Materials Science Forum Vols. 798-799

Abstract: In this work, the yttrium rich rare earth concentrate (Re₂(CO₃)₃) was used as additive aiming stabilization of cubic an tetragonal phases at commercial zirconium oxide with 3% mol of yttrium oxide. The use of high purity rare earth oxide as additive is being commercially used and this work aims to demonstrate the potential use of lower cost additives to produce solid electrolyte for oxygen sensors and fuel cell applications. The powders for the additive production were synthesized by the controlled precipitation method. After synthesis, the powders were de-agglomerated using mechanical grinding and mixed to commercial zirconia to produce the compositions ZrO₂:3% Mol Y₂O₃:ƞ % Mol Re₂O₃ (ƞ=3,4,5,6), followed by uniaxial press and sintering at 1500 ⁰C in two hours. The obtained sintered densities were above 96% of theoretical. X-Ray diffractometric analysis and Rietweld refinement demonstrated the stabilization of cubic and tetragonal phases for all samples with yttrium rich rare earth concentrate additives. Finally the electric behavior of the evaluated samples was carried out with complex impedance spectroscopy, showing conductivity improvement for samples with the chosen additive. At 500 ⁰C the sample A-9% had a conductivity of 1,11E^-3 Ω^-1.cm^-1, well above of the sample without additive with conductivity 5,88E^-4 Ω¹.cm^-1, indicative that use of yttrium rich rare earth concentrate as additive increases considerably the ionic conductivity of comercial zirconium oxide. Key words: rare earth concentrate, controlled precipitation, ionic conductivity

Abstract: The synthesis by polymeric precursors method (Pechini) was used to acquire gadolinium doped ceria forming Ce_0,8Gd_0,2O_1,9 system, reaching high stoichiometric control features and nanosized particles to form dense solid electrolyte of high ionic conductivity. The synthesis was performed with cerium and gadolinium nitrates hexahydrates, citric acid and ethylene glycol. After the pre-calcination at 250°C/18h a resin was obtained like an expanded foam (puff). According to the iterature, this fact indicates that there is a reduction of agglomerates amount in a ceramic powder. A thermogravimetry-differential thermal analysis evaluated the thermal behavior of the resin. Infrared spectroscopy determined the organic matter and nitrates presence, before and after the calcination process. The X-ray diffraction identified the fluorite-type structure and was determined the crystallite size by the Scherrer equation in 22 and 46 nm for the powder calcined respectively at 600 and 800°C. The scanning electron microscopy evaluated the agglomeration degree and the morphology of the powders.

Abstract: Mullite whiskers were obtained by thermal decomposition of powders of natural topaz, pure and doped with 3 and 5% in weight of La₂O₃ and Y₂O₃, at the temperatures of 1300 and 1400^°C, for 1h, in air. Pure and doped mullite whiskers showed a molar ratio Al₂O₃: SiO₂ close to 2:1, rich in alumina. The aspect ratio (AR) of whiskers varies with dopant concentrations and temperatures. The ARs for pure whiskers were 28 and 31.5, at the temperatures of 1300 and 1400°C, respectively, showing no glassy phase. For the doped whiskers, there were observed a reduction in the ARs, ranging from 14.13 to 16.10 (3 and 5% La₂O₃) and from 6.32 to 7.35 (3 and 5% Y₂O₃), for the temperatures of 1300 and 1400°C, respectively. The Y₂O₃ was not entirely incorporated, and part of it formed Y₂Si₂O₇ and Y₂O_3-δ, with δ = 0.33 according to quantitative X-ray diffraction analysis (XRD analysis) with the presence of small amount of vitreous phase.

Abstract: Lithium fluoride as well as calcium oxide were used as sintering additives to magnesium aluminate ceramics in order to provide both transparency and better densification. This work assessed the dynamic behavior of MgAl₂O₄ by performing split Hopkinson bar dynamic tests. The total amount of additives was 1.5 wt% in which the percentage of LiF and CaO varied from 0 to 100 wt% with an increment of 25 wt%. The obtained results indicated that CaO low concentrations induced low strength values to the ceramics of different compositions. By increasing the amount of CaO, the MgAl₂O₄ dynamic strengths were higher. The strain rate was reduced as the amount of CaO increased, indicating a higher trend of energy absorption corroborated by K_Ic measured values. On the other hand, the ceramic strain increased with the increment CaO additions.

Abstract: Lead zirconate titanate, with Zr/Ti ratio of 53/47 was prepared by the polymeric precursor method. It was investigated the barium (II) modification at 0.0, 0.2, 0.4 and 0.6 mol% in substitution to the lead (II) cation in A site of perovskite structure. The powder samples were characterized by XRD and the diffraction patterns were used to Rietveld refinement. The percentages of tetragonal and rhombohedral phases and a systematic study of the effect of barium (II) on the morphology and the dielectric properties of PZT were carried out. The results showed that the tetragonal phase is favored and the ceramic density is improved with the barium (II) insertion. The Curie temperature (Tc) is increased besides the slight reduction of dielectric constant (Kc).

Abstract: We investigated the synthesis of nanosized Co₃O₄ oxide by the polymerization-combustion technique, with different concentrations (3, 12 and 25% w/w) in the ethanol oxidation reaction. Characterization was done by X-ray fluorescence analysis, X-ray diffraction, temperature programmed reduction, scanning and transmission electronic microscopy and CO and H₂ chemisorption. Principal results from physicochemical characterization show that the concentration of the metal oxide influence the product distribution and selectivity under isothermal conditions at 420 °C showed the formation of intermediate etoxi-species and preferential dehydrogenation reaction on stream of material. Specific concentrations result in high conversions and H₂ selectivity under present reaction conditions.

Abstract: The Polymeric Precursor Method has proved suitable for synthesizing reactive powders using low temperatures of calcination, especially when compared with conventional methods. However, during the thermal decomposition of the polymeric precursor the combustion event can be releases an additional heat that raises the temperature of the sample in several tens of degrees Celsius above the set temperature of the oven. This event may be detrimental to some material types, such as the titanium dioxide semiconductor. This ceramic material has a phase transition at around 600 ° C, which involves the irreversible structural rearrangement, characterized by the phase transition from anatase to rutile TiO₂ phase. The control of the calcination step then becomes very important because the efficiency of the photocatalyst is dependent on the amount of anatase phase in the material. Furthermore, use of dopant in the material aims to improve various properties, such as increasing the absorption of radiation and in the time of the excited state, shifting of the absorption edge to the visible region, and increasing of the thermal stability of anatase. In this work, samples of titanium dioxide were synthesized by the Polymeric Precursor Method in order to investigate the effect of Fe (III) doping on the calcination stages. Thermal analysis has demonstrated that the Fe (III) insertion at 1 mol% anticipates the organic decomposition, reducing the combustion event in the final calcination. Furthermore, FTIR-PAS, XRD and SEM results showed that organic matter amount was reduced in the Fe (III)-doped TiO₂ sample, which reduced the rutile phase amount and increased the reactivity and crystallinity of the powder samples.

Abstract: The microstructure of a 1050oC fired clay ceramic added with both argillite and discarded ceramic waste, known as grog, was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The objective was to evaluate not only the developed crystallographic phases but also the ceramic sintering conditions associated with the grog and argillite additions. The XRD results showed the presence of quartz and feldspar existing in the raw materials as well as hematite and mullite transformed at high temperature from the precursor clays. The SEM analysis revealed a consolidated ceramic structure in which the sintering process was effective in reducing the initial space between particles and thus improving the structural compactness.

Abstract: Drill cuttings are wastes produced on a large scale during the drilling of oil wells. Although there are several treatment techniques, there is still no consensus on which one are the best for the economy and environmental. On the other hand, one of the alternatives for the reuse of this waste, and purpose of the present study, is the incorporation of drill cuttings in clay matrixes. The raw materials used in this work, a mixture of clays and drill cuttings, were investigated by two basic techniques of characterization. X-ray fluorescence and X-ray diffraction. In order to evaluate the effect of the content of drill cuttings on the technological properties of sintered ceramics, different formulations containing from 0 wt.% to 100 wt.% of drill cuttings in a clay matrix were obtained. Ceramic samples were obtained by firing at temperatures ranging from 850 °C to 1050 °C. The fired specimens were characterized by water absorption, firing linear shrinkage, resistance to bending three points and scanning electron microscopy analysis. The results indicated that the incorporation of drill cuttings is a viable alternative for the manufacture of several ceramics products, such as solid masonry bricks and ceramic blocks, at certain concentrations and firing temperatures.

Abstract: Banana is a typical fruit that grows in warm tropical regions of the world including everywhere in Brazil. The production of the banana plant takes place year round and its pseudo-stem, mostly made of lignocellulosic fibers, is discarded as waste. The banana fibers posses a relatively higher content of potassium, which is an alkaline element of interest to the production of common clayey ceramics, like red brick, owing to its fluxing action. Therefore, the present work investigated the effect of banana pseudo-stem fiber incorporation on the technological properties of a clayey ceramic fired at 700, 900 and 1050°C. In spite of a possible contribution to liquid phase formation, the incorporation of up to 10 wt% of banana fiber impaired the ceramic properties, especially when fired at 1050°C