RESUMO
The defective fluorite-related Y3NbO7 host lattice was doped with Eu3+ ions to understand the influence of spark plasma sintering (SPS) process on this host lattice. The intrinsic disorder due to the occurrence of oxygen vacancies results in amorphous-type responses of the luminescent cations, and the spectral distribution varies as a function of the niobium content. Two spectral fingerprints of europium emissions were clearly enhanced. The correlation between luminescence, X-ray diffraction, and electron diffraction characterizations shows the existence of local inhomogeneity. Indeed, the particular nonequilibrium sintering conditions allowed pointing out a lack of miscibility within the Y3NbO7 solid solution domain. Thus, the SPS pellet is a composite of two extreme compositions. This phase demixing is mainly induced by the pressure coupled with a current effect that makes possible ionic migration in this Y3NbO7 ionic conductive matrix.
RESUMO
Aluminum matrix composites reinforced with carbon fibers or diamond particles have been fabricated by a powder metallurgy process and characterized for thermal management applications. Al/C composite is a nonreactive system (absence of chemical reaction between the metallic matrix and the ceramic reinforcement) due to the presence of an alumina layer on the surface of the aluminum powder particles. In order to achieve fully dense materials and to enhance the thermo-mechanical properties of the Al/C composite materials, a semi-liquid method has been carried out with the addition of a small amount of Al-Si alloys in the Al matrix. Thermal conductivity and coefficient of thermal expansion were enhanced as compared with Al/C composites without Al-Si alloys and the experimental values were close to the ones predicted by analytical models.
RESUMO
An ecofriendly chemical reduction of graphene oxide (GO) in water is reported. The reducing agent is an electrochemically reduced Keggin-type polyoxometalate (SiW12 O40 5- ). Moreover, this process leads to the fabrication of SiW12 @rGO nanocomposite. This nanohybrid exhibits an electrochemical response which combines high faradic and capacitive currents due to high coverage of polyoxometalates on the rGO sheets. Therefore this material has strong potentiality for energy storage.
RESUMO
Diamond (Dia) films are promising heat-dissipative materials for electronic packages because they combine high thermal conductivity with high electrical resistivity. However, precise knowledge of the thermal properties of the diamond films is crucial to their potential application as passive thermal management substrates in electronics. In this study, modulated photothermal radiometry in a front-face configuration was employed to thermally characterize polycrystalline diamond films deposited onto silicon (Si) substrates through laser-assisted combustion synthesis. The intrinsic thermal conductivity of diamond films and the thermal boundary resistance at the interface between the diamond film and the Si substrate were investigated. The results enlighten the correlation between the deposition process, film purity, film transverse thermal conductivity, and interface thermal resistance.
RESUMO
The quality of diamond films deposited on cemented tungsten carbide substrates (WC-Co) is limited by the presence of the cobalt binder. The cobalt in the WC-Co substrates enhances the formation of nondiamond carbon on the substrate surface, resulting in a poor film adhesion and a low diamond quality. In this study, we investigated pretreatments of WC-Co substrates in three different approaches, namely, chemical etching, laser etching, and laser etching followed by acid treatment. The laser produces a periodic surface pattern, thus increasing the roughness and releasing the stress at the interfaces between the substrate and the grown diamond film. Effects of these pretreatments have been analyzed in terms of microstructure and cobalt content. Raman spectroscopy was conducted to characterize both the diamond quality and compressive residual stress in the films.