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Browsing by Author "Margarido, Fernanda"

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  • Acid leaching of alloys within the quaternary system Fe-Si-Ca-Al
    Publication . Margarido, Fernanda; Figueiredo, Maria Ondina; Queiroz, Ana; Martins, João Pedro de Almeida
    Silicon with high purity and fine particle size can be produced by acid leaching of Fe-Si industrial alloys under the condition that they have adequate chemical composition and structural constitution. Such alloys contain phases that fall within the system Fe-Si-Ca-Al, where the quaternary phase Caalsifer, with aproximate formula (Fe0.8Al0.1 0.1) (Si0.8Ca0.2)2, is found along with several binary and ternary phases (Fe-Si, Ca-Si, Al-Fe-Si, Ca-Al-Si). With the purpose of optimizing the phase, constitution alloys were synthesized within the system Fe-Si-Ca-Al. The results of leaching experiments performed using HCl (150 and 220g/L) at constant temperature (T=102 1 C) and ordinary atmosphere indicate that the Caalsifer plus Al-Fe-Si phases should be maximized whereas the FeSi2 phases should be minimized, by controlling Al/Ca and Fe/Si concentration ratios in the synthesis process.
    1997Journal article Restricted access Show more
  • Acid refining of synthesised alloys within the quaternary system Fe-Si-Ca-Al: effect of ferric ions
    Publication . 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%.
    2002Journal article Restricted access Show more