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 (Fe(3−x)Sn(x)O(4)) was easily formed when SnO(2) and Fe(3)O(4) were roasted under CO-CO(2) 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 SnO(2) and Fe(3)O(4) under CO-CO(2) atmosphere were determined using XRD, VSM, SEM-EDS, XPS, etc. The results indicated that the formation of Fe(3−x)Sn(x)O(4) could be divided into four steps: reduction of SnO(2) to solid phase SnO, volatilization of gaseous SnO, adsorption of gaseous SnO on the surface of Fe(3)O(4), and redox reaction between SnO and Fe(3)O(4). During the roasting process, part of Fe(3+) in Fe(3)O(4) was reduced to Fe(2+) by gaseous SnO, and meanwhile Sn(2+) was oxidized to Sn(4+) and entered into Fe(3−x)Sn(x)O(4). The reaction between SnO(2) and Fe(3)O(4) could be summarized as Fe(3)O(4) + xSnO((g)) → Fe(3−x)Sn(x)O(4) (x = 0–1.0).