In the fields of aerospace, high-temperature industries, and special protective coatings, the coatings must withstand temperatures above 800°C while maintaining high hardness (6-7H), high light transmittance (>95%), and excellent adhesion to the substrate (0 grade by scratch test), and also meet the diverse requirements of different substrates and construction conditions. Although traditional organic silicon resins have good heat resistance, the balance between hardness and light transmittance often requires compromise. The organic polysilazane 9118 utilizes the synergistic cross-linking mechanism of Si-NH-Si bonds and vinyl functional groups, supporting UV curing and multiple heat curing paths (without initiator at 250°C+, platinum catalysis at 80-100°C), with the cured coating clear varnish having a use temperature of <800°C and the formulated coating being ceramicized up to 1600°C, making it a candidate base material for ultra-high temperature and high transparency protective coatings.


Why do polysilazane coatings often fail to meet expectations in high-temperature service, curing, or ceramic conversion?


The mismatch between curing method selection and process window - UV curing has high efficiency but the photoinitiator has limited temperature tolerance (yellowing above 300°C), while heat curing (without initiator at 250°C+, platinum catalysis at 80-100°C) can be flexibly selected based on the substrate's tolerance.


The use of a coating above 300°C with UV curing process leads to yellowing of the coating due to residual photoinitiator, affecting transparency and appearance.


When the film thickness exceeds the resin cracking threshold (100μm+), the coating cracks in high-temperature environments (>800°C) or during ceramicization.


The inappropriate selection of diluent solvents - the product is miscible with most non-polar solvents (alkanes, ethers, ketones, esters), but alcohol ether solvents (such as diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol butyl ether) should not be used.


The mismatch between the cracking atmosphere and the target ceramic phase - nitrogen/argon → SiC/Si₃N₄, ammonia → Si₃N₄, air → SiOCN.


Insufficient curing conditions - if the heat curing does not reach the initiation temperature (without initiator requires 250°C+, platinum catalysis at 80-100°C), the coating cannot complete cross-linking and cannot achieve the target hardness and temperature resistance.


First, determine at which stage the coating problem occurs.


Failure stage Possible reasons Priority inspection direction
Insufficient curing hardness (<6H) Insufficient curing conditions or catalyst/initiator issues Inspection of curing temperature/time, platinum catalysis dosage, UV light dosage
Yellowing of UV-cured coating at >300°C Residual photoinitiator thermal decomposition Assess whether to switch to heat curing process (platinum catalysis at 80-100°C or high temperature 250°C+)
Coating cracking Thickness exceeds 100μm cracking threshold or heating rate is too fast Thickness control, temperature verification, heating rate optimization
Poor adhesion Insufficient substrate surface treatment or solvent residue Surface cleanliness, drying conditions, diluent solvent type
800°C ceramic yield below 50% Matching of cracking atmosphere or heating program Matching of cracking atmosphere (N₂/Ar/NH₃/Air), filler influence assessment
Shortened storage period or resin deterioration Entry of moisture into the container or improper temperature control Container sealing, inert gas replacement, storage temperature control at 0-20°C
Comparison of 9118 and 9108


Comparison item 9118 9108
Functional groups ethylene group (adjusted by special additives) ethylene group + Si-H
Appearance Light yellow transparent liquid (colorless and transparent after curing) Colorless transparent to light yellow liquid
Molecular weight 1200-1400 900-1000
Heat curing (without initiator) 250°C+ 200°C+
Platinum catalysis curing 80-100°C 80°C+
Curing hardness 6-7H 6H
Clear varnish use temperature <800°C <600°C
Ceramic yield (at 800°C) 50-60% 40-60%
Ceramicization rate of the cured product (at 800°C) 60-70% 60-70%
What conditions need to be confirmed before selection and construction?


Condition category Required information
Base material type Metal, alloy, glass, paint film, PP/PC/PVC/PMMA and other plastics
Curing method Ultraviolet light curing, thermal curing (without initiator/peroxide/platinum catalysis)
Curing equipment UV lamp (wavelength/intensity), oven temperature capacity (needs to match 250°C+ or 80-100°C)
Film thickness control Suggested single layer < 100 μm (cracking threshold)
Operating temperature Clear coat < 800°C / formulation coating < 1600°C (after ceramicization)
Target ceramic phase N₂/Ar → SiC/Si₃N₄, NH₃ → Si₃N₄, Air → SiOCN
Saturated solvent Alkanes, ethers, ketones, esters (strictly prohibit alcohol-ether)
Storage conditions 0-20°C, dry and cool, sealed, inert gas protection
Which key indicators should be verified?


Verification item Primary function Content that cannot be replaced
Hardness after curing (6-7H) Verify curing degree and scratch resistance Verification needs to be conducted separately for different curing methods
High-temperature stability (< 800°C for clear coat) Verify the upper limit of operating temperature Thickness affects the cracking temperature
Transmittance (> 95%) Verify optical transparency After curing, the pale yellow color on the coating before curing will react and disappear, and the cured coating is colorless and transparent
Adhesion (grid test 0 grade) Verify the bonding force with the substrate Needs to be verified on different substrates
Ceramic yield (50-60% at 800°C) Evaluate the conversion efficiency of the precursor Dependent on the decomposition atmosphere and fillers
Hydrophobic angle (100-105°) Evaluate the surface hydrophobic effect Needs to be tested after curing
Recommended construction scheme


Ensure the substrate surface is thoroughly cleaned and dried to ensure the presence of active sites for the Si-NH-Si bond reaction.


Choose the appropriate curing method based on the substrate type and process conditions: Ultraviolet light curing (requires a photoinitiator), thermal curing (without initiator at 250°C+/platinum catalysis at 80-100°C).


Adjust the construction viscosity using a dry non-polymer solvent (strictly prohibit alcohol-ether types).


Control the coating film thickness (< 100 μm), and reduce or use multiple thin coatings in high-temperature environments.


For high-temperature ceramicization applications, select the decomposition atmosphere according to the target ceramic phase (N₂/Ar → SiC/Si₃N₄, NH₃ → Si₃N₄, Air → SiOCN).


Intermix with various resins (epoxy silicone resin, organic silicone resin), and use them together to shorten the curing time and increase hardness.


After use, quickly clean the tools with acetone or solvent oil. Once cured, it cannot be washed off with solvents.


Common misunderstandings


The pale yellow color of the product coating indicates that the cured coating is also pale yellow: IOTA 9118 presents a pale yellow color due to vinyl functional groups and special additives. During curing, the additives will react and disappear, and the cured coating is colorless and transparent, with a transmittance > 95%.


The temperature difference between clear coat < 800°C and formulation coating < 1600°C can be ignored: The temperature limit of clear coat and formulation coating (containing fillers) differs by approximately 800°C. The formulation design directly affects the upper limit of high-temperature service.


The high-temperature performance of UV curing and thermal curing coatings is the same: UV curing will yellow at 300°C+ due to residual photoinitiators; thermal curing (especially platinum catalysis or high-temperature without initiator system) has better high-temperature stability > 800°C, and the curing path of thermal curing should be selected when serving at > 800°C.


The thicker the coating, the better the protection: The cracking threshold of the resin is 100 μm+, and a single-layer coating thickness exceeding this value is prone to cracking in high-temperature or ceramicization processes. Multiple thin coatings are better than a single thick coating.


The choice of pyrolysis atmosphere does not affect the final performance: The pyrolysis atmosphere directly determines the composition of the ceramic phase, and has a decisive influence on the temperature resistance and oxidation resistance of the ceramicized material.


FAQ


What is the hardness of IOTA 9118 after curing?
The pencil hardness is 6-7H.


What is the recommended curing temperature for the varnish coating?
<800℃ (related to the film thickness; the higher the film thickness, the easier it cracks at high temperatures).


What ceramic products can be obtained after pyrolysis?
Nitrogen or argon → SiC and Si₃N₄; ammonia → Si₃N₄; air → SiOCN. Below 1400℃, it is amorphous; above 1400℃, it begins to crystallize.


Why is the product appearance pale yellow?
The functional groups contained in IOTA 9118 are mainly vinyl, and it contains special additives, so the color is slightly pale yellow. During the curing process, this additive will react and be removed, and the cured coating is in a colorless and transparent state.


Which substrates is this product suitable for?
It is suitable for metals, alloys, glass, paint films, and various plastic substrates such as PP, PC, PVC, PMMA, etc. The adhesion scratch test grade is 0, and it is recommended to verify separately on different substrates.


Which curing methods are available?
There are two main curing methods: 1) UV curing (requires adding a photoinitiator); 2) Thermal curing, which is divided into three paths: without initiator (baking at 250℃ or above), peroxide initiator (baking at 250℃ or above), and platinum catalysis (80-100℃).