A yttria-stabilized zirconia ceramic slurry and in-situ solidification method

Abstract

This invention discloses a yttrium oxide-stabilized zirconia ceramic slurry and an in-situ solidification method, belonging to the field of ceramic material forming technology. This invention overcomes the technical bias in the field that considers the acid solubility of yttrium oxide as a negative characteristic to be avoided, by dispersing yttrium oxide particles as a solidification inducing agent in the slurry as an independent crystalline phase. Before molding, the slurry is in an alkaline inhibited state, and yttrium oxide does not dissolve significantly; after molding, a pH adjuster switches the slurry to an acidic activated state, triggering the acid dissolution of yttrium oxide and the release of Y³⁺ ions. The released Y³⁺ ions compress the electric double layer on the surface of YSZ particles and bridge the dispersant molecular chains, initiating in-situ solidification of the slurry. This invention achieves solidification triggering solely through pH adjustment, without introducing foreign impurity ions, and the solidification time can be flexibly adjusted within 3-60 minutes, making it particularly suitable for near-net-shape molding of large-sized, complex-shaped, high-purity YSZ ceramic parts.

Description

Technical Field

[0001] This invention relates to the field of ceramic material forming technology, specifically to a yttrium oxide-stabilized zirconia ceramic slurry and an in-situ solidification method. Background Technology

[0002] Yttria-stabilized zirconia (YSZ) ceramics combine excellent mechanical properties, superior wear and corrosion resistance, good biocompatibility, and high-temperature stability, making them valuable for applications in aerospace hot-end components, chemical corrosion-resistant containers, medical devices, semiconductor equipment, and new energy fields. However, as the requirements for the size and structural complexity of ceramic components in high-end equipment continue to rise, the technical threshold for forming processes is also increasing accordingly: on the one hand, it is necessary to achieve near-net-shape forming to save machining costs and material consumption; on the other hand, it is essential to ensure that the microstructure of the green body is uniform and the density is highly consistent during solidification, while maintaining good process controllability throughout the entire process.

[0003] Among numerous molding systems, water-based ceramic slurries, using water as the dispersion medium, possess multiple advantages such as being environmentally friendly, cost-effective, and safe to operate, and have developed into an important branch of ceramic colloidal molding technology. Through in-situ solidification of water-based slurries, complex-shaped green bodies can be directly molded under low-temperature conditions, fundamentally avoiding the volume shrinkage, internal defects, and environmental pollution problems caused by the removal of organic binders in traditional processes.

[0004] Currently, a key strategy for in-situ solidification of water-based ceramic slurries involves pre-introducing a solidification inducing agent in an inhibited state into the slurry. After casting, external conditions (such as temperature and pH) are altered to trigger the release of Ca²⁺ and Mg²⁺ ions, which then interact with the surface charge of the ceramic particles to induce in-situ solidification. However, these residual Ca²⁺ and Mg²⁺ ions can affect the purity, phase stability, and high-temperature performance of zirconia ceramics. This issue is particularly pronounced in high-end applications such as biomedicine and semiconductor equipment, where material purity requirements are extremely stringent.

[0005] To address the aforementioned issue of impurity introduction, existing technologies have attempted to utilize yttrium oxide sol as a binder phase to form YSZ ceramics (see patent CN108101534A). This method achieves slurry solidification by initiating the gelation of the yttrium oxide sol, with the aim of avoiding the introduction of foreign ions. However, the process design principle of this method is entirely focused on maintaining the stability of the yttrium oxide colloid, essentially circumventing rather than utilizing the intrinsic chemical properties of yttrium oxide. Furthermore, in broader transparent ceramic forming systems involving yttrium oxide such as YAG (yttrium aluminum garnet) (see patents CN105218095A and CN118164759A), it can be observed that existing technologies generally maintain the slurry system in a neutral to alkaline range with a pH above 7 during process design.

[0006] The aforementioned prior art collectively reflects a long-standing and prevalent technical bias in this field. Those skilled in the art generally believe that for yttrium oxide-containing ceramic slurries, especially the YSZ system, the dissolution of yttrium oxide as a stabilizer under acidic conditions is a negative process that must be strictly avoided, as it leads to stabilizer loss, uneven slurry composition, and deterioration of the final product's performance. Therefore, existing technologies strictly maintain the slurry within an alkaline or neutral range in process design to actively avoid the acid solubility of yttrium oxide, rather than treating it as an exploitable characteristic. For example, US Patent 8500898 explicitly states that the dissolution of yttrium oxide in water is pH-dependent—under low pH conditions, yttrium oxide dissolves relatively quickly and releases yttrium ions, potentially causing changes in the stabilizer content in the slurry. Based on this understanding, those skilled in the art generally regard the acid solubility of yttrium oxide as a negative characteristic that needs to be suppressed, tending to prevent yttrium oxide dissolution by maintaining an alkaline environment or adding inhibitors to ensure the stability of the slurry's composition and performance. This technical bias limited the further understanding and utilization of the acid solubility of yttrium oxide by those skilled in the art for a considerable period of time.

[0007] Therefore, developing an in-situ forming method with a highly controllable solidification process that does not introduce harmful impurities and can fundamentally overcome existing technological biases has become an urgent technical challenge in the manufacturing of large-size, high-purity YSZ ceramic components. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies, particularly the aforementioned technical bias in the field regarding the acid solubility of yttrium oxide, and to provide a yttrium oxide-stabilized zirconia ceramic slurry and an in-situ solidification method. This invention takes a reverse approach, actively transforming the acid solubility characteristic of yttrium oxide, which has long been considered a "problem" and actively avoided in the field, into a controllable and intrinsic solidification driving force. The "locking" and "release" of yttrium ions can be achieved solely through pH signals, without introducing any foreign impurity elements, fundamentally solving purity concerns in high-end applications.

[0009] The method of this invention disperses YSZ ceramic powder in an aqueous slurry containing yttrium oxide particles of a specific particle size. Before molding, the pH of the slurry is maintained in an inhibition range where yttrium oxide does not dissolve significantly. After molding, external stimuli (such as temperature changes triggering the hydrolysis of pH adjusters or the release of slow-release acids) are used to bring the pH of the slurry into an activation range where yttrium oxide can undergo acid dissolution. The yttrium oxide particles dissolve in a controlled manner, releasing Y³⁺ ions. The released Y³⁺ ions, as high-valence counterions, achieve in-situ solidification through synergistic effects: firstly, by compressing the double layer on the surface of the YSZ ceramic particles, reducing the electrostatic repulsion between particles; and secondly, by bridging the dispersant molecular chains adsorbed on the particle surface, bringing the particles closer together and agglomerating them to form a wet blank with sufficient strength.

[0010] Furthermore, this invention reveals that by synergistically regulating the initial particle size of yttrium oxide particles and the acidification rate of the slurry, precise control over the coagulation rate and coagulation uniformity can be achieved over a wide range. Specifically, finer yttrium oxide particles have a larger specific surface area and faster dissolution kinetics, which can accelerate the coagulation process; while by adjusting the type, concentration, or release rate of the pH adjuster, the temporal-spatial evolution of the slurry pH can be precisely controlled, thereby ensuring uniform coagulation within thick cross-sections or large-sized components.

[0011] The technical solution of the present invention is as follows:

[0012] A yttrium oxide-stabilized zirconia ceramic slurry comprises YSZ ceramic powder, water, yttrium oxide, dispersant, and pH adjuster.

[0013] Among them, yttrium oxide is used as a coagulation inducer, taking advantage of its acid-soluble properties as an alkaline oxide: its solubility is extremely low in alkaline environments, yttrium ions are in an inhibited state, and the slurry maintains good fluidity; in acidic environments, an acid dissolution reaction occurs to generate soluble yttrium salt (Y³⁺), and the release of yttrium ions can be triggered by lowering the pH value. The interaction between yttrium ions and the surface charge of YSZ ceramic particles initiates in-situ coagulation of the slurry.

[0014] It is important to note that the yttrium oxide used as a solidification inducer in this invention is independent of the yttrium oxide component already present as a stabilizer in the YSZ powder. The yttrium oxide in the YSZ powder has already formed a solid solution with zirconium oxide, exhibiting stable chemical properties. The additionally added yttrium oxide exists as independent crystalline particles, possessing greater reactivity. By controlling the slurry to a weakly acidic state (e.g., pH 4–6), only these highly reactive yttrium oxide particles can be selectively dissolved to release Y³⁺ ions without eroding the YSZ solid solution lattice. Furthermore, these additional Y³⁺ ions can further enter the zirconium oxide lattice during subsequent sintering to replenish the stabilizer content, synergistically forming a complete stabilized structure without producing any harmful residues.

[0015] Furthermore, the yttrium oxide has extremely low solubility in a weakly alkaline environment (pH 10–12), and the yttrium ion concentration is less than 10⁻⁻⁶. 5 mol / L, in an inhibited state; in a weakly acidic environment (pH 4–6), the following acid dissolution reaction occurs: Y2O3 + 6H⁺ → 2Y³⁺ + 3H2O, with significant release of yttrium ions.

[0016] Furthermore, the particle size D of the yttrium oxide 50 The particle size ranges from 0.2 to 30 μm. By selecting yttrium oxide of different particle sizes, its acid dissolution reaction rate in the slurry can be independently adjusted, achieving "dual pH-particle size control": small-particle-size yttrium oxide (D... 50 ≤1 μm, D preferred 50 Yttrium oxide (480 nm) has a large specific surface area and reacts rapidly after the pH decreases, enabling rapid solidification and making it suitable for efficient molding of small or simple-shaped parts; large-particle yttrium oxide (D... 50 ≥ 10 μm, D is preferred 50 = 17.2 μm) has a slower reaction rate, enabling gradual solidification, which is especially suitable for molding large-sized or complex structural parts, effectively avoiding internal stress and cracking defects caused by excessively rapid solidification; medium-sized yttrium oxide (D 50 2–8 μm, preferably D 50 = 3.3 μm) The dissolution kinetics are between the two, making it suitable for medium-sized or medium-complex parts, balancing solidification efficiency and uniformity.

[0017] Furthermore, the yttrium oxide can be in the form of a mixture of two or more different particle sizes, wherein the fine-particle component D 50 ≤ 1 μm, coarse-grained component D 50 ≥ 10 μm, with a mass ratio of 1:10 to 1:1, is used to achieve gradient solidification, enabling large-sized blanks to solidify uniformly from the surface to the interior, and eliminating solidification shrinkage stress.

[0018] Furthermore, the particle size D of the solidification inducing yttrium oxide particles is... 50 The particle size D of YSZ ceramic powder 50 The preferred ratio is 0.5:1 to 100:1. When the yttrium oxide particles are smaller than the YSZ powder, they can be more uniformly dispersed in the gaps between the YSZ particles, forming denser ion release points and a more uniform microscopic solidification network, which is beneficial to improving the uniformity of the green body. When the yttrium oxide particles are larger than the YSZ powder, it is beneficial to achieve slow release and gradual solidification, which is suitable for thick-section components. When yttrium oxide of different particle sizes is mixed, the combination of coarse and fine particles can create a microscopically differentiated ion concentration gradient, further optimizing the solidification uniformity of the thick-section green body.

[0019] Further, the YSZ ceramic powder is 3Y-TZP (tetragonal zirconia polycrystalline containing 3 mol% yttrium oxide), 5Y-PSZ (partially stabilized zirconia containing 5 mol% yttrium oxide), 8YSZ (fully stabilized zirconia containing 8 mol% yttrium oxide), or other YSZ powder containing yttrium stabilizers, with a particle size D. 50 The thickness is 0.1–2.0 μm, preferably 0.2–1.0 μm.

[0020] Furthermore, the dispersant is one or more of ammonium polyacrylate, polyethylene glycol, or ammonium citrate, and the amount of dispersant added accounts for 0.2–1.5 wt% of the powder mass, which is used to maintain the good dispersion state of the slurry under alkaline conditions through electrostatic-steric synergistic effect.

[0021] Furthermore, the pH adjuster is a dilute acid solution, preferably dilute acetic acid, dilute lactic acid, or dilute hydrochloric acid, with a concentration of 0.1–2.0 mol / L. When organic acids such as dilute acetic acid or dilute lactic acid are selected, the acid radical ions can be completely thermally decomposed and removed during subsequent drying and sintering processes, further ensuring the purity of the YSZ ceramic components.

[0022] This invention also provides a method for solidifying and molding the above-mentioned yttrium oxide stabilized zirconia ceramic slurry, comprising the following steps:

[0023] (1) Yttrium oxide of a specific particle size is mixed with water under weakly alkaline conditions to form a suspension with extremely low yttrium ion concentration; at this time, yttrium oxide is in an inhibited state and the yttrium ion concentration is less than 10⁻ 5 mol / L;

[0024] (2) Add YSZ ceramic powder and dispersant to the above suspension, stir evenly, adjust pH to weak alkalinity (pH10–12) to obtain a slurry with good fluidity; under this alkaline condition, the dispersant is fully dissociated and adsorbed on the surface of YSZ particles, providing sufficient electrostatic-steric repulsion force, the slurry has low viscosity and good fluidity, which is conducive to mold filling.

[0025] (3) Inject the slurry into a mold of the desired shape, and reduce the pH of the slurry to a weakly acidic level (pH 4–6) by adding a pH adjuster; Yttrium oxide undergoes an acid dissolution reaction in an acidic environment and releases yttrium ions (Y³⁺) at a corresponding rate according to its particle size.

[0026] (4) The released yttrium ions, as trivalent high-valence counterions, compress the double layer and bridge the carboxylate groups of the YSZ particle surface dispersant molecules, thus initiating in-situ solidification of the slurry and forming a ceramic green body with a certain strength.

[0027] (5) Demold the solidified blank, dry and sinter it to obtain dense YSZ ceramic parts.

[0028] Furthermore, the weakly alkaline conditions described in step (1) are pH 10–12, preferably pH 11. The alkaline environment can be achieved by adding ammonia or tetramethylammonium hydroxide.

[0029] Further, the pH adjustment method in step (3) is any one or a combination of the following: injection addition—introducing the pH adjuster into the slurry via injection; pre-positioning in the mold—pre-coating the pH adjuster onto the inner wall of the mold; spray introduction—spraying the pH adjuster into the slurry surface in an atomized form. After adjustment, the pH is controlled at 4–6, preferably pH 5. This pH range ensures effective dissolution of yttrium oxide without damaging the YSZ powder due to excessive acidity.

[0030] Furthermore, the coagulation time mentioned in step (4) is 3–60 minutes, which can be controlled synergistically by three parameters: pH value, yttrium oxide particle size, and yttrium oxide addition amount. Specifically: lowering the target pH value can accelerate the coagulation rate; using smaller yttrium oxide particles can accelerate the coagulation rate; increasing the yttrium oxide addition amount can increase the final yttrium ion concentration and accelerate the coagulation rate.

[0031] Further, the drying in step (5) is room temperature drying or oven drying at 40–60°C, and the drying time is 12–48 hours; the sintering temperature is 1300–1550°C, and the holding time is 2–4 hours.

[0032] Furthermore, the amount of yttrium oxide added is 0.05–0.8 wt% based on the total mass of the slurry, preferably 0.1–0.5 wt%. If the amount added is too low, the released yttrium ions will not be sufficient to effectively initiate coagulation; if the amount added is too high, the slurry may approach the critical coagulation concentration under alkaline conditions, reducing the stability of the slurry and the flowability of the mold filling.

[0033] Furthermore, the amount of yttrium oxide added needs to be adapted according to its particle size: when using small-particle yttrium oxide (D... 50 When the particle size is ≤ 1 μm (e.g., 480 nm), due to its rapid dissolution rate, the amount added can be appropriately reduced, preferably 0.05–0.3 wt% of the total slurry mass; when using large-particle yttrium oxide (D... 50 When the particle size is ≥ 10 μm (e.g., 17.2 μm), due to its slow dissolution rate, the amount added can be appropriately increased, preferably 0.2–0.8 wt% of the total slurry mass; when using medium-sized yttrium oxide (D... 50 When the particle size is 2–8 μm (e.g., 3.3 μm), the preferred addition amount is 0.1–0.5 wt% of the total mass of the slurry.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The solidification driving force is entirely derived from the yttrium element in the bulk component of YSZ ceramics. No foreign impurity ions such as Ca²⁺ and Mg²⁺ are introduced, which realizes true "homologous solidification" and ensures the ultra-high purity of YSZ ceramics. It is particularly suitable for applications with extremely strict requirements on impurity content, such as biomedical applications, solid oxide fuel cell electrolytes, and semiconductor equipment.

[0036] (2) It breaks through the technical prejudice of the field regarding the acid solubility of yttrium oxide, opens up a completely new coagulation path, the process is simple, and the state switching from stable slurry to complete coagulation can be achieved by using only pH as a single variable, which has strong controllability.

[0037] (3) The solidification rate has a wide controllable window and strong process adaptability. By synergistically controlling the particle size, amount of yttrium oxide and pH, the solidification time can be flexibly adjusted from a few minutes to nearly an hour. It can achieve efficient production of small parts through rapid solidification, and ensure uniform solidification of large-size thick-section blanks through slow and gradual solidification, effectively avoiding solidification shrinkage stress and cracking defects.

[0038] (4) The chemical mechanism is clean and there are no organic byproducts. The acid dissolution reaction of yttrium oxide in this invention is a direct inorganic acid-base reaction, which does not involve the decomposition or transformation of organic matter and does not produce organic reaction byproducts. If organic acids that can be decomposed at low temperatures (such as acetic acid and lactic acid) are selected as pH adjusters, all added components in the entire solidification-drying-sintering process can be completely removed or transformed into YSZ ceramic components, achieving "clean solidification". Attached Figure Description

[0039] Figure 1 This diagram illustrates the concentration of yttrium ions released by yttrium oxide under different pH conditions.

[0040] Figure 2 The curves show the comparison of yttrium oxide ion release rates at different particle sizes. Detailed Implementation

[0041] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0042] Example 1

[0043] Take 100 g of 3Y-TZP powder, 0.5 g of ammonium polyacrylate dispersant, and 0.12 g of yttrium oxide (D). 50 = 480 nm), 40 mL of deionized water. First, adjust the pH of the deionized water to 11 with ammonia, then add yttrium oxide and stir to disperse for 15 min to form a yttrium oxide suspension (at this point, the yttrium ion concentration is < 10⁻). 5(Yttrium oxide was in the suppressed state at mol / L). Then, 3Y-TZP powder and dispersant were added, and stirring was continued for 30 min. The slurry pH was 10.8, with low viscosity and good flowability.

[0044] The slurry was injected into a mold with a release agent coated on the inner wall. A dilute acetic acid solution (0.5 mol / L) was added via injection to lower the pH of the slurry to 5.0. The small-particle yttrium oxide (480 nm) has a large specific surface area, resulting in a rapid acid dissolution reaction. Yttrium ions were released quickly within 5 minutes, and the slurry completely solidified within 5 minutes. After demolding, the green body was dried at room temperature for 24 hours, then sintered at 1500℃ for 2 hours to obtain a dense 3Y-TZP ceramic component with a relative density of 98.5%, free from cracks and deformation, and a flexural strength of 1050 MPa.

[0045] Example 2

[0046] Take 100 g of 5Y-PSZ powder, 0.4 g of ammonium citrate dispersant, and 0.40 g of yttrium oxide (D). 50 = 17.2 μm), 42 mL of deionized water. The slurry was prepared at pH 11 according to the method in Example 1, and the slurry had good flowability.

[0047] The slurry was injected into a large-sized, thin-walled, complex-shaped mold (part thickness 10–30 mm, maximum size 250 mm). A dilute lactic acid layer was pre-placed on the inner wall of the mold, gradually lowering the pH to 5.2 during slurry injection. The acid dissolution reaction rate of large-particle yttrium oxide (17.2 μm) was relatively slow, and yttrium ions were gradually released, allowing the slurry to solidify progressively from the surface to the interior within 50 minutes. After demolding, the green body showed no deformation or cracks, and exhibited a uniform internal structure. After drying at 60℃ for 12 h and sintering at 1450℃ for 3 h, the obtained large-sized 5Y-PSZ ceramic parts had a smooth surface, consistent density throughout, and a flexural strength of 960 MPa.

[0048] Example 3

[0049] Take 100 g of 3Y-TZP powder, 0.6 g of polyethylene glycol dispersant, and 0.25 g of yttrium oxide, wherein the fine particles (D... 50 = 480nm) and coarse grains (D 50 = 17.2 μm) with a mass ratio of 1:4, and 41 mL of deionized water. After being mixed evenly under pH 11 conditions, the mixture was poured into a thick cross-section mold with dimensions of 80×80×40 mm, and a dilute hydrochloric acid solution (1.0 mol / L) was introduced by spraying to adjust the pH to 4.8.

[0050] Fine-grained yttrium oxide (480 nm) dissolves rapidly, quickly initiating initial solidification in the surface and near-surface regions of the slurry, forming a solidification front. Coarse-grained yttrium oxide (17.2 μm) continuously and slowly releases yttrium ions within the slurry, driving the solidification front to gradually advance from the surface inwards, achieving gradient solidification. The entire solidification process is completed in approximately 30 minutes. After drying and sintering at 1500℃, the green body exhibits a uniform and dense internal structure, free from central shrinkage cracking defects, with a relative density reaching 99.2%.

[0051] Example 4

[0052] Take 100 g of 8YSZ powder, 0.5 g of ammonium polyacrylate dispersant, and 0.25 g of yttrium oxide (D). 50 = 3.3 μm), 45 mL of deionized water. A slurry with pH 11 was prepared according to the method in Example 1. The 8YSZ powder itself already contains 8 mol% yttrium oxide stabilizer, and the additional yttrium oxide acts as a coagulation inducing agent; the two functions are independent. After the slurry was injected into the mold, a dilute acetic acid solution (0.2 mol / L) was added by injection to lower the pH to 5.5. Due to the use of medium-sized yttrium oxide (3.3 μm) and the relatively high target pH, the acid dissolution reaction rate was moderate, and the coagulation time was 25 min. This method is suitable for molding medium-sized 8YSZ electrolyte sheets, balancing the operating window and production efficiency. After demolding, drying, and sintering at 1500℃, the 8YSZ parts were intact and defect-free, with a relative density of 98.0%, and the ionic conductivity was consistent with that of 8YSZ of the same composition prepared by conventional molding methods, confirming that the coagulation inducing agent yttrium oxide has no adverse effect on the functional properties of the material.

[0053] Example 5

[0054] Take 100 g of 3Y-TZP powder, 0.5 g of ammonium polyacrylate dispersant, and 0.20 g of yttrium oxide (D). 50 = 3.3 μm), and 40 mL of deionized water. A slurry was prepared at pH 11 according to the method in Example 1. The slurry was injected into a medium-sized, complex-shaped mold, and a dilute lactic acid solution (0.5 mol / L) was added by injection to lower the pH to 5.0. The dissolution kinetics of medium-sized yttrium oxide (3.3 μm) are between the nanoscale and microscale, with yttrium ions released at a moderate rate, and the slurry solidified uniformly within 18 min. After demolding, the green body was dried at 50℃ for 20 h and sintered at 1480℃ for 3 h. The resulting medium-sized 3Y-TZP ceramic component had a complete shape, dense interior, a relative density of 98.8%, and a flexural strength of 1020 MPa.

[0055] Comparative Example 1

[0056] According to Example 1, yttrium oxide was omitted, and a slurry was prepared using only 3Y-TZP powder, dispersant, and water at pH 11. After being poured into a mold, dilute acetic acid was added to adjust the pH to 5.0. The slurry did not solidify within 3 hours and could not be molded. This comparative example demonstrates that the acid dissolution reaction of yttrium oxide, which releases yttrium ions, is a necessary condition for initiating slurry solidification.

[0057] Comparative Example 2

[0058] According to Example 1, without any further operation after injection into the mold, the slurry did not solidify within 3 hours and could not be molded. This comparative example demonstrates that a decrease in pH is a necessary condition for triggering the dissolution and solidification of yttrium oxide, verifying the alkaline-to-acidic triggering pathway of the present invention.

[0059] Comparative Example 3

[0060] Take 100 g of 3Y-TZP powder, 0.5 g of ammonium polyacrylate dispersant, and 0.12 g of yttrium oxide (D). 50 = 480 nm), 40 mL of deionized water. Yttrium oxide was directly mixed with water at pH 5, and then powder and dispersant were added. Because yttrium oxide undergoes an acid-dissolving reaction immediately under acidic conditions, yttrium ions are released in large quantities during the slurry preparation stage, resulting in severe flocculation and thickening of the slurry during stirring, loss of fluidity, and inability to complete subsequent molding operations. This comparative example verifies the necessity of the alkaline inhibition state in step (1).

[0061] Figure 1 This diagram illustrates the yttrium ion release concentration of yttrium oxide under different pH conditions. Test conditions: Small-particle yttrium oxide powder (D...) 50 Yttrium (480 nm, purity ≥ 99.9%) 0.15 g was dispersed in 40 mL of deionized water to prepare 12 identical suspensions. The pH was adjusted to 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 7.0, 8.0, 9.0, 10.0, and 11.0 respectively using dilute acetic acid and ammonia. Each suspension was sealed and stirred at 25℃ for 24 h to reach dissolution equilibrium, maintaining a stable pH (± 0.1) during this period. The supernatant was filtered through a 0.22 μm filter membrane, acidified with nitric acid, and the yttrium concentration was determined by ICP-OES.

[0062] Figure 2 Yttrium oxide of different particle sizes (smallest particle size: D) 50 = 480 nm; Medium particle size: D 50 = 3.3 μm; Large particle size: D 50= 17.2 μm) Yttrium ion release rate comparison curves under the same pH change conditions (pH 11 → pH 5). Test conditions: 0.15 g each of small, medium, and large particle sizes of yttrium oxide were dispersed in 40 mL of deionized water. The pH was first adjusted to 11.0 with ammonia water, and stirred for 15 min to form an alkaline inhibited suspension. Under stirring, dilute acetic acid solution (0.5 mol / L) was quickly added to uniformly adjust the pH to 5.0, and this moment was recorded as t = 0. Samples were taken at certain time intervals, immediately filtered through a 0.22 μm filter membrane and acidified with nitric acid, and the yttrium element concentration was determined by ICP-OES.

[0063] Table 1 Raw material formulations and particle size parameters for each embodiment

[0064]

[0065] Table 2 Process conditions and solidification parameters for each embodiment

[0066] serial number pH adjustment method pH adjuster and concentration Target pH solidification time Example 1 Injection Dilute acetic acid, 0.5 mol / L 5.0 5 min Example 2 Pre-set mold inner wall dilute lactic acid layer 5.2 50 min Example 3 Spray introduction Dilute hydrochloric acid, 1.0 mol / L 4.8 30 min Example 4 Injection Dilute acetic acid, 0.2 mol / L 5.5 25 min Example 5 Injection Dilute lactic acid, 0.5 mol / L 5.0 18 min

[0067] Table 3 Drying and sintering parameters of the green body in each embodiment

[0068] serial number Drying conditions Sintering temperature Insulation time Example 1 Dry at room temperature, 24 h 1500℃ 2 h Example 2 Dry in an oven at 60℃ for 12 hours. 1450℃ 3 h Example 3 Drying (details not provided) 1500℃ Not detailed Example 4 Drying (details not provided) 1500℃ Not detailed Example 5 Dry in an oven at 50℃ for 20 hours. 1480℃ 3 h

[0069] Table 4. Product performance and main features of each embodiment

[0070] serial number relative density Bending strength (MPa) No defects Main features Example 1 98.5% 1050 No cracks, no deformation Rapid solidification, suitable for efficient molding of small parts Example 2 — 960 No deformation, no cracks, uniform internal structure Progressive solidification is suitable for large-sized, thin-walled, complex components. Example 3 99.2% — Central shrinkage cracking defects Gradient solidification, suitable for thick cross-section components Example 4 98.0% — Complete and without defects Medium-speed solidification has no effect on ionic conductivity. Example 5 98.8% 1020 Complete exterior and dense interior Medium-speed uniform solidification, suitable for medium-sized complex-shaped parts.

[0071] Table 5 Key parameters and results for each comparative example

[0072]

[0073] Overall Results Summary:

[0074] As shown in the table above, all embodiments of the present invention can achieve controllable in-situ solidification within 3 to 60 minutes. The prepared YSZ ceramic parts have a relative density of 98.0% to 99.2% and a flexural strength of 960 to 1050 MPa, and are free from defects such as cracks and deformation. Through the verification of comparative examples 1 to 3, the necessity of three key elements in the technical solution of the present invention is further established: (1) Yttrium oxide is indispensable as a solidification inducing agent; (2) The pH triggering path from alkaline to acidic is indispensable; (3) Maintaining the alkaline inhibition state during the slurry preparation stage is indispensable. The above results fully demonstrate that the present invention successfully transforms the acid solubility of yttrium oxide, which has long been avoided in the field, into a controllable solidification driving force, realizing clean, efficient, and wide process window in-situ solidification molding of YSZ ceramics.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A yttrium oxide-stabilized zirconia ceramic slurry, characterized in that, It contains YSZ ceramic powder, water, yttrium oxide particles, dispersant, and pH adjuster; The yttrium oxide particles are dispersed in the slurry as a coagulation inducer in the form of an independent crystalline phase. Before molding, the slurry is in an alkaline inhibited state, and the yttrium oxide particles do not dissolve significantly in this state. After molding, the slurry is switched to an acidic activated state by the pH adjuster, which triggers the yttrium oxide particles to undergo an acid dissolution reaction and release Y³⁺ ions, thereby initiating in-situ coagulation of the slurry.

2. The yttrium oxide stabilized zirconia ceramic slurry according to claim 1, characterized in that, The particle size D of the YSZ ceramic powder 50 The particle size D of the yttrium oxide particles is 0.1~2.0 μm. 50 The particle size D of the yttrium oxide particles is 0.2~30 μm. 50 The particle size D of the YSZ ceramic powder 50 The ratio is 0.5:1 to 100:

1.

3. The yttrium oxide stabilized zirconia ceramic slurry according to claim 2, characterized in that, The yttrium oxide particles comprise fine and coarse particles, the fine particles having a D... 50 ≤1μm, the D of the coarse-grained component 50 ≥10μm, the mass ratio of the two is 1:10~1:

1.

4. The yttrium oxide stabilized zirconia ceramic slurry according to claim 1, characterized in that, The amount of yttrium oxide added is 0.05~0.8 wt% based on the total mass of the slurry.

5. The yttrium oxide stabilized zirconia ceramic slurry according to claim 4, characterized in that, When the particle size D of the yttrium oxide particles 50 When the particle size is ≤1μm, the addition amount is 0.05~0.3wt% of the total slurry mass; when the particle size D of the yttrium oxide particles is ≤1μm, the addition amount is 0.05~0.3wt% of the total slurry mass; 50 When the particle size is 2~8μm, the amount added is 0.1~0.5wt% of the total mass of the slurry; when the particle size D of the yttrium oxide particles is... 50 When the particle size is ≥10μm, the amount added is 0.2~0.8wt% of the total mass of the slurry.

6. The yttrium oxide stabilized zirconia ceramic slurry according to claim 1, characterized in that, The pH of the alkaline inhibited state is 10-12, and the pH of the acidic activated state is 4-6.

7. The yttrium oxide stabilized zirconia ceramic slurry according to claim 1, characterized in that, The dispersant is one or more of ammonium polyacrylate, polyethylene glycol, or ammonium citrate, and its addition amount accounts for 0.2 to 1.5 wt% of the mass of the YSZ ceramic powder.

8. A method for solidifying and molding yttrium oxide-stabilized zirconia ceramic slurry as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) The yttrium oxide particles are mixed with water under alkaline conditions to form a suspension in which the yttrium oxide is in an inhibited state; (2) Add the YSZ ceramic powder and the dispersant to the suspension, stir evenly and adjust the pH to alkaline to obtain a slurry; (3) The slurry is injected into the mold, and the pH adjuster is added to reduce the pH of the slurry to acidic, triggering the acid dissolution of the yttrium oxide particles to release Y³⁺ ions; (4) The released Y³⁺ ions compress the double electric layer on the surface of YSZ particles and bridge the dispersant molecular chains, initiating in-situ solidification of the slurry to form a wet blank. (5) Demold, dry and sinter the wet blank to obtain a dense YSZ ceramic component.

9. The solidification molding method according to claim 8, characterized in that, The pH adjustment method in step (3) is any one or a combination of injection, pre-placement in the mold, or spray introduction; the solidification time is 3 to 60 minutes.

10. The solidification molding method according to claim 8, characterized in that, The drying in step (5) is room temperature drying or oven drying at 40~60℃ for 12~48 hours; the sintering temperature is 1300~1550℃ and the holding time is 2~4 hours; the pH adjuster is dilute acetic acid, dilute lactic acid or dilute hydrochloric acid, with a concentration of 0.1~2.0mol / L.

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