900 resultados para Eutectic Carbide Morphology


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The presence of pores in ceramics is directly related to the chosen forming process. So, in the starch consolidation method, the ceramics show, after burning, pores with morphology similar to that presented by this organic material. on the other hand, the increase in solid load leads up to alterations in dispersion viscosity, increasing the thermal stresses during drying and sintering processes. In order to verify the solid percentage influence in ceramic final properties, samples were prepared with silicon carbide in different compositions using or not starch as binder agent and pore forming element. The characterization of the ceramic pieces was performed by superficial roughness measurements, porosity besides by optical and scanning electron microscopy. The results showed ceramics with SiC and starch presented physical and microscopic properties slightly higher in relation to those with only ceramic powder in their composition. The presence of organic material, agglomerated and foam during the forming were essential for the final properties of the studied samples.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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In this work, cellulose nanofibers were extracted from banana fibers via a steam explosion technique. The chemical composition, morphology and thermal properties of the nanofibers were characterized to investigate their suitability for use in bio-based composite material applications. Chemical characterization of the banana fibers confirmed that the cellulose content was increased from 64% to 95% due to the application of alkali and acid treatments. Assessment of fiber chemical composition before and after chemical treatment showed evidence for the removal of non-cellulosic constituents such as hemicelluloses and lignin that occurred during steam explosion, bleaching and acid treatments. Surface morphological studies using SEM and AFM revealed that there was a reduction in fiber diameter during steam explosion followed by acid treatments. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. TGA and DSC results showed that the developed nanofibers exhibit enhanced thermal properties over the untreated fibers. (C) 2010 Elsevier Ltd. All rights reserved.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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The external morphology of eggs of the species Belminus corredori Galvao & Angulo, 2006, Belminus herreri Lent & Wygodzinsky, 1979 and Belminus ferroae Sandoval, Pabon, Jurberg & Galvao, 2007 is described for the first time using scanning electron microscopy (SEM). Females lay one egg at a time; the shape of the egg is oval with lateral flattening, a rounded caudal area and a true and simple convex operculum. The average size of the egg among these species is 0.51-0.58 mm in length and 0.36-0.4 mm in width. As a generic character we highlight the discovery of a chorion rim with one to four grooves always joined to the micropyles. All species present a clear polygonal pattern only in the operculum and in the egg's cephalic region, while the median and caudal regions show a smooth appearance, features that are shared only with the eggs of the genus Alberprosenia. A discriminant analysis of the polygonal design of the operculum proved to be useful for the identification of the species.

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Morphological structures of the head of 1st and 5th instar nymphs of Triatoma circummaculata and Triatoma rubrovaria were revealed by analysis using scanning electron microscopy (SEM). Differences between Ist and 5th instar nymphs of these two species were observed in the postocular callosity, the number of ommatidia and tapered hair, the small segment between antennal segments, the rostrum third segment and slit lines. These slit lines were different only in the 5th instar. Similarities observed were the presence of tapered hairs in the joints, and the type of sensilla in the antennal segments. Only the Ist instar shows anteclypeus and gena sensilla. The antennal segments comprise the following types of sensilla: basiconica, bristles type I, bristles type II, bristles type III, campaniformia, coeloconica, chemosensilla, placodea, trichobothria and trichoidea. We describe here for the first time six (3+3) sensilla basiconica on the dorsal portion of the first segment of the rostrum. (C) 2000 Elsevier B.V. Ltd. All rights reserved.

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Silicon carbide (SiC) has been employed in many different fields such as ballistic armor, thermal coating, high performance mirror substrate, semiconductors devices, among other things. Plasma application over the silicon carbide ceramics is relatively recent and it is able to promote relevant superficial modifications. Plasma expander was used in this work which was supplied by nitrogen and switched by a capacitor bank. Nitrogen plasma was applied over ceramic samples for 20 minutes, in a total medium of 1440 plasma pulses. SiC ceramics were produced by uniaxial pressing method (40 MPa) associated to isostatic pressing (300 MPa) and sintered at 1950 degrees C under argon gas atmosphere. Silicon carbide (beta-sic - BF-12) supplied by HC-Starck and sintering additive (7.6% YAG - Yttrium Aluminum Garnet) were used in order to obtain the ceramics. Before and after the plasma application, the samples were characterized by SEM, AFM, contact angle and surface energy measurement.

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Blends of poly(vinylidene fluoride), PVDF, and poly(o-methoxyaniline), POMA doped with toluene sulfonic acid, TSA, were prepared by casting at various compositions and studied by scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. The blend composition has a great influence on the morphology obtained. As the concentration of POMA-TSA is increased in the blend an interconnecting fibrillar-like morphology is formed and the spherulites characteristic of pure PVDF are destroyed. The variation of blend morphology is further discussed based on X-ray diffraction and differential scanning calorimetry analysis. (C) 1998 Elsevier B.V. Ltd. All rights reserved.

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Diets rich in saturated fatty acids are one of the most important causes of atherosclerosis in men, and have been replaced with diets rich in unsaturated fatty acids (UFA) for the prevention of this disorder. However, the effect of UFA on myocardial performance, metabolism and morphology has not been completely characterized. The objective of the present investigation was to evaluate the effects of a UFA-rich diet on cardiac muscle function, oxidative stress, and morphology. Sixty-day-old male Wistar rats were fed a control (N = 8) or a UFA-rich diet (N = 8) for 60 days. Myocardial performance was studied in isolated papillary muscle by isometric and isotonic contractions under basal conditions after calcium chloride (5.2 mM) and ss-adrenergic stimulation with 1.0 mu M isoproterenol. Fragments of the left ventricle free wall were used to study oxidative stress and were analyzed by light microscopy, and the myocardial ultrastructure was examined in left ventricle papillary muscle. After 60 days the UFA-rich diet did not change myocardial function. However, it caused high lipid hydroperoxide (176 +/- 5 vs 158 +/- 5, P < 0.0005) and low catalase (7 +/- 1 vs 9 +/- 1, P < 0.005) and superoxide-dismutase (18 +/- 2 vs 27 +/- 5, P < 0.005) levels, and discrete morphological changes in UFA-rich diet hearts such as lipid deposits and mitochondrial membrane alterations compared to control rats. These data show that a UFA-rich diet caused myocardial oxidative stress and mild structural alterations, but did not change mechanical function.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)