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

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 52; no. 5; pp. 3477 - 3489
• Main Authors: Yue, Hong-Rui, Xue, Xiang-Xin, Zhang, Wei-Jun
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.10.2021; Springer Nature B.V
• Subjects: Annealing furnaces; Calcification; Calcium ions; Calcium oxide; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium oxides; Diffusion; Electron probe microanalysis; Fourier transforms; Infrared analysis; Interdiffusion; Materials Science; Metallic Materials; Nanotechnology; Original Research Article; Roasting; Slag; Structural Materials; Surfaces and Interfaces; Thin Films; Vacuum furnaces; Vanadium pentoxide
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-021-02276-6

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 V 2 O 5 /CaO systems were studied using the diffusion couple technique. This article, as a supplement, aims to present the diffusion characteristics of Cr 2 O 3 /CaO system and proposes the use of diffusion energy to quantify the competition with V 2 O 5 /CaO system. The Cr 2 O 3 /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 Cr 2 O 3 /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 CaCr 2 O 4 was the main intermediate in the vicinity of the Cr 2 O 3 /CaO interface at 1273 K to 1573 K. The formation of CaCr 2 O 4 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 CaCr 2 O 4 was linearly dependent on the square root of the roasting time, indicating that the solid-solid reaction between Cr 2 O 3 and CaO was governed by the diffusion process. Based on the vacancy mechanism, new equations that involve the diffused Ca 2+ (or Cr 3+ ), undiffused Cr 2 O 3 (or CaO), and undiffused O 2− of the Cr-rich layer (or Ca-rich layer) are proposed to describe the formation of CaCr 2 O 4 . 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  cm 2  s −1 , respectively. The calculated diffusion activity energy of Cr 2 O 3 /CaO system (56.53 ± 2.27 kJ mol −1 ) was only one-fifth of that of V 2 O 5 /CaO system.