Materials Science Forum Vol. 820

Abstract: Each day the water scarcity at the global level is worrying and the industries are faced with the enormous challenge to prevent contamination of existing resources. Separation processes with polymer membranes have been successfully used in separating small quantities of oil in water. The synthesis conditions of UHMWPE tubular membranes, as well as its internal coating of LDPE film with the addition of organophilic clay were evaluated for promoting the generation of micropores, which would allow a more efficient filtration. Through the techniques of flow analysis, it was found that membranes with clay were more effective for filtration. The quantification of the concentration of oil showed the benefits of the application of this technique, resulting in extremely low levels of oil in water.

Abstract: In this study, the influence of type and amount of organoclay in the morphology of the polymer blend PP/EPDM is evaluated. Pure and filled mixtures were prepared by melt intercalation in an internal mixer. The morphology of the hybrids was evaluated by X-ray diffraction and scanning electron microscopy. The results showed that the incorporation of the organophyllic clay to the PP/EPDM blend resulted in new interfacial interactions between components, which contributed to a decrease in the size of the dispersed phase and the compatibility of the blends. Therefore, organoclays may be employed to compatibilize polymeric blends, replacing conventional compatibilizers.

Abstract: Niobates with tetragonal tungsten bronze TTB-type structure have presented great technological potential due to their dielectric, ferroelectric, pyroelectric properties. The preparation by the modified polyol method and structural characterization of K₂Nd_(1-x)Eu_xNb₅O₁₅ nanopowders, where x = 0; 0.0025; 0.025; 0.05 e 0.1, were investigated. The structural parameters were analyzed as a function of concentration of europium ions in the K₂NdNb₅O₁₅ host structure using the Rietveld method. From structural parameters was determined the TTB-type structure with tetragonal symmetry, where the pentagonal sites is occupied by K⁺ and Eu³⁺ ions and tetragonal sites is occupied only by Nd³⁺ ions. The addition of europium in the host structure led to a decrease in the lattice parameters, compatible with the increasing degree of distortion of NbO6 polyhedra. The average crystallite size showed values between 18.25 and 26nm.

Abstract: Ferroelectric niobates with tetragonal tungsten bronze TTB-type structure have shown great technology interest for application in pyroelectric detectors and piezoelectric transducers, sensor/filter in composite. The synthesis and structural characterization of the solid solution of iron doped potassium strontium niobate with stoichiometry KSr₂(Fe_0.25Nb_4.75)O_15-δ prepared by modified polyol method were carried out. The highest crystallinity was obtained for the precursor powder calcined at 1150oC for 10 hours in oxygen atmosphere. The structural characterization was performed by X-Ray diffraction. The average crystallite size obtained was equal to 25 nm. The structural parameters were determined by Rietveld method giving a tetragonal system with space group P4bm. The spontaneous polarization of the solid solution was calculated, being equal to 39.46 μC.cm^-2. Polihedra distortion and its correlation with niobium off-center are discussed.

Abstract: Nanotechnology has been shown as an important tool for developing intelligent devices. In particular, magnetic nanoparticles have been studied due their applications in cancer treatments. However, nanoparticles need to be tightly controlled in relation to size, shape and coating. It makes particles suitable for in vivo applications. In this work, magnetite nanoparticles were used for particle size characterization. Fe₃O₄ crystals were coated by polyethyleneglycol (PEG 4000). Three different techniques were performed to obtain the nanoparticles average diameter: Rietveld Analysis, Scherrer Equation and Nanosight®. Results indicate good properties.

Abstract: Ferroelectric semiconductors oxides with tetragonal tungsten bronze TTB-type structure doped with rare earth ions have been investigated in recent years due their promising optical properties. K₂Nd_(1-x)Eu_xNb₅O₁₅ nanopowders, where x = 0, 0.0025, 0.025, 0.05 and 0.1 were synthesized by the modified polyol method and characterized by X-ray diffraction and diffuse reflectance spectroscopy UV-Vis. Single phase and crystalline powders of tetragonal symmetry with non-centrosymmetric space group P4bm were obtained. The diffuse reflectance spectra were similar to the profile of a semiconductor material with the presence of thin transitions of Eu³⁺ in europium-doped K₂NdNb₅O₁₅, as well as the transitions of Nd³⁺. The method of Kubelka-Munk was used for the estimation of bandgap energy. The values around 3.7 eV showed small variation with the concentration of Eu³⁺ ions in the K₂NdNb₅O₁₅ host structure. The transitions were identified as direct ones type.

Abstract: A functional inorganic-additive modifier of the thermal conductivity of biofuel type alcohol anhydrous was developed based on an amorphous carbon nanocomposite containing dispersed zinc. Dispersion and modification of thermal conductivity in biofuels type anydrous alcohol were considered, as well as in petro-diesel and a blend of biodiesel and petro-diesel. Fuels, alcohol, diesel and biodiesel acted as a continuous medium dispersing the particles of C/Zn. Both thermal conductivity and thermal resistivity measurements were carried out showing that the amorphous nanocomposite particles C/Zn act as an additive to improve the thermal conductivity of alcohol. The same phenomenon has not been identified for diesel, biodiesel and its blends. Increasing the thermal conductivity of the alcohol generated by adding of particles is discussed as a function of the concentration and molecular interactions on the surface of additive particles.

Abstract: Fracture toughness enhancement of ceramic materials through multilayered ceramic composites has been developed since 1990. Toughening mechanisms are based mainly on delamination, deflection, bifurcation or crack arrest effect. Delamination and crack deflection occur by means of weak interfaces. Bifurcation (and deflection as well) and crack arrest effects are result of residual stresses arising from the thermal expansion coefficient mismatch or phase transformation on alternating layers. The main manufacturing methods of these composites are slip casting of two ceramic materials, and stacking and pressing of ceramic tapes obtained by tape casting or rolling technics, followed by suitable sintering process. This review aims to present general aspects of research performed around the theme so far. It is verified that occurs the enhancement of ceramic toughness and reliability with this technic, so it is possible to enlarge its range of application in engineering.

Abstract: In this work, composite ceramic was produced to base Al₂O₃ reinforced with 35% weight TiO₂ and variation 0-2% La₂O₃, were evaluated properties to study their microstructural characteristic and mechanical properties as applicable cutting tools. The ceramic composites were produced by thermo-mechanical process. It was observed from the results of XRD after sintering no new phase is formed, besides the characteristics of the precursor oxides. According to the result of particle size analysis before and 24 hours after milling, there was a reduction of the average diameter of agglomerate 95.25% which is suitable to assist sintering of the composite, because this reduction increases the reaction rate the raw material during firing. At microdurezavickers test it was observed that the sample with 1.5% La₂O₃ showed better hardness results.

Abstract: This study aims to evaluate the hydrophobicity of vulcanized silicone rubber coatings at room temperature (RTV SR) with loads of alumina trihydrate (ATH) and nanosilica (NS) in the polymeric silicone rubber matrix, in order to obtain coatings ATH/NS/RTV SR to cover the surface of glass electrical insulators. The coatings were characterized by scanning electron microscopy (SEM), testing in salt spray chamber, loss test and recovery of hydrophobicity. These coatings showed varying sizes of agglomerates and heterogeneous distribution of particles within the matrix RTV SR. In the test in salt spray chamber smaller leakage current values was observed for the insulator coating with the ATH/NS loads. In the loss and recovery of the hydrophobicity test the best result was observed for insulating load RTV SR / 20: 1 (ATH: NS).