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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
Relevância na Pesquisa
459.17914%
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)

Estudo da síntese convergente de peptídeos em fase sólida: abordagem clássica e uso de temperatura alta; Study of the convergent solid phase peptide synthesis: classical approach and use of high temperature

Ruiz, Cesar Manuel Remuzgo
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 12/12/2003 PT
Relevância na Pesquisa
368.4102%
A síntese de peptídeos em fase sólida passo a passo (SPFS) tem sido aplicada com sucesso na preparação de peptídeos curtos, médios e de determinados sequências contendo mais de 30 resíduos. Entretanto, esta apresenta problemas e limitações que podem ser contornados pela síntese convergente de peptídeos em fase sólida (SCPFS) que se baseia na condensação entre fragmentos peptídicos Nα-acilados protegidos em suas cadeias laterais (doadores de acila) a fragmentos protegidos ligados a um suporte polimérico (receptores de acila). Além de desenvolver outros projetos enfocados na síntese de peptídeos ou no uso de sintéticos para o estudo de peptídeos biologicamente ativos ou proteinas, o nosso grupo de pesquisa tem se dedicado a estudar o emprego de temperaturas altas em SPFS. O objetivo final é propor protocolos ágeis alternativos aos empregados classicamente. Neste trabalho nos propusemos a investigar alguns aspectos da SCPFS e a explorar a possibilidade de agilizá-Ia a 60°C. Para tanto, empregamos como modelos a colecistocinina-33 humana (hCCK-33) não sulfatada e o análogo [Gln1]-gomesina. As seqüências destes peptídeos foram divididas em: doadores de acila (fragmentos central e N-terminal da hCCK-33 não sulfatada de 11 e de 5 resíduos...

Efeito das variáveis de moagem e dos moinhos de alta energia sobre a síntese do composto intermetálico NiAl.; Effect of milling variables and high-energy mills on the NiAl intermetalic compound synthesis.

Kubaski, Evaldo Toniolo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/02/2010 PT
Relevância na Pesquisa
452.06902%
Realizou-se um estudo dos efeitos das variáveis de moagem e dos moinhos de alta energia sobre a síntese do composto intermetálico NiAl. A influência do poder de moagem, tamanho de partícula inicial de Ni, agente controlador de processo e dimensões dos corpos moedores durante a síntese do composto NiAl no moinho Spex foi quantificada utilizando-se um planejamento fatorial. Verificou-se uma significativa influência do poder de moagem no tempo de ignição da reação exotérmica de formação do composto NiAl, além da influência da interação entre o poder de moagem, agente controlador de processo e dimensões dos corpos moedores no tamanho médio de partículas dos produtos das moagens. O rendimento no moinho Attritor demonstrou-se dependente do poder de moagem e também da quantidade de agente controlador do processo durante a moagem de misturas de pós de Ni e Al. A síntese por combustão de pós mecanicamente ativados no moinho Attritor levou à formação de NiAl3, Ni2Al3 e NiAl ou somente NiAl, dependendo da temperatura de síntese. Conduziu-se a tentativa de determinação experimental, através da técnica de calorimetria diferencial de varredura, das entalpias de formação dos compostos intermetálicos NiAl3, Ni2Al3...

Low-temperature synthesis of nanosized bismuth ferrite by the soft chemical method

Aguiar, E. C.; Ramirez, M. A.; Moura, F.; Varela, José Arana; Longo, Elson; Simões, A. Z.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 13-20
ENG
Relevância na Pesquisa
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This paper describes research on a simple low-temperature synthesis route to prepare bismuth ferrite nanopowders by the polymeric precursor method using bismuth and iron nitrates. BiFeO 3 (BFO) nanopowders were characterized by means of X-ray diffraction analyses, (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy (Raman), thermogravimnetric analyses (TG-DTA), ultra-violet/vis (UV/Vis) and field emission scanning electron microscopy (FE-SEM). XRD patterns confirmed that a pure perovskite BiFeO 3 structure with a rhombohedral distorted perovskite structure was obtained by heating at 850 °C for 4 hours. Typical FT-IR spectra for BFO powders revealed the formation of a perovskite structure at high temperatures due to a metal-oxygen bond while Raman modes indicated oxygen octahedral tilts induced by structural distortion. A homogeneous size distribution of BFO powders obtained at 850 °C for 4 hours was verified by FE-SEM analyses. © 2012 Elsevier Ltd and Techna Group S.r.l.

Temperature-enhanced synthesis of DMSO-Melanin

Piacenti-Silva, Marina; Bronze-Uhle, Erika Soares; Paulin, João Vitor; Graeff, Carlos Frederico de Oliveira
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 135-140
ENG
Relevância na Pesquisa
566.3558%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Melanins are a class of pigmentary conjugated macromolecules found in many biological systems. Functionalization of synthetic melanin provides interesting new properties like the greater solubility of melanin synthesized in dimethyl sulfoxide, D-Melanin. In this work we have studied the influence of temperature on D-Melanin synthesis and its properties. To this end, UV-Vis, Fourier-transform infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) techniques have been employed to analyze D-Melanin synthesized within the range of 25-100 degrees C. Our results reveal that by increasing the synthesis temperature up to 100 degrees C, the synthesis time can be decreased by a factor of 7 when compared to room temperature. From FTIR and C-13 CP/MAS NMR analyses the increase in temperature causes a decrease in the number of carbonyl groups from carboxylic acid and from ionized carboxylic acid. The decarboxylation of D-Melanin monomers at higher temperatures shows that the use of higher synthesis temperatures influences the elimination of carbonyls present in the precursor molecules...

Synthesis and functionalization of hydroxyapatite nanoparticles; Síntese e funcionalização de nanopartículas de hidroxiapatite

Santos, Catarina Ferreira dos
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
363.92008%
Graças aos desenvolvimentos na área da síntese de nanomaterais e às potentes técnicas de caracterização à nanoescala conseguimos hoje visualizar uma nanopartícula (NP) como um dispositivo de elevado potencial terapêutico. A melhoria da sua efectividade terapêutica requer no entanto o aprofundamento e sistematização de conhecimentos, ainda muito incipientes, sobre toxicidade, selectividade, efeitos colaterais e sua dependência das próprias características físico-químicas da NP em análise. O presente trabalho, elegendo como alvo de estudo uma substância considerada biocompatível e não tóxica, a hidroxiapatite (Hap), pretende dar um contributo para esta área do conhecimento. Definiram-se como metas orientadoras deste trabalho (i) estudar a síntese de nanoparticulas de Hap (Hap NP), e a modificação das características físico-químicas e morfológicas das mesmas através da manipulação das condições de síntese; (ii) estudar a funcionalização das Hap NP com nanoestruturas de ouro e com ácido fólico, para lhes conferir capacidades acrescidas de imagiologia e terapêuticas, particularmente interessantes em aplicações como o tratamento do cancro (iii) estudar a resposta celular a materiais nanométricos...

Comparative study of Al-MCM materials prepared at room temperature with different aluminium sources and by some hydrothermal methods

Ribeiro Carrott, Manuela; Conceição, Filipe; Lopes, J.M.; Carrott, Peter; Bernardes, C.; Rocha, J.; Ribeiro, F. Ramôa
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: 95816 bytes; application/pdf
ENG
Relevância na Pesquisa
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A comparison of the pore structural properties and catalytic activity of MCM-41 containing aluminium, prepared at room temperature with different aluminium sources, is presented. In addition, they are compared with those of MCM-41 obtained by two conventional hydrothermal procedures and room temperature synthesised Al-MCM-48 grades. Al-MCM-41 samples were prepared by direct synthesis at room temperature with tetraethoxysilane (TEOS) and aluminium isopropoxide, aluminium sulfate or sodium aluminate, and by two hydrothermal routes using silica Ludox suspension and sodium aluminate (at 377K) or Cab-O-Sil silica and alumina (at 377K and 423K). The synthesis of MCM-48 grades was also carried out at room temperature with TEOS and aluminium sulfate or nitrate. The materials were characterised by X-ray diffraction, nitrogen adsorption at 77K and solid-state 27Al MAS NMR. The catalytic activity was evaluated in the reaction of double bond position isomerisation of 1-butene to 2-butenes at 373K. It is concluded that the room temperature synthesis method used resulted in the preparation in a short period of time of well structured MCM-41 materials that contained predominantly tetracoordinated aluminium and presented acidic catalytic activity similar to or better than those prepared by the two hydrothermal procedures. Aluminium sulfate is a good alternative to isoproxide in the room temperature synthesis as it resulted in samples with very uniform pore size...

Temperature-Sensitive Defect of Mutants Isolated from L Cells Persistently Infected with Newcastle Disease Virus

Preble, Olivia T.; Youngner, Julius S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1973 EN
Relevância na Pesquisa
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The temperature-sensitive defects of virus mutants isolated from L cells persistently infected with Newcastle disease virus (NDV) were analyzed. Genetic grouping of the mutants by complementation tests was attempted by using several different methods, including yield analysis, RNA synthesis, and heterozygote formation at 42 to 43 C, the nonpermissive temperature. In each case, specific interference prevented detection of complementation. This interference was shown to occur prior to or at the level of virus RNA synthesis. Temperature-shift experiments with five different NDVpi clones showed that virus replication begun at 37 C could not be completed at the nonpermissive temperature. The activity of the NDV-specific RNA-dependent RNA polymerase in the cytoplasm of infected chicken embryo cells was not stable and could not be demonstrated directly. However, indirect measurement of RNA polymerase activity at the nonpermissive temperature was accomplished by studying the kinetics of virus-specific RNA synthesis in infected cells after temperature shift. Two types of response were obtained: with three NDVpi clones, virus-specific RNA synthesis ceased immediately upon transfer of infected cells to 42 to 43 C, whereas in cells infected with two other NDVpi clones...

Effects of temperature and host cell genetic characteristics on the replication of the lipid-containing bacteriophage PR4 in Escherichia coli.

Sands, J A; Auperin, D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1977 EN
Relevância na Pesquisa
364.21527%
The lipid-containing bacteriophage PR4 is of special intest because it can replicate in various gram-negative bacteria, including Escherichia coli, that carry one of a group of drug resistance plasmids. PR4 grown in E. coli strain PS2R contains about 10% lipid by weight, with the negatively charged phospholipid phosphatidylglycerol being the most abundant lipid in the virion. We now report the following. (i) PR4 attaches to E. coli with an attachment rate constant of Ka approximately 6.2 X 10(-10) ml/min, which is about twice that of the enveloped phage phi6 (to Pseudomonas phaseolicola), but a factor of 5 less than that of phage PM2 (to Pseudomonas BAL-31). (ii) Use of an E. coli glycerol auxotroph indicated that a normal amount of PR4 replication occurs only if glycerol starvation (inhibition of all phospholipid synthesis) begins no earlier than about halfway through the lytic cycle. (iii) Use of an E. coli fatty acid synthesis temperature-sensitive mutant and an E. coli phosphatidylethanolamine synthesis temperature-sensitive mutant indicate that PR4 replication can occur in the absence of either normal fatty acid synthesis or normal phospholipid synthesis if the infection takes place prior to the termination of overall cell growth and the onset of cell death...

Obtenção de ferrita de cobalto através de dois métodos de síntese: método de complexação combinando EDTA/Citrato e método hidrotérmico; Obtaining cobalt ferrite through two synthesis methods: Complexation Method Conbining EDTA/Citrate and Hydrothermal Method

Medeiros, Indira Aritana Fernandes de
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: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
465.4565%
In this work it was synthesized and characterized the cobalt ferrite (CoFe2O4) by two methods: complexation combining EDTA/Citrate and hydrothermal investigating the influence of the synthesis conditions on phase formation and on the crystallite size. The powders were mainly characterized by x-ray diffraction. In specific cases, it was also used scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray fluorescence (XRF) and isotherms of adsorption and desorption of nitrogen (BET method). The study of the crystallite size was based on the interpretation of x-ray diffractograms obtained and estimated by the method of Halder-Wagner-Scherrer and Langford. An experimental design was made in order to assist in quantifying the influence of synthesis conditions on the response variables. The synthesis parameters evaluated in this study were: pH of the reaction medium (8, 9 and 10), the calcination temperature (combined complexation method EDTA/Citrate 600°C, 800°C and 1000°C), synthesis temperature (hydrothermal method 120°C, 140°C and 160°C), calcination time (combined complexation method EDTA/Citrate - 2, 4 and 6 hours) and time of synthesis (hydrothermal method 6, 15 and 24 hours). By the hydrothermal method was possible to produce mesoporous powders with high purity...

The synthesis of polyol from rice bran oil (RBO) through epoxidation and hydroxylation reactions.

Purwanto, Edy
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
363.9428%
Polyurethanes are valuable polymers with a wide variety of applications. They are normally produced from polyol feedstocks derived from petroleum. As petroleum is a non-renewable resource, an alternative source of feedstock is sought. A potential source is rice bran oil. However, far too little attention has been paid to the utilization of rice bran oil as a potential raw material to produce polyol as it contains unsaturated fatty acids that can be converted to polyol and is the by product of rice milling process and available at very low cost. There are two sequential processes to produce polyol from rice bran oil, namely the epoxidation and hydroxylation reactions. In this work, the optimal conditions in the epoxidation reaction were investigated using acetic acid and formic acid as oxygen carriers in terms of reaction time and temperature. Furthermore, the reaction kinetics were also determined using formic acid as an oxygen carrier in the epoxidation step. Finally, the influence of reaction time and temperature in the hydroxylation step were also investigated in this study. In order to determine the optimal condition, the epoxidation reaction was performed in a three neck flask with the use of acetic and formic acid as oxygen carriers. Result shows that the conversion of iodine value increased with reaction time and temperature when acetic acid was used as an oxygen carrier (peroxyacetic acid). Interestingly...

Investigation of the physiological basis of malting quality of grain developing under high temperature conditions

Blesing, Meredith
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado Formato: 1182785 bytes; 4445132 bytes; 4304503 bytes; 746755 bytes; application/pdf; application/pdf; application/pdf; application/pdf
Publicado em //1997 EN
Relevância na Pesquisa
366.7681%
Short periods ( up to 5 days ) of high temperatures have been shown to reduce grain weight in barley although the specific effects on malting quality are still not clearly understood. Controlled environment conditions were used in this study to investigate the physiological and biochemical responses in Schooner barley to 5 days of elevated temperatures during grain filling. Control plants were maintained at 21 / 16 ° C ( 14th day ) from anthesis to harvest ripeness. Plants undergoing heat treatment experienced increasing temperatures for two days ( from 16 days after anthesis ) followed by 3 days at high temperatures (35 ° C day / 25 ° C night ). The period of high temperature reduced individual grain dry weight by 18 %. Schooner barley endosperm ( the grain storage tissue ) exhibited greater sensitivity to high temperatures than the whole grain ( 25 % reduction in dry weight ) in response to high temperatures. Grain development was accelerated by exposure to high temperatures and a reduction of approximately 8 % in the duration of grain filling was observed in heat treated compared with control grain. Changes in endosperm composition provided evidence that exposure to high temperatures altered overall grain metabolism. Reduction in starch...

Effect of synthesis temperature and alkoxy side chain length on molecular structure and photoelectrochemical properties of terthiophenes

Santos,Marcos J. L.; Girotto,Emerson M.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
Relevância na Pesquisa
449.76684%
The photoelectrochemical properties of the alkoxy-substituted terthiophenes poly(4,4"dimethoxy-3'-methyl-2,2':5',2" terthiophene) (PDM) and poly(4,4"dipentoxy-3'-methyl-2,2':5',2" terthiophene) (PDP) have been investigated in terms of the influence of side chain length. Cyclic voltammetry and UV-Vis experiments have suggested that the synthesis temperature affects the molecular organization in different ways and, thus it should not be used as a general rule. The more efficient light harvesting of PDM, results from its improved molecular π-stacking. Due to its short side chain, PDM presents a large chain interaction, which favors electron hopping and the polymer conductivity.

Transition Temperature and Upper Critical Field in SmFeAsO1-xFx Synthesized at Low Heating Temperatures

Singh, S. J.; Shimoyama, J.; Yamamoto, A.; Ogino, H.; Kishio, K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/03/2013
Relevância na Pesquisa
364.21527%
Low-temperature synthesis is a promising and potentially effective method for improving superconducting properties. We report on the fabrication of polycrystalline samples of SmFeAsO1-xFx with nominal x content varying in a wide range of x = 0-0.35 synthesized at 900 deg C. This synthesis temperature is around 300 deg C lower than the conventional synthesis temperature. The variation in the lattice parameters and transition temperature (Tc) of various F-doped samples indicates that reduction of the unit cell volume (V) seems to be the main reason for the rise of Tc up to 57.8 K. Magnetoresistance measurements showed that the upper critical field slope (dHc2/dT) increased with increasing F concentration up to x = 0.2, where it reached a maximum value of -8 T/K corresponding to a coherence length of 10 angstrom. At still higher F doping levels, dHc2/dT and the low field Jc decreased; above 0.5 T, however, Jc had almost the same value. Compared with previous reports, the present synthesis route with low synthesis temperatures and commonly available FeF2 as the source of F is more effective at introducing F into the SmFeAsO system and thereby resulting in improved superconducting properties for the system. In addition, this new sample preparation method also reduces unnecessary problems such as the evaporation of F and reaction between the crucible and superconductor during the solid-state reaction.

Effect of synthesis temperature on superconducting properties of n-SiC added bulk MgB2 superconductor

Vajpayee, Arpita; Jha, R.; Srivastava, A. K.; Kishan, H.; Tropeano, M.; Ferdeghini, C.; Awana, V. P. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
464.21527%
We study the effect of synthesis temperature on the phase formation in nano(n)-SiC added bulk MgB2 superconductor. In particular we study: lattice parameters, amount of carbon (C) substitution, microstructure, critical temperature (Tc), irreversibility field (Hirr), critical current density (Jc), upper critical field (Hc2) and flux pinning. Samples of MgB2+(n-SiC)x with x=0.0, 0.05 & 0.10 were prepared at four different synthesis temperatures i.e. 850, 800, 750, and 700oC with the same heating rate as 10oC/min. We found 750oC as the optimal synthesis temperature for n-SiC doping in bulk MgB2 in order to get the best superconducting performance in terms of Jc, Hc2 and Hirr. Carbon (C) substitution enhances the Hc2 while the low temperature synthesis is responsible for the improvement in Jc due to the smaller grain size, defects and nano-inclusion induced by C incorporation into MgB2 matrix, which is corroborated by elaborative HRTEM (high-resolution transmission electron microscopy) results. We optimized the the Tc(R=0) of above 15K for the studied n-SiC doped and 750 0C synthesized MgB2 under 140 KOe field, which is one of the highest values yet obtained for variously processed and nano-particle added MgB2 in literature to our knowledge.; Comment: 32 pages Text + Figs: comments/suggestions welcome (awana@mail.nplindia.ernet.in)/www.freewebs.com/vpsawana/

Obtención de Si3N4 mediante SHS; Synthesis of Si3N4

Rodríguez Barbero, Miguel Ángel; García Cano, Irene
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 343521 bytes; application/pdf
SPA
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[ES] En el presente trabajo se presentan los resultados obtenidos en el estudio de las reacciones de Síntesis Autopropagada a Alta Temperatura (Self-propagating High-temperature Synthesis, SHS) de Nitruro de Silicio. La síntesis autopropagada a alta temperatura consiste básicamente en la generación de reacciones altamente exotérmicas capaces de automantenerse. Se puede considerar como principal ventaja del método el ahorro energético que supone. La síntesis se realiza sobre una mezcla inicial de silicio metálico sobre la cual se realizan adiciones de diluyente y otros aditivos (sales amónicas) que afectan al desarrollo de la reacción. Se ha estudiado la influencia que en este sistema pueden tener las proporciones de las distintas incorporaciones en la mezcla, tanto en el material resultante como en las condiciones de reacción. Igualmente se ha estudiado la posibilidad de utilización de nuevos aditivos que puedan minimizar el impacto medio ambiental. Se presentan los estudios microestructurales del material obtenido, la identificación cristalográfica de las fases presentes así como los comportamientos de los parámetros que definen la propia reacción. Con la información obtenida se propone el mecanismo predominante de la síntesis del Nitruro de Silicio mediante SHS.; [EN] In the present paper results obtained during synthesis of Silicon Nitride by Self-propagating High-temperature Synthesis (SHS) are shown. Self-propagating High-temperature Synthesis is based on the high enthalpy of certain reactions able to be self-sustained. One of the most important advantages of the method is its very low energy consumption. The synthesis is carried out with a mixture of silicon powder with some additions of diluents and other synthesis aids (ammonium salts). The influence of the mixture composition on reaction parameters and characteristics of the obtained products has been studied. The use of new synthesis aids has been also studied in order to decrease the environmental impact of the process. Microstructural study...

Process Parameters for Successful Synthesis of Carbon Nanotubes by Chemical Vapor Deposition: Implications for Chemical Mechanisms and Life-cycle Assessment

Xue, Ke
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
461.67305%

Manufacturing of carbon nanotubes (CNTs) via chemical vapor deposition (CVD) calls for thermal treatment associated with gas-phase rearrangement and catalyst deposition to achieve high cost efficiency and limited influence on environmental impact. Taking advantage of higher degree of structure control and economical efficiency, catalytic chemical vapor deposition (CCVD) has currently become the most prevailing synthesis approach for the synthesis of large-scale pure CNTs in past years. Because the synthesis process of CNTs dominates the potential ecotoxic impacts, materials consumption, energy consumption and greenhouse gas emissions should be further limited to efficiently reduce life cycle ecotoxicity of carbon naotubes. However, efforts to reduce energy and material requirements in synthesis of CNTs by CCVD are hindered by a lack of mechanistic understanding. In this thesis, the effect of operating parameters, especially the temperature, carbon source concentration, and residence time on the synthesis were studied to improve the production efficiency in a different angle. Thus, implications on the choice of operating parameters could be provided to help the synthesis of carbon nanotubes.

Here, we investigated the typical operating parameters in conditions that have yielded successful CNT production in the published academic literature of over seventy articles. The data were filtered by quality of the resultant product and deemed either "successful" or "unsuccessful" according to the authors. Furthermore...

Effect of blocking protein synthesis at nonpermissive temperatures on temperature-sensitive deoxyribonucleic acid mutants of Escherichia coli

Evans, Irene; Forrest, N.; Lawrence, A.; Eberle, Helen
Fonte: American Society for Microbiology: Journal of Bacteriology Publicador: American Society for Microbiology: Journal of Bacteriology
Tipo: Artigo de Revista Científica Formato: 40553 bytes; application/pdf
EN_US
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When protein synthesis was blocked in temperature-sensitive deoxyribonucleic acid synthesis mutants of Escherichia coli at nonpermissive temperatures, it reduced the amount of apparent subsequent chain elongation to approximately half that observed in the mutants either at nonpermissive temperatures alone or when protein synthesis was blocked at the permissive temperature. Blocking protein synthesis at the nonpermissive temperatures for periods of 40 min caused the loss of ability to reinitiate deoxyribonucleic acid synthesis at the permissive temperature.; Article may be found at: http://jb.asm.org/cgi/reprint/140/2/445; This paper is based on work performed under contract with the U.S. Department of Energy at the University of Rochester Department of Radiation Biology and Biophysics and has been assigned report no. UR-3490-1424.

Exploratory synthesis: crystal chemistry and physical properties of binary, ternary and quaternary alkaline-, rare-earth and group 12 metal tetrelides

Suen, Nian-Tzu
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
459.17914%
Bobev, Svilen; The relationship between crystal structures, compositions and physical properties, together with the reasons determining the formation of one phase among others, still remains as an open question in the realm of solid-state chemistry. The crystal structures and bonding patterns within compounds hold the key to further understanding the physical properties of the compounds in question. Therefore this inspires us to embark on a series of exploratory synthesis of binary, ternary and even quarternary intermetallic compounds containing lanthanide f -block metals (Rare-Earth metals; denote RE hereafter), alkaline-earth metals (Mg, Ca, Sr; denote AE hereafter) or group 12 (Zn) and group 14 elements (Ge, Sn and Pb; group 14 elements are also known as tetrel elements, which we denote Tt hereafter). The compositions and crystal structures of those phases were determined by using different kinds of techniques, such as single-crystal/ powder X-ray diffractions and elemental analysis. The physical properties including magnetic susceptibilities and electrical resistivities of the compounds were reported and discussed herein. In this work, the results can be separated into four chapters including: 1) The binary RE -Ge system: RE 5Ge3 (RE = La and Ce; Pu 5 Rh3 structure type). It was confirmed that RE 5Ge3 could adopt two different structure types depending on the synthesis temperature. It crystalized with Pu 5 Rh3 structure type of low temperature (<600 ??C)...

The synthesis of nitrogen-doped multiwalled carbon nanotubes using an Fe-Co/CaCO3 catalyst

Tetana,Z.N.; Mhlanga,S.D.; Bepete,G.; Krause,R.W.M.; Coville,N.J.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
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A CVD method was used to prepare high-quality nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) using acetonitrile as the nitrogen and carbon source and acetylene as a carbon source over an Fe-Co/CaCO3 catalyst in the temperature range 700-850 °C. This represents a continuation of earlier work in which Fe-Co on CaCO3 was used to make undoped carbon nanotubes. The effect of synthesis parameters (growth temperature and CH3CN vaporization temperature) on the yield, size, quality, morphology and thermal stability of the N-MWCNTs was studied. The resulting materials were characterized by TEM, SEM, TGA, BET, XPS, CN elemental analysis and Raman spectroscopy. TEM analysis revealed that the nanotubes exhibit bamboo-like structures with rough surfaces and a relatively uniform diameter. The bamboo compartment distance decreased with increase in synthesis temperature due to the increased nitrogen content in N-MWCNTs. The SEM examination showed that at high synthesis temperatures carbon spheres (CSs) with chain-like morphology and large sizes were also formed along with the N-MWCNTs. The XPS and CN elemental analysis revealed that nitrogen atoms were successfully doped into the carbon walls. The amount of nitrogen incorporated in the N-MWCNTs varied with increasing growth time and CH3CN vaporization temperature.