Browsing by Author "Martins, J.P."
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- Acid refining of synthesised alloys within the quaternary system Fe-Si-Ca-Al: effect of ferric ionsPublication . Queiroz, Ana; Margarido, Fernanda; Martins, J.P.A systematic study of synthesis of different chemical composition of alloys within the quaternary Fe-Si-Ca-Al system, versus acid leaching refining using HCl with or without FeCl3 has been undertaken. Such study has the aim of achieving an adequate structural composition of Fe-Si alloys, in order to obtain high purity and fine particle size silicon by acid leaching, at more reduced costs. The experimental results show that an adequate control of Fe/Al and Si/Ca concentration ratios can hinder the formation of tetragonal and orthorhombic FeSi2 phases, and consequently promotes a successful refining of ferro-silicon alloys. The presence of ferric ion influences on a distinct way the rate of removal of Al-Fe-Si and Fe-Al-Si-Ca phases, increasing the first and decreasing the second one. The suitable starting composition which could give the expected results must be the following: 92-94% Si; 3-3.5% Fe; 3.5-4% Al and Ca ≤ 0.5%.
- Estudo da corrosão do ferro em meio ácido clorídrico, na presença e ausência de ião férricoPublication . Queiroz, Ana; Martins, J.P.A maior parte dos estudos cinéticos de solubilização do ferro em meios ácidos clorídricos [1-7] foram realizados na ausência de oxigénio. Neste trabalho estudou-se a influência dos iões H+, Cl- e Fe3+ na corrosão de um ferro em meio arejado, utilizando a técnica LSV ("Linear Sweep Voltammetry". Os dados experimentais obtidos, corrente/potencial, permitem determinar as densidades de corrente de corrosão, assim como as ordens da reacção anódica relativamente aos referidos iões.