Creep of CaO/SiO2-containing MgO refractories

Compressive creep of five commercially-available brands of CaO/SiO2-contain ing MgO refractories was measured over a temperature range of 1400-1550 deg rees C and compressive stresses of 0.10-0.30 MPa. All brands had a MgO cont ent greater than 96 wt %, a CaO/SiO2 wt % ratio equal to or greater than 1. 9, and a firing temperature greater than 1535 degrees C. The more creep res istant brands were observed to have a combination of: (1) a larger average grain size and wider grain size distribution, (2) a low iron content, and ( 3) an absence of CaO-MgO-SiO2 compounds. Creep-stress exponents for three o f the five brands indicated their creep was rate-controlled by diffusion, a nd their activation energy values indicated that creep was accommodated by grain boundary sliding through viscous flow of the calcium silicate grain-b oundary phase. Two brands exhibited dramatic time-hardening behavior which resulted in their creep not being well-represented by the power-law creep f ormulation. The observed attributes among the brands were combined and a hy pothetical CaO/SiO2-containing MgO refractory is proposed. (C) 1999 Kluwer Academic Publishers.