2012
DOI: 10.2138/am.2012.4228
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In situ dehydration behavior of zeolite-like cavansite: A single-crystal X-ray study

Abstract: To track dehydration behavior of cavansite, Ca(VO)(Si 4 O 10 )·4H 2 O [space group Pnma, a = 9.6329(2), b = 13.6606(2), c = 9.7949(2) Å, V = 1288.92(4) Å 3 ] single-crystal X-ray diffraction data on a crystal from Wagholi quarry, Poona district (India) were collected up to 400 °C in steps of 25 °C up to 250 °C and in steps of 50 °C between 250 and 400 °C. The structure of cavansite is characterized by layers of silicate tetrahedra connected by V 4+ O 5 square pyramids. This way a porous framework structure is … Show more

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Cited by 16 publications
(54 citation statements)
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“…The dimorphism of cavansite and pentagonite is based on the different linkages in the silicate layer: in cavansite the tetrahedral chains are joined into fourfold and eightfold rings, whereas in pentagonite only sixfold rings are formed (Evans, 1973). In cavansite, the water removal proceeds in four steps preserving the same space group Pnma with only minor framework distortion and contraction (Danisi et al, 2012). Pentagonite undergoes phase transitions to a monoclinic structure at 448 K and to an orthorhombic structure at 498 K with a decrease of the normalized unit-cell volume by 21% (Danisi et al, 2013).…”
Section: Comparison With the Dehydration Behaviour Of Natural Vanadosmentioning
confidence: 99%
See 1 more Smart Citation
“…The dimorphism of cavansite and pentagonite is based on the different linkages in the silicate layer: in cavansite the tetrahedral chains are joined into fourfold and eightfold rings, whereas in pentagonite only sixfold rings are formed (Evans, 1973). In cavansite, the water removal proceeds in four steps preserving the same space group Pnma with only minor framework distortion and contraction (Danisi et al, 2012). Pentagonite undergoes phase transitions to a monoclinic structure at 448 K and to an orthorhombic structure at 498 K with a decrease of the normalized unit-cell volume by 21% (Danisi et al, 2013).…”
Section: Comparison With the Dehydration Behaviour Of Natural Vanadosmentioning
confidence: 99%
“…In contrast to VSH-13Na, the dehydration behaviour of cavansite was Scanning electron microscope (SEM) images of VSH-13Na crystals: (a) crystals covered by unreacted silica particles and (b) a larger crystal after vacuum filtration and washing. extremely well characterized by ex situ single-crystal X-ray diffraction (Rinaldi et al, 1975), in situ single-crystal X-ray diffraction (Danisi et al, 2012) and in situ synchrotron powder diffraction under dynamic conditions (Martucci et al, 2016;Fisch et al, 2016Fisch et al, , 2017.…”
Section: Introductionmentioning
confidence: 99%
“…In their contribution to the issue, Danisi and Armbruster (2018) report on a step-wise dehydration behaviour of VSH-13Na, a framework vanadosilicate structurally related to the minerals cavansite and pentagonite. By analogy with the latter two (Danisi et al 2012(Danisi et al , 2013, the authors observe the formation of new low and dehydrated phases, in which each new dehydrated state corresponds to a new structure type and a new conformation state of an octahedral-tetrahedral framework.…”
mentioning
confidence: 95%
“…However, the manuscript lacks originality and aim and it is also sloppy prepared (1). The paper should be rejected because the quality of the synchrotron data is by far not sufficient (2) to allow any comparison with X-ray single-crystal data of a very recent paper by Danisi et al (2012). In addition, if the authors aim in their manuscript for kinetic aspects of dehydration of cavansite, experiments with only a single heating rate (3) of 5K/min are insufficient for a meaningful interpretation.…”
mentioning
confidence: 99%
“…In general, temperature dependent powder synchrotron diffraction is a useful method to track dehydration of a zeolite if single crystals are not available or kinetic aspects are systematically investigated. However, in case of cavansite such an approach is not useful because temperature dependent X-ray data have previously demonstrated (Danisi et al, 2012) that at elevated temperature the H2O distribution is strongly disordered. The limited spatial resolution of powder synchrotron data (2) does obviously not allow to detect or to model such disordered arrangements.…”
mentioning
confidence: 99%