Microstructures and mechanical properties of Al_2O_3-C refractories with addition of microcrystalline graphite

摘要

Al_2O_3-C refractories were prepared in coke bed in the range from 800 °C to 1400 °C by using tabular alumina, α-Al_2O_3, 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-Al_2O_3 powders, and then partially or totally replaced with graphite flake in Al_2O_3-C refractories. The microstructures and mechanical properties of all the obtained Al_2O_3-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 Al_2O_3-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 Al_2O_3-C refractories. The UMCG powders could accelerate the in-situ formation of A1N, Al_4C_3, and SiC ceramic whiskers in specimens because of their higher reactivity than graphite flake.