Graphene / zirconia calcined composite microsphere modified zirconia ceramics

Abstract

The graphene / zirconia sintered composite microsphere modified zirconia ceramic is prepared by mixing, pressing and sintering stable zirconia powder A and graphene / zirconia sintered composite microspheres accounting for less than 25wt% of the total ceramic powder; the preparation method of the graphene / zirconia sintered composite microspheres is that stable zirconia powder B, graphene and a solvent are matched into a slurry; the graphene / zirconia sintered composite microspheres are obtained through ball milling, spray drying and calcination. The graphene / zirconia sintered composite microspheres and SPS sintering are used in the application, the obtained zirconia composite ceramic has dispersed graphene / zirconia two-phase structure regions in the interior, can consume a large amount of energy of crack propagation, and has a significant toughening effect.

Description

Zirconia ceramics modified with graphene / zirconia calcined composite microspheres Technical Field

[0001] This invention relates to the field of materials, and more specifically to a modified zirconia ceramic. Background Technology

[0002] Zirconia ceramics possess excellent physicochemical properties, are non-irritating to human tissues, do not induce immune responses, and exhibit high strength, high hardness, and good wear resistance; they can be widely used in structural ceramics, cutting tools, medical prosthetic components, and biomedical fields. However, zirconia ceramics also have the disadvantage of relatively low fracture toughness.

[0003] Nanoscale zirconia powder can be used to prepare high-strength zirconia ceramics, and the smaller the grain size, the higher the strength of the zirconia ceramic. Therefore, zirconia powder with a particle size below 100 nm is often favored by researchers and used in scientific research to obtain ceramic materials with better performance. However, the smaller the particle size of zirconia powder, the more expensive it is. In industrial production, the economic indicators of zirconia powder must also be considered. Zirconia powder with a particle size above 200 nm obtained by chemical precipitation is often used in the industrial production of zirconia structural ceramics, but its fracture toughness is low and its flexural strength is far below the theoretical value. If zirconia powder with a larger particle size and lower price can be used to produce zirconia ceramics with better mechanical properties, it will bring significant economic benefits. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a zirconia ceramic modified by graphene / zirconia calcined composite microspheres using large-particle-size zirconia powder as raw material, which has better strength and toughness.

[0005] The technical solution adopted by the present invention to solve its technical problem is as follows: Zirconia ceramic modified by graphene / zirconia calcined composite microspheres is made by mixing, pressing and molding, and sintering stable zirconia powder A and graphene / zirconia calcined composite microspheres accounting for less than 25wt% of the total ceramic powder.

[0006] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene and solvent are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere to obtain graphene / zirconia calcined composite microspheres.

[0007] The graphene content in the calcined graphene / zirconia composite microspheres is less than 3 wt%.

[0008] The graphene / zirconia calcined composite microspheres have a particle size of 10~150µm; the median particle size of the stabilized zirconia powder A is 300~800nm;

[0009] The calcination temperature is 1300~1650℃, and the time is 3~6h;

[0010] The sintering process employs spark plasma sintering (SPS sintering): under an inert atmosphere, with a vacuum degree below 30 Pa, a temperature of 1100℃~1400℃, a pressure of 20MPa~70MPa, and a sintering time of 10min~35min.

[0011] Preferably, the median particle size of the stabilized zirconium oxide powder B is 300~800 nm.

[0012] Preferably, in the preparation method of the graphene / zirconia calcined composite microspheres, the thickness of the graphene is less than 10 nm.

[0013] Preferably, in the preparation method of the graphene / zirconia calcined composite microspheres, the mass ratio of graphene to stable zirconia powder B is less than or equal to 3:97.

[0014] Preferably, the solid content of the slurry is 50wt%~70wt%.

[0015] Preferably, the viscosity of the ball mill II is 2000 mPa·s to 5000 mPa·s.

[0016] Preferably, the ball milling time is 2h to 40h.

[0017] Preferably, the rotational speed of the ball mill I is 100 rpm to 600 rpm.

[0018] Preferably, the ball milling time II is 2h to 40h.

[0019] Preferably, the rotational speed of the ball mill II is 100 rpm to 600 rpm.

[0020] Preferably, the inlet air temperature for the spray drying is 260℃~300℃.

[0021] Preferably, the outlet air temperature of the spray dryer is 90℃~120℃.

[0022] Preferably, the atomization frequency of the spray drying is 15Hz~30Hz.

[0023] Preferably, the solvent is water or ammonium polyacrylate solution.

[0024] Preferably, the adhesive is PVA.

[0025] The present invention has the following beneficial effects: Through the sintering of graphene / zirconia calcined composite microspheres and SPS, the resulting zirconia composite ceramic contains dispersed graphene / zirconia two-phase structural regions within it. These regions contain randomly oriented, even folded or intersecting graphene sheets. When cracks propagate to these two-phase structural regions, due to the high modulus and strength of the graphene sheets, the cracks are unlikely to break through the graphene sheets and can only propagate along the graphene / zirconia two-phase interface. Because of the random orientation, folding, and intersection of the graphene sheets, the cracks can only propagate along the orientation direction of the graphene, constantly deflecting and consuming a large amount of energy for crack propagation. Simultaneously, the residual interfacial micropores on the graphene / zirconia interface can also generate microcracks, inducing the branching of the main crack and consuming energy, resulting in a significant toughening effect. This invention enables the use of larger-particle-size zirconia powder as raw material to obtain zirconia ceramics modified with graphene / zirconia calcined composite microspheres with good strength and toughness, thus reducing production costs.

[0026] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 shows the density and flexural strength test results of the zirconia composite ceramics in Examples 7-9 of the present invention;

[0029] Figure 2 shows the density and flexural strength test results of the zirconia composite ceramics in Examples 4-6 of the present invention;

[0030] Figure 3 shows the density and flexural strength test results of the zirconia composite ceramics in Examples 1-3 of the present invention;

[0031] Figure 4 shows the fracture toughness test results of zirconia composite ceramics in Examples 1-9 of the present invention;

[0032] Figure 5 shows the performance test results of the zirconia composite ceramics of Comparative Examples 7-9; Figure 5(a) shows the density, and Figure 5(b) shows the flexural strength.

[0033] Figure 6 shows the performance test results of the zirconia composite ceramics of Comparative Examples 4-6; Figure 6(a) shows the density, and Figure 6(b) shows the flexural strength.

[0034] Figure 7 shows the performance test results of the zirconia composite ceramics in Comparative Examples 1-3; Figure 7(a) shows the density, and Figure 7(b) shows the flexural strength.

[0035] Figure 8 is a grain distribution diagram of the zirconia composite ceramic of Example 8 of the present invention; Figure 8(a) is an electron microscope image, and Figure 8(b) is a statistical diagram of grain size distribution;

[0036] Figure 9 shows electron microscope images of the zirconia ceramic of Comparative Example 10; Figure 9(a) is a cross-sectional morphology image, and Figure 9(b) is an indentation morphology image.

[0037] Figure 10 shows the cross-sectional morphology of the zirconia composite ceramic of Example 2 of the present invention at different magnifications: Figure 10(a) is 200x, Figure 10(b) is 2000x, Figure 10(c) is 5000x, and Figure 10(d) is 10000x.

[0038] Figure 11 shows the two-phase structure and indentation crack propagation morphology on the polished surface of the zirconia composite ceramic in Embodiment 1 of the present invention: Figure 11(a) shows the two-phase structure on the polished surface, Figure 11(b) is a partial enlarged view of the boxed position in Figure 11(a), Figure 11(c) shows the indentation crack propagation morphology, and Figure 11(d) is a partial enlarged view of the boxed position in Figure 11(c). Detailed Implementation

[0039] To make the objectives, solutions, and beneficial technologies of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be noted that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0040] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0041] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0042] An embodiment of the present invention provides a zirconia ceramic modified with graphene / zirconia calcined composite microspheres, which is formed by mixing, pressing and sintering stable zirconia powder A with graphene / zirconia calcined composite microspheres accounting for less than 25 wt% of the total ceramic powder;

[0043] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene and solvent are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere to obtain graphene / zirconia calcined composite microspheres.

[0044] The graphene content in the calcined graphene / zirconia composite microspheres is less than 3 wt%.

[0045] The graphene / zirconia calcined composite microspheres have a particle size of 10~150µm; the median particle size of the stabilized zirconia powder A is 300~800nm;

[0046] The calcination temperature is 1300~1650℃, and the time is 3~6h;

[0047] The sintering process employs spark plasma sintering (SPS sintering): under an inert atmosphere, with a vacuum degree below 30 Pa, a temperature of 1100℃~1400℃, a pressure of 20MPa~70MPa, and a sintering time of 10min~35min.

[0048] The total ceramic powder includes the stabilized zirconia powder A and the graphene / zirconia calcined composite microspheres.

[0049] In an embodiment of the present invention, the sintering temperature is 1400~1650℃.

[0050] In some embodiments of the present invention, the pressing molding process involves pressing ceramic powder into a compact at a pressure of 30-200 MPa.

[0051] In an embodiment of the present invention, the median particle size of the stabilized zirconium oxide powder B is 300~800 nm.

[0052] In some embodiments of the present invention, the stabilized zirconium oxide powder B is yttrium-stabilized zirconium oxide powder.

[0053] In some embodiments of the present invention, the graphene content in the graphene / zirconia calcined composite microspheres is 0.3~1.5wt%.

[0054] In some embodiments of the present invention, graphene / zirconia calcined composite microspheres account for 8 to 23 wt% of the total ceramic powder.

[0055] In an embodiment of the present invention, the graphene / zirconia calcined composite microspheres are prepared in a method where the thickness of the graphene is less than 10 nm.

[0056] In some embodiments of the present invention, in the preparation method of the graphene / zirconia calcined composite microspheres, the particle size of the graphene is less than 10 μm.

[0057] In some embodiments of the present invention, graphene is pre-prepared as an aqueous solution to facilitate dispersion in the slurry.

[0058] In an embodiment of the present invention, in the preparation method of the graphene / zirconia calcined composite microspheres, the mass ratio of graphene to stable zirconia powder B is less than or equal to 3:97.

[0059] In an embodiment of the present invention, the solid content of the slurry is 50wt%~70wt%.

[0060] In some embodiments of the present invention, the solid content of the slurry is 55wt% to 68wt%.

[0061] In embodiments of the present invention, the viscosity of the ball milling material II is 2000 mPa·s to 5000 mPa·s. Within this range, the graphene / zirconia calcined composite microspheres exhibit a spherical structure. The viscosity of the ball milling material II can be adjusted by modifying the binder or solvent composition. The added binder molecules can form a three-dimensional network structure with the dispersant on the surface of the ceramic powder. The ceramic powder fixed by the network structure shrinks uniformly during droplet drying, making it easier to obtain spherical dried particles. If the amount of binder added is insufficient to bind all the uniformly dispersed ceramic powder, the unfixed ceramic powder will migrate with the evaporation of water in the droplet during droplet drying, producing defective donut-shaped or apple-shaped dried particles. Under this viscosity condition, the zirconia powder and graphene sheets also exhibit good dispersion stability.

[0062] In an embodiment of the present invention, the ball milling time is 2h to 40h.

[0063] In some embodiments of the present invention, the ball milling time is 10h to 40h.

[0064] In an embodiment of the present invention, the rotational speed of the ball mill I is 100 rpm to 600 rpm.

[0065] In some embodiments of the present invention, the rotational speed of the ball mill I is 300 rpm to 400 rpm.

[0066] In an embodiment of the present invention, the ball milling time II is 2h to 40h.

[0067] In some embodiments of the present invention, the ball milling time II is 10h to 40h.

[0068] In an embodiment of the present invention, the rotational speed of the ball mill II is 100 rpm to 600 rpm.

[0069] In some embodiments of the present invention, the rotational speed of the ball mill II is 100 rpm to 200 rpm.

[0070] In an embodiment of the present invention, the inlet air temperature of the spray dryer is 260°C to 300°C.

[0071] In an embodiment of the present invention, the outlet air temperature of the spray dryer is 90°C to 120°C.

[0072] In an embodiment of the present invention, the atomization frequency of the spray drying is 15Hz~30Hz.

[0073] In embodiments of the present invention, the solvent is water or ammonium polyacrylate solution.

[0074] In some embodiments of the present invention, the concentration of the ammonium polyacrylate solution is less than 1 wt%.

[0075] In an embodiment of the invention, the adhesive is PVA. For ease of application, the adhesive may be pre-dissolved.

[0076] The binder and solvent mainly serve to adjust the viscosity of the ball milling material II.

[0077] Raw materials used in each embodiment:

[0078] Stabilized Zirconia Powder B: 3YSZ Zirconia Powder, Guangdong Dongfang Zirconium Industry Technology Co., Ltd., product specification OZ-3Y-7, where d 10 =0.151µm, d 50 =0.625µm, d 90 =2.4µm.

[0079] Stabilized Zirconia Powder A: 3YSZ Zirconia Powder, Guangdong Dongfang Zirconium Industry Technology Co., Ltd., product specification OZ-3Y-7, where d 10 =0.151µm, d 50 =0.625µm, d 90 =2.4µm.

[0080] Graphene was directly applied using a commercially available graphene aqueous solution purchased from Hunan Runxi Technology Co., Ltd., with a concentration of 10 wt%. The graphene particle size was [d]. 10 =0.93µm, d 50 =2.2µm, d 90 =5.0µm; the thickness was measured to be concentrated in the range of 2~5nm.

[0081] Solvent: Ammonium polyacrylate solution dispersant, Dow Chemical, product specification D3019.

[0082] Adhesive: PVA, Sinopharm Group, product specification 1788.

[0083] Example

[0084] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0085] Example 1 (microsphere addition amount 20wt%, microsphere graphene content 2wt%)

[0086] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 80 wt% of stable zirconia powder A and 20 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0087] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0088] The calcination temperature was 1400℃ and the time was 5 hours.

[0089] The graphene / zirconia calcined composite microspheres contain 2 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 63.7:1.3:35; the solid content of the slurry is 65%.

[0090] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0091] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0092] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0093] Example 2 (microsphere addition amount 10wt%, microsphere graphene content 2wt%)

[0094] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 90 wt% of stable zirconia powder A and 10 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0095] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0096] The calcination temperature was 1400℃ and the time was 5 hours.

[0097] The graphene / zirconia calcined composite microspheres contain 2 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 63.7:1.3:35; the solid content of the slurry is 65%.

[0098] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0099] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0100] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0101] Example 3 (microsphere addition amount 5wt%, microsphere graphene content 2wt%)

[0102] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 95 wt% of stable zirconia powder A and 5 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0103] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0104] The calcination temperature was 1400℃ and the time was 5 hours.

[0105] The graphene / zirconia calcined composite microspheres contain 2 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 63.7:1.3:35; the solid content of the slurry is 65%.

[0106] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0107] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0108] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0109] Example 4 (microsphere addition amount 20wt%, microsphere graphene content 1wt%)

[0110] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 80 wt% of stable zirconia powder A and 20 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0111] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0112] The calcination temperature was 1400℃ and the time was 5 hours.

[0113] The graphene / zirconia calcined composite microspheres contain 1 wt% graphene; the mass ratio of stable zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.35:0.65:35.

[0114] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0115] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0116] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0117] Example 5 (microsphere addition amount 10wt%, microsphere graphene content 1wt%)

[0118] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 90 wt% of stable zirconia powder A and 10 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0119] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0120] The calcination temperature was 1400℃ and the time was 5 hours.

[0121] The graphene / zirconia calcined composite microspheres contain 1 wt% graphene; the mass ratio of stable zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.35:0.65:35.

[0122] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0123] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0124] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0125] Example 6 (microsphere addition amount 5wt%, microsphere graphene content 1wt%)

[0126] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 95 wt% of stable zirconia powder A and 5 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0127] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0128] The calcination temperature was 1400℃ and the time was 5 hours.

[0129] The graphene / zirconia calcined composite microspheres contain 1 wt% graphene; the mass ratio of stable zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.35:0.65:35.

[0130] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0131] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0132] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0133] Example 7 (microsphere addition amount 20wt%, microsphere graphene content 0.5wt%)

[0134] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 80 wt% of stable zirconia powder A and 20 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0135] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0136] The calcination temperature was 1400℃ and the time was 5 hours.

[0137] The graphene / zirconia calcined composite microspheres contain 0.5 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.675:0.325:35.

[0138] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0139] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0140] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0141] Example 8 (microsphere addition amount 10wt%, microsphere graphene content 0.5wt%)

[0142] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 90 wt% of stable zirconia powder A and 10 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0143] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0144] The calcination temperature was 1400℃ and the time was 5 hours.

[0145] The graphene / zirconia calcined composite microspheres contain 0.5 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.675:0.325:35.

[0146] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0147] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0148] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0149] Example 9 (microsphere addition amount 5wt%, microsphere graphene content 5wt%)

[0150] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 95 wt% of stable zirconia powder A and 5 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 80 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1300 °C, the pressure is 60 MPa, and the sintering time is 30 min.

[0151] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0152] The calcination temperature was 1400℃ and the time was 5 hours.

[0153] The graphene / zirconia calcined composite microspheres contain 0.5 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.675:0.325:35.

[0154] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0155] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0156] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0157] Example 10 (microsphere addition amount 20wt%, microsphere graphene content 1wt%)

[0158] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 80 wt% of stable zirconia powder A and 20 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 30 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 20 Pa, the temperature is 1250 °C, the pressure is 65 MPa, and the sintering time is 20 min.

[0159] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.6 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0160] The calcination temperature was 1600℃ and the time was 3 hours.

[0161] The graphene / zirconia calcined composite microspheres contain 1 wt% graphene; the mass ratio of stable zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.35:0.65:35.

[0162] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0163] The ball milling time for ball mill I was 40 hours, and the rotation speed of ball mill I was 400 rpm. The ball milling time for ball mill II was 40 hours, and the rotation speed of ball mill II was 200 rpm. The inlet air temperature for spray drying was 300℃, the outlet air temperature for spray drying was 120℃, and the atomization frequency for spray drying was 30Hz.

[0164] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0165] Example 11 (microsphere addition amount 10wt%, microsphere graphene content 1wt%)

[0166] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 90 wt% of stable zirconia powder A and 10 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 200 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 15 Pa, the temperature is 1400 °C, the pressure is 50 MPa, and the sintering time is 30 min.

[0167] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.6 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0168] The calcination temperature was 1500℃ and the time was 5 hours.

[0169] The graphene / zirconia calcined composite microspheres contain 1 wt% graphene; the mass ratio of stable zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.35:0.65:35.

[0170] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0171] The ball milling time for ball mill I was 10 hours, and the rotation speed of ball mill I was 300 rpm. The ball milling time for ball mill II was 10 hours, and the rotation speed of ball mill II was 100 rpm. The inlet air temperature for spray drying was 260℃, the outlet air temperature for spray drying was 90℃, and the atomization frequency for spray drying was 15 Hz.

[0172] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0173] Example 12 (microsphere addition amount 20wt%, microsphere graphene content 0.5wt%)

[0174] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of this embodiment is made by mixing, pressing and sintering 80 wt% of stable zirconia powder A and 20 wt% of graphene / zirconia calcined composite microspheres. The molding pressure is 200 MPa and the pressing time is 1 min. The sintering is carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree is 10 Pa, the temperature is 1200 °C, the pressure is 40 MPa, and the sintering time is 30 min.

[0175] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.6 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0176] The calcination temperature was 1400℃ and the time was 4 hours;

[0177] The graphene / zirconia calcined composite microspheres contain 0.5 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 64.675:0.325:35.

[0178] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0179] The ball milling time for ball mill I was 20 hours, and the rotation speed of ball mill I was 400 rpm. The ball milling time for ball mill II was 30 hours, and the rotation speed of ball mill II was 200 rpm. The inlet air temperature for spray drying was 300℃, the outlet air temperature for spray drying was 90℃, and the atomization frequency for spray drying was 25 Hz.

[0180] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing zirconia composite ceramics in this embodiment.

[0181] Comparative Examples 1-9 (using conventional sintering)

[0182] Comparative Examples 1-9 are set up to correspond to Examples 1-9 respectively. The difference between Comparative Examples 1-9 and Examples 1-9 is that the sintering method of Examples 1-9 is changed to conventional sintering: sintering at 1400℃ for 2 hours; other processes are the same as the corresponding examples. The following detailed description uses Comparative Example 1 as an example:

[0183] Comparative Example 1 (microsphere addition amount 20wt%, microsphere graphene content 2wt%)

[0184] The graphene / zirconia calcined composite microsphere modified zirconia ceramic of Comparative Example 1 was made by mixing, pressing and sintering 80 wt% of stable zirconia powder A and 20 wt% of graphene / zirconia calcined composite microspheres. The molding pressure was 80 MPa and the pressing time was 1 min. The sintering temperature was 1400℃ and the sintering time was 2 h.

[0185] The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stabilized zirconia powder B, graphene aqueous solution and 0.8 wt% ammonium polyacrylate solution are mixed to form a slurry; the obtained slurry is ball-milled I to obtain ball milling material I; ball milling material I and binder (PVA aqueous solution) are ball-milled II together to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere (argon) to obtain graphene / zirconia calcined composite microspheres;

[0186] The calcination temperature was 1400℃ and the time was 5 hours.

[0187] The graphene / zirconia calcined composite microspheres contain 2 wt% graphene; the mass ratio of stabilized zirconia powder B, graphene, and solvent (ammonium polyacrylate solution + aqueous solution) is 63.7:1.3:35; the solid content of the slurry is 65%.

[0188] The viscosity of ball mill II is 2000 mPa·s to 5000 mPa·s (achieved by adjusting the amount of binder).

[0189] The ball milling time for ball mill I was 24 hours, and the rotation speed of ball mill I was 350 rpm. The ball milling time for ball mill II was 24 hours, and the rotation speed of ball mill II was 150 rpm. The inlet air temperature for spray drying was 280℃, the outlet air temperature for spray drying was 105℃, and the atomization frequency for spray drying was 25 Hz.

[0190] The obtained graphene / zirconia calcined composite microspheres were passed through 80-mesh and 350-mesh sieves, and the middle part was taken to obtain graphene / zirconia calcined composite microspheres with a particle size between 43 and 180 µm, which were used as raw materials for firing the comparative zirconia composite ceramics.

[0191] Comparative Example 10 (Zirconium Oxide)

[0192] Comparative Example 10 used pure stable zirconia powder A as ceramic powder, which was pressed and sintered to form zirconia ceramic without the introduction of graphene. The forming pressure was 80 MPa and the pressing time was 1 min. The sintering was carried out by spark plasma sintering: under an inert atmosphere (argon), the vacuum degree was 20 Pa, the temperature was 1300 °C, the pressure was 60 MPa, and the sintering time was 30 min.

[0193] Performance testing

[0194] The ceramic products of Examples 1-9 and Comparative Examples 1-10 were tested. Based on the graphene content in the graphene / zirconia calcined composite microspheres used, Examples 1-9 and Comparative Examples 1-9 were divided into three groups: "2wt%" group (Examples 1-3, Comparative Examples 1-3), "1wt%" group (Examples 4-6, Comparative Examples 4-6), and "0.5wt%" group (Examples 7-9, Comparative Examples 7-9).

[0195] Density was tested according to the national standard "Test Method for Density and Apparent Porosity of Fine Ceramics" (GB / T 25995-2010); bending strength was tested according to the national standard "Test Method for Bending Strength of Fine Ceramics" (GB / T 6569-2006); fracture toughness (K... IC Measurement was performed using the indentation method (Vickers indentation at 98 N); the formula is as follows:

[0196] ;

[0197] Where P is the maximum load, H and E are the hardness and Young's modulus of the ceramic, and c is the average length of the diffusing crack at the four corners of the indentation.

[0198] Figures 1, 2, and 3 show the density and flexural strength (compared to Comparative Example 10) of zirconia composite ceramics in the 0.5 wt% group, the 1 wt% group, and the 2 wt% group, respectively, in relation to the amount of calcined microspheres added.

[0199] As shown in Figure 1, when the graphene content in the graphene / zirconia calcined microspheres is 0.5 wt%, increasing the amount of calcined microspheres initially decreases, then increases, and then slowly decreases again in the relative density of the composite ceramic. When the amount of calcined microspheres is 10 wt%, the density and flexural strength of the composite ceramic are 97.79% and 1097 MPa, respectively, representing the highest values ​​among the composite ceramics with added calcined microspheres. In contrast, the pure zirconia ceramic without added graphene exhibits the highest density and flexural strength, at 98.29% and 1148 MPa, respectively, slightly higher than the former. This indicates that the introduction of graphene reduces the density of the zirconia composite ceramic.

[0200] The effects of the amount of calcined composite microspheres added on the density and flexural strength of the composite ceramics shown in Figures 2 and 3 are similar to those in Figure 1. As the amount of calcined composite microspheres added increases, the density and flexural strength of the composite ceramics first decrease and then increase. In the zirconia composite ceramics with added graphene / zirconia calcined composite microspheres, the highest density and flexural strength (97.46% and 1003 MPa, respectively) are achieved when the graphene content in the calcined microspheres is 1 wt% and the amount of calcined microspheres added is 5 wt%. The highest density and flexural strength (97.12% and 895 MPa, respectively) are achieved when the graphene content in the calcined microspheres is 2 wt% and the amount of calcined microspheres added is 20 wt%. Overall, the density and flexural strength of the zirconia composite ceramics gradually decrease with increasing graphene content in the microspheres.

[0201] Figure 4 shows the fracture toughness of SPS-sintered graphene / zirconia calcined composite microsphere-toughened zirconia composite ceramics (the sample with 0 microspheres is zirconia ceramic, and the ceramic sample is from Comparative Example 10). As can be seen from the figure, the fracture toughness of the composite ceramic gradually increases with the increase of the graphene / zirconia calcined composite microsphere content. When the graphene content in the calcined composite microspheres is 0.5 wt%, the fracture toughness of the composite ceramic increases slowly with the increase of the calcined composite microsphere content. When the composite microsphere content is 20 wt%, the fracture toughness of the composite ceramic reaches 6.48 MPa·m. 1 / 2 When the graphene content in the calcined composite microspheres is 2 wt%, the fracture toughness of the composite ceramic increases at a faster rate with increasing composite microsphere content. The composite ceramic exhibits the highest fracture toughness (7.65 MPa·m) when the calcined composite microsphere content is 20 wt%. 1 / 2 When the graphene content in the composite microspheres is 1 wt%, the fracture toughness of the composite ceramic increases with the increase of the amount of calcined composite microspheres added, and is between the two gradations of ceramics mentioned above. When the amount of calcined composite microspheres added is 20 wt%, the fracture toughness of the composite ceramic reaches 7.28 MPa·m. 1 / 2 .

[0202] Figures 5, 6, and 7 show the relationship between the density and flexural strength of zirconia composite ceramics in the 0.5wt%, 1wt%, and 2wt% comparative examples using conventional sintering and the amount of calcined microspheres added.

[0203] As can be seen from Figure 5, in the comparative example group of 0.5wt%, as the amount of graphene / zirconia calcined composite microspheres added increased from 5wt% to 20wt%, the density of the composite ceramic decreased from 94.9% to 93%, and the flexural strength decreased from 794MPa to 651MPa.

[0204] As can be seen from Figures 6 and 7, the results for the 1wt% and 2wt% comparative examples are similar to those for the 0.5wt% comparative example. The addition of calcined composite microspheres reduces the density and flexural strength of the zirconia composite ceramic. Furthermore, the higher the graphene content in the calcined microspheres, the lower the density and flexural strength of the composite ceramic. When the amount of graphene / zirconia calcined composite microspheres containing 2wt% graphene is 20wt%, the density of the composite ceramic is only 88.8%, and the flexural strength drops to 496MPa.

[0205] The experimental results of Comparative Examples 1 to 9 show that when conventional sintering is used, the addition of calcined composite microspheres significantly deteriorates the mechanical properties of the material.

[0206] Figure 8 shows the grain morphology and size distribution of the zirconia composite ceramic of Example 8. As can be seen from the figure, the grain size of the zirconia composite ceramic after SPS sintering is mostly below 400 nm, with the largest concentration in the 50-250 nm range. Only a small number of grains below 50 nm and above 350 nm exist. This demonstrates that the SPS sintering technology is effective in controlling the grain size of the calcined composite microsphere-graded zirconia composite ceramic. It can be reasonably assumed that the fine-grained zirconia structure resulting from SPS sintering is the main reason for the high flexural strength of the zirconia ceramic and zirconia composite ceramic obtained by SPS sintering.

[0207] Figure 9 shows the cross-sectional and indentation morphology of the zirconia ceramic in Comparative Example 10. As can be seen from Figure 9(a), the cross-section of the pure zirconia sintered by SPS is smooth, indicating that the cracks induced by external force propagate rapidly inside the zirconia with almost no deflection. The indentation morphology in Figure 9(b) also confirms this, with the indentation-induced cracks propagating directly with almost no deflection. The fracture toughness calculated by the indentation method is 4.75 MPa·m. 1 / 2 Low-temperature pressurization of SPS significantly reduces its fracture toughness.

[0208] Testing revealed that the zirconia composite ceramic of Example 10 had a density of 94.48%, a flexural strength of 876 MPa, and a fracture toughness of 6.11 MPa·m. 1 / 2 .

[0209] Testing revealed that the zirconia composite ceramic of Example 11 had a density of 94.91%, a flexural strength of 917 MPa, and a fracture toughness of 5.42 MPa·m. 1 / 2 .

[0210] Testing revealed that the zirconia composite ceramic of Example 12 had a density of 95.26%, a flexural strength of 802 MPa, and a fracture toughness of 5.06 MPa·m. 1 / 2 .

[0211] Figure 10 shows the cross-sectional morphology of the zirconia composite ceramic of Example 2 at different magnifications. As can be seen from Figures 10(a) and (b), the cross-section exhibits rough circular regions, which are approximately the same size as the graphene / zirconia microspheres. Figures 10(c) and (d) show that these rough circular regions also contain micropores with diameters between 1 and 2 µm, and a large number of dispersed sheet-like materials are present near the pores, as indicated by the circular markings in the figures. In Figure 10(d), the intact sheet-like materials sandwiched between zirconia grains and the broken sheet-like materials scattered across the cross-section are also clearly visible within the circular markings. It is reasonable to infer that the circular regions on the cross-section of the composite ceramic are the graphene / zirconia two-phase structure introduced into the composite ceramic by the calcined composite microspheres. The sheet-like materials in the two-phase structure should be graphene sheets, and these graphene sheets were subjected to significant external force and broke during the destruction of the composite ceramic. The image also shows that the circular area is uneven, indicating that the crack was continuously deflected as it propagated within the graphene / zirconia two-phase structure, resulting in this rough cross-sectional structure. Therefore, the graphene / zirconia two-phase structure can induce internal crack deflection, exhibiting a significant toughening effect.

[0212] Figure 11 shows the two-phase structure and indentation crack propagation morphology on the polished surface of the zirconia composite ceramic of Example 1. As can be seen from Figure 11(a), there is an elliptical region covered with black dots on the polished surface of the composite ceramic. This region has no obvious interface with the surrounding zirconia matrix, and its size is basically the same as that of the calcined composite microspheres, only elliptical in shape. From the magnified image of the elliptical region in Figure 11(b), it can be seen that a large number of sheet-like structures are distributed within this region, and some of these sheet-like structures are folded or intersecting. Based on the results and analysis in Figure 10, it can be reasonably inferred that this elliptical region is a two-phase structure introduced into the composite ceramic by the calcined composite microspheres. During the SPS sintering process, the calcined composite microspheres are further compressed under hot pressing, eliminating most of the pore defects inside the calcined composite microspheres. Furthermore, through the enhanced mass transfer effect of SPS, there are no obvious interface defects between the calcined microspheres and the nano-zirconia matrix. Within the two-phase structure, the distribution of graphene sheets is basically the same as that in the calcined composite microspheres, with no obvious orientation, and there are a large number of folded or intersecting graphene sheets. Figures 11(c) and (d) show the propagation morphology of the indentation crack, revealing significant deflection and bifurcation phenomena during crack propagation in the two-phase structure. Combining this with the distribution of graphene sheets in the two-phase structure in Figure 11(b), it is evident that the crack propagation path is largely consistent with the distribution of the graphene sheets. When the crack propagates to the graphene / zirconia two-phase region, the randomly distributed high-modulus and high-strength graphene sheets hinder crack propagation. Therefore, the crack can only propagate along the graphene / zirconia interface, or generate multiple microcracks at the interface micropores, inducing the main crack to bifurcate. When the graphene sheets fold or intersect at grain boundaries, the crack also undergoes a near 90° deflection along the two-phase interface.

[0213] The SPS-sintered graphene / zirconia calcined composite microspheres toughening zirconia composite ceramics contain dispersed graphene / zirconia two-phase structural regions within them, containing randomly oriented, even folded or intersecting graphene sheets. When cracks propagate into these two-phase regions, the high modulus and strength of the graphene sheets prevent them from breaking through and propelling further; instead, the cracks extend along the graphene / zirconia interface. Due to the random orientation, folding, and intersection of the graphene sheets, the cracks can only propagate along the orientation direction of the graphene, constantly deflecting and consuming a large amount of energy for crack propagation. Simultaneously, residual interfacial micropores at the graphene / zirconia interface can also generate microcracks, inducing main crack branching and further consuming energy. Therefore, under SPS sintering conditions, mixing graphene / zirconia calcined composite microspheres with zirconia granulated powder to introduce a less porous graphene / zirconia two-phase structure into the zirconia composite ceramic exhibits a significant toughening effect.

Claims

1. A zirconia ceramic modified with graphene / zirconia calcined composite microspheres, characterized in that, The graphene / zirconia calcined composite microspheres are prepared by mixing, pressing, and sintering stable zirconia powder A with graphene / zirconia calcined composite microspheres comprising less than 25 wt% of the total ceramic powder. The preparation method of the graphene / zirconia calcined composite microspheres is as follows: stable zirconia powder B, graphene, and a solvent are mixed to form a slurry; the resulting slurry is ball-milled (I) to obtain ball milling material I; ball milling material I is ball-milled together with a binder (II) to obtain ball milling material II; ball milling material II is spray-dried and then calcined under an inert atmosphere to obtain graphene / zirconia calcined composite microspheres. The graphene / zirconia calcined composite microspheres contain less than 3 wt% graphene; the particle size of the graphene / zirconia calcined composite microspheres is 10~150 µm; the median particle size of the stable zirconia powder A is 300~800 nm; the calcination temperature is 1300~1650℃, and the time is 3~6 h; the sintering is carried out by spark plasma sintering: under an inert atmosphere, the vacuum degree is below 30 Pa, the temperature is 1100℃~1400℃, the pressure is 20 MPa~70 MPa, and the sintering time is 10 min~35 min.

2. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to claim 1, characterized in that, The median particle size of the stabilized zirconia powder B is 300~800 nm.

3. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to claim 1, characterized in that, In the preparation method of the graphene / zirconia calcined composite microspheres, the thickness of the graphene is less than 10 nm.

4. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to claim 1, characterized in that, In the preparation method of the graphene / zirconia calcined composite microspheres, the mass ratio of graphene to stable zirconia powder B is less than or equal to 3:

97.

5. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to claim 1, characterized in that, In the preparation method of the graphene / zirconia calcined composite microspheres, the solid content of the slurry is 50wt%~70wt%.

6. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to any one of claims 1 to 5, characterized in that, The viscosity of the ball mill II is 2000 mPa·s to 5000 mPa·s.

7. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to any one of claims 1 to 5, characterized in that, The ball milling time for section I is 2 hours to 40 hours; the rotation speed of section I is 100 rpm to 600 rpm; the ball milling time for section II is 2 hours to 40 hours; the rotation speed of section II is 100 rpm to 600 rpm.

8. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to any one of claims 1 to 5, characterized in that, The inlet air temperature of the spray dryer is 260℃~300℃; the outlet air temperature of the spray dryer is 90℃~120℃; and the atomization frequency of the spray dryer is 15Hz~30Hz.

9. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to any one of claims 1 to 5, characterized in that, The solvent is water or ammonium polyacrylate solution.

10. The zirconia ceramic modified with graphene / zirconia calcined composite microspheres according to any one of claims 1 to 5, characterized in that, The adhesive is PVA.

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