Preparation of refractory calcium aluminate cement using the sonochemical process

Calcium aluminate cements (CAC) were prepared using the sonochemical process, followed by heat treatment. A study was made of the action of ultrasonic waves and the influence of thermal treatment conditions on two initial molar compositions of 1:1 and 1:2 of calcia:alumina. The aqueous suspension containing the raw materials (A-50 alumina and CaO) was subjected to an ultrasonic bath, followed by drying and burning at 1000, 1200 and 1300 ºC. These cements were characterized by SEM, XRD and the mechanical strength was evaluated by splitting tensile tests, using commercial cement as a reference. Furthermore, the phases were semi-quantified using the Rietveld method. The results show that hydration and sonochemical action increased the reactivity of the raw materials during firing and that phase formation is dependent on the thermal treatment conditions. The CAC cements were obtained at temperatures at least 200 ºC lower than those used in conventional methods, indicating the potential of this route of synthesis.

Spectrophotometric determination of arsenic in soil samples using 2-(5-bromo-2-pyridylazo)-5-di-ethylaminophenol (Br-PADAP)

Um novo método, simples e sensível para a determinação de arsênio em solo é proposto neste trabalho. Este método é baseado na redução de prata (I) e ferro (III) pela arsina seguida da reação de complexação do ferro (II) com o reagente espectrofotométrico 2-(5-bromo-2-piridilazo)-5-di-etilaminofenol (Br-PADAP). A determinação de arsênio apresentou uma sensitividade de Sandell de 3.1x10^-4 cm^-2, foi linear na faixa de 0.1 µg ml^-1 to 2.0 µg ml^-1 (r₅₆₀ = 0.9995), apresentou uma absortividade molar de 2.45x10⁵ l mol^-1 cm^-1 e um limite de detecção de 1.4 ng ml^-1 (3s) estes dados foram obtidos para 10 ml de amostra. A seletividade foi melhorada com o uso de EDTA com agente mascarante. O método proposto foi aplicado na determinação do arsênio na presença de outros íons e em amostras de solo. Os resultados revelaram que antimônio (III), mercúrio (II), germânio (IV), platina (IV) interferem na análise em todas as proporções analisadas. As interferências podem ser facilmente removidas pelo uso do EDTA. A precisão e a exatidão deram resultados satisfatórios, com desvio padrão relativo abaixo de 5%. As recuperações de arsênio em solo variaram de 95,55 a 102,70% com uma média de 99,63%. Estes resultados demonstraram que o método proposto é aplicável para a análise do arsênio em diferentes amostras de solo.

Ethanolysis optimisation of Jupati (Raphia taedigera Mart.) oil to biodiesel using response surface methodology

In this work, the transesterification of jupati (Raphia taedigera Mart.) oil using ethanol and acid catalyst was examined. The production of biodiesel was performed using a central composite design (CCD). A range of values for catalyst concentration (1 to 4.21%), temperature (70-80 °C), and the molar ratio of alcohol to oil (6:1-13.83:1) were tested, and ester content, viscosity, and yield were the response variables. The synthesis process was optimised using response surface methodology (RSM), resulting in the following optimal conditions for the production of jupati ethyl esters: a catalyst concentration of 3.85% at 80 °C and an alcohol-to-oil molar ratio of 10:1.