| 1. |
- Anderson, Michael W., et al.
(författare)
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Intergrowths of cubic and hexagonal polytypes of faujasitic zeolites
- 1991
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Ingår i: Journal of the Chemical Society, Chemical Communications. - 0022-4936. ; :23, s. 1660-1664
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Tidskriftsartikel (refereegranskat)abstract
- Intergrowths of hexagonal and cubic phases of faujasitic structure have been synthesised using crown ether templates and the phase integrity monitored by high-resolution electron microscopy.
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| 2. |
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| 3. |
- Han, Lu, et al.
(författare)
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Silica-Based Nanoporous Materials
- 2014
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Ingår i: Zeitschrift für Anorganische und Allgemeines Chemie. - : Wiley. - 0044-2313 .- 1521-3749. ; 640:3-4, s. 521-536
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Forskningsöversikt (refereegranskat)abstract
- Ordered nanoporous structures are among the most fascinating and industrially important materials currently in use. The archetypal zeolite material has now been joined by an eclectic array of new structures that exhibit porosity over a wide range of length scales and with order/disorder expressed in a multitude of ways. This raises the bar in terms of characterization and extends a real challenge to the scientific community to fully understand the properties and potential future applications of such materials. In this review we discuss the importance of modern microscopy tools combined with diffraction in this endeavour and show how the details of even the most complex quasi-crystalline nanoporous architectures can be elucidated. We show by using the appropriate spherical aberration (C-s) corrections in scanning transmission electron microscopy it is possible to decipher all the individual silicon and aluminum atoms in a zeolite structure. Automated routines for using large electron diffraction datasets for crystal structure determination of nanocrystals is described making the need for large single crystal synthesis less-and-less important. The power of complementary combinations of surface tools such as atomic force microscopy and high-resolution scanning electron microscopy is discussed to elucidate crystal growth mechanisms. For mesoporous materials synthesized from self-organized organic mesophases electron microscopy reveals the details of the complex hierarchy of porosity so crucial for the functional performance of the structure.
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| 4. |
- Li, Huachun, et al.
(författare)
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Mesoporous silicalite-1 zeolite crystals with unique pore shapes analogous to the morphology
- 2007
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 106:03-jan, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- Thermal/hydrothermal stable silicalite-1 zeolite with high-porosity mesopores analogous to the crystal morphology has been synthesized by using large porous carbon (10-20 nm) as hard template originated from colloidal silica.
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| 5. |
- Muroyama, Norihiro, et al.
(författare)
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Argon adsorption on MCM-41 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:29, s. 10803-10813
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Tidskriftsartikel (refereegranskat)abstract
- Equilibrium argon adsorption from the gas phase on mesoporous MCM-41 silica of hexagonal structure is directly studied by in situ synchrotron powder X-ray diffraction (XRD) measurements at SPring-8. The diffraction intensity data is analyzed by extending the previously developed analytical formula for the crystal structure factors of MCM-41 to account for argon adsorbed in the pores. It is clearly observed that argon adsorbs in layers on the pore walls at low gas pressures and exhibits sudden capillary condensation as the gas pressure increased. The proposed method of interpretation of XRD data allows one to calculate the density ratio between the silica wall and condensed argon, the pore size, and the pore wall fluctuation/roughness, together with the thickness of the adsorbed layer as a function of the gas pressure. The results of in situ XRD experiments are compared with the results of argon adsorption volumetric experiments. The adsorption data are interpreted with the quench solid density functional theory (QSDFT), which takes into account the pore wall roughness. The perfect agreement of the QSDFT isotherm predicted from the adsorption data and the XRD recalculated isotherm suggests that the adsorption porosimetry and XRD measurements can be reconciled provided a proper interpretation of the experimental data.
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| 6. |
- Ohsuna, Tetsu, et al.
(författare)
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TEM image simulation of mesoporous crystals for structure type identification
- 2011
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Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 13:4, s. 736-744
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Tidskriftsartikel (refereegranskat)abstract
- Software, MesoPoreImage, for transmission electron microscope (TEM) image simulation of mesoporous crystals was developed. MesoPoreImage provides two-dimensional (2D) projected potential distributions along any directions as well as corresponding 2D TEM images calculated from a three-dimensional (3D) density distribution of an ideal mesoporous structure. In order to adjust the contrast of simulated TEM images to that observed, a parameter representing surface roughness on the pore surface is introduced. Simulated TEM images of four typical silica mesoporous crystals, MCM-48, AMS-10, SBA-16 and SBA-6 are shown and compared with observed ones, which shows the usefulness of the software for identification of the mesoporous structure type. A procedure for the identification of structure types of mesoporous crystals by using TEM and the simulation software is fully described.
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| 7. |
- Söderberg, Karin, 1976-
(författare)
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Structure and Stability of Bi1-xSbx and CaAl2-xZnx
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused on two intermetallic systems Bi1-xSbx and CaAl2-xZnx. Bi and Sb transform into a peculiar incommensurate composite structure under pressure and our intention was to examine the structure and how alloying influences this incommensurate structure. Our investigation was obscured by the occurrence of a phase separation, which accompanied the transition A7 → Bi III. Most remarkable is the finding that structural parameters of phases with the Bi III composite structure were observed to be almost unaffected by pressure and composition effects. Secondly, phase and structural stability relations within the AB2 pseudo-binary system CaAl2-xZnx was studied. In CaAl2-xZnx, the C36-type Laves phase was observed for the first time, but not the C14-type, and a VEC induced structural transition C15-type → C36-type takes place with increasing x. The exchange of Al by Zn decreases the size of the B-type atom network surrounding Ca and at concentrations x > 0.95, the Laves phase structure is succeeded by the CeCu2 type structure, which tolerates a larger size ratio A/B. The C15-type → C36-type transformation in the CaAl2-xZnx system is induced by the valence electron concentration VEC. Through the analysis of MEM/Rietveld from synchrotron powder X-ray diffraction data, the total charge distributions and deformation charge densities were obtained for cubic and 4H hexagonal Laves phases in CaAl2-xZnx and also for orthorhombic CaZn2. The overlap electrons, which take an important role in stabilising the crystal structures, are clearly observed in the Kagome-net between B-net atoms. The Ca atoms are located in the space formed by the B-net atoms. From the high-pressure experiments it was concluded that at elevated temperatures, 1000-1500 °C, the hexagonal C36 structure type transforms to the C15 structure type between 6.2 and 9.4 GPa, and the orthorhombic CeCu2 phase to a hexagonal Laves phase between 7.5 and 15.5 GPa.
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| 8. |
- Wu, Xiaowei, et al.
(författare)
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A Novel Route for Synthesizing Silica Nanotubes with Chiral Mesoporous Wall Structures
- 2007
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Ingår i: Chemistry of Materials. - 0897-4756 .- 1520-5002. ; 19:7, s. 1577-1583
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Tidskriftsartikel (refereegranskat)abstract
- Right- and left-handed excess chiral mesoporous silica nanotubes with a helical channel in the wall have been formed by the self-assembly of an achiral surfactant sodium dodecyl sulfate (SDS) in the presence of (R)-(+)- and (S)-(-)- 2-amino-3-phenyl-1-propanol ((R)-(+)- and (S)-(-)-APP) chiral molecules. Transmission electron microscopy combined with computer simulations confirmed the presence of ordered chiral channels winding around the central axis of the tubes of similar to 100 nm inner diameter. Furthermore, it has been found that these have been produced through a specific crystallization route that hollows out the chiral mesoporous silica rod, which is different from the tube synthesis pathways reported previously. The enantiomeric excess ee of chiral mesoporous silica has been increased from 0 to a maximum value of 32% with increasing (R)-(+)-APP/SDS molar ratios from 0 to 0.8.
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