A method and apparatus for synthesizing keggin-type heteropolyacid salts

Abstract

The application provides a method and device for synthesizing Keggin type heteropoly acid salt, the method comprises the steps of reaction raw material preparation, microwave assisted ball milling synthesis and product collection, and the solid phase reaction is completed by using an intermittent cycle process of alternating microwave milling and microwave assisted milling. The mechanical chemical action and the microwave thermal field are cooperated to strengthen the intermolecular reaction efficiency, a small solvent reaction system is used to replace the traditional large liquid phase reaction medium, the reaction temperature is accurately controlled in time through the intermittent cycle to avoid excessive heating, and two feeding modes of direct mixing and uniform dropping are matched to cover the synthesis needs of multiple types of heteropoly acid salt, so that the reaction period is greatly shortened and the product reaction sufficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of heteropolyacid salt functional material preparation technology, specifically to a method and apparatus for synthesizing Keggin-type heteropolyacid salts. Background Technology

[0002] Keggin-type heteropolyacids are a class of polyoxometalate compounds with classic cage-like structures. Their unique electronic structure and physicochemical properties have demonstrated significant application value in various fields, including industrial catalysis, metal surface passivation, and functional material preparation. With the continuous expansion of downstream applications, the industry has placed higher demands on the production efficiency, environmental friendliness of the preparation process, and product performance of Keggin-type heteropolyacids. Traditional liquid-phase synthesis processes are gradually becoming insufficient to simultaneously meet the multiple requirements of low cost, large-scale production, and green manufacturing.

[0003] Currently, the mainstream preparation methods for Keggin-type heteropolyacid salts are mainly based on liquid-phase reaction pathways, including acidification-ether extraction, ion exchange, strong acid precipitation, and hydrothermal synthesis. Among these, the acidification-ether extraction method requires the use of flammable, explosive, and toxic ether as the extractant, posing significant safety hazards during production. The ion exchange method requires multiple conversion steps, resulting in a long overall production cycle, high energy consumption, and difficulty in achieving large-scale continuous production. The strong acid precipitation and hydrothermal methods require reactions in strong acid systems or under high temperature and pressure conditions, which not only imposes stringent requirements on the corrosion resistance and pressure resistance of equipment, resulting in high equipment investment and maintenance costs, but also presents problems such as high solubility of some products, difficulty in precipitation separation, and unstable product yields.

[0004] To reduce solvent usage and reaction condition thresholds, existing technologies have begun to explore the use of mechanochemical ball milling to synthesize heteropolyacid salts. However, ball milling alone suffers from limitations in mechanical driving force, slow reaction progress, and incomplete material reaction. Furthermore, the uncontrollable heat release during the reaction process can easily lead to localized temperature anomalies, resulting in the destruction of the product's crystal structure and a decline in performance. Simultaneously, conventional ball milling methods struggle to precisely control the particle size and specific surface area of ​​the product, failing to effectively increase the number of active sites. Summary of the Invention

[0005] In view of the aforementioned problems, this application is made to provide a method and apparatus for synthesizing Keggin-type heteropolyacid salts that overcomes or at least partially solves the aforementioned problems, comprising: A method for synthesizing Keggin-type heteropolyacid salts, characterized by comprising the steps of: preparation of reaction substrate; microwave-assisted ball milling synthesis and product collection; The microwave-assisted ball milling synthesis step includes: The prepared reaction base material is loaded into a ball mill jar, and grinding balls are added according to the preset ball-to-material ratio to obtain the ball milling system to be reacted; The ball milling system to be reacted was placed in a microwave radiation field, the ball milling speed and microwave operating parameters were set, and a solid-phase reaction was carried out by an intermittent cyclic process of alternating microwave-free grinding and microwave-assisted grinding. After the reaction was completed, the solid-phase reaction product was obtained. The solid-phase reaction product was allowed to stand and cool to room temperature to complete the synthesis reaction process.

[0006] Furthermore, the reaction substrate preparation step includes; Keggin-type heteropolyacids and reactants are mixed in a predetermined molar ratio, and a mixed solvent of water and ethanol is added. The mixture is stirred until homogeneous to obtain the reaction substrate. The Keggin-type heteropolyacids include H3PW 12 O 40 or H3PMo 12 O 40 .

[0007] Furthermore, the reaction raw materials are organic cationic compounds or trivalent metal chlorides, and the molar ratio of the reaction raw materials to Keggin-type heteropolyacids is 3:1.

[0008] Furthermore, the organic cationic compound is tyrosine; the trivalent metal chloride is ferric chloride.

[0009] Furthermore, the intermittent cyclic process consists of a 15-minute microwave-free grinding and a 5-minute microwave-assisted grinding cycle, which is repeated until the total reaction time reaches 200 minutes.

[0010] Furthermore, the reaction substrate is a suspension substrate prepared by Keggin-type heteropolyacid and a water-ethanol mixed solvent; In the microwave-assisted ball milling synthesis step, an aqueous solution of metal oxychloride is added dropwise at a uniform rate through a dropper at the top of the ball mill during the solid-phase reaction. The degree of metal substitution of the product is controlled by adjusting the amount of dropper added, thus obtaining a monometallic substitution Keggin-type heteropolyacid salt.

[0011] Furthermore, the metal oxychloride is zirconium oxychloride, and the resulting monometallic substitution Keggin-type heteropolyacid salt has the general formula Zr. x H 3-x PW 12 O 40 , where x ranges from 0.25 to 0.75.

[0012] Furthermore, before adding the aqueous solution of metal oxychloride, the ball milling system to be reacted is pre-ground without microwave for 5 minutes; After the addition is complete, the reaction continues in a cycle unit consisting of 10 minutes of non-microwave grinding and 5 minutes of microwave-assisted grinding, with a total reaction time of 300 minutes.

[0013] Furthermore, the preset ball-to-material mass ratio is 1:1, and the ball milling speed is 400 rpm; the microwave operating parameters are: power 0.8 kW, frequency 2.45 GHz.

[0014] An apparatus for synthesizing Keggin-type heteropolyacid salts, the apparatus being used to perform the method described in any of the preceding claims, the apparatus comprising a microwave oven and a ball mill jar placed in an internal cavity of the microwave oven; The microwave device is used to heat the ball mill jar to provide reaction heat energy. The rated operating power of the microwave device is 0.8kW and the rated operating frequency is 2.45GHz. A drip tube is installed on the top of the ball mill jar, and a control valve for controlling the solution dripping rate is provided on the drip tube.

[0015] This application has the following advantages: In the embodiments of this application, compared with the existing technology where the synthesis of Keggin-type heteropolyacid salts relies on strong acids and toxic organic solvents such as diethyl ether, requires high temperature and high pressure reaction conditions, has a long process flow and low production efficiency, requires multi-step purification of products, has insufficient reaction driving force in the single mechanical ball milling method, has uncontrollable reaction temperature that easily damages the crystal structure of the product, has uneven product particle size and limited specific surface area, and has limited improvement of active sites, and has difficulty in accurately controlling the degree of substitution of single metal substitution products, this application provides a method for synthesizing Keggin-type heteropolyacid salts by microwave-assisted ball milling, including reaction substrate preparation, microwave-assisted ball milling synthesis and product collection steps, and uses an intermittent cyclic process of alternating microwave-free milling and microwave-assisted milling to complete the solid-phase reaction. By synergistically enhancing intermolecular reaction efficiency through mechanochemical action and microwave thermal field, and employing a low-solvent reaction system to replace the traditional large-volume liquid-phase reaction medium, coupled with precise temperature control through intermittent cycling to avoid overheating, this approach adapts to both direct mixing and uniform dropwise feeding modes, covering the synthesis needs of various types of heteropolyacid salts. It significantly shortens the reaction cycle and improves product reaction saturation. Furthermore, all reaction processes require no high-temperature, high-pressure equipment and do not use toxic or harmful extraction reagents. This successfully achieves a Keggin-type heteropolyacid salt synthesis pathway that combines green safety, high reaction efficiency, and high-performance products. The entire reaction process can be completed under ambient pressure and mild conditions, with a minimum total reaction time of 200 minutes. The products can be directly used without purification, exhibiting significantly refined particle size and a substantial increase in specific surface area. The degree of single-metal substitution can be precisely controlled within the range of 0.25–0.75. Simultaneously, it effectively solves the technical challenges of high safety risks, stringent equipment requirements, low production efficiency, insufficient product activity, and difficulty in controlling the degree of substitution inherent in traditional synthesis processes. This provides an ideal synthetic technology solution for the large-scale green production of Keggin-type heteropolyacid salts in fields such as metal surface passivation, industrial catalysis, and functional material preparation. Attached Figure Description

[0016] To more clearly illustrate the technical solution of this application, the drawings used in the description of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of an apparatus for synthesizing Keggin-type heteropolyacid salts according to an embodiment of this application; Figure 2 A comparison diagram of salt spray test results between passivated and unpassivated zinc sheets provided in one embodiment of this application; Explanation of reference numerals in the attached figures: 1. Microwave oven; 2. Grinding jar; 3. Dropper; 4. Control valve. Detailed Implementation

[0018] To make the objectives, features, and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0019] Through analysis of existing technologies, the inventors discovered that single ball milling reactions have drawbacks such as limited mechanical driving force, slow reaction process, and insufficient material reaction. Furthermore, the heat release during the reaction is uncontrollable, which can easily lead to local temperature anomalies that cause damage to the crystal structure of the product and a decline in performance. At the same time, conventional ball milling methods are difficult to precisely control the particle size and specific surface area of ​​the product, and cannot effectively increase the number of active sites in the product.

[0020] An embodiment of this application provides a method for synthesizing Keggin-type heteropolyacid salts, comprising the steps of: preparing reaction substrate; microwave-assisted ball milling synthesis and product collection; The microwave-assisted ball milling synthesis step includes: The prepared reaction base material is loaded into a ball mill jar, and grinding balls are added according to the preset ball-to-material ratio to obtain the ball milling system to be reacted; The ball milling system to be reacted was placed in a microwave radiation field, the ball milling speed and microwave operating parameters were set, and a solid-phase reaction was carried out by an intermittent cyclic process of alternating microwave-free grinding and microwave-assisted grinding. After the reaction was completed, the solid-phase reaction product was obtained. The solid-phase reaction product was allowed to stand and cool to room temperature to complete the synthesis reaction process.

[0021] It should be noted that the core of the intermittent cyclic process, which alternates between microwave-free grinding and microwave-assisted grinding, lies in achieving precise temperature control and efficient advancement of the reaction process through the periodic switching of "mechanical activation - thermally accelerated reaction." In the microwave-free grinding stage, the continuous impact and shearing action of the grinding balls mechanically activates the reactant particles, constantly breaking them down and exposing fresh reaction surfaces, while simultaneously shortening the ion diffusion distance, providing a sufficient kinetic basis for subsequent reactions. In the microwave-assisted grinding stage, the bulk heating properties of microwaves rapidly raise the overall temperature of the material, accelerating ion migration and chemical bonding, and increasing the reaction rate. Alternating between the two processes avoids localized overheating caused by continuous microwave radiation, preventing the cage-like framework of Keggin-type heteropolyacid salts from collapsing and decomposing due to excessively high temperatures, thus ensuring the integrity of the product's crystal structure.

[0022] This method employs a low-solvent solid-phase reaction system, unlike traditional liquid-phase methods which require large amounts of strong acids or organic solvents as reaction media. The reaction is completed simply by wetting the powder with a small amount of mixed solvent. This system avoids the use of toxic extractants and highly corrosive acids from the outset, reducing safety risks and waste treatment costs during production. Furthermore, it generates no large amounts of waste liquid after the reaction, and the product does not require multiple purification steps such as extraction, crystallization, filtration, and recrystallization; it can be directly collected to obtain a qualified product, significantly shortening the production process and reducing overall production costs.

[0023] The preparation of the reaction substrate provides a homogeneous reaction precursor for the ball milling reaction. Microwave-assisted ball milling synthesis is the core step in realizing the solid-phase transformation of heteropoly acid salts, while product collection completes the final product discharge and post-processing. No material transfer is required throughout the process, reducing material loss and the risk of introducing external impurities. It also facilitates continuous and large-scale production operations, meeting the needs of industrial-scale mass production.

[0024] In the embodiments of this application, compared with the existing technology where the synthesis of Keggin-type heteropolyacid salts relies on strong acids and toxic organic solvents such as diethyl ether, requires high temperature and high pressure reaction conditions, has a long process flow and low production efficiency, requires multi-step purification of products, has insufficient reaction driving force in the single mechanical ball milling method, has uncontrollable reaction temperature that easily damages the crystal structure of the product, has uneven product particle size and limited specific surface area, and has limited improvement of active sites, and has difficulty in accurately controlling the degree of substitution of single metal substitution products, this application provides a method for synthesizing Keggin-type heteropolyacid salts by microwave-assisted ball milling, including reaction substrate preparation, microwave-assisted ball milling synthesis and product collection steps, and uses an intermittent cyclic process of alternating microwave-free milling and microwave-assisted milling to complete the solid-phase reaction. By synergistically enhancing intermolecular reaction efficiency through mechanochemical action and microwave thermal field, and employing a low-solvent reaction system to replace the traditional large-volume liquid-phase reaction medium, coupled with precise temperature control through intermittent cycling to avoid overheating, this approach adapts to both direct mixing and uniform dropwise feeding modes, covering the synthesis needs of various types of heteropolyacid salts. It significantly shortens the reaction cycle and improves product reaction saturation. Furthermore, all reaction processes require no high-temperature, high-pressure equipment and do not use toxic or harmful extraction reagents. This successfully achieves a Keggin-type heteropolyacid salt synthesis pathway that combines green safety, high reaction efficiency, and high-performance products. The entire reaction process can be completed under ambient pressure and mild conditions, with a minimum total reaction time of 200 minutes. The products can be directly used without purification, exhibiting significantly refined particle size and a substantial increase in specific surface area. The degree of single-metal substitution can be precisely controlled within the range of 0.25–0.75. Simultaneously, it effectively solves the technical challenges of high safety risks, stringent equipment requirements, low production efficiency, insufficient product activity, and difficulty in controlling the degree of substitution inherent in traditional synthesis processes. This provides an ideal synthetic technology solution for the large-scale green production of Keggin-type heteropolyacid salts in fields such as metal surface passivation, industrial catalysis, and functional material preparation.

[0025] The method for synthesizing Keggin-type heteropolyacid salts in this exemplary embodiment will now be further described.

[0026] In this embodiment, the reaction substrate preparation step includes: Keggin-type heteropolyacids and reactants are mixed in a predetermined molar ratio, and a mixed solvent of water and ethanol is added. The mixture is stirred until homogeneous to obtain the reaction substrate. The Keggin-type heteropolyacids include H3PW 12 O 40 or H3PMo 12 O 40 .

[0027] It should be noted that H3PW 12 O 40 or H3PMo 12 O 40As reaction precursors, they are based on the mature industrial foundation and stable Keggin-type structural characteristics of both. These two heteropolyacids are the most representative Keggin-structured polyoxometalates, with stable molecular structures, tunable acidity, and excellent redox properties. They are currently the two most widely used heteropolyacid precursors in industry. The raw materials are readily available and of stable quality, which can ensure the structural uniformity and performance reliability of the synthesized products.

[0028] The mixed solvent of water and ethanol serves a dual role as both a dispersion medium and a microwave absorption medium in the reaction system. On the one hand, a small amount of the mixed solvent can wet the powder particles, reduce dust emissions during ball milling, improve the mixing uniformity of different components, and avoid localized deviations in the raw material ratio. On the other hand, both water and ethanol are highly polar substances that can efficiently absorb microwave energy, forming microscale high-temperature reaction zones on the particle surface, promoting ion diffusion and reaction. Furthermore, ethanol has a low boiling point and can gradually evaporate during the reaction, leaving no residue in the final product that could affect its purity.

[0029] The amount of mixed solvent added is optimized and controlled to ensure that the material is in a moist and loose powder state, without forming a continuous liquid phase. This amount can play a role in dispersing and promoting the reaction without causing the material to stick to the wall or clump together. It ensures that the mechanical force can act continuously and evenly on the surface of the reactant particles during ball milling, maintain a stable solid-phase reaction environment, and avoid weakening the mechanochemical effect due to excessive liquid phase.

[0030] In this embodiment, the reaction raw material is an organic cationic compound or a trivalent metal chloride, and the molar ratio of the reaction raw material to the Keggin-type heteropolyacid is 3:1.

[0031] It should be noted that the molar ratio of the reactants to Keggin-type heteropolyacids is set at 3:1, which is determined by the molecular structure of Keggin-type heteropolyacids. H3PW 12 O 40 or H3PMo 12 O 40 Each molecule contains three dissociable hydrogen ions. When monovalent organic cations or trivalent metal cations are fed in a molar ratio of 3:1, they can precisely replace the hydrogen ions in the heteropolyacids to generate electrically neutral heteropolyacid salt products, avoiding excessive residue of raw materials and ensuring the purity and stoichiometric accuracy of the products.

[0032] Organic cationic compounds and trivalent metal chlorides are two types of raw materials that correspond to different product performance requirements. Organic cationic compounds can introduce organic functional groups into the structure of heteropolyacid salts to prepare organic-inorganic hybrid heteropolyacid salts, which can effectively improve the interfacial compatibility, dispersibility and surface activity of the products, making them suitable for applications such as metal passivation solutions and composite functional materials. Trivalent metal chlorides are used to prepare pure inorganic heteropolyacid salts, which have better thermal and chemical stability and are more suitable for applications such as high-temperature catalysis and inorganic functional fillers.

[0033] Under the influence of mechanochemistry, reactant particles are continuously refined, the reaction contact area increases exponentially, and the ion diffusion distance is significantly shortened, enabling a complete reaction according to stoichiometry even under solid-phase conditions. Compared to traditional liquid-phase methods that require excessive feed to ensure complete reaction, this method achieves high conversion rates without excessive raw materials, reducing raw material waste and simplifying subsequent purification.

[0034] In this embodiment, the grinding balls are made of zirconium oxide, and the preset ball-to-material mass ratio is 1:1.

[0035] It should be noted that zirconium oxide grinding balls are chosen because they have high strength, high wear resistance, and chemical inertness. They are not easily worn off during long-term ball milling, and will not introduce impurities into the reaction system, thus ensuring product purity. At the same time, zirconium oxide has a high density, which can provide sufficient impact energy to ensure the mechanical activation effect and meet the mechanical driving force required for solid-phase reactions.

[0036] The ball-to-material mass ratio is set at 1:1, which is the result of comprehensive optimization of reaction efficiency and energy consumption. At this ratio, the grinding balls and the material can make full contact, which ensures effective impact and grinding of the material particles and avoids insufficient grinding efficiency and incomplete reaction due to an excessively low ball-to-material ratio; at the same time, it also avoids ineffective collisions between the grinding balls due to an excessively high ball-to-material ratio, reducing unnecessary energy loss and equipment wear, and balancing reaction efficiency and operating economy.

[0037] In this embodiment, the organic cationic compound is tyrosine; the trivalent metal chloride is ferric chloride.

[0038] It should be noted that tyrosine was chosen as the organic cation source because the tyrosine molecule contains an amino group, which can be protonated in a weakly acidic environment to form a positively charged organic cation. This cation can then combine with heteropolyacid anions through electrostatic interactions to form stable organic-inorganic hybrid heteropolyacid salts. Furthermore, tyrosine itself is widely available and has good biocompatibility. Introducing a heteropolyacid salt structure can improve the interfacial dispersion ability of the product, allowing for better compatibility with components such as silane coupling agents in the metal passivation solution system, thereby improving the quality of the passivation film. Ferric chloride was chosen as the inorganic metal source because the charge number of ferric ions matches the number of dissociable hydrogen ions in the heteropolyacid, enabling a one-step substitution reaction to generate FePW. 12 O 40 The reaction pathway is simple and direct. Furthermore, ferric chloride is a low-cost and readily available raw material, and the resulting iron-substituted heteropolyacid salt combines the catalytic properties of heteropolyacids with the characteristics of iron, making it widely applicable in catalytic oxidation and environmental treatment. Both raw materials exhibit good reactivity and, under the synergistic effect of mechanical force and microwaves, can complete a solid-phase reaction with heteropolyacids in a short time without the need for additional catalysts or initiators, further simplifying the reaction system and reducing side reactions.

[0039] In this embodiment, the intermittent cyclic process consists of 15 minutes of microwave-free grinding and 5 minutes of microwave-assisted grinding as one cycle unit, and the cycle is repeated until the total reaction time reaches 200 minutes.

[0040] It should be noted that the cycle unit employing 15 minutes of microwave-free grinding followed by 5 minutes of microwave-assisted grinding is designed based on the matching of material temperature rise patterns with the reaction process. The 15 minutes of microwave-free grinding effectively disperses the material, refines particles, and completes the mechanical activation process, fully exposing the fresh surfaces of the reactants. The subsequent 5 minutes of microwave-assisted grinding rapidly provides the heat energy required for the reaction, promoting ion diffusion and chemical bonding, completing one reaction cycle. This time ratio allows the system temperature to be controlled within a reasonable range, avoiding temperature runaway caused by continuous heating.

[0041] The total reaction time was set at 200 minutes, which is the shortest optimized time to ensure complete reaction. At this time, the material undergoes multiple rounds of activation reaction cycles, and the conversion rate of reactants can reach a high level, with complete product structure and stable performance. Further extending the reaction time has limited effect on improving the conversion rate, but will instead increase energy consumption and equipment wear, and may even lead to excessive fineness of product particles, causing agglomeration and affecting the specific surface area and performance of the product.

[0042] The batch process parameters have been optimized for the synthesis of direct-mixed heteropolyacid salts, and are adapted to the reaction characteristics of both organic-inorganic hybrid and inorganic heteropolyacid salts. This allows for minimizing the production cycle and improving production efficiency while ensuring product performance.

[0043] In one specific implementation, the synthesis of organic-inorganic Keggin-type heteropolyacid salts uses tyrosine (Tyr) as the organic phase, which reacts with H3PW12O40 to yield the product (Try)3PW12O40. The specific reaction formula is as follows: .

[0044] In one specific implementation, the synthesis of inorganic-inorganic Keggin-type heteropolyacid salts Using FeCl3 as the inorganic phase, the reaction with H3PW12O40 yields the product FePW12O40. The specific reaction formula is as follows: .

[0045] In this embodiment, the reaction substrate is a suspension substrate prepared by Keggin-type heteropolyacid and water-ethanol mixed solvent; In the microwave-assisted ball milling synthesis step, an aqueous solution of metal oxychloride is added dropwise at a uniform rate through a dropper at the top of the ball mill during the solid-phase reaction. The degree of metal substitution of the product is controlled by adjusting the amount of dropper added, thus obtaining a monometallic substitution Keggin-type heteropolyacid salt.

[0046] It should be noted that the core advantage of using a uniformly added aqueous solution of metal oxychloride for monometallic substitution reactions lies in the precise control of the amount and rate of metal ion addition, enabling quantitative regulation of the degree of substitution. Unlike direct mixing, which can easily lead to localized excessively high concentrations and uneven substitution, uniform addition allows the metal ions to be evenly dispersed in the reaction system under the stirring action of ball milling, gradually undergoing a substitution reaction with the hydrogen ions of the heteropolyacid, ensuring the uniformity and accuracy of the product's degree of substitution.

[0047] The droplet addition operation, via a dripping pipe at the top of the ball mill jar, allows for the addition of raw materials without interrupting the ball milling reaction or opening the reaction vessel. This avoids temperature loss and material splashing caused by opening the lid during the reaction, maintaining the airtightness of the reaction system and the continuity of the process. Simultaneously, the dropping rate can be flexibly adjusted via a control valve to adapt to metal salt solutions with different reactivity, ensuring the smooth progress of the displacement reaction. This droplet addition process expands the applicability of microwave-assisted ball milling, enabling the synthesis of not only directly mixed heteropolyacid salts but also the preparation of heteropolyacid salts requiring stepwise feeding, such as single-metal substitution types. This allows the same equipment and process system to cover the synthesis needs of multiple types of Keggin-type heteropolyacid salts, improving the versatility of the process and the utilization rate of the equipment.

[0048] In this embodiment, the metal oxychloride is zirconium oxychloride, and the resulting monometallic substitution Keggin-type heteropolyacid salt has the general formula Zr. x H 3-xPW 12 O 40 , where x ranges from 0.25 to 0.75.

[0049] It should be noted that zirconium oxychloride was chosen as the substitution metal source because zirconium ions have a high charge and stable chemical properties. Introducing the Keggin structure can effectively modulate the acidity, redox properties, and thermal stability of heteropolyacid salts, thereby improving the catalytic performance and durability of the product. Furthermore, zirconium oxychloride has good water solubility, making it easy to prepare a homogeneous aqueous solution for dropwise addition, ensuring a uniform substitution reaction.

[0050] The degree of substitution (x) is set within the range of 0.25 to 0.75, based on a comprehensive consideration of product structural stability and performance adjustability. When x is below 0.25, the amount of metal substitution is too small, resulting in an insignificant effect on the performance modulation of heteropolyacid salts and failing to demonstrate the value of substitution modification. When x is above 0.75, excessive zirconium ions disrupt the charge balance of the Keggin-type structure, causing the cage-like framework to collapse and making it impossible to maintain a stable heteropolyacid salt structure. Within the range of 0.25 to 0.75, the degree of substitution can be precisely controlled by adjusting the amount of zirconium salt added, yielding products with different properties to suit various applications. This series of single-metal-substituted heteropolyacid salts retains the basic characteristics of the Keggin structure while optimizing surface acidity and the number of active sites through the introduction of zirconium ions, exhibiting superior performance in catalytic reactions, surface passivation, and other applications, thus expanding the application boundaries of heteropolyacid salts.

[0051] The specific reaction formula is as follows:

[0052] In this embodiment, the ball milling system to be reacted was pre-milled without microwave for 5 minutes before adding the metal oxychloride aqueous solution. After the addition is complete, the reaction continues in a cycle unit consisting of 10 minutes of non-microwave grinding and 5 minutes of microwave-assisted grinding, with a total reaction time of 300 minutes.

[0053] It should be noted that a 5-minute microwave-free pre-grinding step is set before the addition of the metal salt solution. The purpose is to fully disperse and homogenize the heteropolyacid substrate in the tank, forming a uniform suspension dispersion system. This prevents the substrate from clumping, which would lead to uneven dispersion of the added metal salt solution and ensure that the subsequent displacement reaction can proceed uniformly and synchronously. The microwave is not turned on during the pre-grinding stage to prevent premature heating of the substrate, which would cause the solvent to evaporate too quickly and maintain a good dispersion state of the system.

[0054] After the addition was completed, a cycle of 10 minutes of microwave-free grinding followed by 5 minutes of microwave-assisted grinding was used, with the total reaction time set at 300 minutes. This parameter was optimized to suit the process characteristics of the monometallic substitution reaction. Compared to direct mixing reactions, substitution reactions require the gradual diffusion of metal ions into the heteropolyacid structure, resulting in a relatively slow reaction process. Therefore, shortening the microwave-free grinding time per cycle and increasing the number of cycles allows for more precise control of the reaction temperature, ensuring sufficient ion diffusion and substitution reactions, and preventing excessive local reactions that could lead to uneven product structures.

[0055] A total reaction time of 300 minutes ensures that the zirconium ion substitution reaction is fully completed, the product substitution degree reaches the designed value and is uniformly distributed, and the Keggin structure remains intact. This process parameter ensures product quality while avoiding the decrease in production efficiency caused by excessively long reaction time, thus balancing product performance and production economy.

[0056] In one application embodiment of this application, the organic-inorganic Keggin-type heteropolyacid salt synthesized by the microwave-assisted ball milling method described above was used as an additive in the passivation solution for galvanized steel sheets to verify its corrosion resistance and protection effect. The passivation solution was prepared by physical blending and, by mass fraction, consisted of: 10% silane coupling agent with the molecular formula C8H 22 N2O3Si, 5%(Tyr)3PW 12 O 40 The product is an organic-inorganic hybrid Keggin-type heteropolyacid salt, with the balance being deionized water. The passivation process for galvanized steel sheets is as follows: First, the galvanized steel sheets are degreased and placed in 95% ethanol for ultrasonic cleaning at room temperature. After cleaning, they are removed, rinsed with water, and air-dried at room temperature. Then, the air-dried galvanized steel sheets are immersed in a passivation solution at 40°C for 60 seconds, then quickly removed and placed in an 80°C vacuum drying oven for 1 hour to allow the passivation components to solidify into a film on the steel sheet surface. After removal, the sheets are allowed to cool naturally to room temperature.

[0057] Figure 2 This is a comparison chart of salt spray test results between passivated and unpassivated zinc sheets.

[0058] It should be noted that the salt spray test results directly demonstrate the corrosion inhibition effect of the Keggin-type heteropolyacid salt synthesized in this application: the corrosion area of ​​the unpassivated zinc sheet increases rapidly with the extension of the salt spray test time, and large-area corrosion occurs in a short period of time; while the zinc sheet treated with the passivation solution containing the heteropolyacid salt of this application shows a significantly reduced corrosion rate under the same test conditions, and the corrosion area in the same time is much lower than that of the unpassivated sample. This result indicates that the Keggin-type heteropolyacid salt synthesized by the microwave-assisted ball milling method of this application can effectively prevent the corrosive medium from penetrating into the zinc coating, significantly improving the salt spray corrosion resistance of galvanized steel sheets, and can be used as an environmentally friendly passivation additive in the field of metal surface protection. Simultaneously, the organic-inorganic hybrid structure gives this heteropolyacid salt good compatibility with silane coupling agents, and their synergistic film formation can further improve the density and adhesion of the passivation film, balancing environmental friendliness and protective performance, and has good application potential as a replacement for traditional chromium-containing passivation processes.

[0059] Reference Figure 1 In this embodiment, an apparatus for synthesizing Keggin-type heteropolyacid salts is proposed. The apparatus is used to implement the method described in any of the above-mentioned methods. The apparatus includes a microwave oven and a ball mill jar placed in the internal cavity of the microwave oven. The microwave device is used to heat the ball mill jar to provide reaction heat energy. The rated operating power of the microwave device is 0.8kW and the rated operating frequency is 2.45GHz. A drip tube is installed on the top of the ball mill jar, and a control valve for controlling the solution dripping rate is provided on the drip tube.

[0060] It should be noted that the microwave unit 1 is the main heating cavity of the device, and the ball mill jar 2 is coaxially placed in the center of the internal reaction cavity of the microwave unit 1. When the microwave unit is working, the microwaves generated can be uniformly radiated to the outer peripheral wall of the ball mill jar, and heat energy is transferred to the reactants in the jar through bulk heating. Compared with the traditional external jacket heating method, microwave radiation heating has no obvious radial temperature difference. Combined with the mechanical stirring effect of the ball milling process, it can further eliminate local temperature differences in the material, provide a uniform and stable thermal field environment for solid-phase reaction, and avoid local overheating that damages the crystal structure of heteropoly acid salts.

[0061] The drip tube 3 is axially inserted through the top wall of the microwave oven 1, with its lower end extending above the internal cavity of the ball mill jar 2. This allows for the direct dripping of externally prepared reaction solutions into the material inside the jar. A control valve 4 is installed on the section of the drip tube 3 located outside the microwave oven, allowing operators to directly adjust the valve opening from outside the equipment, precisely controlling the dripping rate and total amount of solution added. This structure allows for the addition of liquid raw materials without opening the microwave cavity or interrupting the ball milling reaction. It maintains the airtightness and process continuity of the reaction system while controlling the displacement reaction process through the dripping rate, thus meeting the requirements for the quantitative and controllable synthesis of monometallic substituted heteropolyacid salts.

[0062] The entire device integrates the microwave heating unit and the ball milling reaction unit into one compact and rationally laid-out structure. The addition of a dripping pipe and control valve does not alter the core operating structure of the original ball mill equipment, allowing for modification based on existing microwave ball milling equipment with low cost and high versatility. This device can simultaneously adapt to two process routes: direct mixing synthesis and dropwise displacement synthesis. It can complete the one-step synthesis of organic-inorganic and inorganic heteropolyacid salts, as well as the controlled synthesis of quantitative single-metal displacement heteropolyacid salts. One set of equipment can cover the preparation needs of multiple types of Keggin-type heteropolyacid salts, demonstrating excellent prospects for industrial scale-up applications.

[0063] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0064] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0065] The above provides a detailed description of a low-temperature flowing ultra-low thermal resistance insulating thermal grease and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for synthesizing Keggin-type heteropolyacid salts, characterized in that, The steps include: preparation of the reaction substrate; microwave-assisted ball milling synthesis and product collection; The microwave-assisted ball milling synthesis step includes: The prepared reaction base material is loaded into a ball mill jar, and grinding balls are added according to the preset ball-to-material ratio to obtain the ball milling system to be reacted; The ball milling system to be reacted was placed in a microwave radiation field, the ball milling speed and microwave operating parameters were set, and a solid-phase reaction was carried out by an intermittent cyclic process of alternating microwave-free grinding and microwave-assisted grinding. After the reaction was completed, the solid-phase reaction product was obtained. The solid-phase reaction product was allowed to stand and cool to room temperature to complete the synthesis reaction process.

2. The method according to claim 1, characterized in that, The reaction substrate preparation steps include: Keggin-type heteropolyacids and reactants are mixed in a predetermined molar ratio, and a mixed solvent of water and ethanol is added. The mixture is stirred until homogeneous to obtain the reaction substrate. The Keggin-type heteropolyacids include H3PW 12 O 40 or H3PMo 12 O 40 .

3. The method according to claim 2, characterized in that, The reactants are organic cationic compounds or trivalent metal chlorides, and the molar ratio of the reactants to Keggin-type heteropolyacids is 3:

1.

4. The method according to claim 3, characterized in that, The organic cationic compound is tyrosine; the trivalent metal chloride is ferric chloride.

5. The method according to claim 1, characterized in that, The intermittent cyclic process consists of 15 minutes of microwave-free grinding and 5 minutes of microwave-assisted grinding as one cycle unit, and the cycle is repeated until the total reaction time reaches 200 minutes.

6. The method according to claim 1, characterized in that, The reaction substrate is a suspension substrate prepared by Keggin-type heteropolyacid and water-ethanol mixed solvent; In the microwave-assisted ball milling synthesis step, an aqueous solution of metal oxychloride is added dropwise at a uniform rate through a dropper at the top of the ball mill during the solid-phase reaction. The degree of metal substitution of the product is controlled by adjusting the amount of dropper added, thus obtaining a monometallic substitution Keggin-type heteropolyacid salt.

7. The method according to claim 6, characterized in that, The metal oxychloride is zirconium oxychloride, and the resulting monometallic substitution Keggin-type heteropolyacid salt has the general formula Zr. x H 3-x PW 12 O 40 , where x ranges from 0.25 to 0.

75.

8. The method according to claim 6, characterized in that, Before adding the aqueous solution of metal oxychloride, the ball milling system to be reacted was pre-ground without microwave for 5 minutes. After the addition is complete, the reaction continues in a cycle of 10 minutes of non-microwave grinding followed by 5 minutes of microwave-assisted grinding, with a total reaction time of 300 minutes.

9. The method according to claim 1, characterized in that, The preset ball-to-material mass ratio is 1:1, and the ball milling speed is 400 rpm; the microwave operating parameters are: power 0.8 kW, frequency 2.45 GHz.

10. An apparatus for synthesizing Keggin-type heteropolyacid salts, said apparatus for implementing the method according to any one of claims 1-9, characterized in that, The device includes a microwave oven and a ball mill jar placed inside the cavity of the microwave oven. The microwave device is used to heat the ball mill jar to provide reaction heat energy. The rated operating power of the microwave device is 0.8kW and the rated operating frequency is 2.45GHz. A drip tube is installed on the top of the ball mill jar, and a control valve for controlling the solution dripping rate is provided on the drip tube.

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