High‐Temperature Creep of Polycrystalline Magnesia: I, Effect of Simultaneous Grain Growth *

The creep of pure magnesia (99.9 +% MgO) was tested in transverse bending at temperatures from 1200° to 1500°C, strain rates near 10 −2 %/hr, and grain sizes of 4 to 50μ. In most cases, grain growth during the test affected the apparent creep behavior more than all the other variables combined. An analytical graphical method was used to separate the grain growth effect from other effects and to obtain more meaningful creep data. Creep occurred primarily by a viscous mechanism (Nabarro‐Herring type, cation‐lattice‐diffusion controlling) with a minor amount of plastic creep (dislocation climb). The agreement with previous creep data was good.