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

Improvement of Carbon Nanofibers/ZrO2 Composites Properties with a Zirconia Nanocoating on Carbon Nanofibers by Sol–Gel Method

The development of new carbon nanofibers (CNFs)–ceramic nanocomposite materials with excellent mechanical, thermal, and electrical properties is interesting for a wide range of industrial applications. Among the ceramic materials, zirconia stands out for their excellent mechanical properties. The main limitations in the preparation of this kind of nanocomposites are related with the difficulty in obtaining materials with homogeneous distribution of both phases and the dissimilar properties of CNFs and ZrO2 which causes poor interaction between them. CNFs-reinforced zirconia nanocomposites ZrO2/xCNFs (x=1–20 vol%) were prepared by powder mixture and sintered by spark plasma sintering (SPS). ZrO2-reinforced CNFs nanocomposites CNFs/xZrO2 (x=20 vol%) were prepared by powder mixture and a surface coating of CNFs by the wet chemical route with zirconia precursor is proposed as a very effective way to improve the interaction between CNFs and ZrO2. After SPS sintering, an improvement of 50% in fracture strength was found for similar nanocomposite compositions when the surface coating was used. The improved mechanical properties of these nanocomposites are caused by stronger interaction between the CNFs and ZrO2.This work was financially supported by National Plan Projects MAT2006-01783 and MAT2007-30989-E and the Regional Project FICYT PC07-021. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her research grant BES2007-15033.Borrell Tomás, MA.; Rocha, VG.; Torrecillas, R.; Fernandez, A. (2011). Improvement of Carbon Nanofibers/ZrO2 Composites Properties with a Zirconia Nanocoating on Carbon Nanofibers by Sol–Gel Method. Journal of the American Ceramic Society. 94(7):2048-2052. https://doi.org/10.1111/j.1551-2916.2010.04354.xS20482052947Iijima, S. (1991). Helical microtubules of graphitic carbon. Nature, 354(6348), 56-58. doi:10.1038/354056a0Merkoçi, A. (2005). Carbon Nanotubes in Analytical Sciences. 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Temperature-controlled reversible exfoliation-stacking of titanate nanosheets in an aqueous solution containing tetraalkylammonium ions

Exfoliation and stacking of titanate nanosheets dispersed in aqueous solutions containing tetraalkylammonium ions can be reversibly controlled by adjusting the solution temperature as a tunable physical parameter. That is, the transparent colloidal solution of exfoliated titanates is clouded on the basis of spontaneous stacking of multiple nanosheets when heated at a certain temperature, and cooling of the clouded solution causes regeneration of the original exfoliated state. This cycle repeatedly and rapidly occurs according to the temperature fluctuation. The origin of behavior is qualitatively interpreted with a temperature-dependent variation in the Debye screening length of negatively charged nanosheets that affects the dispersibility of nanosheets

Synthesis and characterization of Ca2CoTaO6, a new monoclinically distorted double perovskite

The new Ca2CoTaO6 double perovskite has been synthesized by a conventional solid state reaction and its unit cell parameters determined by X-ray powder diffractometry. It crystallizes in the monoclinic space group P2(1)/n. The unit cell parameters are: a = 5.507(2) Å; b = 5.564(3) Å; c = 7.798(3) Å; β = 89.99(4)° and Z = 2. The IR spectrum of the material was recorded and is briefly discussed. Some comparisons with Ca2CoNbO6 and other isostructural perovskites are also performed

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