CHEMICAL ATTACK EVALUATION OF ALUMINA-MAGNESIA-GRAPHITE BRICKS BY DYNAMIC TESTS AND THERMODYNAMIC SIMULATION

V. MUÑOZ; CALVO WALTER ANDRÉS; D. GUTIERREZ CAMPOS; S. CAMELLI

Santiago

Congreso; 15th Unified International Technical Conference UNITECR 2017; 2017

Latin-American Association of Refractory Manufacturers (ALAFAR)

Alumina-magnesia-carbon (AMC) refractories used in thesteelmaking ladles support temperatures up to 1600-1700°C andare also exposed to the attack of melts (liquid metal and slag) andoxidant gases of the atmosphere. On the other hand, the highdegradation of the bricks under real conditions in-service isdifficult to reproduce at laboratory scale. For this reason, acombination of analytical methodologies is convenient to face theproblem.In this work, the corrosion of commercial AMC bricks by moltenslag is studied by a combination of methodologies in order toachieve a deep understanding of the corrosion mechanisms and itsrelationship with refractory characteristics such as composition,microstructure and texture.The dipping-test, which reproduces the relative movementbetween the slag and the refractory, is used together with thethermodynamic simulation of the system by commercial software.Prismatic specimens extracted from the brick are subjected to thecorrosion test at 1600°C during 30 min, and a sample speed of 25rpm. A typical industrial slag is evaluated with a CaO/SiO2 ratio of10.6. After the test, the sample wear is evaluated by dimensionalvariations, XRD, TGA, density and porosity measurements. Also,SEM/EDS microscopy is employed. A previous characterization ofthe commercial bricks is performed by the same analyticaltechniques in order to use this information as reference. Thethermodynamic simulation of slag-refractory system is carried outusing FactSage 7.0 commercial package and the chemicalcomposition of the slag and the brick. An iterative procedure isemployed until the amount of equilibrium liquid is null. Thespecimen wear as well as the identification of the new phasesformed at the slag-refractory interface (mainly different calciumaluminates and MgO.Al2O3 spinel) are used as indications ofsample corrosion. Moreover, the equilibrium calculations bringsgood prediction with regard to the phases present at the slagrefractoryinterface, and the degree of corrosion wear taking intoaccount from number the iterative process steps..From these results, the main steps of the corrosion process(mechanisms) are inferred, as well as the relationship betweenchemical attack and AMC bricks characteristics (raw materials,periclase content, etc.).