Method for preparing fireproof coating from fly ash waste and application thereof

Abstract

The application discloses a method for preparing fireproof paint from fly ash waste and application of the fireproof paint, and belongs to the technical field of paint. The method comprises the following steps: pretreating fly ash waste by using a double-frequency plasma; treating the pretreated fly ash by using two-step acid immersion to obtain supernatant containing metal ions and precipitate rich in silicon and aluminum; oxidizing and solidifying the supernatant containing metal ions and the precipitate rich in silicon and aluminum to obtain metal oxides; preparing the metal oxides into a suspension, homogenizing and solvent-thermal crystallizing the suspension to obtain metal oxide nanoparticles, and surface-modifying the metal oxide nanoparticles to obtain metal oxide nanofluid; and compounding the metal oxide nanofluid with a coating base to obtain the fireproof paint. The paint meets the A2-level non-combustible standard of combustion performance.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a method for preparing fire-retardant coatings from fly ash waste and its application. Background Technology

[0002] With the acceleration of urbanization and the improvement of building standards, the fire safety and durability of building facades are becoming increasingly prominent issues. Currently, most building exterior wall insulation materials pose safety hazards such as flammability and aging / detachment. For example, traditional polystyrene board insulation materials have insufficient fire resistance, with a combustion performance rating of only B2. They are prone to fire spread and have poor durability; after 2000 hours of QUV aging testing, 60% of the products showed significant powdering and detachment. In actual use, cracking and detachment occur after 3-5 years of use, resulting in high maintenance costs. On average, repainting is required every 5 years, and the cost of a single maintenance for high-rise buildings can reach 300 yuan / m². 2 .

[0003] my country possesses abundant coal resources and occupies an important position in global coal production. Coal mining, washing, combustion, and coal chemical processes generate a large amount of coal-based solid waste, mainly including coal gangue, fly ash, and gasification slag. Currently, the comprehensive utilization rate of these solid wastes remains low, with stockpiling being the primary method of disposal. This not only occupies significant land resources but also makes them more susceptible to leaching into the aquatic environment through rainwater, as the heavy metals and harmful substances they contain are easily released. Because fly ash contains abundant metal oxides, such as iron, aluminum, and titanium, these valuable resources are not yet fully utilized. To address these issues, researchers have begun to focus on improving the comprehensive utilization rate of coal-based solid waste, achieving its resource recovery and harmless treatment.

[0004] This paper proposes a method that can address the shortcomings of current building facades in terms of fire resistance while reducing the negative environmental impact of coal mine waste. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and application for preparing fire-retardant coatings from fly ash waste, which addresses the shortcomings of the prior art.

[0006] Compared with the prior art, the present invention has the following advantages:

[0007] 1. This invention uses metal oxides extracted from fly ash through plasma activation, acid leaching separation, and nano-processing as raw materials. After nano-fluidization treatment, these oxides are used as fillers and mixed with the coating substrate. The resulting coating meets the A2 non-combustible standard for combustion performance. After 2000 hours of accelerated aging testing, the adhesion is ≥1.5 MPa. After 3000 hours of accelerated aging testing, the coating color difference ΔE <2.0, exhibiting high weather resistance. This invention can specifically address the current problems of flammability and short lifespan of coatings.

[0008] 2. The fire-retardant coating obtained by the method of preparing fire-retardant coating from fly ash waste of the present invention has good thermal stability and structural integrity, and the initial decomposition temperature, residual carbon rate, weather resistance and high temperature expansion rate are significantly improved.

[0009] 3. The fire-retardant coating prepared by the method of the present invention using fly ash waste has high viscosity stability, protective performance and stability in humid environments, long-term corrosion resistance, and good gravity settling stability and long-term storage stability.

[0010] 4. The method for preparing fire-retardant coatings from fly ash waste of the present invention includes increasing the content of amorphous silicon and aluminum components in the waste through high-energy dual-frequency plasma activation, with an amorphous enhancement rate as high as 111.9%. The metal oxide nanoparticles prepared by the method including high-energy dual-frequency plasma activation have a particle size of 20-50 nm and a specific surface area of ​​200-260 m². 2 / g.

[0011] 5. The method for preparing fire-retardant coatings from fly ash waste in this invention relies on fly ash waste. The coatings prepared have high fire resistance, can significantly reduce production costs and facade maintenance costs, and have broad application value.

[0012] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0013] Figure 1 This is a BJH pore size distribution diagram of the metal oxide nanoparticles in Example 1;

[0014] Figure 2 The nitrogen adsorption-desorption isotherm of metal oxide nanoparticles in Example 1;

[0015] Figure 3 Thermogravimetric analysis curves of the coatings used for spraying in Example 1 are shown.

[0016] Figure 4 This is a schematic diagram of the rheological properties test results of the coating for spraying in Example 1;

[0017] Figure 5 This is a schematic diagram of the contact angle test results of the coating used for spraying in Example 1;

[0018] Figure 6 This is a schematic diagram of the stability evaluation results of the coating for spraying in Example 1;

[0019] Figure 7 The image shows the appearance morphology of the coating material used for scraping in Example 1.

[0020] Figure 8Here is an SEM image of the coating material for application in Example 1;

[0021] Figure 9 The image shows the appearance of the coating after the high-temperature expansion performance test of the coating used for spraying in Example 1. Detailed Implementation

[0022] The technical solution will now be clearly and completely described with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.

[0024] In the following description, the terms “including,” “containing,” “having,” and “containing” are open-ended terms, meaning that they include but are not limited to.

[0025] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0026] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] The technical principle adopted in this invention is as follows: based on plasma activation, acid leaching separation and nano-processing, metal oxides are extracted from fly ash, and then dispersed with surfactants to form stable metal oxide nanofluids. These nanofluids are then combined with a coating substrate to prepare a fireproof coating. The coating can rapidly expand and carbonize at high temperatures to form a dense heat insulation layer, which has excellent flame retardant and heat insulation properties and exterior facade application functions.

[0029] A method for preparing fire-retardant coatings from fly ash waste includes:

[0030] Dual-frequency plasma is used for pretreatment of fly ash waste;

[0031] Pretreated fly ash is treated using a two-step acid leaching process to obtain a supernatant containing metal ions and a precipitate rich in silicon and aluminum; the metal ions in the supernatant include Fe. 3+ Ca 2+ and / or Mg 2+ The silicon-aluminum-rich precipitate includes Al(OH)3, silica gel and / or Ti(OH)4, and the silicon-aluminum-rich precipitate contains a silicon-aluminum phase and undissolved titanium.

[0032] Metal oxides are obtained by oxidizing and solidifying a supernatant containing metal ions and a silicon-aluminum-rich precipitate. The oxidation and solidification of the supernatant containing metal ions includes precipitation and calcination, and the oxidation and solidification of the silicon-aluminum-rich precipitate includes sedimentation and heat treatment. The metal oxides include α-Fe2O3, γ-Al2O3 and anatase TiO2.

[0033] The metal oxide was formulated into a suspension, homogenized and solvothermal crystallized to obtain metal oxide nanoparticles, and then surface modified to obtain metal oxide nanofluids.

[0034] Fire-retardant coatings are obtained by combining metal oxide nanofluids with coating substrates.

[0035] Using waste fly ash as raw material, metal oxides are obtained through dual-frequency plasma pretreatment, two-step acid leaching, and curing. Subsequently, the oxides are homogenized, solvothermal crystallized, and modified to obtain metal oxide nanofluids. After mixing with the coating substrate, the resulting coating can be applied to the surface of steel structures, exterior wall panels, or tunnel linings. After curing at room temperature or heat, a dense coating is formed. Under high temperature, the coating can rapidly form an expanding and dense carbon layer, which blocks flame propagation and heat conduction, achieving fire resistance and flame retardancy of building surfaces, with significantly improved flame retardant performance and structural stability.

[0036] By utilizing the excellent thermal stability and catalytic carbonization properties of metal oxide nanofluids, and working synergistically with the coating substrate, heat absorption, smoke suppression, and pyrolysis resistance can be achieved.

[0037] In some embodiments, the dual-frequency plasma power density is 15 W / cm². 3 The carrier gas and its volume ratio are Ar:H2 = 85%:15%, the carrier gas flow rate is 8L / min, and the processing time is 30 minutes; the frequency of the dual-frequency plasma electromagnetic wave is 40kHz / 2.45GHz.

[0038] By introducing high-energy dual-frequency plasma activation, the silicon-aluminum bonds in fly ash are broken and recombined, increasing the proportion of amorphous silicon-aluminum phase. The amorphous silicon-aluminum content is increased from 42wt% to 89wt%, with an amorphous enhancement rate of up to 111.9%. This invention effectively increases the amorphous silicon-aluminum content by pretreating fly ash waste with dual-frequency plasma, laying a highly active foundation for subsequent metal element extraction and nanofluid preparation.

[0039] In some embodiments, the two-step acid leaching includes first leaching in hydrochloric acid and then leaching in hydrofluoric acid, both of which are performed with ultrasonic assistance. In some preferred embodiments, the ultrasonic frequency for ultrasonic assistance is 40 kHz, the power is 500 W, the temperature for hydrochloric acid leaching is 80°C, the leaching time is 8 hours, and the temperature for hydrofluoric acid leaching is 60°C, the leaching time is 1 hour.

[0040] Preferably, the method of the present invention further includes immersing the pretreated fly ash in a hydrochloric acid solution and performing ultrasonic oscillation. Ultrasonic oscillation can effectively promote the leaching of metal ions by hydrochloric acid, further destroy the aggregated structure, and improve the release efficiency of metal ions in the leachate. Furthermore, hydrofluoric acid leaching under ultrasonic-assisted conditions can effectively destroy the solid-phase silicon-aluminum crystal structure, converting the solid-phase silicon-aluminum into soluble H₂SiF₆ and AlF₃; the precipitate is Al(OH)₃, silica gel, and Ti(OH)₄. More preferably, the method further includes centrifugation after hydrochloric acid leaching, and leaching the residue obtained by centrifugation with hydrofluoric acid. Centrifugation ensures thorough liquid-solid separation, providing a stable and high-purity intermediate product for subsequent silicon-aluminum phase extraction and nanomaterial preparation.

[0041] In some embodiments, the precipitation and calcination include: adjusting the pH of the supernatant containing metal ions to 3.5, allowing the precipitate to settle, washing and drying the precipitate, and then calcining it at 600°C to obtain α-Fe₂O₃; the supernatant containing metal ions is a solution containing Fe 3 + Ca 2+ and / or Mg 2+ The hydrochloric acid solution was neutralized by adding ammonia water to bring the pH to 3.5. By strictly controlling the pH of the precipitation and solidification system to 3.5, the system did not reach the critical pH for calcium and magnesium ions to precipitate as hydroxides, thus achieving precipitation of only Fe(OH)3 and Ca. 2+ and Mg 2+It remains stably present in the supernatant in ionic form; and / or, the sedimentation and heat treatment includes: dispersing the silica-alumina-rich precipitate in deionized water, centrifuging to obtain a lower sediment and an upper silica dispersion; in some preferred embodiments, the centrifugation rate is 3000 rpm; further, the present invention also includes recovering calcium and magnesium components to achieve resource recovery of the remaining metal in the system after iron precipitation, specifically including: processing the system after the precipitate is removed by complexation separation, membrane separation or ion exchange separation;

[0042] The lower sediment is redispersed in deionized water, the pH is adjusted to 9-10, stirred and mixed, and centrifuged to obtain a supernatant and a precipitated solid phase. The precipitated solid phase is vacuum dried to obtain Al(OH)3, and Al(OH)3 is calcined to obtain γ-Al2O3. In some preferred embodiments, the centrifugation rate is 3000 rpm, the vacuum drying temperature of the precipitated solid phase is 80°C, the pressure is -0.08 mPa, and the drying time is 6 h. In some preferred embodiments, Al(OH)3 is washed before calcination. In some preferred embodiments, the calcination temperature of Al(OH)3 is 1000°C.

[0043] The pH of the supernatant was adjusted to neutral, centrifuged to obtain a precipitate, and the precipitate was vacuum dried to obtain Ti(OH)4. The Ti(OH)4 was placed in a hydrogen peroxide solution, the pH was adjusted to 8, and the mixture was allowed to stand to form TiO(OH)2 precipitate. The precipitate was then calcined to obtain anatase TiO2. In some preferred embodiments, the centrifugation rate was 3000 rpm, the vacuum drying temperature was 80°C, the pressure was -0.08 mPa, and the drying time was 6 h. In some preferred embodiments, the mass of the hydrogen peroxide solution was 5 times that of Ti(OH)4. In some preferred embodiments, the TiO(OH)2 precipitate was calcined at 500°C for 2 h.

[0044] In some embodiments, preparing a suspension of metal oxides includes ball milling and mixing the metal oxides, dispersing them in a mixed solvent of an organic phase and an aqueous phase, adding a dispersant, and dispersing under pulsed ultrasound. In some specific embodiments, the mixed solvent of the organic phase and the aqueous phase is an aqueous ethanol solution. In some preferred embodiments, the mass ratio of the ball-milled metal oxides to the mixed solvent of the organic phase and the aqueous phase is 3:7. In some preferred embodiments, the dispersant is sodium polyacrylate. In some preferred embodiments, the pulse duration of the pulsed ultrasound is 2s on and 1s off, the ultrasonic frequency of the pulsed ultrasound is 20kHz, and the power is 800W. And / or, the homogenization includes homogenization at 150mPa, and the PDI of the homogenized system is <0.2. High-pressure homogenization is used to further refine the nanoparticles in the preparation of the primary nano-suspension, improving the nanoparticle density. Uniform distribution and stability; and / or, the reaction temperature of solvothermal crystallization is 180℃, and the reaction time is 12h; obtaining nanoparticles by solvothermal crystallization can effectively promote particle crystallization and obtain nanoparticles with stable morphology; and / or, the surface modification is carried out in a modifying solvent, the modifying solvent is anhydrous ethanol or deionized water, and the modifier is gum arabic; in some preferred embodiments, the mass ratio of metal oxide nanoparticles to modifying solvent is (1~3):20; by adding a surface modifier for hydrophobic modification, especially when the surface modifier is gum arabic, the surface functionalization modification of metal oxide nanoparticles is achieved, improving the hydrophobicity and interfacial bonding ability of the particles, endowing the nanofluid with good dispersion stability and rapid composite performance with the coating matrix, and obtaining a hydrophobic nanofluid that can be rapidly composited with the coating matrix. Ball milling and mixing break the primary particles through continuous mechanical and chemical grinding, promote the uniform composite of multiple components, and provide particle-level basic support for the subsequent high stable dispersion and excellent thermal properties of the nanofluid.

[0045] In some embodiments, the mass ratio of metal oxide nanofluid to coating substrate is (3-8):100. In some specific embodiments, the method for obtaining a fire-retardant coating by combining a metal oxide nanofluid with a coating substrate includes: mixing the metal oxide nanofluid with the coating substrate, adding a surfactant, a dispersing stabilizer, a defoamer, and a wetting agent to obtain a composite system; stirring and dispersing the composite system; adding a charring agent and an expansion agent; and dispersing or ultrasonically breaking down the mixture to obtain a fire-retardant coating; the surfactant includes gum arabic, dodecyl glucoside, and / or tea saponin; stirring and dispersing the composite system to promote the full dispersion of the metal oxide nanoparticles and the formation of a stable composite system with the coating substrate; and achieving uniform dispersion of the metal nanoparticles in a high-viscosity substrate through the synergistic effect of the surfactant and the dispersing stabilizer; the charring agent includes one or more of graphite powder, expanded graphite, and silica gel powder, and the expansion agent includes zinc borate and / or silicate; the charring agent can rapidly expand to form a dense carbon layer under fire conditions, and zinc borate can decompose and release moisture when heated, promoting further densification of the carbon layer, working synergistically with the metal oxide nanofluid to impart excellent flame-retardant and heat-insulating properties and structural stability to the coating.

[0046] On the other hand, an application of the aforementioned fire-retardant coating is provided, comprising applying the fire-retardant coating by scraping, brushing, or spraying onto a substrate to be coated, resulting in a fire-retardant coating with a thickness ≥3mm. The coating of this invention can be applied to the surface of steel structures, exterior wall panels, or tunnel linings, forming a dense coating after room temperature or heat curing. Under high temperature, this coating can rapidly form an expanding, dense carbon layer, blocking flame propagation and heat conduction, thus achieving fire resistance and flame retardancy of the building surface. The nano-metal oxides in the coating, through their excellent thermal stability and catalytic char formation ability, synergistically achieve functions such as heat absorption, smoke suppression, and pyrolysis resistance, significantly improving the overall flame retardant performance and structural stability.

[0047] Prior to the application for this invention, a series of experiments were conducted. Some of the experimental results are listed below to provide a more detailed description of the invention. The following is a detailed description in conjunction with the embodiments.

[0048] Example 1

[0049] This embodiment provides a method for preparing fire-retardant coatings from fly ash waste, including:

[0050] Step 1: Pre-treat 500g of fly ash waste using dual-frequency plasma to obtain pre-treated fly ash, specifically including:

[0051] The dual-frequency plasma power density is set to 15 W / cm². 3The carrier gas and its volume ratio were Ar:H2 = 85%:15%, the carrier gas flow rate was maintained at 8L / min, and the treatment time was 30 minutes; the frequency of the dual-frequency plasma electromagnetic wave was 40kHz / 2.45GHz; the amorphous silicon-aluminum content in the pretreated fly ash was 89wt%.

[0052] The preliminary analysis of the fly ash waste composition and content is as follows: SiO2 52.3wt%, Al2O3 28.1wt%, Fe2O3 8.4wt%, CaO 3.2wt%, MgO 1.5wt%, TiO2 1.1wt%, and other impurities totaling 5.4wt%; of which the content of amorphous silicon and aluminum is 42wt%.

[0053] Step 2: A two-step acid leaching process is used to treat the pretreated fly ash, yielding a supernatant containing metal ions and a precipitate rich in silicon and aluminum. Specifically, this includes:

[0054] Step 201: Immerse the pretreated fly ash in a 3 mol / L hydrochloric acid solution at a mass ratio of 1:8. Perform ultrasonic leaching at 80°C with a frequency of 40 kHz and a power of 500 W for 8 hours. Centrifuge the leached system to obtain a supernatant and residue. The supernatant contains Fe. 3+ Ca 2+ and / or Mg 2+ The residue is rich in silicon-aluminum phase and undissolved titanium;

[0055] Step 202: The residue from step 201 is placed in 10% hydrofluoric acid at a mass ratio of 1:6. The mixture is then ultrasonically treated at 60°C with a frequency of 40kHz and a power of 500W for 1 hour to obtain a solution system rich in fluorine complexes. The pH is adjusted to neutral with sodium hydroxide solution to obtain a precipitate rich in silicon and aluminum. Under ultrasonic assistance, the solid-phase silicon and aluminum crystal structure is destroyed by hydrofluoric acid, converting the solid-phase silicon and aluminum into soluble H₂SiF₆ and AlF₃. TiF₆ is also present in the system. 2- A fluorine complex ion system was cured under neutral conditions to obtain a silicon-aluminum-rich precipitate; the silicon-aluminum-rich precipitate consisted of Al(OH)3, silica gel, and Ti(OH)4.

[0056] Step 3: The supernatant containing metal ions and the silicon-aluminum-rich precipitate are oxidized and solidified to obtain metal oxides. This includes precipitation and calcination of the supernatant containing metal ions, and stepwise sedimentation and heat treatment of the silicon-aluminum-rich precipitate. Specifically, this includes:

[0057] Step 301: Adjust the pH of the supernatant from step 201 to 3.5 with ammonia. Allow the solution to stand to allow the precipitate to settle. Maintain the pH of the system at 3.5 during the sedimentation process until no more precipitate forms. Wash and dry the precipitate, then calcine it at 600℃ for 2 hours to obtain α-Fe₂O₃. The pH of the system is 3.5, which is below the critical pH for calcium and magnesium ions to precipitate as hydroxides. 3+ The preferential precipitation is Fe(OH)3, Ca 2+ and Mg 2+ It remains stable in the supernatant in ionic form; after removing the precipitate, the system is separated by membrane separation to recover the calcium and magnesium components.

[0058] Step 302: The silica-alumina-rich precipitate described in step 202 is subjected to stepwise sedimentation to obtain silica gel, Al(OH)3, and Ti(OH)4 sequentially, specifically including:

[0059] Step 3021: Disperse the silica-alumina-rich precipitate described in step 202 in deionized water, stir at room temperature for 30 min, then centrifuge at 3000 rpm for 5 min, collect the lower sediment and the upper silica dispersion, transfer the silica dispersion to an 80℃ vacuum drying oven, dry at -0.08 mPa for 6 h to obtain dried silica gel.

[0060] Step 3022: The lower sediment is redispersed in deionized water, the pH of the system is adjusted to 9.5 with ammonia, stirred evenly at room temperature, and centrifuged at 3000 rpm for 5 min to obtain supernatant and sedimented solid phase. The sedimented solid phase is dried in a vacuum drying oven at 80℃ at -0.08 mPa for 6 h to obtain Al(OH)3.

[0061] Step 3023: Adjust the pH of the supernatant to neutral with hydrochloric acid, centrifuge at 3000 rpm for 5 min to obtain a precipitate, and dry the precipitate in a vacuum drying oven at 80℃ and -0.08 mPa for 6 h to obtain Ti(OH)4.

[0062] Step 303: Wash the Al(OH)3 to remove surface fluoride ions, and calcine it at 1000℃ for 2 hours to obtain γ-Al2O3;

[0063] Step 304: Ti(OH)₄ is placed in a 10wt% hydrogen peroxide solution at a mass ratio of 1:5. The mixture is stirred at room temperature until homogeneous, and the pH is adjusted to 8. The mixture is allowed to stand to form TiO(OH)₂ precipitate until no further precipitate forms. The system is then transferred to a 3000rpm centrifuge and centrifuged for 5 minutes to separate the solid and liquid phases. The TiO(OH)₂ precipitate is calcined at 500℃ for 2 hours to obtain anatase TiO₂. The solution containing titanium-rich fluorine complexes is oxidized with hydrogen peroxide to enhance the reactivity and precipitation stability of Ti species in the system, thereby reducing the concentration of titanium subions (TiO₂). 3+ ) and complexed ions (Ti 4+ It is stabilized by oxidation to TiO. 2+ At pH 8, it hydrolyzes to form TiO(OH)2, which is then calcined to obtain anatase TiO2.

[0064] Step 4: Using the aforementioned metal oxide as the main raw material, prepare metal oxide nanofluids, specifically including:

[0065] Step 401: Mix α-Fe2O3, γ-Al2O3 and anatase TiO2 as described in Step 3 at a mass ratio of 4:3:3, and dry grind them in a high-energy ball mill to reduce the particle size to less than 100 nm. During the dry grinding process, zirconium oxide grinding balls are used as the grinding media, the ball-to-material ratio is 20:1, the rotation speed is 400 rpm, and the process is carried out under a nitrogen protective atmosphere for 6 hours.

[0066] Step 402: Disperse the ball-milled powder in an ethanol-water solution at a mass ratio of 3:7, add a dispersant, and perform dispersion treatment for 30 minutes under pulsed ultrasound at a frequency of 20kHz and a power of 800W to obtain a primary nano-suspension; the ethanol-water solution is a mixture of anhydrous ethanol and water at a volume ratio of 1:1; the concentration of the dispersant in the primary nano-suspension is 0.5wt%, and the dispersant is sodium polyacrylate dispersant; the pulse time is 2 seconds on and 1 second off; the sodium polyacrylate dispersant was purchased from Aladdin, is a white powder, product number P434407, and has a weight-average molecular weight of 2100;

[0067] Step 403: Place the primary nano suspension in a 150 mPa high-pressure homogenizer and circulate it until PDI < 0.2 to obtain a homogenized suspension; the number of cycles is 5.

[0068] Step 404: Transfer the homogenized suspension to a hydrothermal reactor and react at 180°C for 12 hours. After the reaction system is naturally cooled to room temperature, it is centrifuged at 3000 rpm for 5 minutes to obtain metal oxide nanoparticles.

[0069] Step 405: Disperse the metal oxide nanoparticles in anhydrous ethanol at a mass ratio of 1:20, add gum arabic to obtain a modified system, reflux the modified system at 70°C for 4 hours, centrifuge and wash to obtain metal oxide nanofluid; the concentration of gum arabic in the modified system is 5 wt%; the gum arabic was purchased from Aladdin, item number A108975;

[0070] Step 5: Mix with the coating substrate to obtain the fire-retardant coating, specifically including:

[0071] Step 501: The metal oxide nanofluid is slowly added to the epoxy resin at a mass ratio of 5:100 to obtain a matrix material containing nanofluid; the molecular weight of the epoxy resin is 500-700.

[0072] Step 502: Add the surfactant gum arabic, the dispersant and stabilizer sodium polyacrylate, the defoamer silicone, and the wetting agent polyoxyethylene alkyl ether to the matrix material containing nanofluids to obtain a composite system; in the composite system, the mass percentage of gum arabic is 0.5 wt%, the mass percentage of sodium polyacrylate is 0.5 wt%, the mass percentage of silicone is 0.2 wt%, and the mass percentage of polyoxyethylene alkyl ether is 0.3 wt%; the molecular weight of sodium polyacrylate is 4500-5000; the silicone is Simethicone 30, purchased from Dow Corning; the polyoxyethylene alkyl ether is AEO-9, purchased from Guoguang Chemical;

[0073] Step 503: Stir and disperse the composite system in a high-speed disperser at 2000 rpm for 30 minutes to obtain the dispersed composite system;

[0074] Step 504: Add charring agent expanded graphite and expansion aid zinc borate to the dispersed composite system to obtain a flame retardant system; in the flame retardant system, the concentration of charring agent is 15wt% and the concentration of expansion aid is 10wt%; the expanded graphite is purchased from Hebei Guangyou and is EG-20 expanded graphite.

[0075] Furthermore, this embodiment also provides a method for obtaining coatings with corresponding flame retardant grades by adjusting the component ratio in a flame retardant system. When the concentration of expanded graphite in the flame retardant system is 10 wt% and the concentration of zinc borate is 5 wt%, the flame retardant grade of the coating is B1. When the concentration of expanded graphite in the flame retardant system is 15 wt% and the expansion agent is silicate with a concentration of 8 wt%, the flame retardant grade of the coating is A2. The silicate is ALFIBER-WG silicate, purchased from Shandong Jinshi High Temperature Materials Co., Ltd.

[0076] Step 505: The flame retardant system is dispersed and stirred or ultrasonically crushed to obtain a coating. In this embodiment, when the dispersion and stirring time is 30 min, the coating viscosity is 8000-12000 mPa·s, which can be used as a scraping coating. When the dispersion and stirring time is 20 min, the coating viscosity is 3000-5000 mPa·s, which can be used as a brush coating. When the ultrasonic crushing power is 600 W, the frequency is 20 kHz, the ultrasonic time is 30 min, and the operation mode is intermittent operation, i.e., 2 s ultrasonic and 1 s intermittent, the coating viscosity is 500-1000 mPa·s, which can be used as a spray coating. The dispersion and stirring are carried out in a high-speed disperser at a dispersion and stirring rate of 2000 rpm.

[0077] Example 2

[0078] This embodiment provides a method for preparing a fire-retardant coating from fly ash waste, which is the same as in Embodiment 1, except that it further includes constructing an Al2O3 coating layer on the surface of the cured metal oxide. The coating layer has a thickness of 3-5 nm, and the construction method includes:

[0079] The powder from ball milling in step 401 was dispersed in anhydrous ethanol. An aluminum source solution was added at a mass ratio of 1:5 (powder to aluminum source). The mixture was stirred at room temperature for 30 minutes, then deionized water was added dropwise. Stirring continued for 2 hours to allow hydrolysis and deposition. The mixture was filtered, and the filtered material was dried under vacuum at 80°C for 6 hours, followed by calcination at 300°C for 2 hours to complete the construction of an Al2O3 coating layer on the metal oxide surface. The aluminum source solution was an isopropanol solution containing aluminum isopropoxide, with a concentration of 0.1 mol / L. The mass of the anhydrous ethanol was 10 times the mass of the ball-milled powder, and the mass of the deionized water was 3 times the mass of the ball-milled powder. Using the particles with the Al2O3 coating layer as raw material, a fire-retardant coating was prepared through steps 402-505.

[0080] Using an isopropanol solution of aluminum isopropoxide as the aluminum source solution, a coating layer is formed by hydrolysis and deposition on the surface of metal oxide particles. Heat treatment densifies this coating layer, constructing a continuous and stable Al2O3 coating layer on the surface of the metal oxide particles, thus improving the thermal stability and interfacial compatibility of the particles. In particular, when the mass of anhydrous ethanol is controlled to be 10 times the mass of the ball-milled powder, and the mass of deionized water added is 3 times the mass of the ball-milled powder, both sufficient dispersion of the aluminum source and effective control of the hydrolysis rate can be achieved, preventing particle agglomeration and resulting in uniform coating.

[0081] Example 3

[0082] This embodiment provides a method for preparing fire-retardant coatings from fly ash waste, which is the same as in Embodiment 1, except that...

[0083] Step 405 involves dispersing the metal oxide nanoparticles in deionized water at a mass ratio of 1:20, adding gum arabic to obtain a modified system, and then treating the modified system with ultrasound at a frequency of 20 kHz and a power of 800 W for 30 minutes to obtain a preliminarily dispersed nanofluid; the concentration of gum arabic in the modified system is 1 wt%.

[0084] Step five involves slowly adding an aqueous epoxy emulsion to the initially dispersed nanofluid at a mass ratio of 5:100 to obtain a matrix material containing the nanofluid; the aqueous epoxy emulsion has a solid content of 50%, was purchased from BASF, and its model number is [model number missing]. 678;

[0085] Sodium polyacrylate, organosilicon, and polyoxyethylene alkyl ether were added to the matrix material containing nanofluids, and the mixture was stirred at room temperature for 30 min to obtain an aqueous composite system. In the composite system, the mass percentage of sodium polyacrylate was 0.5 wt%, the mass percentage of organosilicon was 0.3 wt%, and the mass percentage of polyoxyethylene alkyl ether was 0.5 wt%.

[0086] Expanded graphite and silicate are added to the aqueous composite system to obtain an aqueous flame retardant system; the concentration of expanded graphite in the aqueous flame retardant system is 15 wt%, and the concentration of silicate is 8 wt%.

[0087] The water-based flame retardant system was placed in a high-speed dispersant and dispersed and stirred at 2000 rpm for 20 minutes to obtain a water-based environmentally friendly coating with a viscosity of 3000-5000 mPa·s that can be used for brushing.

[0088] Example 4

[0089] This embodiment provides a method for preparing fire-retardant coatings from fly ash waste, which is the same as in Embodiment 1, except that in step 405, the mass ratio of metal oxide nanoparticles to anhydrous ethanol is 3:20.

[0090] Comparative Example 1

[0091] This comparative study examines the effect of metal oxide nanofluids on coating performance, specifically providing a coating that does not contain metal oxide nanofluids. The preparation method is the same as steps 502-505 of Example 1, except that step 502 involves adding the surfactant gum arabic, the dispersant and stabilizer sodium polyacrylate, the defoamer organosilicon, and the wetting agent polyoxyethylene alkyl ether to the epoxy resin to obtain a composite system.

[0092] Comparative Example 2

[0093] This comparative study examines the effect of modification on coating performance. The preparation method is the same as in Example 1, except that step 405 is not included. Step 501 involves slowly adding the metal oxide nanoparticles described in step 404 to the epoxy resin at a mass ratio of 5:100 to obtain a matrix material containing metal oxide nanoparticles.

[0094] Comparative Example 3

[0095] This comparative study examines the effect of nanofluidization on coating performance. The preparation method is the same as in Example 1, except that metal oxide nanofluidization is not performed, i.e., steps 402 to 405 are not performed. Step 501 involves slowly adding the powder after ball milling in step 401 to the epoxy resin at a mass ratio of 5:100 to obtain a matrix material containing metal oxide particles.

[0096] Performance Evaluation

[0097] 1.1 Physical properties of metal oxide nanoparticles

[0098] The BJH pore size distribution of the metal oxide nanoparticles prepared in step 404 of Example 1 is shown in the figure below. Figure 1 As shown, the nitrogen adsorption-desorption isotherms are as follows: Figure 2 As shown, the metal oxide nanoparticles have a particle size of 20–50 nm and a specific surface area of ​​200–260 m². 2 / g.

[0099] 1.2 Thermogravimetric Analysis

[0100] The thermal decomposition behavior of the coating used in Example 1 was tested using a thermogravimetric analyzer (TGA). The test procedure was as follows: the coating was sprayed onto the surface of an aluminum alloy sheet with a thickness of 300 μm, dried and cured at room temperature to form a uniform coating, and then the entire coating was peeled off, and samples were cut for thermogravimetric analysis. The thermogravimetric test was conducted under a nitrogen atmosphere (flow rate 50 mL / min), with a heating rate of 10 °C / min and a temperature range of 30–800 °C. The results showed that the initial decomposition temperature of the coating in Example 1 was 312 °C (e.g., ...). Figure 3 As shown in the figure, it exhibits good thermal stability and structural integrity. In comparison, the initial decomposition temperature of the coating sample in Example 2 was 340℃, further improving the heat resistance compared to the coating in Example 1. The initial decomposition temperatures of Comparative Examples 1, 2, and 3 were 276℃, 259℃, and 243℃, respectively. Compared to the comparative examples, the initial decomposition temperature of Example 1 increased by approximately 28%, demonstrating significantly enhanced stability and non-flammability under high-temperature environments. The above results indicate that the fire-retardant coating of the present invention possesses excellent thermal decomposition stability, meets the technical requirements of GB 8624-2012 "Classification Standard for Burning Performance of Building Materials and Products", and is suitable for building protection, energy storage equipment shells, and high-temperature fire protection scenarios.

[0101] The coating formed by the spraying paint in Example 1 had a carbon residue rate of 39.2% at 800°C. The coating formed by the spraying paint in Example 4 had a carbon residue rate of 38.7% at 800°C. The coating of Comparative Example 1 had a carbon residue rate of 24.2% at 800°C. Compared with the conventional product of Comparative Example 1, the carbon residue rate of the paint of the present invention is increased by 60%, indicating that the paint of the present invention can effectively reduce the high-temperature oxidation weight loss rate.

[0102] 1.3 Viscosity Test

[0103] The rheological properties of the spray coating of Example 1 under standard conditions at 25°C were tested using an Anton Paar rotational viscometer. The results showed that the viscosity of the system remained stable at 2500–3500 cP during the standing time of 0–24 h. Figure 4 As shown, it exhibits good construction adaptability and flow stability, and can meet the performance requirements of commonly used construction processes such as high-pressure airless spraying.

[0104] 1.4 Contact Angle Test

[0105] The contact angle of the coating used for spraying in Example 1 was tested, and the test results are as follows: Figure 5 As shown, the coating forms a significant contact angle with water droplets, exhibiting a certain degree of hydrophobicity. It demonstrates protective performance and stability in humid environments, indicating that the coating of this invention meets the waterproof and moisture-proof requirements of building fireproof coatings in various application scenarios.

[0106] 1.5 Corrosion Test

[0107] The corrosivity of the coating for spraying in Example 1 was tested according to GB / T 9274, wherein the corrosive medium was a sodium chloride solution with a mass percentage of 5%, and the coating was soaked at room temperature for 240 hours. The test results showed that after soaking for 240 hours, the adhesion was >90%, and there was no rust, bubbles, or peeling on the coating surface, indicating that the coating of the present invention has excellent corrosion resistance and environmental stability.

[0108] 1.6 Stability Evaluation

[0109] Gravity settling stability tests were conducted on the coating material for spraying in Example 1. The test method included: placing the coating material in a transparent, sealed container, allowing it to stand at room temperature for a preset time, and observing and recording the settling. The results showed that the coating material did not show obvious stratification within 30 days, although there was a small amount of sediment. This sediment was easily restored to a uniformly dispersed state by gentle manual shaking. The sediment was collected and calculated. The results showed that the volume of the sediment was less than 5% of the initial volume of the coating material, indicating that the coating material of the present invention has good gravity settling stability and long-term storage stability, meeting the requirements for storage stability in practical applications. The results are as follows: Figure 6 As shown.

[0110] 1.7 Appearance Characteristics

[0111] The coating used in Example 1 was applied to the substrate surface using a scraper to form a 3mm thick coating. After drying and curing, the coating was measured and observed. The results showed that the coating thickness was uniform, the coefficient of variation was <5%, the porosity was 82%, the surface was dense and smooth, and there were no bubbles, cracks, or peeling. The overall coating had a uniform and aesthetically pleasing black appearance. (See photograph). Figure 7 As shown, the scanning electron microscope image of the coating after drying is as follows: Figure 8 As shown, the coating of the present invention has excellent workability and film appearance quality, and is suitable for fire protection of building exterior walls and structures.

[0112] 1.8 Flame retardant performance test

[0113] Flame retardant performance tests were conducted on the coatings used in each embodiment and comparative example. The test method was based on GB 8624-2012 "Classification of Combustion Performance of Building Materials and Products", and the flame propagation rate and smoke production were determined by the small chamber combustion method. Fire resistance limit tests were also conducted on the coatings used in each embodiment and comparative example. The test method was based on GB / T 9978 "Test Methods for Fire Resistance of Building Components", and the structural integrity and insulation retention time of the samples were measured by heating in a fire-resistant furnace. The test results showed that the coating of Example 1 achieved a fire resistance limit of 3 hours, meeting the A2 non-combustible standard, which is more than 30% higher than the fire resistance limit of the coatings of Comparative Examples 1-3, demonstrating significantly improved high-temperature resistance and overall flame retardant performance. The coating of Example 2 met the A2 non-combustible standard. The water-based environmentally friendly coating of Example 3 achieved a fire resistance limit of 2.8 hours, possessing A1 non-combustible characteristics. The coating of Example 4 achieved a fire resistance limit exceeding 3 hours.

[0114] The accelerated aging performance test results show that after 2000 hours of accelerated aging test (QUV aging test), the coating formed by the paint used in Example 1 still exhibits good adhesion with an adhesion strength ≥1.5 MPa, indicating that the paint of the present invention can specifically solve the defects of current paints, such as flammability and short service life. After 3000 hours of accelerated aging test, the coating formed by the paint of Example 1 has a color difference ΔE <2.0, and the color remains unchanged, indicating that the paint of the present invention can meet the requirement of a color retention period of 10 years+. The coating of Example 2 retains more than 90% of its fire resistance after 5000 hours of QUV aging test, and the coating of Example 3 can withstand 8000 hours of QUV aging, equivalent to at least 25 years of natural aging, showing significantly improved weather resistance.

[0115] 1.9 High-Temperature Expansion Characteristics

[0116] The high-temperature expansion properties of the coating used in Example 1 were tested using a cone calorimeter according to ISO 5660, with a thermal radiation power of 35 kW / m². 2 After testing, the coating appearance is as follows Figure 9 As shown in the figure. The results show that the coating formed by the coating of Example 1 has an expansion rate of 20 times at 800°C, which is more than 50% higher than the expansion rate of the coatings of Comparative Examples 1 to 3. Observation of the expanded coating reveals that its structure is dense and complete, effectively blocking heat transfer and oxygen penetration. This indicates that the coating of the present invention has protective performance in high-temperature environments such as fires.

Claims

1. A method for preparing fire-retardant coatings from fly ash waste, characterized in that, include: Dual-frequency plasma is used for pretreatment of fly ash waste; Pretreated fly ash was treated using a two-step acid leaching process to obtain a supernatant containing metal ions and a precipitate rich in silicon and aluminum. The supernatant containing metal ions and the silicon-aluminum-rich precipitate are respectively oxidized and solidified to obtain metal oxides; the oxidation and solidification of the supernatant containing metal ions includes precipitation and calcination, and the oxidation and solidification of the silicon-aluminum-rich precipitate includes sedimentation and heat treatment; the metal oxides include α-Fe2O3, γ-Al2O3 and anatase TiO2. The metal oxide is formulated into a suspension, homogenized and solvothermal crystallized to obtain metal oxide nanoparticles, and then surface modified to obtain metal oxide nanofluids; the surface modification is carried out in a modifying solvent, which is anhydrous ethanol or deionized water, and the modifier is gum arabic. Fire-retardant coatings are obtained by combining metal oxide nanofluids with coating substrates.

2. The method for preparing fire-retardant coatings from fly ash waste according to claim 1, characterized in that, The precipitation and calcination process includes: adjusting the pH of the supernatant containing metal ions to 3.5, allowing the precipitate to settle, washing and drying the precipitate, and then calcining it at 600°C to obtain α-Fe₂O₃; and / or, the precipitation and heat treatment includes: dispersing the silica-alumina-rich precipitate in deionized water, centrifuging it to obtain a lower precipitate and an upper silica dispersion; redispersing the lower precipitate in deionized water, adjusting the pH to 9-10, stirring and mixing, centrifuging it to obtain a supernatant and a precipitated solid phase, vacuum drying the precipitated solid phase to obtain Al(OH)₃, calcining Al(OH)₃ to obtain γ-Al₂O₃; adjusting the pH of the supernatant to neutral, centrifuging it to obtain a precipitate, vacuum drying the precipitate to obtain Ti(OH)₄, placing the Ti(OH)₄ in a hydrogen peroxide solution, adjusting the pH to 8, allowing it to settle to form TiO(OH)₂ precipitate, and calcining it to obtain anatase TiO₂.

3. The method for preparing fire-retardant coatings from fly ash waste according to claim 1, characterized in that, The dual-frequency plasma power density is 15 W / cm². 3 The carrier gas and its volume ratio are Ar:H2 = 85%:15%, the carrier gas flow rate is 8L / min, and the processing time is 30 minutes; the frequency of the dual-frequency plasma electromagnetic wave is 40kHz / 2.45GHz.

4. The method for preparing fire-retardant coatings from fly ash waste according to claim 1, characterized in that, The two-step acid leaching process includes first leaching in hydrochloric acid and then leaching in hydrofluoric acid, both of which are performed with ultrasonic assistance.

5. The method for preparing fire-retardant coatings from fly ash waste according to claim 1, characterized in that, Preparing a metal oxide suspension includes ball milling and mixing the metal oxides, dispersing them in a mixed solvent of an organic phase and an aqueous phase, adding a dispersant, and dispersing under pulsed ultrasound; and / or, the homogenization includes homogenization at 150 mPa, resulting in a PDI < 0.2 after homogenization; and / or, the solvothermal crystallization reaction temperature is 180 °C, and the reaction time is 12 h.

6. The method for preparing fire-retardant coatings from fly ash waste according to claim 5, characterized in that, The mass ratio of the metal oxide to the modified solvent after ball milling is (1~3):

20.

7. The method for preparing fire-retardant coatings from fly ash waste according to claim 1, characterized in that, The mass ratio of metal oxide nanofluid to coating substrate is (3~8):

100.

8. A method for preparing a fire-retardant coating using the method for preparing fire-retardant coatings from fly ash waste as described in claim 1, characterized in that, This includes applying the fire-retardant coating by scraping, brushing, or spraying onto the substrate to be coated, resulting in a fire-retardant coating with a thickness of ≥3mm.

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