I don't have much of a physics background, so my assumptions might be somewhat incorrect. But I've recently seen how sanding tools can be used on materials that are powerful, such as stainless steel. From a Google search, it seems standard sanding tools are made out of materials like aluminum oxide, which (aluminum) I've generally understood to be a relatively weaker metal. I was hoping to get some clarification regarding the basic process of how the sandpaper does not deform itself, instead doing more damage to the material it's in contact with.

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    $\begingroup$ Aluminum oxide (also known as alumina or, in crystalline form sapphire) is a quite hard ceramic material, very different from aluminum. It has a Moh's hardness of 9. $\endgroup$
    – Jon Custer
    Commented May 28, 2020 at 19:46
  • $\begingroup$ That makes sense; so the material is definitely harder than most other metals that it comes in contact with $\endgroup$
    – Daneolog
    Commented May 28, 2020 at 19:48
  • $\begingroup$ Yes, and if it doesn't work you go with diamond grit. $\endgroup$
    – Jon Custer
    Commented May 28, 2020 at 19:53
  • $\begingroup$ Wow, I did not know that also was an option. Seems a lot more expensive, though $\endgroup$
    – Daneolog
    Commented May 28, 2020 at 19:54
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    $\begingroup$ You may not be aware of this but two naturally occurring forms of aluminium oxide are ruby and sapphire both of which are very hard $\endgroup$
    – slebetman
    Commented May 29, 2020 at 4:47

2 Answers 2


Pure aluminum metal is relatively soft, but aluminum oxide is harder than any steel. The particles of the oxide that are glued to the paper have extremely sharp edges on them, and when you rub the sandpaper on a piece of steel, those sharp edges scrape off tiny pieces of steel.


Aluminum oxide is easily hard enough to cut glass. As a matter of fact, an aluminum oxide crystal with a small chromium oxide impurity is a ruby. With a small titanium oxide impurity, it is a blue sapphire.


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