| 1. |
- Aiello, R., et al.
(författare)
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Zeolite synthesis in microgravity
- 2005
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Ingår i: Topical teams in life & physical sciences. - Noordwijk, Netherlands : ESTEC. - 929092974X ; , s. 78-85
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The results of activities performed by the members of the Topical Team on 'Zeolites synthesis in microgravity' are discussed. A method was developed using a two-temperature synthesis procedure to distinguish between the nucleation and growth phase of the crystallization. The experiments have investigated the possibility of suppressing secondary nucleation by imposing a temperature gradient. Optical thickness of the solution has been monitored by interferometry. The Team, on the basis of findings, has elaborated a research program on zeolite film deposition that includes microgravity experimentation.
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| 2. |
- Andersson, Charlotte, et al.
(författare)
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Silicalite-1 membranes with small crystal size
- 2004
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Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 626-631
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Konferensbidrag (refereegranskat)abstract
- Silicalite-1 membranes with small crystal size were prepared using a multiseeding method, where the support was repeatedly seeded and exposed to a short hydrothermal treatment up to five times. The film were characterized using SEM, single gas permeation, porosimetry and mixture separation experiment Films with three or four layers were of high quality i.e with minor defects according to the porosimetry experiments but showed poor separation of binary mixtures. This result may be attributed to the small crystal size and/or large amount of grain boundaries in the films.
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| 3. |
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| 4. |
- Bjorklund, Robert B., et al.
(författare)
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Vapor adsorption in thin silicalite-1 films studied by spectroscopic ellipsometry
- 1998
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 102:12, s. 2245-2250
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of silicalite-1 grown on silicon substrates were studied by spectroscopic ellipsometry. Analysis of spectra using an optical model consisting of a single porous layer on silicon yielded average film thicknesses of 84 and 223 nm for films synthesized for 10 and 30 h. Void fraction for the films was 0.32-0.33. Vapor adsorption from a nitrogen carrier gas at room temperature was monitored by ellipsometry. Isotherms for different adsorbates were obtained by analysis of spectra taken at different vapor concentrations using an optical model where the void volume was filled with both nitrogen and condensed vapors. Quantification of the condensed vapor amount was based on the changes in refractive index when adsorbates replaced nitrogen in the pores. Adsorbate volumes for water, toluene, 1-propanol, and hexane were 0.12, 0.12, 0.15, and 0.17 cm3 liquid g-1 film, respectively.
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| 5. |
- Dyhr, Kurt, et al.
(författare)
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Effects of zeolite addition on the manganese catalyzed decomposition of hydrogen peroxide
- 1999
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Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 6:4, s. 275-282
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Tidskriftsartikel (refereegranskat)abstract
- Manganese catalyzed decomposition of hydrogen peroxide in the presence of various zeolites was investigated at different pH values, Mn concentrations and zeolite: Mn ratios. Depending upon the level of these parameters the zeolites studied displayed both catalytic and inhibitive effects on the rate of decomposition. At a high pH (10.8) Mordenite 10A in a twofold excess on an ion-exchange capacity basis acted as an inhibitor whereas the other zeolites had little or no effect on the reaction rate. At a lower pH (9.0) zeolite A when added in large excess resulted in a remarkable inhibitive effect whereas the same zeolite resulted in a promotion of the catalytic action of manganese at an intermediate pH (9.9). The complex catalytic nature of zeolite-peroxide-Mn systems is discussed.
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| 6. |
- Dyhr, Kurt, et al.
(författare)
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Use of zeolites in hydrogen peroxide bleaching of pulp
- 1998
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 13:4, s. 257-262
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Tidskriftsartikel (refereegranskat)abstract
- The use of zeolites for inhibition of transition metal catalyzed decomposition of hydrogen peroxide was evaluated. A number of zeolite types (A, P, Y, and mordenite 10A), with different crystal structures and ion-exchange characteristics, were tested as additives in bleaching experiments using a mechanical (TMP) pulp and a chemical (kraft) pulp. For the mechanical pulp, addition of zeolites A and P at a moderate alkali charge resulted in a significant improvement of the bleaching performance as signified by an increase in both brightness and residual peroxide content of the bleaching liquor. The other zeolite types studied did not give any positive effects at the bleaching conditions used. For the chemical pulp, no significant improvements were obtained at any alkali charge using zeolite A as an additive. At high alkali charges, addition of zeolite A resulted in a substantially lower brightness than that reached in a zeolite free reference experiment. The effects of zeolite addition upon the bleaching of pulp are complex and dependent upon a number of factors. Parameters of great importance are the bleaching pH, consistency and the zeolite type and charge
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| 7. |
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| 8. |
- Edin, M., et al.
(författare)
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Hot melt adhesion of liner sized with alkylketene dimer
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 17:4, s. 395-400
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the sizing agent alkylketene dimer (AKD) on hot melt adhesive joint strength was studied. By varying the amount of AKD added, and varying the degrees of beating and calendering, sheets with different surface energies, surface structures, and strength properties, were obtained. The sheets were adhesively bonded using a commercial packaging machine, and the adhesive joints were tested in T-peel and creep tests. Contact angles, water absorptivity, delamination strength, density, and surface roughness were measured to study the way in which the addition of AKD, beating, and calendering influence these paper properties. The results indicate that neither sizing with AKD nor calendering or beating have any pronounced effect on the adhesive joint strength, at least not under the conditions used. Most of the differences observed are within the limits of the experimental error. The greatest influence on the joint strength was observed when samples had been stored at low temperature.
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| 9. |
- Elvin, F.J., et al.
(författare)
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Processes for demetalization of fluid cracking catalysts
- 1988
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Ingår i: Fluid catalytic cracking. - Washington, DC : American Chemical Society (ACS). - 0841215340 ; , s. 229-236
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Konferensbidrag (refereegranskat)abstract
- Three processes, Demet III, Demet X and New Demet, for demetallization of metal poisoned octacat fluid cracking catalysts were investigated. These processes removed a significant part of the V (30-40%) from the catalyst. The New Demet and Demet III were very effective in removing Ni (88% and 80%, respectively) while practically no Ni could be removed by Demet X. The Demet procedures also proved effective in removing other contaminants like Fe and Cu. All Demet methods resulted in increased cracking activities as determined by the micro-activity test. The conversions increased from 65% for the untreated catalyst to 76-78% for samples treated according to the different Demet procedures. The increase in activity was accompanied by a corresponding increase in gasoline yield of 5.0-6.5%.
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| 10. |
- Engström, V., et al.
(författare)
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The effect of seed size on the growth of silicalite-1 films on gold surfaces
- 2000
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 38:1, s. 51-60
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Tidskriftsartikel (refereegranskat)abstract
- Silicalite-1 films grown on gold surfaces seeded with colloidal crystals with a size of 60, 165 and 320 nm were investigated by reflection–absorption infrared spectroscopy, scanning electron microscopy and X-ray diffraction in order to follow up the formation of nano-scale defects and to determine the optimal synthesis conditions for preparation of silicalite-1 films with a low concentration of defects. Using 60-nm-sized colloidal crystals, the seeding method was capable of producing silicalite-1 films with low concentrations of defects and with thicknesses ranging from 100 to 300 nm, which are predominantly oriented with the a-axis perpendicular to the surface. Hydrothermal treatment times of the 60-nm-seeded surfaces longer than 36 h as well as the seeding with 165 or 320 nm colloidal crystals substantially enhanced the formation of defects in the films.
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| 11. |
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| 12. |
- Grahn, Mattias, et al.
(författare)
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Silicalite-1 coated ATR elements as sensitive chemical sensor probes
- 2005
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 81:1-3, s. 357-363
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Tidskriftsartikel (refereegranskat)abstract
- A novel sensitive chemical sensor probe has been fabricated. The sensor principle is based on silicalite-1 coated ATR (attenuated total reflection) elements and FTIR spectroscopy. The microporous silicalite-1 film enriches the analyte to the probe surface, thus increasing the sensitivity. At a relative pressure of n-hexane in helium of 6 × 10−5 the sensitivity of the probe is approximately 85 times higher for the silicalite-1 coated element compared to a 10 cm transmission gas cell and ca. 180 times higher compared to an uncoated element. The performance of the probe is illustrated by determination of an adsorption isotherm for n-hexane in silicalite-1.
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| 13. |
- Haglund, R., et al.
(författare)
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Upgrading of hydropyrolysis coal tar by hydroprocessing
- 1991
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Ingår i: Erdöl Erdgas Kohle. - 0179-3187. ; 107:5, s. 232-235
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Tidskriftsartikel (refereegranskat)abstract
- Upgrading of a hydropyrolysis coal tar by hydroprocessing was investigated using different process conditions. The response of the hydropyrolysis tar to hydroprocessing was compared to those of a conventional coal tar and two heavy oil fractions. At comparable conditions, the removal of heteroatoms from the hydropyrolysis tar was more effective than from the conventional tar and, in particular, than from the oil fractions. Using conditions typical for hydroprocessing of heavy oil fractions, the contents of N, O as well as S in the hydropyrolysis tar were reduced by more than 90%. Hydroprocessing also resulted in a considerable increase in the gasoline fraction of the tar.
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| 14. |
- Hedlund, Jonas, et al.
(författare)
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Controlling the preferred orientation in silicalite-1 films synthesized by seeding
- 1999
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 28:1, s. 185-194
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Tidskriftsartikel (refereegranskat)abstract
- Single crystal silicon (100) wafers were seeded with colloidal silicalite-1 crystals and hydrothermally treated in a precursor solution to grow thin silicalite-1 films. A total of 28 experiments in eight series were investigated with SEM and XRD to evaluate the preferred orientation of the crystals constituting the films. The investigated parameters in the film formation process were seed crystal size, amount of adsorbed seed crystals and film thickness after hydrothermal treatment of the seeded substrates. In thin films, most of the crystalline material is oriented with the b-axis perpendicular to the substrate surface. In thick films, most of the crystalline material is oriented with the a-axis perpendicular to the substrate surface. The change in preferred orientation with film thickness is faster when small seeds are used. The amount of adsorbed seeds has a larger influence on the preferred orientation when large seeds are used. A mechanism explaining these trends is proposed. The choice of size and coverage of seeds can be used to control the preferred orientation of the crystals in a film of given thickness within certain limitations.
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| 15. |
- Hedlund, Jonas, et al.
(författare)
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High-flux MFI membranes
- 2002
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 52:3, s. 179-189
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and evaluation of high performance MFI-type membranes is described. These systems exhibit fluxes that are one to two orders of magnitude higher than previous literature reports, with comparable selectivities, when tested for various single component gases and for mixtures of C4, C6 and xylene isomers.These materials are the result of a rational fabrication approach targeting ultra-thin, defect-free MFI films on open supports by using a two-step support masking technique and a monolayer of colloidal nucleation seeds, followed by in situ hydrothermal growth, producing a defect-free film with a thickness of 0.5 μm. Reproducibility of the membrane preparation was excellent.
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| 16. |
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| 17. |
- Hedlund, Jonas, et al.
(författare)
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Synthesis of thin molecular sieve films
- 1999
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Ingår i: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 12:1-4, s. 413-416
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Tidskriftsartikel (refereegranskat)abstract
- A method to synthesize thin films of various molecular sieves on a number of substrates employing pre-seeding has been developed. The substrate is modified to enable adsorption of seed crystals. Substrates with an originally negative surface charge are charge reversed by adsorption of cationic polymer molecules. Nobel metal substrates are first silanized to obtain a negative surface charge. Nano seed crystals are adsorbed on the modified substrates from a sol and induced to grow in a synthesis solution to form a dense film with controlled thickness. The versatility of the method may be of great value in the development of novel applications. Films have been tested in membrane and sensor applications with successful results.
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| 18. |
- Hedlund, Jonas, et al.
(författare)
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Synthesis of ultra thin films of molecular sieves by the seed film method
- 1997
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Ingår i: Progress in zeolite and microporous materials. - Amsterdam : Elsevier. - 0444823441 ; , s. 2203-2210
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Konferensbidrag (refereegranskat)abstract
- A novel and flexible technique for synthesizing continuous ultra thin (<100 nm) molecular sieve films on substrates has been developed. The technique consists of two steps. A monolayer of discrete colloidal zeolite seed crystals is adsorbed on the substrate, whereafter the crystals are allowed to grow into a continuous film upon hydrothermal treatment in a molecular sieve precursor solution. The technique is exemplified by the formation of silicalite-1 films on silicon wafers. The final film thickness in the examples presented was in the range 80 and 800 nm. The films are continuous and crystalline as confirmed by SEM, Kr-adsorption data, ellipsometry, XRD and FTIR.
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| 19. |
- Hedlund, Jonas, et al.
(författare)
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Thin zeolite NA films by the seed film method
- 1999
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Ingår i: Proceedings of the 12th International Zeolite Conference. - Warrendale, Pa : Materials Research Society. - 1558994637 ; , s. 1857-1862
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Konferensbidrag (refereegranskat)
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| 20. |
- Hedlund, Jonas, et al.
(författare)
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Ultrathin oriented zeolite LTA films
- 1997
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Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; :13, s. 1193-1194
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin oriented films of zeolite LTA are prepared on single-crystal alumina supports by a method including adsorption of LTA seeds on the support followed by hydrothermal film crystallization.
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| 21. |
- Hedlund, Jonas, et al.
(författare)
-
ZSM-5 membranes synthesized without organic templates using a seeding technique
- 1999
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 159:1-2, s. 263-273
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Tidskriftsartikel (refereegranskat)abstract
- Porous α-alumina supports were seeded with colloidal TPA-silicalite-1 crystals and calcined. The supports were treated in a synthesis solution to grow the seed crystals into ZSM-5 films. The synthesis solution was free from organic template molecules in order to avoid the calcination step which often introduces cracks in the synthesized zeolite film. An SEM investigation indicated that the zeolite films on the supports were defect free and that the film thickness was approximately 1.5 μm. XRD data showed that the film consisted of well-crystallized ZSM-5. The permeance in single gas experiments decreased in the order H2O, H2, CO2, O2, N2 and CH4. The difference in permeance between each molecular species in the series was almost one order of magnitude which indicated that the membranes were of a high quality. Molecules larger than CH4 permeated with similar and low rates, independent of their kinetic diameters, indicating a non-selective permeation path through defects in the zeolite films. However, the permeance of these larger molecules was less than 1/10 000 of that for H2O. The highest measured separation factors for binary mixtures of N2/SF6 and H2/i-C4 were 110 and 99.
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| 22. |
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| 23. |
- Jareman, Fredrik, et al.
(författare)
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Effects of aluminum content on the separation properties of MFI membranes
- 2003
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Ingår i: Separation and Purification Technology. - 1383-5866 .- 1873-3794. ; 32:1-3, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- MFI membranes with almost identical film thickness and defect distribution but different Si/Al ratio were evaluated by separation of butane and hexane isomers. Film thickness was evaluated by SEM and defect distribution by porosimetry. When the temperature was varied, the membranes showed similar separation trends for butanes, but clear differences were observed for hexane separation. The hexane separation factor varied with temperature for the silicalite-1 membrane but was constant for the ZSM-5 membrane. It is believed that this difference may be a result of differences in adsorption properties.
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| 24. |
- Jareman, Fredrik, et al.
(författare)
-
Modelling of single gas permeation in real MFI membranes
- 2004
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 236:1-2, s. 81-89
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Tidskriftsartikel (refereegranskat)abstract
- A novel permeation model for flow through defects and zeolite pores in real MFI membranes, also accounting for substrate effects has been developed. Defect distributions for two types of MFI membranes were determined from porosimetry data using the model, which incorporated the Horvath Kawazoe (micropores) or the Kelvin equation (mesopores). The narrowest (1.08 nm) and also most common defects were found to be separated with a distance of 10–40 μm according to the model. Diffusion coefficients for hydrogen, helium, nitrogen and SF6 in the zeolite were further determined from single gas permeation data using the model using the independently determined defect distribution. The coefficients are consistent with values previously reported in the literature.
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| 25. |
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| 26. |
- Kornmann, Xavier, et al.
(författare)
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Nanocomposites based on montmorillonite and unsaturated polyester
- 1998
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Ingår i: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 38:8, s. 1351-1358
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Tidskriftsartikel (refereegranskat)abstract
- The concept of nanoscale reinforcement provides opportunity for synthesis of new polymer materials with unique properties. Montmorilonite (MMT) was derived from bentonite, purified, activated by sodium ions and mixed with reacting unsaturated polyester (UP). X-ray and transmission electron microscopy data were in support of the formation of a partially delaminated nanocomposite material. At an MMT content of only 1.5 vol%, the fracture energy, GQ of the nanocomposite was doubled, 138 J/m2 as compared with 70 J/m2 for the pure UP.
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| 27. |
- Lassinantti-Gualtieri, Magdalena, et al.
(författare)
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Accurate measurement of the thermal expansion of MFI zeolite membranes by in situ HTXRPD
- 2004
-
Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 703-709
-
Konferensbidrag (refereegranskat)abstract
- Template removal by calcination of MFI type membranes is often accompanied by crack formation. The thermal behavior of MFI type membranes, synthesized with and without masking, was studied to understand the mechanism. Masking prevents growth of zeolite in the interior of the Support during membrane synthesis. Rietveld refinements of powder diffraction data collected in situ at high temperature allowed to accurately determine the change in thermal expansion of the MFI film and the porous alpha-alumina support. During heating, a relatively large contraction of the cell volume during template removal occurred in the zeolite powder and in the film of the membrane prepared with masking. The much smaller decrease in the non-masked sample indicates that this membrane is under stress during heating and as a consequence, cracks are formed. The stress imposed in the membrane prepared without masking may be due to the opposite thermal behavior of the Substrate in combination with strong bonds between the membrane and the support.
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| 28. |
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| 29. |
- Lassinantti, Magdalena, et al.
(författare)
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Faujasite-type films synthesized by seeding
- 2000
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 38:1, s. 25-34
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Tidskriftsartikel (refereegranskat)abstract
- Thin and continuous Faujasite-type films were synthesized on α-alumina wafers using a seeding technique. Surface modified wafers were seeded with colloidal zeolite Y crystals prior to film growth in a synthesis mixture. The effects of hydrothermal treatment on film thickness, morphology and preferred orientation of the crystals constituting the film were investigated using scanning electron microscopy and X-ray diffraction. During hydrothermal treatment a precipitate formed rapidly, leaving an almost clear solution in the upper part of the reactor. Experiments at 60–100°C were performed with the sample placed in the upper part of the synthesis solution. An increase in the film growth rate with increasing temperature was observed. Adsorbed seeds were shown to be oriented with the {1 1 1} pyramid, parallel to the substrate surface. A change in the orientation with film growth was noted, probably due to the attachment of secondary crystals to the growing film surface. In one experimental series, film growth was effected at the bottom of the tube at 100°C. Faster film growth and multilayered films were obtained. A decrease in the film thickness after prolonged hydrothermal treatment was observed in all experimental series. This is probably due to the dissolution of the film and formation of zeolite P in the synthesis solution. The thicknesses of the films synthesized in this work are in the range of 150–2700 nm. The films are promising candidates for use in membrane applications.
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| 30. |
- Lassinantti, Magdalena, et al.
(författare)
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Preparation and evaluation of thin ZSM-5 membranes synthesized in the absence of organic template molecules
- 2001
-
Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 67:1-3, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Porous α-alumina supports with a pore size of 100 nm were seeded with colloidal TPA-silicalite-1 crystals with a size of 120 nm. The seeded supports were calcined and treated in a synthesis solution free from organic template molecules to form ZSM-5 films on the supports. According to SEM images, the films were about 2 μm thick and no defects could be found on the as-synthesized membranes. Single gas permeation data was collected and good quality membranes (defined as having a non-detectable permeance of SF6 after drying at 100°C) were further evaluated using binary/ternary gas mixtures. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Water was selectively separated from a helium-diluted vaporized water/ethanol azeotrope with a maximum selectivity of 12.4.
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| 31. |
- Lassinantti, Magdalena, et al.
(författare)
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Synthesis of thin zeolite Y films on polished α-alumina wafers using a seeding technique
- 1999
-
Ingår i: Porous materials in environmentally friendly processes. - Amsterdam : Elsevier. - 0444502440 - 9780444502445 ; , s. 181-187
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Konferensbidrag (refereegranskat)abstract
- Zeolite Y films were synthesized on polished α-alumina wafers by using a seeding technique which includes surface modification, seed adsorption and growth of the seed crystals into a dense film. The film thickness was found to be a linear function of synthesis duration up to a certain point. Further treatment reduced the film thickness. Continuous and crack free films with thicknesses in the range 210 to 2670 nm were synthesized in this work.
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| 32. |
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| 33. |
- Li, Q., et al.
(författare)
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Nucleation period for TPA-silicalite-1 crystallization determined by a two-stage varying-temperature synthesis
- 1999
-
Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 31:1, s. 141-150
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Tidskriftsartikel (refereegranskat)abstract
- A two-stage-varying-temperature synthesis procedure, which involves a rapid change in temperature at some point during the course of crystallization, was applied to the synthesis of discrete colloidal particles of TPA-silicalite-1. As the duration of the period at the initial synthesis temperature was extended, the crystal concentration and ultimate crystal size varied until they were approximately equal to those obtained for a complete synthesis at the initial temperature. At this point in the crystallization, it was concluded that the nucleation stage was completed. For syntheses performed at 60, 80 and 100°C, the duration of the nucleation period determined by this method was about 100 h, between 4 and 6 h and less than 2 h, respectively. Thus, nucleation, for this system, is a continuous process, and it was found that the rate of nucleation, which is initially high, declines, throughout the nucleation period. In all cases, nucleation occurred during an induction period when little or no crystal growth was observed, which explains why the syntheses yielded a product with a rather narrow crystal size distribution. If, for the two-stage syntheses, the temperature change was made after completion of the nucleation period, the second synthesis temperature controlled only the linear growth rate of the crystals and the final yield of silicalite-1 obtained
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| 34. |
- Li, Qinghua, et al.
(författare)
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Synthesis and characterization of zoned MFI films by seeded growth
- 2002
-
Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 56:3, s. 291-302
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Tidskriftsartikel (refereegranskat)abstract
- Supported zoned and sandwiched MFI films were prepared by a two-step crystallization procedure, using seeds. In this work, a zoned MFI film is defined as one assembled by crystals propagating from the support to the film top surface with varying Al content along the length of the crystal. A sandwiched MFI film is referred to as one assembled by at least two layers of crystals. Six types of films were prepared, both zoned and sandwiched, with a high or a low Al-content in the ZSM-5 part and with varying order of the layers, i.e. ZSM-5 coated with silicalite-1 or vice versa. The films were characterized by SEM and TEM. The Al-distribution was measured by cross-sectional EDS, and the preferred orientation of the crystals could be determined by XRD. Truly zoned films are obtained when the compositional difference between the layers is relatively small, and the synthesis conditions are similar or when the first layer is silicalite-1. If the first layer is ZSM-5 and the synthesis conditions and/or the composition vary too much, a discontinuity occurs at the interface between the layers, and sandwiched film results, where nucleation of the second layer is initiated by secondary nucleation or by applying seeds.
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| 35. |
- Li, Qinghua, et al.
(författare)
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The nucleation period for crystallization of colloidal TPA-silicalite-1 with varying silica source
- 2000
-
Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 40:1-3, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- The effect of varying silica source on the nucleation and crystallization of TPA-silicalite-1 was investigated. A direct experimental method, involving a two-stage varying-temperature synthesis, was used to determine the nucleation period for colloidal crystals of TPA-silicalite-1 with different silica sources, including tetraethoxysilane (TEOS) and amorphous silica (Ludox TM and Ludox LS). For syntheses performed at 60°C with TEOS as silica source, the duration of the nucleation was about 72 h, and a very rapid increase in the crystal population occurred during the initial crystallization time. However, with the amorphous silica sources (Ludox TM or Ludox LS), the duration of the nucleation period was extended to about 120 h, and the nucleation profile consisted of a self-accelerating nucleation rate at the beginning of the nucleation period. The two-stage synthesis method could be used to determine the nucleation profile for the various silica sources. However, this technique overestimated the crystal concentration at the earliest stage of nucleation with amorphous silica. The use of amorphous silica gave rise to a broader crystal size distribution compared to that of TEOS. However, it was found that for both TEOS and amorphous silica the vast majority of the nucleation occurred during an induction period when little or no crystal growth was observed. In addition, Raman spectroscopy revealed structural differences between Ludox TM and Ludox LS which may account for differences in the nucleation processes observed for these two amorphous silicas.
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| 36. |
- Li, Qinghua, et al.
(författare)
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The synthesis of small colloidal crystals of TPA-silicalite-1 with short synthesis times and high yields
- 1999
-
Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 125, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- A two-stage varying-temperature crystallization procedure can be used to synthesize particularly small colloidal crystals of TPA-silicalite-1 with reduced synthesis times and high yields. Using this procedure involves starting a synthesis at a reduced temperature which favours the nucleation of a large crystal population. The reduced temperature is maintained throughout the nucleation stage, after which an elevated temperature is used to accelerate the crystal growth and reach higher equilibrium yields favoured by higher temperatures
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| 37. |
- Li, Qinghua, et al.
(författare)
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Zoned MFI films by seeding
- 2001
-
Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; 2001:6, s. 527-528
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of zoned MFI films consisting of intergrown TPA-silicalite-1 and ZSM-5 crystals are described.
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| 38. |
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| 39. |
- Mattsson, Rosa, et al.
(författare)
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Influence of abietic acid, betulinol, sodium oleate and tripalmitine on the migration of akd in paper
- 2003
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 29:8, s. 281-
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Tidskriftsartikel (refereegranskat)abstract
- The migration of alkylketene dimer (AKD) wax through untreated paper and through paper sheets impregnated with extractives was investigated at temperatures above themelting point of the wax. The migration was studied at 80and 105°C by using various combinations of untreated paper sheets, paper sheets impregnated with AKD and sheets impregnated with extractives. The migration was observed by measuring contact angles with distilled water. There is no indication that extractives such as betulinol, oleate or tripalmitine interfere with the migration of AKD. The diffusion coefficient for AKD in paper was estimated to be of the order of 10–11 m2/s at the temperatures investigated.
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| 40. |
- Mattsson, Rosa, et al.
(författare)
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Sizing with pre-flocculated alkylketene dimer (AKD) dispersions.
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 17:3, s. 240-245
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Tidskriftsartikel (refereegranskat)abstract
- Pre-flocculated AKD dispersions were used to size laboratory sheets. The cationic AKD dispersion was pre-flocculated in a Britt Dynamic Drainage Jar. Carboxymethylcellulose and white water from a linerboard mill were used as flocculating agents. The particle size distribution was determined to verify the flocculation. Laboratory sheets sized with pre-flocculated AKD dispersions were made in a dynamic sheet former. The sizing efficiency was evaluated with the 60-second Cobb value, contact angle measurements and quantitative analysis of the total AKD content in the laboratory sheets. The results show that sizing with pre-flocculated AKD improved the sizing efficiency significantly, due to an increased retention. This clearly indicates that agglomerates can be used for internal sizing provided that the flocculation process is controlled. (14 refs.)
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| 41. |
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| 42. |
- Mihailova, B., et al.
(författare)
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Infrared spectroscopic study of a γ-mercaptopropyltrimethoxysilane monolayer on a gold surface
- 1999
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 9:7, s. 1507-1510
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Tidskriftsartikel (refereegranskat)abstract
- Reflectance-absorption infrared spectra of ?-mercaptopropyltrimethoxysilane (?-MPT) adsorbed on Au (111)-oriented films are analyzed on the basis of the calculated vibrational modes of a monomer, a dimer and n-membered rings of SiO3R (R=CH2CH2CH2SAu). The results show that the ?-MPT molecules adsorbed on the Au surface are partially hydrolyzed and that the orientation of the methyl groups and propyl chains are near perpendicular to the surface. After a hydrolysis procedure, the SiO3 groups in ?-MPT form a quasi two-dimensional system built predominantly of 6-membered puckered Si-O rings. Additional treatment of the ?-MPT monolayer with a surface-charge-reversing cationic polymer disrupts the connectivity and increases the topological disorder in the silicate system.
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| 43. |
- Mihailova, B., et al.
(författare)
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Raman scattering in locally inhomogeneous oxide crystals
- 2003
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Ingår i: Phase Transitions. - : Informa UK Limited. - 0141-1594 .- 1029-0338. ; 76:1-2, s. 17-32
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Tidskriftsartikel (refereegranskat)abstract
- Local-scale atomic arrangements in three types of oxide crystalline materials with structural defects, self-bonded molecular sieves, ferroelastics and relaxor ferroelectricity, are investigated by Raman spectroscopy. The experimentally observed spectral data are analysed through normal mode calculations for structural species representative of the intermediate range order in the solid. In the case of molecular sieves, the important role of incipient structural species for producing crystalline silicalite-1 and zeolite beta spheres of mm size is shown. In the case of ferroelastics, further insights on structural perturbation across the domain walls in monoclinic Pb 3(PO4)2 are provided. In the case of relaxors, the local structure and related dynamical effects in PbSc0.5Nb 0.5O3 and PbSc0.5Nb0.5O3 is revealed.
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| 44. |
- Mihailova, B., et al.
(författare)
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Vibrational spectroscopy study of the structure of silicalite-1 films on a gold surface
- 1999
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 32:3, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- The structure of silicalite-1 films grown on seeded gold surfaces is investigated by modelling the observed changes in the infrared reflection absorption (IRRA) spectra of samples treated for different times in the synthesis solution. The results show that a gradual deformation of the five-membered silicon-oxygen rings occurs during the first 11 h of the hydrothermal treatment which leads to breaking of Si---O---Si linkages and to formation of linear defects along the c-axis. Interactions between the dislocations and the grain boundaries during the further growth of the film provoke the appearance of void spaces in the grain boundary interface which may cause incipient cracking in the silicalite-1 films on seeded gold surfaces. The range 1000-1300 cm-1 in the IRRA spectra is found to be appropriate for estimating the quality of silicalite-1 films grown on metal surfaces.
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| 45. |
- Mintova, Svetlana, et al.
(författare)
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Continuous films of zeolite ZSM-5 on modified gold surfaces
- 1997
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Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; :1, s. 15-16
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Tidskriftsartikel (refereegranskat)abstract
- Thin continuous films of zeolite ZSM-5 on gold surfaces are prepared by a novel method including silanization, charge modification and seeding of the surface prior to the hydrothermal crystallization of the zeolite.
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| 46. |
- Mintova, S., et al.
(författare)
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Growth of silicalite-1 films on gold substrates
- 1997
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Ingår i: Microporous Materials. - 0927-6513 .- 1873-3107. ; 11:3-4, s. 149-160
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Tidskriftsartikel (refereegranskat)abstract
- The crystallization of thin continuous silicalite-1 films on modified gold surfaces prepared at 100°C in clear precursor solutions has been studied by grazing angle X-ray diffractometry, infrared spectroscopy, dynamic light scattering, scanning electron microscopy, Kr adsorption and ellipsometry. The gold surfaces were pre-treated with a silane coupling agent, gamma-mercaptopropyltrimethoxysilane, and hydrolysed in an acidic solution, pH < 4, to create a modified negatively charged interface on which positively charged colloidal silicalite-1 seed crystals were adsorbed. The colloidal seed crystals are believed to be preferentially adsorbed with their {010} face parallel to the Au surface. Continued growth of the oriented seed crystals in a following hydrothermal step results in the formation of a continuous thin oriented crystalline film. The mechanism for the formation of silicalite-1 films on Au is discussed
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| 47. |
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| 48. |
- Mintova, Svetlana, et al.
(författare)
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Preparation of zeolite Y-vegetal fiber composite materials
- 1996
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Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 3:3, s. 143-150
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Tidskriftsartikel (refereegranskat)abstract
- Zeolite Y crystallization on chemi thermo mechanical pulp (CTMP) fluff, linen and cotton substrates using two different approaches for the deposition was studied. In the first approach a seed-film method was applied. This method involves surface charge modification of the substrates, adsorption of a monolayer of colloidal zeolite Y crystals onto the surfaces and subsequent growth of these colloidal zeolite crystals into a continuous zeolite film. Application of this method resulted in continuous films of zeolite Y on all substrates investigated. The second approach involved direct synthesis on substrates subjected to chemical or mechanical pretreatment in order to modify their surface properties. Chemical treatment was found to improve the crystallization on cotton and linen fibers but not so for the CTMP. Mechanical pretreatment enhanced the zeolite crystallization on the linen fibers but not on the other substrates. The zeolite Y-vegetal fiber composites were characterized by SEM, XRD, and thermal analysis.
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| 49. |
- Mintova, Svetlana, et al.
(författare)
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Preparation of ZSM-5 films from template free precursors
- 1997
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 7:12, s. 2341-2342
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of zeolite ZSM-5 on quartz substrates have been prepared in the absence of organic templates by growth of adsorbed seed crystals attached to a polymer-modified substrate surface.
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| 50. |
- Mintova, Svetlana, et al.
(författare)
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ZSM-5 films prepared from template free precursors
- 1998
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 8:10, s. 2217-2221
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Tidskriftsartikel (refereegranskat)abstract
- Thin continuous films of zeolite ZSM-5 were synthesized on quartz substrates. The substrates were first surface modified and covered by a monolayer of colloidal silicalite-1 seed crystals. These crystals were grown into continuous films with thicknesses in the range 230-3500 nm by hydrothermal treatment in a synthesis gel free from organic templates. The preferential orientation of the crystals constituting the film was initially one with thec-axis close to parallel to the substrate surface. During the course of crystallization this orientation changed to one with most of the crystals having the c-axes directed approximately 35° from perpendicular to the substrate surface. A mechanism explaining this behavior is proposed. The final thickness of the film was controlled by the synthesis time but also by the addition of seed crystals to the synthesis gel. Films prepared according to this method may be of great value for the development of zeolite based membranes.
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