Humidity has a significant impact on the various properties of the cured product of polysilazane, as follows:
1. Mechanical properties
In terms of hardness:
When the humidity is high, if polysilazane absorbs too much moisture before curing, it may alter the progress of its crosslinking reaction during the curing process. For example, hydroxyl groups and other functional groups generated by hydrolysis can affect the original silicon nitrogen bond cross-linking, resulting in an irregular cross-linking network structure of the cured product and a decrease in hardness. The cured product, which could have reached a pencil hardness of 8H, may only reach a hardness of around 5H after curing in a high humidity environment.
Resilience and brittleness:
The hydrolysis reaction caused by excessive moisture will introduce some polar groups (such as hydroxyl groups) into the cured product, disrupting the originally good interactions between molecular chains, increasing the flexibility of the molecular chains, and improving the toughness but reducing the brittleness of the cured product. However, if there are too many side reactions generated by hydrolysis, which damage the overall cross-linking structure, it may also cause the cured product to become fragile, significantly reduce its impact resistance, and be more prone to cracking when subjected to external impact.
2. Corrosion resistance
Corrosion resistance:
Polysilazane products cured in high humidity environments may introduce more hydrophilic groups (such as hydroxyl groups) due to the involvement of moisture during the curing process, which enhances their hydrophilicity and makes them more susceptible to water infiltration and erosion upon subsequent contact with water. For example, the cured product of polysilazane used for pipeline protective coatings, after curing under high humidity, may experience faster foaming, peeling, and other phenomena when in contact with water for a long time, resulting in a significant decrease in water corrosion resistance.
Chemical corrosion resistance:
The structural changes caused by humidity can deteriorate the chemical stability of the cured product and reduce its tolerance to certain acidic and alkaline chemicals. For example, the cured product of polysilazane, which was originally able to withstand the erosion of a certain concentration of hydrochloric acid and sodium hydroxide solution, may be more susceptible to corrosion, discoloration, dissolution, and other issues when exposed to the same concentration of chemical reagents after curing in a high humidity environment, making it ineffective in providing protection.
3. Thermal stability
High temperature oxidation resistance:
Under high humidity conditions, hydrolysis and other reactions that occur during the solidification process of polysilazane can alter the final ceramic phase structure formed. When cured in a normal low humidity environment, stable ceramic phases such as SiC and SiCN may form, which have good high-temperature oxidation resistance; After curing under high humidity, due to the influence of hydrolysis products, more unstable phases with high oxygen content may be generated, which are more easily oxidized in high temperature environments, resulting in a decrease in the high-temperature oxidation resistance of the cured product and a shortened lifespan in high-temperature use scenarios.
Ceramic yield:
The reaction involving water may consume the active functional groups in polysilazane, which is not conducive to the formation of the target ceramic phase during high-temperature cracking, resulting in a decrease in ceramicization yield. For example, if polysilazane, which could have achieved a 60% ceramicization yield, is cured in a high humidity environment and then subjected to high-temperature treatment, the ceramicization yield may decrease to around 40%, affecting its application effect in high-temperature insulation, wear resistance, and other aspects.
4. Adhesion
Bonding force with substrate:
When the humidity is high, the moisture in contact with the surface of the substrate before the curing of the polysilazane may affect the formation of chemical bonds between it and the substrate. For example, when coating polysilazane on a metal substrate, in high humidity environments, moisture can block the contact between the active sites on the metal surface and the polysilazane. After curing, the adhesion between the polysilazane and the substrate weakens, making it easy for the coating to detach from the substrate and unable to firmly adhere to the substrate for protective purposes.
5. Optical performance
Transparency and glossiness:
For some cured products of polysilazane applied in the field of optics, the uneven structure generated during the curing process in high humidity environments (such as tiny particles produced by hydrolysis) can affect their optical uniformity, leading to a decrease in transparency and glossiness. The high transparency and high gloss cured product of polysilazane used for optical lens protection may become blurry and lose luster after curing under high humidity, affecting its optical performance.

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