Effect of Small Amounts of Porosity on Grain Growth in Hot‐Pressed Magnesium Oxide and Magnesiowustite

Grain growth was studied at 1300°, 1400°, and 1500°C in nearly theoretically dense (0.1 to 0.8% porosity) hot‐pressed magnesium oxide (99.99+%) and magnesiowustite (0.10 and 0.48 wt% Fe 2 O 3 ). Small amounts of porosity had large effects on the kinetics of grain growth. Grain growth is probably porosity‐controlled in MgO at all temperatures and in magnesiowustite at 1400° and 1500°C if pores remain on grain boundaries or at grain intersections. The tendency for the entrapment of porosity is enhanced as the temperature is increased and as the dopant (Fe 2 O 8 ) concentration is decreased. Small amounts of porosity (<1%) can cause limiting growth situations at grain sizes well below 100 μm. The Fe 2 O 3 dopant stabilizes squared grain growth kinetics at 1300°C and decreases the rate of grain growth at all three temperatures.