Materials Science Forum Vols. 727-728

Abstract: This work reports on a novel route to produce porous matrixes for fibre reinforced ceramic matrix composites. This route relies on a reaction bonding process involving an intermediary carbide phase with subsequent oxidation. A slurry was prepared by mixing mullite powder, phenolic resin and aluminium powder in ethanol, which was used to impregnate Nextel fibres 610 (3M) by dip coating under ultrasonic vibration. The composites were vacuum-dried and submitted to a thermal treatment that consisted of a reaction step at 1250°C in Ar-atmosphere to convert the phenolic resin into carbon, which reacted with aluminium, leading to a carbide phase. The samples were then oxidized at 1250°C for 1h in air and subsequently sintered at 1300°C for 2h. Mechanical properties of composites and of matrix were determined at room temperature by 3-and 4-point bending tests, respectively. The microstructure of the composites was evaluated by optical-and scanning electronic microscopy, which revealed an apparent flawless microstructure.

Abstract: s common knowledge that for bundles of fibers, that the bundle strength is always less than the sum of the fiber strengths. This behavior can be explained by load-sharing models. So even when the weakest fiber fails, the remaining fibers share the load, and thus increase the effective stress in these fibers. At this work, different load sharing models were implemented on a simulated tensile test of ceramic oxide fibers using Matlab. The results are in agreement with the theoretical predictions and are a powerful tool for design of composites.

Abstract: The use of hydrogen fuel cell for generating electricity is one of the potential solutions to solve the energy crisis problem. Electrolysis of water is a promising technique to produce hydrogen, however, the large-scale application is, at present, restricted by its high HER (hydrogen evolution reaction) overpotential. Nickel-conductive polymers composites have been proposed as potential electrodes for the electrocatalytic reduction of hydrogen, due to the combination of good mechanical and electrical properties. In this work, it was investigated the electrochemical behavior of Ni and Nickel-Polyaniline (Ni/PAni) composite electrodes. The electrodes were obtained by electrodeposition from a suspension containing PAni particles. The electrocatalytic activity was monitored from polarization curves and the morphology was evaluated by scanning electron microscopy. The results showed that the incorporation of PAni in nickel metal matrix promotes an increase in electrocatalytic activity of HER, compared to nickel electrode.

Abstract: The development of technologies that use clean energy and integrated waste management of the residues domestic and industrial aimed a sustainable engineering in the socio-business concepts is an urgent necessity. This present paper has as objective the production of cement composites trace 1:1,2:0,8 (cement : dust stone: gravel) replacing the sand and dust stone for PET waste in the levels of 3, 6, 9, 12 and 15 %, to evaluate the aging time. The materials were characterized using thermal analysis, FTIR and the composites by particle size analysis, unconfined compression strength, among others. The particle size analysis allowed the calculation of fineness modulus, which was 2.59, 1.66, and 3.99 for the dust stone, gravel and PET, respectively. There was a decreasing trend of resistance with the PET increasing in the composition.

Abstract: Recent findings of Brazilian pre-salt petroleum reservoir has created an intense demand for new materials capable of withstanding direct contact with the crude petroleum as it is a highly corrosive and chemically reactive fluid. Ceramics materials are highly stable in hostile environment and therefore can serve as inert coating to solve some of these problems. In this context, in the present work we have developed La₂O₃ reinforced Al₂O₃-TiO₂ ceramic composites in proportions of 5-20 wt% titanium oxide and 1-2 wt% with high mechanical strength, through thermo-mechanical processing and sintering techniques To assess the quality of these materials as the protective coatings of crude petroleum storage and transportation systems we have studied the physic-chemical and mechanical stability of these materials in crude petroleum, originated from earthen and offshore petroleum wells of Brazil. These studies present satisfactory results for use of 2 wt% La₂O₃ reinforced Al₂O₃-TiO_{2 .}ceramic composites for such applications. Keywords: La₂O₃ reinforced Al₂O₃-TiO_{2 .}ceramic composites, protective coatings, metallic parts, crude petroleum

Abstract: Ceramic materials based on alumina are considered excellent for produce cutting tools used to machining hard metals. However, low mechanical strength and toughness presented by these materials limit their application. Traditionally particles, such as TiC, TiN and ZrO₂, are added to the alumina matrix to improve their mechanical properties, increasing the range of applications. Recent studies have shown that the addition of particles of different sizes in alumina matrix can promote simultaneous increase in mechanical strength and tenacity. In this work sintering behavior of Al₂O₃ micro-nanocomposite containing nanometric particles of NbC and micrometric particles of WC, was studied by dilatometry using heating rate of 20°C/min up to 1800°C. The addition of carbides in alumina matrix is prejudicial to sintering causing an increase in temperature of shrinkage.

Abstract: Alumina and zirconia-alumina composite has been micro-structured in air using femtosecond laser. The threshold fluence of 6.2 J.cm^-2 found in this work is close to that found published in literature [1]. In the case of Al-Zr, the threshold fluence is 2.2 J.cm^-2.Surface femtosecond laser treatment increase the apatite deposition by biomimetic method on alumina and alumina-zirconia composite and depends on the condition of laser treatments.

Abstract: The research in composites attempt to predict the physico-chemical and mechanical a given mixture of materials. In this work, a composite was produced using as the polyamide 6 matrix and how the burden of nickel ferrite was incorporated as powders calcined at 1200°C and concentration of 50 wt.%. This mixture was compacted in a hydraulic press with heating and characterized by XRD, SEM and TG. XRD results showed the characteristic peaks of polyamide 6 and ferrite. SEM results showed a good dispersion of nickel ferrite loading in the matrix, the presence of larger clusters and evenly distributed load for the composite calcined at 1200 ° C. TG curves showed that the addition of loading of calcined nickel ferrite promoted an increase in thermal stability of the composite compared to pure polyamide.

Abstract: There is a growing need for new biomaterials that can gain predictable and controlled tissue response, this is, that as bone graft substitutes should initiate new bone formation, after which they should get reabsorbed and replaced by bone tissue. This combination aims to improve the mechanical properties, degradation rates and absorption rates of biocompatibility and biodegradability. The aim of this study was to propose a synthetic route in which the HA was obtained by reaction of precipitation directly on evaluating the influence of chitosan biopolymer in the middle of precipitation in the characteristics of hydroxyapatite obtained. XRD analysis revealed the presence of HA phase with low crystallinity. In the FTIR analysis identified the characteristic bands of hydroxyapatite, as well as bands that characterize an interaction between chitosan and hydroxyapatite, as the band around 1050cm^-1. SEM analysis of the biocomposites chitosan/HA, showed a dispersion of HA particles in chitosan, revealing a homogenous material and microporous.

Abstract: Ceramics for structural blocks are usually composed of a mixture of clays and sand with addition of water before a final temperature sintering. In the molding stage, the mixtures should attend a packing condition between the different particles sizes, to allow required properties of the ceramic after firing. The introduction of another compatible powder material, with a convenient particle size, may improve the ceramic properties such as the strength and water absorption. The number of variables in this system demands a modeling procedure to optimize conditions for the best results. In this work, a Simplex network modeling was used as an experimental planning to determine the optimum combination of clays, sand and water as well as incorporated granite waste, for ceramic blocks fabrication. The pressing load and firing temperature were also used as variables to determine the best response surfaces for final strength and water absorption of the ceramic blocks.