moisture, polysilazanes decompose more or less quickly. Water molecules attack the silicon atom and the Si–N bond is cleaved. The R3Si–NH–SiR3 forms R3Si–NH2 and HO–SiR3 which can further react (condensation) to form R3Si–O–SiR3 (siloxanes). The rate of the reaction with water (or other OH containing materials like alcohols) depends on the molecular structure of the polysilazanes and the substituents. Perhydropolysilazane [H2Si–NH] n will decompose very quickly and exothermically with contact to water while polysilazanes with large substituents react very slowly. Polysilazanes are not vaporizable because of strong intermolecular forces. Heating polysilazanes results in crosslinking to form higher molecular weight polymers. At temperatures of 100-300 °C, further crosslinking of the molecules takes place with evolution of hydrogen and ammonia. If the polysilazane contains further functional groups such as vinyl units, additional reactions can take place. In general, liquid materials will be converted to solids as the temperature increases. At 400-700 °C, the organic groups decompose with the evolution of small hydrocarbon molecules, ammonia and hydrogen. Between 700 and 1200 °C a three-dimensional amorphous network develops containing Si, C and N ("SiCN ceramics") with a density of ca. 2 g/cm3. A further temperature increase can result in crystallization of the amorphous material and the formation of silicon nitride, silicon carbide and carbon. This so-called pyrolysis of the polysilazanes produces ceramic materials from low-viscosity liquids with very high yield (up to 90%). Due to the organic groups that are often used to give good polymer processability, ceramic yield is normally in the range of 60-80%. Applications For a long time polysilazanes have been synthesized and characterized, and their great potential for many applications was acknowledged. However, up to now, very few products have been developed into a marketable commodity. The development effort for these rather expensive chemicals is relatively high because of changing commercial availability among other things. Nevertheless, for some applications, polysilazanes proved to be competitive products. Taking advantage of their reaction with moisture and polar surfaces, polysilazanes are used as coating materials. Many metals, glass, ceramics or plastics with OH groups on the surface are easily wetted by polysilazanes. Reaction of Si–N with OH leads to the formation of Si–O–metal bonds generating good adhesion of the coating to the substrate. The “free” surface of the coating can react with humidity thereby creating a siloxane-like structure with excellent “easy to clean” properties. TutoProm, an organopolysilazane-based product, is used by Deutsche Bahn on