Effects of temperature on the crystal structure of epidote: a neutron single-crystal diffraction study at 293 and 1070K

The effects of temperature on the crystal structure of a natural epidote [Ca1.925 Fe0.745Al2.265Ti0.004Si3.037O12(OH), a = 8.890(6), b = 5.630(4), c = 10. 50(6) \uc5 and \u3b2 = 115.36(5)\ub0, Sp.Gr. P21/m] have been investigated by means of neutron single-crystal diffraction at 293 and 1,070 K. At room conditions, the structural refinement confirms the presence of Fe3+ at the M3 site [%Fe(M3) = 73.1(8)%] and all attempts to refine the amount of Fe at the M(1) site were unsuccessful. Only one independent proton site was located. Two possible hydrogen bonds, with O(2) and O(4) as acceptors [i.e. O(10)-H(1)\ub7\ub7\ub7O(2) and O(10)-H(1)\ub7\ub7\ub7O(4)], occur. However, the topological configuration of the bonds suggests that the O(10)-H(1)\ub7\ub7\ub7O(4) is energetically more favourable, as H(1)\ub7\ub7\ub7O(4) = 1.9731(28) \uc5, O(10)\ub7\ub7\ub7O(4) = 2.9318(22) \uc5 and O(10)-H(1)\ub7\ub7\ub7O4 = 166.7(2)\ub0, whereas H(1)\ub7\ub7\ub7O(2) = 2.5921(23) \uc5, O(10)\ub7\ub7\ub7O(2) = 2.8221(17)\uc5 and O(10)-H(1)\ub7\ub7\ub7O2 = 93.3(1)\ub0. The O(10)-H(1) bond distance corrected for "riding motion" is 0.9943 \uc5. The diffraction data at 1,070 K show that epidote is stable within the T-range investigated, and that its crystallinity is maintained. A positive thermal expansion is observed along all the three crystallographic axes. At 1,070 K the structural refinement again shows that Fe3+ share the M(3) site along with Al3+ [%Fe(M3)1,070K = 74(2)%]. The refined amount of Fe3+ at the M(1) is not significant [%Fe(M1)1,070K = 1(2)%]. The tetrahedral and octahedral bond distances and angles show a slight distortion of the polyhedra at high-T, but a significant increase of the bond distances compared to those at room temperature is observed, especially for bond distances corrected for "rigid body motions". The high-T conditions also affect the inter-polyhedral configurations: the bridging angle Si(2)-O(9)-Si(1) of the Si2O7 group increases significantly with T. The high-T structure refinement shows that no dehydration effect occurs at least within the T-range investigated. The configuration of the H-bonding is basically maintained with temperature. However, the hydrogen bond strength changes at 1,070 K, as the O(10)\ub7\ub7\ub7O(4) and H(1)\ub7\ub7\ub7O(4) distances are slightly longer than those at 293 K. The anisotropic displacement parameters of the proton site are significantly larger than those at room condition. Reasons for the thermal stability of epidote up to 1,070 K observed in this study, the absence of dehydration and/or non-convergent ordering of Al and Fe3+ between different octahedral sites and/or convergent ordering on M(3) are discussed

Suspension high velocity oxy-fuel spraying of TiO2: a quantitative approach to phase composition

A range of coatings from a water based suspension of anatase has been prepared by suspension high velocity oxy-fuel spraying with the aim to study effects of heat power of the flame on phase composition, microstructure and surface topography. Three most commonly used approaches of quantitative phase analysis have been scrutinized with respect to their applicability and as some of the coatings showed presence of preferred orientation and it was argued that quantitative Rietveld refinement is the most accurate method for phase composition determination. Coatings had a layered duplex anatase/rutile microstructure with fraction of rutile increasing exponentially with heat power. Spraying at the lower heat power led to a lower surface roughness and higher power resulted in surfaces with pronounced humps, which were distributed homogeneously on the surface. The emergence of humps is related to an increase in macroscopic surface area of up to 30% with respect to the flat coating

Influence of fly ash blending on hydration and physical behavior of Belite-Alite-Ye'elimite cements

A cement powder, composed of belite, alite and ye’elimite, was blended with 0, 15 and 30 wt% of fly ash and the resulting lended cements were further characterized. During hydration, the presence of fly ash caused the partial inhibition of both AFt degradation and belite reactivity, even after 180 days. The compressive strength of the corresponding mortars increased by increasing the fly ash content (68, 73 and 82 MPa for mortars with 0, 15 and 30 wt% of fly ash, respectively, at 180 curing days), mainly due to the diminishing porosity and pore size values. Although pozzolanic reaction has not been directly proved there are indirect evidences.This work is part of the Ph.D. of D. Londono-Zuluaga funded by Beca Colciencias 646—Doctorado en el exterior and Enlaza Mundos 2013 program grant. Cement and Building materials group (CEMATCO) from National University of Colombia is acknowledged for providing the calorimetric measurements. Funding from Spanish MINECO BIA2017-82391-R and I3 (IEDI-2016-0079) grants, co-funded by FEDER, are acknowledged

An integrated view of theiInfluence of temperature, pressure, and humidity on the stability of trimorphic cysteamine hydrochloride

Understanding the phase behavior of pharmaceuticals is important for dosage form development and regulatory requirements, in particular after the incident with ritonavir. In the present paper, a comprehensive study of the solid-state phase behavior of cysteamine hydrochloride used in the treatment of nephropathic cystinosis and recently granted orphan designation by the European Commission is presented employing (high-pressure) calorimetry, water vapor sorption, and X-ray diffraction as a function of temperature. A new crystal form (I2/a, form III) has been discovered, and its structure has been solved by X-ray powder diffraction, while two other crystalline forms are already known. The relative thermodynamic stabilities of the commercial form I and of the newly discovered form III have been established; they possess an overall enantiotropic phase relationship, with form I stable at room temperature and form III stable above 37 degrees C. Its melting temperature was found at 67.3 +/- 0.5 degrees C. Cysteamine hydrochloride is hygroscopic and immediately forms a concentrated saturated solution in water with a surprisingly high concentration of 47.5 mol % above a relative humidity of 35%. No hydrate has been observed. A temperature composition phase diagram is presented that has been obtained with the unary pressure temperature phase diagram, measurements, and calculations. For development, form I would be the best form to use in any solid dosage form, which should be thoroughly protected against humidity.Postprint (author's final draft