An efficient MgAl2O4 spinel additive for improved slag erosion and penetration resistance of high-Al2O3 and MgO–C refractories

A stoichiometric dense MgAl2O4 spinel has been prepared according to a conventional double stage firing process using AlCl3 as a sintering aid. A stoichiometric mixture of aluminum trihydroxide and caustic MgO was calcined at 1300 °C for 1 h in order to achieve a desired degree of spinelization. AlCl3 in different amounts, i.e. 0.911, 1.822 and 2.733 wt.%, was coated on spinelized powder using wet-impregnation technique and sintered at different temperatures ranging from 1500 to 1600 °C for 1 h. Among the spinels sintered at 1550 °C for 1 h, spinel incorporated with 2.733 wt% AlCl3 has exhibited superior properties in terms of bulk density, apparent porosity and water absorption. Further, this sintered stoichiometric spinel incorporated with 2.733 wt.% AlCl3 was characterized by means of scanning electron microscopy (SEM), energy dispersive analysis with X-rays (EDAX) and electron probe microanalysis (EPMA). EDAX analysis revealed that AlCl3 as a sintering aid helps in reducing the Na2O present in the raw materials composition after sintering. EPMA studies revealed that spinel prepared in this study is well comparable with the commercial spinel (Alcoa, AR-78, USA). Finally, 20 wt.% of the stoichiometric spinel incorporated with 2.733 wt.% AlCl3 prior to sintering was added to high-Al2O3 and MgO–C refractories to evaluate its effect on slag erosion and penetration resistance as well as on repeated permanent linear change (PLC) of these bricks. By the addition of stoichiometric MgAl2O4 spinel, the slag erosion and penetration resistance of high Al2O3 and MgO–C refractories was improved remarkably, and their PLCs exhibited more steady and stable positive values after spinel addition.