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High pressure behaviour of AIP04-5 in penetrating/ non penetrating pressure medium
Full text linkAluminophosphate are objects of a growing research interest due to their potential technologieal and industriaI applications [e.g 1,2]. Their large channels serve as ideaI host for organie compounds and small polymers. Among those, AIP0-5 is a synthetic zeolite characterized by an open-framework of (P,AI)O4 tetrahedra. The tetrahedra are connected to form six-and twelve-membered rings, in such a way that a large channel (0~7.3À), parallel to the [001] direction, occurs. Klap et al. [3] underlines that every crystal of AIP0-5 is built up by three different microdomains, in which the positions of the framework oxygen atoms are slightly different; the main effect of the structural disorder is the very large anisotropie displacement parameters of the framework oxygens. We performed two in situ single-crystal synchrotron X-ray diffraction experiments using both penetrating (methanol:ethanol:H20 mix, m:e:w) and non-penetrating (silicon oil) pressure media [4]. The structure refinements showed that: 1) for compression in m:e:w mix, H20 molecules are absorbed at low-P regime, forming a H20-network by H-bonding interaction; 2) the elastic parameters of the super-hydrated AIP04 5 are different if compared to the one compressed in silicon oil; 3) the structural deformation mechanisms of super-hydrated and regular AIP04 -5 are different; 4) evidence of a incommensurately modulated structure occur (according to [3]), and there is an evolution of the non-Bragg reflections with pressure.
The author acknowledges the ltalian Ministry of Education, MIUR-Project: "Futuro in Ricerca 2012 -ImPACT-RBFR12CLQD".
[lJ Tang Z.K. et al. Applied Physies Letters 1998; 73, 2287-2289.
[2] Yang W.S. et al. Microporous and mesoporous materials 20i6; 219,87-92. [3J Klap G.J. et al. Mieroporous and mesoporous materials 2000; 38,403-412. [4J Gatta, G.D. Mieroporous and Mesoporous Material 2010; 128, 78-84
Growth Morphology and Segregation of Sucrose Crystals Grown from Aqueous Solutions in the Presence of Raffinose.
No full textSucrose crystals grown from aqueous solutions in the presence of Raffinose are elongated in the [010] direction, together with more and more simpler Morphologies, as higher is the additive concentration in the solution [Craff(sol)]. The Raffinose concentration inside the host crystal [Craff(cryst)] changes both with Craff(sol) and with the different growth sectors. The plot (Craff( cryst) vs Craff(sol)] at T = 40 °C and supersaturation 0,080 is not monoatomic , but can be approximated by two straigh lines with opposite slopes, below and above Craff(sol)= 4%, respectively, according with the strongest habit modifications. The differences between the Raffinose segregated in the complementary sectors (110) and (-1-10) reaches one order of magnitude, according with the strog different ability of surface adsorption on the corresponding faces
Face-by-face growth of sucrose crystals from aqueous solutions in the presence of raffinose-II: Growth morphology and segregation
No full textRaffinose segregation into sucrose crystals is experimentally determined along with the modifications of the quantitative sucrose growth morphology, which are in turn related to the different growth conditions. (Craff, σ) morphodromes nicely represent the conflict between the supersaturation and the raffinose concentration in the solution on the growth morphology, while the overall segregation rate is nearly proportional to the linear overall crystal growth rate. Chernov and Burton-Prim-Slichter models, checked to fit our keff and ln (keff- 1 - 1) coefficients as a function of the supersaturation and of the mean linear overall growth rate, do not allow to know whether the segregation occurs either by a process dominated by surface integration, or by additive transfer dominated by volume diffusion within the boundary layer. The distribution of segregated raffinose strictly depends on the {h k l} growth sectors and doped crystals contain deformed lattice zones, as it comes out from X-ray..
(100) and (111) Forms of NaCl-like Crystals Coexisting in Growth from Pure Aqueous Solution.
No full textThe Authors prove, by means of SEM, the co-existence of (100) and (111) forms in pure aqueous solution in well defined supersaturation range. The consequences of the "octopole hypothesis" is discussed. Finally, according to the calculation of the reconstructed (111) surfaces, the equilibrium shape of the crystals was determined
Face-by-face growth of sucrose crystals from aqueous solutions in the presence of raffinose. I. Experiments and kinetic-adsorption model
No full textExperimental growth kinetics of {1 0 0}, {1 0 1̄}, {1 1 0} and {1̄ 1̄ 0}, the four most important F (flat) forms of sucrose crystal, has been investigated within a range of low supersaturations (0.040 ≤ σ ≤ 0.080) and under varying raffinose concentrations (0.0≤Craff≤8.0% H2O). The comparison with growth isotherms determined in pure solution confirms that raffinose dramatically slows down the growth rates of the first three forms, which still go on growing by the screw dislocation mechanism. Further, dead zones occur for both the {1 0 1̄} and {1 1 0} forms. On the contrary the {1̄ 1̄ 0} form is weakly affected, at least up to Craff≈3% H2O, owing to the low structural compatibility between its surface sites and the adsorbed raffinose molecules. Both Cabrera-Vermilyea and Kubota-Mullin models, associated with Langmuir-type equilibrium isotherms, are tested to find the more suitable description of the kinetic behaviour in the presence of raffinose. The Kubota-Mullin model resulting the be..
Growth kinetics, adsorption and morphology of sucrose crystals from aqueous solutions in the presence of raffinose
No full textExperimental growth kinetics of the most important F forms of sucrose crystal, {100}, {110}, {101̄} and {1̄1̄0}, has been investigated at T = 40&C within a range of supersaturations (σ = 0.040 and 0.080), in the presence of varying raffinose concentrations (0.0 ≤ Craff 8.0 % H2O). Raffinose dramatically slows down the growth rate of the first three forms, modifies the shape of their growth isotherms and can induce dead zones as well, the effects increasing with its concentration. However, the screw dislocation mechanism maintains. The comparison between Kubota-Mullin and Cabrera-Vermilyea kinetic models shows that the first one better describes our experimental data. This allows to deduce that the raffinose adsorption mainly occurs at the kinks sites of all the interested forms. Moreover, the values of the effectiveness coefficient of KM model shows the combined effects of supersaturation and raffinose concentration in the growth solutions. On the contrary, the {1̄1̄0} form is weakly affected by raffinose, owing to the low structural compatibility between its kinks and the additive molecules. Finally, the changes of the crystal morphology, induced by the highly anisotropic kinetic effects, were studied as well. Increasing raffinose concentration and supersaturation produces conflicting effects on the morphology: the first one promotes crystals elongated in the [010] direction and reduces the number of forms on the crystals, while supersaturation acts in the opposite sense. Ratios among the main dimensions of crystals are critically discussed to evaluate their final shapes. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High-P behaviour of zeolites in “penetrating” fluids: Recent insights and new opportunities from XPRESS, the high-P dedicated diffraction beamline at ELETTRA
No full textThe high-pressure behavior of zeolites when compressed in potentially “penetrating” fluids, i.e. those whose molecules can be intruded into the zeolitic structural micropores, has recently been a subject of growing research interest. Pressure-mediated intrusion of molecules can induce changes in the physical and chemical properties of zeolites, thus offering an excellent tool for the tailoring of the properties of these industrially relevant materials. In situ experiments on SiO2-ferrierite (FER; Lotti et al., 2015) and AlPO4-5 (AFI; Lotti et al., 2016) zeolites, conducted in diamond anvil cells (DACs) using “penetrating” pressuretransmitting fluids, showed that theP-induced intrusion of molecules can be readily recognized from the synchrotron single-crystal and powder diffraction data. In case of FER, the complex patterns of phasetransitions at increasing pressure reveal the intrusion, whereas for AFI, the drastically different compressibilities provide evidence of this process. In this scenario, recently commissioned dedicated highpressure diffraction beamline Xpress, at the Elettra synchrotron light-source (Trieste, Italy), represents a new facility for high-pressure investigations in the field of geomaterials, using X-ray diffraction. Xpress is part of a scientific partnership between Italy and India (Indian Institute of Science, Bangalore). At Xpress, a liquid nitrogen cooled silicon single crystal, cut along the [111] direction, intercepts the beam from multipole superconducting wiggler source and deflects it at a fixed energy of 25 keV. The beam is focused using a toroidal mirror of 1.4 m length and 2.9 mrad grazing angle. The mirror is Pt coated to achieve 80% reflectivity at 25 keV. Focused beam from the mirror is further optimized by collimators (ranging from 30 to 200 micrometer in diameter), in order to have intense and well defined monochromatic beam for the HP-XRD experiments. On-line pressure monitoring is achieved through a ruby fluorescence microscope. The present experimental stage is equipped to host different kinds of DACs, in order to permit room-temperature - highpressure experiments in the pressure range 0-50 GPa. An image plate MAR345 with a controllable linear
movement along the beam direction is available for the collection of the diffraction pattern. The setup for hosting in-situ high-P single-crystal X-ray diffraction experiments is under development and will be available for users in the near future
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