Palygorskite is fibrous clay in which the structural tetrahedral and octahedral layers are organized in a way that structural channels are formed, leading to high surface area. However, impurities inside the channels and aggregated ones considerably reduce the available area. In order to increase the surface area, an activation treatment can be considered useful. The goal of this work is the activation of palygorskite from Guadalupe, Piauí, via sulfuric acid treatment using a two-level factorial design. The influence of three parameters (solution molarity, temperature and time) on BET surface area was determined. Moreover, samples were characterized via X-ray diffraction (XRD) and fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The largest surface area (282 m²/g) without considerable changes in clay structure and morphology was found in a sample treated with 5M H2SO4 at 70°C for 1h. The main parameters that favored the improvement of the surface area were the solution's molarity, temperature and their interaction.

Dentre as cerâmicas de uso biomédico destaca-se o fosfato tricálcico do tipo β (β-TCP). Pós cerâmicos são normalmente compactados e sinterizados em altas temperaturas para sua densificação e consequente aumento da resistência mecânica. Uma forma de otimizar a densificação de corpos cerâmicos é analisar a significância das variáveis de processamento por meio de um planejamento de experimentos. O objetivo deste trabalho foi determinar a significância dos seguintes parâmetros: pressão de compactação uniaxial (28 e 111 MPa); calcinação prévia do pó (como recebido - não calcinado e calcinado a 650 °C); temperatura e tempo de sinterização (respectivamente, 900 e 1150 °C, 2 e 4 h). As pastilhas produzidas foram caracterizadas por microscopia eletrônica de varredura, difração de raios X e espectroscopia no infravermelho, enquanto que a microdureza e a retração linear foram consideradas as respostas do planejamento. Observou-se que o aumento da pressão de compactação e da temperatura de sinterização foram os parâmetros mais importantes para a densificação das amostras. As pastilhas sinterizadas a 1150 °C apresentaram tamanho médio de grão entre 1 e 2 µm e retração linear máxima de aproximadamente 20%, bem superior à das amostras sinterizadas a 900 °C, que não apresentaram completa densificação. Não foram identificadas outras fases que não o β-TCP e também não foram observadas microtrincas nas amostras sinterizadas.

Among the ceramic materials for biomedical applications, tricalcium phosphate type β (β-TCP) can be highlighted. Usually, ceramic powders are pressed and densified at high temperatures in order to improve the mechanical strength. One way to optimize the densification of ceramic bodies is to analyze the significance of processing variables using an experimental design. The purpose of this work is to determine the significance of the following parameters: uniaxial pressure (28 and 111 MPa); previous thermal treatment of the powder (as-received -non-calcined and calcined at 650 °C); sintering temperature and time (900 and 1150 °C, 2 and 4 h, respectively). The produced tablets were characterized by scanning electron microscopy, X-ray diffraction and infrared spectroscopy, while linear shrinkage and microhardness results were considered as responses of the experimental design. It was observed that the uniaxial pressure and sintering temperature were the most important parameters for samples densification. The average grain size of the tablets sintered at 1150 °C was approximately 1-2 µm and maximum linear shrinkage of, approximately, 20%, well above the values found for the samples sintered at 900 °C, which did not present complete densification. Phases other than β-TCP were not present in the sintered samples and no cracking was observed.