Artificial corundum is fused aluminum oxide produced by melting alumina in an electric furnace, resulting in a crystalline abrasive material. Standard aluminum oxide (alumina) that has not been fused into corundum form — including calcined, tabular, or Bayer-process alumina — classifies under 281820. The key distinction is the fusion/crystallization process.

Chemically it is the same compound (Al(OH)₃), but classification depends on form and presentation. Bulk aluminum hydroxide for industrial or chemical use classifies under 281830. If it is formulated as a pharmaceutical preparation or antacid, it would likely move to a different chapter. Consult a licensed customs broker when the end-use presentation is ambiguous.