Solidification Behavior of Calcium Ferrite Under Ultrasonic Vibration
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D sinters are widely used as the raw materials in the blast furnace (BF) iron-making process due to their high strength and good reducibility. A sinter with superior reducibility could decrease the fuel consumption of the iron-making process and provide iron-rich raw materials with a suitable porosity to facilitate the smooth operation of the BF. The adhesive phase, a silico-ferrite of calcium and aluminum (SFCA),[1] is the main binder phase in the fluxed sinter and greatly influences the sinter quality and strength. In recent years, with the fluctuation of prices, the depletion of high-grade iron ore in the world, and complex gangue composition, it has become difficult to produce high-quality sinters. As a result, the formation of SFCA is suppressed, leading to a decrease in the yield and strength of the sinter ores. In the steel industry, sintering and BF processes not only consume large amounts of coke and coal, but also produce pollutants. Thus,
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 March 8, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
exploring energy-conservative and environmentally friendly sintering processes is beneficial for the iron-making industry. Iron ore sintering is a high-temperature process which consists of several steps: the formation of a liquid phase, the assimilation of a solid–liquid phase, and the solidification of the liquid phase.[2] The solidification process is a significant step for the formation of acicular SFCA. SFCA is formed through the assimilation[3–5] of the initial liquid-phase calcium ferrite (CaFe2O4, CF) and other solid particles (such as Al2O3, SiO2, and MgO) during the sintering process. Increasing the reducibility of SFCA significantly decreases the consumption of fuel and reductants and reduces the emission of pollutants in the BF process.[6] CF, as the most basic and important composition of SFCA, has an important influence on the formation of SFCA. In addition, the morphology of CF greatly influences the strength and reducibility of SFCA. Thus, modifying the morphology of CF is a possible way to improve the reducibility of SFCA. Power ultrasound is an efficient green technology that has been widely used in the solidification of metals,[7,8] alloys,[9–12] and ceramics[13] to accelerate the heterogeneous reaction rate and to refine grains. Chen et al.[9] investigated the effects of ultrasonic irradiation with an ultrasonic power of 1200 W on the macroscopic morphology, microstructure evolution, solidification behaviors, and mechanical performances of binary TiAl alloys. The results indicated that the coarse lamellar colonies and lamellar space of Ti44Al alloys were refined
from 685 to 52 lm and 1185 nm to 312 nm
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