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Obtaining high purity silica from rice hulls

SILVA JÚNIOR, José da; CUNHA, Carlo R. da; CARVALHO, Flávio L. S. de; RODRIGUES FILHO, Ubirajara P.; OLIVEIRA, Paulo R.; SILVA, Marcos A. Segatto
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica
ENG
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Many routes for extracting silica from rice hulls are based on direct calcining. These methods, though, often produce silica contaminated with inorganic impurities. This work presents the study of a strategy for obtaining silica from rice hulls with a purity level adequate for applications in electronics. The technique is based on two leaching steps, using respectively aqua regia and Piranha solutions, which extract the organic matrix and inorganic impurities. The material was characterized by Fourier-transform infrared spectroscopy (FTIR), powder x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy (SEM), particle size analysis by laser diffraction (LPSA) and thermal analysis.

Er(3+)-doped silica-hafnia films for optical waveguides and spherical resonators

RIGHINI, G. C.; BERNESCHI, S.; CONTI, G. Nunzi; PELLI, S.; MOSER, E.; RETOUX, R.; FERON, P.; GONCALVES, R. R.; SPERANZA, G.; JESTIN, Y.; FERRARI, M.; CHIASERA, A.; CHIAPPINI, A.; ARMELLINI, C.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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In this paper we present some result on sol-gel derived silica-hafnia systems. In particular we focus on fabrication, morphological and spectroscopic assessment of Er(3+)-activated thin films. Two examples of silica-hafnia-derived waveguiding glass ceramics, prepared by top-down and bottom-up techniques are reported, and the main optical properties are discussed. Finally, some properties of activated microspherical resonators, having a silica core, obtained by melting the end of a telecom fiber, coated with an Er(3+)-doped 70SiO(2)-30HfO(2) film, are presented. (C) 2009 Elsevier B.V. All rights reserved.

Interfacial interactions in concretes with silica fume and SBR latex

ROSSIGNOLO, Joao Adriano
Fonte: ELSEVIER SCI LTD Publicador: ELSEVIER SCI LTD
Tipo: Artigo de Revista Científica
ENG
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This paper deals with the effect of silica fume and styrene-butadiene latex (SBR) on the microstructure of the interfacial transition zone (ITZ) between Portland cement paste and aggregates (basalt). Scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis system (EDX) was used to determine the ITZ thickness. In the plain concrete a marked ITZ around the aggregate particles (55 mu m) was observed, while in concretes with silica fume or latex SBR the ITZ was less pronounced (35-40 mu m). However, better results were observed in concretes with silica fume and latex SBR (20-25 mu m). (C) 2008 Elsevier Ltd. All rights reserved.; Research Sponsoring Foundation of Sao Paulo State (Fundacao de Apoio a Pesquisa do Estado de Sao Paulo - FAPESP); Civil Engineering National Laboratory (Laboratorio Nacional de Engenharia Civil - LNEC) in Lisbon, Portugal

Factorial design to optimize microwave-assisted synthesis of FDU-1 silica with a new triblock copolymer

Silva, Luis Carlos Cides da; REIS, T. V. S. dos; COSENTINO, I. C.; Fantini, Marcia Carvalho de Abreu; MATOS, J. R.; BRUNS, R. E.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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The synthesis of FDU-1 silica with large cage-like mesopores prepared with a new triblock copolymer Vorasurf 504 (R) (Eo)(38)(BO)(46)(EO)(38) was developed. The hydrothermal treatment temperature, the dissolution of the copolymer in ethanol, the HCl concentration, the solution stirring time and the hydrothermal treatment time in a microwave oven were evaluated with factorial design procedures. The dissolution in ethanol is important to produce a material with better porous morphology. Increases in the hydrothermal temperature (100 degrees C) and HCl concentration (2 M) improved structural, textural and chemical properties of the cubic ordered mesoporous silica. Also, longer times induced better physical and chemical property characteristics. (C) 2010 Elsevier Inc. All rights reserved.; FAPESP[03/10067-3]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2007/07646-2]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Immobilization of glucose oxidase enzyme (GOD) in large pore ordered mesoporous cage-like FDU-1 silica

Silva, Luis Carlos Cides da; INFANTE, C. M. C.; LIMA, A. W. O.; COSENTINO, I. C.; Fantini, Marcia Carvalho de Abreu; ROCHA, F. R. P.; MASINI, J. C.; MATOS, J. R.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Large pore ordered mesoporous silica FDU-1 with three-dimensional (3D) face-centered cubic, Fm3m arrangement of rnesopores, was synthesized under strong acid media using B-50-6600 poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer (EO(39)BO(47)EO(39)), tetraethyl orthosilicate (TEOS) and trimethyl-benzene (TMB). Large pore FDU-1 silica was obtained by using the following gel composition 1TEOS:0.00735B50-6600:0.00735TMB:6HCl:155H(2)O. The pristine material exhibited a BET specific surface area of 684 m(2) g(-1), total pore volume of 0.89 cm(3) g(-1), external surface area of 49 m(2) g(-1) and microporous volume of 0.09 cm(3) g(-1). The enzyme activity was determined by the Flow Injection Analysis-Chemiluminescence (FIA-CL) method. For GOD immobilized on the FDU-1 silica, GOD supernatant and GOD solution, the FIA-CL results were 9.0, 18.6 and 34.0 U, respectively. The value obtained for the activity of the GOD solution with FIA-CL method is in agreement with the 35 U, obtained by spectrophotometry. (C) 2011 Elsevier B.V. All rights reserved.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2007/07646-2]; FAPESP[2008/09284-3]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Adsorption of Pb(2+), Cu(2+) and Cd(2+) in FDU-1 silica and FDU-1 silica modified with humic acid

Silva, Luis Carlos Cides da; SANTOS, L. B. O. dos; Abate, Gilberto; Cosentino, Ivana Conte; Fantini, Marcia Carvalho de Abreu; MASINI, J. C.; MATOS, J. R.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Ordered mesoporous silica with cubic structure, type FDU-1, was synthesized under strong acid media using B-50-6600 poly(ethylene oxide)-poly(butilene oxide)-poly(ethylene oxide) triblock copolymer (EO(39)BO(47)EO(39)) and tetraethyl orthosilicate (TEOS). Humic acid (HA) was modified to the synthesis process at a concentration of 1.5 mmol per gram of SiO(2). Thermogravimetry, small angle X-ray diffraction, nitrogen adsorption and high resolution transmission electron microscopy were used to characterize the samples. The pristine FDU-1 and FDU-1 with incorporated 1.5 mmol of HA were tested for adsorption of Pb(2+), Cu(2+) and Cd(2+) in aqueous solution. Incorporation of humic acid into the FDU-1 silica afforded an adsorbent with strong affinity for Cd(2+), Cu(2+) and Pb(2+) from single ion solutions. Adsorption of Cu(2+) was significantly enhanced after incorporation of humic acid, a fact that can be explained by the formation of complexes with carboxylic and phenolic groups at low concentrations of the metal cation. The results demonstrated the potential applicability of FDU-1 with incorporated HA in the removal of low concentrations of heavy metal cations from aqueous solution, such as wastewaters, after usual precipitation of metal hydroxides in alkaline medium and proper pH conditioning in the range between 6 and 7. (C) 2007 Elsevier Inc. All rights reserved.

Analysis and risk estimates to workers of Brazilian granitic industries and sandblasters exposed to respirable crystalline silica and natural radionuclides

ESTELLITA, L.; SANTOS, A. M. A.; Anjos, Roberto Meigikos dos; Yoshimura, Elisabeth Mateus; VELASCO, H.; Silva, Almy Anacleto Rodrigues da; AGUIAR, J. G.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
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Occupational exposure to respirable crystalline silica and to radiation emitted by natural radionuclides present both in rocks and sands was studied in the Brazilian extractive process and granite product manufacture. Respirable airborne dust samples were collected in working environments, where workers perform different tasks with distinct commercial granites types, and also in places where sandblasters work with sands from different origins. The free crystalline silica contents were determined using X-ray diffraction of the respirable particulate fraction of each sample. Dust samples from granite cutting and sandblasting ambient had the natural radionuclides concentrations measured by gamma spectrometry. Dust concentrations in the workplaces were quite variable, reaching values up to 10 times higher than the respirable particle mass threshold limit value (TLV) set by the American Conference for Governmental Industrial Hygienists of 3 mg m(-3). Also the free crystalline silica concentrations were high. reaching values up to 48 times the TLV of 0.025 mg m(-3). Additionally, our results suggest that the risk of radiation-induced cancer in the granite or marble industries is negligible. However, the combined exposure to dust, gamma radiation...

Avaliação térmica, mecânica e morfológica de incorporação de nanopartícula de sílica coloidal em matriz de poli(etileno-co-acetato de vinila)

Anton, Jônatan Josué
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
POR
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Neste trabalho foram incorporados nanopartículas de sílica coloidal em matriz de poli(etileno-co-acetato de vinila), através do uso do método de intercalação no estado fundido em câmara de mistura. As seguintes concentrações %/m da nanocarga coloidal adicionadas na matriz de EVA foram avaliadas: 1% (amostra 1L), 3% (3L), 5% (5L) e 10 % (10L). Para efeito de comparação, também foram obtidas amostras com 3% de nanocarga de sílica sólida (3S) e outras com 3% de nanocarga de sílica coloidal em meio aquoso mais 3% de compatibilizante polietileno graftizado com anidrido maléico (PE-g-MA), amostra (3LC). Processou-se também o EVA puro (VP) para que se pudesse estudar o efeito do processamento nas propriedades do polímero. Foram analisadas a influência de adição da nanocarga na forma líquida ou sólida e seus diferentes teores adicionados, com ou sem adição de compatibilizante sobre as propriedades morfológicas, térmicas e mecânicas dos materiais. As técnicas utilizadas foram análise termogravimétrica (TGA), calorimetria diferencial de varredura (DSC), microscopia eletrônica de Varredura (SEM) e ensaio mecânico de tração. Os resultados dos ensaios de tração mostraram que a amostra 10L apresentou melhor valor para o módulo elástico entre as amostras e os piores resultados para deformação máxima e tensão na ruptura. O inverso ocorreu com a amostra 1L. Para a termogravimetria...

Synthesis of silica xerogels with high surface area using acetic acid as catalyst

Arenas, Leliz Ticona; Simm, Carolina Wildner; Gushikem, Yoshitaka; Dias, Silvio Luis Pereira; Moro, Celso Camilo; Costa, Tania Maria Haas; Benvenutti, Edilson Valmir
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
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Nesse trabalho foi estudada a influência do ácido acético na estrutura de poros e na área superficial de sílicas preparadas pelo método sol-gel. Condições experimentais de síntese, tais como temperatura de policondensação e solventes, também foram estudadas. Isotermas de adsorção de N2 das amostras foram classificadas como do tipo 1, típicas de materiais microporosos, o que explica os altos valores de área superficial obtidos. A adição simultânea dos ácidos acético e clorídrico como catalisadores e de acetona como solvente, bem como o emprego de uma temperatura de policondensação de 20 °C, possibilitaram a preparação de sílicas amorfas com valores de área superficial de até 850 m2 g-1. O alto valor de área superficial dessas amostras pode ser explicado principalmente pela microporosidade e também pelo tamanho nanométrico das partículas.; The influence of acetic acid on the pore structure and surface area of silica prepared by the sol-gel method was investigated. Experimental conditions of synthesis, such as gelation temperature and solvents, were also studied. N2 adsorption isotherms of the samples were type 1, typical of microporous materials, explaining the high surface area values (BET) observed. The simultaneous addition of acetic and hydrochloric acids as catalysts and of acetone as solvent...

Materiais híbridos à base de sílica obtidos pelo método sol-gel; Silica based hybrid materials obtained by the sol-gel method

Benvenutti, Edilson Valmir; Moro, Celso Camilo; Costa, Tania Maria Haas; Gallas, Marcia Russman
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
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This review deals with silica based hybrid materials obtained by the sol-gel method. It involves concepts, classifications and important definitions regarding the sol-gel method that allows obtaining materials with organic and inorganic components dispersed in a molecular or nanometric level. We discuss the properties and characteristics of hybrid materials related to experimental synthesis conditions. We devote a special attention to the nanostructured materials, where the self-organization is imposed by the organic component. Finally, we present some important applications of these materials based on their specific properties.

Desenvolvimento de métodos de análise por clae-uv para os antimicrobianos tetraciclina, sulfametoxazol e trimetoprima utilizando materiais à base de sílica como sistemas de pré-concentração; Development of analytical methods for hplc-uv to the antimicrobians tetracycline, sulfamethoxazole and trimethoprim using zirconocene-based silica as pre-concentration/ extraction systems

Pedroso, Rosana Cristina Ribeiro; Peralba, Maria do Carmo Ruaro; Santos, Joao Henrique Zimnoch dos; Pizzolato, Tania Mara; Froehlich, Pedro Eduardo
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
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This paper evaluates the adsorption capacity of zirconocene-based silica materials in the preconcentration of antimicrobians (tetracycline, sulfamethoxazole and trimethoprim) in aqueous medium. These materials were prepared by grafting the zirconocene onto silicas pre-treated at different temperatures. The retention capacity of these materials was evaluated by off line SPE and HPLC-UV and the proposed methodology was validated in ultrapure, tap and river water. The recovery for tetracycline was 72% (in the solid phase A) and, for sulfamethoxazole and trimethoprim was 68 and 95% in the commercial C18, respectively. The target antimicrobians were not detected in the Arroio Diluvio (Porto Alegre . RS).

Sílica quimicamente modificada com os grupos para-anisidina, para-fenitidina e para-fenilenodiamina usada como adsorvente para Pb2+, Cu2+, Cd2+ e Ni2+ em soluções aquosa e etanólica; Silica chemically modified with p-anisidine, p-phenytidine and p-phenylenediamine groups used as adsorbent for pb2+, cu2+, cd2+ and ni2+ in aqueous and ethanol solutions

Vilar, Rossana Borges Cavalcante; Jesus, Alexandre de; Benvenutti, Edilson Valmir; Silva, Marcia Messias da
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
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Silica gel was chemically modified with the aromatic amines p-anisidine, p-phenytidine and p-phenylenediamine, using grafting reactions. The resulting modified silicas were characterized by infrared spectroscopy and N2 adsorption/desorption isotherms. The organic groups were covalently immobilized in a monolayer form. These modified silicas were investigated as adsorbents for Pb2+, Cu2+, Cd2+ and Ni2+ in aqueous and ethanol solutions. In a general way, the adsorption capacity values for all adsorbents presented the following sequence: Pb2+ >> Cu2+~= Cd2+ ~= Ni2+. Adsorption studies for all adsorbents, in competitive medium, showed better selectivity for Cu2+ and Pb2+ in aqueous medium and for Pb2+ in ethanol solution. Desorption studies were carried out using HCl and HNO3 as eluents.

Tunable reinforcement of epoxy-silica nanocomposites with ionic liquids

Donato, Ricardo Keitel; Donato, Katarzyna Joanna Zawada; Schrekker, Henri Stephan; Matejka, Libor
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
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Imidazolium ionic liquids (ILs) have the capacity to exert multiple functions as additives for the formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. This study addresses the effect of ILs on the reinforcement of tensile properties in rubbery epoxy-silica nanocomposites, allowing property tailoring. The use of ILs together with the coupling agent 3-glycidyloxypropyltrimethoxysilane (GTMS) created a synergic action between physical and chemical interfacial bonding, enabling an increase in toughness without a considerable loss of stiffness. The best tensile property balance was obtained with IL 1-triethylene glycol monomethyl ether-3- methylimidazolium methanesulfonate and GTMS. The rubbery nanocomposite produced was remarkably both stiffer and tougher than the unmodified epoxy-silica system, displaying ca. 6 times higher modulus and tensile strength as well as more than 10 times higher energy to break.

Optical properties of an ormosil system comprising methyl- and phenyl-substituted silica

Atkins, Graham; Krolikowska, Maryla; Samoc, Anna
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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We report an organically modified silica (ormosil) system in which the refractive index can be varied from 1.40 to 1.55 by modifying the silica backbone with phenyl and methyl groups, which increase and decrease the refractive index, respectively. By changing the quantities of the phenyl- and methyl-modified precursors in the sol-gel mixture, the refractive index can be varied while keeping the organic fraction of the material constant. Crack-free, dried films up to 15-μm thick have been coated onto silicon and glass substrates, with potential application to optical waveguides for planar integrated circuits. The contributions of SiO-H and C-H absorptions to the attenuation in the communications windows are discussed, along with factors affecting the homogeneity and cracking tendency of the ormosils.

Self-assembly of Carbonate-silica Colloids: Between Living and Non-living Form

Hyde, Stephen; Carnerup, Anna; Larsson, Ann-Kristin; Christy, Andrew; Garcia Ruiz, Juan Manuel
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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We describe self-assembled silica-carbonate aggregates that show a diverse range of morphologies, all of which display complex internal structure, orientational ordering of components, and well-organised, curved global morphologies that bear a strong resemblance to biogenic forms. The internal order is described as a liquid-crystal-like organisation of colloidal particles. We discuss possible causes for the striking morphologies of these inorganic materials, including local nanocrystal packing constraints and global silica membrane templating.

CHARACTERIZATION OF EQUILIBRIUM CONDITIONS OF ADSORBED SILICA–GEL/WATER BED ACCORDING TO DUBININ–ASTAKHOV AND FREUNDLICH

Afonso, M. R. A.; Silveira Jr., V.
Fonte: UFPR Publicador: UFPR
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Peer-reviewed Article Formato: application/pdf
Publicado em 31/08/2005 ENG
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Systems of adsorption have been studied as an alternative for the cooling systems for saving electrical energy. The main advantage is the heat as the driving sources, for example, hot water or waste heat, widely used in the industries, and solar energy. The pair adsorbent/ adsorbate determines the behavior of these systems. Therefore, the knowledge of the equilibrium conditions between the adsorbent and the adsorbate is very important. The pair silica gel/water has the advantage of exploiting low-temperature heat sources. In this paper, the equilibrium conditions of the pair silica gel/water were investigated and the data were used to identify the coefficients of Dubinin-Astakhov equation and Freundlich equation. The experiments consisted of measuring temperature and pressure for different adsorbed mass of water in the adsorbent (silica gel). The amount of adsorbed mass (kg) per adsorbent mass (kg) used were: 0.007, 0.013, 0.024, 0.047, 0.092, 0.162 and 0.209. Both equations showed good agreement with experimental data, the coefficients of regression (R2) were 0.991 on the Dubinin-Astakhov equation and 0.993 for the Freundlich equation.

RECUPERACION DE SILICA PARA CROMATOGRAFIA EN COLUMNA

Rendón P.,Willy J.
Fonte: Revista Boliviana de Química Publicador: Revista Boliviana de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2005 ES
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La recuperación de Sílica Gel (60-200 mesh) J.T.Baker para cromatografía en columna fue realizada por calcinación de residuos orgánicos, lavado con agua y activación final a 110ºC, luego de haber contaminado con extracto alcohólico de la especie botánica Inga ingoides Willd. Con este proceso se logró, la obtener capacidades de separación de hasta el 50 % respecto de una sílica gel nueva, esto es después de haber contaminado la Sílica con un 25 % de material orgánico.

Electrocoagulation to Remove Silica from Cooling Towers Water

Villegas-Mendoza,Iván Emmanuel; Martín-Domínguez,Alejandra; Pérez-Castrejón,Sara; Gelover-Santiago,Silvia Lucila
Fonte: Instituto Mexicano de Tecnología del Agua, Coordinación de Comunicación, Participación e Información Publicador: Instituto Mexicano de Tecnología del Agua, Coordinación de Comunicación, Participación e Información
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
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This paper presents the results of a study carried out about the effect of water quality on the removal of dissolved silica using an electrocoagulation process with aluminum electrodes. Silica is found in replacement water (RW), usually known as make up water, and in cooling tower blowdown water (CTBW). Tests were conducted on a small pilot scale (~2 lmin-1) with a continuous flow device. The treatment train consisted of electrocoagulation (EC), flocculation, sedimentation and sand filtration. Two distinct RW and two CTBW with different physicochemical characteristics were studied. The response variables analyzed were: efficiency of aluminum to remove silica (ratio mgl-1 of dosed Al3+/mgl-1 SiO2 removed), removal efficiency of dosed Al3+, hydraulic head loss throughout the electrochemical reactor and voltage. The cost of the treatment for the four types of water is discussed. The ratio mgl-1 Al3+ dosed /mgl-1 silica removed ranged from 1.09 ± 0.06 to 1.33 ± 0.05 when treating RW and 0.85 ± 0.1 when treating CTBW. The consumption costs of energy, chemicals and electrodes for RW treatment ranged from US$ 0.52 to 0.74 m-3, and was approximately US$0.53 m-3 for CTBW.

Hydrothermal Synthesis of Mesoporous Silica MCM-41 Using Commercial Sodium Silicate

Meléndez-Ortiz,Héctor Iván; Mercado-Silva,Alfonso; García-Cerda,Luis Alfonso; Castruita,Griselda; Perera-Mercado,Yibran Argenis
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2013 EN
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In this work, ordered mesoporous silica MCM-41 was prepared by hydrothermal synthesis using industrial-grade sodium silicate (Na2SiO3) as silica source, hexadecyltrimethyl-ammonium bromide (CTAB) as template agent and ethyl acetate as pH regulator. The influence of CTAB/SiO2 molar ratio, reaction time, aging temperature, and co-surfactant type on the structural and morphological properties of the obtained silica was studied. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-desorption isotherms. Ordered mesoporous MCM-41 silica was obtained at 80 °C by using a range of CTAB/SiO2 molar ratio from 0.35 to 0.71 and reaction times up to 72 h and isopropanol (i-PrOH) as co-surfactant.

Exposição ocupacional à sílica no Brasil no ano de 2001

Ribeiro,Fátima Sueli Neto; Camargo,Esther Archer de; Algranti,Eduardo; Wünsch Filho,Victor
Fonte: Associação Brasileira de Pós -Graduação em Saúde Coletiva Publicador: Associação Brasileira de Pós -Graduação em Saúde Coletiva
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2008 PT
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OBJETIVO: Estimar o número de trabalhadores brasileiros expostos à sílica no ano de 2001. MÉTODO: Informações sobre ocupações e setores econômicos foram reunidas em uma matriz de exposição ocupacional (MEO) com 347 categorias ocupacionais por 25 subsetores econômicos. Informações sobre o número de trabalhadores por ocupação foram extraídas da base de dados Relatório Anual de Informações Sociais (RAIS) do Ministério do Trabalho e Emprego. A exposição à sílica foi avaliada e classificada por dois peritos em quatro categorias, de acordo com a freqüência semanal de exposição no ambiente de trabalho. RESULTADOS: Foram considerados não expostos 31.451.594 trabalhadores (85,7%), possivelmente expostos 976.939 (2,65%), provavelmente expostos 2.404.955 (6,52%) e definitivamente expostos à sílica 2.065.929 (5,6%). Os setores com a maior prevalência de exposição foram: construção civil 65%, extração de pedras 59%, indústria de mineral não metálico 55% e indústria metalúrgica 24%. No setor de serviços de terceiros, a prevalência foi de 2%. CONCLUSÃO: A prevalência de trabalhadores brasileiros definitivamente expostos à sílica é mais alta do que aquela observada em países europeus, onde estudos semelhantes foram conduzidos.