Solidification of Calcium Ferrite Melt Using Ultrasonic Vibration: Effect and Mechanism
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TRODUCTION
IRON ore sintering is a thermal agglomeration process that is applied to a mixture of iron ore fines, recycled iron-making products, fluxes, and solid fuel. The purpose of the sintering process is to produce a product with suitable characteristics (thermal, mechanical, physical, and chemical) to be fed to the blast furnace.[1,2] Calcium ferrite (CaFe2O4, CF) is the most desirable liquid phase among the binding phases, which dominatingly contribute to the improvement of the strength and reducibility of the finished sinters.[3] Solidification, which greatly influences the microstructure of CF, is an important step during the sintering process. Owing to the acoustic cavitation formed by the ultrasonic field, the sonochemical method is an efficient technique and used in many fields[4,5] including (1) synthetic chemistry,[6,7] (2) food technology,[8] (3) biotechnological applications,[9] (4) electrochemical processes,[10] (5) water remediation,[11] (6) spent nuclear fuel
RUIRUI WEI, MINGRUI YANG, JIAN XU, and ZHIXIONG YOU are with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China. XUEWEI LV is with the College of Materials Science and Engineering, Chongqing University and also with the State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing, 400044, China. Contact e-mail: [email protected] Manuscript submitted April 4, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
reprocessing,[12] and (7) metal solidification,[13–15] and others.[16] Wang et al.[17] used high-speed synchrotron X-ray radiography to study the solidification of the primary intermetallic phase of Al2Cu under the effect of ultrasonic melt processing and to understand the dynamic interaction between cavitation bubbles and primary Al2Cu intermetallic particles in situ. The results indicated that acoustic cavitation and streaming flow played a crucial role in the fragmentation of intermetallic dendrite. Cavitation bubbles or bubble clouds contribute to fragmentation not only by mechanically fracturing the dendrites but also by facilitating the effect of acoustic streaming flow on dendrites.[17] Todaro et al.[18] investigated macro-segregation and primary Fe-containing intermetallic peritectic transformations in an Fe alloy with 19 wt pct Al and 4 wt pct Si with and without ultrasonic metal treatment. Macrostructural examination showed the ingot with ultrasonic metal treatment exhibited almost complete homogeneous distribution of both primary and secondary phases. The area fraction, number density, and size distribution of both primary and secondary phases became essentially uniform across the ingot after USMT. Feng et al.[19] studied the formation of non-dendritic structure of Mg alloy solidified with ultrasonic treatment. The results indicated that the ultrasonic cavitation strongly contributed to the grain refinement by improving nucleation, while the acoustic streaming was mainly responsible for the formation of non-dendritic structure. In previous work, the authors reported the effect of
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