Formation mechanisms of Fe 3-x Sn x O 4 by a chemical vapor transport (CVT) process.

Our former study reported that Fe-Sn spinel (Fe3-x Snx O4 ) was easily formed when SnO2 and Fe3 O4 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 Fe3 O4 under CO-CO2 atmosphere were determined using XRD, VSM, SEM-EDS, XPS, etc. The results indicated that the formation of Fe3-x Snx O4 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 Fe3 O4 , and redox reaction between SnO and Fe3 O4 . During the roasting process, part of Fe3+ in Fe3 O4 was reduced to Fe2+ by gaseous SnO, and meanwhile Sn2+ was oxidized to Sn4+ and entered into Fe3-x Snx O4 . The reaction between SnO2 and Fe3 O4 could be summarized as Fe3 O4  + xSnO(g)  → Fe3-x Snx O4 (x = 0-1.0).