CONICET | Buscador de Institutos y Recursos Humanos

Dolomite (MgO.CaO) refractory bricks are widely used in the steelmaking industry from the end of IX century due to their availability and excellent metallurgical properties. After that, in the middle of XX century, the incorporation of coal-tar pitches as binder and oxidation inhibitor was introduced to improve their properties. Later, the addition of graphite increased the performance of these materials (higher thermal conductivity, toughness and slag attack resistance) and extended their lifetime. Nowadays, dolomite-C bricks are claimed mainly because they favor the secondary metallurgy of steel ladles and they also improve the steel cleanliness and quality. However, environmental and shortage drawback linked to these type of materials force the producers to develop dolomite-C materials with improved characteristics. In the present work, the degradation of commercial bricks of dolomite-C thermally treated between 600 and 1400°C is studied. The thermal treatments are carried out in an electrical furnace with SiC heater elements, in controlled atmosphere (coke bed). Prismatic specimens (» 25 mm in length) are used for the tests. These specimens are obtained by cutting from the as-received brick using a diamond wheel and taking special care to prevent hydration. Tests are performed by triplicate. Dolomite-C refractory bricks are resin or synthetic-pitch based materials, with a ratio CaO/MgO close to unity. The as-received bricks are characterized by several techniques: chemical analysis, qualitative phase analysis by X-ray diffraction (DRX), measurement of bulk density and apparent porosity (based on DIN 51056/EN 993-1 standard), picnometry (in kerosene and He), differential thermal and thermogravimetric analyses (up to 1400°C, under flowing air and N2), optical microscopy by reflected light and scanning electron microscopy with EDS. Digital image analysis is performed in order to analyzed some microstructural aspects of the bricks. This method is applied on images of surfaces obtained by cutting with diamond wheel and polishing with kerosene (to prevent hydration). Microstructural degradation of tested specimens are performed with similar techniques to those used for characterization purposes: optical microscopy by reflected light and scanning electron microscopy with EDS, digital image analysis, XRD qualitative phase analysis and density and porosity measurements. In addition, the variation of the specimen weight is also determined. Material degradation is studied in function of the temperature and the time of permanence in each treatment. The experimental results are analyzed considering the difference in the microstructure and composition of tested dolomite-C bricks. Phase equilibrium diagrams available in literature are also considering to explain experimental data.