Colored zirconia artificial gem material and method for producing the same

Abstract

The application discloses a kind of color zirconia artificial gem materials and preparation method thereof, the zirconia artificial gem material contains spinel type coloring nanoparticle generated in situ, with (Co, M) Al2O4, (Fe, M) Al2O4 Or (Cr, M) Al2O4 structure, M is at least one of Zn, Mg, Ni;Spinel type coloring nanoparticle is distributed at the grain boundary of zirconia grain, average particle size 20~150nm;Its preparation method includes, through photocuring 3D printing, then carry out segmented sintering, first stage oxidizing atmosphere oxidation decomposition organic component, second stage reducing atmosphere reduction coloring precursor, third stage oxidizing atmosphere in-situ generation spinel phase and densification sintering.The application realizes the synergistic promotion of coloring uniformity, mechanical property and hydrothermal aging stability by in-situ generation of composite spinel coloring nanoparticle combined with segmented sintering process.

Description

Technical Field

[0001] This invention relates to the field of zirconia materials technology, and more specifically, to a colored zirconia artificial gemstone material and its preparation method, particularly a high-performance colored zirconia artificial gemstone material that achieves coloring through in-situ generation of spinel-type coloring nanoparticles and its photopolymerization 3D printing preparation method. Background Technology

[0002] Zirconia materials are widely used in dental restorations, decorative items, and other fields due to their excellent mechanical properties and biocompatibility. With the increasing demand for personalization, colored zirconia materials have become a research hotspot.

[0003] Current colored zirconia synthetic gemstone materials mainly achieve coloring by adding colorants to the matrix, but face the following technical challenges: High sintering temperatures lead to unstable color due to the decomposition and volatilization of most colorants. Colorant decomposition hinders densification, forming pores and severely reducing fracture toughness and flexural strength. Colorant nanoparticles easily agglomerate, resulting in uneven color and impaired mechanical properties. Existing preparation methods each have their drawbacks: solid-phase mixing methods struggle to overcome agglomeration; chemical co-precipitation methods are complex and prone to forming hard agglomerates; liquid-phase impregnation methods are external coloring methods, resulting in thin, unevenly colored layers and low efficiency. While photopolymerization 3D printing can form complex structures, the high refractive index of dark-colored zirconia powder makes photopolymerization difficult.

[0004] Spinel-type oxides such as CoAl2O4 are commonly used colorants, but current technologies mostly use single-metal ion spinel, making it difficult to precisely control the size and distribution of the colored phase, and the overall mechanical properties need to be improved. In addition, the phase stability problem of existing colored zirconia under hydrothermal aging conditions has not been effectively solved. The low-temperature aging phase transformation from tetragonal to monoclinic phase in a humid environment leads to a significant decrease in material properties.

[0005] Therefore, developing a colored zirconia artificial gemstone material with uniform coloring, excellent mechanical properties, and good resistance to hydrothermal aging, and its efficient and controllable preparation method, has important industrial application value. Summary of the Invention

[0006] The present invention aims to solve the technical problems of existing colored zirconia artificial gemstone materials, such as uneven distribution of coloring phase leading to uneven color and deterioration of mechanical properties, easy decomposition and volatilization of colorants during high-temperature sintering, insufficient comprehensive mechanical properties, and poor phase stability under hydrothermal aging conditions.

[0007] In a first aspect, the present invention provides a colored zirconium oxide artificial gemstone material.

[0008] The zirconia artificial gemstone material comprises in-situ generated spinel-type colored nanoparticles, which have a (Co,M)Al₂O₄, (Fe,M)Al₂O₄, or (Cr,M)Al₂O₄ structure, wherein M is at least one of Zn, Mg, and Ni; the spinel-type colored nanoparticles are distributed at the grain boundaries of zirconia grains, with an average particle size of 20–150 nm; the zirconia artificial gemstone material has a fracture toughness ≥12 MPa·m. 1 / 2 The flexural strength is ≥1200MPa, and after hydrothermal aging treatment at 134℃ for 10 hours, the monoclinic phase content is ≤2%, and the refractive index is 2.15~2.20.

[0009] In the technical solution of this invention, the spinel-type colored nanoparticles generated in situ are composite spinel solid solutions, that is, Zn is introduced into the crystal lattice of cobalt aluminum spinel, iron aluminum spinel or chromium aluminum spinel. 2+ Mg 2+ or Ni 2+ Divalent metal ions, these divalent ions and Co 2+ Fe 2+ or Cr 3+ They collectively occupy the tetrahedral sites of the spinel structure. The colored nanoparticles selectively segregate at the grain boundaries of zirconia grains, with a size of 20–150 nm. This characteristic structure serves several purposes: it prevents the coloring from disrupting the integrity of the zirconia matrix grains, preserving the phase transformation toughening mechanism; it pins the grain boundaries, inhibiting excessive zirconia grain growth and maintaining a fine-grained structure; and it avoids stress concentration caused by excessively large particles. Thus, zirconia synthetic gemstone materials simultaneously achieve a fracture toughness ≥12 MPa·m. 1 / 2 It possesses excellent mechanical properties, including a flexural strength ≥1200MPa, and a high refractive index of 2.15–2.20. Furthermore, the introduction of divalent ions, particularly Mg, with phase-stabilizing effects into the coloring phase further enhances its properties. 2+ It forms a composite stable system with Y2O3 in the matrix, which synergistically inhibits the low-temperature aging phase transformation from tetragonal to monoclinic phase, so that the monoclinic phase content is ≤2% after 10 hours of hydrothermal aging treatment at 134℃.

[0010] Preferably, the molar ratio of Co, Fe, or Cr to M in the spinel-type colored nanoparticles is 1:0.1 to 1, including all endpoint values. This range balances lattice regulation / phase stabilization with preventing weakening of the coloring effect or formation of impurity phases.

[0011] As a further preferred embodiment, the zirconium oxide artificial gemstone material has a relative density ≥99.3% and a Vickers hardness ≥12GPa.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned colored zirconia artificial gemstone material, comprising the following steps:

[0013] (1) Preparation of composite slurry: Zirconia powder, aluminum source, soluble metal salt coloring precursor, sintering aid, dispersant and binder are mixed evenly in a solvent; the sintering aid contains at least one selected from MgO, CaO, TiO2 and Y2O3, and the amount added is 0.1 to 2% of the mass of zirconia powder;

[0014] (2) Molding: The composite slurry is molded by photopolymerization 3D printing to obtain a blank; the printing layer thickness is 10-100μm and the exposure wavelength is 350-450nm;

[0015] (3) Debinding: The raw blank is debinded at a temperature of 300-600°C for 2-6 hours in an atmosphere of air or inert atmosphere.

[0016] (4) Segmented sintering:

[0017] First stage: In an oxidizing atmosphere, the organic components are oxidized and decomposed at 400-600℃ for 0.5-1 hour. The oxidizing atmosphere is air.

[0018] Second stage: In a reducing atmosphere, the coloring precursor is reduced by holding at 600-900℃ for 0.5-3 hours. The reducing atmosphere is a mixture of H2 and N2, with an H2 volume fraction of 5-15%.

[0019] Third stage: Switch to an oxidizing atmosphere and hold at 1300-1500℃ for 1-4 hours to allow the reduction product to react with the aluminum source in situ to generate a spinel-type colored phase, while simultaneously densifying and sintering; the oxidizing atmosphere is air.

[0020] (5) Cooling to obtain colored zirconia artificial gemstone material.

[0021] The core of this invention lies in the segmented sintering process. Unlike traditional one-step sintering or direct oxidation sintering, this invention first reduces the coloring precursor to obtain highly active metal species, and then oxidizes it to generate a spinel phase. This reduction-oxidation sequence makes the nucleation and growth process of the spinel phase more controllable, resulting in uniform nanoparticles of 20–150 nm in size, and promoting their selective segregation at the grain boundaries of zirconia grains, thus achieving both coloring effect and mechanical properties.

[0022] The parameters for each stage have been optimized. In the first stage, if the temperature is too low or the time is too short, organic components will remain, affecting subsequent sintering. In the second stage, if the H2 volume fraction is less than 5%, the reduction will be insufficient, and if it is more than 15%, the zirconium oxide matrix may be over-reduced. In the third stage, if the temperature is less than 1300℃, spinel formation and densification will be insufficient, and if it is more than 1500℃, the grains will coarsen and the performance will be impaired.

[0023] Preferably, the soluble metal salt coloring precursor is a cobalt salt, iron salt, or chromium salt; the aluminum source is alumina, aluminum hydroxide, or boehmite, and its addition amount is 0.5-5% of the mass of the zirconia powder, calculated as Al2O3; the addition amount of the coloring precursor is 0.1-3% of the mass of the zirconia powder, calculated as metal element.

[0024] Preferably, the zirconium oxide powder is tetragonal zirconium oxide containing 2-4 mol% yttrium oxide, with an average particle size of 30-500 nm.

[0025] This invention utilizes a segmented sintering process involving reduction followed by oxidation to generate spinel-type colored nanoparticles in situ and selectively agglomerate them at the grain boundaries of zirconia grains. The size is controlled within the range of 20–150 nm, achieving dual control over the size and spatial distribution of the colored phase. This fundamentally avoids problems such as phase agglomeration, uneven distribution, and thin colored layers found in traditional solid-phase mixing or impregnation coloring methods. The uniformly distributed nanoparticles at the grain boundaries exert a pinning effect on the zirconia grain boundaries, effectively inhibiting excessive grain growth during high-temperature sintering and maintaining a fine-grained structure. Simultaneously, the colored phase agglomerates at the grain boundaries rather than within the grains, avoiding damage to the integrity of the zirconia matrix grains and maximizing the preservation of zirconia's unique phase transformation toughening mechanism. Under these synergistic effects, the fracture toughness of the zirconia artificial gemstone material of this invention is ≥12 MPa·m. 1 / 2 With a flexural strength ≥1200MPa and a refractive index of 2.15~2.20, its comprehensive mechanical properties are significantly superior to existing colored zirconia artificial gemstone materials. Furthermore, this invention introduces Mg into the composite spinel structure... 2+ Divalent ions with phase-stabilizing effects form a composite stable system with Y2O3 in the matrix, which synergistically inhibits the low-temperature aging phase transformation from tetragonal to monoclinic phase. After hydrothermal aging treatment at 134℃ for 10 hours, the monoclinic phase content is ≤2%, while the monoclinic phase content of traditional colored zirconia is usually as high as 8% or more under the same conditions. It can be seen that the hydrothermal aging resistance of the present invention has achieved an unexpected improvement. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the method for preparing colored zirconia artificial gemstone material according to the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Example 1

[0028] This embodiment provides a blue zirconia artificial gemstone material and its preparation method.

[0029] (1) Raw material preparation: Take 100g of tetragonal zirconium powder containing 3mol% Y2O3 with an average particle size of 100nm. The aluminum source is alumina nanoparticles. The amount added is 2.5% of the mass of zirconium powder, i.e., 2.5g, based on Al2O3. The soluble metal salt coloring precursor is cobalt nitrate hexahydrate Co(NO3)2·6H2O. The amount added is 0.8% of the mass of zirconium powder, i.e., 0.8g, based on Co element, which is equivalent to about 4.0g of cobalt nitrate hexahydrate. The sintering aids are Y2O3 powder and MgO powder. The amount of Y2O3 powder added is 0.5% of the mass of zirconium powder, i.e., 0.5g, and the amount of MgO powder added is 0.3% of the mass of zirconium powder, i.e., 0.3g. The dispersant is ammonium polyacrylate, added at 1.5% (1.5g) of the zirconium oxide powder mass; the binder is polyethylene glycol diacrylate (PEGDA), added at 8% (8g) of the zirconium oxide powder mass; the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), added at 3% of the binder mass; the solvent is a mixture of deionized water and ethanol, in a volume ratio of 1:1.

[0030] (2) Preparation of composite slurry: Zirconia powder, Al2O3 nanoparticles, Co(NO3)2·6H2O, Y2O3 powder, MgO powder, dispersant and solvent were mixed evenly in a ball mill jar. Zirconia balls were used as the milling media. The milling speed was 300 rpm and the milling time was 12 hours to obtain a uniformly dispersed zirconia suspension. Then, PEGDA binder and TPO photoinitiator were added to the suspension, and the ball milling was continued for 2 hours to fully disperse the organic components and obtain a uniform composite slurry.

[0031] (3) Photopolymerization 3D printing: The composite slurry obtained in step (2) is loaded into the feed tank of the digital light processing (DLP) 3D printer. The printing layer thickness is set to 50 μm, the exposure wavelength is 405 nm, and the single layer exposure time is 8 seconds. The printing is carried out layer by layer to obtain the blank. After printing, the uncured residual slurry on the surface of the blank is cleaned with ethanol and dried at room temperature.

[0032] (4) Debinding treatment: The green blank obtained in step (3) is placed in a muffle furnace for debinding treatment. The debinding temperature is 500℃, the heating rate is 1℃ / min, the holding time is 3 hours, and the atmosphere is air. After debinding, it is naturally cooled to room temperature.

[0033] (5) Segmented sintering:

[0034] First stage: Place the debinding green blank in a tube sintering furnace and heat it to 500°C at a rate of 5°C / min under air atmosphere. Hold it at this temperature for 1 hour to completely oxidize and decompose the small amount of organic components remaining in the green blank.

[0035] The second stage: The furnace temperature is raised to 800℃ at a heating rate of 5℃ / min, and the atmosphere is switched to a mixed atmosphere of H2 / N2 with a volume fraction of 10% H2 and 90% N2. The temperature is held at 800℃ for 1.5 hours to reduce Co3O4 generated by the decomposition of Co(NO3)2 to metallic Co.

[0036] The third stage: Keep the furnace temperature at 800℃, switch the atmosphere back to air, and raise the furnace temperature to 1400℃ at a heating rate of 3℃ / min. Hold at 1400℃ for 2 hours to allow the reduced metal Co to react with Al2O3 and O2 in the atmosphere, generating CoAl2O4 spinel phase in situ; at the same time, the zirconia matrix is ​​densified and sintered at this temperature.

[0037] (6) Cooling: After sintering, the furnace is cooled to room temperature at a rate of 3℃ / min to obtain blue zirconia artificial gemstone material. Example 2

[0038] This embodiment provides a green zirconia synthetic gemstone material and its preparation method.

[0039] The difference between this embodiment and Example 1 is that the soluble metal salt coloring precursor is ferric nitrate nonahydrate Fe(NO3)3·9H2O, and the addition amount is 1.2% of the zirconia powder mass based on Fe element; the M element is Zn, introduced in the form of zinc nitrate Zn(NO3)2·6H2O, with a Fe to Zn molar ratio of 1:0.5; the aluminum source addition amount is 3% of the zirconia powder mass based on Al2O3; the zirconia powder is tetragonal zirconia containing 3.5 mol% Y2O3, and the sintering aid is MgO, added at 0.5% of the zirconia powder mass. The segmented sintering process parameters are adjusted as follows: the first stage is held at 500℃ for 1 hour, the second stage is held at 850℃ for 1 hour with an H2 volume fraction of 10%, and the third stage is held at 1420℃ for 2 hours. The average particle size of the zirconia powder used is the same as in Example 1, which is 100 nm. The remaining raw material ratios and process parameters are the same as in Example 1, and green zirconia artificial gemstone material is obtained. Example 3

[0040] This embodiment provides a pink zirconia artificial gemstone material and its preparation method.

[0041] The difference between this embodiment and Example 1 is that the soluble metal salt coloring precursor is chromium nitrate nonahydrate Cr(NO3)3·9H2O, and the addition amount is 0.5% of the zirconia powder mass based on Cr element; Mg element is selected as M element and introduced in the form of magnesium nitrate Mg(NO3)2·6H2O, with a Cr to Mg molar ratio of 1:0.3; the aluminum source addition amount is 2% of the zirconia powder mass based on Al2O3; the zirconia powder is tetragonal zirconia containing 2.5 mol% Y2O3, and the sintering aid is Y2O3, added at 0.8% of the zirconia powder mass. The segmented sintering process parameters are adjusted as follows: the first stage is held at 500℃ for 1 hour, the second stage is held at 750℃ for 1 hour with an H2 volume fraction of 8%, and the third stage is held at 1380℃ for 2.5 hours. The average particle size of the zirconia powder used is the same as in Example 1, which is 100 nm. The remaining raw material ratios and process parameters are the same as in Example 1, and a pink zirconia artificial gemstone material is obtained. Example 4

[0042] This embodiment provides a sky-blue zirconia artificial gemstone material and its preparation method, using Co-Ni composite spinel coloring.

[0043] The difference between this embodiment and Example 1 is that the M element is Ni, introduced in the form of nickel nitrate Ni(NO3)2·6H2O, and the molar ratio of Co to Ni is 1:0.6; the amount of aluminum source added is 3.5% of the mass of zirconia powder, calculated as Al2O3; and the sintering aids are TiO2 (0.2%) and MgO (0.3%). The segmented sintering process parameters are adjusted as follows: the first stage is held at 550℃ for 1 hour, the second stage is held at 820℃ for 2 hours with an H2 volume fraction of 12%, and the third stage is held at 1450℃ for 1.5 hours. The average particle size of the zirconia powder used is the same as in Example 1, which is 100 nm. The remaining raw material ratios and process parameters are the same as in Example 1, and a sky-blue zirconia artificial gemstone material is obtained. Example 5

[0044] This embodiment provides a deep blue zirconia artificial gemstone material and its preparation method, using Co-Zn composite spinel coloring.

[0045] The difference between this embodiment and Example 1 is that the M element is Zn, introduced in the form of zinc nitrate Zn(NO3)2·6H2O, and the molar ratio of Co to Zn is 1:0.8; the amount of coloring precursor added is 1.5% of the mass of zirconia powder based on Co; the amount of aluminum source added is 4% of the mass of zirconia powder based on Al2O3; the zirconia powder is tetragonal zirconia containing 4 mol% Y2O3, and the sintering aid is MgO (1.2%). The segmented sintering process parameters are adjusted as follows: the first stage is held at 500℃ for 1 hour, the second stage is held at 780℃ for 2 hours with a H2 volume fraction of 10%, and the third stage is held at 1480℃ for 1 hour. The average particle size of the zirconia powder used is the same as in Example 1, which is 100 nm. The remaining raw material ratios and process parameters are the same as in Example 1, and a deep blue zirconia artificial gemstone material is obtained. Example 6

[0046] The difference between this embodiment and Embodiment 1 is that the average particle size of the zirconia powder is 30 nm, the layer thickness is 10 μm, the exposure wavelength is 350 nm, the binder removal temperature is 300 °C, and the holding time is 6 hours. The first stage is held at 400 °C for 1 hour, the second stage is held at 600 °C for 3 hours with an H2 volume fraction of 5%, and the third stage is held at 1300 °C for 4 hours. Other parameters are the same as in Embodiment 1. Example 7

[0047] The difference between this embodiment and Embodiment 1 is that the average particle size of the zirconia powder is 500 nm, the layer thickness is 100 μm, the exposure wavelength is 450 nm, the binder removal temperature is 600 °C, and the holding time is 2 hours. The first stage involves holding at 600 °C for 0.5 hours, the second stage involves holding at 900 °C for 0.5 hours with an H2 volume fraction of 15%, and the third stage involves holding at 1500 °C for 1 hour. Other parameters are the same as in Embodiment 1.

[0048] Comparative Example 1

[0049] This comparative example provides a blue zirconia synthetic gemstone material prepared using a traditional solid-phase mixing method.

[0050] (1) Raw material ratio: Take 100g of tetragonal zirconium oxide powder containing 3mol% Y2O3 with an average particle size of 100nm; use CoAl2O4 spinel pigment with an average particle size of about 500nm as a colorant, with an addition amount of 2.5% of the mass of zirconium oxide powder; and use Y2O3 (0.5%) and MgO (0.3%) as sintering aids.

[0051] (2) Mixing: The above raw materials were placed in a ball mill jar, using zirconia balls as the milling medium and anhydrous ethanol as the dispersion medium. The ball milling speed was 300 rpm and the milling time was 12 hours to obtain a mixed slurry. After drying, the slurry was passed through a 200-mesh sieve to obtain a mixed powder.

[0052] (3) Molding: The mixed powder is dry-pressed under a pressure of 200MPa to obtain a green body.

[0053] (4) Sintering: The green blank is placed in a muffle furnace and heated to 1400°C at 5°C / min in an air atmosphere. It is held for 2 hours and then cooled with the furnace to obtain blue zirconia artificial gemstone material.

[0054] Comparative Example 2

[0055] This comparative example provides a blue zirconia artificial gemstone material prepared by photopolymerization 3D printing combined with impregnation coloring method.

[0056] (1) Photopolymerization printing of white zirconia blanks: 100g of 3Y-TZP zirconia powder, 15g of resin monomer, 2g of dispersant and 0.5g of photoinitiator are mixed evenly to prepare white zirconia slurry, which is then formed by DLP photopolymerization 3D printing to obtain white zirconia blanks.

[0057] (2) Glue removal: Glue removal at 500℃ for 3 hours.

[0058] (3) Impregnation and coloring: Place the unfinished blank after debinding in a solution containing 0.5 mol / L Co 2+ Immerse in the coloring solution for 24 hours.

[0059] (4) Sintering: Sinter at 1400℃ in air atmosphere for 2 hours to obtain blue zirconium oxide artificial gemstone material.

[0060] Comparative Example 3

[0061] The difference between this comparative example and Example 1 is that the segmented sintering process does not include a second stage; that is, after the binder is removed, the green blank is directly heated to 1400°C in air and held for 2 hours for sintering. Other raw material ratios and process parameters are the same as in Example 1.

[0062] Comparative Example 4

[0063] The difference between this comparative example and Example 1 is that the sintering temperature in the third stage is 1600℃. Other raw material ratios and process parameters are the same as in Example 1.

[0064] Comparative Example 5

[0065] The difference between this comparative example and Example 1 is that the amount of the coloring precursor Co(NO3)2·6H2O added is 4% of the mass of the zirconia powder, i.e., 4g, calculated as Co element. Other raw material ratios and process parameters are the same as in Example 1.

[0066] Performance testing methods

[0067] The following performance tests were performed on the colored zirconium oxide synthetic gemstone materials prepared in the above embodiments and comparative examples:

[0068] (1) Relative density: The Archimedes water displacement method was used for determination, and the test standard was based on ISO 18754. After boiling the sample in distilled water for 30 minutes, its suspended mass and wet mass were determined, and the relative density was calculated.

[0069] (2) Fracture toughness: The single-sided notched beam method was used for determination, and the test standard was based on ASTM C1421. The specimen size was 3mm × 4mm × 30mm. A notch with a depth of about 2mm was machined in the middle of the specimen. A three-point bending loading method was used, with a span of 24mm and a loading rate of 0.5mm / min. The fracture toughness was calculated from the applied fracture load and the specimen size.

[0070] (3) Bending strength: The three-point bending method was used for determination, and the test standard was based on ASTM C1161. The sample size was 3mm×4mm×30mm, the span was 24mm, the loading rate was 0.5mm / min, and the bending strength was calculated from the maximum bending load.

[0071] (4) Vickers hardness: The Vickers hardness tester was used, and the test standard was based on ISO 6507. The test load was 10 kgf, the holding time was 15 seconds, and the average value was taken after measuring at 5 different locations on the sample surface.

[0072] (5) Hydrothermal aging performance: The sample was placed in a high-pressure hydrothermal reactor and treated for 10 hours at 134℃ and 0.2MPa. The phase composition of the sample was determined by X-ray diffraction before and after aging. The monoclinic phase content was calculated based on the integrated intensity of the characteristic peaks of the tetragonal and monoclinic phases in the XRD pattern. The test standard was based on ISO 20203.

[0073] (6) Refractive index: The refractive index was measured at room temperature using an Abbe refractometer or a precision ellipsometer. The test standard was in accordance with GB / T7962.5-2010, Test Method for Refractive Index of Colorless Optical Glass, applicable to transparent ceramic materials. The sample was processed into a thin sheet with parallel sides and a thickness ≥1mm. The test wavelength was 589nm sodium yellow light.

[0074] The performance test results of Examples 1-7 and Comparative Examples 1-5 are summarized in Table 1:

[0075] Table 1

[0076]

[0077] As can be seen from the performance test results of each embodiment and comparative example in Table 1, the colored zirconia artificial gemstone materials of each embodiment of the present invention all exhibit excellent comprehensive performance.

[0078] Regarding the degree of densification, the relative densities of Examples 1-7 were all above 99.3%, with Examples 1, 3, and 6 reaching above 99.5%, indicating that the segmented sintering process and optimized slurry formulation ensured sufficient densification of the zirconia synthetic gemstone material. In contrast, the relative density of Comparative Example 1, using the traditional solid-phase mixing method, was only 97.8%, and that of Comparative Example 2, using the impregnation and coloring method, was only 96.5%, indicating that the introduction of coloring phases in the traditional process hindered the densification of the zirconia matrix to some extent.

[0079] In terms of mechanical properties, the fracture toughness of Examples 1–7 ranges from 12.1 to 13.5 MPa·m. 1 / 2 Within this range, the flexural strength is in the range of 1210–1340 MPa. The fracture toughness of Comparative Example 1 is 7.5 MPa·m. 1 / 2 The flexural strength of Example 1 is 820 MPa; the fracture toughness of Example 2 is only 5.2 MPa·m. 1 / 2 The flexural strength is 560 MPa; the fracture toughness of Comparative Example 3 (omitting the reduction step) is 8.1 MPa·m. 1 / 2 The flexural strength of 780 MPa indicates that the reduction step is crucial for obtaining excellent mechanical properties. Comparative Example 4, sintered at 1600℃, achieved a higher relative density of 99.2%, but its fracture toughness decreased to 9.5 MPa·m due to excessive grain growth. 1 / 2 The flexural strength was 950 MPa, which was still significantly lower than that of the example. In Comparative Example 5, the excessive addition of colorant caused coarsening and agglomeration of the coloring phase particles, which severely impaired the mechanical properties.

[0080] Regarding resistance to hydrothermal aging, the monoclinic phase content of Examples 1-7 was below 1.9% after 10 hours of hydrothermal aging at 134℃, far below the requirement of 2%. Example 3, with its pinkish color, had the lowest monoclinic phase content, at only 1.0%. In contrast, Comparative Example 1 had a monoclinic phase content as high as 8.5%, Comparative Example 2 as high as 12.3%, Comparative Example 3 as high as 9.2%, Comparative Example 4 as high as 4.5%, and Comparative Example 5 as high as 7.8%. This result indicates that the present invention, by introducing divalent ions such as Mg, Zn, and Ni with phase-stabilizing effects into the composite spinel structure, forms a synergistic stabilizing effect with Y2O3 in the matrix, significantly suppressing the monoclinic phase transformation of the tetragonal zirconia phase during hydrothermal aging.

[0081] In terms of optical properties, the refractive indices of Examples 1-7 ranged from 2.17 to 2.20, close to the theoretical refractive index of fully dense zirconia, around 2.18. Furthermore, due to the dense nature of the samples and the absence of internal pores, the measurement results were stable and reliable. Example 3, the pink sample, had the highest refractive index at 2.20, while Example 5, the dark blue sample, had a slightly lower refractive index of 2.17. This is related to slight differences in the amount of coloring phase introduced and the grain boundary structure. However, all examples achieved the high refractive index required for synthetic gemstones (≥2.15), exhibiting a diamond-like luster. In contrast, the refractive indices of Comparative Examples 1-5 ranged from 2.09 to 2.14, significantly lower than the examples. This is mainly due to the insufficient density of Comparative Examples 1, 2, 3, and 5, with relative densities below 98.5%, resulting in light scattering caused by residual pores and lower measured refractive index values. Although Comparative Example 4 had a higher density of 99.2%, its refractive index was only 2.14 due to grain coarsening and the presence of amorphous phases at the grain boundaries, lower than the lowest value of 2.17 in the examples. The above results show that the present invention achieves excellent optical performance while obtaining high density and fine grain structure by generating spinel nanoparticles with grain boundary distribution in situ and combining them with a segmented sintering process. Its refractive index is significantly better than that of existing products, making it suitable for the field of high-end artificial gemstones and decorative items.

[0082] By comparing the test results of Example 1 with those of Comparative Examples 1 to 5, the key technical features and synergistic effects of the present invention that achieve excellent technical results can be clearly revealed.

[0083] First, this invention uses a soluble metal salt coloring precursor and an aluminum source to generate a spinel phase in situ during the segmented sintering process, thus avoiding the inherent particle agglomeration problem of spinel pigments.

[0084] Secondly, the original reduction-oxidation segmented sintering process of this invention is another key element. Comparative Example 3 omitted the reduction step, resulting in an increased spinel phase formation temperature, coarsening of particles, and decreased distribution uniformity, leading to a reduction in fracture toughness and flexural strength to 8.1 MPa·m, respectively. 1 / 2 At 780 MPa, the monoclinic phase content reached as high as 9.2% after hydrothermal aging. This fully demonstrates that the reduction step, by transforming the coloring precursor into highly active metal species, creates the necessary conditions for the low-temperature uniform nucleation of the spinel phase, and is an indispensable core process.

[0085] Furthermore, this invention achieves selective segregation and distribution of spinel-colored nanoparticles at zirconia grain boundaries, forming a unique grain boundary pinning structure. In Comparative Examples 1 and 3, the coloring phase is distributed simultaneously within the grains and at the grain boundaries, resulting in uncontrollable distribution that damages the grain integrity of the zirconia matrix and weakens the phase transformation toughening effect. In Example 1, the coloring phase is strictly distributed at the grain boundaries, avoiding the aforementioned problems and inhibiting grain growth through pinning, thereby achieving a fracture toughness of 13.2 MPa·m. 1 / 2It is much higher than the 7.5 MPa·m of Comparative Example 1. 1 / 2 And 8.1 MPa·m of Comparative Example 3 1 / 2 .

[0086] Finally, this invention optimizes and controls the sintering temperature of the third stage within the range of 1300–1500℃. Comparative Example 4 increased the sintering temperature to 1600℃; although the relative density reached 99.2%, the grains and coloring phases significantly coarsened, and the fracture toughness and flexural strength decreased to 9.5 MPa·m, respectively. 1 / 2 And 950 MPa. This indicates that excessively high sintering temperatures can disrupt grain boundary pinning structures and impair mechanical properties.

[0087] In summary, the colored zirconia artificial gemstone material of the present invention achieves a synergistic improvement in color uniformity, mechanical properties, high refractive index optical properties, and hydrothermal aging stability through in-situ generation of composite spinel coloring nanoparticles, precise control of the reduction-oxidation segmented sintering process, and microstructure design that realizes the segregation distribution of the coloring phase at grain boundaries. Comparative Examples 1-5 lack one or more of the above-mentioned key technical features to varying degrees, and their performance is significantly inferior to the embodiments. In particular, the refractive index of the present invention is stable between 2.15 and 2.20, exhibiting adamantine luster, making it suitable for high-value-added fields such as artificial gemstones and decorative items. This solves the long-standing technical problem in the prior art of achieving both color uniformity and high performance in colored zirconia materials.

[0088] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention. Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A colored zirconium oxide synthetic gemstone material, characterized in that, The colored zirconia artificial gemstone material comprises in-situ generated spinel-type coloring nanoparticles, which have a (Co,M)Al₂O₄, (Fe,M)Al₂O₄, or (Cr,M)Al₂O₄ structure, wherein M is at least one of Zn, Mg, and Ni; the spinel-type coloring nanoparticles are distributed at the grain boundaries of zirconia grains, with an average particle size of 20–150 nm; the fracture toughness of the zirconia artificial gemstone material is ≥12 MPa·m. 1 / 2 The flexural strength is ≥1200MPa, and after hydrothermal aging treatment at 134℃ for 10 hours, the monoclinic phase content is ≤2%, and the refractive index is 2.15~2.

20.

2. The colored zirconium oxide artificial gemstone material according to claim 1, characterized in that, The molar ratio of Co, Fe or Cr to M in the spinel-type colored nanoparticles is 1:0.1 to 1, and the endpoints of the molar ratio are all included.

3. The colored zirconium oxide artificial gemstone material according to claim 1, characterized in that, The relative density of the zirconia artificial gemstone material is ≥99.3%, and the Vickers hardness is ≥12GPa.

4. A method for preparing a colored zirconia artificial gemstone material according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Preparation of composite slurry: Zirconia powder, aluminum source, soluble metal salt coloring precursor, sintering aid, dispersant and binder are mixed evenly in a solvent; the sintering aid contains at least one selected from MgO, CaO, TiO2 and Y2O3, and the amount added is 0.1 to 2% of the mass of zirconia powder; (2) Molding: The composite slurry is molded by photopolymerization 3D printing to obtain a blank; the layer thickness of the photopolymerization 3D printing is 10-100μm and the exposure wavelength is 350-450nm; (3) Debinding: The raw blank is debinded at a temperature of 300-600°C for 2-6 hours in an atmosphere of air or inert atmosphere. (4) Segmented sintering: First stage: In an oxidizing atmosphere, the organic components are oxidized and decomposed at 400-600℃ for 0.5-1 hour. The oxidizing atmosphere is air. Second stage: In a reducing atmosphere, the coloring precursor is reduced by holding at 600-900℃ for 0.5-3 hours. The reducing atmosphere is a mixture of H2 and N2, with an H2 volume fraction of 5-15%. The third stage: switch to an oxidizing atmosphere and hold at 1300-1500℃ for 1-4 hours to allow the reduction product to react with the aluminum source in situ to generate a spinel-type colored phase, while simultaneously densifying and sintering. The oxidizing atmosphere is an air atmosphere. (5) Cooling to obtain colored zirconia artificial gemstone material.

5. The preparation method according to claim 4, characterized in that, The soluble metal salt coloring precursor is a cobalt salt, iron salt, or chromium salt; the aluminum source is alumina, aluminum hydroxide, or boehmite, and its addition amount is 0.5-5% of the mass of the zirconia powder, calculated as Al2O3; the addition amount of the coloring precursor is 0.1-3% of the mass of the zirconia powder, calculated as metal element.

6. The preparation method according to claim 4, characterized in that, The zirconium oxide powder is a tetragonal zirconium oxide containing 2-4 mol% yttrium oxide, with an average particle size of 30-500 nm.

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