Materials Science Forum Vols. 591-593

Abstract: By using the active filler controlled polymer pyrolysis, new and cost-effective composite materials can be obtained. In this work, ceramic matrix composites were prepared by using this precursor route, using a polysiloxane network filled with metallic niobium and aluminum powders as active fillers. The mixtures were blended, uniaxially warm pressed, and pyrolyzed in flowing argon at 1400 °C. Porous ceramic preforms were infiltrated with a LZSA glass material, in order to improve the density of a porous composite material. The properties of the pyrolyzed composite material and the effect of the LZSA infiltration on the Al2O3-NbC-SiOC ceramic composite material were investigated. The results have showed that the infiltration processes has improved the physical and mechanical properties of the composite material.

Abstract: Y-TZP presents excellent properties at room temperature but these properties decrease as the temperature increases. This paper studies the behavior 20vol%Si3N4-SiC when added in YTZP matrix and heated under no pressure system. Al2O3 and Y2O3 were used to maintain the stability of the matrix and as sintering aids. The addition of Si3N4 and SiC in a Y-TZP matrix leads to formation of silicon oxynitride and it increases the mechanical properties like toughness and hardness. The mixture was milled and molded by CIP. Samples were heated at 1500°C, 1600°C and 1700°C for 2h without pressure under atmospheric conditions in bed-powders of Si3N4. Samples were characterized by XRD. Density, hardness, toughness, bending strength were measured. The structure of the material was observed in SEM/EPMA to verify the distribution of the materials in the composite. The formation of Si2N2O was observed in the sintered material and it showed an increment of both hardness and toughness as temperature increases. The samples presented considerable resistance of oxidation at 1000°C.

Abstract: The presence of fissures in the cement material of an oil well due to thermo-mechanic conditions caused by steam injection and acidizing operations, tends to commit the mechanical integrity of the annular space, resulting in the environmental contamination of the phreatic sheets and oil producing zones. However, the development of new materials for oil wells cementing has lead to several researches to achieve the optimization of this process. This work proposes the formulation of portland/polyurethane nonionic composites as a new material for oil wells cementing. The results prove the ability of the formulated composite to improve the mechanical properties when compared with portland/water cement slurry. Also, were obtained significant improvements in mass losses when acids were present.

Abstract: The ceramic matrix composites (CMCs) can be fabricated by the pressure infiltration technique. In this work it was studied porous preforms of quartzite that were infiltrated with aluminum liquid. For to produce the more resistant preforms of quartzite, it was additioned different quantities of bentonite (5 and 10%) and the preforms were firing at 1100°C and 1200°C. For the composites production, the melted aluminum was introduced into preforms under a pressure of 7 MPa. The characterizations of the composites were made by X-ray diffraction, scanning electron microscopy, and flexure strength. All the preforms studied presented sufficient strength for support the pressing during the process of squeeze casting. The results of X-ray diffraction of composites showed the presence of alumina, silicon and aluminum and fully interpenetration aluminum-siliconalumina composites were obtained by infiltration.

Abstract: A comparative study between alumina added niobia ceramics and two alumina zirconia composites from nanostructured TZP (7% and 14% weight) was made. On this composites the zirconia were yttria stabilized and the alumina were submicron structured. As sintering aid a mixture of magnesia, niobia and talc were used on all samples. The sintering was performed at 1450 oC during 60 minutes. The characteristic grain size and shape of an alumina and zirconia powders, aggregates and agglomerates were characterized. The sintering ceramics were evaluated through hardness, fracture toughness and 4 point bending test. Weibull statistic was applied on the flexural results. Although the fracture toughness result from ZTA were lower, and seems to be affected by the liquid fase, the hardness and Weibull modulus were higher than alumina niobia. The grains size and the homogeneity of its distributions on the microstructure of this ceramics was correlated to these higher values. The results from these alumina zirconia composites showed a potential to apply as a ballistic armor material.

Abstract: Several researches have been developed in order to verify the porosity effect over the ceramic material properties. The starch consolidation casting (SCC) allows to obtain porous ceramics by using starch as a binder and pore forming element. This work is intended to describe the porous mathematical behavior and the mechanical resistance at different commercial starch concentration. Ceramic samples were made with alumina and potato and corn starches. The slips were prepared with 10 to 50 wt% of starch. The specimens were characterized by apparent density measurements and three-point flexural test associated to Weibull statistics. Results indicated that the porosity showed a first-order exponential equation e-x/c increasing in both kinds of starches, so it was confirmed that the alumina ceramic porosity is related to the kind of starch used.

Abstract: Structural and functional characteristics of ceramic components highly depend on their microstructure and mechanical properties. In the production of such ceramics sintering plays extremely important role. Recently, we are working on the development and fabrication of temperature sensors for the petroleum wells. In this connection, we have developed a new alumina based ordered complex cubic peroviskite oxide ceramic Ba2AlWO5.5. During our study, we found that Ba2AlWO5.5ceramics compacts could not be densified by normal sintering route. To overcome this hurdle, we have utilized the liquid phase sintering process, using CuO additives. By addition of 1 to 2 wt% CuO, we succeeded to sinter this ceramic in the temperature range 1200 to 14000 C. Sintered Ba2AlWO5.5 ceramics were examined by X-diffraction and scanning electron microscopy to verify the presence of any extra phase due to CuO addition in the Ba2AlWO5.5 matrix. Our studies revealed that CuO addition did not affect the structural characteristics, but considerably modified the densification process, microstrutural characteristics and consequently mechanical properties of the Ba2AlWO5.5 ceramics.

Abstract: The ornamental rock industry generates huge amounts of waste in form of fine powder, demanding adequate alternatives for its final disposal. The possibility of using ornamental rock waste as a flux in porcelain tile has been assessed. The porcelain tile formulations are constituted mainly by kaolin, feldspar and quartz. The waste was added to a typical porcelain tile body, replacing the sodic feldspar by up to 15 wt. %. The prepared pastes were fired of 1240°C using a fast-firing cycle. The specifications of porcelain floor tile in terms of physical properties were achieved.

Abstract: The compound strontium-doped manganite lanthanum (La0,85Sr0,15MnO3 - LSM), deposited in the form of thin films in yttria-stabilized zirconia substrate (Y2O3/ZrO2 - YSZ), is of basic importance as cathodic material of the solid oxide fuel cells (SOFC). In this work, the LSM was synthesized by the citrate technique and characterized by X-ray fluorescence spectroscopy (XRF), phase analysis light scattering granulometry (PALS), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). In the wet powder spraying, was used an airbrush and the LSM sample deposited to the YSZ substrate was sintered and characterized by SEM. The conclusions had allowed to establish preliminary conditions for preparation of LSM suspensions by wet powder spraying.

Abstract: Zirconia stabilized with 8 mol% yttria (YSZ) is the most effective material for use as electrolytes in solid oxide fuel cell. Ceramic powders of YSZ were synthesized in IPEN by coprecipitation route and are composed by fine particles (less than 01μm) with large surface area (~60m2.g-1). These powders have a strong tendency to agglomerate. and it make difficult the compaction process and to achieve a good density. To exert control over the compaction process. the powders were spray dried to obtain spherical granules. Thus the stability of slurries of these powders was studied by adding ammonium polyacrylate (Duramax D3005) as dispersant and the suspension stability was measured by electrophoretic mobilities. Slurries prepared with the better conditions were dried in a laboratory scale spray dryer. The prepared granules were characterized by morphology observation (SEM). surface area (BET). Vickers hardness and sintered ceramics bodies density were measured.