|
| ||
|
|
||
Acid Attack (acid + attack)
Selected AbstractsThe Direct Determination of Rare Earth Elements in Basaltic and Related Rocks using ICP-MS: Testing the Efficiency of Microwave Oven Sample Decomposition ProceduresGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2008Margareth S. Navarro éléments Terres Rares; attaque acide dans un four à micro onde; bombes Parr; ICP-MS; techniques de décomposition Tests are described showing the results obtained for the determination of REE and the trace elements Rb, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th and U with ICP-MS methodology for nine basaltic reference materials, and thirteen basalts and amphibolites from the mafic-ultramafic Niquelândia Complex, central Brazil. Sample decomposition for the reference materials was performed by microwave oven digestion (HF and HNO3, 100 mg of sample), and that for the Niquelândia samples also by Parr bomb treatment (5 days at 200°C, 40 mg of sample). Results for the reference materials were similar to published values, thus showing that the microwave technique can be used with confidence for basaltic rocks. No fluoride precipitates were observed in the microwave-digested solutions. Total recovery of elements, including Zr and Hf, was obtained for the Niquelândia samples, with the exception of an amphibolite. For this latter sample, the Parr method achieved a total digestion, but not so the microwave decomposition; losses, however, were observed only for Zr and Hf, indicating difficulty in dissolving Zr-bearing minerals by microwave acid attack. Les Terres Rares et les éléments en trace suivants: Rb, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th et U, ont été analysés par ICP-MS dans neuf matériaux de référence de composition basaltique et treize basaltes et amphibolites du Complexe basique -ultrabasique Niquelândia (centre du Brésil). Les matériaux de référence ont été mis en solution par attaque acide dans un four à micro ondes (HF et HNO3, 100 mg d'échantillon) et ceux de Niquelândia l'ont été aussi par attaque dans des bombes Parr (5 jours à 200°C, 40 mg d'échantillon). Les résultats obtenus sur les matériaux de référence sont identiques aux valeurs publiées, montrant que la technique d'attaque par micro onde peut être appliquée en toute confiance aux roches basaltiques. Aucun précipité de fluorure n'a été observé dans les solutions résultantes de l'attaque par micro onde. L'extraction des éléments a été totale, même pour Zr et Hf, pour les échantillons de Niquelândia, sauf pour une amphibole où seule la méthode d'attaque avec la bombe Parr a permis une extraction totale. Néanmoins, les pertes ne concernaient que Zr et Hf, révélant donc une certaine difficulté de la technique d'attaque par micro onde à détruire les minéraux contenant Zr. [source] Catalytic cracking, dehydrogenation, and aromatization of isobutane over Ga/HZSM-5 and Zn/HZSM-5 at low pressuresINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2002Yanping Sun Isobutane cracking, dehydrogenation, and aromatization over Ga/HZSM-5 and Zn/HZSM-5 has been investigated in a Knudsen cell reactor and the kinetics of the primary reaction steps for isobutene and propene formation have been accurately determined. Although cracking is the dominant reaction channel, with propene and methane being primary products, methane formation is significantly less than propene formation. This indicates that a proportion of the cracking proceeds via Lewis acid attack at CC bonds, and not just via alkanium ion formation at Bronsted acid sites. This is particularly apparent over Zn/HZSM-5. Intrinsic rate constants for cracking, calculated from the rate of propene formation, are and for dehydrogenation, calculated from the rate of isobutene formation, are Large preexponential factors for cracking and dehydrogenation over Ga/HZSM-5 indicate that either the coverage of active sites is significantly less than the coverage of exposed sites or the intrinsic reaction step involves a large entropy change between reactant and transition state. For Zn/HZSM-5 the small preexponential factors suggest either small entropy changes during activation, perhaps initiated by Lewis acid sites, or a steady-state distribution of active and exposed sites is rapidly reached. Differences in intrinsic activation energies may reflect the ratio of Lewis and Bronsted acid sites on the respective catalyst surfaces. Aromatization is more prolific over Ga/HZSM-5 than over Zn/HZSM-5 under the low-pressure conditions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 467,480, 2002 [source] Determination of the band-gap of MgS and MgS-rich Zn1,xMgxSySe1,y alloys from optical transmission measurementsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010Ian A. Davidson Abstract As part of our development of an epitaxial lift-off process, utilising a sacrificial magnesium sulphide (MgS) layer, we have developed a MgS-rich ZnMgSSe alloy which provides excellent carrier confinement and resists both oxidation and acid attack. Here the optical transmission of the alloy has been measured and its bandgap determined as a direct transition at 4.19,±,0.04,eV. Its composition has also been determined by X-ray interference (XRI) and comparison with simulations. For a range of alloy samples we obtain compositions of the Zn1,xMgxSySe1,y layers which are (x, y),=,(0.80,±,0.02, 0.645,±,0.025). Using the alloy bandgap and composition we have determined direct bandgap transition energy for MgS by extrapolation. This is found to be 4.78,±,0.14,eV. [source] Optimization by response surface methodology (RSM) for toluene adsorption onto prepared acid activated clayTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Abdelfattah Amari Abstract Adsorption of toluene onto acid activated clay was carried out. Modified clay was prepared by acid attack (H2SO4) on raw material. Response surface methodology based on a 2-level, 4-variables central composite orthogonal design was used to evaluate the effects of important parameters on the adsorption of toluene on to activated clay. Temperature (53.8,96.2°C), contact time (0.57,6.93 h), mass ratio of liquid/solid (3.38,7.62) and strength of acid (7.75,57.24%) were chosen as process variables for the optimization. Of these parameters, temperature reaction and time had greater impact on toluene adsorption than did the other parameters. Analysis of variance (ANOVA) shows a good agreement between theoretical analysis and experimental data. The validity of model is verified by an experiment at the optimum conditions. The optimum conditions for the maximum adsorption of toluene onto activated clay are: temperature of 96.2°C, a contact time of 6.93 h, a liquid/solid ratio of 5.98 and strength of acid of 32.94%. Since the predicted values and the actual experimental value obtained for the maximum adsorption of toluene are within 95% confidence intervals, the final model is considered valid and has satisfactory predictive ability. L'adsorption du toluène sur l'argile activée par l'acide est réalisée. L'argile modifiée a été préparée par attaque acide (H2SO4) de la matière première. On a eu recours à la méthodologie de surface de réponse basée sur un plan d'expériences orthogonal composite centré à 2 niveaux et 4 variables afin d'évaluer les effets des paramètres importants pour l'adsorption du toluène sur l'argile activée. La température (53,8°C,96,2°C), le temps de contact (0,57,6,93 h), le rapport massique liquide/solide (3,38,7,62) et la force de l'acide (7,75,57,24%) ont été choisis comme variables de procédé pour l'optimisation. Parmi ces paramètres, le temps de contact et la température ont le plus grand impact sur l'adsorption du toluène. L'analyse de la variance (ANOVA) montre un bon accord avec l'analyse théorique et les données expérimentales. La validité du modèle est vérifiée par une expérience dans les conditions optimales. Les conditions optimales pour l'adsorption du toluène sur l'argile activée sont: la température de 96,2°C, le temps de contact de 6,93 h, le rapport liquide/solide de 5,98 et la force de l'acide de 32,94%. Étant donné que la valeur prédictée et la valeur expérimentale réelle obtenue par l'adsorption maximale du toluène se trouvent dans un intervalle de confiance de 95%, le modèle final est considéré comme valide et possède une capacité de prédiction satisfaisante. [source] | ||||||||||