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Raman evidence of the interaction between multiwalled carbon nanotubes and nanostructured TiO(2)

INOUE, Fabiana; ANDO, Romulo Augusto; CORIO, Paola
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.957114%
Nanocomposites of carbon nanotubes and titanium dioxide (TiO(2)) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO(2). In this work, we show evidence of the attachment of nanostructured TiO(2) to multiwalled carbon nanotubes(MWNTs) by Raman spectroscopy. The nanostructured TiO(2) was characterized by both full-width at half-maximum (FWHM) and the Raman shift of the TiO(2) band at ca 144 cm(-1), whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO(2) shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO(2). To complement the nanocomposite characterization, scanning electronic microscopy and X-ray diffraction were performed. Copyright (C) 2011 John Wiley & Sons, Ltd.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Rede Nacional de Pesquisa em Nanotubos de Carbono; Rede Nacional de Pesquisa em Nanotubos de Carbono

Estudo da aplicação de argilas nanoestruturadas em resinas restauradoras fotoativadas, utilizadas em odontologia; Study of nanostructured clays application in photoactivated restorative resins, used in dentistry

Campos, Luiza Mello de Paiva
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 05/10/2012 PT
Relevância na Pesquisa
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O problema ocasionado pela contração de polimerização é crítico, pois a resina composta deve conservar-se intimamente ligada à cavidade dentária enquanto ganha rigidez e diminui suas dimensões. Forçando-se o material restaurador a se distanciar, ou se separar das paredes da cavidade, a consequente ruptura levaria a uma microinfiltração marginal responsável por outros problemas tais como a cárie secundária, sensibilidade dolorosa pós-operatória, podendo até provocar alterações pulpares. Este processo induz a alteração volumétrica do composto, dado pela união de radicais na formação da macromolécula (polímero), causando uma diminuição em seu volume. Esse estudo teve como objetivo desenvolver novos compósitos experimentais, por meio da adição de nanocomponentes argilominerais em uma matriz polimérica a base de BisGMA/TEGDMA, para que assim se avalie a possibilidade de ocorrer um comportamento dimensional diferenciado no decorrer da polimerização. Foram utilizados nesse estudo matrizes poliméricas adicionadas com nanopartículas argilominerais MMT Cloisite 10A® (nas concentrações de 50, 55, 60, 65 e 70% em massa) e Cloisite 30B® (nas concentrações de 50, 55, 60 e 65% em massa) , que posteriormente foram comparados com o desempenho de compósitos experimentais adicionados com partículas micro-híbridas de Sílica Silanizada Aerosil® OX-50 ( nas concentrações de 50...

Dielectric behavior of epoxy/BaTiO3 composites using nanostructured ceramic fibers obtained by electrospinning

Ávila, H. A.; Ramajo, L. A.; Góes, M. S.; Reboredo, M. M.; Castro, M. S.; Parra, R.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 505-510
ENG
Relevância na Pesquisa
38.747998%
Composite materials made of epoxy resin and barium titanate (BT) electrospun nanostructured fibers were prepared. BT fibers were synthesized from a sol based on barium acetate, titanium isopropoxide, and poly(vinyl pyrrolidone). The fibers were heat-treated at different temperatures and characterized by X-ray diffraction, scanning electron microscopy (SEM), and Raman spectroscopy. Mats of BT fibers heat-treated at 800 C were embedded in epoxy resin into suitable molds. The composites were characterized by SEM, and dielectric measurements were performed by means of dielectric spectroscopy. The dielectric permittivity and dielectric modulus of epoxy resin/BT-fiber composites were measured for two types of samples: with the electrodes parallel and perpendicular to the BT fiber layers. Interestingly, composite samples with electrodes perpendicular to the fiber layers and a BT content as low as 2 vol % led to dielectric permittivities three times higher than that of pure epoxy resin. © 2013 American Chemical Society.

Evaluation of the chemical interaction between carbon nanotubes functionalized with TGDDM tetrafunctional resin and hardener DDS

Edwards, E. R.; Kostov, K. G.; Botelho, E. C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 197-203
ENG
Relevância na Pesquisa
47.97728%
In this work, the chemical interaction between carbon nanotubes (MWCNT) functionalized with acyl chloride (SOCl2) and polymer chain tetrafuncional N,N,N′,N′-tetraglycidyl-4,4′- diaminodiphenylmethane (TGDDM) and hardener 4,4′diaminodiphenyl sulfone (DDS) has been monitored by Fourier transform infrared spectroscopy (FTIR) with a attenuated total reflectance (ATR) coupled. MWCNT were obtained from the pyrolysis of a mixture of camphor and ferrocene into a oven. The functionalization process was done by oxidative treatment in order to incorporate carboxylic group over the walls of MWCNT, before to be used SOCl2. The functionalized carbon nanotubes were evaluated by X-ray photoelectron spectroscopy (XPS), Raman and transmission electron microscopy (TEM). Nanostructured composites were processed by using epoxy resin with MWCNT in varying percentages. In this work it was observed that different percentages of functionalized nanotubes modify the interaction between the composite matrix and curing agent, where can be observed that in specimens with content less than 1 wt% MWCNT the chemical bond occurs preferentially from the opening of the SO double bond of the hardener and when is used MWCNT content higher than 1 wt% there is little chemical interaction with the SO bond of the hardener and most MWCNT binds to amine. © 2013 Elsevier Ltd.

Carbon nanotubes/polyamide 6.6 nanostructured composites crystallization kinetic study

Ribeiro, B.; Nohara, L. B.; Oishi, S. S.; Costa, M. L.; Botelho, E. C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 893-911
ENG
Relevância na Pesquisa
69.066533%
Compared with the traditional composites, the incorporation of carbon nanotubes into polymeric matrices can generate materials with superior properties, especially thermal, electrical and tribological properties. The aim of this study was to study the polyamide 6.6/carbon nanotubes (PA 6.6/CNT) nanostructured composites crystallization kinetics. The solution mixing technique was used to obtain the nanostructured composites studied in this work. PA 6.6 films were produced with amounts of 0.1, 0.5, and 1.0 wt% (weight/weight) CNT. X-ray diffraction analyses were performed in order to determine the crystallographic properties of nanostructured composite. The nanostructured composites crystallization kinetic study was performed using the differential scanning calorimetry under isothermal and nonisothermal (dynamic) conditions. The results have shown addition of CNTs in the PA 6.6 reduces the Avrami exponent, affecting the crystallization process of the composite. © The Author(s) 2012.

Processamento e caracterização de compósitos de resina fenólica com nanotubos de carbono com aplicações aeroespaciais

Botelho, Edson Cocchieri
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Outros Formato: 179 f. : il.
POR
Relevância na Pesquisa
48.748%
Este trabalho de pesquisa consistiu na obtenção de compósitos nanoestruturados utilizando matrizes poliméricas termorrígidas e nanotubos de carbono (CNT) e posterior caracterização de suas propriedades mecânicas, térmicas, elétricas, reológicas e demais características físico-químicas para aplicações aeroespaciais. As atividades experimentais para a realização deste trabalho foram, em sua maioria, conduzidas na Alemanha. Durante o desenvolvimento deste trabalho de pesquisa, foi possível entender melhor como deve ser realizada a purificação, funcionalização e dispersão de CNT em compósitos poliméricos. Desta forma, CNT foram caracterizados e utilizados como reforços para a obtenção de compósitos nanoestruturados em matrizes termorrígidas (resina fenólica). Estes compósitos foram processados, por meio de cura em autoclave e avaliados com relação aos seus desempenhos mecânicos, físico-químicos e morfológicos. Duas metodologias foram utilizadas para permitir a dispersão dos CNT: dispersão em solução aquosa e por calandragem (TRC). Os resultados obtidos mostram que a metodologia mais adequada para dispersar os CNT em resina fenólica é a partir do processo por calandragem e que teores superiores a 0...

Nanostructured Composites Based on Carbon Nanotubes and Epoxy Resin for Use as Radar Absorbing Materials

Silva, Valdirene Aparecida; Folgueras, Luiza de Castro; Candido, Geraldo Mauricio; Paula, Adriano Luiz de; Rezende, Mirabel Cerqueira; Costa, Michelle Leali
Fonte: Univ Fed Sao Carlos, Dept Engenharia Materials Publicador: Univ Fed Sao Carlos, Dept Engenharia Materials
Tipo: Artigo de Revista Científica Formato: 1299-1308
ENG
Relevância na Pesquisa
58.526094%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Nanostructured polymer composites have opened up new perspectives for multifunctional materials. In particular, carbon nanotubes (CNTs) present potential applications in order to improve mechanical and electrical performance in composites with aerospace application. The combination of epoxy resin with multiwalled carbon nanotubes results in a new functional material with enhanced electromagnetic properties. The objective of this work was the processing of radar absorbing materials based on formulations containing different quantities of carbon nanotubes in an epoxy resin matrix. To reach this objective the adequate concentration of CNTs in the resin matrix was determined. The processed structures were characterized by scanning electron microscopy, rheology, thermal and reflectivity in the frequency range of 8.2 to 12.4 GHz analyses. The microwave attenuation was up to 99.7%, using only 0.5% (w/w) of CNT, showing that these materials present advantages in performance associated with low additive concentrations.

Benzoxazine resin and their nanostructured composites cure kinetic by DSC

Bandeira, Cirlene Fourquet; Pereira, Aline Cristina; Botelho, Edson Cocchieri; Costa, Michelle Leali
Fonte: Cambridge University Press Publicador: Cambridge University Press
Tipo: Artigo de Revista Científica Formato: 3094-3099
ENG
Relevância na Pesquisa
48.201943%
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); Benzoxazine resins are a new class of thermosetting phenolic resins that have emerged in recent decades, overcoming the traditional properties of epoxy and phenolic resins applied in the aerospace industry. The incorporation of low mass concentration of carbon nanotube (CNT) in polymer matrices can produce structural materials with superior properties. Thus, this work aims to prepare nanostructured composite benzoxazine resin/CNT and to evaluate the cure kinetic study by differential scanning calorimetry of neat benzoxazine resin and their nanostructured composites produced. Calculations of the activation energy, the reaction order, and kinetic constants are performed by a nonisothermal procedure. In general, it was observed that CNTs act as catalysts for curing the benzoxazine matrix without affecting the initial and final cure temperatures.

Obtenção e caracterização de compósitos nanoestruturados de poli(sulfeto de fenileno) reforçados com nanotubos de carbono

Ribeiro, Bruno
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 159 f. : il.
POR
Relevância na Pesquisa
38.177944%
Pós-graduação em Engenharia Mecânica - FEG; In this work, pristine and functionalized multiwalled carbon nanotubes reinforced poly (phenylene sulfide) composites were successfully obtained by melt mixing technique. The nanostructured composites were characterized by means of electrical, thermal, mechanical, rheological, and morphological methods. The electrical conductivity of neat PPS showed an increase by 11 and 9 orders of magnitude when 3.0 and 4.0 wt% of pristine MWCNT and functionalized MWCNT were incorporated in polymeric matrix, respectively. Moreover, the electrical percolation thresholds found on these systems were 2.1 and 3.6 wt%, suggesting the formation of three-dimensional conductive network within the polymeric matrix. The maximum crystallization temperature of PPS increased by about 19°C and 13°C due the incorporation of pristine (p-MWCNT) and functionalized filler (f- MWCNT), demonstrating the nucleating effect of the nanoparticles. Dynamic mechanical analysis showed an increase in storage modulus and glass transition temperature, due the incorporation of p-MWCNT and f-MWCNT in PPS matrix. However, it is worth to mention that the increment was bigger in p-MWCNT/PPS system. The maximum degradation temperature of PPS increased by about 14°C and 6°C due to the incorporation of 4...

Multiscale Copper-uDiamond Nanostructured Composites

Nunes, D.; Livramento, Vanessa; Fernandes, H.; Silva, C.; Shohoji, Nobumitsu; Correia, J. Brito; Carvalho, P. A.
Fonte: Trans. Tech. Publications Publicador: Trans. Tech. Publications
Tipo: Artigo de Revista Científica
Publicado em //2013 ENG
Relevância na Pesquisa
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Nanostructured copper-diamond composites can be tailored for thermal management applications at high temperature. A novel approach based on multiscale diamond dispersions is proposed for the production of this type of materials: a Cu-nDiamond composite produced by high-energy milling is used as a nanostructured matrix for further dispersion of micrometer sized diamond. The former offers strength and microstructural thermal stability while the latter provides high thermal conductivity. A series of Cu-nDiamond mixtures have been milled to define the minimum nanodiamond fraction suitable for matrix refinement and thermal stabilization. A refined matrix with homogenously dispersed nanoparticles could be obtained with 4 at.% nanodiamond for posterior mixture with ƒÝDiamond and subsequent consolidation. In order to define optimal processing parameters, consolidation by hot extrusion has been carried out for a Cu-nDiamond composite and, in parallel, for a mixture of pure copper and ÝDiamond. The materials produced were characterized by X-ray diffraction, scanning and transmission electron microscopy and microhardness measurements.

Nanostructured composites based on carbon nanotubes and epoxy resin for use as radar absorbing materials

Silva,Valdirene Aparecida; Folgueras,Luiza de Castro; Cândido,Geraldo Maurício; Paula,Adriano Luiz de; Rezende,Mirabel Cerqueira; Costa,Michelle Leali
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
Relevância na Pesquisa
58.526094%
Nanostructured polymer composites have opened up new perspectives for multifunctional materials. In particular, carbon nanotubes (CNTs) present potential applications in order to improve mechanical and electrical performance in composites with aerospace application. The combination of epoxy resin with multiwalled carbon nanotubes results in a new functional material with enhanced electromagnetic properties. The objective of this work was the processing of radar absorbing materials based on formulations containing different quantities of carbon nanotubes in an epoxy resin matrix. To reach this objective the adequate concentration of CNTs in the resin matrix was determined. The processed structures were characterized by scanning electron microscopy, rheology, thermal and reflectivity in the frequency range of 8.2 to 12.4 GHz analyses. The microwave attenuation was up to 99.7%, using only 0.5% (w/w) of CNT, showing that these materials present advantages in performance associated with low additive concentrations.

Ballistic characterization of nanostructured composite materials for aerospace applications

PASTORE, ROBERTO
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN
Relevância na Pesquisa
37.97728%
The manuscript is arranged in three main parts. In the first chapter the nanocomposite manufacturing is described. As far as the CNTfilled polymeric composites are concerned, a carbon nanotube functionalization process by thermal and chemical treatments has been performed, and Scanning Electron Microscopy (SEM) analysis, as well as Raman and FT-IR spectroscopies were used to verify the surface modifications of the CNTs by the added radical groups. Then, the manufacturing of the CNT-reinforced epoxy composite has been carried out, and Differential Scanning Calorimetry (DSC) was used to analyze the polymerization process for the nano-reinforced thermosetting polymer systems. SEM investigations were also performed to assess the nanocomposites quality in terms of nanoparticle dispersion and material homogeneity. Regarding the STF-reinforced materials, STFs have been synthesized in a single step reaction through high power ultrasound technique, and characterized in terms of their rheological properties. The shear thickening fluid is prepared by ultrasound irradiation of silica nanoparticles dispersed in liquid polyethylene glycol polymer. Then, STF-reinforced fabrics have been realized by soaking layers of several types of Kevlar in STF/ethanol solution; the morphology of the as-realized fabrics...

Electrostatic interactions for directed assembly of nanostructured materials: composites of titanium dioxide nanotubes with gold nanoparticles

Yu, J.; Rance, G.; Khlobystov, A.
Fonte: Royal Soc Chemistry Publicador: Royal Soc Chemistry
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
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Interactions of titanium dioxide nanotubes (TiO2NTs) with positively (AuNP+s) and negatively charged (AuNP−s) gold nanoparticles have been investigated using a combination of UV-Vis spectroscopy, ζ potential and transmission electron microscopy analyses. Possessing a negatively charged surface, TiO2NTs show no attractive interactions with AuNP−s, but readily form nanostructured composites with AuNP+s. Using different ratios of TiO2NT : AuNP+, the overall charge of nanotube–nanoparticle composite can be tuned from positive through neutral to negative, which drastically affects the solubility of the resultant material in water. The charge of the nano-composite is related to the density of AuNP+s adsorbed on the surface of the TiO2NTs. At higher densities adsorbed nanoparticles interact with each other and exhibit a red-shift of their surface plasmon resonance, the magnitude of which increases with the density of AuNP+s. This methodology enables precise control over the composition, charge and structure of nanotube–nanoparticle materials.; Jingxian Yu, Graham A. Rance and Andrei N. Khlobystov

Electrical and Thermal study of carbon nanotubes reinforced poly (phenylene sulfide) nanostructured composites

Ribeiro, Bruno; Botelho, Edson Cocchieri; Costa, Michelle Leali
Fonte: Assoc Brasil Polimeros Publicador: Assoc Brasil Polimeros
Tipo: Artigo de Revista Científica Formato: 94-100
POR
Relevância na Pesquisa
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 2008/00171-8; In this work, the crystallization behavior and electrical conductivity of multiwalled carbon nanotubes reinforced poly (phenylene sulfide) nanostructured composites obtained by melt mixing were investigated. The incorporation of nanofiller in polymeric matrix was responsible for an increase in crystallinity due heterogeneous nucleation phenomenon. The electrical conductivity of PPS showed an increase by 11 orders of magnitude when 2.0 wt% of MWCNT was considered. Moreover, the electrical percolation threshold found on this system was 1.4 wt%, suggesting the formation of three-dimensional conductive network within the polymeric matrix.

Estudo da cinética de decomposição de compósitos nanoestruturados de poli (sulfeto de fenileno) reforçados com nanotubos de carbono

Ribeiro, Bruno; Botelho, Edson C.; Costa, Michelle L.
Fonte: Assoc Brasil Polimeros Publicador: Assoc Brasil Polimeros
Tipo: Artigo de Revista Científica Formato: 720-725
POR
Relevância na Pesquisa
47.97728%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 2008/00171- 8; The aim of this work is to obtain nanostructured composites of poly (phenylene sulfide), PPS, reinforced with multiwalled carbon nanotubes, MWCNT, by melt mixing technique and further characterization of their morphological and thermal properties. Transmission Electron Microscopy analysis was carried out to evaluate the quality of MWCNT dispersion throughout the PPS matrix. Thermogravimetry shows an increase in the maximum degradation temperature by the addition of the nanofiller to the polymeric matrix. In addition, Ozawa-Wall-Flynn modeling was used to determine the degradation parameters. The results showed that the maximum degradation temperature increased by ca. 25 degrees C when a very small concentration of MWCNT (0.5 wt %) was considered, contributing to improve the thermal stability of PPS.; O objetivo deste trabalho consiste na obtenção de compósitos nanoestruturados de poli (sulfeto de fenileno) (PPS) reforçados com nanotubos de carbono de paredes múltiplas (MWCNT) por meio da técnica de mistura em fusão, e posterior caracterização de suas propriedades morfológicas e térmicas. A análise por microscopia eletrônica de transmissão foi utilizada com o intuito de avaliar a qualidade da dispersão dos MWCNTs na matriz polimérica. A partir das curvas de termogravimetria obtidas...

Synthesis and characterization of nanostructured TiO2-SnO2 composite

Breve, Joelma Cristina de Souza; Santos, Dayse Iara dos
Fonte: Trans Tech Publications Ltd Publicador: Trans Tech Publications Ltd
Tipo: Conferência ou Objeto de Conferência Formato: 233-237
ENG
Relevância na Pesquisa
47.818857%
Nanostructured composites based on titanium dioxide have been studied in order to improve optical and photo-catalytic properties, as well as their performance in gas sensors. In this work, titanium and tin dioxides were simultaneously synthesized by the polyol method resulting in TiO2 platelet coated with SnO2 nanoparticles as was observed by scanning electron microscopy. The thermal analysis showed that the combined synthesis promotes more easily the crystallization of the TiO2 rutile phase. The composite obtained after heat treatment at 500 degrees C showed to be formed of almost only rutile phases of both oxides. The optical properties analyzed by UV-Vis spectroscopy showed that the combined oxides have higher absorbance, which reinforces a model found in the literature based on the flow of photo-generated electrons to the conduction band of SnO2 delaying the recombination of charges.

Energy Transfer Dynamics of Nanocrystal−Polymer Composites

Warner, Jamie H.; Watt, Andrew; Thomsen, Elizabeth; Heckenberg, Norman Richard; Meredith, Paul; Rubinsztein-Dunlop, Halina
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.749043%
Steady-state and time-resolved photoluminescence spectroscopy are used to examine the photoluminescent properties of nanocrystal-polymer composites consisting of colloidal PbS nanocrystals blended with poly(2-methoxy-5(2- ethylhexyloxy)-p-phenylene vinyle

Carbon-based nanostructured composite films: elastic, mechanical and optoelectronic properties derived from computer simulations

Fyta, Maria; Mathioudakis, Christos; Remediakis, Ioannis N.; Kelires, Pantelis C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/02/2011
Relevância na Pesquisa
38.301428%
In this review, we present our recent computational work on carbon-based nanostructured composites. These materials consist of carbon crystallites embedded in an amorphous carbon matrix and are modeled here through classical and semi-empirical quantum-mechanical simulations. We investigate the energetics, mechano-elastic, and optoelectronic properties of these materials. Once the stability of the composites is discussed, we move on to the calculation of their elastic moduli and constants, their anisotropy and elastic recovery. At a next step, we focus on diamond composites, which were found to be the most stable among the composites studied, and went beyond the elastic regime to investigate their ideal fracture. Finally, for these materials, the electronic density of states, dielectric function, and optical response were calculated and linked to the disorder in the structures. Our findings unveil the high potential of these materials in nanotechnological applications, especially as ultlra-hard coatings.; Comment: 18 pages, 2 tables, 7 figures, Surface & Coatings Technology, 2011, 10.1016/j.surfcoat.2011.02.026

Nanostructured alumina particles synthesized by the Spray Pyrolysis method: microstructural and morphological analysis

Martín Hernández, María Isabel; Gómez, L. S.; Milosevic, O.; Rabanal, M. Eugenia
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 3659722 bytes; application/pdf
ENG
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37.957114%
Ultrafine particles or nanoparticles (ranging between a few nanometers to 100 nm) are of considerable interest for a wide variety of applications, ranking from catalyst to luminescence ceramics, due to their unique and improved properties primarily determined by size, composition and structure. This study presents the preparation and characterization of nanostructured spherical alumina particles by the Spray Pyrolysis method for the application in reinforcements of metal-matrix composites (MMCs). Synthesis procedure includes aerosol formation ultrasonically from alumina nitrate water solution and its decomposition into a tubular flow reactor at 700 ºC. The obtained particles are spherical, smooth, amorphous and in non-agglomerated state. Microstructural and morphological analyses were carried out using X-ray powder diffraction (XRD), scanning electron microscopy (SEM/EDS) and analytical and high resolution transmission electron microscopy (TEM/HRTEM). Keywords: Spray Pyrolysis; Alumina; Nanostructured Particles; Isothermal Treatment; The authors gratefully appreciate the financial support of the Ministry for Education and Science of Spain, Juan de la Cierva Program JCI-2005-1892-13 (M.I. Martín), MAT2006-02458 project, Sabatic Grant SAB 2004-0035 and Project142010...

Preparation, characterization and in vitro evaluation of nanostructured chitosan/apatite and chitosan/Si-doped apatite composites

Solis, Yaimara; Davidenko, Natalia; Carrodeguas, Raul G.; Cruz, Jeny; Hernandez, Andy; Tomas, Miriela; Cameron, Ruth Elizabeth; Peniche, Carlos
Fonte: Universidade de Cambridge Publicador: Universidade de Cambridge
Tipo: Article; not applicable
EN
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38.150366%
Chitosan/apatite composites are attracting great attention as biomaterials for bone repair and regeneration procedures. The reason is their unique set of properties: bioactivity and osteoconductivity provided by apatite and resorbability supplied by chitosan among others. Thus, in this work chitosan/apatite and chitosan/Si-doped apatite composites were prepared and characterized. Particle size, surface area, in vitro physiological stability, enzymatic biodegradation and bioactivity were evaluated. Unimodal particle size distribution was obtained for composites with high chitosan/apatite ratios while bimodal distribution was present in composites with low chitosan/apatite ratio. Physiological stability decreased with Si-doping and with the chitosan content. Acetylation degree and molecular weight of chitosan did not affect in vitro stability. Rate of enzymatic degradation increased with the chitosan content in composites. Si-doped apatite composites also showed increased degradation with respect to non-doped ones. The bioactivity of the composites was evidenced by the deposition on their surface of a calcium phosphate layer with apatite morphology after immersion in simulated body fluid. Both, biodegradation and bioactivity were dependent on the molecular weight of the polymeric chitosan matrix. These results suggest that the chitosan/apatite composites obtained are promising materials for bone regeneration applications