For the synthesis of magnesium borate powder, magnesium carbonate and boric acid powders were mixed in ethanol and then investigated by differential thermal analysis (DTA) and thermogravimetry (TG). X-ray diffraction (XRD) results of the samples showed the formation of Mg2B2O5 phase at 500 oC and Mg3B2O6 at 650 oC. The synthesized powder used as an antioxidant additive in magnesia-graphite bodies containing 20% graphite. After curing at 200 oC and firing at 1200 oC and 1400 oC for 2 hrs in a coke bed environment, its physical and mechanical properties and also microstructural features were investigated. The results showed that after curing at 250 oC, the addition of magnesium borate led to an increase in cold crushing strength at about 20%. Comparing the samples with additives and without any additives at 1200 and 1400 oC showed that the cold crushing strengths were improved about 45%, 35%, respectively. In addition, the results clarified that magnesium borate (Mg3B2O6) phase led to improve oxidation resistance.

Keywords: Magnesium borate, MgO-C refractories, Oxidation resistance.