Preparation of moisture curable polysilazane coatings

Moisture-curing of perhydropolysilazane and polyorganosilazanes to pre-ceramics has been studied at temperatures ranging from room temperature to about 150 °C. Results of FT-IR experiments with a diamond ATR adapter clearly showed that rapid curing required the presence of a moisture-containing atmosphere of about 80% relative humidity and the introduction of a catalytic curing agent such as ammonia or an amine. With respect to the curing rate, the effect of temperature increase can be compensated by a decrease of humidity, that is why moistening furnace are recommended for polysilazane transformation. The mechanism of moisture-cure mainly based on the hydrolysis of Si–H and Si–N bonds by water vapor to promote subsequent cross-linking of intermediately formed silanols via condensation reactions. Compared to neat polyorganosilazanes, blends with perhydropolysilazane revealed both higher curing rate and improved surface hardness. Polysilazane films of about 3 μm thickness coated on polycarbonate plates and cured at 50 °C in air of about 80% relative humidity for 1 h exhibited microhardness of about 450 N mm−2 compared to about 250 N mm−2 obtained for acrylate/silica nano-composite coatings. These findings point to dense polysilazane films what makes them very promising as coatings for technical applications, e.g., reduced gas permeability and improved corrosion resistance.