The Amorphous Form of Salicylsalicylic Acid: Experimental Characterization and Computational Predictability

Amorphous solids challenge our understanding of phase behavior. For small organic molecules, particularly pharmaceuticals, they offer improved solubility and bioavailability. A computational approach to understanding of amorphous stability and ease of formation would be valuable. An apparently ideal test case is salicylsalicylic acid (salsalate), which has been reported to form an amorphous phase that is long-term stable below and above its glass temperature. In this study we report the application of computational crystal structure prediction (CSP) techniques to salsalate, supported by an experimental investigation of the amorphous phase by solid form screening and X-ray derived pair distribution functions (PDFs). CSP reveals a pair of hydrogen bonding motifs that appear to be severely detrimental to the molecule’s ability to pack efficiently and stably, indicating an explanation for salsalate’s formation of a stable amorphous phase. However, experimental data caution against overstating this stability. The amorphous phase is found to crystallize under a wider variety of conditions than has previously been reported. Furthermore the molecule is prone to thermal degradation, giving rise to impurities that may play a role in frustrating crystallization

Persistent deNOx Ability of CaAl2O4:(Eu, Nd)/TiO2-xNy Luminescent Photocatalyst

The properties of the dusty tori in active galactic nuclei (AGNs) have been investigated in detail, mainly focusing on the geometry and components; however, the kinematics of the torus is still not clear. The narrow iron K$\alpha$ line at 6.4 keV is thought to be produced by the X-ray reflection from the torus. Thus, the velocity-resolved reverberation mapping of it is able to constrain the kinematics of the torus. Such effort is limited by the spectral resolution of current CCD detectors and should be possible with the microcalorimeter on the next generation X-ray satellite. In this paper, we first construct the response functions of the torus under a uniform inflow, a Keplerian rotation, and a uniform outflow. Then the energy-dependent light curve of the narrow iron K$\alpha$ line is simulated according to the performance of the X-ray Integral Field Unit in Athena. Finally, the energy-dependent cross-correlation function is calculated to reveal the kinematic signal. According to our results, one hundred observations with 5 ks exposure of each are sufficient to distinguish the above three velocity fields. Although the real geometry and velocity field of the torus could be more complex than we assumed, the present result proves the feasibility of the velocity-resolved reverberation mapping of the narrow iron K$\alpha$ line. The combination of the dynamics of the torus with those of the broad line region and the host galaxy is instructive for the understanding of the feeding and feedback process of AGNs.Comment: 6 pages, 5 figures, ApJ Letters accepte

Aluminum-rich belite sulfoaluminate cements: clinkering and early age hydration

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO2 into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C2S (50-60%), C4A3$(20- 30$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt% of C4A3$, had 19.6, 27.1 and 27.7 wt$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the b-C2S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C4A3$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution

Mode-crystallography analysis and magnetic structures of SrLnFeRuO6 (Ln = La, Pr, Nd) disordered perovskites

The crystal and magnetic structures of SrLnFeRuO6 (Ln = La, Pr, Nd) double perovskites have been investigated. All compounds crystallize with an orthorhombic Pbnm structure at room temperature. These materials show complete chemical disorder of Fe and Ru cations for all compounds. The distortion of the structure, relative to the ideal cubic perovskite, has been decomposed into distortion modes. It has been found that the primary modes of the distortion are octahedral tilting modes: R + 4 and M + 3. The crystal structure of SrPrFeRuO6 has been studied from room temperature up to 1200 K by neutron powder diffraction. There is a structural phase transition from orthorhombic (space group Pbnm) to trigonal (space group ) at T = 1075 K. According to group theory no second-order transition is possible between these symmetries. Magnetic ordering for all the compounds is described by the magnetic propagation vector (0,0,0). SrPrFeRuO6 shows ferrimagnetic order below ca 475 K, while SrLaFeRuO6 (below ca 450 K) and SrNdFeRuO6 (below ca 430 K) exhibit canted-antiferromagnetic order. The magnetic moments at low temperatures are m(Fe/Ru) = 1.88 (3)B for SrLaFeRuO6 (2 K), m(Pr) = 0.46 (4)B and m(Fe/Ru) = 2.24B for SrPrFeRuO6 (2 K), and m(Fe/Ru) = 1.92B for SrNdFeRuO6 (10 K). © 2012 International Union of Crystallography.This work has been supported by ILL (grant MBR-GL/09-056 and MBR-GL/11-050), the Spanish Ministry of Science and Innovation (project MAT2008-05839) and the European Commission under the 7th Framework Program through the ‘Research Infrastructures’ action of the ‘Capacities’ Program, Contract No: CP-CSA_INFRA-2008-1.1.1 Number 226507- NMI3. The authors are grateful to FRMII (exp. 4456), ILL (exp. 5-24-458) and PSI (exp. 20101302) for the beamtime allocation and the instrument local contacts Dr Markus Hoelzel (SPODI, FRMII), Dr Gabriel Cuello (D2B, ILL) and Dr Vladimir Pumjakushin (HRPT, SINQ, PSI) for their kind help and technical assistance.Peer Reviewe

Crystal structure and phase transitions of Sr2CdWO6.

The crystal structure of Sr2CdWO6, prepared by solid state reaction, was determined by high-resolution X-ray diffraction at different temperatures. At room temperature, this compound has a monoclinic structure (space group P2(1)/n) with a = 5.7463(1), b = 5.8189(1), c = 8.1465(1), β = 90.071(1). At 1105 K the structure is converted to tetragonal (space group I4/m). Diffraction data also suggest that a cubic phase exists above 1220K. Comparing the phase transition temperatures of Sr2CdWO6 with those of other compounds of the Sr2MWO6 family reported previously, it was observed that the transition temperatures are higher in compounds with low-tolerance factors. At the same time, the temperature range in which the intermediate tetragonal phase exists is reduced. © 2007, Elsevier Ltd

Aplicación de las técnicas fototérmicas al estudio de materiales

In this paper a general description of the photothermal techniques and its applications is presented. In particular, we concentrate our effort in those developed in our laboratory: infrared radiometry, photothermal reflectance and mirage effect. We also present their application to the measurement of the thermal diffusivity of a wide variety of materials and to the detection and characterization of subsurface features in opaque solids.<br><br>En este trabajo presentamos una descripción detallada de las técnicas fototérmicas y de sus aplicaciones al estudio de materiales. En particular, nos vamos a centrar en aquellas técnicas desarrolladas en nuestro laboratorio: radiometría infrarroja, termorreflectancia y efecto “mirage”, junto con los resultados más importantes que hemos obtenido en el estudio de las propiedades térmicas de una amplia gama de materiales y en la detección y caracterización de defectos subsuperficiales en sólidos opacos