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

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

Vegetal fibers in polymeric composites: a review

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

Monitoring the process of densification of 3D and 4D (tridirectional and tetradirectional) carbon/carbon composites

Carbon fiber reinforced carbon composites can be made by iterative liquid impregnation or gas phase carbon deposition routes. In both cases, at the final processing stage the carbon fiber is embedded in carbon matrix which results in unique properties such as low density, high thermal conductivity and thermal shock resistance, low thermal expansion and high modulus, in relation to other refractory materials. In the present study assembled three-directional and four-directional preforms, having 50% volume of pores, were densified by iterative cycles of thermoset resin impregnation followed by pyrolysis under inert atmosphere, until appropriate densities were achieved. The thermoset resin is converted in a carbon matrix during pyrolysis. The iterative manufacturing process of the carbon fiber reinforced carbon composites is evaluated by means of nondestructive techniques based on X-ray computed tomography and electrical resistivity. X-ray computed tomography gives a general mapping view of the filling pores of the preforms which impacts results of the electrical resistivity. After six processing cycles and heat treatments up to 2000?, the final densities of the three-directional and four-directional carbon fiber reinforced carbon composites were 1.16g/cm(3) and an electrical resistivity of approximate to 0.07m. The configuration of preforms, three-directional or four-directional, did not alter the densification profile, in terms of increasing density and reducing porosity during the processing cycles.

Thermal degradation and lifetime estimation of poly(ether imide)/carbon fiber composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of water immersion and ultraviolet weathering on mechanical and viscoelastic properties of polyphenylene sulfide-carbon fiber composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Morphological characterization by SEM, TEM and AFM of nanoparticles and functional nanocomposites based on natural rubber filled with oxide nanopowders

Nanocomposites were prepared from mixture of different concentrations of ferroelectric nanoparticles in an elastomeric matrix based on the vulcanized natural rubber. The morphological characterization of nanocomposites was carried out using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The nanocrystalline ferroelectric oxide is potassium strontium niobate (KSN) with stoichiometry KSr2Nb5O15, and was synthesized by the chemical route using a modified polyol method, obtaining particle size and microstrain equal to 20 nm and 0.32, respectively. These ferroelectric nanoparticles were added into the natural rubber in concentrations equal to 1, 3, 5, 10, 20 and 50 phr (parts per hundred of rubber) forming ferroelectric nanocomposites (NR/KSN). Using morphological characterization, we identified the maximum value of surface roughness at low concentrations, in particular, sample with 3 phr of nanoparticles and factors such as encapsulation and uniformity in the distribution of nanoparticles into the natural rubber matrix are investigated and discussed.

Anodization mechanism on SiC nanoparticle reinforced al matrix composites produced by power metallurgy

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

Nanostructured TiO2-based composites for light absorption

Metal oxidenanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first processproducesdirectly a two-phase material, while the sol-gelpowder never showed second phase below 600 degrees C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

Electrical, mechanical, and thermal analysis of natural rubber/polyaniline-DBSA composite

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dielectric behaviour of CaCu3Ti4O12-epoxy composites

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

Evaluation of sodium diclofenac release using natural rubber latex as carrier

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

alpha-SiAlON-SiC composites obtained by gas-pressure sintering and hot-pressing

The objective of this work was the obtaining in situ of alpha-SiAlON-SiC composite, using an alternative rare-earth oxide mixture, RE2O3, as sintering additive, by two different sintering processes. As sintering additive, 20 vol.% of AlN-RE2O3 in a molar ratio of 90: 10 was mixed to the alpha-Si3N4 powder. In the Si3N4-AlN-RE2O3 powder mixture, 0, 10, 15 and 20wt.% of SiC were added. The powder batches were milled, dried and compacted by cold isostatic pressing. Two different sintering processes were used: gas-pressure sintering at 1950 degrees C for 1 h under 1.5 MPa of N-2 atmosphere, or uniaxial hot-pressing at 1750 degrees C, for 30 min under pressure of 20 MPa. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy and mechanical properties. XRD patterns indicate only alpha-SiAlON (alpha') and beta-SiC as crystalline phases. It was observed that the SiC addition did not influence the alpha-SiAlON formation, although the growth of elongated alpha'-grains is substantially decreased. The hot-pressed composites presented better mechanical properties, exhibiting fracture toughness of 5 MPa m(1/2) and hardness around 21.5 GPa. (c) 2007 Elsevier B.V. All rights reserved.

Influence of Nd:YAG or Er:YAG laser surface treatment on microtensile bond strength of indirect resin composites to resin cement. Lasers surface treatment of indirect resin composites

This study evaluated the influence of the surface pretreatment of indirect resin composite (Signum, Admira Lab and Sinfony) on the microtensile bond strength of a resin cement. Sixty samples made of each brand were divided into 6 groups, according to surface treatment: (1) control; (2) controlled-air abrasion with Al2O3; (3) Er:YAG Laser 200 mJ, 10 Hz, for 10s; (4) Er: YAG Laser 300 mJ, 10 Hz, for 10 s; (5) Nd:YAG 80 mJ, S15Hz for 1 min; (6) Nd:YAG 120mJ, 15 Hz for 1 min. After treatments, all the groups received an application of 37% phosphoric acid and adhesive. The pair of blocks of the same brand were cemented to each other with dual resin cement. The blocks were sectioned to obtain resin-resin sticks (1 x1 mm) and analyzed by microtensile bond testing. The bond strength values were statistically different, irrespective of the surface treatment performed, with highest values for Sinfony (43.81 MPa) and lowest values for Signum (32.33 MPA). The groups treated with the Nd:YAG laser showed the lowest bond strength values and power did not interfere in the results, both for Nd:YAG laser and Er:YAG. Controlled-air abrasion with Al203 is an efficient surface treatment method and the use of the Nd:YAG and Er:YAG lasers reduced bond strength, irrespective of the intensity of energy used.

Genetic diversity strategy for the management and use of rubber genetic resources: more than 1,000 wild and cultivated accessions in a 100-genotype core collection

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

Polymerization kinetics and polymerization stress in resin composites after accelerated aging as a function of the expiration date

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)