Diffusion coefficient of Ti 4+ in calcium ferrite/calcium titanate diffusion couple
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Diffusion coefficient of Ti4+ in calcium ferrite/calcium titanate diffusion couple Wang Wei, Hong-rui Yue, and Xiang-xin Xue School of Metallurgy, Northeastern University, Shenyang 110819, China (Received: 24 October 2019; revised: 27 March 2020; accepted: 30 March 2020)
Abstract: This study investigated the interdiffusion of calcium ferrite/calcium titanate system in the time range of 0–120 min by the diffusion couple method in a CO/N2 reducing atmosphere at 700°C. The results show that after the diffusion reaction occurred, no longitudinal agglomerations were present on the substrate surface on the calcium titanate side. When the diffusion time was increased to 105 min, a net vacancy flow from calcium titanate to calcium ferrite might have occurred, causing the surface of the calcium ferrite substrate to collapse. The thickness of the diffusion layer of the calcium ferrite/calcium titanate system was about 17–48 μm, which conforms to the parabolic law of diffusion. The diffusion coefficient and the Ti4+ concentration in the calcium ferrite/calcium titanate system are related. This shows an increase in the diffusion coefficient with the increase of Ti4+ concentration, and the diffusion coefficient value was in the range of 10−12–10−11 cm2·s−1. Keywords: vanadium–titanium sinter; diffusion couple; calcium ferrite; calcium titanate; diffusion coefficient
1. Introduction Vanadium–titanium magnetite ore contains a large number of vanadium and titanium, which are strategic elements, and are present in China in large reserves [1]. Vanadium-titanium magnetite resources allow for the efficient recovering vanadium and titanium elements and alleviate the iron ore crisis in China [2–7]. Currently, the main utilization method of vanadium–titanium magnetite in China is still the blast furnace ironmaking process [8], in which sinter is an important raw material. The quality of the sintered ore will greatly affect various economic and technical indicators in the blast furnace smelting [9]. Vanadium–titanium sintered ore has 3%–8% less strength compared with the ordinary iron ore, and its strength (drum index) only is 72% [10]. Compared with the ordinary iron ore, its biggest feature is the presence of TiO2. In response to this feature, several studies have been conducted. Cheng et al. [11] found that with the increase in TiO2 content, the breaking strength of vanadium–titanium magnet pellets significantly decreased. He [12] observed that the strength and yield of the sintered ore decreased following the increase in the mass percentage of TiO2, resulting in poor mineral morphology and structure. Budzik [13] found that reducing the calcium titanate formation in the vanadium–titanium sintered ore could effectively improve the ore utilization rate in the
subsequent blast furnace smelting. Ding et al. [14] found that when the temperature was higher than the melting temperature of calcium ferrite, a large amount of calcium titanate was formed in the CaO–Fe2O3–TiO2 system. When the ore was continuously heated, it would go through two
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