65,495 research outputs found
Microcalorimetric and FT-IR spectroscopic study of benzene adsorption on α-Fe2O3 and γ-Al2O3
No full textThe adsorption of benzene at room temperature on α-Fe2O3 and on γ-Al2O3 powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy. On iron oxide a chemisorption-combustion step is followed by a highly exothermic adsorption step, reversible at r.t. Few combustion centres exist on alumina if reducing pretreatment is not carried out. Two reversible adsorption steps are subsequently observed and were interpreted as due to interaction with two different types of surface hydroxy groups. © 1984 Wiley Heyden Ltd., Chichester and Akadémiai Kiadó, Budapest
Microcalorimetric and FT-IR spectroscopic study of the adsorption of methanol on TiO2 (anatase)
No full textThe adsorption of methanol on TiO2 (anatase) activated under vacuum at different temperatures has been studied by adsorption microcalorimetry and FT-IR spectroscopy. Both dissociative and undissociative chemisorption of methanol molecules have been found corresponding to the evolution of very high adsorption heats (qdiff > 150 kJ mol-1). At higher coverages, hydrogen bonded and dimeric adsorbed species are formed corresponding to differential adsorption heats of 50-120 kJ mol-1. © 1985
FT-IR spectroscopic and calorimetric characterization of the adsorbed forms of water on a-Fe2O3 obtained by thermal decomposition of a-FeOOH
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Preparation and Characterization of Magnesium Chromite and Magnesium Ferrite Aerogels
No full textA supercritical drying process has been used to prepare MgO-Cr2O3 and MgO-Fe2O3 powders from a mixture of magnesium acetate and the metallic acetylacetonates hydrolyzed in a methanolic solvent. The resultant aerogels have small particle sizes in the range of 10 to 20 nm and high surface areas in the range of 50 to 250 m2/g. After removal from the autoclave, characterization by X-ray diffraction (XRD) showed that the MgO-Cr2O3 was amorphous and that the MgO-Fe2O3 was readily in the form of a spinel structure for magnesioferrite (MgFe2O4). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric and differential thermal analyses (TG-DTG-DTA) showed a high level of retained surface methoxy and carboxylate species for the MgO-Cr2O3 aerogel (over 40% by weight). The MgFe2O4, on the otherhand, had less than 10% organic matter. The differences observed between MgO-Cr2O3 and MgFe2O4 have been attributed to the formation of Cr+6 in the former case. After heating in air at 970K. MgO-Cr2O3 crystallized to the spinel structure MgCr2O4. The IR transmittance of pressed disks of MgFe2O4 aerogel showed behavior typical for a n-type semiconductor. The MgCr2O4, however, was a p-type semiconductor due to mainly Cr+6 present on the surface. Lewis acid centers were prevalent on both materials. The acid strength was found to be higher on the MgFe2O4 compare to the MgCr2O4
Islamic Practices, Traditions and Beliefs in Egypt and the Eastern Mediterranean in the Early 16th Century: Georgius Gemnicensis’ Ephemeris
No full textThis article reports several excerpts of Georgius Gemnicensis’ Ephemeris, a travel journal in which the author recounted his experiences in Mamluk Egypt and the Eastern Mediterranean, and provided a number of details about customs, beliefs and Islamic practices in such territories at the beginning of the 16th century
Light response estimation and gamma events reconstruction in gamma-detectors based on continuous scintillators and SiPMs
No full textWe present the implementation of a practical iterative method for optical model estimation in Anger cameras for medical imaging. The optical model, also referred to as light response, represents a fundamental requirement for statistical event reconstruction in gamma detectors implementing monolithic scintillators. Despite we considered several approaches for the response calibration, based either on Monte Carlo optical modelling or experimental scanning of the detectors response, none of them was practical in producing a reliable optical model and, moreover, of practical use when the cameras are installed in the scanner. We therefore propose a more effective approach for optical model estimation. We designed and tested it on detectors based on Silicon PhotoMultipliers (SiPMs) and adopted in the INSERT project, aiming at the development of a non-rotational SPECT insert for MR scanners, composed by 10 detectors (preclinical version). The iterative method calibrates the light response starting from an experimental acquisition of a non-collimated source. Thus, the model is reliable, keeping the calibration procedure fast and simple. This permits to estimate, within the same session, the optical models for every gamma camera populating the SPECT in few tens of minutes. The estimated optical model feeds a Maximum Likelihood algorithm for optimal event reconstruction, providing better uniformity and linearity together with recovery of the field of view. We tested the reconstructed images quality by acquiring irradiation profiles with a gamma-camera designed for the preclinical version of the INSERT SPECT. The maximum deviation from linearity results inferior to 1 mm. Deviation from uniformity is less than the 15 % of the average number of counts. The optical model is also well adaptable to the variability of detection response thanks to the well uniform behavior of the SiPMs adopted
Infrared spectroscopic study of micronised geothite
No full textInfrared spectra of micronised goethite between 4000 cm-1 and 20 cm-1 were studied. Stretching and bending vibrations of structural hydroxy-groups were assigned using data on deuterated samples and comparison with α-Fe2O3 obtained by thermal decomposition. The existence of two different kinds of surface hydroxyls was also confirmed and an interpretation of their nature proposed. Various measured low-frequency bands were assigned to vibrations of the structural FeO6 blocks. © 1978
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