Formation mechanisms of Fe3−xSnxO4 by a chemical vapor transport (CVT) process

摘要

Our former study reported that Fe-Sn spinel (Fe3−xSnxO4) was easily formed when SnO2 and Fe3O4 were roasted under CO-CO2 atmosphere at 900–1100 °C. However, the formation procedure is still unclear and there is a lack of theoretical research on the formation mechanism of the Fe-Sn spinel. In this work, the reaction mechanisms between SnO2 and Fe3O4 under CO-CO2 atmosphere were determined using XRD, VSM, SEM-EDS, XPS, etc. The results indicated that the formation of Fe3−xSnxO4 could be divided into four steps: reduction of SnO2 to solid phase SnO, volatilization of gaseous SnO, adsorption of gaseous SnO on the surface of Fe3O₄, and redox reaction between SnO and Fe₃O₄. During the roasting process, part of Fe³⁺ in Fe₃O₄ was reduced to Fe²⁺ by gaseous SnO, and meanwhile Sn²⁺ was oxidized to Sn⁴⁺ and entered into Fe_3−xSn_xO₄. The reaction between SnO₂ and Fe₃O₄ could be summarized as Fe₃O₄ + xSnO_(g) → Fe_3−xSn_xO₄ (x = 0–1.0).