Preparation method of layered aluminum triphosphate antirust pigment

Abstract

The invention discloses a preparation method of a layered aluminum triphosphate antirust pigment, and belongs to the technical field of design and synthesis of inorganic materials. The method comprises the following steps: S1, mixing an aluminum source compound and a phosphorus source compound in water at room temperature to form turbid liquid; s2, adding one or more structure-directing agents into the turbid liquid, and adjusting the pH value of the mixed liquid to 3.0-5.0; s3, putting the mixed solution into a high-pressure reaction kettle, and carrying out hydrothermal crystallization reaction for 7-13 hours at the pressure of 1-3 MPa and the temperature of 190-230 DEG C; and S4, filtering, washing and drying the reaction product to obtain the aluminum triphosphate anti-rust pigment with the layered structure. The method is simple in process, the product morphology is regular, and the layered pigment effectively improves the compactness and flatness of a coating in the anti-corrosion application process, has a synergistic effect with a chemical anti-rust effect, remarkably improves the protective performance of the coating and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of inorganic material design and synthesis technology, specifically to a method for preparing a layered aluminum tripolyphosphate anti-rust pigment. Background Technology

[0002] Aluminum tripolyphosphate, as an environmentally friendly and pollution-free rust-preventing pigment, has become an important alternative to traditional toxic rust-preventing pigments due to its absence of heavy metals such as lead and chromium and its excellent rust-preventing effect. Its rust-preventing mechanism mainly relies on the phosphate ions it releases in the presence of water. These ions react with iron ions on the surface of the metal substrate (such as iron) to form a dense, insoluble passivation film, thereby effectively blocking anodic corrosion current and inhibiting further corrosion of the metal.

[0003] Aluminum tripolyphosphate products prepared by traditional methods typically exhibit an irregular, amorphous particle morphology. This morphology presents inherent defects: irregular particles struggle to achieve effective directional alignment within the coating, potentially affecting the final coating's density, smoothness, and mechanical properties. Corrosive media can penetrate the coating relatively directly to reach the metal interface. Furthermore, the relatively limited specific surface area of ​​conventional morphologies may hinder the rate and efficiency of dissociation of corrosion-inhibiting ions in aqueous media, thus impairing the rapid development of its initial rust-preventive capabilities. In addition, the irregular particle morphology can sometimes lead to poor dispersibility in resin bases, making agglomeration more likely.

[0004] To improve the performance of aluminum tripolyphosphate, researchers have made various modification attempts, including doping with metal ions such as zinc and strontium to enhance its chemical activity, or using silicon dioxide, zinc oxide and other materials for surface coating to improve its early water resistance.

[0005] Chinese patent document “A method for preparing modified aluminum tripolyphosphate” (publication number: CN103525135B) describes an invention that uses aluminum tripolyphosphate as raw material and modifies it with one or more of zinc modifier, magnesium modifier, calcium modifier and silicon modifier. The aluminum tripolyphosphate and the modifier are mixed in water to form a slurry, which is then ground to obtain modified aluminum tripolyphosphate.

[0006] Chinese patent application document "Modified Aluminum Tripolyphosphate Rust-Inhibiting Pigment and its Preparation Method" (Publication No.: CN103468048A) specifies the following raw material components and weight parts: 100 parts aluminum tripolyphosphate, 20-50 parts zinc oxide, 30-300 parts powder containing 10-30% basic potassium aluminum sulfate, and 200-500 parts water. The modified aluminum tripolyphosphate rust-inhibiting pigment is prepared by changing the type and amount of filler without adding other fillers. A chemical modification reaction is then carried out to change the acidity of aluminum dihydrogen phosphate.

[0007] However, most of these methods focus on changing the chemical composition or surface state, without fundamentally altering the geometry of the particles, and thus contribute little to significantly enhancing the physical barrier properties of the coating.

[0008] The application of layered fillers in heavy-duty anti-corrosion coatings has proven that layered pigments can align parallel to the substrate surface in the coating, forming a dense physical barrier with overlapping layers. This significantly extends the diffusion path of corrosive media and substantially improves the coating's impermeability and durability. Therefore, developing a method for controllably preparing aluminum tripolyphosphate with a regular layered structure, combining the chemical passivation ability of aluminum tripolyphosphate with the excellent physical shielding properties of layered fillers, holds promise for developing synergistically effective high-performance anti-rust pigments. Summary of the Invention

[0009] To address the aforementioned shortcomings, this invention provides a method for preparing layered aluminum tripolyphosphate anti-rust pigments. By combining high-pressure hydrothermal treatment with structure-directing agents, the method solves the problems of irregular morphology, poor coating protection, and poor dispersibility of traditional aluminum tripolyphosphate pigments.

[0010] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0011] A method for preparing a layered aluminum tripolyphosphate anti-rust pigment includes the following steps:

[0012] S1. Disperse or dissolve the aluminum source compound in water, and add the phosphorus source compound under stirring at room temperature to form a suspension;

[0013] S2. Add a structure-directing agent to the suspension, stir to form a mixture, and adjust the pH value of the mixture with a pH adjuster;

[0014] S3. Place the mixture obtained in step S2 into a high-pressure reactor for hydrothermal crystallization reaction;

[0015] S4. The reaction product of step S3 is subjected to solid-liquid separation, washing and drying to obtain the layered aluminum tripolyphosphate anti-rust pigment.

[0016] Preferably, in step S1, the aluminum source compound is selected from at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum isopropoxide, boehmite, and industrial aluminum hydroxide.

[0017] Preferably, in step S1, the phosphorus source compound is selected from at least one of phosphoric acid and sodium tripolyphosphate; the molar ratio of the aluminum source compound to the phosphorus source compound is 1:(2.8~3.2) in Al / P.

[0018] Preferably, in step S2, the structure directing agent is one or more of the following: cationic surfactant, nonionic surfactant, organic acid, or urea.

[0019] Preferably, the cationic surfactant is hexadecyltrimethylammonium bromide; the nonionic surfactant is polyvinylpyrrolidone or polyethylene glycol; and the organic acid is citric acid.

[0020] Preferably, in step S2, the amount of the structure-directing agent added is 1% to 5% of the mass of the aluminum source compound.

[0021] Preferably, in step S2, the pH adjuster is ammonia, urea, sodium hydroxide, hydrochloric acid, or nitric acid; the pH value of the mixture is adjusted to 3.0~5.0.

[0022] Preferably, in step S3, the conditions for the hydrothermal crystallization reaction are: pressure 1-3 MPa, temperature 190-230°C, and reaction time 7-13 h.

[0023] Preferably, in step S3, the filling degree of the mixture in the high-pressure reactor is 60% to 85% of the effective volume of the reactor.

[0024] Preferably, in step S4, the washing includes washing with water and alcohol solvent in sequence; the drying is hot air drying.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] I. Innovate technological approaches to break through traditional limitations

[0027] This invention breaks through the existing approach of "emphasizing chemical composition while neglecting morphology control" in the preparation of aluminum tripolyphosphate, and constructs a novel synergistic technology scheme of structure-directing agents and high-pressure hydrothermal crystallization. Even when using hydrothermal methods, existing technologies do not utilize structure-directing agents to control crystal growth, resulting in products that are mostly irregular particles. This invention utilizes cationic / nonionic surfactants, organic acids, or urea as directing agents, leveraging their selective adsorption to different crystal faces to directionally inhibit the growth of high surface energy crystal faces and induce the formation of a regular layered structure. Simultaneously, the synergistic use of parameters such as 1-3 MPa high pressure, 190-230℃ temperature, and 60%-85% reactor filling provides sufficient thermodynamic driving force for directional crystal growth, avoiding impurity phases easily generated in atmospheric pressure processes, thus forming a unique technical feature distinct from traditional processes.

[0028] II. Addressing industry pain points and adapting to industry needs

[0029] Traditional aluminum tripolyphosphate coatings suffer from poor density, poor dispersion, and low initial rust prevention efficiency due to their irregular morphology. This invention addresses these shortcomings with targeted breakthroughs and strong practicality. Firstly, the layered pigments can be oriented and stacked parallel to the substrate within the coating, forming a dense physical barrier. This extends the penetration path of corrosive media, fills coating pores, and improves impermeability and mechanical strength, solving the problems of easy cracking and short protective lifespan of traditional coatings. Secondly, the layered structure reduces the tendency for particle agglomeration, ensuring uniform dispersion in the resin and avoiding uneven coating appearance and weak protective areas, thus guaranteeing stable rust prevention performance. Thirdly, the high specific surface area of ​​the layered structure accelerates phosphate ion dissociation, achieving a synergistic effect of physical shielding and chemical passivation. This solves the problems of slow initial rust prevention and weak long-term protection of traditional pigments, making it suitable for solvent-based, water-based, and other types of anti-corrosion coatings, applicable to heavy-duty anti-corrosion fields such as marine engineering and steel structures. Furthermore, the raw materials used in the process are common industrial products, the steps are simple, parameters are easy to control, and it can be scaled up industrially.

[0030] III. Reconstructing the rust prevention mechanism to achieve a technological leap.

[0031] In terms of technical concept, this invention breaks away from the inertia of existing technologies that only optimize chemical properties, achieving dual performance enhancement through morphology control. Technically, it solves three major pain points of traditional products in one go: the improved dispersibility brought by the layered structure indirectly enhances the chemical passivation effect; and the dual protection significantly improves the long-term corrosion resistance of the coating, exceeding conventional expectations. Furthermore, its "structure-guided high-pressure crystallization" principle can be extended to the preparation of other layered inorganic pigments, providing a general approach for morphology control of inorganic materials. Its technological radiation value is significant, promoting the green and high-performance development of the anti-corrosion coating industry. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the layered aluminum tripolyphosphate pigment sample Y-1 prepared in Example 1 of the present invention;

[0033] Figure 2 This is a scanning electron microscope (SEM) image of the layered aluminum tripolyphosphate pigment sample Y-2 prepared in Example 2 of the present invention;

[0034] Figure 3 This is a scanning electron microscope (SEM) image of sample D-1 prepared in Comparative Example 1;

[0035] Figure 4 This is a scanning electron microscope (SEM) image of sample D-2 prepared in Comparative Example 2. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0037] In this invention, a method for preparing a layered aluminum tripolyphosphate anti-rust pigment includes the following steps:

[0038] S1. Raw material mixing and suspension preparation: The aluminum source compound is dispersed or dissolved in water. Under room temperature and mechanical stirring conditions, the phosphorus source compound is slowly added to form a homogeneous suspension system. During this process, the feeding rate is controlled to avoid excessively high local concentrations that could lead to difficult-to-disperse precipitates.

[0039] S2. Structure Direction and pH Adjustment: Add a certain mass of structure directing agent to the suspension obtained in step S1. The mass of the structure directing agent is 1% to 5% of the mass of the aluminum source compound. Continue stirring to ensure that the structure directing agent is fully dispersed and adsorbed on the surface of the nascent particles or affects the solution environment, forming a mixture. Then, use a pH adjuster to precisely adjust the pH of the mixture to an acidic range of 3.0 to 5.0.

[0040] S3. Hydrothermal Crystallization Reaction: Transfer the pH-adjusted mixture from step S2 to a high-pressure reactor. Control the filling degree of the reactor (i.e., the percentage of the mixture volume to the effective volume of the reactor liner) between 60% and 85%. Conduct the hydrothermal crystallization reaction under pressure of 1–3 MPa and temperature of 190–230°C for 7–13 hours.

[0041] S4. Post-processing of the product: After the hydrothermal reaction is completed, the reactor is allowed to cool naturally to room temperature. Then, solid-liquid separation is carried out by suction filtration or pressure filtration. The obtained filter cake is washed repeatedly with a large amount of water 3-5 times, and then washed with anhydrous ethanol 1-2 times. Finally, the washed filter cake is placed in a hot air environment to dry for 2-4 hours, thus obtaining aluminum tripolyphosphate anti-rust pigment with a regular layered morphology.

[0042] The working mechanism of each step in this invention is as follows:

[0043] I. Raw material mixing and suspension preparation: laying the foundation for the reaction and ensuring the accuracy of element ratios

[0044] The selection and mixing of aluminum source compounds (aluminum nitrate, aluminum chloride, etc.) and phosphorus source compounds (phosphate, sodium tripolyphosphate) in step S1 are the core material basis for constructing aluminum tripolyphosphate crystal growth. The aluminum source provides aluminum ions required for crystal growth, and the phosphorus source provides phosphate ions. The two are fed at an Al / P molar ratio of 1:(2.8~3.2), which ensures that the concentrations of aluminum ions and phosphate ions in the reaction system are within the stoichiometric equilibrium range. This avoids the generation of impurities caused by excess of a single ion (such as the formation of aluminum hydroxide byproducts due to excess aluminum ions, and the formation of hydrogen phosphate due to excess phosphate ions), and provides elemental ratio assurance for the subsequent accurate synthesis of aluminum tripolyphosphate.

[0045] Slow mixing at room temperature with stirring forms a suspension, which avoids instantaneous precipitation caused by excessively high local concentrations. If mixing is too fast, the concentration of aluminum ions and phosphate ions in local areas will rise sharply, which will easily form amorphous aggregates that are difficult to participate in the subsequent crystallization reaction. The room temperature environment can inhibit the premature amorphization reaction of the raw materials, maintain the stability of the system, and create a uniform precursor environment for the uniform action of the structure-directing agent in step S2.

[0046] II. Structure Guidance and pH Regulation: Directional Control of Crystal Growth and Optimization of Crystallization Environment

[0047] Step S2 is the core regulatory step to achieve layered morphology. The structure-directing agent and pH adjuster work together to ensure the formation of layered structure from two aspects: "crystal growth direction" and "reaction environment compatibility".

[0048] Structure-directing agents function through selective adsorption and inhibition of crystal facet growth: specific functional groups in their molecules (such as quaternary ammonium salt groups of cationic surfactants, ether bonds of nonionic surfactants, and carboxyl groups of organic acids) can selectively interact with different crystal faces of aluminum tripolyphosphate crystals, preferentially adsorbing onto crystal faces with higher surface energy. The adsorption layer forms steric hindrance, hindering the deposition of aluminum and phosphate ions on this crystal facet, thereby inhibiting longitudinal growth; while lateral crystal faces with lower surface energy, due to weaker adsorption, can normally accept ion deposition, achieving lateral directional expansion of the crystal, ultimately forming a layered structure. The dosage of the structure-directing agent should be controlled at 1%–5% of the aluminum source mass. Too low a dosage results in insufficient adsorption and cannot effectively inhibit the growth of high surface energy crystal faces; too high a dosage easily leads to molecular aggregation, which in turn interferes with the orderly growth of the crystal.

[0049] The pH adjuster adjusts the system pH to 3.0–5.0. This acidic range is crucial for the stable growth of aluminum tripolyphosphate crystals: on the one hand, the acidic environment inhibits the hydrolysis of aluminum ions to form aluminum hydroxide, ensuring that aluminum ions participate in the crystallization reaction in a free state; on the other hand, this pH range optimizes the solubility and activity of structure-directing agents—for example, cationic surfactants are more likely to dissociate into cationic forms under weakly acidic conditions, enhancing their charge interaction with the crystal surface; at the same time, the acidic environment can regulate the existing form of phosphate ions, making them more likely to combine with aluminum ions in proportion to form tripolyphosphate, avoiding crystal structure deviations caused by excessive protonation or deprotonation of phosphate ions.

[0050] III. Hydrothermal crystallization reaction: Provides thermodynamic driving force, ensuring stable formation of layered crystals.

[0051] The high-pressure hydrothermal environment in step S3 is the key thermodynamic guarantee for the transformation of layered crystals from "directional growth" to "stable formation". The synergistic effect of pressure, temperature and filling parameters breaks through the limitations of atmospheric pressure process.

[0052] The hydrothermal system formed by high pressure (1–3 MPa) and high temperature (190–230 °C) can enhance the "solventization capacity" and "ion diffusion rate" of the reaction system: high temperature increases the kinetic energy of water molecules, enhancing their ability to dissolve raw materials and promoting the full dissociation of aluminum and phosphate ions in the precursors into free ions, providing sufficient "raw material supply" for crystal growth; the high-pressure environment keeps water in a liquid state at high temperature and enhances intermolecular forces, which can lower the activation energy of crystal growth, accelerate the deposition rate of aluminum and phosphate ions on the transverse crystal plane regulated by the structure-directing agent, and inhibit disordered crystal aggregation. If the pressure is too low, water is easily vaporized at high temperature, the system is in a gas-liquid two-phase state, ion diffusion is uneven, and amorphous products are easily formed; if the temperature is too low, the ion activity is insufficient, the crystallization reaction is slow, and impurity phases are easily generated.

[0053] The reactor filling degree is controlled between 60% and 85% to ensure uniform temperature and pressure distribution during the reaction. If the filling degree is too low, the excessive gas space under high pressure can easily lead to localized temperature fluctuations, affecting the consistency of crystal growth. If the filling degree is too high, the system expansion during the reaction can easily cause a sudden pressure rise, posing a safety risk and hindering heat transfer, resulting in incomplete crystallization. A reaction time of 7–13 hours provides sufficient growth time for the crystals, ensuring the entire process of layered structure development from initial nucleation to complete expansion, avoiding incomplete layered structures due to too short a reaction time or excessive crystal growth and agglomeration due to too long a reaction time.

[0054] IV. Product Post-processing: Purify and stabilize the layered structure to ensure product performance.

[0055] Step S4, consisting of solid-liquid separation, washing, and drying, is crucial for removing impurities and preserving the integrity of the layered structure. Solid-liquid separation (vacuum filtration / pressure filtration) quickly separates unreacted raw materials from crystallized products, preventing unreacted raw materials from adhering to the crystal surface and affecting performance. Washing with water and alcohol solvents sequentially removes residual soluble impurities from the system; if impurities remain, they can lead to decreased product dispersibility in the coating. Alcohol washing reduces the surface tension of the product, minimizing capillary forces generated during drying due to water evaporation, preventing the layered crystals from wrinkling or agglomerating under stress. Furthermore, the volatility of alcohols shortens subsequent drying time.

[0056] Hot air drying can quickly remove moisture and alcohol solvents from the product, and the drying process is gentle, avoiding the collapse of the layered structure caused by high-temperature baking. Ultimately, this step yields a structurally intact and highly pure layered aluminum tripolyphosphate anti-rust pigment, laying the foundation for its synergistic anti-rust effect of "physical shielding and chemical passivation" in coatings.

[0057] To make the present invention more fully disclosed, more specific embodiments are described below.

[0058] Example 1

[0059] 24.14 g of aluminum chloride was dissolved in 175 mL of deionized water. 34.3 g of phosphoric acid was slowly added under stirring at room temperature to form a suspension. Then, 0.24 g of hexadecyltrimethylammonium bromide (CTAB) was added, and stirring continued for 1 hour to obtain a mixture. The pH of the mixture was adjusted to 4.0 with ammonia. The mixture was transferred to a 300 mL high-pressure reactor (65% filling) and reacted at 1 MPa and 210 °C for 8 hours. After the reaction, the reactor was allowed to cool naturally to room temperature. The product was then removed and filtered, washed three times with deionized water and twice with anhydrous ethanol. Finally, the filter cake was placed in a drying oven and dried at 105 °C for 4 hours to obtain layered aluminum tripolyphosphate pigment sample Y-1.

[0060] Compositional analysis of sample Y-1 showed that its aluminum and phosphorus contents were basically consistent with the theoretical values ​​of aluminum tripolyphosphate (see Table 2). Scanning electron microscopy (SEM) revealed that the product consisted of numerous thin-layered crystals with clear outlines and relatively uniform size (see Table 2). Figure 1 ).

[0061] Example 2

[0062] 37.53 g of aluminum nitrate was dissolved in 200 mL of deionized water. 34.3 g of phosphoric acid was slowly added under stirring at room temperature to form a suspension. Then, 0.75 g of polyvinylpyrrolidone (PVP K30) was added, and stirring continued for 1 hour. The pH of the system was adjusted to 4.5 with ammonia. The resulting mixture was transferred to a 300 mL high-pressure reactor (approximately 75% filling) and reacted at 2 MPa and 200 °C for 12 hours. After the reaction, the reactor was allowed to cool naturally to room temperature. The product was then removed and filtered, washed three times with deionized water and twice with anhydrous ethanol. Finally, the filter cake was placed in a drying oven and dried at 105 °C for 4 hours to obtain layered aluminum tripolyphosphate pigment sample Y-2.

[0063] Component analysis showed that its aluminum and phosphorus contents were basically consistent with the theoretical values ​​of aluminum tripolyphosphate (see Table 2), and SEM characterization ( Figure 2 The results show that the Y-2 sample also exhibits a distinct layered structure.

[0064] Example 3

[0065] 7.8 g of industrial aluminum hydroxide was dispersed in 220 mL of deionized water, and 34.3 g of phosphoric acid was slowly added under stirring at room temperature to form a suspension. 0.39 g of cetyltrimethylammonium bromide (CTAB) was added, and after stirring for 2 h, the pH was adjusted to 3.5 with ammonia. The mixture was transferred to a 300 mL high-pressure reactor (80% filling) and reacted at 2 MPa and 220 °C for 10 h. After the reaction, the reactor was allowed to cool naturally to room temperature, and the product was removed and filtered. The product was washed three times with deionized water and twice with anhydrous ethanol. Finally, the filter cake was placed in a drying oven and dried at 105 °C for 4 h to obtain layered aluminum tripolyphosphate pigment sample Y-3.

[0066] Composition analysis (Table 2) shows that its aluminum and phosphorus contents are basically consistent with the theoretical values ​​of aluminum tripolyphosphate.

[0067] Comparative Example 1

[0068] 7.8 g of industrial aluminum hydroxide was dispersed in 220 mL of water, and 34.3 g of phosphoric acid was slowly added while stirring to form a suspension. After stirring for 2 hours, the pH of the mixture was adjusted to 3.5 with ammonia. The mixture was then transferred to a 300 mL high-pressure reactor (approximately 80% filling) and reacted at 2 MPa and 220 °C for 10 hours. After the reaction was completed, the crude product was post-processed as in Example 1, and sample D-1 was finally obtained.

[0069] Compositional analysis (Table 2) shows that the aluminum and phosphorus contents of Comparative Example 1 sample are basically consistent with the theoretical values ​​of aluminum tripolyphosphate. SEM characterization ( Figure 3The results show that it mainly consists of irregularly shaped particles and a small number of short rod-shaped crystals, without forming a regular and complete layered structure. This indicates that even with high-pressure hydrothermal methods, aluminum tripolyphosphate crystals tend to grow randomly without the induction of a structure-directing agent, and the layered morphology of the present invention cannot be obtained.

[0070] Comparative Example 2

[0071] 7.8 g of industrial-grade aluminum hydroxide was dispersed in 220 mL of deionized water, and 34.3 g of phosphoric acid was slowly added with stirring to form a suspension. Then, 0.39 g of hexadecyltrimethylammonium bromide (CTAB) was added, and stirring continued for 2 hours to form a mixture. The pH of the mixture was adjusted to 3.5 with sodium hydroxide. The mixture was transferred to a 300 mL atmospheric pressure reactor (80% filling) and placed in a muffle furnace. The reactor was reacted at 220 °C for 10 hours. After the reactor cooled naturally to room temperature, the reaction product was transferred to a beaker, dispersed with deionized water, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol, respectively. The filter cake was then dried in a 105 °C drying oven for 4 hours to obtain sample D-2.

[0072] SEM image of sample D-2 ( Figure 4 The results showed that the product was an amorphous aggregate with almost no obvious layered morphology. Chemical analysis (see Table 2) showed that its aluminum content (calculated as Al2O3) was 21.3% and its phosphorus content (calculated as P2O5) was 61.6%, which differed significantly from the theoretical values ​​for aluminum tripolyphosphate pigment, but was basically consistent with the elemental composition of the intermediate product aluminum dihydrogen phosphate. This indicates that under normal pressure conditions, even in the presence of a structure-directing agent, the necessary reaction and crystallization environment for the formation of aluminum tripolyphosphate cannot be provided, making it difficult to generate the target product.

[0073] Summary of experimental results:

[0074] (a) Test Results

[0075]

[0076] The test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 2.

[0077]

[0078] (II) Data Comparison and Analysis

[0079] 1. Analysis of active ingredient content

[0080] As shown in Table 2, the aluminum content (calculated as Al2O3) of Examples 1-3 is 17.5%~17.9%, and the phosphorus content (calculated as P2O5) is 70.2%~72.2%, both of which are basically consistent with the theoretical values ​​of aluminum tripolyphosphate. However, the aluminum content of Comparative Example 2 is 21.3%, and the phosphorus content is only 61.6%, which deviates significantly from the composition of the target product. From a principle perspective, this invention ensures the formation of effective components through aluminum-phosphorus ratio control and a high-pressure hydrothermal environment: the aluminum source and phosphorus source are fed at Al / P=1:(2.8~3.2), providing a precise elemental ratio for the combination of tripolyphosphate and aluminum ions; the high pressure of 1~3MPa combined with the temperature of 190~230℃ improves the solubility of raw materials and the ion diffusion rate, promoting the full combination of aluminum ions and phosphate ions to form aluminum tripolyphosphate. In contrast, Comparative Example 2, due to the use of atmospheric pressure reaction, could not provide the thermodynamic conditions for stable crystal growth. Aluminum ions and phosphate ions only partially combined to form aluminum dihydrogen phosphate (Al(H2PO4)3), resulting in a high aluminum content and a low phosphorus content, thus failing to generate the target product.

[0081] 2. Product morphology analysis

[0082] The products of Examples 1-3 all exhibited regular layered morphology, while Comparative Example 1 was a mixture of irregular particles and rods, and Comparative Example 2 was an amorphous aggregate. This difference stems from the synergistic regulation mechanism of "structure-directing agent and high-pressure hydrothermal treatment" in this invention: the structure-directing agent (CTAB, PVP K30) selectively adsorbs high surface energy crystal faces, inhibiting longitudinal growth and promoting lateral expansion, thus inducing the formation of a layered structure; the high-pressure hydrothermal environment provides sufficient driving force for the directional growth of crystals, ensuring the stable expansion of layered crystal faces. Comparative Example 1, lacking a structure-directing agent, lacked the constraint of directional growth, resulting in a randomly growing irregular morphology; although a structure-directing agent was added to Comparative Example 2, insufficient ionic activity and weak crystallization driving force under normal pressure prevented the structure-directing agent from playing a directional regulatory role, and the raw materials were not fully crystallized, ultimately forming amorphous aggregates.

[0083] (III) Performance Verification Experiment

[0084] 1. Experimental Objective

[0085] The purpose of this invention is to verify the rust-preventive properties and impermeability of the layered aluminum tripolyphosphate anti-rust pigment (hereinafter referred to as "the product of this invention") in coatings, and to clarify its advantages over non-layered aluminum tripolyphosphate (traditional products).

[0086] 2. Experimental Samples and Testing Methods

[0087] (1) Experimental samples: The samples prepared in Example 1 (Y-1), Example 2 (Y-2) and Example 3 (Y-3) of this invention were selected as experimental groups; the non-layered aluminum tripolyphosphate (sample D-1) prepared in Comparative Example 1 and the commercially available conventional aluminum tripolyphosphate (sample S-1) were selected as control groups.

[0088] (2) Coating preparation: The above 5 pigments were mixed into the same type of water-based epoxy resin coating at the same mass fraction (20%) and coated on the surface of Q235 steel sheet using the same process. The dry film thickness of the coating was controlled to be 80±5μm. After curing at room temperature for 72h, it was ready for use.

[0089] (3) Test method:

[0090] Rust prevention performance: Neutral salt spray test (NSS) was conducted according to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", and the time when red rust appeared on the steel sheet was recorded (salt spray resistance time).

[0091] Water absorption resistance: The water absorption rate of the coating after immersion in water for 72 hours was tested according to GB / T 1766-2008 "Rating method for aging of paint and varnish coatings".

[0092] 3. Experimental Data

[0093]

[0094] 4. Conclusion Analysis

[0095] As shown in Table 3:

[0096] Significant advantages in rust prevention performance: Samples Y-1, Y-2, and Y-3 in the experimental group showed bubble points after 780h, 730h, and 720h salt spray time, respectively, far exceeding the control groups D-1 and S-1. The core reason lies in the layered structure of the product of this invention, which is oriented parallel to the substrate in the coating, forming a dense physical barrier that significantly prolongs the penetration path of corrosive media such as chloride ions and moisture. Simultaneously, the high specific surface area of ​​the layered structure accelerates the dissociation of phosphate ions, rapidly forming a stable passivation film on the steel substrate surface, achieving dual protection of physical shielding and chemical passivation, and greatly improving rust prevention durability.

[0097] Significantly improved water resistance: The water absorption rate of the experimental group coating after immersion in water for 72 hours was only 2.3%~2.8%, while that of the control group was as high as 4.2%~4.6%. This is because the layered pigment of this invention can fill the tiny pores inside the coating, reducing coating defects. Compared with the loose accumulation of traditional non-layered particles, the coating structure formed is more dense, effectively blocking the penetration channels of water and further strengthening the anti-rust foundation.

[0098] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a layered aluminum tripolyphosphate anti-rust pigment, characterized in that, Includes the following steps: S1. Disperse or dissolve the aluminum source compound in water, and add the phosphorus source compound under stirring at room temperature to form a suspension; S2. Add a structure-directing agent to the suspension, stir to form a mixture, and adjust the pH value of the mixture with a pH adjuster; S3. Place the mixture obtained in step S2 into a high-pressure reactor for hydrothermal crystallization reaction; S4. The reaction product of step S3 is subjected to solid-liquid separation, washing and drying to obtain the layered aluminum tripolyphosphate anti-rust pigment.

2. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S1, the aluminum source compound is selected from at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum isopropoxide, boehmite, and industrial aluminum hydroxide.

3. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S1, the phosphorus source compound is selected from at least one of phosphoric acid and sodium tripolyphosphate; the molar ratio of the aluminum source compound to the phosphorus source compound is 1:(2.8~3.2) in Al / P.

4. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S2, the structure directing agent is one or more of the following: cationic surfactant, nonionic surfactant, organic acid, or urea.

5. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 4, characterized in that, The cationic surfactant is hexadecyltrimethylammonium bromide; the nonionic surfactant is polyvinylpyrrolidone or polyethylene glycol; and the organic acid is citric acid.

6. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S2, the amount of the structure-directing agent added is 1% to 5% of the mass of the aluminum source compound.

7. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S2, the pH adjuster is ammonia, urea, sodium hydroxide, hydrochloric acid, or nitric acid; the pH value of the mixture is adjusted to 3.0~5.

0.

8. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S3, the conditions for the hydrothermal crystallization reaction are: pressure 1-3 MPa, temperature 190-230°C, and reaction time 7-13 h.

9. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S3, the filling degree of the mixture in the high-pressure reactor is 60% to 85% of the effective volume of the reactor.

10. The method for preparing a layered aluminum tripolyphosphate anti-rust pigment according to claim 1, characterized in that, In step S4, the washing includes washing with water and alcohol solvent in sequence; the drying is hot air drying.

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