Materials Science Forum Vols. 660-661

Abstract: Among the researches applied to the sustainable production of construction materials there are the incorporation of rejects from the civil construction to clayey masses to make bricks, tiles and other products of structural ceramics. Main objective of this paper is to show the results of these mixtures. Spherical samples had been conformed incorporating 1%, 5%, 10%, 20% and 30% of reject from the civil construction in mass. These samples had been evaluated on compressive strength after dried to 110°C and to color and compressive strength after burns to 950°C. The composition that presented better results had been conformed by extrusion in prismatic samples. Then, the dried to 110°C and burnt to 950°C samples had been evaluated on flexion strength and in linear retraction too. Industrial test was made having produced 1500 ceramic blocks that show similar or better properties of blocks without incorporation. It was measured the ceramic and leaching properties of the blocks. The mixture with 5% of rejects in the clayey mass show the better results in all tests.

Abstract: In this work itria stabilized ZrO2 based ceramics for dental applications has been sintered and characterized in terms of physical and mechanical properties. Nanostructured blocks were sintered at 1400 0C and microstrutured blocks sintered at 1600 0C. Both nanostructured and microstructured materials were characterized in terms of densification, crystalline phases, mechanical properties and microstructure. Fracture toughness and four point bending strength were evaluated and compared. For the nanostructured zirconia, the reduced grain size allowed the increase of its toughening capacity, generated from maximization of volumetric fraction of retained tetragonal zirconia particles. For this material higher bending flexural strength is related to induced nucleation of microcracks, increase of energy absorption during crack propagation and developed compressive surface stress. The fracture toughness obtained at nanostructured samples sintered at 1400 0C is approximately 20% higher when compared to microstrucutured samples. These results represent the toughening ability of nanostructured zirconia, originated from higher amount of retained tetragonal phase and grain boundary microcracks. The higher Weibull moduli in this case are indicative of material reliability improvement and these results are correlated to grain size and its influence at mechanical strength.

Abstract: Paraíba is the main natural bentonite producing state of Brazil. Besides the advantage of abundance of bentonite clays, its transformation in organoclay is a simple method and there is only little study about the commercialization of Brazilian organoclays. In this work, Brazilian bentonite clay was organophilized with different quantity of a quaternary ammonium salt, such as 100, 125 and 150 wt.% in relation to Cationic Exchange Capacity (CEC) of the clay. The clays were characterized by X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Thermogravimetry (TG) and Nuclear Magnetic Resonance (NMR). It was observed that with increasing amount of salt the degree of dispersion of the clay increased, leading in some cases to the delamination of the clay layers and its loss of thermal stability.

Abstract: The selective reaction of CO oxidation (PROX) was named as the most attractive way to reduce the CO concentration, thereby purifying the hydrogen. The aim of this work is to make the structural and morphologic characterization of the NiFe2O4 spinel synthesized by combustion reaction, using glycine as fuel, and to evaluate as catalyst in the reaction of selective oxidation of carbon monoxide in the presence of hydrogen, oxygen and carbon monoxide. The powder was prepared by using a vitreous silica crucible on a hot plate at 480°C and according to stoichiometry established by theory of propellants and explosive. The powder was characterized by X-ray diffraction (XRD), FTIR, textural analyses, transmission electron microscopy (TEM) and catalytic measurements. The results from XRD show characteristic peaks of spinel phase without presence of secondary phases. The morphologic results show surface area of 3.1 m2/g and particle size calculated by TEM of 21.72 nm. The catalyst was active and selective for O2, reaching 100% of conversion.

Abstract: The effect of nylon 6 (Ny6) molecular weight on the development of polymer/layered silicates nanocomposites prepared by the melt intercalation technique was studied in this work. The nylon6/organoclay nanocomposites were prepared in the counter-rotational twin screw extruder. The results of torque rheometry showed that the presence of organoclay in the nylon 6 increased the torque. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed exfoliated and/or partially exfoliated structures.

Abstract: In this work, it was produced hybrids organic/inorganic membranes of nylon6 and clay mineral constituted of silicate layers, from the interior of the Paraiba. The sodic clay was used in the untreated and treated (with quaternary ammonium salts) form (to become compatible with polymer). Commercial salts Genamin and Cetremide were used to prepare organoclay by cationic exchange reaction in aqueous phase. The nanocomposites were obtained by melt intercalation and from these nanocomposites it was synthesized the membranes for dissolution in predetermined amounts of formic acid and a precipitation in a non-solvent, also called immersion-precipitation technique to prepare thin films. Thus, on the basis of the results, it can be observed that the presence of the treated and untreated clay confer a significant alteration in the structure/morphology of the pores and the porosity of the membrane.

Abstract: Titania ceramics have many applications due to its surface properties and, recently, its nanostructured compounds, prepared by hydrothermal treatments, have been described to improve these properties. In this work, commercial titanium dioxide was treated with 10% sodium hydroxide solution in a pressurized reactor at 150°C for 24 hours under vigorous stirring and then washed following two different procedures. The first one consisted of washing with water and ethanol and the second with water and hydrochloric acid solution (1%). Resulting powders were characterized by X-ray diffraction, N2 gas adsorption and field emission gun scanning and transmission electronic microscopy. Results showed that from an original starting material with mainly rutile phase, both anatase and H2Ti3O7 phase could be identified after the hydrothermal treatment. Surface area of powders presented a notable increase of one order of magnitude and micrographs showed a rearrangement on the microstructure of powders.

Abstract: Drug delivery systems involving microcapsules provide an attractive way to improve the performance of many chemical and biological substances. These systems may be used for several industrial segments, especially medical, pharmaceuticals and cosmetics. PHB is a polyhydroxyalkanoate available in powder form, biocompatible, biodegradable and inert towards animal tissues. The obtained PHB/smectite clay nanocomposite improved the physical-chemical properties of PHB, including its biodegradability. In this work, we describe the preparation of microcapsules from two nanocomposites systems: a) PHB and Cloisite 20A organoclay (PHB1) and b) PHB and natural Brazilian green policationic clay (PHB2). When analyzed by XRD, the films and microcapsules did not show a d(001) peak, demonstrating an exfoliated structure for the nanocomposites. The films have shown by SEM an homogeneous distribution with the clay mineral particles spread homogeneously by the PHB film. The new microcapsules/nanocomposites showed an “hydrangea” morphology. The diameter of the microcapsules was variable between 0.5-15 µm.

Abstract: This work has as its objective to add sand, up to 25 wt.%, to a clayey ceramic body used for roofing tiles fabrication. Specimens were prepared by extrusion and fired at 850oC. The evaluated properties were: plasticity, water absorption and flexural rupture strength. The microstructure of the fired ceramic was evaluated by scanning electron microscopy. The results indicated that the sand improved the evaluated properties of the ceramic as well as its processing. The microstructure of the ceramic presented a minor amount of porosity as a function of the sand addition.

Abstract: Samaria-doped ceria is a candidate solid electrolyte for applications in intermediate-temperature solid oxide fuel cells. One of the main concerns related to this solid electrolyte is its low sinterability, even when prepared by chemical methods. In this work, an alternative method of sintering was used aiming obtaining high densification with negligible grain growth in the late stage of sintering. Commercial samaria-doped ceria powder was pressed into pellets and sintered following the two-step sintering process. The first (peak) temperature was varied from 1100 to 1500 °C and the dwell temperature between 1050 and 1400 °C with soaking time of 5 h. The sintered ceramics were characterized by several techniques to correlate the processing-property characteristics. Relatively high densification has been obtained. Electrical conductivity data obtained by impedance spectroscopy could account for the observed improved densification.