Assessing and tailoring the dilatometric profile of novel chromium-free refractory raw materials

Reducing dependence on toxic electrofused magnesia-chromium aggregates is essential to meet demands for eco-friendly refractories. Some authors have proposed alternative compositions using lab-scale electrofusion to produce small specimens (< 0.5 g). However, this size limits the evaluation of key refractory properties, such as thermal expansion. As an alternative, this study explored conventional sintering at 1600 degrees C for 5 h and both methods resulted in equivalent chemical and mineralogical compositions. Despite presenting higher porosity (24 % - 30 %) than the electrofused ones (4 % - 6 %), consistent microstructural parameters supported using the sintering route to produce larger specimens (5 x 5 x 25 mm(3)), which were assessed for dilatometric profiles up to 1400 degrees C. Combined with thermodynamic calculations, Rietveld's refining of X-ray diffraction patterns and differential scanning calorimetry, the dilatometric analysis indicated that spinel dissolution in the periclase causes a high expansion during heating, whereas its re-precipitation results in shrinkage. As this behavior could result in challenges for the refractory lining design, computational thermodynamics was used to find additives capable of increasing this transition temperature. TiO2 was identified as a promising candidate and its effectiveness was attested.