Magnesium-stabilized zirconium oxide composite powder and preparation method of ceramic of magnesium-stabilized zirconium oxide composite powder

Abstract

The invention relates to the technical field of ceramic material preparation, in particular to magnesium-stabilized zirconia composite powder and a preparation method of ceramic thereof, and the preparation method of the ceramic comprises the following steps: (1) raw material preparation and sol preparation; (2) gelation reaction; (3) drying the gel; (4) calcining; (5) sanding; (6) spray granulation; (7) forming; and (8) sintering to obtain a finished product. The magnesium-stabilized zirconia powder is prepared by adopting a gel method, and zirconium and magnesium ions are subjected to molecular-level uniform complexing according to the molar ratio of 94.5-96.5: 3.5-5.5 through an organic acid-alcohol gel system, so that the defect of non-uniform mixing of components in a coprecipitation method is overcome, uniform distribution of the components in the final powder is ensured, the crystal phase stability is remarkably improved, and the preparation method has the advantages that the preparation process is simple, the preparation cost is low, and the preparation method is suitable for industrial production. The magnesium-stabilized zirconia ceramic prepared by the invention has the advantages of high bending strength, high density, high tetragonal phase ratio, uniform microstructure, high chemical stability, low raw material cost and the like.

Description

Technical Field

[0001] This application relates to the field of ceramic material preparation technology, and in particular to a method for preparing magnesium-stabilized zirconia composite powder and ceramic thereof. Background Technology

[0002] Zirconia (ZrO2), as a high-performance ceramic material, possesses excellent high-temperature resistance, wear resistance, chemical stability, and good mechanical properties, making it widely used in aerospace, electronics, biomedicine, and energy fields. Zirconia exists in three crystalline phases: monoclinic (m-ZrO2), tetragonal (t-ZrO2), and cubic (c-ZrO2). The monoclinic phase, stable at room temperature, is prone to phase transformation and volume changes during temperature variations, leading to material cracking and performance degradation. Therefore, stabilizers are typically added to zirconium oxide to obtain a room-temperature stable tetragonal or cubic phase structure.

[0003] Commonly used zirconia stabilizers include yttrium oxide (Y₂O₃), magnesium oxide (MgO), and calcium oxide (CaO). While yttrium-stabilized zirconia (YSZ) exhibits excellent thermal stability and mechanical properties, it suffers from higher costs and sintering temperatures. Magnesium-stabilized zirconia (Mg-PSZ), on the other hand, is less expensive and its stability and mechanical properties can be guaranteed through appropriate manufacturing processes, making it widely used in general-purpose ceramics. In acidic media, Mg-stabilized zirconia also demonstrates better stability. Low-yttrium-content YSZ shows a 91.4% loss in flexural strength after 14 days of corrosion in simulated acidic and humid marine environments; even high-yttrium-content YSZ still faces the risk of performance degradation under strong acid or prolonged acidic conditions. In contrast, the magnesium oxide in Mg-PSZ produces a weakly alkaline buffer through slow hydrolysis, gently neutralizing localized acidic media and preventing excessive surface corrosion by strong acids. Simultaneously, its crystalline structure effectively blocks the penetration of acidic molecules, reducing internal corrosion.

[0004] Currently, the main methods for preparing magnesium-stabilized zirconia powder include co-precipitation, combustion synthesis, and gelation. Co-precipitation suffers from poor component mixing uniformity, wide particle size distribution, and significant powder loss during washing. Combustion synthesis results in low product purity and insufficient crystal phase stability. Gelation, through sol-gel conversion, achieves molecular-level uniform mixing of components, effectively overcoming these shortcomings and producing high-quality powder with controllable particle size and uniform composition. However, existing gelation methods for preparing magnesium-stabilized zirconia generally suffer from difficulties in controlling the gelation process, easy cracking during gel drying, and severe powder agglomeration after calcination, limiting their industrial application.

[0005] Therefore, developing a method for preparing magnesium-stabilized zirconia composite powder that is simple in process, low in cost, has uniform composition, and stable performance is of great practical significance. Summary of the Invention

[0006] Based on this, the purpose of this application is to provide a method for preparing magnesium-stabilized zirconia composite powder and its ceramics. This method achieves molecular-level uniform mixing of composite powder components, narrow particle size distribution, and stable crystal phase by optimizing the gelation system, precisely controlling gel conversion conditions, and improving drying and post-treatment processes. Furthermore, the process is simple, low-cost, and easily scalable for industrial mass production.

[0007] The technical solution of this application is as follows: A method for preparing magnesium-stabilized zirconium oxide composite powder includes the following steps: Step (1) Raw material preparation and sol preparation a. Preparation of zirconium-magnesium mixed salt solution: Dissolve zirconium source and magnesium source in deionized water and stir until completely dissolved to obtain zirconium-magnesium mixed salt solution.

[0008] Specifically, the molar ratio of zirconium source to magnesium source is 94.5-96.5∶3.5-5.5, and the total concentration of the mixed salt solution is 0.6-1.2 mol / L; the zirconium source is selected from one or more of zirconium nitrate (Zr(NO3)4·5H2O), zirconium oxychloride (ZrOCl2·8H2O), zirconium sulfate (Zr(SO4)2·4H2O), and zirconium acetate (Zr(CH3COO)4); the magnesium source is selected from one or more of magnesium nitrate (Mg(NO3)2·6H2O), magnesium chloride (MgCl2·6H2O), magnesium sulfate (MgSO4·7H2O), and magnesium acetate ((CH3COO)2Mg·4H2O).

[0009] Furthermore, the optimal zirconium source is zirconium nitrate (Zr(NO3)4·5H2O), and the optimal magnesium source is magnesium nitrate (Mg(NO3)2·6H2O). The optimal molar ratio of the two is 96.5∶3.5, and the optimal total concentration of the mixed salt solution is 0.9 mol / L.

[0010] b. Preparation of gelling solution: Dissolve the complexing agent and crosslinking agent in deionized water and stir until homogeneous to obtain a gelling solution.

[0011] Specifically, the molar ratio of the complexing agent to the crosslinking agent is 1:1.2-2.0, and the concentration of the gelling agent solution is 0.4-0.8 mol / L; the complexing agent is selected from one or more of lactic acid, citric acid, malic acid, tartaric acid, and ethylenediaminetetraacetic acid (EDTA); the crosslinking agent is selected from one or more of glycerol, ethylene glycol, xylitol, and sodium glycerophosphate.

[0012] Furthermore, the optimal complexing agent is lactic acid, the optimal cross-linking agent is glycerol, the optimal molar ratio of the two is 1:1.6, and the optimal concentration of the gelling agent solution is 0.6 mol / L.

[0013] c. Preparation of mixed sol: Slowly add the gelling agent solution dropwise to the zirconium magnesium mixed salt solution while stirring (150-250 r / min). After the addition is complete, add the dispersant and continue stirring for 30-60 min.

[0014] Specifically, the volume ratio of the gelling agent solution to the zirconium-magnesium mixed salt solution is 1:1.8-2.8, and the amount of dispersant used is 0.8-1.8% of the total mass of the zirconium-magnesium mixed salt; the dispersant is selected from one or more of polyethylene glycol 4000 (PEG4000), polyethylene glycol 6000 (PEG6000), sodium polyacrylate (PAAS, molecular weight 2000-5000), sodium dodecylbenzene sulfonate (SDBS), and sodium citrate.

[0015] Furthermore, the optimal volume ratio of the gelling agent solution to the zirconium-magnesium mixed salt solution is 1:2.2, the optimal dispersant is polyethylene glycol 4000 (PEG4000), and its optimal dosage is 1.2% of the total mass of the zirconium-magnesium mixed salt.

[0016] (2) Gelation reaction: The mixed sol was transferred to a constant-temperature reactor with a stirrer and stirred at a constant temperature (50-100 r / min) under a water bath heating condition of 60-80℃ to carry out the gelation reaction. The viscosity of the system was monitored in real time during the reaction. When the viscosity of the system reached 500-800 mPa·s, heating and stirring were stopped, and the system was allowed to stand at room temperature for 12-24 h to obtain a stable magnesium-zirconium composite gel.

[0017] Furthermore, in step (2), the optimal gelation conditions are: water bath temperature 65℃, stirring speed 80 r / min, aging time 18 h, and the final viscosity of the system at the gelation endpoint is 600-650 mPa·s.

[0018] This invention uses an organic acid-alcohol system as a gelling agent. The core of this invention is that the carboxyl group in the organic acid molecule can form a stable complex with zirconium ions and magnesium ions. Alcohols, as crosslinking agents, can undergo esterification with the carboxyl group of the organic acid to gradually build a three-dimensional network structure, laying the foundation for subsequent gelation. Dispersants such as PEG4000 prevent ion aggregation through steric hindrance, thereby improving the uniformity of the sol.

[0019] Key points of operation: ① When dissolving the zirconium-magnesium mixed salt, stirring at room temperature is required to avoid heating, which would cause zirconium oxychloride to hydrolyze and form ZrO(OH)2 precipitate. If slight turbidity occurs, 1-2 drops of concentrated hydrochloric acid can be added to adjust the pH to 2-3 to promote the dissolution of the precipitate; ② When adding the gelling agent solution, it should be slowly added along the vicinity of the stir bar to ensure immediate mixing with the salt solution and avoid excessively high local concentrations of gelling agent that would lead to premature gelation; ③ The dispersant should be added after the gelling agent has been added. At this time, the ions have been initially complexed, and the dispersant can be more evenly adsorbed on the surface of the complexed ions, improving the dispersion effect.

[0020] Gelation is the process by which complexed ions form a three-dimensional network structure through esterification cross-linking. Increasing the temperature can accelerate the esterification reaction rate, but excessively high temperatures can lead to an overly vigorous reaction and a loose gel structure. Excessive stirring speed will destroy the formed network structure, while too low a speed will result in uneven mixing of components. Therefore, it is necessary to precisely control the temperature and stirring speed.

[0021] Key points of operation: ① Viscosity monitoring should be performed using a rotational viscometer. Before each measurement, the viscometer probe should be fully immersed in the sol to avoid air bubbles affecting the measurement results. It is recommended to measure every 15 minutes, and every 5 minutes when approaching the endpoint (viscosity ≥ 400 mPa·s); ② The gelation endpoint is judged by "the viscosity reaches 500-800 mPa·s and the sol can be pulled into threads as a whole". If the viscosity meets the standard but cannot be pulled into threads, stirring should continue for 10-20 minutes; ③ The aging process should be carried out in a sealed container to avoid cracking caused by the evaporation of moisture on the gel surface. The aging temperature should be controlled at 20-25℃ to avoid high temperature accelerating gel degradation.

[0022] If the gel cracks, it may be due to excessively rapid heating or excessively high stirring rate. The heating rate should be reduced to 30-40℃ / h, and the stirring rate adjusted to below 50 r / min. The sol should be prepared again for gelation. If a gel cannot be formed, the amount of gelling agent may be insufficient. The gelling agent solution should be added until the volume ratio of gelling agent to salt solution is ≥1:2.5, and the reaction should continue to be stirred.

[0023] (3) Gel drying: Cut the composite gel into 1-2 cm pieces. 3 The gel block was placed in a vacuum drying oven for segmented drying: first, it was dried at 40-50℃ for 8-12 h, then the temperature was raised to 60-70℃ for 12-16 h, and finally the temperature was raised to 80℃ for 4-6 h. The vacuum degree was controlled at -0.08--0.09 MPa during the drying process. After drying, the dry gel precursor was obtained.

[0024] Furthermore, in step (3), the optimal segmented drying conditions are: drying at 45℃ for 10 h → drying at 65℃ for 14 h → drying at 80℃ for 5 h, with a vacuum degree of -0.085 MPa.

[0025] The core of segmented drying is to gradually remove free and bound water from the gel. In the low-temperature segment (40-50℃), free water is removed first to prevent rapid evaporation and internal stress caused by high temperatures. In the medium-temperature segment (60-70℃), bound water is removed to prepare for subsequent removal of organic components. The high-temperature segment (80℃) further dries the gel, ensuring a moisture content of ≤1%. Vacuum drying lowers the boiling point of water, accelerates evaporation, and reduces oxidation.

[0026] Key points of operation: ① Stainless steel blades must be used for gel cutting, and the cutting size should be uniform (1-2 cm). 3 ① To avoid uneven drying rates due to inconsistent sizes; ② During the drying process, the condensate in the vacuum drying oven needs to be drained periodically to prevent moisture from flowing back to the gel surface; ③ The heating rate should be controlled at 5-10℃ / h, and the temperature should be kept constant for 1-2 hours after each drying stage before proceeding to the next stage.

[0027] If some gels crack or pulverize, it may be due to an excessively rapid heating rate or insufficient vacuum. The heating rate should be reduced to below 5℃ / h, and the vacuum should be increased to -0.085 to -0.09 MPa. If some gels have an excessively high water content (>1%), the final drying time should be extended by 2-3 hours.

[0028] (4) Calcination: The dry gel precursor was placed in a muffle furnace and subjected to a staged heating and calcination process: the temperature was increased to 300-400℃ at a rate of 2-5℃ / min and held for 1-2 h (to remove organic components); then the temperature was increased to 900-1200℃ at a rate of 5-8℃ / min and held for 2-4 h (to crystallize and form); the mixture was then naturally cooled to room temperature to obtain magnesium-stabilized zirconia coarse powder; the specific surface area of ​​the magnesium-stabilized zirconia coarse powder was 5-10 m². 2 / g, and the proportion of tetragonal zirconium oxide is greater than 60%. The high proportion of stable phase can significantly improve the densification efficiency in the subsequent sintering process, ensuring the mechanical properties and thermal stability of ceramic products.

[0029] Pure zirconia exists as a monoclinic phase at room temperature. Heating to approximately 1170°C transforms it into a tetragonal phase, and further heating to 2370°C transforms it into a cubic phase. This transformation is reversible; upon cooling, the tetragonal phase reverts to the monoclinic phase around 1000°C, accompanied by a volume expansion of about 3-5%, which is the cause of cracking. Adding stabilizers such as magnesium oxide ensures that the high-temperature tetragonal or cubic phase remains metastable at room temperature, thus preventing phase transformation and cracking upon cooling. Compared to commonly used yttrium oxide, magnesium oxide has lower solid solubility in zirconia and relatively weaker stabilizing ability. This means that magnesium-stabilized zirconia powder prepared by conventional methods (such as co-precipitation) easily contains a large amount of incompletely stabilized monoclinic phase after calcination. Therefore, commercially available products typically contain around 50% tetragonal phase.

[0030] If the powder is entirely monoclinic (such as the 50% portion found in commercially available products), its sintering activity is low, making densification difficult. Even if a 100% cubic phase powder is forcibly obtained through extremely high-temperature calcination, although the phase is stable, the powder has been over-sintered, resulting in particle size growth and loss of activity (commonly known as "dead burning"), making densification equally difficult. In contrast, the magnesium-stabilized zirconia powder obtained in this application has a tetragonal zirconia phase content greater than 60%, preferably 60-65%. This indicates that the present invention achieves molecular-level uniform mixing through a gelation method, allowing the magnesium oxide stabilizer to function efficiently, stabilizing most of the zirconia in a metastable tetragonal phase with high sintering activity, rather than an inert monoclinic phase. A tetragonal zirconia phase content of 60-65% achieves a perfect balance between high activity and controllability.

[0031] The powder obtained in this application, after calcination, has a composition of 60-65% metastable tetragonal phase and 35-40% highly active monoclinic phase. During the sintering stage, at a high temperature of 1350-1600℃, all the monoclinic phase transforms into the tetragonal phase. At this point, the green body reaches complete density, becoming a 100% tetragonal phase structure. During the cooling stage, slow cooling and holding at key temperature points such as 1200℃ allow sufficient time for magnesium oxide ions to diffuse uniformly in the zirconia lattice. The purpose of this process is not to revert the tetragonal phase back to the monoclinic phase, but to "freeze" the high-temperature tetragonal phase to room temperature, further improving its stability. The final ceramic product aims to be as close as possible to 100% tetragonal phase, or contain a very small amount of cubic phase, but the monoclinic phase content should be extremely low (e.g., <2%) to ensure the best performance of the ceramic. The final ceramic product has a high tetragonal phase content (>98%).

[0032] Furthermore, in step (4), the optimal calcination conditions are: heating at 2℃ / min to 350℃ and holding for 1.5 h, then heating at 6℃ / min to 1100℃ and holding for 3 h. At this time, the stable phase content in the obtained powder is 65%, which is beneficial for subsequent sintering.

[0033] Segmented heating and calcination can avoid the rapid decomposition of organic components (such as citric acid, ethylene glycol, PEG4000) in the dry gel caused by a single high temperature, which would generate a large amount of gas, causing powder agglomeration or structural damage. The low temperature segment (300-400℃) mainly removes organic components, while the high temperature segment (900-1200℃) achieves crystallization and forms stable tetragonal zirconia.

[0034] Key points of operation: ① Before calcination, the dry gel precursor should be evenly spread in the alumina crucible with a thickness of ≤2cm to avoid uneven local temperature caused by excessive stacking; ② During the low-temperature holding process, the gas should be discharged through the muffle furnace's own exhaust valve or by connecting to the external ventilation system to facilitate the discharge of gases generated by the decomposition of organic components; ③ The heating rate in the high-temperature section should be controlled at 5-8℃ / min to avoid insufficient phase transformation due to excessive heating. The holding time should be adjusted according to the amount of powder. For every 5 kg increase in powder amount, the holding time should be extended by 0.5 h.

[0035] If the powder exhibits severe agglomeration after calcination, it may be due to an excessively rapid heating rate in the high-temperature section or insufficient holding time. The heating rate should be reduced to below 5℃ / min, and the holding time extended by 1-2 hours. If the powder has an impure crystalline phase (including monoclinic phase), it may be due to insufficient calcination temperature. The high-temperature section temperature should be increased by 50-100℃, and the holding time extended by 1 hour.

[0036] (5) Sanding: Magnesium-stabilized zirconia coarse powder is added to a sand mill, with deionized water as the dispersion medium, and a grinding dispersant (0.5-1.5% of the mass of coarse powder) is added. Grinding media are added, and the mass ratio of grinding media (zirconia beads, particle size 0.1-0.5 mm) to coarse powder is controlled at 5-8:1. The sand milling speed is 2000-3000 r / min, and the sand milling time is 1-3 h. After sand milling, the grinding media is removed by centrifugation to obtain magnesium-stabilized zirconia slurry. Further, in step (5), the grinding dispersant is one or more of ammonium polyacrylate (NH4-PAA), ammonium polymethacrylate, sodium hexametaphosphate, and sodium pyrophosphate. It is suitable for water-based sand milling of nano / micron-sized zirconia. Among them, ammonium polyacrylate is one of the optimal choices, with a molecular weight of 1000–5000 Da. The addition amount is 1.0% of the powder mass, and the solid content of the slurry after sand milling can be increased to over 60%, with excellent sedimentation stability. The mass ratio of the sand milling media to the coarse powder is 6:1, the sand milling speed is 2500 r / min, the sand milling time is 2 h, and the sand milling media are 0.3 mm zirconia beads.

[0037] The sand mill refines coarse powder to the target particle size (80-200nm) through the high-speed impact and grinding action of zirconia beads; the grinding dispersant ammonium polyacrylate can be adsorbed on the powder surface and prevent the agglomeration of refined powder through steric hindrance effect; deionized water is used as a dispersion medium to reduce grinding resistance and improve grinding efficiency.

[0038] Key operating points: ① Before sand milling, the coarse powder must be mixed evenly with the dispersing medium and dispersant to form a slurry with a solid content of 30-40% to avoid uneven grinding caused by directly adding dry powder to the sand mill; ② High-purity zirconia beads (purity ≥99.9%) must be used as the sand milling medium to avoid contamination by impurities; ③ The slurry temperature must be monitored during sand milling and controlled between 30-50℃. If the temperature is too high (>50℃), sand milling must be stopped and continued after the slurry cools down.

[0039] If the particle size distribution of the powder after sand milling is too wide (>200 nm), it may be due to insufficient sand milling time or insufficient amount of medium. The sand milling time needs to be extended by 1-2 hours, and zirconium oxide beads need to be added to make the mass ratio of medium to coarse powder 6-8:1. If the slurry separates, it may be due to insufficient amount of dispersant. 0.3-0.5% of ammonium polyacrylate needs to be added, and sand milling should continue for 30 minutes.

[0040] If the mixed sol shows stratification, it indicates that the stirring rate is insufficient or the amount of dispersant is insufficient. It is necessary to add 0.2-0.3% of ammonium polyacrylate and increase the stirring speed to 300 r / min, and continue stirring for 30 min. If a large amount of precipitation occurs in the sol, it may be that the salt solution concentration is too high or the pH is abnormal. It is necessary to dilute the salt solution to a total concentration ≤1.2 mol / L and adjust the pH to 2-4.

[0041] Detection methods: ① Concentration detection of mixed salt solution: Using the gravimetric method, accurately transfer 10 mL of mixed salt solution into a pre-weighed crucible, dry it at 105℃ to constant weight, calculate the mass of the residue, and then obtain the total concentration of the solution; ② Sol uniformity detection: Using a laser particle size analyzer, take a small amount of mixed sol, dilute it, and test the particle size distribution. If the particle size distribution span ((D90-D10) / D50) ≤ 1.0, it can be judged as having a narrow distribution and good uniformity; ③ pH value detection: Using a precision pH meter (accuracy 0.01), calibrate it with standard buffer solutions (pH=2.00, 4.00) before measurement, and directly insert it into the sol to read the value.

[0042] (6) Spray granulation: The milled magnesium-stabilized zirconium oxide slurry is pumped into a spray dryer for spray granulation. The inlet air temperature is controlled at 180-220℃, the outlet air temperature at 80-100℃, the feed rate at 10-30 kg / h, and the atomization pressure at 0.3-0.6 MPa. After granulation, well-flowing magnesium-stabilized zirconium oxide particles are obtained, with a particle size of 50-200 μm and a loose packing density of 1.3-1.8 g / cm³. 3 .

[0043] Further, in step (6), the optimal spray granulation parameters are: inlet air temperature 200℃, outlet air temperature 90℃, feed rate 20 kg / h, and atomization pressure 0.4 MPa; the optimal granulated particle size is 80-150 μm, and the loose packing density is 1.3-1.5 g / cm³. 3 .

[0044] Spray granulation disperses the slurry after sand milling into tiny droplets through an atomizer. The moisture evaporates rapidly in a hot air stream, causing the powder particles to agglomerate and form spherical particles with good flowability. This process can solve the problems of easy agglomeration and poor flowability of powder after sand milling, providing high-quality raw materials for subsequent molding processes. The inlet air temperature, outlet air temperature, and atomization pressure directly affect the morphology and density of the particles. If the temperature is too high, the particle surface will easily melt and form a shell. If the temperature is too low, the moisture will not evaporate sufficiently, and the particles will easily break.

[0045] Key operating points: ① Before spray granulation, the solid content of the slurry after sand milling needs to be adjusted to 35-40%. Too low a solid content will result in low granulation efficiency and low particle density, while too high a solid content will result in high slurry viscosity, which will easily clog the atomizer; ② The atomizer needs to be preheated to 80-100℃ in advance to avoid the slurry from solidifying instantly due to a cold atomizer, which will affect the atomization effect; ③ During the drying process, the inlet and outlet air temperatures need to be kept stable with a fluctuation range of ≤±5℃. At the same time, the residual powder on the inner wall of the drying tower should be cleaned regularly to avoid cross-contamination.

[0046] If the particle size after granulation is too small (<50 μm), it indicates that the atomization pressure is too high or the feeding rate is too slow. The atomization pressure needs to be reduced to 0.3-0.4 MPa or the feeding rate needs to be increased to 25-30 kg / h. If the particle size is too large (>200 μm), it indicates that the atomization pressure is too low or the feeding rate is too fast. The atomization pressure needs to be increased to 0.5-0.6 MPa or the feeding rate needs to be reduced to 10-15 kg / h. If the particle flowability is poor (angle of repose >35°), it indicates that the outlet air temperature is too low and there is too much residual moisture. The outlet air temperature needs to be increased to 95-100℃ and the drying time needs to be extended.

[0047] Testing methods: ① Particle size detection: Using a laser particle size analyzer, the granulated particles are dispersed in anhydrous ethanol, and the particle size distribution is tested and the D50 particle size is recorded; ② Loose packing density detection: Using the volumetric method, 50 g of granulated particles are accurately weighed and poured into a graduated cylinder of known volume. The graduated cylinder is gently tapped until the particle volume stabilizes, and the loose packing density is calculated; ③ Moisture content detection: Using the oven drying method, 2 g of granulated particles are accurately weighed and dried in an oven at 110℃ for 2 h. The mass loss rate is calculated to ensure that the moisture content is ≤0.5%.

[0048] A method for preparing magnesium-stabilized zirconia ceramic further includes the following steps: (7) Molding: Magnesium-stabilized zirconia particles after spray granulation are added to a molding die, and a green body is prepared by dry pressing or isostatic pressing. The dry pressing pressure is 80-150 MPa and the holding time is 10-30 s. The isostatic pressing pressure is 200-300 MPa and the holding time is 2-5 min. The relative density of the green body after molding is ≥65%.

[0049] Furthermore, in step (7), the optimal molding process is isostatic pressing with a molding pressure of 250 MPa and a holding time of 3 min; the relative density of the blank after optimal molding is ≥70%.

[0050] Molding is the process of using external force to make granulated particles compactly stacked to form a green body with a certain shape and strength. External force can overcome the gaps and friction between particles and increase the density of the green body. Dry pressing is suitable for preparing green bodies with simple shapes and is a simple and efficient process. Isostatic pressing can make the green body be subjected to uniform stress in all directions and have a more uniform density distribution, making it suitable for preparing green bodies with complex shapes or high performance requirements.

[0051] Key points of operation: ① Before molding, the granulated particles should be passed through an 80-mesh sieve to remove large agglomerates and avoid affecting the uniformity of the green body; ② During dry pressing, a small amount of zinc stearate release agent should be applied to the inner wall of the mold to prevent the green body from sticking to the mold; during isostatic pressing, the particles should be loaded into an elastic mold to expel air from the mold and prevent air holes from appearing in the green body after molding; ③ The molding pressure should be gradually increased. The pressure increase rate for dry pressing is 20-30 MPa / s, and the pressure increase rate for isostatic pressing is 50-100 MPa / min to avoid cracking of the green body due to a sudden increase in pressure.

[0052] If cracks appear in the green body after molding, it may be due to excessively rapid pressure increase or excessively high particle moisture content. The pressure increase rate needs to be reduced or the particles need to be re-dried (drying at 110℃ for 2 hours). If the green body density is too low (<55%), it indicates that the molding pressure is insufficient or the holding time is too short. The molding pressure needs to be increased by 20-50 MPa or the holding time needs to be extended by 10-20 s (dry pressing) / 1-2 min (isostatic pressing). If the surface of the green body is uneven, it indicates that the particle size distribution of the granulated particles is too wide. The slurry particle size needs to be adjusted by re-grinding before spray granulation.

[0053] Testing methods: ① Relative density test of billet: The water displacement method is used to accurately weigh the dry weight, water weight, and weight after saturation water absorption of the billet, and calculate the relative density; ② Strength test of billet: A compressive strength tester (model: WDW-100) is used, and a cylindrical billet (diameter 10 mm, height 20 mm) is selected. The compressive strength test is carried out at a rate of 2 mm / min to ensure that the compressive strength of the billet is ≥2 MPa; ③ Dimensional accuracy test of billet: A digital display vernier caliper (accuracy 0.01 mm) is used to measure the key dimensions of the billet, and the error is controlled within ±0.1 mm.

[0054] (8) Sintering: The shaped green body is placed in a high-temperature sintering furnace for sintering to finally obtain magnesium-stabilized zirconia ceramic products; the ceramic products have a relative density ≥96% and a bending strength ≥600 MPa, and the high-performance products have a relative density ≥97% and a bending strength ≥800 MPa.

[0055] Further, in step (8), the optimal sintering conditions are: heating to 700℃ at 3℃ / min and holding for 1.5 h, then heating to 1500℃ at 3℃ / min and holding for 3 h; the relative density of the ceramic product after optimal sintering is ≥98%, and the bending strength is ≥800 MPa.

[0056] By adjusting sintering process parameters (such as high-temperature densification temperature), this invention can flexibly prepare general-purpose (sintered at 1400-1450℃) or high-performance (sintered at 1550-1600℃) products to meet the needs of different application scenarios.

[0057] The sintering process in step (8) is as follows: ① Preheating and impurity removal stage: Heat to 200℃ at a rate of 2℃ / min and hold for 30 min to remove free moisture adsorbed on the surface of the green body; continue to heat to 400℃ at a rate of 2℃ / min and hold for 1 h to preliminarily decompose the low-boiling-point organic impurities (such as small molecule fragments of dispersant that have not been completely removed) remaining in the green body, thereby preventing cracking and internal defects in the green body. ②Deep impurity removal stage: Heat to 600-800℃ at 3℃ / min and hold for 1-2 hours to deeply remove residual high-boiling-point organic components and adsorbed impurities in the green body, so as to avoid the presence of pores or crystal phase defects in the sintered product due to the residue of impurities. ③ Low-temperature sintering neck formation stage: Heat to 1100-1200℃ at a heating rate of 2-3℃ / min, hold for 1-1.5h to promote initial contact between particles and form a stable sintering neck, and inhibit abnormal particle growth. ④ Medium-temperature densification stage: Heat to 1350-1450℃ at a heating rate of 1.5-2℃ / min, hold for 1.5-2 h to accelerate atomic diffusion and promote the growth of sintering neck and pore closure. ⑤ High-temperature densification stage: Heat to 1400-1600℃ at a rate of 1℃ / min (precisely controlled according to the performance requirements of the product; 1550-1600℃ for high-performance products and 1400-1450℃ for general-purpose products), and hold for 2-4 hours; In this stage, the high temperature achieves full densification between particles, while promoting the uniform diffusion of magnesium ions in the zirconia lattice, further increasing the proportion of the tetragonal stable phase. ⑥ Gradient Cooling Stage: After sintering, the temperature is lowered to 1200℃ at a rate of 2℃ / min and held for 1 hour to release internal thermal stress; then lowered to 800℃ at a rate of 3℃ / min and held for 1 hour to stabilize the crystal structure; finally, the temperature is lowered to 400℃ at a rate of 5℃ / min and allowed to cool naturally to room temperature. Gradient cooling effectively releases thermal stress, prevents product cracking, stabilizes the crystal structure, and prevents phase transformation cracking.

[0058] The "multi-stage heating-gradient cooling" synergistic sintering process employed in this invention is fundamentally optimized through precise temperature parameter control, achieving a complete process from "precise impurity removal to orderly growth of the sintering neck, thorough densification, and stable crystal phase control." Multi-stage slow heating (preheating → impurity removal → sintering neck formation → densification) avoids rapid temperature increases that could lead to intense thermal stress and pore expansion within the green body, ensuring structural integrity. Gradient cooling releases thermal stress through segmented heat preservation, preventing rapid cooling that could cause phase transformation and product cracking, further stabilizing the tetragonal phase structure. The heating rate must be matched to the processes of impurity decomposition, phase transformation, and atomic diffusion to ensure sufficient reaction at each stage, achieving simultaneous improvement in densification and crystal phase stability. Ultimately, high-density (≥96%), high-strength (≥700 MPa), stable crystal phase (high tetragonal phase content), crack-free, and uniformly structured high-quality magnesium-stabilized zirconia ceramics are obtained.

[0059] Key operating points: ① Before sintering, the green bodies should be evenly placed in the alumina crucible, with a gap of ≥5 mm between them to prevent sticking during sintering; use alumina ceramic gaskets to support the green bodies, and apply a small amount of zirconia slurry (20% solid content) to the contact area between the gaskets and the green bodies to further prevent sticking; ② The heating rate should be precisely controlled by a programmable temperature controller. Each heating stage should be kept at a constant temperature for 10 minutes before continuing heating, ensuring the furnace temperature is uniform; ③ During the gradient cooling stage, the furnace temperature change should be monitored in real time. The cooling rate should be controlled by adjusting the water temperature and flow rate of the furnace cooling water pipes, ensuring a deviation from the set rate of ≤±0.3℃ / min; ④ During sintering, the furnace temperature data should be recorded in real time to form a sintering process curve, facilitating subsequent process optimization and quality traceability.

[0060] ① If carbon residue (black spots) appears on the surface of the sintered product, it indicates insufficient deep impurity removal. The holding time for the deep impurity removal stage needs to be extended to 2-2.5 h, or the impurity removal temperature increased by 50-100℃. ② If a large number of pores appear inside the product (density <95%), it may be due to an excessively rapid heating rate during the medium / high temperature densification stage. The heating rate needs to be reduced to 1-1.5℃ / min, or the high-temperature densification holding time extended by 1-2 h. ③ If the product exhibits uneven crystal phase (tetragonal phase <98%), it indicates insufficient high-temperature densification temperature or insufficient holding time. The high-temperature section temperature needs to be increased by 50-80℃, and the holding time extended by 1-2 h. Simultaneously, the gradient cooling parameters should be optimized, extending the holding time at 1200℃ to 1.5 h. ④ If cracks appear in the product, it is mostly due to an excessively rapid cooling rate or insufficient thermal stress release. A 1-h holding platform needs to be added at 800℃ and 400℃ respectively, and the cooling rate reduced to 2-3℃ / min. ⑤ If the products stick together, it indicates that the zirconia slurry applied to the support pad is insufficient or the sintering temperature is too high. It is necessary to apply more zirconia slurry and reduce the high-temperature densification temperature by 30-50℃.

[0061] Testing methods: ① Relative density test: using the drainage method, the same relative density test method as the green body; ② Bending strength test: using a three-point bending test, the sample size is 3 mm × 4 mm × 36 mm, the span is 30 mm, and the loading rate is 0.5 mm / min; ③ Crystal phase structure test: using an X-ray diffractometer, Cu Kα radiation, scanning range 2θ=20°-90°, to confirm that the crystal phase is a single tetragonal zirconia phase; ④ Microstructure test: using a scanning electron microscope to observe the cross-sectional microstructure of the product to ensure uniform grains and no obvious pores or cracks.

[0062] Compared with the prior art, this application has the following advantages and positive effects: 1. This invention uses a gel method to prepare magnesium-stabilized zirconium oxide powder. The organic acid-alcohol gel system achieves molecular-level uniform complexation of zirconium and magnesium ions, which solves the defect of uneven component mixing in the co-precipitation method. This ensures that zirconium oxide (96.5%) and magnesium oxide (3.5%) are uniformly distributed in the final powder, and the crystal phase stability is significantly improved.

[0063] 2. This invention precisely controls the temperature, stirring rate, and final viscosity during the gelation process. Combined with a segmented aging process, it avoids gel cracking and delamination, ensuring the stability of the gel structure. The segmented drying process can slowly remove moisture and organic components from the gel, further reducing dry gel cracking and improving the integrity of the precursor.

[0064] 3. A segmented heating and calcination process is adopted, first removing organic impurities at low temperature and then crystallizing and shaping at high temperature, avoiding powder agglomeration and crystal phase defects caused by one-time high-temperature calcination. The product is a single stable tetragonal phase zirconia with good crystallinity.

[0065] 4. Using magnesium oxide as a stabilizer avoids the introduction of rare earth elements, significantly reducing raw material costs; the process does not require high-temperature and high-pressure equipment, the reaction conditions are mild, and the gelation and subsequent processing steps are easy to scale up industrially, making it suitable for large-scale production.

[0066] 5. By combining sand milling process to further refine the powder particle size, the product has a narrow particle size distribution (80-200 nm), good powder dispersibility, and excellent subsequent sintering and molding performance, and can be directly used to prepare high-performance magnesium-stabilized zirconia ceramic devices.

[0067] 6. The magnesium-stabilized zirconia ceramic prepared by this invention has the advantages of high flexural strength, high density, high tetragonal phase ratio, uniform microstructure, high chemical stability (especially in acidic environments), and low raw material cost, making it suitable for large-scale production and application. Attached Figure Description

[0068] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0069] Figure 1 The image shows the XRD pattern of the magnesium-stabilized zirconium oxide powder prepared in Example 3.

[0070] Figure 2 The image shows the XRD pattern of the magnesium-stabilized zirconia ceramic prepared in Example 3.

[0071] Figure 3 This is a SEM image of the fracture surface of the magnesium-stabilized zirconia ceramic prepared in Example 3. Detailed Implementation

[0072] The present application is further described below with reference to embodiments and examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Furthermore, it should be understood that after reading the teachings of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the protection scope of the appended claims.

[0073] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0074] The term “and / or” as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, wherein any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items.

[0075] In this application, terms such as "further" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0076] In this application, terms such as "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0077] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0078] In this application, unless otherwise specified, the numerical intervals (i.e., numerical ranges) involved are considered continuous within the aforementioned numerical intervals, and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges may be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0079] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range controlled by the instrument.

[0080] In this application, weight can be a well-known unit of mass in the pharmaceutical, health product, or food industry, such as μg, mg, g, or kg.

[0081] Example 1 The preparation method of magnesium-stabilized zirconium oxide composite powder according to this embodiment includes the following steps: Step (1) Raw material preparation and sol preparation a. Preparation of zirconium-magnesium mixed salt solution: Dissolve zirconium source and magnesium source in deionized water and stir until completely dissolved to obtain zirconium-magnesium mixed salt solution.

[0082] The molar ratio of zirconium source to magnesium source is 94.5:5.5, and the total concentration of the mixed salt solution is 0.7 mol / L; the zirconium source is zirconium oxychloride (ZrOCl2·8H2O); the magnesium source is magnesium chloride (MgCl2·6H2O).

[0083] b. Preparation of gelling solution: Dissolve the complexing agent and crosslinking agent in deionized water and stir until homogeneous to obtain a gelling solution.

[0084] The molar ratio of the complexing agent to the crosslinking agent is 1:1.3, and the concentration of the gelling agent solution is 0.5 mol / L; the complexing agent is citric acid; and the crosslinking agent is ethylene glycol.

[0085] c. Preparation of the mixed sol: The gelling agent solution is slowly added dropwise to the zirconium-magnesium mixed salt solution at a volume ratio of 1:2, while stirring (160 r / min). After the addition is complete, a dispersant is added at a rate of 1.0% of the total mass of the zirconium-magnesium mixed salt solution, and stirring is continued for 60 min. The dispersant is polyethylene glycol 6000 (PEG6000).

[0086] (2) Gelation reaction: The mixed sol was transferred to a constant temperature reactor with a stirrer and stirred at a constant temperature (100 r / min) under a water bath heating condition at 60℃ to carry out the gelation reaction. The viscosity of the system was monitored in real time during the reaction. When the viscosity of the system reached 550 mPa·s, heating and stirring were stopped, and the system was allowed to stand at room temperature for 24 h to obtain a stable magnesium-zirconium composite gel.

[0087] (3) Gel drying: Cut the composite gel into 1-2 cm pieces. 3 The gel block was placed in a vacuum drying oven for segmented drying: first dried at 40℃ for 12 h, then heated to 60℃ for 16 h, and finally heated to 80℃ for 4 h. The vacuum degree was controlled at -0.09 MPa during the drying process. After drying, a dry gel precursor was obtained.

[0088] (4) Calcination: The dry gel precursor was placed in a muffle furnace and subjected to a segmented calcination process: the temperature was increased to 300°C at a rate of 5°C / min and held for 2 hours (to remove organic components); then the temperature was increased to 1000°C at a rate of 8°C / min and held for 2 hours (to crystallize and form); the mixture was then naturally cooled to room temperature to obtain magnesium-stabilized zirconia coarse powder; the specific surface area of ​​the magnesium-stabilized zirconia coarse powder was 5 m². 2 / g, and the tetragonal zirconium oxide accounts for 60%. The high proportion of stable phase can significantly improve the densification efficiency in the subsequent sintering process, ensuring the mechanical properties and thermal stability of ceramic products.

[0089] (5) Sanding: Magnesium-stabilized zirconia coarse powder was added to a sand mill, with deionized water as the dispersion medium. A grinding dispersant (0.6% of the mass of the coarse powder) was added, and grinding media was added. The mass ratio of the grinding media (zirconia beads, 0.3 mm in diameter) to the coarse powder was controlled at 5:1. The sand milling speed was 2000 r / min, and the sand milling time was 3 h. After sand milling, the grinding media was removed by centrifugation to obtain magnesium-stabilized zirconia slurry. The grinding dispersant was polymethyl methacrylate ammonium salt.

[0090] (6) Spray granulation: The milled magnesium-stabilized zirconia slurry was pumped into a spray dryer for spray granulation. The inlet air temperature was controlled at 180℃, the outlet air temperature at 80℃, the feed rate at 10 kg / h, and the atomization pressure at 0.3 MPa. After granulation, magnesium-stabilized zirconia particles with good flowability were obtained, with a particle size of 80-100 μm and a loose packing density of 1.3 g / cm³. 3 .

[0091] The method for preparing magnesium-stabilized zirconia ceramics in this embodiment further includes the following steps: (7) Molding: Magnesium-stabilized zirconium oxide particles after spray granulation were added into a molding die, and a green body was prepared by dry pressing or isostatic pressing. The dry pressing pressure was 100 MPa and the holding time was 20 s. The relative density of the green body after molding was 65%.

[0092] (8) Sintering: The sintering process in step (8) is as follows: ① Preheating and impurity removal stage: Heat to 200℃ at a heating rate of 2℃ / min, hold for 30 min to remove free moisture adsorbed on the surface of the billet; continue to heat to 400℃ at a rate of 2℃ / min, and hold for 1 h. ② Deep impurity removal stage: Increase the temperature to 600℃ at 3℃ / min and hold for 2 hours. ③ Low-temperature sintering neck formation stage: Heat to 1200℃ at a heating rate of 2℃ / min and hold for 1-h. ④ Medium-temperature densification stage: Heat to 1350℃ at a heating rate of 1.5℃ / min and hold for 2 hours.

[0093] ⑤ High-temperature densification stage: Heat to 1400℃ at a heating rate of 1℃ / min and hold for 4 hours. ⑥ Gradient cooling stage: After sintering, the temperature is reduced to 1200℃ at a rate of 2℃ / min and held for 1 h to release the internal thermal stress of the product; then the temperature is reduced to 800℃ at a rate of 3℃ / min and held for 1 h to stabilize the crystal phase structure; then the temperature is reduced to 400℃ at a rate of 5℃ / min and allowed to cool naturally to room temperature.

[0094] The shaped green body is placed in a high-temperature sintering furnace for sintering, and finally magnesium-stabilized zirconia ceramic products are obtained; the ceramic products have a relative density of 96% and a bending strength of 600 MPa.

[0095] Example 2 The difference between this embodiment and Embodiment 1 is that: In step (1)a, the molar ratio of zirconium source to magnesium source is 95:5, and the total concentration of the mixed salt solution is 0.9 mol / L; the zirconium source is zirconium sulfate (Zr(SO4)2·4H2O); the magnesium source is magnesium sulfate (MgSO4·7H2O).

[0096] In step (1)b, the molar ratio of the complexing agent to the crosslinking agent is 1:1.5, and the concentration of the gelling agent solution is 0.7 mol / L; the complexing agent is ethylenediaminetetraacetic acid (EDTA); and the crosslinking agent is sodium glycerophosphate.

[0097] In step (1)c, the volume ratio of the gelling agent solution to the zirconium-magnesium mixed salt solution is 1:2.5, the stirring speed is 180 r / min, the amount of dispersant is 1.5% of the total mass of the zirconium-magnesium mixed salt, and stirring is continued for 40 min. The dispersant is sodium polyacrylate (PAAS, molecular weight 2000-5000).

[0098] (2) During the gelation reaction, the water bath temperature was 70℃, the stirring speed was 70 r / min, the aging time was 16 hh, and the final viscosity of the system at the gelation endpoint was 600 mPa·s.

[0099] (3) During gel drying, the segmented drying conditions are: 45℃ drying for 9 h → 65℃ drying for 13 h → 80℃ drying for 5 h, with a vacuum degree of -0.085 MPa.

[0100] (4) Calcination: The calcination conditions are as follows: heat up to 350℃ at 4℃ / min and hold for 1-2 h, then heat up to 1100℃ at 7℃ / min and hold for 3 h. At this time, the content of stable phase in the obtained powder is 62%, and the specific surface area of ​​magnesium-stabilized zirconia coarse powder is 6m². 2 / g.

[0101] (5) In the sand milling, the amount of grinding dispersant is 0.8% of the mass of coarse powder, the mass ratio of sand milling medium to coarse powder is controlled at 7:1, the sand milling speed is 2500 r / min, and the sand milling time is 2 h; the grinding dispersant is sodium hexametaphosphate.

[0102] (6) In spray granulation, the inlet air temperature is controlled at 210℃, the outlet air temperature at 90℃, the feed rate at 20 kg / h, and the atomization pressure at 0.4 MPa; the resulting magnesium-stabilized zirconium oxide particles have a particle size of 90-110 μm and a loose packing density of 1.4 g / cm³. 3 .

[0103] The method for preparing magnesium-stabilized zirconia ceramics in this embodiment further includes the following steps: (7) Molding: The dry pressing pressure is 120 MPa and the holding time is 25 s; the relative density of the blank after molding is 68%.

[0104] (8) Sintering: Deep impurity removal stage: heating to 700℃ at a rate of 3℃ / min and holding for 1.5 h. Low-temperature sintering neck formation stage: heating to 1150℃ at a rate of 3℃ / min and holding for 1.5 h. Medium-temperature densification stage: heating to 1400℃ at a rate of 2℃ / min and holding for 1.5 h. High-temperature densification stage: heating to 1450℃ at a rate of 1℃ / min and holding for 3 h. The ceramic product has a relative density of 97% and a flexural strength of 700 MPa.

[0105] The rest of the content of this embodiment is the same as that of Embodiment 1, and will not be repeated here.

[0106] Example 3 The difference between this embodiment and Embodiment 1 is that: In step (1)a, the molar ratio of zirconium source to magnesium source is 96.5:3.5, and the total concentration of the mixed salt solution is 0.9 mol / L; the zirconium source is zirconium nitrate (Zr(NO3)4·5H2O); the magnesium source is magnesium nitrate (Mg(NO3)2·6H2O).

[0107] In step (1)b, the molar ratio of complexing agent to crosslinking agent is 1:1.6, and the concentration of gelling agent solution is 0.6 mol / L; the complexing agent is lactic acid; and the crosslinking agent is glycerol.

[0108] In step (1)c, the volume ratio of the gelling agent solution to the zirconium-magnesium mixed salt solution is 1:2.2, the stirring speed is 200 r / min, the amount of dispersant is 1.2% of the total mass of the zirconium-magnesium mixed salt, and stirring is continued for 50 min. The dispersant is polyethylene glycol 4000 (PEG4000).

[0109] (2) During the gelation reaction, the water bath temperature was 65℃, the stirring speed was 80 r / min, the aging time was 18 hh, and the final viscosity of the system at the gelation endpoint was 650 mPa·s.

[0110] (3) During gel drying, the segmented drying conditions are: 45℃ drying for 10 h → 65℃ drying for 14 h → 80℃ drying for 5 h, with a vacuum degree of -0.085 MPa.

[0111] (4) Calcination: The calcination conditions were as follows: heating at 2℃ / min to 350℃ and holding for 1.5 h, then heating at 6℃ / min to 1100℃ and holding for 3 h. At this time, the stable phase content in the obtained powder was 65%, and the specific surface area of ​​the magnesium-stabilized zirconia coarse powder was 8m². 2 / g.

[0112] (5) In the sand milling, the amount of grinding dispersant is 1.0% of the mass of coarse powder, the mass ratio of sand milling medium to coarse powder is controlled at 6:1, the sand milling speed is 2500 r / min, and the sand milling time is 2 h; the grinding dispersant is ammonium polyacrylate (NH4-PAA) with a molecular weight of 1000–5000 Da.

[0113] (6) In spray granulation, the inlet air temperature is controlled at 200℃, the outlet air temperature at 90℃, the feed rate at 20 kg / h, and the atomization pressure at 0.4 MPa; the resulting magnesium-stabilized zirconium oxide particles have a particle size of 130-150 μm and a loose packing density of 1.5 g / cm³. 3 .

[0114] The method for preparing magnesium-stabilized zirconia ceramics in this embodiment further includes the following steps: (7) Molding: The isostatic pressing pressure is 250MPa, and the holding time is 3min; the relative density of the blank after molding is 73%.

[0115] (8) Sintering: Deep impurity removal stage: heating to 700℃ at a rate of 3℃ / min and holding for 1.5 h. Low-temperature sintering neck formation stage: heating to 1200℃ at a rate of 3℃ / min and holding for 1.5 h. Medium-temperature densification stage: heating to 1450℃ at a rate of 2℃ / min and holding for 1.5 h. High-temperature densification stage: heating to 1560℃ at a rate of 1℃ / min and holding for 3 h. The ceramic product has a relative density of 98.5% and a flexural strength of 850 MPa.

[0116] The rest of the content of this embodiment is the same as that of Embodiment 1, and will not be repeated here.

[0117] Example 4 The difference between this embodiment and Embodiment 1 is that: In step (1)a, the molar ratio of zirconium source to magnesium source is 996.5:3.5, and the total concentration of the mixed salt solution is 1.0 mol / L; the zirconium source is a mixture of zirconium nitrate (Zr(NO3)4·5H2O) and zirconium acetate (Zr(CH3COO)4) in a 2:1 ratio; the magnesium source is a mixture of magnesium nitrate (Mg(NO3)2·6H2O) and magnesium acetate ((CH3COO)2Mg·4H2O) in a 2:1 ratio.

[0118] In step (1)b, the molar ratio of complexing agent to crosslinking agent is 1:1.8, and the concentration of gelling agent solution is 0.8 mol / L; the complexing agent is a mixture of lactic acid and tartaric acid in a 3:1 ratio; the crosslinking agent is a mixture of glycerol and xylitol in a 3:1 ratio.

[0119] In step (1)c, the volume ratio of the gelling agent solution to the zirconium-magnesium mixed salt solution is 1:2.5, the stirring speed is 230 r / min, the amount of dispersant used is 1.8% of the total mass of the zirconium-magnesium mixed salt, and stirring is continued for 30 min. The dispersant is a mixture of polyethylene glycol 4000 (PEG4000), sodium dodecylbenzenesulfonate (SDBS), and sodium citrate in a ratio of 2:1:1.

[0120] (2) During the gelation reaction, the water bath temperature was 75℃, the stirring speed was 60 r / min, the aging time was 13hh, and the final viscosity of the system at the gelation endpoint was 800 mPa·s.

[0121] (3) During gel drying, the segmented drying conditions are: 50℃ drying for 8h → 70℃ drying for 12h → 80℃ drying for 6h, with a vacuum degree of -0.08 MPa.

[0122] (4) Calcination: The calcination conditions were as follows: heating at 3℃ / min to 400℃ and holding for 1 h, then heating at 5℃ / min to 1200℃ and holding for 2 h. At this time, the content of stable phase in the obtained powder was 63%, and the specific surface area of ​​magnesium-stabilized zirconia coarse powder was 9m². 2 / g.

[0123] (5) In the sand milling, the amount of grinding dispersant is 1.2% of the mass of coarse powder, the mass ratio of sand milling media to coarse powder is controlled at 8:1, the sand milling speed is 3000 r / min, and the sand milling time is 1 h; The grinding and dispersing agent is a mixture of ammonium polyacrylate (NH4-PAA) and sodium pyrophosphate in a 3:2 ratio.

[0124] (6) In spray granulation, the inlet air temperature is controlled at 220℃, the outlet air temperature at 100℃, the feed rate at 30 kg / h, and the atomization pressure at 0.6 MPa; the resulting magnesium-stabilized zirconium oxide particles have a particle size of 150-180 μm and a loose packing density of 1.6 g / cm³. 3 .

[0125] The method for preparing magnesium-stabilized zirconia ceramics in this embodiment further includes the following steps: (7) Molding: The isostatic pressing pressure is 250 MPa, and the holding time is 4 min; the relative density of the blank after molding is 70%.

[0126] (8) Sintering: Deep impurity removal stage: heating to 800℃ at a rate of 3℃ / min and holding for 1 h. Low-temperature sintering neck formation stage: heating to 1200℃ at a rate of 2℃ / min and holding for 1 h. Medium-temperature densification stage: heating to 1400℃ at a rate of 2℃ / min and holding for 1.5 h. High-temperature densification stage: heating to 1600℃ at a rate of 1℃ / min and holding for 2.5 h. The ceramic product has a relative density of 98% and a flexural strength of 800 MPa.

[0127] The rest of the content of this embodiment is the same as that of Embodiment 1, and will not be repeated here.

[0128] The preparation methods described in Examples 1-4 above all successfully produced high-performance magnesium-stabilized zirconia powder and magnesium-stabilized zirconia ceramics. Specific technical parameters are as follows:

[0129] And from Figure 1 As can be seen, the magnesium-stabilized zirconia powder prepared in this application has a high proportion of zirconia stabilized phase. XRD analysis was performed on the ceramic product. The final ceramic product was analyzed by XRD. Figure 2 The structure was confirmed to be a single tetragonal phase with no monoclinic phase present. All zirconia ceramics obtained after sintering in this application are stable phases. SEM images of the ceramic fracture surface (…) Figure 3 As can be seen, its grains are fine and uniform with low porosity, which is consistent with the high density and uniform microstructure described in this invention.

[0130] This invention employs a gel method to prepare magnesium-stabilized zirconia powder. An organic acid-alcohol gel system is used to achieve uniform molecular-level complexation of zirconium and magnesium ions at a molar ratio of 94.5-96.5:3.5-5.5, overcoming the defect of uneven component mixing in the co-precipitation method. This ensures uniform distribution of all components in the final powder, significantly improving crystal phase stability. Furthermore, the magnesium-stabilized zirconia ceramic prepared by this invention possesses advantages such as high flexural strength, high density, high tetragonal phase ratio, uniform microstructure, high chemical stability, and low raw material cost.

[0131] All references to this application are incorporated herein by reference as if each document were individually incorporated herein by reference. Unless they conflict with the purpose and / or technical solution of this application, all cited references are incorporated herein by reference in their entirety and for all purposes. When references are cited in this application, the definitions of relevant technical features, terms, nouns, phrases, etc., are also incorporated herein by reference. Examples and preferred embodiments of the cited technical features may also be incorporated herein by reference, but only to the extent that they enable the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, this application shall prevail or modifications shall be made adaptably to the description in this application.

[0132] The technical features of the above-described embodiments and examples can be combined in any suitable manner. For the sake of brevity, not all possible combinations of the technical features in the above-described embodiments and examples are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0133] The embodiments described above merely illustrate several implementation methods of this application and should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Furthermore, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to this application, and the equivalent forms obtained also fall within the protection scope of this application. It should also be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the protection scope of the appended claims. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing magnesium-stabilized zirconium oxide composite powder, characterized in that, Includes the following steps: Step (1) Raw material preparation and sol preparation a. Preparation of zirconium-magnesium mixed salt solution: Dissolve zirconium source and magnesium source in deionized water and stir until completely dissolved to obtain zirconium-magnesium mixed salt solution; b. Preparation of gelling agent solution: Dissolve the complexing agent and crosslinking agent in deionized water and stir until homogeneous to obtain a gelling agent solution; c. Preparation of mixed sol: The gelling agent solution is added dropwise to the zirconium magnesium salt mixed salt solution while stirring. After the addition is complete, the dispersant is added and stirring is continued. (2) Gelation reaction: The mixed sol was stirred at a constant temperature under water bath heating to carry out the gelation reaction; when the viscosity of the system reached 500-800 mPa·s, heating and stirring were stopped, and the system was allowed to stand at room temperature for aging to obtain a stable magnesium-zirconium composite gel. (3) Gel drying: The composite gel was cut into gel blocks and dried in stages to obtain a dry gel precursor. (4) Calcination: The dry gel precursor was calcined in stages to obtain magnesium-stabilized zirconia coarse powder. (5) Sanding: Magnesium-stabilized zirconia coarse powder was added to a sand mill, with deionized water as the dispersion medium, a grinding dispersant and grinding media were added, and after sand milling, the grinding media were removed by centrifugation to obtain magnesium-stabilized zirconia slurry. (6) Spray granulation: The milled magnesium-stabilized zirconium oxide slurry was pumped into a spray dryer for spray granulation to obtain magnesium-stabilized zirconium oxide particles with a particle size of 50-200 μm and a loose packing density of 1.3-1.8 g / cm³. 3 .

2. The method for preparing magnesium-stabilized zirconium oxide composite powder according to claim 1, characterized in that, In step (1)a, the molar ratio of zirconium source to magnesium source is 94.5-96.5∶3.5-5.5, and the total concentration of the mixed salt solution is 0.6-1.2 mol / L; the zirconium source is selected from one or more of zirconium nitrate (Zr(NO3)4·5H2O), zirconium oxychloride (ZrOCl2·8H2O), zirconium sulfate (Zr(SO4)2·4H2O), and zirconium acetate (Zr(CH3COO)4); the magnesium source is selected from one or more of magnesium nitrate (Mg(NO3)2·6H2O), magnesium chloride (MgCl2·6H2O), magnesium sulfate (MgSO4·7H2O), and magnesium acetate ((CH3COO)2Mg·4H2O).

3. The method for preparing magnesium-stabilized zirconia composite powder according to claim 1, characterized in that, In step (1)b, the molar ratio of the complexing agent to the crosslinking agent is 1:1.2-2.0, and the concentration of the gelling agent solution is 0.4-0.8 mol / L; the complexing agent is selected from one or more of lactic acid, citric acid, malic acid, tartaric acid, and ethylenediaminetetraacetic acid (EDTA); the crosslinking agent is selected from one or more of glycerol, ethylene glycol, xylitol, and sodium glycerophosphate.

4. The method for preparing magnesium-stabilized zirconium oxide composite powder according to claim 1, characterized in that, In step (1)c, the volume ratio of the gelling agent solution to the zirconium-magnesium mixed salt solution is 1:1.8-2.8, and the amount of dispersant used is 0.8-1.8% of the total mass of the zirconium-magnesium mixed salt; the dispersant is selected from one or more of polyethylene glycol 4000 (PEG4000), polyethylene glycol 6000 (PEG6000), sodium polyacrylate (PAAS, molecular weight 2000-5000), sodium dodecylbenzene sulfonate (SDBS), and sodium citrate.

5. The method for preparing magnesium-stabilized zirconium oxide composite powder according to claim 1, characterized in that, In step (3), the segmented drying process is as follows: first, dry at 40-50℃ for 8-12 h, then heat up to 60-70℃ for 12-16 h, and finally heat up to 80℃ for 4-6 h. During the drying process, the vacuum degree is controlled at -0.08--0.09 MPa.

6. The method for preparing magnesium-stabilized zirconium oxide composite powder according to claim 1, characterized in that, In step (4), the segmented heating and calcination process is as follows: the temperature is raised to 300-400℃ at a heating rate of 2-5℃ / min, and held for 1-2 h to remove organic components; then the temperature is raised to 900-1200℃ at a heating rate of 5-8℃ / min, and held for 2-4 h to crystallize and form; and then naturally cooled to room temperature to obtain magnesium-stabilized zirconia coarse powder.

7. The method for preparing magnesium-stabilized zirconium oxide composite powder according to claim 1, characterized in that, In step (5), the dispersant is one or more of ammonium polyacrylate (NH4-PAA), ammonium polymethacrylate, sodium hexametaphosphate, and sodium pyrophosphate. The mass ratio of the grinding media to the coarse powder is 5-8:1, the grinding speed is 2000-3000 r / min, and the grinding time is 1-3 h.

8. The method for preparing magnesium-stabilized zirconium oxide composite powder according to claim 1, characterized in that, In step (6), the spray granulation process specifically involves controlling the inlet air temperature to 180-220℃, the outlet air temperature to 80-100℃, the feed rate to 10-30 kg / h, and the atomization pressure to 0.3-0.6 MPa.

9. A method for preparing a magnesium-stabilized zirconia ceramic according to any one of claims 1-8, characterized in that, It also includes the following steps: (7) Molding: Magnesium-stabilized zirconium oxide particles after spray granulation are added to a molding die, and a blank is prepared by dry pressing or isostatic pressing. (8) Sintering: The shaped green body is placed in a high-temperature sintering furnace for sintering to finally obtain magnesium-stabilized zirconia ceramic products; the relative density of the ceramic products is ≥96%, and the bending strength is ≥600 MPa.

10. The method for preparing magnesium-stabilized zirconia ceramic as described in claim 9, characterized in that, The sintering process in step (8) is as follows: ① Preheating and impurity removal stage: Heat to 200℃ at a heating rate of 2℃ / min and hold for 30 min to remove the free moisture adsorbed on the surface of the green body; continue to heat to 400℃ at a heating rate of 2℃ / min and hold for 1 h to preliminarily decompose the low-boiling-point organic impurities remaining in the green body. ② Deep impurity removal stage: Heat to 600-800℃ at 3℃ / min and hold for 1-2 h to deeply remove residual high-boiling-point organic components and adsorbed impurities in the green body; ③ Low-temperature sintering neck formation stage: Heat to 1100-1200℃ at a heating rate of 2-3℃ / min, hold for 1-1.5 h to promote initial contact between particles and form a stable sintering neck, and inhibit abnormal particle growth. ④ Medium-temperature densification stage: Heat to 1350-1450℃ at a heating rate of 1.5-2℃ / min, hold for 1.5-2 h to accelerate atomic diffusion and promote the growth of sintering neck and pore closure; ⑤ High-temperature densification stage: The temperature is increased to 1400-1600℃ at a heating rate of 1℃ / min and held for 2-4 hours. In this stage, the high temperature achieves full densification between particles and promotes the uniform diffusion of magnesium ions in the zirconia lattice, further increasing the proportion of the tetragonal stable phase. ⑥ Gradient cooling stage: After sintering, the temperature is reduced to 1200℃ at a rate of 2℃ / min and held for 1 h to release the internal thermal stress of the product; then the temperature is reduced to 800℃ at a rate of 3℃ / min and held for 1 h to stabilize the crystal phase structure; then the temperature is reduced to 400℃ at a rate of 5℃ / min and allowed to cool naturally to room temperature.

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