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High performance solar collectors are those with high selectivity surfaces, high solar radiation absorption and that do not thermally reemit to the external environment. Strategies to enhance this performance might involve surface porosity modification. In this work, a plasma treatment technique called plasma electrolytic oxidation (PEO) has been tested to produce porosity on aluminium surfaces in a controlled manner. The porosity control was made by varying the intensity, frequency and duty cycle of the applied voltage pulses. The aluminium sample was placed in a solution of 1 g/L Na2SiO3. Voltage of 500 V and current density of 0.17 A cm2 was applied between electrodes. Three duty cycles were used: 33.33%, 50.00% and 67.77%. After treatment, the size, number and distribution of pores were evaluated. These parameters were correlated with both surface reflectance and optical absorbance. It was possible to control the porosity by controlling the electrical parameters of the process. While the mean pore size was directly related to the duty cycle, the inverse occurred for the number of pores. Surface treated with duty cycle of 33.33% presented higher values of absorption for all wavelength range.

This work aims to evaluate through technological tests the use of quartzite residues as component at the the production of porcelain stoneware. Were collected five samples of quartzites called of green quartzite, black quartzite, pink quartzite, goldy quartzite, white quartzite. After, the raw materials were milled, passed by a sieve with a Mesh of 200# (Mesh) and characterized by chemical analysis in fluorescence of x-rays and also analysis of the crystalline phases by diffraction of x-rays. The porcelain tiles mass is composed of five formulations containing 57% of feldspar, 37% of clay and 6% of residues of quartzite with different coloration. For the preparation of the specimens, it was used uniaxial pressing, which afterwards were synthesized at 1150°C, 1200°C and 1250°C. After the sintering, the specimens were submit for tests of technological characterization like: water absorption, linear shrinkage, apparently porosity, density and flexural strain at three points. The results presented in the fluorescence of x-rays showed a high-content of iron oxide on black quartzite that is why it was discarded the utilization of it in porcelain stoneware. All quartzite formulations had low water absorption achieved when synthesized at 1200°C, getting 0.1 to 0.36% without having gone through the atomization process. At the tests of flexural strain, all the quartzite had in acceptance limits, according to the European norm EN 100, overcoming 27 MPA at 1200°C

Compósitos cerâmicos a base de Al2O3 - Co apresentam propriedades específicas como baixa densidade, alta resistência à oxidação, alta dureza da fase cerâmica com a excelente tenacidade e boa trabalhabilidade da fase metálica, bem como, a boa biocompatibilidade de ambas as fases. O compósito alumina – cobalto apresenta ser um material promissor para ser aplicado em biomateriais ou ferramenta de corte. Este trabalho tem como objetivo avaliar o efeito do teor de cobalto na sinterização do compósito Al2O3 – Co. Os pós de partida de alumina e cobalto foram moídos e homogeneizados com teores de 5% e 20% cobalto, em seguida prensados no formato de corpos de prova circular com diâmetro de 5 mm a uma pressão uniaxial de 25 MPa e sinterizados a 1050°C durante 1h com taxa de aquecimento de 10°C/min em forno resistivo. As matérias-primas foram caracterizadas por difração de raios X (DRX), termogravimetria (TG/ DSC) e microscopia eletrônica de varredura (MEV). Os corpos de prova sinterizados foram submetidos a ensaios tecnológicos (AA, PA, MEA) e microscopia eletrônica de varredura. Os resultados evidenciam o efeito significativo do teor de cobalto na sinterização do compósito cerâmico Al2O3–Co, apresentando valores satisfatórios para o compósito Al2O3 – 5% Co.