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‣ Estudo da reocinética de cura de resinas epoxídicas por meio de diferentes técnicas de análise; Study of cure reokinetic of epoxy resins by different analytical techniques

Abreu, Mariane Martim Sobrosa Passos de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 24/09/2008 Português
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As aplicações comerciais e científicas das resinas epoxídicas dependem diretamente da combinação entre resina/endurecedor/acelerador, tornando-o um sistema reativo bastante complexo, cuja determinação dos seus parâmetros de cura é um problema multivariável de tempo, temperatura e concentração de reagentes. É necessário o conhecimento de suas etapas de cura e de seu mecanismo cinético para obtenção das melhores propriedades mecânicas, elétricas e térmicas, com a finalidade de conseguir uma resina epoxídica de alto desempenho. As técnicas analíticas comumente empregadas na determinação da cura de resinas epoxídicas como também de diversas outras resinas poliméricas são: a calorimetria exploratória diferencial (DSC) e a análise dinâmico-mecânica (DMA). Neste trabalho, dois sistemas reativos foram analisados: o primeiro, resultante da combinação de resina DGEBA com endurecedor à base de amina alifática; o segundo composto pela resina DGEBA reagida com endurecedor à base de anidrido e catalisado por amina terciária. É apresentada a metodologia empregada na determinação dos parâmetros cinéticos para os dois sistemas epóxi utilizando a análise por DSC isotérmica e não isotérmica, a técnica DMA isotérmica...

‣ Understanding the Crystallization Mechanism of a Wollastonite Base Glass Using Isoconversional, IKP Methods and Master Plots

Perez, Juan M.; Teixeira, Silvio R.; Rincon, Jesus Ma.; Romero, Maximina
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 3441-3447
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 08/04368-4; The complex development of crystals found in the crystallization of SiO2-Al2O3-CaO-Na2O glass has been explained using Differential Thermal Analysis. The crystal growth process has been studied using isoconversional, invariant kinetic parameters, and master plots methods. The applied kinetic models have revealed activation energy values that are over 360 and 385 kJ/mol by employing the integral and differential kinetic methods, respectively. The crystallization process schedule that was previously observed using scanning electron microscopy has been corroborated in this study using the kinetic methods. The crystallization of wollastonite occurs through a complex two-stage mechanism, with early three-dimensional growth of crystals (A(3) mechanism) on the surface of glass particles followed by one-dimensional growth of needles (A(3/2) mechanism) toward the interior of grains. The results presented in this article are in agreement with a previous paper that employed the Kissinger non-isothermal method and the Ligero approximation.

‣ Kinetic parameters for thermal decomposition of supramolecular polymers derived from flunixin-meglumine adducts

Cassimiro, Douglas L.; Ribeiro, Clovis A.; Capela, Jorge M. V.; Crespi, Marisa S.; Capela, Marisa V.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 405-410
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Meglumine, (2R,3R,4R,5S)-6-methylaminohexane-1,2,3,4,5-pentol, is a carbohydrate derived from sorbitol in which the hydroxyl group in position one is replaced by a methylamine group. It forms binary adducts with substances having carboxyl groups, which have in common the presence of hydrogen bonding as the main force in the stabilization of these species. During melting, adducts of meglumine with flunixin (2-[[2-methyl-3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid) polymerize or self-assemble in amorphous supramolecular structures with molecular weights around 2.0 x 10(5) kDa. DSC curves, in a first heating, show isomorphic transitions where the last one at 137 A degrees C for the flunixin-meglumine adduct originated the supramolecular amorphous polymers with glass transition around 49.5 A degrees C. The kinetic parameters for the thermal decomposition step of the polymers were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15, and 20 A degrees C min(-1), the E (alpha) and B (alpha) terms could be determined and, consequently, the pre-exponential factor, A(alpha), as well as the kinetic model, g(alpha).

‣ Application of Nonisothermal Cure Kinetics to the Interaction of Poly(ethylene terephthalate) with Alkyd Resin Varnish

Dias, D. S.; Crespi, M. S.; Ribeiro, C. A.; Kobelnik, M.
Fonte: John Wiley & Sons Inc Publicador: John Wiley & Sons Inc
Tipo: Artigo de Revista Científica Formato: 1316-1321
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Samples of varnish (V), poly(ethylene terephthalate) from recycled soft drink bottles (PET-R), and varnish/poly(ethylene terephthalate) from recycled soft drink bottles mixtures (VPET-Rs) were evaluated with differential scanning calorimetry (DSC) to verify their physicochemical properties and thermal behavior. Films from V and VPET-R were visually similar. The maximum amount of PET-R that we could add to V without significantly altering its filming properties, such adherence and color in glass sheets, was 2%. The cure process (80-203 degrees C) was identified through the DSC curves. The kinetic parameters, activation energy (E), and Arrhenius parameter (A) for the samples containing 0.5-2% PET-R were calculated with the Flynn-Wall-Ozawa isoconversional method. With greater amounts of PET-R added, there was a small change in E for the curing process. A kinetic compensation effect, represented by the equation ln A = -10.5 + 0.29E, was observed for all of the samples. The most suitable kinetic model to describe this curing process was the autocatalytic Sestak-Berggren model, which is applied to heterogeneous systems governed by nucleation and growth. (C) 2010 Wiley Periodicals...

‣ Decomposition kinetics of iron (III)-diclofenac compound

Kobelnik, M.; Bernabe, Giseli Aparecida; Ribeiro, C. A.; Capela, J. M. V.; Fertonani, Fernando Luís
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 493-496
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Non-isothermal decomposition of iron (III)-diclofenac anhydrous salt was investigated by thermogravimetry (TG) under different conditions in opened and closed alpha-alumina pans under nitrogen atmosphere. To estimate the activation energy of decomposition, the Capela and Ribeiro isoconversional method was applied. The results show that due to the lid cover different activation energies were obtained. From these curves a tendency can be seen where the plots maintain the same profile for closed lids and almost run parallel to each other. Independently of the different experimental conditions no remarkably different results have been obtained.

‣ Kinetic parameters for thermal decomposition of microcrystalline, vegetal, and bacterial cellulose

Barud, Hernani S.; Ribeiro, Clovis A.; Capela, Jorge M. V.; Crespi, Marisa S.; Ribeiro, Sidney. J. L.; Messadeq, Younes
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 421-426
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Cellulose can be obtained from innumerable sources such as cotton, trees, sugar cane bagasse, wood, bacteria, and others. The bacterial cellulose (BC) produced by the Gram-negative acetic-acid bacterium Acetobacter xylinum has several unique properties. This BC is produced as highly hydrated membranes free of lignin and hemicelluloses and has a higher molecular weight and higher crystallinity. Here, the thermal behavior of BC, was compared with those of microcrystalline (MMC) and vegetal cellulose (VC). The kinetic parameters for the thermal decomposition step of the celluloses were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and at heating rates of 5, 10, and 20 A degrees C/min, the E(alpha) and B(alpha) terms could be determined and consequently the pre-exponential factor A(alpha) as well as the kinetic model g(alpha). The pyrolysis of celluloses followed kinetic model g(alpha) = [-ln(1 - alpha)](1.63) on average, characteristic for Avrami-Erofeev with only small differences in activation energy. The fractional value of n may be related to diffusion-controlled growth, or may arise from the distributions of sizes or shapes of the reactant particles.

‣ Kinetic study of crystallization of PHB in presence of hydroxy acids

Souza, Josiane de Lima; Kobelnik, Marcelo; Ribeiro, Clovis Augusto; Vieira Capela, Jorge Manoel; Crespi, Marisa Spirandeli
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 525-528
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid (TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear fitting to obtain the estimation for activation energy (E (a) ) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 A degrees C at 5 A degrees C/min, and results obtained to the average activation energy, 73 +/- A 9 kJ mol(-1) and 63 +/- A 1 kJ mol(-1), to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain. PHB/TA show increase in the medium value of E (a), 119 +/- A 2 kJ mol(-1) and T (c) = 48.2 A degrees C (at 5 A degrees C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E (a)=73 +/- A 9 kJ mol(-1), T (c) = 44.8 A degrees C at 5 A degrees C/min).

‣ Thermal Study in Solid State of Zn(II)-Diclofenac Complex: Behavior Kinetic of the Dehydration, Transition Phase and Thermal Decomposition

Kobelnik, Marcelo; Quarcioni, Valdecir Angelo; Ribeiro, Clovis Augusto; Vieira Capela, Jorge Manuel; Dias, Diogenes dos Santos; Crespi, Marisa Spirandeli
Fonte: Chinese Chemical Soc Publicador: Chinese Chemical Soc
Tipo: Outros Formato: 384-390
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The dehydration, thermal decomposition and transition phase stage of Zn(II)-diclofenac compound were studied by simultaneous TG-DTA and DSC techniques. The TG and DSC curves of this compound were obtained with the mass of sample of 2 and 5 mg. Additionally, DSC curves were carried out in opened and closed alpha-alumina pans under static and nitrogen atmosphere. The DTA and DSC curves show that this compound possesses exothermic transition phase between 170-180 degrees C, which it is irreversible (monotropic reaction) The kinetics study of this transition phase stage was evaluated by DSC under non-isothermal conditions. The obtained data were evaluated with the isoconversional method, where the values of activation energy (E(a) / kJ mol(-1)) was plotted in function of the conversion degree (alpha). The results show that due to mass sample, different activation energies were obtained From these curves a tendency can be seen where the plots maintain the same profile for closed lids and almost run parallel to each other.

‣ Study of the thermal behavior of the transition phase of Co(II)-diclofenac compound by non-isothermal method

Kobelnik, Marcelo; Ribeiro, Clovis A.; Dias, Diogenes dos Santos; de Almeida, Sonia; Crespi, Marisa Spirandeli; Capela, Jorge M. V.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 467-471
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The Co(II)-diclofenac complex was evaluated by simultaneous thermogravimetry-differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC). The DTA curve profile shows one exothermic peak because of the transition phase of the compound between 170 and 180 A degrees C, which was confirmed by X-ray powder diffractometry. The transition phase behavior was studied by DSC curves at several heating rates of a sample mass between 1 and 10 mg in nitrogen atmosphere and in a crucible with and without a lid. Thus, the kinetic parameters were evaluated using an isoconversional non-linear fitting proposed by Capela and Ribeiro. The results show that the activation energy and pre-exponential factor for the transition phase is dependant on the different experimental conditions. Nevertheless, these results indicate that the kinetic compensation effect shows a relationship between them.

‣ Non-isothermal kinetic for lyophilized leachate from sanitary landfill and composting usine

Lima, Evaneide Nascimento; Crespi, Marisa Spirandeli; Ribeiro, C. A.; de Almeida, Sonia
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 823-826
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Leachate samples from a sanitary landfill of Araraquara city and composting usine of Vila Leopoldina, São Paulo, Brazil were lyophilized to remove the water content. TG/DTG curves at different heating rates were recorded. The second step of the thermal decomposition of leachate from the Araraquara landfill (CB1), from the composting usine from Vila Leopoldina (CB2) from the organic phase extracted (FO) and aqueous phase (FA) were all kinetically evaluated using the non-isothermal method.By Flynn-Wall isoconversional method the following values were obtained: E=234 +/- 3.65 kJ mol(-1) and logA=29.7 +/- 0.58 min(-1) for CB1; E=129 +/- 1.66 kJ mol(-1) and logA=11.8 +/- 0.10 min(-1) for CB2; E=51.6 +/- 1.35 kJ mol(-1) and logA=6.09 +/- 0.09 min(-1) for FO and E=76.91 +/- 6.33 kJ mol(-1) and logA=8.88 +/- 0.7 min(-1) for FA with 95% confidence level. Applying the procedures of Malek and Koga, SB kinetic model (Sestak-Berggren) is the most appropriate to describe the decomposition of CB1, CB2, FO and FA.

‣ Non-isothermal kinetic applied to thermal decomposition of commercial alkyd varnish

Amaral, GCA; Crespi, M. S.; Ribeiro, C. A.; Hikosaka, M. Y.; Guinesi, L. S.; Santos, A. F.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 375-377
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Samples of commercial alkyd resin varnish were spread in a film form on slides, dried at room temperature and exposed to solar radiation from one day up to seven months.Thermogravimetric measurements have been done. Based on the TG data, the Flynn-Wall isoconversional method was applied. The activation energy varied between 176-154 kJ mol(-1) and logA was between 15.5-12.9 min(-1) for A, B and C samples at 95% confidence level.

‣ Kinetic of thermal decomposition of residues from different kinds of composting

Silva, A. R.; Crespi, M. S.; Ribeiro, C. A.; Oliveira, S. C.; Silva, MRS
Fonte: Kluwer Academic Publ Publicador: Kluwer Academic Publ
Tipo: Artigo de Revista Científica Formato: 401-409
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Non-isothermal kinetic parameters regarding to the thermal decomposition of the ligninocellulosic fraction present in compost from urban solid residues (USR) obtained through stack covered (SC) with composted material, comes from the usine in composing of Araraquara city, São Paulo state, Brazil, and from stack containing academic restaurant organic solid residues (SAR). The samples were periodically revolved round 132 days of composting.Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the lignocellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated during that process. The lignocellulosic fraction decomposition, between 200 and 400degreesC, were kinetically evaluated through non-isothermal methods of analysis.By using the Flynn-Wall and Ozawa isoconversional method, the medium activation energy, E-a, and pre-exponential factor, IgA, were 283.0+/-4.6, 257.6+/-1.3 U mol(-1) and 25.4+/-0.8, 23.2+/-0.2 min(-1),to the SC and SAR, respectively, at 95% confidence level.From E-a, and IgA values and DSC curves, Malek procedure could be applied, Suggesting that the SB (Sestik-Berggren) kinetic model is suitable for the first thermal decomposition step.

‣ Kinetic parameters for thermal decomposition of hydrazine

Santos, L. B.; Ribeiro, C. A.; Capela, J. M V; Crespi, M. S.; Pimentel, M. A S; De Julio, M.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 1209-1216
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The propulsion of most of the operating satellites comprises monopropellant (hydrazine - N2H4) or bipropellant (monometilydrazine - MMH and nitrogen tetroxide) chemical systems. When some sample of the propellant tested fails, the entire sample lot shall be rejected, and this action has turned into a health problem due to the high toxicity of N2H 4. Thus, it is interesting to know hydrazine thermal behavior in several storage conditions. The kinetic parameters for thermal decomposition of hydrazine in oxygen and nitrogen atmospheres were determined by Capela-Ribeiro nonlinear isoconversional method. From TG data at heating rates of 5, 10, and 20 C min-1, kinetic parameters could be determined in nitrogen (E = 47.3 ± 3.1 kJ mol-1, lnA = 14.2 ± 0.9 and T b = 69 C) and oxygen (E = 64.9 ± 8.6 kJ mol-1, lnA = 20.7 ± 3.1 and T b = 75 C) atmospheres. It was not possible to identify a specific kinetic model for hydrazine thermal decomposition due to high heterogeneity in reaction; however, experimental f(α)g(α) master-plot curves were closed to F 1/3 model. © 2013 Akadémiai Kiadó, Budapest, Hungary.

‣ Estudo de degradação térmica e caracterização de lodos provenientes de diferentes sistemas de tratamento de esgotos

Torquato, Lilian Danielle de Moura
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 109 f.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Química - IQ; Neste trabalho foram caracterizadas as amostras de lodo dos sistemas de tratamento de efluentes sanitários de Araraquara-SP e São José do Rio Preto-SP com o intuito de: 1- investigar, por meio de técnicas termoanalíticas (TG/DTG, DTA e DSC), a ocorrência dos eventos que compreendem sua degradação térmica, além da obtenção de parâmetros que norteiam o entendimento da cinética dessa degradação; 2- avaliar os aspectos estruturais e morfológicos das partículas sólidas que os compõem, com o suporte de técnicas como: DRX, EDX, EAA, IV, EDL e MEV. A amostra de lodo LM (ETE Araraquara) apresentou apenas 7% de perda de massa atribuída à presença de matéria orgânica, com caráter predominantemente cristalino reafirmado por todas as técnicas utilizadas. Em relação às amostras LU e LF (ETE São José do Rio Preto), pôde-se observar o caráter predominantemente amorfo por DRX confirmado por perfis de decomposição térmica muito semelhantes com perda de massa de até 57% referente ao conteúdo orgânico. A aplicação do método isoconversional de Flynn-Wall-Ozawa revelou diferenças na cinética de degradação entre as amostras LU e LF atribuídas à presença da poliacrilamida aplicada no processo de desidratação do lodo. Observou-se ainda a ocorrência de efeito de compensação cinética...

‣ Caracterização e estudo do comportamento térmico de chorume, de composto maturado e derivados

Lima, Evaneide Nascimento
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 148 f. : il.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Química - IQ; Chorume é um líquido produzido durante a decomposição anaeróbia dos resíduos sólidos que tem potencial impacto ao ambiente devido a larga variedade de substâncias orgânicas e inorgânicas contidas nesta matriz. Dessa forma, o presente estudo apresenta a caracterização e estudo térmico de amostras de chorume de diferentes procedências as quais foram coletadas nos aterros de Araraquara (CA), São Carlos (CSC), Campinas (CC) e da usina de compostagem na Vila Leopoldina-SP (CSP). Adicionalmente foram estudados os extratos solúveis (ES) obtidos de composto maturado (CM) e o chorume de sistemas anaeróbios (SA1 e SA2) preenchidos com resíduos sólidos provenientes de restaurante universitário simulando as condições acidogênicas de decomposição anaeróbia de aterros. Os resultados obtidos da análise térmica (TG, DTA e DSC) evidenciaram que as amostras de chorume com características acidogênicas (CC, SA1, SA2) apresentaram-se menos estáveis termicamente quando comparadas as CA e CSP que estão em condições metanogênicas. O método isoconversional de Flynn-Wall permitiu a determinação dos parâmetros cinéticos (E e A) para reações de desidratação em intervalos fixos de temperatura. Os valores de E e lnA associados ao procedimento desenvolvido por Málek e Koga conduziu ao modelo mais aproximado para as reações em estudo. O modelo cinético SB (Sesták- Berggren) foi indicado para as reações de decomposição das amostras de extratos solúveis do composto maturado...

‣ Estudo térmico e caracterização química de amostras de resíduos sólidos de aterro sanitário

Almeida, Sonia de
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 107 f. : il.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Química - IQ; Os resíduos sólidos domiciliares são classificados como IIA de acordo com a ABNT (NBR 10004, 2004), que são resíduos não inertes. A pesquisa de campo foi realizada no aterro sanitário de São Carlos, em duas etapas: a primeira, em 2004 e a segunda, em 2006, cujo objetivo central foi a amostragem de resíduos dispostos entre o anos de 1999 até 2006. A fração orgânica dos resíduos domiciliares dispostos em aterros sanitários, sofre decomposição e gera o biogás e o chorume, que são fontes de poluição. As amostras foram retiradas do aterro em várias células de diversos anos, que após tratamentos, foram submetidas à análise de metais, difratometria de raios X, determinação da Demanda Química de Oxigênio e a determinação dos parâmetros cinéticos utilizando o método isoconversional de Flynn-Wall-Ozawa e determinação da alcalinidade total. As diferenças de alcalinidade encontradas nas amostras se devem às diferentes etapas de degradação da matéria orgânica presentes nos resíduos coletados no aterro sanitário. As curvas termogravimétricas (TG) e as curvas termogravimentricas derivadas (DTG) obtidas nessa pesquisa...

‣ Kinetic modeling of self-hydrolysis of aqueous NaBH4 solutions by model-based isoconversional method 

Retnamma, Rajasree; Novais, Augusto Q.; Rangel, C. M.; Yu, Lin; Matthews, Michael A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2014 Português
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The present work reports the kinetic modeling of self-hydrolysis of non-buffered, nonstabilized NaBH4 solutions by model-based isoconversional method. The overall kinetics is described by a ‘reaction-order’ model in a practical operating window of 10-20 wt% NaBH4 solutions at 25-80 ºC and 0-50% conversions. The apparent activation energy and preexponential factor are interrelated through a kinetic compensation effect (KCE). The apparent reaction order remains constant at a given temperature irrespective of extent of conversion and decreases with increase in temperature. It decreases from first-order to 0.26 with increase in temperature from 25 to 80 ºC. 

‣ Preparação de poliuretana à base de óleo de mamona

Rodrigues, Jucélia Maria Emerenciano
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Tese de Doutorado Formato: application/pdf
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Polyurethanes are very versatile macromolecular materials that can be used in the form of powders, adhesives and elastomers. As a consequence, they constitute important subject for research as well as outstanding materials used in several manufacturing processes. In addition to the search for new polyurethanes, the kinetics control during its preparation is a very important topic, mainly if the polyurethane is obtained via bulk polymerization. The work in thesis was directed towards this subject, particularly the synthesis of polyurethanes based castor oil and isophorone diisocianate. As a first step castor oil characterized using the following analytical methods: iodine index, saponification index, refraction index, humidity content and infrared absorption spectroscopy (FTIR). As a second step, test specimens of these polyurethanes were obtained via bulk polymerization and were submitted to swelling experiments with different solvents. From these experiments, the Hildebrand parameter was determined for this material. Finally, bulk polymerization was carried out in a differential scanning calorimetry (DSC) equipment, using different heating rates, at two conditions: without catalyst and with dibutyltin dilaurate (DBTDL) as catalyst. The DSC curves were adjusted to a kinetic model...

‣ Kinetics of sodium borohydride hydrolysis in aqueous-basic solutions

Retnamma, Rajasree; Rangel, C. M.; Novais, Augusto Q.; Matthews, Michael A.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 Português
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Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kinetics. The estimation of kinetic parameters is performed by gPROMS (general PRocess Modeling System) parameter estimation tool. The reaction kinetics differs from low to highly-concentrated NaOH solutions. In highly-basic (.10 wt% NaOH), aqueous solutions of NaBH4, the rate is independent of NaOH concentration, while for lower-basic (< 10 wt% NaOH) solutions, the dependence is -0.57, confirming the inhibition of hydrolysis kinetics by NaOH.

‣ Potential metallurgical treatment of copper concentrates with high arsenic contents

Mihajlovic,I; Strbac,N; Nikolic,D; Zivkovic,Z
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2011 Português
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SYNOPSIS This paper investigates a potential method for arsenic removal from copper concentrates using hypochlorite leaching. The problems concerning pyrometallurgical processing of copper concentrates with high arsenic contents are discussed. A possible solution to the problem by leaching of natural enargite crystals with sodium hypochlorite under alkaline oxidizing conditions, with enargite converted into crystalline CuO and the soluble arsenic forming AsO4(3-), was experimentally investigated and results are presented. Kinetic parameters were calculated for enargite leaching, using a model-free approach. Advanced isoconversional methods were used to investigate the dependence of activation energy (Ea) on reaction rate (α).