The physical properties of silicone resin will undergo a series of changes under high temperature environment, as follows:
Appearance changes
During the process of gradually increasing temperature, the silicone resin can initially maintain its original appearance, such as the smoothness and color of its surface remaining basically unchanged. But when the temperature approaches or exceeds its tolerance limit, discoloration may occur, such as the originally transparent or light colored resin turning yellow, brown, or even carbonization and blackening. Meanwhile, under prolonged exposure to high temperatures, the surface of the resin may become rough and lose its original luster, due to internal structural changes caused by high temperatures and the volatilization of some low molecular weight substances.
Hardness change
As the temperature increases, the hardness of silicone resin shows a gradually decreasing trend. At room temperature, it has a certain hardness and can provide physical protection such as wear resistance and scratch resistance for the substrate. However, when the temperature rises to a certain level, the activity ability of the molecular chain segments increases, and the originally relatively fixed structure becomes relaxed, making the resin softer and the hardness significantly decrease. For example, the organic silicon resin coating that could have resisted external scratching may be more susceptible to scratches and abrasions due to reduced hardness in high temperature environments, resulting in a weakened protective ability.
Change in elastic modulus
The elastic modulus reflects the ability of a material to resist elastic deformation, and the elastic modulus of silicone resin decreases in high temperature environments. This means that it is more prone to elastic deformation when subjected to external forces, gradually transitioning from a relatively rigid state to a more flexible state. For example, in some scenarios where it is used as a sealing material, silicone resin, which can maintain the shape of the sealing structure and prevent medium leakage well at room temperature, is more prone to deformation under external forces (such as pressure, vibration, etc.) due to the decrease in elastic modulus at high temperatures, which may lead to poor sealing effect and potential leakage hazards.
Changes in thermal expansion characteristics
Organic silicone resin expands when heated, and although its thermal expansion coefficient is relatively stable, the degree of volume expansion gradually increases with increasing temperature. In high-temperature environments, if there is a significant difference in the thermal expansion coefficient between the resin and the matrix material, and there is no reasonable buffering design, the internal stress generated by thermal expansion may cause peeling, cracking, and other phenomena between the resin and the matrix, affecting their performance and service life. For example, on some metal products coated with organic silicon resin, during high-temperature use, the resin coating is subjected to significant stress at the junction with the metal substrate due to thermal expansion, which can easily cause cracks and result in the coating losing its protective effect on the substrate.
Density variation
Generally speaking, under high temperature conditions, the density of silicone resin will decrease to a certain extent. This is because high temperature causes some small molecular components inside the resin to evaporate and escape, resulting in a relative decrease in the content of substances per unit volume, leading to a decrease in density. However, this density change is relatively subtle under conventional high-temperature use, unless it is under extreme high temperature and long-term exposure conditions, the density change will be more significant and further affect its related physical properties and usage effects.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150K. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.