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

Abstract

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% Fe2O3). 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 (Fe2O8) concentration is decreased. Small amounts of porosity (<1%) can cause limiting growth situations at grain sizes well below 100 μm. The Fe2O3 dopant stabilizes squared grain growth kinetics at 1300°C and decreases the rate of grain growth at all three temperatures.