China's Refractories

Abstract: To improve the performance of low-carbon magnesia carbon refractories, specimens were prepared using fused magnesia with particle sizes of 3-1, ≤ 1, and ≤ 0.074 mm, flake graphite with a particle size of ≤ 0.15 mm as the main raw materials, phenolic resin as the binder, and adding alumina micropowder with mass percentages of 1%, 3%, 5%, 7%, and 9%, respectively. The obtained green specimens were then cured at 200 °C for 24 h and heat-treated at 950 °C or 1 550 °C for 3 h. The effects of the alumina micropowder addition on the properties (including the apparent porosity, bulk density, cold compressive strength, cold modulus of rupture, hot modulus of rupture, and thermal shock resistance) as well as on the phase composition and microstructure of the low-carbon magnesia carbon specimens were investigated. The results show that the physical properties of the specimens are improved as the alumina micropowder addition increases, mainly due to the in-situ reaction between magnesia and alumina to form spinel, which enhances the bonding of the matrix and thus strengthens the overall bonding of the specimens. After the heat treatment at 1 550 °C, the bulk density, cold compressive strength, and cold modulus of rupture of the specimens first increase and then decrease with the increase of the alumina micropowder addition, reaching the optimal values when the addition is 7%. Both the linear change rate and volume change rate of the specimens increase with the increasing alumina micropowder addition.

Key words: alumina, low-carbon magnesia carbon materials, spinel