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1

Catalytic dewaxing of oils containing ammonia over highly siliceous porous crystalline materials of the zeolite ZSM-5 type  

SciTech Connect

Straight-chain hydrocarbons and slightly branched chain hydrocarbons are selectively converted utilizing highly siliceous porous crystalline materials of the zeolite type having SiO/sub 2//Al/sub 2/O/sub 3/ ratio of greater than 200, unique molecular sieving properties and superior resistance to ammonia deactivation. The catalyst preferably contains acidic cations and can also contain a component having a hydrogenation/dehydrogenation function. The process of this invention is particularly useful for the dewaxing of hydrocarbon oils, including removal of high freezing point paraffins from jet fuel to lower freezing point, as well as improving the octane rating of naphtha fractions.

Dwyer, F.G.; Garwood, W.E.

1984-04-10

2

An x-ray diffraction study of zeolite-containing metal silicates  

SciTech Connect

An x-ray diffraction study of zeolites and zeolite-containing metal silicates showed that a reaction occurs in the preparation of zeolite-containing systems between the zeolite crystallites and the metal silicate base, which depends on the means of the introduction of the zeolite in the chemical composition of the base and the zeolite.

Mel'nikov, V.B.; Chukin, G.D.; Netedov, B.K.

1986-10-01

3

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

4

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

5

Crystalline silicate dust around evolved stars. III. A correlations study of crystalline silicate features  

Microsoft Academic Search

We have carried out a quantitative trend analysis of the crystalline\\u000asilicates observed in the ISO spectra of a sample of 14 stars with different\\u000aevolutionary backgrounds. We have modeled the spectra using a simple dust\\u000aradiative transfer model and have correlated the results with other known\\u000aparameters. We confirm the abundance difference of the crystalline silicates in\\u000adisk and

F. J. Molster; L. B. F. M. Waters; A. G. G. M. Tielens; C. Koike; H. Chihara

2002-01-01

6

Multitechnique Analysis of the Lattice Structures of Highly Siliceous Zeolites  

Microsoft Academic Search

The combined use of high-resolution solid state NMR techniques (both 1D and 2D) with synchrotron-based powder x-ray diffraction studies yields detailed information on the lattice structures of highly siliceous zeolites. The two methods are complementary, the former probing short range ordering and structures while the latter is sensitive to long range orderings and periodicities.

C. A. Fyfe; H. Gies; G. T. Kokotailo; Y. Feng; H. Strobl; B. Marler; D. E. Cox

1999-01-01

7

Multitechnique Analysis of the Lattice Structures of Highly Siliceous Zeolites  

SciTech Connect

The combined use of high-resolution solid state NMR techniques (both 1D and 2D) with synchrotron-based powder x-ray diffraction studies yields detailed information on the lattice structures of highly siliceous zeolites. The two methods are complementary, the former probing short range ordering and structures while the latter is sensitive to long range orderings and periodicities.

Fyfe, C. A.; Gies, H.; Kokotailo, G. T.; Feng, Y.; Strobl, H.; Marler, B.; Cox, D. E.

1999-08-26

8

Tracking Dust in an Evolving Disk: Implications for Crystalline Silicates  

Microsoft Academic Search

Samples returned from comet Wild 2 by the Stardust mission confirm that when the comet formed it incorporated substantial quantities of crystalline silicates. Crystalline silicates require high processing temperatures and therefore likely originated interior to the comet-forming region. We present numerical models of radial transport of grains combining advection and turbulent diffusion at the disk midplane. We employ one-dimensional disk

Anna L. Hughes; P. J. Armitage

2010-01-01

9

Microprobe study of the surface of a zeolite-containing zirconium-silicate catalyst  

SciTech Connect

X-ray microprobe techniques have been used to study the chemical and phase compositions of a zeolite-containing zirconium-silicate catalyst synthesized by introducing crystallites of the zeolite into the hydrosol and hydrogel of the zirconium silicate. It is shown that dispersion of the zeolite crystallites occurs in this process.

Mel'nikov, V.B.; Chukin, G.D.; Nefedov, B.K.

1987-02-01

10

Crystalline galliosilicate with the zeolite omega structure  

SciTech Connect

This patent describes a process for preparing a crystalline, galliosilicate molecular sieve free of an organic templating agent and having the zeolite omega structure. It comprises mixing a hydrogel free of an organic templating agent and having the following oxide mole ratios of components: SiO{sub 2}/Ga{sub 2}O{sub 3} = 5 to 40, M{sub 2}O/Ga{sub 2}O{sub 3} = 2 to 10, H{sub 2}O/Ga{sub 2}O{sub 3} = 80 to 800 with a galliosilicate solution free of an organic templating agent and substantially free of alumina, the solution having the following oxide mole ratios of components SiO{sub 2}/Ga{sub 2}O{sub 3} = 5 to 30, M{sub 2}O/Ga{sub 2}O{sub 3} = 6 to 20, H{sub 2}O/Ga{sub 2}O{sub 3} = 200 to 800 to form a mixture of the hydrogel and the solution, wherein M is an alkali metal and the mixture has oxide mole ratios of components falling within the same ranges as the oxide mole ratios of components in the hydrogel; and crystallizing the mixture to form a galliosilicate molecular sieve free of an organic templating agent and having the zeolite omega structure.

Occelli, M.L.

1991-07-09

11

Final report on the safety assessment of aluminum silicate, calcium silicate, magnesium aluminum silicate, magnesium silicate, magnesium trisilicate, sodium magnesium silicate, zirconium silicate, attapulgite, bentonite, Fuller's earth, hectorite, kaolin, lithium magnesium silicate, lithium magnesium sodium silicate, montmorillonite, pyrophyllite, and zeolite.  

PubMed

This report reviews the safety of Aluminum, Calcium, Lithium Magnesium, Lithium Magnesium Sodium, Magnesium Aluminum, Magnesium, Sodium Magnesium, and Zirconium Silicates, Magnesium Trisilicate, Attapulgite, Bentonite, Fuller's Earth, Hectorite, Kaolin, Montmorillonite, Pyrophyllite, and Zeolite as used in cosmetic formulations. The common aspect of all these claylike ingredients is that they contain silicon, oxygen, and one or more metals. Many silicates occur naturally and are mined; yet others are produced synthetically. Typical cosmetic uses of silicates include abrasive, opacifying agent, viscosity-increasing agent, anticaking agent, emulsion stabilizer, binder, and suspending agent. Clay silicates (silicates containing water in their structure) primarily function as adsorbents, opacifiers, and viscosity-increasing agents. Pyrophyllite is also used as a colorant. The International Agency for Research on Cancer has ruled Attapulgite fibers >5 microm as possibly carcinogenic to humans, but fibers <5 microm were not classified as to their carcinogenicity to humans. Likewise, Clinoptilolite, Phillipsite, Mordenite, Nonfibrous Japanese Zeolite, and synthetic Zeolites were not classified as to their carcinogenicity to humans. These ingredients are not significantly toxic in oral acute or short-term oral or parenteral toxicity studies in animals. Inhalation toxicity, however, is readily demonstrated in animals. Particle size, fibrogenicity, concentration, and mineral composition had the greatest effect on toxicity. Larger particle size and longer and wider fibers cause more adverse effects. Magnesium Aluminum Silicate was a weak primary skin irritant in rabbits and had no cumulative skin irritation in guinea pigs. No gross effects were reported in any of these studies. Sodium Magnesium Silicate had no primary skin irritation in rabbits and had no cumulative skin irritation in guinea pigs. Hectorite was nonirritating to the skin of rabbits in a Draize primary skin irritation study. Magnesium Aluminum Silicate and Sodium Magnesium Silicate caused minimal eye irritation in a Draize eye irritation test. Bentonite caused severe iritis after injection into the anterior chamber of the eyes of rabbits and when injected intralamellarly, widespread corneal infiltrates and retrocorneal membranes were recorded. In a primary eye irritation study in rabbits, Hectorite was moderately irritating without washing and practically nonirritating to the eye with a washout. Rats tolerated a single dose of Zeolite A without any adverse reaction in the eye. Calcium Silicate had no discernible effect on nidation or on maternal or fetal survival in rabbits. Magnesium Aluminum Silicate had neither a teratogenic nor adverse effects on the mouse fetus. Female rats receiving a 20% Kaolin diet exhibited maternal anemia but no significant reduction in birth weight of the pups was recorded. Type A Zeolite produced no adverse effects on the dam, embryo, or fetus in either rats or rabbits at any dose level. Clinoptilolite had no effect on female rat reproductive performance. These ingredients were not genotoxic in the Ames bacterial test system. In primary hepatocyte cultures, the addition of Attapulgite had no significant unscheduled DNA synthesis. Attapulgite did cause significant increases in unscheduled DNA synthesis in rat pleural mesothelial cells, but no significant increase in sister chromosome exchanges were seen. Zeolite particles (<10 microm) produced statistically significant increase in the percentage of aberrant metaphases in human peripheral blood lymphocytes and cells collected by peritoneal lavage from exposed mice. Topical application of Magnesium Aluminum Silicate to human skin daily for 1 week produced no adverse effects. Occupational exposure to mineral dusts has been studied extensively. Fibrosis and pneumoconiosis have been documented in workers involved in the mining and processing of Aluminum Silicate, Calcium Silicate, Zirconium Silicate, Fuller's Earth, Kaolin, Montmorillonite, Pyrophyllite, and Zeolite. The Cosmetic Ingre

Elmore, Amy R

2003-01-01

12

The Crystalline Fraction Of Interstellar Silicates In Starburst Galaxies  

NASA Astrophysics Data System (ADS)

We present a model using the evolution of the stellar population in a starburst galaxy to predict the crystallinity of the silicates in the interstellar medium of this galaxy. We take into account dust production in stellar ejecta, and amorphization and destruction in the interstellar medium and find that a detectable amount of crystalline silicates may be formed using relatively extreme input parameters. We discuss the effect of dust destruction and amorphisation of supernovae, and the relatively low dust-production efficiency of supernovae, and find that when taking this into account, crystallinity in the interstellar medium becomes hard to detect. Levels of 6.5-13% crystallinity in the interstellar medium of Ultraluminous Infrared Galaxies have been observed (Spoon et al. 2006, ApJ 638, 759). We conclude that not all these crystalline silicates can be of stellar (e.g. starburst related) origin, and additional crystallisation must be asociated with AGN activity.

Kemper, Francisca; Markwick, A. J.; Woods, P. M.

2011-01-01

13

Multiple episodes of zeolite deposition in fractured silicic tuff  

SciTech Connect

Fractures in silicic tuffs above the water table at Yucca Mountain, Nevada, USA contain two morphologies of heulandite with different compositions. Tabular heulandite is zoned, with Sr-rich cores and Mg-rich rims. Later prismatic heulandite is nearly the same composition as the more magnesian rims. Heulandite and stellerite may occur between layers of calcite, and calcite occurs locally between generations of heulandite. Thermodynamic modeling, using estimated thermodynamic data and observed chemical compositions for heulandite and stellerite, shows that stellerite is the favored zeolite unless Ca concentrations are reduced or Mg and/or Sr concentrations are significantly elevated above current Yucca Mountain waters.

Carlos, B.A.; Chipera, S.J.; Snow, M.G.

1995-04-01

14

Amorphous to crystalline transition of magnesium silicate and silica nanoparticles  

NASA Astrophysics Data System (ADS)

Amorphous magnesium silicate and silica nanoparticles (smoke) have been transformed into the crystalline state by the process of thermal annealing. It has been shown that the magnesium silicate smoke evolves 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. Amorphous silica nanoparticles have been annealed at 1220 K and are characterized by distinctly lower rates of thermal evolution compared to the magnesium silicates. Silica changed into cristobalite and tridymite.

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

2000-11-01

15

Crystalline oxyfluorinated open-framework compounds: Silicates, metal phosphates, metal fluorides and metal-organic frameworks (MOF)  

Microsoft Academic Search

This contribution is dedicated to a short overview on the utilization of fluorine for the preparation of crystalline microporous frameworks including different families of solids: zeolites, metal phosphates and metal-organic frameworks (MOF-type). Beside the silicates compounds, this presentation is focused on the different types of fluorinated aluminum or gallium phosphates hydrothermally obtained in the presence of organic structure-directing agent or

Thierry Loiseau; Gérard Férey

2007-01-01

16

An ordered mesoporous aluminosilicate with completely crystalline zeolite wall structure.  

PubMed

An ordered mesoporous aluminosilicate with completely crystalline zeolite pore wall structure, denoted as OMZ-1, was successfully synthesized by recrystallization of SBA-15 using in situ formed CMK-5 as the hard template. The role of carbon material not only serves as a hard template to preserve ordered mesoporous structure but also kinetically controls the crystallization process to form large crystals. PMID:16910631

Fang, Yunming; Hu, Haoquan

2006-08-23

17

Crystalline-amorphous transition in silicate perovskites  

Microsoft Academic Search

CaSiO3 and MgSiO3 perovskites are known to undergo solid-state crystal to amorphous transitions near ambient pressure when decompressed from their high-pressure stability fields. In order to elucidate the mechanistic aspects of this transition we have performed detailed molecular-dynamics simulations and lattice-dynamical calculations on model silicate perovskite systems using empirical rigid-ion pair potentials. In the simulations at low temperatures, the model

Mahin Hemmati; Andrew Chizmeshya; George H. Wolf; Peter H. Poole; Jun Shao; C. Austen Angell

1995-01-01

18

The leading role of association in framework modification of highly siliceous zeolites with adsorbed methylamine.  

PubMed

Affinity index (AT value), adsorption heat, X-ray diffraction (XRD), and 13C and 29Si magic-angle spinning (MAS) NMR, FTIR, and Raman spectroscopies were used to study the interaction of highly siliceous MFI-, FAU-, and FER-type zeolites with adsorbed methylamine (MA). Compared with the data for methanol, the much higher AT values and adsorption heats, and significant changes in XRD patterns, 29Si MAS NMR spectra, and FTIR spectra for the zeolites after adsorption of MA, revealed a strong hydrogen-bonding interaction between the perfect framework of the zeolites and the adsorbed MAs. This interaction results from the fact that the H atom of the amine group attacks the [Si-O] framework to form a Si-OHN bond, which leads to the appearance of Si-N bonds in the zeolites at 323 K. Therefore, the zeolite framework can be modified with MA under mild conditions. The highly siliceous MFI zeolite and the H-ZSM-5 zeolite with SiO2/Al2O3=31:1 were modified with MA and investigated by temperature-programmed desorption of CO2. The modified zeolites exhibited greatly enhanced basic properties in comparison with those of the raw materials. The influence of defects in the zeolite on the adsorption and the interaction with MA is discussed. PMID:16456902

Han, Ai-Jie; Guo, Juan; Yu, Hui; Zeng, Yu; Huang, Yue-Fang; He, He-Yong; Long, Ying-Cai

2006-03-13

19

INTERSTELLAR SILICATE DUST IN THE z = 0.89 ABSORBER TOWARD PKS 1830-211: CRYSTALLINE SILICATES AT HIGH REDSHIFT?  

SciTech Connect

We present evidence of a >10{sigma} detection of the 10 {mu}m silicate dust absorption feature in the spectrum of the gravitationally lensed quasar PKS 1830-211, produced by a foreground absorption system at redshift 0.886. We have examined more than 100 optical depth templates, derived from both observations of Galactic and extragalactic sources and laboratory measurements, in order to constrain the chemical structure of the silicate dust. We find that the best fit to the observed absorption profile is produced by laboratory crystalline olivine, with a corresponding peak optical depth of {tau}{sub 10} = 0.27 {+-} 0.05. The fit is slightly improved upon by including small contributions from additional materials, such as silica, enstatite, or serpentine, which suggests that the dust composition may consist of a blend of crystalline silicates. Combining templates for amorphous and crystalline silicates, we find that the fraction of crystalline silicates needs to be at least 95%. Given the rarity of extragalactic sources with such a high degree of silicate crystallinity, we also explore the possibility that the observed spectral features are produced by amorphous silicates in combination with other molecular or atomic transitions, or by foreground source contamination. While we cannot rule out these latter possibilities, they lead to much poorer profile fits than for the crystalline olivine templates. If the presence of crystalline interstellar silicates in this distant galaxy is real, it would be highly unusual, given that the Milky Way interstellar matter contains essentially only amorphous silicates. It is possible that the z = 0.886 absorber toward PKS 1830-211, well known for its high molecular content, has a unique star-forming environment that enables crystalline silicates to form and prevail.

Aller, Monique C.; Kulkarni, Varsha P.; Som, Debopam [Department of Physics and Astronomy, University of South Carolina, 712 Main Street, Columbia, SC 29208 (United States); York, Donald G.; Welty, Daniel E. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 (United States); Vladilo, Giovanni, E-mail: ALLERM@mailbox.sc.edu [Osservatorio Astonomico di Trieste, Via Tiepolo 11, 34143 Trieste (Italy)

2012-03-20

20

Measurement of zeolite, silicate, and phosphate in laundry detergent products by inductively coupled plasma atomic emission spectrometry  

Microsoft Academic Search

This paper reports the development of a method for simultaneously measuring zeolite, silicate, and phosphate in laundry detergent\\u000a products by inductively coupled plasma atomic emission spectrometry. A sample is decomposed under alkaline oxidative conditions\\u000a to decompose zeolite, silicate, phosphate, and organic substances. Then hydrochloric acid is added to the decomposed solution\\u000a to dissolve aluminum hydroxide precipitate before analysis. This sample

Akihiko Kawauchi; Masahiro Ishida

1996-01-01

21

Radiation and thermal effects on zeolites, smectites and crystalline silicotitanates  

NASA Astrophysics Data System (ADS)

Long-term radiation and thermal effects on materials in the near-field of a nuclear waste repository have been evaluated using accelerated laboratory experiments by energetic electron or ion beam irradiations. The materials studied include: zeolites, smectites, and crystalline silicotitanates (CST). In situ transmission electron microscopy (TEM) during irradiation by 200 keV electrons has shown that all of the studied materials are susceptible to radiation-induced amorphization. At room temperature, complete amorphization was observed after ionizing doses of 1010˜10 12 Gy or displacement doses of ˜0.1 dpa. The critical amorphization dose increased with temperature for CST. A peak amorphization dose was found at ˜400°C for the smectites. A new experimental approach was developed using a combination of proton irradiation, TEM, and electron microprobe analysis techniques to overcome the difficulties in studying the chemical properties in the radiation-damaged region. A clear correlation between the structural damage and changes in ion-exchange and desorption capacities has been established for zeolite-Y, which maybe useful for predicting the long-term behavior of the near-field materials in a nuclear waste repository. Radiation-induced decrease in the release rate of radionuclides has been observed for the first time in the damaged materials, indicating that the structural damage in near-field materials may be beneficial for retarding the release of radionuclides from geologic disposal repository into biosphere. Possible mechanisms for radiation-induced changes in structure, ion exchange and desorption capacities have been proposed.

Gu, Binxi

22

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

23

Differences Between Charge Trapping States in Irradiated NanoCrystalline HfO2 and Non-Crystalline Hf Silicates  

Microsoft Academic Search

This paper provides an explanation for qualitative differences between radiation-induced charge trapping states in nano-crystalline HfO 2 and non-crystalline Hf silicate alloys in high-kappa gate stacks by combining electrical measurements with spectroscopic studies and theory. Differences in the observed electrical response to X-ray and gamma-ray irradiation are consistent with fundamental differences in electronic structures between high-kappa dielectrics that are nano-crystalline

G. Lucovsky; D. M. Fleetwood; S. Lee; H. Seo; R. D. Schrimpf; J. A. Felix; J. Lning; L. B. Fleming; M. Ulrich; D. E. Aspnes

2006-01-01

24

Comet Samples Returned by Stardust, Insight into the Origin of Comets and Crystalline Silicates in Disks  

Microsoft Academic Search

The comet samples returned by the NASA Stardust mission contain abundant crystalline silicates that are very similar to inner solar materials found in primitive asteroidal meteorites. Isotopic compositions indicate that the bulk of the silicates from comet Wild 2 formed in the solar nebula and that the pre-solar content is less than in primitive meteorites. It appears that the bulk

D. E. Brownlee; D. Joswiak; G. Matrajt; P. Tsou

2009-01-01

25

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

26

Cooked Gems Insights into the Hot Origin of Crystalline Silicates in Circumstellar Disks and the Cold Orgin Gems.  

National Technical Information Service (NTIS)

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 circums...

D. E. Brownless D. J. Joswiak J. P. Bradley

2005-01-01

27

X-Ray Emission Spectroscopy Study of Iron Silicate Catalyst FeZSM-5.  

National Technical Information Service (NTIS)

Iron silicate analogs of the zeolite ZMS-5 may be directly synthesized from iron silicate gels in a manner which differs slightly from the alumino-silicate ZSM-5. The resultant white, crystalline iron silicate is referred to as FeZSM-5 in the as-synthesiz...

R. Csencsits C. E. Lyman R. Gronsky

1988-01-01

28

Discovery of Crystalline Silicates in Comet C\\/2001 Q4 (NEAT)  

Microsoft Academic Search

We present the 10 mum silicate feature of the dynamically new Oort Cloud comet C\\/2001 Q4 (NEAT) 5 days prior to perihelion (rh=0.97 AU, Delta=0.35 AU, 2004 May 11.25 and 11.30 UT) observed with the NASA Ames HIFOGS spectrophotometer. The silicate feature of comet Q4 contains strong crystalline peaks at 10.0 and 11.2 mum, along with weaker peaks at 9.3,

Diane H. Wooden; Charles E. Woodward; David E. Harker

2004-01-01

29

Hydrothermal synthesis and characterization of copper containing crystalline silicate mesoporous materials from gel mixture  

Microsoft Academic Search

Novel copper-containing crystalline silicate mesoporous materials (SCMM) have been synthesized by the hydrothermal treatment of slurries of silicon–magnesium–copper hydroxide precipitates along with quaternary ammonium salt. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed a house-of-cards type structure consists of very thin platy silicates. Nitrogen adsorption–desorption isotherms of calcined material show that it has a high surface area (?550 m2

M Chatterjee; T Iwasaki; Y Onodera; H Hayashi; Y Ikushima; T Nagase; T Ebina

2004-01-01

30

[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

31

Methodology for synthesizing crystalline metallosilicates with expanded pore windows through molecular alkoxysilylation of zeolitic lamellar precursors.  

PubMed

Postalkoxysilylation with diethoxydimethylsilane has been carried out on the zeolitic lamellar precursors of various topologies such as MWW, FER, CDO and MCM-47 aiming to construct new crystalline structures with expanded pore apertures between the layers. The silylation process and the crystalline and pore structures of the resulting materials have been investigated with the techniques of XRD, IR, (13)C and (29)Si MAS NMR, ICP, SEM, HRTEM, elemental analyses, and N 2 adsorption. In contrast to forming known three-dimensional zeolite structures after direct calcination of the lamellar precursors, the silylation led to new crystalline structures with opener pores, as evidenced by the shift of layer-related diffractions to the lower-angle region in XRD patterns and the enlarged interlayer pores found by HRTEM images. After optimizing the treatment conditions, particularly the amount of silane agent, a maximum and homogeneous silylation was realized, which guaranteed the phase purity in interlayer expanded zeolites. The expanded structures were well preserved after calcination at 823 K or reflux in water for 1 to 2 weeks, indicating a high thermal stability and also a hydrothermal stability. The interlayer expanded zeolites prepared from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and solid acid-catalyzed reactions of bulky molecules than that of their counterparts with conventional MWW topology. PMID:18528990

Wu, Peng; Ruan, Juanfang; Wang, Lingling; Wu, LeiLei; Wang, Yong; Liu, Yueming; Fan, Weibin; He, Mingyuan; Terasaki, Osamu; Tatsumi, Takashi

2008-06-04

32

Polycyclic Aromatic Hydrocarbons and Crystalline Silicates in the Bipolar Post-Asymptotic Giant Branch Star IRAS 16279-4757  

Microsoft Academic Search

IRAS 16279-4757 belongs to a group of post-asymptotic giant branch (post-AGB) stars showing both polycyclic aromatic hydrocarbon (PAH) bands and crystalline silicates. We present mid-infrared images that resolve the object for the first time. The morphology is similar to that of the ``Red Rectangle'' (HD 44179), the prototype object with PAHs and crystalline silicates. A two-component model and images suggest

M. Matsuura; A. A. Zijlstra; F. J. Molster; S. Hony; L. B. F. M. Waters; F. Kemper; J. E. Bowey; H. Chihara; C. Koike; L. P. Keller

2004-01-01

33

Carbonate versus silicate weathering in the Raikhot watershed within the High Himalayan Crystalline Series  

NASA Astrophysics Data System (ADS)

The major element and Sr isotope geochemistry of surface waters, bedrock, and river sands was investigated in the Raikhot watershed within the High Himalayan Crystalline Series (HHCS) in northern Pakistan. Mass-balance calculations of mineral-weathering contributions to the dissolved flux of ions from the watershed indicate that 82% of the HCO3- flux is derived from the weathering of carbonate minerals and only 18% is derived from silicate weathering, even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only ˜1% carbonate in the watershed. This study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds. We suggest that the flux of Sr with a high 87Sr/86Sr ratio in the major Himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate HHCS. Models that use the flux of radiogenic Sr from the Himalayas as a proxy for silicate weathering rates may, therefore, overestimate the amount of CO2 consumption due to silicate weathering in the Himalaya.

Blum, Joel D.; Gazis, Carey A.; Jacobson, Andrew D.; Page Chamberlain, C.

1998-05-01

34

Crystalline Silicates and Dust Processing in the Protoplanetary Disks of the Taurus Young Cluster  

NASA Astrophysics Data System (ADS)

We characterize the crystalline-silicate content and spatial distribution of small dust grains in a large sample of protoplanetary disks in the Taurus-Auriga young cluster, using the Spitzer Space Telescope mid-IR spectra. In turn we use the results to analyze the evolution of structure and composition of these 1-2 Myr old disks around Solar- and later-type young stars, and test the standard models of dust processing which result in the conversion of originally amorphous dust into minerals. We find strong evidence of evolution of the dust-crystalline mass fraction in parallel with that of the structure of the disks, in the sense that increasing crystalline mass fraction is strongly linked to dust settling to the disk midplane. We also confirm that the crystalline silicates are confined to small radii, r lsim 10 AU. However, we see no significant correlation of crystalline mass fraction with stellar mass or luminosity, stellar-accretion rate, disk mass, or disk/star mass ratio, as would be expected in the standard models of dust processing based upon photoevaporation and condensation close to the central star, accretion-heating-driven annealing at r lsim 1 AU, or spiral-shock heating at r lsim 10 AU, with or without effective large-scale radial mixing mechanisms. Either another grain-crystallizing mechanism dominates over these, or another process must be at work within the disks to erase the correlations they produce. We propose one of each sort that seems to be worth further investigation, namely X-ray heating and annealing of dust grains, and modulation of disk structure by giant-planetary formation and migration.

Watson, Dan M.; Leisenring, Jarron M.; Furlan, Elise; Bohac, C. J.; Sargent, B.; Forrest, W. J.; Calvet, Nuria; Hartmann, Lee; Nordhaus, Jason T.; Green, Joel D.; Kim, K. H.; Sloan, G. C.; Chen, C. H.; Keller, L. D.; d'Alessio, Paola; Najita, J.; Uchida, Keven I.; Houck, J. R.

2009-01-01

35

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

36

Chemically feasible hypothetical crystalline networks  

Microsoft Academic Search

Our systematic enumeration of 4-connected crystalline networks (that is, networks in which each atom is connected to exactly four neighbours) used recent advances in tiling theory to evolve over 900 topologies. The results are relevant to the structures of zeolites and other silicates, aluminophosphates (AlPOs), oxides, nitrides, chalcogenides, halides, carbon networks, and even to polyhedral bubbles in foams. Given their

Martin D. Foster; Alexandra Simperler; Robert G. Bell; Olaf Delgado Friedrichs; Filipe A. Almeida Paz; Jacek Klinowski

2004-01-01

37

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

38

Destruction of Massive Fragments in Protostellar Disks and Crystalline Silicate Production  

NASA Astrophysics Data System (ADS)

We present a mechanism for the crystalline silicate production associated with the formation and subsequent destruction of massive fragments in young protostellar disks. The fragments form in the embedded phase of star formation via disk fragmentation at radial distances gsim50-100 AU and anneal small amorphous grains in their interior when the gas temperature exceeds the crystallization threshold of ~800 K. We demonstrate that fragments that form in the early embedded phase can be destroyed before they either form solid cores or vaporize dust grains, thus releasing the processed crystalline dust into various radial distances from sub-AU to hundred-AU scales. Two possible mechanisms for the destruction of fragments are the tidal disruption and photoevaporation as fragments migrate radially inward and approach the central star and also dispersal by tidal torques exerted by spiral arms. As a result, most of the crystalline dust concentrates to the disk inner regions and spiral arms, which are the likely sites of fragment destruction.

Vorobyov, Eduard I.

2011-02-01

39

An electrokinetic study on a synthetic adsorbent of crystalline calcium silicate hydrate and its mechanism of endotoxin removal  

Microsoft Academic Search

A synthetic, disposable adsorbent of crystalline calcium silicate hydrate, LRA® product by Advanced Minerals Corp., has been found highly effective for endotoxin removal from aqueous solutions. Endotoxin removal by this adsorbent is greatly enhanced by the addition of an electrolyte, such as NaCl or Tris–HCl. The electrophoretic method has been used to study the mechanism of endotoxin adsorption. In many

Qun Wang; John P. Zhang; Timothy R. Smith; William E. Hurst; Thomas Sulpizio

2005-01-01

40

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

2013-05-30

41

Synthesis and properties of crystalline silver nanoparticles supported in natural zeolite chabazite  

NASA Astrophysics Data System (ADS)

A simple, low-temperature, hydrothermal method for the synthesis of silver nanoparticles supported on the surfaces of the natural zeolite chabazite has been developed. The synthesis method includes two ion exchange processes: the first is a conditioning process to exchange the natural cations included in the chabazite tuff with NH4 ions, and the second exchanges the latter ions with silver. The precipitation of silver nanoparticles is achieved by thermal annealing of the silver-exchanged chabazite at 400 °C for 1 h. The samples were studied with X-ray diffraction, Fourier-transform infrared spectroscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and diffuse reflectance spectroscopy. The results show the presence of both silver cations and nanoparticles in the chabazite matrix, the silver nanoparticles being located at the surface of the chabazite microcrystals. The silver nanoparticles are crystalline with an average size of 8 nm and show cube-truncated shapes. The absorption spectra of the silver nanoparticles display several plasmon resonance transitions due to their geometry. The silver-supporting chabazite powders have bactericide properties against several types of bacteria as was shown by the inhibition of bacteria growth on conventional agar medium.

Flores-López, N. S.; Castro-Rosas, J.; Ramírez-Bon, R.; Mendoza-Córdova, A.; Larios-Rodríguez, E.; Flores-Acosta, M.

2012-11-01

42

Zealous zeolites  

SciTech Connect

Zeolites have made significant inroads in fluid cracking catalysts for gasoline and have pushed phosphates out of laundry detergents. But these crystalline aluminosilicate structures are just beginning to make their mark in chemical processes and environmental applications. Ideally suited for work as molecular sieves and catalysts, zeolites sport uniform surface pores and channels that are receptive only to molecules of a specific size and shape. This high selectivity makes zeolites a good alterative to some of the conventional products used for chemical reaction and filtration. One of the most potentially lucrative markets for zeolites is chemical catalyst replacements for liquid acids, such as hydrofluoric acid and sulfuric acid, and aluminum chloride in a number of alkylation and acrylation reactions. Zeolites are also being considered for oligomerization,isomerization, amination and condensation processes for the manufacture of chemical intermediates. The paper discusses the market and manufacturers of zeolites, justifying the cost of converting to zeolite catalysts, and natural zeolites.

Hairston, D.W.

1996-07-01

43

Diffusive characterization of large pore mesoporous materials with semi- crystalline zeolitic framework  

Microsoft Academic Search

Diffusion (kinetics) characterization of composite mesoporous materials that contain nano- zeolite particles in the mesoporous walls (UL-zeolite) is considered very important to further assess their potential as unique materials for separation and catalysis. Two different bimodal materials were investigated using two probe molecules, i.e., n-heptane and toluene of different kinetic diameter. Results showed varied behavior with respect to diffusion rates,

H. V. Thang; A. Malekian; M. Ei?; D. Trong On; S. Kaliaguine

2003-01-01

44

Catalytic properties of crystalline titanium silicalites. 1. Synthesis and characterization of titanium-rich zeolites with MFI structure  

SciTech Connect

Crystalline titanium silicalites with the MFI structure and high titanium content (Si/Ti{double bond}10) have been prepared using improved synthesis procedures. The monoclinic lattice symmetry of silicalite-1 changes to orthorhombic on introduction of titanium. The titanium silicalites retain their orthorhombic symmetry even after calcination in air. On progressive incorporation of titanium, (1) the unit cell dimensions and volume (from XRD) increase linearly, (2) the crystal size decreases progressively, (3) the intensity of the framework IR band at 960 cm{sup {minus}1} increases, (4) a band around 47,000 c{sup {minus}1} appears in the electronic spectra due to charge transfer transitions involving Ti(IV) sites, (5) the hydrophilicity of the zeolite (from water adsorptions measurements) increases, (6) the adsorption capacity for cyclohexane increases, (7) the {sup 29}Si MAS NMR lines exhibit progressive broadening, and finally (8) the catalytic activity in the hydroxylation of phenol to catechol and hydroquinone also increases markedly. Based on these observations, it is concluded that a significant fraction of titanium in these samples is situated in framework positions. The catalytic properties of these well-defined titanium-modified zeolites will be described in more detail in the subsequent parts of this series.

Thangaraj, A.; Kumar, R.; Mirajkar, S.P.; Ratnasamy, P. (National Chemical Lab., Pune (India))

1991-07-01

45

Review of the thermal stability and cation exchange properties of the zeolite minerals clinoptilolite, mordenite, and analcime; applications to radioactive waste isolation in silicic tuff  

SciTech Connect

Silicic tuffs of the southern Great Basin and basalts of the Columbia River Plateau are under investigation as potential host rocks for high- and intermediate-level radioactive wastes. Nonwelded and partially welded tuffs may contain major amounts (> 50%) of the zeolite minerals clinoptilolite, mordenite, and analcime. Densely welded tuffs and some basalt flows may contain clinoptilolite as fracture filling that limits the permeability of these rocks. The cation exchange properties of these zeolite minerals allow them to pose a formidable natural barrier to the migration of cationic species of various radionuclides in aqueous solutions. However, these minerals are unstable at elevated temperatures and at low water-vapor pressures and may break down either by reversible dehydration or by irreversible mineralogical reactions. All the breakdown reactions occurring at increased temperature involve a net volume reduction and evolution of fluids. Thus, they may provide a pathway (shrinkage fractures) and a driving force (fluid pressure) for release of radionuclides to the biosphere. These reactions may be avoided by keeping zeolite-bearing horizons saturated with water and below about 85{sup 0}C. This may restrict allowable gross thermal loadings in waste repositories in volcanic rocks.

Smyth, J.R.; Caporuscio, F.A.

1981-06-01

46

Steps toward interstellar silicate mineralogy. VI. Dependence of crystalline olivine IR spectra on iron content and particle shape  

NASA Astrophysics Data System (ADS)

Crystalline olivines are an important component of silicate dust particles in space. ISO observations revealed the presence of crystalline silicates in comets, protoplanetary accretion disks, and outflows from evolved stars. For the interpretation of astronomical spectra, the relevant material data at a variety of temperatures and over a broad wavelength range, are urgently needed. In contrast to this need, optical properties of the astronomically interesting olivines are scarcely available at present. In order to close this gap, we studied the optical properties of three minerals of the olivine group by reflection spectroscopy on single crystals in the infrared spectral range. We measured the iron endmember (fayalite, Fe2SiO4), an Mg-rich olivine (Mg1.9Fe0.1SiO4), and the magnesium endmember (forsterite, Mg2SiO4) of the (Mg,Fe)2SiO4 series. For a direct comparison with astronomical observations, we present calculated mass absorption coefficients in the Rayleigh limit for different shapes and varying iron content of the dust particles. The laboratory data together with a set of ISO data for envelopes around evolved stars (Molster 2000) are used to constrain the properties of circumstellar silicates. We find that essentially all band positions are shifted to larger wavelengths with increasing iron content. The particle shape influences very significantly the strong bands such as the B1u:nu3 mode that appears as the ``11.4 mu m'' band of forsterite, whereas e.g. the two FIR modes longward of 40 mu m remain practically unaffected by the particle shape but shift due to increasing iron content. The comparison with the band positions in ISO spectra points to the presence of olivine crystals strongly elongated along the crystallographic c-axis. In addition, we apply the calculated mass absorption coefficients to evaluate transmission measurements of particles embedded in a matrix - a technique which is frequently used in laboratory astrophysics. All data shown in this paper will be made available in digital form via the electronic database http://www.astro.uni-jena.de.

Fabian, D.; Henning, T.; Jäger, C.; Mutschke, H.; Dorschner, J.; Wehrhan, O.

2001-10-01

47

Elucidation of the role of potassium fluoride in the chemical and physical nature of ZSM-5 zeolite  

Microsoft Academic Search

This investigation synthesized the ZSM-5 zeolite using sodium silicate, aluminum sulfate and tetrapropylammonium bromide. In addition to examining how the KF additive affected the crystal structure, crystallinity, crystal size and crystal morphology by XRPD and SEM measurements, this work investigated how the KF additive affected the specific surface area, Al contents and zeolite framework through BET, ICP-MS, SIMS, 29Si, 27Al-MAS

Jun-An Ke; Ikai Wang

2001-01-01

48

Crystalline and electronic structures of lithium silicates: A density functional theory study  

NASA Astrophysics Data System (ADS)

Lithium silicates, such as Li2SiO3 and Li4SiO4, are considered as favorable candidates for the tritium breeding materials of a deuterium-tritium type nuclear fusion reactor. Their bulk structural and electronic properties are investigated using pseudopotential plane wave (PPW) method within density functional theory (DFT). The optimized crystal structure parameters are well consistent with the experimental results. The results indicate that Li2SiO3 and Li4SiO4 are insulators with band gaps of about 5.36 and 5.53 eV, respectively. The valence electrons density of state reveal the covalency properties mainly resulting from the overlapping of O 2p and Si 3p orbital electrons in both lithium silicates. The nonbridging O (NBO) atoms and bridging O (BO) atoms of Li2SiO3 exhibit significantly different electron distributions. The Si 3s and 3p hybridization is observed in Li2SiO3, but not in Li4SiO4. The mechanical elastic constants reflected Li4SiO4 might be unstable in some degrees.

Tang, Tao; Chen, Piheng; Luo, Wenhua; Luo, Deli; Wang, Yu

2012-01-01

49

Characterization of the structural and electronic properties of crystalline lithium silicates  

SciTech Connect

Structures of several lithium silicate crystals were fully optimized by minimizing the total energy with respect to atom position and lattice parameters using density functional theory (DFT) calculations within the generalized gradient approximation (GGA). Electronic density of states and atomic charges were calculated on the optimized structures. The relative stability of two forms of lithium disilicate determined from density functional theory calculations agree well with experimental results. Partial electronic density of states of different elements and crystallographical sites were determined. The results show bridging and non-bridging oxygen (oxygen ions that bond to two or one silicon ions, respectively) have distinguishable contributions to the oxygen 2s and upper valence bands. Hirshfeld and Bader population analysis were performed to obtain atomic charges of the crystals. Combining the understanding of the silicate crystal chemistry, we found that the Hirshfeld method correctly predicts relative charges of bridging and non-bridging oxygen ions thus provide additional evidence that the Hirshfeld charges better represent the bond ionicity of the silicon-oxygen bonds.

Du, Jincheng; Corrales, Louis R.

2006-10-14

50

Methyl rotational tunneling dynamics of p-xylene confined in a crystalline zeolite host  

NASA Astrophysics Data System (ADS)

The methyl rotational tunneling spectrum of p-xylene confined in nanoporous zeolite crystals has been measured by inelastic neutron scattering (INS) and proton nuclear magnetic resonance (NMR), and analyzed to extract the rotational potential energy surfaces characteristic of the methyl groups in the host-guest complex. The number and relative intensities of the tunneling peaks observed by INS indicate the presence of methyl-methyl coupling interactions in addition to the methyl-zeolite interactions. The INS tunneling spectra from the crystals (space group P212121 with four crystallographically inequivalent methyl rotors) are quantitatively interpreted as a combination of transitions involving two coupled methyl rotors as well as a transition involving single-particle tunneling of a third inequivalent rotor, in a manner consistent with the observed tunneling energies and relative intensities. Together, the crystal structure and the absence of additional peaks in the INS spectra suggest that the tunneling of the fourth inequivalent rotor is strongly hindered and inaccessible to INS measurements. This is verified by proton NMR measurements of the spin-lattice relaxation time which reveal the tunneling characteristics of the fourth inequivalent rotor.

Nair, Sankar; Dimeo, Robert M.; Neumann, Dan A.; Horsewill, Anthony J.; Tsapatsis, Michael

2004-09-01

51

Fluorine-19 NMR Results on Crystalline Models for Fluoride Sites in Silicate and Aluminosilicate Glasses and Melts.  

NASA Astrophysics Data System (ADS)

As part of an ongoing effort to apply Fluorine-19 NMR to understanding the effects of fluoride on the structures and properties of silicate glasses and melts, the local environment of fluorine anions in several fluorosilicate and fluoroaluminate crystals and silicate glasses has been explored using F-19 MAS NMR. A compilation of this work with recent F-19 NMR chemical shift data has yielded several trends in the chemical shift. The chemical shift generally increases with the radius of the adjoining cation, which is qualitatively similar to the trends for oxygen anions in simple metal oxides and chlorine anions in crystalline chlorides. This effect was less pronounced in the fluoroaluminates and fluorosilicates (about 220 ppm from NaF to CsF versus about 60 ppm from Na2SiF6 to Cs2SiF6), implying that the strong bond to the Al or Si dominates the electron distribution around the fluorine anion. Another effect on the chemical shift was the coordination number of the fluorine, although it was difficult to establish a simple relationship between coordination number and chemical shift. In F-La(n) and F-Ca(n) sites (where "n" is the coordination number), increasing the coordination of the fluorine atom shifts the chemical shift to lower frequencies. In Na, Ca, and Ba fluoroaluminates, however, increasing coordination in Al-F-M(n) sites (where "M" is the coordinating cation) increases the chemical shift. The latter is also observed in Al-F-Al sites in Ba fluoroaluminates; as the number of coordinating Ba atoms increased, the position of peak maximum increased from -173 to -145.9 ppm. This may not have been due solely to the increasing coordination by Ba atoms, however, since the Al-F-Al bond angle decreases as the number of surrounding cations increases. Using this compilation of crystalline model compound F-19 peak positions, we were able to analyze spectra for several silicate and aluminosilicate glasses and identify the coordination environments of the fluorine anions. The major feature in the barium silicate glass spectrum is a broad peak (at -19 ppm) near that of crystalline BaF2 (-15 ppm). This implies that the Ba silicate glass contains a similar coordination environment as BaF2 (F-Ba(4)) but with a range of bond lengths and, possibly, coordination numbers. A low intensity shoulder at -131 ppm was attributed to the structural unit Si-F-Ba(n) due to its proximity to the Si-F-Ba(2) site in crystalline BaSiF6 ( -112 ppm). The main feature in the Ba aluminosilicate glass overlapped the ranges for Al-F-Ba(n), Si-F-Ba(n), and Al-F-Al structural units, so assignment of this peak to a particular structural unit is impossible. However, it is possible to say that this glass has a minimal amount of F-Ba(n) structural units. The studied Ca aluminosilicate glass contains a different fluorine environment than the Ba aluminosilicate. Our data for Ca aluminosilicate glass corroborates previous work on glasses of this composition, with the major feature of the spectrum (-152 ppm) within the observed range for Al-F-Ca(n) structural units (-143 to -154 ppm). There was also an unresolved shoulder centered at -126 ppm near the ranges of Si-F-Ca(n) (-123.4 to -134.5 ppm) and F-Ca(n) (-104 to -112.4 ppm) structural units. An additional intensity in the higher frequency spinning sidebands also suggests a considerable contribution from sites similar to those found in the Ca silicate glass (F-Ca(n) sites). The presence of F-M(n) sites in the Ca aluminosilicate but not in the Ba aluminosilicate suggests that the higher field strength cation can more effectively compete with Al cations for bonding with F anions. This supports previous conclusions about partial ordering of F anions around higher field strength cations.

Kiczenski, T. J.; Stebbins, J. F.

2001-12-01

52

Influence of aluminum content, crystallinity and crystallite size of zeolite Pd\\/H-ZSM-5 on the catalytic performance in the dehydroalkylation of toluene with ethane  

Microsoft Academic Search

Pd\\/H-ZSM-5 zeolites with different aluminum contents and nSi\\/nAl ratios between 11 and 122, different crystallinities and crystallite sizes, including a nanocrystalline sample, were used as catalysts in the dehydroalkylation of toluene with ethane to the isomeric ethyltoluenes. This reaction was chosen as an industrially relevant test reaction for the non-oxidative activation of light alkanes. The catalysts were physicochemically characterized using

Arne Bressel; Thomas Donauer; Sarah Sealy; Yvonne Traa

2008-01-01

53

A simple and general route for the preparation of pure and high crystalline nanosized lanthanide silicates with the structure of apatite at low temperature  

NASA Astrophysics Data System (ADS)

Rare earth silicates with the structure of apatite are attracting considerable interest since they show oxygen ion conductivities higher than that of yttria-stabilized zirconia (YSZ) at moderate temperature. Based on the hydrothermal synthesis we presented a simple one step process for the direct preparation of the pure and the high crystalline nanosized rare earth silicates with the structure of apatite under a mild condition (230 °C). Since the preparation of the high crystalline silicon based rare earth apatites is performed at high temperature previously and accompanied by subsequent process of grinding, results of this work provide a promising alternative of the existing methodology. Furthermore, due to the relatively low temperature of the preparation of these materials, high doping of monovalent cation can be done, which was not achieved before.

Ferdov, Stanislav; Rauwel, Protima; Lin, Zhi; Ferreira, Rute A. Sá; Lopes, Augusto

2010-11-01

54

First step towards the growth of single-crystal oxides on Si: Formation of a two-dimensional crystalline silicate on Si(001)  

NASA Astrophysics Data System (ADS)

We have investigated the structural and chemical properties of reconstructed Sr/Si(001) surfaces at different Sr coverages using low energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy. The results show that upon low temperature oxidation and subsequent UHV annealing of the Sr/Si(001)-(2×1) surface, a crystalline Sr2SiO4 silicate-like layer formed. Using this layer as a template, single-crystal SrO thin films were grown on Si(001) substrates. Our results provide microscopic and spectroscopic evidence of the formation of a uniform, stable, two-dimensional crystalline silicate that can be used for growth of single-crystal oxides on Si(001) substrates.

Liang, Y.; Gan, S.; Engelhard, M.

2001-11-01

55

Crystalline Silicate-perovskite in S6 L6 Chondrite ACFER 040: A Relatively High Shock Pressure of Only 25-26GPa  

NASA Astrophysics Data System (ADS)

Many L6 chondrites are highly shocked and contain high-pressure minerals in and adjacent to shock melt veins and melt pockets. Pressure and duration estimates from shock features are used to understand impact events on the L chondrite parent body (Sharp and DeCarli, 2004; Xie et al, 2006; Ohtani et al, 2004). The crystallization assemblages in shock melt veins and pockets constrain the shock pressures to a maximum of about 25 GPa in most L6 chondrites. Acfer 040 is a highly shocked (S6) L5-6 chondrite with numerous melt veins and pockets. Akimotoite and vitrified silicate-perovskite were identified in Acfer 040 suggesting a relatively high shock pressure relative to other L6 S6 chondrites (Sharp et al, 1997). However, that study was limited to a very small amount of melt-vein material and no crystalline perovskite was found. Tomioka and Fujino (1997) also found silicate perovskite in Tenham, but they were unable to get sufficient diffraction data to fully characterize it. Recently, Miyahara et al (2011) found olivine that transformed to perovskite plus magneseowustite in a Martian meteorite. They also have limited electron diffraction data from the perovskite. In this study, we use laser-Raman spectroscopy, FESEM and FIB-TEM to reinvestigate the melt-vein matrix and high-pressure mineralogy of Acfer 040 and search for crystalline-silicate perovskite. Two distinct crystallization assemblages are identified in the melt veins and pockets: 1) akimotoite + vitrious silicate-perovskite and 2) ringwoodite + vitrious silicate-perovskite. Transformed fragments of high- and low-Ca pyroxenes are also amorphous, suggesting that both pyroxenes transformed to perovskite that subsequently vitrified during decompression. Some of transformed pyroxenes appear crystalline in SEM images. Preliminary TEM data from a FIB sample suggest that some of the silicate perovskite has survived. Detailed analysis of diffraction data will be presented. The abundance of vitrified silicate perovskite in Acfer 040 suggests that the shock pressure was higher than the 20 - 25 GPa pressure of most highly shocked L6 chondrites. The perovskite bearing crystallization assemblages in Acfer 040 suggest a relatively high pressure of 25-26 GPa, but not an extremely high pressure.

Hu, J.; Sharp, T. G.; Trickey, R.

2011-12-01

56

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

Microsoft Academic Search

Very high temperature, Ca-rich alkaline magma intruded an argillite formation at Colle Fabbri, Central Italy, producing cordierite-tridymite\\u000a metamorphism in the country rocks. An intense Ba-rich sulphate-carbonate-alkaline hydrothermal plume produced a zone of mineralization\\u000a several meters thick around the igneous body. Reaction of hydrothermal fluids with country rocks formed calcium-silicate-hydrate\\u000a (CSH), i.e., tobermorite-afwillite-jennite; calcium-aluminum-silicate-hydrate (CASH) — “cement” phases - i.e., thaumasite,

Francesco Stoppa; Fernando Scordari; Ernesto Mesto; Victor V. Sharygin; Giorgio Bortolozzi

2010-01-01

57

High temperature synthesis of high silica zeolite Y with good crystallinity in the presence of N-methylpyridinium iodide.  

PubMed

A novel synthetic route is designed, employing both high temperature and a nontoxic organic structure-directing agent (SDA), for the synthesis of high silica zeolite Y. The N-methylpyridinium used as an organic SDA is stable during the synthesis, and the high silica zeolite Y shows high hydrothermal stability and good catalytic performance, as well as excellent adsorptive properties. PMID:24087828

Zhu, Longfeng; Ren, Limin; Zeng, Shangjing; Yang, Chengguang; Zhang, Haiyan; Meng, Xiangju; Rigutto, Marcello; Made, Alexander van der; Xiao, Feng-Shou

2013-10-15

58

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

59

Chemically feasible hypothetical crystalline networks.  

PubMed

Our systematic enumeration of 4-connected crystalline networks (that is, networks in which each atom is connected to exactly four neighbours) used recent advances in tiling theory to evolve over 900 topologies. The results are relevant to the structures of zeolites and other silicates, aluminophosphates (AlPOs), oxides, nitrides, chalcogenides, halides, carbon networks, and even to polyhedral bubbles in foams. Given their importance as molecular sieves, ion exchangers, catalysts and catalyst supports, we have applied the results to microporous aluminosilicates and aluminophosphates (zeolites). Zeolite chemistry has to date produced 152 distinct types of structure. However, it was always clear that although many further structures can be synthesised, only a fraction of the mathematically generated networks would be chemically feasible (many are 'strained' frameworks requiring unrealistic bond lengths and bond angles), and that an effective 'filtering' process is needed to identify the most plausible frameworks. Here, we describe the use of computational chemistry methods to calculate optimized structural parameters, framework energies relative to alpha-quartz, volumes accessible to sorption, and X-ray diffraction patterns for systematically enumerated hypothetical 4-connected crystalline frameworks. Structures were treated as silica polymorphs with the empirical formula SiO(2), and their energies were minimized. PMID:15048108

Foster, Martin D; Simperler, Alexandra; Bell, Robert G; Friedrichs, Olaf Delgado; Paz, Filipe A Almeida; Klinowski, Jacek

2004-03-28

60

Oxygen isotopes in crystalline silicates of comet Wild 2: A comparison of oxygen isotope systematics between Wild 2 particles and chondritic materials  

NASA Astrophysics Data System (ADS)

Oxygen three-isotope ratios of nine crystalline silicate particles from comet Wild 2 were measured to investigate oxygen isotope systematics of cometary materials. We are able to analyze particles as small as 4 ?m using an ion microprobe with a˜1×2 ?m beam by locating the analysis spots with an accuracy of ±0.4 ?m. Three particles of Mn-rich forsterite, known as low-iron, manganese-enriched (LIME) olivine, showed extremely 16O-rich signatures (?18O, ?17O˜-50‰), similar to refractory inclusions in chondrites. The three Mn-rich forsterite particles may have formed by condensation from an 16O-rich solar nebula gas. Other particles consist of olivine and/or pyroxene with a wide range of Mg# [=molar MgO/(FeO+MgO) %] from 60 to 96. Their oxygen isotope ratios plot nearly along the carbonaceous chondrite anhydrous mineral (CCAM) and Young and Russell lines with ?17O(=?17O-0.52×?18O) values of -3.0‰ to +2.5‰. These data are similar to the range observed from previous analyses of Wild 2 crystalline silicates and those of chondrules in carbonaceous chondrites. Six particles extracted from Stardust track 77 show diverse chemical compositions and isotope ratios; two Mn-rich forsterites, FeO-poor pigeonite, and three FeO-rich olivines with a wide range of ?17O values from -24‰ to +1.6‰. These results confirmed that the original projectile that formed track 77 was an aggregate (>6 ?m) of silicate particles that formed in various environments. The ?17O values of ferromagnesian Wild 2 particles (including data from previous studies) increase from ˜-23‰ to+2.5‰ with decreasing Mg#: ?17O values of Mn-rich forsterite particles (Mg#=98-99.8) cluster at -23‰, those of FeO-poor particles (Mg#=95-97) cluster at -2‰, and those of FeO-rich particles (Mg#?90) scatter mainly from -1.5‰ to+2.5‰. Compared to chondrules in primitive chondrites, the systematic trend between Mg# and ?17O among the Wild 2 particles is most similar to that reported for CR chondrite chondrules. We argue that CR chondrites and some cometary materials share multiple common chemical and isotope characteristics. We suggest that many of the crystalline silicate particles formed in the outer regions of the asteroid belt, or regions that share the common properties, and were transported to comet-forming regions and accreted into comet Wild 2.

Nakashima, Daisuke; Ushikubo, Takayuki; Joswiak, David J.; Brownlee, Donald E.; Matrajt, Graciela; Weisberg, Michael K.; Zolensky, Michael E.; Kita, Noriko T.

2012-12-01

61

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

62

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

63

Rates of Exchange of Cs and Sr for Poorly Crystalline Sodium Titanium Silicate (CST) in Nuclear Waste Systems  

Microsoft Academic Search

The compound sodium titanium silicate, popularly known as CST, is highly selective for Cs. It was synthesized for the purpose of removing Cs from basic nuclear waste systems. This compound has a tunnel structure in which the Cs ion just fits but diffusion through the tunnels is relatively slow. CST loses its ability to sequester Cs in the strongly basic

Abraham Clearfield; Dmitry G. Medvedev; Steven Kerlegon; Timothy Bosser; Jonathan D. Burns; Milton Jackson

2012-01-01

64

Hexavalent chromium in tricalcium silicate: Part I Quantitative X-ray diffraction analysis of crystalline hydration products  

Microsoft Academic Search

The hydration products of CrVI-doped tricalcium silicate (C3S)? have been investigated. C3S is the main constituent of Portland cement responsible for the strength and stability of hardened Portland cement paste. Chromium trioxide (CrO3), added as a dopant to C3S, simulates hexavalent chromium waste that may be stabilized in ordinary Portland cement. X-ray diffraction was used to monitor the development of

O. E Omotoso; D. G Ivey; R Mikula

1998-01-01

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

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

67

Raman spectroscopic study of the synthesis of zeolite Y  

SciTech Connect

The formation of zeolite Y from colloidal silica and soluble silicate species was investigated by Raman spectroscopy. The role of aging of the reactant mixture was studied. During the nucleation period, the solid amorphous phase consists of predominantly six-membered aluminosilicate rings, which act as building blocks for the formation of zeolite Y. It is essential to have polymeric, highly condensed silicate units as a reactant if zeolite Y crystallization is to take place.

Dutta, P.K.; Shieh, D.C.; Puri, M.

1987-04-23

68

Entrapment of ionic tris(2,2'-bipyridyl) ruthenium(II) in hydrophobic siliceous zeolite: O2 sensing in biological environments.  

PubMed

Synthesis of the ionic dye, tris(2,2'-bipyridyl) ruthenium(II) chloride (Ru(bpy) 3 2+.2Cl (-)) within the supercages of a highly hydrophobic zeolite Y is reported. Use of the neutral precursor Ru(bpy)Cl 2(CO) 2 allowed for high loading levels of Ru(bpy) 3 2+ (1 per 7 and 25 supercages). The emission quenching of the Ru(bpy) 3 2+-zeolite crystals dispersed in polydimethoxysiloxane (PDMS) films by dissolved oxygen in water was examined. The quenching data as a function of oxygen concentration was fit to a linear Stern-Volmer plot ( R2 = 0.98). Using the Stern-Volmer plot as calibration, changes in concentration of dissolved oxygen due to reaction with glucose in the presence of glucose oxidase was monitored. Human monocyte-derived macrophages internalized the submicron-sized Ru(bpy) 3 2+-zeolite crystals, and intracellular oxygen concentrations initiated by zymosan-mediated oxidative burst could be monitored by measuring the emission from Ru(bpy) 3 2+ by confocal fluorescence microscopy. PMID:18642937

Ruda-Eberenz, Toni A; Nagy, Amber; Waldman, W James; Dutta, Prabir K

2008-07-22

69

Adsorption, Diffusion and Reaction Studies of Hydrocarbons on Zeolite Catalysts  

Microsoft Academic Search

Zeolites are crystalline microporous materials that are widely applied as catalysts in industries like oil refining, basic petrochemistry and fine chemistry. The major benefit of the use of zeolites as catalysts lies in their unique microporous structures. However, in some cases the presence of micropores limits the catalytic performance of zeolites due to diffusion limitation. This is caused by the

Sander van Donk

2002-01-01

70

Structural characteristics of modified natural zeolite  

Microsoft Academic Search

Natural zeolite of Slovak provenience has been modified with magnetic nanoparticles at selected temperatures of 20, 50 and\\u000a 85 °C with the aim to enhance its sorption properties. The pore, surface and structural properties of zeolite\\/iron oxide composite\\u000a were characterized using nitrogen adsorption measurements, electron probe microanalysis and powder X-ray diffraction. The\\u000a crystallinity of the host zeolite was strongly influenced by

Annamária Mockov?iaková; Marek Matik; Zuzana Orolínová; Pavol Hudec; Erika Kmecová

2008-01-01

71

Template synthesis and characterization of mesoporous zeolites  

Microsoft Academic Search

Well-crystalline ZSM-5 and zeolite Y having uniform mesopores were synthesized with template route method using carbon aerogels of different mesoporosities. These mesoporous zeolites were characterized with X-ray diffraction, FT-IR spectroscopy, field emission scanning electron microscopy, and N2 adsorption. ZSM-5 having mesopore volume of 0.2–1cm3g?1 was obtained. Mesoporous ZSM-5 synthesized by heating at 423K for 96h was well-crystalline, which had mesopores

Yousheng Tao; H Kanoh; Y Hanzawa; K Kaneko

2004-01-01

72

Applications of NMR spectroscopy to the Study of Zeolite Synthesis.  

National Technical Information Service (NTIS)

NMR spectroscopy is a powerful technique for identifying the structure and concentration of silicate and aluminosilicate anions in gels and solution used for zeolite synthesis. A review is presented of the types of species that have been observed and the ...

A. T. Bell

1989-01-01

73

Magnesium Silicate  

Microsoft Academic Search

A comprehensive profile of magnesium silicate with 80 references is reported. A full description including nomenclature, formulae, and appearance is included. Methods for magnesium silicate preparation including precipitation, hydrothermal precipitation, and mechanochemical dehydration are reviewed. Physical characteristics, compendia and non-compendia analytical methods, uses, stability and incompatibilities, biodegradability, toxicity, and substances related to magnesium silicate are also discussed.

Iyad Rashid; Nidal H. Daraghmeh; Mahmoud M. Al Omari; Babur Z. Chowdhry; Stephen A. Leharne; Hamdallah A. Hodali; Adnan A. Badwan

2011-01-01

74

Magnesium silicate.  

PubMed

A comprehensive profile of magnesium silicate with 80 references is reported. A full description including nomenclature, formulae, and appearance is included. Methods for magnesium silicate preparation including precipitation, hydrothermal precipitation, and mechanochemical dehydration are reviewed. Physical characteristics, compendia and non-compendia analytical methods, uses, stability and incompatibilities, biodegradability, toxicity, and substances related to magnesium silicate are also discussed. PMID:22469264

Rashid, Iyad; Daraghmeh, Nidal H; Al Omari, Mahmoud M; Chowdhry, Babur Z; Leharne, Stephen A; Hodali, Hamdallah A; Badwan, Adnan A

2011-06-23

75

Case Series Describing Thermal Injury Resulting From Zeolite Use for Hemorrhage Control in Combat Operations.  

National Technical Information Service (NTIS)

Four cases are presented to illustrate cutaneous burns sustained with the use of zeolite in the treatment of major hemorrhage secondary to combat wounds. Zeolite, a microporous crystalline aluminosilicate granular hemostatic agent, can cause secondary the...

A. Pusateri J. McManus K. J. Knoop T. Hurtado

2007-01-01

76

Heavy ion bombardment of silicates and nitrides  

Microsoft Academic Search

Several silicates, including ?-quartz, zirconium silicate, thorium silicate, LiAlSiO, a silicate glass and several nitrides, ? and ? Si3N4, AlN, ZrN as well as Si2N2O and ThO2, have been irradiated by 10-10 Krypton(3MeV)ions\\/m The damaged powders of original particle size less than 5 ?m, have been examined by x-ray diffraction and electron microscope methods. The silicates and Si2N2O become non-crystalline

L. Cartz; F. G. Karioris; R. A. Fournelle

1981-01-01

77

Effect of crystal size on physical and catalytic properties of ZSM-5 type zeolites  

NASA Astrophysics Data System (ADS)

Diffusion of C6-alkanes in zeolite ZSM-5 and its aluminum free variant silicate-1 receives the greatest attention in the thesis. A physical property of zeolite like the ability to sorb, in particular, nonpolar compounds, was utilized in studying hydrocarbon diffusion by performing adsorption and desorption experiments. The diffusional behavior of the zeolite ZSM-5 and of aluminated silicate-1 at catalytically relevant temperatures was studied by way of a catalytic property of the zeolite. Descriptions of physical studies on nitrogen sorption in ZSM 5 type zeolites and of catalytic studies on the conversion of ethanol to hydrocarbons complete the thesis which tries to give a better understanding of adsorptive, diffusional, and catalytic behavior by describing experiments in which only one parameter has been varied, the zeolite crystal size. Discussions and conclusions are directed towards the industrial application of zeolite ZSM-5, as a catalyst.

Voogd, P.

1991-09-01

78

On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium  

Microsoft Academic Search

The abundance of both amorphous and crystalline silicates in very small grains is limited by the fact that the 10 mum silicate emission feature is not detected in the diffuse interstellar medium (ISM). On the basis of the observed IR emission spectrum for the diffuse ISM, the observed ultraviolet extinction curve, and the 10 mum silicate absorption profile, we obtain

Aigen Li; B. T. Draine

2001-01-01

79

Synthesis of NaY zeolite on preformed kaolinite spheres. Evolution of zeolite content and textural properties with the reaction time  

SciTech Connect

The synthesis of NaY zeolite was carried out on fired kaolinite microspheres. Changes in porosity, chemical composition, and crystallinity of the solid show zeolite growth on both internal and external microsphere surfaces. It was also observed that, as a consequence of the alkaline treatment, the SiO[sub 2]/Al[sub 2]O[sub 3] ratio in the solid diminishes prior to the appearance of the zeolite, but increases when the zeolite begins to crystallize.

Basaldella, E.I.; Bonetto, R.; Tara, J.C. (Centro de Investigacion y Desarrollo en Procesos Cataliticos, La Plata (Argentina))

1993-04-01

80

Hydrocarbon cracking with catalyst containing a CO oxidation promoter in ultra-stable zeolite particles  

Microsoft Academic Search

A cracking catalyst for promoting the oxidation of carbon monoxide to carbon dioxide during regeneration of the catalyst by the burning of coke therefrom, comprises two distinct crystalline aluminosilicate zeolite particles embedded in an inorganic porous oxide matrix material. The first zeolite is the ultra-stable variety of Y-type zeolite which contains a CO oxidation promoter, such as a Group VIII

Gladrow

1979-01-01

81

Properties of Zeolite A Obtained from Powdered Laundry Detergent: An Undergraduate Chemistry Experiment  

Microsoft Academic Search

Zeolites, crystalline porous aluminosilicates, are valued for their ability to absorb ions and molecules as well as function as catalysts. A number of laboratory experiments using zeolites filtered from a suspension of powdered laundry detergent are described. The various experiments illustrate the myriad uses of zeolites as desiccants, ion exchange materials, and catalysts.

David A. Lindquist; Alison L. Smoot

1997-01-01

82

Mass spectrometric investigation of small silicate polyhedra in solution  

NASA Astrophysics Data System (ADS)

The hydrolysis of tetra-methyl-ortho-silicate (TMOS) or tetra-ethyl-ortho-silicate (TEOS) in aqueous solutions at pH values of 1-2 was investigated by electrospray mass spectroscopy. In this study, small oligomer intermediates of silicates were formed and detected. Some of the structures are secondary building units as found in zeosils and zeolites. Here, we present the first H/D-exchange mass spectrometric experiments to determine the structure of silicates formed in acidic solution. Most of the observed oligomers take on polyhedral geometries. The results are compared with experiments of other groups, which have performed complementary experiments in alkaline solutions in presence of template molecules.

Eggers, K.; Eichner, T.; Woenckhaus, J.

2005-06-01

83

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

84

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

85

Novel long-term immobilization method for radioactive iodine-129 using a zeolite/apatite composite sintered body.  

PubMed

The amount of radioactive iodine generated from nuclear power plants is expected to increase with the proliferation of nuclear energy production, and long-term immobilization methods for such radioactive elements need to be developed to make nuclear energy sustainable. The standard immobilization method of radioactive elements, vitrification, is not very effective for radioactive iodine-129 because of the low solubility of iodine in silicate melts, its very high volatility at standard vitrification process temperatures, and its instability in the alkaline environment of deep geological layers below 300 m. We have developed a novel three-phase ceramic composite produced by a sintering process. Iodine adsorbed onto Ca-type zeolite A was covered with a hydroxyapatite nanolayer through the exchange reaction of ammonium with calcium. Clusters of iodine of 30 nm within the zeolite structure were found to be thermally stable up to 1253 K because of the partial blockage of the alpha-cage apertures by ammonium ions and the partial change from a crystalline phase to an amorphous phase at 473 K. No gasification of iodine molecules was found to occur during the sintering process. The outer phase was highly crystalline hydroxyfluorapatite in which the hydroxyapatite nanolayer plays an important role for successful sintering. The elution of iodine in low-dioxygen water, similar to that found within the Earth's crust, was investigated and was found to occur only in the surface layer of the sintered body. PMID:20355964

Watanabe, Yujiro; Ikoma, Toshiyuki; Yamada, Hirohisa; Suetsugu, Yasushi; Komatsu, Yu; Stevens, Geoffrey W; Moriyoshi, Yusuke; Tanaka, Junzo

2009-07-01

86

Titanium silicate molecular sieve oxidation catalysts and the production thereof  

US Patent & Trademark Office Database

Disclosed are novel crystalline molecular sieves having the framework of ETS-10 titanium silicate which contain both octahedral and tetrahedral titanium atoms and are in acid form. The sieves are prepared by adding a complexing agent such as hydrogen peroxide during synthesis or by treating a synthesized titanium silicate molecular sieve with a reagent that replaces tetrahedral silicon with tetrahedral titanium atoms.

Thangaraj; Appadurai (Colonia, NJ); Kuznicki; Steven M. (Whitehouse Station, NJ); Koermer; Gerald S. (Roseland, NJ)

2000-07-11

87

Solubility and structure of calcium silicate hydrate  

Microsoft Academic Search

The poorly crystalline calcium silicate hydrate (C-S-H) phases that form near room temperature, which include the technically important C-S-H gel phase formed during the hydration of Portland cement, have a broad similarity to the crystalline minerals tobermorite and jennite, but are characterized by extensive atomic imperfections and structural variations at the nanometer scale. Relationships between the aqueous solubility and chemical

Jeffrey J. Chen; Jeffrey J. Thomas; Hal F. W. Taylor; Hamlin M. Jennings

2004-01-01

88

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

89

Zeolite coatings on metal alloys for corrosion resistance, hydrophilicity, and microbiocidal activity  

NASA Astrophysics Data System (ADS)

The recent advent of polycrystalline zeolite coatings on metal alloys has heralded a paradigm shift in zeolitic application and function as well as their requisite synthesis. The prevailing paradigm for zeolite utilization and employment was through the exploitation of their uniform microporosity. We have demonstrated the utility of the non-porous as-synthesized form of high-silica-zeolite (HSZ) MFI coatings on aluminum alloys for corrosion resistance. A single chemical formulation was able to generate excellent corrosion-resistant HSZ MFI coatings on all aluminum alloys studied. Functional zeolite coatings have traditionally been synthesized as coatings comprised of single zeolite species. We have successfully generated functional zeolite hybrid coatings comprised of disparate zeolite species with controlled composition. A three-layer zeolite coating was developed to apply a low-silica-zeolite (LSZ), zeolite Y (ZY), to aluminum substrates. The middle layer was a zeolite hybrid coating of ZY crystals embedded within a MFI matrix. The mixed zeolite middle layer allowed for the adhesion of the single species HSZ MFI bottom layer to the single species LSZ ZY, top layer. A two-layer hydrophilic and antimicrobial hybrid zeolite coating on aluminum alloys was also developed. The base layer was a HSZ MFI coating and the top layer consisted of zeolite A (ZA) crystals embedded within a matrix of HSZ MFI. The ZA crystals are still present at the surface of the hybrid layer, as such; their hydrophilicity is accessible and can be exploited for their hydrophilic and antimicrobial potential. The great utility of the zeolite hybrid layer is realized with the formation of single-layer hybrid coatings on metal alloys. The hybrid coating is made of mixed inorganic crystalline species imbedded in a matrix of HSZ MFI. The inorganic species used is not limited to zeolite types; other inorganic crystalline species can be used. We have generated hybrid coatings made from LSZ ZY and HSZ MR, and hybrid coatings made from hydrotalcite, an inorganic crystalline species distinctly different from zeolite, and HSZ MFI. The single layer hybrid coatings have great utility and their function and application can be easily tuned by changing the zeolite or crystalline inorganic species used to generate them.

Beving, Derek Eugene

90

Isomerization of ?-pinene over dealuminated ferrierite-type zeolites  

Microsoft Academic Search

Isomerization of ?-pinene was performed on a series of dealuminated ferrierite (FER)-type zeolites in liquid phase at 363 K using a batch reactor. The course of zeolite dealumination was followed in detail using 29Si, 27Al, 1H MAS NMR, XRD, FTIR, and sorption of nitrogen. The ammonium form of FER was dealuminated with aqueous solutions of HCl. While retaining the crystallinity

Rafal Rachwalik; Zbigniew Olejniczak; Jian Jiao; Jun Huang; Michael Hunger; Bogdan Sulikowski

2007-01-01

91

Skeletal isomerization of 1?butene on synthetic clinoptilolite zeolite  

Microsoft Academic Search

A pure, highly crystalline clinoptilolite (CLI) zeolite with a Si\\/Al ratio of 5.8 has been synthesized using a small amount\\u000a (1%) of seed crystals and tested as a catalyst for the skeletal isomerization of 1?butene at 623–723 K at atmospheric pressure.\\u000a The catalytic results are compared to those obtained from a ferrierite (FER) zeolite with a Si\\/Al ratio of 7.6.

Gon Seo; Byung Joon Ahn; Suk Bong Hong; Young Sun Uh

1998-01-01

92

Interpreting the 10 micron Astronomical Silicate Feature  

NASA Astrophysics Data System (ADS)

10micron spectra of silicate dust in the diffuse medium towards Cyg OB2 no. 12 and towards field and embedded objects in the Taurus Molecular Cloud (TMC) were obtained with CGS3 at the United Kingdom Infrared Telescope (UKIRT). Cold molecular-cloud silicates are sampled in quiescent lines of sight towards the field stars Taurus-Elias 16 and Elias 13, whilst observations of the embedded young stellar objects HL Tau, Taurus-Elias 7 (Haro6-10) and Elias 18 also include emission from heated dust. To obtain the foreground silicate absorption profiles, featureless continua are estimated using smoothed astronomical and laboratory silicate emissivities. TMC field stars and Cyg OB2 no. 12 are modelled as photospheres reddened by foreground continuum and silicate extinction. Dust emission in the non-photospheric continua of HL Tau and Elias 7 (Haro6-10) is distinguished from foreground silicate absorption using a 10micron disk model, based on the IR-submm model of T Tauri stars by Adams, Lada & Shu (1988), with terms added to represent the foreground continuum and silicate extinction. The absorption profiles of HL Tau and Elias 7 are similar to that of the field star Elias 16. Fitted temperature indices of 0.43 (HL Tau) and 0.33 (Elias 7) agree with Boss' (1996) theoretical models of the 200-300K region, but are lower than those of IR-submm disks (0.5-0.61; Mannings & Emerson 1994); the modelled 10micron emission of HL Tau is optically thin, that of Elias 7 is optically thick. A preliminary arcsecond-resolution determination of the 10micron emissivity near ?1 Ori D in the Trapezium region of Orion and a range of emission temperatures (225-310K) are derived from observations by T. L. Hayward; this Ney-Allen emissivity is 0.6micron narrower than the Trapezium emissivity obtained by Forrest et al. (1975) with a large aperture. Published interstellar grain models, elemental abundances and laboratory studies of Solar System silicates (IDPs, GEMS and meteorites), the 10micron spectra of comets, interstellar silicates, synthetic silicates and terrestrial minerals, and the effects of laboratory processing on the 10micron spectra of crystalline and amorphous silicates are reviewed to provide insight into the mineralogy of interstellar silicate dust. The wavelengths of the peaks of the 10micron silicate profiles decrease between circumstellar, diffuse medium and molecular-cloud environments, indicating (after Gürtler & Henning 1986) that the amorphous pyroxene content of initially olivine-rich interstellar dust increases with time. This is accompanied by an increase in the FWHM of the features which indicates an increase in grain size and/or an increasing fraction of chemically-varied crystalline pyroxene. Fine structure in the Cyg OB2 no. 12, Elias 16, Elias 7, HL Tau profiles indicate that hydrated layer silicates similar to terrestrial serpentines, clays and talc may be a ubiquitous component of interstellar dust. At 10microns the narrow bands of mixed crystalline pyroxenes blend, making their identification difficult. Since no fine structure is observed near 11.2microns, the fraction of crystalline olivine is small. In geology direct olivine-plus-SiO2 to pyroxene reactions occur only at high pressure within the terrestrial mantle. Therefore the fraction of amorphous pyroxene is probably increased by the hydration of Mg-rich olivine to form a serpentine-like hydrated silicate, which is subsequently annealed to form a mixture of amorphous pyroxene and olivine. Terrestrial and laboratory olivine samples are readily converted to serpentine in the presence of water, and (after extended annealing) the first crystalline band to appear is the 11.2micron olivine feature frequently observed in cometary spectra.

Bowey, Janet E.

1998-11-01

93

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

94

ZEOLITE STRUCTURE ANALYSIS WITH POWDER X-RAY DIFFRACTION AND SOLID-STATE NMR TECHNIQUES  

Microsoft Academic Search

Large advances in the development of catalytic materials were made with the synthesis of zeolites, which are porous crystalline materials that can be used as catalysts, catalyst supports, sorbents and ion exchangers. Zeolite structures consist of T-atoms tetrahedrally coordinated to oxygen atoms, where T can be AI, Si, or any other element capable of isomorphous substitution for Si. The unavailability

G. T. KOKOTAILO; C. A. FYFE

95

Viscoelastic characterisation of zeolite modified asphalt binder considering phase transformation and air void interaction  

Microsoft Academic Search

A recent warm mix asphalt technology uses zeolite powders as an additive to reduce production temperature and improve workability. With an increase in temperature, water is released from the zeolite crystalline structure and vaporised into bubbles within the binder, and thus gas, fluid, and solid phases simultaneously exist in the modified binders. The effective complex modulus of the modified binders

H. M. Yin; B. Lai

2012-01-01

96

Zeolite collapse and polyamorphism  

Microsoft Academic Search

The phenomenology of zeolite collapse is outlined, drawing on recent synchrotron x-ray diffraction experiments and computer simulations of low density cage structures like zeolite A and zeolite Y. Attention is drawn to the importance of polyamorphism in destabilizing this type of microporous crystal and its role in order disorder as well as amorphous amorphous transitions, together with associated differences in

G. Neville Greaves; F. Meneau; F. Kargl; D. Ward; P. Holliman; F. Albergamo

2007-01-01

97

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...

98

Phase studies of pozzolanic stabilized calcium silicate hydrates at 180 °C  

Microsoft Academic Search

Phase studies of calcium silicate hydrates formed at elevated temperature and pressure have been well documented. At 180 °C, the initially formed amorphous calcium silicate gel [C-S-H] transforms into well-defined crystalline phases, the stability of which is primarily dependent on the C\\/S ratio in the CaO-SiO2-H2O system and the hydrothermal conditions. Hillebrandite [C2SH], ?-dicalcium silicate hydrate [?-C2SH] and ?-tricalcium silicate

K. Luke

2004-01-01

99

Directing zeolite structures into hierarchically nanoporous architectures.  

PubMed

Crystalline mesoporous molecular sieves have long been sought as solid acid catalysts for organic reactions involving large molecules. We synthesized a series of mesoporous molecular sieves that possess crystalline microporous walls with zeolitelike frameworks, extending the application of zeolites to the mesoporous range of 2 to 50 nanometers. Hexagonally ordered or disordered mesopores are generated by surfactant aggregates, whereas multiple cationic moieties in the surfactant head groups direct the crystallization of microporous aluminosilicate frameworks. The wall thicknesses, framework topologies, and mesopore sizes can be controlled with different surfactants. The molecular sieves are highly active as catalysts for various acid-catalyzed reactions of bulky molecular substrates, compared with conventional zeolites and ordered mesoporous amorphous materials. PMID:21764745

Na, Kyungsu; Jo, Changbum; Kim, Jeongnam; Cho, Kanghee; Jung, Jinhwan; Seo, Yongbeom; Messinger, Robert J; Chmelka, Bradley F; Ryoo, Ryong

2011-07-15

100

Zeolite catalysis  

SciTech Connect

This patent describes a process for preparing hydrocarbons boiling in the gasoline and/or distillate range by contacting a feedstock comprising lower molecular weight olefins in a reaction zone under conditions of elevated temperature and pressure with a shape selective crystalline aluminosilicate catalyst, comprising: reducing the non-shape selective surface-cracking and/or surface isomerization activity of the aluminosilicate catalyst by a process comprising: preparing an aqueous solution comprising colloidal silica, optionally an organic directing agent, and a source of hydroxide ions; mixing the aqueous solution with an aqueous dispersion of shape-selective crystalline aluminosilicate to form a homogeneous mixture which is subsequently heated; adding an aqueous solution comprising a source of fluoride ions to the homogeneous mixture to form a reactive composition; heating the reactive composition at a temperature to effectively form a surface-deactivated catalyst comprising a crystalline fluoride-containing silica outer shell on an aluminosilicate; withdrawing the surface-deactivated catalyst from the reactive composition for washing, drying, and calcining of the catalyst; and removing the catalyst to the reaction zone for contact with the olefin feedstock.

Chu, P.; Garwood, W.E.; Schwartz, A.B.

1988-11-29

101

Zeolite catalysis: technology  

SciTech Connect

Zeolites have been used as catalysts in industry since the early nineteen sixties. The great majority of commercial applications employ one of three zeolite types: zeolite Y; Mordenite; ZSM-5. By far the largest use of zeolites is in catalytic cracking, and to a lesser extent in hydrocracking. This paper reviews the rapid development of zeolite catalysis and its application in industries such as: the production of gasoline by catalytic cracking of petroleum; isomerization of C/sub 5/ and C/sub 6/ paraffin hydrocarbons; alkylation of aromatics with olefins; xylene isomerization; and conversion of methanol to gasoline.

Heinemann, H.

1980-07-01

102

Design and generation of extended zeolitic metal-organic frameworks (ZMOFs): synthesis and crystal structures of zinc(II) imidazolate polymers with zeolitic topologies.  

PubMed

Attempts to create metal-organic frameworks (MOFs) with zeolitic topologies, metal (zinc(II) and cobalt(II)) imidazolates have repeatedly been used as the metal-organic motifs of inorganic silicate analogues. By modulating the synthetic strategy based on the solvothermal and liquid diffusion method, seven further MOFs (including at least three zeolitic MOFs) of zinc(II) imidazolates, [Zn(im)2.x G] (G=guest molecule, x=0.2-1) 1 a-7 a, have been successfully synthesized. Of these, 1 a-3 a are isostructural with the previously reported cobalt analogues 1 b-3 b, respectively, while 4 a-7 a are new members of the metal imidazolate MOF family. Complex 4 a exhibits a structure related to silicate CaAl2Si2O8 of CrB4 topology, but with a higher network symmetry; complex 5 a has a structure with zeolitic DFT topology that was discovered in zeolite-related materials of DAF-2, UCSB-3, and UCSB-3GaGe; complex 6 a demonstrates an unprecedented zeolite-like topology with one dimensional channels with 10-rings; and 7 a displays a structure of natural zeolite GIS (gismondine) topology. All of these polymorphous MOFs were created only by using certain solvents as structure-directing agents (SDAs). Further extensive metal-organic frameworks with zeolitic topologies can be envisaged if other solvents were to be used. PMID:17397024

Tian, Yun-Qi; Zhao, Yu-Ming; Chen, Zhen-Xia; Zhang, Guang-Ning; Weng, Lin-Hong; Zhao, Dong-Yuan

2007-01-01

103

Effects of the synthesis hydrogel on the formation of zeolite LTA membranes  

Microsoft Academic Search

A zeolite\\/polymer composite hollow fiber (CHF) support is used to investigate the effects of three different silica sources (sodium metasilicate nonahydrate, silica sol and sodium silicate) of the synthesis hydrogel on the properties of zeolite LTA membrane prepared on the outer surface of the support by in situ hydrothermal synthesis at 100°C. The as-synthesized membranes and powders from the synthesis

Qinqin Ge; Jia Shao; Zhengbao Wang; Yushan Yan

104

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

105

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

106

Zeolite collapse and polyamorphism  

NASA Astrophysics Data System (ADS)

The phenomenology of zeolite collapse is outlined, drawing on recent synchrotron x-ray diffraction experiments and computer simulations of low density cage structures like zeolite A and zeolite Y. Attention is drawn to the importance of polyamorphism in destabilizing this type of microporous crystal and its role in order disorder as well as amorphous amorphous transitions, together with associated differences in entropy and density between polyamorphic phases and the precursor zeolite. Magic angle spinning NMR and inelastic x-ray scattering are used to highlight changes in structural order and mechanical rigidity between the starting zeolite and the final high density polyamorph. In conclusion, two-level systems detected with inelastic neutron scattering are described and their involvement in dictating the dynamics of the collapse of zeolitic cage structures.

Neville Greaves, G.; Meneau, F.; Kargl, F.; Ward, D.; Holliman, P.; Albergamo, F.

2007-10-01

107

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

108

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

109

Mg/Fe FRACTIONATION IN CIRCUMSTELLAR SILICATE DUST INVOLVED IN CRYSTALLIZATION  

SciTech Connect

Infrared astronomical observations of oxygen-rich young and evolved stars show that only magnesium-rich crystalline silicates exist in circumstellar regions, and iron, one of the most important dust-forming elements, is extremely depleted. The compositional characteristic of circumstellar crystalline silicates is fundamentally different from that of primitive extraterrestrial materials in our solar system, such as chondritic meteorites and interplanetary dust particles. Amorphous silicates are ubiquitous and abundant in space, and are a promising carrier of iron. However, since the first detection of crystalline silicates, there has been an unsolved inconsistency due to differing compositions of coexisting crystalline and amorphous phases, considering that amorphous silicates have been expected to be precursors of these crystals. Here we show the first experimental evidence that Fe-depleted olivine can be formed by crystallization via thermal heating of FeO-bearing amorphous silicates under subsolidus conditions. Mg/Fe fractionation involved in crystallization makes possible to coexist Mg-rich crystalline silicates with Fe-bearing amorphous silicates around stars.

Murata, K.; Takakura, T.; Chihara, H.; Koike, C.; Tsuchiyama, A. [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)], E-mail: keisuke@astroboy.ess.sci.osaka-u.ac.jp

2009-05-10

110

Formulation of cracking catalyst based on zeolite and natural clays  

SciTech Connect

Domestically manufactured cracking catalysts are based on a synthetic amorphous aluminosilicate matrix and Y zeolite. A multistage {open_quotes}gel{close_quotes} technology is used in manufacturing the catalysts. The process includes mixing solutions of sodium silicate and acidic aluminum sulfate, forming, syneresis, and activation of the beaded gel. In the manufacture of bead catalysts, the next steps in the process are washing, drying, and calcining; in the manufacture of microbead catalysts, the next steps are dispersion and formation of a hydrogel slurry, spray-drying, and calcining. The Y zeolite is either introduced into the alumina-silica sol in the stage of forming the beads, or introduced in the dispersion stage. With the aim of developing an active and selective cracking catalyst based on Y zeolite and natural clays, with improved physicomechanical properties, the authors carried out a series of studies, obtaining results that are set forth in the present article.

Aliev, R.R.; Lupina, M.I.

1995-11-01

111

Synthesis and characterization of the tellurium\\/calcium silicate nanocomposite  

Microsoft Academic Search

A novel tellurium\\/calcium silicate nanocomposite with tellurium nanorods homogeneously dispersed in the calcium silicate matrix has been successfully synthesized using corresponding tellurium nanorods, Ca(NO3)2·4H2O, and Na2SiO3·9H2O in ethanol\\/water mixed solvents at room temperature for 48h. The new material consists of a single crystalline Te core and an amorphous calcium silicate shell. The products were characterized by X-ray powder diffraction (XRD),

Ming-Guo Ma; Jie-Fang Zhu; Run-Cang Sun; Feng Chen; Ying-Jie Zhu

2011-01-01

112

Sodium clusters in zeolites  

NASA Astrophysics Data System (ADS)

The method of loading sodium clusters in zeolites, consisting of the controlled thermal decomposition of physisorbed sodium azide, is discussed. The influence of the azide loading, the azide decomposition rate and the sintering process on the amount of ionic and metallic sodium clusters in zeolite Y was followed by ESR. The method is compared to other metal deposition techniques.

Grobet, P. J.; Martens, L. R. M.; Vermeiren, W. J. M.; Huybrechts, D. R. C.; Jacobs, P. A.

1989-03-01

113

Comparison of competition between T = O and T-OH groups in vanadium, niobium, tantalum BEA zeolite and SOD based zeolites  

NASA Astrophysics Data System (ADS)

The investigation of intra framework substitution of Si by group V transition metals (V, Nb, Ta) is an important strategy to modify or to tune the catalytic properties of zeolites. Theoretically one of the limitations is the size of the zeolite unit cell. In this study the energy and geometry of silicate BEA modified with group V metals is investigated and compared with the results obtained for smaller zeolite models, in particular the SOD structure. The group V substituted T framework sites in BEA zeolite structure with T = O and/or T-OH groups are confirmed: i.e. T = O for T = vanadium, and T-OH for T = niobium or tantalum.

Wojtaszek, Anna; Ziolek, Maria; Dzwigaj, Stanislaw; Tielens, Frederik

2011-09-01

114

Pyrolytic Synthesis of Carbon Nanotubes from Sucrose on a Mesoporous Silicate  

Microsoft Academic Search

Multi?wall carbon nanotubes were synthesized from sucrose by a pyrolytic technique using mesopourous 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 multi?wall nanotubes showed them to be 15 nm in diameter, 200 nm in length and close?ended. There was variation in crystallinity

Emilie J. Siochi; Roy E. Crooks

2006-01-01

115

Investigations of the adsorption of n-pentane in several representative zeolites.  

PubMed

We have examined the adsorption of n-pentane in several representative zeolites such as silicalite (MFI), ferrierite (FER), zeolite L (LTL), and faujasite zeolites with FAU structure including siliceous Y (Si-Y) and Na-Y by using FT-Raman spectroscopy in combination with thermogravimetric analysis (TGA) with particular attention being paid to the conformational and dynamic behavior of the guest molecule. The results indicate that the framework topology mainly dictates the conformation of n-pentane in a zeolite. For the zeolites with channel systems such as silicalite, ferrierite, and zeolite L, the population of the all-trans conformer increases upon loading, given that the geometry of the isomer fits better in the channel. When n-pentane is adsorbed in zeolites with a large cavity, such as Si-Y and Na-Y, the distribution of the all-trans (TT) and trans-gauche (TG) conformers is similar to that of pure liquid, suggesting that the large supercage in the framework imposes minimal effect on the conformational equilibrium. The dynamics of the guest molecule is, however, influenced significantly by the existence of cations. Adsorption of n-pentane in a siliceous framework such as silicalite and Si-Y results in extensive molecular motion at room temperature, the degree of which decreases with decreasing temperature. In zeolites ferrierite, L, and Na-Y, the presence of cations in the framework markedly hinders the overall molecular motion. The cations clearly play a role in the observed static disorder of the guest molecule in zeolite L. Important information regarding the location of the n-pentane molecules within silicalite and ferrierite is also obtained. PMID:16623502

Wang, Haiyan; Turner, Elizabeth A; Huang, Yining

2006-04-27

116

Formation of Magnesium Silicates is Limited around Evolved Stars  

NASA Astrophysics Data System (ADS)

Laboratory experiments suggest that magnesium silicide (Mg2Si) grains could be produced in the hydrogen dominant gas outflow from evolved stars in addition to amorphous oxide minerals. Astronomical observations have shown the existence of abundant silicate grains around evolved stars and we have long realized that most of the silicate grains are amorphous, based on the observed infrared features. Only high mass loss stars show the feature attributed to magnesium-rich crystalline silicate about 10-20 % respect to total silicates, so far. The lower degree of crystallinity observed in silicates formed in outflows of lower mass-loss-rate stars might be caused by the formation of magnesium silicide in this relatively hydrogen-rich environment. As a result of predominant distribution of magnesium into the silicide, the composition of interstellar amorphous silicates could be magnesium poor compared with silicon. Indeed, the chemical composition of isotopically anomalous GEMS (glass with embedded metal and sulfides) is magnesium poor with respect to a forsteritic composition (Floss et al. 2006; Keller & Messenger 2007). Infrared observations suggest that there is little or no crystalline forsterite in interstellar environments while there is an abundance of crystalline forsterite in our Solar System. If the forsterite is a result of the oxidation of interstellar magnesium silicide, then it is clear both why crystalline forsterite is stoichiometric olivine and why the chemical composition of isotopically anomalous GEMS is magnesium poor with respect to a forsteritic composition. In addition, it may also explain why the chemical composition of olivine is iron poor. Unfortunately, magnesium silicide has never been detected via astronomical observation or in the analysis of primitive meteorites. I would suggest that future analysis of meteorites and theoretical calculations could confirm the possibility of the formation of magnesium silicide grains around evolved stars.

Kimura, Yuki; Nuth, J. A., III

2009-05-01

117

Molecular chemistry in a zeolite: genesis of a zeolite Y-supported ruthenium complex catalyst.  

PubMed

Dealuminated zeolite Y was used as a crystalline support for a mononuclear ruthenium complex synthesized from cis-Ru(acac)2(C2H4)2. Infrared (IR) and extended X-ray absorption fine structure spectra indicated that the surface species were mononuclear ruthenium complexes, Ru(acac)(C2H4)2(2+), tightly bonded to the surface by two Ru-O bonds at Al(3+) sites of the zeolite. The maximum loading of the anchored ruthenium complexes was one complex per two Al(3+) sites; at higher loadings, some of the cis-Ru(acac)2(C2H4)2 was physisorbed. In the presence of ethylene and H2, 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)(C2H4)2(2+) species was dissociated and captured by an Al(3+) site. Ethylene dimerization proceeded approximately 600 times faster with a cofeed of ethylene and H2 than without H2. These results provide evidence of the importance of the cooperation of the Al(3+) sites in the zeolite and the H2 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. PMID:18785737

Ogino, Isao; Gates, Bruce C

2008-09-12

118

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

119

Selective sorption by zeolites  

SciTech Connect

An improved adsorptive separation process by the selective sorption properties of certain members of a novel class of zeolites is provided. The novel class of zeolites is characterized by a silica to alumina mole ratio greater than 12 and a Constraint Index within the approximate range of greater than 2 to about 12. The process of this invention involves selective separation of waxy paraffinic compounds in admixture with stocks containing paraffinic compounds, e.g. crude oils, heavy oils, distillate oils and lube base oils, by contacting the mixture with a zeolite having a SiO/sub 2//Al/sub 2/O/sub 3/ mole ratio of at least about 12 and a Constraint Index within the range of greater than 2 to about 12 to effect the selective sorption of said waxy paraffinic compounds by said zeolite.

Dessau, R.M.

1984-05-15

120

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

121

Zeolites for reforming catalysts  

Microsoft Academic Search

This patent describes a reforming catalyst exhibiting enhanced selectivity, activity, and activity maintenance. It comprises: zeolite crystals having a pH within the range of 9.4 to 10.0, wherein the pH is determined by measuring pH of supernatent liquid from a mixture of one part of the zeolite crystals with ten parts of dionized water by weight, and comprising exchangeable cations

J. L. Kao; M. Nadler; M. J. Potter; R. V. Martir

1991-01-01

122

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves  

NASA Astrophysics Data System (ADS)

Zeolites are microporous crystalline materials that find wide application in industry, for example, as catalysts and gas separators, and in our daily life, for example, as adsorbents or as ion exchangers in laundry detergents. The tetrahedrally coordinated silicon and aluminium atoms in the zeolite unit cell occupy the so-called crystallographic T-sites. Besides their pore size, the occupation of specific T-sites by the aluminium atoms determines the performance of the zeolites. Despite its importance, the distribution of aluminium over the crystallographic T-sites remains one of the most challenging, unresolved issues in zeolite science. Here, we report how to determine unambiguously and directly the distribution of aluminium in zeolites by means of the X-ray standing wave technique using brilliant, focused X-rays from a third-generation synchrotron source. We report in detail the analysis of the aluminium distribution in scolecite, which demonstrates how the aluminium occupancy in zeolites can systematically be determined.

van Bokhoven, Jeroen A.; Lee, Tien-Lin; Drakopoulos, Michael; Lamberti, Carlo; Thieß, Sebastian; Zegenhagen, Jörg

2008-07-01

123

Bromides in zeolite synthesis \\/ zeolites in bromide synthesis and conversion  

Microsoft Academic Search

Quaternary ammonium bromides and hydroxides (quats) are applied as templates in the synthesis of zeolites with relatively high Si\\/Al ratio. Examples will be given of the use of mon-, di-, poly- and associated quats as templates in zeolite growth. Templated zeolites of the MFI-type can be grown in a lateral or in an axial way onto metal supports, providing promising

H. Van Bekkum

1995-01-01

124

Preparation of functionalized zeolitic frameworks  

SciTech Connect

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

125

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

126

Fluoroalkyleneether Silicate Copolymers.  

National Technical Information Service (NTIS)

Fluoroalkyleneether silicate copolymers are synthesized by the polycondensation of a bis-dimethylcarbinol containing a fluoroalkyleneether segment and bis-(dimethylamino) methylvinylsilane. The copolymers are useful in applications, e.g., as seals and sea...

R. E. Cochoy

1978-01-01

127

X-ray photoelectron spectroscopic investigation of nanocrystalline calcium silicate hydrates synthesised by reactive milling  

SciTech Connect

X-ray photoelectron spectroscopy (XPS) has been used to analyse a series of mechanochemically synthesised, nanocrystalline calcium silicate hydrates (C-S-H). The samples, with Ca/Si ratios of 0.2 to 1.5, showed structural features of C-S-H(I). XPS analysis revealed changes in the extent of silicate polymerisation. Si 2p, Ca 2p and O 1s spectra showed that, unlike for the crystalline calcium silicate hydrate phases studied previously, there was no evidence of silicate sheets (Q{sup 3}) at low Ca/Si ratios. Si 2p and O 1s spectra indicated silicate depolymerisation, expressed by decreasing silicate chain length, with increasing C/S. In all spectra, peak narrowing was observed with increasing Ca/Si, indicating increased structural ordering. The rapid changes of the slope of FWHM of Si 2p, {delta} {sub Ca-Si} and {delta} {sub NBO-BO} as function of C/S ratio indicated a possible miscibility gap in the C-S-H-solid solution series between C/S 5/6 and 1. The modified Auger parameter ({alpha}') of nanocrystalline C-S-H decreased with increasing silicate polymerisation, a trend already observed studying crystalline C-S-H. Absolute values of {alpha}' were shifted about - 0.7 eV with respect to crystalline phases of equal C/S ratio, due to reduced crystallinity.

Black, Leon [Forschungszentrum Karlsruhe GmbH, Institut fuer Technische Chemie, Bereich Thermische Abfallbehandlung (ITC-TAB), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany) and Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB (United Kingdom)]. E-mail: l.black@shu.ac.uk; Garbev, Krassimir [Forschungszentrum Karlsruhe GmbH, Institut fuer Technische Chemie, Bereich Thermische Abfallbehandlung (ITC-TAB), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Beuchle, Guenter [Forschungszentrum Karlsruhe GmbH, Institut fuer Technische Chemie, Bereich Thermische Abfallbehandlung (ITC-TAB), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Stemmermann, Peter [Forschungszentrum Karlsruhe GmbH, Institut fuer Technische Chemie, Bereich Thermische Abfallbehandlung (ITC-TAB), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Schild, Dieter [Forschungszentrum Karlsruhe GmbH, Institut fuer Nukleare Entsorgung (INE), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

2006-06-15

128

Crystalline solids.  

PubMed

Many drugs exist in the crystalline solid state due to reasons of stability and ease of handling during the various stages of drug development. Crystalline solids can exist in the form of polymorphs, solvates or hydrates. Phase transitions such as polymorph interconversion, desolvation of solvate, formation of hydrate and conversion of crystalline to amorphous form may occur during various pharmaceutical processes, which may alter the dissolution rate and transport characteristics of the drug. Hence it is desirable to choose the most suitable and stable form of the drug in the initial stages of drug development. The current focus of research in the solid-state area is to understand the origins of polymorphism at the molecular level, and to predict and prepare the most stable polymorph of a drug. The recent advances in computational tools allow the prediction of possible polymorphs of the drug from its molecular structure. Sensitive analytical methods are being developed to understand the nature of polymorphism and to characterize the various crystalline forms of a drug in its dosage form. The aim of this review is to emphasize the recent advances made in the area of prediction and characterization of polymorphs and solvates, to address the current challenges faced by pharmaceutical scientists and to anticipate future developments. PMID:11325474

Vippagunta, S R; Brittain, H G; Grant, D J

2001-05-16

129

Palagonite-like Alteration Products on the Earth and Mars 2: Secondary Mineralogy of Crystalline Basalts Weathered Under Semi-Arid Conditions  

NASA Astrophysics Data System (ADS)

In weathering rinds of crystalline basalts, we find poorly crystalline secondary silicates, similar to palagonites. Small volumes of these products cause rinds to have "glassy" thermal-IR spectra. Similar spectral surfaces on Mars may be altered.

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

2005-03-01

130

Adamantanes from petroleum with zeolites  

Microsoft Academic Search

Experiments with zeolite Beta and zeolite Y demonstrate that adamantane and methyl adamantanes can be isolated very effectively from modern refinery streams by mild hydrocracking over Pt-and Pd-containing large pore zeolites. Yield depends importantly on individual refinery crude source and process configuration. Heavy crudes and refineries with conventional hydrocracking and FCC feed hydrotreater facilities are particularly desirable, and an ideal

L. Deane Rollmann; Larry A. Green; Robert A. Bradway; Hye Kyung C. Timken

1996-01-01

131

Estudio de zeolitas de hierro por el efecto Moessbauer y la resonancia paramagnetica electronica. (Study of iron exchanged zeolites by Moessbauer effect and electron spin resonance spectroscopy).  

National Technical Information Service (NTIS)

Crystalline iron exchanged NaY zeolites, prepared from aqueous solutions and calcined at atmospheric conditions, have been studied and characterized by XRD, Moessbauer and EPR spectroscopies and TGA analysis. Three iron sites are clearly distinguished fro...

C. E. Aguirre Campuzano

1993-01-01

132

Tumbling approach towards template-free synthesis of EMT zeolite  

Microsoft Academic Search

The zeolite EMT has been synthesized with 18-crown-6\\/Al2O3 ratios as low as 0.14, by applying continuous tumbling of the synthesis mixture during the entire aging and crystallization period. The crystalline product contained only two crown ether molecules per unit cell, and the mother liquor was essentially free of crown ether. It was found that the lower the amount of crown

Rune Wendelbo; Michael Stöcker; Hanne Junggreen; Helle B Mostad; Duncan E Akporiaye

1999-01-01

133

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

134

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

135

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

136

Hydrogen storage enhanced in Li-doped carbon replica of zeolites: A possible route to achieve fuel cell demand  

NASA Astrophysics Data System (ADS)

We first report the atomistic grand canonical Monte Carlo simulations of the synthesis of two realistic ordered microporous carbon replica in two siliceous forms of faujasite zeolite (cubic Y-FAU and hexagonal EMT). Atomistic simulations of hydrogen adsorption isotherms in these two carbon structures and their Li-doped composites were carried out to determine their storage capacities at 77 and 298 K. We found that these new forms of carbon solids and their Li-doped versions show very attractive hydrogen storage capacities at 77 and 298 K, respectively. However, for a filling pressure of 300 bars and at room temperature, bare carbons do not show advantageous performances compared to a classical gas cylinder despite of their crystalline micropore network. In comparison, Li-doped nanostructures provide reversible gravimetric and volumetric hydrogen storage capacities twice larger (3.75 wt % and 33.7 kg/m3). The extreme lattice stiffness of their skeleton will prevent them from collapsing under large external applied pressure, an interesting skill compared to bundle of carbon nanotubes, and metal organic frameworks (MOFs). These new ordered composites are thus very promising materials for hydrogen storage issues by contrast with MOFs.

Roussel, Thomas; Bichara, Christophe; Gubbins, Keith E.; Pellenq, Roland J.-M.

2009-05-01

137

Aromatization of propene on modified montmorillonite-containing catalysts based on high-silica NTsVM zeolite  

SciTech Connect

Much attention is given today to the properties and uses of semiartificial lamellar silicates. The authors have examined the influence of additions of metal ions (Zn{sup 2+}, Ga{sup 3+}, Cr{sup 3+}) on catalytic properties of samples prepared from high-silica zeolite NTsVM and lamellar-pillared montmorillonite in aromatization of propene.

Stepanova, E.A.; Bolotnikova, E.V.; Rat`ko, A.I. [Institute of General and Inorganic Chemistry, Minsk (Belarus)

1995-10-10

138

Hydrogen storage enhanced in Li-doped carbon replica of zeolites: A possible route to achieve fuel cell demand  

Microsoft Academic Search

We first report the atomistic grand canonical Monte Carlo simulations of the synthesis of two realistic ordered microporous carbon replica in two siliceous forms of faujasite zeolite (cubic Y-FAU and hexagonal EMT). Atomistic simulations of hydrogen adsorption isotherms in these two carbon structures and their Li-doped composites were carried out to determine their storage capacities at 77 and 298 K.

Thomas Roussel; Christophe Bichara; Keith E. Gubbins; Roland J.-M. Pellenq

2009-01-01

139

Laboratory spectra of amorphous and crystalline olivine: An application to comet Halley IR spectrum.  

National Technical Information Service (NTIS)

Among the various silicates proposed as components of cosmic dust grains, olivine is considered one of the most likely materials. In this work we present the infrared spectra of three different types of olivine grains: crystalline, amorphous, and syntheti...

A. Blanco V. Orofino E. Bussoletti S. Fonti L. Colangeli

1990-01-01

140

Zeolite-Hydraulic Cement Containment Medium.  

National Technical Information Service (NTIS)

The invention generally relates to a zeolite-hydraulic cement containment medium for hazardous wastes. In particular, the invention relates to a process for preparing a zeolite-portland cement containment medium from a paste prepared by mixing zeolite in ...

P. M. Brown M. A. Maginnis C. R. Furlong M. G. Bakker G. L. Turner

1994-01-01

141

Adhesion of Hydrated Silicate Films.  

National Technical Information Service (NTIS)

We used fracture mechanics test techniques to measure the adhesive bond energy formed between hydrated silica glass surfaces and silicate species deposited from solution. In the case of silicate surfaces hydrated in room temperature water vapor, intermole...

T. A. Michalske K. D. Keefer

1988-01-01

142

Praseodymium silicate formed by postdeposition high-temperature annealing  

SciTech Connect

Praseodymium silicate (Pr silicate) has been synthesized by molecular-beam deposition of Pr{sub 2}O{sub 3} layers on Si(111) substrates and subsequent high-temperature postdeposition annealing at 1000 deg. C. This thermal treatment drastically changes the film texture from the crystalline Pr{sub 2}O{sub 3} epitaxially grown on Si, into Pr silicate with completely amorphized structures, resulting from intermixing of Si from the substrate. It was found that the electrical characteristics of Pr silicate were critically dependent on the quality of the as-deposited Pr{sub 2}O{sub 3} films. A typical dielectric constant and a leakage current density of Pr silicate grown under an optimal condition were, respectively, 19.7 and 3x10{sup -9} A cm{sup -2} at +1 V relative to the flatband voltage for an equivalent oxide thickness of 1.9 nm. Using x-ray photoelectron spectroscopy, a valence-band offset at the Pr-silicate/Si(111) interface of 2.75 eV and a band gap of 6.50 eV were obtained. The large band gap and the highly symmetric band alignment account for the observed low leakage current density.

Sakai, Akira; Sakashita, Shinsuke; Sakashita, Mitsuo; Yasuda, Yukio; Zaima, Shigeaki; Miyazaki, Seiichi [Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Center for Cooperative Research in Advanced Science and Technology, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Department of Electrical Engineering, Graduate School of Advanced Science of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530 (Japan)

2004-11-29

143

Mesoporous templated silicates: an overview of their synthesis, catalytic activation and evaluation of the stability  

Microsoft Academic Search

The most recent developments in the formation of new mesoporous templated zeolitic materials, characterized by surfaces of more than 1000 m2\\/g, are discussed in this paper. By adapting the synthesis parameters, such as type of silicium source, type of template, pH, temperature,… different materials can be synthesized with varying porosity and crystallinity. Besides the synthesis, much attention is focused on

T Linssen; K Cassiers; P Cool; E. F Vansant

2003-01-01

144

Capped Mesoporous Silicates.  

National Technical Information Service (NTIS)

The invention provides an article comprising, a mesoporous silicate matrix, such as a particle, having one or more pores; and one or more releasable caps obstructing one or more of the pores. The articles are useful as delivery vehicles for encapsulated a...

C. Y. Lai D. M. Jeftinija S. Jeftinija V. S. Y. Lin

2004-01-01

145

Calcium silicate insulation structure  

DOEpatents

An insulative structure including a powder-filled evacuated casing utilizes a quantity of finely divided synthetic calcium silicate having a relatively high surface area. The resultant structure-provides superior thermal insulating characteristics over a broad temperature range and is particularly well-suited as a panel for a refrigerator or freezer or the insulative barrier for a cooler or a insulated bottle.

Kollie, Thomas G. (Oak Ridge, TN); Lauf, Robert J. (Oak Ridge, TN)

1995-01-01

146

In-situ growth of porous alumino-silicates and fabrication of nano-porous membranes  

Microsoft Academic Search

Feasibility of depositing continuous films of nano-porous alumino-silicates, primarily zeolites and MCM-41, on metallic and non-metallic substrates was examined with an aim to develop membranes for separation of gaseous mixtures and also for application as hydrogen storage material. Mesoporous silica was deposited in-side the pores of these nano-porous disks with an aim to develop membranes for selective separations. Our study

Pradeep Kodumuri

2009-01-01

147

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

148

Experimental Proof for Resonant Diffusion of Normal Alkanes in LTL and ZSM-12 Zeolites  

Microsoft Academic Search

The intra-crystalline diffusion of normal alkanes in LTL and ZSM-12 zeolite was experimentally studied via gravimetric measurements performed at different temperatures. A periodic dependence of the diffusion coefficient on the number of carbon atoms in alkane was detected, which is an experimental proof for resonant diffusion. The present observations were described on the base of the existing theory of the

Kyesang Yoo; Roumen Tsekov; P. G. Smirniotis

2003-01-01

149

Monoethanol amine modified zeolite 13X for CO adsorption at different temperatures  

Microsoft Academic Search

Zeolite 13X has been modified with monoethanol amine (MEA). MEA loadings of 0.5-25 wt % have been achieved using the impregnation method in different solvents. The mode of incorporation based on methanol with stirring at room temperature appears to be the most feasible. The adsorbent has been characterized for crystallinity, surface area, pore volume, and pore size. The thermal stability

P. D. Jadhav; R. V. Chatti; R. B. Biniwale; N. K. Labhsetwar; S. Devotta; S. S. Rayalu

2007-01-01

150

Resonant diffusion of normal alkanes in zeolites: effect of the zeolite structure and alkane molecule vibrations  

Microsoft Academic Search

Diffusion of normal alkanes in one-dimensional zeolites is theoretically studied on the basis of the stochastic equation formalism. The calculated diffusion coefficient accounts for the vibrations of the diffusing molecule and zeolite framework, molecule-zeolite interaction, and specific structure of the zeolite. It is shown that when the interaction potential is predominantly determined by the zeolite pore structure, the diffusion coefficient

Roumen Tsekov; Panagiotis G. Smirniotis

1998-01-01

151

European Microgravity Facilities for ZEOLITE Experiments on the International Space Station  

NASA Astrophysics Data System (ADS)

Synthetic zeolites are complex porous silicates. Zeolites are applied as catalysts, adsorbents and sensors. Whereas the traditional applications are situated in the petrochemical area, zeolite catalysis and related zeolite-based technologies have a growing impact on the economics and sustainability of products and processes in a growing number of industrial sectors, including environmental protection and nanotechnology. A Sounding Rocket microgravity experiment led to significant insight in the physical aggregation patterns of zeolitic nanoscopic particles and the occurrence of self-organisation phenomena when undisturbed by convection. The opportunity of performing longer microgravity duration experiments on zeolite structures was recently offered in the frame of a Taxi-Flight to the ISS in November 2002 organized by Belgium and ESA. Two facilities are currently under development for this flight. One of them will use the Microgravity Science Glovebox (MSG) in the US Lab. Destiny to achieve thermal induced self-organization of different types of Zeosil nanoslabs by heating and cooling. The other facility will be flown on the ISS Russian segment and will allow to form Zeogrids at ambient temperature. On the other hand, the European Space Agency (ESA) is studying the possibility of developing a dedicated insert for zeolite experiments to be used with the optical and diagnostic platform of the Protein Crystallisation Diagnostic Facility (PCDF), that will fly integrated in the European Drawer Rack on the Columbus Laboratory starting in 2004. This paper will present the approach followed by ESA to prepare and support zeolite investigations in microgravity and will present the design concept of these three facilities.

Pletser, V.; Minster, O.; Kremer, S.; Kirschhock, C.; Martens, J.; Jacobs, P.

2002-01-01

152

Catalytic cracking of hydrocarbons with oxygen promoted alkali metal zeolite cracking catalyst  

SciTech Connect

This patent describes a process for the catalytic cracking of a hydrocarbon oil. It comprises contacting the oil with 0.001 to 0.1 weight parts of oxygen for each weight of oil at a temperature in excess 1000 {degrees} F. with a catalyst which is essentially free of shape selective combustion catalyst and comprising a large pore, alkali metal silicate zeolite cracking catalyst.

Chen, N.Y.; Degnan, T.F.

1989-11-21

153

Synthesis, Ion-exchange, Structural Characterization and Adsorption of K, Na-FER Type Zeolite  

Microsoft Academic Search

Synthesis of K, Na -FER type zeolite wasstudied in the reactant system ofK 2O-–Na 2O-–Al 2O 3-–SiO 2-–CO 3-–HCO 3-ndash;H 2O.Sodium silicate, silica sol andfumed silica were tested as the silica source, andsolid aluminum sulfate, aluminum hydroxide andmeta-kaolinite as the alumina source. The startingmaterials, the composition of the reactant, and thesynthesis temperature greatly influence the phasescrystallized. A pure phase of

Yingcai Long; Minghua Ma; Yaojun Sun; Huiwen Jiang

2000-01-01

154

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

155

Improved zeolitic isocracking catalysts  

SciTech Connect

Chevron Research Company introduced the first low pressure, low temperature catalytic hydrocracking process--ISOCRACKING--in 1959. Within the last four years, Chevron has developed and commercialized three new zeolitic ISOCRACKING catalysts. ICR 209 is Chevron`s latest noble metal ISOCRACKING catalyst. It offers improved liquid yield stability, longer life, and superior polynuclear aromatics control compared to its predecessor. ICR 209`s high hydrogenation activity generates the highest yields of superior quality jet fuel of any zeolitic ISOCRACKING catalyst. The second new ISOCRACKING catalyst, ICR 208, is a base metal catalyst which combines high liquid selectivity and high light naphtha octane in hydrocrackers operating for maximum naphtha production. ICR 210 is another new base metal catalyst which offers higher liquid yields and longer life than ICR 208 by virtue of a higher hydrogenation-to-acidity ratio. Both ICR 208 and ICR 210 have been formulated to provide higher liquid yield throughout the cycle and longer cycle length than conventional base metal/zeolite catalysts. This paper will discuss the pilot plant and commercial performances of these new ISOCRACKING catalysts.

Dahlberg, A.J.; Habib, M.M.; Moore, R.O. [Chevron Research and Technology Co., Richmond, CA (United States); Law, D.V. [Chevron International Oil Co., San Francisco, CA (United States); Convery, L.J. [ABB Lummus Crest, Bloomfield, NJ (United States)

1995-09-01

156

Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts.  

PubMed

Zeolites-microporous crystalline aluminosilicates-are widely used in petrochemistry and fine-chemical synthesis because strong acid sites within their uniform micropores enable size- and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion. This has been realized by synthesizing zeolite nanocrystals, by exfoliating layered zeolites, and by introducing mesopores in the microporous material through templating strategies or demetallation processes. But except for the exfoliation, none of these strategies has produced 'ultrathin' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications. PMID:19741706

Choi, Minkee; Na, Kyungsu; Kim, Jeongnam; Sakamoto, Yasuhiro; Terasaki, Osamu; Ryoo, Ryong

2009-09-10

157

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

158

Zeolite modification II - direct fluorination  

Microsoft Academic Search

Over the past thirty years, zeolite science has grown into a major branch of chemistry. A large number of new zeolite materials have been made by both direct hydrothermal synthesis and by post-synthesis modification. This has led to a large number of new applications in such diverse fields as catalysis, adsorption and ion exchange. In synthesis alone, over one hundred

B. M. Lok; F. P. Gortsena; P. J. Izod; C. A. Messina; H. Rastelli

1982-01-01

159

Zeolitic basanite from southeastern California  

Microsoft Academic Search

In a belt of Quaternary volcanism within the Mojave Desert, California, lavas of alkali-olivine basalt have been extruded from many centers. Also three small volcanoes erupted alkaline lavas similar to basanite, except that the zeolites phillipsite and chabazite crystallized in the groundmass instead of the usual feldspathoid. These zeolite-bearing lavas, more alkaline than the olivine basalts, brought many peridotitic nodules

W. S. Wise

1966-01-01

160

The safety of synthetic zeolites used in detergents.  

PubMed

Synthetic zeolites are replacing phosphates as builders in laundry detergents; workers and consumers may, therefore, increasingly be exposed to these materials and it is important to assess their safety. This article puts mechanistic, toxicological and exposure data into context for a safety assessment. Zeolites are hygroscopic compounds with ion-exchanging properties. They may partially decompose under acidic conditions such as in the stomach releasing sodium ions, silicic acid and aluminum salts. The intact molecule is not bioavailable after oral intake or exposure through the dermal and inhalational routes. Under current conditions of manufacture and use, no systemic toxicity is to be expected from neither the intact molecule nor the degradation products; a significant effect on the bioavailability of other compounds is not likely. Zeolites may cause local irritation. It is, therefore, important to minimise occupational exposure. The co-operation of detergent manufacturers with the manufacturers of washing machines is necessary to find the right balance between environmental aspects such as energy and water savings and the occurrence of detergent residues on textiles due to insufficient rinsing. PMID:18563391

Fruijtier-Pölloth, Claudia

2008-06-18

161

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

162

Small-angle neutron scattering studies of the template-mediated crystallization of ZSM-5 type zeolite  

SciTech Connect

Small-angle neutron scattering is a useful new approach to the study of zeolite crystallization from aluminosilicate gels and the action of template molecules. It has been applied to gels for synthesis of zeolite ZSM-5 using tetrapropylammonium ions as templates where the scattering length densities of the gel particles and their texture were determined using contrast variation methods. Gels formulated from soluble silicate incorporate template molecules promptly into an amorphous embryonic'' structure and crystallization ensues via a solid hydrogel transformation mechanism. Gels formulated from colloidal silica show different scattering behavior, and a liquid phase transport mechanism is inferred. 8 refs., 4 figs., 2 tabs.

Iton, L.E.; Brun, T.O.; Epperson, J.E. (Argonne National Lab., IL (USA). Materials Science and Technology Div.); Trouw, F. (Argonne National Lab., IL (USA). Intense Pulsed Neutron Source (IPNS) Program); White, J.W.; Henderson, S.J. (Australian National Univ., Canberra (Australia))

1988-03-01

163

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

164

Properties and applications of zeolites.  

PubMed

Zeolites are aluminosilicate solids bearing a negatively charged honeycomb framework of micropores into which molecules may be adsorbed for environmental decontamination, and to catalyse chemical reactions. They are central to green-chemistry since the necessity for organic solvents is minimised. Proton-exchanged (H) zeolites are extensively employed in the petrochemical industry for cracking crude oil fractions into fuels and chemical feedstocks for other industrial processes. Due to their ability to perform cation-exchange, in which the cations that are originally present to counterbalance the framework negative charge may be exchanged out of the zeolite by cations present in aqueous solution, zeolites are useful as industrial water-softeners, in the removal of radioactive Cs+ and Sr2+ cations from liquid nuclear waste and in the removal of toxic heavy metal cations from groundwaters and run-off waters. Surfactant-modified zeolites (SMZ) find particular application in the co-removal of both toxic anions and organic pollutants. Toxic anions such as arsenite, arsenate, chromate, cyanide and radioactive iodide can also be removed by adsorption into zeolites that have been previously loaded with co-precipitating metal cations such as Ag+ and Pb2+ which form practically insoluble complexes that are contained within the zeolite matrix. PMID:21047018

Rhodes, Christopher J

2010-01-01

165

Nanoparticle formation and zeolite growth in TEOS/Organocation/water solutions.  

PubMed

This work investigates nanoparticle formation and zeolite growth in several tetraethyl orthosilicate (TEOS)/organocation/water solutions heated at 368 K using small-angle X-ray scattering. The effect of several synthesis parameters including organocation identity, hydroxide content, alkali content, synthesis temperature, ethanol content, and seeding are investigated. In all cases the TEOS/organocation/water solutions lead to colloidal silica nanoparticles both after aging at room temperature and after hydrothermal treatment. In addition, the size, number density, and shape of the colloidal particles depend on the organocation identity. However, in contrast to TEOS/TPAOH/water mixtures that rapidly form silicalite-1 at 368 K, none of the investigated solutions can direct the formation of a zeolite phase at 368 K. The key point that emerges from this investigation is that it is not straightforward to synthesize siliceous zeolites from clear solutions at 368 K with the investigated organocations under the conditions where silicalite-1 forms in a matter of hours. These results suggest that the zeolite community may wish to take pause before formulating a "general" description of zeolite nucleation and growth from the studies of silicalite-1 grown from clear solution at 368 K. PMID:16851831

Cheng, Chil-Hung; Shantz, Daniel F

2005-04-21

166

Crystallinity in starch bioplastics  

Microsoft Academic Search

Thermoplastic starch (TPS) materials have been prepared by kneading, extrusion, compression moulding and injection moulding of several native starches with the addition of glycerol as a plasticizer. Two types of crystallinity can be distinguished in TPS directly after processing: (i) residual crystallinity: native A-, B- or C-type crystallinity caused by incomplete melting of starch during processing; (ii) processing-induced crystallinity: amylose

Jeroen J. G. van Soest; S. H. D. Hulleman; D. de Wit; J. F. G. Vliegenthart

1996-01-01

167

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

168

Two stage process for improving the catalyst life of zeolites in the synthesis of lower olefins from alcohols and their ether derivatives  

SciTech Connect

A process is described for converting an alcohol and/or ether feed as hereinafter defined to a hydrocarbon mixture rich in olefins which comprises contacting, under conversion conditions at a conversion reaction temperature of from about 300/sup 0/ to 350/sup 0/C., a feed comprising one or more monohydric alcohols having from about 1 to about 4 carbon atoms, ethers derived therefrom, or mixtures of the alcohols and ethers, with a modified crystalline metalosilicate shape selective acidic zeolite. The metalosilicate is selected from the group consisting of aluminum, gallium, and mixtures thereof, and the zeolite, prior to modification and in the absence of any coke deposited thereon, possesses: (a) the capability of catalyzing the alcohol and/or other conversion reaction; (b) a channel size and structure such as to permit (i) entry of the feed into the zeolite and diffusion to the active acid sites within the zeolite, and (ii) formation of olefin products within the zeolite and diffusion of the products out of the zeolite; and (c) hydrothermal stability at temperatures of at least about 290/sup 0/C. The modification of the zeolite is conducted in a manner sufficient to increase the catalyst life of the zeolite, relative to the absence of the modification when the zeolite is employed as a catalyst for the alcohol and/or ether conversion reaction.

Pieters, W.J.M.; Okumura, Y.

1987-01-20

169

Stardust silicates from primitive meteorites  

Microsoft Academic Search

Primitive chondritic meteorites contain material (presolar grains), at the level of a few parts per million, that predates the formation of our Solar System. Astronomical observations and the chemical composition of the Sun both suggest that silicates must have been the dominant solids in the protoplanetary disk from which the planets of the Solar System formed, but no presolar silicates

Kazuhide Nagashima; Alexander N. Krot; Hisayoshi Yurimoto

2004-01-01

170

The first examples of X-ray phosphors, and C-band infrared emitters based on microporous lanthanide silicates  

Microsoft Academic Search

The synthesis and luminescence characterisation of microporous Tb3+- and Er3+-silicates (Na4K2Ln2Si16O38·10H2O, AV-9 materials) are reported. These solids possess a structure related to the structure of mineral montregianite and are the first examples of siliceous materials combining zeolite-like properties with X-ray induced luminescence and infrared emission. The photoluminescence (PL) integrated intensity of Tb-AV-9 is 60% of the integrated intensity of the

D Ananias; J. P Rainho; A Ferreira; J Rocha; L. D Carlos

2004-01-01

171

Electron microscopy study of zeolite ZK-14; a synthetic chabazite  

NASA Astrophysics Data System (ADS)

The defect structure of zeolite (K+, TMA+) — ZK-14, a synthetic chabazite, has been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM together with TEM bright field (BF) and dark field (DF) micrographs indicate that the hexagonal, platelet ZK-14 crystals are built up of crystalline blocks joined by twinning along (00.1). High resolution transmission electron microscopy (HRTEM) reveals faulting of the ideal AABBCC single 6-ring stacking sequence of ZK-14. This is consistent with an observed line broadening in its X-ray powder diffraction profile. Channel apertures are imaged, even for thick specimens.

Cartlidge, S.; Wessicken, R.; Nissen, H.-U.

1983-03-01

172

Effects of step-change of synthesis temperature on synthesis of zeolite 4A from coal fly ash  

Microsoft Academic Search

Pure form, single phase and high crystalline zeolite 4A samples were synthesized by applying step-change of synthesis temperature during hydrothermal treatment of coal fly ash prepared solution. The results indicate that step-change of synthesis temperature during hydrothermal treatment plays an important role in reducing the overall synthesis time while maintaining a high degree of crystallinity for the samples. In order

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

2006-01-01

173

Stimulated short-wave emission of charged particles in natural hollow crystalline channels  

Microsoft Academic Search

A quantum theory of the spontaneous and stimulated emission of relativistic and nonrelativistic charged particles moving in natural hollow cylindrical crystalline channels is elaborated with reference to the development of X-ray and gamma lasers. The example of channels in zeolite and chrysolite-asbestos is used to illustrate the features of the quantized motion of particles in such structures, as well as

V. I. Vysotskii; P. N. Kuzmin

1983-01-01

174

Zeolitic basanite from southeastern California  

Microsoft Academic Search

In a belt of Quaternary volcanism within the Mojave Desert, California, lavas of alkali-olivine basalt have been extruded\\u000a from many centers. Also three small volcanoes erupted alkaline lavas similar to basanite, except that the zeolites phillipsite\\u000a and chabazite crystallized in the groundmass instead of the usual feldspathoid. These zeolite-bearing lavas, more alkaline\\u000a than the olivine basalts, brought many peridotitic nodules

W. S. Wise

1966-01-01

175

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

176

Electronic structure calculations of calcium silicate hydrates  

SciTech Connect

Many phases in the calcium-silicate-hydrate system can develop in cement exposed over long periods of time to temperatures above 25 C. As a consequence, chemical reactions involving these phases can affect the relative humidity and water chemistry of a radioactive waste repository that contains significant amounts of cement. In order to predict and simulate these chemical reactions, the authors are developing an internally consistent database of crystalline Ca-Si-hydrate structures. The results of first principles electronic structure calculations on two such phases, wollastonite (CaSiO{sub 3}) and xonotlite (Ca{sub 6}Si{sub 6}O{sub 17}(OH){sub 2}), are reported here. The calculated ground state properties are in very good agreement with experiment, providing equilibrium lattice parameters within about 1--1.4% of the experimentally reported values. The roles of the different types of oxygen atoms, which are fundamental to understanding the energetics of crystalline Ca-Si-hydrates are briefly discussed in terms of their electronic state densities. The good agreement with experiment for the lattice parameters and the consistency of the electronic density of states features for the two structures demonstrate the applicability of these electronic structure methods in calculating the fundamental properties of these phases.

Sterne, P.A. [Univ. of California, Davis, CA (United States). Dept. of Physics]|[Lawrence Livermore National Lab., CA (United States); Meike, A. [Lawrence Livermore National Lab., CA (United States)

1995-11-01

177

Siliceous cements and their timing relations in arkosic arenites, Lobo formation (Paleocene-Eocene), southwestern New Mexico  

SciTech Connect

Arkoses (Q/sub 46/F/sub 53/L/sub 1/) with subequal amounts of K-feldspar and plagioclase contain a variety of siliceous cements composing over 96% of those authigenic products present. Textural intergrowths and cement stratigraphy indicate siliceous phases overlap or postdate pure limonite and feldspar overgrowth formation and predate zeolites, albitization, and calcite constituents. Four siliceous phases are present: (1) impure siliceous cement, (2) microquartz, (3) chalcedony, and (4) quartz overgrowths. The impure siliceous cement is 1-30 ..mu..m, subhedral to euhedral, equant to bladed microquartz intermixed with chlorite and/or limonite. The cement is pore filling and grain replacing. Microquartz is compositionally pure, equant, often euhedral, and less than 30 ..mu..m. It mainly lines pores. Bladed to fibrous habits with spherulitic fan textures are typical of chalcedony. Quartz overgrowths are larger sized and optically clear and possess optical continuity with host quartz grains. Although siliceous phases overlap in timing, the impure siliceous cement was the first precipitated followed by a dissolution event and growth of pure microquartz or chalcedony. Often pore-filling chalcedony postdates an isopachous grain coating of microquartz. Euhedral quartz overgrowths postdate all other siliceous phases. Precipitation of siliceous components may in part be related to pH decreases and/or the increasing activity of iron, aluminum, and magnesium constituents. Although previous studies have suggested the proportion of impurities present as the principal determinant for morphology of resultant siliceous phases, nucleation site density and geometry likely had a greater influence in this specific case.

James, W.C.; Russo, J.

1989-03-01

178

Aftereffects in zeolite-encapsulated 57Co-complexes  

NASA Astrophysics Data System (ADS)

Tris(2,2'-bipyridyl)-57CoII and bis(2,2':6',2'-terpyridine)-57CoII complexes were synthesised in the supercages of zeolite-Y in order to study the effect of molecular isolation on the aftereffects of the 57Co(EC)57Fe decay. As compared to the regular crystalline salts of the complex ions where, according to the emission Mössbauer spectra, the most abundant species is low-spin FeII, the molecular isolation in the zeolite resulted in a larger fraction of low-spin FeIII and a varying amount of high-spin Fe2+ species. In the investigated temperature range, 20 K to 295 K, the majority of the changes was observed above 80 K. In the case of tris (2,2'-bipyridyl)-57CoII-Y, the most characteristic change occurred in valence states, while for bis (2,2':6',2'-terpyridine)-57CoII-Y, the temperature dependence of the spin states was more prominent. The change in the low spin valence states is explained partly by donor-acceptor properties of the zeolite lattice. The variation in the high spin fraction is explained by radiation damage of the ligand sphere and/or fragmentation of the complex ion followed by incomplete recombination in the supercage. Molecular isolation itself did not seem to increase the chance of fragmentation (as a consequence of charge neutralization following Auger ionization) of these highly conjugated complex molecules.

Homonnay, Z.; Vankó, Gy.; Vértes, A.; Nath, A.; Spiering, H.; Gütlich, P.

1998-08-01

179

Metal-supported aluminosilicate ultrathin films as a versatile tool for studying the surface chemistry of zeolites.  

PubMed

The application of a variety of "surface-science" techniques to elucidate surface structures and mechanisms of chemical reactions at zeolite surfaces has long been considered as almost impossible because of the poor electrical and thermal conductivity of those materials. Here, we show that the growth of a thin aluminosilicate film on a metal single crystal under controlled conditions results in adequate and well-defined model systems for zeolite surfaces. In principle, silicate films that contain metals other than Al (e.g. Ti, Fe, etc) may be prepared in a similar way. We believe that this approach opens up a new playground for experimental and theoretical modeling of zeolites, aimed at a fundamental understanding of structure-reactivity relationships in such materials. PMID:23143912

Shaikhutdinov, Shamil; Freund, Hans-Joachim

2012-11-09

180

Effect of high-pressures on the electrical resistivity of natural zeolites from Deccan Trap, Maharashtra, India  

Microsoft Academic Search

We report here the electrical resistivity measurements on two natural zeolites–natrolite and scolecite (from the Killari borehole, Maharashtra, India) as a function of pressure up to 8 GPa at room temperature. High-pressure electrical resistivity studies on hydrous alumino-silicate minerals are very helpful in understanding the role of water in deep crustal conductivities obtained from geophysical models. The results obtained by

G. Parthasarathy

2006-01-01

181

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

182

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

183

Splitting Aluminosilicates with Silicate Bacteria.  

National Technical Information Service (NTIS)

An experiment was conducted to demonstrate the ability of silicate bacteria to break down the aluminosilicate nucleus in soils and the subsequent liberation of potassium. The equipment and procedures used in the experiment are described along with the res...

M. I. Ternovskaya R. N. Blagodyr V. G. Aleksandrov

1973-01-01

184

Mbosi: An anomalous iron with unique silicate inclusions  

NASA Astrophysics Data System (ADS)

The Mbosi iron meteorite contains millimeter size silicate inclusions. Mbosi is an ungrouped iron meteorite with a Ge/Ga ratio >10, which is an anomalous property shared with the five-member IIF iron group, the Eagle Station pallasites and four other ungrouped irons. Neither the IIF group nor the four other ungrouped irons are known to have silicate inclusions. Chips from three Mbosi inclusions were studied, but most of the work concentrated on a whole 3.1 mm circular inclusion. This inclusion consists of a mantle and a central core of different mineralogies. The mantle is partially devitrified quartz-normative glass, consisting of microscopic crystallites of two pyroxenes and plagioclase, which are crystalline enough to give an x-ray powder diffraction pattern but not coarse enough to permit analyses of individual minerals. The core consists of silica. The bulk composition does not match any known meteorite type, although there is a similarity in mode of occurrence to quartz-normative silicate inclusions in some HE irons. Mbosi silicate appears to be unique. The bulk rare earth element (REE) pattern of the mantle is flat at ? 7×C1; the core is depleted in REE but shows a small positive Eu anomaly. The O-isotope composition of bulk silicate lies on a unit slope mixing line (parallel and close to the C3 mixing line) that includes the Eagle Station pallasites and the iron Bocaiuva (related to the IIF irons); all of these share the property of having Ge/Ga ratios >10. It is concluded that Mbosi silicate represents a silica-bearing source rock that was melted and injected into metal. Melting occurred early in the history of the parent body because the metal now shows a normal Widmanstätten structure with only minor distortion that was caused when the parent body broke up and released meteorites into interplanetary space. The cause of Ge/Ga ratios being >10 in these irons is unknown. The fact that silicates in Mbosi, Bocaiuva (related to IIF irons) and the Eagle Station trio of pallasites, all characterized by a Ge/Ga ratio >10, lie on a unit slope mixing line in the O-isotope diagram suggests that their origins are closely related. The C3 chondrites appear to be likely precursors for silicates in Mbosi, Bocaiuva and the Eagle Station pallasites.

Olsen, Edward J.; Clayton, Robert N.; Mayeda, Toshiko K.; Davis, Andrew M.; Clarke, Roy S., Jr.; Wasson, John T.

1996-09-01

185

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

186

Characterisation of crystalline CSH phases by X-ray photoelectron spectroscopy  

Microsoft Academic Search

We have prepared a number of crystalline calcium-silicate-hydrate (C-S-H) phases hydrothermally, with calcium–silicon ratios varying from approximately 0.5 (K-phase) to 2.0 (hillebrandite and ?-dicalcium silicate hydrate). The phases were then analysed using X-ray photoelectron spectroscopy (XPS). Increasing calcium–silicon ratios resulted in decreased silicon binding energies. Additionally, changes in the O 1s spectra could be explained in terms of bridging (BO)

Leon Black; Krassimir Garbev; Peter Stemmermann; Keith R. Hallam; Geoffrey C. Allen

2003-01-01

187

Adhesion of hydrated silicate films  

SciTech Connect

We used fracture mechanics test techniques to measure the adhesive bond energy formed between hydrated silica glass surfaces and silicate species deposited from solution. In the case of silicate surfaces hydrated in room temperature water vapor, intermolecular bonding between hydrated surfaces can be attributed to either hydrogen bonding interactions between adsorbed water molecules (0.15 Jm/sup 2/) or electrostatic bonds formed between adsorbed cations and anionic-nonbridging surface oxygen groups (2.0 Jm/sup 2/). The bonding interaction observed at room temperature depends upon the glass surface composition and the degree of surface hydration. When hydrated silicate solution species are added to the interface and heat treated, adhesion energies as large as the cohesive energy of silica glass can be obtained with heat treatments as low as 200/degree/C. The adhesion of the silicate interfacial film produced by the addition of solution species is greatest for silicate precursors showing a low degree of molecular crosslinking. In addition, the presence of alkali in the silicate solution greatly enhances interface adhesion for heat treatments below 200/degree/C. 9 refs., 10 figs.

Michalske, T.A.; Keefer, K.D.

1988-01-01

188

THE BIOCOMPATIBILITY OF MESOPOROUS SILICATES  

PubMed Central

Micro- and nano- mesoporous silicate particles are considered potential drug delivery systems because of their ordered pore structures, large surface areas and the ease with which they can be chemically modified. However, few cytotoxicity or biocompatibility studies have been reported, especially when silicates are administered in the quantities necessary to deliver low-potency drugs. The biocompatibility of mesoporous silicates of particle sizes ~ 150 nm, ~ 800 nm and ~ 4 µm and pore sizes of 3 nm, 7 nm and 16 nm respectively are examined here. In vitro, mesoporous silicates showed a significant degree of toxicity at high concentrations with mesothelial cells. Following subcutaneous injection of silicates in rats, the amount of residual material decreased progressively over three months, with good biocompatibility on histology at all time points. In contrast, intra peritoneal and intra venous injections in mice resulted in death or euthanasia. No toxicity was seen with subcutaneous injection of the same particles in mice. Microscopic analysis of the lung tissue of the mice indicates that death may be due to thrombosis. Although local tissue reaction to mesoporous silicates was benign, they caused severe systemic toxicity. This toxicity could be mitigated by modification of the materials.

Hudson, Sarah; Padera, Robert F.; Langer, Robert; Kohane, Daniel S.

2008-01-01

189

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

190

Analysis of an altered simple silicate glass using different mineral and glass standards  

SciTech Connect

Quantitative analyses of alteration products formed during the aqueous corrosion of glass were performed using four different sets of standards: relevant mineral standards, an NBS glass standard, and the unreacted center of the reacted glass. A simple silicate glass (containing Na, Mg, Al, Si, and Ca) was reacted in water vapor at 200/degree/C for 14 days. Up to eight alteration phases, including a Mg-rich smectite clay and a zeolite intermediate in composition between Ca-harmotome and phillipsite, formed on the glass surface. A set of EDS spectra of the bulk glass, the clay, and the zeolite were collected from a polished cross-section of the reacted sample. Results are discussed. 6 refs., 2 figs., 3 tabs.

Mazer, J.J.; Bates, J.K.

1989-03-01

191

A model for the formation of point defects in zeolites  

NASA Astrophysics Data System (ADS)

Using ab initio DFT periodic and molecular cluster models, we investigate transformations of Brønsted acid sites (Al substitutionals compensated by H) in aluminium silicates upon steaming and calcination, possibly assisted by gamma-irradiation. These treatments can result in formation of (i) hydroxyl nest (hydrogarnet) defects; (ii) oxygen vacancies coupled with Al impurities; or (iii) over-coordinated Al substitutionals. We concentrate on process (ii) which involves either spin or charge separation at the defect site. For zeolites with high Si/Al ratios, we show that two paramagnetic centres are formed preferentially: an electron bound to Si adjacent to the O vacancy site, the E' centre (trigonal Si+ being a counterpart), and an electron hole localised on oxygens at the dehydrogenated Brønsted site (the V1.2, or X1.2 centre). Energetics, geometries and electron and hole distributions are calculated.

Catlow, C. R. A.; Sinclair, P. E.; Sokol, A. A.

192

Flexibility of ideal zeolite frameworks.  

PubMed

We explore the flexibility windows of the 194 presently-known zeolite frameworks. The flexibility window represents a range of densities within which an ideal zeolite framework is stress-free. Here, we consider the ideal zeolite to be an assembly of rigid corner-sharing perfect tetrahedra. The corner linkages between tetrahedra are hard-sphere oxygen atoms, which are presumed to act as freely-rotating, force-free, spherical joints. All other inter-tetrahedral forces, such as coulomb interactions, are ignored. Thus, the flexibility window represents the null-space of the kinematic matrix that governs the allowable internal motions of the ideal zeolite framework. We show that almost all of the known aluminosilicate or aluminophosphate zeolites exhibit a flexibility window. Consequently, the presence of flexibility in a hypothetical framework topology promises to be a valuable indicator of synthetic feasibility. We describe computational methods for exploring the flexibility window, and discuss some of the exceptions to this flexibility rule. PMID:20589266

Kapko, V; Dawson, C; Treacy, M M J; Thorpe, M F

2010-06-29

193

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

194

A novel concept for photovoltaic cells: clusters of titanium dioxide encapsulated within zeolites as photoactive semiconductors.  

PubMed

Discrete clusters of TiO(2) (of only a few titanium atoms) are prepared within the internal micropore space of zeolite Y (4.8 wt % Ti loading) and characterized by Raman spectroscopy (rutile- and anatase-like structures), electron microscopy combined with elemental analyses (coincident Si and Ti spatial distribution), and X-ray diffraction (minor zeolite crystallinity decrease). The parent TiO(2)@Y sample is modified either by adsorption of acid-organic compounds (benzoic and 4-aminobenzoic acids or catechol) or by nitrogen doping. After modification, the optical UV/Vis spectrum of the parent TiO(2)@Y (onset of the absorption band at wavelengths <300 nm and bandgap of 4.2 eV) changes, and the appearance of new bands expanding to the visible region is observed. In contrast to the inactive zeolite Y matrix, all the zeolite-encapsulated TiO(2) species exhibit a photovoltaic response. The influence of the I(2)/I(3) (-) concentration in the electrolyte solution on the temporal profile of the photovoltage clearly shows that I(2)/I(3) (-) is also a suitable carrier for the positive charge in zeolite-based photovoltaic devices. The photocurrent response and the efficiency of the photovoltaic cell based on zeolite-encapsulated TiO(2) materials depend on the nature of the organic modifier and on the N-doping. The most efficient photovoltaic cell is that based on N-doped TiO(2)@Y, which exhibits a V(OC) (voltage at open circuit) of 270 mV, an I(SC) of 5.8 muA (current at short circuit), and a fill factor (FF) of 0.4. Although these values are low compared to current dye-sensitized TiO(2) solar cells, our findings could open up a promise for a stimulating research on the photovoltaic activity of zeolite-based host-guest solids. PMID:16921574

Alvaro, Mercedes; Carbonell, Esther; Atienzar, Pedro; García, Hermenegildo

2006-09-11

195

Low-voltage bendable pentacene thin-film transistor with stainless steel substrate and polystyrene-coated hafnium silicate dielectric.  

PubMed

The hafnium silicate and aluminum oxide high-k dielectrics were deposited on stainless steel substrate using atomic layer deposition process and octadecyltrichlorosilane (OTS) and polystyrene (PS) were treated improve crystallinity of pentacene grown on them. Besides, the effects of the pentacene deposition condition on the morphologies, crystallinities and electrical properties of pentacene were characterized. Therefore, the surface treatment condition on dielectric and pentacene deposition conditions were optimized. The pentacene grown on polystyrene coated high-k dielectric at low deposition rate and temperature (0.2-0.3 Å/s and R.T.) showed the largest grain size (0.8-1.0 ?m) and highest crystallinity among pentacenes deposited various deposition conditions, and the pentacene TFT with polystyrene coated high-k dielectric showed excellent device-performance. To decrease threshold voltage of pentacene TFT, the polystyrene-thickness on high-k dielectric was controlled using different concentration of polystyrene solution. As the polystyrene-thickness on hafnium silicate decreases, the dielectric constant of polystyrene/hafnium silicate increases, while the crystallinity of pentacene grown on polystyrene/hafnium silicate did not change. Using low-thickness polystyrene coated hafnium silicate dielectric, the high-performance and low voltage operating (<5 V) pentacene thin film transistor (?: ~2 cm(2)/(V s), on/off ratio, >1 × 10(4)) and complementary inverter (DC gains, ~20) could be fabricated. PMID:22462593

Yun, Dong-Jin; Lee, Seunghyup; Yong, Kijung; Rhee, Shi-Woo

2012-04-10

196

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

197

Adsorption of Dye from Wastewater by Zeolites Synthesized from Fly Ash: Kinetic and Equilibrium Studies  

Microsoft Academic Search

The removal performance of a basic dye, methylene blue (MB), in aqueous solution was investigated by adsorption process on single-phase and high-crystalline zeolite A (FA-ZA) and X (FA-ZX). Both adsorbents FA-ZA and FA-ZX were synthesized from fly ash prepared aluminosilicate gel followed by the hydrothermal treatment at 100°C with the control of Si\\/Al molar ratio, respectively. The properties of the

Chunfeng WANG; Jiansheng LI; Lianjun WANG; Xiuyun SUN; Jiajia HUANG

2009-01-01

198

Hiding Silicates in Saturn's Rings  

NASA Astrophysics Data System (ADS)

A series of numerical simulations are presented that look at the impact of replacing some of the ice particles in Saturn's rings with silicate particles. All particles are modeled as perfect spheres with no tangential friction. Collisions and particle self-gravity are considered and regions in both the A and B rings have been explored. The particles that represent silicates are given a density of 3 g/cm3 while the icy particles have a density of 0.5 g/cm3. Simulations were done using particles of a single size as well as size distributions and parameters were picked to roughly match measured surface densities. The primary conclusion of this work is that silicate material is well hidden from observations as it collapses down to form core-like structures in the ephemeral gravity wakes. When 4% of the particles are silicates, less than 1% of the reflected light is reflected from the silicate bodies. The light reflected from silicates preferentially comes from particles that are not currently in gravity wakes. Higher percentages of high density material can also be very effectively hidden. Hence, direct observation of spectra does not serve as a strong bound on ring composition. However, having even 4% silicate material does change the pitch angle and structure of gravity wakes and this might serve as an indirect diagnostic of the presence of higher density material. This is especially relevant in the A ring where gravity wake pitch angle affects the azimuthal brightness asymmetry. This work supported by NASA PG&G.

Lewis, Mark C.; Stewart, G. R.

2009-09-01

199

Osmium(0) nanoclusters stabilized by zeolite framework; highly active catalyst in the aerobic oxidation of alcohols under mild conditions.  

PubMed

Osmium(0) nanoclusters stabilized by zeolite-Y framework were reproducibly prepared by a simple two step procedure involving the incorporation of osmium(III) cations into the zeolite matrix by ion-exchange, followed by their reduction within the cavities of zeolite with sodium borohydride in aqueous solution all at room temperature. The composition and morphology of osmium(0) nanoclusters stabilized by zeolite framework, as well as the integrity and crystallinity of the host material were investigated by using ICP-OES, XRD, XPS, SEM, TEM, HRTEM, TEM/EDX, mid-IR, far-IR spectroscopies, and N(2)-adsorption/desorption technique. The results of the multiprong analysis reveal the formation of osmium(0) nanoclusters within the cavities of zeolite-Y without causing alteration in the framework lattice, formation of mesopores, or loss in the crystallinity of the host material. More importantly, far-IR studies showed that after the reduction of Os(3+) cations by sodium borohydride the Na(+) cations reoccupy their authentic cation sites restoring the integrity of zeolite-Y. The catalytic activity of osmium(0) nanoclusters stabilized by zeolite framework was tested in the aerobic oxidation of activated, unactivated and heteroatom containing alcohols to carbonyl compounds and was found to provide high activity and selectivity even under mild conditions (80 degrees C and 1 atm O(2) or air). Moreover, they were found to be stable enough to be isolated and bottled as solid material, which can be reused as active catalyst under the identical conditions of the first run. PMID:20614055

Zahmakiran, Mehmet; Akbayrak, Serdar; Kodaira, Tetsuya; Ozkar, Saim

2010-07-07

200

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

201

Investigation of the physicochemical changes preceding zeolite nucleation in a sodium-rich aluminosilicate gel.  

PubMed

All industrially available zeolites are obtained from hydrogel systems. Unfortunately the level of understanding of the events preceding zeolite crystallization is far from satisfactory. In this respect, revealing the nature of the processes taking place in the precursor gel is of paramount importance to understanding zeolite nucleation. The investigation of the gel structure, however, is a difficult task due to the complexity of the object in terms of both composition and topology. Therefore, a combination of hyperpolarized (HP) (129)Xe NMR-N(2) adsorption-high-resolution transmission electron microscopy-energy-dispersive spectrometry methods complemented by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and chemical analyses has been employed to study the changes in composition and structure of sodium hydroxide rich aluminosilicate gel yielding zeolite A. The role of each component in the system and the entire sequence of events during the induction, nucleation, and crystallization stages have been revealed. The high concentration of sodium hydroxide in the studied system has been found to control the size and structure of the gel particles in the beginning stage. During the initial polymerization of aluminosilicate species a significant part of the sodium hydroxide is expelled from the gel into the solution, which restricts extensive polymerization and leads to formation of small aluminosilicate particles with open pore structure. The induction period that follows is marked by incorporation of Na back in the bulk gel. The combined action of the Na ion as a structure-directing agent and the hydroxyl group as a mobilizer results in partial depolymerization of the gel and formation of voids with mesopore sizes. The nucleation maximum coincides temporally with development of pores with sizes in the range of 2-5 nm. The amorphous gel undergoes into crystalline zeolite only after these pores have disappeared and the chemistry of the gel has evolved to reach the stoichiometric zeolite composition. It was established unambiguously by high-resolution transmission electron microscopy and HP (129)Xe NMR that the nucleation of zeolite occurs in the solid part of the system and the succeeding crystallization commences only after the nuclei are released into the liquid, which is consistent with the autocatalytic mechanism. Also this investigation has demonstrated the unrivaled sensitivity of HP (129)Xe NMR that is capable of identifying presence of small amounts of crystalline zeolite material in amorphous medium with detection limit extending below 1 wt %. PMID:19572709

Itani, Lama; Liu, Yong; Zhang, Weiping; Bozhilov, Krassimir N; Delmotte, Luc; Valtchev, Valentin

2009-07-29

202

Coagulation and crystallization of silicates in protoplanetary disks: a c2d Spitzer/IRS survey  

NASA Astrophysics Data System (ADS)

Silicates are observed in almost every place where dust can survive: in the interstellar medium (ISM), in the Earth mantle, in comets and it is now common knowledge that there are also present in circumstellar disks around young stars. The ISM sub-micron sized silicates are highly amorphous (>99%), while the silicate Mg-rich crystallinity fraction can reach 60% in comets like Hale-Bopp in the Solar System. The silicates have to be exposed to high temperatures to crystallize, and their presence in long-period comets suggests that dust has been heavily processed and transported in the disk. Statistical studies of planet forming disks are keys on understanding if these processes are generic and can occur in other protoplanetary systems. As part of the Cores to Disks (c2d) Legacy Program, we obtained more than a hundred of Spitzer/IRS spectra of T Tauri stars, in the spectral range 5-35 ?m, where many crystalline features are present. We find that most of these objects (˜ 70%) show silicate emission features, either attributed to amorphous or crystalline grains. Studying the 10 ?m feature, we find that grain growth has occured and their quasi-systematic presence in the disks upper layers indicate ongoing turbulent vertical mixing. We will also show that crystalline dust grains are present in the outer/deeper cold regions of the disk, with typical temperatures of about 100 K, which suggests efficient radial transport mechanisms. Overall, our study shows that vertical and radial transport seem to be generic dynamical processes in disks, challenging theoretical disk evolution and planet formation models.

Olofsson, J.; Augereau, J.-C.; Monin, J.-L.; C2d Irs Team

2008-11-01

203

Influence of the size of extraframework monovalent cations in X-type zeolite on their thermal behavior  

Microsoft Academic Search

Pure and well crystalline NaX zeolite with Si\\/Al=1.5 was prepared by hydrothermal crystallization from the Na2O–Al2O3–SiO2–H2O system. The hydrothermal crystallization was carried out under autogeneous pressure and at static condition at 368K. The post-synthesis modification was achieved by following conventional ion-exchange technique to obtain K+, Rb+ and Cs+-exchanged forms of NaX zeolite. Compositional and structural investigations of parent sample and

U. D. Joshi; P. N. Joshi; S. S. Tamhankar; V. P. Joshi; B. B. Idage; V. V. Joshi; V. P. Shiralkar

2002-01-01

204

Effect of silicate anion distribution in sodium silicate solution on silicate conversion coatings of hot-dip galvanized steels  

Microsoft Academic Search

Silicate conversion coatings are prepared by immersing hot-dip galvanized (HDG) steel sheets in sodium silicate solutions with 5wt.% SiO2 and SiO2:Na2O molar ratio in the range of 1.00 to 4.00. The coating with better corrosion resistance is usually obtained in silicate solution with higher molar ratio (3.00–4.00). In this article, the distribution of types of silicate anion in solutions is

Mei-rong Yuan; Jin-tang Lu; Gang Kong; Chun-shan Che

2011-01-01

205

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

206

Structural investigations and luminescence properties of nanocrystalline europium-doped yttrium silicates prepared by a sol–gel technique  

Microsoft Academic Search

Luminescent yttrium silicate powders doped with europium ions (EuxY2?xSiO5) were obtained by a sol–gel method after thermal treatment at 1300°C. The crystalline phases retrieved from X-ray diffraction (XRD) patterns were quantitatively evaluated through Rietveld analysis, which showed that the formation and stability of high-temperature crystalline phases is affected by the europium ions. In fact, the X2 monoclinic oxyorthosilicate Y2SiO5 is

Carla Cannas; Marina Mainas; Anna Musinu; Giorgio Piccaluga; Stefano Enzo; Marco Bazzoni; Adolfo Speghini; Marco Bettinelli

2007-01-01

207

Battery components employing a silicate binder  

SciTech Connect

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); Reinhardt, Frederick W. (Albuquerque, NM); Odinek, Judy G. (Rio Rancho, NM)

2011-05-24

208

Stability of crystalline Gd2O3 thin films on silicon during rapid thermal annealing  

Microsoft Academic Search

We investigate the impact of rapid thermal anneals on structural and electrical properties of crystalline Gd2O3 layers grown on Si with different orientations. Due to additional oxygen from the annealing ambient, a structureless two-layer stack (silicon-oxide-like and silicate-like) between the silicon and the crystalline oxide will be formed. The degradation of layers can be significantly reduced by sealing the layer

M. Czernohorsky; D. Tetzlaff; E. Bugiel; R. Dargis; H. J. Osten; H. D. B. Gottlob; M. Schmidt; M. C. Lemme; H. Kurz

2008-01-01

209

CRYSTALLINE HEXOKINASE (HETEROPHOSPHATESE)  

PubMed Central

1. Crystalline hexokinase has been isolated from baker's yeast. 2. Crystalline hexokinase is a protein of albumin type of a molecular weight of 96,000. Its isoelectric point is at about pH 4.8. 3. The method of isolation consists in separating the proteins of an aqueous extract of toluene-treated yeast by means of fractional precipitation with ammonium sulfate and with alcohol. 4. The procedure involves also the separation of several crystalline proteins, including one yellow crystalline protein, which do not possess hexokinase activity. The biological and the physicochemical properties of these proteins are still under investigation. 5. The crystallization of hexokinase proceeds at about 5°C. in the presence of ammonium sulfate and dilute phosphate buffer pH 7.0. 6. Crystalline hexokinase becomes relatively pure after 2 or 3 recrystallizations as tested by solubility, sedimentation in the ultracentrifuge, and electrophoresis. The enzymatic activity remains constant on repeated crystallization. 7. The enzymatic activity is associated with the protein nature of the material. Inactivation is accompanied by denaturation of the protein. 8. Crystalline hexokinase is relatively stable when stored in the form of crystalline filter cake. Solutions of hexokinase in dilute buffers are most stable at pH 5.0. 9. Crystalline hexokinase requires the presence of magnesium ions for its catalytic activity.

Kunitz, M.; McDonald, Margaret R.

1946-01-01

210

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

211

Fallout fractionation in silicate soils  

Microsoft Academic Search

The existing models for testing radiochemical fractionation in nuclear weapon debris are discussed and compared. A method which extends the existing theory for the case of surface bursts over silicate soils is developed and validated with weapons test data. There is evidence that fission product absorption by soil and weapon debris is diffusion controlled. There is also evidence that there

1985-01-01

212

Core formation in silicate bodies  

Microsoft Academic Search

Differentiation of a body into a metallic core and silicate mantle occurs most efficiently if temperatures are high enough to allow at least the metal to melt [1], and is enhanced if matrix deformation occurs [2]. Elevated temperatures may occur due to either decay of short-lived radio-isotopes, or gravitational energy release during accretion [3]. For bodies smaller than the Moon,

F. Nimmo; D. P. O'Brien; T. Kleine

2008-01-01

213

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

214

Physical, Chemical and Structural Evolution of Zeolite-Containing Waste Forms Produced from Metakaolinite and Calcined Sodium Bearing Waste (HLW and/or LLW)  

SciTech Connect

Zeolites are extremely versatile. They can adsorb liquids and gases and serve as cation exchange media. They occur in nature as well cemented deposits. The ancient Romans used blocks of zeolitized tuff as a building material. Using zeolites for the management of radioactive waste is not a new idea, but a process by which the zeolites can be made to act as a cementing agent is. Zeolitic materials are relatively easy to synthesize from a wide range of both natural and man-made substances. The process under study is derived from a well known method in which metakaolin (an impure thermally dehydroxylated kaolinite heated to {approx}700 C containing traces of quartz and mica) is mixed with sodium hydroxide (NaOH) and reacted in slurry form (for a day or two) at mildly elevated temperatures. The zeolites form as finely divided powders containing micrometer ({micro}m) sized crystals. However, if the process is changed slightly and only just enough concentrated sodium hydroxide solution is added to the metakaolinite to make a thick crumbly paste and then the paste is compacted and cured under mild hydrothermal conditions (60-200 C), the mixture will form a hard ceramic-like material containing distinct crystalline tectosilicate minerals (zeolites and feldspathoids) imbedded in an X-ray amorphous hydrated sodium aluminosilicate matrix. Due to its lack of porosity and vitreous appearance we have chosen to call this composite a ''hydroceramic''.

Grutzeck, Michael W.

2005-06-27

215

Process for preparing silicon substituted zeolite compositions  

SciTech Connect

This patent describes the process for substituting silicon into the crystal lattice of zeolites in place of extracted lattice aluminum atoms to achieve zeolite products of higher silicon content. It comprises: providing a starting aluminosilicate zeolite having a framework SiO{sub 2}/Al{sub 2}O{sub 3} molar ratio of at least 2 and pore diameters of at least 3 Angstroms; contacting the starting zeolite at a temperature of 25{degrees} C. to 95{degrees} C. with an aqueous solution of a fluorosilicate salt containing from 0.5 to 1.5 moles per liter of the fluorosilicate salt dissolved therein, the proportions of zeolite and fluorosilicate salt being at least 0.1 moles of salt per 100 grams of anhydrous zeolite; maintaining contact between the zeolite and the salt solution for a period not in excess of 5 hours; removing from contact with the zeolite the liquid medium containing at least 90 percent of the by-product fluoroaluminate salt produced by the reaction of the fluorosilicate salt with the zeolite.

Skeels, G.W.

1991-02-26

216

Tribochemical reactions of erionite and Na-LTA zeolites with Fe2(SO4)3.5H2O: A mössbauer study  

NASA Astrophysics Data System (ADS)

The tribochemical reactions between Na-LTA and natural erionite with Fe2(SO4)3·5H2O were studied by Mössbauer spectroscopy, X-ray powder diffraction, IR spectroscopy and NH3 adsorption experiments. The reactions occur with the consequent zeolite dealumination and the formation of a crystalline compound, a product of the extracted aluminum and the sulfate.

de Oñate Martínez, J.; Aguila, C. Díaz; Bertrán, J. Fernández; Ruíz, E. Reguera; Vergara, C. Portilla; Malherbe, R. Roque

1992-10-01

217

Mineralogy of the Dhofar 489 Lunar Meteorite, Crystalline Matrix Breccia with Magnesian Anorthositic Clasts  

NASA Astrophysics Data System (ADS)

Dhofar 489, a crystalline matrix feldspathic breccia gives the mg# of mafic silicates higher than those of FAN trend in the An vs. mg# diagram, but D489 does not show granulitic texture. We examine the origin of this magnesian anorthosite.

Takeda, H.; Saiki, K.; Ishii, T.; Otsuki, M.

2003-03-01

218

Mineralogy of the Dhofar 489 Lunar Meteorite, Crystalline Matrix Breccia with Magnesian Anorthositic Clasts  

Microsoft Academic Search

Dhofar 489, a crystalline matrix feldspathic breccia gives the mg# of mafic silicates higher than those of FAN trend in the An vs. mg# diagram, but D489 does not show granulitic texture. We examine the origin of this magnesian anorthosite.

H. Takeda; K. Saiki; T. Ishii; M. Otsuki

2003-01-01

219

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

220

Liquid crystalline bispropargyl thermosets  

SciTech Connect

A series of rigid-rod bispropargyl thermoset monomers have been synthesized. These monomers were examined by differential scanning calorimetry (DSC) and hot stage polarized optical microscopy. Enantiotropic or monotropic nematic liquid crystalline phases were observed for all but two monomers. Partial curing of these reactive liquid crystalline monomers resulted in the formation of stable liquid crystalline phases with broad nematic phase after partial curing. DSC investigations indicated that the onset temperature of thermally induced cross-linking was approximately 260 C and insensitive to the phase type. The rate of cure was insensitive to the phase in which the cure occurred due to the unusual reaction mechanism for the propargyl end group.

Langlois, D.A.; Benicewicz, B.C. [Los Alamos National Lab., NM (United States). Polymers and Coatings Group; Douglas, E.P. [Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering

1998-11-01

221

Improved epitaxy of ultrathin praseodymia films on chlorine passivated Si(111) reducing silicate interface formation  

SciTech Connect

Ultrathin praseodymia films have been deposited on both Cl-passivated and nonpassivated Si(111) substrates by molecular beam epitaxy. Comparative studies on the crystallinity and stoichiometry are performed by x-ray photoelectron spectroscopy, x-ray standing waves, and x-ray reflectometry. On nonpassivated Si(111) an amorphous silicate film is formed. In contrast, praseodymia deposited on Cl-passivated Si(111) form a well-ordered crystalline film with cubic-Pr{sub 2}O{sub 3} (bixbyite) structure. The vertical lattice constant of the praseodymia film is increased by 1.4% compared to the bulk value. Furthermore, the formation of an extended amorphous silicate interface layers is suppressed and confined to only one monolayer.

Gevers, S.; Bruns, D.; Weisemoeller, T.; Wollschlaeger, J. [Department of Physics, University of Osnabrueck, Barbarastrasse 7, D-49069 Osnabrueck (Germany); Flege, J. I.; Kaemena, B.; Falta, J. [Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen (Germany)

2010-12-13

222

Biogenic silicate accumulation in sediments, Jiazhou Bay  

NASA Astrophysics Data System (ADS)

It has been widely recognized that low silicate content in seawater is a major limiting factor to phytoplankton primary production in Jiaozhou Bay. However the reason of Si-limitation remains poorly understood. In the present study we measured the biogenic silicate content and discussed the accumulation of silicate in Jiaozhou Bay sediment. The results show that the biogenic silica content in the sediment of the Jiaozhou Bay is obviously much higher than those in the Yellow Sea and the Bohai Sea. The Bsi:TN ratios and BSi:16P ratios in the sediment are>1 and the OC:BSi ratio in sediment is lower than these of Redfield ratio (106?16), indicating that the decomposition rate of OC is much higher than that for BSi in similar conditions. Therefore, the majority of the biogenic silicate was buried and thus did not participate in silicate recycling. Silicate accumulation in sediment may explain why Si limits the phytoplankton growth in the Jiaozhou Bay. Comparing the flux of biogenic silicate from sediments with primary production rate, it can be concluded that only 15.5% of biogenic silicate is hydrolyzed during the journey from surface to bottom in seawater, thus approximate 84.5% of biogenic silicate could reach the bottom. The silicate releasing rate from the sediment to seawater is considerably lower than that of sedimentation of biogenic silicate, indicating silicate accumulation in sediment too. In a word, the silicate accumulation in sediment is the key reason of silicate limiting to phytoplankton growth in Jiaozhou Bay.

Li, Xuegang; Song, Jinming; Dai, Jicui; Yuan, Huamao; Li, Ning; Li, Fengye; Sun, Song

2006-09-01

223

Detailed investigation of the lattice structure of zeolite ZSM-11 by a combination of solid-state NMR and synchrotron X-ray diffraction techniques  

Microsoft Academic Search

The lattice structure of a pure and completely siliceous sample of zeolite ZSM-11 has been investigated by a combination of high-resolution solid-state ²⁹Si MAS NMR and synchrotron-based X-ray powder diffraction techniques. The structure is temperature dependent in the range 263-363 K and a good fit to the diffraction data at 363 K is obtained with space group I{anti 4}m2 and

Colin A. Fyfe; Hermann Gies; George T. Kokotailo; Connie Pasztor; Harald Strobl; David E. Cox

1989-01-01

224

Liquid-crystalline terpyridines.  

PubMed

5,5"-Disubstitution of the terpyridine core leads to the first inherently liquid-crystalline terpyridines. Mesophases characteristic of bent-core and calamitic systems may be obtained depending on the core structure employed. PMID:18217660

Kozhevnikov, Valery N; Whitwood, Adrian C; Bruce, Duncan W

2007-10-01

225

Liquid Crystalline Polymers.  

National Technical Information Service (NTIS)

This research produced the first quantitative approach to the elucidation of the structure-properties relationship in the field of side chain liquid crystalline polymers via a molecular engineering approach. The elucidation of the mechanisms required for ...

V. Percec

1995-01-01

226

Synthesis and characterization of nano-sized copper-silicate with mel structure  

Microsoft Academic Search

Nano-sized copper silicalite with MEL structure has been hydrothermally synthesized for the first time under static conditions. The physicochemical property of this novel material was characterized by means of XRD, TEM, FT-IR, ESR, TG-DTA and NH3-TPD techniques. The results revealed that the as-synthesized copper silicalite was highly thermally stable owing to its siliceous nature. This monophased crystalline material was quite

Xiang-Hai Tang; Jing-Zhong Wang; He-Xuan Li

2004-01-01

227

Silicates of the rare earths  

Microsoft Academic Search

of Silicate Chemistry, we have plotted phase diagrams for binary systems of silica with oxides of lanthanum, samarium, ga0olinium, dysprosium, yttrium, erbium, and ytterbium. The investigations showed similarities in the structure of these systems: the existence of three types of compounds - the oxyorthosilicates (Ln~O[SiO4] or Ln20 s ?9 sin2), the orthosilicates (Ln4[SiO4]s or 2Ln20 s ?9 3SIO2), the diorthosilicates

F. Ya. Galakhov; N. A. Toropov

1962-01-01

228

The potential application of natural zeolite for greywater treatment  

Microsoft Academic Search

Natural zeolites are good potential material for water and wastewater treatment. It is due to the advantages of low cost, ion-exchange and adsorption capability of the natural zeolites. It can also be modified and regenerated. This paper thus looks at efforts made in exploring the potential application of natural zeolites and modified natural zeolites in water and wastewater treatment especially

Nurul Widiastuti; Hongwei Wu; Ming Ang; Dong-ke Zhang

2008-01-01

229

Zeolite-based discriminating gas sensors  

Microsoft Academic Search

The use of zeolites to enhance the discriminating power of solid state gas sensors is demonstrated. Screen printed tungsten trioxide (WO3) and chromium titanium oxide (CTO) thick films overlaid and admixed (CTO only) with different forms of zeolites are shown to give different and in some cases, enhanced responses to a variety of gases. We attempt to rationalise the noted

Sheena Dungey; Ayo Afonja; Dewi W. Lewis; Russell Binions; Ivan P. Parkin; Themis Paraskeva; David E. Williams

2008-01-01

230

Hydrophilic and hydrophobic adsorption on Y zeolites  

Microsoft Academic Search

The uniform large micropores of hydrothermally stable Y zeolites are used widely to confine both polar and non-polar molecules. This paper compares the physisorption of water, methanol, cyclohexane, benzene and other adsorbates over various Y zeolites. These adsorbents are commercial products with reproducibly controllable physical and chemical characteristics. Results indicate that the type I isotherms typical for micropore adsorption can

Istvan Halasz; Song Kim; Bonnie Marcus

2002-01-01

231

The flexibility of zeolites for Hydrogen storage  

NASA Astrophysics Data System (ADS)

The flexibility window is a newly discovered theoretical measure which can provide a valuable selection criterion when evaluating hypothetical zeolite framework structures as potential synthetic targets. Today synthetic zeolites are the most important catalysts in petrochemical refineries. There have been considerable efforts to synthesize new zeolites with specific pore geometries, to add to the 167 available at present. Millions of hypothetical structures have been generated on the basis of energy minimization, and there is an ongoing search for criteria capable of predicting new zeolite structures. The flexibility window appears to be a property of existing zeolite frameworks not shared by many hypothetical structures. It provides a valuable selection criterion when evaluating hypothetical zeolite framework structures as potential synthetic targets. We are investigating the use of zeolites as hydrogen storage materials, as small molecules such as molecular hydrogen and ammonia can be easily absorbed into a flexible framework of zeolites. An exiting possibility is the use of framework flexibility to control hydrogen uptake, storage and release. This would allow a safe use of hydrogen for fuel cells.

Sartbaeva, Asel; Wells, Stephen Anthony; Edwards, Peter P.

2008-03-01

232

Chemical Interactions in Multimetal\\/Zeolite Catalysts  

Microsoft Academic Search

This two-year project has led to a significant improvement in the fundamental understanding of the catalytic action of zeolite-supported redox catalysts. It turned out to be essential that we could combine four strategies for the preparation of catalysts containing transition metal (TM) ions in zeolite cavities: (1) ion exchange from aqueous solution; (2) chemical vapor deposition (CVD) of a volatile

Sachtler; Wolfgang M. H

2004-01-01

233

Influence of the porous structure of zeolite-containing catalysts on their activity and selectivity. Zeolite-containing catalysts based on a Y zeolite  

SciTech Connect

The catalytic activity and selectivity of zeolite-containing catalysts based on zeolite CaY-78 and amorphous aluminosilicates with various compositions and porous structures in the conversion of n-hexane at 400/sup 0/C have been determined. The differences in the activity and selectivity of the zeolite in the zeolite-containing catalysts in comparison to the zeolite without a matrix have been attributed to the blocking of part of the zeolite by the matrix material and matrix-zeolite cation jumps, whose rate is influenced by the macroporous structure of the matrix. The activity and selectivity of such zeolite-containing catalysts with an inactive matrix are determined by the effects of a mixture of CaY zeolites with different cationic compositions.

Rosolovskaya, E.N.; Barsukov, O.V.

1985-10-01

234

Design of zeolite by inverse sigma transformation  

NASA Astrophysics Data System (ADS)

Although the search for new zeolites has traditionally been based on trial and error, more rational methods are now available. The theoretical concept of inverse ? transformation of a zeolite framework to generate a new structure by removal of a layer of framework atoms and contraction has for the first time been achieved experimentally. The reactivity of framework germanium atoms in strong mineral acid was exploited to selectively remove germanium-containing four-ring units from an UTL type germanosilicate zeolite. Annealing of the leached framework through calcination led to the new all-silica COK-14 zeolite with intersecting 12- and 10-membered ring channel systems. An intermediate stage of this inverse ? transformation with dislodged germanate four-rings still residing in the pores could be demonstrated. Inverse ? transformation involving elimination of germanium-containing structural units opens perspectives for the synthesis of many more zeolites.

Verheyen, Elke; Joos, Lennart; van Havenbergh, Kristof; Breynaert, Eric; Kasian, Nataliia; Gobechiya, Elena; Houthoofd, Kristof; Martineau, Charlotte; Hinterstein, Manuel; Taulelle, Francis; van Speybroeck, Veronique; Waroquier, Michel; Bals, Sara; van Tendeloo, Gustaaf; Kirschhock, Christine E. A.; Martens, Johan A.

2012-12-01

235

Entropic inflation of ideal zeolitic frameworks  

NASA Astrophysics Data System (ADS)

Ideal zeolites can be viewed as flexible networks of rigid, corner-sharing tetrahedra. Recent studies have shown that such systems can exist at a range of densities (termed the "flexibility window") without breaking topology or deforming the comprising tetrahedra. They also have shown that densities of real zeolites almost always correspond to the lowest densities within this range. This anomalous behavior is usually attributed to coulombic repulsion between oxygen atoms in framework cavities and channels. In this paper we show that the inflation of ideal zeolites can be driven by entropy. This effect is closely related to displacive phase transitions often observed in zeolites and related materials like quartz, which cannot be explained by potential energy minimization alone. We show that periodicity and high symmetry in ideal zeolites is a result of entropy maximization. An estimation of entropy using a harmonic oscillator model with a realistic force field is given.

Kapko, Vitaliy; Dawson, Colby; Treacy, Michael

2011-03-01

236

[Research on the mineral phase and component of non-crystalline and nano-crystalline corrosion products on bronzes unearthed from Shang Tomb in Xingan].  

PubMed

The patinas on bronzes in Shang Tomb of Xingan were powdery, pale green, which were more like "bronze disease", but the mineral composition of patinas was not paratacamite or atacamite. Micro X-ray diffraction (XRD) and high performance transmission electroscope (HTEM) showed that the patinas were mainly composed of non-crystalline and nano-crystalline SnO2, and the size of nano-crystalline particle was in the range of 4-5.7 nm; Moreover, the energy-dispersive X-ray spectrometry showed that element tin is the primary ingredient of the sample, as well as little copper, silicon, lead and iron were detected. By studying the crystal lattice stripe image of the nanometer SnO2, it was deduced that the chemical formula of nano-crystalline SnO2 did not include other elements; The Raman spectrum of the sample showed that there were not any characteristic peaks of SnO2, the spectrum was more like non-crystalline SnO2, and the weak and broad peak of 973 cm(-1) indicated that the sample may contain silicate grains, It was inferred that little of copper, silicon, lead and iron should exist in the form of non-crystalline silicate particles. PMID:22827070

Cheng, Xiao-lin; Pan, Lu

2012-05-01

237

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

238

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

239

Small-angle neutron-scattering studies of the template-mediated crystallization of ZSM-5-type zeolite  

SciTech Connect

Small-angle neutron-scattering scattering is a useful new approach to the study of zeolite crystallization from aluminosilicate gels and the action of template molecules. It has been applied to gels for synthesis of zeolite ZSM-5 using tetrapropylammonium ions as templates where the scattering length densities of the gel particles and their texture were determined by using contrast variation methods. Gels formulated from soluble silicate incorporate template molecules promptly into an amorphous {open_quotes}embryonic{close_quotes} structure, and crystallization ensues via a solid hydrogel transformation mechanism. Gels formulated from colloidal silica show different scattering behavior, and a liquid-phase transport mechanism is inferred. 8 refs., 4 figs., 2 tabs.

Iton, L.E.; Trouw, F.; Brun, T.O. [Argonne National Lab., IL (United States)] [and others

1992-04-01

240

Zeolite inorganic supports for BSA immobilization: comparative study of several zeolite crystals and composite membranes.  

PubMed

Zeolites due to their low toxicity and high compatibility are considered new biomaterials for medical applications. The surface adsorption behaviour of zeolite crystals and composite membranes was discussed in this research. The zeolite materials were synthesized by hydrothermal syntheses using different reaction gels to modulate the Brönsted acidity of the microporous structures. Spectrophotometric analyses were used to evaluate protein adsorption on these surfaces. This study revealed that zeolite chemical composition and structure influenced the kinetics of protein adsorption. Zeolite Y surface adsorbed greater amount of BSA than the other structures. The percentage of adsorption increases with temperature and depends on the pH of the solution, being highest at the pI of the protein. The influence of the membrane configuration on the protein adsorption was studied using different zeolite structures and crystallization types. It seems that the observed differences could depend on the type of hydrothermal crystallization inside the inorganic support. PMID:17194574

Tavolaro, Adalgisa; Tavolaro, Palmira; Drioli, Enrico

2006-11-17

241

Zeolite catalyst deactivation by coking  

SciTech Connect

Deactivation of a lanthanum exchanged zeolite Y catalyst for isopropylbenzene (cumene) cracking was studied with a thermobalance. The kinetics of coke formation and the main reaction were determined. The Froment Bischoff approach to modeling catalyst deactivation was used. The deactivation function giving the best fit to both the cracking and coking reaction data was an exponential one related to the coke content of the catalyst. The kinetic mechanism for coking that gave the best fit was one in which parallel and consecutive coking reactions occurred simultaneously. Apparently, more coke forms from products than reactants, especially at higher temperature.

Lin, C.C.; Hatcher, W.J.; Park, S.W.

1983-10-01

242

17O NMR Studies of Zeolites  

NASA Astrophysics Data System (ADS)

Multiple-quantum magic-angle spinning (MQMAS) and double rotation (DOR) techniques were applied in the fields of 17.6 T and 11.7 T to the study the 17O NMR of oxygen-17 enriched zeolites A, LSX and sodalite. In addition, some 29Si and 1H MAS NMR experiments were performed. Zeolites with the ratio Si/Al = 1 were chosen, in order to have an alternating distribution of silicon and aluminum atoms. A linear correlation between the isotropic value of the chemical shift and the Si-O-Al bond angle (taken from X-ray data) could be found for the zeolites A and LSX, but not for sodalites. Hydration of the zeolites causes a downfield 17O NMR chemical shift of about 8 ppm with respect to the dehydrated zeolites. Ion exchange of the hydrated zeolites generates stronger chemical shift effects. The increase of the basicity of the oxygen framework of the zeolite LSX is reflected by a downfield shift of ca. 10 ppm going from the lithium to the cesium form, and the substitution of sodium by thallium in the zeolite A causes a shift of 34 ppm for the O3 site. 17O DOR NMR spectra are superior to 17O 3QMAS NMR spectra, featuring a resolution increase by a factor of two and are about equal with respect to the sensitivity. The residual linewidths of the signals in the 17O DOR and 17O 5QMAS NMR spectra can be explained by a distribution of the Si-O-Al angles in the zeolites.

Freude, Dieter; Loeser, Thomas

243

Photochemical charge separation in zeolites: Electron transfer dynamics, nanocrystals and zeolitic membranes. Final technical report  

SciTech Connect

Aluminosilicate zeolites provide an excellent host for photochemical charge separation. Because of the constraints provided by the zeolite, the back electron transfer from the reduced acceptor to the oxidized sensitizer is slowed down. This provides the opportunity to separate the charge and use it in a subsequent reaction for water oxidation and reduction. Zeolite-based ruthenium oxide catalysts have been found to be efficient for the water splitting process. This project has demonstrated the usefulness of zeolite hosts for photolytic splitting of water.

Dutta, Prabir K.

2001-09-30

244

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

245

Photoinduced electron transfer reactions in zeolite cages  

SciTech Connect

This report summarizes work in the two areas of zeolites and layered double hydroxides. Results of studies on structural aspects of Ru(bpy)[sub 3][sup 2+]-zeolite Y are summarized. Photoinduced electron transfer between entrapped Ru(bpy)[sub 3][sup 2+] and methylviologen (MV) in neighboring supercages was examined. Benzylviologen was also used. Since molecules larger than 13 [angstrom] cannot be accomodated in zeolite cages, the layered double metal hydroxides (LDH) LiAl[sub 2](OH)[sub 6][sup +]X[sup [minus

Dutta, P.K.

1992-01-01

246

Synthesis, characterization and energetics of zeolites  

NASA Astrophysics Data System (ADS)

Zeolites are microporous aluminosilicates, and Al or Si can be substituted by other elements, such as Ge, Ga, or P. Zeolites have been studied for more than two hundred years, because of their wide application and importance in mineralogy and technology. With high acidity and special pore system, zeolite beta (IZA code BEA) receives much attention. In the dissertation, the formation and dehydration enthalpy of cation exchanged zeolite beta, Li/Na/K/Rb/Cs/Mg/Ca/Sr/Ba -BEA 14 (14 is the Si/Al ratio), Mg/Ca - BEA 4 (4 is the Si/Al ratio), were studied by high-temperature oxide melt solution calorimetry. From an energetic point of view, zeolites beta are less stable than other zeolites of similar Si/Al ratio and cation content. Their enthalpies of formation and dehydration become more endothermic with increasing average ionic potential of the cations in the channels. The unfavorable enthalpy of low silica Mg-BEA 4 and Ca-BEA 4 suggests a possible energy barrier in their direct synthesis. The formation and partial molar dehydration enthalpy of Li-BEA 3 and Na-BEA 3.67 are also investigated by high temperature calorimetry. The partial molar dehydration enthalpies are a linear function of water content. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents. Ga substitution is of great interest due to the special catalytic character of Ga zeolites and the directing agent effect of Ga atoms. The energetics of gallosilicate zeolites Ga-NaSOD, Ga-NaFAU, Ga-NaNAT, Ga-KNAT, Ga-KLTL and Ga-KTUN-1 were studied. The lattice parameters and adsorbed water content increase after Ga substitution of Al. Compared to analogous aluminosilicate zeolites, the gallosilicate zeolites have a similar dehydration enthalpy per mole of tetrahedra, but a less endothermic dehydration enthalpy per mole of water. The gallosilicate zeolites also have less exothermic formation enthalpies from oxide components. The energetics of Ga zeolites are further discussed in terms of Si/Ga ratio, framework density and cation effects.

Sun, Pingping

247

Zeolite based arsine storage and delivery system  

SciTech Connect

A method of storing and subsequently delivering arsine is described, which comprises the steps of: (a) contacting arsine at a temperature of between about -30/sup 0/C and about +30/sup 0/C with a zeolite having a pore size of between about 5 and about 15 angstroms to provide arsine-adsorbed zeolite suitable to be stored, and (b) heating the arsine-adsorbed zeolite to an elevated temperature of no greater than about 175/sup 0/C for a time sufficient to release at least a portion of the adsorbed arsine to provide free arsine.

Knollmueller, K.O.

1988-05-17

248

Gas adsorption isotherm for dealuminated zeolites  

SciTech Connect

Adsorption is a current technique to remove volatile organic compounds from process gas streams. In industrial applications hydrophobic dealuminated zeolites are often used as adsorbents, because of their specific advantages in comparison to activated carbon or polar zeolites. A new equation for complex adsorption isotherms was developed by using a mathematical method well-known in control engineering. On the basis of this analogy, it is possible to describe the transitional region between Langmuir isotherms and isotherms following Henry`s law. Development and verification of the equation are based on experimental data of the system zeolite DAY-ethanol-air.

Bathen, D.; Schmidt-Traub, H.; Simon, M. [Univ. of Dortmund (Germany). Dept. of Chemical Engineering

1997-09-01

249

Luminescence quenching measurements on zeolite L monolayers  

NASA Astrophysics Data System (ADS)

The luminescence quenching of the oxygen sensitive Ru2+ complex (Ru-ph4-TMS) used as a stopcock and attached to a zeolite L monolayer has been investigated. The luminescence lifetime of the attached Ru-ph4-TMS was the same under N2 and under O2 atmosphere. This remarkable result is attributed to the shielding provided by the channels of the zeolite L crystals arranged as a monolayer. The emitting 3MLCT state of the Ru-ph4-TMS stopcock is localized on the ligand bearing the phenyl groups forming the tail of this complex, which deeply penetrates into the zeolite L channel.

Albuquerque, Rodrigo Q.; Zabala Ruiz, Arantzazu; Li, Huanrong; De Cola, Luisa; Calzaferri, Gion

2006-05-01

250

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

Code of Federal Regulations, 2013 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...

2013-07-01

251

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

252

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

253

Carbon substitution for oxygen in silicates in planetary interiors.  

PubMed

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. PMID:24043830

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

2013-09-16

254

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

NASA Astrophysics Data System (ADS)

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, M. S.; Lynch, D. K.; Russell, R. W.

1994-04-01

255

Diffusion in crystalline materials  

Microsoft Academic Search

Recently nuclear scattering of synchrotron radiation proved to be a powerful new method to study the elementary diffusion jump in crystalline solids. The scattered radiation decays faster when atoms move on the time scale of the excited-state lifetime of a Mössbauer isotope because of a loss of coherence. The acceleration of the decay rate differs for different crystal orientations relative

G. Vogl; B. Sepiol

1999-01-01

256

Crystalline Xenon Particle Detector  

Microsoft Academic Search

The sensitivity necessary to measure single photon electrons may be achieved through ionization produced in a crystalline xenon based particle detector. Following crystal formation and the application of an electric field, the ionization drifts to the surface and can be extracted from the solid xenon. Quantification of the ions is accomplished by utilizing a silicon PIN diode scintillation detector with

J. A. Maxin; R. Blessitt; J. Gao; J. Miller; G. Salinas; J. Seifert; J. T. White

2004-01-01

257

Diffusion of Water in Silicate Melts  

Microsoft Academic Search

Diffusion of water in silicate melts and glasses has significant impact on both high temperature igneous and low temperature alteration processes. Water diffusivity in silicates is complicated by its strong, complex dependence on composition, including water content, which has been used to infer molecular level mechanisms of water diffusion. Very little has been done on mafic melts, but such studies

S. Newman; E. Persikov; E. Stolper; P. Bukhtiyarov; Y. Zhang

2005-01-01

258

Tectonic and climatic controls on silicate weathering  

Microsoft Academic Search

Understanding the controls on chemical weathering, especially of silicate minerals, remains a major challenge, despite its importance in controlling the evolution of the Earth's surface. In particular, it has proved hard to distinguish the temperature sensitivity of silicate weathering rates from other factors. Here we present a new compilation of chemical and physical erosion rates in small catchments and show

A. Joshua West; Albert Galy; Mike Bickle

2005-01-01

259

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

260

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

261

Zeolite structure type EAB: Crystal structure and mechanism for the topotactic transformation of the Na, TMA form  

NASA Astrophysics Data System (ADS)

Synthetic zeolite (Na, TMA)-E represents a new structure type designated EAB. Detailed structure analyses based on X-ray powder diffraction data have been carried out at room temperature, 220°C, and 350°C. The silicate framework, having maximum symmetry P63/mmc, consists of parallel 6-rings in ABBACC sequence as opposed to AABAAC in erionite (with which it has mistakenly been identified). Large changes in conformation of the EAB framework precede the transformation of (Na, TMA)-E to a sodalite-type product above 360°C. There are also strong indications for this reaction to be topotactic, whereby only one-twelfth of the original siloxane bridges are broken. Details of an acid-base reaction mechanism proceeding in characteristic loops of the structure are discussed. This process brings about the inversion of one-third of the tetrahedra in the silicate framework. The presence of water appears to be essential in this model-type reaction.

Meier, W. M.; Groner, M.

1981-04-01

262

Astrobiological relevance of phenols and their silicates  

NASA Astrophysics Data System (ADS)

We have prepared solid silicates of various phenols and have studied them by the IR (infra-red) spectroscopy. Phenols are organic compounds that are important in biology. Only very recently phenols have been synthesized in prebiotic manner. They are formed under the hydrothermal conditions and also under the simulated conditions of the interstellar space. Solid phenol silicates, which we have prepared, are ideally suited for the preservation of phenols on prebiotic Earth and in space, and for their transportation in space. The reflectance IR spectra of phenol silicates were taken and are currently being analyzed. Our goal is to determine if phenols are entombed, covalently bound, or both, in respect to the silicate matrix. We have also prepared fluorescent phenol silicates.

Kolb, Vera M.; Liesch, Patrick J.

2008-08-01

263

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

264

Methylcyclohexane conversion over ZSM-11 zeolite  

Microsoft Academic Search

ZSM-11 zeolite samples differing by their active sites (H+ and Zn2+) have been studied in the conversion of methylcyclohexane. It was observed that both the conversion and the selectivity to aromatic hydrocarbons are increased with the zinc content. It has been shown that dehydrogenation of the hydrocarbon, leading directly to toluene, is the initial stage for Zn-ZSM-11 zeolite showing very

Oscar A. Anunziata; Liliana B. Pierella; Raul G. Marino

1995-01-01

265

Strategies for high throughput, templated zeolite synthesis  

Microsoft Academic Search

The design and redesign of high throughput experiments for zeolite synthesis are addressed. A model that relates materials function to the chemical composition of the zeolite and the structure directing agent is introduced. Using this model, several Monte Carlo-like design protocols are evaluated. Multi-round protocols are bound to be effective, and strategies that use a priori information about the structure-directing

Ligang Chen; Michael W. Deem

2002-01-01

266

Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale-Bopp) Pre- and Postperihelion  

NASA Astrophysics Data System (ADS)

We present 7.5-13.4 ?m infrared (IR) spectrophotometry (R~=180-360) of the 10 ?m silicate emission from dust in the inner coma (i.e., within a diameter of 3") of comet C/1995 O1 (Hale-Bopp) at four temporal epochs from 1996 October through 1997 June during Hale-Bopp's approach to, arrival at, and recession from perihelion. Hale-Bopp's silicate feature is the strongest observed from any comet to date: the flux-to-continuum ratio at 10.0 ?m is 2.5 at 2.8 AU preperihelion, increases to 3.0 at 0.93 AU, and then decreases to 2.4 at 1.7 AU postperihelion, dropping more rapidly in strength than expected from preperihelion spectra and indicating a diminishment in the relative abundance of submicron sized grains by perihelion passage. The silicate feature also evolves with heliocentric distance. When far from perihelion, at ~2.8 AU, the High Efficiency Faint Object Grating Spectrometer (HIFOGS) 10 ?m silicate feature contains a 9.3 ?m shoulder attributable to amorphous pyroxene, broad emission from amorphous olivine (9.7 ?m), and the 11.2 ?m peak associated with crystalline olivine. Concurrent with the HIFOGS spectra at 2.8 AU, the Infrared Space Observatory (ISO) Short Wavelength Spectrometer (SWS) spectrum also shows the strong far-IR peaks of crystalline olivine at 18 mum, 23 mum, and 33 mum. When close to perihelion the HIFOGS spectra include a newly discovered 9.3 ?m peak, identifiable as Mg-rich crystalline pyroxene. We hypothesize that the crystalline pyroxenes are cooler than the other silicates, too cool to be detected at 9.3 ?m at 2.8 AU but warm enough to be detected at 1.2 AU. The best-fit empirical model for the temporal evolution of Hale-Bopp's silicate feature constrains the Mg-rich crystalline pyroxenes to be dominated by ortho-pyroxene rather than clino-pyroxene. The crystalline pyroxenes have a color temperature that is 0.6 times cooler than and an abundance that is about 9 times greater than the other silicates at all epochs, assuming equivalent particle size distributions for all components. Comparing crystalline ortho-pyroxene and crystalline olivine in radiative equilibrium, both with Mg number 0.9, the ortho-pyroxene crystals are cooler because they are less absorbing at visible and near-IR wavelengths. Thus, it is the high Mg content of the crystalline pyroxenes that accounts for their cooler temperature. The dominance of Mg-rich pyroxenes among Hale-Bopp's cometary silicates is consistent with PUMA-1 mass spectrometer measurements of comet P/Halley 1986 III and with cometary interplanetary dust particles. The high Mg content of the pyroxenes in comet Hale-Bopp implies that they are either pristine solar nebula condensates or presolar grains such as the Mg-rich crystals recently discovered by ISO around asymptotic giant branch stars.

Wooden, Diane H.; Harker, David E.; Woodward, Charles E.; Butner, Harold M.; Koike, Chiyoe; Witteborn, Fred C.; McMurtry, Craig W.

1999-06-01

267

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)

2007-05-08

268

Zeolite-based catalysts for hydrocracking  

SciTech Connect

A zeolite/amorphous dual catalyst system was developed which effectively hydrocracked feeds with wide boiling range to extinction. In this dual catalyst system, the zeolite and the amorphous catalysts operate complementally. The good character of zeolite catalyst can be realized without its bad features. Feeds with higher nitrogen content can be hydrocracked, and product yield with good selectivity for naphthas can be obtained. This scheme was derived from diagnosis of the problems associated with zeolite-based hydrocracking catalysts. A zeolitic hydrocracking catalyst, nickel tungsten on rare earth exchanged X-type zeolite (NiW/REX), was found to be ineffective for extinction recycle hydrocracking of feeds containing heavy components. The process performance was poor as indicated by high catalyst aging rate and poor naphtha selectivity and high hydrogen consumption. The polynuclear ring compounds are refractory to NiW/REX due to steric hindrance resulting from the small pore size of the catalyst, but they are easily hydrocracked with high selectivity to naphtha by amorphous catalyst.

Yan, T.Y.

1983-01-01

269

Preparation of an asymmetric zeolite L film  

SciTech Connect

Zeolites and molecular sieves are widely used for catalysis and gas separations. An elusive but highly rewarding goal is the fabrication of zeolite films for selective membranes, electrodes, sensors, and optoelectronic devices. Recently, a variety of techniques tailored to specific applications has emerged (postsynthesis preparations as well as in situ film deposition); however, to date, no general preparative methods exist. Here we report on a new processing scheme which involves the use of zeolite nanosols (colloidal suspensions of zeolite nanoparticles) for film casting, combined with controlled secondary growth of the nanoparticles. Decoupling film deposition from crystal growth provides added flexibility for tailoring the film microstructure and ease for scaleup. Implementation of this scheme, using zeolite L nanosols, led to the preparation of self-supported asymmetric zeolite L films. These films exhibit a regular decrease in crystal grain size and an increase in interzeolitic porosity proceeding from the intergrown surface of the film down into the bulk of the film. In this regard, we refer to these films as asymmetric, using the term as applied in membrane technology. 35 refs., 4 figs.

Lovallo, M.C.; Tsapatsis, M. [Univ. of Massachusetts, Amherst, MA (United States); Okubo, T. [Univ. of Tokyo (Japan)

1996-08-01

270

Kinetics of zeolite dealumination in steam  

SciTech Connect

Zeolite dealumination is a well known phenomenon that contributes to the deactivation or activation of catalysts in several different applications. The most obvious effect is in acid catalysis where dealumination under reaction conditions removes the Broensted sites, thus deactivating the catalyst. The authors are interested in the use of cation exchanged zeolites as selective reduction catalysts for removal of NO{sub x} from exhaust streams, particularly from automotive exhaust. In this case, copper exchanged ZSM-5 has been shown to be an effective catalyst for the generic reaction of NO{sub x} with hydrocarbons. However, high temperature and steam in combustion exhaust causes dealumination and consequent migration of copper out of the zeolite structure resulting in rapid deactivation of the catalyst. Dealumination of zeolites has been reported by many authors in uncountable papers and cannot be reviewed here. However, to the authors` knowledge there are no reports on the kinetics of dealumination under varying conditions of temperature and steam. By measuring the kinetics of dealumination with different zeolites and exchange cations they expect to develop working models of the dealumination process that will allow control of zeolite deactivation. This manuscript is a description of the basic techniques used and a progress report on the very beginning of this study.

Hughes, C.D.; Labouriau, A.; Crawford, S.N.; Romero, R.; Quirin, J.; Earl, W.L.

1998-08-01

271

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

272

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

273

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

274

Comparison absorption of new methylene blue dye in zeolite and nanocrystal zeolite  

Microsoft Academic Search

Mordenite and mordenite nanocrystal, were employed as effective adsorbents for new methylene blue (NMB) from an aqueous solution. The adsorption kinetics was investigated. The adsorption capacity of mordenite nanocrystal zeolite for NMB dye is more than that of the mordenite zeolite. Kinetic and adsorption isotherm studies demonstrate that the adsorption follows the pseudo second-order kinetics. The intraparticle diffusion rate coefficient

Sh. Sohrabnezhad; A. Pourahmad

2010-01-01

275

Crystalline oxides on silicon.  

PubMed

This review outlines developments in the growth of crystalline oxides on the ubiquitous silicon semiconductor platform. The overall goal of this endeavor is the integration of multifunctional complex oxides with advanced semiconductor technology. Oxide epitaxy in materials systems achieved through conventional deposition techniques is described first, followed by a description of the science and technology of using atomic layer-by-layer deposition with molecular beam epitaxy (MBE) to systematically construct the oxide-silicon interface. An interdisciplinary approach involving MBE, advanced real-space structural characterization, and first-principles theory has led to a detailed understanding of the process by which the interface between crystalline oxides and silicon forms, the resulting structure of the interface, and the link between structure and functionality. Potential applications in electronics and photonics are also discussed. PMID:20432223

Reiner, James W; Kolpak, Alexie M; Segal, Yaron; Garrity, Kevin F; Ismail-Beigi, Sohrab; Ahn, Charles H; Walker, Fred J

2010-07-20

276

Activated cation motions in zeolites  

NASA Astrophysics Data System (ADS)

We apply a Monte Carlo technique specialized for the simulation of rare events to study the activated counterions motions in the aluminosilicate Na+-mordenite. Mean activation barriers are obtained from minimum energy paths calculated on realistic potential energy surfaces by using a Metropolis algorithm. Energy barriers for Na+ hops calculated for lattices with various Si/Al ratio are found in good agreement with the Na+ detrapping energies measured by thermally stimulated current spectroscopy. One shows that the dielectric activated motions of Na+ proceed between degenerated many-body ground states with different dipolar moment by either sequential or collective hopping motions. This provides a first microscopic description of dielectric relaxation measured in zeolites.

Maurin, G.; Devautour, S.; Henn, F.; Giuntini, J. C.; Senet, P.

2002-07-01

277

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, Rayford G. (Bryan, TX); Dosch, Robert G. (Albuquerque, NM)

1993-01-01

278

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

279

Catalytic processes in the presence of zeolites of increased internal acid activity and decreased external acid activity  

SciTech Connect

A process is described for aromatizing a C[sub 2+] aliphatic hydrocarbon stream in the presence of a catalyst which comprises ZSM-5 which becomes coked and deactivated during a catalytic aromatization cycle, the improvement comprising reducing production of coke, and increasing product yield by contacting said C[sub 2+] aliphatic hydrocarbon with a zeolite catalyst, in acid form, consisting of a silicate exhibiting the X-ray diffraction pattern of ZSM-5, and recovering a product effluent which comprises benzene, toluene, and at least one xylene selected from the group consisting of o-xylene, m-xylene, and p-xylene, wherein the silicate is formed by a method consisting essentially of the steps of providing as a reactant an aluminosilicate exhibiting the X-ray diffraction pattern of an ZSM-5 wherein said reactant exhibits an alpha value which is effective to crack hydrocarbons under cracking conditions and exhibits an activity to dealkylate 1,3,5-tri-t-butylbenzene, as measured by the rate of dealkylation of 1,3,5-tri-t-butylbenzene in the presence of said reactant; treating the reactant, in hydrogen form, with a solution of nitric acid at reflux temperature or lower; and recovering said silicate; which silicate exhibits an alpha value greater than that of said reactant and a rate for dealkylation of 1,3,5-tri-t-butylbenzene which is less than that rate of dealkylation of 1,3,5-tri-t-butylbenzene by said reactant.

Rodewald, P.G.

1993-06-15

280

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

2011-08-24

281

The behaviour of water confined in zeolites: molecular dynamics simulations versus experiment  

NASA Astrophysics Data System (ADS)

In order to study the behaviour of water adsorbed in zeolites, which are microporous crystalline aluminosilicates, whose channels and cavities of nanometric dimensions can host many different molecules, we developed a sophisticated empirical potential for water, including the full flexibility of the molecule and the correct response to the electric field generated by the cations and by the charged atoms of the aluminosilicate framework. The reproduction of experimental data by our potential model is similar or even better than that obtained from the first principles methods. The results of molecular dynamics simulations of water confined in a variety of zeolites (worm-like clusters in silicalite, spherical nanoclusters in zeolite A and ice-like nanotubes in AlPO4-5 and SSZ-24) at different temperatures and coverage (loading) are discussed in connection with the experimental data, whose overall good reproduction encourages the attempt of an atomic-scale description of structural and dynamical phenomena occurring in confined water, in particular in the supercooled regime. The results are also compared with simulations and experimental data on bulk water.

Demontis, P.; Gulín-González, J.; Masia, M.; Suffritti, G. B.

2010-07-01

282

Photoassisted catalytic oxidation of isopropyl alcohol by uranyl-exchanged zeolites  

SciTech Connect

Suspensions of uranyl-exchanged zeolites mixed with solutions of isopropyl alcohol and acetonitrile undergo selective photocatalytic conversion of the alcohol to acetone. The photoassisted catalytic oxidation is sustained for over 300 h. Bulk photolysis experiments show that aging does occur. X-ray photoelectron spectroscopy experiments indicate the uranyl ions on the surface are slightly reduced with respect to the bulk. Luminescence lifetime measurements yield a range of long-lived components between 10 and 700 ..mu..s for the different zeolites. Quenching experiments show that the shortest lived components of crystalline uranyl-exchanged zeolites are responsible for this conversion to acetone. Liquid nitrogen and liquid helium temperature luminescence emission spectra show splitting of the vibrational rotational fine structure as the temperature is diminished. These splittings are indicative of site symmetry, and in the case of the uranyl-exchanged HZSM-5 with the isopropyl alcohol mixture, evidence is presented that the isopropyl alcohol binds to the excited uranyl ion. The nature of the active site and factors that are important in the mechanism of this reaction are described.

Suib, S.L.

1984-03-21

283

Zeolites US market to reach $1 billion by 2000  

SciTech Connect

This article describes the growth of the U.S. market for zeolites, specifically sodium aluminosilicate. The largest application for zeolites is for petrochemical and petroleum catalysts; however, detergents are also a specific application addressed in the article.

Morris, G.D.L.

1997-02-05

284

Determination of water content in natural zeolites by reflection method.  

National Technical Information Service (NTIS)

Water content in natural zeolites collected from different site places in Cuba has been determined by neutron reflection method. Results show that it is possible to separate the minerals abundant in zeolite from the surrounding barren rocks. Water content...

L. P. Sarria V. Desdin Garcia V. Freixas Lemus O. Dominguez Ley G. Csikai

1989-01-01

285

Dual zeolite fluid cracking catalyst composition for improved gasoline octane  

SciTech Connect

A fluid cracking catalyst is described useful for the production of high octane gasoline comprising a hydrothermally or chemically stabilized Y zeolite component and a stabilized Omega zeolite component having a silica to alumina ratio greater than 15 wherein the weight ratio of the Y zeolite to the stabilized Omega zeolite is 1:3 to 20: 1, said catalyst not having a hydrogenation component. A fluid cracking catalyst is described according to claim 1, wherein the fluid cracking catalyst comprises either (a) a composite of a Y zeolite and a stabilized Omega zeolite in an inorganic matrix, or (b) a mixture of a matrixed Y zeolite component and a matrixed stabilized Omega zeolite component.

Gatte, R.R.

1993-08-17

286

Catalytic Oxidation by Transition Metal Ions in Zeolites.  

National Technical Information Service (NTIS)

The regular cavities of zeolites form a unique environment for carrying out both stoichiometric and catalytic oxidation reactions. Transition metal ions such as molybdenum and cobalt may be introduced into the zeolite, and, as well, the acidity may be var...

J. H. Lunsford

1988-01-01

287

Experiments on Photochemical Energy Storage with Metal-Coated Zeolites.  

National Technical Information Service (NTIS)

Photo-oxidation of water to oxygen using silver zeolite catalysts resulted in a pH-dependence and inherent sensitivity of the photo-redox system depending on the type of zeolite used. (ERA citation 09:037443)

B. Sulzberger

1983-01-01

288

Optical and microhardness measurement of lead silicate  

NASA Astrophysics Data System (ADS)

Lead silicate glasses, PbO-SiO2, are interesting because these glasses exhibit thermal, optical, and mechanical properties different than other silicate glasses, and they form a thermally and chemically stable glass over a wide composition range. They are also interesting as PbO acts as glass modifier and as glass former depending on the concentration. In the present work we have prepared lead silicate glasses (xPbO-(1-x).SiO2) by melt quenching. We measured UV absorbance, Vickers hardness, and glass transition for these samples. It is found that band gap is proportional to glass transition.

Jogad, Rashmi M.; Kumar, Rakesh; Krishna, P. S. R.; Jogad, M. S.; Kothiyal, G. P.; Mathad, R. D.

2013-02-01

289

A Mechanism of Crystallization of Cometary Silicates  

NASA Astrophysics Data System (ADS)

We propose a mechanism of crystallization of cometary silicate grains on the basis of the Greenberg model of cometary dust which is composed of a silicate core an organic mantle and an outermost icy mantle. The crystallization mechanism we propose is due to energy release by polymerization of the organic mantle when the grains are released from a cometary nucleus and heated by solar radiation. We formulate the crystallization mechanism and calculate the degree of crystallization of the silicate core. We show the results of the calculations of the crystallization degree for plausible values of the physical parameters and of the infrared emission spectra.

Yamamoto, Tetsuo; Chigai, Takeshi

2005-01-01

290

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

291

Absorption and desorption characteristic of zeolites in gas sensor system  

Microsoft Academic Search

Nanosized zeolites as a novel absorbent were investigated targeting for the nerve agent sarin stimulant gas DMMP. Quartz crystal microbalance (QCM) gas sensors modified with Silicalite-1 or Cu-ZSM-5 zeolites synthesized as micro-porous absorbents were fabricated and their gas response characteristics were examined to study the absorption capability of zeolites. The results indicated that Cu-ZSM-5 zeolite has stronger absorption capacity than

Wei Yao; Yuanyuan Hu; Xinming Ji; Nan Ren; Jia Zhou; Yiping Huang; Yi Tang

2008-01-01

292

Zeolite catalysis in the synthesis of isobutylene from hydrous ethanol  

Microsoft Academic Search

This work deals with the synthesis of isobutylene from a hydrous ethanol feedstock over zeolites. The synthesis is accomplished in three steps: (1) low-temperature direct ethanol conversion to ethylene on H-ZSM-5 zeolite, (2) ethylene conversion to butene products over metal-exchanged zeolites, and (3) butene skeletal rearrangement to isobutylene over FER zeolites. The key to understanding and optimizing each synthesis step

Cory Bernard Phillips

1999-01-01

293

Basic sites in zeolites followed by IR studies of NO +  

Microsoft Academic Search

The basic properties of zeolitic oxygens were examined by IR studies of NO+ ions. NO+ were formed by the disproportionation of N2O4 (N2O4?NO++NO3?). NO+ were stabilized by zeolitic oxygens and NO3? by the zeolitic cations or positively charged extraframework Al species. The spectra of NO+ in zeolite NaY show three maxima that indicate the presence of oxygens of various negative

Barbara Gil; Karolina Mierzy?ska; Monika Szczerbi?ska; Jerzy Datka

2007-01-01

294

Substitution clustering in a non-stoichiometric celsian synthesized by the thermal transformation of barium exchanged zeolite X  

SciTech Connect

The thermal transformation of Ba exchanged zeolite X to celsian has been studied by {sup 27}Al and {sup 29}Si MAS NMR spectroscopy. Evidence for the degradation of the zeolite framework is present in the {sup 29}Si NMR spectra after thermal treatment at 850 deg. C. Confirmation is provided by the {sup 29}Si NMR data that synthesis of celsian via the decomposition of Ba exchanged zeolite leads to a single defect phase. Clustering of the isomorphous replacement of aluminium by silicon must occur to explain the observed {sup 29}Si chemical shifts. The {sup 27}Al NMR data show distorted aluminium co-ordination sites upon the thermal transformation of Ba exchanged zeolite X. The distortions present in the amorphous matrix are greater than those present in the monoclinic and hexagonal crystalline phases of celsian. - Graphical abstract: Monte Carlo simulation of the Q {sub 4}(mAl) silicon connectivity in the {alpha}-hexagonal celsian lattice, for a Si/Al ratio of 1:1. Si atoms are shown in yellow and the Al atoms in black.

Clayden, Nigel J. [School of Chemical Sciences and Pharmacy, University of East Anglia, NR4 7TJ (United Kingdom)]. E-mail: N.Clayden@uea.ac.uk; Esposito, Serena [Laboratorio Materiali del Dipartimento di Meccanica, Strutture, Ambiente e Territorio, Facolta di Ingegneria dell'Universita di Cassino, Via G. Di Biasio 43, 03043 Cassino (FR) (Italy); Ferone, Claudio [Laboratorio Materiali del Dipartimento di Meccanica, Strutture, Ambiente e Territorio, Facolta di Ingegneria dell'Universita di Cassino, Via G. Di Biasio 43, 03043 Cassino (FR) (Italy); Pansini, Michele [Laboratorio Materiali del Dipartimento di Meccanica, Strutture, Ambiente e Territorio, Facolta di Ingegneria dell'Universita di Cassino, Via G. Di Biasio 43, 03043 Cassino (FR) (Italy)

2006-07-15

295

Corrosion protection property of colloidal silicate film on galvanized steel  

Microsoft Academic Search

Chemical conversion treatment of galvanized steel using colloidal silica was investigated as an alternative treatment to chromate conversion. The solution used for the colloidal silicate coating consisted of colloidal silicate, titanium sulfate, and nitrate ions to maintain good corrosion resistance. Adding CoSO4 to the colloidal silicate solution enhanced the adhesion between the silicate film and the zinc coat on the

Motoaki Hara; Ryoichi Ichino; Masazumi Okido; Nobuaki Wada

2003-01-01

296

Silicate Abundance and its Significance in the Hooghly-Matla Estuary, India (Invited)  

NASA Astrophysics Data System (ADS)

Sea water contains in suspension a wide spectrum of siliceous materials. The surface water abounds with organisms such as diatoms and radiolarians having skeletons composed of non-crystalline form of hydrated silica. A very high level of silicate (130-140 ?M) noticed in the Bay of Bengal nearer the confluence of the rivers, where nutrient levels are appreciably higher during southwest monsoon period (March-October) in contrast to other seasons (CSMCRI, 2007). The relatively high (>5 µg) silicate values at the Ganges head (Bay of Bengal) is attributable to river runoff during the same period (CSMCRI, 2007). In general, the concentration of inorganic phosphate, nitrate and silicate increased in the direction of Antarctic Sea, particularly around 40° S latitude, in the proximity of sub-tropical convergence. In comparison to Atlantic and Pacific oceans, the concentration of nutrients in the Indian Ocean is almost twice (Venkataramana, 2007). The mean value of 102.9±43.2 ?M for silicate in Hooghly estuary is found lower than worldwide average river water concentration of 147.8±93.6 ?M (Gems, 2002). Seasonal variation of river runoff of silicate shows maximum value of 12.6×109 mol during monsoon; thereafter, its value decreased to 2.54 and 1.33×109 mol during post-monsoon and pre-monsoon, respectively. The net residual flows of 4.91, 1.47 and 0.5×109 mol and the exchange flux of 6.95, 0.94 and 0.51×109 mol is found at the estuary during monsoon, post-monsoon and pre-monsoon, respectively. The annual flux of silicate out of the estuary is estimated to be 15.28×109 mol (428×103 t), about 93% of the total fluvial flux. The non-conservative flux of silicate removed from the water column is found to be 1.12 × 109 mol (31.0×103 t), which is about 5% in the global scale (0.6×106 t year-1) (Tregguer et al.,1995). Nitrate, Phosphate and Silicate, have been studied in the Hooghly-Matla estuarine complex and compared with selected previous studies. It is observed that both nitrate and phosphate concentrations remained almost stable varied (between 19.28 and 19.4?M for DIN and between 1.61and 1.99?M for DRP) during the period between 1975 and 2001, but silicate shows a distinct increasing trend from 35.6 to 102.9?M (Nandy et al., 1983; NIO, 1986; Ghosh et al., 1992). These also conforms our study, with the concentration of silicate from 19.97 µ M to 72.73 µ M during pre-monsoon and 48.26 µ M to 103.19 µ M during the monsoon in the Hooghly-Matla estuarine complex. High concentrations of biogenic silica in tidal marshes are necessary for maximum benthic diatom production which in turn helps high secondary production of commercial fish and crustaceans (Courtney, 2007). The Gross Primary Productivity is found to be increased in three stations of these estuaries (27.32±5.06 mg/m3/ hr in 1990, 33.58±14 mg/m3/ hr in 2000 and 44.36±5.91 mg/m3/ hr in 2007) (Biswas et. al., 2009), with the increasing trend of silicate within this estuarine complex. The increasing trend of total catches in the Eastern and Western Indian Ocean (FAO, 1998), of which the Bay of Bengal is an important part (Islam, 2003), justify the interrelation. Thus, these findings are ascertaining the interrelation between the increasing trend of silicate concentration with the enhanced primary productivity, which in turn increase the fish yield in the Hooghly-Matla estuarine complex on the Bay of Bengal.

Ghosh, T.; Akhand, A.

2010-12-01

297

Zeolites as transformation elements in discriminating semiconductor metal oxide sensors  

Microsoft Academic Search

The effectiveness of using zeolites as a method of introducing variance in the gas responses of semiconductor metal oxide gas sensors is demonstrated. Screen printed tungsten trioxide (WO3) and chromium titanium oxide (CTO) thick films overlaid with the hydrogen form of different zeolites were exposed to organic vapours with similar functional groups. The composite metal oxide-zeolite gas sensors responses exhibit

A. Afonja; R. Binions; S. Dungey; I. P. Parkin; D. W. Lewis; D. E. Williams

2010-01-01

298

Computer modeling of the infrared spectra of zeolite catalysts  

Microsoft Academic Search

The paper describes the applications of computer modeling methods to the interpretation of the infrared spectra of zeolite frameworks. The correlation of the breathing vibration of ring structures in zeolitic lattices with their infrared spectra was investigated by the molecular dynamics method. The calculations reveal that in periodic zeolite lattices the ring-breathing vibrations participate in many normal modes. Despite the

Konstantin S. Smirnov; Daniel Bougeard

2001-01-01

299

Nanostructured zeolite 4A molecular sieving air separation membranes.  

PubMed

A novel membrane forming strategy is reported to probe the intrinsic O2/N2 selectivity of zeolite 4A membrane and to fabricate highly selective nanocomposite membranes by using a nanocrystal-derived hierarchical porous zeolite 4A membrane whose non-zeolitic mesoporsity is filled with a nonpermeable polymer material (polyfurfuryl alcohol). PMID:12196960

Wang, Huanting; Huang, Limin; Holmberg, Brett A; Yan, Yushan

2002-08-21

300

Synthesis of ionic liquid templated zeolite like structures  

Microsoft Academic Search

This study describes the utilization of the alkyl substituted imidazolium based ionic liquid as a structure directing agent of the MFI type zeolite structure in water rich environment. The resulted zeolite like structure presents some similarities with the parent MFI structure, but grows preferentially in 1D leading to zeolite like nanofibers.

Amando Martín; Svetlana Ivanova; Francisca Romero Sarria; Miguel Ángel Centeno; Jose Antonio Odriozola

2010-01-01

301

Crystallization of neodymium-rich phases in silicate glasses developed for nuclear waste immobilization  

NASA Astrophysics Data System (ADS)

Glass-ceramics containing neodymium-rich crystalline phases can be obtained by crystallization of silicate glasses (nucleation + crystal growth heat treatments) or by controlled cooling of melts. Such materials could be envisaged as durable matrices for conditioning minor actinides- and Pu-rich nuclear wastes if the partitioning ratio of the wastes between crystalline phase and residual glass is high (principle of double containment barrier). In radioactive waste forms, Nd would be partially substituted by actinides and neutron absorbers (Gd). In this work, two silicate glass compositions leading to efficient nucleation and crystallization of either zirconolite (Ca1-xNdxZrTi2-xAlxO7, x < 1) or apatite (Ca2Nd8Si6O26) in their bulk were studied as potential waste forms. The effect of the method used to prepare glass-ceramics (controlled cooling from the melt or nucleation + crystal growth from the glass) on both the microstructure and the structure of the neodymium-rich crystalline phase was studied. The highest number of zirconolite or apatite crystals in the bulk was obtained using the nucleation + crystal growth method. However, the percentage of neodymium incorporated in zirconolite crystals remained too small to make realistic the use of such materials for the conditioning of actinides in comparison with more durable bulk ceramics.

Caurant, D.; Majerus, O.; Loiseau, P.; Bardez, I.; Baffier, N.; Dussossoy, J. L.

2006-08-01

302

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

303

On the exceptional time-on-stream stability of HZSM-12 zeolite: relation between zeolite pore structure and activity  

Microsoft Academic Search

ZSM-12 and several other 12-membered ring large-pore zeolites have been tested for the reforming of naphthenic hydrocarbon\\u000a mixtures. It was found that ZSM-12 possesses a surprisingly higher coking resistance than other large pore zeolites tested\\u000a such as USY, L-zeolite, mordenite, and ?=zeolite for reforming of hydrocarbon mixtures. This superior performance is due to\\u000a the unique non-interconnecting tubular-like linear channels of

Wenmin Zhang; Panagiotis G. Smirniotis

1999-01-01

304

Infrared spectra of hydrated silicates, carbonaceous chondrites, and amorphous carbonates compared with interstellar dust absorptions  

NASA Astrophysics Data System (ADS)

The infrared spectra of C1 and C2 carbonaceous chondrites are similar but not identical to the serpentines, montmorillonites, and chamosites. Hydroxyl or bound water features at 2.7, 2.9 and 6 microns do not change at temperatures from 15 to 300 K; absorption bands at 2.7 and near 2.8 microns can be applied for the determination of a hydrated silicate component in the interstellar dust. The interstellar 3.07-micron band is a broad feature between the 3.1 and 4 micron lines in hydrated silicates; a band at 7 microns in carbonaceous chondrites is probably a carbonate absorption. Finally, an amorphous calcite was produced to investigate order-disorder effects on the infrared carbonate spectra and its spectrum compared with crystalline carbonates.

Knacke, R. F.; Kraetschmer, W.

1980-12-01

305

Fluorine-19 NMR Study of the Environment of Fluorine in Silicate and Aluminosilicate Oxyfluoride Glasses.  

NASA Astrophysics Data System (ADS)

Using a compilation of F-19 NMR chemical shift values for crystalline model compounds, we have explored the local fluorine environment in several silicate and aluminosilicate oxyfluoride glasses. The F-19 MAS NMR spectrum of the Mg-silicate glass consists of a broad peak centered at -170 ppm, which encompasses the F-Mg(3) environments (where "3" is the number of Mg neighbors) of crystalline MgF2 (-195 ppm) and phlogopite (-175 ppm). The predominant environment in the glass is consequently assigned to F-Mg(n), where "n" indicates an unknown number of nearest neighbors. The magnesium aluminosilicate glass spectra all consist of a major feature at about -175 ppm and a shoulder at approximately -145 ppm. Based on the model compound data, the shoulder lies in the region attributed to Al-F-M2+ sites, and it was observed that glasses with a higher Al/Mg ratio featured extra intensity in the high-frequency shoulder. The shoulder is consequently assigned to Al-F-Mg(n), while the major feature is attributed to F-Mg(n) sites. This indicates that Mg is decidedly more effective in bonding to fluorine than either Ca or Ba in aluminosilicate glasses, following the trend established in our previous work on the Ba- and Ca-aluminosilicate glasses (the higher field strength modifier cation is more effective in competing with Al). Fluorine preferentially bonding with the modifier cation over aluminum has, to our knowledge, never been previously observed in aluminosilicate glasses. Spectra for Na-La-silicate glasses are characterized by an extremely wide peak (hundreds of ppm) and a relatively narrow peak at -220 ppm. The narrow peak at -220 ppm is assigned to F-Na(n) due to its proximity to the chemical shift of F-Na(6) (-225 ppm, from crystalline NaF). The small relative area of the F-Na(n) peak indicates a pronounced preference for F-La bonds over F-Na bonds, which is consistent with the findings of the previously discussed aluminosilicates. The massive, broad feature encapsulates the region described by the mixed fluorine environments of crystalline NaLaF4 (-30 to -63 ppm), and has therefore been assigned to a wide variety of fluorine environments, consisting of F-La bonds in a mixed environment with some number of F-Na bonds. In order to explore La-F clustering we have employed "echo" experiments, which can provide information about F-F distances. In the Na-La-silicates, the broad feature decays much faster than the F-Na(n) peak, indicating a shorter F-F distance in the sites associated with La. This is not consistent with random anion distribution but can be easily explained by the formation of fluorine-rich clusters. This may provide insight into the mechanism for the onset of crystallization in glass ceramics. In the long echo-time experiments on the Na-La-silicate glasses, the intensity of the broad feature was virtually gone, and the intensity of the F-Na(n) peak was largely decreased. This allowed us to clearly observe another peak centered at -140 ppm. This is near the peak found for the Si-F-Na(2) structure (-152 ppm) in the model compounds. Further examination of the original one-pulse spectra revealed the presence of this peak in small quantities in all compositions. Its relative intensity (about 2 percent of the total intensity) is comparable to that of Si-F-Ba(n) and Si-F-Na(n) bonding found in the fluorine containing Ba-silicate and Na-silicate glasses (respectively) from our previous studies. This suggests that Si-F bonding is independent of composition and may be an intrinsic characteristic of fluorine-containing silicate glasses.

Kiczenski, T. J.; Stebbins, J. F.

2002-12-01

306

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

307

Magnesium silicates adsorbents of organic compounds  

NASA Astrophysics Data System (ADS)

Studies were presented on production of highly dispersed magnesium silicate at a pilote scale. The process of silicate adsorbent production involved precipitation reaction using water glass (sodium metasilicate) solution and appropriate magnesium salt, preceded by an appropriate optimization stage. Samples of best physicochemical parameters were in addition modified (in order to introduce to silica surface of several functional groups) using the dry technique and various amounts of 3-isocyanatepropyltrimethoxysilane, 3-thiocyanatepropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane. The so prepared samples were subjected to a comprehensive physicochemical analysis. At the terminal stage of studies attempts were made to adsorb phenol from its aqueous solutions on the surface of unmodified and modified magnesium silicates. Particle size distributions were determined using the ZetaSizer Nano ZS apparatus. In order to define adsorptive properties of studied magnesium silicates isotherms of nitrogen adsorption/desorption on their surfaces were established. Efficiency of phenol adsorption was tested employing analysis of post-adsorption solution.

Ciesielczyk, Filip; Krysztafkiewicz, Andrzej; Jesionowski, Teofil

2007-08-01

308

Highly silicic compositions on the Moon.  

PubMed

Using data from the Diviner Lunar Radiometer Experiment, we show that four regions of the Moon previously described as "red spots" exhibit mid-infrared spectra best explained by quartz, silica-rich glass, or alkali feldspar. These lithologies are consistent with evolved rocks similar to lunar granites in the Apollo samples. The spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar. The variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the Moon. Basaltic underplating is the preferred mechanism for silicic magma generation, leading to the formation of extrusive landforms. This mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies. PMID:20847267

Glotch, Timothy D; Lucey, Paul G; Bandfield, Joshua L; Greenhagen, Benjamin T; Thomas, Ian R; Elphic, Richard C; Bowles, Neil; Wyatt, Michael B; Allen, Carlton C; Donaldson Hanna, Kerri; Paige, David A

2010-09-17

309

High Pressure Response of Siliceous Materials.  

National Technical Information Service (NTIS)

Several siliceous (i.e., materials containing, resembling, relating to or consisting of silica or silicon dioxide) materials were examined in this study conducted by Oak Ridge National Laboratory and sponsored by the US Army TARDEC. Some were glasses: fus...

A. A. Wereszczak E. A. Rodgers K. P. Bortle M. K. Ferber T. G. Morrissey

2013-01-01

310

21 CFR 872.6670 - Silicate protector.  

Code of Federal Regulations, 2013 CFR

...6670 Section 872.6670 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6670 Silicate protector. (a)...

2013-04-01

311

Fine tuning of the dimensionality of zinc silicate nanostructures and their application as highly efficient absorbents for toxic metal ions  

Microsoft Academic Search

The controllable synthesis of materials with the desired crystal structure and dimensionality is of great significance in\\u000a material science. In this work we report the successful synthesis of amorphous and crystalline zinc silicates with different\\u000a dimensionalities and well-defined shapes, including hollow spheres, nanowires and membranes. The structure-related absorption\\u000a properties have been studied. A detailed study of their ability to remove

Yan Yang; Yuan Zhuang; Yunhua He; Bo Bai; Xun Wang

2010-01-01

312

Protein adsorption on the mesoporous molecular sieve silicate SBA15: effects of pH and pore size  

Microsoft Academic Search

A mesoporous molecular sieve silicate, SBA-15, with three pore sizes (38.1Å, 77.3Å, and 240Å) has been synthesized using a non-ionic, tri-block copolymer as a template in a sol–gel method. The effects of synthesis conditions on the pore size and pore-size distribution of this adsorbent have been described. The adsorption of proteins on these crystalline, ordered, materials has been studied. The

Amit Katiyar; Lei Ji; Panagiotis Smirniotis; Neville G. Pinto

2005-01-01

313

Water Solubility in Octahedrally Coordinated Silicates  

Microsoft Academic Search

The incorporation of water into nominally anhydrous silicates, associated with mechanical weakening and lowered melting points, can serve as a significant volatile reservoir in the planet. Using density functional theory, we performed a series of first-principles, calculations to address the substitution mechanism of hydrogen coupled with aluminum in octahedrally coordinated silicates (SiO2 stishovite and MgSiO3 perovskite). We additionally consider the

W. R. Panero; L. Stixrude

2006-01-01

314

Silicates characterization as potential bacteriocin-carriers  

Microsoft Academic Search

Two different silicates, zeosil and expanded perlite, were characterized as potential carriers of a bacteriocin with anti-Listeria monocytogenes activity, produced by Enterococcus faecium CRL1385. Specific surface areas showed a value significantly higher for zeosil (146m2 g?1) than for perlite (0.65m2 g?1). Potential zeta measurements revealed that both silicates had negatively charged surfaces between pH 2 and 11, but zeosil presented

Carolina Ibarguren; M. Carina Audisio; E. Mónica Farfán Torres; María C. Apella

2010-01-01

315

Molecular simulations and experimental studies of zeolites  

NASA Astrophysics Data System (ADS)

Zeolites are microporous aluminosilicate tetrahedral framework materials that have symmetric cages and channels with open-diameters between 0.2 and 2.0 nm. Zeolites are used extensively in the petrochemical industries for both their microporosity and their catalytic properties. The role of water is paramount to the formation, structure, and stability of these materials. Zeolites frequently have extra-framework cations, and as a result, are important ion-exchange materials. Zeolites also play important roles as molecular sieves and catalysts. For all that is known about zeolites, much remains a mystery. How, for example, can the well established metastability of these structures be explained? What is the role of water with respect to the formation, stabilization, and dynamical properties? This dissertation addresses these questions mainly from a modeling perspective, but also with some experimental work as well. The first discussion addresses a special class of zeolites: pure-silica zeolites. Experimental enthalpy of formation data are combined with molecular modeling to address zeolitic metastability. Molecular modeling is used to calculate internal surface areas, and a linear relationship between formation enthalpy and internal surface areas is clearly established, producing an internal surface energy of approximately 93 mJ/m2. Nitrate bearing sodalite and cancrinite have formed under the caustic chemical conditions of some nuclear waste processing centers in the United States. These phases have fouled expensive process equipment, and are the primary constituents of the resilient heels in the bottom of storage tanks. Molecular modeling, including molecular mechanics, molecular dynamics, and density functional theory, is used to simulate these materials with respect to structure and dynamical properties. Some new, very interesting results are extracted from the simulation of anhydrous Na6[Si6Al 6O24] sodalite---most importantly, the identification of two distinct oxygen sites (rather than one), and formation of a new supercell. New calorimetric measurements of enthalpy are used to examine the energetics of the hydrosodalite family of zeolites---specifically, formation enthalpies and hydration energies. Finally, force-field computational methods begin the examination of water in terms of energetics, structure, and radionuclide containment and diffusion.

Moloy, Eric C.

316

A new active zeolite structure for the selective catalytic reduction (SCR) of nitrogen oxides: ITQ7 zeolite  

Microsoft Academic Search

The activity of a new zeolite material, ITQ7, has been studied for the selective catalytic reduction (SCR) of NO. The pore topology of this material is similar to the structure of a beta zeolite, with a tridirectional system with 12-member rings. ITQ7 exchanged with copper or cobalt shows a catalytic behaviour very similar to a beta zeolite exchanged with copper

Antonio E Palomares; J. G Prato; A Corma

2002-01-01

317

The catalytic effect of boron substitution in ZSM-5 type zeolites  

SciTech Connect

A homologous series of boron-containing MFI-type zeolites has been prepared and studied for catalytic activity. The authors find that boron is incorporated into the catalyst lattice and exhibits catalytic activity for one of the least demanding hydrogen conversions, double bond shift. It shows no activity for the next more demanding process, skeletal isomerization. The authors also find that boron enhances the formation of surface oligomers but lacks the acidity to crack these species. The result is that the presence of boron in an aluminum-containing MFI catalyst causes enhanced coke formation and an increased rate of catalyst decay. These results are confirmed by runs done on a silicate synthesized from the same starting materials as those of the other catalysts. This sample showed no detectable catalytic activity.

Cornaro, U. (Snamprogetti, Milan (Italy)); Wojciechowski, B.W. (Queen's Univ., Kingston, Ontario (Canada))

1989-11-01

318

Italian zeolitized rocks of technological interest  

NASA Astrophysics Data System (ADS)

Large areas of Italian territory are covered by thick and widespread deposits of zeolite-bearing volcaniclastic products. The main zeolites are phillipsite and chabazite spread over the whole peninsula, and clinoptilolite recorded only in Sardinia. A trachytic to phonolitic glassy precursor accounts for the formation of the former zeolites characterized by low Si/Al ratios (?3.00), while clinoptilolite is related to more acidic volcanism. The genesis of most of these zeolitized deposits is linked to pyroclastic flow emplacement mechanisms characterized by quite high temperatures and by the presence of abundant fluids. The main utilization of these materials has been and still is as dimension stones in the building industry. Currently, limited amounts are also employed in animal farming (dietary supplement, pet litter and manure deodorizer) and in agriculture as soil improvement and slow-release fertilizers. New fields of application have been proposed for these products on account of their easy availability, very low cost, their high-grade zeolites (50 70%), and good technological features such as high cation exchange capacities and adsorption properties.

de'Gennaro, M.; Langella, A.

1996-09-01

319

Molecular simulation of alkene adsorption in zeolites  

NASA Astrophysics Data System (ADS)

The adsorption isotherms of various alkenes and their mixtures in zeolites such as silicalite-1 (MFI-type), theta-1 (TON-type), and deca-dodecasil 3R (DDR-type) were calculated using the grand canonical Monte Carlo (GCMC) approach. Additionally, the adsorption of alkene-alkane mixtures was simulated. The GCMC approach was combined with the configurational-bias Monte Carlo (CBMC) method. Effective Lennard-Jones parameters for the interaction between the oxygen atoms of all-silica zeolites and the sp2-hybridized groups of linear alkenes were determined using a united atom force field. They were adjusted to the experimental adsorption data of silicalite-1 (MFI). The inflection behaviour of the 1-heptene isotherm was investigated in detail. It is shown that, in the inflection region, the 1-heptene molecules alter their end-to-end length depending on their location. The occurrence of a maximum in the mixture adsorption isotherms is attributed to two effects: entropic effects and non-ideality effects. From the mixture simulations some general conclusions concerning the separation of hydrocarbons with silicalite-1 can be drawn. The transferability of the Lennard-Jones parameters to other zeolites was investigated. Simulations of adsorption isotherms in the zeolites theta-1 and DD3R and their comparison with experimental data indicate the possibility of transferring the parameters to other all-silica zeolites.

Jakobtorweihen, Sven; Hansen, Niels; Keil, Frerich J.

320

Molecular recognition in cation-exchanged zeolites  

NASA Astrophysics Data System (ADS)

The concepts of confinement- and molecular recognition-driven chemical reactivity of cation-exchanged zeolites is illustrated by our recent results from periodic and cluster density functional theory (DFT) calculations. The reactivity of alkali-earth- and alkaline-exchanged low-silica zeolites for selective photo-oxidation of alkenes with molecular oxygen and for N2O4 disproportionation is shown to be mainly due to the specific arrangement and the size of the cations in the zeolite cage. An attempt is made to separate the effects of basicity of the framework, the Lewis acidity of the extra-framework cations and the electrostatic field in the zeolite cage as well as its geometrical properties for the respective reactions. The importance of the favorable adsorption fashion of the reagents controlled by noncovalent interactions with the microporous matrix is shown. The role of the weak interactions with the zeolite walls and the factors, which determine the preference for a particular adsorption mode, are discussed by the example of light alkanes adsorption to Mg- and Ca-exchanged faujasites.

Pidko, Evgeny A.; van Santen, Rutger A.

321

Crystalline silicon thin-film solar cells on ZrSiO 4 ceramic substrates  

Microsoft Academic Search

The development of a low-cost substrate is one of the major technological challenges for crystalline Si thin-film solar cells. Zirconium silicate (ZrSiO4) ceramics is a material which can meet the demanding physical requirements as well as the cost goals. Thin microcrystalline Si films were deposited by atmospheric pressure CVD on ZrSiO4-based ceramic substrates coated with barrier layers. The Si film

T Kieliba; S Bau; R Schober; D Oßwald; S Reber; A Eyer; G Willeke

2002-01-01

322

Characterisation of crystalline C-S-H phases by X-ray photoelectron spectroscopy  

SciTech Connect

We have prepared a number of crystalline calcium-silicate-hydrate (C-S-H) phases hydrothermally, with calcium-silicon ratios varying from approximately 0.5 (K-phase) to 2.0 (hillebrandite and {alpha}-dicalcium silicate hydrate). The phases were then analysed using X-ray photoelectron spectroscopy (XPS). Increasing calcium-silicon ratios resulted in decreased silicon binding energies. Additionally, changes in the O 1s spectra could be explained in terms of bridging (BO) and nonbridging oxygen (NBO) moieties. Finally, the modified Auger parameter has proved particularly useful in determining the extent of silicate anion polymerisation. Of note also are the apparently unusual spectra for 11 A tobermorite. The silicon and oxygen photoelectron spectra indicate a phase with a lower degree of silicate polymerisation than predicted from its composition. The main contributing factor is the intrinsic disorder within the tobermorite structure. This study has shown how XPS may be used to obtain valuable structural information from C-S-H phases, and our analysis of the crystalline phases is the first step towards the analysis of real C-S-H-based cement systems.

Black, Leon; Garbev, Krassimir; Stemmermann, Peter; Hallam, Keith R.; Allen, Geoffrey C

2003-06-01

323

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  

NASA Astrophysics Data System (ADS)

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, however, as some NICs also have weak features like most ECs. Grains with lower porosities (lower fraction of vacuum) can explain weaker silicate features (Kelley and Wooden 2009; Kolokolova et al. 2007). Alternatively, omitting the smallest (submicron) solid grains can reduce the contrast of the silicate feature (Lisse et al. 2006). However, so far, only models for solid submicron crystals fit the crystalline peaks in spectra of comets with weak silicate features. This presents a dilemma: how can the coma be devoid of small grains except for the crystals? The Spitzer spectra of the Deep Impact event with EC 9P/Tempel 1 provides a data set to model larger porous grains with crystal inclusions because the post-impact coma was a time-of-flight experiment: an impulsive release of grains were size-sorted in time by their respective gas velocities so that the smaller grains departed the inner coma quicker than larger grains. A velocity law derived from fitting small beam Gemini spectra (Harker et al. 2007) indicates that at 20 hour post-impact the (pre-impact subtracted) Spitzer IRS spectrum contained grains larger than 10-20 micron radii, moving at 20 m/s, that produced a weak silicate feature with an 11.2 micron crystalline olivine peak. Furthermore, this feature looks like the silicate feature from the nominal coma. We present some results of a computational effort to model discrete crystals and mixed-mineral porous aggregate grains with silicate crystal inclusions using DDSCAT on the NAS Pleiades supercomputer.

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

2010-10-01

324

Laser processing of siliceous materials  

NASA Astrophysics Data System (ADS)

Laser processing of siliceous materials becomes increasingly important. Analogous to the laser processing of conventional materials there are applications in the fields of cleaning, surface processing, cutting, etc. The present paper concerns the state of the art and new applications: (1) Laser cleaning of natural stone surfaces. The good disability allows restoration work to be carried out conveniently, as for example the complete removal of crusts or the removal to such degree that moisture is not trapped beneath. (2) Non-slip finish of polished natural stone surfaces: The excellent focusing of laser beams on spots as small as 100 micrometer and below can be exploited to produce macroscopically invisible structures on the surfaces of different materials. This permits microscopically small craters and lentil shaped depressions to be generated on the stone surface. Therefore it is possible to provide a non-slip finish to polished natural stone surfaces without noticeably impairing the gloss. (3) Concrete cutting: In Europe, and particularly in Germany, there is a growing demand for redevelopment of concrete apartment buildings, involving the removal of non-bearing walls and the cutting of openings. The temporal relocation of residents due to the noise and moisture from the use of diamond tools could be avoided by applying a laser cutting technology. With a 3 kW-Nd-YAG-laser, 70 mm concrete can be cut with rates up to 25 mm/min.

Panzner, Michael; Lenk, Andreas; Wiedemann, Guenter R.; Hauptmann, Jan; Weiss, Hans J.; Ruemenapp, Thomas; Morgenthal, Lothar; Beyer, Eckhard

2000-08-01

325

The development of electrical treeing in LDPE and its nanocomposites with spherical silica and fibrous and laminar silicates  

NASA Astrophysics Data System (ADS)

Electrical treeing in LDPE and three LDPE nanocomposites, with spherical silica and fibrous and laminar phyllosilicates, has been studied. Electrical tests were performed at a 50 Hz frequency and voltages between 8 and 29 kV, and the time to inception of the first electrical partial discharges (TTI) of the electrical trees and the time to breakdown (TBD), related to the electrical stability of the insulator, were determined. Above 15 kV all the nanocomposites show longer inception times and shorter tree growth times than LDPE. It is proposed that both observations are caused by the modification of the polymer crystalline morphology induced by the presence of the fillers and by the development of a large number of interfacial structures, both organo-inorganic and amorphous-crystalline. Below 15 kV the TBD is increased in the nanocomposites with the laminar silicate because of tortuosity and the TTI is increased in the fibrous silicate containing a nanocomposite because of the LDPE crystalline morphology in the presence of the silicate. The nanosilica particles decrease the electrical stability in the whole voltage range by decreasing both TTI and TBD.

Tiemblo, Pilar; Hoyos, Mario; Gómez-Elvira, Jose Manuel; Guzmán, Julio; García, Nuria; Dardano, Andrea; Guastavino, Francesco

2008-06-01

326

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

327

Phenylalanine and arginine adsorption in zeolites X, Y, and Beta.  

PubMed

This paper documents a continuation of work published in Langmuir 2005, 21, 8743-8750. We report new aspects of this amino acid adsorption study, including the effect of changing zeolite framework type and results from adsorption of mixed amino acids. In single-amino-acid adsorption experiments, zeolite Y (Si/Al=2.5) was found to adsorb no phenylalanine while admitting arginine to a similar extent as observed with zeolite beta. Using this zeolite Y, we measured mixed-amino-acid separation selectivities for arginine/phenylalanine as large as 25,000 or 2 orders of magnitude larger than the corresponding selectivities measured with zeolite beta. PMID:17042553

Krohn, John E; Tsapatsis, Michael

2006-10-24

328

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

329

Determination of the bulk modulus of hydroxycancrinite, a possible zeolitic precursor in geopolymers, by high-pressure synchrotron X-ray diffraction  

Microsoft Academic Search

Crystalline zeolitic materials, such as hydroxycancrinite, hydroxysodalite, herschelite and nepheline, are often synthesized from geopolymerization using fly-ash and solutions of NaOH at high temperatures. Comprised mainly of 6-membered aluminosilicate rings that act as basic building units, their crystal structures may provide insight into the reaction products formed in NaOH-activated fly ash-based geopolymers. Recent research indicates that the hydroxycancrinite and hydroxysodalite

Jae Eun Oh; Simon M. Clark; Paulo J. M. Monteiro

2011-01-01

330

Natural zeolite reactivity towards ozone: the role of compensating cations.  

PubMed

Among indoor pollutants, ozone is recognised to pose a threat to human health. Recently, low cost natural zeolites have been applied as alternative materials for ozone abatement. In this work, the effect of compensating cation content of natural zeolite on ozone removal is studied. A Chilean natural zeolite is used here as starting material. The amount of compensating cations in the zeolite framework was modified by ion exchange using an ammonium sulphate solution (0.1 mol L(-1)). Characterisation of natural and modified zeolites were performed by X-ray powder diffraction (XRD), nitrogen adsorption at 77K, elemental analysis, X-ray fluorescence (XRF), thermogravimetric analysis coupled with mass spectroscopy (TGA-MS), and temperature-programmed desorption of ammonia (NH(3)-TPD). Ozone adsorption and/or decomposition on natural and modified zeolites were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results show that the zeolite compensating cation content affects ozone interaction with zeolite active sites. Ammonium ion-exchange treatments followed by thermal out-gassing at 823 K, reduces ozone diffusion resistance inside the zeolite framework, increasing ozone abatement on zeolite surface active sites. Weak and strong Lewis acid sites of zeolite surface are identified here as the main active sites responsible of ozone removal. PMID:22633878

Valdés, Héctor; Alejandro, Serguei; Zaror, Claudio A

2012-05-05

331

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

332

Modelling of the prebiotic synthesis of oligopeptides: silicate catalysts help to overcome the critical stage  

NASA Astrophysics Data System (ADS)

On the basis of experimental studies of the initial stages of glycine oligomerization in aqueous suspension of zeolite and kaolinite catalysts, a model is suggested for the prebiotic synthesis of oligopeptides from ?-amino acids. The formation of linear dipeptides by hydrolysis of one amide bond in the cyclic piperazinedione intermediate (formed from glycine spontaneously) is found to be the critical stage of the reaction. This stage is base catalyzed and its rate increases when pH of the medium goes up. The linear glycyl-glycine yield rises under effect of hydroxyl anions generated from different sources including insoluble silicates and soluble sodium bicarbonate. During prebiotic evolution silicates capable of cation-exchange can serve as local sources of the hydroxyl anions which dramatically accelerate formation of linear dipeptides from cyclic ones. Oligopeptides of higher molecular weight are then easily formed from the linear dipeptides at neutral pH, even in the absence of catalysts or sources of energy (e.g. such as light). The described catalytic synthesis could occur in the proximity of submarine hydrothermal vents.

Zamaraev, Kirill I.; Romannikov, Vyacheslav N.; Salganik, Rudolph I.; Wlassoff, Wjatschesslaw A.; Khramtsov, Valeriy V.

1997-08-01

333

Endo- to exo-isomerization of tetrahydrodicyclopentadiene catalyzed by commercially available zeolites  

Microsoft Academic Search

This paper presents the results of catalytic endo- to exo-isomerization of tetrahydrodicyclopentadiene. Several zeolites were tested and influences of calcinations temperatures, Si\\/Al ratio and cations of the zeolites on the reaction were investigated. The results showed that HY zeolites were more active than other zeolites and Y zeolites with other cations, because of its large pore size and relative strong

Enhui Xing; Zhentao Mi; Chengwei Xin; Li Wang; Xiangwen Zhang

2005-01-01

334

Effect of Zeolite Chemical Surface Properties on Catalytic Ozonation of Methylene Blue Contaminated Waters  

Microsoft Academic Search

Heterogeneous catalytic ozonation using natural zeolite has been recently reported. However, there is a lack in the information related to the influence of zeolite active surface sites in this combined system. This work presents experimental results on the effect of zeolite chemical surface properties on catalytic ozonation. Zeolite samples with different chemical surface compositions were prepared from natural zeolite. The

Héctor Valdés; Rolando F. Tardón; Claudio A. Zaror

2010-01-01

335

Gadolinium Borosilicate Glass-Bonded Gd-Silicate Apatite: A Glass-Ceramic Nuclear Waste Form for Actinides  

SciTech Connect

A Gd-rich crystalline phase precipitated in a sodium gadolinium alumino-borosilicate glass during synthesis. The glass has a chemical composition of 45.39-31.13 wt% Gd2O3, 28.80-34.04 wt% SiO2, 10.75-14.02 wt% Na2O, 4.30-5.89 wt% Al2O3, and 10.75-14.91 wt% B2O3. Backscattered electron images revealed that the crystals are hexagonal, elongated, acicular, prismatic, skeletal or dendritic, tens of mm in size, some reaching 200 mm in length. Electron microprobe analysis confirmed that the crystals are chemically homogeneous and have a formula of NaGd9(SiO4)6O2 with minor B substitution for Si. The X-ray diffraction pattern of this phase is similar to that of lithium gadolinium silicate apatite. Thus, this hexagonal phase is a rare earth silicate with the apatite structure. We suggest that this Gd-silicate apatite in a Gd-borosilicate glass is a potential glass-ceramic nuclear waste form for actinide disposition. Am, Cm and other actinides can easily occupy the Gd-sites. The potential advantages of this glass-ceramic waste form include: (1) both the glass and apatite can be used to immobilize actinides, (2) silicate apatite is thermodynamically more stable than the glass, (3) borosilicate glass-bonded Gd-silicate apatite is easily fabricated, and (4) the Gd is an effective neutron absorber.

Zhao, Donggao (Michigan, Univ Of - Ann Arbor); Li, Liyu (BATTELLE (PACIFIC NW LAB)); Davis, Linda L. (ASSOC WESTERN UNIVERSITY); Weber, William J. (BATTELLE (PACIFIC NW LAB)); Ewing, Rodney C. (Michigan, Univ Of - Ann Arbor); KP Hart and GR Lumpkin

2001-01-01

336

Reaction of sodium hydroxide with silicate minerals  

SciTech Connect

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 montmorillonite). Bottle tests were conducted at 24/sup 0/ and 70/sup 0/C using three different sodium hydroxide concentrations: 0.01, 0.1, and 1 equiv/dm/sup 3/. Changes in the concentrations of the following aqueous species were monitored with time: sodium, silicate, aluminate, and hydroxide. Experimental results show that all of the silicate minerals cited above dissolve in caustic solution, but the extent of dissolution varies from one mineral to another. The extent of dissolution increases with increasing pH and temperature. Caustic consumption by kaolinite was observed: 1.0 N NaOH solution was found to precipitate at 0.03 equiv/(kg kaolinite)/h when mixed with kaolinite at 70/sup 0/C. Caustic solution was injected through a Berea core, and silicate and aluminate were observed in the effluent, indicating silicate-mineral dissolution in a flowing mode. A model was developed to predict the kinetics of caustic consumption by a mixture of three minerals: quartz, kaolinite, and phillipsite. The model illustrates mineral dissolution and precipitation in a simplified system without including all of the known reservoir minerals. With knowledge of the reaction kinetics between sodium hydroxide and individual silicate minerals, one can extrapolate caustic consumption data beyond the laboratory time scale to the time scale of oilfield operations. Implications of the kinetic model to alkaline flooding are discussed. 18 refs., 3 figs., 21 tabs.

Thornton, S.D.

1986-04-01

337

H2O Inner-Surface Interactions in Micro/Nanoporous Silicates: Thermodynamic Behavior and Low Energy Molecular Vibrations  

NASA Astrophysics Data System (ADS)

Macroscopic thermodynamic and molecular-scale behavior related to silicate surface-fluid interactions in nature is complex and poorly understood. The study of confined H2O at inner surfaces in micro/ nanoporous silicates is helpful for understanding outer-surface interactions, because such phases offer simpler physicochemical systems for investigation. We are investigating the nature of H2O in various micro/nanoporous silicates. Low temperature calorimetric heat capacity (Cp) determinations have been made to determine thermodynamic behavior. Powder IR and polarized single-crystal Raman spectroscopy are used to investigate local features such as bonding and dynamics. In this report, Cp behavior and low energy external H2O modes related to van der Waals and/or hydrogen bonding at inner surfaces are emphasized. The first group of microporous silicates that includes cordierite, Mg2Al4Si5O18· xH2O, and beryl, Be2Al3Si6O18· xH2O, where x = 0 to 1, can hold single H2O molecules in small structural microcavities and exchange them with the environment with no change in volume. The Cp behavior of the confined H2O, which is characterized by weak van der Waals forces to the aluminosilicate framework, is roughly similar to that of steam at T > 100 K up to moderate T's. Cp is greater than that for ice at T < 100 K. Raman, IR and inelastic neutron scattering measurements show that the H2O molecule is quasi free in both phases. In cordierite, low energy T(H2O) modes occur at ~80 and ~48 cm-1 (Winkler and Hennion, 1994), and possibly at ~31 cm-1 . For beryl, for an external mode T(H2O) at ~ 10 cm-1 is present. The second type of microporous silicate, namely zeolites (those studied are bikitaite Li2[Al2Si4O12]·2H2O, natrolite - Na16[Al16Si24O80]·16H2O, scolecite - Ca8[Al16Si24O80]·24H2O, gmelinite - (Na2,Ca)[Al2Si4O12]·6H2O) are strongly hydrophilic and their intrachannel H2O molecules are hydrogen bonded. Zeolites show measurable changes in volume with loss or gain of H2O. The Cp behavior of H2O in natrolite is similar to that for ice at T < 100 K, but its Cp increases roughly linearly with increasing T and is greater than the Cp of ice at T > 100 K and also for H2O in cordierite at T > 250 K. At 298 K, T(H2O) modes between 45 and 180 cm-1 occur in natrolite and scolecite. Gmelinite shows similar Cp behavior at T < 100 K but anomalously high Cp behavior above 170 K. Conclusions from our investigations are: 1) At T < 200 K, Cp behavior of confined H2O is controlled by low-energy external T(H2O) modes. 2) T(H2O) mode energies reflect weak van-der-Waals to moderately strong hydrogen-bond forces at inner-surfaces. 3) The marked increase in Cp in some zeolites with increasing T indicates a change in hydrogen-bonding behavior from more "ice-like" to increasing "liquid- water-like". It is possible that this "transition" can account for the Cp behavior observed at T > 170 K in gmelinite. 4) Cp and entropy values for confined H2O in silicates cannot be considered similar, as is done in crystal-chemical-based schemes used for calculating thermodynamic properties of H2O-bearing silicates.

Geiger, C. A.; Paukov, I. E.; Kovalevskaya, Y. A.; Kolesov, B. A.

2007-12-01

338

Zeolites as supports for enzymatic hydrolysis reactions. Comparative study of several zeolites  

Microsoft Academic Search

Fusarium solani pisi recombinant cutinase was immobilised by adsorption on different zeolites and its activity towards the hydrolysis reaction of tricaprylin was measured. It was observed that the enzyme immobilised over most of the zeolites used (NaA, NaX, NaY, NaUSY and modified forms) was active for this reaction, although the specific activity depended strongly on the structure and composition of

A. P. V. Gonçalves; J. M. Lopes; F. Lemos; F. Ramôa Ribeiro; D. M. F. Prazeres; J. M. S. Cabral; M. R. Aires-Barros

1996-01-01

339

Nanocomposites of Poly(vinylidene Fluoride) with Organically Modified Silicate  

SciTech Connect

We report a study of the impact of cold crystallization on the structure of nanocomposites comprising poly(vinylidene fluoride) (PVDF) and Lucentite STN{trademark} organically modified silicate (OMS). Nanocomposites were prepared from solution over a very wide composition range, from 0.01 to 20% OMS by weight. Thermal preparation involved cold crystallization at 145 degC of quenched, compression-molded plaques. Static and real-time wide and small angle X-ray scattering (WAXS, SAXS), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) were used to investigate the crystalline phase of PVDF. For OMS content greater than 0.50 wt%, WAXS studies show that that the silicate gallery spacing increases modestly in the nanocomposites compared to neat OMS film, indicating a level of polymer intercalation. Using Gaussian peak fitting of WAXS profiles, we determine that the composition range can be divided into three parts. First, for OMS greater than 0.5 wt%, alpha phase fraction, {phi}{sub {alpha}}, is insignificant ({phi}{sub {alpha}}{approx}0-0.01). Second, at the intermediate range, for OMS between 0.5 wt% down to 0.025 wt%, beta phase dominates and the beta fraction,{phi}{sub {beta}}, is related to alpha by {phi}{sub {beta}}>{phi}{sub {alpha}}. Third, below 0.025 wt% OMS, alpha dominates and {phi}{sub {alpha}}>{phi}{sub {beta}}. The ability of small amounts of OMS ({le}0.025 wt%) to cause beta crystal domination is remarkable. Overall, crystallinity index (from the ratio of WAXS crystal peak area to total area) ranges from about 0.36 to 0.51 after cold crystallization. Real-time WAXS studies during heating of initially cold crystallized nanocomposites show that there is no inter-conversion between the alpha and beta phase PVDF crystals, where these crystals coexist at room temperature. While all samples showed a strong SAXS Bragg peak, indicating existence of two-phase lamellar stacks, the sample containing predominantly beta phase had poorly correlated lamellar stacks, compared to samples containing predominantly alpha phase.

Buckley,J.; Cebe, P.; Cherdack, D.; Crawford, J.; Ince, B.; Jenkins, M.; Pan, J.; Reveley, M.; Washington, N.; Wolchover, N.

2006-01-01

340

Structural Environments of Chloride in Silicate and Aluminosilicate Glasses: Cl-35 NMR of a Volatile Species  

NASA Astrophysics Data System (ADS)

As a volatile species, chloride behavior affects the nature and timing of magmatic degassing. Chloride is also recognized as an important complexing agent for metals in hydrothermal ore fluids and is directly related to many mineral deposits. In silicate melts, chloride solubilities have been observed to be strongly dependent on melt composition, and from these studies chlorine speciation has been inferred. However, little direct spectroscopic data is available to constrain the chemical and structural environments of chlorine in these systems. As such, the local environments of chlorine anions in several silicate and aluminosilicate glasses were probed using chlorine-35 MAS NMR. NMR spectra were obtained at 14.1 and 18.8 T fields for a series of Na- and Ca- silicate and aluminosilicate glasses with 1 wt % Cl. Peaks are roughly Gaussian in shape, much narrower than the total chemical shift range for the nuclei, and contributions to peak widths are primarily from quadrupole interactions (Wq) and to a lesser extent chemical shift distribution (Wcsd). Peak widths (FWHM), Wq, and Wcsd at 14.1 T, isotropic chemical shifts (relative to 1 M aq. NaCl), and mean quadrupole coupling constants (? =.7) for the samples probed are: Na-silicate (6210+/-80 Hz, 92+/-3 ppm, 50+/-2 ppm, -70+/-5 ppm, 3.3+/-.1 Hz), Ca-Na-silicate (11750+/-70 Hz, 186+/-4 ppm, 72+/-5 ppm, -50+/-15ppm, 3.2+/-.4 Hz), Ca-silicate (11250+/-590 Hz, 175+/-16 ppm, 78+/-6 ppm, 81+/-20 ppm, 4.4+/-.4 Hz), and Ca-aluminosilicate (12900+/-240 Hz, 217+/-6 ppm, 33+/-10 ppm, 14+/-39 ppm, 3.5+/-.9 Hz). Modeling of the mixed cation (Ca-Na) silicate glass suggests that most (>60%) Cl in the sample is in a mixed bonding environment with a significant amount (~25%) completely Na-coordinated and a minor amount (<10%) completely Ca-coordinated. There is no evidence for significant Cl-Al bonding and quantization of peak intensities suggests that there is little to no "NMR-invisible" Cl in the samples due to peak broadening caused by a large quadrupolar coupling constant. This observation is mirrored in the relative instability of Cl-Al bonds in crystalline solids.

Sandland, T. O.; Du, L.-; Stebbins, J. F.

2002-12-01

341

The effect of zeolite A supplementation in the dry period on periparturient calcium, phosphorus, and magnesium homeostasis.  

PubMed

One potential way of preventing parturient hypocalcemia in the dairy cow is to feed dry cow rations very low in calcium (<20 g/d); but, because it is difficult to formulate rations sufficiently low in calcium, this principle has been almost abandoned. Recent studies have shown, however, that it is possible to prevent milk fever, as well as subclinical hypocalcemia, by supplementing the dry cow ration with sodium aluminium silicate (zeolite A), which has the capacity to bind calcium. The aim of this study was to further evaluate the effect, if any, of such supplementation on other blood constituents, feed intake, and milk production in the subsequent lactation. A total of 31 pregnant dry cows about to enter their third or later lactation were assigned as experimental or control cows according to parity and expected date of calving. The experimental cows received 1.4 kg of zeolite pellets per d (0.7 kg of pure zeolite A) for the last 2 wk of pregnancy. Blood samples were drawn from all cows 1 wk before the expected date of calving, at calving, at d 1 and 2 after calving, and 1 wk after calving. Additionally, a urine sample was drawn 1 wk before the expected date of calving. Zeolite supplementation significantly increased the plasma calcium level on the day of calving, whereas plasma magnesium as well as inorganic phosphate was suppressed. Serum 1,25(OH)2D was significantly increased 1 wk before the expected date of calving among the experimental cows, whereas there was no difference in the urinary excretion of the bone metabolite deoxypyridinoline between the two groups. Feed intake was decreased among the zeolite-treated cows during the last 2 wk of pregnancy. No effect was observed on milk yield, milk fat, and milk protein in the subsequent lactation. The mechanisms and interactions involved in zeolite supplementation are discussed in relation to the observed improvement in parturient calcium homeostasis and to the observed depression in blood magnesium and inorganic phosphate. PMID:12201536

Thilsing-Hansen, T; Jørgensen, R J; Enemark, J M D; Larsen, T

2002-07-01

342

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

343

Zeolite 5A Catalyzed Etherification of Diphenylmethanol  

ERIC Educational Resources Information Center

|An experiment for the synthetic undergraduate laboratory is described in which zeolite 5A catalyzes the room temperature dehydration of diphenylmethanol, (C[subscript 6]H[subscript 5])[subscript 2]CHOH, producing 1,1,1',1'-tetraphenyldimethyl ether, (C[subscript 6]H[subscript 5])[subscript 2]CHOCH(C[subscript 6]H[subscript 5])[subscript 2]. The…

Cooke, Jason; Henderson, Eric J.; Lightbody, Owen C.

2009-01-01

344

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

345

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, W.M.H.; Tzou, M.S.; Jiang, H.J.

1987-03-31

346

Adsorption of pyridine on dealuminated zeolite HY  

Microsoft Academic Search

Infrared spectra showed that over 80% of aluminum atoms on the surface of zeolite HY were extracted by a exposure of SiCl4 vapor at elevated temperatures. The dealumination of the HY surface resulted in an appreciable change in its acidic properties. Infrared spectra of adsorbed pyridine indicated the formation of various kinds of Lewis acid sites on the delauminated HY

H. Paul Wang

1999-01-01

347

On the templating of curvature in zeolites  

Microsoft Academic Search

The cage and tunnel descriptions of some zeolite crystal structures have previously been shown to be succinctly described as structural networks lying on periodic minimal surfaces, which are saddle-shaped surfaces whose average curvature vanishes everywhere on the surface. The authors establish here that the vanishing average curvature of these structures is due to the templating effect of typical cations (e.g.,

Z. Blum; S. Hyde

2009-01-01

348

Polyphosphonium Salts as Templates for New Zeolites  

Microsoft Academic Search

Zelites have conventionally been prepared using quaternary ammonium salts as templates which control the pore size nnd structure of the resulting material. A range of polyammonium and -phoaphonium salts of the types shown have been prepared for evaluation in directing the formation of new zeolite structiires, particularly those with large pore sizes which may be useful a, ciitalysts for organic

R. Alan Aitken; Véronique Patinec; Paul A. Wright

1999-01-01

349

Zeolite synthesis from pre-treated coal fly ash in presence of soil as a tool for soil remediation  

Microsoft Academic Search

The study reports the synthesis of zeolites from pre-treated coal fly ash in presence of a natural agricultural soil. The synthetic process of zeolites formation in soil was studied for a period of 6 months at 30 and 60 °C. The synthesis of zeolite P (zeolite belonging to the Gismondine series) and zeolite X (zeolite belonging to the Faujasite series)

R. Terzano; M. Spagnuolo; L. Medici; F. Tateo; P. Ruggiero

2005-01-01

350

Spectroscopic and XRD characterisation of zeolite catalysts active for the oxidative methylation of benzene with methane.  

PubMed

The benzene methylation with methane over zeolite catalysts was previously shown in our laboratory to require the presence of oxygen. Thus, a two-step mechanism involving the intermediate formation of methanol by partial oxidation of methane followed by the methylation of benzene with methanol in the second step, was postulated. This paper now reports the results of the characterisation of the zeolite catalysts used for the oxidative benzene methylation reaction in order to provide some information about their composition, structure, properties and their behaviour before and after the reaction. The catalysts were characterised by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence (XRF), FT-IR and solid state NMR. XRD results indicate that the crystalline structures of all the ZSM-5 and H-beta catalysts remained unchanged after batch reaction of benzene with methane over the catalysts in agreement with the observation that the catalysts recovered from the reactor could be reused without loss of activity. Elemental analyses and FT-IR data show that as the level of metal ion exchange increases, the Brönsted acid concentration decreases but this metal ion exchange does not totally remove Brönsted acidity. FT-IR results further show that only a small amount of acid sites is actually necessary for a catalyst to be active since used catalysts containing highly reduced Brönsted acidity are found to be reusable without any loss of their activity. 29Si and 27Al magic angle spinning (MAS) NMR together with FT-IR spectra also show that all the active zeolites catalysts contain some extra-framework octahedral aluminium in addition to the normal tetrahedral framework aluminium. The presence of this extra-lattice aluminium does not, however, have any adverse effect on the crystallinity of the catalysts both before and after oxidative benzene methylation reaction. There appears also to be no significant dealumination of the zeolite catalysts during reaction since their catalytic performance was retained after use. PMID:15036089

Adebajo, Moses O; Long, Mervyn A; Frost, Ray L

2004-03-01

351

The influence of silicate melt composition on distribution of siderophile elements among metal and silicate liquids  

NASA Astrophysics Data System (ADS)

Liquid metal-liquid silicate partitioning of Fe, Ni, Co, P, Ge, W and Mo among a carbon-saturated metal and a variety of silicate melts (magnesian-tholeiitic-siliceous-aluminous-aluminosiliceous basalts) depends modestly to strongly upon silicate melt structure and composition. Low valency siderophile elements, Fe, Ni and Co, show a modest influence of silicate melt composition on partitioning. Germanium shows a moderate but consistent preference for the depolymerized magnesian melt. High valency siderophile elements, P, Mo, and W, show more than an order of magnitude decrease in metal-silicate partition coefficients as the silicate melt becomes more depolymerized. Detailed inspection of our and other published W data shows that polymerization state, temperature and pressure are more important controls on W partitioning than oxidation state. For this to be true for a high and variable valence element implies a secondary role in general for oxidation state, even though some role must be present. Equilibrium core segregation through a magma ocean of ‘ultrabasic’ composition can provide a resolution to the ‘excess’ abundances of Ge, P, W and Mo in the mantle, but the mantle composition alone cannot explain the excess abundances of nickel and cobalt in chondritic proportions.

Jana, Dipayan; Walker, David

1997-08-01

352

New Laboratory-Based Optical Functions of Cosmic Abundance Glass: Comparison to “Astronomical Silicates” and Application to Post-AGB Object HD 161796  

NASA Astrophysics Data System (ADS)

Complex refractive indices (optical functions) for amorphous silicates are used to model and interpret a wide variety of astrophysical environments including H II regions, circumstellar dust around evolved stars and in disks around young stellar objects (YSOs), and active galactic nuclei (AGN). However, the most widely-used optical functions in the literature have been derived using 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. Furthermore, these previous optical functions often include portions derived from astronomical observations rather than laboratory spectra. 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 radiation field 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.

Speck, Angela; Pitman, K. M.; Hofmeister, A. M.; Whittington, A. G.

2013-06-01

353

Low-temperature crystallization of thin silicate layer on crystalline Fe dust  

NASA Astrophysics Data System (ADS)

The crystallization of an amorphous SiO layer covering Fe crystal grains has been clarified by high-resolution transmission electron microscopic (HRTEM) observation. Cristobalite crystals were produced preferentially on the (110) surface of Fe particles by the oxidation of silicon crystallites in the SiO layer, i.e. the oxidation energy of the silicon crystallites resulted in the epitaxial growth of the oxide layer on the Fe surface. The chemical reaction energy due to the oxidation of silicon crystallites in the SiO layer was concentrated at the interface of the crystal and the amorphous layer. Crystal growth took place from the Fe grain surface.

Kaito, C.; Kumamoto, A.; Saito, Y.; Ono, R.

2010-01-01

354

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

Microsoft Academic Search

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

Hideo Usui; Yuichi Niibori; Hitoshi Mimura; Osamu Tochiyama

2007-01-01

355

29Si and 17O NMR investigation of the structure of some crystalline calcium silicate hydrates  

Microsoft Academic Search

This paper presents the results of a systematic investigation of the structure of 17O-enriched, hydrothermally synthesized 1.1-nm tobermorite, 1.4-nm tobermorite, jennite, calciochondrodite, xonotlite, and hillebrandite, using 29Si magic angle spinning (MAS) NMR, 1H-29Si cross-polarization magic angle spinning (CPMAS) NMR, and 17O MAS NMR. The 17O and most of the 1H-29Si CPMAS results are the first reported for these phases. Six

Xiandong Cong; R. James Kirkpatrick

1996-01-01

356

Deactivation Behavior of Bifunctional Pt\\/H-Zeolite Catalysts during Cyclopentane Hydroconversion  

Microsoft Academic Search

Cyclopentane hydroconversion was used as a probe reaction to study the coking behavior of selected large-pore zeolites loaded with 0.5% Pt under identical conditions. The zeolites studied, namely, Y zeolite, zeolite beta, mordenite, LTL, and ZSM-12, were also tested at several different Si\\/Al ratios. The zeolite pore structure was the most important factor determining the deactivation behavior. Zeolites like Y

Srikant Gopal; Panagiotis G. Smirniotis

2002-01-01

357

Core formation in silicate bodies  

NASA Astrophysics Data System (ADS)

Differentiation of a body into a metallic core and silicate mantle occurs most efficiently if temperatures are high enough to allow at least the metal to melt [1], and is enhanced if matrix deformation occurs [2]. Elevated temperatures may occur due to either decay of short-lived radio-isotopes, or gravitational energy release during accretion [3]. For bodies smaller than the Moon, core formation happens primarily due to radioactive decay. The Hf-W isotopic system may be used to date core formation; cores in some iron meteorites and the eucrite parent body (probably Vesta) formed within 1 My and 1-4~My of solar system formation, respectively [4]. These formation times are early enough to ensure widespread melting and differentiation by 26Al decay. Incorporation of Fe60 into the core, together with rapid early mantle solidification and cooling, may have driven early dynamo activity on some bodies [5]. Iron meteorites are typically depleted in sulphur relative to chondrites, for unknown reasons [6]. This depletion contrasts with the apparently higher sulphur contents of cores in larger planetary bodies, such as Mars [7], and also has a significant effect on the timing of core solidification. For bodies of Moon-size and larger, gravitational energy released during accretion is probably the primary cause of core formation [3]. The final stages of accretion involve large, stochastic collisions [8] between objects which are already differentiated. During each collision, the metallic cores of the colliding objects merge on timescales of a few hours [9]. Each collision will reset the Hf-W isotopic signature of both mantle and core, depending on the degree to which the impactor core re-equilibrates with the mantle of the target [10]. The re-equilibration efficiency depends mainly on the degree to which the impactor emulsifies [11], which is very uncertain. Results from N-body simulations [8,12] suggest that significant degrees of re- equilibration are required [4,10]. Re-equilibration is also suggested by mantle siderophile abundances [13], though simple partitioning models do not capture the likely complex P,T evolution during successive giant impacts. The timescale of Martian core formation is currently uncertain (0-10 My) [14], though it is clear that Martian core formation ended before that of the Earth. [1] Stevenson, in Origin of the Earth, 1990. [2] Groebner and Kohlstedt, EPSL 2006. [3] Rubie et al., Treatise Geophys. 2007. [4] Kleine et al., GCA submitted. [5] Weiss et al., LPSC 39, 2008. [6] Keil and Wilson, EPSL 1993 [7] Wanke and Dreibus, PTRSL, 1984. [8] Agnor et al. Icarus 1999 [9] Canup and Asphaug, Nature 2001 [10] Nimmo and Agnor, EPSL 2006. [11] Rubie et al., EPSL 2003 [12] O'Brien et al, Icarus 2006 [13] Righter, AREPS 2003. [14] Nimmo and Kleine, Icarus 2007.

Nimmo, F.; O'Brien, D. P.; Kleine, T.

2008-12-01

358

Solubility of Zinc Silicate and Zinc Ferrite in Aqueous Solution to High Temperatures  

SciTech Connect

Crystalline zinc silicate, Zn{sub 2}SiO{sub 4}, and zinc ferrite, ZnFe{sub 2}O{sub 4}, were prepared and characterized. The solubilities of these phases were measured using flow-through apparatus from 50 to 350 C in 100 C intervals over a wide range of pH. Both solid phases dissolve incongruently, presumably to form ZnO(s) and Fe{sub 2}O{sub 3}(s) (or the corresponding hydroxide phases at low temperature), respectively. The respective concentrations of zinc(II) and iron(III) matched those of ZnO(cr) and Fe{sub 2}O{sub 3}(s) ({ge}150 C) reported in the literature, whereas the corresponding Si(IV) and Zn(II) concentrations were at least an order of magnitude below the solubility limits for their pure oxide phases. Therefore, the solubility constants for zinc silicate and ferrite were determined with respect to the known solubility constants for ZnO(cr) and Fe{sub 2}O{sub 3}(s) ({ge}150 C), respectively, and the corresponding concentrations of Si(IV) and Zn(II) measured in this study. The results of independent experiments, as well as those reported in the literature provide insights into the mechanism(s) of formation of zinc silicate and ferrite in the primary circuits of nuclear reactors.

Palmer, Donald [ORNL; Anovitz, Lawrence {Larry} M [ORNL

2009-07-01

359

Density of mechanisms within the flexibility window of zeolites.  

PubMed

By treating idealized zeolite frameworks as periodic mechanical trusses, we show that the number of flexible folding mechanisms in zeolite frameworks is strongly peaked at the minimum density end of their flexibility window. 25 of the 197 known zeolite frameworks exhibit an extensive flexibility, where the number of unique mechanisms increases linearly with the volume when long wavelength mechanisms are included. Extensively flexible frameworks therefore have a maximum in configurational entropy, as large crystals, at their lowest density. Most real zeolites do not exhibit extensive flexibility, suggesting that surface and edge mechanisms are important, likely during the nucleation and growth stage. The prevalence of flexibility in real zeolites suggests that, in addition to low framework energy, it is an important criterion when searching large databases of hypothetical zeolites for potentially useful realizable structures. PMID:22107389

Kapko, V; Dawson, C; Rivin, I; Treacy, M M J

2011-10-12

360

Zeolite and swine inoculum effect on poultry manure biomethanation  

NASA Astrophysics Data System (ADS)

Poultry manure is an ammonia-rich substrate that inhibits methanogenesis, causing severe problems to the anaerobic digestion process. In this study, the effect of different natural zeolite concentrations on the mesophilic anaerobic digestion of poultry waste inoculated with well-digested swine manure was investigated. A significant increase in methane production was observed in treatments where zeolite was added, compared to the treatment without zeolite.Methane production in the treatment with 10 g dm-3 of natural zeolite was found to be 109.75% higher compared to the treatment without zeolite addition. The results appear to be influenced by the addition of zeolite, which reduces ammonia toxicity in anaerobic digestion and by the ammonia-tolerant swine inoculum.

Kougias, P. G.; Fotidis, I. A.; Zaganas, I. D.; Kotsopoulos, T. A.; Martzopoulos, G. G.

2013-03-01

361

Structural and hydration properties of amorphous tricalcium silicate  

SciTech Connect

Mechanical milling was carried out to synthesize amorphous tricalcium silicate (Ca{sub 3}SiO{sub 5}) sample, where Ca{sub 3}SiO{sub 5} is the most principal component of Portland cement. The partial phase transformation from the crystalline to the amorphous state was observed by X-ray and neutron diffractions. Moreover, it was found that the structural distortion on the Ca-O correlation exists in the milled Ca{sub 3}SiO{sub 5}. The hydration of the milled Ca{sub 3}SiO{sub 5} with D{sub 2}O proceeds as follows: the formation of hydration products such as Ca(OD){sub 2} rapidly occurs in the early hydration stage, and then proceeds slowly after about 15 h. The induction time for the hydration of the milled Ca{sub 3}SiO{sub 5} is approximately one half shorter than that for the hydration of the unmilled one. This result means that the mechanical milling brings about the chemical activity of Ca{sub 3}SiO{sub 5} for hydration, and may be particularly useful for increasing the reactivity in the early hydration stage.

Mori, K. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan)]. E-mail: kmori@rri.kyoto-u.ac.jp; Fukunaga, T. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Shiraishi, Y. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Iwase, K. [Department of Materials Structure Science, Graduate University for Advanced Studies, Tsukuba, Ibaraki 305-0801 (Japan); Xu, Q. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Oishi, K. [Institute of Technology, Shimizu Corporation, 3-4-17, Etchujima, Koto-ku, Tokyo 135-8530 (Japan); Yatsuyanagi, K. [Institute of Technology, Shimizu Corporation, 3-4-17, Etchujima, Koto-ku, Tokyo 135-8530 (Japan); Yonemura, M. [Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801 (Japan); Itoh, K. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Sugiyama, M. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Ishigaki, T. [Department of Materials Science and Engineering, Muroran Institute for Technology, Muroran 050-8585 (Japan); Kamiyama, T. [Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801 (Japan); Kawai, M. [Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801 (Japan)

2006-11-15

362

Structural and diffusion characterizations of steam-stable mesostructured zeolitic UL-ZSM-5 materials.  

PubMed

A series of mesoporous UL-ZSM-5 materials (Si/Al = 50) with different micro- and mesoporosity as well as crystallinity was prepared following the procedure proposed in one of our recent studies (Trong-On, D.; Kaliaguine, S. Angew. Chem. Int. Ed. 2001, 40, 3248-3251. Trong-On, D.; Kaliaguine, S. U.S. Patent 6,669,924, B1, 2003). These materials have zeolitic structure in the form of nanoparticles intergrown in the walls of the amorphous wormhole-like aluminosilicate mesopores of Al-Meso-50, which was used as a precursor in the synthesis. The structure, crystallinity, and textural properties of the synthesized materials, as well as a reference ZSM-5 zeolite sample, were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM)/scanning electron microscoy (SEM) analyses, Fourier transform infrared spectroscopy (FTIR), 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), and nitrogen adsorption/desorption techniques. The acid properties were examined by FTIR of adsorbed pyridine. UL-ZSM-5 materials were shown to be highly hydrothermally stable. The diffusion of two C7 hydrocarbons, i.e., n-heptane and toluene, in four UL-ZSM-5 materials with different microporosities, related acidities, and crystallinities were investigated using the zero-length column (ZLC) method. Furthermore, the wormhole-like mesostructured aluminosilicate precursor (Al-Meso-50) and a reference MFI zeolite sample were also investigated using the same technique. A theoretical model considering a combination of mesopore diffusion (with surface slip in the main channels) with an activated, mainly surface diffusion mechanism in the intrawall biporous structure, was proposed and employed to interpret the experimental ZLC results. A classical Knudsen type of diffusion was replaced by an activated surface slip type of diffusion mechanism in the mesopores. The transport of n-heptane in UL-ZSM-5 materials was found to be mainly controlled by mesopore diffusion in the main-channel structure, while that of toluene was dominated by the intrawall diffusion process. Diffusion activation energies of n-heptane are about 2 times higher in comparison to toluene, which has a larger kinetic diameter. The main mesopore channel structure seems to appreciably contribute to the overall mass transport. Furthermore, the effect of hydrothermal treatment (20% steam at 800 degrees C for 24 h) on the diffusion of these two sorbates on UL-ZSM-5 materials was also evaluated. PMID:16649795

Vinh-Thang, Hoang; Huang, Qinglin; Ungureanu, Adrian; Ei?, Mladen; Trong-On, Do; Kaliaguine, Serge

2006-05-01

363

Chemical Interactions in Multimetal/Zeolite Catalysts  

SciTech Connect

This two-year project has led to a significant improvement in the fundamental understanding of the catalytic action of zeolite-supported redox catalysts. It turned out to be essential that we could combine four strategies for the preparation of catalysts containing transition metal (TM) ions in zeolite cavities: (1) ion exchange from aqueous solution; (2) chemical vapor deposition (CVD) of a volatile halide onto a zeolite in its acidic form; (3) solid state ion exchange; and (4) hydrothermal synthesis of a zeolite having TM ions in its lattice, followed by a treatment transporting these ions to ''guest positions''. Technique (2) enables us to position more TM ions into cavities than permitted by the conventional technique (1).viz one positive charge per Al centered tetrahedron in the zeolite lattice. The additional charge is compensated by ligands to the TM ions, for instance in oxo-ions such as (GaO){sup +} or dinuclear [Cu-O-Cu]{sup 2+}. While technique (3) is preferred over CVD where volatile halides are not available, technique (4) leads to rather isolated ''ex lattice'' oxo-ions. Such oxo-ions tend to be mono-nuclear, in contrast to technique (2) which preferentially creates dinuclear oxo-ions of the same TM element. A favorable element for the present research was that the PI is also actively engaged in a project on the reduction of nitrogen oxides, sponsored by EMSI program of the National Science Foundation and the US Department of Energy, Office of Science. This combination created a unique opportunity to test and analyze catalysts for the one step oxidation of benzene to phenol and compare them with catalysts for the reduction of nitrogen oxides, using hydrocarbons as the reductant. In both projects catalysts have been used which contain Fe ions or oxo-ions in the cavities the zeolite MFI, often called ZSM-5. With Fe as the TM-element and MFI as the host zeolite we found that catalysts with high Fe content, prepared by technique (2) were optimal for the De-NO{sub x} reaction, but extremely unselective for benzene oxidation to phenol. Conversely, the catalysts prepared with (4) had the highest turnover frequency for benzene oxidation, but performed very poorly for NO{sub x} reduction with so-butane. In fact the Fe concentration in the former catalysts were so low that it was necessary to design a special experimental program for the sole purpose of showing that it is really the Fe which catalyzes the benzene oxidation, not some acid center as has been proposed by other authors. For this purpose we used hydrogen sulfide to selectively poison the Fe sites, without deactivating the acidic sites. In addition we could show that the hydrothermal treatment of catalysts prepared by technique (4) is essential to transform iron ions in the zeolite lattice to ''ex lattice ions'' in guest positions. That line of the work required very careful experimentation, because a hydrothermal treatment of a zeolite containing Fe ions in its cavities can also lead to agglomeration of such ions to nano-particles of iron oxide which lowers the selectivity for the desired formation of phenol. This part of the program showed convincingly that indeed Fe is responsible for the benzene oxidation catalysis. The results and conclusion of this work, including the comparison of different catalysts, was published in a number of papers in the scientific literature, listed in the attached list. In these papers also our analysis of the reaction orders and the possible mechanism of the used test reaction are given.

Sachtler, Wolfgang M. H.

2004-04-16

364

Silicic acid: boric acid complexes as wood preservatives  

Microsoft Academic Search

Wood was treated with a low molecular-weight silicic acid: boric acid agent and examined for increased resistance to termites and combustion. Wood treated with silicic acid only exhibited increased termite resistance, but not to the marked extent observed after treatment with a mixture of silicic and boric acids. Increasing the quantity of boric acid also increased the termite mortality rate

Haruhiko Yamaguchi

2003-01-01

365

Soluble-silicate mud additives inhibit unstable clays  

Microsoft Academic Search

Although drilling fluids with soluble-silicate additives are not used as often as in the past, experiments in China indicate these additives can help stabilize problem clays in some well bores, and therefore warrant further attention. The earlier silicate muds contained more than 30% sodium silicate. Their rheological properties were hard to control, and their high alkalinity was a hazard. In

Ding Rui; Qiu Zhengsong; Li Jianying

1996-01-01

366

A preliminary investigation of chlorine XANES in silicate glasses  

Microsoft Academic Search

Chlorine speciation in silicate melts affects volatile exsolution, rheology, and thermodynamic properties of the melt but is poorly known. X-Ray Absorption Near Edge Structure (XANES) spectra have been used to investigate Cl speciation in 26 silicate glasses and to test the hypothesis that Cl in silicate melts is hosted by species that combine Cl and network-modifying cations such as Ca

K. A. Evans; J. A. Mavrogenes; H. S. O'Neill; N. S. Keller; L.-Y. Jang

2008-01-01

367

40 CFR 721.10495 - Metal silicate (generic).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Metal silicate (generic). 721.10495 ...Specific Chemical Substances § 721.10495 Metal silicate (generic). (a) Chemical...chemical substance identified generically as metal silicate (PMN P-05-634) is...

2013-07-01

368

Behavior and sitting of sodium ion in ZSM-5 zeolite  

Microsoft Academic Search

The behavior of sodium ion in ZSM-5 zeolite was studied by MAS-NMR, ion-exchange, thermal analyses and energy dispersive X-ray analysis (EDX). The samples used were free from surface defects and hence the Na ion in the zeolite was not present in a form of Si-O-Na. In the ion-exchange of the Na ion in the ZSM-5 zeolite with tetramethylammonium (TMA) or

Tatsuo Ohgushi; Toshiyuki Niwa; Hiromi Araki; Satomi Ichino

1997-01-01

369

Separation of water\\/UDMH mixtures using hydroxysodalite zeolite membranes  

Microsoft Academic Search

Dehydration of water\\/1-1-dimethylhydrazine (UDMH) mixtures using hydroxysodalite (HS) zeolite membranes is presented and its performance during separation of water\\/UDMH mixtures was evaluated. HS zeolite was coated on an external surface of porous supports by hydrothermal synthesis. The tubular supports were made of mullite. Water\\/UDMH mixtures were separated at ambient temperature and atmospheric pressure by pervaporation using the HS zeolite membranes.

Mansoor Kazemimoghadam; Toraj Mohammadi

2005-01-01

370

Preparation and characterization of antibacterial zeolite-polyurethane composites  

Microsoft Academic Search

In this study, antibacterial properties were induced in polyurethane (PU) films by the incorporation of Agþ-loaded zeolites as fillers. The mechanical and ther- mal properties of the prepared composites were also investigated. For this purpose, two different types of zeo- lite microparticles, high-silica zeolite beta crystals and low-silica zeolite A crystals, were synthesized. Agþ was added by ion exchange, and

K. Kamõsog; E. A. Aksoy; B. Akata; N. Hasirci; N. Bac

2008-01-01

371

Effects of zeolites on cultures of marine micro-algae  

Microsoft Academic Search

Goal, Scope and Background  The cation-exchange capacity of zeolites is well known and has been increasingly explored in different fields with both economic\\u000a and environmental successes. In aquatic medium with low salinity, zeolites have found multiple applications. However, a review\\u000a of the literature on the applications of zeolites in salt waters found relatively few articles, including some recently published\\u000a papers. The

Adriano Fachini; Maria Teresa S. D. Vasconcelos

2006-01-01

372

Retention of molecular oxygen in zeolites at high temperature  

Microsoft Academic Search

X-ray photoelectron spectroscopy and residual gas analysis experiments were carried out on NaY zeolite at temperatures between -196 and 400°C. The objective of this work was to further understand the 0 1s transition for zeolites since contributions can arise from zeolitic oxygen as well as trapped water. The residual gas analysis data show that molecular oxygen is retained by NaY

S. L. Suib; B. E. Morse

2009-01-01

373

Tetrahedrally coordinated cupric ion in A-zeolites  

Microsoft Academic Search

Electron spin resonance and electron spin echo studies on Cu2+ in four A-zeolites exchanged with K+, Cs+ and NH4+ indicate the formation of a new tetrahedral species, Cu(Oz)3(H2O)2+ where Oz is a zeolite oxygen and the water molecule is probably in the beta cage. The preferential formation of this tetrahedral species in these zeolites instead of the usually observed Cu(H2O)62+

M. Narayana; L. Kevan

1983-01-01

374

Reactivity of trimethyltin manganese pentacarbonyl in zeolite cavities  

Microsoft Academic Search

The anchoring chemistry, thermal stability, and reactivity of MeâSnMn(CO)â in zeolite NaY and acid forms of zeolite Y was studied with X-ray absorption spectroscopy (Sn, Mn edge EXAFS) and in situ FTIR\\/TPD-MS techniques. In the NaY host, the precursor is physically adsorbed from hexane solution into the dehydrated zeolite cages at room temperature without further chemical reaction. Symmetry changes of

A. Borvornwattananont; Thomas Bein

1992-01-01

375

Influence of zeolite additive on properties of autoclaved aerated concrete  

Microsoft Academic Search

In this experimental study, the effect of zeolite on the properties of autoclaved aerated concrete (AAC) was investigated. Zeolite was used as a quartzite replacement in conventional AAC mixtures. The zeolite containing AAC (ZAAC) specimens were prepared at bulk densities of 270–500kg\\/m3. The specimens were examined by X-ray diffraction, X-ray fluorescence, and thermal analysis. Bulk density, compressive strength and thermal

Mustafa Albayrak; Abdulkerim Yörüko?lu; Serdar Karahan; Sema Atl?han; H. Y?lmaz Arunta?; ?smail Girgin

2007-01-01

376

Modeling diffusive dissolution in silicate melts  

Microsoft Academic Search

Here empirical models for calculating self-diffusion coefficients and diffusion matrices are combined with MELTS, a thermodynamic model for silicate minerals and melts, to estimate diffusive dissolution rates, interface melt compositions and melt diffusivities. Simulations of olivine dissolution experiments in basalt show that the overall model is capable of accurately reproducing diffusive dissolution rates, and the resulting diffusion profiles, over a

Conel M. O’D. Alexander

2011-01-01

377

Variable Transmission Silicate Glasses Sensitive to Sunlight.  

PubMed

The process of variable transmission in silicate glasses has been accomplished by optically pumping color centers by electron transfer from europium (II) or cerium (III) which absorb sunlight at higher energies than the color center. Absorbed energy quickly pumps the visible color center band to a maximum. Upon removal of activating light, the visible color spontaneously decays. PMID:17782734

Cohen, A J; Smith, H L

1962-09-21

378

Silicates and Silicones. Compounds for the Future.  

National Technical Information Service (NTIS)

'Silicates and Silicones - Compounds for the Future' is the title of a report containg six lectures given at a symposium arranged in Stockholm on May 21, 1984, by the Royal Swedish Academy of Engineering Sciences, IVA. Silicon organic compounds with three...

1985-01-01

379

Rheology of polymer layered silicate nanocomposites  

Microsoft Academic Search

Layered silicate based polymer nanocomposites have gained significant technological interest because of the recent commercialization of nylon 6 and polypropylene based materials. Aside from the natural interests in understanding and improving the processing of these hybrids, viscoelastic measurements have also proven to be a sensitive tool to probe the mesoscale structure and the strength of polymer–nanoparticle interactions.

Ramanan Krishnamoorti; Koray Yurekli

2001-01-01

380

Dental Silicate Cements: III. Environment and Durability  

Microsoft Academic Search

The nature of the aqueous environment has considerable effect on the durability of dental silicate cements. When free from soluble reaction products, cements show little dissolution in the pH range associated with normal saliva, but are drastically attacked by acids and citrates. These observations suggest that phosphates are important constituents of the gel matrix.

Alan D. Wilson; Reginald F. Batchelor

1968-01-01

381

Cordierite- and beryl-types silicates (Text)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I3 'Cyclosilicates' 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 on cordierite- and beryl-types silicates (Text).

Burzo, E.

382

Cordierite- and beryl-types silicates (Figures)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I3 'Cyclosilicates' 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 on cordierite- and beryl-types silicates (Figures).

Burzo, E.

383

Cordierite- and beryl-types silicates (Tables)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume I3 'Cyclosilicates' 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 on cordierite- and beryl-types silicates (Tables).

Burzo, E.

384

Natural Weathering Rates of Silicate Minerals  

Microsoft Academic Search

Silicates constitute more than 90% of the rocks exposed at Earth's land surface (Garrels and Mackenzie, 1971). Most primary minerals comprising these rocks are thermodynamically unstable at surface pressure\\/temperature conditions and are therefore susceptible to chemical weathering. Such weathering has long been of interest in the natural sciences. Hartt (1853) correctly attributed chemical weathering to \\

A. F. White

2003-01-01

385

Thermoset polymer-layered silicic acid nanocomposites  

NASA Astrophysics Data System (ADS)

Nanocomposites are formed when phase mixing occurs on a nanometer length scale. Due to the improved phase morphology and interfacial properties, nanocomposites exhibit mechanical properties superior to conventional composites. Toyota researchers first demonstrated that organoclay could be exfoliated in a nylon-6 matrix to greatly improve the thermal and mechanical properties of the polymer, which has resulted in a practical application in the automobile industry. A great deal of research has been conducted on organic-inorganic hybrid composites in which smectite clays are used as reinforcement agents. However, little work has been devoted to derivatives of other layered inorganic solids. In the present work, the first examples of organic polymer-layered silicic acid nanocomposites have been prepared by formation of a cured epoxy polymer network in the presence of organo cation exchange forms of magadiite. The exfoliation of silicate nanolayers in the epoxy matrix was achieved by in-situ intragallery polymerization during the thermosetting process. In general, the tensile properties, solvent resistance, barrier properties and chemical stability of the polymer matrix are greatly improved by the embedded silicate nanolayers when the matrix is flexible (sub-ambient Tg). The improvement of properties are dependent on the silicate loading, the degree of nanolayer separation and interfacial properties. Interestingly, the exfoliation also affects the polymer elasticity in a favorable way. The mechanism leading to nanocomposite formation is proposed. One exfoliated epoxy-magadiite nanocomposite/composition possessed unique transparent optical properties. The exfoliation chemistry was successfully extended to the other members of the layered silicic acid family. A new approach also was developed to prepare thermoset epoxy polymer-layered silicate nanocomposites in which curing agents can be directly intercalated into the intragallery without the need for alkylammonium ions on the exchange sites. This new development has resulted in a greater improvement in the overall properties of thermoset polymer-clay nanocomposites. The exfoliation chemistry was extended further to other thermoset silicone polymer systems. The new polysiloxane-layered silicic acid nanocomposites were prepared with promising mechanical properties. Some fundamental chemistry and physics issues regarding nanocomposite formation were elucidated by this research work, particularly with regard to the relationship of microstructure and interfacial factors to the mechanical properties of the nanocomposites.

Wang, Zhen

386

``Central Atoms'' models for ternary silicate and alumino-silicate melts  

NASA Astrophysics Data System (ADS)

The “Central Atoms” model presented by the authors in an earlier paper is extended to ternary silicate and alumino-silicate melts. The model is applied to the CaO-FeO-SiO2 and the CaO-Al2O3-SiO2 system. Use is made of the parameters from the relevant binaries only. The agreement between experimental and calculated isoactivity curves is good in all cases.

Sastri, P.; Lahiri, A. K.

1986-01-01

387

Preparation, characterization and catalytic properties of Pd-Fe-zeolite and Pd-Ce-zeolite composite catalysts.  

PubMed

Highly effective composite catalysts for removal of CO by catalytic oxidation have been designed through constructing active centers on the support of zeolite. Performances of the derived Pd-Fe-zeolite and Pd-Ce-zeolite composite catalysts for CO removal under different heterogeneous conditions were studied. The results indicate that the two kinds of promoted catalysts, including special chemical states of Pd and surface active oxygen, show high catalytic activities not only for the low temperature oxidation of CO, but also for CO electro-oxidation. The typical light-off temperatures of Pd-Fe-zeolite and Pd-Ce-zeolite for low temperature CO oxidation are 270 and 273 K. Their characteristic peak potentials for CO electro-oxidation are both around 0.70 V. The promotional effects are associated with the special interaction among Pd, modifier and zeolite, which can be firmly supported by the detailed characterizations using XRD, BET, XPS, TPD and TPR. PMID:22727393

Bi, Yu-Shui; Dang, Guang-Yao; Zhao, Xiao-Hong; Meng, Xian-Feng; Lu, Hui-Jie; Jin, Jian-Tao

2012-06-06

388

Ion exchange properties of Japanese natural zeolites in seawater.  

PubMed

Ion exchange properties of five different Japanese natural zeolites in seawater were examined. Sodium ions could be reduced by all zeolites, although anions, Cl(-) and SO(4)(2-), in seawater showed barely changes. Natural zeolite desalination treatment mainly depends on the ion exchange between Na(+), K(+) and Mg(2+) in seawater and Ca(2+) in natural zeolite. This study found that mordenite is superior to clinoptilolite for use in Na(+) reduction. Mordenite with high cation exchange capacity containing Ca(2+) resulted in the highest Na(+) reduction from seawater. PMID:23303099

Wajima, Takaaki

2013-01-01

389

Regeneration of zeolite catalysts of isobutane alkylation with butenes  

SciTech Connect

The industrial adoption of alkylation of isoalkanes with alkenes is held back by the rapid and irreversible deactivation of the zeolite catalysts appropriate to the process. This paper is aimed specifically at the restoration of the catalytic activity and increase in the service life of zeolite alkylation catalysts. The catalyst chosen for the investigation was HLaCaNaX zeolite both unmodified and modified with various multivalence cations. The thermochemical and oxidative regeneration process as well as the equipment utilized are described. Both the advantages and the drawbacks of the method are given; explanations for the possibly irreversible losses of the catalytic properties in the regenerated zeolites are also put forward.

Manza, I.A.; Tsupryk, I.N.; Bartyshevskii, V.A.; Gaponenko, O.I.; Petrilyak, K.I.

1986-12-10

390

Influencing the selectivity of zeolite Y for triglycine adsorption.  

PubMed

In prior work we studied the adsorption of triglycine on zeolite Y under reference conditions. This study aims to solve the question of which adsorbent properties and process conditions influence the adsorption triglycine from an aqueous solution by zeolite Y. Relevant zeolite parameters to study are: the amount of acidic sites (Si/Al(2) ratio), counter ion, micropore structure. Process conditions that may influence triglycine adsorption are pH, other components such as sugars, amino acids and salts, and temperature. Adsorption of triglycine on zeolite HY is dominated by ionic interaction. The capacity and selectivity of zeolite HY for triglycine can be changed by choosing different Si/Al(2) ratios or changing the counter ion. The presence of cations and basic anions in solutions reduces triglycine adsorption. Fructose and glycine have no significant influence on triglycine adsorption. Temperature only has a slight influence. The pore structure of zeolite Y is not a critical factor for triglycine adsorption, provided pores are accessible to triglycine and in the micropore range (<2 nm). While this allows other zeolites than zeolite Y to be applied, the presence of the supercage structure of zeolite Y is beneficial to obtain better adsorption of triglycine in its neutral form. PMID:17092513

Wijntje, R; Bosch, H; de Haan, A B; Bussmann, P J T

2006-11-07

391

Dry method for recycling iodine-loaded silver zeolite  

DOEpatents

Fission product iodine is removed from a waste gas stream and stored by passing the gas stream through a bed of silver-exchanged zeolite until the zeolite is loaded with iodine, passing dry hydrogen gas through the bed to remove the iodine and regenerate the bed, and passing the hydrogen stream containing the hydrogen iodide thus formed through a lead-exchanged zeolite which adsorbs the radioactive iodine from the gas stream and permanently storing the lead-exchanged zeolite loaded with radioactive iodine.

Thomas, Thomas R. (Idaho Falls, ID); Staples, Bruce A. (Idaho Falls, ID); Murphy, Llewellyn P. (Idaho Falls, ID)

1978-05-09

392

Dispersion of Silicate in Tricalcium Phosphate Elucidated by Solid-State NMR  

SciTech Connect

The dispersion of silicate in tricalcium phosphate, a resorbable bioceramics for bone replacement, has been investigated by various solid-state nuclear magnetic resonance (NMR) methods. In samples prepared with 5 and 10 mol% of both {sup 29}SiO{sub 2} and ZnO, three types of silicate have been detected: (i) SiO{sub 4}{sup 4-} (Q{sub 0} sites) with long longitudinal (T{sub 1,Si}) relaxation times ({approx} 10,000 s), which substitute for {approx}1% of PO{sub 4}{sup 3-}; (ii) silicate nanoinclusions containing Q{sub 2}, Q{sub 1}, and Q{sub 0} sites with T{sub 1,Si} 100 s, which account for most of the silicon; and (iii) crystalline Q{sub 4} (SiO{sub 2}) with long T{sub 1,Si}. Sensitivity was enhanced >100-fold by {sup 29}Si enrichment and refocused detection. The inclusions in both samples have a diameter of {approx}8 nm, as proved by {sup 29}Si{l_brace}{sup 31}P{r_brace} REDOR dephasing on a 30-ms time scale, which was simulated using a multispin approach specifically suited for nanoparticles. {sup 29}Si CODEX NMR with 30-s {sup 29}Si spin diffusion confirms that an inclusion contains >10 Si (consistent with the REDOR result of >100 Si per inclusion). Overlapping signals of silicate Q{sub 2}, Q{sub 1}, and Q{sub 0} sites were spectrally edited based on their J-couplings, using double-quantum filtering. The large inhomogeneous broadening of the Q{sub 2}, Q{sub 1}, and Q{sub 0} {sup 29}Si subspectra indicates that the nanoinclusions are amorphous.

Rewal, A.; Wei, X.; Akinc, M.; Schmidt-Rohr, K.

2008-03-12

393

Electrical Response of PEDOT-PSS/FAU Zeolite Composites toward SO2: Controlling the Adsorption Properties of FAU Zeolite  

NASA Astrophysics Data System (ADS)

In our work, we propose to combine a conductive polymer, Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT-PSS), with FAU zeolites to investigate the potential of the composites for use as SO2 sensing materials.Composites with PEDOT-PSS as a matrix containing faujasite zeolites of various cation types (divalent transition metal ions: Fe^2+, Co^2+, Ni^2+ and Cu^2+), were fabricated to investigate the effect of the cation type of the faujasite zeolites on the electrical conductivity response when exposed to SO2. The composite was tested through repeated sensing and recovery processes to investigate the reversibility and reproducibility. During the recovery process, the electrical conductivity of the composites were recovered, which proves that the sensing characteristics are repeatable. Responses and the interaction mechanism of the conductive polymer/zeolite composites were investigated. The composite with 20% (v/v) of zeolite content gives the highest sensitivity. The electrical conductivity responses of PEDOT-PSS/Zeolite composites can be altered due to the available adsorption sites for gas molecules. The addition of zeolites to the pristine PEDOT-PSS improved the electrical conductivity sensitivity of the composites by enhancing the interaction between PEDOT-PSS and SO2. The type of cation in the zeolite pores effected the sensitivity of the composites, depending on the acidity of the ion-exchanged zeolites.

Chanthaanont, Pojjawan; Sirivat, Anuvat

2012-02-01

394

Mg-Rich Silicate Crystals in Comet Hale-Bopp: ISM Relics or Solar Nebula Condensates?  

NASA Astrophysics Data System (ADS)

We compare the HIFOGS 10-?m spectra of Comet C/1995 (O1) (Hale-Bopp) to the mid-IR spectra of interplanetary dust particles (IDPs). The four epochs of Hale-Bopp silicate features, at 2.8 AU (pre-perihelion), 1.2 AU (pre-perihelion), 0.93 AU (10 days after perihelion), and 1.7 AU (post-perihelion) have different spectral shapes. At smaller heliocentric distances, rh?1.7 AU, there appears to be enhanced mid-IR emission (i.e., 9.3- and 10.5-?m peaks) from Mg-rich pyroxene crystals. A two-temperature model of warm amorphous and crystalline olivines, warm amorphous pyroxenes, and ˜165 K cooler pyroxene crystals is successful with laboratory silicate minerals (D. H. Wooden et al. 1999, Astrophys. J.517, 1034-1058). A two-temperature model using IDPs as cometary dust particle analogs also fits Comet Hale-Bopp's silicate features, with the pyroxene IDP ˜50 K cooler than the olivine and layer-lattice silicate IDPs. The warm layer-lattice silicate IDP contributes a broad 20-?m feature which is not in the Infrared Space Observatory Short Wavelength Spectrometer (ISO SWS) spectrum of Hale-Bopp at 2.8 AU, making it a questionable cometary component. On the other hand, members of the ``cluster IDP" subclass of pyroxene IDPs fit Hale-Bopp's 10-?m spectra better than other pyroxene IDPs. Cluster IDPs are highly fragile and contain significant deuterium enrichments, indicating their presolar origin. By spectroscopic analogy, Comet Hale-Bopp's Mg-rich pyroxene crystals may also be relic interstellar grains. The IDP and mineral models for Comet Hale-Bopp indicate the importance of multiple grain components at different temperatures to explaining the temporal evolution of the observed infrared features. Relative abundances of minerals depend on their relative temperatures. Cooler grains may be more abundant than warmer grains and yet may remain hidden from detection in the 10-?m silicate feature because of their cooler temperatures. The deduced larger abundance of cooler, pyroxene-dominated grains in Comet Hale-Bopp affects the interpretation of the origin of cometary dust, and dust evolution during protoplanetesimal accumulation and disk dissipation.

Wooden, Diane H.; Butner, Harold M.; Harker, David E.; Woodward, Charles E.

2000-01-01

395

Infrared spectroscopy and hydrogen isotope geochemistry of hydrous silicate glasses. Progress report, June 1, 1996--May 31, 1999  

SciTech Connect

This DOE-funded project (DE-FG03-ER13445, 6/1/96-5/31/99) emphasizes study of the behavior of volatiles in magmatic systems. The project is explicitly focused on the combined application of IR spectroscopy, experimental petrology, and stable isotope geochemistry to understanding the behavior and properties of the volatile components dissolved in silicate melts and glasses, although in recent years, our emphasis has broadened to include non-volatile aspects of stable isotope geochemistry. Results obtained during the current grant and previous grant periods confirm that when applied to study of well-chosen synthetic and natural systems, the combination of these approaches and techniques can yield insights of general petrological and volcanological value and of practical value to DOE. In particular, the results of our DOE-funded work has led to a deeper understanding of the physical chemistry of silicate melts as well as specific constraints on the thermal and chemical evolution of high-level magmatic systems of the sort being evaluated as potential geothermal and magmathermal energy sources. Moreover, our work has also contributed to understanding the behavior of H-, C-, and O-bearing species in amorphous and crystalline silicates, including the kinetics of their interactions; we believe these results will contribute to efforts to use silicates in the development of nuclear waste disposal strategies.

Epstein, S.; Stolper, E.

1998-06-01

396

Zeolitic catalyst with improved regeneration properties  

Microsoft Academic Search

An experimental batch of Tseokar-4 bead catalyst was prepared from the zeolitic catalyst Tseokar-2 by adding 0.15% chromic oxide by weight. Finds that the use of the Tseokar-4 (with better regeneration properties because of the addition of chromium), in a commercial unit made it possible to increase the coke burnoff rate in the regenerator quite substantially, particularly in the upper

V. R. Zinovev; L. V. Bryzgalina; S. N. Khadzhiev; A. P. Kosolapova

1983-01-01

397

Solar energy application of natural zeolites  

Microsoft Academic Search

The utilization of solar energy for cooling is usually achieved by means of sorption-refrigeration cycles. However, the conventional cycles using ammonia-water or lithium bromide-water solutions are inefficient because of the low solution temperatures obtainable with solar radiation and the high condenser temperatures required by air-cooled condensers. Zeolites provide a unique opportunity for a solid-gas adsorption cooling system because of their

D. I. Tchernev

1978-01-01

398

The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers  

SciTech Connect

The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 deg. C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na.

Oh, Jae Eun [Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720 (United States); Monteiro, Paulo J.M., E-mail: monteiro@berkeley.ed [Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720 (United States); Jun, Ssang Sun [Global Leading Offshore Plant Education Center, Korea Maritime University, Busan, 606-791 (Korea, Republic of); Choi, Sejin [Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720 (United States); Clark, Simon M. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 20015 (United States); Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720 (United States)

2010-02-15

399

Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3/Si multilayer deposited on Si substrates.  

PubMed

Eu2O3/Si multilayer nanostructured films are deposited on Si substrates by magnetron sputtering. Transmission electron microscopy and X-ray diffraction measurements demonstrate that multicrystalline Eu silicate is homogeneously distributed in the film after high-temperature treatment in N2. The Eu2+ silicate is formed by the reaction of Eu2O3 and Si layers, showing an intense and broad room-temperature photoluminescence peak centered at 610 nm. It is found that the Si layer thickness in nanostructures has great influence on Eu ion optical behavior by forming different Eu silicate crystalline phases. These findings open a promising way to prepare efficient Eu2+ materials for photonic application. PMID:23618344

Li, Leliang; Zheng, Jun; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

2013-04-26

400

Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3/Si multilayer deposited on Si substrates  

NASA Astrophysics Data System (ADS)

Eu2O3/Si multilayer nanostructured films are deposited on Si substrates by magnetron sputtering. Transmission electron microscopy and X-ray diffraction measurements demonstrate that multicrystalline Eu silicate is homogeneously distributed in the film after high-temperature treatment in N2. The Eu2+ silicate is formed by the reaction of Eu2O3 and Si layers, showing an intense and broad room-temperature photoluminescence peak centered at 610 nm. It is found that the Si layer thickness in nanostructures has great influence on Eu ion optical behavior by forming different Eu silicate crystalline phases. These findings open a promising way to prepare efficient Eu2+ materials for photonic application.

Li, Leliang; Zheng, Jun; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

2013-04-01

401

Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3/Si multilayer deposited on Si substrates  

PubMed Central

Eu2O3/Si multilayer nanostructured films are deposited on Si substrates by magnetron sputtering. Transmission electron microscopy and X-ray diffraction measurements demonstrate that multicrystalline Eu silicate is homogeneously distributed in the film after high-temperature treatment in N2. The Eu2+ silicate is formed by the reaction of Eu2O3 and Si layers, showing an intense and broad room-temperature photoluminescence peak centered at 610 nm. It is found that the Si layer thickness in nanostructures has great influence on Eu ion optical behavior by forming different Eu silicate crystalline phases. These findings open a promising way to prepare efficient Eu2+ materials for photonic application.

2013-01-01

402

Monoethanol amine modified zeolite 13X for CO{sub 2} adsorption at different temperatures  

SciTech Connect

Zeolite 13X has been modified with monoethanol amine (MEA). MEA loadings of 0.5-25 wt % have been achieved using the impregnation method in different solvents. The mode of incorporation based on methanol with stirring at room temperature appears to be the most feasible. The adsorbent has been characterized for crystallinity, surface area, pore volume, and pore size. The thermal stability of the adsorbent is studied using a thermal analyzer. The CO{sub 2} adsorption capacity of adsorbents is evaluated using the breakthrough adsorption method with a packed column on a 10 g scale. The adsorption capacities of adsorbents are estimated in the temperature range 30-120{sup o}C. The adsorbents show improvement in CO{sub 2} adsorption capacity over the unmodified zeolite by a factor of ca. 1.6 at 30{sup o}C, whereas at 120{sup o}C the efficiency improved by a factor of 3.5. For adsorption at these temperatures, different MEA loading levels were found to be suitable as per the governing adsorption phenomena, that is, physical or chemical. The adsorbent is also studied for CO{sub 2} selectivity over N{sub 2} at 75{sup o}C. The MEA-modified adsorbent shows better CO{sub 2} selectivity, which was improved further in the presence of moisture. 25 refs., 6 figs., 3t abs.

P.D. Jadhav; R.V. Chatti; R.B. Biniwale; N.K. Labhsetwar; S. Devotta; S.S. Rayalu [National Environmental Engineering Research Institute, Nagpur (India)]. s_rayalu@neeri.res.in

2007-12-15

403

Zeolite compositions as proxies for eruptive paleoenvironment  

NASA Astrophysics Data System (ADS)

We report chemical compositions of authigenic alteration minerals in subglacially erupted hyaloclastite breccias from James Ross Island, Antarctica, which provide a geochemical proxy for paleoenvironment. Analyses of zeolites (phillipsite and chabazite) from several lava-fed deltas on the island were compared with published compositions of zeolites from known freshwater and marine environments. Using values of (Na + K)/Ca = 3.0 (for phillipsites) and 1.0 (for chabazites), the data successfully distinguish between marine and freshwater alteration. However, our study also suggests that volcanic breccias may not be sealed to fluids, even when the pore spaces are completely filled. The James Ross Island data show that, at higher elevations in lava-fed deltas, the zeolites preserve their original freshwater-influenced (i.e., glacial) compositions, whereas at lower elevations, (Na + K)/Ca ratios are generally higher and indicate a later marine influence. We suggest that water may penetrate several kilometers into the volcanic pile by movement along fractures and/or grain boundaries.

Johnson, Joanne S.; Smellie, John L.

2007-03-01

404

Anchoring strategies for bimetallic species in zeolites  

SciTech Connect

We explore a new approach by introducing heterobinuclear organometallic compounds for linking catalytic functions to zeolite frameworks. With two different metals present, the complexes are being anchored to the support via one oxophilic metal, ligand exchange and catalytic reactions may proceed at the second metal center. Anchoring chemistry, thermal stability and reactivity of Me[sub 3]SnMn(CO)[sub 5] in zeolite NaY and acid forms of zeolite Y was studied with X-ray absorption spectroscopy (Sn, Mn edge EXAFS) and in-situ FTIR/TPD-MS techniques. Subsequently, the tin-cobalt complex Me[sub 3]SnCo(CO)[sub 4] has been a focus of detailed synthetic and spectroscopic studies. The reactivity of tricarbonyl (cyclopentadienyl) (trimethylstannyl) molybdenum in new mesoporous hosts has been explored. A recent development is the design of vanadium oxo species in different micro- and mesoporous hosts. These are of great interest for the selective reduction of nitrogen oxides by ammonia, and selective oxidation of different hydrocarbons, such as xylenes, olefines and alkanes. Combination analytical techniques used to probe local structural changes at the molecular level, include EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy utilizing synchrotron radiation, in situ FT-IR coupled to thermodesorption/MS, UV-NIR, and CCD Raman.

Bein, T.

1993-03-01

405

Silicate Feature Variation in LPV Stars  

NASA Astrophysics Data System (ADS)

Silicate dust, found around oxygen-rich stars, produces a hallmark mid-infrared spectral feature resulting from the bend or stretch in the SiO_4 tetrahedron. Long Period Variable (LPV) stars on the Asymptotic Giant Branch produce copious quantities of silicate dust over this short stage of their stellar evolution. A study of 31 oxygen-rich LPVs was conducted over a sixteen month period using the University of Denver's TNTCAM. The study has been supplemented with spectral data from UKIRT CGS3 service observations and IRAS LRS archives. Observations of the silicate features in the circumstellar environment indicate a possible evolutionary sequence for the stars, inferred from the changes of the dust spectra. These new observations suggest a relationship between the dust spectral signature and the stage of the dust formation process. There is evidence that acoustic shocks from the LPV are a catalyst in the dust formation process. Follow-on work is already occuring in the form of ISO SWS data on a selected subgroup of LPVs. To enhance this study, a mid-infrared, cross-dispersed spectrometer, TGIRS, was built. TGIRS covers a wavelength range of 7 to 14 microns at a resolving power of 750. The instrument utilizes a Boeing-Rockwell Si:As BIB HFPA as its detector. It is cooled using a two-stage Gifford-McMahon cryocooler, eliminating the need for liquid cryogens. All of the optics in the system are aluminum, permitting ambient alignment and focusing with a laser. A description of the design and building phases of TGIRS is presented. Brief descriptions concerning the evolution of LPVs, theories of dust formation, and the signatures of the silicate dust are given. Data acquisition and reduction are described, including a new method for removing telluric attenuation from the data. Spectral energy distributions are shown, including graphs of the silicate features with respect to stellar phase. Finally, results of the statistical analysis of the sample and conclusions are drawn, including a new scenario for silicate dust growth.

Creech-Eakman, M. J.

1997-08-01

406

Crystalline plutonium hosts derived from high-level waste formulations.  

SciTech Connect

The Department of Energy has selected immobilization for disposal in a repository as one approach for disposing of excess plutonium (1). Materials for immobilizing weapons-grade plutonium for repository disposal must meet the ''spent fuel standard'' by providing a radiation field similar to spent fuel (2). Such a radiation field can be provided by incorporating fission products from high-level waste into the waste form. Experiments were performed to evaluate the feasibility of incorporating high-level waste (HLW) stored at the Idaho Chemical Processing Plant (ICPP) into plutonium dispositioning materials to meet the spent fuel standard. A variety of materials and preparation techniques were evaluated based on prior experience developing waste forms for immobilizing HLW. These included crystalline ceramic compositions prepared by conventional sintering and hot isostatic pressing (HIP), and glass formulations prepared by conventional melting. Because plutonium solubility in silicate melts is limited, glass formulations were intentionally devitrified to partition plutonium into crystalline host phases, thereby allowing increased overall plutonium loading. Samarium, added as a representative rare earth neutron absorber, also tended to partition into the plutonium host phases. Because the crystalline plutonium host phases are chemically more inert, the plutonium is more effectively isolated from the environment, and its attractiveness for proliferation is reduced. In the initial phase of evaluating each material and preparation method, cerium was used as a surrogate for plutonium. For promising materials, additional preparation experiments were performed using plutonium to verify the behavior of cerium as a surrogate. These experiments demonstrated that cerium performed well as a surrogate for plutonium. For the most part, cerium and plutonium partitioned onto the same crystalline phases, and no anomalous changes in oxidation state were observed. The only observed difference in behavior between cerium and plutonium was that plutonium partitioned more completely into the major host phases than cerium. Where cerium was sometimes observed at up to a few atom percent in crystalline or glassy phases, plutonium could not be detected in these phases. The crystalline plutonium host phases identified in this work included zirconolite, cubic zirconia, sphene, and an anorthite-like calcium aluminosilicate. Zirconia has been suggested as a possible material for immobilizing actinides (3), but this appears to be the first synthesis of such a material. Plutonium appears to stabilize the cubic (fluorite) structure through abroad solid solution range. Samarium can also be incorporated into this material, but is not necessary to stabilize the cubic structure. Plutonium leach rates, as measured by the Product Consistency Test (4), were on the order of 10{sup {minus}5} to 10{sup {minus}6} g/m{sup 2}/day.

O'Holleran, T. P.

1998-04-24

407

Solar energy storage by natural zeolites: I. Dehydration of zeolitic tuff  

SciTech Connect

In the perspective of a possible utilization of natural zeolites in the solar energy exploitation as materials suitable for heat storage, the behaviours of chabazitic and phillipsitic tuffs in the isothermal dehydration have been studied, evaluating the influence of temperature, heating rate and cationic form of the zeolite on the water desorption process. The possibility of achieving an almost complete desorption at temperatures of 200/250/sup 0/C in times of the order of two hours or less has been emphasized and indications on the heat amount storable by a chabazitic tuff in its original cationic form have been at last given.

Nastro, A.; Aiello, R.; Colella, C.; Conte, M.; Fittipaldi, F.

1980-12-01

408

Process wastewater treatment with hydrogen-form CST and chabazite zeolite  

SciTech Connect

Ion-exchange materials have been investigated for the removal of radionuclides from near-neutral-pH wastewaters containing competing cations at concentrations greater than those of the targeted species. Natural chabazite zeolite was chosen as the baseline material for the removal of fission products, namely {sup 90}Sr and {sup 137}Cs, from wastewater and groundwater. The sorbent IONSIV{reg_sign} IE-911, a crystalline silicotitanate manufactured by UOP, was recently tested in this capacity and found to compare extremely well against the baseline material in removing {sup 90}Sr and {sup 137}Cs from process wastewater. This paper presents results of similar column tests performed using both materials, as well as results from batch experiments on actual wastewaters using IONSIV{reg_sign} IE-911.

DePaoli, S.M.; Bostick, D.T.

1998-05-01

409

Sodic and Acidic Crystalline Lamellar Magadiite Adsorbents for the Removal of Methylene Blue from Aqueous Solutions: Kinetic and Equilibrium Studies  

Microsoft Academic Search

The present study reports the feasibility of two synthetic crystalline lamellar nano-silicates, sodic magadiite (Na-mag) and its converted acidic form (H-mag), as alternative adsorbents for the removal of the dye methylene blue (MB) from aqueous solutions. The ability of these adsorbents for removing the dye was explored through the batch adsorption procedure. Effects such as the pH and the adsorbent

Betina Royer; Natali F. Cardoso; Eder C. Lima; Thais R. Macedo; Claudio Airoldi

2009-01-01

410

PHYSICAL, CHEMICAL AND STRUCTURAL EVOLUTIION OF ZEOLITE-CONTAINING WASTE FORMS PRODUCED FROM METAKAOLINITE AND CALCINED SODUIM BEARING WASTE (HLW AND/OR LLW)  

SciTech Connect

Zeolites are extremely versatile. They can adsorb liquids and gases and serve as cation exchange media. They occur in nature as well cemented deposits. The Romans used blocks of zeolitized tuff as a building material. Using zeolites for the management of radioactive waste is not new, but a process by which the zeolites can be made to act as a cementing agent is. Zeolitic materials are relatively easy to synthesize from a wide range of both natural and man-made precursors. The process under study is derived from a well known method in which metakaolin (thermally dehydroxylated kaolin a mixture of kaolinite and smaller amounts of quartz and mica that has been heated to {approx}700 C) is mixed with sodium hydroxide (NaOH) and water and reacted in slurry form (for a day or two) at mildly elevated temperatures. The zeolites form as finely divided powders containing micrometer ({micro}m) sized crystals. However, if the process is changed slightly and just enough concentrated sodium hydroxide solution is added to the metakaolinite to make a thick paste and then the paste is cured under mild hydrothermal conditions (60-200 C), the mixture forms a concrete-like ceramic material made up of distinct crystalline tectosilicate minerals (zeolites and feldspathoids) imbedded in an X-ray amorphous hydrated sodium aluminosilicate matrix. Due to its vitreous character we have chosen to call this composite a ''hydroceramic''. Similar to zeolite powders, a hydroceramic is able to sequester cations in both lattice positions and within the channels and voids present in its tectosilicate framework structure. It can also accommodate a wide range of salt molecules (e.g., sodium nitrate) within these same openings thus rendering them insoluble. Due to its fine crystallite size and cementing character, the matrix develops significant physical strength. The obvious similarities between a hydroceramic waste form and a waste form based on solidified Portland cement grout are only superficial because their chemistries are entirely different. In addition to being vastly superior to conventional Portland cement grouts with respect to salt retention, standard radwaste leach protocols (PCT, TCLP, etc.) have shown that hydroceramics also do a better job of immobilizing the RCRA-toxic and radioactive components of ''sodium bearing wastes'' (SBWs).

Grutzeck, Michael W.

2004-06-10

411

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

National Technical Information Service (NTIS)

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

M. G. Howden

1981-01-01

412

Influence of zeolites in PDMS membranes. Pervaporation of water\\/alcohol mixtures  

Microsoft Academic Search

A strong influence of the zeolite was found on the pervaporation of alcohol\\/water mixtures using filled PDMS membranes. In all cases, the zeolites reduced the swelling of the PDMS. Incorporation of the hydrophilic zeolite Y increased water fluxes, while ZSM-5 reduced both water and alcohol fluxes due to a partial retention of these molecules in the zeolite. For branched alcohols,

Ivo F. J. Vankelecom; Dirk Depre; Stijn De Beukelaer; Jan B. Uytterhoeven

1995-01-01

413

Influence of Chemical Surface Characteristics of Natural Zeolite on Catalytic Ozone Abatement  

Microsoft Academic Search

In this article, the effect of zeolite chemical surface properties on gaseous ozone removal was investigated. Zeolite samples with different surface chemical composition were prepared from a Chilean natural zeolite. Such treatments included acid de-alumination, and thermal treatment at 400 °C and 550 °C prior to contact with ozone. Chemical modification of natural zeolite showed that the generation of new

Héctor Valdés; Eder E. Padilla; Claudio A. Zaror

2011-01-01

414

Removal of Ca and Zn from aqueous solutions by zeolites NaP and KP  

Microsoft Academic Search

Zeolites P in sodium (NaP) and potassium (KP) forms were used as adsorbents for the removal of calcium (Ca) and zinc (Zn) cations from aqueous solutions. Zeolite KP was prepared by ion exchange of K with Na which neutralizes the negative charge of the zeolite P framework structure. The ion exchange capacity of K on zeolite NaP was determined through

Alias Mohd Yusof; Nik Ahmad Nizam Nik Malek; Nurul Asyikin Kamaruzaman; Muhammad Adil

2010-01-01

415

Separation of 1-butanol\\/2,3-butanediol using ZSM-5 zeolite-filled polydimethylsiloxane membranes  

Microsoft Academic Search

Mixed matrix membranes were prepared by incorporating ZSM-5 zeolite particles into polydimethylsiloxane. A uniform dispersion of the zeolite in the membrane was obtained. The membranes were characterized with scanning electron microscopy, and the effects of zeolite loading on membrane performance were evaluated. It was found that 80wt.% ZSM-5 loading was optimal for selectivity. Further increase in the zeolite loading either

Pinghai Shao; Ashwani Kumar

2009-01-01

416

Effect of Na and Al on the phase composition and morphology of autoclaved calcium silicate hydrates ? ? This paper was originally submitted to Advanced Cement Based Materials. The paper was received at the Editorial Office of Cement and Concrete Research on 5 November 1998 and accepted in final form on 16 July 1999  

Microsoft Academic Search

The hydrated materials were synthesized at 160–240°C in hydrothermal conditions. The series of samples with differing CaO\\/SiO2 ratios and doped with NaOH and Al(OH)3 (used as Na- and Al-bearing compounds) were produced, yielding materials consisting of the ill-crystallized calcium silicate hydrates and\\/or more crystalline calcium silicate phases. Generally, in the presence of sodium ions the acceleration of reactions leads to

Wieslawa NocuÒ-Wczelik

1999-01-01

417

Diverse topics in crystalline beams  

SciTech Connect

Equations of motion are presented, appropriate to interacting charged particles of diverse charge and mass, subject to the external forces produced by various kinds of magnetic fields and radio-frequency (rf) electric fields in storage rings. These equations are employed in the molecular dynamics simulations to study the properties of crystalline beams. The two necessary conditions for the formation and maintenance of crystalline beams are summarized. The transition from ID to 2D, and from 2D to 3D is explored, and the scaling behavior of the heating rates is discussed especially in the high temperature limit. The effectiveness of various cooling techniques in achieving crystalline states has been investigated. Crystalline beams made of two different species of ions via sympathetic cooling are presented, as well as circulating ``crystal balls`` bunched in all directions by magnetic focusing and rf field. By numerically reconstructing the original experimental conditions of the NAP-M ring, it is found that only at extremely low beam intensities, outside of the range of the original measurement, proton particles can form occasionally-passing disks. The proposed New ASTRID ring is shown to be suitable for the formation and maintenance of crystalline beams of all dimensions.

Wei, Jie [Brookhaven National Lab., Upton, NY (United States); Draeseke, A.; Sessler, A.M. [Lawrence Berkeley Lab., CA (United States); Li, Xiao-Ping [BIOSYM Technologies Inc., San Diego, CA (United States)

1995-11-27

418

Recycle of silicate waste into mesoporous materials.  

PubMed

Template synthesis of porous carbon materials usually requires selective removal of template silica from the carbon/silica composites. It not only involves waste of valuable chemicals, but also poses significant environmental concerns including high waste treatment cost. Recycling of silicates released from such nanocasting methods is successfully performed for the first time to regenerate valuable mesoporous MCM and SBA type silica materials, which will not only help in saving valuable chemicals, but also in decreasing chemical waste, contributing in improvement of our environmental standards. This approach can thus improve cost effectiveness for the mass production of nanostructured carbon and others utilizing silica directed nanocasting method by recycling otherwise silicate waste into highly desirable valuable mesoporous silica. PMID:21417445

Kim, Jung Ho; Kim, Minwoo; Yu, Jong-Sung

2011-03-21

419

Al speciation in silicate glasses and melts  

NASA Astrophysics Data System (ADS)

The first human glasses were made 3500 BC. It was essentially sodo-lime silicate glass. To improve the chemical resistance, the thermal properties and increase the viscosity it is interesting to add aluminum in these silicates. But what is the speciation of the aluminum and how it varies according to the chemical composition and to the temperature? The aluminum appears essentially in four or five fold coordination in glasses and melts melted. The proportion of [5]Al varies according to the alkaline or to the earth-alkaline content and to the temperature. We shall present in a first part the influence of the network-modifier on the proportion of [5]Al and then we shall present some new results of absorption of high-temperature using NMR and XANES spectroscopy at the Al K-edge. Finally, from glass transition temperature measurements we propose to explain that [5]Al can be a new network former.

Neuville, Daniel; Florian, Pierre; Montouillout, Valérie; Le Losq, Charles; Massiot, Dominique

2010-05-01

420

Lithium alumino-silicate ion source development  

NASA Astrophysics Data System (ADS)

We report experimental progress on Li+ source development in preparation for warm dense matter heating experiments. To uniformly heat targets to electron-volt temperatures for the study of warm dense matter, we are pursuing the use of a low (E < 5 MeV) kinetic energy singly ionized lithium beam and a thin target. Two kinds of lithium (Li+) alumino-silicate ion sources, ?-spodumene and ?-eucryptite, each of area 0.31 cm2, have been fabricated for ion emission measurements. These surface ionization sources are heated to 1200 to 1300 C where they preferentially emit singly ionized alkali ions. Tight process controls were necessary in preparing and sintering the alumino-silicate to the porous tungsten substrate to produce an emitter that gives uniform ion emission, sufficient current density and low beam emittance. Current density limit of the two kinds have been measured, and ion species identification of possible contaminants has been verified with a Wien (E x B) filter.

Roy, Prabir Kumar; Seidl, Peter A.; Kwan, Joe W.; Greenway, Wayne G.; Waldron, William L.; Wu, James K.; Mazaheri, Kavous

2009-11-01

421

Synthesis of zeolites from coal fly ash: an overview  

Microsoft Academic Search

Coal combustion by-products production in USA and EU is estimated in around 115 million tons per year. A large portion of this production is accounted for the coal fly ash (CFA). Cement and concrete manufacturing consumes most of the CFA produced. Zeolite synthesized from CFA is a minor but interesting product, with high environmental applications. Zeolites may be easily obtained

X Querol; N Moreno; J. C Umaña; A Alastuey; E Hernández; A López-Soler; F Plana

2002-01-01

422

Use of natural zeolite as a supplementary cementitious material  

Microsoft Academic Search

Natural zeolite, a type of frame-structured hydrated aluminosilicate mineral, is used abundantly as a type of natural pozzolanic material in some regions of the world. In this work, the effectiveness of a locally quarried zeolite in enhancing mechanical and durability properties of concrete is evaluated and is also compared with other pozzolanic admixtures. The experimental tests included three parts: In

Babak Ahmadi; Mohammad Shekarchi

2010-01-01

423

Support effects on CO hydrogenation over Ru/zeolite catalysts  

SciTech Connect

Hydrogenation of carbon monoxide at 101.3 kPa has been studied over a series of ion-exchanged Ru catalysts supported on NaX, NaY, KL, Na mordenite, and HY zeolites. The type of zeolite had pronounced effects on the activity and selectivity of the Ru. The specific activity would appear to be related to the dispersion of reduced ruthenium in the zeolite. Methane selectivity, however, seems to be strongly influenced by the type and concentration of alkali cations remaining in the ion-exchanged zeolite. These cations appear to promote chain growth much as traditional alkali promoters would, though perhaps more indirectly. Due to bifunctional properties of the zeolite-supported catalysts, a significant fraction of C/sub 4/ was in the form of isobutane. Formation of isobutane seems to be related to either the Si/Al ratio in the zeolites or the concentration of the remaining alkali cations, but not to the OH concentration. In addition, H/sub 2/ chemisorption at 25/sup 0/C was increasingly suppressed as the Se/Al ratio of the zeolite support increased. Both the formation of isobutane and the suppression of H/sub 2/ chemisorption may be related to the acid strength of the OH groups present, which is a function of the Si/Al ratio of the zeolite.

Chen, Y.W.; Wang, H.T.; Goodwin, J.G. Jr.

1984-02-01

424

Ion exchange in a zeolite-molten chloride system  

SciTech Connect

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 ion exchange. To date, the molten chloride ion-exchange properties of four zeolites have been investigated for this process: zeolite A, IE95{reg_sign}, clinoptilolite, and mordenite. Of these, zeolite A has been the most promising. Treating zeolite 4A, the sodium form of zeolite A , with the solvent salt for the waste stream-lithium-potassium chloride of eutectic melting composition, is expected to provide a material with favorable ion-exchange properties for the treatment of the waste salt. The authors constructed a pilot-plant system for the ion-exchange column. Initial results indicate that there is a direct relationship between the two operating variable of interest, temperature, and initial sodium concentration. Also, the mass ratio has been about 3--5 to bring the sodium concentration of the effluent below 1 mol%.

Woodman, R.H.; Pereira, C. [Argonne National Lab., IL (United States). Chemical Technology Div.

1997-07-01

425

The adsorption of SOâ by zeolites synthesized from fly ash  

Microsoft Academic Search

Zeolites X, Y, and Na-Pl (90 C) and analcime and sodalite (150 C) were synthesized from Class F fly ash using 3 M sodium hydroxide solutions and autogenous pressures. The partially zeolitized fly ashes were dried overnight in air at room temperature and then characterized using X-ray diffraction and SEM. On occasion, a few samples were dried to constant weight

Anand Srinivasan; Michael W. Grutzeck

1999-01-01

426

Zeolitic coatings and their potential use in catalysis  

Microsoft Academic Search

The formation of zeolitic coatings and their properties, such as the thickness, continuity and orientation of the crystals, are related to the presence and macro-organization of a precursor phase. Based on this view, preshaped zeolitic coatings can be prepared which may be either active catalysts themselves or an inert thin membrane on an existing catalyst. They can be applied in

J. C. Jansen; J. H. Koegler; H. van Bekkum; H. P. A. Calis; C. M. van den Bleek; F. Kapteijn; J. A. Moulijn; E. R. Geus; N. van der Puil

1998-01-01

427

Investigation of zeolites by solid state quadrapole NMR.  

National Technical Information Service (NTIS)

The subject of this thesis is the NMR investigation of zeolites. The nature and properties of zeolites are discussed. Some of the basic priniples of NMR techniques on quadrupole nuclei are presented. A special technique, namely a two-dimensional nutation ...

R. Janssen

1990-01-01

428

Removal of ammonium from greywater using natural zeolite  

Microsoft Academic Search

This paper focuses on the effectiveness of removing ammonium ion and the theoretical aspects of adsorption including adsorption isotherm, kinetics and thermodynamics as well as desorption–regeneration studies. Results have demonstrated that natural zeolite shows good performance with up to 97% for ammonium removal depending on contact time, zeolite loading, initial ammonium concentration and pH. The adsorption kinetics is best approximated

Nurul Widiastuti; Hongwei Wu; Ha Ming Ang; Dongke Zhang

2011-01-01

429

Preparation and characterization of ton type zeolite catalysts  

Microsoft Academic Search

The reduction of air pollutants emitted at the engine exhaust is an imperative goal for the coming years. The traditional Pt-Rh three-way catalysts are not able to operate in lean burn condition working engines. Copper and cobalt zeolites show high activity and selectivity for both reduction of NOx and hydrocarbon combustion. The TON type zeolite presents a high hydrophobicity and

F. Cosentino; A. Katovic; G Giordano; P. Lentz; J. B. Nagy

1999-01-01

430

Selective thermal and photooxidation of hydrocarbons in zeolites by oxygen  

DOEpatents

A process is described for selective thermal oxidation or photooxidation of hydrocarbons adsorbed onto zeolite matrices. A highly selective thermal oxidation and photooxidation of unsubstituted or alkyl substituted alkanes, alkenes, aromatics and cycloalkyls in solvent free zeolites under dark thermal conditions or under irradiation with visible light. The process oxidizes hydrocarbons almost completely selectively without substantial production of byproducts. 19 figs.

Frei, H.; Blatter, F.; Sun, H.

1999-06-22

431

Co-ZSM-5 Zeolites: Characterization and Magnetic Properties  

Microsoft Academic Search

ZSM-5 zeolites modified with Co cations were synthesized. They were characterized by AA, XRD, Raman Spectroscopy, TPR, FTIR and BET. The Co ions were introduced in the zeolitic matrix by wet impregnation or ion-exchange methods, followed by thermal treatments. The incorporation of cobalt ions into ZSM-5 does not affect the high degree of purity, cristallinity and orthorhombic symmetry of the

L. B. Pierella; M. Fernández García; P. Bercoff; H. R. Bertorello

432

Adsorption of Pb and Cd by amine-modified zeolite  

Microsoft Academic Search

Natural zeolites, known for their excellent sorption properties towards metal cations, are widely used for the purification of wastewaters. The selectivity of clinoptilolite, a common zeolite mineral, for Pb is known to be particularly high, whereas its selectivity for Cd is often lower. Extraordinarily high sorption capacities for soft metal cations were observed in the case of thiol-functionalized silica gels

Ulla Wingenfelder; Bernd Nowack; Gerhard Furrer; Rainer Schulin

2005-01-01

433

Antibacterial activity of heavy metal-loaded natural zeolite.  

PubMed

The antibacterial activity of natural zeolitized tuffs containing 2.60wt.% Cu(2+), 1.47 Zn(2+) or 0.52 Ni(2+) were tested. Antibacterial activities of the zeolites against Escherichia coli and Staphylococcus aureus were tested after 1h and 24h of exposure to 1g of the zeolite in 100mL of three different media, namely Luria Bertani, synthetic wastewater and secondary effluent wastewater. The antibacterial activities of the zeolites in Luria Bertani medium were significantly lower than those in the other media and negatively correlated with the chemical oxygen demand of the media. The Ni-loaded zeolite showed high leaching of Ni(2+) (3.44-9.13wt.% of the Ni(2+) loaded) and weak antibacterial activity in the effluent water. Since Cu-loaded zeolite did not leach Cu(2+) and the leaching of Zn(2+) from Zn-loaded zeolite was low (1.07-1.61wt.% of the Zn(2+) loaded), the strong antibacterial activity classified the Cu- and Zn-loaded zeolite as promising antibacterial materials for disinfection of secondary effluent water. PMID:22178285

Hrenovic, Jasna; Milenkovic, Jelena; Ivankovic, Tomislav; Rajic, Nevenka

2011-12-01

434

Selective thermal and photooxidation of hydrocarbons in zeolites by oxygen  

Microsoft Academic Search

A process is described for selective thermal oxidation or photooxidation of hydrocarbons adsorbed onto zeolite matrices. A highly selective thermal oxidation and photooxidation of unsubstituted or alkyl substituted alkanes, alkenes, aromatics and cycloalkyls in solvent free zeolites under dark thermal conditions or under irradiation with visible light. The process oxidizes hydrocarbons almost completely selectively without substantial production of byproducts. 19

H. Frei; F. Blatter; H. Sun

1999-01-01

435

CHARACTERISTICS OF ZEOLITE WASHCOATS ON CORDIERITE MONOLITHS FOR ENVIRONMENTAL APPLICATIONS  

Microsoft Academic Search

Several preparation variables were analyzed which might affect the characteristics of zeolite coatings on cordierite monolith structures obtained by was hcoating. It was found that zeolite type, suspension concentration, number of immersions, solvent, particle size, and additives impinge on coating quality. When the suspension concentration is increased, a non-linear increment of the load is obtained. At the same time, the

J. M. Zamaro; M. A. Ulla; E. E. Miró

436

Exploratory study of mesopore templating with carbon during zeolite synthesis  

Microsoft Academic Search

Here we present an exploratory study on the generation of mesopores in zeolite crystals by templating with carbon during synthesis. With nitrogen physisorption, scanning electron microscopy and (three-dimensional) transmission electron microscopy we have studied the influence of the carbon source and zeolite synthesis conditions on the mesopores generated after the carbon has been burned off. In particular, silicalite-1 crystals have

A. H. Janssen; I. Schmidt; C. J. H. Jacobsen; A. J. Koster; K. P. de Jong

2003-01-01

437

Raman studies of the templated synthesis of zeolites  

Microsoft Academic Search

The application of confocal Raman and FT-Raman in the understanding of zeolite synthesis is a goal that can be reached by studying different levels of complexity. First, the Raman properties of TEOS and its polymerization products under acid conditions is investigated. Structural characterization of zeolite framework vibrations is related to their building blocks such as prisms and sodalite cages. The

P. P. H. J. M. Knops-Gerrits; M. G. L. J. Cuypers

2000-01-01

438

Structure descriptors for organic templates employed in zeolite synthesis  

Microsoft Academic Search

A structural analysis has been carried out upon 130 organic templating agents employed in the synthesis of zeolites from 18 different framework types. The orthogonal principal axes of inertia of these molecules provide quantitative structure descriptors which can be plotted to produce three-dimensional ‘shape-space’ diagrams. Groups of templates which produce different zeolite framework architectures plot in discrete areas of these

R. E. Boyett; A. P. Stevens; M. G. Ford; P. A. Cox

1997-01-01

439

Minerals Yearbook 1991: Wollastonite and Zeolites.  

National Technical Information Service (NTIS)

Wollastonite is natural calcium silicate and has a theoretical composition of CaOSiO2. It has developed a significant role as a high-performance mineral filler in paint, plastics, and thermal board. It is used in asbestos replacement and in ceramics such ...

M. J. Potter R. L. Virta

1992-01-01

440

Mechanical properties of calcium silicate hydrates  

Microsoft Academic Search

The dynamic mechanical properties of compacted samples of synthetic calcium