One cannot simply rely on the data of the product H21500 indicating a temperature resistance greater than 1500°C or the shear strength at a certain temperature to directly determine that it is suitable for all bonding and sealing systems between graphite, metal, ceramic or composite materials. One should first confirm the type of substrate, surface treatment, the ratio of the two components and the homogeneity of the mixture, the thickness of the adhesive layer, the curing temperature curve, the operating temperature and atmosphere, the thermal cycling conditions, and the sealing structure, before determining whether the problem is caused by poor interface wetting, uneven mixing, incomplete curing, thermal expansion mismatch, high-temperature oxidation, or adhesive layer defects, or due to poor compatibility with the substrate and the working conditions. Product H21500 can be considered as a candidate for poly-carbon-silane type high-temperature adhesive, but it must be confirmed through small-scale tests, bonding strength tests and actual high-temperature working conditions verification.


1. Why do poly-carbon-silane type adhesives often experience strength reduction in ultra-high temperature bonding or sealing?


The surface of the substrate is not cleaned or there is oil, release agent, oxide layer, or dust, which affects the wetting of the adhesive to graphite, metal or ceramic and the interface bonding.


The graphite material has a high porosity, and when the viscosity and coating amount of the adhesive do not match, the adhesive layer may over-penetrate or be locally deficient, forming a weak interface.


The two-component ratio is inaccurate or the mixture is not uniform, resulting in incomplete curing in some areas, insufficient cross-linking density or inconsistent behavior of high-temperature ceramicization.


The curing temperature curve does not match the product requirements and is not executed as 220°C × 2 hours, leading to incomplete curing or the generation of internal stress.


The thickness of the adhesive layer is improperly controlled. If it is too thick, the shrinkage and thermal mismatch at high temperatures increase, and if it is too thin, it fails to fill adequately, both of which will reduce the shear strength.


Using temperatures beyond the long-term tolerance range of the materials or undergoing high-temperature cycling repeatedly causes the adhesive layer to develop micro-cracks and gradually expand.


The improper control of the high-temperature atmosphere, such as oxidation in an oxidative atmosphere, leads to a decrease in interface strength.


Switching from phosphate-based adhesives, organic silicon adhesives, phenolic resins or other high-temperature adhesives without re-adjusting the surface treatment, ratio, adhesive layer thickness and curing curve results in deviation from the target strength.


The thermal expansion coefficients of metals, ceramics or composite materials differ significantly from that of graphite. No buffer for thermal stress is provided through the adhesive layer thickness, transition layer or structural design.


In the sealing structure, the adhesive layer is subjected to pressure, shear and thermal cycling simultaneously. Selecting based solely on a single shear strength data and not verifying the actual sealing conditions.


Storage conditions do not meet the requirements of cool and dry storage or exceeding the shelf life of one year, leading to a decrease in the adhesive material's activity, fluctuations in curing quality and high-temperature strength.


The two-component adhesive does not confirm the ratio and expiration date according to the effective TDS, and is mixed for too long, resulting in a decrease in fluidity or premature reaction.


2. Determine which stage the problem of high-temperature bonding or sealing occurs


Failure stage Possible causes Preferred inspection direction
The adhesive layer does not wet or is locally deficient after coating Unclean substrate, porosity of graphite, high viscosity of adhesive Surface treatment, adhesive viscosity, coating amount
The adhesive becomes thickened or the expiration date is insufficient after mixing Incorrect two-component ratio, prolonged mixing time Ratio accuracy, mixing uniformity, expiration date
The room temperature strength after curing is insufficient at 500-900°C Deviation of curing curve, thick adhesive layer, interface contamination Temperature curve, adhesive layer thickness, substrate treatment
The shear strength at 500-900°C is lower than expected Incomplete curing, thermal mismatch, adhesive layer defect Curing quality, thermal expansion matching, adhesive layer uniformity
The shear strength rapidly decreases at 1100-1400°C High-temperature ceramicization shrinkage, oxidation, micro-crack expansion Operating atmosphere, thermal cycling, structural design
The adhesive layer cracks or detaches after thermal cycling Thermal expansion coefficient difference, thick adhesive layer, rapid temperature increase Thermal expansion matching, adhesive layer thickness, temperature rise and cooling rate
Leakage of the sealing structure Discontinuous adhesive layer, pores, interface detachment Coating process, curing curve, sealing structure
Variations in strength or curing behavior between batches Discrepancies in two-component batches, imprecise ratios or uneven coating Inspection upon entry, ratio records, curing curve records
If only focusing on "whether product H21500 was used", without recording substrate treatment, ratios of the two components, layer thickness, curing curve, usage atmosphere and thermal cycling conditions, it is usually difficult to accurately determine whether it is a material issue or a process issue.


III. Why is it not necessarily effective to only increase the curing temperature or increase the layer thickness?


Product H21500 plays a role as a high-temperature ceramicizing adhesive in the bonding system. It is influenced by the substrate, ratio, layer thickness, curing curve, usage temperature and atmosphere. Simply increasing the temperature or adding thickness may bring side effects.


Increasing the curing temperature may accelerate curing, but exceeding the recommended curve may lead to increased layer shrinkage, internal stress concentration or substrate damage.


Extending the curing time may improve the curing degree, but it may affect production efficiency and is ineffective for contaminated, expired or unevenly mixed adhesive materials.


Increasing the layer thickness may enhance filling capacity, but too thick will increase high-temperature shrinkage and thermal mismatch, reducing shear strength.


Reducing the layer thickness may lower thermal stress, but it may result in missing adhesive, pores or discontinuous sealing.


When the substrate surface is not cleaned, only adjusting the curing temperature or layer thickness cannot solve the interface wetting and bonding problems.


When the ratio of the two components deviates or the mixture is uneven, only adjusting the curing curve cannot restore the crosslink density and high-temperature strength.


When the graphite porosity is high, increasing the adhesive quantity may cause excessive penetration of the adhesive material and insufficient surface layer.


When high-temperature oxidation or thermal cycling leads to microcracks, only increasing the curing temperature cannot restore strength.


When the adhesive is expired or its activity decreases, only adjusting the process cannot restore the original performance.


Therefore, when optimizing, one should observe the substrate treatment, ratio of the two components, adhesive viscosity, layer thickness, curing curve, usage atmosphere and thermal cycling conditions, rather than only adjusting a single parameter.


IV. What are the differences in product selection between H21500 and H11500 and similar high-temperature adhesive solutions?


Comparison direction Product H21500 (polycarbosilane type) Product H11500 (borosilinonitrogen type) Phosphate-based adhesive Organic silicone adhesive Epoxy adhesive Selection boundary
Temperature range Marked as greater than 1500℃ in the data Marked as 1300-1500℃ Up to 1000℃ Usually 200-400℃ Usually 150-200℃ Prioritize polycarbosilane or borosilinonitrogen system for ultra-high temperature applications
Number of components Two-component Unicomponent Usually single-component or dual-component Unicomponent or dual-component Dual-component Requires control of ratio and shelf life
Curing temperature 220℃×2 hours 170℃×2 hours Medium-high temperature curing At room temperature or heating At room temperature or heating Depending on substrate's high-temperature resistance and production line
Graphite bonding strength >10MPa at room temperature, >15MPa at 500-900℃, >12MPa at 1100℃, >10MPa at 1400℃ >5MPa at room temperature, >8MPa at 400-1000℃, >2MPa at 1500℃ High-temperature strength is better High-temperature strength is limited Insufficient high-temperature resistance Prioritize H21500 for high-load graphite bonding
Metal/ceramic/composite materials Used for bonding and sealing Used for bonding and sealing Used Used Used for medium-low temperatures Prioritize based on substrate and temperature
Solvent-free Yes Yes Usually water-based or solvent-based Varies by product Varies by product Solvent-free requirement prioritizes this product
Storage conditions Shaded and dry, with a shelf life of 1 year Shaded and dry, with a shelf life of 1 year Varies by product Varies by product Varies by product Manage according to storage conditions
V. What parameters should be confirmed when using product H21500?


Parameter category Required information
Application direction Graphite bonding, metal bonding, ceramic bonding, composite material bonding, sealing, high-temperature resistant coating
Base material type Graphite, metal, ceramic, composite material and surface condition
Surface treatment Cleaning method, degreasing, oxide removal, drying degree, pore treatment
Two-component mixing ratio Confirm the ratio according to the effective TDS, measurement accuracy and mixture uniformity
Gelatin applicability period Usable time after mixing, viscosity change and coating window
Coating process Gel application amount, gel layer thickness, uniformity, whether multiple coatings are required
Curing curve 220℃×2 hours, heating and cooling rate and holding conditions
Operating temperature Long-term temperature, peak temperature, short-term exposure condition above 1500℃
Operating atmosphere Air, inert gas, vacuum, oxidation or reduction atmosphere
Thermal cycling Heating and cooling rate, number of cycles, high and low temperature holding time
Sealing structure Gap, pressure, bearing mode, leakage requirement
Storage conditions Cool and dry place, sealed, shelf life 1 year
Acceptance indicators Room temperature bonding strength, 500/900/1100/1400℃ shear strength, sealing performance, strength retention rate after thermal cycling
VI. What should be mainly verified when using product H21500?


Two-component mixing ratio accuracy and mixture uniformity.


Applicable period of gel after mixing and coating window.


Wetting property of base material surface after surface treatment and continuity of gel layer.


Whether the curing curve is executed according to 220℃×2 hours, and whether the heating and cooling are controlled.


Whether the room temperature bonding strength is greater than 10 MPa.


Whether the 500℃ and 900℃ shear strength is greater than 15 MPa.


Whether the 1100℃ shear strength is greater than 12 MPa and 1400℃ shear strength is greater than 10 MPa.


The influence of gel layer thickness on shear strength and thermal mismatch.


The strength retention rate and interface integrity after thermal cycling.


The influence of operating atmosphere on gel layer oxidation, graphite oxidation and sealing performance.


The consistency of bonding between graphite, metal, ceramic and composite materials.


The leakage rate and pressure holding capacity of sealing structure.


The consistency of gel viscosity, curing behavior and high-temperature strength among batches.


VII. How to design tests before using product H21500?


Establish a reference for the current high-temperature resistant adhesive, record the model, surface treatment, mixing ratio, gel layer thickness, curing curve and failure performance.


Uniform test conditions: Base material, surface treatment, two-component mixing ratio, mixing method, gel layer thickness, curing curve, operating temperature, atmosphere and thermal cycling conditions.


Set candidate samples: Current adhesive, product H21500, different gel layer thickness or curing curve gradients.


Complete the full process test: Surface treatment → Mixing → Mixing → Coating → Curing → Room temperature strength → High-temperature shear strength → Thermal cycling → Sealing performance test.


Evaluate actual results: Room temperature strength, shear strength at various temperatures, strength retention rate after thermal cycling, sealing performance.


Test items Uniform requirements
Base material and surface treatment Keep consistent or set gradients according to the test design
Two-component mixing ratio Confirm and maintain consistency according to the effective TDS
Mixing method Set gradients according to the test design
Gel layer thickness Set gradients according to the test design
Curing curve Set gradients according to the 220℃×2h benchmark
Operating temperature Set according to 500/900/1100/1400℃
Operating atmosphere Set according to actual working conditions
Thermal cycling conditions Set according to actual heating and cooling rate and cycle number
Measurement method Uniform room temperature strength, shear strength, sealing performance, strength retention rate after thermal cycling
VIII. Under which circumstances should product H21500 not be directly used?


If the base material surface is not cleaned or has oil stains, oxide layer, or release agent, it will affect the interface bonding.


The porosity of graphite has not been evaluated, and the viscosity of the rubber compound and the coating amount cannot be matched.


The two sets of mixing ratios cannot be accurately controlled according to the effective TDS or the mixture is not uniform.


After mixing, the coating and assembly cannot be completed within the applicable period.


The curing curve cannot be executed according to 220℃×2 hours or the temperature rise and cooling conditions are not available.


The use temperature exceeds the material's tolerance range for a long time, and the high-temperature creep and oxidation have not been evaluated.


The use atmosphere is highly oxidizing, and the antioxidant capacity of the rubber layer and the substrate has not been verified.


The sealing structure can withstand high pressure or strong vibration, but the actual sealing condition has not been verified.


Specific food contact, medical or airworthiness approval is required, but the corresponding data has not been obtained.


Only the use temperature is known, without the substrate, ratio, rubber layer thickness, curing curve and atmosphere data.


The customer requests to directly mix it into the in-use system, but the surface treatment, ratio, coating and curing conditions cannot be controlled.


When switching from phosphate, organic silicon, borosilicon nitrogen alkanes or other high-temperature adhesives, the process needs to be re-adjusted.


Storage conditions do not meet the requirements of cool and dry, or the shelf life exceeds 1 year.


The safety factor and load-bearing design for the shear strength at 1400-1500℃ are not evaluated.


IX. What selection support can our company provide?


As a provider of the entire organic silicon value chain, our company can assist in comparing the applicability of poly-carbon-silane type adhesives in different substrates, two sets of mixing ratios, rubber layer thickness, curing curves and high-temperature conditions for product H21500.


For projects that need to consider bonding and sealing of graphite, metal, ceramic or composite materials, as well as the preparation of high-temperature coatings, before selection, the following information should be provided:


Application direction and substrate type.


Target room temperature bonding strength and shear strength at 500-1400℃.


Surface treatment method and porosity of graphite.


Two sets of mixing ratios, mixing methods and shelf life requirements.


Rubber layer thickness and coating process.


Curing curve and temperature rise and cooling conditions.


Use temperature, atmosphere and thermal cycling requirements.


Sealing structure, pressure and leakage requirements.


Current adhesive model, process and failure performance.


Acceptance method and applicable standards.


After receiving complete data, it can be determined whether to prioritize testing a certain ratio, coating and curing scheme of product H21500, or to choose product H11500, phosphate or other high-temperature adhesives.


X. Common Misunderstandings


A material with a temperature resistance greater than 1500℃ can be used at 1500℃ continuously.
The data provided shows that the shear strength at 1400℃ is greater than 10 MPa, and the strength may continue to decrease at higher temperatures. It should be evaluated based on actual load, safety factor and time, and not just judged by the upper limit of temperature resistance.


Two-component adhesives can be mixed randomly by proportion.
The two sets of mixing ratios need to be confirmed according to the effective TDS. Deviations in the ratio or uneven mixing can lead to incomplete curing, decreased high-temperature strength, and require precise measurement and thorough stirring.


The higher the curing temperature, the higher the strength.
The curing should be carried out according to 220℃×2 hours. Exceeding the recommended curve may cause shrinkage, internal stress and damage to the substrate.


The thicker the rubber layer, the stronger the bonding.
An excessively thick rubber layer will increase high-temperature shrinkage and thermal mismatch, reducing shear strength, and the thickness should be optimized according to the substrate and structure.


A rough graphite surface does not necessarily mean a strong bond.
The porosity and surface contamination of the graphite will affect the penetration of the rubber material and interface bonding, and the graphite surface needs to be cleaned and evaluated for coating amount.


Compatibility with the substrate means direct coating.
It is still necessary to confirm the surface treatment, two sets of mixing ratios, rubber layer thickness, curing curve, use atmosphere and thermal cycling conditions.


Equal strength at 25℃ can be substituted.
The high-temperature strength, thermal mismatch, number of components and curing behavior of different high-temperature adhesives are different, and replacement requires re-verification.
This product is suitable for bonding and sealing of graphite, metals, ceramics, and composite materials, as well as for high-temperature resistant coatings. For systems that are subject to strong oxidation, high-pressure sealing, or have special industry approval requirements, specific verification is necessary.


The product can be used after being mixed and left for a period of time.


The applicable period after the mixing of the two components is limited. If left for too long, it may result in a decrease in fluidity or premature reaction, affecting the coating and curing quality.


XIV. Recommended Selection Steps


Confirm the application direction: graphite bonding, metal/ceramic/composite material bonding, sealing, or high-temperature resistant coating.


Confirm the type of substrate, surface treatment, and graphite porosity.


Confirm the ratio of the two components, mixing method, and applicable period requirements.


Confirm the state of the adhesive, viscosity, and storage period.


Confirm the thickness of the coating and the coating process.


Confirm the curing curve as 220℃×2 hours and temperature rise and drop.