Inhibition of Sintering and Surface Area Loss in Phosphorus‐Doped Corundum Derived from Diaspore

The influence of magnesium, phosphorus, and iron additions on the low‐temperature (≤1000°C) sintering of nanocrystalline α‐Al 2 O 3 derived from α‐AlOOH has been investigated. α‐AlOOH powder with a surface area of 50 m 2 /g yielded α‐Al 2 O 3 products with surface areas of 150 and 80 m 2 /g after dehydration at temperatures of 400° and 500°C, respectively. However, these products were prone to sintering at >600°C, and the surface area was reduced to 15 m 2 /g within only 1 h at 1000°C. Although magnesium and iron doping had no discernible effect, the presence of phosphorus inhibited sintering and surface‐area loss significantly. Samples doped with 1%–2% phosphorus had surface areas of >31 m 2 /g after 100 h at 1000°C. Atomic force microscopy studies of α‐Al 2 O 3 pseudomorphs derived from α‐AlOOH single crystals also demonstrated the inhibiting effect of phosphorus, as the rate of crack elimination was reduced on phosphorus‐modified surfaces. The effects of the dopants are discussed with regard to their potential influence on α‐Al 2 O 3 surface energy and diffusivity.