High‐Temperature Creep of Polycrystalline Magnesia: II, Effects of Additives *

The creep of magnesia doped with 0.035 to 2.26 cation % of nine other oxides and three binary mixtures thereof and of three seawater products (about 96, 98, and 99.5y0 MgO) was evaluated in transverse bending at 1200° to 1500°C, with strain rates of about 10− 2 %/hr, and average grain sizes of 5 to 50p. The results obtained were compared with those for pure magnesia. Most additives accentuated the plastic (diffusion‐controlled) nature of the creep process presumably by pinning dislocations and/or slowing grain growth. In most cases the rate‐determining diffusing species seemed to be the cation, Mg, but in two cases it was suspected that oxygen boundary diffusion was controlling. Porosities above ˜10% appear to increase the temperature dependence of creep, probably by introducing boundary sliding. The agreement of the creep data with those of other diffusion‐controlled processes (electrical conductivity, sintering, and grain growth) is demonstrated.