oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 17 )

2018 ( 23 )

2017 ( 32 )

2016 ( 36 )

Custom range...

Search Results: 1 - 10 of 19270 matches for " Cristina Volzone "
All listed articles are free for downloading (OA Articles)
Page 1 /19270
Display every page Item
Structural Changes by Thermal Treatment up to Glass Obtention of P2O5-Na2O-CaO-SiO2 Compounds with Bioglass Composition Types  [PDF]
Cristina Volzone, Franco Matías Stábile
New Journal of Glass and Ceramics (NJGC) , 2013, DOI: 10.4236/njgc.2013.31009
Abstract: P2O5-Na2O-CaO-SiO2 compounds are the base of certain glass types. Glasses are solids obtained by fast cooling of melted mix of certain compounds. Different compositions give origin to many products with a variety of applications such as: bottles, coatings, windows, tools for chemical industry, laboratory equipment, optics, as bioceramics, etc. The aim of this work was to analyze structural changes of different composition in the P2O5-Na2O-CaO-SiO2 systems thermally treated up to 1250?C, that is to say, before glass formation, by X ray diffraction. Intermediate and final developed phases up to 1100?C thermal treatment in samples were generated as a function of Na2O/CaO (1 and 1.62) and P2O5/Na2O ratios (0, 0.2 and 0.245). High-and low-combeites, calcium and sodium-calcium silicate were found at the highest studied temperature.
Influence of organobentonite structure on toluene adsorption from water solution
Vidal, Nuria;Volzone, Cristina;
Materials Research , 2012, DOI: 10.1590/S1516-14392012005000126
Abstract: due to increase water pollution by organic compound derived from hydrocarbons such as toluene, several alternative technologies for remediation of polluted water have been originated. in this work natural bentonites were modified with cetyltrimethylammonium (ctma+) for obtaining organophilic bentonites. the obtained ctma-bentonites would be suitable for use as adsorbents of toluene present in water. the influence of structural characteristics of ctma-bentonites on their adsorption capacity was studied. it was shown that adsorption of toluene depended on homogeneous interlayer space associated with arrangements of ctma+ paraffin-monolayer and bilayer models, accompanied by a high degree ordering of the carbon chain of organic cation in both arrangements. however, packing density would not have an evident influence on the retention capacity of these materials. the solids obtained were characterized by chemical analysis, x-ray diffractions and infrared spectroscopy. toluene adsorption was measured by uv-visible spectrophotometer. adsorption capacity was studied by determining adsorption isotherms and adsorption coefficient calculation. the adsorption isotherms were straight-line indicating a partition phenomenon of toluene between the aqueous and organic phase present in organophilic bentonites.
Thermal behaviour of titanium in host matrix clay
Volzone, Cristina;Cesio, Ana María;
Materials Research , 2009, DOI: 10.1590/S1516-14392009000200013
Abstract: titanium in hosted by a clay matrix has important applications in a variety of catalysts. however, there is insufficient information about of textural and structural characteristics of the titanium in matrix clay at room temperature and after thermal treatment. in this study, titanium in host matrix clay was obtained by treating montmorillonite clay minerals with different oh-ti solutions. the titanium-solutions containing partially hydrolyzed titanium were obtained using a ticl4 solution with and without the addition of glycerol. the amount of ti added to the solid was 20 mmol ti per gram of clay. thermal treatments were carried out at 500 and 1,000 °c in an air atmosphere. the solids were characterized by x ray diffraction, thermal analyses, infrared spectroscopy, n2 adsorption-desorption isotherms. the products presented different structural and textural characteristics and, after calcination at 1,000 °c, anatase and rutile in different proportions were present in the samples.
Adsorción de Cadmio en Solución utilizando como Adsorbente Material Tobáceo Modificado
Rueda,Monica L; Volzone,Cristina; Martinez,Susana Y;
Información tecnológica , 2010, DOI: 10.4067/S0718-07642010000400010
Abstract: the adsorption of cd ions from solution by a tuffaceous material (in natural and after clay concentration) from neuquén province, argentine was tested. the solid was used as collected and after being concentrated in the clay fraction. the chemical analysis was performed by plasma couple inductively and the mineralogical composition was identified by x-ray diffraction. the adsorption isotherms were carried out by using concentrations of cd solutions in the range of 100 to 1000 ppm. the solid/liquid ratio was 2 % w/v and the contact time was 24 hours. the amount of metal ion retained was obtained by difference between the initial concentration and supernatant concentration after contacting metal ions solution with the solid. the metal concentrations were determined by atomic absorption spectrometry. the main mineralogical components of the sample were smectite/illite (clay minerals), quartz and feldspar. the purification of the tuffaceous material in clay minerals increased the adsorption capacity from 15.75 to 22.86 mg·g-1.
Influence of thermal treatment on bentonite used as adsorbent for Cd, Pb, Zn retention from mono-solute and poly-solute aqueous solutions
Martinez Stagnaro, Susana Yamila;Volzone, Cristina;Rueda, Mónica Luciana;
Materials Research , 2012, DOI: 10.1590/S1516-14392012005000074
Abstract: the retentions of zn, cd and pb cations by one treated bentonite up to 750 °c were analyzed. the retentions were evaluated by using mono-and poly-solute aqueous solutions of such cations. the adsorptions were carried out in batch system at room temperature. the solid/liquid ratio was 2% wt.v-1. the solids were characterized by x-ray diffraction, thermal and chemical analyses. the zn cation from mono- or polysolute-solutions was retained in higher amount than cd and pb cations in similar solution types by bentonite. the retentions were effective up to 450 °c calcined bentonite, after that, the retention capacity decreased in concordance with dehydroxylation of the structure of clay minerals.
Adsorción de Cadmio en Solución utilizando como Adsorbente Material Tobáceo Modificado Adsorption of Cadmium in Solution using a Modified Tuffaceous Material as Adsorbent
Monica L Rueda,Cristina Volzone,Susana Y Martinez
Información Tecnológica , 2010,
Abstract: Se estudia la adsorción de iones de cadmio en solución por un mineral tobáceo, procedente de la Provincia de Neuquén, Argentina, utilizado en forma natural y luego de concentrado en fracción arcilla. El análisis químico fue efectuado por Plasma Acoplado Inductivamente y la composición mineralógica fue identificada por Difracción de Rayos X. La isoterma de adsorción fue obtenida usando cadmio en solución en el rango de concentración de 100 a 1000 ppm. El ensayo experimental se llevó a cabo con una relación sólido/liquido de 2 % p/v y tiempo de contacto de 24 horas. La retención de cadmio se determinó por diferencia entre la concentración inicial y la concentración luego del contacto con el sólido, lectura efectuada por espectrometría de absorción atómica. La mayor proporción de fracción arcillosa (esmectita e illita) lograda por la purificación, permitió reducir el contenido de cuarzo y feldespato y aumentar la capacidad de adsorción de 15.75 a 22.86 mg·g-1. The adsorption of Cd ions from solution by a tuffaceous material (in natural and after clay concentration) from Neuquén Province, Argentine was tested. The solid was used as collected and after being concentrated in the clay fraction. The chemical analysis was performed by Plasma Couple Inductively and the mineralogical composition was identified by X-ray diffraction. The adsorption isotherms were carried out by using concentrations of Cd solutions in the range of 100 to 1000 ppm. The solid/liquid ratio was 2 % w/v and the contact time was 24 hours. The amount of metal ion retained was obtained by difference between the initial concentration and supernatant concentration after contacting metal ions solution with the solid. The metal concentrations were determined by atomic absorption spectrometry. The main mineralogical components of the sample were smectite/illite (clay minerals), quartz and feldspar. The purification of the tuffaceous material in clay minerals increased the adsorption capacity from 15.75 to 22.86 mg·g-1.
Obten??o e caracteriza??o de materiais argilosos quimicamente ativados para utiliza??o no descoramento de óleo vegetal
Foletto, Edson L.;Volzone, Cristina;Morgado, Ayres F.;Porto, Luismar M.;
Materials Research , 2001, DOI: 10.1590/S1516-14392001000300012
Abstract: a natural bentonite sample from argentina was activated by sulfuric acid in different concentrations (20 and 40 wt%) and different contact time (120 and 210 min), at the same temperature (90 °c) . the ratio of the mass of clay to the volume of acid solution was 1:10 (w/v). these materials were tested to verify its bleaching (decolorization) capacity of soybean oil, which was compared to a standard commercial bleaching material fulmont premiere. differential thermal analysis and thermogravimetric techniques, infrared spectrometry and chemical analysis showed that the acid activation modified the clay material structural properties. bleaching capacity was found to be dependent on the acid concentration and treatment time used. the activated argentine material showed superior bleaching performance compared to the commercial clay used by vegetable oil refiners.
Obten o e caracteriza o de materiais argilosos quimicamente ativados para utiliza o no descoramento de óleo vegetal
Foletto Edson L.,Volzone Cristina,Morgado Ayres F.,Porto Luismar M.
Materials Research , 2001,
Abstract: A natural bentonite sample from Argentina was activated by sulfuric acid in different concentrations (20 and 40 wt%) and different contact time (120 and 210 min), at the same temperature (90 °C) . The ratio of the mass of clay to the volume of acid solution was 1:10 (w/v). These materials were tested to verify its bleaching (decolorization) capacity of soybean oil, which was compared to a standard commercial bleaching material Fulmont Premiere. Differential thermal analysis and thermogravimetric techniques, infrared spectrometry and chemical analysis showed that the acid activation modified the clay material structural properties. Bleaching capacity was found to be dependent on the acid concentration and treatment time used. The activated Argentine material showed superior bleaching performance compared to the commercial clay used by vegetable oil refiners.
Comparison results for solutions of parabolic equations with a singular potential COMPARISON RESULTS FOR SOLUTIONS OF PARABOLIC EQUATIONS WITH A SINGULAR POTENTIAL
Roberta Volpicelli,Bruno Volzone
Le Matematiche , 2007,
Abstract: We consider the solution u of the Cauchy-Dirichlet problem for a class of linear parabolic equations in which the coefficient of the zero order term could have a singularity at the origin of the type 1/|x|^2 . We prove that u can be compared “in the sense of rearrangements” with the solution v of a problem whose data are radially symmetric with respect to the space variable. We consider the solution u of the Cauchy-Dirichlet problem for a class of linear parabolic equations in which the coef cient of the zero order term could have a singularity at the origin of the type 1/|x|^2. We prove that u can be compared “in the sense of rearrangements” with the solution v of a problem whose data are radially symmetric with respect to the space variable.
Improved Poincaré inequalities
Jean Dolbeault,Bruno Volzone
Mathematics , 2011,
Abstract: Although the Hardy inequality corresponding to one quadratic singularity, with optimal constant, does not admit any extremal function, it is well known that such a potential can be improved, in the sense that a positive term can be added to the quadratic singularity without violating the inequality, and even a whole asymptotic expansion can be build, with optimal constants for each term. This phenomenon has not been much studied for other inequalities. Our purpose is to prove that it also holds for the gaussian Poincar\'e inequality. The method is based on a recursion formula, which allows to identify the optimal constants in the asymptotic expansion, order by order. We also apply the same strategy to a family of Hardy-Poincar\'e inequalities which interpolate between Hardy and gaussian Poincar\'e inequalities.
Page 1 /19270
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.