ABSTRACT Alumina refractories are constantly subject to abrupt temperature variations and to high mechanical stresses. In this context, the search for solutions that prevent or reduce the degradation of refractories from industrial processes. The alumina-mullite-zirconia refractory materials exhibit excellent thermal shock resistance and enable high performance in wear and corrosion applications. In this work, we evaluated high-alumina refractories with 5.0 wt.% of nanometric zirconia, verifying the influence of the granulometry of the mullite aggregates, kept at 20 wt.%. Mullite aggregates up to 1 mm and fines of the order of 75 μm were separately used, partially replacing the alumina, and the specimens were sintered at 1600 °C for 5 h. We use scanning electron microscopy and X-ray diffraction techniques to identify the phases present. The fracture energy was evaluated using a three-point bending test, while the resistance to thermal shock damage using a thermal gradient of 800 °C for samples submitted up to fifteen thermal cycles combined with bending tests. The composition containing fine mullite and agglomerated zirconia aggregate provides higher fracture energy than the refractory, however, the aggregate with coarse particle size tends to offer good resistance to thermal shock damage due to the presence of lateral porosity to the aggregates.

RESUMO Os refratários de alumina estão constantemente sujeitos a variações bruscas de temperatura e elevados esforços mecânicos. Nesse contexto, busca-se por soluções que evitem ou diminuam a degradação dos refratários provenientes dos processos industriais. Os materiais refratários do sistema alumina-mulita-zircônia apresentam excelente resistência ao choque térmico e possibilitam alto desempenho em solicitações de desgaste e corrosão. Neste trabalho, avaliamos refratários de alta-alumina com 5,0 %m. de zircônia nanométrica, verificando a influência da granulometria dos agregados de mulita, mantida em 20 %m. Utilizou-se separadamente agregados de mulita de até 1 mm e de finos da ordem de 75 mm, substituindo parcialmente a alumina, e os corpos de prova foram sinterizados a 1600 °C por 5 horas. Utilizamos as técnicas de microscopia eletrônica de varredura e a difração de raios X para identificação e das fases presentes. A energia de fratura foi avaliada utilizando ensaio de flexão em três pontos, enquanto a resistência ao dano por choque térmico, utilizando-se gradientes térmicos de 800 °C para amostras submetidas até quinze ciclos térmicos combinados com ensaios de flexão. A composição contendo agregado de mulita fina e de zircônia aglomerada proporciona energia de fratura superior ao refratário, no entanto, o agregado com granulometria grossa tende a oferecer boa resistência ao dano por choque térmico devido a presença de porosidade lateral aos agregados.

Abstract Introduction The aim of this pilot study based on convenience sampling was to analyze the feasibility to quantitatively discriminate Trendelenburg sign (TS), a characteristic drop in pelvic position during gait in hip disfunctions, in patients with total hip arthroplasty (THA), by assessing gait variability and symmetry using inertial sensors. Methods Thirteen patients with right THA, divided into two groups with (GTS, n=4) and without TS (GnTS, n=9) assessed by experienced physician, were enrolled in the study. Harris Hip Score was applied for specific evaluation of THA. The protocol consisted in walking on a level treadmill during 3 minutes with two inertial sensors attached at anterior superior iliac spine of both sides. For each left and right step, features were extracted from the Y-axis gyroscope signals: peak value, mean absolute value, standard deviation and range. For each feature, a symmetry ratio was calculated as the ratio between left and right side. Results No significant differences were found in Harris Hip Score between groups. The variability assessed by standard deviation for left step, contralateral to the replaced side, was significantly larger for GTS group (p<0.001). Significant differences in the symmetry ratios were found between GTS and GnTS for all features extracted from gyroscopes Y-axis (W=144, p<0.001). The symmetry ratios for GnTS group were approximately equal one (except for range), whereas for the GTS group they exceed the 10% criterion. Conclusion The variability and symmetry ratios of gait features extracted from inertial sensors were successful to discriminate TS in THA patients.

RESUMO Este trabalho tem por objetivo caracterizar o desempenho de resistência mecânica e absorção de água de blocos solo-cimento para alvenaria, após 28 dias de cura, com a incorporação limite dos seguintes coprodutos siderúrgicos em substituição parcial ao solo: adições de até 20 % em massa do pó de balão coletado em alto-forno, até 10 % de poeiras de despoeiramento de aciaria elétrica, e até 20 % de escória granulada de forno elétrico a arco. As formulações propostas incluem adições simultâneas de pós obtidos do descarte da produção de blocos solo-cimento, onde a substituição parcial ao solo foi de até 20 % em massa. Os resultados obtidos sugerem a potencialidade de uso dos resíduos siderúrgicos em blocos intertravados de solo-cimento para alvenaria sustentável, como alternativa de aplicação para esses resíduos. Verificou-se a possibilidade de bons resultados confrontando os valores exigidos por norma (absorção de água < 20% e resistência mecânica > 2,0 MPa) com destaque quando se utilizou 20% pó de balão juntamente com 10% de reuso do bloco solo-cimento; 10% de escória de aciaria ou 20% de escória de aciaria juntamente com 10% de reuso do bloco solo-cimento; e 2,5% de pó de despoeiramento juntamente com 20% de reuso do bloco solo-cimento.

ABSTRACT This work aims to characterize the mechanical resistance performance and water absorption of soil-cement blocks for masonry, after 28 days of moist curing, with the incorporation limit of the following steel co-products to partial replacement of soil: up to 20% by weight of balloon blast furnace dust powder additions, 10% of dedusting dust secondary from electric arc furnace, and 20% of granulated slag of electric arc furnace. The proposed formulations also evaluated simultaneous additions of soil-cement blocks discarded, after granulated by crushing, with partial replacement of soil in up to 20% by mass. The results suggest the potential use of steel residues in soil-cement interlocked blocks for sustainable masonry, as applying alternative to this waste. It was found that the results that stood out, comparing standard specification (water absorption < 20% and strength > 2.0 MPa), the results that stood out were using 20% powder flask along with a 10% reuse of the soil-cement block; 10% of steel slag or 20% of steel slag with 10% reuse of soil-cement block; and 2.5% dusting powder with 20% reuse of the soil-cement block.

Polycrystalline strontium-doped lanthanum manganite (LSM) powders with 0.15, 0.22, and 0.30 mol % Sr were synthesized by the polymeric precursor route using a molar ratio of 3:1 citric acid and metal cations. The powders were characterized by Fourier transform infrared spectroscopy, thermal analysis, high-temperature X-ray diffraction to determine the crystalline perovskite phase and crystallite sizes, scanning electron microscopy for the morphological analysis, nitrogen adsorption to determine the specific surface area, and laser scattering to evaluate the particle size distribution. The LSM perovskite-type oxides containing intermediate 0.22 mol % Sr were found to exhibit a tendency to decrease in crystallite size and increase in specific surface area and, when calcined at 700-900 ºC exhibited a pure phase of perovskite, had a crystallite size of about 17-20 nm and a specific surface area for 900 ºC of 34.3 m².g-1.

As Manganitas de Lantânio são óxidos cerâmicos semicondutores intrínsecos do tipo p com estrutura perovsquita. A dopagem adequada nos sítios A, nesse material, aumenta a condutividade elétrica tornando-o apropriado para ser utilizado na produção de células a combustível de óxido sólido (solid oxide fuel cell - SOFC), operando em temperaturas próximas de 1000 °C. Em geral, a propriedades dos materiais variam com a composição e com o método de síntese. Nesse trabalho, foi sintetizado o composto La1-xSrxMnO3 (x = 0,20-0,22) via método citrato, visando investigar o efeito do teor de dopante na formação da fase perovsquita. O método citrato foi utilizado, uma vez que permite a obtenção de pós homogêneos e fases cristalinas a temperaturas mais baixas que os métodos tradicionais de síntese. Os pós-sintetizados foram caracterizados por difração de raios X (DRX), análise termogravimétrica (TG), microscopia eletrônica de varredura (MEV) e análise de área superficial específica pelo método BET. Os pós sintetizados com substituição de 22% de lantânio apresentaram melhores resultados em relação a obtenção da fase perovsquita.

Lanthanum manganite is a type p intrinsic semiconductor ceramic oxide with perovskite structure. The partial substitution in A-site of that material increases it’s electrical conductivity, becoming appropriate to be used in production of solid oxide fuel cells (SOFC) component for working at temperatures around at 1000 °C. In general, the properties of materials change with composition and synthesis method. In the present work, the synthesis of La1-xSrxMnO3 (x = 0,20-0,22) has been carried out by citrate method, aiming at to investigate the percentage effect of the dopante in the formation of the perovskite phase. This method allows to obtain homogenous powders and crystalline phase in lower temperatures than traditional methods of synthesis. The sample was characterized by X-ray diffraction (XRD), thermal gravimetric analyses (TGA), scanning electron microscopy (SEM) and analysis by specific surface area by BET method. The powders synthesized with 22% partial substitution of strontium showed better results relative to obtain perovskite phase.