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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 140 (2000), S. 16-27 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Frequent inclusions of ferropericlase, some coexisting with phases of MgSiO3, CaSiO3 and SiO2 composition, suggest that a large proportion of diamonds from Guinea are derived from the lower mantle. Low aluminium contents in MgSiO3 inclusions indicate derivation from the uppermost lower mantle, where Al solubility in perovskite is low. Trace element analyses (SIMS) of CaSiO3 inclusions reveal extreme degrees of LREE (200–2000 times chondritic) and Sr enrichment (70–1000 times chondritic) together with negative and positive Eu anomalies. This implies a highly enriched lower mantle source, possibly a product of a subducted oceanic slab. A number of phases that are only stable in the upper mantle are found to coexist with lower mantle phases and thereby indicate retrograde equilibration during slow exhumation within a rising plume or convection cell. In one case, however, an inclusion paragenesis of ferropericlase and olivine can be shown to have formed within the upper mantle, indicating that the occurrence of ferropericlase inclusions alone is an unreliable indicator of lower mantle origin.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0044-2313
    Keywords: Vanadium phosphate ; mixed valence compound V4+/V5+ ; microporosity ; disorder ; open framework ; crystal structure ; single crystal X-ray diffraction ; anti-Keggin group ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Das System Na/V/P/N(C2H5)3/H2O bei 473 K und die neue offene Struktur der Vanadiumphosphat-Phase Nav[((V4-w4+V1+w5+) O9)(PO4)2] · (PO4)x · (OH)y · zH2O (v = 2,8 bis 4,0; w = -0,1 bis 1,1; x = 0 bis 0,2; y = 0 bis 2,1; z = 7 bis 10)Eine Untersuchung des Na/V/P/N(C2H5)3/H2O-Systems bei 473 K unter hydrothermalen Bedingungen ergibt verschiedene Phasen im pH-Bereich von 2,65 bis 12. Bei niedrigen pH-Werten wurde die NaV4+OPO4-Phase erhalten. Im schwach sauren, neutralen und schwach basischen Bereich wurde die Nav[((V4-w4+V1+w5+) O9)(PO4)2] · (PO4)X · (OH)y · zH2O-Phase (oder kurz FVP-1) (mit v = 2.8 bis 4.0, w = -0.1 bis 1.1, x = 0 bis 0.2, y = 0 bis 2.1 and z = 7 bis 10) gefunden. Ihre Kristallstruktur wurde in der Raumgruppe Im3m mit a = 16.025 Å gelöst. Die Kristallstruktur enthält V4+V5+O9(PO4)2-Gruppen, in welchen die Vanadiumatome in quadratisch pyramidaler Koordination mit den Sauerstoffatomen vorliegen. Die Gruppen besitzen die Gestalt einer Pickelhaube, wobei die Spitze die Vanadylgruppe des zentralen V5+ Polyeders ist. Sie sind statistisch um eine Spiegelebene angeordnet und bilden eine V10/2O18/2(PO4)2-Gruppe. Diese sind über die Phosphattetraeder miteinander verknüpft und bilden dabei ein offenes poröses Gerüst, das die Topologie des NbO-Netzes hat. Das Gerüst hat einen freien mittleren Kanaldurchmesser von 4.1 Å und eine Dichte von 10.2 Vanadium- und Phosphatpolyedern pro 1000 Å3. Dieses und zwei verwandte kürzlich gefundene Strukturen sind mikroporöse Gerüste mit der bisher größten gefundenen Porösität. Kein Aluminosilicat oder Aluminophosphat mit einem ähnlich großen Porenanteil ist bisher bekannt geworden. Die FVP-1 Phase kollabiert nicht beim Heizen in Luft bis 523 K und im Vakuum bis 623 K. Sie dehydratisiert und rehydratisiert reversibel. Redoxtitrationen von 19 Proben zeigten, daß das V4+/V5+ Verhältnis zwischen 4.1(2)/0.9(2) un d2.9(2)/2.1(2) variiert. Synthesen mit V25+O5 als Vanadiumquelle ergaben kleinere V4+/V5+ Verhältnisse als solche mit V4+OSO4. Die Tatsache, daß FVP-1 Unordnungserscheinungen zeigt, macht es möglicherweise für katalytische Anwendungen interessant.
    Notes: An examination of the Na/V/P/N(C2H5)3/H2O system at 473 K under hydrothermal conditions yields several different phases in the pH range of 2.65 to 12. At low pH values a NaV4+OPO4 phase was obtained. In the weakly acid, neutral or low basic pH ranges the Nav[((V4-w4+V1+w5+) O9)(PO4)2] · (PO4)x · (OH)y · zH2O (or FVP-1 for short) phase was found (with v = 2.8 to 4.0, w = -0.1 to 1.1, x = 0 to 0.2, y = 0 to 2.1 and z = 7 to 10). Its crystal structure was solved in space group Im3m with a = 16.025 Å. It contains V44+V5+O9(PO4)2 groups in which the vanadium atoms have a square pyramidal coordination of oxygen atoms in the shape of a spiked helmet, where the spike is the vanadyl group of the central V5+ coordination polyhedron. These groups are statistically arranged around a mirror plane yielding an V10/2O18/2(PO4)2 grouping and connect to form an open porous framework by bridging via the phosphate groups following the topology of the NbO type net. The framework has a mean free channel diameter of about 4.1 Å and a density of 10.2 vanadium and phosphorus polyhedra per 1000 Å3. This makes it, together with two other recently found related frameworks, the most open microporous framework described so far. No aluminosilicates or aluminophosphates of similar openness are known. In air the FVP-1 phase does not collapse when heated to 523 K, in vacuum it remains stable to 623 K. It dehydrates and rehydrates reversibly. Redox titrations of 19 samples show that the V4+/V5+ ratios vary from 4.1(2)/0.9(2) to 2.9(2)/2.1(2). Syntheses using V2O5 as a source of vanadium yield samples with lower V4+/V5+ ratios than those based on VOSO4. The fact that FVP-1 displays disorder makes the compound possibly interesting for potential catalytic applications.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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