Published online by Cambridge University Press: 28 February 2011
The structure of sol-gel derived silica coatings was investigated using nanoindentation. chemical etching. and cross-sectional TEM. For coatings heated at 100°C. the surfaces were harder, etched slower, and appeared less porous than the interior of the coatings. For samples fired at higher temperatures (400–800°C). the surfaces remained harder and etched slower than the interior. even though the porosity appeared to be evenly distributed throughout the thickness of the coating. It is proposed that this difference is due to inhomogeneities on two scales in the coatings: bulk porosity and skeletal strain.