WO2025056619A1

WO2025056619A1 - A composition for an intumescent coating

Info

Publication number: WO2025056619A1
Application number: PCT/EP2024/075395
Authority: WO
Inventors: Aixiao FU; Burak ULUSOY; Hao Wu; Kim A. DAM-JOHANSEN; Hafeez AHMADI
Original assignee: Danmarks Tekniske Universitet
Current assignee: Danmarks Tekniske Universitet
Priority date: 2023-09-12
Filing date: 2024-09-11
Publication date: 2025-03-20
Anticipated expiration: 2026-03-12

Abstract

Disclosed is a composition for intumescent coating. The composition comprises a silicon-based binder, an expandable agent, a thixotropic agent, and a silicate filler. The expandable agent is hydrated alkali silicate particles. Furthermore, an intumescent coating system is disclosed. The intumescent coating system comprises a primer, the composition for intumescent coating according to this disclosure, and optionally a top coat. Furthermore, a method for preparing a composition for intumescent coating is disclosed.

Description

A COMPOSITION FOR AN INTUMESCENT COATING

The present disclosure pertains to the field of fire protection of structures. The present disclosure relates to a composition for intumescent coating, an intumescent coating system and a method for preparing the composition for intumescent coating.

BACKGROUND

Structural steel loses about 50% of its load bearing capacity at higher temperatures, such as around 500 °C, which may cause the steel to buckle and collapse at said high temperature. To protect steel structures, such as buildings, bridges, offshore constructions, ships, and aircraft, and thereby prevent the loss of life and property in the event of fire, intumescent coatings may be applied to a surface of the steel structure. At high temperatures, intumescent coatings swell and act as thermal barriers due to their high porosity and low thermal conductivity. Current state-of-the-art intumescent coatings are predominantly based on organic systems which provide efficient protection under severe fire scenarios. However, these state-of-the-art intumescent coatings have disadvantages, such as potential combustion (expanded coating burns), toxic gas release, toxic species incorporation (Boron-species), and low mechanical strength. There is thus room for improvement of the intumescent coatings.

SUMMARY

Accordingly, there is a need for an intumescent coating, which mitigates, alleviates or addresses the existing shortcomings and provides an improved fire protection and reduced toxicity.

Disclosed is a composition for intumescent coating. The composition comprises a silicon- based binder, an expandable agent, wherein the expandable agent is hydrated alkali silicate particles, a thixotropic agent, wherein the thixotropic agent is hydrophobic fumed silica, and a silicate filler.

Disclosed is an intumescent coating system. The intumescent coating system comprises a primer, the composition for intumescent coating disclosed herein. In one or more examples, the intumescent coating system may be used in or as a layered coating system, such as may comprise a top layer, such as a top coat, and/or one or more intermediate layers, and/or a bottom layer, such as a bottom coat. The composition for intumescent coating disclosed herein may, in one or more examples, be one of the one or more intermediate layers, and/or the top layer.

Disclosed is a method for preparing a composition for intumescent coating. In one or more example methods, the method comprises curing an alkali silicate solution to prepare a hydrated alkali silicate solid. In one or more example methods, the method comprises reducing the size of the hydrated alkali silicate solid to obtain hydrated alkali silicate particles in a size up to 300 pm, such as in a range of 63 to 300 pm. The method comprises mixing a silicon-based binder with an expandable agent, a thixotropic agent, a silicate filler, wherein the expandable agent is the hydrated alkali silicate particles, and the thixotropic agent is hydrophobic fumed silica. The silicon-based binder may, in one or more example methods, comprise a silicon-based resin, a crosslinker and a catalyst. In one or more example methods, the method comprises mixing a silicon-based resin, a crosslinker and a catalyst to obtain the silicon-based binder. The method comprises curing the mixed composition through crosslinking of silicone. In one or more example methods, the crosslinking is performed through a condensation reaction.

It is an advantage of the present disclosure that the components of the composition, such as the expandable agent, the thixotropic agent, and the silicate filler, causes a ceramification process of the composition when subjected to heat, and thus yields a ceramic product with a low thermal conductivity and a high mechanical strength. Selected formulations of the invention provide significantly better fire protection as compared to a commercial organic alternative. The composition for the intumescent coating and the intumescent coating system thus provide an expanded coating with higher thermal stability and minimal decomposition which offers a better protection of a coated structure against fire. Since the composition is based on a silicon-based binder comprising expandable alkali silicate particles instead of the commonly used expandable graphite, the use of boron to improve the mechanical stability of the coating is no longer required. Thereby, a less toxic composition than known intumescent coatings is provided, and a release of toxic components, such as of boron, upon expansion of the coating can be reduced or even eliminated. In other words, present disclosure may advantageously provide an intumescent coating having one or more non-toxic components. The composition, the intumescent coating system, and/or the method for preparing the composition can provide a safe means of fire protection of materials, such as for coating of steel or for use as a sealant for sealing a cavity, thereby minimizing the loss of life and property during the event of fire. Moreover, the application of the composition disclosed herein is straightforward, and reduces the amount of toxic material and solvents being released during application, thereby allowing a safer handling of the composition and the coating system. Lastly, the composition according to this disclosure incorporates a silicon- based binder in contrast to the traditional epoxy binders, making the composition and the coating system more sustainable since epoxy is formed from crude oil while silicone is produced from quartz sand. A further advantage of the present disclosure relates to the provision of alkali silicate, such as sodium silicate, in the expandable agent and/or as the expandable agent. It may be appreciated that the sodium silicate improves the expansion properties of the expandable agent and in turn of the coating. For example, as the alkali silicate becomes solid expanded, spherical particles may improve the mechanical properties of the char. In other words, the solid expanded alkali silicate particles may improve the mechanical properties of the char.

Further, it is an advantage of the present disclosure that the components of the intumescent coating may enable a reduction in the amount of smoke released when it is heated. Furthermore, the raw materials used for the intumescent coating disclosed herein may have an increased availability and/or versatility in comparison with other coatings used for fire protection.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosure will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the attached drawings, in which:

Fig. 1 is a diagram illustrating a comparison of steel temperature-time curves for blank steel and example compositions according to this disclosure,

Fig. 2 is a diagram illustrating a comparison of steel temperature-time curves for steel coated example compositions according to this disclosure and existing intumescent coating systems, Figs. 3A-3B is a starfish diagram comparing five different product features for the example compositions and the existing intumescent coating systems of Fig. 2,

Fig. 4A-4C is a diagram illustrating a comparison of steel temperature-time curves for a plurality of example compositions according to this disclosure,

Fig. 5 is a diagram illustrating a thermal behavior of different types of example silicate particles according to this disclosure,

Fig. 6 is a diagram illustrating a comparison of steel temperature-time curves for a plurality of example compositions according to this disclosure having different amount of alkali silicate particles,

Fig. 7 is a diagram illustrating the influence of different types of alkali silicate particles on steel temperature-time curves for a plurality of example compositions according to this disclosure,

Fig. 8 is a diagram illustrating the influence of different types of mixed alkali silicate particles on steel temperature-time curves for a plurality of example compositions according to this disclosure,

Fig. 9 is a diagram illustrating the influence of the particle size on steel temperature-time curves for a plurality of example compositions according to this disclosure,

Fig. 10 is a diagram illustrating the influence of a gas atmosphere on steel temperaturetime curves for a plurality of example compositions according to this disclosure,

Fig. 11 is a diagram illustrating the durability of one or more example compositions according to this disclosure, and

Fig. 12 is a diagram illustrating a comparison of steel temperature-time curves for an example commercial coating and an example composition according to this disclosure,

Fig. 13 is a flow-chart illustrating an example method for preparing a composition for an intumescent coating according to this disclosure.

DETAILED DESCRIPTION Various exemplary embodiments and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not to have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

The figures are schematic and simplified for clarity, and they merely show details which aid understanding the disclosure, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts.

Known intumescent coatings come with a variety of disadvantages. The known intumescent coatings are typically based on organic ingredients. For organic coatings used against hydrocarbon fires, the binder is predominantly epoxy based with several additional ingredients to ensure good fire protection. Common for hydrocarbon intumescent coatings, i.e. intumescent coatings used for protection against hydrocarbon fires, is that they employ toxic species, such as various forms of boron. Another common disadvantage with the known intumescent coatings is potential combustion, where the expanded coating burns, which can cause it to disintegrate and lose its protective properties. A further disadvantage is toxic gas release upon expansion of the coating when subjected to fire, such as release of one or more of ammonia (NH3), carbon monoxide (CO), and others, which may be harmful to people. Furthermore, the known intumescent coatings typically comprise organic material which have a low mechanical strength.

A composition for an intumescent coating is disclosed. The composition comprises a silicon-based binder, an expandable agent, a thixotropic agent, and a silicate filler. The expandable agent is hydrated alkali silicate particles. The thixotropic agent is a fumed silica, such as a hydrophobic fumed silica. The intumescent coating may be seen as a coating that expands as a result of a chemical reaction generated by heat exposure, for example due to fire, thus leading to an increase in volume and decrease in density. The expansion of the intumescent coating leads to an expanded coating which forms an insulating layer on a surface of a material. The material may be a material used for building structures, such as one or more of steel, wood, stone, cement, bricks, etc. When the intumescent coating expands, the heat transfer through the coating may be reduced, thereby protecting the underlying structure that has been coated with the intumescent coating from the heat. The interactions between the components of the composition when subjected to high temperatures, such as under harsh fire scenarios described by the UL 1709 standard relating to “Rapid Rise Fire Tests of Protection Materials for Structural Steel”, or a cellulosic fire scenario according to ISO 834, ultimately yield a ceramic product with a low thermal conductivity and a high mechanical strength, such as to protect the structure. The resulting ceramic product may eliminate the drawbacks of traditional organic coatings.

The silicon-based binder, such as a silicone binder, binds the composition together at lower temperatures, such as at temperatures lower than 300 °C, such as at room temperature. While silicone decomposes when exposed to high temperatures, such as temperatures above 300 °C, incorporation of one or more inorganic constituents, such as the expandable agent, the thixotropic agent, and the silicate filler, into the composition provides intumescence and ceramification of the intumescent coating upon heat exposure. The ceramification can increase the mechanical strength of the coating such that the expanded coating is held together due to the ceramification of the composition when the silicone binder has decomposed. The silicon-based binder may be inorganic. Silicon-based polymers can be seen as a material comprising both organic (such as CH3) and inorganic groups (such as Si-O-Si, Si-N-Si, or Si-Si). In one or more examples, the silicon-based binder may be a silicone with backbone consisting of Si-O-Si which, in one or more examples, can be seen as an inorganic or hybrid compound. Hence, the compound can be seen as an inorganic compound. The silicon-based binder may comprise one or more of polysilanes, polysiloxanes, and polysilazanes.

Upon being exposed to heating, the expandable agent, which can be based on hydrated alkali silicates, provides a high expansion through the release of water (H2O). In some examples, the expansion of the expandable agent may be influenced by the heating rate, such as the rate at which the temperature of the expandable agent increases. The interactions between all the constituents ultimately yields a ceramic product with a low thermal conductivity and high mechanical strength to protect the steel, which eliminates the drawbacks of traditional organic coatings. The expandable agent is configured to allow for expansion of the composition when the composition is subjected to heat, for example due to a fire. In one or more example compositions, the hydrated alkali silicate particles comprise one or more of sodium (Na) silicate, potassium (K) silicate, and lithium (Li) silicate. For an example composition comprising lithium silicate particles as the only silicate particles, the expansion of the composition, when subjected to heat, is around 37%. For an example composition comprising potassium silicate particles as the only silicate particles, the expansion of the composition, when subjected to heat, is around 66%. For an example composition comprising sodium silicate particles as the only silicate particles, the expansion of the composition, when subjected to heat, is around 308%. In one or more example compositions, the hydrated alkali silicate particles comprise a mixture of potassium silicates and lithium silicates. In one or more example compositions, the hydrated alkali silicate particles comprises a mixture of potassium and sodium silicates. In one or more example compositions, the hydrated alkali silicate particles comprises a mixture of sodium and lithium silicates. In one or more example compositions, the hydrated alkali silicate particles comprises a mixture of potassium, sodium and lithium silicates. For an example composition comprising the mixture of potassium, sodium and lithium silicate particles, the expansion of the composition, when subjected to heat, is around 1256 %. The expansion of the composition can thus be increased by adding a mixture of alkali silicate particles to the composition. In one or more example compositions herein, the hydrated alkali silicate particles comprise a mixture of two or more different alkali silicates are hydrated alkali silicates being chemically bonded in a single particle, such as potassium, sodium and lithium silicate being chemically bonded into single particles. In one or more example compositions herein, the hydrated alkali silicate particles comprising a mixture of two or more different alkali silicates are mechanically mixed. Mechanically mixed can herein be seen as a particle of one alkali silicate, such as a potassium silicate particle, a sodium silicate particle, or a lithium silicate particle, being mechanically mixed with particles of one or more other alkali silicates. In one or more example compositions, the wt.% of the expandable agent is in the range 17 % to 42 %, such as 25 % to 33 %.

In one or more example compositions, a size of the hydrated alkali silicate particles is in the range of up to 300 pm, such as in the range of 63 pm to 300 pm, such as in the range of 212 pm and 300 pm. By providing hydrated alkali silicate particles with a size up to 300 pm, such as in the range of 63 pm - 300 pm, such as in the range of 212 pm - 300 pm, the fire protection capability of the composition increased. A critical time, such as the time it takes for a steel surface coated with the composition to reach an example critical temperature of 500 °C when subjected to fire, increased from around 50 minutes for the composition having particles with a size <63 pm to 84 minutes for the composition having particles with a size of 212 pm - 300 pm. Experiments performed by the applicant and described in further detail with regards to Fig. 1-9, show that the expansion of the composition increased from 500 % for particles with a size < 63 pm to more than 800 % for particles with a size in the range of 212 pm - 300 pm. Increasing the particle size (up to 300 pm) lead to increasingly uniform expansion of the coating when subjected to heat, which leads to better fire protection capability of the composition. However, further increasing the size of the particles, such as to a size in the range of 300 pm to 850 pm, causes the fire protection capability, such as the critical time, of the composition to decrease. By decreasing the particle size (from 300 pm towards 63 pm) a more dense and compact expanded coating and a better adhesion to steel can be achieved. The performance of the example compositions of this disclosure can thus be significantly affected by the silicate particle size. The one or more example compositions according to this disclosure, comprising a silicone coating having alkali silicate particles in the size range of 63 pm to 300 pm provided very good fire protection capabilities, while providing the alkali silicate particles in the size range of 212 pm to 300 pm further improved the fire protection capability of the composition. Smaller sized alkali silicate particles expand less but create a compact layer with better steel adhesion. Hence, by adding alkali silicate particles in the size range of 63 pm to 300 pm a composition having the required fire protection capabilities and adhesion to steel can be provided.

The thixotropic agent is a component that is added to the composition to give the composition thixotropic properties. Thixotropic properties can herein be seen as the composition being in a gelatinous state when being undisturbed but becoming a fluid when the composition is disturbed, such as when the composition is shaken or stirred. If left to rest, the composition will revert to the gelatinous state. In one or more example compositions, fumed silica, such as hydrophobic fumed silica, is used as thixotropic agent. Fumed silica (SiO?) can be seen as a form of silicon dioxide that consists of microscopic droplets of amorphous silica that may be fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. In one or more example compositions, the wt.% of the thixotropic agent is in the range 4.5 % to 20 %.

In one or more example compositions, the silicate filler is one or more of an aluminosilicate, such as one or more of kaolin and metakaolin, mica, feldspar, and talc. The silicate filler may bond the composition together after the silicone binder has decomposed at high temperatures. The silicate filler may increase the integrity and adhesion of the coating when the coating is exposed to heat and expands. The silicate filler may cause the composition to bond by ceramification at higher temperatures, such as at temperatures above 400 °C. By adding the aluminosilicate, such as kaolin and/or metakaolin, to the composition, the fire protection, mechanical properties, and thermal stability of the coating can be enhanced. In one or more example compositions, the wt.% of the silicate filler is in the range of 0 % to 22 %.ln one or more example compositions, the silicon-based binder comprises a silicon based resin, such as a polysilanes, polysiloxanes, or polysilazane, a crosslinker, and a catalyst. The silicon-based binder may, in one or more example compositions, be silanol terminated polydimethylsiloxane. In one or more example compositions, the wt.% of the silicone binder is in the range 40 % and 70 %. In one or more example compositions, the catalyst is a titanium-based catalyst or a tin-based catalyst. The titanium-based catalyst may, in one or more example compositions, be one or more of titanium 2-ethylhexoxide and titanium 2-ethylhexanol. The crosslinker is a chemical compound containing alkoxy groups (-OR) used to create a cross-linking with the silicon-based binder by forming Si-O-Si bonds with the release of ROH.

In one or more example compositions, the composition comprises a strengthening agent and/or a reinforcing agent. The strengthening agent and/or reinforcing agent may comprise one or more of calcium carbonate (CaCOs), sodium carbonate (Na2CO3), sodium hydrogen carbonate (NaHCOs), potassium chloride (KCI), zinc oxide (ZnO), magnesium oxide (MgO), potassium carbonate (K2CO3), and phosphate-derived compounds, such as ammonium polyphosphate ([NH4PO3]_n(OH)2), diammonium hydrogen phosphate ((NH^HPC ), calcium phosphate (Ca3(PC>4)2), potassium dihydrogen phosphate (KH2PO4), and/or aluminum phosphate (AIPO4). In one or more example compositions, the wt.% of the strengthening agent and/or reinforcing agent is in the range 0 % to 22 %, such as 0-15%, such as 0-11 %. The strengthening agent and/or reinforcing agent can increase the fire protection, the integral strength, such as a compressional strength, and/or an adhesion strength of the composition. In one or more example compositions, the strengthening agent and/or reinforcing agent comprises a mixture of t^CCh and (NH^HPC . The strengthening agent and/or reinforcing agent may be seen as a component added to enhance the physical and mechanical properties of the coating, for example its durability, adhesion, and resistance to cracking, deformation, or flaking when exposed to heat or fire. The strengthening agent and/or reinforcing agent helps maintain the integrity of the char layer formed during a fire, ensuring the char layer remains protective throughout the fire exposure.

In one or more example compositions, the composition comprises a flame retardant. The flame retardant may comprise one or more of, potassium carbonate (K2CO3), aluminum hydroxide (AI(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), and phosphate-derived compounds, such as ammonium polyphosphate ([NH4PO3]_n(OH)2), diammonium hydrogen phosphate ((NH^HPC ), calcium phosphate (Ca3(PC>4)2), potassium dihydrogen phosphate (KH2PO4), aluminum phosphate (AIPO4). In one or more example compositions, the wt.% of the flame retardant is in the range 0 % to 22 %, such as 0-15 %, such as 0-11 %.

In one or more example compositions, the composition comprises a wetting agent. The wt.% of the wetting agent may be in the range 0 % to 2.5 %. The wetting agent can be seen as a chemical substance, such as a surface-active molecule, that increases the spreading and penetrating properties of a liquid, such as water, by lowering its surface tension. The wetting agent may thus improve the release of water from the composition which improves the expansion of the composition at high temperatures.

In one or more example compositions, the composition comprises a filler material, such as a waste material. The filler material may be one or more of fly ash, ferric oxide (Fe2C>3), ferric oxyhydroxide (FeO(OH)), straw, pine wood, lignin and sewage. By replacing a part of the silicon-based binder with the filler material the cost of the composition can be reduced. By adding lignin to the one or more example compositions according to this disclosure, the fire protection capability of the composition can be improved due to the release of gas upon heating (pyrolysis, de-volatilization). In one or more example compositions, the wt.% of the filler material is in the range 0 % to 22 %, such as 0-15 %, such as 0-11 %.

An intumescent coating system is disclosed. The intumescent coating system comprises a primer, the inorganic composition for intumescent coating according to any one of the examples disclosed herein, and optionally a top coat. The intumescent coating system is configured to be applied to a metal surface or structure, such as a building, for protecting the structure from collapsing when subjected to high temperatures, such as temperatures above 500°C, during a fire. The intumescent coating system may be a layered coating system where the primer constitutes a first layer configured to improve the adhesion of the coating to the structure that is to be protected. The primer may be configured to face the steel structure. The inorganic composition may constitute a second, such as an intermediate layer, of the intumescent coating system. The top coat may constitute a third layer and may be configured to face away from the steel structure. The top coat may be configured to protect the composition from the environment, such as against weathering. In one or more examples, the intumescent coating may comprise a plurality of intermediate layers. In one or more examples, the intumescent coating system may be used in or as a layered coating system, such as may comprise a top layer, such as a top coat, and/or one or more intermediate layers, and/or a bottom layer, such as a bottom coat. The composition for intumescent coating disclosed herein may, in one or more examples, be one of the one or more intermediate layers, and/or the top layer.

A method for preparing a composition for intumescent coating is disclosed. In one or more example methods, the method comprises mixing and/or curing an alkali silicate solution to prepare a hydrated alkali silicate solid. The hydrated alkali silicate solid may for example have a water content, such as a wt.%, in the range of 5-40%. In one or more example methods, the hydrated alkali silicate solid comprises one or more additives, such as reinforcing agents, silicate fillers, and/or flame retardants. In one or more example methods, alkali silicate solution is poured in petri dishes and placed in a climate chamber at a temperature in the range of 20-50 °C, such as in the range of 20-40 °C, such as in the range of 25-35 °C, such as at 25 °C, and 50 RH%. These may then be left in the climate chamber until the alkali silicate solution is cured, which may take up to four days depending on the temperature used, after which the hydrated alkali silicate solids, such as the cured alkali silicate solution, may be crushed, and/or sieved and/or used in coating formulation.

In one or more example methods, the method comprises obtaining hydrated alkali silicate particles in a size range of 63 pm to 300 pm. In one or more example methods, the method comprises obtaining hydrated alkali silicate particles in a size range of 63 pm to 300 pm and/or with a water content in the range of 5-40%. In one or more example methods, obtaining the hydrated alkali silicate particles comprises reducing a size of the hydrated alkali silicate solid to obtain hydrated alkali silicate particles in a size range of 63 pm to 300 pm. The size of the hydrated alkali silicate solid may be reduced by milling, such as ball milling, the hydrated alkali silicate solid until the hydrated alkali silicate particles have been obtained.

The method comprises mixing a silicon-based binder with an expandable agent, a thixotropic agent, a silicate filler, such as to prepare a composition for an intumescent coating. In one or more example methods, the silicon-based binder may comprise a silicon-based resin, a crosslinker and a catalyst, which may be mixed to obtain the silicon- based binder. The silicon-based resin may be a polydimethylsiloxane (PDMS), such as silanol terminated polydimethylsiloxane. The expandable agent is the hydrated silicate particles and the thixotropic agent is hydrophobic fumed silica. In one or more example methods, the silicon-based resin is mixed with the expandable agent, the thixotropic agent, the silicate filler, and/or the crosslinker using a dissolver. The silicon-based resin may be mixed with the expandable agent, the thixotropic agent, the silicate filler, and/or the crosslinker at a rotational speed of 500 rpm to 12000 rpm. In one or more example methods, the silicon-based resin is mixed with the expandable agent, the thixotropic agent, the silicate filler, and/or the crosslinker for 5-15 minutes. In one or more example methods, the catalyst is added, during continued mixing, after the silicon-based resin has been mixed with the expandable agent, the thixotropic agent, the silicate filler, and/or the crosslinker.

The method comprises curing the mixed composition, such as the composition comprising the expandable agent, the thixotropic agent, the silicate filler, the crosslinker and the catalyst, through a crosslinking reaction. The crosslinking reaction may be performed at a temperature in the range of 20 °C to 40 °C, such as at 25 °C. The crosslinking reaction may be performed at a relative humidity in the range of 40-80 %. The time for curing may be in the range of 2-10 days.

In one or more examples, the composition disclosed herein may be used as an intumescent coating of a surface, such as of an inner or an outer surface of an item, and/or a structure.

In one or more examples, the composition disclosed herein may be used as an intumescent coating for sealing a cavity. The composition may be used as an intumescent coating applied to an inside of the cavity. Upon being subjected to heat, such as in case of a fire, the intumescent coating on the inside of the cavity may expand, so that the cavity is sealed by the intumescent coating. Thereby, the cavity, or any items located in the cavity can be sealed from the fire. In one or more examples, the cavity may be a shaft, such as an electrical shaft comprising a plurality of cables, and/or a pipe shaft comprising a plurality of pipes, and/or a ventilation shaft, in a structure, such as in a building.

Fig. 1 illustrates a fire protection capability, such as a steel temperature over time, for a plurality of furnace tests without coating and with a plurality of example coatings on the steel surface. During the furnace tests the temperature of a test substrate, in this example steel, increased until a critical temperature was reached. The behavior, such as an expansion, of the coating when subjected to the heat in the furnace was studied. A critical temperature of 500°C was defined and the corresponding time it took the steel to reach the critical temperature was monitored and defined as the critical time, such as the fire protection time, of the respective coating. A slow increase (e.g., a slow rate of increase) of the steel temperature, such as a longer critical time, can be seen as indicative of good fire protection capability, while a fast increase of the steel temperature is indicative of a poor fire protection capability. A blank steel test without coating was performed to demonstrate the fire protective capabilities of the tested coatings. In addition, a commercial organic hydrocarbon coating, was tested for reference. A first example composition for the intumescent coating according to the current disclosure, herein referred to as Form6- N1 M, showed comparable fire protection with the commercial coating, with a critical time of approximately 45 minutes. The N1 M coating comprises condensation cured silicone, hydrophobic fumed silica, kaolin, CaCOs, (NH^HPC and hydrated alkali silicate particles in the form of hydrated sodium silicate particles (particle size is 63-300 pm) as an expandable agent. A key ingredient of this formulation is the hydrated alkali silicate particles. A reference composition without the hydrated alkali silicate particles, in Fig. 1 referred to as “Form 12” exhibited significantly poorer fire protection and a critical time of around 25 minutes. A second example composition for the intumescent coating according to the current disclosure, herein referred to as Form6-Mix-212-300, based on the Form6- N1 M composition was further optimized in terms of type and size of the hydrated alkali silicate particles surprisingly exhibited almost twice as good fire protection than the Form6-N1 M composition and the commercial coating, namely a critical time of >80 min. The Form6-Mix-212-300 composition comprised hydrated mixed alkali silicate particles, prepared by mixing, such as chemically mixing, Na, K, and Li-silicate solutions, and having a size in the range of 212-300 pm.

Fig. 2 illustrates a comparison of the steel temperature over time for steel coated with five different formulations:

“With ZnB” refers to a silicone coating comprising zinc borate (ZnB). The composition is summarized in Table 1 below.

“Lille-EG” refers to a coating prepared as described in the work of Gardelle et al., i.e. using silicone and expandable graphite. The coating is described in ’’Gardelle B, Duquesne S, Vandereecken P, Bourbigot S. Characterization of the carbonization process of expandable graphite/silicone formulations in a simulated fire. Polym Degrad Stab 2013; 98:1052-63. https://doi.Org/10.1016/j.polymdegradstab.2013.02.001.”.

“Commercial coating” refers to the commercial coating previously discussed.

“Form 6” refers to an example base silicone coating employing hydrated sodium silicate particles according to this disclosure. The ’’Form 6”-coating is similar in composition to the Form6-N1M coating shown in Fig. 1 with slight differences in curing conditions of silicate particles. The silicate particles used in Form6-N1 M was cured in smaller petri dishes while the one in Form 6 was cured in bigger petri dishes, resulting in slightly difference in the water content of the particles followed by the critical time. “Form6-Mix-212-300” is the example composition according to this disclosure and is similar to the base silicone coating ’’Form 6” with a mixture of silicate particles in the specified size range 212 pm to 300 pm.

A plurality of furnace tests on a steel surface coated with the different coatings were performed. The furnace was heated in the same way as discussed for Fig. 1 until the critical temperature was reached. As can be seen in Fig. 2, the silicone-expandable graphite intumescent coating (Lille-EG) developed by a research group at the University of Lille was repeated and tested. The coating exhibited a significantly worse performance compared to the example coatings of this disclosure (Form 6 and Form6-Mix-212-300) under similar testing conditions. Besides the poor protection time of about 20 min (see Fig. 2), the silicone-expandable graphite intumescent coating (Lille-EG) in the expanded state after being subjected to the heat in the furnace test proved to be fragile and easily destroyed. It was observed that the composition comprising expandable graphite exhibited a very high expansion, however, the coatings comprising expandable graphite tends to be very fragile and unable to resist external forces. To improve the mechanical stability of coatings comprising expandable graphite, boron (B) is often incorporated. Boron is commonly applied in organic and silicone-based intumescent coatings, for example in the form of ZnB. However, due to the toxicity of boron, and a difficulty in recycling of boron, it is generally unwanted in coatings. Furthermore, a release of SO2 from the graphite during the expansion process is also unwanted. Incorporation of ZnB into a tested silicone coating did not provide any benefits compared to the example silicone coatings according to this disclosure in terms of fire protection and mechanical strength. In fact, the coating with ZnB proved to be slightly worse in fire protection compared to the example base coating (Form 6).

As can be seen in Fig. 2, the example base coating Form 6 provided a slightly better fire protection than the commercial coating, while the example coating Form 6-Mix- 212-300 with the optimized hydrated alkali silicate mixture as the intumescent material exhibited a significantly better fire protection. The critical time, such as the time it took the steel to reach the critical temperature, for the Form 6-Mix- 212-300 composition was almost double the time of the commercial coating and the Form 6 coating.

Table 1 discloses the formulations of the silicone based coatings ’’with ZnB”, ’’Form 6” and ’’Form 6-Mix-212-300” previously discussed. Form 6 and Form 6-N1 M (shown in Figure 1 ) have a similar composition with slight differences in curing conditions. The formulations are given in wt.% of the composition.

Table 1: Compositions of the example formulation ‘with ZnB’, ‘form 6-N1M (Form 6)’, and ‘M1M 212-300 pm’.

Figs. 3A-3B illustrates starfish diagrams comparing the product features “fire protection”, “thermal stability”, “mechanical strength”, “sustainability”, and “affordability” of the coatings compared in Fig. 2. The coatings comprising the example compositions according to this disclosure exhibit a better performance in a majority of product features compared to the commercial coating and the Lille-EG coating.

Figs. 4A-4C illustrate a comparison of the steel temperature over time for steel coated with example compositions according to this disclosure having different formulations, namely Form 3 to Form 8 shown in Fig. 4A-4C and Table 2 below. Form 6 in Table 2 corresponds to the Form 6-N1 M compound described in Table 1. The example compositions according to this disclosure were compared to two reference compositions with the formulations Form 1 and Form 2. All of the coatings shown in Figs. 4A-4C are silicone based coatings. The composition of each coating is provided in Table 2. The coatings were prepared using a step-by-step approach from condensation cured silicone and thereafter one component was added at a time.

Initially, a promising silicone based intumescent coating was obtained by combining the compounds in Form 8. The coating exhibited similar or slightly better fire protection and higher compressional strength compared to the commercial coating. In addition, the expanded coating of the invention formed a product with good adhesion to the steel.

As can be seen in Figs. 4A-4C the presence of both a thixotropic agent, in these example compositions in the form of hydrophobic fumed silica, and hydrated alkali silicate particles as an expandable agent, in these example compositions in the form of hydrated sodium silicate particles, drastically improved the fire protection over the reference compositions which only comprised one of the thixotropic agent and the hydrated alkali silicate particles respectively. The coatings with both fumed silica and hydrated sodium silicate particles (such as Form 3) had an almost equally good fire protection as the commercial coating, however, removing one of them (Form 1 and Form 2) led to a significantly worse performance. This is demonstrated by the better performance of Form 3 compared to Form 1 and Form 2 in Fig. 4A.

The addition of kaolin (in form 4) improved the fire protection further (compared to Form 3) and also increased the mechanical strength of the expanded coating. Using kaolin as the filler increased the flame resistance further (Form 4) and the coating was comparable with commercial coating in terms of fire protection. Moreover, heating stage coupled with digital microscopy results indicated that, the presence of kaolin can prevent a melting of the coating caused by hydrated sodium silicate particles, which improved the thermal stability of the coating.

The addition of a strengthening agent and/or reinforcing agent, in the form of CaCC (in Form 5 and 6) or in the form of K2CO3 (in Form 7 and 8) enhanced the integrity, such as a compressional and cohesion strength, of the expanded coating. The addition of the strengthening agent and/or reinforcing agent may also increase the adhesion of the coating to the steel. Even though the addition of CaCOs did not lead to further improvements in fire protection, the addition of CaCC enhanced the integrity of the expanded coating (Form 5).

It was further observed that the addition of (NFU^HPC in coatings employing K2CO3 increased performance of these coatings, which can be observed from the poorer performance of Form 7 not comprising (NH4)2HPO4 compared to Form 8 comprising (NH₄)₂HPO₄. Studies on the working mechanisms of these coatings have shown that K2CO3 enhances the structural integrity of the coating, but may also accelerate degradation of the silicone. An interaction between (NH4)2HPO4 and K2CO3 results in the effect of K2CO3 on silicone degradation diminishing, while providing a coating having a similar expansion with Form 6 when exposed to heat.

The (NH₄)₂HPO₄ proved to be less important in coatings comprising CaCOs, visualized by the comparable performance of Form 5 and Form 6. However, (NH4)₂HPO4 may improve the adhesion of the coating to the steel.

Table 2: Compositions of example formulations from Form 1 to Form 8 and Form 12.

Fig. 5 illustrates the behavior of the different types of hydrated alkali silicate particles. An in-depth investigation of the hydrated alkali silicate particles was performed using available furnace and heated stage setups, to map the physical changes, such as a relative expansion, that different alkali silicate particles undergo upon heating. Four different types of alkali silicates were compared, sodium (Na) silicates, lithium (Li) silicates, potassium (K) silicates and a mixed silicates (Na + K + Li). The different phases of the physical change of the hydrated alkali silicate particles are indicated as:

0 - 1 : Initial shrinkage 1 - 2: Expansion

2 - 3: No total changes 3 - 4: second shrinkage

4 - 5: Silicate melting (not observed for lithium silicate)

Of the investigated silicates, the highest expansion was observed for the mixed alkali silicates, up to 2000 % expansion. The corresponding expansion was around 37 % for the lithium silicate particles, around 308 % for the sodium silicate particles, and around 66 % for the potassium silicate particles. The mixed silicate particles thus provided a significantly higher expansion than any of the silicate particles by their own.

Further, the effect of the amount of alkali silicate particles in the compound was studied.

Fig. 6 shows the fire protection capabilities of three example silicone coatings with varying hydrated sodium silicate content. The three example compositions, namely Form 3 as previously discussed, Form 10 and Form 11 are summarized in Table 3.

Table 3: Compositions of example formulation Form 3, Form 10 and Form 11.

As can be seen in Fig. 6, an increase of alkali silicate particles from 30.7 wt.%, as in Form

3, to 41.2 wt.%, as in Form 10, showed similar result with regards to the fire protection capability. However, increasing the amount of alkali silicate particles to 46.5 wt.% as in

Form 11 yielded a significantly worse fire protection capability. Hence, according to one or more example compositions according to this disclosure, the wt.% of the alkali silicate particles is in the range of 17 % to 42 %. The poorer performance of Form 11 may be caused by an increased expansion leading to a poor char structure due to the presence of a larger amount of hydrated sodium silicate particles. Hence, a wt.% of alkali silicate particles above 50 % would not be applicable under the severe conditions of hydrocarbon fires.

The effect of the type of silicate particles was further investigated. Fig. 7 illustrates the fire protection capability, such as the temperature profiles, of example compositions comprising different types of single alkali silicate particles Li, K and Na. In Fig. 7 the molar ratio of the silicate particles of the alkali silicate particles in the respective composition is indicated. The molar ratio can be defined as the ratio in moles between the silica (SiO?) and the respective alkali silicate Na, K, or Li. In other words, the molar ratio can be defined as the SiC^/IVbO ratio, where M = Na, K, or Li. In the example compositions shown in Fig. 7, lithium silicate particles were provided with a molar ratio of 4.2, sodium silicate particles were provided with a molar ratio of 3.38 and potassium silicate particles were provided with two different molar ratios, such as 3.1 and 4.8. Sodium silicates provided the best fire protection of the four compositions with an average protection time of 42 min and an expansion of about 250 %. In comparison, lithium silicates and potassium silicates provided a protection time of around 30 minutes.

Fig. 8 illustrates the fire protection capability, such as the temperature profiles, of different types of mixed silicate particles, such as a mix M of all three silicates Li, K and Na, a mix of potassium and lithium silicate (K+L), a mix of potassium and sodium silicate (K+Na) and a mix of sodium and lithium silicate (Na+L). The mixed silicate types M=(K + Na + Li) provided almost double as good fire protection as the commercial coating, with an average critical time of around 70 minutes compared to an average critical time of around 42 min for commercial coating. The mixed silicate types M provided a significant expansion (up to 800 %) with a uniform internal structure. The mixtures of potassium and sodium silicates, and potassium and lithium silicates also provided a better fire protection than the commercial composition, with a critical time of around 62 min and 50 minutes, respectively. The potassium silicate can provide a significant expansion of the composition when subjected to heat during for example a fire scenario. However, the expanded char is of poor cohesive strength. Lithium silicates can provide heat resistance and uniformity due to its high melting point of approximately 1200 °C. In addition, lithium can act as an H₂O carrier to improve evaporation of water from the compound when subjected to heat during for example a fire scenario. Hence, by combining these alkali silicate particles in the composition, the fire protection capability of the composition can be significantly improved.

In general, increased expansion of the coating results in increased fire protection. The different alkali silicates exhibit different expansion in silicone coatings. Herein, low molar ratio silicates provide more expansion with one exception for high molar ratio potassium silicates that created a hollow body upon rapid expansion. Lithium and lower molar ratio potassium silicates do not provide the same expansion as sodium silicates and mixed silicates. Sodium silicates can also provide uniform expansion. As is shown in Fig. 5, lithium silicate does not melt at high temperatures, but is distributed in the expanded coating to improve the structural integrity of the expanded coating. By mixing the different types of silicates solution a significantly better result was achieved with expansions of up to 800 % volume and more than one hour fire protection, shown by the critical time of M and K+L in Fig. 8 being more than 60 minutes. Here, the uniform expansion of the coating with mixed silicate particles M slows down the effect of the heat from the fire, thereby allowing slow heating rates especially around a steel temperature of around 400 °C, a temperature where all the silicate particles in the coating are expected to be fully expanded. However, an increased expansion generally leads to a lower mechanical strength, and this therefore creates a trade-off between fire protection and mechanical properties.

Furthermore, the effect of the size of the alkali silicate particles was studied. The effect of the size of the alkali silicate particles is illustrated in Fig. 9, where the composition comprising mixed silicate particles M with particle sizes of <63 pm, 63 pm to 212 pm, 212 pm to 300 pm and 63-300 pm was compared. As can be seen in Fig. 9, the particle size of the already well-performing mixed silicate particles M (Li, Na, K) had a significant influence on the expansion and fire protection parameters. The increase of particle size in the ranges <63 pm, 63 pm to 212 pm, and 212 pm to 300 pm results in better critical time values going from 50 to 84 minutes. Accordingly, the coating expansion increased from 500 % for the range <63 pm to more than 800 % for the range 212 pm to 300 pm. It was further observed that an increasingly uniform expansion leads to better fire protection. Increasing the particle size (up to 300 pm) leads to increasingly uniform expansion of the coating when subjected to heat. Larger particle sizes, such as in the range of 300 pm to 850 pm, leads to poorer fire protection. By decreasing the particle size (from 300 pm) a more dense and compact expanded coating may be achieved. By decreasing the particle size (from 300 pm) a better adhesion to steel may also be achieved, due to a formation of -Si-O-Fe bonds formed by a reaction of -Si(OH) to the surface of the structure, such as to a steel surface.

The performance of the example compositions of this disclosure can thus be significantly affected by the silicate particle size. For example, a silicone coating having alkali silicate particles in the size range of 63 pm to 300 pm provided very good fire protection capabilities, while providing the alkali silicate particles in the size range of 212 pm to 300 pm further improved the fire protection capability. Smaller sized alkali silicate particles expand less but creates a compact layer with better steel adhesion. The cohesion and expansion properties of the one or more example compositions according to this disclosure, can thus be tailored to different requirements by adjusting the size of the alkali silicate particles within the range of 63 pm to 300 pm.

Fig. 10 shows the influence of atmospheric conditions on the fire protection capability of two example compositions according to this disclosure, such as Form 6 and an example Form 9, compared to the commercial composition. Silicone has different degradation behavior under oxidizing and reducing conditions, which can lead to different fire protection performance of the silicone based coatings. As the example coatings provided herein are relatively thick (such as around 6 mm), the surface of the coating may in the event of a fire be in an oxidizing atmosphere, while reducing conditions may be prominent beneath the surface of the coating. Thus, the influence of gas atmosphere was investigated to get a better understanding of the working mechanism of the example compositions, the results of which are summarized in Fig. 10 with the compositions shown in Table 4. Table 4: Compositions of example formulation Form 6 and Form 9.

The results show that both the commercial coating and the example silicone coatings Form 6 had better performance under nitrogen (N2) atmosphere. Compared to the commercial coating, the example composition Form 6 performed better under oxidizing conditions and worse under reducing atmosphere conditions, such as under the N2 atmosphere condition. By replacing the (NH^HPC with APP as flame retardant, such as in the example composition Form 9, in the same formulation, the fire protection was improved. The mechanical properties of Form 6 and Form 9 were better under oxidizing atmosphere conditions than under reducing atmosphere conditions. In reducing atmosphere, the strength of the example compositions Form 6 and Form 9 are comparable with the commercial coating, while under oxidizing conditions the mechanical properties were higher. The example compositions according to this disclosure can thus be tailored to meet the requirements of a certain atmosphere depending on the employed ingredients, such as based on the applied flame retardant. This may be relevant for protection of structures in spaces where oxygen supply may be limited.

Silicone is known to possess good weathering stability and water resistance, while silicate systems are generally sensitive towards weathering including H2O and CO2. Intumescent coatings in general are required to be stable on substrates for at least ten years.

Weathering stability of the developed coating was therefore evaluated. Fig. 11 illustrates the weathering stability of the example compositions disclosed herein, in Fig. 11 shown for the example composition Form 6. After being applied to a metal substrate and aged in a climate chamber for 3 month, the coating (Form 6) exhibited the same fire protection capability as when tested immediately after curing.

Hence, by transforming the silicate solution into silicate particles and then embedding the silicate particles into the silicone according to the one or more example methods disclosed in this document, the silicate particles can be stabilized against weathering. Thereby, the example compositions disclosed herein are less prone to change due to environmental conditions, such as H2O and CO2 concentration, thus improving durability of the one or more example compositions, and/or one or more example coatings comprising the one or more example compositions.

Fig. 12 describes the fire protection performance of Form 6 in a pilot-scaled furnace named as CoaST-FIRE in our group, which has radiation dominated heating. Coating F6 has similar critical time with the commercial coating, indicating its promising fire protection performance under different testing conditions.

The one or more example coatings based on the one or more example compositions comprising a silicone binder with incorporated alkali silicate particles withstand the effects of a simulated hydrocarbon fire (UL 1709) for an extended period of time by the formation of an expanded, physical barrier. The expanded barrier consists of a brittle surface layer mainly comprising silicate melt. In one or more example coatings, the brittle surface layer may comprise degraded amorphous silica and additives, such as a minimal amount of degraded amorphous silica and additives, such as substantially less than the amount of silicate melt. As silicone degrades from 300 °C, the degraded amorphous silica on the coating surface is released, some of which is captured by the components of the coating forming a solid, heat-resistant surface. Hereof, the temperature profile decreases from the surface down to the steel as the coating expansion relies mainly on expanded silicate particles in the expanded coating body. With the clarification of the degradation process of the one or more example compositions according to this disclosure, it is possible to modify the expansion mechanism of the one or more example compositions by varying the type of silicate particles, their particle size, etc. This can be done to adapt a degradation, an expansion and/or an encapsulation of (or reaction/bonding with) degraded amorphous silica. Moreover, specific additives are to be incorporated to improve certain properties of the one or more example compositions, such as thermal, physical, and mechanical. Fig. 13 is a flow diagram of an example method 100 for preparing a composition for intumescent coating is disclosed. The method may comprise curing S101 an alkali silicate solution to prepare a hydrated alkali silicate solid.

The method may comprise obtaining S103 hydrated alkali silicate particles in a size range of 63 to 300 pm, such as in the range of 212 to 300 pm. In one or more example methods, obtaining 300 comprises reducing S103A a size of the hydrated alkali silicate solid to obtain hydrated alkali silicate particles in a size range of 63 to 300 pm, such as in the range of 212 to 300 pm. In one or more example methods, reducing S103A the size of the hydrated alkali silicate solid may comprise reducing the size by milling S103AA, such as ball milling, the hydrated alkali silicate solid until the hydrated alkali silicate particles have been obtained.

The method comprises mixing S105 silicon-based binder with an expandable agent, a thixotropic agent, a silicate filler, a crosslinker and a catalyst to form a composition. The silicon-based binder may be a polydimethylsiloxane (PDMS), such as silanol terminated polydimethylsiloxane. The expandable agent is hydrated alkali silicate particles, such as hydrated alkali silicate particles in a size range of 63 to 300 pm, such as in the range of 212 to 300 pm. The thixotropic agent is fumed silica, such as hydrophobic fumed silica. In one or more example methods, the silicon-based binder is mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker using a dissolver. The silicon-based binder may be mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker at a rotational speed of 500 to 12000 rpm. In one or more example methods, the silicon-based binder is mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker for 5-15 minutes. In one or more example methods, the catalyst is added, during continued mixing, after the silicon-based binder has been mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker.

The method comprises curing S107 the composition through a condensation reaction.

The condensation reaction may be performed at a temperature in the range of 20 to 40°C, such as at 25 °C. The condensation reaction may be performed at a relative humidity in the range of 40-80 %.

It shall be noted that the features mentioned in the embodiments described in Figs. 1-13 are not restricted to these specific embodiments. Any features relating to optional components and the effects achieved by the respective component and mentioned in relation to one or more example compositions of Figs. 1-12, are thus also applicable to the any of the other example compositions described in relation to Figs. 1-12.

It shall be noted that in Table 1 , Table 2, Table 3, and Table 4 herein, the amount of the respective constituents is given as a wt.% of the composition. It shall be noted that for any composition where the amount of the constituents does not add up to a 100%, the deviation may be due to, such as caused by, other elements and/or inevitable impurities in the composition. In some example compositions, the composition may include other elements and inevitable impurities at less than 1 wt.%.

Embodiments of products (composition for an intumescent coating, intumescent coating system and method for preparing a composition for intumescent coating) according to the disclosure are set out in the following items:

Item 1 . A composition for intumescent coating, the composition comprising: a silicon-based binder; an expandable agent, wherein the expandable agent comprises hydrated alkali silicate particles, a thixotropic agent, and a silicate filler.

Item 2. The composition according to Item 1 , wherein the thixotropic agent is one or more of hydrophobic fumed silica and organobentonite.

Item 3. The composition according to Item 1 or 2, wherein a size of the hydrated alkali silicate particles is up to 300 pm, such as in the range of 63 pm and 300 pm, such as in the range of 212 pm and 300 pm.

Item 4. The composition according to any one of the previous Items, wherein the silicate filler is one or more of an alumino silicate, kaolin, metakaolin, mica, feldspar, wollastonite, and talc.

Item 5. The composition according to any one of the previous Items, wherein the silicon-based binder comprises a silicon-based resin, a crosslinker, and a catalyst.

Item 6. The composition according to Item 5, wherein the catalyst is a Titanium- based catalyst or a Tin-based catalyst.

Item 7. The composition according to any of the previous Items, wherein the hydrated alkali silicate particles comprise sodium silicate.

Item 8. The composition according to any of the previous Items, wherein the hydrated alkali silicate particles comprise potassium silicate.

Item 9. The composition according to Item 7 or 8, wherein the hydrated alkali silicate particles comprise lithium silicate.

Item 10. The composition according to any of the previous Items, wherein the composition comprises a reinforcing agent.

Item 11. The composition according to Item 10, wherein the reinforcing agent comprises one or more of phosphate-derived compounds (such as (NH^HPC , Ca₃(PO₄)₂, KH2PO4, AIPO4, and APP), K2CO3, CaCO₃, Na₂CO₃, NaHCO₃, KCI, ZnO, MgO, and TiC>2. Item 12. The composition according to any one of the previous Items, wherein the composition comprises a flame retardant.

Item 13. The composition according to Item 12, wherein the flame retardant comprises one or more of phosphate-derived compounds (such as (NH^HPC , and APP), AI(OH)₃, Mg(OH)₂, and Ca(OH)₂.

Item 14. The composition according to Item 12 or 13, wherein the wt.% of the flame retardant is in the range 0 % to 22 %.

Item 15. The composition according to any of the previous Items, wherein the wt.% of the silicon-based binder is in the range 40 % and 70 %.

Item 16. The composition according to any of the previous Items, wherein the wt.% of the expandable agent is in the range 17 % to 42 %.

Item 17. The composition according to any of the previous Items, wherein the wt.% of the thixotropic agent is in the range 4.5 % to 20 %.

Item 18. The composition according to any of the previous Items, wherein the wt.% of the reinforcing agent is in the range 0 % to 22 %.

Item 19. The composition according to any of the previous Items, wherein the wt.% of the silicate filler is in the range of 0 % to 22 %.

Item 20. The composition according to any of the previous Items, wherein the composition comprises a wetting agent.

Item 21. The composition according to Item 19, wherein the wt.% of the wetting agent is in the range 0 % to 2.5 %.

Item 22. The composition according to any of the previous Items, wherein the composition comprises waste material.

Item 23. The composition according to any of the previous Items, wherein the composition comprises lignin.

Item 24. An intumescent coating system, the intumescent coating system comprising: a primer, the composition for intumescent coating according to any one of the Items 1-23, and optionally a top coat.

Item 25. A method for preparing a composition for intumescent coating, the method comprising: obtaining hydrated alkali silicate particles in a size of up to 300 pm, mixing a silicon-based binder with an expandable agent, a thixotropic agent, a silicate filler, wherein the expandable agent comprises the hydrated silicate particles and the thixotropic agent is hydrophobic fumed silica, and curing the mixed composition through a crosslinking reaction.

Item 26. The method for preparing the composition for intumescent coating according to Item 25, wherein the silicon-based binder is mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker using a dissolver at a rotational speed of 500 to 12000 rpm.

Item 27. The method for preparing the composition for intumescent coating according to Item 25 or 26, wherein the silicon-based binder is mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker for 5-15 minutes.

Item 28. The method for preparing the composition for intumescent coating according to any one of the Items 25 to 27, wherein, after the silicon-based binder has been mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker adding, during continued mixing, the catalyst.

Item 29. The method for preparing the composition for intumescent coating according to any one of the Items 25 to 28, wherein the condensation reaction is performed at a temperature in the range of 20 to 40°C, and at a relative humidity in the range of 40-80 %. Item 30. The method for preparing the composition for intumescent coating according to any one of the Items 25 to 29, wherein the method comprises: curing an alkali silicate solution to prepare a hydrated alkali silicate solid.

Item 31. The method for preparing the composition for intumescent coating according to Item 30, wherein obtaining the hydrated alkali silicate particles in the size of up to 300 pm comprises reducing the size of the hydrated alkali silicate solid to obtain the hydrated alkali silicate particles in the size of up to 300 pm.

Item 32. The method for preparing the composition for intumescent coating according to any one of the Items 25 to 31 , wherein the method comprises mixing a silicon- based resin, a crosslinker and a catalyst to obtain the silicon-based binder.

Item 33. Use of the composition according to any one of Items 1 to 23, as an intumescent coating of a surface.

Item 34. Use of the composition according to any one of Items 1 to 23, as an intumescent coating for sealing a cavity.

The use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not imply any particular order, but are included to identify individual elements. Moreover, the use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not denote any order or importance, but rather the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used to distinguish one element from another. Note that the words “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering. Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.

It is to be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed.

It is to be noted that the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than or equal to 10% of, within less than or equal to 5% of, within less than or equal to 1% of, within less than or equal to 0.1 % of, and within less than or equal to 0.01% of the stated amount. If the stated amount is 0 (e.g., none, having no), the above recited ranges can be specific ranges, and not within a particular % of the value. For example, within less than or equal to 10 wt./vol. % of, within less than or equal to 5 wt./vol. % of, within less than or equal to 1 wt./vol. % of, within less than or equal to 0.1 wt./vol. % of, and within less than or equal to 0.01 wt./vol. % of the stated amount.

Although features have been shown and described, it will be understood that they are not intended to limit the claimed disclosure, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the claimed disclosure. The specification and drawings are, accordingly to be regarded in an illustrative rather than restrictive sense. The claimed disclosure is intended to cover all alternatives, modifications, and equivalents.

Claims

1. A composition for intumescent coating, the composition comprising: a silicon-based binder; an expandable agent, wherein the expandable agent comprises hydrated alkali silicate particles, a thixotropic agent, and a silicate filler.

2. The composition according to claim 1 , wherein the thixotropic agent is one or more of hydrophobic fumed silica and organobentonite.

3. The composition according to claim 1 or 2, wherein a size of the hydrated alkali silicate particles is up to 300 pm.

4. The composition according to any one of the previous claims, wherein the silicate filler is one or more of an alumino silicate, kaolin, metakaolin, mica, feldspar, wollastonite, and talc.

5. The composition according to any one of the previous claims, wherein the silicon- based binder comprises a silicon-based resin, a crosslinker, and a catalyst.

6. The composition according to claim 5, wherein the catalyst is a Titanium-based catalyst or a Tin-based catalyst.

7. The composition according to any of the previous claims, wherein the hydrated alkali silicate particles comprise sodium silicate.

8. The composition according to any of the previous claims, wherein the hydrated alkali silicate particles comprise potassium silicate.

9. The composition according to any of the previous claims, wherein the hydrated alkali silicate particles comprise one or more of sodium silicate, potassium silicate, and lithium silicate.

10. The composition according to any of the previous claims, wherein the composition comprises a reinforcing agent.

11. The composition according to claim 10, wherein the reinforcing agent comprises one or more of phosphate-derived compounds (such as (NH^HPC , Ca3(PC>4)2, KH2PO4, AIPO4, and APP), K2CO3, CaCO₃, Na₂CO₃, NaHCO₃, KCI, ZnO, MgO, and TiC>2.

12. The composition according to any one of the previous claims, wherein the composition comprises a flame retardant.

13. The composition according to claim 12, wherein the flame retardant comprises one or more of phosphate-derived compounds (such as (NH4)2HPO4, and APP), AI(OH)₃, Mg(OH)₂, and Ca(OH)₂.

14. The composition according to claim 12 or 13, wherein the wt.% of the flame retardant is in the range 0 % to 22 %.

15. The composition according to any of the previous claims, wherein the wt.% of the silicon-based binder is in the range 40 % and 70 %.

16. The composition according to any of the previous claims, wherein the wt.% of the expandable agent is in the range 17 % to 42 %.

17. The composition according to any of the previous claims, wherein the wt.% of the thixotropic agent is in the range 4.5 % to 20 %.

18. The composition according to any of the previous claims, wherein the wt.% of the reinforcing agent is in the range 0 % to 22 %.

19. The composition according to any of the previous claims, wherein the wt.% of the silicate filler is in the range of 0 % to 22 %.

20. The composition according to any of the previous claims, wherein the composition comprises a wetting agent.

21. The composition according to claim 19, wherein the wt.% of the wetting agent is in the range 0 % to 2.5 %.

22. The composition according to any of the previous claims, wherein the composition comprises waste material.

23. The composition according to any of the previous claims, wherein the composition comprises lignin.

24. An intumescent coating system, the intumescent coating system comprising:

- a primer, the composition for intumescent coating according to any one of the claims 1-23, and optionally a top coat.

25. A method for preparing a composition for intumescent coating, the method comprising: obtaining hydrated alkali silicate particles in a size up to 300 pm, mixing a silicon-based binder with an expandable agent, a thixotropic agent, a silicate filler, wherein the expandable agent comprises the hydrated silicate particles, and curing the mixed composition through a crosslinking reaction.

26. The method for preparing the composition for intumescent coating according to claim 25, wherein the silicon-based binder is mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker using a dissolver at a rotational speed of 500 to 12000 rpm.

27. The method for preparing the composition for intumescent coating according to claim 25 or 26, wherein the silicon-based binder is mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker for 5-15 minutes.

28. The method for preparing the composition for intumescent coating according to any one of the claims 25 to 27, wherein, after the silicon-based binder has been mixed with the expandable agent, the thixotropic agent, the silicate filler, and the crosslinker adding, during continued mixing, the catalyst.

29. The method for preparing the composition for intumescent coating according to any one of the claims 25 to 28, wherein the condensation reaction is performed at a temperature in the range of 20 to 40°C, and at a relative humidity in the range of 40-80 %.

30. The method for preparing the composition for intumescent coating according to any one of the claims 25 to 29, wherein the method comprises: curing an alkali silicate solution to prepare a hydrated alkali silicate solid.

31. The method for preparing the composition for intumescent coating according to claim 30, wherein obtaining the hydrated alkali silicate particles in the size of up to 300 pm comprises reducing the size of the hydrated alkali silicate solid to obtain the hydrated alkali silicate particles in the size of up to 300 pm.

32. The method for preparing the composition for intumescent coating according to any one of the claims 25 to 31 , wherein the method comprises mixing a silicon- based resin, a crosslinker and a catalyst to obtain the silicon-based binder.

33. Use of the composition according to any one of claims 1 to 23, as an intumescent coating of a surface.

34. Use of the composition according to any one of claims 1 to 23, as an intumescent coating for sealing a cavity.