An abrasive is any material used to cut, grind, or polish a softer material by abrasion – the wearing down of a surface when a harder surface rubs over it. Mild abrasives such as chalk are incorporated as a fine powder in toothpaste, and others such as silica, pumice, and aluminum oxide, are used in household cleaners; but various industrial applications demand even harder abrasives such as carborundum (silicon carbide), borazon (boron nitride), or synthetic diamond.

 

Some abrasives are used in solid blocks, as in the case of knife-grinding stones; but coated abrasives such as sandpaper in which abrasive granules are stuck onto a carrier make more economic use of the material.

 

Sandblasting exemplifies a third technique in which abrasive particles are thrown against the workpiece in a stream of compressed air or steam. Sandblasting is used for cleaning buildings and engraving glass.

 

Unwanted abrasion in bearings can be prevented by lubrication.