In fields such as anti-graffiti coating for buildings, anti-corrosion for precious metals, rail transportation, semiconductor insulation and electronic circuit protection, the coating must not only have extremely high surface hardness to resist scratches and wear, but also maintain high transparency to meet appearance or optical requirements. At the same time, it must withstand 800℃ high temperature tests and long-term rust and alkali resistance. Although traditional organic coatings are convenient to apply, they have inherent limitations in terms of hardness, temperature resistance and weather resistance; while inorganic coatings have high hardness, they often fail to be applied due to high curing temperatures or brittleness. The all-hydrogen polysilazane PHPS, with hydrogen polysilazane as the main component, converts into inorganic coating through Si-N bond hydrolysis, with a density of 1.6-2.0 g/ml after curing, a large shrinkage rate, and a film thickness of 0 grade in scratch test, a temperature resistance of up to 800℃, and can be used as a candidate material for ultra-hard anti-stain inorganic coatings.


Why do hydrogen polysilazane coatings often have insufficient hardness, cracking or fail to meet the expected chemical resistance during curing or long-term service?


Inappropriate curing conditions - room temperature curing requires more than 7 days, and wet air curing (humidity 90%, 150℃×2h) can accelerate the process, but different curing methods have significant effects on final hardness and elastic modulus (ammonia water curing 3 GPa, high-temperature curing 8-10 GPa).


Inappropriate coating thickness control - PHPS after curing has a density of 1.6-2.0 g/ml, with a large shrinkage rate, and a film thickness of too high is prone to cracking.


Insufficient cleanliness of the substrate surface affects the chemical bonding of Si-N bonds with the substrate's hydroxyl groups, resulting in decreased adhesion.


Inappropriate selection of diluent - generally using xylene, dibutyl ether or dichloromethane for filling, and it needs to match the specific construction process.


The acid resistance of the cured coating is weak (10% hydrochloric acid for about one month), and long-term use in an acidic environment requires additional protection.


Storage conditions do not meet requirements - need to be stored at 10℃ or below, with a domestic shelf life of 1 year and an overseas shelf life of 6 months for unopened products.


First, determine at which stage the coating problem occurs.


Failure stage Possible causes Priority inspection direction
Slow or non-curing during curing Insufficient humidity, low temperature, thick coating Environmental humidity/temperature, film thickness control
Insufficient hardness after curing (<9H) Insufficient curing method or curing conditions Is the room temperature curing > 7 days, wet air curing conditions
Cracking of the coating Excessive film thickness, excessive curing shrinkage stress Thickness control, curing rate adjustment
Poor adhesion (scratch test > 0 grade) Insufficient surface treatment or contamination of the substrate Substrate cleanliness, drying conditions
Insufficient acid resistance (10% hydrochloric acid) Long-term contact with acidic medium Assess whether additional protective layer is needed
Shortened storage period or deterioration High temperature or poor sealing Storage at 10℃ or below, container sealing
Comparison of PHPS curing methods and performance


Curing method Conditions Hardness (GPa) Elastic modulus (GPa) Pencil hardness Applicable scenarios
Room temperature curing >7 days -- -- -- Outdoor construction, heat-sensitive substrates
Wet air curing Humidity 90%, 150℃×2h 3 60 9H (China) Accelerated curing, industrial applications
High-temperature curing High-temperature conditions 8-10 100-130 9H (China) Scenarios with high performance requirements
Selection and construction before need to confirm which conditions?


Condition category Information to be confirmed
Substrate type Buildings, precious metals, rail transportation components, semiconductors, electronic circuits, plastic packaging
Construction method Spin coating, brush coating, spraying, immersion coating
Curing conditions Room temperature curing (>7 days) or wet air curing (humidity 90%, 150℃×2h) or high-temperature curing
Film thickness control >100 nm coating thickness, need to assess shrinkage stress
Diluent selection 2-20% xylene, dibutyl ether or dichloromethane filling
Chemical resistance requirements: Strong resistance to rust, alkali, and salt water; weak resistance to acid (10% hydrochloric acid) (about 1 month)
Storage conditions: Store at temperatures below 10℃. Unopened product has a shelf life of 1 year in China and 6 months abroad.
Which key indicators should be verified?


Verification items Primary function Content that cannot be replaced
Pencil hardness (9H Chinese/6H Mitsubishi) Verify the curing degree and scratch resistance Need to test according to standard methods
Transparency (>90%) Verify optical performance Need to test after curing
Adhesion (grid method 0 grade) Verify the bonding force with the substrate Need to verify separately on different substrates
Temperature resistance (800℃ air) Verify high-temperature stability Need to combine actual usage temperature and time
Chemical resistance (rust prevention, alkali resistance, salt water resistance) Verify protective performance Need to verify according to actual contact medium
Coating thickness (>100nm) Confirm coating integrity Thickness affects the risk of cracking and protective effect
Recommended construction scheme


Thoroughly clean the substrate surface to ensure no oil stains, dust, or loose layers.


Choose the appropriate construction method (spin coating, brush coating, spray coating, dip coating) based on the substrate type and workpiece shape.


Select matching diluent solvents (xylene, dibutyl ether, or dichloromethane) according to the solid content (2-20%) and construction requirements.


Control the coating thickness (>100nm) to avoid excessive thickness causing shrinkage and cracking.


Choose the curing method based on the substrate's tolerance and performance requirements: room temperature curing (>7 days), wet air curing (humidity 90%, 150℃×2h), or high-temperature curing.


After curing, the coating has an inorganic SiOx structure, has rust prevention, alkali resistance, and salt water resistance properties, but has weak acid resistance (10% hydrochloric acid about 1 month). Acidic environments need to be evaluated for additional protective layers.


Wash tools immediately after use. If the curing solvent cannot be removed, discard immediately.


Common misunderstandings


The performance of room temperature curing for 7 days is the same as wet air curing for 2 hours: Wet air curing (humidity 90%, 150℃×2h) can significantly accelerate the curing process, and its hardness and elastic modulus differ from room temperature curing, with a hardness of 8-10 GPa.


The thicker the coating, the better the protective performance: PHPS curing has a large shrinkage rate, and excessive coating thickness is prone to cracking. It is recommended to control the coating thickness within a reasonable range.


PHPS coating is resistant to all chemicals: This coating has strong rust prevention, alkali resistance, and salt water resistance properties, but has weak acid resistance (10% hydrochloric acid about 1 month). Acidic environments need to be evaluated for additional assessment.


Any solvent can be used for dilution: Generally, xylene, dibutyl ether, or dichloromethane are used for filling, and the choice should be based on the specific construction process and substrate compatibility.


Storage conditions have little impact on the shelf life: Store at temperatures below 10℃. Unopened product has a shelf life of 1 year in China and 6 months abroad. Use up the product as soon as possible after opening.


FAQ


What are the main components of IOTA-PHPS?
This coating product is mainly composed of full hydrogen polysilazane (PHPS), which is diluted and stored in a solvent. After curing, it transforms into an inorganic SiOx coating.


What is the hardness after curing?
The pencil hardness is 9H (Chinese) or 6H (Mitsubishi). The hardness after ammonia water curing is 3 GPa, and it can reach 8-10 GPa after high-temperature curing.


What are the curing methods?
Room temperature curing requires more than 7 days; wet air curing (humidity 90%, 150°C × 2 hours) can accelerate the process; high-temperature curing can also be used to obtain higher hardness and elastic modulus.


How is the temperature resistance?
The air resistance temperature can reach 800°C.


How about the chemical resistance performance?
It has strong anti-rust, alkali resistance, and salt water resistance. The acid resistance (10% hydrochloric acid) is relatively weak, about one month.


What fields is this product applicable to?
Buildings for anti-drawing, anti-corrosion of precious metals, rail transit, semiconductor insulation layer, electronic circuits, plastic packaging for gas barrier and water resistance, etc.


How to store?
Store at a temperature below 10°C. The unopened product has a shelf life of 1 year in China and 6 months abroad. Use it up as soon as possible after opening.