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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Time-dependent release of iron from soot particles by acid extraction and the reduction of fe3+ by elemental carbon

Drake, Stephen James 15 May 2009 (has links)
Elemental carbon reduces Fe3+ to Fe2+ in aqueous solutions. This process has potential implications in the adverse health effects of fine particles in air pollution, because both elemental carbon and iron are major components in atmospheric particulate matter. In this study we measured the time-dependent release of iron from laboratory flames and standard reference soot particles that contained iron, and the reduction of Fe3+ to Fe2+ in an acid extraction process. The concentration of Fe3+ and Fe2+ ions in the extraction solutions was measured by a spectrophotometric method. The results showed that while Fe3+ was the dominant valence state in the dry soot particles, significant fraction of iron was reduced to Fe2+ in the aqueous solution. Further investigation is needed to assess the significance of this phenomenon in the biological effects of particles that contain iron and elemental carbon.
2

Soft X-ray photoemission study of thermoelectric alloys Fe2−x−yIryV1+xAl and Fe2−xV1+x−yTiyAl

Nishino, Yoichi, Sugiura, Takahiro, Tanaka, Suguru, Tamada, Yuko, Sandaiji, Yusuke, Miyazaki, Hidetoshi, Inukai, Manabu, Yagi, Shinya, Kato, Masahiko, Harada, Shota, Soda, Kazuo 04 1900 (has links)
Advances in Vacuum Ultraviolet and X-ray Physics The 37th International Conference on Vacuum Ultraviolet and X-ray Physics (VUVX2010)
3

Perdas em ferritas de manganês zinco: o papel da sinterização e de parâmetros microestruturais. / Magnetic losses in maganese zinc ferrites: the role of sinterization and microstructural parameters.

Lázaro Colán, Victoria Amelia 21 May 2010 (has links)
O uso das ferritas de manganês zinco em fontes de potência de carregadores de bateria vem crescendo nos últimos anos, devido a suas baixas perdas magnéticas em induções da ordem de 0,2 T. Estas ferritas pertencem à categoria de ferritas moles, são óxidos ferrimagnéticos, policristalinos com estrutura cúbica tipo espinélio. Pós desse material foram compactados em prensa uniaxial e em prensa automática de produção para anel e toróide, respectivamente. Foram realizados dois ciclos de queima variando o teor de oxigênio entre 5 e 15%, no patamar de sinterização, com o propósito de avaliar seu efeito na densidade, microestrutura, perdas magnéticas em altas induções (0,2 T) e permeabilidade. Amostras sinterizadas em posições mais quentes do forno resultaram em maior densidade e maior tamanho de grão, conforme esperado, mas resultaram em maiores perdas a 25 °C. O aumento do teor de oxigênio entre 5 e 15% não alterou sistematicamente a densidade, mas resultou num pequeno aumento do tamanho de grão. Já a correlação entre teor de oxigênio e perdas foi complexa. Foi observado que existe uma temperatura de mínimo nas perdas totais por volta de 60 °C. O mesmo comportamento foi observado na curva da perda histerética, compatível com a variação da constante de anisotropia magnetocristalina (K1). Foram realizados ensaios de curvas de histerese a partir de 25 até 100 °C, a 0,2 T com o objetivo de avaliar o efeito da temperatura nas duas parcelas da perda histerética. Amostras sinterizadas a 1290 °C com a menor pressão de oxigênio apresentaram menor temperatura de mínimo de perda. As técnicas de análise química do teor de Fe2+ não foram capazes de estabelecer, inequivocamente, a esperada relação entre essa variável e o teor de oxigênio da atmosfera de sinterização. / The use of manganese zinc ferrite in power sources of battery chargers is growing, due to its low magnetic power losses at inductions around 0.2 T. These ferrites belong to the soft magnetic materials group, they are polycrystalline ferromagnetic oxides with face centered cubic structure. Powders of this material were compacted in uniaxial press and in automatic press of production, by ring and toroidal form, respectively. Two firing cycles, varying the atmosphere oxygen content between 5 and 15%, were applied to evaluate its effect on microstructure, density, magnetic losses in high induction and permeability. Samples sintered in warmer positions inside the furnace resulted in higher density and larger grain size, as expected, but higher losses at 25 °C were achieved. Increasing the atmosphere oxygen content from 5 to 15% did not alter density significantly, but resulted in a slight increase in grain size. On the other hand, the correlation between oxygen content and losses was complex. There are lower losses, at 60 °C. Similar behavior was observed with hysteresis loss, which is compatible with the change in magnetocrystalline magnetic anisotropy (K1). Measurements were performed from 25 to 100 °C, at 0.2 T, aiming at the evaluation of the effect of temperature on the two parcels of hysteresis loss. Samples sintered at 1290 °C with low atmosphere oxygen content showing a minimum on the losses versus temperature curve. The available techniques to analyze Fe2+ content were not capable of establishing, unequivocally, the expected relation between this variable and the oxygen content of the sintering atmosphere.
4

Perdas em ferritas de manganês zinco: o papel da sinterização e de parâmetros microestruturais. / Magnetic losses in maganese zinc ferrites: the role of sinterization and microstructural parameters.

Victoria Amelia Lázaro Colán 21 May 2010 (has links)
O uso das ferritas de manganês zinco em fontes de potência de carregadores de bateria vem crescendo nos últimos anos, devido a suas baixas perdas magnéticas em induções da ordem de 0,2 T. Estas ferritas pertencem à categoria de ferritas moles, são óxidos ferrimagnéticos, policristalinos com estrutura cúbica tipo espinélio. Pós desse material foram compactados em prensa uniaxial e em prensa automática de produção para anel e toróide, respectivamente. Foram realizados dois ciclos de queima variando o teor de oxigênio entre 5 e 15%, no patamar de sinterização, com o propósito de avaliar seu efeito na densidade, microestrutura, perdas magnéticas em altas induções (0,2 T) e permeabilidade. Amostras sinterizadas em posições mais quentes do forno resultaram em maior densidade e maior tamanho de grão, conforme esperado, mas resultaram em maiores perdas a 25 °C. O aumento do teor de oxigênio entre 5 e 15% não alterou sistematicamente a densidade, mas resultou num pequeno aumento do tamanho de grão. Já a correlação entre teor de oxigênio e perdas foi complexa. Foi observado que existe uma temperatura de mínimo nas perdas totais por volta de 60 °C. O mesmo comportamento foi observado na curva da perda histerética, compatível com a variação da constante de anisotropia magnetocristalina (K1). Foram realizados ensaios de curvas de histerese a partir de 25 até 100 °C, a 0,2 T com o objetivo de avaliar o efeito da temperatura nas duas parcelas da perda histerética. Amostras sinterizadas a 1290 °C com a menor pressão de oxigênio apresentaram menor temperatura de mínimo de perda. As técnicas de análise química do teor de Fe2+ não foram capazes de estabelecer, inequivocamente, a esperada relação entre essa variável e o teor de oxigênio da atmosfera de sinterização. / The use of manganese zinc ferrite in power sources of battery chargers is growing, due to its low magnetic power losses at inductions around 0.2 T. These ferrites belong to the soft magnetic materials group, they are polycrystalline ferromagnetic oxides with face centered cubic structure. Powders of this material were compacted in uniaxial press and in automatic press of production, by ring and toroidal form, respectively. Two firing cycles, varying the atmosphere oxygen content between 5 and 15%, were applied to evaluate its effect on microstructure, density, magnetic losses in high induction and permeability. Samples sintered in warmer positions inside the furnace resulted in higher density and larger grain size, as expected, but higher losses at 25 °C were achieved. Increasing the atmosphere oxygen content from 5 to 15% did not alter density significantly, but resulted in a slight increase in grain size. On the other hand, the correlation between oxygen content and losses was complex. There are lower losses, at 60 °C. Similar behavior was observed with hysteresis loss, which is compatible with the change in magnetocrystalline magnetic anisotropy (K1). Measurements were performed from 25 to 100 °C, at 0.2 T, aiming at the evaluation of the effect of temperature on the two parcels of hysteresis loss. Samples sintered at 1290 °C with low atmosphere oxygen content showing a minimum on the losses versus temperature curve. The available techniques to analyze Fe2+ content were not capable of establishing, unequivocally, the expected relation between this variable and the oxygen content of the sintering atmosphere.
5

Méthode EF2 et hyperréduction de modèle : vers des calculs massifs à l'échelle micro / FE2 method and hyperreduction : towards intensive computations at the micro scale

Peyre, Georges 22 September 2015 (has links)
Des méthodes de réduction de modèle sont utilisées pour diminuer le coût de calcul associé à des analyses paramétriques de structures qui requièrent un très grand nombre de simulations quasi-identiques. Parmi ces méthodes, l'hyperréduction de modèle est efficace pour attaquer les problèmes de mécanique non-linéaire. Une approche orientée objet de cette méthode dans le cadre d'un code éléments finis modulaire a été développée. L'architecture logicielle s'appuie sur un algorithme qui se déroule en deux étapes : une étape extit{offline} dans laquelle le modèle réduit est construit à partir d'états du système mécanique et une étape extit{online} de calcul réduit qui exploite le modèle réduit. La structure du code qui repose sur l'utilisation d'un élément réduit permet d'améliorer la performance, de simplifier la prise en main et de favoriser sa réutilisation dans les développements futurs de la méthode. En outre, la méthode d'hyperréduction est revisitée et améliorée : des bases réduites vectorielles et tensorielles sont mises en oeuvre pour traiter les champs de contraintes et de variables internes des calculs éléments finis non-linéaires. En particulier, l'accent est mis sur la prise en compte des conditions aux limites périodiques et des conditions de bord libre. Dans cette démarche, les conditions aux limites au bord du domaine réduit sont imposées dans l'équation de l'équilibre mécanique réduit. Des exemples d'inclusions élastiques fibre/matrice sont fournis ainsi qu'un calcul complet adaptatif non-linéaire sur plaque perforée. Pour prendre en compte les effets de la microstructure, les méthodes éléments finis au carré ($EF^{2}$) divisent le problème mécanique en deux échelles. A l'échelle microscopique, les équations de comportement sont intégrées sur le volume élémentaire représentatif (VER) sollicité en condition périodique. Le comportement de la structure macroscopique est déterminé par homogénéisation. Une méthode d'hyperréduction multidimensionnelle est appliquée au problème microscopique constitué de l'ensemble des volumes élémentaires représentatifs. On se sert d'un algorithme de Broyden-Fletcher-Goldfarb-Shanno (BFGS) pour mettre à jour les matrices tangentes macroscopiques en chaque point de Gauss. On parvient ainsi à diminuer le temps de calcul sur des modèles de faible dimension. Cependant, quand le nombre de degrés de liberté augmente, on démontre que l'hyperréduction de modèle multidimensionnelle ne parvient pas à réduire suffisamment les coûts de calcul. / Model Order Reduction (MOR) methods are used to cope with high computational costs typically involved in parametric analysis of structures requiring a huge number of almost similar simulations. Among them, a so-called hyperreduction method suitable for non-linear mechanical finite element (FE) problems is studied. An objected-oriented approach to deal with it in the framework of a FE software is carried out. The software design takes advantage of a two-level process : a so-called offline computation step in which the reduced model is set up based on collected snapshots of mechanical system states and an online high-speed reduced computation which runs the reduced model. The code design relying on a reduced element is expected to enhance performance, to give a clearer view over the process and to favour code reuse in subsequent developments of the method. Futhermore, the hyperreduction method is reviewed and is deeply improved : vector and tensor bases are introduced to deal with non-scalar fields which arise in non-linear mechanical FE problems and the mechanical balance is ensured in the extrapolation phase. A particular emphasis is placed on the treatment of free and periodic boundary conditions. In this approach, the boundary conditions at the edge of the reduced integration domain are enforced in the reduced balance equations. Numerical toy examples of elasticity fiber/matrix inclusions as well as a full adaptative non-linear simluation are provided to show the capabilities of the implementation. To take into account microstructural behaviors, FE2 methods consist in splitting the computation into two scales. At the micro scale the material constitutive equations are integrated over periodic RVEs. The behavior of the macro structure is carried out by a homogeneized process. A multidimensional hyperreduction method is applied to the massive micro problem composed of the set of the periodic RVEs. A BFGS algorithm is used to update the macro tangent matrices at each integration Gauss point. Some speed-ups are recorded for low dimensional models. However, as the number of degrees of freedom increases, the multidimensional hyperreduction method is proved to be far less efficient to cut computational costs down.
6

1H NMR spectroscopic elucidation in solution of the kinetics and thermodynamics of spin crossover for an exceptionally robust Fe2+ complex

Petzold, Holm, Djomgoue, Paul, Hörner, Gerald, Speck, J. Matthäus, Rüffer, Tobias, Schaarschmidt, Dieter 15 September 2016 (has links) (PDF)
A series of Fe2+ spin crossover (SCO) complexes [Fe(5/6)]2+ employing hexadentate ligands (5/6) with cis/trans-1,2-diamino cyclohexanes (4) as central building blocks were synthesised. The ligands were obtained by reductive amination of 4 with 2,2′-bipyridyl-6-carbaldehyde or 1,10-phenanthroline-2-carbaldehyde 3. The chelating effect and the rigid structure of the ligands 5/6 lead to exceptionally robust Fe2+ and Zn2+ complexes conserving their structure even in coordinating solvents like dmso at high temperatures. Their solution behavior was investigated using variable temperature (VT) 1H NMR spectroscopy and VT Vis spectroscopy. SCO behavior was found for all Fe2+ complexes in this series centred around and far above room temperature. For the first time we have demonstrated that the thermodynamics as well as kinetics for SCO can be deduced by using VT 1H NMR spectroscopy. An alternative scheme using a linear correction term C1 to model chemical shifts for Fe2+ SCO complexes is presented. The rate constant for the SCO of [Fe(rac-trans-5)]2+ obtained by VT 1H NMR was validated by Laser Flash Photolysis (LFP), with excellent agreement (1/(kHL + kLH) = 33.7/35.8 ns for NMR/LFP). The solvent dependence of the transition temperature T1/2 and the solvatochromism of complex [Fe(rac-trans-5)]2+ were ascribed to hydrogen bond formation of the secondary amine to the solvent. Enantiomerically pure complexes can be prepared starting with R,R- or S,S-1,2-diaminocyclohexane (R,R-trans-4 or S,S-trans-4). The high robustness of the complexes reduces a possible ligand scrambling and allows preparation of quasiracemic crystals of [Zn(R,R-5)][Fe(S,S-5)](ClO4)4·(CH3CN) composed of a 1 : 1 mixture of the Zn and Fe complexes with inverse chirality. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
7

Nanoparticules d'oxydes de fer PEGylées pour la délivrance de la doxorubicine : développement et évaluation de leur potentiel théragnostique. / PEGylated iron oxide nanoparticles for doxorubicin delivery : development and evaluation of a potential theragnostic system

Gautier, Juliette 19 June 2013 (has links)
Des nanoparticules d’oxydes de fer superparamagnétiques (SPIONs) PEGylées ont servi de plateforme pour la formulation de nanovecteurs théragnostiques pour la délivrance d’un agent anticancéreux, la doxorubicine (DOX). Le chargement de la DOX sur les nanovecteurs à l’aide d’un complexe avec l’ion fer (II) a été optimisé. Ce complexe se dissocie en milieu acide, typique des compartiments intracellulaires. La spectroscopie Raman exaltée de surface (SERS) a confirmé que les nanovecteurs libèrent la DOX sous forme non complexée. La cytotoxicité in vitro induite par la libération de la DOX a été évaluée sur différentes lignées cellulaires de cancer du sein, et comparée à celle de la DOX en solution. Les voies d’internalisation des nanovecteurs ont été explorées en microscopie électronique en transmission (MET), et le devenir intracellulaire de la DOX a été suivi en imagerie confocale multispectrale (ICMS). Enfin, un protocole thérapeutique in vivo chez la souris tumorisée a permis d’évaluer la capacité de la nanoformulation à limiter la croissance tumorale, la possibilité d’un ciblage magnétique, et la réduction des effets secondaires induits par la DOX. / PEGylated superparamagnetic iron oxide nanoparticles (SPIONs) were used as a platform to build theranostic nanovectors for the delivery of an anticancer drug, doxorubicin (DOX). The DOX loading on nanocarriers via a DOX-iron (II) complex was optimized. The complex dissociates at low pH, typical of intracellular compartments. Surface enhanced Raman scattering (SERS) confirmed that the nanovectors released DOX under free form. In vitro cytotoxicity due to DOX loaded on nanocarriers was performed on different breast cancer cells, and compared to that of DOX in solution. Internalization pathways of nanovectors were explored with transmission electron microscopy (TEM), and intracellular fate of DOX was monitored by confocal spectral imaging (CSI). To finish, a therapeutical protocol was performed on tumorized mice, in order to evaluate the efficacy of the nanoformulation on tumor reduction, the possibility of magnetic targeting, and the decrease of side effects induced by DOX.
8

Nouveaux matériaux d’électrodes pour microbatteries au sodium / New electrode materials for sodium microbatteries

Pelé, Vincent 25 November 2016 (has links)
Les futures générations de microbatteries devant fonctionner à des tensions plus faibles, ces travaux sont dédiés à l’étude de matériaux d’électrodes en couche mince pour accumulateurs au Na et Na-ion pouvant répondre à ce nouveau cahier des charges. Ce manuscrit décrit ainsi le choix, l’élaboration et la caractérisation de matériaux d’électrode massifs et en couches minces. Les matériaux présentés ont été sélectionnés pour leur potentiel de fonctionnement et du mécanisme régissant l’insertion des ions alcalins. Pour chaque matériau, notre démarche a impliqué l’élaboration d’une cible permettant le dépôt par pulvérisation cathodique magnétron RF. Les différents paramètres de dépôt ont été optimisés pour obtenir les propriétés physico-chimiques et électrochimiques désirées et dresser une comparaison entre la configuration massive et en couche mince. L’étude du Fe2(MoO4)3 montre les différences de mécanismes selon l’ion alcalin employé. Le bismuth (mécanisme d’alliage), étudié en couches minces, nous a permis d’élucider des réactions électrolytiques parasites ; nos travaux s’attardant également sur les composés NaBi et Na3Bi. Enfin, cette thèse présente 2 sulfures, le matériau « de conversion » FeS2 et un nouveau matériau lamellaire : le Na2TiS3. / As the next generations of microbatteries are expected to power microelectronics devices working at lower voltages, we address the elaboration and characterization of electrode materials for sodium microbatteries. The described materials were selected according to several criterions including their working potentials and insertion mechanisms. For each material, the deposition of thin films was performed using RF magnetron sputtering, the deposition parameters being optimised in order to reach the targeted properties and to highlight the special features of thin film electrodes. The study of the intercalation compound Fe2(MoO4)3 shows the differences in mechanism between Li and Na insertion; while the alloying compound Bi undergoes parasitic electrolytic reactions. Our work also addresses two sulphides: the conversion compound FeS2 and the new layered material Na2TiS3.
9

1H NMR spectroscopic elucidation in solution of the kinetics and thermodynamics of spin crossover for an exceptionally robust Fe2+ complex

Petzold, Holm, Djomgoue, Paul, Hörner, Gerald, Speck, J. Matthäus, Rüffer, Tobias, Schaarschmidt, Dieter 15 September 2016 (has links)
A series of Fe2+ spin crossover (SCO) complexes [Fe(5/6)]2+ employing hexadentate ligands (5/6) with cis/trans-1,2-diamino cyclohexanes (4) as central building blocks were synthesised. The ligands were obtained by reductive amination of 4 with 2,2′-bipyridyl-6-carbaldehyde or 1,10-phenanthroline-2-carbaldehyde 3. The chelating effect and the rigid structure of the ligands 5/6 lead to exceptionally robust Fe2+ and Zn2+ complexes conserving their structure even in coordinating solvents like dmso at high temperatures. Their solution behavior was investigated using variable temperature (VT) 1H NMR spectroscopy and VT Vis spectroscopy. SCO behavior was found for all Fe2+ complexes in this series centred around and far above room temperature. For the first time we have demonstrated that the thermodynamics as well as kinetics for SCO can be deduced by using VT 1H NMR spectroscopy. An alternative scheme using a linear correction term C1 to model chemical shifts for Fe2+ SCO complexes is presented. The rate constant for the SCO of [Fe(rac-trans-5)]2+ obtained by VT 1H NMR was validated by Laser Flash Photolysis (LFP), with excellent agreement (1/(kHL + kLH) = 33.7/35.8 ns for NMR/LFP). The solvent dependence of the transition temperature T1/2 and the solvatochromism of complex [Fe(rac-trans-5)]2+ were ascribed to hydrogen bond formation of the secondary amine to the solvent. Enantiomerically pure complexes can be prepared starting with R,R- or S,S-1,2-diaminocyclohexane (R,R-trans-4 or S,S-trans-4). The high robustness of the complexes reduces a possible ligand scrambling and allows preparation of quasiracemic crystals of [Zn(R,R-5)][Fe(S,S-5)](ClO4)4·(CH3CN) composed of a 1 : 1 mixture of the Zn and Fe complexes with inverse chirality. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
10

Prognóstico da toxidez por ferro em arroz irrigado a partir da análise química do solo / Prognosis of iron toxicity in irrigated rice from soil chemical analysis

Wolter, Roberto Carlos Doring 22 August 2014 (has links)
Submitted by Gabriela Lopes (gmachadolopesufpel@gmail.com) on 2018-05-17T17:27:26Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_Roberto Carlos Doring Wolter.pdf: 2034054 bytes, checksum: d53dff149845c79db461dd69fc6b8806 (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2018-05-18T20:34:58Z (GMT) No. of bitstreams: 2 Tese_Roberto Carlos Doring Wolter.pdf: 2034054 bytes, checksum: d53dff149845c79db461dd69fc6b8806 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-05-18T20:34:58Z (GMT). No. of bitstreams: 2 Tese_Roberto Carlos Doring Wolter.pdf: 2034054 bytes, checksum: d53dff149845c79db461dd69fc6b8806 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2014-08-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / A toxidez por ferro é um dos mais importantes estresses abióticos em solos de várzea. Depois do surgimento dos sintomas de toxidez na lavoura, apenas medidas paliativas podem ser tomadas para diminuir o efeito do problema. Os objetivos do trabalho foram verificar se os critérios de interpretação para prognóstico do risco de ocorrência da toxidez por ferro em arroz irrigado por alagamento baseado na porcentagem de saturação da CTC por Fe2+ (PSFe2+), que é calculada a partir da estimativa do ferro trocável, proveniente da determinação do ferro extraído por oxalato de amônio pH 6,0 de uma amostra coletada anterior ao alagamento, são válidos para um grupo de solos de várzea do Rio Grande do Sul. Além disso, se a inclusão de outras variáveis melhora a estimação e o prognóstico, e ainda se a relação das classes de riscos está de acordo com a ocorrência da toxidez nas plantas. Para isso foram conduzidos quatro experimentos com plantas usando diferentes solos em casa de vegetação e um experimento em solução nutritiva em laboratório. Os resultados do experimento em solução nutritiva mostram que o surgimento dos sintomas de toxidez por ferro nas plantas de arroz apenas ocorreram a partir da fração entre 0,45 e 0,60 de ferro pelos cátions divalentes, diferente do valor de 0,40 da fração de ferro na solução definido como crítico para a toxidez pelo método, no entanto, não foi detectada mudança nos teores de ferro no tecido das plantas quando se variou a fração molar de ferro na solução nutritiva. Com os resultados dos experimentos com plantas em solos verificou-se que a alta PSFe2+ de uma amostra de solo está relacionada a uma maior probabilidade de ocorrência de toxidez por ferro, e em amostra com baixa PSFe2+ quase não ocorrem sintomas de toxidez por ferro, indicando que o método foi eficiente para prever a ocorrência de sintomas de toxidez por ferro nas plantas de arroz, para o grupo de solos. Também foi constatado que o uso das variáveis: C orgânico, ferro e manganês extraídos por oxalato de amônio pH 6 melhora a exatidão da estimação do ferro trocável comparado a estimação apenas pela extração de ferro, porém, isso não se refletiu em melhores prognósticos do risco de ocorrência de toxidez por ferro nas plantas de arroz do grupo de solos estudados, observou-se que as correlações com as duas formas de estimativas de ferro trocável com os atributos relacionados com a toxidez por ferro tiveram coeficientes bem próximos, impossibilitando a definição do melhor método. Pelo menor número de variáveis a serem determinadas, ou seja, pela maior facilidade de execução, a estimação do ferro trocável obtido apenas pelo ferro extraído por oxalato de amônio pH 6,0 é o método mais eficiente para prognosticar o risco de ocorrência de toxidez por ferro para o arroz irrigado. / The iron toxicity is one of the most important abiotic stress in lowland soils. After the appearance of toxicity symptoms in the field, only palliative measures can be taken to lessen the effect of the problem. The aims of this work were to verify if the interpretation criteria for predicting the risk of iron toxicity occurrence in rice plants by flooding based on the percentage saturation of CEC by Fe2+ (PSFe2+), which is calculated from the estimated exchangeable iron from the determination of iron extracted by ammonium oxalate pH 6.0 in a sample collected prior to flooding, are valid for a group of lowland soils from of Rio Grande do Sul. Furthermore, if the inclusion of other variables improves the estimation and prognosis, and if the relation of the classes of risks is consistent with the occurrence of toxicity in plants. For this, four experiments were conducted with plants, using different soils in a greenhouse and an experiment in nutrient solution in laboratory. The results of the experiment in nutrient solution have shown that the emergence of symptoms of iron toxicity in rice plants occurred only for the 0.45 and 0.60 molar ratio of iron to divalent cations, different from the 0.40 molar ratio of iron in solution defined as critical to the toxicity by the method. However, no change was detected for the iron levels on plant tissue when varying the molar ratio of iron in the nutrient solution. With the results of experiments with plants in soil one could verify that the higher the PSFe2+ of a soil sample the greater the probability of toxicity by iron, and for samples with low PSFe2+ almost no symptoms of toxicity occurred, indicating that the method was efficient in predicting the occurrence of iron toxicity symptoms in rice plants, for the group of soils. It was also found that the use of the variables: organic C, iron and manganese extracted by ammonium oxalate pH 6 improve the accuracy of the exchangeable iron estimation, when compared to estimating only by the iron extraction. However, it was not reflected in better prognostic of the risk of iron toxicity occurrence in rice plants, for the group of soils. It was observed that the correlations with the two forms of estimating exchangeable iron-related attributes of toxic iron coefficients were very close, making impossible the definition of the best method. By the small number of variables to be determined, ie, by the easiness of implementation, the estimation of exchangeable iron obtained only by the iron extracted by ammonium oxalate pH 6.0 is the most efficient method to predict the risk of iron toxicity for rice crop.

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