A gradient alumina-based grinding ball based on shape-modulated properties, its preparation method, and its recycling method after disposal.

Abstract

This invention provides a shape-controlled gradient alumina-based grinding ball, its preparation method, and a method for recycling the grinding ball after it has been disposed of, relating to the field of ceramic materials. The shape-controlled gradient alumina-based grinding ball comprises a three-layer gradient structure from the outside in: a surface layer, a transition layer, and a core layer. The surface layer is a composite layer of dot-like h-BN, linear h-BN, and plate-like h-BN with Al2O3. The transition layer is a composite layer of yttrium-stabilized zirconia (YSZ) with Al2O3. The core layer is composed of industrial α-Al2O3. The shape-controlled gradient alumina-based grinding ball of this invention possesses excellent self-lubricating properties, wear resistance, hardness, and toughness, and also enables effective recycling after the grinding ball has been disposed of.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials, and in particular to a gradient alumina-based grinding ball based on shape and property control, its preparation method, and a method for recycling the grinding ball after it is discarded. Background Technology

[0002] As a core consumable in industrial wet and dry grinding processes, ceramic grinding balls directly determine grinding efficiency, energy consumption, and final product quality. Currently, commercial grinding balls are mainly divided into two categories: high-alumina balls and zirconia balls. While high-alumina balls offer advantages such as high hardness and low cost, their poor toughness makes them prone to brittle fracture under impact loads, limiting their application in heavy-load or high-impact conditions. Zirconia balls, on the other hand, exhibit excellent toughness due to their unique phase transformation toughening mechanism; however, their relatively low hardness and high friction coefficient during high-speed grinding can easily lead to increased energy consumption and localized overheating, affecting the quality of the ground material. To balance hardness and toughness, zirconia-toughened alumina ceramic balls (ZTA ceramic balls) have been developed, achieving a certain degree of performance balance. However, they are still homogeneous or simple composite materials, with little difference between the surface and bulk properties, making it difficult to simultaneously meet the contradictory requirements of "low friction coefficient and high wear resistance on the surface" and "high toughness and impact resistance overall."

[0003] In recent years, the concept of functionally graded materials (FJTs) has been introduced into the design of grinding balls. By creating continuous or stepped changes in composition and structure along the radial direction of the grinding ball, different regions of the material can undertake different functions. However, existing gradient grinding ball designs mostly focus on the gradient transition of macroscopic mechanical properties, and there are still shortcomings in the design of surface functionalization, especially in failing to systematically solve the synergistic problem of "self-lubrication" and "reinforcement and toughening" at the microscopic scale. This problem is mainly reflected in two aspects:

[0004] Firstly, regarding the synergistic improvement of surface self-lubrication and reinforcement, boron nitride (h-BN) is considered an ideal solid lubricant due to its graphite-like layered structure, extremely low coefficient of friction, and good high-temperature stability. Existing techniques have attempted to introduce flake-like h-BN into ceramic surfaces to reduce friction. While this can provide some lubrication, the inventors have found that flake-like h-BN tends to aggregate in-plane within the alumina matrix, easily disrupting the matrix's continuity. This not only weakens the material's mechanical strength but may also lead to crack initiation due to the flakes being pulled out under stress, thus impairing the material's intrinsic toughness. It can be seen that existing techniques using flake-like h-BN to reduce ceramic ball friction improve lubrication at the expense of mechanical properties, failing to maintain or enhance the surface's mechanical properties while providing effective lubrication.

[0005] Secondly, regarding the stress buffering and toughening balance of the transition layer, yttrium-stabilized zirconia (YSZ) is a commonly used toughening phase, and its stress-induced phase transformation toughening mechanism has been widely utilized. In gradient structure design, the transition layer needs to effectively alleviate the residual stress caused by the difference in thermal expansion coefficient and elastic modulus between the surface layer and the core layer, and prevent surface cracks from propagating inward. However, in traditional ZTA materials or simple gradient structures, the toughening potential of yttrium-stabilized zirconia has not been fully realized. Analysis shows that the main reason is that the phase transformation behavior of yttrium-stabilized zirconia strongly depends on its particle size, stabilizer content, and the constraints of the surrounding matrix. Under non-optimal conditions, the phase transformation may occur prematurely or be difficult to be effectively induced by external stress, resulting in unstable toughening effects and poor controllability. On the other hand, if the content and distribution of yttrium-stabilized zirconia in the transition layer fail to achieve a smooth gradient transition in mechanical properties with the surface h-BN / Al2O3 composite layer and the pure Al2O3 layer in the core layer, stress concentration may occur at the interface due to abrupt property changes, forming new structural weaknesses and reducing overall reliability.

[0006] Furthermore, from a life-cycle perspective, high-performance grinding balls are expensive, and after they are scrapped, they are usually landfilled as solid waste, resulting in a huge waste of valuable resources such as h-BN, zirconium oxide, and alumina, as well as environmental pollution. Existing recycling methods are mostly limited to physical crushing and use as low-grade fillers, which cannot achieve closed-loop high-value regeneration of "waste grinding balls - high-performance new balls", nor can they specifically purify the surface of waste ball powder, restore its sintering activity, and combine it with new raw materials to achieve a systematic green cycle for high-quality remanufacturing.

[0007] In summary, the core challenges facing existing technologies are: how to solve the technical bottleneck of balancing surface lubrication, wear resistance, and overall toughness and impact resistance in gradient composite grinding balls; how to achieve effective enhancement of gradient composite grinding balls by h-BN through "shape control" so that the grinding balls simultaneously possess excellent self-lubrication, wear resistance, hardness, and toughness; and how to further overcome the problem that existing grinding balls cannot be recycled after being scrapped, and achieve effective recycling of the grinding balls after they are scrapped. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention provides a gradient alumina-based grinding ball based on shape-modulation and its preparation method. Through "shape-modulation," h-BN effectively enhances the gradient composite grinding ball, enabling it to simultaneously possess excellent self-lubricating properties, wear resistance, hardness, and toughness. This overcomes the technical bottleneck of gradient composite grinding balls where surface lubrication and wear resistance are difficult to balance with overall toughness and impact resistance. This invention also provides a method for recycling the aforementioned shape-modulated gradient alumina-based grinding ball after it has been scrapped, achieving effective recycling of the grinding ball after it has been scrapped.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A gradient alumina-based grinding ball based on shape regulation comprises a three-layer gradient structure from the outside to the inside: a surface layer, a transition layer, and a core layer;

[0011] The surface layer is a composite layer of dot-shaped h-BN, linear h-BN, sheet-like h-BN and Al2O3;

[0012] The transition layer is a composite layer of yttrium oxide-stabilized zirconium oxide (YSZ) and Al2O3.

[0013] The core layer is composed of industrial α-Al2O3.

[0014] Preferably, the thickness ratio of the surface layer, transition layer, and core layer is (0.5-1.5):(1-3):(8-10).

[0015] A method for preparing gradient alumina-based grinding balls based on shape regulation, as described above, includes the following steps: raw material pretreatment and slurry preparation, gradient molding, drying treatment, and sintering treatment;

[0016] The method for raw material pretreatment and slurry preparation is as follows: Dot-like h-BN, linear h-BN, flake-like h-BN, and Al2O3 powder are mixed to obtain a surface layer raw material; yttrium-stabilized zirconium oxide and Al2O3 powder are mixed to obtain a transition layer raw material; industrial α-Al2O3 powder is used as the core layer raw material; binder, dispersant, and deionized water are added to the surface layer raw material, transition layer raw material, and core layer raw material respectively, and the mixture is ball-milled uniformly to obtain surface slurry, transition layer slurry, and core layer slurry with a solid content of 50-60 wt% respectively.

[0017] The gradient forming method is as follows: core layer slurry is injected into a spherical mold and centrifuged to form the core layer; transition layer slurry is injected into the spherical mold and centrifuged to form the transition layer; surface layer slurry is injected into the spherical mold and centrifuged to form the surface layer, thereby obtaining a composite preform with a three-layer gradient structure.

[0018] The composite preform is subjected to drying and sintering processes in sequence to obtain gradient alumina-based grinding balls.

[0019] Preferably, in the surface material, the total weight of dot-shaped h-BN, linear h-BN and flake-shaped h-BN to the mass ratio of Al2O3 powder is (10-25):(75-90).

[0020] The mass ratio of dot-shaped h-BN, linear h-BN, and sheet-like h-BN is (3-5):(1-3):(6-8).

[0021] Preferably, in the transition layer raw material, the mass percentage content of yttrium oxide-stabilized zirconium oxide is 10-20%, and the balance is Al2O3 powder;

[0022] The Y₂O₃ content in yttrium oxide-stabilized zirconium oxide is 3-5 wt%.

[0023] Preferably, in the gradient molding process, the centrifugal speed of the centrifugal molding is 800-1200 r / min;

[0024] The centrifugal molding time after the core layer slurry is injected into the spherical mold is 25-35 minutes.

[0025] The centrifugal molding time after the transition layer slurry is injected into the spherical mold is 20-30 minutes.

[0026] The centrifugal molding time after the surface slurry is injected into the spherical mold is 15-25 minutes.

[0027] Furthermore, the drying process is as follows: the composite green body is dried at 60-65℃ for 8-10 hours, then heated to 80-85℃ and kept at that temperature for 12-16 hours, then heated to 100-105℃ and kept at that temperature for 4-6 hours to obtain the dried composite green body.

[0028] The sintering process involves placing the dried composite blank in a sintering furnace and heating it to 1500-1600℃ at a heating rate of 5-8℃ / min in an air atmosphere, holding it at that temperature for 2-4 hours; then cooling it to 800℃ at a cooling rate of 3-5℃ / min and allowing it to cool naturally to obtain gradient alumina-based grinding balls.

[0029] A method for recycling and utilizing the aforementioned gradient alumina-based grinding balls based on shape control includes the following steps: crushing and grading, surface cleaning, batching and mixing, microwave reheating, and molding processing.

[0030] The crushing and grading method involves crushing the discarded gradient alumina-based grinding balls to a particle size of less than 100 μm to obtain regenerated powder.

[0031] The surface cleaning method is to use argon and oxygen as working gases to perform plasma cleaning on the regenerated powder to obtain the surface-cleaned regenerated powder.

[0032] The method of mixing the ingredients is to mix the surface-cleaned regenerated powder with industrial α-Al2O3 powder and sintering aid evenly to obtain a mixed powder;

[0033] The microwave re-firing method involves placing the mixed powder in a microwave sintering furnace, controlling the furnace pressure to be 0.1-0.5 MPa and the microwave frequency to be 2.45 GHz under a nitrogen protective atmosphere, and then performing microwave re-firing to obtain the sintered material.

[0034] The processing and forming method is as follows: the material is ground, shaped, and then sintered in a sintering furnace to obtain recycled grinding balls.

[0035] Preferably, in the surface cleaning process, the volume percentage of oxygen in the working gas is controlled to be 5-10%, the working gas flow rate is 50-60 sccm, the plasma radio frequency power is 500-600W, and the plasma cleaning time is 10-30min.

[0036] In the microwave reheating process, the temperature is increased to 1150-1250℃ at a heating rate of 50-100℃ / min, and then held at that temperature for 25-35 minutes.

[0037] Preferably, in the ingredient mixing process, the amount of regenerated powder after surface cleaning added is controlled to be 5-10% of the total mass of the mixed powder; the amount of sintering aid added is 0.4-0.6% of the total mass of the mixed powder;

[0038] The sintering aid is a MgO-CaO-SiO2 composite aid, and the mass ratio of MgO, CaO and SiO2 in the sintering aid is 1:1:1.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The gradient alumina-based grinding balls of this invention, based on shape-modified technology, achieve excellent self-lubricating properties, wear resistance, hardness, and toughness through the synergistic regulation of multi-morphological h-BN with other raw materials and its gradient design. The specific effects achievable are detailed below based on experimental data and process mechanisms:

[0041] I. Achieve synergistic breakthroughs in core product performance, characterized by "self-lubrication, high wear resistance, and high toughness":

[0042] 1. Excellent tribological and wear performance (a direct manifestation of surface shape control)

[0043] The surface layer is composed of h-BN with three morphologies: dots, lines, and sheets, in a specific mass ratio. Among them, the dominant sheet-like h-BN is highly susceptible to slippage along the (002) crystal plane under shear force during friction, forming a continuous and stable solid lubrication transfer film on the surface of the sphere and between the material being ground. This fundamentally transforms sliding friction into internal friction between h-BN layers, significantly reducing the coefficient of friction.

[0044] In ball-disc friction and wear tests under simulated laboratory conditions, the steady-state friction coefficient of the gradient alumina-based grinding balls of this invention can be reduced to 0.13-0.18, which is more than 50% lower than that of traditional 95% alumina balls (with a friction coefficient typically >0.5). Under the same grinding time and load, the wear weight loss is reduced by more than 30%. This is directly attributed to the synergistic effect of "flaky h-BN friction reduction" and "dot-like h-BN matrix reinforcement / refinement," the latter of which refines the alumina grains to the submicron level through a pinning effect, significantly improving the surface hardness and resistance to plastic deformation.

[0045] 2. Excellent impact resistance and fracture toughness (synergistic result of gradient structure and dual-phase toughening):

[0046] First, the linear h-BN in the surface layer, acting as a one-dimensional toughening phase, effectively bridges and deflects microcracks induced by surface defects, consuming crack propagation energy. Second, the transition layer (10-20 wt% YSZ content) plays a crucial dual role: firstly, it utilizes the moderate difference in thermal expansion coefficients between YSZ and Al2O3 to alleviate thermal stress between the surface and core layers during sintering and cooling; secondly, the metastable tetragonal zirconia particles contained within it undergo stress-induced martensitic transformation (t→m) under impact or stress field at the crack tip, accompanied by approximately 3-5% volume expansion, generating a compressive stress closure effect on the crack and significantly hindering crack propagation inward.

[0047] Through drop ball impact fatigue testing, a Φ20mm ball was repeatedly dropped freely from a height of 2 meters onto a steel plate. The grinding ball of this invention achieved an average failure impact count exceeding 21,000 times, which is 3-5 times that of a high-purity alumina ball of the same specifications. The fracture toughness (K1c), tested by the indentation method, reached 6.7-7.6 MPa·m. 1 / 2 It is far superior to that of ordinary alumina ceramics (approximately 3-4 MPa·m). 1 / 2 This achieves a performance leap that is "rigid but not brittle".

[0048] 3. Significant economic benefits and energy-saving effects:

[0049] ① Long service life and reduced overall cost: Due to the dual improvement in wear resistance and impact resistance, the service life of the grinding balls of this invention is expected to be extended by 1-2 times under high-wear conditions such as mining and ceramic raw materials. Although the initial cost may be slightly higher than that of ordinary high-alumina balls, the cost of grinding media consumption per ton of material can be reduced by more than 30%.

[0050] ② Energy saving and consumption reduction: The self-lubricating properties of the surface directly reduce frictional resistance and ineffective work conversion during the grinding process. In actual industrial ball mill applications, it is expected to reduce the main motor current by 5-10%, achieving direct energy savings.

[0051] II. In terms of remanufacturing cycles, achieve a closed loop of "high-performance recovery and efficient resource utilization":

[0052] 1. Restoration of the performance of regenerated grinding balls

[0053] In the aforementioned method for recycling and utilizing graded alumina-based grinding balls, a combination of "plasma cleaning" and "microwave reheating" is employed. Plasma cleaning efficiently removes organic contaminants and weakly chemically adsorbed layers from the surface of the waste powder, activating the powder surface. Subsequent microwave reheating utilizes the volumetric heating characteristics of microwaves to rapidly and uniformly repair lattice defects in the powder, restoring its sintering activity. Simultaneously, the added composite sintering aid (MgO-CaO-SiO2) promotes interfacial bonding between the regenerated powder and the new powder.

[0054] The regenerated grinding balls prepared by this process have a recovery rate of key properties (wear resistance and impact toughness) that is no less than 94% or higher than that of the original new balls (i.e., gradient alumina-based grinding balls).

[0055] 2. Outstanding resource and environmental benefits

[0056] ① High resource utilization rate: The waste recycling method of this invention can effectively recover the most valuable ceramic components such as alumina, zirconium oxide, and h-BN from waste grinding balls. Through the process of "crushing-grading-purification-reuse", the comprehensive utilization of high-value raw materials is effectively achieved (about 80%), which is far higher than the traditional method of crushing and using as filler (utilization rate <10%).

[0057] ②Significant carbon emission reduction: Since the long and energy-intensive front-end process from bauxite smelting, chemical synthesis to high-temperature calcination to prepare alumina powder is eliminated in the recycling of the grinding balls, only a short-time, medium-temperature activation treatment of the recycled powder is required to prepare high-performance grinding balls, which significantly reduces carbon dioxide emissions compared to the preparation of grinding balls with the same performance. Detailed Implementation

[0058] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0060] This invention provides a gradient alumina-based grinding ball based on shape control, which includes a three-layer gradient structure from the outside to the inside: a surface layer, a transition layer, and a core layer; the thickness ratio of the surface layer, the transition layer, and the core layer is (0.5-1.5):(1-3):(8-10).

[0061] The surface layer is a self-lubricating reinforcing layer composed of h-BN and Al2O3, with a mass ratio of h-BN to Al2O3 of (10-25):(75-90). The h-BN includes dot-like h-BN (nano boron nitride), linear h-BN (boron nitride whiskers), and plate-like h-BN (plate-like boron nitride); the mass ratio of dot-like h-BN, linear h-BN, and plate-like h-BN is (3-5):(1-3):(6-8).

[0062] The transition layer is a yttrium oxide-stabilized zirconia (YSZ)-Al₂O₃ dual-phase toughening buffer layer, with the yttrium oxide-stabilized zirconia (YSZ) content in the transition layer being 10-20 wt%. The Y₂O₃ content in the yttrium oxide-stabilized zirconia (YSZ) is 3-5 wt%.

[0063] The core layer is composed of industrial α-Al2O3.

[0064] The present invention also provides the aforementioned method for preparing gradient alumina-based grinding balls based on shape regulation, comprising the following steps: raw material pretreatment and slurry preparation, centrifugal gradient molding, segmented drying, and sintering treatment.

[0065] S101. Raw material pretreatment and slurry preparation

[0066] Prepare surface layer raw materials, transition layer raw materials and core layer raw materials separately. Add 3-5% of binder (such as polyvinyl alcohol) and 0.5-1% of dispersant (such as triethanolamine) to each layer raw material according to the total mass of the raw material of that layer, and then add deionized water. After ball milling in a planetary ball mill for 2-4 hours, remove impurities by passing through a 200-mesh sieve to obtain surface layer slurry, transition layer slurry and core layer slurry with a solid content of 50-60wt%.

[0067] The surface material consists of dot-shaped h-BN, linear h-BN, flake-shaped h-BN, and Al2O3 powder; the total weight of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN to the mass ratio of Al2O3 powder is (10-25):(75-90); the mass ratio of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is (3-5):(1-3):(6-8).

[0068] The Al2O3 powder used in the surface material has a purity of ≥99.0wt%, an average grain size of 0.8-1.5μm, and a specific surface area of ​​12-18m². 2 / g, loose bulk density is 0.8-1.0g / cm³ 3 The high purity of Al2O3 powder prevents impurities from affecting the surface density and lubrication performance; at the same time, the submicron-sized grain size can form a tight composite with multi-morphological h-BN, improving the surface hardness; and the specific specific surface area and loose packing density ensure uniform dispersion of the slurry, avoiding component agglomeration during the molding process.

[0069] The dotted h-BN used in the surface material consists of nano-boron nitride particles with a purity ≥99.5wt%, an average particle size of 50-100nm, a particle size distribution range (D90-D10) ≤30nm, and a specific surface area of ​​50-80m². 2 / g, with an absolute zeta potential ≥30mV (pH=7). It fills the surface matrix pores with nano-sized particles, refines the grains, and improves hardness; and ensures the dispersion stability of the slurry and avoids agglomeration through a specific narrow particle size distribution and high zeta potential.

[0070] The linear h-BN used in the surface material is boron nitride whisker, with a diameter of 0.5-2 μm, a length of 10-30 μm, an aspect ratio of 15-40, a purity ≥99.3 wt%, a tensile strength ≥800 MPa, an elastic modulus ≥400 GPa, and an oxygen content ≤0.4 wt%. By controlling the aspect ratio, it can achieve crack bridging and deflection, improving surface toughness; its high mechanical properties ensure that it does not fracture under friction and impact conditions, avoiding becoming a crack initiation point.

[0071] The flake-shaped h-BN used in the surface material is flake-shaped boron nitride with a purity ≥99.5wt%, a flake diameter of 5-15μm, a thickness of 0.1-0.5μm, an aspect ratio of 20-50, an interlayer spacing of 0.335-0.340nm, an oxygen content ≤0.3wt%, and a moisture content ≤0.2wt%. Its specific flake diameter and thickness ensure the formation of a continuous lubricating film during friction. An excessively large aspect ratio can easily lead to matrix cracking, while an excessively small aspect ratio results in insufficient lubrication. Simultaneously, selecting high purity and low oxygen and moisture content avoids affecting sintering density and interfacial bonding strength.

[0072] The transition layer raw materials are yttria-stabilized zirconia (YSZ) and Al₂O₃ powder; the mass percentage content of yttria-stabilized zirconia (YSZ) in the transition layer raw materials is 10-20%, with the balance being Al₂O₃ powder. The Y₂O₃ content in yttria-stabilized zirconia (YSZ) is 3-5 wt%.

[0073] The Al2O3 powder used in the transition layer has a purity of ≥98.5wt%, an average grain size of 1.2-2.0μm, and a specific surface area of ​​8-12m². 2 / g; Simultaneously, the difference in the coefficient of thermal expansion between the Al2O3 powder used in the transition layer and the industrial α-Al2O3 powder used in the core layer is controlled to be ≤0.5×10. -6 / ℃ (25-1000℃). Since the transition layer needs to be compatible with the interface of the surface layer and the core layer, the grain size of the Al2O3 powder used is between that of the surface layer and the core layer, which is conducive to a smooth transition of mechanical properties. At the same time, controlling the difference in the thermal expansion coefficient of the Al2O3 powder between the transition layer and the core layer can reduce the residual stress at the interface during sintering and avoid cracking.

[0074] The core layer material is industrial α-Al2O3 powder with an alumina purity of ≥98.5wt% and an average grain size of 1-3μm.

[0075] S102. Gradient molding

[0076] A gradient composite molding process is employed, with the following steps: The core layer slurry is injected into a spherical mold and centrifuged at 800-1200 r / min for 25-35 min. During this process, under centrifugal force, the solid particles in the core layer slurry move towards the inner wall of the mold due to centrifugal sedimentation, forming the core region (core layer) of the sphere. After centrifugal molding, the core layer slurry has initially solidified (slurry viscosity reaches 5000-8000 mPa·s). A transition layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for another 20-30 min. During this process, the solid particles of the transition layer slurry adhere to the surface of the core layer under centrifugal force, forming the transition layer. After centrifugal molding, the transition layer slurry has been initially solidified (slurry viscosity reaches 4000-6000 mPa·s). Continue to inject the surface slurry into the spherical mold, and continue centrifugation for 15-25 minutes while maintaining the same rotation speed. After centrifugation molding, the surface slurry has been initially solidified (slurry viscosity reaches 3000-5000 mPa·s), resulting in a composite preform with a three-layer gradient structure.

[0077] During the gradient molding process, the thickness ratio of each layer is controlled by the injection amount of each layer of slurry, and the thickness ratio of the surface layer, transition layer and core layer is controlled to be (0.5-1.5):(1-3):(8-10).

[0078] During the gradient molding process, as the slurry is centrifuged, the water in the slurry gradually separates and is discharged through the mold's filter screen. The solid particles inside the mold gradually accumulate and become dense, and the viscosity slowly increases. When the set viscosity is reached, a preliminary physical bond is formed between the particles, which can withstand the impact force of subsequent slurry injection and avoid interlayer mixing.

[0079] S103. Drying treatment

[0080] The composite green body is placed in a drying oven and a segmented drying process is adopted to avoid cracks caused by rapid drying. The specific operation is as follows: first, dry at 60-65℃ for 8-10 hours, then raise the temperature to 80-85℃ for 12-16 hours, and finally raise the temperature to 100-105℃ for 4-6 hours until the moisture content of the composite green body is ≤0.5%, and the dried composite green body is obtained.

[0081] S104. Sintering treatment

[0082] The dried composite preform is placed in a box sintering furnace or an atmosphere sintering furnace and heated to 1500-1600℃ in an air atmosphere at a heating rate of 5-8℃ / min, and held for 2-4 hours. Then it is cooled to 800℃ at a cooling rate of 3-5℃ / min without holding and continues to cool naturally to room temperature to obtain gradient alumina-based grinding balls based on shape control.

[0083] During the sintering process, after cooling to 800℃ at a specific rate, the thermal stress release of the material is basically completed. Then, through a natural cooling process with a gradual temperature gradient, secondary stress concentration caused by rapid cooling is avoided.

[0084] The method for preparing gradient alumina-based grinding balls based on shape-modulated properties solves the aforementioned technical problems through the following technical means:

[0085] (1) Synergistic regulation of the multimorphology of surface materials by h-BN:

[0086] By using three specific morphologies (dot-like, linear, and sheet-like) of h-BN for compounding and combining them with Al2O3 powder, the synergistic regulation of multi-morphology h-BN in the surface material is achieved. This allows for the simultaneous exertion of in-situ synergistic effects of "dot-like particle refinement and reinforcement", "linear fiber bridging and toughening" and "sheet-like layer slippage and friction reduction" within a single material layer, thus resolving the contradiction between self-lubrication and strength and toughness at the microscale.

[0087] (2) Stress matching and phase transformation toughening optimization of gradient structure interface:

[0088] The transition layer not only serves as a compositional transition zone but also as a functional stress buffer and toughening layer. By combining YSZ with Al2O3 powder, the material retains a sufficient amount of metastable tetragonal zirconium oxide after sintering. This not only enables "phase transformation toughening" under stress during service but also achieves a smooth transition in elastic modulus and thermal expansion coefficient from the high-toughness surface layer to the high-strength core layer through its content and distribution. This effectively avoids interface stress concentration and maximizes the advantages of the gradient structure.

[0089] This invention also provides a method for recycling and reusing the aforementioned gradient alumina-based grinding balls based on shape control, comprising the following steps:

[0090] S201. Crushing and Grading

[0091] After mechanically crushing the waste gradient alumina-based grinding balls, an air classifier was used for classification and screening. The speed of the classifying wheel was controlled at 3000-6000 rpm to obtain regenerated powder with a particle size of less than 100 μm.

[0092] S202. Surface cleaning

[0093] The regenerated powder is placed in the processing chamber (volume 10-15L) of the plasma cleaning device using a tray-laying method, maintaining the thickness of the regenerated powder on the tray ≤3cm. Argon and oxygen are used as working gases, and the pressure of the processing chamber is controlled at 48-52Pa, the working gas flow rate is 50-60sccm, and the plasma radio frequency power is 500-600W. The regenerated powder is plasma cleaned for 10-30min to obtain surface-cleaned regenerated powder.

[0094] The working gas contains 5-10% oxygen by volume.

[0095] S203. Ingredient Mixing

[0096] The surface-cleaned regenerated powder is mixed with new industrial α-Al2O3 powder and sintering aid. The amount of surface-cleaned regenerated powder added is controlled to be 5-10% of the total material mass, and the amount of sintering aid added is 0.4-0.6% of the total material mass, to obtain mixed powder.

[0097] The sintering aid is a MgO-CaO-SiO2 composite aid, and the mass ratio of MgO, CaO and SiO2 in the sintering aid is 1:1:1.

[0098] S204. Microwave reheating

[0099] The mixed powder is placed in a microwave sintering furnace for microwave re-firing. Specifically, under a nitrogen protective atmosphere, the furnace pressure is controlled at 0.1-0.5 MPa, the microwave frequency is 2.45 GHz, the temperature is raised to 1150-1250℃ at a heating rate of 50-100℃ / min, and then held at that temperature for 25-35 minutes to obtain the sintered material.

[0100] During the microwave reheating process, the microwave power is controlled at 3-5kW.

[0101] S205. Molding and processing

[0102] After grinding the sintering material to a particle size D50 of 1-2 μm, it is cold isostatically pressed to obtain a shaped green body. The shaped green body is placed in an atmosphere sintering furnace and heated to 550-600℃ at a heating rate of 4-5℃ / min, and sintered at that temperature for 1-1.5 h. Then, the temperature is further increased to 1500-1550℃ at a heating rate of 6-7℃ / min, and sintered at that temperature for 2-2.5 h. Subsequently, the temperature is decreased to 800℃ at a cooling rate of 3-4℃ / min, without holding, and allowed to cool naturally to room temperature to obtain regenerated grinding balls with a homogeneous structure.

[0103] Among them, the molding pressure of cold isostatic pressing is 180-220MPa.

[0104] The aforementioned method for recycling and utilizing waste gradient alumina-based grinding balls based on shape and property control takes into account that after the waste gradient alumina-based grinding balls are crushed, the high-value components (such as h-BN, YSZ, Al2O3, etc.) are uniformly dispersed in the regenerated powder, making it difficult to reconstruct the gradient structure. Therefore, through a homogenized preparation process and by combining various technical means, the wear resistance and impact toughness of the regenerated grinding balls are ensured to reach 94% or more of the initial new balls, so as to meet the requirements of conventional grinding conditions and realize the closed-loop high-value regeneration of "waste grinding balls - high-performance new balls".

[0105] In its end-of-life recycling process, a combination of "plasma cleaning" and "microwave re-firing" is used, especially the microwave re-firing step, where the temperature (1150-1250℃) and time (25-35min) are much lower than the sintering temperature of brand-new ceramics. Plasma cleaning non-destructively and thoroughly cleans and activates the powder surface, removing impurity layers that affect re-sintering. The subsequent microwave re-firing utilizes its volumetric heating and selective heating characteristics to rapidly and uniformly repair powder lattice defects and restore sintering activity at low temperatures. With the help of trace composite additives, a good combination of new and old powders is achieved. Thus, the wear resistance and impact toughness of the prepared recycled grinding balls can be restored to 94% or more of the original new balls using a "low-temperature, short-process" method. This effectively realizes the comprehensive utilization of high-value raw materials, and the carbon emissions of the production process are effectively reduced compared to the preparation of brand-new grinding balls.

[0106] The present invention will be further described below with reference to some specific embodiments.

[0107] Example 1

[0108] This invention provides a gradient alumina-based grinding ball based on shape control, which has a three-layer gradient structure from the outside to the inside: a surface layer, a transition layer, and a core layer; the thickness ratio of the surface layer, the transition layer, and the core layer is 1:2:9.

[0109] The surface layer is a self-lubricating reinforcing layer composed of h-BN and Al2O3, with a mass ratio of h-BN to Al2O3 of 20:80. The h-BN comprises dot-like h-BN (nano boron nitride), linear h-BN (boron nitride whiskers), and plate-like h-BN (plate-like boron nitride); the mass ratio of dot-like h-BN, linear h-BN, and plate-like h-BN is 4:2:7.

[0110] The transition layer is a yttrium oxide-stabilized zirconia (YSZ)-Al₂O₃ dual-phase toughening buffer layer, with a YSZ content of 15 wt%. The Y₂O₃ content in the YSZ is 4 wt%.

[0111] The core layer is composed of industrial α-Al2O3.

[0112] This invention also provides a method for preparing the aforementioned shape-controlled gradient alumina-based grinding balls, the specific steps of which are as follows:

[0113] S101. Raw material pretreatment and slurry preparation

[0114] Prepare surface layer raw materials, transition layer raw materials and core layer raw materials separately. Add 4% of the total mass of the binder (polyvinyl alcohol) and 0.8% of the dispersant (triethanolamine) to each layer raw material, and then add deionized water. After ball milling for 3 hours in a planetary ball mill, remove impurities by passing through a 200-mesh sieve to obtain surface layer slurry, transition layer slurry and core layer slurry with a solid content of 55wt%.

[0115] The surface material consists of dot-shaped h-BN, linear h-BN, flake-shaped h-BN, and Al2O3 powder; the total weight of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is 20:80 with the mass ratio of Al2O3 powder; the mass ratio of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is 4:2:7.

[0116] The specifications of the raw materials used in the surface layer are as follows: Al2O3 powder with a purity of 99.3 wt%, an average grain size of 1.2 μm, and a specific surface area of ​​15.4 m². 2 / g, loose bulk density is 0.89g / cm³ 3The dot-like h-BN consists of nano-sized boron nitride particles with a purity of 99.6 wt%, an average particle size of 87 nm, a particle size distribution span (D90-D10) ≤ 30 nm, and a specific surface area of ​​72 m². 2 / g, with an absolute zeta potential of 33mV (at pH=7). Linear h-BN consists of boron nitride whiskers with a diameter of 1.5μm, a length of 27μm, an aspect ratio of 18, a purity of 99.5wt%, a tensile strength of 822MPa, an elastic modulus of 417GPa, and an oxygen content of 0.2wt%. Flaky h-BN consists of flaky boron nitride with a purity of 99.6wt%, a flake diameter of 12μm, a thickness of 0.3μm, an aspect ratio of 40, an interlayer spacing of 0.336nm, an oxygen content of 0.2wt%, and a moisture content of 0.1wt%.

[0117] The transition layer raw materials are yttria-stabilized zirconia (YSZ) and Al₂O₃ powder; the mass percentage content of yttria-stabilized zirconia (YSZ) in the transition layer raw materials is 15%, and the balance is Al₂O₃ powder. The Y₂O₃ content in yttria-stabilized zirconia (YSZ) is 4 wt%.

[0118] The specifications of the raw materials used in the transition materials are as follows: Al2O3 powder with a purity of 98.9 wt%, an average grain size of 1.8 μm, and a specific surface area of ​​10.4 m². 2 / g; Simultaneously, the difference in the coefficient of thermal expansion between the Al2O3 powder used in the transition layer and the industrial α-Al2O3 powder used in the core layer is controlled to be ≤0.5×10. -6 / ℃ (25-1000℃).

[0119] The core layer material is industrial α-Al2O3 powder with an alumina purity of 99.0 wt% and an average grain size of 2 μm.

[0120] S102. Gradient molding

[0121] A gradient composite molding process is employed, with the following steps: The core layer slurry is injected into a spherical mold and centrifuged at 1000 r / min for 30 min. During this process, under centrifugal force, the solid particles in the core layer slurry move towards the inner wall of the mold due to centrifugal sedimentation, forming the core region (core layer) of the sphere. After centrifugation, the core layer slurry has initially solidified. A transition layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for 25 min. During this process, the solid particles in the transition layer slurry adhere to the surface of the core layer under centrifugal force, forming the transition layer. After centrifugation, the transition layer slurry has initially solidified. A surface layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for 20 min. After centrifugation, the surface layer slurry has initially solidified, resulting in a composite preform with a three-layer gradient structure.

[0122] During the gradient molding process, the thickness ratio of each layer is controlled by the injection amount of each layer of slurry, and the thickness ratio of the surface layer, transition layer and core layer is controlled to be 1:2:9.

[0123] S103. Drying treatment

[0124] The composite green body is placed in a drying oven and a segmented drying process is adopted to avoid cracks caused by rapid drying. The specific operation is as follows: first, dry at 60℃ for 9 hours, then raise the temperature to 80℃ for 14 hours, and finally raise the temperature to 100℃ for 5 hours until the moisture content of the composite green body is ≤0.5%, and the dried composite green body is obtained.

[0125] S104. Sintering treatment

[0126] The dried composite preform is placed in a box sintering furnace or an atmosphere sintering furnace and heated to 1550°C at a heating rate of 6°C / min in an air atmosphere environment, and held for 3 hours. Then it is cooled to 800°C at a cooling rate of 4°C / min without holding and continues to cool naturally to room temperature to obtain gradient alumina-based grinding balls based on shape control.

[0127] The performance of the shape-controlled gradient alumina-based grinding ball of this embodiment was tested. The results showed that the surface friction coefficient of the gradient alumina-based grinding ball was 0.13, exhibiting excellent self-lubricating properties; and its impact toughness reached 3.2 MPa·m. 1 / 2 Compared to traditional 95 alumina grinding balls, its impact toughness is improved by 45%; its fracture toughness (K1c) is 6.8 MPa·m. 1 / 2 The ball impact fatigue cycle (Φ20mm, 2m height) is 21,500 times; under the working conditions of 300r / min rotation speed and grinding quartz sand for 2h, the wear amount is 0.75g, which is 38% lower than that of 95 traditional alumina grinding balls; the amount of impurities introduced into the ground quartz sand is 0.018wt%, which is 52% lower than that of traditional processes, fully meeting the requirements of high-precision powder processing.

[0128] Example 2

[0129] This invention provides a gradient alumina-based grinding ball based on shape control, which has a three-layer gradient structure from the outside to the inside: a surface layer, a transition layer, and a core layer; the thickness ratio of the surface layer, the transition layer, and the core layer is 0.5:1:8.

[0130] The surface layer is a self-lubricating reinforcing layer composed of h-BN and Al2O3, with a mass ratio of h-BN to Al2O3 of 15:85. The h-BN comprises dot-like h-BN (nano boron nitride), linear h-BN (boron nitride whiskers), and plate-like h-BN (plate-like boron nitride); the mass ratio of dot-like h-BN, linear h-BN, and plate-like h-BN is 3:1:6.

[0131] The transition layer is a yttrium oxide-stabilized zirconia (YSZ)-Al₂O₃ dual-phase toughening buffer layer, with the yttrium oxide-stabilized zirconia (YSZ) content in the transition layer being 10 wt%. Specifically, the Y₂O₃ content in the yttrium oxide-stabilized zirconia (YSZ) is 3 wt%.

[0132] The core layer is composed of industrial α-Al2O3.

[0133] This invention also provides a method for preparing the aforementioned shape-controlled gradient alumina-based grinding balls, the specific steps of which are as follows:

[0134] S101. Raw material pretreatment and slurry preparation

[0135] Prepare surface layer raw materials, transition layer raw materials and core layer raw materials separately. Add 3% of the total mass of the binder (polyvinyl alcohol) and 0.6% of the dispersant (triethanolamine) to each layer raw material, and then add deionized water. After ball milling for 3 hours in a planetary ball mill, remove impurities by passing through a 200-mesh sieve to obtain surface layer slurry, transition layer slurry and core layer slurry with a solid content of 55wt%.

[0136] The surface material consists of dot-shaped h-BN, linear h-BN, flake-shaped h-BN, and Al2O3 powder; the total weight of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is 15:85 with the mass ratio of Al2O3 powder; the mass ratio of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is 3:1:6.

[0137] The specifications of the raw materials used in the surface layer are as follows: Al2O3 powder with a purity of 99.3 wt%, an average grain size of 1.2 μm, and a specific surface area of ​​15.4 m². 2 / g, loose bulk density is 0.89g / cm³ 3 The dot-like h-BN consists of nano-sized boron nitride particles with a purity of 99.6 wt%, an average particle size of 87 nm, a particle size distribution span (D90-D10) ≤ 30 nm, and a specific surface area of ​​72 m². 2 / g, with an absolute zeta potential of 33mV (at pH=7). Linear h-BN consists of boron nitride whiskers with a diameter of 1.5μm, a length of 27μm, an aspect ratio of 18, a purity of 99.5wt%, a tensile strength of 822MPa, an elastic modulus of 417GPa, and an oxygen content of 0.2wt%. Flaky h-BN consists of flaky boron nitride with a purity of 99.6wt%, a flake diameter of 12μm, a thickness of 0.3μm, an aspect ratio of 40, an interlayer spacing of 0.336nm, an oxygen content of 0.2wt%, and a moisture content of 0.1wt%.

[0138] The transition layer raw materials are yttria-stabilized zirconia (YSZ) and Al₂O₃ powder; the mass percentage content of yttria-stabilized zirconia (YSZ) in the transition layer raw materials is 10%, and the balance is Al₂O₃ powder. The Y₂O₃ content in yttria-stabilized zirconia (YSZ) is 3 wt%.

[0139] The specifications of the raw materials used in the transition materials are as follows: Al2O3 powder with a purity of 98.9 wt%, an average grain size of 1.8 μm, and a specific surface area of ​​10.4 m². 2 / g; Simultaneously, the difference in the coefficient of thermal expansion between the Al2O3 powder used in the transition layer and the industrial α-Al2O3 powder used in the core layer is controlled to be ≤0.5×10. -6 / ℃ (25-1000℃).

[0140] The core layer material is industrial α-Al2O3 powder with an alumina purity of 99.0 wt% and an average grain size of 2 μm.

[0141] S102. Gradient molding

[0142] A gradient composite molding process is employed, with the following steps: The core layer slurry is injected into a spherical mold and centrifuged at 800 rpm for 35 minutes. During this process, under centrifugal force, the solid particles in the core layer slurry move towards the inner wall of the mold due to centrifugal sedimentation, forming the core region (core layer) of the sphere. After centrifugation, the core layer slurry has initially solidified. A transition layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for another 30 minutes. During this process, the solid particles in the transition layer slurry adhere to the surface of the core layer under centrifugal force, forming the transition layer. After centrifugation, the transition layer slurry has initially solidified. A surface layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for another 25 minutes. After centrifugation, the surface layer slurry has initially solidified, resulting in a composite preform with a three-layer gradient structure.

[0143] During the gradient molding process, the thickness ratio of each layer is controlled by the injection amount of each layer of slurry, and the thickness ratio of the surface layer, transition layer and core layer is controlled to be 0.5:1:8.

[0144] S103. Drying treatment

[0145] The composite green body is placed in a drying oven and a segmented drying process is adopted to avoid cracks caused by rapid drying. The specific operation is as follows: first, dry at 60℃ for 8 hours, then raise the temperature to 80℃ for 12 hours, and finally raise the temperature to 100℃ for 4 hours until the moisture content of the composite green body is ≤0.5%, and the dried composite green body is obtained.

[0146] S104. Sintering treatment

[0147] The dried composite preform is placed in a box sintering furnace or an atmosphere sintering furnace and heated to 1500℃ at a heating rate of 5℃ / min in an air atmosphere environment, and held for 2.5h; then cooled to 800℃ at a cooling rate of 3℃ / min without holding, and continued to cool naturally to room temperature to obtain gradient alumina-based grinding balls based on shape control.

[0148] The performance of the shape-controlled gradient alumina-based grinding ball of this embodiment was tested. The results showed that the surface friction coefficient of the gradient alumina-based grinding ball was 0.18, exhibiting excellent self-lubricating properties; and the impact toughness reached 2.9 MPa·m. 1 / 2 Compared to traditional 95 alumina grinding balls, its impact toughness is improved by 36%; its fracture toughness (K1c) is 6.7 MPa·m. 1 / 2 The ball impact fatigue test (Φ20mm, 2m height) is 21,300 times; under the working conditions of 300r / min and grinding quartz sand for 2h, the wear amount is 0.82g, which is 32% lower than that of 95 traditional alumina grinding balls; the amount of impurities introduced into the ground quartz sand is 0.022wt%, which is 45% lower than that of traditional processes, fully meeting the requirements of high-precision powder processing.

[0149] Example 3

[0150] This invention provides a gradient alumina-based grinding ball based on shape control, which has a three-layer gradient structure from the outside to the inside: a surface layer, a transition layer, and a core layer; the thickness ratio of the surface layer, the transition layer, and the core layer is 1.5:3:10.

[0151] The surface layer is a self-lubricating reinforcing layer composed of h-BN and Al2O3, with a mass ratio of h-BN to Al2O3 of 25:75. The h-BN comprises dot-like h-BN (nano boron nitride), linear h-BN (boron nitride whiskers), and plate-like h-BN (plate-like boron nitride); the mass ratio of dot-like h-BN, linear h-BN, and plate-like h-BN is 5:3:8.

[0152] The transition layer is a yttrium oxide-stabilized zirconia (YSZ)-Al₂O₃ dual-phase toughening buffer layer, with a YSZ content of 20 wt%. The Y₂O₃ content in the YSZ is 5 wt%.

[0153] The core layer is composed of industrial α-Al2O3.

[0154] This invention also provides a method for preparing the aforementioned shape-controlled gradient alumina-based grinding balls, the specific steps of which are as follows:

[0155] S101. Raw material pretreatment and slurry preparation

[0156] Prepare surface layer raw materials, transition layer raw materials and core layer raw materials separately. Add 5% binder (polyvinyl alcohol) and 1% dispersant (triethanolamine) of the total mass of each layer raw material to each layer raw material, and then add deionized water. After ball milling for 4 hours in a planetary ball mill, remove impurities by passing through a 200-mesh sieve to obtain surface layer slurry, transition layer slurry and core layer slurry with a solid content of 55wt%.

[0157] The surface material consists of dot-shaped h-BN, linear h-BN, flake-shaped h-BN, and Al2O3 powder; the total weight of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is 25:75 to the mass ratio of Al2O3 powder; the mass ratio of dot-shaped h-BN, linear h-BN, and flake-shaped h-BN is 5:3:8.

[0158] The specifications of the raw materials used in the surface layer are as follows: Al2O3 powder with a purity of 99.3 wt%, an average grain size of 1.2 μm, and a specific surface area of ​​15.4 m². 2 / g, loose bulk density is 0.89g / cm³ 3 The dot-like h-BN consists of nano-sized boron nitride particles with a purity of 99.6 wt%, an average particle size of 87 nm, a particle size distribution span (D90-D10) ≤ 30 nm, and a specific surface area of ​​72 m². 2 / g, with an absolute zeta potential of 33mV (at pH=7). Linear h-BN consists of boron nitride whiskers with a diameter of 1.5μm, a length of 27μm, an aspect ratio of 18, a purity of 99.5wt%, a tensile strength of 822MPa, an elastic modulus of 417GPa, and an oxygen content of 0.2wt%. Flaky h-BN consists of flaky boron nitride with a purity of 99.6wt%, a flake diameter of 12μm, a thickness of 0.3μm, an aspect ratio of 40, an interlayer spacing of 0.336nm, an oxygen content of 0.2wt%, and a moisture content of 0.1wt%.

[0159] The transition layer raw materials are yttria-stabilized zirconia (YSZ) and Al₂O₃ powder; the mass percentage content of yttria-stabilized zirconia (YSZ) in the transition layer raw materials is 20%, and the balance is Al₂O₃ powder. The Y₂O₃ content in yttria-stabilized zirconia (YSZ) is 5 wt%.

[0160] The specifications of the raw materials used in the transition materials are as follows: Al2O3 powder with a purity of 98.9 wt%, an average grain size of 1.8 μm, and a specific surface area of ​​10.4 m². 2 / g; Simultaneously, the difference in the coefficient of thermal expansion between the Al2O3 powder used in the transition layer and the industrial α-Al2O3 powder used in the core layer is controlled to be ≤0.5×10. -6 / ℃ (25-1000℃).

[0161] The core layer material is industrial α-Al2O3 powder with an alumina purity of 99.0 wt% and an average grain size of 2 μm.

[0162] S102. Gradient molding

[0163] A gradient composite molding process is employed, with the following steps: The core layer slurry is injected into a spherical mold and centrifuged at 1200 r / min for 25 min. During this process, under centrifugal force, the solid particles in the core layer slurry move towards the inner wall of the mold due to centrifugal sedimentation, forming the core region (core layer) of the sphere. After centrifugation, the core layer slurry has initially solidified. A transition layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for 20 min. During this process, the solid particles in the transition layer slurry adhere to the surface of the core layer under centrifugal force, forming the transition layer. After centrifugation, the transition layer slurry has initially solidified. A surface layer slurry is then injected into the spherical mold, and centrifugation continues at the same speed for 15 min. After centrifugation, the surface layer slurry has initially solidified, resulting in a composite preform with a three-layer gradient structure.

[0164] During the gradient molding process, the thickness ratio of each layer is controlled by the injection amount of each layer of slurry, and the thickness ratio of the surface layer, transition layer and core layer is controlled to be 1.5:3:10.

[0165] S103. Drying treatment

[0166] The composite green body is placed in a drying oven and a segmented drying process is adopted to avoid cracks caused by rapid drying. The specific operation is as follows: first, dry at 65℃ for 8 hours, then raise the temperature to 85℃ for 12 hours, and finally raise the temperature to 105℃ for 4 hours until the moisture content of the composite green body is ≤0.5%, and the dried composite green body is obtained.

[0167] S104. Sintering treatment

[0168] The dried composite preform is placed in a box sintering furnace or an atmosphere sintering furnace and heated to 1600℃ at a heating rate of 8℃ / min in an air atmosphere environment, and held for 4 hours; then cooled to 800℃ at a cooling rate of 5℃ / min without holding, and continued to cool naturally to room temperature to obtain gradient alumina-based grinding balls based on shape control.

[0169] The performance of the shape-controlled gradient alumina-based grinding ball of this embodiment was tested. The results showed that the surface friction coefficient of the gradient alumina-based grinding ball was 0.14, exhibiting excellent self-lubricating properties; and the impact toughness reached 3.5 MPa·m. 1 / 2 Compared to traditional 95 alumina grinding balls, its impact toughness is improved by 59%; its fracture toughness (K1c) is 7.6 MPa·m. 1 / 2 The number of impact fatigue cycles (Φ20mm, 2m height) is 24,800; under the working conditions of 300r / min rotation speed and grinding quartz sand for 2h, the wear amount is 0.68g, which is 43% lower than that of 95 traditional alumina grinding balls; the amount of impurities introduced into the ground quartz sand is 0.015wt%, which is 58% lower than that of traditional processes, fully meeting the requirements of high-precision powder processing.

[0170] Example 4

[0171] This embodiment provides a method for recycling and reusing waste alumina-based grinding balls based on shape and property control. The specific steps are as follows:

[0172] S201. Crushing and Grading

[0173] After mechanically crushing the waste gradient alumina-based grinding balls from Example 1, a classifier was used for classification and screening. The speed of the classifier wheel was controlled at 3000 rpm to obtain regenerated powder with a particle size of less than 100 μm.

[0174] S202. Surface cleaning

[0175] The regenerated powder was placed in the processing chamber (volume 15L) of the plasma cleaning device using a tray-laying method, maintaining a 3cm thickness of regenerated powder on the tray. Argon and oxygen were used as working gases, and the pressure in the processing chamber was controlled at 50Pa, the working gas flow rate at 55sccm, and the plasma radio frequency power at 600W. The regenerated powder was plasma cleaned for 20 minutes to obtain surface-cleaned regenerated powder.

[0176] The working gas contains 9% oxygen by volume.

[0177] S203. Ingredient Mixing

[0178] The surface-cleaned regenerated powder is mixed with new industrial α-Al2O3 powder and sintering aid. The amount of surface-cleaned regenerated powder added is controlled at 8% of the total material mass, and the amount of sintering aid added is controlled at 0.5% of the total material mass to obtain mixed powder.

[0179] The sintering aid is a MgO-CaO-SiO2 composite aid, and the mass ratio of MgO, CaO and SiO2 in the sintering aid is 1:1:1.

[0180] S204. Microwave reheating

[0181] The mixed powder was placed in a microwave sintering furnace for microwave re-firing. Specifically, under a nitrogen protective atmosphere, the furnace pressure was controlled at 0.3 MPa, the microwave frequency was 2.45 GHz, the temperature was raised to 1200℃ at a heating rate of 80℃ / min, and microwave re-firing was carried out for 30 minutes to obtain the sintered material.

[0182] During the microwave reheating process, the microwave power is controlled at 4kW.

[0183] S205. Molding and processing

[0184] The sintering material was ground to a particle size D50 of 1.5 μm and then cold isostatically pressed to obtain a shaped green body. The shaped green body was placed in an atmosphere sintering furnace and heated to 600℃ at a heating rate of 5℃ / min, and sintered at that temperature for 1-1.5 h. Then, the temperature was increased to 1550℃ at a heating rate of 6℃ / min and sintered at that temperature for 2.5 h. Subsequently, the temperature was decreased to 800℃ at a cooling rate of 4℃ / min without holding, and then allowed to cool naturally to room temperature to obtain regenerated grinding balls with a homogeneous structure.

[0185] The forming pressure for cold isostatic pressing is 200 MPa.

[0186] The performance of the regenerated grinding balls prepared in this embodiment was tested, and the results showed that the impact toughness of the regenerated grinding balls was 3.1 MPa·m. 1 / 2 (96.9% of the performance of new graded alumina-based grinding balls); under the working conditions of 300 r / min and grinding quartz sand for 2 hours, the wear amount is 0.78 g (96.2% of the performance of new graded alumina-based grinding balls), which can meet the basic processing requirements of powder.

[0187] Example 5

[0188] This embodiment provides a method for recycling and reusing waste alumina-based grinding balls based on shape and property control. The specific steps are as follows:

[0189] S201. Crushing and Grading

[0190] After mechanically crushing the waste gradient alumina-based grinding balls from Example 3, a classifier was used for classification and screening. The speed of the classifier wheel was controlled at 3000 rpm to obtain regenerated powder with a particle size of less than 100 μm.

[0191] S202. Surface cleaning

[0192] The regenerated powder was placed in the processing chamber (15L volume) of the plasma cleaning device using a tray-laying method, maintaining a 3cm thickness of regenerated powder on the tray. Argon and oxygen were used as working gases, and the processing chamber pressure was controlled at 50Pa, the working gas flow rate at 50sccm, and the plasma radio frequency power at 500W. The regenerated powder was plasma cleaned for 15 minutes to obtain surface-cleaned regenerated powder.

[0193] The working gas contains 8.2% oxygen by volume.

[0194] S203. Ingredient Mixing

[0195] The surface-cleaned regenerated powder is mixed with new industrial α-Al2O3 powder and sintering aid. The amount of surface-cleaned regenerated powder added is controlled at 5% of the total material mass, and the amount of sintering aid added is controlled at 0.5% of the total material mass to obtain mixed powder.

[0196] The sintering aid is a MgO-CaO-SiO2 composite aid, and the mass ratio of MgO, CaO and SiO2 in the sintering aid is 1:1:1.

[0197] S204. Microwave reheating

[0198] The mixed powder was placed in a microwave sintering furnace for microwave re-firing. Specifically, under a nitrogen protective atmosphere, the furnace pressure was controlled at 0.1 MPa, the microwave frequency was 2.45 GHz, the temperature was raised to 1150℃ at a heating rate of 50℃ / min, and microwave re-firing was carried out for 25 minutes to obtain the sintered material.

[0199] During the microwave reheating process, the microwave power is controlled at 3kW.

[0200] S205. Molding and processing

[0201] The sintering material was ground to a particle size D50 of 1.5 μm and then cold isostatically pressed to obtain a shaped green body. The shaped green body was placed in an atmosphere sintering furnace and heated to 600℃ at a heating rate of 4℃ / min, and held for sintering for 1 hour. The temperature was then increased to 1500℃ at a heating rate of 6.5℃ / min and held for sintering for 2 hours. Subsequently, the temperature was decreased to 800℃ at a cooling rate of 3℃ / min without holding, and then allowed to cool naturally to room temperature to obtain regenerated grinding balls with a homogeneous structure.

[0202] The forming pressure for cold isostatic pressing is 180 MPa.

[0203] The performance of the regenerated grinding balls prepared in this embodiment was tested, and the results showed that the impact toughness of the regenerated grinding balls was 3.3 MPa·m. 1 / 2 (94.3% of the performance of new graded alumina-based grinding balls); under the working conditions of 300 r / min and grinding quartz sand for 2 hours, the wear amount is 0.72 g (94.1% of the performance of new graded alumina-based grinding balls), which can meet the basic processing requirements of powder.

[0204] Comparative Example 1

[0205] Comparative Example 1 adopts the scheme of Example 1, except that the addition of dot-shaped h-BN (nano boron nitride) and linear h-BN (boron nitride whiskers) is omitted in the surface material, and sheet-like h-BN is used to make up for the missing weight parts of dot-shaped h-BN and linear h-BN.

[0206] The performance of the shape-controlled gradient alumina-based grinding ball of Comparative Example 1 was tested. The results showed that the surface friction coefficient of the gradient alumina-based grinding ball was 0.28, and the impact toughness was 2.1 MPa·m. 1 / 2 The fracture toughness (K1c) is 4.5 MPa·m. 1 / 2 The number of impact fatigue cycles (Φ20mm, 2m height) is 9500; the wear amount is 1.23g under the working conditions of 300r / min rotation speed and grinding quartz sand for 2h.

[0207] Analysis showed that in Comparative Example 1, omitting the combination of dot-shaped h-BN with other h-BNs weakened the surface grain refinement effect, reduced hardness, and increased wear. Simultaneously, omitting the combination of linear h-BN with other h-BNs resulted in the disappearance of crack bridging and deflection effects, significantly reducing toughness. Furthermore, single-plate h-BNs tended to agglomerate, leading to an increase in the friction coefficient, fully demonstrating the necessity of the multi-morphology h-BN synergistic control employed in this invention.

[0208] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0209] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gradient alumina-based grinding ball based on shape-modulated properties, characterized in that, It consists of three gradient layers from the outside in: surface layer, transition layer, and core layer; The surface layer is a composite layer of dot-shaped h-BN, linear h-BN, sheet-like h-BN and Al2O3; the total weight of dot-shaped h-BN, linear h-BN and sheet-like h-BN to the mass ratio of Al2O3 is (10-25):(75-90); the mass ratio of dot-shaped h-BN, linear h-BN and sheet-like h-BN is (3-5):(1-3):(6-8); The transition layer is a composite layer of yttrium-stabilized zirconium oxide and Al2O3; the content of yttrium-stabilized zirconium oxide in the transition layer is 10-20 wt%. The core layer is composed of industrial α-Al2O3.

2. The gradient alumina-based grinding ball based on shape-controlled grinding according to claim 1, characterized in that, The thickness ratio of the surface layer, transition layer, and core layer is (0.5-1.5):(1-3):(8-10).

3. A method for preparing gradient alumina-based grinding balls based on shape control as described in claim 1 or 2, characterized in that, The process includes the following steps: raw material pretreatment and slurry preparation, gradient molding, drying, and sintering. The method for raw material pretreatment and slurry preparation is as follows: Dot-like h-BN, linear h-BN, flake-like h-BN, and Al2O3 powder are mixed to obtain a surface layer raw material; yttrium-stabilized zirconium oxide and Al2O3 powder are mixed to obtain a transition layer raw material; industrial α-Al2O3 powder is used as the core layer raw material; binder, dispersant, and deionized water are added to the surface layer raw material, transition layer raw material, and core layer raw material respectively, and the mixture is ball-milled uniformly to obtain surface slurry, transition layer slurry, and core layer slurry with a solid content of 50-60 wt% respectively. The gradient forming method is as follows: core layer slurry is injected into a spherical mold and centrifuged to form the core layer; transition layer slurry is injected into the spherical mold and centrifuged to form the transition layer; surface layer slurry is injected into the spherical mold and centrifuged to form the surface layer, thereby obtaining a composite preform with a three-layer gradient structure. The composite preform is subjected to drying and sintering processes in sequence to obtain gradient alumina-based grinding balls.

4. The method for preparing gradient alumina-based grinding balls based on shape-controlled properties according to claim 3, characterized in that, In the transition layer material, the Y2O3 content in yttrium oxide-stabilized zirconium oxide is 3-5 wt%.

5. The method for preparing gradient alumina-based grinding balls based on shape-controlled properties according to claim 3, characterized in that, In the gradient molding process, the centrifugal speed for centrifugal molding is 800-1200 r / min; The centrifugal molding time after the core layer slurry is injected into the spherical mold is 25-35 minutes. The centrifugal molding time after the transition layer slurry is injected into the spherical mold is 20-30 minutes. The centrifugal molding time after the surface slurry is injected into the spherical mold is 15-25 minutes.

6. The method for preparing gradient alumina-based grinding balls based on shape-controlled properties according to claim 3, characterized in that, The drying process is as follows: the composite green body is dried at 60-65℃ for 8-10 hours, then heated to 80-85℃ and kept at that temperature for 12-16 hours, then heated to 100-105℃ and kept at that temperature for 4-6 hours to obtain the dried composite green body. The sintering process involves placing the dried composite blank in a sintering furnace and heating it to 1500-1600℃ at a heating rate of 5-8℃ / min in an air atmosphere, holding it at that temperature for 2-4 hours; then cooling it to 800℃ at a cooling rate of 3-5℃ / min and allowing it to cool naturally to obtain gradient alumina-based grinding balls.

7. A method for recycling and utilizing waste alumina-based grinding balls based on shape-controlled gradient as described in claim 1 or 2, characterized in that, The process includes the following steps: crushing and grading, surface cleaning, ingredient mixing, microwave reheating, and molding. The crushing and grading method involves crushing the discarded gradient alumina-based grinding balls to a particle size of less than 100 μm to obtain regenerated powder. The surface cleaning method is to use argon and oxygen as working gases to perform plasma cleaning on the regenerated powder to obtain the surface-cleaned regenerated powder. The method of mixing the ingredients is to mix the surface-cleaned regenerated powder with industrial α-Al2O3 powder and sintering aid evenly to obtain a mixed powder; The microwave re-firing method involves placing the mixed powder in a microwave sintering furnace, controlling the furnace pressure to be 0.1-0.5 MPa and the microwave frequency to be 2.45 GHz under a nitrogen protective atmosphere, and then performing microwave re-firing to obtain the sintered material. The forming process involves grinding and forming the sintered material, followed by sintering to obtain recycled grinding balls.

8. The method for recycling and utilizing waste alumina-based grinding balls based on shape-controlled gradient as described in claim 7, characterized in that, In the surface cleaning process, the volume percentage of oxygen in the working gas is controlled to be 5-10%, the working gas flow rate is 50-60 sccm, the plasma radio frequency power is 500-600W, and the plasma cleaning time is 10-30min. In the microwave reheating process, the temperature is increased to 1150-1250℃ at a heating rate of 50-100℃ / min, and then held at that temperature for 25-35 minutes.

9. The method for recycling and utilizing waste alumina-based grinding balls based on shape-controlled gradient as described in claim 7, characterized in that, During the mixing process, the amount of recycled powder after surface cleaning is controlled to be 5-10% of the total mass of the mixed powder; the amount of sintering aid is controlled to be 0.4-0.6% of the total mass of the mixed powder. The sintering aid is a MgO-CaO-SiO2 composite aid, and the mass ratio of MgO, CaO and SiO2 in the sintering aid is 1:1:1.