Sample records for hydrogen ions
from WorldWideScience.org

Sample records 1 - 11 shown.



1

Cinética de dissolução da superfície de aço SAE-AISI 1005 em meio ácido/ Kinetic of the surface dissolution of SAE-AISI 1005 steel in acid media

Magnani, Marina; Fugivara, Cecílio Sadao; Garcia, Roberto; Benedetti, Assis Vicente
2002-01-01

Resumo em português O setor automotivo é um dos mais competitivos e um grande consumidor de materiais ferrosos, que exigem uma eficiente proteção contra a corrosão. Esta proteção é alcançada aplicando revestimentos adequados. Para se aplicar revestimentos se requer uma cuidadosa preparação da superfície que pode ser feita por ataque químico. Neste trabalho, determinou-se a velocidade de reação do aço extra-doce, SAE-AISI 1005, laminado a frio (CFF) utilizando várias soluçõe (mais) s ácidas, de baixo custo, baixa agressividade ao meio ambiente e que geram pouco hidrogênio. O estudo cinético foi realizado medindo-se a perda de massa (deltam/mg cm-2) de chapas de aço CFF em função do tempo (s) de reação nas diferentes soluções, com e sem agitação, a 30ºC. Os resultados foram interpretados considerando-se os efeitos de transporte de massa, o efeito oxidante dos íons Me3+ e inibidor dos íons Fe2+. Dentre as várias soluções estudadas a que apresentou maior velocidade de reação foi a solução de H2SO4 2 M + MeCl3 1 M, v = 15,44 x 10-6 g cm-2s-1 para tempos até 1800 s. Resumo em inglês The automotive sector is one of the biggest consumers of ferrous materials, which require an efficient protection against corrosion. This protection can be reached applying adequate coatings. A careful surface preparation is required to apply any kind of coatings on surfaces. The surface preparation can be done by a chemical attack. In this work, reaction rates of cold-rolled steel with different acid solutions were determined. The solutions used have low cost, are enviro (mais) nmental friendly and some of them generate low quantity of hydrogen. The kinetic study was performed measuring the loss of mass (deltam/mg cm-2) of cold-rolled steel samples with time (s) reaction in the different solutions, with and without solution stirring, at 30 ºC. The results were interpreted considering the mass transfer effect, the Me3+ oxidizing and Fe2+ inhibitor effects on the steel dissolution. Among the different solutions studied, the 2 M H2SO4 + 1 M MeCl3 solution was the one that showed the highest rate, v = 15.44 x 10-6 g cm-2 s-1 for times up to 1800 s.

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2

Importância da ventilação pulmonar no transporte de 0(2) e equilíbrio ácido-base após desclampeamento intermitente de aorta na revascularização cirúrgica do miocárdio: desclamping in coronary artery bypass graft/ Importance of lung ventilation on oxygen transport and acid-base balance after intermittent aortic cross

Piccioni, Marilde de Albuquerque; Jatene, Fábio B; Auler Júnior, José Otávio C; Jatene, Marcelo B; Oliva, José Luís; Jatene, Adib D
1991-12-01

Resumo em português Na revascularização cirúrgica do miocárdio, empregando-se a técnica de pinçamento intermitente de aorta, após o desclampeamento e a recuperação dos batimentos cardíacos, surgiu a polêmica da necessidade da ventilação pulmonar na prevenção de hipoxemia. O objetivo deste trabalho foi analisar a importância da ventilação pulmonar no transporte de oxigênio e equilíbrio ácido-base do sangue que irá perfundir o miocárdio após desclampeamento de aorta e r (mais) ecuperação dos batimentos cardíacos. Foram estudados dez pacientes submetidos a revascularização cirúrgica do miocárdio, empregando-se a técnica de pinçamento intermitente de aorta com hipotermia moderada (± 32ºC). Em cinco pacientes (Grupo I), após o 1º desclampeamento de aorta, a ventilação pulmonar foi realizada simultaneamente à recuperação dos batimentos cardíacos. Nos outros cinco pacientes (Grupo II) não se realizou a ventilação pulmonar. Foram analisados (Saturação de O2, PO2, PCO2 e pH) do sangue do átrio direito (AD), tronco pulmonar (AP), átrio esquerdo (AE), aorta (Ao), artéria radial (art. radial) e circuito da circulação extracorpórea (CEC) (arterial [art. CEC] e venoso [ven. CEC]), comparando-se os dois grupos. Não houve diferença estatisticamente nos valores de saturação de 02 em ambos os grupos. No Grupo I, os valores do PO2 aumentaram significativamente. Houve aumento significante da PO2 no Grupo II, contribuindo para redução significante de pH neste grupo. Os autores concluem que, embora não tenha ocorrido hipoxemia, a acidose respiratória observada no Grupo II permite recomendar a ventilação pulmonar ao utilizar-se do pinçamento intermitente de aorta como forma de proteção miócardica, pois sabese dos efeitos deletérios do aumento da concentração de íons hidrogênio ([H+]) na função contrátil do miocárdio. Resumo em inglês In coronary artery bypass graft employing the surgical technique of intermittent aortic cross-clamping appeared the controversy of the need of lung ventilation on prevention of the hypoxemia. The purpose of this work was to verify the importance of lung ventilation on oxygen transport and acidbase balance in blood that will reperfuse the myocardium following aortic desclamping. Ten patients undergoing coronary artery bypass graft under moderate hypothermia were divided in (mais) two groups: I - Lung ventilation was carried out after aortic desclamping. II - Lung ventilation wasn't done following aortic desclamping. Blood samples were collected from the left right atrium, aorta, radial and pulmonary artery and the both sides of bypass circuit (venous and arterial). Oxygem saturation, oxygen tension, carbon dioxide tension, and blood pH were evaluated in the both groups. The results showed no statistical difference between groups concerning oxygen saturation. The pH decreases significantly in patients of Group II, due to a sharp elevation of PCO2. Although no significative hypoxemia could be observed, the respiratory acidosis that appeared in Group II suggests the importance of ventilation of the lungs as soon as possible after aortic desclamping. It is important to remember that myocardial contractility may be depressed by hydrogen ions (H+) in excess.

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3

Uso da casca de coco verde como adsorbente na remoção de metais tóxicos/ The use of green coconut shells as absorbents in the toxic metals

Sousa, Francisco W.; Moreira, Sarah A.; Oliveira, André G.; Cavalcante, Rivelino M.; Nascimento, Ronaldo F.; Rosa, Morsyleide F.
2007-10-01

Resumo em inglês Green coconut shells were treated with acid, base and hydrogen peroxide solutions for 3, 6, 12 and 24 h for removing toxic metals from synthetic wastewater. The removal of ions by the adsorbent treated with 0.1 mol L-1 NaOH/ 3h was 99.5% for Pb2+ and 97.9% for Cu2+. The removal of Cd2+, Ni2+, Zn2+, using adsorbent treated with 1.0 mol L-1 NaOH/3 h, was 98.5, 90.3 and 95.4%, respectively. Particle size, adsorbent concentration and adsorption kinetics were also studied. An (mais) adsorbent size of 60-99 mesh and a concentration of 30-40 g/L for 5 min exposure were satisfactory for maximum uptake of Pb2+, Ni2+, Cd2+, Zn2+ and Cu2+ and can be considered as promising parameters for treatment the aqueous effluents contaminated with toxic metals.

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4

Síntese e caracterização de copolímeros de estireno e divinilbenzeno clorometilados/ Synthesis and characterization of chloromethylated styrene-divinylbenzene copolymers

Teixeira, Viviane G.; Coutinho, Fernanda M. B.; Gomes, Ailton S.
2004-01-01

Resumo em português A reação de clorometilação de copolímeros de estireno e divinilbenzeno (S-DVB) em presença de HCl, formaldeído e cloreto de zinco foi estudada em meios aquoso e orgânico. O copolímero S-DVB foi, primeiramente, sintetizado por polimerização em suspensão e caracterizado quanto às suas propriedades porosas. Em meio aquoso, o copolímero foi clorometilado borbulhando-se HCl na mistura de solução aquosa de formaldeído a 37% (formalina 37%) e solução aquosa de (mais) cloreto de zinco (catalisador). Em meio orgânico (1,2-dicloroetano), foram usados HCl (borbulhado na solução reacional), paraformaldeído e cloreto de zinco sólido. A presença de grupos clorometila foi identificada por espectroscopia na região do infravermelho e o teor desses grupos foi determinado por titulação potenciométrica dos íons cloreto, liberados após a reação de quaternização com piridina. A reação em meio aquoso originou copolímeros com baixos graus de clorometilação, mesmo sob condições drásticas (uso do catalisador sólido e ácido clorídrico concentrado como meio reacional). Em meio orgânico, devido à maior estabilidade do eletrófilo, foram originados copolímeros com teores mais altos de grupos clorometila. Foi estudada a influência dos parâmetros reacionais sobre o grau de clorometilação dos copolímeros em meio orgânico. A temperatura e a razão copolímero/catalisador foram parâmetros determinantes do grau de clorometilação obtido. Resumo em inglês Cloromethylation of styrene-divinylbenzene copolymer (S-DVB) in presence of hydrogen chloride, formaldehyde and zinc chloride was studied in aqueous and organic media. S-DVB was first synthesized by suspension polymerization and its porosity was characterized. In aqueous medium, S-DVB was chloromethylated by using a mixture of hydrogen chloride, aqueous formaldehyde solution (formalin 37%) and aqueous zinc chloride solution as catalyst. In organic medium (1,2-dichloroetha (mais) ne), a mixture of hydrogen chloride, paraformaldehyde and solid zinc chloride was employed. The presence of chloromethyl groups in the copolymer was investigated by infrared spectroscopy analysis and titration of chloride ions, after a quaternization reaction between the chloromethylated copolymer and pyridine. The reaction in aqueous medium seems to be very difficult to occur even in the presence of solid zinc chloride (catalyst) and concentrated hydrochloric acid as reaction medium. Organic medium offers a better condition for aromatic eletrophilic substitution, where the reaction occurred in a more satisfactory way. The influence of reaction parameters was studied. Temperature and copolymer/catalyst ratio were the main responsible factors for the attained chloromethylation degree.

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5

Reciclagem do crômio de resíduos químicos provenientes da determinação de carbono oxidável em fertilizantes orgânicos/ Recycling of chromium in chemical waste from oxidizable carbon determination in organic fertilizer

Machado, Jeane M. C; Oliveira, Lenita M. C. P. E; Kamogawa, Marcos Y
2011-01-01

Resumo em inglês This work proposes a separation, recovery and reuse procedure of chemical residues with chromium. This residue was generated by the determination of oxidizable carbon in organic fertilizers samples. The Cr(VI) of the residue was reduced with ethanol and precipitated with NaOH. The Cr(OH)3 precipitate was separated and oxidized to dichromate ions with hydrogen peroxide. This solution was used another time in organic carbon determination. The uses of recycled dichromate sol (mais) ution were appropriated in four successive recycling. The accuracy was proven using potassium hydrogen phthalate and ten organic fertilizer samples. The organic carbon results, determined with recycled solutions, were similar the conventional solution.

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6

Potencialidades do dióxido de chumbo eletrodepositado como sensor potenciométrico/ Potentialities of electrodeposited lead dioxide as a potentiometric sensor

Capelato, Milton Duffles; Cassiano, Neila Maria
1998-07-01

Resumo em inglês This paper proposes an experiment to be performed in both instrumental analysis and experimental physical-chemistry curricular disciplines in order to open options to develop challenging basic research activities. Thus the experimental procedures and the results obtained in the preparation of electrodeposited lead dioxide onto graphite and its evaluation as potentiometric sensor for H3O+ and Pb2+ ions, are presented. The data obtained in acid-base titrations were compared (mais) with those of the traditional combination glass electrode at the same conditions. Although a linear sub-Nernstian response to free hydrogen ions was observed for the electrodeposited PbO2 electrode, a good agreement was obtained between them. Working as lead(II) sensing electrode, the PbO2 showed a linear sub-Nernstian behavior at total Pb2+ concentrations ranging from 3,5 x 10-4 to 3,0 x 10-2 mol/L in nitrate media. For the redox couple PbO2/Pb(II) the operational slope converges to the theoretical one, as the acidity of the working solution increases.

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7

Metodologia analítica para a determinação de sulfato em vinhoto/ When sulfate is present in high concentrations, it acts as an inhibitor in the production of methane (biogas formation) in anaerobic biodigestion processes

Prada, Sílvio Miranda; Guekezian, Márcia; Suárez-Iha, Maria Encarnación. V.
1998-06-01

Resumo em inglês In this way it is very important to know the sulfate concentration in vinasse samples before to make the biodigestor design. A previous developed and indirect method (Anal. Chim. Acta. 1996, 329, 197), was used to determine sulfate in samples of vinasse, after previous treatments, done in order to eliminate organic matter with hydrogen peroxide 30% and concentrated nitric acid mixture (3:1), under heating. Interferent cationic ions were isolated by using ion exchange colu (mais) mns. The results obtained for some samples from Araraquara and Penápolis are here presented. The phosphate concentration was also determined.

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8

Estudos da eletrodeposição de metais em regime de subtensão/ Studies of the underpotential deposition of metals

Santos, Mauro C.; Machado, Sergio A. S.; Avaca, Luis A.; Mascaro, Lucia H.
2000-06-01

Resumo em inglês This work reviews recent studies of underpotential deposition (UPD) of several metals on Pt and Au substrates performed in the Grupo de Materiais Eletroquímicos e Métodos Eletroanalíticos (IQSC -- USP, São Carlos). The UPD Cu, Cd and Pb on Pt were analysed in terms of their influence in the oxygen evolution reaction. Partial blockage of surface active sites, promoted by Pb ad-atoms, resulted in a change from water to hydrogen peroxide as the final product. The Ag UPD (mais) on Pt and Au substrates was also discussed in this work. A detailed model of charge calculation for Ag monolayer was developed and confirmed by the rotating ring-disk data. The partial charge transfer in UPD studies was analysed in the Cd/Pt and Cd/Au systems and a value of 0.5 was found for the adsorption electrovalence of Cd ad-ions. The Sn/Pt UPD systems were studied from the point of view of the valences of metallic ions in solution. The deposition from Sn(IV) generates a full monolayer with a maximum occupation of approximately 40% of the surface active sites (340 µC cm-2) plus 105 µC cm-2 of Hads (half monolayer). Changing the metallic ion for Sn(II), it was possible to deposit a full monolayer (210 µC cm-2) without any detectable Hads. Finally, the effect of anions was discussed in the Zn/Pt and Zn/Au systems. Here, the hydrogen evolution reaction (her) and the hydrogen adsorption/desorption were used in order to investigate the maximum coverage of the surface with Zn ad-atoms. The full monolayer, characterised by the complete absence of Hads, was achieved only in 0.5 M HF solutions.

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9

Estudo da adsorção de hidrogênio e sulfeto na superfície de paládio: aspectos experimentais (eletroquímica) e teóricos (ab initio e Teoria do Funcional da Densidade)/ Experimental (electrochemistry) and theoretical (ab initio and Density Functional Theory) studies of hydrogen and sulfide adsorption on palladium (100) surface

Ângelo, Antônio Carlos D.; Souza, Aguinaldo R. de; Morgon, Nelson H.; Sambrano, Júlio R.
2001-08-01

Resumo em inglês The adsorption of H and S2- species on Pd (100) has been studied with ab initio, density-functional calculations and electrochemical methods. A cluster of five Pd atoms with a frozen geometry described the surface. The computational calculations were performed through the GAUSSIAN94 program, and the basis functions adapted to a pseudo-potential obtained by using the Generator Coordinate Method adapted to the this program. Using the cyclic voltammetry technique through a M (mais) odel 283 Potentiostat/Galvanostat E.G.&G-PAR obtained the electrochemical results. The calculated chemisorption geometry has a Pd-H distance of 1.55Å, and the potential energy surface was calculated using the Becke3P86//(GCM/DFT/SBK) methodology. The adsorption of S2- ions on Pd surface obtained both through comparison between the experimental and theoretical results, at MP2 level, suggest a S2- absorption into the metallic cluster. The produced Pd-(S2-) system was show to be very stable under the employed experimental conditions. The paper has shows the powerful aid of computational methods to interpret adsorption experimental data.

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10

Comparação de dois tipos de amostragem de chuva: deposição total e deposição apenas úmida em àrea costeira tropical/ Comparison of two types of rain sampling: total deposition and wet only deposition

Campos, Vânia P.; Costa, Angela C. A.; Tavares, Tania M.
1998-07-01

Resumo em inglês In a tropical coastal area. During 6 months the composition of rain samples collected simultaneously over 24h with an open collector and with an automatic opened collector (KFA - J¸lich Type) at 500m of the Atlantic coastline of Salvador were compared. All average concentrations were higher for the "total" samples than for the "wet only" samples, except for hydrogen ions, nitrate and ammonium.

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11

Caracterização e classificação de solos desenvolvidos de arenitos da formação Aquidauana-MS/ Characterization and classification of soils developed from sandstone of the Aquidauana formation

Schiavo, Jolimar Antonio; Pereira, Marcos Gervásio; Miranda, Luiz Paulo Montenegro de; Dias Neto, Antonino Hypólito; Fontana, Ademir
2010-06-01

Resumo em português A formação Aquidauana é constituída por um conjunto de sedimentos com até 500 m de espessura, predominando arenito de granulometria fina a média, intercalado com conglomerado arenoso. Nesse ambiente, o relevo é um dos principais fatores condicionantes na formação de solos. Objetivou-se, neste trabalho, caracterizar e classificar os solos desenvolvidos desses arenitos. Para isso, foram estudados quatro perfis ao longo de uma topossequência, de uma pendente repres (mais) entativa das colinas suaves onduladas verificadas na área de estudo. Os perfis localizavam-se no terço superior (P1), terço médio (P2), terço inferior (P3) e sopé de encosta (P4). Eles foram morfologicamente descritos, e os horizontes, caracterizados quanto às propriedades físicas e químicas. Os solos estudados apresentaram predomínio da fração areia (> 680 g kg-1), com textura variando de franco-arenosa (P4) a franco-argiloarenosa. Os valores de pH em água variaram de 4,2 a 6,5. Os valores de capacidade de troca catiônica variaram de 1,6 cmol c kg-1 no P4 a 10,3 cmol c kg-1 no P2, com predomínio dos íons H+ no P1 e P4 e Ca2+ no P2 e P3. Os horizontes subsuperficiais do P1 e P4 são distróficos, enquanto em P2 e P3 verificou-se elevada saturação por bases, evidenciando caráter eutrófico. À exceção do P2, os demais apresentaram argila de baixa atividade. Em todos os perfis verificaram-se atributos morfológicos, físicos, químicos e mineralógicos condicionados pelo material de origem e relevo, demonstrando a influência desses fatores na pedogênese. Resumo em inglês The Aquidauana geological formation consists of a set of up to 500 m thick sediments predominantly composed of sandstone with fine to medium grain size, interspersed with sandy conglomerates. In this environment, the topography is one of the main conditioning factors of the formation of different soil types in the landscape. The objective of this study was to characterize and classify soils developed from these sandstones. Four soils profiles along a representative topose (mais) quence of gentle slopes were sampled and studied. The profiles were located on the shoulder (P1), backslope (P2), footslope ( P3) and toeslope (P4). The soil profiles were morphologically described and physical and chemical properties of their horizons evaluated. The sand fraction was predominant in all profiles (> 680 g kg-1), with textures ranging from sandy loam (P4) to clay sandy loam. The water pH values ranged from 4.2 to 6.5. The cation exchange capacity values ranged from 1.6 cmol c kg-1(in P4) to 10.3 cmol c kg-1 (in P2), with a predominance of hydrogen ions in P1 and P4, and calcium in profile P2 and P3. The P1 and P4 pedons were dystrophic, whereas in P2 and P3, a high base saturation status evidenced an eutrophic character. Except in P2, the profiles presented low activity clays. In all soil profiles the morphological, physical, chemical and mineralogical properties were conditioned by the parent material and relief, demonstrating the influence of these factors on the pedogenesis.

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