol solution. PMID:24941707

Panitchakarn, Panu; Laosiripojana, Navadol; Viriya-Umpikul, Nawin; Pavasant, Prasert

2014-05-01

247

Experiments on metal-silicate plumes and core formation.  

PubMed

Short-lived isotope systematics, mantle siderophile abundances and the power requirements of the geodynamo favour an early and high-temperature core-formation process, in which metals concentrate and partially equilibrate with silicates in a deep magma ocean before descending to the core. We report results of laboratory experiments on liquid metal dynamics in a two-layer stratified viscous fluid, using sucrose solutions to represent the magma ocean and the crystalline, more primitive mantle and liquid gallium to represent the core-forming metals. Single gallium drop experiments and experiments on Rayleigh-Taylor instabilities with gallium layers and gallium mixtures produce metal diapirs that entrain the less viscous upper layer fluid and produce trailing plume conduits in the high-viscosity lower layer. Calculations indicate that viscous dissipation in metal-silicate plumes in the early Earth would result in a large initial core superheat. Our experiments suggest that metal-silicate mantle plumes facilitate high-pressure metal-silicate interaction and may later evolve into buoyant thermal plumes, connecting core formation to ancient hotspot activity on the Earth and possibly on other terrestrial planets. PMID:18826918

Olson, Peter; Weeraratne, Dayanthie

2008-11-28

248

Molecular silicate and aluminate species in anhydrous and hydrated cements.  

PubMed

The compositions and molecular structures of anhydrous and hydrated cements are established by using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy methods to distinguish among different molecular species and changes that occur as a result of cement hydration and setting. One- and two-dimensional (2D) solid-state (29)Si and (27)Al magic-angle spinning NMR methodologies, including T(1)-relaxation-time- and chemical-shift-anisotropy-filtered measurements and the use of very high magnetic fields (19 T), allow resonances from different silicate and aluminate moieties to be resolved and assigned in complicated spectra. Single-pulse (29)Si and (27)Al NMR spectra are correlated with X-ray fluorescence results to quantify the different crystalline and disordered silicate and aluminate species in anhydrous and hydrated cements. 2D (29)Si{(1)H} and (27)Al{(1)H} heteronuclear correlation NMR spectra of hydrated cements establish interactions between water and hydroxyl moieties with distinct (27)Al and (29)Si species. The use of a (29)Si T(1)-filter allows anhydrous and hydrated silicate species associated with iron-containing components in the cements to be distinguished, showing that they segregate from calcium silicate and aluminate components during hydration. The different compositions of white Portland and gray oilwell cements are shown to have distinct molecular characteristics that are correlated with their hydration behaviors. PMID:20455533

Rawal, Aditya; Smith, Benjamin J; Athens, George L; Edwards, Christopher L; Roberts, Lawrence; Gupta, Vijay; Chmelka, Bradley F

2010-06-01

249

Microsphere zeolite materials derived from coal fly ash cenospheres as precursors to mineral-like aluminosilicate hosts for 135,137Cs and 90Sr  

NASA Astrophysics Data System (ADS)

Hollow microsphere zeolite materials with a bilayered zeolite/glass crystalline shell bearing NaP1 zeolite were synthesized by the hydrothermal treatment of coal fly ash cenospheres (Si/Al = 2.7) in an alkaline medium. Cs+ and/or Sr2+ forms of zeolitized cenospheres with the different Cs+ and/or Sr2+ loading were prepared by the ion exchange from nitrate solutions. The resulted (Cs,Na)P1, (Sr,Na)P1 and (Cs,Sr,Na)P1 bearing microsphere zeolites were converted to glass ceramics by heating at 900-1000 °C. The differential scanning calorimetry and quantitative phase analysis were used to monitor the solid-phase transformation of the initial and ion exchanged zeolite materials. It was established that the final solidified forms of Cs+ and/or Sr2+ are glass-crystalline ceramic materials based on pollucite-nepheline, Sr-feldspar-nepheline and Sr-feldspar-pollucite composites including ˜60 wt.% of the major host phases (pollucite, Sr-feldspar) and 10-20 wt.% of glass. The 137Cs leaching rate of 4.1 × 10-7 g cm-2 day-1 was determined for the pollucite glass-ceramic according to Russian State Standard (GOST) No. 52126 P-2003 (7 day, 25 °C, distilled water).

Vereshchagina, Tatiana A.; Vereshchagin, Sergei N.; Shishkina, Nina N.; Vasilieva, Nataly G.; Solovyov, Leonid A.; Anshits, Alexander G.

2013-06-01

250

Characterization and comparison of pore landscapes in crystalline porous materials.  

PubMed

Crystalline porous materials have many applications, including catalysis and separations. Identifying suitable materials for a given application can be achieved by screening material databases. Such a screening requires automated high-throughput analysis tools that characterize and represent pore landscapes with descriptors, which can be compared using similarity measures in order to select, group and classify materials. Here, we discuss algorithms for the calculation of two types of pore landscape descriptors: pore size distributions and stochastic rays. These descriptors provide histogram representations that encode the geometrical properties of pore landscapes. Their calculation involves the Voronoi decomposition as a technique to map and characterize accessible void space inside porous materials. Moreover, we demonstrate pore landscape comparisons for materials from the International Zeolite Association (IZA) database of zeolite frameworks, and illustrate how the choice of pore descriptor and similarity measure affects the perspective of material similarity exhibiting a particular emphasis and sensitivity to certain aspects of structures. PMID:23876827

Pinheiro, Marielle; Martin, Richard L; Rycroft, Chris H; Jones, Andrew; Iglesia, Enrique; Haranczyk, Maciej

2013-07-01

251

Increased thermal conductivity monolithic zeolite structures  

DOEpatents

A monolith comprises a zeolite, a thermally conductive carbon, and a binder. The zeolite is included in the form of beads, pellets, powders and mixtures thereof. The thermally conductive carbon can be carbon nano-fibers, diamond or graphite which provide thermal conductivities in excess of about 100 W/mK to more than 1,000 W/mK. A method of preparing a zeolite monolith includes the steps of mixing a zeolite dispersion in an aqueous colloidal silica binder with a dispersion of carbon nano-fibers in water followed by dehydration and curing of the binder is given.

Klett, James (Knoxville, TN); Klett, Lynn (Knoxville, TN); Kaufman, Jonathan (Leonardtown, MD)

2008-11-25

252

Analysis of a Sheet Silicate.  

ERIC Educational Resources Information Center

Describes a student project in analytical chemistry using sheet silicates. Provides specific information regarding the use of phlogopite in an experiment to analyze samples for silicon, aluminum, magnesium, iron, potassium, and fluoride. (CS)

Adams, J. M.; Evans, S.

1980-01-01

253

The Silicate Structures: Chalkboard Demonstration  

NSDL National Science Digital Library

Three-dimensional, magnetic representations of SiO tetrahedra and cations are manipulated on a chalkboard to create five basic silicate structures. Students are expected to complete a worksheet accompanying the exercise, which addresses silicate structures, bond types and strengths, physical properties (e.g. fracture, cleavage), Si:O ratio and introduction to vocabulary such as "felsic" and "mafic," and mineral formulae. The worksheet and chalkboard demonstration are designed to simplify silicate structures from complex ball-and-stick models typically used in textbook figures, and to grant students a visual, three-dimensional, manipulable, perspective on what tends to be a confusing concept. This exercise may be simplified or expanded to suit timeframe and the needs of the audience. Benefits of this approach include reinforcement of lecture concepts, broad appeal for a student group with multiple learning styles and degrees of knowledge, and strengthened understanding of the silicate structures.

Stevens, Liane

254

Ion implantation in silicate glasses  

SciTech Connect

This review examines the effects of ion implantation on the physical properties of silicate glasses, the compositional modifications that can be brought about, and the use of metal implants to form colloidal nanosize particles for increasing the nonlinear refractive index.

Arnold, G.W.

1993-12-01

255

Kaolin group and related silicates  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I5? `Phyllosilicates - Part ?' of Volume 27 `Magnetic properties of non-metallic inorganic compounds based on transition elements` of Landolt-Börnstein - Group III `Condensed Matter'. It presents silicates belonging to the kaolin group and related silicates, presenting their crystal structure and lattice parameters, magnetic properties, nuclear gamma resonance (NGR), nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) data, dielectric properties, heat capacity, infrared and Raman data, and optical absorption spectra.

Burzo, E.

256

Is ``Silicate Life'' Possible?  

NASA Astrophysics Data System (ADS)

The simplest theory of chemical reactions (including also structural isomerisation reactions) is based on the model of potential barrier overcoming which separates combining states (chemical forms) of molecular objects. In a more complicated model not only the zero but other oscillation level positions are taken into account that in the theory of temperature reactions leads to the statistical sum changes on the states. In all traditional models only energetic factors are taken into consideration. A close structural similarity of some organic and silicon organic compositions (for example, paraffins and silans) and similarity of electron building of carbon and silicon atoms, that also reflects in the similarity of their atomic orbitals, were noticed by researchers long ago. These options cause an idea of a possibility of what can be called “the silicate life”. In connection with new visions at the mechanism of the elementary act at chemical reactions there was an opportunity to consider some chemical factors which influence the run of the reactions that earlier had slipped out from the attention.

Gribov, L.; Baranov, V.; Magarshak, Yu.

257

Synthesis and crystal structure of a layered silicate HUS-1 with a halved sodalite-cage topology.  

PubMed

A new layered silicate, HUS-1, was synthesized by hydrothermal synthesis using decomposed FAU- and *BEA-type zeolites as nanosized silica parts. Structural analyses by X-ray powder diffractometry and solid-state magic-angle-spinning (MAS) NMR spectroscopy revealed that HUS-1 has a layered structure containing a silicate layer per unit cell along a stacking direction. Its framework topology is similar to that of SOD-type zeolites and consists of a halved sodalite cage, which includes four- and six-membered Si rings. Structure refinement by the Rietveld method showed that tetramethylammonium (TMA) ions used as a structure-directing agent (SDA) were incorporated into the interlayer. The four methyl groups of the TMA molecule were located orderly in a hemispherical cage in the silicate layer, which suggests restraint of molecular motion. The interlayer distance is estimated at about 0.15 nm, which is unusually short in comparison with that in other layered silicates (e.g., ?-HLS or RUB-15) with similar framework topologies. The presence of hydrogen bonding between adjacent terminal O atoms was clearly revealed by the (1)H MAS NMR spectroscopy and by electron-density distribution obtained by the maximum entropy method. PMID:21294579

Ikeda, Takuji; Oumi, Yasunori; Honda, Koutaro; Sano, Tsuneji; Momma, Koichi; Izumi, Fujio

2011-03-21

258

Observation of muonium in zeolites  

Microsoft Academic Search

Muonium has been directly detected over a range of temperatures and fields by transverse field muSR in different zeolites: 3A, 13X, USY, ZSM-5, and S-115 (a high-silica form of ZSM-5), as well as in silica gel. The polarizations determined from data at 75 and 150 G were independent of both field and temperature. The amounts of Mu seen vary from

D. J. Arseneau; D. G. Fleming; C. A. Fyfe; M. Senba

2003-01-01

259

Observation of muonium in zeolites  

Microsoft Academic Search

Muonium has been directly detected over a range of temperatures and fields by transverse field ?SR in different zeolites: 3A, 13X, USY, ZSM-5, and S-115 (a high-silica form of ZSM-5), as well as in silica gel. The polarizations determined from data at 75 and 150 G were independent of both field and temperature. The amounts of Mu seen vary from

D. J. Arseneau; D. G. Fleming; C. A. Fyfe; M. Senba

2003-01-01

260

Zeolites Remove Sulfur From Fuels  

NASA Technical Reports Server (NTRS)

Zeolites remove substantial amounts of sulfur compounds from diesel fuel under relatively mild conditions - atmospheric pressure below 300 degrees C. Extracts up to 60 percent of sulfur content of high-sulfur fuel. Applicable to petroleum refineries, natural-gas processors, electric powerplants, and chemical-processing plants. Method simpler and uses considerably lower pressure than current industrial method, hydro-desulfurization. Yields cleaner emissions from combustion of petroleum fuels, and protects catalysts from poisoning by sulfur.

Voecks, Gerald E.; Sharma, Pramod K.

1991-01-01

261

An Equation of State for Silicate Melts Under Compression  

NASA Astrophysics Data System (ADS)

Density of silicate melts at elevated pressures and temperatures (i.e., equation of state) is critical to our understanding of melting processes such as the generation and differentiation of silicate melts in Earth and is a key parameter to the thermodynamic and dynamic models of melting at high pressures. In the past, equations of state of silicate melts were often treated in analogy with that of crystalline solids for which the change in internal energy due to the change in inter-atomic distance plays an important role. However, liquids are different from solids in their ability to change structures, which implies the importance of entropy contribution to compression in addition to the internal energy contribution. This results in the distinct compressional properties of liquids such as (1) Liquids have much smaller bulk moduli than solids and do not follow the Birch's law of corresponding state (the relationship between bulk modulus and density) as opposed to solids; (2) The Grüneisen parameter increases with increasing pressure for (non-metallic) liquids but decreases for solids. In this work, we propose a new equation of state for multi-component silicate melts based on the hard sphere mixture model of a liquid to account for the role of entropic contribution. We assign a hard sphere for each cation species that moves in the liquid except for the volume occupied by other spheres. The geometrical arrangements of these spheres give the entropic contribution to compression, while the Columbic attraction between the spheres and the uniformly distributed oxygen background provides the internal energy contribution to compression. We calibrate the equation of state for the SiO2-Al2O3-FeO-MgO-CaO 5-component melts. The effective size of a hard sphere for each component is determined. The temperature and volume dependencies of sphere diameters are also included in the model in order to explain the melt density data at high pressures. We have also investigated the influences of other melt components such as Na2O, K2O, and H2O. All compressional properties of a silicate melt can be calculated using the calibrated sphere diameters. This equation of state provides a unified explanation for most of compressional behaviors of silicate melts and the experimental observations cited above including the uniformly small bulk moduli of silicate melts as well as the pressure dependence of Grüneisen parameters. With additional data to better constrain the key parameters, this equation of state will serve as a first step toward the unified equation of state for silicate melts.

Jing, Z.; Karato, S.

2011-12-01

262

Synthesis and Properties of Nanoparticle Forms Saponite Clay, Cancrinite Zeolite and Phase Mixtures Thereof  

PubMed Central

The low-temperature synthesis (90°C) of nanoparticle forms of a pure phase smectic clay (saponite) and zeolite (cancrinite) is reported, along with phase mixtures thereof. A synthesis gel corresponding to the Si:Al:Mg unit cell composition of saponite (3.6:0.40:3.0) and a NaOH/Si ratio of 1.39 affords the pure phase clay with disordered nanolayer stacking. Progressive increases in the NaOH/Si ratio up to a value of 8.33 results in the co-crystallization of first garronite and then cancrinite zeolites with nanolath morphology. The resulting phase mixtures exhibit a compound particulate structure of intertwined saponite nanolayers and cancrinite nanolaths that cannot be formed through physical mixing of the pure phase end members. Under magnesium-free conditions, pure phase cancrinite nanocrystals are formed. The Si/Al ratio of the reaction mixture affects the particle morphology as well as the chemical composition of the cancrinite zeolite. Ordinarily, cancrinite crystallizes with a Si/Al ratio of 1.0, but a silicon-rich form of the zeolite (Si/Al=1.25) is crystallized at low temperature from a silica rich synthesis gel, as evidenced by 29Si NMR spectroscopy and XEDS-TEM. Owing to the exceptionally high external surface areas of the pure phase clay (875 m2/g) and zeolite end members (8.9 - 40 m2/g), as well as their unique mixed phase composites (124 - 329 m2/g), these synthetic derivatives are promising model nanoparticles for studies of the bioavailability of poly-aromatic hydrocarbons immobilized in silicate bearing sediments and soils.

Shao, Hua

2010-01-01

263

The crystalline revolution :ISO's finding opens a new research field, "astro-mineralogy"  

NASA Astrophysics Data System (ADS)

Silicate minerals were known to be a main component of dust in space, but detecting them in a crystallised state has been a surprise. It allows the identification of precise silicates in astronomical objects, which will open "a totally new field in astronomy: astro-mineralogy. This is the crystalline revolution", said the author, Dutch astronomer Rens Waters of Amsterdam university. "It's really fantastic, this possibility of identifying the silicates. Before ISO everybody thought that all silicates in space were amorphous, without a well-ordered internal structure; that means you cannot differentiate among the many different silicates existing. Now we can try to identify them and track their presence in different regions. A whole new research field is starting", said Rens Waters, who brought to the press conference samples of several terrestrial crystalline silicates: olivine and pyroxene, the most common silicates on Earth. Crystals give key clues about the physical conditions and evolutionary history of crystal-bearing objects. The precise mechanisms for crystal-making are now being researched now very actively in the laboratories, although some working-hypotheses are already being used. For instance, crystals can be made by heating the material to temperatures above 1 300 degrees Centigrade and then cooling it down slowly. Those found so far by ISO are at -170 degrees Centigrade, both in stellar envelopes and in protoplanetary discs. In the case of the old stars -red giant stars, where crystals are found to account for as much as 20% of all the surrounding dust, astronomers think that that the high temperatures near the star triggered the crystallisation of the silicates. In the protoplanetary discs some experts postulate that electric shocks - like lightning flashes - heated the dust, which cooled afterwards. "The crystals detected by ISO in these discs have a size of about a thousandth of a millimetre. They collide with each other, forming bigger and bigger bodies. Models predict that in about ten to one hundred million years they will make planets", Waters says. "In fact, crystalline silicates are very common in our own Solar System. You also have them in the comet Hale Bopp!". The reason why crystalline silicates had not been detected before in stars has to do with their low temperatures. Cold material emits mostly infrared light, which means an infrared space telescope like ESA's ISO was needed. The two high-resolution spectrometers on-board the satellite, able to detect the 'chemical fingerprint' of the crystals, did the rest. Astronomers are sure about the discovery because those chemical fingerprints, the spectra, can be compared in laboratories with spectra from crystalline silicates found on Earth. This method has demonstrated the crystalline structure and has even already allowed the identification of some of the crystals, such as forsterite and enstatite. However, crystalline silicates are a large family and their chemical signatures can be very similar; to enlarge the list of precise crystals more work will be needed, say experts in space chemistry. That is just one of the open questions requiring lab work. There's at least another one: crystalline silicates are found around old stars, in protoplanetary disks and in our own Solar System, but not in the space among the stars; astronomers can't explain it yet. "Crystalline silicates are synthesised around the stars; then that dust goes into the interstellar space, and enriches the raw material out of which more stars and planets will form. So you would expect crystals also to be in the interstellar medium! Crystals will certainly make us learn a lot...", says Waters. "This finding shows that ISO is really unveiling the chemistry of the Universe", says ESA astronomer Alberto Salama, chairman of the workshop about ISO results in spectroscopy held this week at ESA's Villafranca station in Madrid where the results were presented to the scientific community. "This is becoming more and more a 'hot

2000-02-01

264

Mixing of zeolite powders and molten salt.  

National Technical Information Service (NTIS)

Transuranics and fission products in a molten salt can be incorporated into zeolite A by an ion exchange process and by a batch mixing or blending process. The zeolite is then mixed with glass and consolidated into a monolithic waste form for geologic dis...

C. Pereira V. N. Zyryanov M. A. Lewis J. P. Ackerman

1996-01-01

265

Oxygen and hydrogen isotope geochemistry of zeolites  

Microsoft Academic Search

Zeolites are widespread minerals and occur in a large variety of rock types. More than 40 naturally occurring species have been described. Zeolites are hydrous aluminosilicates which possess unique properties such as reversible dehydration, selective sorption, molecular sieving, ion exchange, and catalysis. While we known a great deal about their occurrence, chemistry, crystal structure, and physical properties, we know relatively

H. R. Karlsson; R. N. Clayton

1990-01-01

266

Chemical interactions in multimetal\\/zeolite catalysts  

Microsoft Academic Search

Mechanistic explanations have been found for the migration of atoms and ions through the zeolite channels leading to specific distribution of ions and the metal clusters. In this report, we summarize the state of understanding attained on a number of topics in the area of mono- and multimetal\\/zeolite systems, to which our recent research has made significant contributions. The following

Sachtler; W. M. H

1992-01-01

267

Fly Ash Zeolites as Sulfur Dioxide Adsorbents  

Microsoft Academic Search

Air protection technologies generate massive amounts of solid wastes, including fly ash (FA). Zeolite synthesis from FA seems to be an effective method for FA utilization. In addition, fly ash zeolites (FAZs) could be used for sulfur dioxide (SO2) adsorption. Since there is a lack of sufficient information about SO2 uptake on FAZs, we investigated this phenomenon in detail. Two

T. T. Suchecki; T. Wa?ek; M. Banasik

268

Metal/zeolite catalysts of methane dehydroaromatization  

NASA Astrophysics Data System (ADS)

Results of studying methane dehydroaromatization over metal/zeolite catalysts have been reviewed. Special attention has focused on molybdenum catalysts based on HZSM-5 zeolites. The effect of catalyst synthesis and reaction conditions on the catalytic properties of the systems has been scrutinized. Information on the mechanism of the process and the nature of active sites has been reported. The bibliography includes 137 references.

Mamonov, N. A.; Fadeeva, E. V.; Grigoriev, D. A.; Mikhailov, M. N.; Kustov, Leonid M.; Alkhimov, S. A.

2013-06-01

269

[Morphology of pneumoconiosis induced by natural zeolite].  

PubMed

Pneumoconiosis was induced in white rats through intratracheal administration of natural zeolite. It was characterized by intensive phagocytosis of the specks of dust, moderate cytotoxic action on the macrophages, as well as inflammatory processes in the vascular system and alveolar epithelium. Zeolite induced fibrosis did not develop to the extent as in case with quartz induced massive collagen formation. PMID:2165972

Kruglikov, G G; Velichkovski?, B T; Garmash, T I

1990-01-01

270

Ion exchange equilibria in zeolite minerals  

Microsoft Academic Search

Cation exchange equilibria of the most common sedimentary zeolites are reviewed. Selected exchange isotherms and thermodynamic equilibrium constants are reported and interpreted in terms of selectivity of one cation over another. Selectivity sequences of various zeolites are compared with each other in the light of Eisenman's theory and utilized to predict or explain specific practical performances.

C. Colella; Napoli Federico; Piazzale V. Tecchio

1996-01-01

271

Octane-enhancing zeolitic FCC catalysts  

Microsoft Academic Search

While particular aspects of octane- enhancing catalysts and zeolites are often described in detail in different articles and patents, this book provides a comprehensive, unified view of this topic. The author has organized the wealth of disparate data and information from the literature by the frequent use of classifications. For example, high-silica Y zeolites were classified according to their preparation

Scherzer

1990-01-01

272

Synthesis of crystalline polyaniline  

SciTech Connect

The synthesis of crystalline polyaniline base using a water-in-oil type microemulsion as a medium of polymerization is reported. The polymer exhibits well defined crystalline phase whose observed orthorhombic lattice parameters are a = 7.65, b = 5.75, c = 10.22{angstrom} and V = 450{angstrom}{sup 3}. The polymer obtained has been characterized by XRD, FTIR, UV and Cyclic Voltammetry (CV) confirming the crystalline phase, surfactant stabilized nature, base form and dopability.

Selvan, S.T.; Mani, A.; Athinarayanasamy, K.; Phani, K.L.N.; Pitchumani, S. [Central Electrochemical Research Inst., Karaikudi (India)] [Central Electrochemical Research Inst., Karaikudi (India)

1995-06-01

273

Dealumination of hexagonal (EMT)/cubic (FAU) zeolite intergrowth materials: A SEM and HRTEM study  

SciTech Connect

The aim of this paper is to describe the effects of mild dealumination of the end members (FAU, EMT) and intergrowths produced using crown ethers on the nature of the resultant zeolite. The end members and intergrowths were prepared as described previously and dealuminated according to the following procedure. The intergrowth was prepared from a mixture of crown ethers; 66% 18-crown-6 and 33% 15-crown-5 to give an ordered intergrowth. The zeolites were first calcined to remove the crown ether template (600{degree}C, flowing air, 16 h) and then exchanged with ammonium ions. The zeolite (6 g) was slurried in ammonium acetate solution (450 cm{sup 3}, 0.8 M), and to this was added slowly 15.6 cm{sup 3} of ammonium hexafluorosilicate solution (0.5 M). The mixture was stirred at 75{degree}C for 3 h. The zeolite was collected and carefully washed with water (3 x 100 cm{sup 3}). The dealuminated samples were characterized by {sup 29}Si and {sup 27}Al MAS NMR, X-ray powder diffraction and adsorption measurements. These data indicate that the resultant materials are highly crystalline and showed no signs of structural degradation both in short-range order ({sup 27}Al, {sup 29}Si MAS NMR) and long-range order (XRD). However, the SEM and high-resolution images were particularly informative.

Ohsuna, Tetsu; Watanabe, Denjiro [Iwaki Meisei Univ., Fukushima (Japan); Terasaki, Osamu [Tohoku Univ., Sendai (Japan); Anderson, M.W. [UMIST, Manchester (United Kingdom); Carr, S.W. [Unilever Research, Merseyside (United Kingdom)

1994-12-01

274

Phosphatation of zeolite H-ZSM-5: a combined microscopy and spectroscopy study.  

PubMed

A variety of phosphated zeolite H-ZSM-5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse (27)Al, (29)Si, (31)P, (1)H-(31)P cross polarization (CP), (27)Al-(31)P CP, and (27)Al 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X-ray microscopy (STXM) and N2 physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H-ZSM-5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue. Phosphatation of pre-steamed H-ZSM-5 gives rise to the formation of a crystalline tridymite AlPO4 phase, which is found in the mesopores of dealuminated H-ZSM-5. Framework aluminum species interacting with phosphorus are not affected by hydrothermal treatment. Dealuminated H-ZSM-5, containing AlPO4 , retains relatively more framework Al atoms and acid sites during hydrothermal treatment than directly phosphated H-ZSM-5. PMID:24402742

van der Bij, Hendrik E; Aramburo, Luis R; Arstad, Bjørnar; Dynes, James J; Wang, Jian; Weckhuysen, Bert M

2014-02-01

275

UTILITY OF ZEOLITES IN ARSENIC REMOVAL FROM WATER  

EPA Science Inventory

Zeolites are well known for their ion exchange and adsorption properties. So far the cation exchanger properties of zeolites have been extensively studied and utilized. The anion exchanger properties of zeolites are less studied. Zeolite Faujasite Y has been used to remove arseni...

276

Silver supported on natural Mexican zeolite as an antibacterial material  

Microsoft Academic Search

The antimicrobial effect of the Mexican zeolitic mineral from Taxco, Guerrero exchanged with silver ions was investigated. The zeolitic mineral as well as sodium and silver zeolitic minerals were characterized by using X-ray diffraction, electron microscopy and IR spectroscopy techniques. The elementary composition of the zeolitic mineral was determined by atomic absorption and microanalyses (EDAX). Escherichia coli and Streptococcus faecalis

M Rivera-Garza; M. T Olgu??n; I Garc??a-Sosa; D Alcántara; G Rodr??guez-Fuentes

2000-01-01

277

What Is Crystalline Silica?  

MedlinePLUS

... loss, which often leads to death. Where are construction workers exposed to crystalline silica? Exposure occurs during many different construction activities. The most severe exposures generally occur during ...

278

Comparative pathology of silicate pneumoconiosis.  

PubMed Central

A simple pneumoconiosis with lamellar birefringent crystals was observed in animals dying in the San Diego Zoo. We studied 100 autopsies from 11 mammalian and eight avian species. In mammals, mild pulmonary lesions comprised crystal-laden macrophages in alveoli and lymphatics. Interstitial fibrosis was present in 20% of cases. There were no nodules. In birds, dust retention produced large granulomas around tertiary bronchi without fibrosis. Mineralogic analysis using scanning and transmission electron microscopy showed most of the crystals to be silicates. Ninety percent were complex silicates, with aluminum-potassium silicates comprising 70% of the analyzed particles. Electron and x-ray diffraction showed the silicates to be muscovite mica and its hydrothermal degradation product, ie, illite clay. This mica was also present on filtration membranes of atmospheric air samples obtained from the San Diego Zoo. The amount of dust retention was related to the animal's age, anatomic or ecologic variances, and length of stay in the San Diego Zoo. Its semidesert atmosphere is rich in silicates, which are inhaled and deposited in the lungs. Similar mica-induced lesions are found in humans living in this region or the Southwest of the USA. This simple pneumoconiosis is likely to be widespread in human populations living in desert or semidesert climates. Images Figure 9 Figure 10 Figure 7 Figure 8 Figure 5 Figure 6 Figure 1 Figure 2 Figure 3 Figure 4

Brambilla, C.; Abraham, J.; Brambilla, E.; Benirschke, K.; Bloor, C.

1979-01-01

279

Coating crystalline nuclear waste forms to improve inertness  

SciTech Connect

Crystalline waste forms of high simulated waste loading were successfully coated with layers of pyrolytic carbon and silicon carbide. Sol-gel technology was used to produce microspheres that contained simulated waste. A separate process for cesium immobilization was developed, which loads 5 wt % Cs onto zeolite particles for subsequent coating. The chemical vapor deposition process was developed for depositing thin layers of carbon and silicon carbide onto particles in a fluidized-bed coater. Pyrolytic carbon-coated particles were extremely inert in numerous leach tests. Aqueous leach test results of coated waste forms were below detection limits of such sensitive analytical techniques as atomic absorption and inductively coupled plasma atomic emission.

Stinton, D.P.; Angelini, P.; Caputo, A.J.; Lackey, W.J.

1981-01-01

280

Coating of crystalline nuclear waste forms to improve inertness  

SciTech Connect

Microspheres of a crystalline waste form prepared by sol-gel processing were successfully coated with layers of pyrolytic carbon and silicon carbide to isolate the radioactive wastes from the biosphere. A separate process for cesium immobilization was developed, which loads 5 wt% Cs onto zeolite particles for subsequent coating. Pyrolytic carbon-coated particles showed leach rates approx. =2 to 4 orders of magnitude less than the candidate reference borosilicate glass waste form. Aqueous leach-test results of coated waste forms were below detection limits of such sensitive analytical techniques as atomic absorption and inductively coupled plasma atomic emission.

Stinton, D.P.; Angelini, P.; Caputo, A.J.; Lackey, W.J.

1982-08-01

281

Post-synthetic preparation of Sn-, Ti- and Zr-beta: a facile route to water tolerant, highly active Lewis acidic zeolites.  

PubMed

A two-step procedure for the post-synthetic preparation of Lewis acidic Sn-, Zr- and Ti-zeolite ? is reported. Dealumination of a commercially available Al-? zeolite leads to the formation of highly siliceous material containing silanol nests, which can be filled in a second step via the solid-state ion-exchange or impregnation of an appropriate metal precursor. Spectroscopic studies indicate that each metal is subsequently coordinated within the zeolite framework, and that little or no bulk oxides are formed--despite the high metal loadings. The synthesised catalysts demonstrate excellent activity for the isomerisation of glyceraldehyde to dihydroxyacetone, a key model reaction for the upgrading of bio-renewable feedstocks, and the epoxidation of bulky olefins. PMID:24407516

Wolf, Patrick; Hammond, Ceri; Conrad, Sabrina; Hermans, Ive

2014-03-21

282

An ESCA study of rhodium(III)-exchanged zeolite catalysts  

SciTech Connect

An ESCA study of rhodium(III)-exchanged zeolite catalysts which are active in hydrogenation and other reactions, showed that activation at 300/sup 0/C and 0.002 mm Hg reduced rhodium(III) in Y zeolite to metallic rhodium but did not affect rhodium(III) in A zeolite. This reduction occurred under milder conditions than known for other metal ions in zeolites, and the reduced species is probably the active catalyst in rhodium-exchanged zeolite.

Kuznicki, S.M.; Eyring, E.M.

1980-09-01

283

Liquid crystalline cellulose derivatives  

SciTech Connect

Following the observation that (hydroxypropyl)cellulose in water forms an ordered cholesteric liquid crystalline phase at high polymer concentrations, reports that many other cellulose derivatives in a wide variety of solvents also form liquid crystalline solutions have appeared in the scientific and patent literature. A tabulation of cellulose-based liquid crystalline systems is presented. The formation of the ordered phase is attributed to the limited flexibility of the cellulose chain. However, some cellulose derivatives form liquid crystalline phases only in specific solvents; concentrated solutions in other solvents remain isotropic. Other cellulose derivatives, such as (hydroxypropyl)cellulose, appear to form liquid crystalline solutions in any solvent that dissolves sufficiently high concentrations of the polymer. It has been suggested that the role of flexible side-chain substituents is to allow the main chains to achieve their equilibrium orientational order. The presence of many large substituents on the cellulose backbone also increases the effective chain radius and may change the chain conformation. The effect of side-chain structure on the properties of cellulose liquid crystalline phases is thus of interest. A series of esters of (hydroxypropyl)cellulose have been prepared. In addition to forming liquid crystalline solutions in organic solvents, these materials also were found to form cholesteric thermotropic phases in the absence of solvent. The thermotropic phases show spontaneous molecular orientation and cholesteric reflection. On heating, a transformation to the isotropic melt occurs. The liquid crystalline state of cellulose and its derivatives is thus widely observed. 42 references, 4 figures, 3 tables.

Gray, D.G.

1983-01-01

284

Framework-incorporated Mn and Co analcime zeolites: Synthesis and characterization  

SciTech Connect

The framework-substituted cobalt and manganese analcime zeolites were synthesized via a direct hydrothermal approach. The obtained samples were characterized by XRD powder, SEM-EDX, nitrogen physical adsorption, Raman microscopy, diffuse reflectance UV-Vis and IR spectroscopy which complementarily demonstrated the incorporation of cobalt and manganese into the zeolites framework. The results showed that substitution of Mn and Co could be placed in two synthesis gels with same compositions containing Al/Mn=5 and Al/Co=4 mol ratios, respectively. In addition, with replacing Al with Mn and synthesis of Mn-modified analcime, zeolite with higher surface area and pore volume could be achieved than the Co modified analcime. - Graphical abstract: The images and adsorption-desorption isotherms of N{sub 2} at 77 K for (a) Co (b) Mn modified analcime. Highlights: Black-Right-Pointing-Pointer Synthesis of Co and Mn modified analcime for the first time. Black-Right-Pointing-Pointer Framework-incorporation of Co and Mn using the same silicate gel composition. Black-Right-Pointing-Pointer Applying several techniques to provide proofs for the characterization.

Azizi, Seyed Naser, E-mail: azizi@umz.ac.ir [Analytical Division, Faculty of Chemistry, University of Mazandaran, P.O. Box 47416-95447, Babolsar (Iran, Islamic Republic of); Ehsani Tilami, Salma [Analytical Division, Faculty of Chemistry, University of Mazandaran, P.O. Box 47416-95447, Babolsar (Iran, Islamic Republic of)] [Analytical Division, Faculty of Chemistry, University of Mazandaran, P.O. Box 47416-95447, Babolsar (Iran, Islamic Republic of)

2013-02-15

285

Nanocrystalline zeolite beta and zeolite Y as catalysts in used palm oil cracking for the production of biofuel  

Microsoft Academic Search

Nanocrystalline zeolites with crystal size smaller than 100 nm are potential replacement for conventional zeolite catalysts\\u000a due to their unique characteristics and advantages. In this study, the synthesis of nanocrystalline zeolite Y (FAU) and nanocrystalline\\u000a zeolite beta (BEA) under hydrothermal conditions is reported. The effect of crystal size on the physico-chemical characteristics\\u000a of the zeolite, Y (FAU), and beta (BEA) is

Niken Taufiqurrahmi; Abdul Rahman Mohamed; Subhash Bhatia

286

FORMATION OF COSMIC CRYSTALS IN HIGHLY SUPERSATURATED SILICATE VAPOR PRODUCED BY PLANETESIMAL BOW SHOCKS  

SciTech Connect

Several lines of evidence suggest that fine silicate crystals observed in primitive meteorite and interplanetary dust particles (IDPs) nucleated in a supersaturated silicate vapor followed by crystalline growth. We investigated evaporation of {mu}m-sized silicate particles heated by a bow shock produced by a planetesimal orbiting in the gas in the early solar nebula and condensation of crystalline silicate from the vapor thus produced. Our numerical simulation of shock-wave heating showed that these {mu}m-sized particles evaporate almost completely when the bow shock is strong enough to cause melting of chondrule precursor dust particles. We found that the silicate vapor cools very rapidly with expansion into the ambient unshocked nebular region; for instance, the cooling rate is estimated to be as high as 2000 K s{sup -1} for a vapor heated by a bow shock associated with a planetesimal of radius 1 km. The rapid cooling of the vapor leads to nonequilibrium gas-phase condensation of dust at temperatures much lower than those expected from the equilibrium condensation. It was found that the condensation temperatures are lower by a few hundred K or more than the equilibrium temperatures. This explains the results of the recent experimental studies of condensation from a silicate vapor that condensation in such large supercooling reproduces morphologies similar to those of silicate crystals found in meteorites. Our results strongly suggest that the planetesimal bow shock is one of the plausible sites for formation of not only chondrules but also other cosmic crystals in the early solar system.

Miura, H.; Yamada, J.; Tsukamoto, K.; Nozawa, J. [Department of Earth Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai 980-8578 (Japan); Tanaka, K. K.; Yamamoto, T. [Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819 (Japan); Nakamoto, T., E-mail: miurah@m.tohoku.ac.j [Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan)

2010-08-10

287

The Deep Impact Coma of Comet 9P\\/Tempel 1 as a Time-of-Flight Experiment Motivates DDSCAT Models for Porous Aggregate Grains with Silicate Crystal Inclusions  

Microsoft Academic Search

Spitzer IRS spectra of short-period Ecliptic Comets (ECs) have silicate features, and many have distinct crystalline silicate peaks. These Spitzer spectra, when fitted with thermal models after subtraction of the relatively strong contribution of the nuclear flux to the IR spectrum (e.g., Harker et al. 2007), demonstrate ECs have weaker silicate features than long-period Nearly-Isotropic Comets (NICs). There are exceptions,

Diane H. Wooden; S. S. Lindsay; D. E. Harker; M. S. Kelley; C. E. Woodward; D. T. Richard; L. Kolokolova; F. Moreno

2010-01-01

288

Zeolites on Mars: Prospects for remote sensing  

NASA Technical Reports Server (NTRS)

The Martian surface composition measured by Viking can be represented by several combinations of minerals incorporating major fractions of zeolites known to occur in altered mafic rocks and polar soils on Earth. The abundant occurrence of zeolites on Mars is consistent with what is known about both the physical and chemical environment of that planet. The laboratory reflectance spectra (0.65 to 2.55 microns) of a number of relatively pure zeolite minerals and some naturally occurring zeolite-clay soils were measured. All of the spectra measured are dominated by strong absorption near 1.4 and 1.9 microns and a steep reflectance drop longward of about 2.2 microns, all of which are due to abundant H2O. Weaker water overtone bands are also apparent, and in most cases there is spectral evidence for minor Fe(3+). In these features the zeolite spectra are similar to spectra of smectite clays which have abundant interlayer water. The most diagnostic difference between clay and zeolite spectra is the total absence in the zeolites of the weak structural OH absorption.

Gaffney, E. S.; Singer, R. B.; Kunkle, T. D.

1985-01-01

289

Reaction of Sodium Hydroxide with Silicate Minerals.  

National Technical Information Service (NTIS)

The reactions of individual silicate minerals with caustic solution were measured over a 1-week period. These silicate minerals included: two feldspars (microcline and albite), two micas (biotite and muscovite), and three clays (chlorite, Kaolinite and mo...

S. D. Thornton

1986-01-01

290

Battery components employing a silicate binder  

DOEpatents

A battery component structure employing inorganic-silicate binders. In some embodiments, casting or coating of components may be performed using aqueous slurries of silicates and electrode materials or separator materials.

Delnick, Frank M. (Albuquerque, NM) [Albuquerque, NM; Reinhardt, Frederick W. (Albuquerque, NM) [Albuquerque, NM; Odinek, Judy G. (Rio Rancho, NM) [Rio Rancho, NM

2011-05-24

291

TRANSMISSION ELECTRON MICROSCOPY OF Al-RICH SILICATE STARDUST FROM ASYMPTOTIC GIANT BRANCH STARS  

SciTech Connect

We report on transmission electron microscopy (TEM) investigations of two mineralogically unusual stardust silicates to constrain their circumstellar condensation conditions. Both grains were identified by high spatial resolution nano secondary ion mass spectrometry (NanoSIMS) in the Acfer 094 meteorite, one of the most pristine carbonaceous chondrites available for study. One grain is a highly crystalline, highly refractory (Fe content < 0.5 at%), structurally undisturbed orthopyroxene (MgSiO{sub 3}) with an unusually high Al content (1.8 {+-} 0.5 at%). This is the first TEM documentation of a single crystal pyroxene within the complete stardust silicate data set. We interpret the microstructure and chemistry of this grain as being a direct condensate from a gas of locally non-solar composition (i.e., with a higher-than-solar Al content and most likely also a lower-than-solar Mg/Si ratio) at (near)-equilibrium conditions. From the overabundance of crystalline olivine (six reported grains to date) compared to crystalline pyroxene (only documented as a single crystal in this work) we infer that formation of olivine over pyroxene is favored in circumstellar environments, in agreement with expectations from condensation theory and experiments. The second stardust silicate consists of an amorphous Ca-Si rich material which lacks any crystallinity based on TEM observations in which tiny (<20 nm) hibonite nanocrystallites are embedded. This complex assemblage therefore attests to the fast cooling and rapidly changing chemical environments under which dust grains in circumstellar shells form.

Vollmer, Christian [Institute for Mineralogy, University of Muenster, Correnssstr. 24, D-48149 Muenster (Germany); Hoppe, Peter [Max Planck Institute for Chemistry, Particle Chemistry Department, Hahn-Meitner-Weg 1, D-55128 Mainz (Germany); Brenker, Frank E., E-mail: christian.vollmer@wwu.de [Institute of Geoscience/Mineralogy, Goethe-University Frankfurt, Altenhoeferallee 1, D-60438 Frankfurt (Germany)

2013-05-20

292

Cracking Activity of Zeolite Y Catalysts Synthesized from a South African Kaolinite.  

National Technical Information Service (NTIS)

Rare earth cation exchanged zeolite Y catalysts, rare earth acidic exchanged zeolite Y catalysts, and ultrastable zeolite Y catalysts with or without exchanged rare earth cations were prepared from ceramic microspheres which contained 24% NaY zeolites. A ...

M. G. Howden

1981-01-01

293

Facile synthesis of mesoporous aluminosilicates constructed with crystalline microporous frameworks  

NASA Astrophysics Data System (ADS)

A hierarchically micro-mesoporous structured ZSM-5 zeolite has been synthesized from assembly of aluminosilcate species with a tetra-quaternary ammonium type surfactant, in which the surfactant acts as two-level structure-directing templates for generating micropores and mesopores simultaneously. The synthesized samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption isotherms, scanning electron microscopy, transmission electron microscopy, 27Al magic angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, Thermogravimetric analysis and Quantum chemical calculation. X-ray diffraction as well as nitrogen sorption analyses indicated the dual-porosity of samples, one is from intra-crystalline micropores, and the other is from mesopores. Quantum chemical calculation results showed that the inner ammonium groups of surfactant had more higher molecular degrees of freedom for the zeolite-structure-directing function. Moreover, on the basis of the same concept, this method could be extended to investigate other hierarchically structured zeolites.

Liu, Baoyu; Ren, Yanqun; Duan, Qianqian; Chen, Fei; Xi, Hongxia; Qian, Yu

2013-08-01

294

Molecular-sieving effect of zeolite 3A on adsorption of H 2, HD and D 2  

Microsoft Academic Search

Synthetic zeolite 3A has the molecular-sieving windows of nominal diameter 0.3nm in its crystal lattice framework, which obstruct the crystalline adsorption of molecules of diameter larger than 0.3nm, except water, hydrogen and helium. The window's diameter slightly varies with temperature, however, that is endorsed in experimental results that hydrogen cannot be adsorbed at the liquid-nitrogen temperature. Authors measured the range

K. Kotoh; S. Takashima; Y. Nakamura

2009-01-01

295

Lithologic mapping of silicate rocks using TIMS  

NASA Technical Reports Server (NTRS)

Common rock-forming minerals have thermal infrared spectral features that are measured in the laboratory to infer composition. An airborne Daedalus scanner (TIMS) that collects six channels of thermal infrared radiance data (8 to 12 microns), may be used to measure these same features for rock identification. Previously, false-color composite pictures made from channels 1, 3, and 5 and emittance spectra for small areas on these images were used to make lithologic maps. Central wavelength, standard deviation, and amplitude of normal curves regressed on the emittance spectra are related to compositional information for crystalline igneous silicate rocks. As expected, the central wavelength varies systematically with silica content and with modal quartz content. Standard deviation is less sensitive to compositional changes, but large values may result from mixed admixture of vegetation. Compression of the six TIMS channels to three image channels made from the regressed parameters may be effective in improving geologic mapping from TIMS data, and these synthetic images may form a basis for the remote assessment of rock composition.

Gillespie, A. R.

1986-01-01

296

Copper-Exchanged Zeolite L Traps Oxygen  

NASA Technical Reports Server (NTRS)

Brief series of simple chemical treatments found to enhance ability of zeolite to remove oxygen from mixture of gases. Thermally stable up to 700 degrees C and has high specific surface area which provides high capacity for adsorption of gases. To increase ability to adsorb oxygen selectively, copper added by ion exchange, and copper-exchanged zeolite reduced with hydrogen. As result, copper dispersed atomically on inner surfaces of zeolite, making it highly reactive to oxygen, even at room temperature. Reactivity to oxygen even greater at higher temperatures.

Sharma, Pramod K.; Seshan, Panchalam K.

1991-01-01

297

Pulsed laser deposition of zeolitic membranes  

SciTech Connect

The pulsed laser deposition of zeolites to form zeolitic thin films is described. Films were grown using both mordenite and faujasite targets and were deposited on various substrates. The optimal films were obtained when the target and substrate were separated by 5 cm. These films are comprised of small crystallites embedded in an amorphous matrix. Transmission electron microscopy reveals that the amorphous material is largely porous and that the pores appear to be close to the same size as the parent zeolite. Zeolotic thin films are of interest for sensor, gas separation, and catalytic applications.

Peachey, N.M.; Dye, R.C. [Los Alamos National Lab., NM (United States); Ries, P.D. [Dow Chemical Co., Midland, MI (United States)

1995-02-01

298

Role of structural similarity between starting zeolite and product zeolite in the interzeolite conversion process.  

PubMed

GIS- and LTL- (the three capital characters indicate the framework type-code) type zeolites were obtained by organic structure-directing agent free hydrothermal conversion of FAU-type zeolite at 125 degrees C in the presence of NaOH and KOH, respectively. MOR-type zeolite was found coexisting with GIS-type when the hydrothermal conversion with NaOH was carried out at 140 degrees C. There was a common building unit consisting of four-membered ring chain such as d6r, dsc, and dcc (the three characters indicate the composite building unit-code) units present in both the starting zeolite (FAU-type zeolite) and the product zeolites (GIS- and LTL-type zeolites), which was the crucial factor for crystal growth through interzeolite conversion. In the case of severe hydrothermal synthesis conditions such as high temperature, however, the crystallization behavior was similar to that observed in conventional hydrothermal synthesis using amorphous materials because the starting zeolite was excessively decomposed. The hypothesis was confirmed by successful interzeolite conversion of *BEA- to MFI-type zeolite which shared the common composite building unit mor. PMID:23763196

Honda, Koutaro; Itakura, Masaya; Matsuura, Yumiko; Onda, Ayumu; Ide, Yusuke; Sadakane, Masahiro; Sano, Tsuneji

2013-04-01

299

Tobermorite group of silicates (Text)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I4 'Inosilicates' of Volume 27 'Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III Condensed Matter. It contains the data of the tobermorite group of silicates (Text)

Burzo, E.

300

Tobermorite group of silicates (Figures)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I4 'Inosilicates' of Volume 27 'Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III Condensed Matter. It contains the data of the tobermorite group of silicates (Figures)

Burzo, E.

301

Tobermorite group of silicates (Tables)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I4 'Inosilicates' of Volume 27 'Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III Condensed Matter. It contains the data of the tobermorite group of silicates (Tables)

Burzo, E.

302

Ionic Transport in Liquid Silicates  

Microsoft Academic Search

OME uncertainty exists concerning the presence of semi­ conduction in the electric conduction of liquid silicates. This may be resolved only by measurements of the applicability of Faraday's Laws to the electric transport processes in the melt. Such measurements are considered to be difficult at 800°C in liquid salts.' A method has been devised in these laboratories whereby the oxygen

J. O'M. Bockris; J. A. Kitchener; A. E. Davies

1951-01-01

303

Amended Silicated for Mercury Control  

SciTech Connect

Amended Silicates{trademark}, a powdered, noncarbon mercury-control sorbent, was tested at Duke Energy's Miami Fort Station, Unit 6 during the first quarter of 2006. Unit 6 is a 175-MW boiler with a cold-side electrostatic precipitator (ESP). The plant burns run-of-the-river eastern bituminous coal with typical ash contents ranging from 8-15% and sulfur contents from 1.6-2.6% on an as-received basis. The performance of the Amended Silicates sorbent was compared with that for powdered activated carbon (PAC). The trial began with a period of baseline monitoring during which no sorbent was injected. Sampling during this and subsequent periods indicated mercury capture by the native fly ash was less than 10%. After the baseline period, Amended Silicates sorbent was injected at several different ratios, followed by a 30-day trial at a fixed injection ratio of 5-6 lb/MMACF. After this period, PAC was injected to provide a comparison. Approximately 40% mercury control was achieved for both the Amended Silicates sorbent and PAC at injection ratios of 5-6 lbs/MMACF. Higher injection ratios did not achieve significantly increased removal. Similar removal efficiencies have been reported for PAC injection trials at other plants with cold-side ESPs, most notably for plants using medium to high sulfur coal. Sorbent injection did not detrimentally impact plant operations and testing confirmed that the use of Amended Silicates sorbent does not degrade fly ash quality (unlike PAC). The cost for mercury control using either PAC or Amended Silicates sorbent was estimated to be equivalent if fly ash sales are not a consideration. However, if the plant did sell fly ash, the effective cost for mercury control could more than double if those sales were no longer possible, due to lost by-product sales and additional cost for waste disposal. Accordingly, the use of Amended Silicates sorbent could reduce the overall cost of mercury control by 50% or more versus PAC for locations where fly ash is sold as a by-product.

James Butz; Thomas Broderick; Craig Turchi

2006-12-31

304

Liquid Crystalline Polymers.  

National Technical Information Service (NTIS)

The remarkable mechanical properties and thermal stability of fibers fabricated from liquid crystalline polymers (LCPs) have led to the use of these materials in structural applications where weight savings are critical. Advances in processing of LCPs cou...

1990-01-01

305

Crystalline color superconductivity  

SciTech Connect

In any context in which color superconductivity arises in nature, it is likely to involve pairing between species of quarks with differing chemical potentials. For suitable values of the differences between chemical potentials, Cooper pairs with nonzero total momentum are favored, as was first realized by Larkin, Ovchinnikov, Fulde, and Ferrell (LOFF). Condensates of this sort spontaneously break translational and rotational invariance, leading to gaps which vary periodically in a crystalline pattern. Unlike the original LOFF state, these crystalline quark matter condensates include both spin-zero and spin-one Cooper pairs. We explore the range of parameters for which crystalline color superconductivity arises in the QCD phase diagram. If in some shell within the quark matter core of a neutron star (or within a strange quark star) the quark number densities are such that crystalline color superconductivity arises, rotational vortices may be pinned in this shell, making it a locus for glitch phenomena.

Alford, Mark; Bowers, Jeffrey A.; Rajagopal, Krishna

2001-04-01

306

Factors affecting drug adsorption on beta zeolites.  

PubMed

The adsorption behaviour of three commonly used drugs, namely ketoprofen, hydrochlorothiazide and atenolol, from diluted aqueous solutions on beta zeolites with different SiO2/Al2O3 ratio (i.e. 25, 38 and 360) was investigated by changing the ionic strength and the pH, before and after thermal treatment of the adsorbents. The selective adsorption of drugs was confirmed by thermogravimetry and X-ray diffraction. The adsorption capacity of beta zeolites was strongly dependent on both the solution pH and the alumina content of the adsorbent. Such a remarkable difference was interpreted as a function of the interactions between drug molecules and zeolite surface functional groups. Atenolol was readily adsorbed on the less hydrophobic zeolite, under pH conditions in which electrostatic interactions were predominant. On the other hand, ketoprofen adsorption was mainly driven by hydrophobic interactions. For undissociated molecules the adsorption capability increased with the increase of hydrophobicity. PMID:23436460

Pasti, Luisa; Sarti, Elena; Cavazzini, Alberto; Marchetti, Nicola; Dondi, Francesco; Martucci, Annalisa

2013-05-01

307

Mixing of zeolite powders and molten salt  

SciTech Connect

Transuranics and fission products in a molten salt can be incorporated into zeolite A by an ion exchange process and by a batch mixing or blending process. The zeolite is then mixed with glass and consolidated into a monolithic waste form for geologic disposal. Both processes require mixing of zeolite powders with molten salt at elevated temperatures (>700 K). Complete occlusion of salt and a uniform distribution of chloride and fission products are desired for incorporation of the powders into the final waste form. The relative effectiveness of the blending process was studied over a series of temperature, time, and composition profiles. The major criteria for determining the effectiveness of the mixing operations were the level and uniformity of residual free salt in the mixtures. High operating temperatures (>775 K) improved salt occlusion. Reducing the chloride levels in the mixture to below 80% of the full salt capacity of the zeolite significantly reduced the free salt level in the final product.

Pereira, C.; Zyryanov, V.N.; Lewis, M.A.; Ackerman, J.P.

1996-05-01

308

Crystalline Raman Lasers  

Microsoft Academic Search

In this paper, we review the developments of crystalline Raman lasers over the past five years. Average powers exceeding 5 W and pulse energies above 1 J in the near infrared have been demonstrated for larger scale devices. There has been a rapid development of all-solid-state sources based on the standard diode-pumped lasers, especially intracavity crystalline Raman lasers, which offer

James A. Piper; Helen M. Pask

2007-01-01

309

Effects of ionization on silicate glasses. [Silicate glasses  

SciTech Connect

This evaluation of radiation effects in silicate glasses caused by ionization is based on our own investigations, on material collected in our files (reports, articles, and notes), and on a computer literature search through recent issues of Physics Abstracts and Chemical Abstracts (and the apparently pertinent references which appeared). Some of our recent results, available heretofore only in internal correspondence, are presented in some detail. It is concluded that research into the behavior of silicate glasses generally will be required before the specific effects in the radioactive waste storage glasses can be properly understood and evaluated. Two particular neglected areas of investigation are targeted for immediate concern: a kinetic analysis of annealing data and the acquisition of data on effects of irradiation at controlled elevated temperatures.

Primak, W.

1982-02-01

310

Important yet Overlooked Topological Mechanisms of Compression in Silicate Liquids at Low Pressure (0-5 GPa)  

Microsoft Academic Search

The compressibility of silicate liquids has long been known to be larger than corresponding solids (especially pronounced at low pressures; 0-5 GPa), with important consequences for the increase in the density difference between partial melts vs. crystalline mantle with decreasing pressure, which in turn has consequences for decompressional mantle melting and an increased buoyancy drive for partial melts. Despite the

R. A. Lange

2007-01-01

311

Acetylene hydration on different Cd-zeolites  

Microsoft Academic Search

Various Cd-zeolite preparations, containing adsorbed water in controlled amounts, were contacted with acetylene in an IR cell at 0.03 bar. The activity of the zeolites was estimated from the formation rate of adsorbed acetaldehyde at 50 °C detected by FTIR. Cd-derivatives of MOR, MFI, and clinoptilolite were prepared by conventional ion exchange and by a novel method which is based

Gy. Onyestyák; G. Pál-Borbély; D. Kalló

2004-01-01

312

Three Mile Island zeolite vitirification demonstration program  

SciTech Connect

The cleanup of the high-activity-level water at Three Mile Island (TMI) provides an opportunity to further develop waste management technology. Approximately 790,000 gallons of high-activity-level water at TMI's Unit-2 Nuclear Power Station will be decontaminated at the site using the submerged demineralizer system (SDS). In the SDS process, the cesium and strontium in the water are sorbed onto zeolite that is contained within metal liners. The Department of Energy has asked the Pacific Northwest Laboratory (PNL) to take a portion of the zeolite from the SDS process and demonstrate, on a production scale, that this zeolite can be vitrified using the in-can melting process. This paper is a brief overview of the TMI zeolite vitrification program. The first section discusses the formulation of a glass suitable for immobilizing SDS zeolite. The following section describes a feed system that was developed to feed zeolite to the in-can melter. It also describes the in-can melting process and the government owned facilities in which the demonstrations will take place. Finally, the schedule for completing the program activities is outlined.

Siemens, D.H.; Knowlton, D.E.; Shupe, M.W.

1981-06-01

313

The zeolite deposits of Greece  

USGS Publications Warehouse

Zeolites are present in altered pyroclastic rocks at many localities in Greece, and large deposits of potential economic interest are present in three areas: (1) the Evros region of the province of Thrace in the north-eastern part of the Greek mainland; (2) the islands of Kimolos and Poliegos in the western Aegean; and (3) the island of Samos in the eastern Aegean Sea. The deposits in Thrace are of Eocene-Oligocene age and are rich in heulandite and/or clinoptilolite. Those of Kimolos and Poliegos are mainly Quaternary and are rich in mordenite. Those of Samos are Miocene, and are rich in clinoptilolite and/or analcime. The deposits in Thrace are believed to have formed in an open hydrological system by the action of meteoric water, and those of the western Aegean islands in a similar way but under conditions of high heat flow, whereas the deposits in Samos were formed in a saline-alkaline lake.

Stamatakis, M. G.; Hall, A.; Hein, J. R.

1996-01-01

314

Zeolite membranes for gas separations  

SciTech Connect

Silicalite-1, a pure silica zeolite, was deposited on a tubular, asymmetric, {gamma}-alumina support. Single gas permeation experiments with N{sub 2}, CH{sub 4}, and CO{sub 2} were carried out on the membrane. Separation experiments for N{sub 2}/CH{sub 4} mixtures were also conducted. Single-gas permeation of H{sub 2} and separation of H{sub 2}/SF{sub 6} mixture were also carried out with the membrane. Composite membranes of silicalite and Ni-SAPO-34 were also fabricated, but no CO{sub 2}/H{sub 2} selectivity was found. It is proposed to use these membranes for methanol synthesis and separation, and for separating H{sub 2} from gasification products for use as fuel cell fuel, etc.

Falconer, J.; Noble, R.

1995-06-01

315

Salt-occluded zeolite waste forms: Crystal structures and transformability  

SciTech Connect

Neutron diffraction studies of salt-occluded zeolite and zeolite/glass composite samples, simulating nuclear waste forms loaded with fission products, have revealed complex structures, with cations assuming the dual roles of charge compensation and occlusion (cluster formation). These clusters roughly fill the 6--8 {angstrom} diameter pores of the zeolites. Samples are prepared by equilibrating zeolite-A with complex molten Li, K, Cs, Sr, Ba, Y chloride salts, with compositions representative of anticipated waste systems. Samples prepared using zeolite 4A (which contains exclusively sodium cations) as starting material are observed to transform to sodalite, a denser aluminosilicate framework structure, while those prepared using zeolite 5A (sodium and calcium ions) more readily retain the zeolite-A structure. Because the sodalite framework pores are much smaller than those of zeolite-A, clusters are smaller and more rigorously confined, with a correspondingly lower capacity for waste containment. Details of the sodalite structures resulting from transformation of zeolite-A depend upon the precise composition of the original mixture. The enhanced resistance of salt-occluded zeolites prepared from zeolite 5A to sodalite transformation is thought to be related to differences in the complex chloride clusters present in these zeolite mixtures. Data relating processing conditions to resulting zeolite composition and structure can be used in the selection of processing parameters which lead to optimal waste forms.

Richardson, J.W. Jr. [Argonne National Lab., IL (United States). Intense Pulsed Neutron Source Div.

1996-12-31

316

Mechanism of Zeolite Crystallization and Thermochemical Properties of Some Synthetic Zeolites. Final Report.  

National Technical Information Service (NTIS)

During the period of 4/1/82 to 9/30/84, the Department of Energy has provided support for laboratory synthesis of zeolites, calorimetric determinations, and thermal analyses on synthetic zeolites. This Final Report to the DOE is written as 6 independent s...

J. G. Liou

1984-01-01

317

An efficient synthesis of nanocrystalline MFI zeolite using different silica sources: A green approach  

SciTech Connect

Nanocrystalline MFI zeolite was synthesized with a very broad range of silica to alumina ratios using an autoclave for periods of 7 h at 473 K under autogeneous pressure without seeding gel, promoter, organic solvent or sulfuric acid. The procedure has been successfully employed for the synthesis of MFI samples using fumed silica, colloidal silica, aerosil and tetraethylorthosilicate as silica sources. The synthesized samples were characterized by different techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy. Their average crystallite size ranges from about 26 to 55 nm and they exhibit high crystallinity.

Kalita, Banani [Department of Chemistry, Gauhati University, Guwahati 781014, Assam (India); Talukdar, Anup K. [Department of Chemistry, Gauhati University, Guwahati 781014, Assam (India)], E-mail: anup_t@sify.com

2009-02-04

318

Brittle micas and related silicates  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I5a `Phyllosilicates' of Volume 27 `Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III `Condensed Matter'. It presents brittle micas and related silicates with regard to their crystal structures, lattice parameters, nuclear gamma resonance (NGR) data, nuclear magnetic resonance (NMR) data, X-ray absorption spectra and optical properties.

Burzo, E.

319

Pyrophyllite, talc and related silicates  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I5a `Phyllosilicates' of Volume 27 `Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III `Condensed Matter'. It presents pyrophyllite, talc and related silicates with regard to their crystal structures, lattice parameters, neutron diffraction data, magnetic properties, nuclear gamma resonance (NGR) data, nuclear magnetic resonance (NMR) data, heat capacities and optical properties.

Burzo, E.

320

First-principles study of structural, electronic, dynamical, and dielectric properties of zirconium silicates  

Microsoft Academic Search

We investigate structural, electronic, dynamical, and dielectric properties of zirconium silicates (ZrSi_xO_y) within density-functional theory. As a first step, we consider crystalline ZrSiO_4, which presents all the principal bonding features occuring in ZrSi_xO_y. For this crystal, the atomic structure is fully relaxed and the structural parameters are found to differ by less than 1.5% from the experimental data. The associated

Gian-Marco Rignanese; Xavier Gonze; Alfredo Pasquarello

2001-01-01

321

Interconnectivity of Fe–O–S liquid in polycrystalline silicate perovskite at lower mantle conditions  

Microsoft Academic Search

An important aspect of planetary core formation concerns whether interconnectivity of liquid metal can occur in crystalline silicates, which at low melt fractions requires that the dihedral angle between the two phases is <60°. [Shannon, M.C., Agee, C.B., 1998. Percolation of core melts at lower mantle conditions. Science 280, 1059–1061] previously reported that dihedral angles in mantle assemblages decrease from

Hidenori Terasaki; Daniel J. Frost; David C. Rubie; Falko Langenhorst

2007-01-01

322

Application of Metastable Phase Diagrams to Silicate Thin Films for Alternative Gate Dielectrics  

Microsoft Academic Search

Using the concept of metastable phase diagrams, we discuss the microstructure evolution during annealing of amorphous ZrO2-SiO2 and HfO2-SiO2 thin films for gate dielectric applications. These systems are characterized by a low solid solubility, a liquid miscibility gap and a kinetic barrier to the formation of the complex, crystalline silicate. We show that phase partitioning is expected for most compositions.

Susanne Stemmer; Zhiqiang Chen; Carlos G. Levi; Patrick S. Lysaght; Brendan Foran; John A. Gisby; Jeff R. Taylor

2003-01-01

323

The asteroid albedo scale. II - Laboratory polarimetry of dark carbon-bearing silicates  

NASA Technical Reports Server (NTRS)

Laboratory reflection polarimetry is presented for eight samples of artificial, poorly crystalline magnesian silicates with varying admixtures of carbon black. The polarimetric slope-albedo law saturates for geometric albedos lower than about 0.05, and good agreement with the telescopic polarization-phase curves of C-type asteroids is found for albedos as low as 0.02. Thus the conclusion from thermal radiometry is confirmed that the C objects are very dark, darker than any known carbonaceous chondrite.

Zellner, B.; Lebertre, T.; Day, K.

1977-01-01

324

Shock-enhanced dissolution of silicate minerals: An important planetary surface process  

SciTech Connect

This study was undertaken to examine the effect of shock loading on rock-water interactions and on the dissolution of silicate phases. Shock-recovery experiments were carried out on oligoclase, hornblende, and labradorite. No additional crystalline phases or glass were produced, although mean grain size was decreased and specific surface area increased. Dissolution experiments were conducted; the extracted solutions are being analyzed. (DLC)

Boslough, M.B.; Cygan, R.T.

1987-01-01

325

The human crystallin gene families  

PubMed Central

Crystallins are the abundant, long-lived proteins of the eye lens. The major human crystallins belong to two different superfamilies: the small heat-shock proteins (?-crystallins) and the ??-crystallins. During evolution, other proteins have sometimes been recruited as crystallins to modify the properties of the lens. In the developing human lens, the enzyme betaine-homocysteine methyltransferase serves such a role. Evolutionary modification has also resulted in loss of expression of some human crystallin genes or of specific splice forms. Crystallin organization is essential for lens transparency and mutations; even minor changes to surface residues can cause cataract and loss of vision.

2012-01-01

326

Interactions between Tetraalkylammonium Ions and Silicates.  

National Technical Information Service (NTIS)

In zeolite syntheses Tetraalkylammonium (TAA) ions are used as a template. The operation is based on specific interactions between the template and the precursor phase. In order to obtain insight in these interactions viscosity measurements were performed...

J. C. J. Vanderdonck

1992-01-01

327

Hot isostatic pressing of glass-zeolite composites.  

National Technical Information Service (NTIS)

Glass-zeolite waste forms are being developed for immobilizing the chloride waste salt generated from the electrometallurgical treatment of spent fuel. Glass-zeolite composites with high densities were made using hot isostatic pressing (HIP) techniques. P...

M. C. Hash C. Pereira M. A. Lewis

1996-01-01

328

11. EASTERN END OF ZEOLITE BUILDING. NOTE DIAL TO LEFT ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. EASTERN END OF ZEOLITE BUILDING. NOTE DIAL TO LEFT OF CLOCK GAUGING TOTAL ZEOLITE INFLUENT IN MILLIONS OF GALLONS PER DAY. - F. E. Weymouth Filtration Plant, 700 North Moreno Avenue, La Verne, Los Angeles County, CA

329

Branched vs. linear hydrocarbon separations with novel modified zeolites.  

SciTech Connect

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.

Gray, Gary R.; Noble, Richard D.; Nenoff, Tina Maria; Arruebo, Manuel; Ulutagay-Kartin, Mutlu; Johnston, Kaylynn; Anderson, Thomas M.

2005-06-01

330

Branched vs. linear hydrocarbon separations with novel modified zeolites.  

SciTech Connect

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.

Gray, Gary R.; Noble, Richard D.; Nenoff, Tina Maria; Arruebo, Manuel; Ulutagay-Kartin, Mutlu; Anderson, Thomas M.

2004-08-01

331

Separation of xylene mixtures using polyurethane—zeolite composite membranes  

Microsoft Academic Search

Fractionation of o- and p-xylene isomeric mixtures was performed using pervaporation (PV) with polyurethane (PU) membranes containing ZSM zeolite. The xylene vapor sorption isotherms exhibited a Henry's law relationship in this PU–zeolite blend. In binary solutions the individual xylene uptake was also proportional to the solvent composition. Although incorporating zeolite into the PU–zeolite membrane rendered a decrease in xylene solubility

Shingjiang Jessie Lue; Tsai-hsin Liaw

2006-01-01

332

Preparation and characterization of zeolite framework stabilized cuprous oxide nanoparticles  

Microsoft Academic Search

Zeolite framework stabilized copper(I) oxide nanoparticles (4.8±2.6 nm) were prepared for the first time by using a four step procedure: the ion exchange of Cu2+ ions with the extra framework Na+ ions in Zeolite-Y, the reduction of the Cu2+ ions within the cavities of zeolite with sodium borohydride in aqueous solution, the dehydration of Zeolite-Y with the copper(0) nanoclusters, and the

Mehmet Zahmakiran; Saim Özkar

2009-01-01

333

Comparative sorption kinetic studies of ammonium onto zeolite  

Microsoft Academic Search

The sorption kinetics of ammonium onto three types of zeolite, natural zeolite, natural zeolite covered by biofilm and ammonium-bearing zeolite covered by biofilm, at two particle sizes were studied. The pseudo-first order and pseudo-second order models were fitted to the results by a non-linear method. The batch sorption model, based on a pseudo-second order mechanism, was applied to predict the

Donghui Wen; Yuh-Shan Ho; Xiaoyan Tang

2006-01-01

334

A designed organic–zeolite hybrid acid–base catalyst  

Microsoft Academic Search

An organic–zeolite hybrid catalyst was synthesised via solid-state impregnation of the zeolite with an amount of melamine corresponding to 20mol% of the aluminium content. A high density of basic sites is formed in the zeolite. From infrared spectroscopy and TGA measurements we infer that melaminium cations are formed in the zeolite which are highly thermally stable. IR spectroscopic and TGA

Andrew C. Brooks; Liam France; Cecile Gayot; Jerry Pui Ho Li; Ryan Sault; Andrew Stafford; John D. Wallis; Michael Stockenhuber

335

Monolithic nanoporous crystalline aerogels.  

PubMed

Monolithic aerogels can be easily obtained by drying physical gels formed by linear uncross-linked polymers. Preparation methods, structure, and properties of these physically cross-linked polymeric aerogels are reviewed, with particular emphasis to those whose cross-linking knots are crystallites and, more in particular, crystallites exhibiting nanoporous-crystalline forms. The latter aerogels present beside disordered amorphous micropores (typical of all aerogels) also all identical nanopores of the crystalline phases. Their outstanding guest transport properties combined with low material cost, robustness, durability, and ease of handling and recycle make these aerogels suitable for applications in chemical separations, purification, and storage as well as in biomedicine. Scientific, technological, and industrial perspectives for monolithic nanoporous-crystalline polymeric aerogels are also discussed. PMID:23913316

Daniel, Christophe; Longo, Simona; Ricciardi, Rosa; Reverchon, Ernesto; Guerra, Gaetano

2013-08-01

336

Crystalline molecular flasks  

NASA Astrophysics Data System (ADS)

A variety of host compounds have been used as molecular-scale reaction vessels, protecting guests from their environment or restricting the space available around them, thus favouring particular reactions. Such molecular 'flasks' can endow guest molecules with reactivities that differ from those in bulk solvents. Here, we extend this concept to crystalline molecular flasks, solid-state crystalline networks with pores within which pseudo-solution-state reactions can take place. As the guest molecules can spontaneously align along the walls and channels of the hosts, structural changes in the substrates can be directly observed by in situ X-ray crystallography during reaction. Recently, this has enabled observation of the molecular structures of transient intermediates and other labile species, in the form of sequential structural snapshots of the chemical transformation. Here, we describe the principles, development and applications of crystalline molecular flasks.

Inokuma, Yasuhide; Kawano, Masaki; Fujita, Makoto

2011-05-01

337

Fly ash zeolite catalyst support for Fischer-Tropsch synthesis  

NASA Astrophysics Data System (ADS)

This dissertation research aimed at evaluating a fly ash zeolite (FAZ) catalyst support for use in heterogeneous catalytic processes. Gas phase Fischer-Tropsch Synthesis (FTS) over a fixed-bed of the prepared catalyst/FAZ support was identified as an appropriate process for evaluation, by comparison with commercial catalyst supports (silica, alumina, and 13X). Fly ash, obtained from the Wabash River Generating Station, was first characterized using XRD, SEM/EDS, particle size, and nitrogen sorption techniques. Then, a parametric study of a two-step alkali fusion/hydrothermal treatment process for converting fly ash to zeolite frameworks was performed by varying the alkali fusion agent, agent:flyash ratio, fusion temperature, fused ash/water solution, aging time, and crystallization time. The optimal conditions for each were determined to be NaOH, 1.4 g NaOH: 1 g fly ash, 550 °C, 200 g/L, 12 hours, and 48 hours. This robust process was applied to the fly ash to obtain a faujasitic zeolite structure with increased crystallinity (40 %) and surface area (434 m2/g). Following the modification of fly ash to FAZ, ion exchange of H+ for Na+ and cobalt incipient wetness impregnation were used to prepare a FTS catalyst. FTS was performed on the catalysts at 250--300 °C, 300 psi, and with a syngas ratio H2:CO = 2. The HFAZ catalyst support loaded with 11 wt% cobalt resulted in a 75 % carbon selectivity for C5 -- C18 hydrocarbons, while methane and carbon dioxide were limited to 13 and 1 %, respectively. Catalyst characterization was performed by XRD, N2 sorption, TPR, and oxygen pulse titration to provide insight to the behavior of each catalyst. Overall, the HFAZ compared well with silica and 13X supports, and far exceeded the performance of the alumina support under the tested conditions. The successful completion of this research could add value to an underutilized waste product of coal combustion, in the form of catalyst supports in heterogeneous catalytic processes.

Campen, Adam

338

Production of biofuel from waste cooking palm oil using nanocrystalline zeolite as catalyst: process optimization studies.  

PubMed

The catalytic cracking of waste cooking palm oil to biofuel was studied over different types of nano-crystalline zeolite catalysts in a fixed bed reactor. The effect of reaction temperature (400-500 °C), catalyst-to-oil ratio (6-14) and catalyst pore size of different nanocrystalline zeolites (0.54-0.80 nm) were studied over the conversion of waste cooking palm oil, yields of Organic Liquid Product (OLP) and gasoline fraction in the OLP following central composite design (CCD). The response surface methodology was used to determine the optimum value of the operating variables for maximum conversion as well as maximum yield of OLP and gasoline fraction, respectively. The optimum reaction temperature of 458 °C with oil/catalyst ratio=6 over the nanocrystalline zeolite Y with pore size of 0.67 nm gave 86.4 wt% oil conversion, 46.5 wt% OLP yield and 33.5 wt% gasoline fraction yield, respectively. The experimental results were in agreement with the simulated values within an experimental error of less than 5%. PMID:21924606

Taufiqurrahmi, Niken; Mohamed, Abdul Rahman; Bhatia, Subhash

2011-11-01

339

Hydrogen isotope separation using molecular sieve of synthetic zeolite 3A  

SciTech Connect

It is known that hydrogen isotope molecules can be adsorbed easily onto synthetic zeolite 4A, 5A, and 13X at the liquid-nitrogen temperature of 77.4 K. We show here that hydrogen and deuterium are not adsorptive onto zeolite 3A at the same temperature. This phenomenon is explained by assuming the molecular sieve function in zeolite-3A-crystalline lattice structure. From a series of pseudo-isobaric experiments, it is also shown that the sieving phenomenon appears in a range above 77.4 K. This behavior is interpreted as resulting on the dependence of sieve's mesh size on temperature, where the sieving effect is considered to appear at a certain temperature. In this interpretation, an isotopic difference between hydrogen and deuterium is suggested to exist in the sieving effect appearance temperatures. This is endorsed in the result of pseudo-isobaric experiments. This temperature deference is very significant because that indicates the possibility of an effective method of hydrogen isotope separation. This possibility is verified through an experimental series of adsorption-desorption with a mixture of H{sub 2} and D{sub 2}, where the gas samples adsorbed through the sieve operated at intentionally selected temperatures are isolated and then analyzed. The result demonstrates remarkable values of isotope separation factor. (authors)

Kotoh, K.; Kimura, K.; Nakamura, Y.; Kudo, K. [Faculty of Engineering, Kyushu Univ., 744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan)

2008-07-15

340

Characterization and environmental application of a Chilean natural zeolite  

Microsoft Academic Search

The use of natural zeolites for environmental applications is gaining new research interests mainly due to their properties and significant worldwide occurrence. The present work describes the characterization of a natural Chilean zeolite and the results as adsorbent for ammonia from aqueous solutions. The zeolitic-rich tuff sample, mainly composed of clinoptilolite and mordenite, consisted of 13 ?m mean volumetric particle

A. H. Englert; J. Rubio

2005-01-01

341

Zeolite membranes – state of their development and perspective  

Microsoft Academic Search

An ideal zeolite membrane combines the general advantages of inorganic membranes (temperature stability, solvent resistance) with a perfect shape selectivity. Due to their “molecular sieve” function, zeolite membranes can principally discriminate the components of gaseous or liquid mixtures dependent on their molecular size. This molecular sieving principle requires a pinhole- and crack-free zeolite membrane. Remarkable separation effects can also be

J Caro; M Noack; P Kölsch; R Schäfer

2000-01-01

342

Removing nitrosamines from mainstream smoke of cigarettes by zeolites  

Microsoft Academic Search

The adsorption of volatile nitrosamines in mainstream smoke of cigarettes by the use of zeolites and other porous materials has been investigated. Zeolites are shown to possess the ability of selectively adsorbing nitrosamines from the mainstream (MS) smoke, and among them, zeolites NaY and ZSM-5 exhibit excellent capacities. The impact of the porous structure and acidity of the adsorbent, the

Yang Xu; Jian Hua Zhu; Li Li Ma; An Ji; Yi Lun Wei; Xi Yong Shang

2003-01-01

343

The efficiency of Jordanian natural zeolite for heavy metals removal  

Microsoft Academic Search

The capability of Jordanian natural zeolite to remove nickel from aqueous solutions was experimentally investigated using a packed bed column. The zeolite samples were obtained from Jabal AL Aritayn in the northeast of Jordan. The effects of the initial concentration of nickel (C0), the packed bed length (L) and the zeolite grain size (Dp) on the adsorption process were considered.

Yazan Taamneh; Yazan TaamnehReyad Al Dwairi

2013-01-01

344

Ion exchange in a zeolite-molten chloride system  

Microsoft Academic Search

Electrometallurgical treatment of spent nuclear fuel results in a secondary waste stream of radioactive fission products dissolved in chloride salt. Disposal plans include a waste form that can incorporate chloride forms featuring one or more zeolites consolidated with sintered glass. A candidate method for incorporating fission products in the zeolites is passing the contaminated salt over a zeolite column for

R. H. Woodman; C. Pereira

1997-01-01

345

Development of Desiccant System using Wakkanai Siliceous Shale  

NASA Astrophysics Data System (ADS)

The aim of this study is to develop a desiccant system using Wakkanai siliceous shale. A honeycombed desiccant rotor containing this shale's powder and chlorides was made and evaluated. However a specific surface area and a pore volume were smaller than a silica-gel rotor or a zeolite rotor, the maximum amount of water adsorption was twice as other rotors. We have verified the function of this desiccant rotor concerning adsorption and desorption of moisture from the draft experiments. The rotor containing the shale could adsorb moisture stably in the cyclic test, and be regenerated by 40°C air under this experimental condition. This means that the exhaust heat from the heat pump can be used for regenerating rotor. Furthermore, the numerical simulation was carried out on the assumption that this rotor was used for a dehumidification for the residential air conditioning in Tokyo. This rotor could adsorb 37.1% moisture of the required dehumidification amount for the hottest day in 2008. When we employed a pre-cooling before dehumidification, the amount of adsorption increased to 66.2%.

Nakabayashi, Saya; Nagano, Katsunori; Nakamura, Makoto; Togawa, Junya; Kurokawa, Asami

346

Erupted silicic cumulates in large ignimbrites  

NASA Astrophysics Data System (ADS)

If chemical diversity in igneous rocks is dominated by crystal-liquid separation in open-system magma reservoirs, a significant number of crystal accumulation zones must be preserved in the crust and upper mantle. Such cumulates are conspicuous in mafic lithologies (MOR, layered mafic intrusions, lower crustal arc sections), but have rarely been described and/or are controversial in the silicic upper crust. Although it is possible to recognize signs of crystal accumulations in plutonic exposures, the fact that these batholiths are typically: 1) at least several millions of years old, 2) multi-stage, 3) deformed and 4) biased towards the youngest intrusive episodes, some ambiguity remains in how to interpret geochemical and textural observations. We have chosen to explore large zoned ignimbrites, which represent an instantaneous evacuation of an upper crustal magma reservoir, to isolate potential crystal accumulation zones. Late-erupted, crystal-rich scoria with unusual chemistries (e.g., high Ba, Zr, Eu/Eu*) have been found in multiple examples of these zoned ignimbrites around the world, including the 900+ km3 Ammonia Tanks and Carpenter Ridge Tuffs, both erupted during the Tertiary magmatic flare-up in the Western USA. As already suggested for the 7700 BP Crater Lake ignimbrite, such crystal-rich scoria have mineralogical and geochemical characteristics that are most convincingly explained by accumulation of low temperature minerals as highly-evolved melt escapes upward and pools at the top of large crystalline mushes. To account for the eruption of such crystal-rich zones (technically uneruptible with >50vol% crystals), some melting of low-temperature mineral phases is required; evidence for resorption textures in sanidine and quartz is commonplace in these scoria. The presence of mafic enclaves and/or mingling textures in such scoria indicate that recharge from below ultimately drove melting of part of the mineral assemblage within the cumulate rootzone, while simultaneously triggering eruption of the voluminous crystal-poor cap.

Bachmann, O.; Deering, C. D.; Huber, C.; Dufek, J.

2011-12-01

347

Formation of NaA and -X zeolites from waste solutions in conversion of coal fly ash to zeolites  

Microsoft Academic Search

Na-A and -X zeolites were synthesized from waste solutions in conversion of coal fly ash (Fa) to zeolite. The amorphous SiO2 and Al2O3 of Fa were completely dissolved to form Po, Pt, and Pc type zeolites in NaOH solutions at 85°C. Only 24% of Si4+ eluted from Fa were converted to the zeolites and the remaining waste solutions contained high

Hidekazu Tanaka; Yasuhiko Sakai; Ryozi Hino

2002-01-01

348

Preparation, Processing, and Characterization of Oriented Polycrystalline Zeolite and Aluminophosphate Membranes  

NASA Astrophysics Data System (ADS)

Since the advent of zeolite membranes, speculation on their industrial applicability has been closely monitored, although widespread commercialization has been hampered by limitations in fabrication and post-synthesis processing. Economical, energy-efficient technology breakthroughs require an evaluation of a range of material candidates which show robustness and reliability. Straightforward manufacturing techniques should be devised to generate thousands of square meters of membrane area; however, this demands control of structural characteristics on the scale of nanometers. As described in this dissertation, the path forward will be forged by exploiting the intrinsic crystalline properties of zeolites or aluminophosphates for the next advancement in membrane technology. A facile method is described for the preparation of silicalite-1 (MFI zeolite type) membranes using the secondary growth technique on symmetric porous stainless steel tubes. Activation through rapid thermal processing (RTP), a lamp-based heat-treatment process used as a critical fabrication step in silicon integrated circuit manufacturing, is proven to reduce the density of non-zeolitic transport pathways which are detrimental to high-resolution molecular sieving. RTP-treated membranes are shown to have enhanced performance in the binary separation of vapor-phase isomers (p-/o-xylene), gas-phase isomers (n-/i-butane), and alcohol/water when compared to membranes activated at a much slower heating rate but otherwise similarly-prepared. The performance is discussed in the context of the market potential for industrially-attractive separations: the recovery of p-xylene from an isomeric mixture or alcohol biofuels from aqueous post-fermentation streams. Hydrothermal growth techniques for the preparation and characterization of continuous aluminophosphate (AFI zeolite type) membranes with a preferential crystallographic alignment on porous alpha-Al2O3 disc supports are demonstrated. A mechanism is proposed for flake-like crystal formation in the early stages of in-plane crystalline intergrowth between oriented columnar crystals by electric heating. It is shown that elevated temperatures induce a phase transformation to a densified aluminophosphate phase despite framework metal substitution or alternative heat-treatment conditions. Additionally, stability and membrane characteristics following in situ microwave growth using a TiO2-coated support are examined. Indications of improved quality validate the candidacy of the microwave-grown membranes with regard to the potential for carbon nanotube synthesis in the aligned one-dimensional channels for high flux, high separation factor membrane fabrication.

Stoeger, Jared Andrew

349

Competing mechanisms of catalytic H2 formation and dissociation on ultrasmall silicate nanocluster dust grains  

NASA Astrophysics Data System (ADS)

Silicate dust grains are thought to be essential in catalysing the formation of H2. Ultrasmall silicates (diameter ?1.5 nm) are fundamental intermediates in silicate dust formation in stellar outflows, and are ubiquitous in the interstellar medium. To investigate the catalytic formation and dissociation of H2 on such nanosilicates, we have performed ab initio quantum chemical calculations of hydrogen interacting with a stable 21 atom nanosilicate cluster having the stoichiometry of forsterite, (MgO)6(SiO2)3. Due to its small size and high percentage of surface atoms, our particle inherently does not exhibit the bulk forsterite crystal structure and possesses a range of chemisorption and physisorption sites, presumably similar to those that larger amorphous silicates would offer. We find a number of exothermic H2 formation routes and pathways for H2 catalytic dissociation on the nanosilicate. In particular, we discover some H2 formation routes that are energetically more favourable than that reported for the forsterite (010) surface. Further, we find a linear correlation between the dissociative chemisorption of two H atoms and the dissociation transition state, suggestive of a general Brønsted-Evans-Polanyi relation for H2 dissociation on bare silicates independent of dust grain size and/or crystallinity.

Kerkeni, Boutheïna; Bromley, Stefan T.

2013-10-01

350

Silicon Kedge XANES spectra of silicate minerals  

Microsoft Academic Search

Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measured using synchrotron radiation (SR). The spectra are qualitatively interpreted based on MO calculation of the tetrahedral SiO44-cluster. The Si K-edge generally shifts to higher energy with increased polymerization of silicates by about 1.3 eV, but with considerable overlap for silicates of

Dien Li; G. M. Bancroft; M. E. Fleet; X. H. Feng

1995-01-01

351

SEDIMENTATION AND WETTABILITY OF SYNTHETIC MAGNESIUM SILICATES  

Microsoft Academic Search

In the paper studies were presented which aimed at obtaining synthetic magnesium silicate, which could be applied as a selective adsorbent, polymer filler or a filler of paper-coating masses. Synthetic magnesium silicate was obtained by precipitation using solutions of MgSO4·7H2O and Na2SiO3 (water glass). In view of specific application of the precipitated silicates, the process of their production was broadened

Filip CIESIELCZYK; Andrzej KRYSZTAFKIEWICZ; Teofil JESIONOWSKI

2006-01-01

352

Controlling chemistry with cations: photochemistry within zeolites.  

PubMed

The alkali ions present in the supercages of zeolites X and Y interact with included guest molecules through quadrupolar (cation-pi), and dipolar (cation-carbonyl) interactions. The presence of such interactions can be inferred through solid-state NMR spectra of the guest molecules. Alkali ions, as illustrated in this article, can be exploited to control the photochemical and photophysical behaviors of the guest molecules. For example, molecules that rarely phosphoresce can be induced to do so within heavy cation-exchanged zeolites. The nature (electronic configuration) of the lowest triplet state of carbonyl compounds can be altered with the help of light alkali metal ions. This state switch (n pi*-pi pi*) helps to bring out reactivity that normally remains dormant. Selectivity obtained during the singlet oxygen oxidation of olefins within zeolites illustrates the remarkable control that can be exerted on photoreactions with the help of a confined medium that also has active sites. The reaction cavities of zeolites, like enzymes, are not only well-defined and confined, but also have active sites that closely guide the reactant molecule from start to finish. The examples provided here illustrate that zeolites are far more useful than simple shape-selective catalysts. PMID:12934881

Ramamurthy, V; Shailaja, J; Kaanumalle, Lakshmi S; Sunoj, R B; Chandrasekhar, J

2003-08-21

353

Zeolite-templated Pt/C electrocatalysts  

SciTech Connect

In an effort to reduce the amount of platinum required in low temperature fuel cells, we have prepared electrocatalysts of platinum nanoparticles-on-carbon through zeolite-templating methods. Several different zeolite structure-types, as well as clays and mesoporous silicas were investigated as hosts for the preparation of small Pt clusters through thermal decomposition of ion exchanged (NH{sub 3}){sub 4}Pt{sup 2+}. Several factors relating to cluster confinement and mobility influence cluster size, and clusters below 1 nm with narrow size distribution have been prepared. To enable electrochemical application, the pores of the Pt cluster-containing zeolite were filled with electrically conductive carbon via infiltration with carbon precursors, polymerization, and pyrolysis. The zeolite host was then removed by acid digestion, to leave a micro-/mesoporous Pt/C electrocatalyst possessing Pt clusters of controlled size. Preliminary electrochemical evaluation of these catalysts is reported. The energetics of thermal decomposition of (NH{sub 3}){sub 4}Pt{sup 2+} to form Pt clusters in zeolite X have been investigated through Differential Scanning Calorimetry, and apparent activation energies calculated. The relationship between (NH{sub 3}){sub 4}Pt{sup 2+} decomposition and conditions of calcination has been explored in an effort to better control Pt cluster sizes.

Coker, Eric N.; Steen, William A.; Miller, James E. (Sandia)

2008-06-16

354

Effect of silicate ions on electrode overvoltage  

NASA Technical Reports Server (NTRS)

The influence of the addition of a silicate to a caustic solution (KOH) is studied in order to determine the degree to which silicates inhibit the corrosion of chrysotile under conditions of electrolysis at working temperatures of 100 C and above. In an alkaline solution containing various silicate concentrations, current density was increased and electrode overvoltage was measured. Results show that silicate ion concentrations in the electrolyte increase with temperature without effecting electrochemical performance up to 115 C at 700 MA/sqcm. At this point the concentration is about 0.5 g Si/100 g KOH. Beyond this limit, electrolytic performance rapidly degenerates due to severe oxidation of the electrodes.

Gras, J. M.; Seite, C.

1979-01-01

355

Models for silicate melt viscosity  

NASA Astrophysics Data System (ADS)

The prediction of viscosity in silicate liquids, over the range of temperatures and compositions encountered in nature, remains one of the most challenging and elusive goals in Earth Sciences. Recent work has demonstrated that there are now sufficient experimental measurements of melt viscosity to create new viscosity models to replace previous Arrhenian models [1],[2] and extend the compositional range of more recent non-Arrhenian models [3]. Most recently, [4] have developed an empirical strategy for accurately predicting viscosities over a very wide range of anhydrous silicate melt compositions (e.g., rhyolite to basanite). Future models that improve upon this work, will probably extend the composition range of the model to consider, at least, H2O and other volatile components and may utilize a compositional basis that reflects melt structure. In preparation for the next generation model, we explore the attributes of the three most common equations that could be used to model the non-Arrhenian viscosity of multicomponent silicate melts. The equations for the non-Arrhenian temperature dependence of viscosity (? ) include: a) Vogel-Fulcher-Tammann (VFT): log ? = A + B/(T - C) b) Adam and Gibbs (AG): log ? = A + B/[T log (T/C)], and c) Avramov (Av): log ? = A + [B/T]? We use an experimental database of approximately 900 high-quality viscosity measurements on silicate melts to test the ability of each equation to capture the experimental data. These equations have different merits [5]. VFT is purely empirical in nature. The AG model has a quasi-theoretical basis that links macroscopic transport properties directly to thermodynamic properties via the configurational entropy. Lastly, the model proposed by Avramov adopts a form designed to relate the fit parameter (? ) to the fragility of the melt. [1] Shaw, H.R., 1972. Am J Science, 272, 438-475. [2] Bottinga Y. and Weill, D., 1972. Am J Science, 272, 438-475. [3] Hess, K.U. and Dingwell, D.B, 1996, Am Min, 81, 1297-1300. [4] D. Giordano & D.B. Dingwell, 2003. EPSL. 208, 337 (and related corrige EPSL 221, 449) [5] J.K. Russell, D. Giordano & D.B. Dingwell, 2003. Am Min 88, 1390

Giordano, D.; Russell, K.; Moretti, R.; Mangiacapra, A.; Potuzak, M.; Romano, C.; Dingwell, D. B.

2004-12-01

356

Capturing Ultrasmall EMT Zeolite from Template-Free Systems  

NASA Astrophysics Data System (ADS)

Small differences between the lattice energies of different zeolites suggest that kinetic factors are of major importance in controlling zeolite nucleation. Thus, it is critical to control the nucleation kinetics in order to obtain a desired microporous material. Here, we demonstrate how careful investigation of the very early stages of zeolite crystallization in colloidal systems can provide access to important nanoscale zeolite phases while avoiding the use of expensive organic templates. We report the effective synthesis of ultrasmall (6- to 15-nanometer) crystals of the large-pore zeolite EMT from template-free colloidal precursors at low temperature (30°C) and very high yield.

Ng, Eng-Poh; Chateigner, Daniel; Bein, Thomas; Valtchev, Valentin; Mintova, Svetlana

2012-01-01

357

Towards a sustainable manufacture of hierarchical zeolites.  

PubMed

Hierarchical zeolites have been established as a superior type of aluminosilicate catalysts compared to their conventional (purely microporous) counterparts. An impressive array of bottom-up and top-down approaches has been developed during the last decade to design and subsequently exploit these exciting materials catalytically. However, the sustainability of the developed synthetic methods has rarely been addressed. This paper highlights important criteria to ensure the ecological and economic viability of the manufacture of hierarchical zeolites. Moreover, by using base leaching as a promising case study, we verify a variety of approaches to increase reactor productivity, recycle waste streams, prevent the combustion of organic compounds, and minimize separation efforts. By reducing their synthetic footprint, hierarchical zeolites are positioned as an integral part of sustainable chemistry. PMID:24520034

Verboekend, Danny; Pérez-Ramírez, Javier

2014-03-01

358

Crystal engineering of zeolites with graphene.  

PubMed

Achieving control over the morphology of zeolite crystals at the nanoscale is crucial for enhancing their performance in diverse applications including catalysis, sensors and separation. The complexity and sensitivity of zeolite synthesis processes, however, often make such control both highly empirical and difficult to implement. We demonstrate that graphene can significantly alter the morphology of titanium silicalite (TS-1) particles, in particular being able to reduce their dimensions from several hundreds to less than 10 nm. Through electron microscopy and molecular mechanics simulations we propose a mechanism for this change based on the preferential interaction of specific TS-1 surfaces with benzyl-alcohol-mediated graphene. These findings suggest a facile new means of controlling the zeolite morphology and thereby also further demonstrate the potential of graphene in hybrid materials. Moreover, the generality of the mechanism points the way to a new avenue of research in using two-dimensional materials to engineer functional inorganic crystals. PMID:24853328

Gebhardt, Paul; Pattinson, Sebastian W; Ren, Zhibin; Cooke, David J; Elliott, James A; Eder, Dominik

2014-06-12

359

Reorientational dynamics of water confined in zeolites.  

PubMed

We present a detailed molecular-dynamics study of water reorientation and hydrogen-bond dynamics in a strong confinement situation, within the narrow pores of an all-silica Linde type A (LTA) zeolite. Two water loadings of the zeolite are compared with the bulk case. Water dynamics are retarded in this extreme hydrophobic confinement and the slowdown is more pronounced at higher water loading. We show that water reorientation proceeds mainly by large-amplitude angular jumps, whose mechanism is similar to that determined in the bulk. The slowdown upon hydrophobic confinement arises predominantly from an excluded-volume effect on the large fraction of water molecules lying at the interface with the zeolite matrix, with an additional minor contribution coming from a structuring effect induced by the confinement. PMID:24449592

Fogarty, Aoife C; Coudert, François-Xavier; Boutin, Anne; Laage, Damien

2014-02-24

360

Spontaneous proton transfer in Na zeolites  

NASA Astrophysics Data System (ADS)

First-principles room-temperature molecular dynamics (MD) simulations are conducted to investigate proton transfer (PT) in Na zeolites. The MD are performed on the unit cell containing two Al-sites, one of them saturated with H (acid site) and the second one with Na coordinated with three water molecules. The creation of the charged H 3O + cations is suppressed by the Na cation. Spontaneous barrierless PT between the O-sites in the zeolite, however, is possible. The lifetime of the hydronium cation is extremely short (?5 fs). The presence of Na + cations leads to a modified mechanism but does not suppress the proton transfer around the Al-site in zeolites.

Benco, L.; Demuth, T.; Hafner, J.; Hutschka, F.

2000-11-01

361

Studies of anions sorption on natural zeolites.  

PubMed

This work presents results of FT-IR spectroscopic studies of anions-chromate, phosphate and arsenate - sorbed from aqueous solutions (different concentrations of anions) on zeolites. The sorption has been conducted on natural zeolites from different structural groups, i.e. chabazite, mordenite, ferrierite and clinoptilolite. The Na-forms of sorbents were exchanged with hexadecyltrimethylammonium cations (HDTMA(+)) and organo-zeolites were obtained. External cation exchange capacities (ECEC) of organo-zeolites were measured. Their values are 17mmol/100g for chabazite, 4mmol/100g for mordenite and ferrierite and 10mmol/100g for clinoptilolite. The used initial inputs of HDTMA correspond to 100% and 200% ECEC of the minerals. Organo-modificated sorbents were subsequently used for immobilization of mentioned anions. It was proven that aforementioned anions' sorption causes changes in IR spectra of the HDTMA-zeolites. These alterations are dependent on the kind of anions that were sorbed. In all cases, variations are due to bands corresponding to the characteristic Si-O(Si,Al) vibrations (occurring in alumino- and silicooxygen tetrahedra building spatial framework of zeolites). Alkylammonium surfactant vibrations have also been observed. Systematic changes in the spectra connected with the anion concentration in the initial solution have been revealed. The amounts of sorbed CrO4(2-), AsO4(3-) and PO4(3-) ions were calculated from the difference between their concentrations in solutions before (initial concentration) and after (equilibrium concentration) sorption experiments. Concentrations of anions were determined by spectrophotometric method. PMID:25002191

Barczyk, K; Mozgawa, W; Król, M

2014-12-10

362

Crystal engineering of zeolites with graphene  

NASA Astrophysics Data System (ADS)

Achieving control over the morphology of zeolite crystals at the nanoscale is crucial for enhancing their performance in diverse applications including catalysis, sensors and separation. The complexity and sensitivity of zeolite synthesis processes, however, often make such control both highly empirical and difficult to implement. We demonstrate that graphene can significantly alter the morphology of titanium silicalite (TS-1) particles, in particular being able to reduce their dimensions from several hundreds to less than 10 nm. Through electron microscopy and molecular mechanics simulations we propose a mechanism for this change based on the preferential interaction of specific TS-1 surfaces with benzyl-alcohol-mediated graphene. These findings suggest a facile new means of controlling the zeolite morphology and thereby also further demonstrate the potential of graphene in hybrid materials. Moreover, the generality of the mechanism points the way to a new avenue of research in using two-dimensional materials to engineer functional inorganic crystals.Achieving control over the morphology of zeolite crystals at the nanoscale is crucial for enhancing their performance in diverse applications including catalysis, sensors and separation. The complexity and sensitivity of zeolite synthesis processes, however, often make such control both highly empirical and difficult to implement. We demonstrate that graphene can significantly alter the morphology of titanium silicalite (TS-1) particles, in particular being able to reduce their dimensions from several hundreds to less than 10 nm. Through electron microscopy and molecular mechanics simulations we propose a mechanism for this change based on the preferential interaction of specific TS-1 surfaces with benzyl-alcohol-mediated graphene. These findings suggest a facile new means of controlling the zeolite morphology and thereby also further demonstrate the potential of graphene in hybrid materials. Moreover, the generality of the mechanism points the way to a new avenue of research in using two-dimensional materials to engineer functional inorganic crystals. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00320a

Gebhardt, Paul; Pattinson, Sebastian W.; Ren, Zhibin; Cooke, David J.; Elliott, James A.; Eder, Dominik

2014-06-01

363

THE EFFECT OF HEAVY COSMIC-RAY IONS ON SILICATE GRAINS IN THE INTERSTELLAR DUST  

SciTech Connect

Electronmicroscopic samples of crystalline Mg{sub 2}SiO{sub 4} forsterite were irradiated by energetic Ar, Fe, Kr, and Xe ions at room temperature. Tracks with a mean radius R{sub e} = 1.36 nm were observed after irradiation by 56 MeV Fe ions, while no tracks were induced by a 48 MeV Ar beam. Amorphization of forsterite grains by cosmic-ray (CR) Fe ions are discussed, including the effects of low temperature, ion velocity, and ion-induced crystallization. CR Fe ions induce amorphous tracks in crystalline forsterite only in the range 40-140 MeV, and the period of time for complete amorphization is tau{sub cr} approx 13,400 Myr. Our estimate is tau{sub cr} approx 1300 Myr for enstatite. Thus, heavy CR particles do not reduce the crystallinity of silicate grains within a reasonable time, as supposed previously. However, energetic ions can induce crystallization in amorphous solids, and this may be partially or fully responsible for the estimated 0.2% crystallinity of silicates in the interstellar medium.

Szenes, G. [Department of Materials Physics, Eoetvoes University, P.O. Box 32, H-1518 Budapest (Hungary); Kovacs, V. K.; Pecz, B. [Research Institute for Technical Physics and Materials Science, H-1525 Budapest, P.O. Box 49 (Hungary); Skuratov, V., E-mail: szenes@metal.elte.h [Flerov Laboratory of Nuclear Reactions, JINR, 141980 Dubna (Russian Federation)

2010-01-01

364

Photophysical properties of metal ion functionalized NaY zeolite.  

PubMed

A series of luminescent ion exchanged zeolite are synthesized by introducing various ions into NaY zeolite. Monometal ion (Eu(3+), Tb(3+), Ce(3+), Y(3+), Zn(2+), Cd(2+), Cu(2+)) exchanged zeolite, rare-earth ion (Eu(3+), Tb(3+), Ce(3+)) exchanged zeolite modified with Y(3+) and rare-earth ion (Eu(3+), Tb(3+), Ce(3+)) exchanged zeolite modified with Zn(2+) are discussed here. The resulting materials are characterized by Fourier transform infrared spectrum radiometer (FTIR), XRD, scanning electronic microscope (SEM), PLE, PL and luminescence lifetime measurements. The photoluminescence spectrum of NaY indicates that emission band of host matrix exhibits a blueshift of about 70 nm after monometal ion exchange process. The results show that transition metal ion exchanged zeolites possess a similar emission band due to dominant host luminescence. A variety of luminescence phenomenon of rare-earth ion broadens the application of zeolite as a luminescent host. The Eu(3+) ion exchanged zeolite shows white light luminescence with a great application value and Ce(3+) exchanged zeolite steadily exhibits its characteristic luminescence in ultraviolet region no matter in monometal ion exchanged zeolite or bimetal ions exchanged zeolite. PMID:24392790

Duan, Tian-Wei; Yan, Bing

2014-01-01

365

Photocatalytic activity of undoped and Ag-doped TiO{sub 2}-supported zeolite for humic acid degradation and mineralization  

SciTech Connect

Highlights: {yields} Hybrid materials based on natural zeolite and TiO{sub 2} obtained by solid-state reaction. {yields} XRD proved the presence of anatase form of undoped and Ag-doped TiO{sub 2} onto zeolite. {yields} FT-IR spectra evidenced the presence on TiO{sub 2} bounded at the zeolite network. {yields} Ag-doped TiO{sub 2} onto zeolitic matrix exhibited an enhanced photocatalytic activity. -- Abstract: The hybrid materials based on natural zeolite and undoped and Ag-doped TiO{sub 2}, i.e., Z-Na-TiO{sub 2} and Z-Na-TiO{sub 2}-Ag, were successfully synthesized by solid-state reaction in microwave-assisted hydrothermal conditions. Undoped TiO{sub 2} and Ag-doped TiO{sub 2} nanocrystals were previously synthesized by sol-gel method. The surface characterization of undoped TiO{sub 2}/Ag-doped TiO{sub 2} and natural zeolite hybrid materials has been investigated by X-ray diffraction, DRUV-VIS spectroscopy, FT-IR spectroscopy, BET analysis, SEM microscopy and EDX analysis. The results indicated that anatase TiO{sub 2} is the dominant crystalline type as spherical form onto zeolitic matrix. The presence of Ag into Z-Na-TiO{sub 2}-Ag was confirmed by EDX analysis. The DRUV-VIS spectra showed that Z-Na-TiO{sub 2}-Ag exhibited absorption within the range of 400-500 nm in comparison with Z-Na-TiO{sub 2} catalyst. The enhanced photocatalytic activity of Z-Na-TiO{sub 2}-Ag catalyst is proved through the degradation and mineralization of humic acid under ultraviolet and visible irradiation.

Lazau, C. [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1, 300254 Timisoara (Romania)] [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1, 300254 Timisoara (Romania); Ratiu, C. [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1, 300254 Timisoara (Romania) [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1, 300254 Timisoara (Romania); National Institute for Research and Development in Microtechnologies, Erou Iancu Nicolae Street, 077190 Bucharest (Romania); Orha, C. [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1, 300254 Timisoara (Romania)] [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1, 300254 Timisoara (Romania); Pode, R. ['Politehnica' University of Timisoara, P-ta Victoriei no.2, 300006 Timisoara (Romania)] ['Politehnica' University of Timisoara, P-ta Victoriei no.2, 300006 Timisoara (Romania); Manea, F., E-mail: florica.manea@chim.upt.ro ['Politehnica' University of Timisoara, P-ta Victoriei no.2, 300006 Timisoara (Romania)

2011-11-15

366

Carbon substitution for oxygen in silicates in planetary interiors  

PubMed Central

Amorphous silicon oxycarbide polymer-derived ceramics (PDCs), synthesized from organometallic precursors, contain carbon- and silica-rich nanodomains, the latter with extensive substitution of carbon for oxygen, linking Si-centered SiOxC4-x tetrahedra. Calorimetric studies demonstrated these PDCs to be thermodynamically more stable than a mixture of SiO2, C, and silicon carbide. Here, we show by multinuclear NMR spectroscopy that substitution of C for O is also attained in PDCs with depolymerized silica-rich domains containing lithium, associated with SiOxC4-x tetrahedra with nonbridging oxygen. We suggest that significant (several percent) substitution of C for O could occur in more complex geological silicate melts/glasses in contact with graphite at moderate pressure and high temperature and may be thermodynamically far more accessible than C for Si substitution. Carbon incorporation will change the local structure and may affect physical properties, such as viscosity. Analogous carbon substitution at grain boundaries, at defect sites, or as equilibrium states in nominally acarbonaceous crystalline silicates, even if present at levels at 10–100 ppm, might form an extensive and hitherto hidden reservoir of carbon in the lower crust and mantle.

Sen, Sabyasachi; Widgeon, Scarlett J.; Navrotsky, Alexandra; Mera, Gabriela; Tavakoli, Amir; Ionescu, Emanuel; Riedel, Ralf

2013-01-01

367

40 CFR 721.9513 - Modified magnesium silicate polymer (generic).  

Code of Federal Regulations, 2010 CFR

... false Modified magnesium silicate polymer (generic). 721.9513 Section 721...721.9513 Modified magnesium silicate polymer (generic). (a) Chemical substance...generically as modified magnesium silicate polymer (PMN P-98-604) is subject to...

2010-07-01

368

21 CFR 182.2122 - Aluminum calcium silicate.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Aluminum calcium silicate. 182.2122 Section 182.2122...Anticaking Agents § 182.2122 Aluminum calcium silicate. (a) Product. Aluminum calcium silicate. (b) Tolerance. 2...

2013-04-01

369

21 CFR 582.2122 - Aluminum calcium silicate.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Aluminum calcium silicate. 582.2122 Section 582.2122...Anticaking Agents § 582.2122 Aluminum calcium silicate. (a) Product. Aluminum calcium silicate. (b) Tolerance. 2...

2013-04-01

370

Thermal properties of zeolites: effective thermal conductivity of dehydrated powdered zeolite 4A  

Microsoft Academic Search

The determination of the subambient effective thermal conductivity of evacuated powdered zeolite 4A is described. The results are modelled successfully in terms of boundary scattering, point defects and three-phonon Umklapp processes.

Vladimir V. Murashov; Mary Anne White

2002-01-01

371

The 8-13 micron spectra of comets and the composition of silicate grains  

NASA Technical Reports Server (NTRS)

We have analyzed the existing spectra of seven comets which show an emission feature at 7.8-13 micrometers. Most have been converted to a common calibration, taking into account the SiO feature in late-type standard stars. The spectra are compared with spectra of the Trapezium, interplanetary dust particles (IDPs), laboratory mineral samples, and small particle emission models. The emission spectra show a variety of shapes; there is no unique 'cometary silicate'. A peak at 11.20-11.25 micrometers, indicative of small crystalline olivine particles, is seen in only three comets of this sample, P/Halley, Bradfield 1987 XXIX, and Levy 1990 XX. The widths of the emission features range from 2.6 to 4.1 micrometers (FWHM). To explain the differing widths and the broad 9.8 micrometers maximum, glassy silicate particles, including both pyroxene and olivine compositions, are the most plausible candidates. Calculations of emission models confirm that small grains of glassy silicate well mixed with carbonaceous material are plausible cometary constituents. No single class of chondritic aggregate IDPs exhibits spectra closely matching the comet spectra. A mixture of IDP spectra, particularly the glass-rich aggregates, approximately matches the spectra of comets P/Halley, Levy, and Bradfield 1987 XXIX. Yet, if comets are simply a mix of IDP types, it is puzzling that the classes of IDPs are so distinct. None of the comet spectra match the spectrum of the Trapezium. Thus, the mineralogy of the cometary silicates is not the same as that of the interstellar medium. The presence of a component of crystalline silicates in comets may be evidence of mixing between high- and low-temperature regions in the solar nebula.

Hanner, Martha S.; Lynch, David K.; Russell, Ray W.

1994-01-01

372

Liquid crystalline composites containing phyllosilicates  

DOEpatents

The present invention provides barrier films having reduced gas permeability for use in packaging and coating applications. The barrier films comprise an anisotropic liquid crystalline composite layer formed from phyllosilicate-polymer compositions. Phyllosilicate-polymer liquid crystalline compositions of the present invention can contain a high percentage of phyllosilicate while remaining transparent. Because of the ordering of the particles in the liquid crystalline composite, barrier films comprising liquid crystalline composites are particularly useful as barriers to gas transport.

Chaiko; David J. (Naperville, IL) [Naperville, IL

2007-05-08

373

Peralkaline Silicic Volcanic Rocks in Northwestern Nevada  

Microsoft Academic Search

Late Tertiary silicic ashflow tuffs and lavas peralkaline in chemical character (atomic Na + K greater than Al), mainly comendites, occur over wide areas in northwestern Nevada and appear to be widespread in southeastern Oregon. Such peralkaline rocks-which are not uncommon in the western United States-and other chemically unusual silicic rocks are found near the margins rather than toward the

Donald C. Noble; David W. Chipman; David L. Giles

1968-01-01

374

The speciation of water in silicate melts  

Microsoft Academic Search

Previous models of water solubility in silicate melts generally assume essentially complete reaction of water molecules to hydroxyl groups. In this paper a new model is proposed that is based on the hypothesis that the observed concentrations of molecular water and hydroxyl groups in hydrous silicate glasses reflect those of the melts from which they were quenched. The new model

Edward Stolper

1982-01-01

375

Decomposition of NO over [Co]-ZSM-5 zeolite: Effect of co-adsorbed O{sub 2}  

SciTech Connect

The decomposition of NO over four Co-containing ZSM-5 zeolites and Pr, Ga-, and Cu-exchanged ZSM-5 zeolites was investigated using the isotope labeled {sup 15}N{sup 18}O and a temperature-programmed desorption (TPD) technique. The authors found that [Co]-ZSM-5 that contains Co in the framework had the highest activity for NO decomposition, almost an order of magnitude greater than that previously reported for a zeolite catalyst, namely Cu-ZSM-5 obtained under steady-state conditions. The phenomenally high activity of [Co]-ZSM-5 is due to the unique incorporation of Co{sup 2+} in the siliceous MFI structure. For all the catalysts investigated, co-adsorption of NO and O{sub 2} led to a substantial increase in the amount of NO{sub x} adsorbed. However, the adsorbed species were not necessarily NO{sub 2} as reported by others. The authors believe that the interaction between adsorbed NO{sub x} species and O{sub 2} is responsible for enhancing the rate of NO{sub x} decomposition. It is obvious that the framework Co{sup 2+} behaves very differently from Co{sup 2+} in the countercation position and from extra-framework CoO such as that supported on or dispersed on the surface of silicalite also having the same MFI structure.

Chang, Y. [ABB Lummus Global, Inc., Bloomfield, NJ (United States)] [ABB Lummus Global, Inc., Bloomfield, NJ (United States); McCarty, J.G. [Catalytica, Inc., Mountain View, CA (United States)] [Catalytica, Inc., Mountain View, CA (United States)

1998-09-10

376

Coalescence of Crystalline Drops  

NASA Astrophysics Data System (ADS)

We present the first experimental analysis of drop coalescence in a case where the dynamics is not governed by viscous dissipation in the bulk nor by the inertia of the fluid flow, only by the geometry and mobility of surfaces. We found such a situation in the physics of 3He crystals near 0.32K where the latent heat of crystallization vanishes. Two crystalline drops of 3He coalesce if their crystalline orientations are identical: a neck forms after the contact at time t=0, and the shape evolves towards that of one convex crystal by local growth and melting in a fraction of a second. We have found that the neck radius initially increases as t1/3, as predicted by Maris. This behavior is also expected for superfluid drops. It is clearly distinguished from the logarithmic behavior and from the t1/2 power law which have been predicted by Eggers et al. in more usual situations.

Ishiguro, R.; Graner, F.; Rolley, E.; Balibar, S.

2004-11-01

377

Crystalline color superconductors  

NASA Astrophysics Data System (ADS)

Inhomogeneous superconductors and inhomogeneous superfluids appear in a variety of contexts including quark matter at extreme densities, fermionic systems of cold atoms, type-II cuprates, and organic superconductors. In the present review the focus is on properties of quark matter at high baryonic density, which may exist in the interior of compact stars. The conditions realized in these stellar objects tend to disfavor standard symmetric BCS pairing and may favor an inhomogeneous color superconducting phase. The properties of inhomogeneous color superconductors are discussed in detail and in particular of crystalline color superconductors. The possible astrophysical signatures associated with the presence of crystalline color superconducting phases within the core of compact stars are also reviewed.

Anglani, Roberto; Casalbuoni, Roberto; Ciminale, Marco; Ippolito, Nicola; Gatto, Raoul; Mannarelli, Massimo; Ruggieri, Marco

2014-04-01

378

Silicate emission feature in the spectrum of comet Mueller 1993a  

NASA Technical Reports Server (NTRS)

An 8- to 13-micron spectrum of comet Mueller 1993a, a dynamically new comet, was acquired when the comet was at R = 2 AU. Strong, structured silicate emission is present, closely resembling that seen in Comet P/Halley at smaller R. For the first time in a new comet, the 11.2-micron peak of crystalline olivine was detected, demonstrating that crystalline olivine particles were widespread in the solar nebula. Crystalline olivine particles could have formed in the inner protosolar nebula at temperatures greater than 1200 K; extensive radial mixing would have been required to transport these grains to the region of comet formation. Either there was more radial mixing in the solar nebula than some current theories predict or the olivine grains have a presolar origin.

Hanner, Martha S.; Hackwell, John A.; Russell, Ray W.; Lynch, David K.

1994-01-01

379

Better Alternatives to “Astronomical Silicate”: Laboratory-Based Optical Functions of Cosmic Abundance Glass with Application to HD 161796  

NASA Astrophysics Data System (ADS)

“Astronomical” or “cosmic” silicate optical (dielectric) functions over a large fraction of the electromagnetic spectrum are critical for interpreting the radiative environments of systems as varied as H II regions, circumstellar dust around evolved stars and in disks around young stellar objects (YSOs), and active galactic nuclei (AGN). However, the optical functions that have been previously derived by the community to address this need are for compositionally and structurally disparate materials, and were prepared with inconsistent methodology, kludging observational data and laboratory data with different experimental methods to populate the wavelength space. New quantitative laboratory data are available to build up wavelength coverage for amorphous silicates in a more systematic way. We present optical functions and extinction cross-sections derived from mid-UV to far-IR laboratory transmission spectra of cosmic abundance silicate glass. The advantages of using these data are that our glass sample was synthesized especially with cosmic (solar) abundances in mind and excludes iron. We compare these results to other popular optical functions used to model amorphous silicates (e.g., “astronomical” or “cosmic” silicate by Draine & Lee 1984, Draine 2003, Ossenkopf et al. 1992), both directly and in application to HD 161796, a spherically symmetric, O-rich system with a visible central star, optically thin dust shell, and energy intermediate to AGB and PN class targets. The new cosmic silicate optical functions have much lower UV-vis and NIR opacity than the traditionally used functions necessitating significantly more dust (1 or 2 orders of magnitude for mass) to model an object like HD 161796. Furthermore, the lower opacity has an impact on the fraction of crystalline material needed to match the observed spectrum. Previous models produced using older optical functions will underestimate the dust mass and overestimate the importance of crystalline silicates. This work is supported through NSF AST-1009544 and NASA APRA04-000-0041.

Pitman, Karly M.; Speck, A.; Hofmeister, A. M.; Buffard, A. S.; Whittington, A. G.

2013-01-01

380

Skeletal isomerization of 1-butene over ferrierite and ZSM-5 zeolites: influence of zeolite acidity  

Microsoft Academic Search

Three ferrierite (FER) and five ZSM-5 (MFI) zeolites with SiO2Al2O3 ratio ranging from 27 to 2000 are tested as catalysts for the skeletal isomerization of 1-butene at 350–450°C and atmospheric total pressure in order to study the influence of acidity and pore structure of zeolite on conversion and selectivity. The catalytic and NH3 temperature-programmed desorption results from FER and MFI

Gon Seo; Hwan Seok Jeong; Suk Bong Hong; Young Sun Uh

1996-01-01

381

Effect of zeolites on chitosan\\/zeolite hybrid membranes for direct methanol fuel cell  

Microsoft Academic Search

Zeolites including 3A, 4A, 5A, 13X, mordenite, and HZSM-5 were incorporated into chitosan (CS) matrix to fabricate the hybrid membranes for direct methanol fuel cell (DMFC). Due to the presence of hydrogen bonds between CS and zeolite, the hybrid membranes displayed desirable thermal and mechanical stabilities. Through free volume characteristics analysis by positron annihilation lifetime spectroscopy (PALS) technique, it was

Jingtao Wang; Xiaohong Zheng; Hong Wu; Bin Zheng; Zhongyi Jiang; Xiaopeng Hao; Baoyi Wang

2008-01-01

382

Dynamic crystallization of silicate melts  

NASA Technical Reports Server (NTRS)

Two types of furnaces with differing temperature range capabilities were used to provide variations in melt temperatures and cooling rates in a study of the effects of heterogeneous nucleation on crystallization. Materials of chondrule composition were used to further understanding of how the disequilibrium features displayed by minerals in rocks are formed. Results show that the textures of natural chondrules were duplicated. It is concluded that the melt history is dominant over cooling rate and composition in controlling texture. The importance of nuclei, which are most readily derived from preexisting crystalline material, support an origin for natural chondrules based on remelting of crystalline material. This would be compatible with a simple, uniform chondrule forming process having only slight variations in thermal histories resulting in the wide range of textures.

Russell, W. J.

1984-01-01

383

Crystalline titanate catalyst supports  

DOEpatents

A series of new crystalline titanates (CT) are shown to have considerable potential as catalyst supports. For Pd supported catalyst, the catalytic activity for pyrene hydrogenation was substantially different depending on the type of CT, and one was substantially more active than Pd on hydrous titanium oxide (HTO). For 1-hexene hydrogenation the activities of the new CTs were approximately the same as for the hydrous metal oxide supports.

Anthony, R.G.; Dosch, R.G.

1993-01-05

384

Crystalline beam ground state  

SciTech Connect

In order to employ molecular dynamics (MD) methods, commonly used in condensed matter physics, we have derived the equations of motion for a beam of charged particles in the rotating rest frame of the reference particle. We include in the formalism that the particles are confined by the guiding and focusing magnetic fields, and that they are confined in a conducting vacuum pipe while interacting with each other via a Coulomb force. Numerical simulations using MD methods has been performed to obtain the equilibrium crystalline beam structure. The effect of the shearing force, centrifugal force, and azimuthal variation of the focusing strength are investigated. It is found that a constant gradient storage ring can not give a crystalline beam, but that an alternating-gradient (AG) structure can. In such a machine the ground state is, except for one-dimensional (1-D) crystals, time dependent. The ground state is a zero entropy state, despite the time-dependent, periodic variation of the focusing force. The nature of the ground state, similar to that found by Schiffer et al. depends upon the density and the relative focusing strengths in the transverse directions. At low density, the crystal is 1-D. As the density increases, it transforms into various kinds of 2-D and 3-D crystals. If the energy of the beam is higher than the transition energy of the machine, the crystalline structure can not be formed for lack of radial focusing.

Wei, Jie [Brookhaven National Lab., Upton, NY (United States); Li, Xiao-Ping [Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics; Sessler, A.M. [Lawrence Berkeley Lab., CA (United States)

1993-06-11

385

IMPROVED CATALYSTS FOR HEAVY OIL UPGRADING BASED ON ZEOLITE Y NANOPARTICLES ENCAPSULATED IN STABLE NANOPOROUS HOST  

SciTech Connect

Composite materials of SBA-15/zeolite Y were synthesized from zeolite Y precursor and a synthesis mixture of mesoporous silicate SBA-15 via a hydrothermal process in the presence of a slightly acidic media of pH 4-6 with 2M H{sub 2}SO{sub 4}. The SBA-15/ZY composites showed Type IV adsorption isotherms, narrow BJH average pore size distribution of 4.9 nm, surface areas up to 800 m{sup 2}2/g and pore volumes 1.03 cm{sup 3}, all comparable to pure SBA-15 synthesized under similar conditions. Chemical analysis revealed Si/Al ratio down to 8.5 in the most aluminated sample, and {sup 27}AlSS MAS NMR confirmed aluminum was in tetrahedral coordination. This method of introduction of Al in pure T{sub d} coordination is effective in comparison to other direct and post synthesis alumination methods. Bronsted acid sites were evident from a pyridinium peak at 1544 cm-1 in the FTIR spectrum after pyridine adsorption, and from NH{sub 3} -TPD experiments. SBA-15/ZY composites showed significant catalytic activities for the dealkylation of isopropylbenzene to benzene and propene, similar to those of commercial zeolite Y. It was observed that higher conversion for catalysts synthesized with high amount of ZY precursor mixture added to the SBA-15. Over all the composites has shown good catalytic activity. Further studies will be focused on gaining a better understand the nature of the precursor, and to characterize and to locate the acid sites in the composite material. The composite will also be evaluated for heavy oil conversion to naphtha and middle distillates.

Conrad Ingram; Mark Mitchell

2005-11-15

386

Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars  

PubMed Central

Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; = Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars.

Smith, Joseph V.

1998-01-01

387

Electronic structure calculations of ammonia adsorption in H-ZSM-5 zeolites  

SciTech Connect

The structural and electronic properties of acid sites in zeolites are important in determining their catalytic behavior. Kohn-Sham density functional theory calculations are used to probe the local environment of the acid site in realistic zeolite clusters and to study its interaction with ammonia. The long-range electrostatic effects on the adsorption are incorporated self-consistently in the electronic structure calculations. We examine their effect on the acidity of the cluster and on both the structure and the energetics of adsorption. Systematic structural relaxations of the aluminum-substituted framework show that there are significant structural rearrangements from the entirely siliceous cluster, in the vicinity of the substitution site. In the case of ammonia adsorption, the energetics of adsorption are sensitive to the structural arrangement of the ammonia. Configurations where the adsorbed molecule interacts with three lattice bridging oxygen molecules are favored. The theoretical predictions are compared to recent solid state NMR and microcalorimetry experiments. 57 refs., 10 figs., 8 tabs.

Kyrlidis, A.; Cook, S.J.; Chakraborty, A.K.; Bell, A.T.; Theodorou, D.N. (Lawrence Berkeley Lab., CA (United States) Univ. of California, Berkeley, CA (United States))

1995-02-02

388

Toxic elements in silicate cements.  

PubMed

Six brands of silicate cements have been characterized by means of optical emission spectrography with respect to the contents of elements in minor or trace quantities in a search for presence of possible toxic elements. Beryllium was observed in two powders at levels of 1.3 and 1.6% Cadmium was found in two powders at levels of 0.02 and 0.03%. Lead was measured in three powders at levels of 0.001-0.003%. Bismuth, boron, copper, gallium, iron, manganese, titanium, tin and zirconium were found in various brands in either powder or liquid at levels of 0.001-0.1%. Upper limits of the amounts of the various elements that might be transferred to the gastrointestinal tract after dissolution of the cement matrix in the oral cavity have been calculated. PMID:296570

Brune, D

1979-12-01

389

Mesoporous Silicate Materials in Sensing  

PubMed Central

Mesoporous silicas, especially those exhibiting ordered pore systems and uniform pore diameters, have shown great potential for sensing applications in recent years. Morphological control grants them versatility in the method of deployment whether as bulk powders, monoliths, thin films, or embedded in coatings. High surface areas and pore sizes greater than 2 nm make them effective as adsorbent coatings for humidity sensors. The pore networks also provide the potential for immobilization of enzymes within the materials. Functionalization of materials by silane grafting or through co-condensation of silicate precursors can be used to provide mesoporous materials with a variety of fluorescent probes as well as surface properties that aid in selective detection of specific analytes. This review will illustrate how mesoporous silicas have been applied to sensing changes in relative humidity, changes in pH, metal cations, toxic industrial compounds, volatile organic compounds, small molecules and ions, nitroenergetic compounds, and biologically relevant molecules.

Melde, Brian J.; Johnson, Brandy J.; Charles, Paul T.

2008-01-01

390

Dispersion enhanced metal/zeolite catalysts  

DOEpatents

Dispersion stabilized zeolite supported metal catalysts are provided as bimetallic catalyst combinations. The catalyst metal is in a reduced zero valent form while the dispersion stabilizer metal is in an unreduced ionic form. Representative catalysts are prepared from platinum or nickel as the catalyst metal and iron or chromium dispersion stabilizer.

Sachtler, Wolfgang M. H. (Evanston, IL); Tzou, Ming-Shin (Evanston, IL); Jiang, Hui-Jong (Evanston, IL)

1987-01-01

391

Electrical properties of zeolitized volcaniclastic materials  

Microsoft Academic Search

The interpretation of electromagnetic anomalies associated with volcanic activity requires a good understanding of two rock properties, the electrical conductivity and the streaming potential coupling coefficient. We measured these properties on 22 consolidated tuff samples containing clays and zeolites typically found in hydrothermal systems or in other areas of high water-rock interactions associated with active volcanic areas. These rocks exhibit

A. Revil; D. Hermitte; E. Spangenberg; J. J. Cochemé

2002-01-01

392

Silver clusters and chemistry in zeolites  

SciTech Connect

The spectroscopic work done on silver clusters trapped in solid noble gas matrices at low temperature has been extensively reviewed by Ozin, and Henglein has done the same for photochemical studies of colloidal silver particles in solution. This article will review the chemistry of silver in zeolite hosts, including the synthesis and structures of silver clusters. 127 refs.

Sun, T.; Seff, K. (Univ. of Hawaii, Honolulu, HI (United States). Dept. of Chemistry)

1994-06-01

393

ARSENIC SEPARATION FROM WATER USING ZEOLITES  

EPA Science Inventory

Arsenic is known to be a hazardous contaminant in drinking water. The presence of arsenic in water supplies has been linked to arsenical dermatosis and skin cancer . Zeolites are well known for their ion exchange capacities. In the present work, the potential use of a variety of ...

394

Reactions of aliphatic ketones on zeolites  

Microsoft Academic Search

Reactions of some ketones (acetone, methyl ethyl ketone and diethyl ketone) on the H-form of ZSM-5, ZSM-11, mordenite and erionite have been studied in an integral reactor. At a reaction temperature of 300 or 350°C acetone is selectively transformed on all these zeolites into isobutene, while with higher ketones substantial amounts of aromatics are formed.

K. Nedomová; S. Beran

1986-01-01

395

ARSENIC SEPARATION FROM WATER USING ZEOLITES: SYMPOSIUM  

EPA Science Inventory

NRMRL-ADA-01134 Shevade, S, Ford*, R., and Puls*, R.W. "Arsenic Separation from Water Using Zeolites." In: 222nd ACS National Meeting, ACS Environmental Chemistry Division Symposia, Chicago, IL, 08/26-30/2001. 2001. 04/23/2001 This...

396

Multicomponent liquid ion exchange with chabazite zeolites  

SciTech Connect

In spite of the increasing commercial use of zeolites for binary and multicomponent sorption, the understanding of the basic mass-transfer processes associated with multicomponent zeolite ion-exchange systems is quite limited. This study was undertaken to evaluate Na-Ca-Mg-Cs-Sr ion exchange from an aqueous solution using a chabazite zeolite. Mass-transfer coefficients and equilibrium equations were determined from experimental batch-reactor data for single and multicomponent systems. The Langmuir isotherm was used to represent the equilibrium relationship for binary systems, and a modified Dubinin-Polyani model was used for the multicomponent systems. The experimental data indicate that diffusion through the microporous zeolite crystals is the primary diffusional resistance. Macropore diffusion also significantly contributes to the mass-transfer resistance. Various mass-transfer models were compared to the experimental data to determine mass-transfer coefficients. Effective diffusivities were obtained which accurately predicted experimental data using a variety of models. Only the model which accounts for micropore and macropore diffusion occurring in series accurately predicted multicomponent data using single-component diffusivities. Liquid and surface diffusion both contribute to macropore diffusion. Surface and micropore diffusivities were determined to be concentration dependent.

Robinson, S.M.; Arnold, W.D. Jr.; Byers, C.W.

1993-10-01

397

MERCURY SEPARATION FROM POLLUTANT WATER USING ZEOLITES  

EPA Science Inventory

Arsenic is known to be a hazardous contaminant in drinking water that causes arsenical dermatitis and skin cancer. In the present work, the potential use of a variety of synthetic zeolites for removal of arsenic from water has been examined at room temperature. Experiments have...

398

Coating of crystalline nuclear waste forms to improve inertness  

SciTech Connect

Microspheres of a crystalline waste form prepared by sol-gel processing were successfully coated with layers of pyrolytic carbon and silicon carbide to isolate the radioactive wastes from the biosphere. A separate process for cesium immobilization was developed which loads 5 wt% Cs onto zeolite particles for subsequent coating. Pyrolytic carbon-coated particles showed leach rates approx. =2 to 4 orders of magnitude less than the candidate reference borosilicate glass waste form. Aqueous leach-test results of coated waste forms were below detection limits of such sensitive analytical techniques as atomic absorption and inductively coupled plasma atomic emission. Significant progress was made in applying sol-gel and fluidized bed coating technology to the solidification of high-level nuclear wastes. The authors successfully prepared microspheres containing simulated wastes of Synroc-B, Synroc-D, a modified Synroc-D where alumina was previously removed from the waste, and a very high waste-loading composition containing 90% waste and 10% ZrO/sub 2/. Each of these compositions was sintered at 1000/sup 0/C and coated with pyrocarbon at temperatures as low as 1000/sup 0/C. Silicon carbide can be applied to these pyrocarbon-coated particles at temperatures as low as 900/sup 0/C for additional inertness or for oxidation resistance. Cesium was isolated by pyrocarbon-coating cesium-loaded zeolite. Pyrocarbon and SiC coatings successfully reduced the leach rates to below detection limits.

Stinton, D.P.; Angelini, P.; Caputo, A.J.; Lackey, W.J.

1982-08-01

399

PHYSICAL, CHEMICAL AND STRUCTURAL EVOLUTION OF ZEOLITE-CONTAINING WASTE FORMS PRODUCED FROM METAKAOLINITE AND CALCINED HLW  

SciTech Connect

Natural and synthetic zeolites are extremely versatile materials. They can adsorb a variety of liquids and gases, and take part in cation exchange reactions. Zeolites are relatively easy to synthesize from a wide range of natural and man-made materials. One such combination is a mixture of metakaolinite and concentrated sodium hydroxide solution. Once mixed and cured at elevated temperatures, these ingredients react to form a hard, dense, ceramic-like material that contains significant amounts of crystalline tectosilicates (zeolites and feldspathoids) imbedded in an X-ray amorphous sodium aluminosilicate hydrate matrix. This rather unique composite material has been termed a ''hydroceramic.'' The crystalline phases in the hydroceramic have the ability to sequester alkali, alkaline earth and a variety of higher valance cations in lattice positions or within networks of channels and voids. The matrix plays host to the crystallites and to residual amounts of insoluble hydroxide phases. Due to its gel-like character, the matrix also provides considerable strength. A previous publication has established the fact that a mixture of a calcined equivalent ICPP waste (sodium aluminate/hydroxide solution containing {approx}3:1 Na:Al) and fly ash and/or metakaolinite could be cured at various temperatures to produce a monolith containing Zeolite A (80 C) or Na-P1 plus hydroxy sodalite (130 C) dispersed in the alkali aluminosilicate hydrate matrix. Dissolution tests (PCT type) have shown these materials have superior retention of alkali, alkaline earth and heavy metal ions. The zeolitization process is a simple one. Metakaolinite is mixed with a calcined sodium-bearing waste and enough water to make a thick paste. The paste is transferred to a metal canister and ''soaked'' for a few hours at 90 C prior to conventional oven heating or steam autoclaving at -200 C for varying periods of time. Hydroceramics could well be a viable alternative for fixation of low activity sodium-bearing waste (SBW) calcines. The objective of the current study is to adapt this technology for use on site remediation and clean up of caustic waste solutions now in storage in tanks at Hanford and Savannah River. The proposed work is meant to develop a clearer understanding of the advantages and limitations of producing a zeolite-containing hydroceramic from treated low activity SBW, i.e. the effect of processing variables, reaction kinetics, crystal and phase chemistry, and microstructure on the performance of the waste form.

Grutzeck, Michael W.; Kwan, Stephen

2001-06-01

400

UTILITY OF ZEOLITES IN REMOVAL OF INORGANIC AND ORGANIC WATER POLLUTANTS  

EPA Science Inventory

Zeolites are well known for their ion exchange, adsorption and acid catalysis properties. Different inorganic and organic pollutants have been removed from water at room temperature using various zeolites. Synthetic zeolite Faujasite Y has been used to remove inorganic pollutants...

401

Studying the effect of zeolite inclusion in aluminum alloy on measurement of its surface hardness using laser-induced breakdown spectroscopy technique  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) has been used to study the surface hardness of special aluminum alloys containing zeolite. The aluminum alloy has acquired pronounced changes in its metallurgical properties due to the zeolite inclusion. The surface hardness of the samples under investigation is determined by measuring the spectral intensity ratios of the ionic to atomic spectral lines in the LIBS spectra of samples having different surface hardness values that have been conventionally measured before for comparison. The presence of aluminum silicate mineral in the studied alloys enabled material volume to expand under compression. This feature gave new results in the measurement of hardness via LIBS. It has been proven that the trend of the alloy density change complies with the increase of ionic to atomic spectral line intensity ratio.

Khalil, Osama Mostafa; Mingareev, Ilya; Bonhoff, Tobias; El-Sherif, Ashraf F.; Richardson, Martin C.; Harith, Mohamed Abdel

2014-01-01

402

A time-resolved diffuse reflectance study of the photo-reduction of 2,2$prime;-bipyridine in faujasitic zeolites  

NASA Astrophysics Data System (ADS)

The siting location and conformation of 2,2'-bipyridine sorbed alone and co-sorbed with 1,4-diazabicyclo(2.2.2)octane (DABCO) in several faujasitic zeolites with different aluminium content were determined by a Raman spectroscopic study and Monte Carlo simulations. Theoretical and experimental results clearly indicate a trans ? cis conformational change of the 2,2'-bpy molecule upon sorption into dehydrated Na nFAU ( n = 56, 85) whereas the trans conformation is retained in the purely siliceous zeolite FAU ( n = 0). The UV photolysis of 2,2'-bpy molecules sorbed alone generates a triplet excited state via singlet states, whereas in the case of co-sorbed DABCO, the photo-reduction of 2,2'-bpy by the amine leads to the radical anion.

Brémard, C.; Buntinx, G.; Coustillier, G.; Ginestet, G.

1997-06-01

403

Order and disorder in calcium-silicate-hydrate  

NASA Astrophysics Data System (ADS)

Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C-S-H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue of C-S-H, and to an artificial ideal glass. The results clearly indicate that C-S-H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C-S-H retains some signatures of a tobermorite-like layered structure, hydrated species are completely amorphous.

Bauchy, M.; Qomi, M. J. Abdolhosseini; Ulm, F.-J.; Pellenq, R. J.-M.

2014-06-01

404

Order and disorder in calcium-silicate-hydrate.  

PubMed

Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C-S-H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue of C-S-H, and to an artificial ideal glass. The results clearly indicate that C-S-H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C-S-H retains some signatures of a tobermorite-like layered structure, hydrated species are completely amorphous. PMID:24908022

Bauchy, M; Qomi, M J Abdolhosseini; Ulm, F-J; Pellenq, R J-M

2014-06-01

405

CO2 SEPARATIONS USING ZEOLITE MEMBRANES  

SciTech Connect

Zeolite and other inorganic molecular sieve membranes have shown potential for separations based on molecular size and shape because of their small pore sized, typically less than 1 nm, and their narrow pore size distribution. The high thermal and chemical stability of these inorganic crystals make them ideal materials for use in high temperature applications such as catalytic membrane reactors. Most of the progress with zeolite membranes has been with MFI zeolites prepared on porous disks and tubes. The MFI zeolite is a medium pore size structure having nearly circular pores with diameters between .53 and .56 nm. Separation experiments through MFI membranes indicate that competitive adsorption separates light gas mixtures. Light gas selectivities are typically small, however, owing to small differences in adsorption strengths and their small sizes relative to the MFI pore opening. Furthermore, competitive adsorption does not work well at high temperature where zeolite membranes are stable and have potential application. Separation by differences in size has a greater potential to work at high temperature than competitive adsorption, but pores smaller than those in MFI zeolites are required. Therefore, some studies focused on the synthesis of a small, 8-membered-pore structures such as zeolite A (0.41-nm pore diameter) and SAPO-34, a chabazite (about .4-nm pore diameter with about 1.4 nm cages) analog. The small pore size of the zeolite A and SAPO-34 structures made the separation of smaller molecules by differences in size possible. Zeolite MFI and SAPO-34 membranes were prepared on the inside surface of porous alumina tubes by hydrothermal synthesis, and single gas and binary mixture permeances were measured to characterize the membrane's performance. A mathematical diffusion model was developed to determine the relative quantities of zeolite and non-zeolite pores in different membranes by modeling the permeation date of CO{sub 2}. This model expresses the total flux through the membrane as the sum of surface diffusion through zeolite pores and viscous flow and Knudsen diffusion through non-zeolite pores. As predicted by the model, the permeance of CO{sub 2} decrease with increasing pressure at constant pressure drop for membranes with few non-zeolite pores, but the permeance increased through viscous flow pores and was constant through pores allowing Knudsen diffusion. Membranes having more non-zeolite pores had lower CO{sub 2}/CH{sub 4} selectivities. The SAPO-34 membranes were characterized for light gas separation applications, and the separation mechanisms were identified. Single gas permeances of CO{sub 2}, N{sub 2}, and CH{sub 4} decreased with increasing kinetic diameter. For the best membrane at 300K, the He and H{sub 2} permeances were less than that of CO{sub 2}, because He, H{sub 2} and CO{sub 2} were small compared to the SAPO-34 pore, and differences in the heat of adsorption determined the permeance order. The small component permeated the fastest in CO{sub 2}/CH{sub 4}, CO{sub 2}/N{sub 2}, N{sub 2}/CH{sub 4}, H{sub 2}/CH{sub 4}, and H{sub 2}/N{sub 2} mixtures between 300 and 470 K. For H{sub 2}/CO{sub 2} mixtures, which were separated by competitive adsorption at room temperature, the larger component permeated faster below 400K. The room temperature CO{sub 2}/CH{sub 4} selectivity was 36 and decreased with temperature. The H{sub 2}/CH{sub 4} mixture selectivity was 8 and constant with temperature up to 480 K. Calcination, slow temperature cycles, and exposure to water vapor had no permanent effect on membrane performance, but temperature changes of approximately 30 K/min decreased the membrane's effectiveness. The effects of humidity on gas permeation were studied with SAPO-34 membranes of different qualities. Membranes with high CO{sub 2}/CH{sub 4} selectivities (greater than 20) were stable in water vapor under controlled conditions, but degradation was seen for some membranes. The degradation opened non-SAPO-34 pores that were larger than SAPO-34 pores as shown by the IC{sub 4}H{sub 10} permeance, C

Richard D. Noble; John L. Falconer

2001-06-30

406

First Principles Simulations of Hydrocarbon Conversion Processes in Functionalized Zeolitic Materials  

NASA Astrophysics Data System (ADS)

With increasing demand for chemicals and fuels, and finite traditional crude oil resources, there is a growing need to invent, establish, or optimize chemical processes that convert gasifiable carbon-based feedstocks (e.g., coal, natural gas, oil sands, or biomass) into the needed final products. Catalysis is central to almost every industrial chemical process, including alkane metathesis (AM) and the methanol-to-hydrocarbons (MTH) process, which represent final steps in a sequence of hydrocarbon conversion reactions. An in depth understanding of AM and MTH is essential to the selective production of the desired end products. In this dissertation, ab initio density functional theory simulations provide unique mechanistic and thermodynamic insight of specific elementary steps involved in AM and MTH as performed on zeolite supports. Zeolites have been employed throughout the petroleum industry because of their ability to perform acid-catalyzed reactions (e.g., cracking or MTH). The crystalline structure of zeolites imparts regular microporous networks and, in turn, the selective passage of molecules based on shape and functionality. Many different elements can be grafted onto or substituted into zeolites, resulting in a broad range of catalytic behavior. However, due to the variety of competing and secondary reactions that occur at experimental conditions, it is often difficult to extract quantitative information regarding individual elementary steps. ab initio calculations can be particularly useful for this purpose. Alkane metathesis (i.e., the molecular redistribution or chain length averaging of alkanes) is typically performed by transition metal hydrides on amorphous alumina or silica supports. In Chapter 3, the feasibility of AM in zeolites is assessed by using a grafted Ta-hydride complex to explore the full catalytic cycle in the self-metathesis of ethane. The decomposition of a Ta-metallacyclobutane reaction intermediate that forms during olefin metathesis is responsible for the largest activation energy of the catalytic cycle. This assessment is similar to the findings of alkane metathesis studies on alumina/silica supports and indicates that the entire AM cycle can be performed in zeolites by isolated single-atom transition metal hydrides. Performed over acid form zeolites, MTH is used in the conversion of methanol into a broad range of hydrocarbons, including alkenes, alkanes, and aromatics. For reasons that are not yet rigorously quantified, product selectivities vary dramatically based on the choice of catalyst and reaction conditions. The methylation of species containing double bonds (i.e., co-catalysts) is central to the overall process. Distinct structure-function relationships were found with respect to the elementary steps in the methylation and beta-scission of olefins. In Chapter 4, the role of zeolite topology in the step-wise methylation of ethene by surface methoxides is investigated. Elementary steps are studied across multiple frameworks (i.e., BEA, CHA, FER, MFI, and MOR) constituting a wide variety of confinement environments. The reaction of surface methoxides with ethene is found to require a transition state containing a primary carbocation. The barrier height is found to decrease nearly monotonically with respect to the degree of dispersion interactions stabilizing the primary carbocationic species in the transition state. In addition, quantification of the ``local'' dispersion energy indicates that confinement effects can not be simply correlated to pore size. The beta-scission of olefins plays an important role in the product selectivities of many important chemical processes, including MTH. In Chapter 5, beta-scission modes involving C6 and C8 isomers are investigated at a single, isolated Bronsted acid site within H-ZSM-5. We find that the relative enthalpic barriers of beta-scission elementary steps can be rationalized by the substitution order of the two different carbocationic carbon atoms that are present in the reactant (C+) and transition states (betaC). In fact, the increase in c

Mazar, Mark Nickolaus

407

Alkali Silicate Vehicle Forms Durable, Fireproof Paint  

NASA Technical Reports Server (NTRS)

The problem: To develop a paint for use on satellites or space vehicles that exhibits high resistance to cracking, peeling, or flaking when subjected to a wide range of temperatures. Organic coatings will partially meet the required specifications but have the inherent disadvantage of combustibility. Alkali-silicate binders, used in some industrial coatings and adhesives, show evidence of forming a fireproof paint, but the problem of high surface-tension, a characteristic of alkali silicates, has not been resolved. The solution: Use of a suitable non-ionic wetting agent combined with a paint incorporating alkali silicate as the binder.

Schutt, John B.; Seindenberg, Benjamin

1964-01-01

408

Layered zeolitic materials: an approach to designing versatile functional solids.  

PubMed

Relevant layered zeolites have been considered in this perspective article from the point of view of the synthesis methodologies, materials characterization and catalytic implications, considering the unique physico-chemical characteristics of lamellar materials. The potential of layered zeolitic precursors to generate novel lamellar accessible zeolites through swelling, intercalation, pillarization, delamination and/or exfoliation treatments is studied, showing the chemical, functional and structural versatility exhibited by layered zeolites. Recent approaches based on the assembly of zeolitic nanosheets which act as inorganic structural units through the use of dual structural directing agents, the selective modification of germanosilicates and the direct generation of lamellar hybrid organic-inorganic aluminosilicates are also considered to obtain layered solids with well-defined functionalities. The catalytic applications of the layered zeolites are also highlighted, pointing out the high accessibility and reactivity of active sites present in the lamellar framework. PMID:24457617

Díaz, Urbano; Corma, Avelino

2014-07-21

409

Zeolite catalysis in conversion of cellulosics. Annual report  

SciTech Connect

The authors have studied the kinetics of oxylose/xylulose isomerization in significant detail over a variety of zeolites and obtained the pseudo-first order reaction rate constants. The authors have found that HY zeolite is still the best material and zeolites are more selective than homogeneous acid catalysts where decomposition of the sugar compounds is much faster. They have completed, as described in the Year 2 Work Plan, the study of cellobiose hydrolysis with an ion exchange resin. The kinetics of the solid-catalyzed reaction is qualitatively similar to that for catalysis by homogeneous acids. The planned program of NMR studies has revealed the dynamics of sugar molecules within the zeolite cavities. Two chemisorbed and a physisorbed state have been identified in HY zeolite. A new state, accounting for as much as a half of the sugar, has been found in ZSM-5 zeolite.

Tsao, G.T.

1994-02-01

410

Atomic sites and stability of Cs+ captured within zeolitic nanocavities  

PubMed Central

Zeolites have potential application as ion-exchangers, catalysts and molecular sieves. Zeolites are once again drawing attention in Japan as stable adsorbents and solidification materials of fission products, such as 137Cs+ from damaged nuclear-power plants. Although there is a long history of scientific studies on the crystal structures and ion-exchange properties of zeolites for practical application, there are still open questions, at the atomic-level, on the physical and chemical origins of selective ion-exchange abilities of different cations and detailed atomic structures of exchanged cations inside the nanoscale cavities of zeolites. Here, the precise locations of Cs+ ions captured within A-type zeolite were analyzed using high-resolution electron microscopy. Together with theoretical calculations, the stable positions of absorbed Cs+ ions in the nanocavities are identified, and the bonding environment within the zeolitic framework is revealed to be a key factor that influences the locations of absorbed cations.

Yoshida, Kaname; Toyoura, Kazuaki; Matsunaga, Katsuyuki; Nakahira, Atsushi; Kurata, Hiroki; Ikuhara, Yumi H.; Sasaki, Yukichi

2013-01-01

411

Preparation of Robust, Thin Zeolite Membrane Sheet for Molecular Separation  

SciTech Connect

This paper reports a feasibility study on the preparation of zeolite membrane films on a thin, porous metal support sheet (50-{micro}m thick). Zeolite sodium A (NaA) and silicalite zeolite frameworks are chosen to represent synthesis of respective hydrophilic-type and hydrophobic-type zeolite membranes on this new support. It is found that a dense, continuous inter-grown zeolite crystal layer at a thickness less than 2 {micro}m can be directly deposited on such a support by using direct and secondary growth techniques. The resulting membrane shows excellent adhesion on the metal sheet. Molecular-sieving functions of the prepared membranes are characterized with ethanol/water separation, CO2 separation, and air dehumidification. The results show great potential to make flexible metal-foil-like zeolite membranes for a range of energy conversion and environmental applications.

Liu, Wei; Zhang, Jian; Canfield, Nathan L.; Saraf, Laxmikant V.

2011-10-19

412

Interaction of hydrogen with surfaces of silicates: single crystal vs. amorphous.  

PubMed

We have studied how the formation of molecular hydrogen on silicates at low temperature is influenced by surface morphology. At low temperature (<30 K), the formation of molecular hydrogen occurs chiefly through weak physical adsorption processes. Morphology then plays a role in facilitating or hindering the formation of molecular hydrogen. We studied the formation of molecular hydrogen on a single crystal forsterite and on thin films of amorphous silicate of general composition (Fe(x)Mg((x-1)))(2)SiO(4), 0 < x < 1. The samples were studied ex situ by Atom Force Microscopy (AFM), and in situ using Thermal Programmed Desorption (TPD). The data were analysed using a rate equation model. The main outcome of the experiments is that TPD features of HD desorbing from an amorphous silicate after its formation are much wider than the ones from a single crystal; correspondingly typical energy barriers for diffusion and desorption of H, H(2) are larger as well. The results of our model can be used in chemical evolution codes of space environments, where both amorphous and crystalline silicates have been detected. PMID:21808801

He, Jiao; Frank, Paul; Vidali, Gianfranco

2011-09-21

413

Necrotizing infundibular crystalline folliculitis.  

PubMed

We describe a 22-year-old woman with a background of acne who developed multiple folliculocentric facial papules associated with sharply demarcated waxy, keratotic plugs. Multiple skin biopsies showed umbilicated craters that were filled with dispersed bundles of eosinophilic filaments embedded in a pale amorphous matrix forming a plug. The plugs bulged into the upper dermis. Serial sections showed vacuolar and filamentous destruction of the infundibular and adjacent perifollicular epithelium and a close relationship of the crystalline necrosis to follicles. Electron microscopy revealed that the filamentous bundles were tonofilaments. No fresh material was available for polarization and the paraffin sections failed to polarize. The clinical and pathological findings of the lesions in our patient were identical to those reported as a new perforating disorder with urate-like crystals. Our case indicates that the process may represent crystalline folliculocentric necrosis rather than a primary perforating disorder. The nature and basis of the crystals that have a urate-like appearance remain to be determined. PMID:11453930

Kossard, S; Scurry, J; Killingsworth, M

2001-07-01

414

Silicate mineralogy of martian meteorites  

NASA Astrophysics Data System (ADS)

Basalts and basaltic cumulates from Mars (delivered to Earth as meteorites) carry a record of the history of that planet - from accretion to initial differentiation and subsequent volcanism, up to recent times. We provide new microprobe data for plagioclase, olivine, and pyroxene from 19 of the martian meteorites that are representative of the six types of martian rocks. We also provide a comprehensive WDS map dataset for each sample studied, collected at a common magnification for easy comparison of composition and texture. The silicate data shows that plagioclase from each of the rock types shares similar trends in Ca-Na-K, and that K 2O/Na 2O wt% of plagioclase multiplied by the Al content of the bulk rock can be used to determine whether a rock is "enriched" or "depleted" in nature. Olivine data show that meteorite Y 980459 is a primitive melt from the martian mantle as its olivine crystals are in equilibrium with its bulk rock composition; all other olivine-bearing Shergottites have been affected by fractional crystallization. Pyroxene quadrilateral compositions can be used to isolate the type of melt from which the grains crystallized, and minor element concentrations in pyroxene can lend insight into parent melt compositions. In a comparative planetary mineralogy context, plagioclase from Mars is richer in Na than terrestrial and lunar plagioclase. The two most important factors contributing to this are the low activity of Al in martian melts and the resulting delayed nucleation of plagioclase in the crystallizing rock. Olivine from martian rocks shows distinct trends in Ni-Co and Cr systematics compared with olivine from Earth and Moon. The trends are due to several factors including oxygen fugacity, melt compositions and melt structures, properties which show variability among the planets. Finally, Fe-Mn ratios in both olivine and pyroxene can be used as a fingerprint of planetary parentage, where minerals show distinct planetary trends that may have been set at the time of planetary accretion. Although the silicate mineralogical data alone cannot support one specific model of martian magmatism over another, the data does support the basic igneous reservoirs proposed for Mars, and may also be used to constrain some aspects of specific petrogenetic models. Examples include enriched and depleted reservoirs that can be identified by plagioclase K, Na and Al composition, multivalent element partitioning in olivine and pyroxene (V, Cr) elucidates oxygen fugacity conditions of the reservoirs, and minor element concentrations (i.e., Cr in pyx) show that proposed fractional crystallization models linking Y 980459 to QUE 94201 will not work.

Papike, J. J.; Karner, J. M.; Shearer, C. K.; Burger, P. V.

2009-12-01

415

Bis-GMA/TEGDMA Dental Composites Reinforced with Electrospun Nylon 6 Nanocomposite Nanofibers Containing Highly Aligned Fibrillar Silicate Single Crystals  

PubMed Central

The objective of this research was to study the reinforcement of electrospun nylon 6/fibrillar silicate nanocomposite nanofibers on Bis-GMA/TEGDMA dental composites. The hypothesis was that the uniform distribution of nano-scaled and highly aligned fibrillar silicate single crystals into electrospun nylon 6 nanofibers would improve the mechanical properties of the resulting nanocomposite nanofibers, and would lead to the effective reinforcement of dental composites. The nylon 6/fibrillar silicate nanocomposite nanofibers were crystalline, structurally oriented and had an average diameter of approximately 250 nm. To relatively well distribute nanofibers in dental composites, the nanofiber containing composite powders with a particle structure similar to that in interpenetration networks were prepared first, and then used to make the dental composites. The results indicated that small mass fractions (1 % and 2 %) of nanofiber impregnation improved the mechanical properties substantially, while larger mass factions (4 % and 8 %) of nanofiber impregnation resulted in less desired mechanical properties.

Tian, Ming; Gao, Yi; Liu, Yi; Liao, Yiliang; Xu, Riwei; Hedin, Nyle E.; Fong, Hao

2007-01-01

416

Development of low-cost integrated zeolite collector  

NASA Astrophysics Data System (ADS)

The optimum zeolite loading and the best zeolite for this purpose were determined by careful mathematical analysis, followed by experimental test, to confirm the theoretical results. The integrated collector design was then completed and the collector was constructed. After sealing and vacuum testing the zeolite panels and heat exchanges, the collector was coated with flat black paint and provided with double glazing, aluminum frame and insulation. Preliminary testing indicates close agreement with theoretical predictions of its performance.

Tchernev, D. I.

1981-07-01

417

Random walk theory of reaction kinetics in zeolites  

Microsoft Academic Search

We discuss application of the continuous-time random walk (CTRW) model to studying the kinetics of pseudo-first-order reactions in zeolites. The model includes distance-dependent reaction mechanism, details of the zeolite structure, and dynamics of migration of guest molecules between adsorption sites. Diffuse-reflectance transient-absorption study of triplet anthracene quenching by azulene in NaY zeolite shows that quenching can occur when reactants are

A. V. Barzykin; S. Hashimoto

2000-01-01

418

Large zeolites - Why and how to grow in space  

NASA Technical Reports Server (NTRS)

The growth of zeolite crystals which are considered to be the most valuable catalytic and adsorbent materials of the chemical processing industry are discussed. It is proposed to use triethanolamine as a nucleation control agent to control the time release of Al in a zeolite A solution and to increase the average and maximum crystal size by 25-50 times. Large zeolites could be utilized to make membranes for reactors/separators which will substantially increase their efficiency.

Sacco, Albert, Jr.

1991-01-01

419

Abnormalities of cation movements in 3A zeolite  

Microsoft Academic Search

The dielectric spectra of dehydrated and partially hydrated 3A zeolites with the cation composition of Na6.1K5.9-A were measured to investigate movements of cations in the zeolite (‘A’ stands for the framework of A zeolite). The spectra of dehydrated state showed two relaxations (relax I in the lower frequency side and relax II in the higher frequency side) in the ranges

Tatsuo Ohgushi; Yuya Sakai; Yoshimichi Adachi

420

Polyfuran\\/zeolite LTA composites and adsorption properties  

Microsoft Academic Search

Composites of polyfuran (PFu) with LTA type (3A, 4A, 5A) zeolites were prepared via chemical oxidative polymerization of furan (Fu) in the presence of a dispersion of zeolites (powder) in ACN solvent using anhydrous FeCl3 oxidant at an ambient temperature. The composites were characterized by Fourier transform infrared spectroscopic (FTIR) analysis. FTIR results showed that the composites of 3A zeolite

Songül ?en; Belgin Bardakç?; Ay?e Gül Yavuz; Ay?egül Uygun Gök

2008-01-01

421

Adsorption of CO on LTA zeolite adsorbents: An IR investigation  

Microsoft Academic Search

The low temperature adsorption of CO on the zeolites K-LTA (3A) Na-LTA (4A) and Ca,Na-LTA (5A) has been investigated by IR spectroscopy. For comparison, the adsorption of CO on K-MOR, Na-MOR and Ca-MOR has also been studied. CO adsorption on K-LTA zeolite is mostly limited at the external surface. In the case of Na-LTA zeolite, terminal Na+ carbonyls are formed.

Tania Montanari; Isabel Salla; Guido Busca

2008-01-01

422

Predicting locations of non-framework species in zeolite materials  

Microsoft Academic Search

A new grid-based algorithm developed at Molecular Simulations, and mol