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 pseudo-morphs 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 a-Al 2 O 3 surface energy and diffusivity.

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