Microstructures and mechanical properties of Al2O3–C refractories with addition of microcrystalline graphite

Al2O3–C refractories were prepared in coke bed in the range from 800 °C to 1400 °C by using tabular alumina, α-Al2O3, Al, Si powder, silica fume, natural graphite flake and microcrystalline graphite as starting materials. Firstly the ultrafine microcrystalline graphite (UMCG) powders were produced by high-energy ball milling natural microcrystalline graphite and micron sized α-Al2O3 powders, and then partially or totally replaced with graphite flake in Al2O3–C refractories. The microstructures and mechanical properties of all the obtained Al2O3–C specimens were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and three-point bending test. The results showed that UMCG with less than 5 μm in size could be obtained by a high-energy ball milling process. The mechanical properties such as cold modulus of rupture (CMOR), modulus of elasticity (E), force and displacement of Al2O3–C refractories with UMCG powders were improved in comparison with those without UMCG. This improvement was attributed to the fact that the addition of UMCG affected the microstructural evolution of Al2O3–C refractories. The UMCG powders could accelerate the in-situ formation of AlN, Al4C3, and SiC ceramic whiskers in specimens because of their higher reactivity than graphite flake.