A magnesium phosphate fire-resistant composite coating based on industrial solid waste and a preparation method thereof

Abstract

The application discloses a magnesium phosphate fire-resistant composite coating based on industrial solid wastes and a preparation method thereof, and belongs to the technical field of building materials and solid waste resource utilization. The magnesium phosphate fire-resistant composite coating is prepared from the following raw materials in parts by weight: 40-60 parts of magnesium phosphate cement, 15-55 parts of fly ash, 8-15 parts of expanded graphite, 5-9 parts of nano silicon dioxide, 3-6 parts of ceramic fiber, 5-12 parts of ammonium polyphosphate, 2-5 parts of silane coupling agent and 15-30 parts of water. The magnesium phosphate cement is prepared from the following raw materials in parts by weight: 60-180 parts of burnt magnesia, 20-60 parts of potassium dihydrogen phosphate, 5-15 parts of borax, 13-39 parts of phosphogypsum and 2-6 parts of sodium lignosulfonate. The magnesium phosphate fire-resistant composite coating has the characteristics of high-value utilization of solid wastes, doubled fire resistance, no wastewater and waste gas emission in the production process, low cracking coefficient, good bonding performance and the like, and meets the sustainable development concept of green environmental protection and low carbon.

Description

Technical Field

[0001] This invention belongs to the field of building materials and solid waste resource utilization technology, specifically relating to a magnesium phosphate fire-resistant composite coating based on industrial solid waste and its preparation method. Background Technology

[0002] Among various disasters, fire is one of the most frequent and widespread major disasters threatening public safety and social development. Its harm is characterized by suddenness, chain reaction, and persistent damage. Globally, the economic losses caused by building fires exceed hundreds of billions of US dollars every year, and problems such as steel structure softening and collapse, concrete cracking and failure, and fire spreading through exterior wall materials may occur.

[0003] In building fires, the most effective way to prevent fires is to directly spray fire-retardant coatings. However, traditional fire-retardant coatings are difficult to meet the standards for high-rise buildings and green building materials due to problems such as toxicity release, poor durability, and high cost. Pure magnesium phosphate coatings have become a new type of inorganic substrate with their characteristics of fast hardening and high strength. However, they are expensive, brittle, and have weak thermal stress resistance. There is an urgent need to improve their comprehensive performance through low-cost modification.

[0004] The Chinese patent with publication number CN117736593A shows a magnesium phosphate fireproof and anti-corrosion coating, which adopts a gradient structure of magnesium phosphate cement fireproof and anti-corrosion coating, combining high temperature performance and anti-corrosion performance. However, it does not involve the utilization of industrial solid waste, resulting in low solid waste utilization rate, failure to achieve resource recycling and cost reduction, and difficulty in meeting the "dual carbon" target requirements.

[0005] Chinese patent CN112552015A discloses a magnesium phosphate fire-retardant coating, which uses ammonium dihydrogen phosphate and deburned magnesia as the main ingredients, and incorporates wollastonite and polypropylene fibers to improve high-temperature resistance and bonding strength. This patent uses only wollastonite, resulting in a single type of solid waste with a very small proportion. Furthermore, the high proportion of deburned magnesia in the raw materials leads to high costs, and the use of ammonium dihydrogen phosphate is accompanied by the release of ammonia, posing a threat to human health.

[0006] The Chinese patent with publication number CN114891381A discloses a magnesium phosphate cement-based anti-corrosion and fire-retardant coating that primarily uses chemical raw materials such as recalcined magnesium oxide, dihydrogen phosphate, and polyphosphate to achieve both anti-corrosion and fire-retardant functions. However, this patent does not incorporate the application of industrial solid waste products, resulting in higher raw material costs and insufficient environmental friendliness. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in the existing technology by providing a magnesium phosphate fire-resistant composite coating based on industrial solid waste and its preparation method. This invention uses potassium dihydrogen phosphate, borax, phosphogypsum, sodium lignosulfonate, and overburned magnesium oxide to prepare magnesium phosphate cement. Then, expanded graphite, fly ash, nano-silica, ceramic fiber, ammonium polyphosphate, and a silane coupling agent are added to prepare a magnesium phosphate fire-resistant composite coating that utilizes industrial solid waste for high-value purposes. The magnesium phosphate fire-resistant composite coating prepared by this invention features high-value utilization of solid waste, significantly enhanced fire resistance, no wastewater or waste gas emissions during production, a low cracking coefficient, and good adhesion. It realizes the integrated concept of "solid waste recycling - fire resistance enhancement - low-carbon emission reduction," conforming to the green, environmentally friendly, and low-carbon sustainable development concept.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A magnesium phosphate fire-resistant composite coating based on industrial solid waste is composed of the following raw materials in parts by weight:

[0010] 40-60 parts magnesium phosphate cement, 15-55 parts fly ash, 8-15 parts expanded graphite, 5-9 parts nano silica, 3-6 parts ceramic fiber, 5-12 parts ammonium polyphosphate, 2-5 parts silane coupling agent, and 15-30 parts water.

[0011] The magnesium phosphate cement is composed of the following raw materials in parts by weight: 60-180 parts of overburned magnesium oxide, 20-60 parts of potassium dihydrogen phosphate, 5-15 parts of borax, 13-39 parts of phosphogypsum, and 2-6 parts of sodium lignosulfonate.

[0012] Preferably, the overburned magnesium oxide is obtained by calcining magnesite at 1700℃ and then grinding it to a particle size of 10-100μm.

[0013] Preferably, the purity of potassium dihydrogen phosphate is ≥98%.

[0014] Preferably, the purity of borax is ≥98%.

[0015] Preferably, the phosphogypsum has a purity of ≥85% and a particle size of 20-30μm.

[0016] Preferably, the purity of sodium lignosulfonate is ≥98%.

[0017] Preferably, the fly ash is Grade I fly ash with a specific surface area ≥500m² / kg.

[0018] Preferably, the expanded graphite is of industrial grade, with a carbon content ≥98% and a sulfur content <0.5%.

[0019] Preferably, the nano-silica particles have a diameter of 10-30 nm and a SiO2 content of ≥99%.

[0020] Preferably, the ceramic fiber has a diameter of 3-5 μm and a length of 50-200 μm.

[0021] Preferably, the ammonium polyphosphate has a purity of ≥95% and a particle size of 10-20μm.

[0022] Preferably, the silane coupling agent is KH-550 with a purity ≥98%.

[0023] This invention also provides a method for preparing the above-mentioned magnesium phosphate fire-resistant composite coating based on industrial solid waste, comprising the following steps:

[0024] S1. Pretreatment of phosphogypsum:

[0025] ① Rinse the phosphogypsum with water to remove soluble phosphorus and fluorine (reduce the content by 30%-50%).

[0026] ② Calcination at 200-300℃ removes some of the water of crystallization, transforming it into hemihydrate gypsum (CaSO4·0.5H2O), thereby increasing the reactivity.

[0027] ③ Neutralize the residual acidity with lime (Ca(OH)2) to avoid reacting with the phosphate in magnesium phosphate to produce gas.

[0028] S2. Mix overburned magnesium oxide, potassium dihydrogen phosphate, borax, phosphogypsum, and sodium lignosulfonate to obtain a mixture. Pour the mixture into a mixer and stir slowly for 1-2 minutes to obtain magnesium phosphate cement powder.

[0029] S3. Then, add fly ash, nano silica, expanded graphite, and ammonium polyphosphate to the magnesium phosphate cement powder in sequence, and then stir quickly for 1 to 2 minutes to make the mixture evenly dispersed.

[0030] S4. Dissolve the silane coupling agent (KH-550) in water to obtain an additive solution.

[0031] S5. Add the additive solution to the mixture and stir quickly with a mixer for 1-2 minutes to obtain a uniform slurry.

[0032] S6. Add the ceramic fiber in three equal portions to the mixed slurry to avoid agglomeration. After adding all the ceramic fiber, continue to stir rapidly for 1-2 minutes to form a sprayable slurry, which is a magnesium phosphate fire-resistant composite coating based on industrial solid waste.

[0033] Preferably, the slow stirring speed is 135~145 r / min, and the fast stirring speed is 275~295 r / min.

[0034] Further, in step S3, the fly ash is modified as follows before use: sodium caseinate is dissolved in warm water at 40-55℃ to form a sodium caseinate solution with a mass concentration of 3-5%; sodium hydroxide is dissolved in water to prepare a sodium hydroxide solution with a pH of 12.3-12.8; fly ash is added to the sodium hydroxide solution, the mass ratio of the sodium hydroxide solution to the fly ash is 0.5-1:1, and the mixture is stirred at 1000-1200 r / min for 1-3 min, then the sodium caseinate solution, sucrose, and hydrogen peroxide are added, and the mixture is stirred at 1000-1200 r / min for 1-2 min to obtain a mixture, wherein the amount of sodium caseinate added is 0.3-0.5% of the mass of fly ash; the amount of sucrose added is 15-20% of the mass of sodium caseinate, and the amount of hydrogen peroxide added is 1.5-2% of the mass of the mixture; the mixture is allowed to stand for 1-3 h, dried, and passed through a 325 mesh sieve to obtain the modified fly ash.

[0035] The beneficial effects of this invention are as follows:

[0036] (1) This invention replaces part of the magnesium phosphate cement substrate with industrial solid waste products such as fly ash and phosphogypsum, which can significantly reduce raw material costs, increase the density of magnesium phosphate cement substrate, reduce the environmental pressure of solid waste pile-up, reduce carbon dioxide emissions, and realize the high-value utilization of solid waste. The composite flame retardant system adopts the synergistic effect of expanded graphite and ammonium polyphosphate to form a dual flame retardant mechanism of "gas phase (foamed insulation) + solidified phase (magnesium phosphate ceramic layer)", which effectively improves the fire resistance limit of the coating; the addition of nano silica can effectively fill microcracks and reduce porosity, and improve flexural strength; the addition of ceramic fiber can enhance the toughness of the coating, inhibit the propagation of microcracks, maintain structural stability in fire, and prevent the coating from softening and collapsing at high temperature; the addition of sodium lignosulfonate can prevent the flame retardant from agglomerating and optimize the uniformity of the slurry; the addition of silane coupling agent (KH-550) allows the amino group to react with the phosphate in magnesium phosphate, thereby improving the interfacial bonding strength of solid waste filler.

[0037] (2) In fires, the shortcomings of traditional fire-retardant coatings and pure magnesium phosphate coatings become increasingly apparent. This invention uses magnesium phosphate as a base material and incorporates industrial solid waste products such as fly ash and phosphogypsum into pure magnesium phosphate coatings, achieving high-value utilization of solid waste. This not only controls the setting time of magnesium phosphate coatings but also improves their density, significantly reducing the high cost of pure magnesium phosphate coatings, thus achieving the goals of cost reduction, environmental protection, and carbon emission reduction. In summary, the magnesium phosphate fire-resistant composite coating prepared by this invention features high-value utilization of solid waste, enhanced fire resistance, no wastewater or waste gas emissions during production, low cracking coefficient, and good adhesion. It realizes the three-in-one concept of "solid waste regeneration - fire resistance enhancement - low carbon emission reduction," conforming to the concept of green, environmentally friendly, and low-carbon sustainable development. Its application prospects in building fire prevention, comprehensive utilization of solid waste, and environmental economy are very broad. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments.

[0039] In the following examples and comparative examples: overburned magnesium oxide was obtained by calcining magnesite at 1700℃ and then grinding it to a particle size of 10-100μm; potassium dihydrogen phosphate purity ≥98%; borax purity ≥98%; phosphogypsum purity ≥85% and particle size of 20-30μm; sodium lignosulfonate purity ≥98%; fly ash was Grade I fly ash with a specific surface area ≥500m² / kg; expanded graphite was industrial grade with a carbon content ≥98% and a sulfur content <0.5%; nano silica had a particle size of 10-30nm and a SiO2 content ≥99%; ceramic fiber had a fiber diameter of 3-5μm and a length of 50-200μm; ammonium polyphosphate purity ≥95% and particle size of 10-20μm; silane coupling agent was KH-550 with a purity ≥98%; the stirring speed was 140r / min for rapid stirring and 280r / min for fast stirring.

[0040] Example 1:

[0041] The raw materials consist of the following components: 500g magnesium phosphate cement, 200g fly ash, 100g expanded graphite, 60g nano silica, 40g ceramic fiber, 80g ammonium polyphosphate, 20g silane coupling agent (KH-550), and 180g water.

[0042] Magnesium phosphate cement is composed of the following raw materials by weight: 300g of overburned magnesium oxide, 100g of potassium dihydrogen phosphate, 25g of borax, 65g of phosphogypsum, and 10g of sodium lignosulfonate.

[0043] The preparation method includes the following steps:

[0044] S1. Pretreatment of phosphogypsum:

[0045] ① Rinse with clean water to remove soluble phosphorus and fluorine (reduce content by 30%-50%).

[0046] ② Calcination at 250℃ removes some of the water of crystallization, transforming it into hemihydrate gypsum (CaSO4·0.5H2O), thereby increasing the reactivity.

[0047] ③ Neutralize the residual acidity with lime (Ca(OH)2) to avoid reacting with the phosphate in magnesium phosphate to produce gas.

[0048] S2. Mix overburned magnesium oxide, potassium dihydrogen phosphate, borax, phosphogypsum, and sodium lignosulfonate to obtain a mixture. Pour the mixture into a mixer and stir slowly for 2 minutes to obtain magnesium phosphate cement powder.

[0049] S3. Then, fly ash, nano silica, expanded graphite, and ammonium polyphosphate are added to the magnesium phosphate cement powder in sequence, and then the mixture is stirred quickly for 1 minute to make the mixture evenly dispersed.

[0050] S4. Dissolve the silane coupling agent (KH-550) in water to obtain an additive solution.

[0051] S5. Add the additive solution to the mixture and stir rapidly for 2 minutes to obtain a uniform slurry.

[0052] S6. Add the ceramic fiber in three equal portions to the mixed slurry to avoid agglomeration. After adding all the ceramic fiber, continue to stir rapidly for 1 minute to form a sprayable slurry, which is a magnesium phosphate fire-resistant composite coating based on industrial solid waste.

[0053] The magnesium phosphate fire-resistant composite coating prepared in this embodiment, based on industrial solid waste, has a density of 1.55 g / cm³. 3 It has a fire resistance limit of 150 minutes, a solid waste content of 26%, and a combustion performance rating of Class A (non-combustible).

[0054] Example 2:

[0055] The raw materials consist of the following components: 540g magnesium phosphate cement, 300g fly ash, 120g expanded graphite, 72g nano silica, 48g ceramic fiber, 96g ammonium polyphosphate, 24g silane coupling agent (KH-550), and 216g water.

[0056] Magnesium phosphate cement is composed of the following raw materials by weight: 324g of overburned magnesium oxide, 108g of potassium dihydrogen phosphate, 27g of borax, 70.2g of phosphogypsum, and 10.8g of sodium lignosulfonate.

[0057] The preparation method includes the following steps:

[0058] S1. Pretreatment of phosphogypsum:

[0059] ① Rinse with clean water to remove soluble phosphorus and fluorine (reduce content by 30%-50%).

[0060] ② Calcination at 300℃ removes some of the water of crystallization, transforming it into hemihydrate gypsum (CaSO4·0.5H2O), thereby increasing the reactivity.

[0061] ③ Neutralize the residual acidity with lime (Ca(OH)2) to avoid reacting with the phosphate in magnesium phosphate to produce gas.

[0062] S2. Mix overburned magnesium oxide, potassium dihydrogen phosphate, borax, phosphogypsum, and sodium lignosulfonate to obtain a mixture. Pour the mixture into a mixer and stir slowly for 1 minute to obtain magnesium phosphate cement powder.

[0063] S3. Add fly ash, nano silica, expanded graphite, and ammonium polyphosphate to the magnesium phosphate cement powder in sequence, and then stir quickly for 2 minutes to disperse the mixture evenly.

[0064] S4. Dissolve the silane coupling agent (KH-550) in water to obtain an additive solution.

[0065] S5. Add the additive solution to the mixture and stir rapidly for 1 minute to obtain a uniform slurry.

[0066] S6. Add the ceramic fiber in three equal portions to the mixed slurry to avoid agglomeration. After adding all the ceramic fiber, continue to stir rapidly for 2 minutes to form a sprayable slurry, which is a magnesium phosphate fire-resistant composite coating based on industrial solid waste.

[0067] The magnesium phosphate fire-resistant composite coating prepared in this embodiment, based on industrial solid waste, has a density of 1.50 g / cm³. 3 It has a fire resistance limit of 138 minutes, a solid waste content of 31%, and a combustion performance rating of Class A (non-combustible).

[0068] Example 3:

[0069] The raw materials consist of the following components: 600g magnesium phosphate cement, 450g fly ash, 150g expanded graphite, 90g nano silica, 60g ceramic fiber, 120g ammonium polyphosphate, 30g silane coupling agent (KH-550), and 270g water.

[0070] Magnesium phosphate cement is composed of the following raw materials by weight: 360g of overburned magnesium oxide, 120g of potassium dihydrogen phosphate, 30g of borax, 78g of phosphogypsum, and 12g of sodium lignosulfonate.

[0071] The preparation method includes the following steps:

[0072] S1. Pretreatment of phosphogypsum:

[0073] ① Rinse with clean water to remove soluble phosphorus and fluorine (reduce content by 30%-50%).

[0074] ② Calcination at 300℃ removes some of the water of crystallization, transforming it into hemihydrate gypsum (CaSO4·0.5H2O), thereby increasing the reactivity.

[0075] ③ Neutralize the residual acidity with lime (Ca(OH)2) to avoid reacting with the phosphate in magnesium phosphate to produce gas.

[0076] S2. Mix overburned magnesium oxide, potassium dihydrogen phosphate, borax, phosphogypsum, and sodium lignosulfonate to obtain a mixture. Pour the mixture into a mixer and stir slowly for 1 minute to obtain magnesium phosphate cement powder.

[0077] S3. Add fly ash, nano silica, expanded graphite, and ammonium polyphosphate to the magnesium phosphate cement powder in sequence, and then stir quickly for 2 minutes to disperse the mixture evenly.

[0078] S4. Dissolve the silane coupling agent (KH-550) in water to obtain an additive solution.

[0079] S5. Add the additive solution to the mixture and stir rapidly for 1 minute to obtain a uniform slurry.

[0080] S6. Add the ceramic fiber in three equal portions to the mixed slurry to avoid agglomeration. After adding all the ceramic fiber, continue to stir rapidly for 2 minutes to form a sprayable slurry, which is a magnesium phosphate fire-resistant composite coating based on industrial solid waste.

[0081] The magnesium phosphate fire-resistant composite coating prepared in this embodiment, based on industrial solid waste, has a density of 1.45 g / cm³. 3 It has a fire resistance limit of 120 minutes, a solid waste content of 35%, and a combustion performance rating of Class A (non-combustible).

[0082] Example 4:

[0083] The raw materials consist of the following components: 600g magnesium phosphate cement, 570g fly ash, 150g expanded graphite, 90g nano silica, 60g ceramic fiber, 120g ammonium polyphosphate, 30g silane coupling agent (KH-550), and 300g water.

[0084] Magnesium phosphate cement is composed of the following raw materials by weight: 360g of overburned magnesium oxide, 120g of potassium dihydrogen phosphate, 30g of borax, 78g of phosphogypsum, and 12g of sodium lignosulfonate.

[0085] The preparation method includes the following steps:

[0086] S1. Pretreatment of phosphogypsum:

[0087] ① Rinse with clean water to remove soluble phosphorus and fluorine (reduce content by 30%-50%).

[0088] ② Calcination at 300℃ removes some of the water of crystallization, transforming it into hemihydrate gypsum (CaSO4·0.5H2O), thereby increasing the reactivity.

[0089] ③ Neutralize the residual acidity with lime (Ca(OH)2) to avoid reacting with the phosphate in magnesium phosphate to produce gas.

[0090] S2. Mix overburned magnesium oxide, potassium dihydrogen phosphate, borax, phosphogypsum, and sodium lignosulfonate to obtain a mixture. Pour the mixture into a mixer and stir slowly for 1 minute to obtain magnesium phosphate cement powder.

[0091] S3. Dissolve sodium caseinate in warm water at 50°C to form a sodium caseinate solution with a mass concentration of 4%; dissolve sodium hydroxide in water to prepare a sodium hydroxide solution with a pH of 12.5; add fly ash to the sodium hydroxide solution, wherein the mass ratio of sodium hydroxide solution to fly ash is 0.8:1, stir at 1200 r / min for 2 min, then add sodium caseinate solution, sucrose and hydrogen peroxide, stir at 1200 r / min for 1 min to obtain a mixture, wherein the amount of sodium caseinate added is 0.4% of the mass of fly ash; the amount of sucrose added is 16% of the mass of sodium caseinate, and the amount of hydrogen peroxide added is 1.8% of the mass of the mixture; let the mixture stand for 2 h, dry it, and pass it through a 325 mesh sieve to obtain modified fly ash; add the modified fly ash, nano silica, expanded graphite and ammonium polyphosphate sequentially to magnesium phosphate cement powder, and then stir rapidly for 2 min to disperse the mixture evenly.

[0092] S4. Dissolve the silane coupling agent (KH-550) in water to obtain an additive solution.

[0093] S5. Add the additive solution to the mixture and stir rapidly for 1 minute to obtain a uniform slurry.

[0094] S6. Add the ceramic fiber in three equal portions to the mixed slurry to avoid agglomeration. After adding all the ceramic fiber, continue to stir rapidly for 2 minutes to form a sprayable slurry, which is a magnesium phosphate fire-resistant composite coating based on industrial solid waste.

[0095] The magnesium phosphate fire-resistant composite coating prepared in this embodiment, based on industrial solid waste, has a density of 1.50 g / cm³. 3 It has a fire resistance limit of 157 minutes, a solid waste content of 40%, and a combustion performance rating of Class A (non-combustible).

[0096] Comparative Example 1:

[0097] Mass of each component of raw materials: 500g magnesium phosphate cement, 200g fly ash, 100g expanded graphite, 60g nano silica, 40g ceramic fiber, 80g ammonium polyphosphate, and 180g water.

[0098] Magnesium phosphate cement is composed of the following raw materials by weight: 300g of overburned magnesium oxide, 100g of potassium dihydrogen phosphate, 25g of borax, 65g of phosphogypsum, and 10g of sodium lignosulfonate.

[0099] Compared with Example 1, Comparative Example 1 differs in that the raw material components do not contain silane coupling agents, while the mass ratios of the remaining components are the same as in Example 1. The preparation method is the same as in Example 1.

[0100] Compared to Example 1, the magnesium phosphate fire-resistant composite coating provided in this comparative example lacks a silane coupling agent. The molecular structure of the silane coupling agent (KH-550) contains amino groups. ) and siloxane ( ), amino ( ) can react with phosphates in MPC, siloxane ( After hydrolysis, it bonds with the hydroxyl groups (-OH) on the surface of fly ash / phosphogypsum, forming a "chemical bridge". Without silane, the interfacial bonding relies solely on mechanical interlocking and physical adsorption, which leads to a significant decrease in the interfacial bonding ability of the coating and makes it prone to interfacial delamination.

[0101] The magnesium phosphate fire-resistant composite coating prepared in this comparative example based on industrial solid waste was found to have a density of 1.55 g / cm³. 3 It has a fire resistance limit of 128 minutes, a solid waste content of 26%, and a combustion performance rating of Class A (non-combustible).

[0102] Comparative Example 2:

[0103] Mass of each component of raw materials: 540g magnesium phosphate cement, 300g fly ash, 120g expanded graphite, 48g ceramic fiber, 96g ammonium polyphosphate, 24g silane coupling agent (KH-550), and 216g water.

[0104] Magnesium phosphate cement is composed of the following raw materials by weight: 324g of overburned magnesium oxide, 108g of potassium dihydrogen phosphate, 27g of borax, 70.2g of phosphogypsum, and 10.8g of sodium lignosulfonate.

[0105] Compared to Example 2, Comparative Example 2 differs in that it does not contain nano-silica in its raw material components, while the remaining components and their mass ratios are the same as in Example 2. The preparation method is the same as in Example 2.

[0106] Compared to Example 2, the magnesium phosphate fire-resistant composite coating provided in this comparative example lacks nano-silica. Without nano-silica, the increased porosity of the coating leads to increased thermal conductivity and deterioration of fire resistance. Furthermore, the internal pores cannot be effectively filled, resulting in significantly worsened mechanical properties. Consequently, the high-temperature stability and density of the coating are reduced.

[0107] The magnesium phosphate fire-resistant composite coating prepared in this comparative example based on industrial solid waste was found to have a density of 1.50 g / cm³. 3 It has a fire resistance limit of 117 minutes, a solid waste content of 31%, and a combustion performance rating of Class A (non-combustible).

[0108] Comparative Example 3:

[0109] The raw materials consist of the following components: 600g magnesium phosphate cement, 450g fly ash, 150g expanded graphite, 90g nano silica, 120g ammonium polyphosphate, 30g silane coupling agent (KH-550), and 270g water.

[0110] Magnesium phosphate cement is composed of the following raw materials by weight: 360g of overburned magnesium oxide, 120g of potassium dihydrogen phosphate, 30g of borax, 78g of phosphogypsum, and 12g of sodium lignosulfonate.

[0111] Compared to Example 3, Comparative Example 3 differs in that it does not contain ceramic fibers in its raw material components, while the remaining components and their mass ratios are the same as in Example 3. The preparation method is the same as in Example 3.

[0112] Compared to Example 3, the magnesium phosphate fire-resistant composite coating provided in this comparative example lacks ceramic fibers. Without ceramic fibers, the coating exhibits brittleness, with cracks penetrating directly through the coating, significantly affecting its crack resistance and toughness. Ceramic fibers possess high-temperature resistance, which can suppress the high-temperature shrinkage of the coating; their absence would affect the high-temperature stability of the coating.

[0113] The magnesium phosphate fire-resistant composite coating prepared in this comparative example based on industrial solid waste was found to have a density of 1.45 g / cm³. 3 It has a fire resistance limit of 102 min, a solid waste content of 36%, and a combustion performance rating of Class A (non-combustible).

[0114] Comparative Example 4

[0115] Mass of each component of raw materials: 600g magnesium phosphate cement, 450g fly ash, 150g expanded graphite, 90g nano silica, 60g ceramic fiber, 120g ammonium polyphosphate, 30g silane powder, and 270g water.

[0116] Magnesium phosphate cement is composed of the following raw materials by weight: 360g of overburned magnesium oxide, 120g of potassium dihydrogen phosphate, 30g of borax, 78g of phosphogypsum, and 12g of sodium lignosulfonate.

[0117] Compared with Example 3, the difference in Comparative Example 4 is that the silane coupling agent in the raw material components is replaced with silane powder, while the mass ratio of the remaining components is the same as in Example 4. The preparation method is the same as in Example 4.

[0118] Compared to Example 3, the magnesium phosphate fire-resistant composite coating provided in this comparative example uses silane powder instead of silane coupling agent. Silane powder lacks the bifunctional reactive properties of silane coupling agents and cannot form an effective bond between the solid waste filler and the magnesium phosphate substrate. It can only rely on physical filling, resulting in a significant weakening of the interfacial bonding strength between the solid waste filler and the magnesium phosphate substrate. This leads to delamination and peeling of the coating. Due to the reduced interfacial bonding strength, cracks are easily generated inside the coating under thermal stress in high-temperature fire environments, and these cracks propagate rapidly along the weak interface, reducing the fire resistance limit. Furthermore, silane coupling agents can improve the dispersibility of solid waste fillers in the coating, while silane powder cannot achieve a similar effect, potentially leading to agglomeration of the solid waste fillers and affecting the uniformity and performance stability of the coating.

[0119] The magnesium phosphate fire-resistant composite coating prepared in this comparative example based on industrial solid waste was found to have a density of 1.55 g / cm³. 3 It has a fire resistance limit of 103 min, a solid waste content of 35%, and a combustion performance rating of Class A (non-combustible).

[0120] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be defined by the claims.

Claims

1. A magnesium phosphate fire-resistant composite coating based on industrial solid waste, characterized in that, Composed of the following raw materials in parts by weight: 40-60 parts magnesium phosphate cement, 15-55 parts fly ash, 8-15 parts expanded graphite, 5-9 parts nano silica, 3-6 parts ceramic fiber, 5-12 parts ammonium polyphosphate, 2-5 parts silane coupling agent, and 15-30 parts water. The magnesium phosphate cement is composed of the following raw materials in parts by weight: 60-180 parts of overburned magnesium oxide, 20-60 parts of potassium dihydrogen phosphate, 5-15 parts of borax, 13-39 parts of phosphogypsum, and 2-6 parts of sodium lignosulfonate. The preparation method of the magnesium phosphate fire-resistant composite coating based on industrial solid waste includes the following steps: S1. Pretreatment of phosphogypsum: First, rinse the phosphogypsum with clean water, then calcine it at a low temperature of 200-300℃ to remove some of the water of crystallization until it is converted into hemihydrate gypsum, and then neutralize the residual acidity with lime; S2. Mix overburned magnesium oxide, potassium dihydrogen phosphate, borax, phosphogypsum, and sodium lignosulfonate to obtain a mixture. Pour the mixture into a mixer and stir slowly for 1-2 minutes to obtain magnesium phosphate cement powder. S3. Dissolve sodium caseinate in warm water at 40-55℃ to form a sodium caseinate solution with a mass concentration of 3-5%; dissolve sodium hydroxide in water to prepare a sodium hydroxide solution with a pH of 12.3-12.8; add fly ash to the sodium hydroxide solution, wherein the mass ratio of sodium hydroxide solution to fly ash is 0.5-1:1, stir at 1000-1200 r / min for 1-3 min, then add the sodium caseinate solution, sucrose, and hydrogen peroxide, and stir at 1000-1200 r / min for 1-2 min. After n, a mixture is obtained, wherein the amount of sodium caseinate added is 0.3-0.5% of the mass of fly ash; the amount of sucrose added is 15-20% of the mass of sodium caseinate; and the amount of hydrogen peroxide added is 1.5-2% of the mass of the mixture. After the mixture is allowed to stand for 1-3 hours, it is dried and passed through a 325-mesh sieve to obtain modified fly ash. Modified fly ash, nano silica, expanded graphite, and ammonium polyphosphate are added sequentially to magnesium phosphate cement powder, and then the mixture is stirred rapidly for 1-2 minutes to disperse the mixture evenly. S4. Dissolve the silane coupling agent in water to obtain an additive solution; S5. Add the additive solution to the mixture and stir quickly for 1-2 minutes to obtain a uniform slurry; S6. Add ceramic fibers in three equal portions to the mixed slurry. After all the ceramic fibers have been added, continue to stir rapidly for 1-2 minutes to form a sprayable slurry, which is a magnesium phosphate fire-resistant composite coating based on industrial solid waste.

2. The magnesium phosphate fire-resistant composite coating based on industrial solid waste according to claim 1, characterized in that: The over-burned magnesium oxide is obtained by calcining magnesite at 1700℃ and then grinding it to a particle size of 10-100μm.

3. The magnesium phosphate fire-resistant composite coating based on industrial solid waste according to claim 1, characterized in that: The purity of the potassium dihydrogen phosphate is ≥98%; the purity of the borax is ≥98%; the purity of the phosphogypsum is ≥85%, and the particle size is 20-30μm; the purity of the sodium lignosulfonate is ≥98%; the fly ash is Grade I fly ash, with a specific surface area ≥500m² / kg; the expanded graphite is industrial grade, with a carbon content ≥98% and a sulfur content <0.5%; the nano-silica has a particle size of 10-30nm and a SiO2 content ≥99%; the ceramic fiber has a fiber diameter of 3-5μm and a length of 50-200μm; and the ammonium polyphosphate has a purity ≥95% and a particle size of 10-20μm.

4. The magnesium phosphate fire-resistant composite coating based on industrial solid waste according to claim 1, characterized in that: The silane coupling agent is KH-550 with a purity ≥98%.

5. The magnesium phosphate fire-resistant composite coating based on industrial solid waste according to claim 1, characterized in that: The slow stirring speed is 135~145 r / min, and the fast stirring speed is 275~295 r / min.