The best replacement for alumina is silica.

The best alternatives to alumina are rated as following:
★★★★★  silica
★★★  zirconia
★★★  silica gel
★  aluminum nitride
★  mullite
★  molecular sieve
★  bates
  bone char
  arctic silver 5
  steatite
  arctic silver
  aluminum oxide
  corundum
  bauxite
  silver 5

Your alternative for alumina is not listed? Suggest!
Speaking about alumina, one probably shouldn't forget about silica.

Other search terms related to alumina and their ratings are:
★★★★★ silica
You have in mind a companion for alumina and it is not yet here? Propose!



Google Trends

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alumina
silica
zirconia