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Search Results: 1 - 10 of 1027 matches for " Mirabel Cerqueira; "
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Multilayer radar absorbing material processing by using polymeric nonwoven and conducting polymer
Folgueras, Luiza de Castro;Rezende, Mirabel Cerqueira;
Materials Research , 2008, DOI: 10.1590/S1516-14392008000300003
Abstract: this study shows the processing of radar absorbing multilayer structures based on nonwoven substrates of polyacrylonitrile and poly (ethylene terephthalate) impregnated with a polyaniline and polyurethane mixture. processed materials with different parameters - layer stacking and impregnated faces - were evaluated considering the incident radiation attenuation in the frequency range of 8 to 12 ghz. the results show the influence of the quantity, types and thickness of the impregnated layers. scanning electronic microscopy observations evaluated the anchorage of the absorbing center (polyaniline) in the substrate. in a general way, the different obtained structures presented incident radiation attenuation values between 87 and 99%. this result allows its use as microwave absorbers.
Complex permeability and permittivity variation of carbonyl iron rubber in the frequency range of 2 to 18 GHz
Adriana Medeiros Gama,Mirabel Cerqueira Rezende
Journal of Aerospace Technology and Management , 2010,
Abstract: The complex dielectric permittivity (e) and magnetic permeability (m) of Radar Absorbing Materials (RAM) based on metallic magnetic particles (carbonyl iron particles) embedded in a dielectric matrix (silicon rubber) have been studied in the frequency range of 2 to 18 GHz. The relative permeability and permittivity of carbonyl iron-silicon composites for various mass fractions are measured by the transmission/reflection method using a vector network analyzer. The concentration dependence of permittivity and permeability on the frequency is analyzed. In a general way, the results show that e′ parameter shows a more significant variation among the evaluated parameters (e”, m”, m’). The comparison of dielectric and magnetic loss tangents (e”/e” and m”/m’, respectively) shows more clearly the variation of both parameters (e and m) according to the frequency. It is also observed that higher carbonyl iron content fractions favor both dielectric and magnetic loss tangents.
Dielectric properties of microwave absorbing sheets produced with silicone and polyaniline
Folgueras, Luiza de Castro;Alves, Mauro Angelo;Rezende, Mirabel Cerqueira;
Materials Research , 2010, DOI: 10.1590/S1516-14392010000200013
Abstract: the aim of this study was to produce sheets of microwave absorbing materials using conductive polyaniline dispersed in a silicone rubber matrix and to characterize the electromagnetic properties (absorption, transmission and reflection of electromagnetic energy; and electric permittivity and magnetic permeability) of these sheets in the x-band (8 - 12 ghz). two sheets were produced: one 2.80 mm thick and the other 4.39 mm thick. the thinner sheet absorbed incident microwave energy more efficiently, attenuating up to 88% of the incident electromagnetic energy. also, calculations were performed in order to determine the electromagnetic parameters that optimize the absorbent properties of these sheets. these calculations showed that these materials can be combined and altered to produce absorbing materials with a wide range of absorbing characteristics.
Evaluation of mechanical properties of four different carbon/epoxy composites used in aeronautical field
Paiva, Jane Maria Faulstich de;Mayer, Sergio;Rezende, Mirabel Cerqueira;
Materials Research , 2005, DOI: 10.1590/S1516-14392005000100016
Abstract: four families of carbon fiber reinforced composites (cfrc) used in aeronautical industry were evaluated by flexural and interlaminar shear tests. it is also characterized three families of non-conditioned and conditioned cfrc by compression test. the composites were obtained by hand lay-up process in autoclave by using prepregs based on epoxy matrices (f155 and f584) and carbon fiber fabric reinforcements (pw-"plain weave" and 8hs-"eight harness satin"). the f155-epoxy matrix was cured at 121 °c and the f584-epoxy type at 177 °c. after molding, the laminates were cut in specimens attending the astm d790 for the flexural test, the astm d2344 for the interlaminar shear test (ilss) and the astm d3410 for the compressive test. the compressive tests were performed for testing the specimens before and after hygrothermal conditioning. the results show that the f584-epoxy matrix laminates present higher mechanical properties when compared to the f155-epoxy ones. the shear-tested samples observed by scanning electron microscopy and that ones tested in flexural, analyzed by stereoscopy, revealed that the fractured surfaces present typical aspects. the compressive results show that the hygrothermal conditioning caused the decrease of the compressive strength in, approximately, 8-20% depending on the laminate type. the failure modes of the tested specimens were evaluated showing good agreement with the literature.
Influence of aromatic amine hardeners in the cure kinetics of an epoxy resin used in advanced composites
Costa, Michelle Leali;Pardini, Luiz Claudio;Rezende, Mirabel Cerqueira;
Materials Research , 2005, DOI: 10.1590/S1516-14392005000100012
Abstract: composite structures for aerospace applications are mainly made by the well-known prepreg technology. in order to achieve adequate prepreg processing schedules, and consequently maximum fiber strength utilization, one has to know in deep the cure kinetics of matrix, which held the fibers together. this work describes a procedure to study the cure kinetic and has as example how aromatic amine hardeners influence the cure kinetics of an epoxy resin used in advanced composites. the investigation was carried out by using the dsc technique and it was found that depending on the system used the cure kinetics of the formulation obeys order n or autocatalytic order.
Rheological analysis of the phenolic and furfuryl resins used in the carbon materials processing
Botelho, Edson Cocchieri;Scherbakoff, Natália;Rezende, Mirabel Cerqueira;
Materials Research , 2000, DOI: 10.1590/S1516-14392000000200004
Abstract: carbon materials processing is an advanced technology due to its aerospace and medical applications. in the aerospace area one can mention the carbon/carbon composites used in rockets and aeronautical brakes; in the medical area one can mention the intrabody implant tools such as heart and hydrocephalic valves and pacemaker electrode tips. the highly sophisticated purpose of its application requires a very tight processing control, which defines the microstructure the mechanical, thermal and electrical characteristics of the final material. the objective of this study is to correlate rheological, chromatographic and thermal analysis of phenolic and furfuryl resins, aiming their use as raw materials in carbon/carbon composite and glassy carbon processing. the obtained results are correlated and used directly in the establishment of the adequate parameters for carbon reinforcement impregnation and to prepare glassy carbon samples with controlled porosity.
Estudo da influência do diluente reativo PGE na cinética de cura de resina epóxi utilizada em compósitos estruturais
Costa, Michelle Leali;Rezende, Mirabel Cerqueira;Pardini, Luiz Claudio;
Química Nova , 2000, DOI: 10.1590/S0100-40422000000300008
Abstract: phenil glycidyl ether (pge), a monofunctional diluent, has been used in epoxy resins formulations in order to increase the toughness of the epoxy molded composite. in a systematic study concerning its influence in the cure kinetics of the epoxy resin, it was used in concentrations of 2,5; 5,0; 10 and 20% in relation to a diglycidyl ether bisphenol-a (dgeba)/diamino diphenil-sulfone (dds) base matrix. dynamic and isothermal scanning analysis were carried out using a differential scanning calorimety (dsc) equipment. for all the concentrations of pge, a n order kinetics was observed, with n varing between 0,35 ? 0,91 as a function of the increase in the pge concentration.
Rheological analysis of the phenolic and furfuryl resins used in the carbon materials processing
Botelho Edson Cocchieri,Scherbakoff Natália,Rezende Mirabel Cerqueira
Materials Research , 2000,
Abstract: Carbon materials processing is an advanced technology due to its aerospace and medical applications. In the aerospace area one can mention the carbon/carbon composites used in rockets and aeronautical brakes; in the medical area one can mention the intrabody implant tools such as heart and hydrocephalic valves and pacemaker electrode tips. The highly sophisticated purpose of its application requires a very tight processing control, which defines the microstructure the mechanical, thermal and electrical characteristics of the final material. The objective of this study is to correlate rheological, chromatographic and thermal analysis of phenolic and furfuryl resins, aiming their use as raw materials in carbon/carbon composite and glassy carbon processing. The obtained results are correlated and used directly in the establishment of the adequate parameters for carbon reinforcement impregnation and to prepare glassy carbon samples with controlled porosity.
Estudo da influência do diluente reativo PGE na cinética de cura de resina epóxi utilizada em compósitos estruturais
Costa Michelle Leali,Rezende Mirabel Cerqueira,Pardini Luiz Claudio
Química Nova , 2000,
Abstract: Phenil glycidyl ether (PGE), a monofunctional diluent, has been used in epoxy resins formulations in order to increase the toughness of the epoxy molded composite. In a systematic study concerning its influence in the cure kinetics of the epoxy resin, it was used in concentrations of 2,5; 5,0; 10 and 20% in relation to a diglycidyl ether bisphenol-A (DGEBA)/diamino diphenil-sulfone (DDS) base matrix. Dynamic and isothermal scanning analysis were carried out using a differential scanning calorimety (DSC) equipment. For all the concentrations of PGE, a n order kinetics was observed, with n varing between 0,35 -- 0,91 as a function of the increase in the PGE concentration.
Methodology for DSC calibration in high heating rates
Carlos Isidoro Braga,Mirabel Cerqueira Rezende,Michelle Leali Costa
Journal of Aerospace Technology and Management , 2011,
Abstract: Despite the large use of differential scanning calorimetry (DSC) technique in advanced polymer materials characterization, the new methodology called DSC in high heating rates was developed. The heating rate during conventional DSC experiments varying from 10 to 20oC.min-1, sample mass from 10 to 15mg and standard aluminum sample pan weighting, approximately, 27mg. In order to contribute to a better comprehension of DSC behavior in different heating rates, this work correlates as high heating rate influences to the thermal events in DSC experiments. Samples of metallic standard (In, Pb, Sn and Zn) with masses varying from 0.570mg to 20.9mg were analyzed in multiples sample heating rate from 4 to 324°C. min-1. In order to make properly all those experiments, a precise and careful temperature and enthalpy calibrations were performed and deeply discussed. Thus, this work shows a DSC methodology able to generate good and reliable results on experiments under any researcher choice heating rates to characterize the advanced materials used, for example, for aerospace industry. Also it helps the DSC users to find in their available instruments, already installed, a better and more accurate DSC test results, improving in just one shot the analysis sensitivity and resolution. Polypropylene melting and enthalpy thermal events are also studied using both the conventional DSC method and high heating rate method.
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