Bentonite composite ultrafine grinding medium and preparation method

Abstract

A bentonite composite ultrafine grinding medium and a preparation method thereof. The medium is made of 12-25 parts of composite modified bentonite, 60-75 parts of alpha-alumina powder, 8-15 parts of zirconium silicate powder and 3-8 parts of nano titanium oxide. The composite modified bentonite is prepared through acid activation, titanium ion pillaring, in-situ hydrolysis to generate TiO2 crystal seeds and calcium carbonate powder shearing anchoring steps. The preparation method comprises dosing ball milling, granulation molding, step-by-step sintering and temperature control annealing: the first temperature rising stage makes calcium carbonate decompose and release CaO, and the second temperature rising stage generates perovskite phase in-situ at the soft-hard phase interface. In the grinding process, when the microcrack extends to the CaTiO3 particle, the crack tip stress induces the lattice distortion and volume expansion of CaTiO3, and the expansion generates compressive stress on the crack surface to prevent the crack from further expanding. The self-wear rate of the obtained medium is lower than 0.005%, and the service life is more than 50% higher than that of the traditional alumina-based medium.

Description

Technical Field

[0001] This invention relates to the field of grinding media technology, specifically to a bentonite composite ultrafine grinding media and its preparation method. Background Technology

[0002] In the field of ultrafine grinding, grinding media are the core medium for energy transfer between the mill and the material, and their performance directly determines grinding efficiency and product quality. As downstream applications place increasingly stringent requirements on powder purity, whiteness, and particle size distribution, high-performance, low-wear grinding media have become a key industry need.

[0003] Existing grinding media are mainly classified into several categories, including glass beads, alumina beads, zirconia beads, and composite ceramic beads. Among them, alumina-based composite ceramic media are widely used due to their high hardness, moderate density, and relatively low manufacturing cost. However, traditional alumina-based media face a common problem during long-term service: the accumulation and propagation of fatigue microcracks. Under repeated impact and shear stress, microcracks inevitably form inside and on the surface of the media. These cracks gradually expand and connect, eventually leading to particle spalling or even overall fragmentation. This not only significantly shortens the service life of the media, but the spalled abrasive debris also contaminates the color and purity of the slurry.

[0004] To address this issue, existing technologies primarily focus on two approaches: increasing hardness to resist crack initiation and toughening to delay crack propagation. For example, Chinese Patent Publication No. CN118895100B enhances hardness and wear resistance by introducing a layered aluminum silicate structure through modified muscovite; while Chinese Patent Publication No. CN118909594B reduces chemical wear by forming an anti-corrosion protective film within the medium through modified kaolin. However, these methods are essentially passive protection strategies; once cracks occur, they cannot be actively repaired. Summary of the Invention

[0005] (a) Technical problems to be solved This invention aims to provide a bentonite composite ultrafine grinding media and its preparation method. By designing the composite modified bentonite and using a stepwise sintering process, a perovskite phase activation layer is constructed inside the media. During the grinding process, when microcracks extend to this area, stress-induced volume expansion generates compressive stress on the crack surface, thereby limiting further crack extension and significantly improving service life.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: This invention provides a bentonite composite ultrafine grinding media, which is made of the following components in parts by weight: 12-25 parts of composite modified bentonite; 60-75 parts of α-alumina micro powder; 8-15 parts of zirconium silicate micro powder; and 3-8 parts of nano titanium oxide.

[0007] The preparation method of composite modified bentonite includes the following steps A1 to A5.

[0008] A1. The purified sodium-based bentonite is placed in a hydrochloric acid solution with a mass concentration of 5% to 12%, stirred at 55 to 65°C for 2.5 to 3.5 hours, filtered and washed until neutral to obtain acid-activated bentonite.

[0009] The purpose of acid activation treatment is to remove impurities from bentonite and open interlayer channels, resulting in appropriate structural defects and dangling bonds at the edges of bentonite sheets. The hydrochloric acid concentration is preferably 8% to 10%. When the concentration is below 5%, interlayer activation is insufficient, and there are not enough titanium ion exchange sites; when the concentration is above 12%, the bentonite sheets may be over-etched, damaging their structural integrity and thus affecting the mechanical properties of the subsequent ceramic matrix.

[0010] A2. Prepare a titanium oxysulfate solution with a mass concentration of 8% to 15%. Disperse the acid-activated bentonite obtained in step A1 into the solution at a solid-liquid ratio of 1:8 to 12. Stir at 45 to 55°C to carry out a titanium ion exchange pillaring reaction for 3 to 5 hours.

[0011] This step utilizes the cation exchange capacity of bentonite to allow titanium ions to enter the interlayer and replace the exchangeable cations. The pillaring effect expands the interlayer spacing of bentonite to over 1.5 nm, providing structural conditions for the subsequent embedding of calcium carbonate particles and mass transfer of reactants in the sintering stage. The preferred concentration of the titanium oxysulfate solution is 10%–12%, the preferred solid-liquid ratio is 1:9–10, and the preferred reaction temperature is 48–52 °C. Under these conditions, the titanium ion exchange rate reaches 65%–80% of the cation exchange capacity of bentonite.

[0012] A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension obtained in step A2 until the pH is 5.5-6.5, so that the interlayer titanium ions are hydrolyzed in situ. After aging for 10-14 hours, TiO2 pillared bentonite slurry is obtained.

[0013] Slowly adding dilute ammonia allows for the gentle and uniform hydrolysis of titanium ions within the bentonite layers, preferentially generating anatase TiO2 seed crystals with a particle size of 5–10 nm. These seed crystals are chemically bonded to the bentonite layers, rather than physically adsorbed, thus reducing the likelihood of grain growth and deactivation due to thermal aging during subsequent high-temperature sintering. The preferred aging time is 11–13 hours to ensure complete hydrolysis and full nucleation.

[0014] A4. Weigh out 10% to 20% of the dry weight of bentonite and add it to the slurry obtained in step A3. Shear and disperse it at a high speed of 15 to 25 m / s for 40 to 80 minutes to anchor the calcium carbonate particles to the edges of the bentonite lamellae and cleavage defects.

[0015] Through the action of a high shear force field, calcium carbonate microparticles are forcibly driven into the edges of bentonite sheets and the surface defect sites formed in step A1, achieving physical interlocking and anchoring. If ordinary stirring or dry mixing is used, the calcium carbonate particles only adhere to the surface of the bentonite aggregates. During subsequent sintering, the CaO produced by decomposition will accumulate on the outside of the particles, failing to achieve a site-specific reaction at the interface between the soft and hard phases. The preferred amount of calcium carbonate is 13% to 17% of the dry weight of the bentonite. When the amount is less than 10%, the subsequently generated CaTiO3 is insufficient to form a continuous interfacial bonding layer; when the amount is more than 20%, the excessive CO2 produced by decomposition may lead to excessively high porosity inside the medium, reducing the overall strength. The preferred particle size D50 of the lightweight calcium carbonate micropowder is 1 to 3 μm.

[0016] A5. Spray dry the slurry obtained in step A4 to obtain composite modified bentonite. The spray drying process produces composite modified bentonite in the form of aggregated particles. At the same time, the rapid drying process fixes the calcium carbonate anchoring structure formed in step A4, preventing the calcium carbonate particles from settling or migrating during the slow drying process.

[0017] In the preparation process of the aforementioned composite modified bentonite, steps A1 to A5 are interconnected, collectively constructing the structure of an interlayer pre-embedded active reactant precursor. Acid activation provides active sites, ion exchange pillars anchor the titanium source in the interlayer domain, in-situ hydrolysis generates seed crystals, shearing anchors and embeds calcium carbonate microparticles, and finally, spray drying synergistically fixes all functional components into a single unit. This process endows the composite modified bentonite with the ability to drive in-situ interfacial chemical reactions during subsequent sintering, which cannot be achieved by implementing each step individually.

[0018] Furthermore, the present invention provides a method for preparing the above-mentioned bentonite composite ultrafine grinding media, comprising the following steps S1 to S4.

[0019] S1. Ingredients and ball milling. Weigh 12-25 parts by weight of composite modified bentonite, 60-75 parts by weight of α-alumina micro powder, 8-15 parts by weight of zirconium silicate micro powder, and 3-8 parts by weight of nano titanium dioxide according to the formula. Add polyvinyl alcohol aqueous solution as a temporary binder and perform wet ball milling to mix until the slurry particle size D90 < 2 μm.

[0020] Preferably, the α-alumina micropowder has a particle size D50 of 0.4–0.8 μm, the zirconium silicate micropowder has a particle size D50 of 0.8–1.5 μm, and the nano-titanium oxide has a particle size of 15–30 nm and a mixed crystal form of anatase and rutile. The polyvinyl alcohol aqueous solution preferably has a mass concentration of 3%–5%, and its addition amount is 1.5%–3.5% of the total mass of the powder.

[0021] In this invention, nano-titanium oxide possesses a dual function. First, a portion of the nano-titanium oxide is uniformly dispersed in the matrix during ball milling, and during the sintering stage, it primarily synergistically promotes densification sintering with alumina and zirconium silicate, acting as a conventional sintering aid. Second, another portion of the nano-titanium oxide participates in the perovskite phase formation reaction at the interface during the sintering stage, combining with anatase TiO2 seeds pre-embedded in bentonite and CaO decomposed from calcium carbonate to generate CaTiO3 in situ at the soft-hard phase interface.

[0022] S2. Granulation and molding. The slurry obtained in S1 is spray-dried and granulated, and the precursor particles are sieved to obtain 40-200 mesh. Then, it is dry-pressed or rolled to form spherical green bodies with a diameter of 0.5-5.0 mm.

[0023] During the spray drying granulation process, the composite modified bentonite, as the soft phase component, forms a uniform coating layer on the surface of the hard alumina-zirconium silicate particles, constructing an initial soft-phase-encapsulated hard-phase microstructure. This structure lays the spatial foundation for site-specific reactions at the soft-hard phase interface during subsequent sintering.

[0024] S3, step-by-step sintering.

[0025] The spherical blanks obtained from S2 are placed in a kiln for stepwise sintering, specifically including a first heating stage and a second heating stage.

[0026] First heating stage: Heat to 900-1100℃ at a rate of 2-4℃ / min, and hold for 1.5-2.5 hours. More preferably, heat to 950-1050℃ at a rate of 2.5-3.5℃ / min, and hold for 1.5-2.5 hours.

[0027] The main event occurring in this stage is the thermal decomposition of the lightweight calcium carbonate anchored in the composite-modified bentonite, generating calcium oxide and carbon dioxide. CO2 gas slowly escapes from the bentonite interlayer and edge defect sites, forming uniformly distributed submicron-sized closed pores within the medium, with a pore size of approximately 0.1–0.5 μm. These closed pores provide the medium with a certain elastic strain tolerance, giving it better energy absorption capacity when subjected to abrasive impacts, thereby reducing the probability of brittle fracture. The decomposition product, CaO, is highly reactive and, because it is confined in situ within the bentonite interlayer, does not undergo long-range diffusion and migration; it is precisely stored in the soft-hard phase interface region, awaiting a chemical reaction with adjacent TiO2 seed crystals in the second heating stage.

[0028] Preferably, the heating rate in the first heating stage is 2.5–3.5 °C / min, and the holding temperature is 950–1050 °C. The holding time is preferably 1.5–2.5 hours to ensure complete decomposition of calcium carbonate and allow sufficient time for CO2 to diffuse out through the matrix without causing localized pressure concentration. If the holding time is too short, the residual calcium carbonate may suddenly decompose at subsequent higher temperatures, potentially leading to a sudden increase in gas pressure and cracking. A heating rate that is too slow reduces production efficiency; a heating rate that is too fast results in excessive gas release, which may induce microcracks inside the billet.

[0029] Second heating stage: Continue heating at a rate of 3-6℃ / min to 1250-1380℃, and hold for 2-3 hours. More preferably, heat to 1280-1350℃ at a rate of 4-5℃ / min, and hold for 2-3 hours.

[0030] This stage is the functional structure shaping stage, during which the following synergistic processes occur. First, the hard matrix undergoes sintering and densification. Under the combined promotion of zirconium silicate and some nano-titanium oxide, the α-alumina matrix undergoes liquid-phase sintering, achieving densification. Zirconium silicate forms a eutectic liquid phase above 1200℃, promoting mass transfer; the added nano-titanium oxide forms a solid solution with alumina, accelerating grain boundary diffusion. Second, the perovskite phase is generated in situ. Anatase TiO2 seeds embedded in the bentonite layers react with CaO released in the first heating stage at the soft-hard phase interface to generate CaTiO3. Because the TiO2 seeds and CaO are precisely confined in a nearby region at the nanometer to submicron scale, this reaction requires approximately 50–80℃ less temperature than the traditional solid-state synthesis of CaTiO3. The in-situ generated CaTiO3 forms a continuous interfacial bonding layer between the soft and hard phases, achieving metallurgical-grade bonding between the two phases. The interfacial bonding strength is higher than the bulk strength of the soft phase, effectively preventing particle peeling caused by interfacial debonding during the grinding process.

[0031] Preferably, the heating rate in the second heating stage is 4–5 °C / min, and the holding temperature is 1280–1350 °C. Holding temperatures above 1380 °C may cause excessive growth of the perovskite phase, resulting in the loss of its phase transformation activity under grinding stress. The holding time is preferably 2–3 hours to ensure the interfacial chemical reaction is fully completed, while simultaneously achieving matrix densification and microstructure homogenization.

[0032] S4. Annealing and post-processing.

[0033] The temperature is controlled at a rate of 1.5 to 3℃ / min to retain residual compressive stress inside the medium. After exiting the kiln, the medium is self-polished and screened to obtain the finished product.

[0034] Controlling the cooling rate is crucial for constructing the residual stress field. A slower cooling rate causes the surface of the medium to cool and contract first, while the core cools more slowly, forming a residual compressive stress layer with a thickness of approximately 20–80 μm on the surface. This compressive stress layer makes the Vickers hardness of the medium surface 15%–25% higher than that of the core. The presence of surface residual compressive stress has a dual effect: on the one hand, it enhances the impact fatigue resistance of the medium surface; on the other hand, during subsequent grinding operations, when the medium is subjected to stress and microcracks are generated and propagated, the residual compressive stress gradually releases elastic strain energy, providing a mechanical driving force for the stress-induced phase transformation of the perovskite phase at the crack tip.

[0035] Preferably, the cooling rate is 2 to 2.5 °C / min. When the cooling rate is lower than 1.5 °C / min, the production cycle is too long and energy consumption increases; when the cooling rate is higher than 3 °C / min, the surface compressive stress layer is not formed sufficiently and may cause thermal stress cracks to occur inside the medium.

[0036] The preferred method for self-polishing is to place the sintered spheres in a rotating drum and rotate them for 2 to 4 hours by mutual friction between the spheres to remove slight surface adhesions and improve surface smoothness.

[0037] In grinding operations, the bentonite composite ultrafine grinding media prepared by this invention induces micro-lattice distortion in CaTiO3 when fatigue microcracks extend to the dispersed perovskite phase particles. This distortion occurs as a partial transformation from an orthorhombic to a rhombohedral or monoclinic crystal system, accompanied by a volume expansion of approximately 0.5% to 1.2%. This volume expansion generates compressive stress on the crack surface, creating a clamping and healing effect that effectively prevents further crack propagation. This effect results in a self-wear rate of less than 0.005% and a service life that is more than 50% longer than that of traditional alumina-based grinding media of the same hardness.

[0038] The aforementioned effect relies on the complete synergy between steps A1 to A5 and steps S1 to S4. If calcium carbonate is simply mechanically mixed instead of being anchored between bentonite layers through high-speed shearing, or if TiO2 is entirely added without pre-embedding interlayer seeds, precise proximity and site-specific combination of CaO and TiO2 at the nanoscale cannot be achieved. Consequently, a continuous CaTiO3 bonding layer cannot be constructed at the interface, ultimately failing to achieve the function of inhibiting crack propagation. This inseparable synergistic process characteristic results in unforeseen and unexpected technical effects from the present invention compared to the simple superposition of components.

[0039] (III) Beneficial Effects The purpose of this invention is to provide a bentonite composite ultrafine grinding media and its preparation method. It has the following beneficial effects: First, this invention utilizes a synergistic pretreatment process in the preparation of composite modified bentonite—including titanium ion pillaring, in-situ hydrolysis to generate TiO2 seed crystals, and interlayer anchoring of calcium carbonate particles—combined with a step-by-step sintering process, to generate a dispersed perovskite phase (CaTiO3) in situ at the soft-hard phase interface within the medium. During the grinding process, when fatigue microcracks propagate to the perovskite phase particles, stress concentration at the crack tip induces micro-lattice distortion in CaTiO3, accompanied by volume expansion. This results in a clamping and healing effect on the crack, effectively preventing further crack propagation. This effect leads to a self-wear rate of less than 0.005% and a service life more than 50% longer than traditional alumina-based grinding media of the same hardness. This effect is the result of the synergistic action of four stages: titanium ion pillaring, TiO2 seed pre-embedding, calcium carbonate interlayer anchoring, and step-by-step sintering; the absence of any single stage would prevent its achievement.

[0040] Secondly, this invention achieves precise in-situ combination of CaTiO3 at the interface between the soft and hard phases by pre-embedding TiO2 seed crystals between bentonite layers and anchoring calcium carbonate at the defect sites of the bentonite lamellae during the second heating stage of stepwise sintering. The generated CaTiO3 forms a continuous interfacial bonding layer, achieving metallurgical-grade bonding between the soft and hard phases, with an interfacial bonding strength higher than the bulk strength of the soft phase. Compared to the weak interfacial bonding resulting from simple mechanical mixing and sintering of soft and hard phases in traditional ceramic grinding media, this invention fundamentally eliminates particle detachment caused by interfacial debonding during the grinding process.

[0041] Finally, this invention utilizes a heat preservation design in the first heating stage of the step-by-step sintering process to ensure the complete decomposition of calcium carbonate and the safe escape of CO2 gas, forming uniformly distributed submicron-level closed pores within the medium. These closed pores do not reduce the macroscopic strength of the medium but provide it with a certain elastic strain tolerance, giving it better energy absorption capacity when subjected to abrasive impacts and reducing the probability of brittle fracture. Simultaneously, controlled cooling during the annealing stage forms a residual compressive stress layer on the medium surface, further enhancing its impact fatigue resistance. Test results from the embodiments show that the fracture strength of the medium of this invention can reach up to 1320 N. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] Example 1: This embodiment provides a bentonite composite ultrafine grinding media and its preparation method.

[0044] I. Preparation of Composite Modified Bentonite A1. The purified sodium-based bentonite was placed in a 5% hydrochloric acid solution and stirred at 55°C for 3.5 hours. After filtration and washing until neutral, acid-activated bentonite was obtained.

[0045] A2. Prepare an 8% (w / w) titanium oxysulfate solution. Disperse the acid-activated bentonite obtained in step A1 in the solution at a solid-liquid ratio of 1:8. Stir at 45°C to carry out a titanium ion exchange pillaring reaction for 5 hours.

[0046] A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension obtained in step A2 until the pH reaches 5.5, so that the interlayer titanium ions are hydrolyzed in situ. After aging for 10 hours, TiO2 pillared bentonite slurry is obtained.

[0047] A4. Weigh out 10% of the dry weight of bentonite and add it to the slurry obtained in step A3. Shear and disperse it at a linear velocity of 15m / s for 80 minutes to anchor the calcium carbonate particles to the edge of the bentonite lamellae and cleavage defects.

[0048] A5. Spray dry the slurry obtained in step A4 to obtain the composite modified bentonite.

[0049] II. Preparation of Abrasive Media S1. Ingredient preparation and ball milling.

[0050] Weigh out 12 parts by weight of composite modified bentonite, 75 parts by weight of α-alumina micro powder (D50=0.4μm), 8 parts by weight of zirconium silicate micro powder (D50=0.8μm), and 8 parts by weight of nano titanium oxide (particle size 15nm, mixed anatase and rutile crystal form). Add polyvinyl alcohol aqueous solution as a temporary binder. The mass concentration of polyvinyl alcohol aqueous solution is 3%, and the amount added is 1.5% of the total mass of powder. Wet ball milling is performed to mix until the slurry particle size D90 < 2μm.

[0051] S2, Granulation and molding.

[0052] The slurry obtained from S1 is spray-dried and granulated, and the precursor particles are sieved to a mesh size of 40-200. Then, it is rolled and molded to produce a spherical preform with a diameter of 0.5 mm.

[0053] S3, step-by-step sintering.

[0054] The spherical blanks obtained in S2 are placed in a kiln for stepwise sintering.

[0055] First heating stage: Heat to 900℃ at a rate of 2℃ / min and hold for 2.5 hours.

[0056] Second heating stage: Continue heating at a rate of 3℃ / min to 1250℃ and hold for 3 hours.

[0057] S4. Annealing and post-processing.

[0058] The temperature was controlled at a rate of 1.5℃ / min. After exiting the kiln, the product underwent self-grinding and polishing (the spheres were placed in a rotating drum and rotated for 2 hours by mutual friction) and then screened to obtain the finished product.

[0059] Example 2 This embodiment provides a bentonite composite ultrafine grinding media and its preparation method.

[0060] I. Preparation of Composite Modified Bentonite A1. The purified sodium-based bentonite was placed in a 12% hydrochloric acid solution and stirred at 65°C for 2.5 hours. After filtration and washing until neutral, acid-activated bentonite was obtained.

[0061] A2. Prepare a 15% (w / w) titanium oxysulfate solution. Disperse the acid-activated bentonite obtained in step A1 into the solution at a solid-liquid ratio of 1:12. Stir at 55°C to carry out a titanium ion exchange pillaring reaction for 3 hours.

[0062] A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension obtained in step A2 until the pH reaches 6.5, so that the interlayer titanium ions are hydrolyzed in situ. After aging for 14 hours, TiO2 pillared bentonite slurry is obtained.

[0063] A4. Weigh 20% of the dry weight of bentonite into light calcium carbonate micro powder (D50=3μm), add it to the slurry obtained in step A3, and disperse it at a high speed of 25m / s for 40 minutes to anchor the calcium carbonate microparticles to the edge of the bentonite lamellae and cleavage defects.

[0064] A5. Spray dry the slurry obtained in step A4 to obtain the composite modified bentonite.

[0065] II. Preparation of Abrasive Media S1. Ingredient preparation and ball milling.

[0066] Weigh out 25 parts by weight of composite modified bentonite, 60 parts by weight of α-alumina micro powder (D50=0.8μm), 15 parts by weight of zirconium silicate micro powder (D50=1.5μm), and 3 parts by weight of nano titanium oxide (particle size 30nm, mixed anatase and rutile crystal form). Add polyvinyl alcohol aqueous solution as a temporary binder. The mass concentration of polyvinyl alcohol aqueous solution is 5%, and the amount added is 3.5% of the total mass of powder. Wet ball milling is performed until the slurry particle size D90 < 2μm.

[0067] S2, Granulation and molding.

[0068] The slurry obtained from S1 is spray-dried and granulated, and the precursor particles are sieved to obtain 40-200 mesh. Then, it is dry-pressed to form a spherical green body with a diameter of 5.0 mm.

[0069] S3, step-by-step sintering.

[0070] The spherical blanks obtained in S2 are placed in a kiln for stepwise sintering.

[0071] First heating stage: Heat to 1100℃ at a rate of 4℃ / min and hold for 1.5 hours.

[0072] Second heating stage: Continue heating at a rate of 6℃ / min to 1380℃, and hold for 2 hours.

[0073] S4. Annealing and post-processing.

[0074] The temperature was controlled at a rate of 3℃ / min. After exiting the kiln, the balls were self-polished (the balls were placed in a rotating drum and rotated by mutual friction for 4 hours) and then screened to obtain the finished product.

[0075] Example 3 This embodiment provides a bentonite composite ultrafine grinding media and its preparation method.

[0076] I. Preparation of Composite Modified Bentonite A1. The purified sodium-based bentonite was placed in an 8% hydrochloric acid solution and stirred at 60°C for 3 hours. After filtration and washing until neutral, acid-activated bentonite was obtained.

[0077] A2. Prepare a 12% (w / w) titanium oxysulfate solution. Disperse the acid-activated bentonite obtained in step A1 into the solution at a solid-liquid ratio of 1:10. Stir at 50°C to carry out a titanium ion exchange pillaring reaction for 4 hours.

[0078] A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension obtained in step A2 until the pH reaches 6.0, so that the interlayer titanium ions are hydrolyzed in situ. After aging for 12 hours, TiO2 pillared bentonite slurry is obtained.

[0079] A4. Weigh out 15% of the dry weight of bentonite and add it to the slurry obtained in step A3. Shear and disperse it at a linear velocity of 20m / s for 60 minutes to anchor the calcium carbonate particles to the edge of the bentonite lamellae and cleavage defects.

[0080] A5. Spray dry the slurry obtained in step A4 to obtain the composite modified bentonite.

[0081] II. Preparation of Abrasive Media S1. Ingredient preparation and ball milling.

[0082] Weigh out 20 parts by weight of composite modified bentonite, 65 parts by weight of α-alumina micro powder (D50=0.6μm), 12 parts by weight of zirconium silicate micro powder (D50=1.0μm), and 5 parts by weight of nano titanium oxide (particle size 25nm, anatase and rutile mixed crystal form). Add polyvinyl alcohol aqueous solution as a temporary binder. The mass concentration of polyvinyl alcohol aqueous solution is 4%, and the amount added is 2.5% of the total mass of powder. Wet ball milling is performed to mix until the slurry particle size D90 < 2μm.

[0083] S2, Granulation and molding.

[0084] The slurry obtained from S1 is spray-dried and granulated, and the precursor particles are sieved to obtain 40-200 mesh. Then, it is rolled and molded to produce a spherical preform with a diameter of 2.0 mm.

[0085] S3, step-by-step sintering.

[0086] The spherical blanks obtained in S2 are placed in a kiln for stepwise sintering.

[0087] First heating stage: Heat to 1000℃ at a rate of 3℃ / min and hold for 2 hours.

[0088] Second heating stage: Continue heating at a rate of 4.5℃ / min to 1320℃ and hold for 2.5 hours.

[0089] S4. Annealing and post-processing.

[0090] The temperature was controlled to decrease at a rate of 2℃ / min. After exiting the kiln, the product underwent self-grinding and polishing (the spheres were placed in a rotating drum and rotated for 3 hours by mutual friction) and then screened to obtain the finished product.

[0091] Example 4 This embodiment provides a bentonite composite ultrafine grinding media and its preparation method.

[0092] I. Preparation of Composite Modified Bentonite A1. The purified sodium-based bentonite was placed in a 10% hydrochloric acid solution and stirred at 58°C for 2.8 hours. After filtration and washing until neutral, acid-activated bentonite was obtained.

[0093] A2. Prepare a 10% (w / w) titanium oxysulfate solution. Disperse the acid-activated bentonite obtained in step A1 in the solution at a solid-liquid ratio of 1:9. Stir at 52°C to carry out a titanium ion exchange pillaring reaction for 4.5 hours.

[0094] A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension obtained in step A2 until the pH reaches 6.2, so that the interlayer titanium ions are hydrolyzed in situ. After aging for 13 hours, TiO2 pillared bentonite slurry is obtained.

[0095] A4. Weigh out 13% of the dry weight of bentonite and add it to the slurry obtained in step A3. Shear and disperse it at a linear velocity of 18m / s for 70 minutes to anchor the calcium carbonate particles to the edge of the bentonite lamellae and cleavage defects.

[0096] A5. Spray dry the slurry obtained in step A4 to obtain the composite modified bentonite.

[0097] II. Preparation of Abrasive Media S1. Ingredient preparation and ball milling.

[0098] Weigh out 18 parts by weight of composite modified bentonite, 68 parts by weight of α-alumina micro powder (D50=0.5μm), 10 parts by weight of zirconium silicate micro powder (D50=1.2μm), and 6 parts by weight of nano titanium oxide (particle size 20nm, mixed anatase and rutile crystal form). Add polyvinyl alcohol aqueous solution as a temporary binder. The mass concentration of polyvinyl alcohol aqueous solution is 4%, and the amount added is 2.0% of the total mass of powder. Wet ball milling is performed until the slurry particle size D90 < 2μm.

[0099] S2, Granulation and molding.

[0100] The slurry obtained from S1 is spray-dried and granulated, and the precursor particles are sieved to obtain 40-200 mesh. Then, it is dry-pressed to form a spherical green body with a diameter of 3.0 mm.

[0101] S3, step-by-step sintering.

[0102] The spherical blanks obtained in S2 are placed in a kiln for stepwise sintering.

[0103] First heating stage: Heat to 950℃ at a rate of 2.5℃ / min and hold for 2.2 hours.

[0104] Second heating stage: Continue heating at a rate of 4℃ / min to 1280℃ and hold for 2.8 hours.

[0105] S4. Annealing and post-processing.

[0106] The temperature is controlled at a rate of 2.5℃ / min. After exiting the kiln, the product is subjected to self-grinding polishing (the sphere is placed in a rotating drum and rotated by mutual friction for 2.5 hours), and then screened to obtain the finished product.

[0107] Example 5 This embodiment provides a bentonite composite ultrafine grinding media and its preparation method.

[0108] I. Preparation of Composite Modified Bentonite A1. The purified sodium-based bentonite was placed in a 7% hydrochloric acid solution and stirred at 62°C for 3.2 hours. After filtration and washing until neutral, acid-activated bentonite was obtained.

[0109] A2. Prepare a 14% (w / w) titanium oxysulfate solution. Disperse the acid-activated bentonite obtained in step A1 into the solution at a solid-liquid ratio of 1:11. Stir at 48°C to carry out a titanium ion exchange pillaring reaction for 3.5 hours.

[0110] A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension obtained in step A2 until the pH reaches 5.8, so that the interlayer titanium ions are hydrolyzed in situ. After aging for 11 hours, TiO2 pillared bentonite slurry is obtained.

[0111] A4. Weigh out 17% of the dry weight of bentonite and add it to the slurry obtained in step A3. Shear and disperse it at a linear velocity of 22m / s for 50 minutes to anchor the calcium carbonate particles to the edge of the bentonite lamellae and cleavage defects.

[0112] A5. Spray dry the slurry obtained in step A4 to obtain the composite modified bentonite.

[0113] II. Preparation of Abrasive Media S1. Ingredient preparation and ball milling.

[0114] Weigh out 22 parts by weight of composite modified bentonite, 62 parts by weight of α-alumina micro powder (D50=0.7μm), 14 parts by weight of zirconium silicate micro powder (D50=1.3μm), and 4 parts by weight of nano titanium oxide (particle size 28nm, mixed anatase and rutile crystal form). Add polyvinyl alcohol aqueous solution as a temporary binder. The mass concentration of polyvinyl alcohol aqueous solution is 3.5%, and the amount added is 3.0% of the total mass of powder. Wet ball milling is performed until the slurry particle size D90 < 2μm.

[0115] S2, Granulation and molding.

[0116] The slurry obtained from S1 is spray-dried and granulated, and the precursor particles are sieved to obtain 40-200 mesh. Then, it is rolled and molded to produce a spherical preform with a diameter of 1.5 mm.

[0117] S3, step-by-step sintering.

[0118] The spherical blanks obtained in S2 are placed in a kiln for stepwise sintering.

[0119] First heating stage: Heat to 1050℃ at a rate of 3.5℃ / min and hold for 1.8 hours.

[0120] Second heating stage: Continue heating at a rate of 5℃ / min to 1350℃ and hold for 2.2 hours.

[0121] S4. Annealing and post-processing.

[0122] The temperature was controlled to decrease at a rate of 2℃ / min. After exiting the kiln, the product underwent self-grinding and polishing (the spheres were placed in a rotating drum and rotated for 3 hours by mutual friction) and then screened to obtain the finished product.

[0123] Comparative Example 1 The difference between this comparative example and Example 3 is that in the preparation process of the composite modified bentonite, steps A2 and A3 are omitted, that is, titanium ion exchange pillaring and in-situ hydrolysis are not performed. The acid-activated bentonite is directly sheared and mixed with light calcium carbonate micro powder in step A4. The remaining components and preparation steps are the same as in Example 3.

[0124] Comparative Example 2 The difference between this comparative example and Example 3 is that step A4 is omitted in the preparation process of the composite modified bentonite, that is, the shear anchoring of calcium carbonate micro powder is not performed. The remaining components and preparation steps are the same as in Example 3.

[0125] Comparative Example 3 The difference between this comparative example and Example 3 is that in the preparation process of the composite modified bentonite, the light calcium carbonate micro powder in step A4 is not anchored by high-speed shearing, but is mixed by ordinary stirring. The stirring speed is 300 rpm and the stirring time is 60 minutes. The remaining components and preparation steps are the same as in Example 3.

[0126] Comparative Example The difference between this comparative example and Example 3 is that in the preparation process of the grinding media, step S3 does not use stepwise sintering, but directly heats to 1320°C at a rate of 4.5°C / min and holds for 4.5 hours, that is, the holding platform in the first heating stage is eliminated. The remaining components and preparation steps are the same as in Example 3.

[0127] Comparative Example 5 The difference between this comparative example and Example 3 is that the composite modified bentonite is replaced with an equal mass of unmodified purified sodium-based bentonite, and the amount of nano-titanium oxide is increased from 5 parts by mass to 7 parts by mass. That is, the additional 2 parts by mass of nano-titanium oxide are used to compensate for the lack of pre-embedded TiO2 seeds in the original composite modified bentonite. The remaining components and preparation steps are the same as in Example 3.

[0128] Comparative Example 6 The difference between this comparative example and Example 3 is that the composite modified bentonite is replaced with an equal mass of ordinary commercially available bentonite, and no other components are adjusted. The remaining components and preparation steps are the same as in Example 3.

[0129] Comparative Example 7: Commercially available 92% alumina balls Application and performance testing The grinding media prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were respectively applied to a sand mill under the same conditions to conduct ultrafine grinding experiments on calcium carbonate slurry. Meanwhile, a commercially available 92% alumina grinding ball was selected as a control example of traditional alumina-based media, and tests were conducted under the same conditions to verify the lifespan improvement effect of the present invention. The grinding conditions were: sand mill volume 5L, media filling rate 70%, slurry solid content 60%, grinding speed 1500rpm, continuous operation for 200 hours. The following performance indicators were tested: (1) Self-wear rate: Referring to the industry's common method, weigh the initial mass of the grinding media, take out the media after running for 200 hours, clean and dry it, weigh it again, and calculate the mass loss rate.

[0130] (2) Crushing strength: 50 media particles were randomly selected and subjected to single-particle crushing test on a universal testing machine. The arithmetic mean was taken.

[0131] (3) Grinding efficiency retention rate: Samples were taken at 50 hours and 200 hours of operation to determine the D50 particle size of calcium carbonate in the slurry, and the grinding efficiency retention rate at 200 hours was calculated relative to that at 50 hours. Grinding efficiency is measured by the decrease in particle size per unit time. Retention rate = (Particle size decrease per unit time at 200 hours ÷ Particle size decrease per unit time at 50 hours) × 100%.

[0132] (4) Cross-sectional morphology observation: After running for 200 hours, medium particles were randomly selected to prepare cross-sectional samples. The internal microcrack morphology and structural changes of the perovskite phase region were observed using a scanning electron microscope.

[0133] The performance test results are shown in Table 1.

[0134] Table 1 Performance test results of each embodiment and comparative example in conclusion: As shown in Table 1, the self-wear rate of Examples 1 to 5 was significantly lower than that of the comparative examples, while the crushing strength and grinding efficiency retention rates were significantly higher than those of the comparative examples. Furthermore, scanning electron microscopy revealed the presence of new biophase filling in the microcrack areas in all examples. Compared to Comparative Example 7 (traditional alumina medium), the self-wear rate of the embodiments of the present invention was reduced by approximately 80% or more, the grinding efficiency retention rate was increased by approximately 30%, and the service life was significantly improved.

[0135] Example 3 exhibits the best performance across all parameters, indicating that when the concentration of hydrochloric acid is 8%, the concentration of titanium oxysulfate is 12%, the amount of calcium carbonate is 15% of the dry weight of the bentonite, and the holding temperature during the first heating stage of sintering is 1000℃ and the holding temperature during the second heating stage is 1320℃, the synergistic effect of each process parameter is optimal, and the function of inhibiting crack propagation is most fully realized.

[0136] Compared to Example 3, Comparative Example 1 omitted the titanium ion exchange pillar and in-situ hydrolysis steps, resulting in the absence of TiO2 seed crystals embedded in the bentonite interlayer. Consequently, a sufficient amount of CaTiO3 could not be generated at the interface between the soft and hard phases during subsequent sintering, leading to a significant increase in the self-wear rate to 0.028% and a decrease in the grinding efficiency retention rate to 82.5%. Furthermore, no crack filler was observed under electron microscopy. This indicates that titanium ion pillar and hydrolysis seed crystal pre-embedding are necessary pretreatment steps for achieving CaTiO3 generation at the interface.

[0137] Compared to Example 3, Comparative Example 2 omitted the anchoring step of calcium carbonate micropowder, resulting in no decomposable CaO source between the bentonite layers. Consequently, CaTiO3 could not be generated at the interface during sintering, leading to a self-wearing rate of 0.025%, and no crack filler was observed. This indicates that calcium carbonate anchoring is a crucial step in providing a CaO source and achieving site-specific synthesis.

[0138] Compared to Example 3, Comparative Example 3, which used ordinary stirring instead of high-speed shear anchoring, showed a self-wear rate of 0.018%, higher than Example 3, with only occasional discontinuous fillers observed under electron microscopy. This indicates that high-speed shear anchoring is crucial for ensuring that calcium carbonate particles are embedded in the defect sites of bentonite lamellars, and ordinary stirring cannot achieve the same anchoring effect.

[0139] Compared to Example 3, Comparative Example 4 lacked a holding platform during the first heating stage of the sintering process. Calcium carbonate decomposition occurred simultaneously with matrix sintering, resulting in insufficient CO2 escape and inadequate CaO release at the designated location. The self-wear rate was 0.015%, and the crack filling effect was significantly weakened. This indicates that the holding period during the first heating stage in the step-by-step process plays a crucial role in ensuring the full release of CaO and the safe escape of CO2.

[0140] Compared to Example 3, Comparative Example 5 replaced the composite modified bentonite with unmodified bentonite and added an additional 2 parts by mass of nano-titanium oxide. Although the total amount of TiO2 was increased, since all TiO2 was introduced externally and calcium carbonate was not composite-anchored with bentonite, TiO2 and CaO could not form precise proximity at the nanoscale, resulting in a self-wearing rate as high as 0.032%. This indicates that the spatial synergistic effect of pre-embedded TiO2 seeds and anchored calcium carbonate in the composite modified bentonite cannot be replaced by simply increasing the amount of components.

[0141] Compared with Example 3, Comparative Example 6 directly used ordinary commercially available bentonite, and all its properties were the worst, with a self-wearing rate as high as 0.045%, a crushing strength of only 720N, and a grinding efficiency retention rate of 71.4%.

[0142] The comparative results of the above comparative examples and embodiments show that the crack propagation inhibition function of the bentonite composite ultrafine grinding media prepared by the present invention depends entirely on the complete synergy between the composite modified bentonite preparation process and the step-by-step sintering process. The absence or substitution of any link will lead to a significant reduction or even complete loss of the effect. This inseparable process synergy characteristic makes the present invention produce unpredictable and unexpected technical effects compared to the simple superposition of the components.

[0143] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bentonite composite ultrafine grinding media, characterized in that, Made from the following components in parts by weight: Composite modified bentonite: 12-25 parts; α-Alumina micro powder: 60-75 parts; Zirconium silicate micro powder: 8-15 parts; Nano titanium dioxide: 3-8 parts; The preparation method of the composite modified bentonite includes the following steps: A1. The purified sodium-based bentonite is placed in a hydrochloric acid solution with a mass concentration of 5% to 12%, stirred at 55 to 65°C for 2.5 to 3.5 hours, filtered and washed until neutral to obtain acid-activated bentonite; A2. Prepare a titanium oxysulfate solution with a mass concentration of 8% to 15%, disperse the acid-activated bentonite obtained in step A1 in it at a solid-liquid ratio of 1:8 to 12, and carry out a titanium ion exchange pillaring reaction at 45 to 55°C for 3 to 5 hours. A3. Under continuous stirring, dilute ammonia water is slowly added dropwise to the suspension of step A2 until the pH is 5.5-6.5, so that the interlayer titanium ions are hydrolyzed in situ. Then, the mixture is aged for 10-14 hours to obtain TiO2 pillared bentonite slurry. A4. Weigh out 10% to 20% of the dry weight of bentonite and add it to the slurry obtained in step A3. Shear and disperse it at a high speed of 15 to 25 m / s for 40 to 80 minutes to allow the calcium carbonate particles to enter and anchor in the edge of the bentonite lamellae and cleavage defects. A5. Spray dry the slurry obtained in step A4 to obtain the composite modified bentonite.

2. The bentonite composite ultrafine grinding media according to claim 1, characterized in that, The particle size D50 of the α-alumina micro powder is 0.4-0.8 μm; the particle size D50 of the zirconium silicate micro powder is 0.8-1.5 μm; the particle size of the nano titanium oxide is 15-30 nm, and the crystal form is a mixed crystal form of anatase and rutile.

3. A method for preparing the bentonite composite ultrafine grinding media as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Ingredients and ball milling: Weigh out the composite modified bentonite, α-alumina micro powder, zirconium silicate micro powder and nano titanium oxide according to the formula, add polyvinyl alcohol aqueous solution as temporary binder, and perform wet ball milling to mix until the slurry particle size D90 < 2μm. S2. Granulation and molding: The slurry obtained in S1 is spray-dried and granulated, and the precursor particles with a mesh size of 40-200 are obtained by sieving. Then, the spherical green bodies with a diameter of 0.5-5.0 mm are formed by dry pressing or rolling molding. S3, Step-by-step sintering: The green body obtained in S2 is placed in a kiln for step-by-step sintering; S4. Annealing and post-treatment: Control the cooling rate to retain residual compressive stress inside the medium. After exiting the kiln, the spheres are self-polished and screened to obtain the finished product.

4. The method for preparing bentonite composite ultrafine grinding media according to claim 3, characterized in that, The stepwise sintering described in step S3 includes the following steps: First heating stage: Increase the temperature to 950-1050℃ at a rate of 2.5-3.5℃ / min, and hold for 1.5-2.5 hours; Second heating stage: Increase the temperature to 1280-1350℃ at a rate of 4-5℃ / min, and hold for 2-3 hours.

5. The method for preparing bentonite composite ultrafine grinding media according to claim 3, characterized in that, In step S4, the cooling rate is 1.5–3 °C / min.

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