Kinetics and Mechanism of Oxidation Induced Contraction of MgAl₂O₄ Spinel Carbon Composites Reinforced by Al₄C₃ in situ Reaction

Abstract

Kinetics and mechanism of oxidation induced contraction of MgAl₂O₄ spinel carbon composites reinforced by Al₄C₃ in situ reaction were researched in air using vertical high temperature thermal dilatometer from 25 °C to 1 400 °C. It is shown that oxidation induced contraction of MgAl₂O₄ spinel carbon composites reinforced Al₄C₃ in situ reaction is the common logarithm of oxidation time t and the oxygen partial pressure P inside MgAl₂O₄ spinel carbon composites reinforced by Al₄C₃ in situ reaction in air at 1 400 °C is as follows: P=F(−2.75×10⁻⁴ A+2.13×10⁻³) lnt. The nonsteady diffusion kinetic equation of O₂ at 1 400 °C inside the composites is as follows: J=D _e lnt. Acceleration of the total diffusional flux of oxygen inside the composites at 1 400 °C is in inverse proportion to the oxidation time. The nonsteady state effective diffusion coefficient D _e of O₂(g) inside the composites decreases in direct proportional to the increase of the amount of metallic aluminium. The method of preventing the oxidation induced contraction of MgAl₂O₄ spinel carbon composites reinforced by Al₄C₃ in situ reaction is to increase the amount of Al. The slag erosion index of MgO-Al₂O₃ spinel carbon composite reinforced by Al₄C₃ in situ reaction is 0.47 times that of MgO-CaO brick used in the lining above slag line area of a VOD stainless steel-making vessel. HMOR of MgO-Al₂O₃ spinel carbon composite reinforced by Al₄C₃ in situ reaction is 26.7 MPa, HMOR of the composite is 3.6 times the same as that of MgO-CaO brick used in the lining above slag line area of a VOD vessel. Its service life is two times as many as that of MgO-CaO brick.

Keywords

kinetics / mechanism / oxidation / contraction / MgAl₂O₄ spinel / carbon / Al₄C₃ in situ reaction