Materials Science Forum Vols. 530-531

Abstract: A process for synthesis of fine zirconium titanate powders by chemical route is described. Zirconium/titanium molar ratio was varied from 0.67 to 1.5 and the powders produced were analyzed. The precipitation process comprises the mixture of zirconium and titanium metal salt solutions to ammonium hydroxide solution, followed by washing of the precipitate, calcination and grinding to result in zirconium titanate. The ceramic powder is then uniaxially pressed as cylindrical samples and sintered at 1400°C for 5 hours. The microstructure of fractured and thermally etched ceramic was observed by scanning electron microscopy, and crystal phase identifications were done by X-ray diffraction. At least two different zirconium titanate phases, ZrTiO4 and Zr5Ti7O24, were identified. Ceramic hardness was measured by Vickers indentation.

Abstract: The titanium affinity by oxygen is one of main factors that limit the application of their alloys as structural materials at high temperatures. Notables advances have been obeserved in the development of titanium alloys with the objective of improving the specific high temperature strength and creep-resistance properties. However, the surface oxidation limits the use of these alloys in temperatures up to 600°C. The objective of this work was estimate the influence of the plasma-sprayed coatings for oxidation protection on creep of the Ti-6Al-4V alloy, focusing on the determination of the experimental parameters related to the primary and secondary creep states. Constant load creep tests were conducted with Ti-6Al-4V alloy in air for coated and uncoated samples and in nitrogen atmosphere for uncoated samples at 500°C to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V specimens. Results indicated the creep resistance of the coated alloy was greater than uncoated in air, but nitrogen atmosphere was more efficient in oxidation protection. Previously reported results about the activation energies and the stress exponents values indicate that the primary and stationary creep, for both test conditions, was probably controlled by dislocation climb. Occurred a decreasing of steady state creep in function of the reduction of oxidation process, showing that Ti-6Al-4V alloy lifetime was strongly affected by the atmosphere due the oxidation suffered by the material.

Abstract: The aim of this contribution was to evaluate the synthesis of perovskites containing cerium by the combustion synthesis methodology as well as their catalytic behaviour in the methane combustion. Cerium was introduced partially replacing lanthanum into A position of perovskites with general formula AxA’1-xCoO3. The formation of cubic perovskites was confirmed by XRD. The powder containing only lanthanum and strontium in A sites showed a structure transition to orthorhombic at temperatures above 700 °C. The addition of cerium, instead of strontium, induced a structural stabilisation and only a cubic phase was detected up to 1100 °C. High cerium loadings led to the formation of cerium oxide, revealing its up limit into the structure. All samples showed to be active in methane combustion. The results indicated that over the perovskites loaded with cerium the oxygen adsorbed onto the catalyst surface plays a role in the reaction.

Abstract: Nanocomposites containing nylon 66 and montmorillonite clay organically modified with quaternary ammonium salts were obtained via direct melt intercalation. A montmorillonite sample from Boa Vista/PB, Northeast of Brazil, was treated with three types of quaternary ammonium salts such as Genamin, Praepagen and Cetremide. After the treatment, the powder was characterized by X-ray diffraction (XRD). The produced nanocomposites were characterized by Torque Rheometer, Infrared Spectroscopy (FTIR), mechanical properties and HDT. The obtained results for rheological characterization showed that the nanocomposites did not present deterioration with the presence of modified clay. Generally, the mechanical properties of tensile of the systems presented superior values compared to that of pure Ny 66. HDT's properties presented very interesting values for the nanocomposites and significantly larger than for pure nylon 66.

Abstract: In this work, polyethylene/montmorillonite clay nanocomposites were produced by melt intercalation. The clays were treated with quaternary ammonium salts and then treated and untreated clays were introduced in polyethylene. The clays were characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR). The nanocomposites were characterized by mechanical and flammability properties. The results showed that the mechanical properties were improved by introduction of organoclay in polyethylene matrix. By adding only 3wt% montmorillonite, the burning rate of the nanocomposites was reduced by 17% in relation to PE matrix.

Abstract: The aim of this paper was to study the characterization of sludge affected by different thermal treatment, on selected physical and chemical properties. Sludge incinerated ash has been fired at different temperatures. This material was fired at 1050 °C for 3 h and until a peak of 1010°C. After thermal treatment the ash were screened at 200 mesh. The ash was characterized by X-ray fluorescence and trace elements like Cr, Pb, Zn, Cu, and some oxides like quartz(SiO2), Al2O3, P2O5, Fe2O3 were found. Scanning electron microscopy (SEM) has shown one change of particle between 2μm at 90μm and apparent porosity.

Abstract: This paper studies the main well-know technological types of kaolins clays from the Republic of Cuba and compares it with one from Brazil. A simple description from the Cuban geology and from the involved kaolins deposits is showed. The basic characterization of each kind of kaolin, includes, chemical analyzes, grain size distribution, scanning electronic microscopy, X-ray diffraction and X-ray fluorescence for chemicals. For special assays it had conformed, by a simple axis hand press up to 5 t, test bodies, which had been burnt to the temperatures of 950, 1250 and 1450°C. These results include refractory and contraction results.

Abstract: This study shows a possibility of using sewage sludge after thermal treatment (at 1050°C for 3h) in the production of a building material. The use of dehydrated sewage sludge as a component in building materials, like in the sludge-clay mixture employed in the manufacture of bricks, tiles and cements, has been frequently done around the world. During sludge-clay mixture firing, which was done by controlled heating at a temperature above of 1000°C for 3h, organic substances of the sludge were completely eliminated. After thermal treatment, the micropores formed due to the released expansive gases, are responsible for the acoustic and thermal isolation properties of the resulting material. A problem found in the ashes was the high concentration of toxic compounds like Zn, Ni, Cr, Cu, Al oxides. The aim of the present work was to observe through scanning electron microscopy (SEM), X-ray fluorescence (XRF) and inductively coupled plasma optical emission spectrometer (ICP-OES) the integration of these oxides into the sintered ceramic matrix of sludge. Oxide integration is an important factor in brick manufacturing used as building materials.

Abstract: Municipal sludge waste combustion was studied by thermogravimetry (TG) and differential thermal analysis (DTA), to better understand the two main stages which occur during the combustion process, and to evaluate how much of the total and significant generated heat is released is during each combustion stage. A method to measure the lower heating value (LHV) on a dried basis was developed from the TG/DTA data and it was applied to the whole process and to each combustion stage. Chemical analysis of the residual products after each step shows that nitrogen organic compounds are burnt only from 350°C to 550°C, and that the organics which are released and burnt in the previous step, which begins by 150°C, present a heating value of about 32MJ/kg. The nitrogen containing compounds present a lower LHV.