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Amorphous Samples (amorphous + sample)

Distribution by Scientific Domains

Physics and Astronomy	60%
Chemistry	40%

Selected Abstracts

Structure, texture and surface acidity studies of a series of mixed zinc,aluminum (60,90 molar % Al) phosphate catalysts

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2001
Karim Mtalsi
Abstract A series of mixed zinc,aluminum phosphate (ZnAlP) catalysts containing 40,90 aluminum molar % were synthesized by a coprecipitation method and characterized by nitrogen adsorption,desorption, X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) of ammonia. The presence of aluminum greatly affected the surface properties of Zn3(PO4)2 by delaying the crystallization process of Zn3(PO4)2. All amorphous samples were shown to be mesoporous and they contained two types of aluminum surface hydroxyl groups and one type of phosphorus hydroxyl group, as shown by DRIFT spectra. The specific surface area and the acidity of ZnAlP increased on increasing the aluminum content. On the other hand, a great difference in the texture and the concentration of surface acid sites was found by changing the precipitating agent and calcination temperature. Thus these factors also play an important role in the final properties of these catalysts. © 2001 Society of Chemical Industry [source]

Characterisation of indomethacin and nifedipine using variable-temperature solid-state NMR

MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2005
David C. Apperley
Abstract We have characterised the stable polymorphic forms of two drug molecules, indomethacin (1) and nifedipine (2) by 13C CPMAS NMR and the resonances have been assigned. The signal for the CCl carbon of indomethacin has been studied as a function of applied magnetic field, and the observed bandshapes have been simulated. Variable-temperature 1H relaxation measurements of static samples have revealed a T1, minimum for indomethacin at 17.8 °C. The associated activation energy is 38 kJ mol,1. The relevant motion is probably an internal rotation and it is suggested that this involves the COCH3 group. Since the two drug compounds are potential candidates for formulation in the amorphous state, we have examined quench-cooled melts in detail by variable-temperature 13C and 1H NMR. There is a change in slope for and at the glass transition temperature (Tg) for indomethacin, but this occurs a few degrees below Tg for nifedipine, which is perhaps relevant to the lower real-time stability of the amorphous form for the latter compound. Comparison of relaxation time data for the crystalline and amorphous forms of each compound reveals a greater difference for nifedipine than for indomethacin, which again probably relates to real-time stabilities. Recrystallisation of the two drugs has been followed by proton bandshape measurements at higher temperatures. It is shown that, under the conditions of the experiments, recrystallisation of nifedipine can be detected already at 70 °C, whereas this does not occur until 110 °C for indomethacin. The effect of crushing the amorphous samples has been studied by 13C NMR; nifedipine recrystallises but indomethacin does not. The results were supported by DSC, powder XRD, FTIR and solution-state NMR measurements. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Cu/Ti base multicomponent amorphous Cu47Ti33Zr11Ni8Si1 and nanocrystalline silver composites

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010
Jan Dutkiewicz
Abstract An easy glass-forming alloy based on Cu,Ti of composition Cu47Ti33Zr11Ni8Si1 was ball milled for 40,h to obtain amorphous powder. X-ray diffraction and differential scanning calorimetry (DSC) measurements confirmed the dominant presence of the amorphous phase after ball milling. However, transmission electron microscopy from powders allowed identification of Si particles and intermetallic phases a few nanometre in diameter, often of CuNi2Ti or Cu,Ti structures. The powder was then hot pressed in vacuum at temperature of 460,°C between the glass transition and the crystallization point to form bulk amorphous samples. Composites were prepared in the same way from mixed milled amorphous powders and nanocrystalline silver powder prepared by ball milling. Various ratios of amorphous to silver powder were applied with a maximum of 60% of nanocrystalline silver The microhardness of the amorphous phase component was near 1100,HV, much higher than the 90,HV of silver. Composites containing 20% of nanosilver have shown a much higher compression strength of 850,MPa, as compared to the 450,MPa of the composite containing 60% of silver, however, the latter has better ductility, near 5%, before fracture. [source]

Phase structure and crystallization of the bulk glassy FeCoZrWB alloys

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2010
Katarzyna Pawlik
Abstract In the present work, the high-energy X-ray diffraction (XRD) measurements performed using monochromatic synchrotron radiation of 112 keV (,=0.110696 Å), were utilized to compare a phase constitution of melt-spun ribbon and suction-cast rods of Fe61Co10+xZr5W4,xB20 alloys (where x = 0, 2, 3 at.%). For bulk amorphous samples of the investigated alloys DSC studies allowed to determine the activation energies of crystal growth and differences in crystallization kinetics at constant heating rates. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ab-initio modeling of a-Si and a-Si:H

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2010
Ricardo M. Ribeiro
Abstract The simulation of a-Si is complicated because there is no direct experimental data, as there are for crystals. Our approach to simulate a-Si is to build several relatively small amorphous samples and, later, the properties we wish to calculate are averaged over all samples. We applied the Wooten, Winer and Weaire bond switch to 64 atom cubic supercell of crystalline silicon. This mechanism was used to create 15 samples of continuous random network of silicon. For each supercell, the volume and atomic relaxation were allowed in order to minimize the total energy, using a density functional-pseudopotential code. The radial and angular distributions, the electronic and vibrational density of states, and the Raman spectra were calculated. The radial distribution agrees very well with experimental data. The angular distribution has its maximum at 109.4 degree. The experimental positions and relative intensities of the Transverse Optical (TO) and Transverse Acoustic vibrational modes are well reproduced, with 14 and 25 cm -1 peak deviations, respectively. The shape of the calculated Raman spectra agrees well with experimental data, being the intense TO peak shifted by 50 cm -1. The TO width at half-weight is very well reproduced. Introducing hydrogen in the a-Si samples, decorating all the undercoordinated Si atoms and at bond centres of floating bonds, the hydrogen vibrational frequencies of the relaxed structures agree very well with experimental data. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]