Solidification of Calcium Ferrite Melt Using Ultrasonic Vibration: Effect and Mechanism

Calcium ferrite (CF) is a very important binder phase in iron ore sintering processes. To improve the microstructure of CF, power ultrasound was introduced during its solidification process, and the effect of immersion depth of ultrasonic probe (IDUP) on the properties of CF was investigated in detail. The results indicated that the microstructure of CF was greatly refined; the grain size decreased from 2864 μm without ultrasonic vibration to 841 μm with ultrasonic vibration at an immersion depth of 30 mm. Without ultrasonic vibration, the density and compressive strength of CF slag were 3904 kg/m³ and 38.3 MPa, respectively. When the IDUP was increased from 10 to 30 mm, the density and compressive strength of CF increased from 4049 to 4452 kg/m³ and 52.5 to 87.3 MPa, respectively. Further, the reducibility of CF was examined. The reduction time, at the same reduction rate, decreased from 347 minutes without ultrasonic vibration to 200 minutes with ultrasonic vibration at an IDUP of 30 mm. The rate-limiting step was obviously improved, which may be attributable to the grain refinement of CF and composition segregation in the slag. In general, the properties of CF were greatly improved due to the cavitation and acoustic streaming of ultrasonic waves.