Densification of ceramic composite films coated on steel by a wet process

The densification of a ceramic coating based on SiO ₂-Al ₂O ₃-TiO ₂ by using wet processing was investigated by adding excess alkali silicates. Ceramic composite films (80-100 μm thick) were deposited on a steel plate by slurry coating with a doctor blade, followed by drying and calcination. The corrosion test in 1 mol/l HCl solution revealed that the number of through-holes in the coating decreased drastically with increasing amount of alkali silicates in the range of 26 to 33 or 40 wt.%. The coatings involving alkali silicates of 33 or 40 wt.% were stable to heating up to 800°C in air. The adhesive strength was also found to increase by three times with increasing amounts of alkali silicates.