Martensitic transformation, magnetic entropy, and adiabatic temperature changes in bulk and ribbon Ni48Mn39.5Sn12.5−xInx (x = 2, 4, 6) metamagnetic shape memory alloys

Martensitic transformation, magnetic entropy, and direct adiabatic temperature changes in Ni48Mn39.5Sn12.5− xInx (x = 2, 4, 6) metamagnetic Heusler bulk and grain-constrained ribbon alloys were studied. All alloys showed a typical L21 structure in austenite and the 4O structure in martensite. Their relative volume contributions changed depending on In content. With increasing In concentration, the martensitic transformation temperature increased, whereas the Curie temperature of austenite decreased. The magnetic entropy change under magnetic field of 5 T attained maximum of 20 J/kgK in the bulk and 14.4 J/kgK in the ribbon alloys with the Ni48Mn39.5Sn8.5In4 nominal composition. The corresponding adiabatic temperature change under 1.7 T yielded 1.3 K for the Ni48Mn39.5Sn8.5In4 bulk alloy. Despite grain confinement, melt spinning was found to stabilize martensite phase. Changes observed were discussed with relation to strengthened covalency imposed by In substitution

Effect of Cryogrinding on Chemical Stability of the Sparingly Water-Soluble Drug Furosemide

Purpose To investigate the effect of cryogrinding on chemical stability of the diuretic agent furosemide and its mixtures with selected excipients. Methods Furosemide was ground at liquid nitrogen temperature for 30, 60, 120 and 180 min. Mixtures of furosemide-PVP and furosemide-inulin (1:1) were milled under cryogenic conditions. Materials were analyzed by XRD, UPLC, MS and NMR. Results Upon increasing the milling time, a significant build-up of an unidentified impurity 1, probably the main degradation product, was noticed. Cogrinding of furosemide with PVP and inulin worsened chemical stabilization of the pharmaceutical. The main degradation product formed upon cryomilling was subsequently identified as 4-chloro-5-sulfamoylanthranilic acid (CSA). Based on some theoretical considerations involving specific milling conditions, the milling intensity and an expected specific milling dose have been calculated. Results indicate that cryogenic grinding is capable to initiate mechanically induced decomposition of furosemide.Conclusions Cryogenic grinding can activate and accelerate not only structural changes (solid state amorphization) but also chemical decomposition of pharmaceuticals. A cryogenic milling device should be considered as a chemical reactor, where under favourable conditions chemical reactions could be mechanically initiated

Simulation study of topological point defects in graphitic layer - curvature effect and pair correlation function analysis

The effect of three types of topological defects, single vacancy, double vacancy and the Stone-Thrower-Wales defect on the atomic arrangement in a single graphitic layer is studied using computer simulations. The topological defects were positioned on the perfect hexagonal graphitic layer 20 Å in diameter with different distance from the layer edge and then the geometry of the system was independently optimized using the reactive bond order potential, the semi-empirical quantum-chemical PM7 and the density functional theory method. Curvature and the distortion of the graphitic layer caused by the defects are analyzed and their influence on the pair correlation function is discussed

Reduction of the graphite crystal dimension by ultrasounds irradiation

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Fullerene-like structure of activated carbons

The structure of the commercial activated carbons AX21 and BP71 has been studied using the high-energy X-ray diffraction and molecular dynamics techniques. The diffraction measurements were carried up to a maximum value of the scattering vector K-max=24 angstrom(-1). The obtained diffraction data have been converted to a real space representation in the form of the radial distribution function. Structural models containing 2 and 4 graphene layers, approximately 16-20 angstrom in size, were computer generated and then relaxed using the reactive empirical bond order potential for carbon-carbon interactions and the Lennard-Jones potential with parameters for inter-layer interactions. The molecular dynamics simulations were performed at 300 K to account for the thermal oscillations. For Such models the intensity and radial distribution functions were computed. The correctness of the models was verified by comparison of the simulations with the experimental data both in real and reciprocal space. The effects of hydrogen, saturating dangling bonds of edge atoms, the presence of non-six membered rings and the sp(3) defects on the resulting structure were investigated

Structural studies of nanodiamond by high-energy X-ray diffraction

The atomic scale structure of explosive diamond nanoparticles has been studied using high-energy X-ray diffraction. The diffraction data have been converted to the real space representation in the form of the radial distribution function. Spherical and truncated octahedron nanodiamond clusters containing from 729 to 1182 atoms have been computer generated and then relaxed using the molecular dynamics method with the reactive empirical bond order potential for carbon-carbon interaction and the Lennard-Jones potential with parameters for inter-layer interactions. Validity of such constructed models has been verified by comparison of the simulations and the experimental data in both real and reciprocal space. The obtained results show that the structure of the investigated diamond nanoparticles cannot be satisfactorily described in terms of the model based on the perfect diamond lattice. The core-shell model with an average size of 22.5-23.4 angstrom, consisting of the diamond core and the graphite-like shell, accounts very well for the experimental data

Application of image plate for structural studies of carbon nanotubes by high-energy X-ray diffraction

An image plate detector coupled with high-energy synchrotron radiation was used to determine the structure factor and the radial distribution function of carbon nanotubes obtained by a template CVD process. The image plate detector has proved to be a very efficient tool for structural studies of nanotubes providing diffraction data of good quality in relatively short time. The diffraction data were converted to real space yielding the radial distribution function which can be used for quantitative analysis of the atomic arrangement of the carbon nanotubes. The obtained results are compared to those of traditional experiments using a conventional point Ge detector

Cleavage and size reduction of graphite crystal using ultrasound radiation

International audienceThe influence of ultrasound radiation on graphite structure was studied by laser light scattering, X-ray diffraction, Raman spectroscopy and Transmission Electron Microscopy. Irradiations of polycrystalline graphite powder suspensions at frequencies of 20 kHz and 500 kHz, were carried out in three different solvents: water (as the best medium for cavitation), a surfactant (OMImBr) aqueous solution and also a mixture of sulfuric and nitric acids which caused the exfoliation by intercalation. The average basal particle size of 168 lm was reduced to 4 lm after ultrasonication delivering a huge energy density up to 1.2 MW/m2. Change of the sonication time and the nature of the solvents produced different reduction of the graphite crystals dimensions, affecting the out of plane thickness and the basal width as well. The ultrasonication promoted the disordering of the graphite tridimensional stacking for all solvents used, with the strongest effect in acidic medium. Turbostratic structures formation and exfoliation of graphene flakes have been observed after the use of surfactant for sonication medium. Intercalation in acid medium prior to the ultrasound treatment produced similar effects