123 resultados para Cr3
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PVTPVTPVTMajoriteMg-PerovskiteCa-PerovskitePVT XPVT 1Fe2+Mg2+Mn2+Mg2+1.36ÅFe2+1.17ÅMg2+O2.270ÅFe2+O2.299Å Mn2+1.17ÅFe2+1.17ÅMn2+O2.326ÅFe2+O2.299Å 2(Mg0.6766Fe0.2808Na0.0073Ti0.0014)0.9661(Cr1.4874Al0.5367)2.0241O4Fe2+Mg2+Cr3+Al3+Fe2+Mg2+ 32102.214203745 4CinnabarB33 5SSeTe 6ZnSFe2+Zn2+Sb2S3Bi2S3MoS2WS2
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As piroxenas so um vasto grupo de silicatos minerais encontrados em muitas rochas gneas e metamrficas. Na sua forma mais simples, estes silicatos so constitudas por cadeias de SiO3 ligando grupos tetrahdricos de SiO4. A frmula qumica geral das piroxenas M2M1T2O6, onde M2 se refere a caties geralmente em uma coordenao octadrica distorcida (Mg2+, Fe2+, Mn2+, Li+, Ca2+, Na+), M1 refere-se a caties numa coordenao octadrica regular (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), e T a caties em coordenao tetrahdrica (Si4+, Al3+, Fe3+). As piroxenas com estrutura monoclnica so designadas de clinopiroxenes. A estabilidade das clinopyroxenes num espectro de composies qumicas amplo, em conjugao com a possibilidade de ajustar as suas propriedades fsicas e qumicas e a durabilidade qumica, tm gerado um interesse mundial devido a suas aplicaes em cincia e tecnologia de materiais. Este trabalho trata do desenvolvimento de vidros e de vitro-cermicos baseadas de clinopiroxenas para aplicaes funcionais. O estudo teve objectivos cientficos e tecnolgicos; nomeadamente, adquirir conhecimentos fundamentais sobre a formao de fases cristalinas e solues slidas em determinados sistemas vitro-cermicos, e avaliar a viabilidade de aplicao dos novos materiais em diferentes reas tecnolgicas, com especial nfase sobre a selagem em clulas de combustvel de xido slido (SOFC). Com este intuito, prepararam-se vrios vidros e materiais vitro-cermicos ao longo das juntas Enstatite (MgSiO3) - diopsdio (CaMgSi2O6) e diopsdio (CaMgSi2O6) - Ca - Tschermak (CaAlSi2O6), os quais foram caracterizados atravs de um vasto leque de tcnicas. Todos os vidros foram preparados por fuso-arrefecimento enquanto os vitro-cermicos foram obtidos quer por sinterizao e cristalizao de fritas, quer por nucleao e cristalizao de vidros monolticos. Estudaram-se ainda os efeitos de vrias substituies inicas em composies de diopsdio contendo Al na estrutura, sinterizao e no comportamento durante a cristalizao de vidros e nas propriedades dos materiais vitro-cermicos, com relevncia para a sua aplicao como selantes em SOFC. Verificou-se que Foi observado que os vidros/vitro-cermicos base de enstatite no apresentavam as caractersticas necessrias para serem usados como materiais selantes em SOFC, enquanto as melhores propriedades apresentadas pelos vitro-cermicos base de diopsdio qualificaram-nos para futuros estudos neste tipo de aplicaes. Para alm de investigar a adequao dos vitro-cermicos base de clinopyroxene como selantes, esta tese tem tambm como objetivo estudar a influncia dos agentes de nucleao na nucleao em volume dos vitro-cermicos resultantes base de diopsdio, de modo a qualific-los como potenciais materiais hopedeiros de resduos nucleares radioactivos.
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O trabalho de investigao apresentado nesta dissertao foi desenvolvido tendo como objectivo a sntese e funcionalizao de meso-triarilcorris para utilizao como quimiossensores. Este trabalho encontra-se apresentado ao longo de cinco captulos. No primeiro captulo so apresentadas as caractersticas gerais, as metodologias de sntese e de funcionalizao de macrociclos de tipo corrlico, e descrevemse algumas aplicaes em que tm sido utilizados. So ainda abordadas algumas das propriedades e caractersticas dos quimiossensores e os mecanismos de deteo de diversos analtos. No segundo captulo, aps uma pequena introduo s reaes de Wittig e de Diels-Alder, escolhidas para a funcionalizao do macrociclo corrlico, descreve-se o estudo efectuado para a obteno do complexo de glio(III) do 3- vinil-5,10,15-tris(pentafluorofenil)corrol e o seu comportamento como dieno, em reaes de Diels-Alder na presena dos dienfilos 1,4-benzoquinona e 1,4- naftoquinona. Desses estudos resultaram dois aductos cuja habilidade sensorial, bem como a dos seus precursores, foi estudada, em soluo, na presena de anies esfricos (F-, Br-, Cl-), lineares (CN-) e volumosos (CH3COO-, H2PO4 -). Dos macrociclos estudados verificou-se que o corrol base-livre 5,10,15-tris(pentafluorofenil)corrol apresenta uma elevada sensibilidade para o anio fluoreto (F-), e que a coordenao do ncleo corrlico com glio(III) diminui a afinidade para este anio. Em geral, todos os compostos mostraram afinidade para o anio cianeto (CN-) mesmo quando em suportes polimricos. O gel de poliacrilamida revelou-se muito promissor na determinao de CN- em amostras de gua. No terceiro captulo avaliada a reatividade do complexo de glio(III) do 3- vinil-5,10,15-tris(pentafluorofenil)corrol ainda como dieno mas agora na presena de um dienfilo linear, o acetilenodicarboxilato de dimetilo. Desse estudo resultaram dois novos derivados corrlicos. A habilidade sensorial dos mesmos perante os anies fluoreto, cianeto, acetato, e fosfato foi avaliada por espectroscopia de absoro e emisso tendo um dos aductos mostrado ser colorimtrico para o anio cianeto. No quarto captulo descreve-se a sntese e caracterizao de dois conjugados do tipo corrol-cumarina, resultantes de reaes de Hetero-Diels-Alder entre o 3-vinil-5,10,15-tris(pentafluorofenil)corrolatoglio(III)(piridina) e orto-quinonasmetdeos gerados in situ a partir de reaces de Knoevenagel entre cumarinas e paraformaldedo. Realizaram-se estudos de afinidade sensorial para anies e caties com estes macrociclos, bem como com conjugados porfirinacumarina anlogos. A insero de uma unidade cumarina conferiu uma excepcional solubilidade tendo os novos derivados apresentado solubilidade em etanol. No quinto e ltimo captulo desta dissertao avaliada a capacidade sensorial do 5,10,15-tris(pentafluorofenil)corrol e da sua espcie monoaninica, para os caties metlicos Na+, Ca2+, Cu2+, Cd2+, Pb2+, Hg2+, Ag+, Al3+, Zn2+, Ni2+, Cr3+, Ga3+, Fe3+ em tolueno e acetonitrilo. Os macrociclos corrlicos mostraram ser selectivos e colorimtricos para o catio Hg2+. Neste trabalho descreve-se ainda a sntese do derivado -iminocorrol, que aps funcionalizao com o 3-isocianatopropiltrimetoxisilano originou um derivado do tipo alcoxisilano, que foi, posteriormente, ancorado a nanopartculas comerciais de slica. As novas nanopartculas ancoradas com o alcoxisilano corrol foram estudadas na presena de Cu2+, Hg2+ e Ag+. Na presena do catio Ag+ assistiu-se a uma mudana de cor, de verde para amarelo.
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A new series of nano-sized Ce1-xEuxCrO3 (x = 0.0 to 1.0) with an average particle size of 50 - 80 nm were synthesized using a solution combustion method. Nano-powders Ce1-xEuxCrO3 with the canted antiferromagnetic property exhibited interesting magnetic behaviours including the reversal magnetization and the exchange bias effect. The effect of europium doping as the ion with the smaller radius size and different electron con figuration on structural, magnetic and thermal properties of Ce1-xEuxCrO3 were investigated using various experimental techniques, i.e. DC/AC magnetic susceptibility, heat capacity, thermal expansion, Raman scattering, X-ray photoemission spectroscopy, transmission/scanning electron microscopy, X-ray powder diffraction and neutron scattering. An exchange bias effect, magnetization irreversibility and AC susceptibility dispersion in these samples confirmed the existence of the spin disorder magnetic phase in Ce1-xEuxCrO3 compounds. The exchange bias phenomenon, which is assigned to the exchange coupling between glassy-like shell and canted antiferromagnetic core, showed the opposite sign in CeCrO3 and EuCrO3 at low temperatures, suggesting different exchange interactions at the interfaces in these compounds. The energy level excitation of samples were examined by an inelastic neutron scattering which was in good agreement with the heat capacity data. Neutron scattering analysis of EuCrO3 was challenging due to the large neutron absorption cross-section of europium. All diffraction patterns of Ce1-xEuxCrO3 showed the magnetic peak attributed to the antiferromagnetic Cr3+ spins while none of the diffraction patterns could detect the magnetic ordering of the rare-earth ions in these samples.
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A new chromium-antimony-sulfide, [Cr(C6H18N4)(SbS3)], has been synthesised under solvothermal conditions from CrCl3. 6H(2)O, Sb2S3 and S in the presence of triethylenetetramine at 433 K and characterised by single-crystal X-ray diffraction, thermogravimetry, elemental analysis and SQUID magnetometry. The structure of [Cr(C6H18N4)(SbS3)] consists of neutral mononuclear chromium-centred complexes, in which the Cr3+ is chelated by one tetradentate triethylenetetramine molecule and a bidentate SbS33- ligand, yielding distorted octahedral coordination. Intermolecular hydrogen bonds link individual molecules into layers within the ac plane. Within a layer, molecules occur in pairs with each member related by a centre of inversion. The Cr...Cr separation within a pair is approximately 6.5 Angstrom. Magnetic susceptibility data reveal Curie-Weiss behaviour with mu(eff) = 3.819(3)/mu(B) and a negligible Weiss constant, indicative of non-interacting Cr3+ ions. (C) 2003 Elsevier Science Ltd. All rights reserved.
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The rutile TiO2(110) surface has been doped with sub-monolayer metallic Cr, which oxidises and donates charge to specific surface Ti ions. X-Ray and ultra violet photoemission spectroscopy and first principles density functional theory with Hubbard U are used to assign the oxidation states of Cr and surface Ti and we find that Cr2+ forms on bridging oxygen ions and a 5-fold coordinated surface Ti atom is reduced to Ti3+ and the Cr ions readily react with oxygen (to Cr3+), which leads to depletion of surface Ti3+ 3d electrons.
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We have employed a combination of experimental surface science techniques and density functional calculations to study the reduction of TiO2(110) surfaces through the doping with submonolayer transition metals. We concentrate on the role of Ti adatoms in self doping of rutile and contrast the behaviour to that of Cr. DFT+U calculations enable identification of probable adsorption structures and their spectroscopic characteristics. Adsorption of both metals leads to a broken symmetry and an asymmetric charge transfer localised around the defect site of a mixed localised/delocalised character. Charge transfer creates defect states with Ti 3d character in the band gap at similar to 1-eV binding energy. Cr adsorption, however, leads to a very large shift in the valence-band edge to higher binding energy and the creation of Cr 3d states at 2.8-eV binding energy. Low-temperature oxidation lifts the Ti-derived band-gap states and modifies the intensity of the Cr features, indicative of a change of oxidation state from Cr3+ to Cr4+. Higher temperature processing leads to a loss of Cr from the surface region, indicative of its substitution into the bulk.
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The Kagome lattice, comprising a two-dimensional array of corner-sharing equilateral triangles, is central to the exploration of magnetic frustration. In such a lattice, antiferromagnetic coupling between ions in triangular plaquettes prevents all of the exchange interactions being simultaneously satisfied and a variety of novel magnetic ground states may result at low temperature. Experimental realization of a Kagome lattice remains difficult. The jarosite family of materials of nominal composition AM3(SO4)2(OH)6 (A = monovalent cation; M= Fe3+, Cr3+), offers perhaps one of the most promising manifestations of the phenomenon of magnetic frustration in two dimensions. The magnetic properties of jarosites are however extremely sensitive to the degree of coverage of magnetic sites. Consequently, there is considerable interest in the use of soft chemical techniques for the design and synthesis of novel materials in which to explore the effects of spin, degree of site coverage and connectivity on magnetic frustration.
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In the present work, the trivalent and hexavalent chromium phytoaccumulation by three living free floating aquatic macrophytes Salvinia auriculata, Pistia stratiotes, and Eicchornia crassipes was investigated in greenhouse. These plants were grown in hydroponic solutions supplied with non-toxic Cr3+ and Cr6+ chromium concentrations, performing six collections of nutrient media and plants in time from a batch system. The total chromium concentrations into Cr-doped hydroponic media and dry roots and aerial parts were assayed, by using the Synchrotron radiation X-ray fluorescence technique. The aquatic plant-based chromium removal data were described by using a nonstructural kinetic model, obtaining different bioaccumulation rate, ranging from 0.015 to 0.837 1 mg(-1) d(-1). The Cr3+ removal efficiency was about 90%, 50%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata, respectively; while it was rather different for Cr6+ one, with values about 50%, 70%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata.
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The heavy metals are used in many industrial processes and when discharged to the environment can cause harmful effects to human, plants and animals. The adsorption technology has been used as an effective methodology to remove metallic ions. The search for new adsorbents motivated the development of this research, accomplished with the purpose of removing Cr (III) from aqueous solutions. Diatomite, chitosan, Filtrol 24TM and active carbon were used as adsorbents. To modify the adsorbent surface was used a bicontinuous microemulsion composed by water (25%), kerosene (25%), saponified coconut oil (10%) and as co-surfactant isoamyl or butyl alcohols (40%). With the objective of developing the best operational conditions the research started with the surfactant synthesis and after that the pseudo-ternary diagrams were plotted. It was decided to use the system composed with isoamyl alcohol as co-surfactant due its smallest solubility in water. The methodology to impregnate the microemulsion on the adsorbents was developed and to prepare each sample was used 10 g of adsorbent and 20 mL of microemulsion. The effect of drying time and temperature was evaluated and the best results were obtained with T = 65 C and t = 48 h. After evaluating the efficiency of the tested adsorbents it was decided to use chitosan and diatomite. The influence of the agitation speed, granule size, heavy metal synthetic solution concentration, pH, contact time between adsorbent and metal solution, presence or not of NaCl and others metallic ions in the solution (copper and nickel) were evaluated. The adsorption isotherms were obtained and Freundlich and Langmuir models were tested. The last one correlated better the data. With the purpose to evaluate if using a surfactant solution would supply similar results, the adsorbent surface was modified with this solution. It was verified that the adsorbent impregnated with a microemulsion was more effective than the one with a surfactant solution, showing that the organic phase (kerosene) was important in the heavy metal removal process. It was studied the desorption process and verified that the concentrated minerals acids removed the chromium from the adsorbent surface better than others tested solutions. The treatment showed to be effective, being obtained an increase of approximately 10% in the chitosan s adsorption capacity (132 mg of Cr3+ / g adsorbent), that was already quite efficient, and for diatomite, that was not capable to remove the metal without the microemulsion treatment, it was obtained a capacity of 10 mg of Cr3+ / g adsorbent, checking the applied treatment effectiveness
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In this work were synthesized matrix-based commercial white clay in its composition having large amounts of kaolinite and quartz, with a certain percentage of iron oxide for use as an adsorbent for hydrogen sulfide (H2S). To characterize the effect of initial matrix techniques were used to characterize XRD, FTIR, XRF and TG. The initial clay mineral matrix was placed in contact with 0.1 molar solutions of the salts of Co2+, Ni2+, Cr3+ and a solution 0.1 g / 100ml rhodamine B. During the synthesis process, the solutions were placed in contact with the initial matrix for a period of 48 hours in order to have ion exchange with the clay mineral. To check the amount of exchanged metals, we used the technique of X-ray Fluorescence (XRF). After synthesis was initiated the process of adsorption of H2S, where the arrays were placed in the reactor, then by passing a stream of hydrogen sulfide. The matrix along with the reactor was weighed before and after to measure the amount of gas adsorbed. Based on the gravimetric data the matrix which had the highest performance of the adsorption matrix was exchanged with Ni2+ ions, obtaining a result of 11.13 mg H2S / g matrix, then the matrix coated with rhodamine B which was reached 10.13 mg H2S / g matrix
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The contamination by metal ions has been occurring for decades through the introduction of liquid effluent not treated, mainly from industrial activities, rivers and lakes, affecting water quality. For that the effluent can be disposed in water bodies, environmental standards require that they be adequately addressed, so that the concentration of metals does not exceed the limits of standard conditions of release in the receptor. Several methods for wastewater treatment have been reported in the literature, but many of them are high cost and low efficiency. The adsorption process has been used as effective for removal of metal ions. This paper presents studies to evaluate the potential of perlite as an adsorbent for removing metals in model solution. Perlite, in its natural form (NP) and expanded (EP), was characterized by X-ray fluorescence, X-ray diffraction, surface area analysis using nitrogen adsorption (BET method), scanning electron microscopy and Fourier transform infrared spectroscopy. The physical characteristic and chemical composition of the material presented were appropriate for the study of adsorption. Adsorption experiments by the method of finite bath for model solutions of metal ions Cr3+, Cu2+, Mn2+ and Ni2+ were carried out in order to study the effect of pH, mass of the adsorbent and the contact time on removal of ions in solution. The results showed that perlite has good adsorption capacity. The NP has higher adsorption capacity (mg g-1) than the EP. According to the values of the constant of Langmuir qm (mg g-1), the maximum capacity of the monolayer was obtained and in terms of proportion of mass, we found the following order experimental adsorption: Cr3+ (2.194 mg g- 1) > Ni2+ (0.585 mg g-1) > Mn2+ (0.515 mg g-1) > Cu2+ (0.513 mg g-1) and Cr3+ (1.934 mg g-1)> Ni2+ (0.514 mg g-1) > Cu2+ (0.421 mg g-1) > Mn2+ (0.364 mg g-1) on the NP and EP, respectively. The experimental data were best fitted the Langmuir model compared to Freundlich for Cu2+, Mn2+ and Ni2+. However, for the Cr3+, both models fit the experimental data
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Fundao de Amparo Pesquisa do Estado de So Paulo (FAPESP)
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Cr-doped xerogels were obtained by sol-gel process from the acid-catalyzed and ultrasound-stimulated hydrolysis of tetraethoxysilane (TEOS) with addition of CrCl3.6H(2)O in water solution during the liquid step of the process. The gels were aged immersed in different pH solutions for about 30 days, after that they were allowed to dry. The samples were annealed at temperatures ranging from 40 to 600degreesC and analyzed by UV-visible absorption spectroscopy. Cr3+ is the preferable oxidation state of the chromium ion in the gels annealed up to 250-300degreesC, in the case of aging in solutions of pH=5 and 11. A high UV absorption below similar to320 nm, due to the host gel, and different absorption bands, depending on the temperature, due to the chromium ion were observed in the xerogels at temperatures below similar to250degreesC, in the case of aging in solutions of pH=1 and 2. These absorption bands have not been assigned. Above 300degreesC up to 600degreesC, Cr5+, and possibly Cr6+, are the preferable oxidation states of the chromium ion independent of the pH of the aging solution, so the xerogels turn to a yellowish appearance in all cases.
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In this work, the polymeric precursor method Was used to obtain disordered Zn2TiO4 powders, either Undoped or doped with Sn4+, Cr3+ and V5+, to be applied its photoluininescent material. The characterization was undertaken by means of thermal analysis (TG and DTA), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). Previous works stated that titanate octahedra containing a short Ti-O distance show efficient luminescence at roorn temperature if these octahedra are isolated from each other. In the present work, the phenomenon was observed in condensed octahedra, sharing edges. The room temperature PL noticed in undoped Zn2TiO4 had its intensity increased by the dopant addition-the increase was of about 300% for V5+ doping 400% for Cr3+ and 800% for Sn4+. (c) 2005 Elsevier B.V. All rights reserved.