34 research outputs found

    Controlling the spatial distribution of aluminum in ZSM-5 crystals

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    The spatial distribution of aluminum over ZSM-5 crystals was systematically studied using electron microprobing on polished crystals. Crystals synthesized with TPABr as template exhibit a pronounced enrichment of aluminum in the crystal rim, essentially irrespective of the aluminum source employed, although aluminum sources with organic anions are favoring less inhomogeneous profiles. With 1,6-hexanediol or from totally inorganic reaction gels, crystals with completely homogeneous aluminum profiles are obtained, even if the crystals grow larger than 50 μm. In the 1,6-hexanediol system the homogeneous profiles could be changed to profiles similar to the TPABr system by addition of KNO3. The results are explained with the competition between the different cations for silicate and alumosilicate species. As long as alkali ions are present in the synthesis gel, they interact favorably with the alumosilicate species. In TPA-based reactions, the TPA primarily induces the structure, incorporating predominantly silicate species, because the alumosilicate species are blocked by alkali ions. In the absence of TPA, i.e., in hexanediol-based syntheses or in inorganic reaction gels, the structure is induced by Na+ ions which also interact favorably with the alumosilicate species, thus incorporating them into the structure already at a very early stage of the synthesis

    Element distribution and growth mechanism of large SAPO-5 crystals

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    The spatial distribution of silicon as T-atom substituent in large optically clear crystals with the AFI structure was studied by electron microprobing. The silicon concentration in the center of the crystals is lower by a factor of two to three than in the other part of the crystals. This is the second example of a microporous material, for which an inhomogeneous heteroelement distribution was observed. This corresponds to the findings of our kinetic studies and previous findings concerning the correlation between silicon content and crystal size. During the early stages of AFI crystal growth we found ‘pencil type’ crystals which develop into hexagonal prisms by flattening of the tips during crystal growth. Increasing silicon content accelerates the morphological change and inhibits lengthwise growth of the crystallites

    Phosphine-Coordinated Pure-Gold Clusters: Diverse Geometrical Structures and Unique Optical Properties/Responses

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    Synthetic techniques, geometrical structures, and electronic absorption spectra of phosphine-coordinated pure-gold molecular clusters (PGCs) accumulated over 40 years are comprehensively collected especially for those with unambiguous X-ray crystal structures available. Inspection of the electronic absorption spectra from geometrical aspects reveals that their optical properties are highly dependent on the cluster geometries rather than the nuclearity. Recent examples of unusual clusters that show unique color/photoluminescence properties and their utilization for stimuli-responsive modules are also presented

    Further characterisation of the 91500 zircon crystal

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    This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses

    Further characterisation of the 91500 zircon crystal

    No full text
    This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and lase
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