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Aluminum exposed to air very quickly grows a thin passive layer of aluminum oxide (unlike steel rust, this layer is stable). Anodizing forces it to grow a thick
by yuubi 10y ago
Aluminum exposed to air very quickly grows a thin passive layer of aluminum oxide (unlike steel rust, this layer is stable). Anodizing forces it to grow a thicker layer.
Aluminum oxide is hard stuff: 9 on the Mohs hardness scale (talc = 1, diamond = 10). https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness
- sbierwagen 10y agoAlso note that pure crystalline aluminum oxide is called corundum, or when doped with other elements, the precious gemstones ruby and sapphire, rocks of exceptional hardness and chemical resistance.
- yuubi 10y ago> chemical resistance I remember from a freshman chem lab that trying to dissolve aluminum into acid doesn't work because acid promotes oxide growth, so we dissolved it in NaOH, which was supposed to attack the oxide, then acidified the solution. Are the aluminum oxide minerals similarly susceptible, or do they also resist alkali?