A Comprehensive Guide to Polysilazane Antioxidant Properties: Research on High-Performance Applications of Silazane Polymers in Multiple Fields

With the rapid development of modern industrial technology, the requirements for material performance are increasingly stringent, especially regarding durability and functionality in extreme environments. Building upon previous in-depth discussions of the unique value of polysilazane as a "solid ceramic resin"—its transformation from a processable polymer state into a ceramic material with excellent properties through heat treatment—this article systematically elucidates its application principles and practical achievements in key technology areas such as carbon material oxidation resistance, high-temperature metal protection, and high-temperature sealing, further revealing its important role in solving cutting-edge problems in materials science.

I. Innovative Applications of Polysilazane in Carbon Material Oxidation Resistance

Carbon materials, mainly including graphite, carbon fiber, and their composites, have become indispensable key materials for high-temperature structural components in aerospace, high-speed transportation, and other high-end equipment manufacturing industries due to their significant performance advantages, such as low density, high specific strength, no creep, excellent ultra-high temperature resistance in non-oxidizing environments, excellent fatigue resistance, unique specific heat and electrical conductivity between non-metals and metals, low coefficient of thermal expansion, and excellent corrosion resistance. However, an inherent and fatal weakness of these materials lies in their poor oxidation resistance. When temperatures rise to approximately 400 degrees Celsius or higher in air, carbon materials begin to undergo significant oxidation, leading to a series of problems such as weight loss and a sharp decline in structural strength. Particularly for carbon fiber reinforced composites, when the oxidation weight loss rate reaches the critical range of 2% to 5%, key mechanical properties can decline by as much as 40% to 50%. This technological bottleneck severely restricts the application potential and development space of carbon materials in broader aerobic, high-temperature environments.

To solve this global problem, materials scientists have conducted extensive and in-depth research. Among these efforts, the method of converting polysilazane precursors into ceramic coatings has shown great promise. An experiment led by a German research team is particularly representative. This study uniformly coated liquid polysilazane onto the surface of a single carbon fiber filament, then cured and crosslinked it through a specific room-temperature process, forming a dense protective film. To scientifically evaluate the protective effect of this coating, the researchers designed a rigorous isothermal weight loss test in a muffle furnace. The experimental results are encouraging: carbon fibers treated with polysilazane showed a significant increase in initial oxidation temperature and a widened thermal stability temperature window to 750 degrees Celsius. Compared to untreated fibers, their high-temperature mass retention rate showed a qualitative leap. To verify the engineering applicability of this technology, researchers further applied the method to carbon fiber roving (an assembly of multiple fiber bundles). They cured the coating at approximately 200 degrees Celsius, and the results again confirmed that the polysilazane coating can effectively improve the overall oxidation resistance and long-term stability of the fiber bundles under high-temperature conditions. This opens up new possibilities for the application of carbon fiber composites in extreme environments such as engine hot-end components and hypersonic aircraft skin.

II. The Outstanding Performance of Polysilazane in High-Temperature Metal Protection

High-temperature corrosion and oxidation protection of metallic materials has long been a core issue plaguing industry and science. At high temperatures, metals react with oxygen, sulfides, and other environmental media to form loose oxide scale or undergo internal oxidation, leading to changes in component dimensions, degradation of mechanical properties, and ultimately equipment failure. Polysilazane has demonstrated unique advantages in this field. The core mechanism lies in the fact that, after appropriate heat treatment, polysilazane can be transformed into an inorganic ceramic layer with silicon dioxide (SiO₂) or silicon carbon nitride (SiCN) as its main components. These ceramic materials possess excellent chemical inertness, effectively resisting the corrosion of oxidizing media. Furthermore, due to the polar nature of the silicon-nitrogen (Si-N) bonds in the polysilazane molecular structure, it can form stable chemical bonds and good physical adhesion with metal substrates (such as steel, aluminum alloys, and nickel-based alloys) before and after transformation, thus ensuring the longevity and reliability of the coating.

Based on these superior properties, commercially available high-temperature protective coating materials with polysilazane as the core component are now available on the market. These products have undergone rigorous performance testing and process optimization and are widely used in applications requiring extremely high heat resistance. For example, in the automotive industry, they are coated on the metal surfaces of engine exhaust pipes, turbocharger components, piston tops, and various heat exchangers, significantly improving the service life of these components in high-temperature, corrosive exhaust environments, while also contributing to improved energy efficiency of the entire powertrain. 

III. The Key Role of Polysilazane in High-Temperature Sealing Technology

In advanced ceramic manufacturing and surface engineering, whether through traditional inorganic powder sintering or modern plasma spraying methods, the ceramic components or coatings produced often inevitably contain a certain amount of micropores and through cracks. These defects significantly reduce the material's airtightness and insulation, and become stress concentration points and channels for corrosive media penetration, severely affecting its performance and service safety under high temperature, high pressure, or corrosive environments. Therefore, effective sealing of these porous ceramic materials is a key post-processing step to improve their overall performance and expand their application range.

Traditional sealing agents are mainly divided into two categories. One category is organic sealing agents, mostly epoxy resins and silicone resins. Although they can provide good sealing effects under low or medium temperature conditions, once the ambient temperature exceeds their decomposition limit, the organic components will carbonize or volatilize, resulting in the complete loss of sealing function. Another type is inorganic adhesives, typically composed of inorganic nanoparticles (such as silica sol and alumina sol) and a small amount of organic additives. Their upper temperature resistance is higher than that of organic adhesives, but as the temperature rises further, the residual organic adhesive decomposes, and the gaps originally filled between the inorganic nanoparticles are re-exposed, forming new microchannels, leading to a decrease or even failure of the sealing effect.

To address the limitations of traditional sealing agents, researchers have explored the application of polysilazane in this field. M.R. Mucalo and his collaborators conducted a pioneering study. They used a polysilazane solution to coat porous alumina substrates, followed by high-temperature pyrolysis treatment in a protective atmosphere or air. Experimental results showed that polysilazane successfully transformed into continuous silicon nitride (Si₃N₄) or silicon oxynitride (Si₂N₂O) ceramic layers on the alumina surface. Microstructural observation using high-resolution scanning electron microscopy clearly showed that the porosity of the treated alumina material surface was significantly reduced, and the densification degree was significantly improved. The study also found that through a cyclic process of multiple coatings and pyrolysis, the thickness and uniformity of the coating can be further increased, thereby effectively sealing deeper pores and obtaining a nearly completely dense surface state. This method provides solid technical support for the reliable application of ceramic components in higher temperatures and harsher environments.

IV. Exploration of the Application of Polysilazane in Other Functional Coatings

Besides the three core application areas mentioned above, polysilazane, with its inherent high-temperature resistance and designability, is showing potential in other functional coating fields. One important direction is high-temperature thermal insulation coatings. While pure polysilazane coatings have a certain thermal insulation effect, their thermal insulation performance can be significantly enhanced by functionalizing them, such as by adding fillers with specific proportions and morphologies, such as hollow glass microspheres and ceramic hollow spheres. These hollow fillers introduce a large number of microscopic air gaps, which can effectively reflect thermal radiation and hinder heat conduction. In practice, polysilazane slurries containing such fillers can be applied to the surface of composite material substrates requiring protection using conventional air spraying or dip coating processes. Subsequently, a curing process is carried out at a moderate temperature of approximately 200 degrees Celsius, causing the polysilazane to crosslink and form a robust coating. This composite coating system can form an effective thermal barrier for the underlying composite material during subsequent high-temperature service, preventing it from degrading or failing due to overheating. This has significant application value in fields such as thermal protection systems for aerospace vehicles and high-performance brake pads.