High-volume-stability phosphate fireproof coating and application thereof

Abstract

The invention discloses a phosphate fireproof coating with high volume stability and application thereof. The coating is prepared from the following raw materials in parts by weight: 1-5 parts of aluminum dihydrogen phosphate, 1-4 parts of magnesium oxide, 0.1-0.3 part of wollastonite fiber, 0.1-1 part of aluminum powder paste, 1-3 parts of vermiculite, 0.1-1 part of dolomite, 0.1-0.5 part of organic modified montmorillonite, 0.1-0.5 part of zinc borate and 0.1-0.3 part of expanded graphite. The preparation method comprises the following steps: firstly, premixing the magnesium oxide, the vermiculite, the dolomite, the organic modified montmorillonite, the zinc borate and the expanded graphite to obtain a mixed material; dissolving aluminum dihydrogen phosphate in a proper amount of water, adding wollastonite fibers and the aluminum powder paste, fully stirring to obtain a mixed solution, and carrying out ultrasonic treatment on the mixed solution until the mixed solution is not agglomerated; and finally, adding the mixed material into the mixed solution to obtain the slurry. The coating disclosed by the invention has excellent fire resistance and heat insulation property, high volume stability and excellent crack resistance, and is suitable for the field of fire prevention of steel structures with extremely high requirements on integrity of protective layers.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically a high volume stability phosphate fire retardant coating and its application. Background Technology

[0002] With the advancement of industrialized construction and the continuous improvement of urban safety standards, the demand for fire-retardant coatings for steel structures continues to grow in high-rise buildings, petrochemical facilities, and power facilities. Existing intumescent fire-retardant coatings can form an expanded char layer when heated to block heat conduction; however, under long-term exposure to high temperatures, humidity, or chemical corrosion, the coating is prone to cracking or peeling due to volume changes, thus weakening its fire-retardant effect. While non-intumescent inorganic fire-retardant coatings possess good weather resistance and stability, their thick coatings and complex application methods make them difficult to meet the combined requirements of lightweighting and long-term durability in steel structure protection. Therefore, developing a phosphate-based fire-retardant coating that combines high volume stability, environmental friendliness, and long-lasting flame-retardant properties has become a technological breakthrough for addressing key pain points in the field of steel structure fire protection.

[0003] Magnesium phosphate cement (MPC) is a novel cementitious material formed by the curing of reburned magnesium oxide, phosphate, retarders, and functional components through an acid-base reaction. It possesses advantages such as high strength, excellent high-temperature resistance, and good adhesion to steel interfaces, making it widely used in fire-retardant coatings and repair materials. However, MPC systems generally suffer from high density, high carbon emissions, and high production costs, limiting their widespread application in large-scale projects. To address these shortcomings, existing research often introduces lightweight components such as expanded perlite and glass microspheres into the system to reduce material density and thermal conductivity, thereby improving its thermal insulation and fire-retardant properties. The porous structure of lightweight fillers reduces heat conduction and improves the compactness of the MPC matrix through a filling effect, reducing surface cracking under high-temperature conditions and increasing residual bond strength. On the other hand, some studies have proposed using unburned low-grade brucite powder to partially or completely replace reburned magnesium oxide to reduce energy consumption and carbon emissions, achieving green production. These studies have, to some extent, promoted the performance optimization of phosphate fire-retardant coatings, laying the foundation for their industrial application.

[0004] Despite this, phosphate-based fire-retardant coatings still exhibit significant shortcomings in high-temperature volume stability. Particularly in environments above 800°C, the mismatch in thermal expansion coefficients between the coating and the steel substrate easily leads to irreversible shrinkage stress, resulting in the propagation of internal microcracks and interlayer delamination. This phenomenon primarily stems from lattice distortion of the phosphate network structure and the densification process during sintering under high-temperature conditions. In traditional systems, the magnesium aluminum phosphate phase formed by the reaction of magnesium oxide and phosphate is prone to volume shrinkage under thermal cycling, compromising the integrity of the coating structure. While existing technologies improve the crack resistance of coatings by adding fiber reinforcements or modified fillers, they cannot fundamentally solve the volume instability problem caused by high-temperature phase transformations from the intrinsic structure of the material system, thus limiting the long-term protective application of phosphate-based fire-retardant coatings in extreme high-temperature environments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high volume stability phosphate fire retardant coating and its application, which addresses the shortcomings of the prior art and enables the substrate to have fire resistance and heat insulation properties, high volume stability and excellent crack resistance.

[0006] To solve the aforementioned technical problems, the present invention adopts the following technical solution: a high volume stability phosphate fire retardant coating, which is composed of the following raw materials in parts by weight: 1-5 parts aluminum dihydrogen phosphate, 1-4 parts magnesium oxide, 0.1-0.3 parts wollastonite fiber, 0.1-1 parts aluminum powder paste, 1-3 parts vermiculite, 0.1-1 parts dolomite, 0.1-0.5 parts organically modified montmorillonite, 0.1-0.5 parts zinc borate, and 0.1-0.3 parts expanded graphite;

[0007] In the preparation process, magnesium oxide, vermiculite, dolomite, organically modified montmorillonite, zinc borate, and expanded graphite are first premixed to obtain a mixture; then aluminum dihydrogen phosphate is dissolved in an appropriate amount of water and wollastonite fiber and aluminum powder paste are added and stirred thoroughly to obtain a mixed solution. The mixed solution is ultrasonically treated until there is no agglomeration; finally, the mixture is added to the mixed solution to obtain a slurry.

[0008] The phosphate fire-retardant coating of this invention exhibits excellent workability. While maintaining the inherent rapid-hardening and early-strength characteristics of the phosphate system, the introduction of organically modified montmorillonite as a rheology modifier effectively solves the technical problems of easy sedimentation and poor anti-sagging properties in high-solids-content inorganic coatings. In an aqueous system, the organically modified montmorillonite can peel off to form a lamellar structure and construct a three-dimensional network framework, endowing the coating system with thixotropic properties. In a static state, the network structure locks in the filler particles, inhibiting delamination and sedimentation, and improving the system's storage stability. Under the high-shear conditions of spray application, the network structure is temporarily disrupted, reducing the system viscosity and thus providing excellent atomization and leveling performance. The application process employs a high-pressure airless spraying technique, allowing the coating to be fully atomized under high pressure and generate significant spray kinetic energy, enabling it to penetrate the microscopic unevenness of the substrate surface and form a dense, uniform, and strongly adherent coating. This spraying method avoids interference from moisture or oil contamination caused by compressed air mixing. Once the shear force is removed, the thixotropic network structure is quickly rebuilt and the viscosity is restored, which can effectively suppress the sagging phenomenon in vertical surface construction, enabling a uniform film thickness of 2-3mm to be achieved in a single spraying, thereby improving construction efficiency and coating density.

[0009] The phosphate fire-retardant coating of this invention exhibits excellent resistance to high-temperature shrinkage, effectively overcoming the bulk shrinkage problem of traditional phosphate ceramics at high temperatures through a multi-mechanism synergistic effect. The coating employs a dynamic volume compensation strategy combining physical and chemical methods. Expanded graphite undergoes intense interlayer expansion above 200℃, resulting in a rapid increase in volume that directly offsets the thermal shrinkage of the matrix. Zinc borate decomposes above 300℃, releasing water of crystallization, which not only absorbs heat but also forms numerous micron-sized pores within the coating, buffering the shrinkage stress generated by sintering densification through the introduction of controllable porosity. Furthermore, a multi-scale reinforcing network is constructed to suppress shrinkage strain. Wollastonite fibers are uniformly distributed three-dimensionally within the matrix; their high modulus and aspect ratio enable them to effectively bridge cracks at high temperatures. Through mechanisms such as fiber pull-out and interfacial friction, they absorb and disperse thermal stress, mechanically inhibiting the formation and propagation of macroscopic shrinkage cracks. The staged endothermic decomposition of dolomite (CaMg(CO3)2) in the 350-750℃ range also helps alleviate localized thermal stress. The above mechanism, through the synergy of micropore control and macro-fiber reinforcement, enables the coating to maintain near-zero shrinkage volume stability during high-temperature service.

[0010] The phosphate fire-retardant coating of this invention exhibits excellent high-temperature resistance. During temperature rise, each component undergoes a series of beneficial physicochemical changes, synergistically enhancing the fire resistance limit. Initially, zinc borate melts and reacts with phosphate to form high-temperature resistant complex salts such as aluminum borophosphate. This glass-ceramic phase covers the surface of unreacted fillers, providing both high-temperature bonding and oxygen isolation. As the temperature continues to rise, wollastonite fibers not only maintain their fibrous morphology above 1000°C, acting as high-temperature reinforcing materials, but their surface also reacts with phosphate to form thermally more stable silicate phosphates, further stabilizing the ceramic skeleton. Simultaneously, aluminum powder paste and vermiculite are activated within a specific temperature range, synergistically expanding graphite to form a carbonaceous-ceramic composite insulation layer with increased thickness, high porosity, and excellent strength. This insulation layer effectively blocks the transmission of high flame temperature to the steel structure substrate, ensuring that the temperature of the unexposed surface remains below the critical temperature for an extended period during standard fire resistance tests. Ultimately, the entire system generates a series of high-melting-point ceramic phases and stable glass phases through in-situ reactions, giving the coating excellent fire resistance integrity and thermal insulation.

[0011] Preferably, the aluminum dihydrogen phosphate is an industrially pure powder with a purity of not less than 95%, wherein the P2O5 content is 31-33%, the Al2O3 content is 6-7.5%, and the pH value is 1.3-1.5.

[0012] Preferably, the magnesium oxide has a particle size of 1-5 μm, a purity of 85%-92%, and an activity content of ≥95%.

[0013] Preferably, the wollastonite fiber has a length of 100-300 μm, an aspect ratio of 10:1-15:1, and a heat resistance temperature ≥1000℃.

[0014] Preferably, the aluminum powder paste has a solid content of ≥65% and a gas generation rate of ≥85% within 40 minutes in an alkaline solution.

[0015] Preferably, the vermiculite is unexpanded phlogopite type, with a particle size of 80-150μm, an expansion ratio of ≥10 times, and an initial expansion temperature of 200-300℃.

[0016] Preferably, the dolomite contains ≥95% CaMg(CO3)2 and has a decomposition temperature of 350-750℃.

[0017] Preferably, the interlayer spacing of the organically modified montmorillonite is 2.5-3.5 nm, and the content of the organic modifier is 15-35 wt%.

[0018] Preferably, the zinc borate contains 37-40% ZnO and 45-48% B2O3, and has a decrystallization temperature ≥300℃; the expanded graphite has an initial expansion temperature of 200-220℃ and an expansion volume ≥150mL / g.

[0019] The present invention also provides the application of the above-mentioned high volume stability phosphate fire retardant coating, wherein the coating is sprayed onto the surface of the substrate using high pressure airless spraying, and the film thickness is controlled at 2-3 mm.

[0020] The beneficial effects of this invention are as follows: It utilizes an aluminum dihydrogen phosphate-magnesium oxide system to form a high-strength ceramic bonding skeleton, providing a foundation for the volume stability of the coating; through the synergistic and efficient expansion of aluminum powder paste, vermiculite, and expanded graphite, a robust and dense heat-insulating carbon layer is formed during fire; the three-dimensional network reinforcement of wollastonite fibers and the high-temperature decomposition and heat absorption of dolomite synergistically inhibit cracking, deformation, and shrinkage of the coating at high temperatures; and the thixotropic properties of organically modified montmorillonite ensure the storage stability and anti-sagging performance of the coating system during application. High-pressure airless spraying is used during application, ensuring a dense, uniform coating that is firmly bonded to the substrate. The coating of this invention possesses excellent fire resistance and heat insulation, high volume stability, and outstanding crack resistance, making it suitable for fire protection applications of steel structures where the integrity of the protective layer is extremely important. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments, but the embodiments should not be regarded as limiting the rights of the present invention.

[0022] Example 1

[0023] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0024] Example 2

[0025] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 5 parts aluminum dihydrogen phosphate, 2.5 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0026] Example 3

[0027] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 1 part aluminum dihydrogen phosphate, 1 part magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0028] Example 4

[0029] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.3 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0030] Example 5

[0031] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 1 part aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.3 parts expanded graphite.

[0032] Example 6

[0033] A high volume-stability phosphate fire-retardant coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.1 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.1 parts expanded graphite.

[0034] Example 7

[0035] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 3 parts vermiculite, 1 part dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0036] Example 8

[0037] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.5 parts zinc borate, and 0.2 parts expanded graphite.

[0038] Example 9

[0039] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.5 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0040] Example 10

[0041] A high volume-stability phosphate fire-retardant coating comprises, by weight, the following components: 4 parts aluminum dihydrogen phosphate, 3 parts magnesium oxide, 0.25 parts wollastonite fiber, 0.8 parts aluminum powder paste, 2.5 parts vermiculite, 0.8 parts dolomite, 0.4 parts organically modified montmorillonite, 0.4 parts zinc borate, and 0.25 parts expanded graphite.

[0042] In the preparation of the coatings described in Examples 1-10, magnesium oxide, vermiculite, dolomite, organically modified montmorillonite, zinc borate, and expanded graphite are first premixed to obtain a mixture; then aluminum dihydrogen phosphate is dissolved in an appropriate amount of water, and wollastonite fiber and aluminum powder paste are added and stirred thoroughly to obtain a mixed solution. The mixed solution is ultrasonically treated until there is no agglomeration; finally, the mixture is added to the mixed solution to obtain a slurry.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that this comparative example does not use wollastonite fibers.

[0045] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that this comparative example does not use aluminum powder paste.

[0048] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0049] Comparative Example 3

[0050] The difference between this comparative example and Example 1 is that this comparative example does not use expanded graphite.

[0051] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, and 0.3 parts zinc borate.

[0052] Comparative Example 4

[0053] The difference between this comparative example and Example 1 is that vermiculite is not used in this comparative example.

[0054] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0055] Comparative Example 5

[0056] The difference between this comparative example and Example 1 is that this comparative example does not use dolomite.

[0057] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0058] Comparative Example 6:

[0059] The difference between this comparative example and Example 1 is that this comparative example does not use organically modified montmorillonite.

[0060] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0061] Comparative Example 7

[0062] The difference between this comparative example and Example 1 is that zinc borate is not used in this comparative example.

[0063] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, and 0.2 parts expanded graphite.

[0064] Comparative Example 8

[0065] The difference between this comparative example and Example 1 is that this comparative example uses 1 part aluminum dihydrogen phosphate and 4 parts magnesium oxide.

[0066] A coating, by weight, comprises the following components: 1 part aluminum dihydrogen phosphate, 4 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0067] Comparative Example 9

[0068] The difference between this comparative example and Example 1 is that this comparative example uses 5 parts aluminum dihydrogen phosphate and 1 part magnesium oxide.

[0069] A coating, by weight, comprises the following components: 5 parts aluminum dihydrogen phosphate, 1 part magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts aluminum powder paste, 2 parts vermiculite, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, 0.3 parts zinc borate, and 0.2 parts expanded graphite.

[0070] Comparative Example 10

[0071] The difference between this comparative example and Example 1 is that this comparative example does not use aluminum powder paste, expanded graphite, and vermiculite.

[0072] A coating, by weight, comprises the following components: 3 parts aluminum dihydrogen phosphate, 2 parts magnesium oxide, 0.2 parts wollastonite fiber, 0.5 parts dolomite, 0.3 parts organically modified montmorillonite, and 0.3 parts zinc borate.

[0073] The methods for preparing the coatings in Comparative Examples 1-10 are similar to those in Examples 1-10.

[0074] The test methods for the compressive strength, bond strength, dry density, and fire resistance limit of the coatings of Examples 1-10 and Comparative Examples 1-10 are as follows:

[0075] The compressive strength was tested according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar"; the tensile bond strength was tested according to JGJ144-2019 "Technical Standard for External Wall Insulation Engineering"; the dry density was tested according to GB 14907-2018 "Fireproof Coating for Steel Structures"; and the fire resistance limit was tested according to GB 14907-2018 "Fireproof Coating for Steel Structures".

[0076] Compressive strength: Hardened specimens with dimensions of 40*40*40mm were prepared according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar". The specimens were placed on a press and uniformly loaded at a rate of 2400 N / s until failure, and the pressure on the testing machine was recorded.

[0077] Tensile bond strength: In accordance with the requirements of JGJ144-2019 "Technical Standard for External Thermal Insulation Engineering", the prepared thermal insulation wall repair material slurry was applied to a 45mm thick thermal insulation board or concrete wall surface with a coating thickness of 8mm. The sample was then installed on a tensile testing machine with a tensile speed of 0.1mm / min, and the tensile force at failure was recorded.

[0078] Dry density: According to GB 14907-2018 "Fireproof Coatings for Steel Structures" standard, a thin layer of machine oil was first applied to the inner wall of a metal mold with dimensions of 70.7mm×70.7mm×70.7mm. The mixed coating was then poured into the mold, gently shaken, and tamped to smooth the surface. After basic drying and curing, the mold was removed. After the curing period under the specified environmental conditions, the mold was placed in an oven at (60±5)℃ for 48 hours, and then placed in a desiccator to cool to room temperature. The volume and mass of the specimens were measured using calipers and an electronic balance, and the dry density of each specimen was calculated using the formula ρ=m / v. The dry density result is expressed as the average value after removing gross errors from the five test values.

[0079] Fire resistance time: Specimens for fire resistance testing were prepared according to the requirements of GB 14907-2018 "Fire-retardant Coatings for Steel Structures". After 28 days of curing, the fire-retardant coated steel components were installed in a fire resistance testing furnace. Thermocouples were installed at the web and flanges to measure the average temperature of the unexposed surface of the steel components. The fire resistance testing furnace was then activated, and heating was performed according to the ISO 834 standard temperature rise curve. The temperature changes and deformation of the steel components were recorded. The test was terminated when the average temperature of the steel components reached the critical temperature of 540℃ or when the steel components lost their load-bearing capacity. The time from the start to the end of the test was recorded as the fire resistance time, expressed in minutes (min).

[0080] The main performance indicators of the coatings prepared according to the above performance testing methods are shown in Table 1.

[0081] Table 1 Main Performance Indicators of Coatings

[0082]

[0083]

[0084] As shown in Table 1, the experimental results of Example 1 and Comparative Example 1 indicate that the absence of wollastonite fibers significantly reduced the compressive strength, bond strength, and fire resistance limit of the coating. This may be because wollastonite fibers, as a reinforcing phase, can form a three-dimensional network structure in the coating, effectively improving the mechanical strength and toughness of the matrix. Without them, the coating's internal microstructure becomes loose, resulting in reduced load-bearing capacity and worsened thermal stability, thus affecting overall performance.

[0085] As shown in Table 1, the experimental results of Example 1 and Comparative Example 2 indicate that the absence of aluminum powder paste increases the dry density and reduces the fire resistance limit. This is because aluminum powder paste can undergo a foaming reaction in an alkaline environment, forming a porous insulating layer, reducing the coating density and enhancing the thermal barrier effect. Without it, the coating density increases, heat conduction accelerates, and the fire resistance deteriorates.

[0086] As shown in Table 1, the experimental results of Example 1 and Comparative Example 3 indicate that the absence of expanded graphite leads to a decrease in compressive strength and fire resistance limit, while increasing dry density. This is because expanded graphite expands upon heating in a fire to form a dense carbon layer, effectively blocking heat and oxygen and enhancing the expansion fireproof mechanism of the coating. Without it, the coating lacks this protective effect, resulting in a fragile structure and reduced thermal insulation performance.

[0087] As shown in Table 1, the experimental results of Example 1 and Comparative Example 4 indicate that the absence of vermiculite resulted in a decrease in compressive strength, bond strength, and fire resistance limit, while increasing dry density. This is because vermiculite, as an expanding mineral, expands in volume at high temperatures to fill pores, enhancing the thermal insulation and volume stability of the coating. Its absence weakens the coating's thermal buffering capacity, leading to performance degradation.

[0088] As shown in Table 1, the experimental results of Example 1 and Comparative Example 5 indicate that the refractory limit is reduced and the dry density is increased without the addition of dolomite. This is because the decomposition reaction of dolomite at high temperatures is endothermic, which can temporarily enhance the thermal buffering capacity. However, its absence damages the high-temperature resistance of the structure, thus reducing the refractory limit.

[0089] As shown in Table 1, the experimental results of Example 1 and Comparative Example 6 indicate that the absence of organically modified montmorillonite leads to a decrease in bond strength, a slight reduction in compressive strength and fire resistance limit, and little change in dry density. This is because organically modified montmorillonite improves the rheology and adhesion of the coating, enhancing its bonding performance with the substrate. Its absence deteriorates the coating's workability and adhesion, affecting its durability.

[0090] As shown in Table 1, the experimental results of Example 1 and Comparative Example 7 indicate that the absence of zinc borate has little impact on the conventional mechanical properties of the coating, but it does lead to a slight decrease in its fire resistance limit. This suggests that zinc borate mainly contributes to the fire resistance of the system through its role in promoting char formation and glass phase formation at high temperatures, rather than through its mechanical enhancement at very low temperatures.

[0091] As shown in Table 1, the experimental results of Example 1 and Comparative Example 8 indicate that an improper ratio of aluminum dihydrogen phosphate to magnesium oxide significantly reduced compressive strength, bond strength, and fire resistance limit, while increasing dry density. This is because the imbalanced ratio affects the hydration process of phosphate cement, leading to a less dense structure and increased shrinkage stress, thereby reducing mechanical properties and fire resistance durability.

[0092] As shown in Table 1, the experimental results of Example 1 and Comparative Example 9 indicate that an improper ratio of aluminum dihydrogen phosphate to magnesium oxide leads to a decrease in compressive strength, bond strength, and refractory limit, while increasing dry density. This is because excessive aluminum dihydrogen phosphate may result in excessive acidity, inhibiting the hydration reaction balance and forming a fragile structure. Conversely, a lack of adequate magnesium oxide prevents the formation of stable bonds, affecting overall performance.

[0093] As shown in Table 1, the experimental results of Example 1 and Comparative Example 10 indicate that the absence of aluminum powder paste, expanded graphite, and vermiculite resulted in a decrease in compressive strength and bond strength, a significant increase in dry density, and a substantial reduction in fire resistance. This is because the lack of various expanding components prevents the coating from forming an effective expansion insulation system at high temperatures, leading to rapid heat conduction. The lack of a porous structure and char layer protection further deteriorates the overall fire resistance and mechanical strength.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-volume-stability phosphate fire-retardant coating, characterized in that, It is composed of the following raw materials in parts by weight: 1-5 parts aluminum dihydrogen phosphate, 1-4 parts magnesium oxide, 0.1-0.3 parts wollastonite fiber, 0.1-1 parts aluminum powder paste, 1-3 parts vermiculite, 0.1-1 parts dolomite, 0.1-0.5 parts organically modified montmorillonite, 0.1-0.5 parts zinc borate, and 0.1-0.3 parts expanded graphite; In the preparation process, magnesium oxide, vermiculite, dolomite, organically modified montmorillonite, zinc borate, and expanded graphite are first premixed to obtain a mixture; then aluminum dihydrogen phosphate is dissolved in an appropriate amount of water and wollastonite fiber and aluminum powder paste are added and stirred thoroughly to obtain a mixed solution. The mixed solution is ultrasonically treated until there is no agglomeration; finally, the mixture is added to the mixed solution to obtain a slurry.

2. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The aluminum dihydrogen phosphate contains 31-33% P2O5, 6-7.5% Al2O3, and has a pH of 1.3-1.

5.

3. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The magnesium oxide has a particle size of 1-5 μm, a purity of 85%-92%, and an activity content of ≥95%.

4. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The wollastonite fibers have a length of 100-300μm, an aspect ratio of 10:1-15:1, and a heat resistance temperature ≥1000℃.

5. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The aluminum powder paste has a solid content of ≥65% and a gas evolution rate of ≥85% within 40 minutes in an alkaline solution.

6. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The vermiculite has a particle size of 80-150μm, an expansion ratio of ≥10 times, and an initial expansion temperature of 200-300℃.

7. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The dolomite contains ≥95% CaMg(CO3)2 and has a decomposition temperature of 350-750℃.

8. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The organically modified montmorillonite has an interlayer spacing of 2.5-3.5 nm and an organic modifier content of 15-35 wt%.

9. The high volume stability phosphate fire-retardant coating as described in claim 1, characterized in that, The zinc borate contains 37-40% ZnO and 45-48% B2O3, and has a decrystallization temperature ≥300℃; the expanded graphite has an initial expansion temperature of 200-220℃ and an expansion volume ≥150mL / g.

10. The application of the high volume stability phosphate fire-retardant coating according to any one of claims 1-9, characterized in that, The coating is applied to the surface of the substrate using high-pressure airless spraying, with the film thickness controlled at 2-3 mm.

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