Polysilazane is a kind of highly active polymer with Si-N bond as the main chain, which can react strongly with water, oxygen and many polar substances. This material has a wide range of applications in the ceramic, aviation, aerospace and coatings industries. According to its structure, polysilazanes can be divided into two major categories: organic and inorganic. Organic polysilazanes have side chains with organic groups, while inorganic polysilazanes, also known as perhydrogen polysilazanes or PHPS, have molecules that contain only three elements: silicon, nitrogen, and hydrogen. Due to its simple structure and high market value, PHPS is mainly used to make ceramic precursors and thermal insulation materials. PHPS do not contain organic groups, so they can be converted at lower temperatures by a variety of methods and have good adhesion to the substrate. Its converted coating features include corrosion resistance, high and low temperature resistance, gas isolation, long-term durability, transparency and scratch resistance, so it is widely used in the preparation of coatings. In photoelectric technology, an important branch of modern science, the development of coating technology is a challenge, and PHPS coating technology plays a vital role in improving the performance of photoelectric equipment and solving the key technical problems in the field of photoelectric technology.

In an environment of oxygen or water, PHPS can be converted to a silicon oxide coating by high-temperature treatment or light, regardless of the presence of a catalyst. Many researchers have explored the mechanism of coating formation by PHPS under different conditions, including chemical reactions and phase transitions of PHPS to silicon oxide at high temperatures. The diagram shows the phase separation in the PHPS transformation process, showing the transition from the PHPS phase to the silicon oxide phase, including the continuous phase of PHPS and the island structure, and the island structure of silicon oxide. The chemical reaction diagram shows the hydrolysis, condensation and oxidation reactions in the transformation process. It is found that when the conversion temperature is lower than 180°C, the hydrolytic condensation reaction of Si-H and Si-N mainly occurs, and the conversion is insufficient, forming the structure of silicon oxide as a dispersed phase. At this time, the refractive index is high, but the modulus and hardness are low. In the temperature range of 180°C to 300°C, the conversion is mainly the oxidation reaction of Si-H and Si-N, the silicon oxide phase gradually grows, forming a bicontinuous phase structure, and at more than 200°C, the silicon oxide phase becomes dominant, thus significantly improving the mechanical properties of the material. In the temperature range of 300°C to 600°C, the network structure of silicon oxide is basically formed and further densified at high temperatures.

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