The formation of strontium hexaferrite SrFe12O19from pure iron oxide and strontium carbonate

The formation of strontium hexaferrite SRFE
12
O
19
from pure iron oxide and strontium carbonate has been studied by means of dynamic high temperature X-ray diffraction, thermal analysis, and thermogravimetry. The formation in air passes through two endothermal reactions: SrCo
3
+6α-Fe
2
O
3
+(0.5-x)
\frac{1}{2}
O
2
→ SrCo
3
+5.5α-Fe
2
O
3
+CO
2
(A) SrFeO
3-x
+5.5α-Fe
2
O
3
→ SrFe
12
O
19
+(0.5-x)
\frac{1}{2}
O
2
(B) The solid state reaction of the formation of the perovskite SrFeO
3-x
starts between 660 C (0.13°/min) and 730 C (20°/min) depending on the heating rate. Above 810 C or 1000 C, resp., the perovskite reacts with the excess iron oxide forming the hexaferrite. During the process a part of the iron becomes tetravalent and is again reduced into the trivalent state. The phase Sr
7
Fe
10
O
22
or Sr
4
Fe
6
O
13
, resp., observed in quenched samples could not be detected during the formation in air.