Core-shell structure nano-powder toughened zirconia ceramic and preparation method thereof

Abstract

The application discloses a kind of core-shell structure nanometer powder toughened zirconia ceramics and preparation method thereof, belong to ceramic material technical field, the method includes using three-dimensional network gel to realize washing-free co-precipitation method to prepare high-activity, ZrO2@SiO2Core-shell structure nanometer zirconia raw material powder, and stable agent is mixed ball milling, drying, sieving, shaping, cold isostatic pressing and gets green body, green body is placed in vacuum furnace and sintering, annealing and obtains toughened zirconia ceramic target product, realizes the efficient preparation of jade quality feeling simulation ceramic tooth of integral penetration.The application avoids the repeated washing steps of precursor in the traditional co-precipitation preparation process, reduces the introduction of impurities, the sintering temperature is lower, the powder yield is high, the process is simple, the cost is low, and is suitable for the industrial production of toughened zirconia ceramics.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a core-shell structured nanopowder-toughened zirconia ceramic and its preparation method. Background Technology

[0002] Dental restorations have always been an essential part of people's oral health. Currently, restoration materials have shifted from traditional and expensive metal materials (all-metal or porcelain-fused-to-metal crowns) to all-ceramic or resin composite materials. In clinical applications, most doctors and patients prioritize all-ceramic restorations, making them the primary form of fixed dental restorations. Zirconia ceramics, due to their excellent biocompatibility, superior aesthetics, excellent flexural strength, and wear resistance, almost dominate the all-ceramic restoration market. To ensure that the color and translucency of the restoration closely resemble natural tooth enamel, achieving a more realistic and perfect aesthetic performance, zirconia all-ceramic restorations consist of a zirconia framework base ceramic (often using yttrium-stabilized tetragonal polycrystalline zirconia 3Y-TZP) and a relatively thin zirconia veneer. Clinical investigations have revealed that porcelain chipping in zirconia ceramics is a fatal flaw, primarily occurring in the zirconia veneer, which severely affects the lifespan and stability of the restoration in the patient's mouth. The main reason for the failure of all-ceramic restorations is their low toughness. It has also been found that sintering temperature and grain size have a significant impact on ceramic properties. High temperatures and large grains directly lead to crack lengthening, which in turn destabilizes the properties of zirconia ceramics. Therefore, enhancing the toughness of zirconia ceramics, lowering the sintering temperature, and controlling the grain size are key to solving the problem of ceramic chipping.

[0003] To address the aforementioned issues, Chinese patent application CN114394830A discloses a method for preparing high-strength zirconia ceramics. This method uses a chemical co-precipitation method to prepare yttrium-stabilized zirconia nanopowder. The resulting sintered yttrium-stabilized zirconia ceramic has uniform grain size with an average size less than 500 nm. While this method improves the flexural strength and hardness of zirconia ceramics without altering their phase composition, its toughness remains unimproved. Furthermore, the precursor requires multiple cleaning processes with deionized water and ethanol, resulting in a complex process and low production efficiency. Chinese patent application CN109503186A discloses a method for preparing a strong and tough zirconia ceramic material for dental restorations. This method involves adding a tourmaline second phase and sintering to obtain a strong and tough zirconia ceramic material with mullite whiskers. Although this method effectively improves the strength and toughness of zirconia ceramics, the addition of the second phase reduces the density of the sintered body, affecting its overall mechanical properties, and may also affect its color and transparency, making it unsuitable for direct use as a dental restoration. Chinese patent CN214735424U discloses a whisker-toughened zirconia ceramic. By using a special interface layer preparation method, an interface layer that is not actively reacting with the zirconia ceramic matrix is ​​set on the surface of the whisker, which solves the problem of secondary sintering reaction between oxide whiskers and zirconia ceramic matrix. Although it improves the strength and toughness of ceramic materials, this method cannot guarantee the uniformity of whisker distribution, cannot guarantee product quality and yield, and does not fundamentally solve the problem of low toughness of zirconia ceramic. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing core-shell structured nanopowder-toughened zirconia ceramics, which has a lower sintering temperature, higher powder yield, simpler process, and lower cost, and is suitable for the industrial production of toughened zirconia ceramics.

[0005] The second objective of this invention is to provide core-shell structured nanopowder-toughened zirconia ceramics prepared by the above method, fundamentally solving the problem of zirconia ceramics being prone to chipping due to low toughness. The properties of the prepared zirconia ceramics all meet the requirements of the dental ceramics standard ISO6872:2015.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing core-shell structured nanopowder-toughened zirconia ceramic, comprising the following steps:

[0008] S1: Using zirconium oxychloride octahydrate as raw material, ammonia and magnesium hydroxide solution are added as precipitants; TEOS solution is added as silicon source; the solid content of the slurry is controlled at 30-60 vol.%, heated in a water bath and magnetically stirred, pH adjuster is added, and after precipitation and aging, the slurry is filtered to obtain highly active ZrO2@SiO2 core-shell structured nanopowder.

[0009] S2: After drying the nanoparticles obtained in step S1, place them in a vacuum muffle furnace for calcination. First, calcine them in a vacuum environment for 1-2 hours, and then calcine them in an air or oxygen atmosphere for 1-2 hours. After calcination, place them in a ball mill jar, add micron-sized yttrium oxide as a stabilizer, add ball milling media, mix and ball mill, dry, sieve, shape, and then perform cold isostatic pressing to obtain a dense green blank.

[0010] S3: The green blank obtained in step S2 is sintered in a vacuum sintering furnace and air-annealed. After cooling, toughened zirconia ceramic is obtained. Preferably, in step S1, the mass ratio of precipitant to zirconium oxychloride octahydrate is 1:1, the mass ratio of ammonia water to magnesium hydroxide solution is 2:1, the mass ratio of TEOS solution to zirconium oxychloride octahydrate is 2:1 to 3:1, the heating temperature in the water bath is 50 to 80°C, the stirring time is 2 hours, the pH adjuster is urea, the pH is controlled to be 8.0 to 9.0, and the precipitation aging time is 12 hours.

[0011] Preferably, in step S2, the calcination temperature in the vacuum muffle furnace is 200–400°C and the vacuum degree is 200–400 Pa; then air or oxygen is introduced to raise the calcination temperature to 600–700°C.

[0012] Preferably, the amount of micron-sized yttrium oxide added in step S2 is 2 to 4 wt.% of the mass of the nanoparticles obtained in step S1.

[0013] Preferably, in step S2, the milling medium is anhydrous ethanol; the milling speed is 180-280 rpm; and the milling time is 8-10 h.

[0014] Preferably, in step S3, the sintering temperature is 1200–1300℃, the holding time is 3–5 hours, and the vacuum degree is not less than 1×10⁻⁶. -3 Pa; air annealing temperature is 800~1100℃, and holding time is 1~2h.

[0015] Secondly, the present invention provides a core-shell structured nanopowder-toughened zirconia ceramic prepared by the above method.

[0016] This invention discloses a method for preparing core-shell structured nanoparticle-toughened zirconia ceramics. This method utilizes a three-dimensional network gel encapsulation to achieve a wash-free co-precipitation process to prepare highly active ZrO2@SiO2 core-shell structured nano-zirconia raw material powder. The powder is then mixed with a stabilizer, ball-milled, dried, sieved, shaped, and cold isostatically pressed to obtain a green body. The green body is then sintered and annealed in a vacuum furnace to obtain the target toughened zirconia ceramic product, achieving efficient preparation of seamless, jade-like, simulated ceramic teeth. This invention avoids the repeated washing steps of the precursor in traditional co-precipitation processes, reducing the introduction of impurities, allowing for lower sintering temperatures, higher powder yield, simpler processes, and lower costs, making it suitable for the industrial production of toughened zirconia ceramics.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. This invention uses TEOS solution as the silicon source. After TEOS is mixed with water, it undergoes hydrolysis. Then, under the catalysis of ammonia, the hydroxyl groups (OH-) attack the Si atoms with fewer alkoxy groups, thereby achieving a three-dimensional network structure of silica gel encapsulating zirconium hydroxide. In the initial stage of calcination, zirconium hydroxide and its encapsulated polymer three-dimensional network are in a low vacuum environment. The lack of oxygen prevents the decomposition of polymeric organic matter, promoting the preferential decomposition of zirconium hydroxide into zirconium oxide powder. The polymer three-dimensional network remains encapsulated on the surface of the zirconium oxide powder. As the temperature continues to rise and air or oxygen is introduced, the polymers decompose and adhere on the zirconium oxide surface, forming a structurally stable ZrO2@SiO2 core-shell powder. This preparation method avoids the need for repeated washing of the precursor in the traditional co-precipitation preparation process to remove excess waste ions, impurities, and other byproducts, thus avoiding large precursor particle size and low activity. On the other hand, the use of a SiO2 shell replaces the added sintering aid, simplifying the preparation process of dental ceramics and reducing the introduction of impurities into zirconium oxide ceramics, promoting the sintering densification of ceramics, and achieving efficient preparation of one-piece transparent jade-like simulated ceramic teeth.

[0019] 2. This invention uses urea as a pH adjuster. Urea can be slowly hydrolyzed into ammonia at low temperature to act as an alkali source, without affecting the functional groups on the surface of ZrO2@SiO2 core-shell structure powder.

[0020] 3. The toughened zirconia ceramic prepared by this invention has a flexural strength that is 20 MPa higher than that of traditional toughened zirconia ceramics (test method: GB / T 6569-2006), a fracture toughness that is more than 25% higher (test method: 23806-2009), and a flexural strength that is more than 10% higher than that of cubic or tetragonal zirconia ceramics stabilized by yttrium oxide or magnesium oxide.

[0021] 4. The toughened zirconia ceramics prepared by this method have a lower sintering temperature, smaller and more uniform crystal size, higher powder yield, simpler process, and lower cost, making them suitable for the industrial production of toughened zirconia ceramics. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 Flowchart of the preparation process for toughened zirconia ceramics using core-shell structured nanopowder.

[0024] Figure 2 This is a SEM image of the ZrO2@SiO2 core-shell structured nanopowder in Example 1.

[0025] Figure 3 This is a SEM image of the core-shell structured nanopowder-toughened zirconia ceramic from Example 1. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The following examples are all based on Figure 1 The process shown is used to prepare core-shell structured nanopowder-toughened zirconia ceramics.

[0028] Example 1

[0029] S1: Using 100 parts of zirconium oxychloride octahydrate as raw material, 100 parts of precipitant were added, with the mass ratio of ammonia water to magnesium hydroxide solution being 2:1; 200 parts of TEOS solution were added as a silicon source, and the solid content of the slurry was controlled at 30 vol.%. The mixture was heated in an 80℃ water bath and magnetically stirred for 2 hours. Urea was added as a pH adjuster to control the pH at 8.0. After precipitation and aging for 12 hours, the resulting slurry was filtered to obtain highly active ZrO2@SiO2 core-shell structured nanopowders. The SEM image of the ZrO2@SiO2 core-shell structured nanopowder is shown below. Figure 2 As shown;

[0030] S2: The nanoparticles obtained in step S1 are dried and calcined in a vacuum muffle furnace at a rate of 5℃ / min to 200℃ for 2 hours with a vacuum degree of 200Pa. Then, air is introduced and the calcination temperature is increased to 600℃ and held for 1 hour. The nanoparticles are then placed in a ball milling jar, and 2wt.% of micron-sized yttrium oxide is added as a stabilizer. Anhydrous ethanol is added as the ball milling medium. The ball milling speed is 180 rpm and the ball milling time is 8 hours. The mixture is then ball-milled, dried, sieved, and shaped. Finally, it is cold isostatically pressed at 300MPa and held for 10 minutes to obtain a dense green body.

[0031] S3: Sinter the green blank obtained in step S2 in a vacuum sintering furnace, heating to 1200℃ at a rate of 5℃ / min and sintering for 3 hours, with a vacuum degree not less than 1×10⁻⁶. -3 Pa; then air is introduced and the temperature is lowered to 800℃ at a rate of 5℃ / min for annealing for 1 hour. After cooling, toughened zirconia ceramic is obtained. SEM image of core-shell structured nanopowder toughened zirconia ceramic is shown below. Figure 3 As shown.

[0032] Example 2

[0033] S1: Using 100 parts of zirconium oxychloride octahydrate as raw material, add 100 parts of precipitant with a mass ratio of ammonia water to magnesium hydroxide solution of 2:1; add 200 parts of TEOS solution as silicon source, control the solid content of slurry to 45 vol.%, heat in an 80℃ water bath and react with magnetic stirring for 2 hours, add urea as pH adjuster to control pH to 8.5, precipitate and age for 12 hours, filter the obtained slurry to obtain highly active ZrO2@SiO2 core-shell structured nanopowder;

[0034] S2: The nanoparticles obtained in step S1 are dried and calcined in a vacuum muffle furnace at a rate of 5℃ / min to 200℃ for 2 hours with a vacuum degree of 200Pa. Then, oxygen is introduced and the calcination temperature is increased to 650℃ and held for 1 hour. The nanoparticles are then placed in a ball mill jar, and 2wt.% of micron-sized yttrium oxide is added as a stabilizer. Anhydrous ethanol is added as the ball milling medium. The ball milling speed is 180 rpm and the ball milling time is 8 hours. The mixture is then ball-milled, dried, sieved, and shaped. Finally, it is cold isostatically pressed at 300MPa and held for 10 minutes to obtain a dense green body.

[0035] S3: Sinter the green blank obtained in step S2 in a vacuum sintering furnace, heating to 1200℃ at a rate of 5℃ / min and sintering for 3 hours, with a vacuum degree not less than 1×10⁻⁶. -3 Pa; then air is introduced and the temperature is lowered to 1000℃ at a rate of 5℃ / min for annealing for 1h. After cooling, toughened zirconia ceramic can be obtained.

[0036] Example 3

[0037] S1: Using 100 parts of zirconium oxychloride octahydrate as raw material, add 100 parts of precipitant with a mass ratio of ammonia water to magnesium hydroxide solution of 2:1; add 300 parts of TEOS solution as silicon source, control the solid content of slurry to 60 vol.%, heat in an 80℃ water bath and react with magnetic stirring for 2 hours, add urea as pH adjuster to control pH to 8.5, precipitate and age for 12 hours, filter the obtained slurry to obtain highly active ZrO2@SiO2 core-shell structured nanopowder;

[0038] S2: The nanoparticles obtained in step S1 are dried and calcined in a vacuum muffle furnace at a rate of 5℃ / min to 400℃ for 2 hours with a vacuum degree of 400Pa. Then, air is introduced and the calcination temperature is increased to 600℃ and held for 1 hour. The nanoparticles are then placed in a ball milling jar, and 4wt.% of micron-sized yttrium oxide is added as a stabilizer. Anhydrous ethanol is added as the ball milling medium. The ball milling speed is 180 rpm and the ball milling time is 8 hours. The mixture is then ball-milled, dried, sieved, and shaped. Finally, it is cold isostatically pressed at 300MPa and held for 10 minutes to obtain a dense green body.

[0039] S3: Sinter the green blank obtained in step S2 in a vacuum sintering furnace, heating to 1300℃ at a rate of 5℃ / min and sintering for 3 hours, with a vacuum degree not less than 1×10⁻⁶. -3 Pa; then air is introduced and the temperature is lowered to 1100℃ at a rate of 5℃ / min for annealing for 1h. After cooling, toughened zirconia ceramic can be obtained.

[0040] Comparative Example 1 (Compared with Example 1, the difference in Comparative Example 1 is that urea is not added in step S1 as a pH adjuster to adjust the pH value of the slurry)

[0041] S1: Using 100 parts of zirconium oxychloride octahydrate as raw material, add 100 parts of precipitant and the mass ratio of ammonia water and magnesium hydroxide solution is 2:1; add 200 parts of TEOS solution as silicon source, control the solid content of slurry to 30 vol.%, heat in an 80℃ water bath and react with magnetic stirring for 2 hours, after precipitation and aging for 12 hours, filter the obtained slurry to obtain highly active ZrO2@SiO2 core-shell structured nanopowder;

[0042] S2: The nanoparticles obtained in step S1 are dried and calcined in a vacuum muffle furnace at a rate of 5℃ / min to 200℃ for 2 hours with a vacuum degree of 200Pa. Then, air is introduced and the calcination temperature is increased to 600℃ and held for 1 hour. The nanoparticles are then placed in a ball milling jar, and 2wt.% of micron-sized yttrium oxide is added as a stabilizer. Anhydrous ethanol is added as the ball milling medium. The ball milling speed is 180 rpm and the ball milling time is 8 hours. The mixture is then ball-milled, dried, sieved, and shaped. Finally, it is cold isostatically pressed at 300MPa and held for 10 minutes to obtain a dense green body.

[0043] S3: Sinter the green blank obtained in step S2 in a vacuum sintering furnace, heating to 1200℃ at a rate of 5℃ / min and sintering for 3 hours, with a vacuum degree not less than 1×10⁻⁶. -3 Pa; then air is introduced and the temperature is lowered to 800℃ at a rate of 5℃ / min for annealing for 1 hour. After cooling, toughened zirconia ceramic can be obtained.

[0044] Comparative Example 2 (The difference between Comparative Example 2 and Example 3 is that the powder is not subjected to cold isostatic pressing after molding in step S2)

[0045] S1: Using 100 parts of zirconium oxychloride octahydrate as raw material, add 100 parts of precipitant with a mass ratio of ammonia water to magnesium hydroxide solution of 2:1; add 300 parts of TEOS solution as silicon source, control the solid content of slurry to 60 vol.%, heat in an 80℃ water bath and react with magnetic stirring for 2 hours, add urea as pH adjuster to control pH to 8.5, precipitate and age for 12 hours, filter the obtained slurry to obtain highly active ZrO2@SiO2 core-shell structured nanopowder;

[0046] S2: The nanoparticles obtained in step S1 are dried and calcined in a vacuum muffle furnace at a rate of 5℃ / min to 400℃ for 2 hours with a vacuum degree of 400Pa. Then, air is introduced and the calcination temperature is increased to 600℃ and held for 1 hour. The nanoparticles are then placed in a ball milling jar, and 4wt.% of micron-sized yttrium oxide is added as a stabilizer. Anhydrous ethanol is added as the ball milling medium. The ball milling speed is 180 rpm and the ball milling time is 8 hours. The mixture is then ball milled, dried, sieved, and shaped to obtain a dense green body.

[0047] S3: Sinter the green blank obtained in step S2 in a vacuum sintering furnace, heating to 1300℃ at a rate of 5℃ / min and sintering for 3 hours, with a vacuum degree not less than 1×10⁻⁶. -3 Pa; then air is introduced and the temperature is lowered to 1100℃ at a rate of 5℃ / min for annealing for 1h. After cooling, toughened zirconia ceramic can be obtained.

[0048] The test results of the toughened zirconia ceramics obtained in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in Table 1. The number of samples used for the bending strength and fracture toughness tests was 10 each.

[0049] Table 1 Performance Tests of Toughened Zirconia Ceramics

[0050] Flexural strength / MPa <![CDATA[Fracture toughness / MPa·m 1 / 2 > Grain size / nm Example 1 1191.7±12.5 5.7±0.3 70～85 Example 2 1213.4±11.0 6.3±0.2 67～77 Example 3 1209.4±9.3 5.5±0.0 77～87 Comparative Example 1 1170.0±10.2 4.0±0.1 300～425 Comparative Example 2 1057.6±13.7 3.7±0.1 150～300

[0051] The test results in Table 1 show that the pH value of the slurry affects various properties of zirconia ceramics. This is because under weakly alkaline conditions, the nanoparticles have smaller particle sizes, more uniform distribution, larger specific surface areas, and higher surface activity, ultimately resulting in a denser sintered body. As the sintering temperature increases, the grain size increases accordingly; therefore, lowering the sintering temperature can effectively reduce the grain size, thereby improving the performance of zirconia ceramics. Simultaneously, the cold isostatic pressing process can further improve the density of the formed green body, effectively enhancing the flexural strength and fracture toughness of zirconia ceramics.

Claims

1. A method for preparing core-shell structured nanopowder-toughened zirconia ceramic, characterized in that, Includes the following steps: S1: Using zirconium oxychloride octahydrate as raw material, ammonia and magnesium hydroxide solution are added as precipitants; TEOS solution is added as a silicon source; the solid content of the slurry is controlled at 30-60 vol.%, heated in a water bath and magnetically stirred, a pH adjuster is added, and after precipitation and aging, the resulting slurry is filtered to obtain highly active ZrO2@SiO2 core-shell structured nanopowder; in step S1, the mass ratio of precipitant to zirconium oxychloride octahydrate is 1:1, the mass ratio of ammonia and magnesium hydroxide solution is 2:1, the mass ratio of TEOS solution to zirconium oxychloride octahydrate is 2:1-3:1, the heating temperature in the water bath is 50-80℃, the stirring time is 2h, the pH adjuster is urea, the pH is controlled at 8.0-9.0, and the precipitation and aging time is 12h; S2: After drying the nanoparticles obtained in step S1, place them in a vacuum muffle furnace for calcination. First, calcine them in a vacuum environment for 1-2 hours, and then calcine them in an air or oxygen atmosphere for 1-2 hours. After calcination, place them in a ball mill jar, add micron-sized yttrium oxide as a stabilizer, add ball milling media, mix and ball mill, dry, sieve, shape, and then perform cold isostatic pressing to obtain a dense green blank. S3: The green blank obtained in step S2 is sintered in a vacuum sintering furnace and air annealed. After cooling, toughened zirconia ceramic is obtained.

2. The method for preparing core-shell structured nanopowder-toughened zirconia ceramic according to claim 1, characterized in that, In step S2, the calcination temperature in the vacuum muffle furnace is 200–400°C, and the vacuum degree is 200–400 Pa; then air or oxygen is introduced to raise the calcination temperature to 600–700°C.

3. The method for preparing core-shell structured nanopowder-toughened zirconia ceramic according to claim 1, characterized in that, In step S2, the amount of micron-sized yttrium oxide added is 2-4 wt.% of the mass of the nanoparticles obtained in step S1.

4. The method for preparing core-shell structured nanopowder-toughened zirconia ceramic according to claim 1, characterized in that, In step S2, the milling medium is anhydrous ethanol; the milling speed is 180–280 rpm; and the milling time is 8–10 h.

5. The method for preparing core-shell structured nanopowder-toughened zirconia ceramic according to claim 1, characterized in that, In step S3, the sintering temperature is 1200–1300℃, the holding time is 3–5 hours, and the vacuum degree is not less than 1×10⁻⁶. -3 Pa; air annealing temperature is 800~1100℃, and holding time is 1~2h.

6. The core-shell structured nanopowder-toughened zirconia ceramic prepared by the preparation method according to any one of claims 1 to 5.

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