Creep of CaO/SiO2-containing MgO refractories

Compressive creep of five commercially-available brands of CaO/SiO2-containing MgO refractories was measured over a temperature range of 1400-1550°C and compressive stresses of 0.10–0.30 MPa. All brands had a MgO content greater than 96 wt%, a CaO/SiO2 wt% ratio equal to or greater than 1.9, and a firing temperature greater than 1535°C. The more creep resistant 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 of the five brands indicated their creep was rate-controlled by diffusion, and their activation energy values indicated that creep was accommodated by grain boundary sliding through viscous flow of the calcium silicate grain-boundary phase. Two brands exhibited dramatic time-hardening behavior which resulted in their creep not being well-represented by the power-law creep formulation. The observed attributes among the brands were combined and a hypothetical CaO/SiO2-containing MgO refractory is proposed.