WEAR OF PYROLYTIC TIN OXIDE AND ANODIZED ALUMINUM-OXIDE COATINGS ON ALUMINUM

Tin oxide and anodized aluminium oxide coatings intended for the protection of aluminium in optical applications have been investigated with respect to their hardness and their resistance to erosive and abrasive wear. The influence of wear on the reflectance of coated and uncoated specimens has also been studied. The hardness of the tin oxide coating was found to be somewhat higher than that of the anodic layer, which in turn was harder than the aluminium substrate. In the erosion tests, the tin oxide coating displayed a lower erosion resistance than the anodic layer, mainly owing to insufficient adhesion to the substrate. Both coating materials displayed a low intrinsic resistance to abrasive wear. The reflectance of the two coated specimens was more or less unchanged after a test time sufficient to decrease the reflectance of uncoated aluminium by almost 50%.