Diffusion Characteristics of Intermediate in Cr2O3/CaO System and Its Formation Mechanism

• DOI: 10.1007/s11663-021-02276-6
• Publication Date: 2021-07-27T17:02:31Z
• Authors: Hong-Rui Yue; Xiang-Xin Xue; Wei-Jun Zhang
• Keywords: Roasting; Microanalysis

Cr has a disadvantage in competing with V for CaO during calcification roasting of V-Cr slag. However, there are almost no quantitative indicators that can directly describe the competing relationships. In previous studies, V-Cr slag/CaO and V2O5/CaO systems were studied using the diffusion couple technique. This article, as a supplement, aims to present the diffusion characteristics of Cr2O3/CaO system and proposes the use of diffusion energy to quantify the competition with V2O5/CaO system. The Cr2O3/CaO diffusion couple was prepared by the hot-pressing method and annealed in a vacuum furnace at 1173 K to 1573 K for 30 to 120 minutes. The Cr2O3/CaO interfaces under different annealing conditions were analyzed through electron probe microanalysis, X-ray diffraction, and Fourier transform infrared spectroscopy. The analysis results showed that CaCr2O4 was the main intermediate in the vicinity of the Cr2O3/CaO interface at 1273 K to 1573 K. The formation of CaCr2O4 was very slight (compared with V) at 1173 K, which verified that Cr was indeed at a disadvantage (compared with V) for occupying CaO during roasting. The diffusion thickness of CaCr2O4 was linearly dependent on the square root of the roasting time, indicating that the solid-solid reaction between Cr2O3 and CaO was governed by the diffusion process. Based on the vacancy mechanism, new equations that involve the diffused Ca2+ (or Cr3+), undiffused Cr2O3 (or CaO), and undiffused O2− of the Cr-rich layer (or Ca-rich layer) are proposed to describe the formation of CaCr2O4. The interdiffusion coefficients at 1273 K, 1373 K, 1473 K, and 1573 K were determined to be 6.04 × 10−10, 8.4 × 10−10, 1.09 × 10−9, and 1.72 × 10−9 cm2 s−1, respectively. The calculated diffusion activity energy of Cr2O3/CaO system (56.53 ± 2.27 kJ mol−1) was only one-fifth of that of V2O5/CaO system.