Search results for "nuclear chemistry"
showing 10 items of 1124 documents
MTA HP Repair stimulates in vitro an homogeneous calcium phosphate phase coating deposition
2019
Background To study the mineralization capacity in vitro of the bioceramic endodontic material MTA HP Repair. Material and methods Bioactivity evaluation in vitro was carried out, by soaking processed cement disk in simulated body fluid (SBF) during 168 h. The cement surface was studied by Fourier transform infrared spectroscopy (FT-IR), field emission gun scanning electron microscopy (FEG-SEM) and energy dispersive X-ray analysis (EDX). Release to the SBF media of ionic degradation products was monitored using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Results FT-IR showed increasing formation of phosphate phase bands at 1097, 960, 607 and 570 cm-1 with prolonged SB…
SHORT-TERM PROCESSES OF RADIONUCLIDE IMMOBILIZATION IN CEMENT - A CHEMICAL APPROACH
1992
Abstract The ions released in solution by the constituents of cement (principally silicate, aluminate, OH and Ca ions) can combine with the anions and cations from nuclear wastes present in the mixing water to give very insoluble compounds that can fix these ions in the concrete matrix. In order to understand some of the particular physico-chemical processes involved in cement hydration in the presence of analogue elements, tricalcium silicate (C 3 S) was used instead of cement, which is too complex a mixture. It was found that the salt of a chemical analogue, a lanthanide salt, showed some accelerating effects when present in dilute amounts but resulted in large accelerating effects on QS …
Bond strength of lithium disilicate after cleaning methods of the remaining hydrofluoric acid
2020
Background Complex implant treatments have steadily increased within implant prosthodontics. Based on the lower implant mobility, implant impressions need high accuracy in the model transfer to receive a high passive fit within the final prosthodontic restoration. To analyze the accurate 3-dimensional (3D) inter-implant-positions, a reference point is indispensable. However, there is no reference in the patients mouth, so the aim of the present study was to develop a new method based on a custom-made-measuring-aid (CMA) to assess the inter implant dimensions (InID) in patients. Material and Methods Initially an implant master model (IMM/patient equivalent) was digitized by computed tomograp…
Influence of barium and cerium oxides on alumina supported Pd catalysts for hydrocarbon combustion
2002
Abstract The effects of baria and ceria additions to alumina-supported palladium catalysts have been investigated. Two series of binary Al 2 O 3 –BaO and ternary oxides Al 2 O 3 –CeO 2 –BaO were prepared using a sol–gel method and then characterized, after high-temperature treatments, by XRD, BET, TG, TEM and EDXS analyses. The influence of baria and ceria on the thermal stability and morphology of the supports was examined. A baria content of 12 wt.% appears the most effective for alumina stabilization. Palladium catalysts were prepared by impregnation method using Pd(NH 3 ) 4 (NO 3 ) 2 and were characterized by XRD and TEM. The catalysts showed high activity in the total oxidation of meth…
Effect of Impurities (Carbon and Manganese) on Iron Oxidation at High Temperature: Impurities-Rare Earth Element (Cerium) Interactions
1997
Apres oxydation du fer pur revetu d'un depot de CeO 2 , (T = 7000C, pO 2 = 0,04 Pa), le cerium se trouve localise dans la couche de wustite sous la forme de CeFeO 3 . La dissolution de cette phase assure l'introduction homogene du cerium a l'interieur de la couche de FeO. Sa formation est attribuee a un processus d'oxydo-reduction entre le depot de CeO 2 et les premiers germes de FeO. Dans le cas des echantillons d'acier Fe-Mn-C, recouverts de CeO 2 , le cerium n'est pas incorpore dans la couche d'oxyde de fer de facon homogene et se retrouve sous la forme de CeO 2 a l'interface oxyde-gaz. Le role de chaque impurete est maintenant bien etabli: le manganese inhibe l'incorporation du cerium d…
The influence of various synthesis methods on the catalytic activity of cerium oxide in one-pot synthesis of diethyl carbonate starting from CO2, eth…
2013
Different synthesis methods such as homogeneous precipitation at room temperature and supercritical water (T > 647 K and P > 22.1 MPa) were employed for cerium oxide preparation. Additionally, deposition of ceria on silica mesoporous material, SBA-15, was carried out. The obtained materials were characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physisorption, X-ray photoelectron spectroscopy and CO2 temperature programmed desorption. Considerable variations in physico-chemical properties of the resulting materials were observed. The catalytic activities of pristine cerium oxide and ceria loaded on SBA-15 support were…
The effect of the fused-ring substituent on anthracene chalcones: crystal structural and DFT studies of 1-(anthracen-9-yl)-3-(naphthalen-2-yl)prop-2-…
2018
Two new anthracene chalcones, namely 1-(anthracen-9-yl)-3-(naphthalen-2-yl)prop-2-en-1-one and 1-(anthracen-9-yl)-3-(pyren-1-yl)prop-2-en-1-one, have been successfully synthesized and the effect of the different fused ring substituent system attached to the anthracene chalcone derivative investigated. These compounds show a very narrow band gap due to the large p-conjugated systems, making them promising candidates as optoelectronic materials. Hirshfeld surface analysis has been carried out to show the contribution of intermolecular contacts and weak interactions to supramolecular stabilization.
Extraction of uranyl ions from aqueous solutions using silica-gel-bound macrocycles for alpha contaminated waste water treatment
2004
Abstract The efficiency for the extraction of U(VI) of new modified silica gels, namely N-tripropionate (or N-triacetate)-substituted tetraazamacrocycles-bound silica gels, has been studied. The effect of the nature of the ligand, the pH and the temperature was studied both in batch experiments as well as in continuous extraction. These silica gels are good candidates for the extraction of U(VI) when compared to a commercially available acid-type chelating resin. The breakthrough and regeneration tests showed that the total removal of U(VI) from a contaminated solution can be achieved by using a column packed with such tetraazamacrocycles-bound silica gels. Finally, the use of a modified si…
Sequestration of organomettalic compounds by synthetic and naturally occuring polycarboxylate ligands. Binding of monomethylmercury(II) by polyacryli…
2007
The sequestering capacity of synthetic and naturally occurring polycarboxylate ligands towards mono- methylmercury(II) was evaluated by stability quantitative data on the interaction of CH3Hgþ with different molecular weight synthetic polyacrylates (2 and 20 kDa average M.wt) and alginate (70– 100 kDa) extracted from brown algae Macrocystis pyrifera. The influence of ionic medium was evaluated by measurements on the CH3Hgþ-polyacrylate systems in NaNO3 medium at different ionic strengths (0.10, 0.25, 0.50 and 0.75mol Lÿ1), and a Debye–Hu¨ ckel type equation was used for the dependence of complex formation constants on ionic strength. Measurements on the CH3Hgþ - alginate system were carried…
Ascorbic acid degradation kinetics in mushrooms in a high-temperature short-time process controlled by a thermoresistometer
2004
Abstract The degradation of ascorbic acid was studied in mushrooms heated at temperatures between 110 and 140°C, high-temperature short-time conditions, in a five-channel computer-controlled thermoresistometer. The kinetics parameters were calculated on the assumption that there are 2 degradation mechanisms, one aerobic (during the first few seconds of the process) and the other anaerobic. The 2 stages followed first-order reaction kinetics, with E a =46.36 kJ/mol for aerobic degradation and E a =49.57 kJ/mol for anaerobic degradation.