Potassium sulfate-based low-temperature reaction composite binder for casting and preparation method thereof

Abstract

This application provides a potassium sulfate-based low-temperature reactive composite binder for casting and its preparation method, belonging to the field of casting materials. The composite binder is composed of the following chemical components: anhydrous potassium sulfate micropowder: 68-75%, potassium aluminum sulfate: 3.0-5.0%, sodium silicate: 12-15%, γ-alumina nanosheets: 4-6%, 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2-3%, lithium / zirconium composite conductive agent: 0.8-1.2%, α-zirconium phosphate: 1.0-2.0%, potassium persulfate: 0.3-0.6%, and sodium phytate aqueous solution: 0.5%-1.0%. This overcomes the contradiction between "low-temperature curing efficiency and high-temperature service performance" and "high strength and good collapsibility" present in water glass-based casting binders used in intelligent casting island production.

Description

Technical Field

[0001] This application relates to the field of casting materials technology, and in particular to a potassium sulfate-based low-temperature reactive composite binder for casting and its preparation method. Background Technology

[0002] In the production system of modern intelligent foundry islands, the efficient and high-quality manufacturing of complex precision castings of light alloys (such as aluminum alloys and magnesium alloys) (such as motor housings for new energy vehicles and thin-walled components for aero engines) places far more stringent demands on the performance of casting binders than on traditional production lines. Water glass-based casting binders, due to their low cost, wide availability, and good environmental compatibility, have long been used as the core bonding material for light alloy casting cores. However, their inherent performance contradictions are further amplified in the automated, high-precision, and continuous production scenarios of intelligent foundry islands, becoming a key bottleneck restricting the improvement of intelligent casting efficiency and casting quality.

[0003] On the one hand, intelligent casting islands rely on automated core-making production lines to achieve efficient and continuous operation, which places clear demands on the low-temperature curing efficiency of binders. The production line cycle usually requires the core to be quickly cured and shaped within a low-temperature range of 60-90℃ to avoid the core-making process becoming a bottleneck in production. However, existing water glass-based binders, if relying solely on traditional ion exchange curing, have high reaction activation energy and slow curing rate at low temperatures, making it difficult to match the cycle of intelligent production lines. If high-activity curing agents (such as strong acids or high-concentration salts) are added to accelerate low-temperature curing, it will lead to a significant decrease in the high-temperature service performance of the core. During the pouring of molten metal (temperatures often exceed 600℃), the gel network formed too quickly is prone to thermal depolymerization due to its loose structure and low bond energy, resulting in softening, creep, or even collapse of the core, which in turn causes defects such as dimensional deviations and internal cavity deformation in the casting. This seriously conflicts with the goal of "one-time molding with high precision" pursued by intelligent casting islands and increases subsequent rework costs. On the other hand, the cores of complex thin-walled castings produced by intelligent casting islands must possess sufficient strength at both room temperature and high temperature: at room temperature, they must withstand the mechanical stress during automated handling and assembly to prevent core breakage; at high temperatures, they must resist the scouring and thermal shock of molten metal to ensure the integrity of the casting's internal cavity contour. However, existing water glass-based binders often improve strength by increasing the water glass modulus, increasing the amount of curing agent, or introducing inorganic rigid particles (such as ordinary alumina powder). This results in a dense and poorly soluble bond bridge structure formed after the core cools, with extremely poor disintegration properties. In the sand removal process of intelligent casting islands, traditional mechanical vibration and shot blasting methods not only fail to completely remove residual cores from complex internal cavities but also easily cause mechanical damage to thin-walled castings and precision hole systems, failing to meet the quality requirements of "non-destructive sand removal" in intelligent casting. At the same time, the dust and noise pollution generated by mechanical sand removal also contradicts the "clean workshop" concept pursued by intelligent casting islands, increasing the cost of workshop environmental management.

[0004] In summary, the two core contradictions commonly found in existing water glass-based casting binders—"low-temperature curing efficiency versus high-temperature service performance" and "high strength versus good collapsibility"—are irreconcilable in the context of automated, high-precision, and green production in intelligent casting islands. There is an urgent need to develop a new type of water glass-based binder that can adapt to the production requirements of intelligent casting islands and simultaneously resolve the aforementioned performance contradictions, in order to break through the technical bottleneck in the manufacturing of intelligent casting light alloy precision castings. Summary of the Invention

[0005] This application provides a potassium sulfate-based low-temperature reactive composite binder for casting and its preparation method, in order to solve the following technical problem: how to overcome the contradiction between "low-temperature curing efficiency and high-temperature service performance" and "high strength and good collapsibility" in water glass-based casting binders used in intelligent casting island production.

[0006] In a first aspect, embodiments of this application provide a potassium sulfate-based low-temperature reactive composite binder for casting. The composite binder, by mass fraction, comprises the following chemical components: anhydrous potassium sulfate micropowder: 68–75%, potassium aluminum sulfate: 3.0–5.0%, sodium silicate: 12–15%, γ-alumina nanosheets: 4–6%, 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2–3%, lithium / zirconium composite conductive agent: 0.8–1.2%, α-zirconium phosphate: 1.0–2.0%, potassium persulfate: 0.3–0.6%, and sodium phytate aqueous solution: 0.5%–1.0%.

[0007] Optionally, the modulus of the sodium silicate is 3.0 to 3.4.

[0008] Optionally, the γ-alumina nanosheets are two-dimensional sheet structures with an aspect ratio of not less than 50:1.

[0009] Optionally, the preparation method of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer includes the following steps:

[0010] 3-Aminopropyltriethoxysilane and boric acid were reacted in an alcohol solvent at 60–80 °C for 2–4 h to obtain the 3-aminopropyltriethoxysilane-boric acid hybrid prepolymer.

[0011] Optionally, the molar ratio of 3-aminopropyltriethoxysilane to boric acid is 1:(0.3-0.5).

[0012] Optionally, the lithium / zirconium composite conductive agent is composed of nano-zirconium oxide and lithium sulfate, wherein the mass ratio of nano-zirconium oxide to lithium sulfate is 1:(1.5~2.5).

[0013] Optionally, the nano-zirconia has a mixed crystal structure of monoclinic and tetragonal phases, and an average particle size of 20–50 nm.

[0014] Optionally, the mass concentration of the sodium phytate aqueous solution is 10-20%.

[0015] Secondly, embodiments of this application provide a method for preparing the potassium sulfate-based low-temperature reactive composite binder for casting as described in any one of the first aspects, the method comprising the following steps:

[0016] S1. Under an inert atmosphere, the γ-alumina nanosheets are calcined and activated at 300-400°C for 1 hour to obtain activated alumina;

[0017] S2. Using a portion of the anhydrous potassium sulfate micro powder as a carrier, grind it together with the lithium / zirconium composite conductive agent and the α-zirconium phosphate for 5 to 10 minutes to make the ultrafine powder uniformly adhere to the surface of the potassium sulfate carrier, thus obtaining a pre-coated composite powder.

[0018] S3. The remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina are subjected to primary low-speed dry mixing to obtain primary mixed dry material;

[0019] S4. Add the pre-coated composite powder to the primary mixed dry material, and then perform secondary low-speed dry mixing to obtain secondary mixed dry material.

[0020] S5. Add the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary mixed dry material and stir at medium speed to wet and coat the surface of the solid particles with the hybrid prepolymer to obtain a mixed wet material.

[0021] S6. Add the sodium silicate and the sodium phytate aqueous solution to the mixed wet material and stir at low speed to obtain the composite binder.

[0022] Optionally, in step S2, the mass of a portion of the anhydrous potassium sulfate micro powder is 25-35% of the total mass of the anhydrous potassium sulfate micro powder;

[0023] In step S3, the rotation speed of the primary low-speed dry mixer is 200-300 rpm, and the mixing time is 5-8 min.

[0024] In step S4, the rotation speed of the secondary low-speed dry mixer is 200-300 rpm, and the mixing time is 5-8 min.

[0025] In step S5, the speed of the medium-speed stirring is 400-600 rpm, and the stirring time is 8-10 min;

[0026] In step S6, the low-speed stirring speed is 200-300 rpm, and the stirring time is 5-8 min.

[0027] The technical solutions provided in this application have the following advantages compared with the prior art:

[0028] This application provides a potassium sulfate-based low-temperature reactive composite binder for casting. Through the synergistic design of multiple components in the formulation, it precisely solves the two core contradictions of existing water glass-based casting binders for intelligent casting islands: "low-temperature curing efficiency versus high-temperature service performance" and "high strength versus good collapsibility." The specific implementation path is as follows:

[0029] To address the contradiction between low-temperature curing efficiency and high-temperature service performance, this application designs components from two dimensions: accelerating the low-temperature reaction and constructing a high-temperature stable structure. In the low-temperature curing stage, potassium persulfate decomposes at a lower temperature to generate free radicals, rapidly stimulating the cross-linking reaction of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer, thus constructing the primary covalent network in advance and shortening the initial curing time. Simultaneously, the Li+ in the lithium / zirconium composite conductive agent accelerates the release of K+ from anhydrous potassium sulfate. + Na in sodium silicate + In terms of ion exchange, the layered structure of α-zirconium phosphate provides pre-established channels for cation migration, further reducing the curing activation energy and ensuring rapid molding at low temperatures. During high-temperature service, the two-dimensional structure of γ-alumina nanosheets can act as a "nanoskeleton" interspersed within the system, physically hindering network deformation at high temperatures; the Al dissociation of potassium aluminum sulfate... 3+ It can replace part of the Si in the silicon-oxygen network. 4+ This forms a more stable Al-O-Si ternary network; ZrO2 in the lithium / zirconium composite conductive agent also forms high-bond-energy Zr-O-Si bonds with the silicon-oxygen network. These structures work together to resist high-temperature shocks, prevent system softening or creep, and achieve a synergy between low-temperature rapid solidification and high-temperature stability.

[0030] To address the contradiction between "high strength and good collapseability," this application achieves a balance between "constructing a strong interpenetrating network" and "retaining a water-soluble matrix" through design. Regarding strength enhancement, ionic crosslinking (the phosphate ester groups of sodium phytate and K...) is employed. + Al 3+ The dynamic ionic bonds, covalent crosslinks (condensation reaction of hybrid prepolymer with sodium silicate and γ-alumina), and nano-reinforcement (γ-alumina and α-zirconium phosphate) form a three-dimensional interpenetrating network, providing both green strength at room temperature and residual strength at high temperatures, meeting the mechanical requirements of the casting process. Regarding collapsibility, the main component, anhydrous potassium sulfate, is water-soluble, and the glass phase formed after cooling sodium silicate is also water-soluble. Simultaneously, sodium phytate can regulate the aggregation state of metal ions in α-zirconium phosphate and the lithium / zirconium composite conductive agent, preventing the formation of insoluble structures. Ultimately, after the casting cools, the core can be rapidly dissolved and collapsed by immersion in warm water, eliminating the need for mechanical sand removal and achieving a balance between high strength and easy collapse. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic flowchart illustrating a method for preparing a potassium sulfate-based low-temperature reactive composite binder for casting, as provided in an embodiment of this application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] This application provides a potassium sulfate-based low-temperature reactive composite binder for casting. The composite binder, by mass fraction, comprises the following chemical components: anhydrous potassium sulfate micropowder: 68-75%, potassium aluminum sulfate: 3.0-5.0%, sodium silicate: 12-15%, γ-alumina nanosheets: 4-6%, 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2-3%, lithium / zirconium composite conductive agent: 0.8-1.2%, α-zirconium phosphate: 1.0-2.0%, potassium persulfate: 0.3-0.6%, and sodium phytate aqueous solution: 0.5%-1.0%.

[0036] It should be noted that the mass fraction of sodium phytate aqueous solution is based on the total mass of sodium phytate aqueous solution.

[0037] In some embodiments, the modulus of the sodium silicate is 3.0 to 3.4.

[0038] In some embodiments, the γ-alumina nanosheets are two-dimensional sheet structures with an aspect ratio of not less than 50:1.

[0039] In some embodiments, the preparation method of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer includes the following steps:

[0040] 3-Aminopropyltriethoxysilane and boric acid were reacted in an alcohol solvent at 60–80 °C for 2–4 h to obtain the 3-aminopropyltriethoxysilane-boric acid hybrid prepolymer.

[0041] In some embodiments, the molar ratio of the 3-aminopropyltriethoxysilane to the boric acid is 1:(0.3 to 0.5).

[0042] In some embodiments, the lithium / zirconium composite conductive agent is composed of nano-zirconium oxide and lithium sulfate, wherein the mass ratio of the nano-zirconium oxide to the lithium sulfate is 1:(1.5-2.5).

[0043] In some embodiments, the nano-zirconia has a mixed crystal structure of monoclinic and tetragonal phases, and an average particle size of 20–50 nm.

[0044] In some embodiments, the mass concentration of the sodium phytate aqueous solution is 10-20%.

[0045] This application presents a rationally designed chemical composition for a potassium sulfate-based low-temperature reactive composite adhesive, with the core functions of each component as follows:

[0046] (I) Main Matrix Components: Constructing the Basic Framework and Ion Source of the System

[0047] Anhydrous potassium sulfate powder (K2SO4) has an ionic crystal structure as its core, with strong intramolecular ionic bonds (K... + With SO4 2- This determines two main functions: first, as a "skeleton filler" of the system, it disperses in the form of micro-powder at room temperature, providing physical support for the sand core; although it partially melts at high temperatures, the crystal structure fragments can still maintain the core outline; second, as an "ion reservoir," it releases K+ after dissolution. + It can exchange cations with other components, while SO4 2- Can react with metal cations (such as Al) 3+ Zr 4+ It forms a weak coordination effect, which helps stabilize the dispersion of the system.

[0048] The key to the molecular structure of potassium aluminum sulfate (KAl(SO4)2) lies in the Al released after dissociation. 3+ Its ionic potential (charge / radius ratio) is much higher than that of K. + Na + It can bind more strongly to oxygen atoms. On the one hand, Al 3+ It can replace part of the Si in the silicon-oxygen network. 4+It forms a [AlO4] tetrahedral structure, which enhances the thermodynamic stability of the network through stronger Al-O bonds; on the other hand, the Al(OH)3 colloidal particles generated by its hydrolysis are positively charged and can adsorb negatively charged silicate and phosphate ions in the system, preventing solid particles from settling and improving suspension uniformity.

[0049] (ii) Gel network components: forming the binding core structure

[0050] The molecular core of sodium silicate (Na2O·nSiO2) is a linear or branched silicate anion (such as SiO3). 2- Si2O5 2- These anions are linked by Si-O-Si bonds, and each Si atom retains 1-2 Si-OH groups, which are the key active sites for forming the gel network. At room temperature, silicate exists in a dissolved state; when it encounters K... + Li + When the cations are equal, Si-OH undergoes dehydration condensation, and the Si-O-Si bonds further crosslink, gradually forming a three-dimensional potassium silicate gel network that "bonds" the sand particles to other components into a whole. The design of its modulus (SiO2 / Na2O ratio) of 3.0 to 3.4 ensures both the degree of polymerization of silicate (sufficient to form a strong network) and a certain degree of water solubility (facilitating subsequent sand cleaning).

[0051] The molecular structural advantages of γ-alumina nanosheets lie in their two-dimensional sheet-like morphology and abundant Al-OH groups on the surface: the sheet-like structure gives them a much larger specific surface area than ordinary powders, allowing them to be interwoven in the silica gel network like "nano-steel bars," physically hindering network deformation; while the surface Al-OH can undergo condensation reactions with the Si-OH of sodium silicate and the -Si-OH of hybrid prepolymers (forming Al-O-Si bonds), firmly anchoring the inorganic nanosheets in the gel network, while enhancing the network's density and reducing the channels for gas escape at high temperatures.

[0052] (III) Functional regulation components: Optimizing curing and high-temperature performance

[0053] The molecular structure of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer is an "organic-inorganic bifunctional" design: the -Si(OEt)3 group at one end can hydrolyze to -Si-OH, which condenses with the hydroxyl groups of sodium silicate and γ-alumina, achieving covalent bonding between the "inorganic end" and the gel network; the organic amine chain (-CH2CH2CH2NH2) in the middle is flexible and can form "molecular ligaments" in the rigid inorganic network, relieving internal stress during the curing process; the -B(OH)2 group (boronic acid residue) at the other end can form hydrogen bonds with amino groups and participate in the formation of BO-Si bonds at high temperatures, further enhancing the network's high-temperature resistance. The 1:(0.3~0.5) molar ratio of aminopropyltriethoxysilane to boric acid in its preparation process is precisely to balance the ratio of organic flexibility to inorganic rigidity.

[0054] The molecular interaction of lithium / zirconium composite conductive agents stems from the synergistic effect of two components: Lithium sulfate (Li₂SO₄) dissociates into Li₂. + With its small radius (approximately 0.076 nm) and high migration rate, it can serve as an "ion catalyst" to accelerate K+ ionization. + Na in sodium silicate + The exchange of ions reduces the activation energy for gel solidification. The monoclinic-tetragonal mixed-crystal structure of nano-zirconia (ZrO2) results in a large number of Zr-OH groups on its surface. These groups can react with the Si-OH groups of silicate to form Zr-O-Si bonds. The bond energy of this bond (approximately 640 kJ / mol) is much higher than that of the Si-O-Si bond (approximately 460 kJ / mol), which can act as a "stabilizing crosslinking point" at high temperatures, preventing the thermal depolymerization of the silicon-oxygen network. At the same time, the particle size of 20–50 nm ensures uniform dispersion and avoids local stress concentration. The mass ratio of 1:(1.5–2.5) ensures that Li + It has high catalytic efficiency and can provide sufficient high-temperature support through ZrO2.

[0055] The layered crystal structure of α-zirconium phosphate (Zr(HPO4)2·H2O) is its functional core: exchangeable H atoms exist between the layers. + With free water molecules, it can adsorb Li + K + The presence of cations forms "pre-placed ion channels," which accelerate cation diffusion within the system and shorten curing time. Simultaneously, the layered, sheet-like morphology synergizes with γ-alumina nanosheets to further enhance the network's creep resistance. The PO4 in its molecules... 3- The group can also react with Al 3+ Zr 4+ They form coordinate bonds, which help stabilize the dispersion of these metal ions and prevent them from becoming excessively aggregated.

[0056] The key to the molecular structure of potassium persulfate (K2S2O8) lies in the peroxy bond (-OO-), which is easily broken at 60–90°C, releasing sulfate free radicals (·SO4). - These free radicals have strong oxidizing properties and can attack the amino groups (-NH2) in the hybrid prepolymer, converting them into amino free radicals (-NH·). The amino free radicals can further initiate cross-linking reactions of silicate and boric acid groups, constructing a "primary covalent network" in advance before the formation of ion exchange gel, significantly improving the green strength (demolding strength) of the sand core and shortening the initial solidification time.

[0057] The molecular core of sodium phytate aqueous solution (mass concentration 10-20%) is a polyphosphate ester structure (containing 6 -PO4 groups). 3- Groups): Each phosphate ester group can react with K + Al 3+ Dynamic ionic bonds are formed, which can break and recombine when the sand core is subjected to external force, dissipating stress like "molecular springs" and improving the system's toughness. Simultaneously, the multidentate phosphate groups can adsorb onto the surface of solid particles, forming a steric hindrance layer to prevent the sedimentation of anhydrous potassium sulfate, nano-zirconia, and other particles. At high temperatures, its phosphate groups can also react with Zr. 4+ By combining and regulating the growth size of ZrO2 nanoclusters, excessive aggregation can be avoided, which may affect their disintegration properties.

[0058] Meanwhile, the synergistic interactions of the chemical components of the potassium sulfate-based low-temperature reactive composite adhesive in this application are as follows:

[0059] (I) Ion exchange and gel network construction: synergy between the host matrix and gel components

[0060] K released by anhydrous potassium sulfate + With Na in sodium silicate + First, ion exchange occurs, K + The ionic radius (0.138 nm) is slightly larger than that of Na. + (0.098nm) has a stronger binding force with silicate ions, which can promote the condensation and cross-linking of silicate ions and accelerate the formation of potassium silicate gel; at the same time, the Al dissociation of potassium aluminum sulfate 3+ It will preferentially combine with silicate ions, replacing some of the Si. 4+ The formation of [AlO4] tetrahedra, through Al-O-Si bonds, transforms the originally linear silicon-oxygen chains into a three-dimensional network, significantly improving the gel's strength and high-temperature resistance. During this process, the phosphate groups of sodium phytate react with K... + Al 3+ The formation of dynamic ionic bonds not only helps stabilize the distribution of these cations, but also alleviates the internal stress caused by gel shrinkage.

[0061] (II) Covalent cross-linking and reinforcement: the binding of functional regulatory components to the gel network

[0062] The Al-OH on the surface of γ-alumina nanosheets undergoes dehydration condensation with the Si-OH of sodium silicate and the -Si-OH of the hybrid prepolymer to form Al-O-Si covalent bonds. This action "anchors" the inorganic nanosheets to the silicon-oxygen network, transforming it from "physical filling" to "chemical reinforcement," significantly improving the network's tensile and creep resistance. In addition to reacting with inorganic components, the -Si-OH of the hybrid prepolymer can also react with free radicals generated by potassium persulfate to form NC covalent bonds, allowing organic chain segments to interweave in the inorganic network. This not only enhances the integrity of the network but also improves brittleness through the flexibility of the organic chains.

[0063] In lithium / zirconium composite conductive agents, Li + It enters the interlayer channels of α-zirconium phosphate, forming a "lithium-ion highway," which accelerates the combustion of lithium ions. + Diffusion into the silicon-oxygen network further catalyzes K + -Na + The exchange and condensation of silicate groups occur simultaneously. At the same time, the Zr-OH on the surface of nano-zirconia reacts with the Si-OH of silicate groups to form Zr-O-Si bonds, which become the "thermally stable cross-linking points" of the network at high temperatures (>400℃), preventing the thermal depolymerization of silicon-oxygen bonds. Meanwhile, the layered structure of α-zirconia phosphate works synergistically with ZrO2 to further enhance the skeletal support capacity at high temperatures.

[0064] (III) Dynamic Regulation and Collapse Protection: Synergy of Dispersing and Regulating Components

[0065] In addition to initiating cross-linking, the free radicals released by potassium persulfate can also slightly oxidize the hydroxyl groups of sodium phytate, enhancing its coordination ability with metal cations and further improving the suspension stability of the system; while the phosphate ester groups of sodium phytate react with the PO4 groups of α-zirconium phosphate at high temperatures. 3- Collaboration, through Zr 4+ Al 3+ The coordination effect regulates the aggregation state of these metal ions, preventing both excessive dispersion leading to insufficient high-temperature strength and excessive agglomeration affecting water solubility. Ultimately, after the casting cools, the system contains a large amount of K₂SO₄ (water-soluble), potassium silicate glass phase (water-soluble), and Zr ions regulated by phosphate groups. 4+ Al 3+ (Easily dissolved in warm water), together they ensure that the core can quickly disintegrate in warm water, achieving sand removal without residue.

[0066] Figure 1 This is a schematic flowchart illustrating a method for preparing a potassium sulfate-based low-temperature reactive composite binder for casting, as provided in an embodiment of this application.

[0067] Based on a general inventive concept, such as Figure 1 As shown, this application provides a method for preparing the potassium sulfate-based low-temperature reactive composite binder for casting as described in any one of the first aspects, the method comprising the following steps:

[0068] S1. Under an inert atmosphere, the γ-alumina nanosheets are calcined and activated at 300-400°C for 1 hour to obtain activated alumina;

[0069] S2. Using a portion of the anhydrous potassium sulfate micro powder as a carrier, grind it together with the lithium / zirconium composite conductive agent and the α-zirconium phosphate for 5 to 10 minutes to make the ultrafine powder uniformly adhere to the surface of the potassium sulfate carrier, thus obtaining a pre-coated composite powder.

[0070] S3. The remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina are subjected to primary low-speed dry mixing to obtain primary mixed dry material;

[0071] S4. Add the pre-coated composite powder to the primary mixed dry material, and then perform secondary low-speed dry mixing to obtain secondary mixed dry material.

[0072] S5. Add the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary mixed dry material and stir at medium speed to wet and coat the surface of the solid particles with the hybrid prepolymer to obtain a mixed wet material.

[0073] S6. Add the sodium silicate and the sodium phytate aqueous solution to the mixed wet material and stir at low speed to obtain the composite binder.

[0074] In some embodiments, in step S2, the mass of a portion of the anhydrous potassium sulfate micro powder is 25-35% of the total mass of the anhydrous potassium sulfate micro powder;

[0075] In step S3, the rotation speed of the primary low-speed dry mixer is 200-300 rpm, and the mixing time is 5-8 min.

[0076] In step S4, the rotation speed of the secondary low-speed dry mixer is 200-300 rpm, and the mixing time is 5-8 min.

[0077] In step S5, the speed of the medium-speed stirring is 400-600 rpm, and the stirring time is 8-10 min;

[0078] In step S6, the low-speed stirring speed is 200-300 rpm, and the stirring time is 5-8 min.

[0079] It should be noted that the S1 step, which involves calcination activation at 300–400℃ for 1 hour, effectively removes physically adsorbed water molecules from the nanosheet surface through heat treatment. Simultaneously, it promotes the rearrangement of surface Al-O bonds, increasing the density of chemically more active Al-OH groups. These hydroxyl groups, acting as core active sites, will undergo condensation reactions with the silicon-oxygen network and hybrid prepolymers in subsequent reactions to form Al-O-Si bonds, directly enhancing the chemical bonding strength between the nanosheets and other components.

[0080] The S2 step, involving the pre-dispersion and coating of the active components, employs a "carrier coating" strategy to address the agglomeration problem of highly active ultrafine powders and establishes a "delayed activation" mechanism to ensure they function effectively during the optimal reaction stage. Specifically, a portion of dried anhydrous potassium sulfate micropowder is used as a carrier; its moderate particle size (as the main component) provides sufficient surface area to support the ultrafine powder. This carrier is then co-ground with a lithium / zirconium composite conductive agent and α-zirconium phosphate under inert gas protection for 5-10 minutes. Through mechanochemical action, the nanoscale conductive agent and zirconium phosphate particles are uniformly adhered to the surface of the potassium sulfate carrier via van der Waals forces and mechanical intercalation, forming a stable pre-coated composite powder. This coating method not only avoids agglomeration of the ultrafine powders due to their high surface energy but also reduces premature contact with subsequent components (especially water glass) through physical isolation. The active component is only gradually released after the aqueous phase permeates during the wet mixing stage, achieving "on-demand activation."

[0081] The stepped sequential mixing in steps S3 to S6 achieves an orderly transition from physical dispersion to chemical pre-reaction by controlling the feeding sequence, stirring intensity, and temperature in stages, thus ensuring system uniformity and process stability.

[0082] The initial dry mixing in step S3 involves stirring at a low speed of 200–300 rpm for 5–8 minutes to mix the remaining anhydrous potassium sulfate micro powder, potassium aluminum sulfate, potassium persulfate, and activated alumina. The low-speed stirring avoids electrostatic agglomeration of the powder due to high-speed collisions, while the gentle shearing force achieves a macroscopically uniform distribution of the dry materials, laying the foundation for the subsequent introduction of active components.

[0083] In step S4, the secondary dry mixing continues at a low speed for 5-8 minutes. The pre-coated composite powder is then added. Continuing to mix at a low speed ensures that the coated powder is evenly dispersed in the dry material system, avoids local enrichment, and prevents the coating layer from falling off due to violent mechanical action, thus maintaining the "delayed activation" effect.

[0084] In step S5, the primary wet mixing speed is increased to 400-600 rpm and stirred for 8-10 minutes. Then, the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer is added. The shear force generated by the medium-speed stirring can promote the rapid wetting of all solid particle surfaces by the hybrid prepolymer, so that it forms a uniform organic-inorganic transition layer. This transition layer provides a large number of active sites for the subsequent condensation reaction with the silicon-oxygen network, and also improves the toughness of the system through the flexibility of the organic segments.

[0085] In step S6, the secondary trigger wet mixing is carried out at a low speed of 200-300 rpm for 5-8 minutes. At the same time, ultrasonically treated sodium silicate and sodium phytate aqueous solution are added. The low temperature environment can inhibit the premature decomposition of potassium persulfate (avoiding premature cross-linking by free radicals), and the low speed stirring reduces the temperature rise of the system, ensuring that physical wetting is the main process at this time. This allows the water glass and sodium phytate to penetrate evenly into the interparticle gaps and gradually come into contact with the transition layer and coated powder formed in the previous stage. The stirring time of 5-8 minutes is sufficient to form uniform and loose wet particles, which not only ensures the fluidity during subsequent core making, but also reserves sufficient activity for the orderly reaction in the use stage (core making and curing).

[0086] In summary, the potassium sulfate-based low-temperature reactive composite binder for casting in this application, through the deep coupling of formulation design and preparation process, forms a comprehensive advantage covering performance, process, environmental protection and industrialization. It significantly breaks through many contradictions between the core performance and practical application of traditional casting binders, demonstrating distinct technological innovation and practical value.

[0087] At the formulation design level, its core advantage lies in constructing a multi-network interpenetrating system with "precise synergy at the molecular level," rather than a simple mixture of components. By introducing active components with specific structures, the system can orderly form three major networks at different temperature stages: ionic cross-linking, covalent condensation, and high-temperature glass phase. These networks achieve deep synergy through chemical bond anchoring and spatial interpenetration. At low temperatures, the ionic network quickly completes core shaping while reserving active sites for subsequent reactions. At medium temperatures, the covalent network, relying on an organic-inorganic hybrid structure, enhances strength while injecting flexibility and alleviating internal stress during curing. At high temperatures, the glass phase network fills pores and fuses with the preceding network, relying on high-bond-energy chemical bonds to ensure creep resistance. This design not only solves the pain points of traditional binders such as "slow curing at low temperatures" and "easy softening at high temperatures," but also ensures that the core can quickly disintegrate under mild conditions after the casting cools through the combination of a water-soluble matrix and controllable active components. This completely avoids the risk of damage to the casting cavity caused by mechanical sand removal, while also avoiding interference from residual binder on casting quality, achieving a unified performance of "fast curing, high strength, and easy disintegration."

[0088] At the manufacturing process level, this application transforms process advantages into a stable guarantee of product performance through refined process design. The raw material pretreatment stage features customized treatment schemes for different component characteristics. For example, calcination activation of γ-alumina nanosheets increases the density of surface active sites, ultrasonic dispersion of sodium silicate breaks up agglomeration, and drying and cooling of anhydrous potassium sulfate prevents moisture absorption, laying the foundation for uniformity in subsequent reactions from the source. The active component pre-coating strategy innovatively solves the agglomeration problem of nanoscale highly active powders. Utilizing the physical isolation of an inert carrier, the active components are activated "on demand," preventing premature reactions with other components that could lead to system instability. Simultaneously, it ensures uniform nanoscale dispersion in the final product, fully realizing… It plays an enhancing and catalytic role; the step-by-step sequential mixing process achieves an orderly transition from physical dispersion to chemical pre-reaction through precise control of the feeding sequence, stirring intensity and temperature. The primary dry mixing ensures the macroscopic uniformity of dry materials, the secondary dry mixing maintains the stability of the pre-coated structure, the primary wet mixing constructs an organic-inorganic transition layer, and the secondary trigger wet mixing achieves uniform wetting of aqueous components in a low-temperature environment. The entire process avoids the "premature occurrence" or "localized intensity" of the reaction, which not only ensures the consistency of product performance, but also extends the usable time of the mixed materials, and is suitable for the continuous production needs of automated core making.

[0089] From the perspective of practical application and environmental value, the advantages of this application extend further to the entire production cycle. The formula contains no toxic components such as phenols and aldehydes, and the preparation and casting processes release no irritating or harmful gases, significantly improving the production environment and aligning with the development trend of green casting. The waste sand generated after core collapse can be recycled through simple washing because the binder's main component is water-soluble, greatly reducing solid waste treatment costs and resource consumption, thus balancing economic benefits and environmental responsibility. Simultaneously, its excellent low-temperature curing efficiency, high-temperature stability, and collapse properties precisely meet the needs of high-end casting scenarios such as complex thin-walled castings and high-speed automated core making, solving the problems of "difficult molding, poor quality, and low efficiency" of traditional binders in these scenarios, and providing a reliable binder solution for high-end casting production.

[0090] The potassium sulfate-based low-temperature reactive composite binder of this application can be widely used in the casting field for core preparation of light alloy castings such as aluminum alloys and magnesium alloys, especially suitable for the production needs of complex thin-walled castings (such as engine blocks, gearbox housings, and new energy vehicle motor housings). In the core-making process, its low-temperature rapid curing characteristics are compatible with automated core-making production lines, shortening the core forming cycle. Furthermore, the mixed materials have a long usable time, ensuring continuous production efficiency. During the pouring process, thanks to its excellent high-temperature creep resistance and low gas evolution, it can withstand the high-temperature impact of molten metal without softening or deformation, avoiding defects such as porosity and incomplete filling, ensuring the dimensional accuracy and internal quality of the castings. After the casting cools, the core can be quickly dissolved by soaking in warm water, eliminating the need for mechanical vibration or shot blasting, thus avoiding damage to the casting's internal cavity and simplifying the sand removal process. Simultaneously, its environmentally friendly formula releases no toxic gases, and the old sand can be recycled through simple water washing, helping casting companies achieve green production, reducing solid waste treatment costs and resource consumption. Overall, it meets the multiple demands of high-end casting for efficiency, quality, and environmental protection.

[0091] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0092] Example 1

[0093] This embodiment provides a potassium sulfate-based low-temperature reactive composite binder for casting, which, by mass fraction, comprises the following chemical components:

[0094] Anhydrous potassium sulfate micro powder: 71%, particle size: 100-150 mesh;

[0095] Potassium aluminum sulfate: 4%;

[0096] Sodium silicate: 13.5%, modulus: 3.2, density: 1.45 g / cm³ 3 Source: Foshan Zhongfa Water Glass Factory;

[0097] γ-alumina nanosheets: 5%, aspect ratio: ≥60:1, morphology: two-dimensional sheet;

[0098] 3-Aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2.5%, preparation method: 3-aminopropyltriethoxysilane (CAS No.: 919-30-2) and boric acid are dissolved in anhydrous ethanol at a molar ratio of 1:0.4 and reacted at 70°C for 3 h to obtain the prepolymer.

[0099] Lithium / zirconium composite conductive agent: 1%, composition: nano-zirconium oxide and lithium sulfate are compounded in a mass ratio of 1:2, nano-zirconium oxide specifications: monoclinic and tetragonal mixed crystals, average particle size 30nm;

[0100] Zirconium α-phosphate: 1.5%, morphology: layered powder;

[0101] Potassium persulfate: 0.5%;

[0102] Sodium phytate aqueous solution: 1.0%, solvent: deionized water, mass concentration: 15%, sodium phytate CAS number: 14306-25-3.

[0103] Based on the chemical composition of the above-mentioned binder, this embodiment also provides a method for preparing a potassium sulfate-based low-temperature reactive composite binder for casting, comprising the following steps:

[0104] S1. Place γ-alumina nanosheets in a tube furnace and heat to 350°C at a rate of 4°C / min under nitrogen protection. Calcinate and activate at this temperature for 1 hour to obtain activated alumina. Then allow the furnace to cool naturally to below 80°C, remove the nanosheets, and seal for storage.

[0105] S2. Weigh out dried anhydrous potassium sulfate micro powder (approximately 33% of the total potassium sulfate mass) as a carrier, and add it together with all of the lithium / zirconium composite conductive agent and α-zirconium phosphate into a vibratory mill. Grind together for 8 minutes under a nitrogen atmosphere to obtain a pre-coated composite powder. The powder should be uniformly white and free of visible spots.

[0106] S3, Primary Dry Mixing: Add the remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina to a high-speed mixer. Dry mix at 250 rpm for 6 minutes to obtain the primary dry mixture.

[0107] S4. Secondary dry mixing: Add all the pre-coated composite powder obtained in step S2 to the above primary dry mixture and continue to dry mix at 250 rpm for 6 minutes to obtain the secondary dry mixture.

[0108] S5, Primary Wet Mixing: Add all of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary dry mixture. Increase the mixer speed to 500 rpm and stir for 9 minutes. During this process, control the material temperature to remain below 35°C using jacketed water cooling until the material is a uniform, moist powder, thus obtaining the wet mixture.

[0109] S6, Secondary Trigger Wet Mixing: Sodium silicate and sodium phytate aqueous solution are pre-mixed and then slowly added to the wet mixture. Simultaneously, the mixer speed is adjusted back to 250 rpm, and stirring is continued for 6 minutes. During this stage, the material temperature is further controlled to remain below 35°C through cooling, ultimately yielding a uniformly colored, loose, and lumpy wet granular composite binder.

[0110] Example 2

[0111] This embodiment provides a potassium sulfate-based low-temperature reactive composite binder for casting, which, by mass fraction, comprises the following chemical components:

[0112] Anhydrous potassium sulfate micro powder: 69.4%, particle size: 100-150 mesh;

[0113] Potassium aluminum sulfate: 4.5%;

[0114] Sodium silicate: 14.5%, modulus: 3.3, density: 1.46 g / cm³ 3 Source: Foshan Zhongfa Water Glass Factory;

[0115] γ-alumina nanosheets: 5.5%, aspect ratio: ≥55:1, morphology: two-dimensional sheet;

[0116] 3-Aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2.0%, preparation method: 3-aminopropyltriethoxysilane and boric acid are dissolved in anhydrous ethanol at a molar ratio of 1:0.35 and reacted at 65°C for 3.5 h to obtain the prepolymer.

[0117] Lithium / zirconium composite conductive agent: 1.2%, composition: nano-zirconium oxide and lithium sulfate are composited at a mass ratio of 1:2.2, nano-zirconium oxide specifications: monoclinic and tetragonal mixed crystals, average particle size 25nm;

[0118] Zirconium α-phosphate: 1.3%, morphology: layered powder;

[0119] Potassium persulfate: 0.6%;

[0120] Sodium phytate aqueous solution: 1.0%, solvent: deionized water, mass concentration: 18%.

[0121] Based on the chemical composition of the above-mentioned binder, this embodiment also provides a method for preparing a potassium sulfate-based low-temperature reactive composite binder for casting, comprising the following steps:

[0122] S1. Place γ-alumina nanosheets in a tube furnace and heat to 380°C at a rate of 3°C / min under nitrogen protection. Activate the nanosheets at this temperature for 1 hour to obtain activated alumina. Then allow the furnace to cool naturally to below 80°C, remove the nanosheets, and seal them for storage.

[0123] S2. Weigh out dried anhydrous potassium sulfate micro powder (approximately 30% of the total potassium sulfate mass) as a carrier, and add it together with all of the lithium / zirconium composite conductive agent and α-zirconium phosphate into a vibratory mill. Grind together for 10 minutes under a nitrogen atmosphere to obtain a pre-coated composite powder. This powder should be uniformly white and free of visible spots.

[0124] S3, Primary Dry Mixing: Add the remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina to a high-speed mixer. Dry mix at 220 rpm for 7 minutes to obtain the primary dry mixture.

[0125] S4. Secondary dry mixing: Add all the pre-coated composite powder obtained in step S2 to the above primary dry mixture and continue to dry mix at 220 rpm for 5 minutes to obtain the secondary dry mixture.

[0126] S5, Primary Wet Mixing: Add all of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary dry mixture. Increase the mixer speed to 450 rpm and stir for 10 minutes. During this process, control the material temperature to remain below 35°C using jacketed water cooling until the material is a uniform, moist powder, thus obtaining the wet mixture.

[0127] S6, Secondary Trigger Wet Mixing: Sodium silicate and sodium phytate aqueous solution are pre-mixed and then slowly added to the wet mixture. Simultaneously, the mixer speed is adjusted back to 220 rpm, and stirring is continued for 7 minutes. During this stage, the material temperature is further controlled to remain below 35°C through cooling, ultimately yielding a uniformly colored, loose, and lumpy wet granular composite binder.

[0128] Example 3

[0129] This embodiment provides a potassium sulfate-based low-temperature reactive composite binder for casting, which, by mass fraction, comprises the following chemical components:

[0130] Anhydrous potassium sulfate micro powder: 73%, particle size: 100-150 mesh;

[0131] Potassium aluminum sulfate: 3.5%;

[0132] Sodium silicate: 12.5%, modulus: 3.1, density: 1.44 g / cm³ 3 Source: Foshan Zhongfa Water Glass Factory;

[0133] γ-alumina nanosheets: 4.5%, aspect ratio: ≥65:1, morphology: two-dimensional sheet;

[0134] 3-Aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 3.0%, preparation method: 3-aminopropyltriethoxysilane and boric acid are dissolved in anhydrous ethanol at a molar ratio of 1:0.45 and reacted at 75°C for 2.5 h to obtain the prepolymer.

[0135] Lithium / zirconium composite conductive agent: 0.9%, composition: nano-zirconium oxide and lithium sulfate in a mass ratio of 1:1.8, nano-zirconium oxide specifications: monoclinic and tetragonal mixed crystals, average particle size 35nm;

[0136] Zirconium α-phosphate: 1.7%, morphology: layered powder;

[0137] Potassium persulfate: 0.3%;

[0138] Sodium phytate aqueous solution: 0.6%, solvent: deionized water, mass concentration: 12%.

[0139] Based on the chemical composition of the above-mentioned binder, this embodiment also provides a method for preparing a potassium sulfate-based low-temperature reactive composite binder for casting, comprising the following steps:

[0140] S1. Place γ-alumina nanosheets in a tube furnace and heat to 320°C at a rate of 5°C / min under nitrogen protection. Activate the nanosheets at this temperature for 1 hour to obtain activated alumina. Then allow the furnace to cool naturally to below 80°C, remove the nanosheets, and seal them for storage.

[0141] S2. Weigh out dried anhydrous potassium sulfate micro powder (approximately 35% of the total potassium sulfate mass) as a carrier, and add it together with all of the lithium / zirconium composite conductive agent and α-zirconium phosphate into a vibratory mill. Grind together for 6 minutes under a nitrogen atmosphere to obtain a pre-coated composite powder. This powder should be uniformly white and free of visible spots.

[0142] S3, Primary Dry Mixing: Add the remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina to a high-speed mixer. Dry mix at 280 rpm for 5 minutes to obtain the primary dry mixture.

[0143] S4. Secondary dry mixing: Add all the pre-coated composite powder obtained in step S2 to the above primary dry mixture and continue to dry mix at 280 rpm for 4 minutes to obtain the secondary dry mixture.

[0144] S5, Primary Wet Mixing: Add all of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary dry mixture. Increase the mixer speed to 550 rpm and stir for 8 minutes. During this process, control the material temperature to remain below 35°C using jacketed water cooling until the material is a uniform, moist powder, thus obtaining the wet mixture.

[0145] S6, Secondary Trigger Wet Mixing: Sodium silicate and sodium phytate aqueous solution are pre-mixed and then slowly added to the wet mixture. Simultaneously, the mixer speed is adjusted back to 280 rpm, and stirring is continued for 5 minutes. During this stage, the material temperature is further controlled to remain below 35°C through cooling, ultimately yielding a uniformly colored, loose, and lumpy wet granular composite binder.

[0146] Example 4

[0147] This embodiment provides a potassium sulfate-based low-temperature reactive composite binder for casting, which, by mass fraction, comprises the following chemical components:

[0148] Anhydrous potassium sulfate micro powder: 71.5%, particle size: 100-150 mesh;

[0149] Potassium aluminum sulfate: 4.0%;

[0150] Sodium silicate: 13.0%, modulus: 3.2, density: 1.45 g / cm³ 3 Source: Foshan Zhongfa Water Glass Factory;

[0151] γ-alumina nanosheets: 5.0%, aspect ratio: ≥60:1, morphology: two-dimensional sheet;

[0152] 3-Aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2.5%, preparation method: 3-aminopropyltriethoxysilane and boric acid are dissolved in anhydrous ethanol at a molar ratio of 1:0.4 and reacted at 70°C for 3 h to obtain the prepolymer.

[0153] Lithium / zirconium composite conductive agent: 1.0%, composition: nano-zirconium oxide and lithium sulfate are composited in a mass ratio of 1:2, nano-zirconium oxide specifications: monoclinic and tetragonal mixed crystals, average particle size 30nm;

[0154] Zirconium α-phosphate: 1.5%, morphology: layered powder;

[0155] Potassium persulfate: 0.5%;

[0156] Sodium phytate aqueous solution: 1.0%, solvent: deionized water, mass concentration: 15%.

[0157] Based on the chemical composition of the above-mentioned binder, this embodiment also provides a method for preparing a potassium sulfate-based low-temperature reactive composite binder for casting, comprising the following steps:

[0158] S1. Place γ-alumina nanosheets in a tube furnace and heat to 350°C at a rate of 4°C / min under nitrogen protection. Calcinate and activate at this temperature for 1 hour to obtain activated alumina. Then allow the furnace to cool naturally to below 80°C, remove the nanosheets, and seal for storage.

[0159] S2. Weigh out dried anhydrous potassium sulfate micro powder (approximately 33% of the total potassium sulfate mass) as a carrier, and add it together with all of the lithium / zirconium composite conductive agent and α-zirconium phosphate into a vibratory mill. Grind together for 8 minutes under a nitrogen atmosphere to obtain a pre-coated composite powder. The powder should be uniformly white and free of visible spots.

[0160] S3, Primary Dry Mixing: Add the remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina to a high-speed mixer. Dry mix at 250 rpm for 6 minutes to obtain the primary dry mixture.

[0161] S4. Secondary dry mixing: Add all the pre-coated composite powder obtained in step S2 to the above primary dry mixture and continue to dry mix at 250 rpm for 5 minutes to obtain the secondary dry mixture.

[0162] S5, Primary Wet Mixing: Add all of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary dry mixture. Increase the mixer speed to 500 rpm and stir for 9 minutes. During this process, control the material temperature to remain below 35°C using jacketed water cooling until the material is a uniform, moist powder, thus obtaining the wet mixture.

[0163] S6, Secondary Trigger Wet Mixing: Sodium silicate and sodium phytate aqueous solution are pre-mixed and then slowly added to the wet mixture. Simultaneously, the mixer speed is adjusted back to 250 rpm, and stirring is continued for 6 minutes. During this stage, the material temperature is further controlled to remain below 35°C through cooling, ultimately yielding a uniformly colored, loose, and lumpy wet granular composite binder.

[0164] Comparative Example 1

[0165] This comparative example is modified from the one disclosed in Example 1 as follows:

[0166] The γ-alumina nanosheets in the binder were removed, and the remaining components and their mass fractions were adjusted as follows: 76% anhydrous potassium sulfate micro powder, 4% potassium aluminum sulfate, 13.5% sodium silicate, 2.5% 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer, 1% lithium / zirconium composite conductive agent, 1.5% α-zirconium phosphate, 0.5% potassium persulfate, and 1.0% sodium phytate aqueous solution.

[0167] Comparative Example 2

[0168] This comparative example is modified from the one disclosed in Example 1 as follows:

[0169] The 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer in the binder was removed, and the remaining components and their mass fractions were adjusted as follows: 73.5% anhydrous potassium sulfate micro powder, 4% potassium aluminum sulfate, 13.5% sodium silicate, 5% γ-alumina nanosheets, 1% lithium / zirconium composite conductive agent, 1.5% α-zirconium phosphate, 0.5% potassium persulfate, and 1.0% sodium phytate aqueous solution.

[0170] Comparative Example 3

[0171] This comparative example is modified from the one disclosed in Example 1 as follows:

[0172] The sodium phytate aqueous solution in the binder was removed, and the remaining components and their mass fractions were adjusted as follows: 71% anhydrous potassium sulfate micro powder, 4% potassium aluminum sulfate, 14.5% sodium silicate, 5% γ-alumina nanosheets, 2.5% 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer, 1% lithium / zirconium composite conductive agent, 1.5% α-zirconium phosphate, and 0.5% potassium persulfate.

[0173] Comparative Example 4

[0174] This comparative example is modified from the one disclosed in Example 1 as follows:

[0175] The lithium / zirconium composite conductive agent in the binder was removed, and the remaining components and their mass fractions were adjusted as follows: 72% anhydrous potassium sulfate micro powder, 4% potassium aluminum sulfate, 13.5% sodium silicate, 5% γ-alumina nanosheets, 2.5% 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer, 1.5% α-zirconium phosphate, 0.5% potassium persulfate, and 1.0% sodium phytate aqueous solution.

[0176] Comparative Example 5

[0177] This comparative example is modified from the one disclosed in Example 1 as follows:

[0178] The calcination and activation step of γ-alumina nanosheets is omitted, and unactivated γ-alumina nanosheets are used directly.

[0179] Comparative Example 6

[0180] This comparative example is modified from the one disclosed in Example 1 as follows:

[0181] The preparation step of the pre-coated composite powder (i.e., step S2) is omitted. All anhydrous potassium sulfate micro powder, potassium aluminum sulfate, potassium persulfate, activated alumina, lithium / zirconium composite conductive agent and α-zirconium phosphate are directly added to a high-speed mixer for primary dry mixing (250 rpm, 12 min). The subsequent steps (S5-S6) are the same as in Example 1.

[0182] The adhesives obtained in Examples 1-4 and Comparative Examples 1-6 were subjected to performance testing. The performance results are shown in Table 1. The performance testing methods are as follows:

[0183] Tensile strength at room temperature: The binder and standard foundry quartz sand were mixed at a mass ratio of 3:97 to form a standard figure-eight shaped specimen. After step curing (80℃ / 1.5h + 110℃ / 0.75h), the tensile strength (MPa) was measured at room temperature using a smart strength tester (SWY type).

[0184] Curing time: Record the time (min) required from the time the sample enters the 80℃ oven until its strength reaches 0.5MPa (the strength at which it can be safely demolded).

[0185] High-temperature compressive strength at 600℃: The cured cylindrical specimen (Φ30×50mm) was placed in a box-type resistance furnace and heated to 600℃ at a rate of 10℃ / min and held for 15min. Then it was immediately taken out and its compressive strength (MPa) was measured using a universal testing machine.

[0186] Gas Emission: Take 1.0g (accurate to 0.01g) of cured adhesive sand sample and place it in a tube furnace of an 850℃ gas emission meter (SFL type) to determine its gas emission (mL / g).

[0187] Collapsibility (sand drop performance): The cured standard tensile test specimen was immersed in a constant temperature water bath at 80°C, and the time (min) from the start of immersion to complete self-disintegration and natural sand drop was recorded.

[0188] Demolding pass rate: Under industrialized core-making production conditions, 100 complex cores are pressed, and the percentage (%) of the cores that are intact, without cracks or defects after demolding is counted.

[0189] Table 1. Performance of the adhesives in Examples 1-4 and Comparative Examples 1-6

[0190]

[0191] As shown in Table 1, the room temperature tensile strength of Examples 1-4 is stable at 1.7-1.9 MPa, which meets the mechanical requirements for core handling and assembly; the curing time is only 11-14 min, demonstrating high efficiency in low-temperature curing, which is suitable for the continuous production cycle of intelligent casting islands; the high-temperature compressive strength at 600℃ is maintained at 1.1-1.3 MPa, which can withstand the high-temperature impact during molten metal pouring; the gas generation is controlled at 13.8-15.2 mL / g, which effectively avoids porosity defects in castings; the collapse time is less than 4 min (2.9-3.8 min), which can be quickly cleaned with warm water without residue; the demolding qualification rate is 96-98%, indicating that the core has good integrity after molding and very little cracking or breakage, which fully verifies the advantages of the present invention in balancing the performance of "low-temperature rapid curing, high-temperature toughness, and easy collapse".

[0192] The production line cycle of 30 molds per hour in the intelligent casting island must meet the requirement that the total cycle time of a single mold is ≤2 minutes. Data from Examples 1-4 shows good compatibility with this cycle time: the curing time of 11-14 minutes can be handled by the multi-station continuous curing furnace of the intelligent casting island (a 12-station furnace can produce one mold every 1.2 minutes), eliminating the need for waiting for each mold; a demolding pass rate of 96-98% reduces the risk of rework and avoids cycle interruptions; a warm water dissipation time of <4 minutes, combined with parallel sand cleaning tanks, allows for rapid connection to subsequent processes; and the low gas generation of 13.8-15.2 mL / g eliminates the need for additional venting time, while the room temperature tensile strength of 1.7-1.9 MPa ensures undamaged handling by the robotic arm. There are no significant bottlenecks throughout the entire process, allowing for stable matching of the 30 molds per hour production rhythm.

[0193] Comparative Example 1, lacking γ-alumina nanosheets, exhibits a significant performance deficiency primarily due to a sharp deterioration in high-temperature compressive strength. Its compressive strength at 600℃ is only 0.6 MPa, a mere 50% of the average of Examples 1-4 (1.2 MPa). γ-alumina nanosheets, as a two-dimensional sheet-like nano-reinforcing phase, can normally form Al-O-Si covalent bonds with the silicon-oxygen network and hybrid prepolymers through surface hydroxyl groups, constructing a "high-temperature skeleton" in the system and hindering the softening and creep of the gel network at high temperatures. Without this component, the silicon-oxygen network loses its nanoscale physical support at high temperatures, making it prone to structural deformation and resulting in a substantial decrease in high-temperature load-bearing capacity. Simultaneously, its auxiliary reinforcing effect on room-temperature tensile strength also disappears, causing the room-temperature tensile strength to drop to 1.3 MPa, a 27.8% decrease compared to the average of the examples (1.8 MPa), further demonstrating the crucial supporting value of this component for the mechanical properties of the system.

[0194] Comparative Example 2, lacking the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer, exhibits performance limitations primarily in demolding success rate and room-temperature tensile strength. The demolding success rate is only 85% (compared to an average of 97.2% in other examples), and the room-temperature tensile strength drops to 1.5 MPa. The core function of the hybrid prepolymer is to provide "flexible toughening" through organic amine segments, while its… The functional groups can form covalent crosslinks with the silicon-oxygen network and γ-alumina nanosheets, improving the overall integrity of the system. When these functional groups are missing, the core loses the buffering effect of the organic flexible chain segments, significantly increasing its brittleness. During demolding, it is prone to cracking, chipping, and other defects under mechanical stress, leading to a sharp drop in the yield rate. Simultaneously, the covalent crosslinking density decreases, making it difficult for the system to form a stable mechanical structure at room temperature. This results in a 16.7% decrease in room temperature tensile strength compared to the average of the examples, and the curing reaction is slightly delayed due to insufficient crosslinking sites (curing time 15 min, 36.4% longer than the shortest time of 11 min in the examples).

[0195] Comparative Example 3, lacking sodium phytate aqueous solution, exhibited performance degradation primarily manifested as prolonged curing time and increased gas evolution. The curing time reached 18 min (average of 12.5 min in the examples), and the gas evolution was 16.5 mL / g (average of 14.5 mL / g in the examples), while the collapse time was extended to 4.1 min. The polyphosphate groups of sodium phytate could originally interact with… , The formation of "dynamic ionic bonds" provides initial strength to accelerate the curing process and regulates the crystal growth of potassium sulfate and the silicon-oxygen network, preventing excessive structural density. Without these bonds, the "ionic spring" effect disappears, resulting in insufficient initial reaction kinetics and a significantly prolonged curing time. Furthermore, uncontrolled crystal growth leads to the formation of numerous closed pores within the system, making it difficult for gas to escape during casting and increasing gas evolution. In addition, structural densification increases the difficulty of warm water penetration, with the collapse time increasing by 24.2% compared to the average of the previous examples (3.3 min), further demonstrating the crucial role of sodium phytate in regulating the reaction process and structure.

[0196] Comparative Example 4, lacking a lithium / zirconium composite conductive agent, exhibited performance defects primarily in curing efficiency and high-temperature stability, with a curing time as long as 22 minutes (the average of the examples was 12.5 minutes), and a high-temperature compressive strength at 600°C dropping to 0.8 MPa. In this composite conductive agent, It can act as an "ionic catalyst" to accelerate the release of anhydrous potassium sulfate. In sodium silicate The exchange reaction reduces the curing activation energy; Nanoparticles can form high-energy Zr-O-Si bonds with the silicon-oxygen network at high temperatures, creating high-temperature crosslinking points. The absence of these bonds significantly slows down the ion exchange reaction rate, hindering the curing process and resulting in a 57.1% increase in curing time compared to the longest value (14 min) in the previous examples. Simultaneously, without Zr-O-Si bond support at high temperatures, the silicon-oxygen network is prone to thermal depolymerization, and the high-temperature compressive strength is only 66.7% of the average value (1.2 MPa) of the previous examples, failing to meet the high-temperature load-bearing requirements during molten metal casting.

[0197] Comparative Example 5, by omitting the calcination activation step of the γ-alumina nanosheets, showed a significant decrease in both room temperature and high temperature strength. The room temperature tensile strength was 1.5 MPa, and the 600℃ high-temperature compressive strength was 0.9 MPa, representing decreases of 16.7% and 25% respectively compared to the average values ​​of the examples. The core purpose of calcination activation is to remove physically adsorbed water from the surface of the γ-alumina nanosheets, while simultaneously promoting Al-O bond rearrangement and increasing the density of chemically more active Al-OH groups—these hydroxyl groups are the core sites for forming Al-O-Si covalent bonds with the silicon-oxygen network and hybrid prepolymers. When unactivated nanosheets are used directly, the insufficient number of surface hydroxyl groups leads to a significant weakening of the interfacial bonding force with other components in the system. This prevents the full utilization of the reinforcing effect of the "nanoskeleton," making it difficult to provide effective mechanical support at room temperature and unable to prevent network creep at high temperatures, ultimately resulting in a double degradation in strength at both room temperature and high temperatures.

[0198] Comparative Example 6, due to omitting the pre-coating composite powder preparation step, became the group with the worst overall performance. Its room temperature tensile strength was 1.2 MPa, its 600℃ high-temperature compressive strength was 0.7 MPa, its gas evolution was 16.8 mL / g, its collapse time was 4.5 min, and its demolding pass rate was 82%, all significantly lower than those of the Example. The original pre-coating step used anhydrous potassium sulfate micropowder as a carrier to uniformly attach the nano-sized lithium / zirconium composite conductive agent and α-zirconium phosphate through mechanochemical action, preventing their agglomeration. When omitted, these two nano-components agglomerate severely due to their high surface energy, making it impossible to disperse uniformly in the system. Agglomerated lithium / zirconium composite conductive agents cause local catalytic failure, uneven curing reaction, slow reaction and low strength in some areas, resulting in a sharp drop in strength at both room temperature and high temperature. Agglomerated α-zirconium phosphate cannot form uniform "ion channels," and structural defects are easily generated around the agglomerates, making it difficult for gas to escape and increasing gas generation. At the same time, the agglomerates hinder the penetration of warm water, prolonging the disintegration time. Structural defects also make it easy to crack during demolding, resulting in a significant decrease in the pass rate. This fully demonstrates that the pre-coating process is the core link to ensure the dispersibility of nano-components and the stability of system performance.

[0199] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0200] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A potassium sulfate based low temperature reactive composite binder for foundry, characterized by, The composite adhesive, by mass fraction, comprises the following chemical components: anhydrous potassium sulfate micro powder: 68–75%, potassium aluminum sulfate: 3.0–5.0%, sodium silicate: 12–15%, γ-alumina nanosheets: 4–6%, 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer: 2–3%, lithium / zirconium composite conductive agent: 0.8–1.2%, α-zirconium phosphate: 1.0–2.0%, potassium persulfate: 0.3–0.6%, and sodium phytate aqueous solution: 0.5%–1.0%. The preparation method of the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer includes the following steps: 3-Aminopropyltriethoxysilane and boric acid were reacted in an alcohol solvent at 60–80 °C for 2–4 h to obtain the 3-aminopropyltriethoxysilane-boric acid hybrid prepolymer. The molar ratio of 3-aminopropyltriethoxysilane to boric acid is 1:(0.3-0.5); The lithium / zirconium composite conductive agent is composed of nano-zirconium oxide and lithium sulfate, wherein the mass ratio of nano-zirconium oxide to lithium sulfate is 1:(1.5~2.5). The preparation method of the potassium sulfate-based low-temperature reactive composite binder for casting includes the following steps: S1. Under an inert atmosphere, the γ-alumina nanosheets are calcined and activated at 300-400°C for 1 hour to obtain activated alumina; S2. Using a portion of the anhydrous potassium sulfate micro powder as a carrier, grind it together with the lithium / zirconium composite conductive agent and the α-zirconium phosphate for 5 to 10 minutes to make the ultrafine powder uniformly adhere to the surface of the potassium sulfate carrier, thus obtaining a pre-coated composite powder. S3. The remaining anhydrous potassium sulfate powder, potassium aluminum sulfate, potassium persulfate, and activated alumina are subjected to primary low-speed dry mixing to obtain primary mixed dry material; S4. Add the pre-coated composite powder to the primary mixed dry material, and then perform secondary low-speed dry mixing to obtain secondary mixed dry material. S5. Add the 3-aminopropyltriethoxysilane-boronic acid hybrid prepolymer to the secondary mixed dry material and stir at medium speed to wet and coat the surface of the solid particles with the hybrid prepolymer to obtain a mixed wet material. S6. Add the sodium silicate and the sodium phytate aqueous solution to the mixed wet material and stir at low speed to obtain the composite binder.

2. The potassium sulfate based low temperature reactive composite binder for casting according to claim 1, characterized in that, The modulus of the sodium silicate is 3.0 to 3.

4.

3. The potassium sulfate based low temperature reactive composite binder for casting according to claim 1, characterized in that, The γ-alumina nanosheets are two-dimensional sheet structures with a diameter-to-thickness ratio of not less than 50:

1.

4. The potassium sulfate based low temperature reactive composite binder for casting according to claim 1, characterized in that, The nano-zirconia has a mixed crystal structure of monoclinic and tetragonal phases, and the average particle size is 20-50 nm.

5. The potassium sulfate-based low-temperature reactive composite binder for casting according to claim 1, characterized in that, The mass concentration of the sodium phytate aqueous solution is 10-20%.

6. The potassium sulfate based low temperature reactive composite binder for casting according to claim 1, characterized in that, In step S2, the mass of a portion of the anhydrous potassium sulfate micro powder is 25-35% of the total mass of the anhydrous potassium sulfate micro powder; In step S3, the rotation speed of the primary low-speed dry mixer is 200-300 rpm, and the mixing time is 5-8 min. In step S4, the rotation speed of the secondary low-speed dry mixer is 200-300 rpm, and the mixing time is 5-8 min. In step S5, the speed of the medium-speed stirring is 400-600 rpm, and the stirring time is 8-10 min; In step S6, the low-speed stirring speed is 200-300 rpm, and the stirring time is 5-8 min.

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