Study On The Effect Of Cab₆ And B₄c Addition On Anti-oxidation Resistance Of Mgo-cao-c Refractory

CaO has the properties of high melting point, high thermodynamic stability as well as the performance of removing inclusion from molten steel, and thus MgO-CaO-C refractoriy is considered to be an important type of refractory for clean steel production. As carbon containing refractories, carbon oxidation is one of the key issue affecting their application, and how to improve the oxidation resistance of the refractories is an important subject to be solved.The present work studied the effect of B4C and CaB6 addition on oxidation resistance of MgO-CaO-C refractories. And the thermal behaviors of the two additives and the mechanism of these additions on improving the oxidation resistance of the refractories was studied by investigating change of the microstructure and phase composition, and the following conclusions have been drawn.(1) CaB6 began to be oxidized at 700℃while heating in air condition, and the oxidation products B2O3 and CaB4O7 further reacted with CaO and MgO to form Ca3B2O6 and Mg3B2O6. These reactions could be conducted until elevated to 1762℃.(2) B4C began to be oxidized at 600℃, and the oxidation products B2O3 reacted with CaO and MgO to form Ca3B2O6 and Mg3B2O6.These reactions could be conducted until elevated to 1565℃.(3) The oxidation resistance of the refractories was improved by addition of CaB6 and B4C due to the following two aspects. On the aspect of thermodynamics, the oxidation of carbon in the refractories was protected due to the priority of the oxidation of these anti-oxidants. And on the aspect of dynamics, the oxidation resistance of the refractories was improved due to decease of porosity and formation of dense oxides layer near surface of the refractories.(4) While CaB6 and B4C were added respectively, the proper addition amount was around 4%, and the performance of the combined addition was between the two kind of anti-oxidant added respectively.(5) Considering the temperature ranges, that the oxides of these two additives, it is considered that the combined addition contribute to obtain a satisfied performance.