A method for preparing yttrium oxide ceramics by gel casting

Abstract

This invention discloses a method for preparing yttrium oxide ceramics by gel casting. The method first prepares modified yttrium oxide powder, then adds calcium carbonate for mixing, and finally uses Isobam gelling agent for green gel casting, followed by sintering to obtain yttrium oxide ceramics. Through powder pretreatment, an aqueous suspension containing yttrium oxide and calcium oxide is obtained, solving the dual problems of challenging sintering characteristics and thermal shock susceptibility of yttrium oxide. The preparation process of this invention is simple, the gel system used is non-toxic and harmless, environmentally friendly, and has high production efficiency. The prepared ceramics possess advantages such as high strength, good toughness, and good wear resistance.

Description

Technical Field

[0001] This invention relates to the field of inorganic ceramic material preparation technology, specifically to a gel casting yttrium oxide ceramic and its preparation method. Background Technology

[0002] Currently, ceramic materials have become an indispensable key in alloy smelting and casting, especially in titanium-aluminum alloy smelting and casting. Due to the high chemical reactivity of molten titanium alloys, they can interact with almost all refractory materials. Commonly used oxide refractory materials exhibit good thermodynamic stability when reacting with titanium-aluminum alloys. Y₂O₃ and CaO are the most promising ceramic shell materials for titanium-aluminum alloy castings.

[0003] Studies have shown that the reaction between calcium oxide and titanium liquid is relatively weak; however, the practical application of yttrium oxide as a shell material faces challenges. Yttrium oxide shells are hygroscopic and prone to volume expansion and cracking upon contact with high temperatures. Therefore, stringent humidity requirements must be met, which increases the complexity of practical applications of yttrium oxide as a shell material. Although yttrium oxide is recognized as the most stable oxide refractory material, its limitations in thermal shock resistance and high sintering temperatures hinder its widespread adoption.

[0004] Traditional methods for preparing yttrium oxide composite ceramics, such as injection molding and slip casting, are insufficient for producing high-performance yttrium oxide ceramics. Currently, green gel casting is widely used. This method utilizes internal chemical reactions in the slurry to form a macromolecular or ceramic network structure, allowing the ceramic slurry poured into a non-porous mold to rapidly solidify into a ceramic green body. The resulting products exhibit uniform structure and density, short casting cycles, and reliable performance, making them suitable for industrial applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing yttrium oxide ceramics by gel casting. This invention utilizes a gel casting method to prepare oxide refractory materials, enabling the multifunctional production of yttrium oxide refractory products with various complex shapes. Through a powder pretreatment process, an aqueous suspension containing yttrium oxide and calcium oxide was successfully obtained, which also solves the dual problems of challenging sintering characteristics and susceptibility to thermal shock of yttrium oxide. The preparation process of this invention is simple, the gel system used is non-toxic and harmless, environmentally friendly, and has high production efficiency. The prepared ceramics possess advantages such as high strength, good toughness, and good wear resistance.

[0006] The technical solution adopted in this invention is as follows: A method for preparing yttrium oxide ceramics by gel casting, comprising the following steps:

[0007] Step 1: First, the yttrium oxide powder is ultrasonically dispersed in a boric acid solution at 45-60℃, and then dried and sieved to obtain modified yttrium oxide powder;

[0008] Step 2: Add deionized water, modified yttrium oxide powder, and calcium carbonate to a ball mill jar, mix and disperse, dry and sieve, and calcine to obtain calcium oxide-doped modified yttrium oxide powder;

[0009] Step 3: Mix Isobam gelling agent with ultrapure water, then adjust the pH value to 8-10 with lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add calcium oxide-doped modified yttrium oxide powder and sintering aid to the premixed solution, and mix by ball milling to obtain a slurry.

[0010] Step 4: After vacuum degassing, the slurry is injected into a mold and cured under microwave heating. After demolding, it is dried to obtain a yttrium oxide ceramic green body. Finally, the ceramic green body is sintered in a vacuum sintering furnace and then annealed in a muffle furnace to obtain yttrium oxide ceramic.

[0011] Preferably, in step one, the yttrium oxide powder has three different particle sizes (d50 of 50μm, 3μm, and 550nm respectively), and the ratio of the different particle sizes added is 5:3:2; the amount of yttrium oxide added is 40-60wt%; the heating and ultrasonication time is 0.5-1h; the boric acid solution mass concentration is 5-10%; the drying temperature is 80-100℃; the drying time is 18-24h; and it is passed through a 120-mesh sieve.

[0012] Preferably, in step two, the modified yttrium oxide powder accounts for 40-60% of the mass of the mixture, and the calcium carbonate accounts for 5%-10% of the mass of the modified yttrium oxide powder; the drying temperature is 80-100℃, the drying time is 18-24h, and it passes through a 120-mesh sieve; the calcination temperature is 800-850℃, and the calcination time is 8-10h.

[0013] Preferably, in step three, the Isobam gelling agent is one or more of Isobam104, Isobam110, and Isobam304, which are fully dissolved in ultrapure water to prepare a solution with a concentration of 10-20 wt%, and the pH value is adjusted to 8-10 by lactic acid and tetramethylammonium hydroxide.

[0014] Preferably, in step three, the solid content of the calcium oxide-doped modified yttrium oxide powder in the slurry is 60-75% by mass; the sintering aid is zirconium oxide, and the amount added is 0.5-1 wt% of the calcium oxide-doped modified yttrium oxide powder.

[0015] Preferably, in step four, the vacuum degassing pressure is -0.5 to -1 MPa, the vacuum degassing time is 40-60 min; the microwave heating temperature is 30-40℃, the curing time is 5-10 min; the specific drying process is: drying in a constant temperature and humidity chamber with humidity of 70-85% and temperature of 35-50℃ for 15-20 h.

[0016] Preferably, in step four, the sintering process is as follows: the temperature is increased to 800℃ at a rate of 1-5℃ / min and held for 1-2 hours, and then increased to 1650-1720℃ at a rate of 1-3℃ / min and held for 2-4 hours.

[0017] Preferably, in step four, the sintered ceramic is placed in a muffle furnace and annealed in air at 1000-1100°C for 2-3 hours.

[0018] Preferably, in steps two and three, the grinding balls used in the ball mill are zirconia balls, the ball-to-material ratio is 1:1 to 3, the ball milling speed is 300-500 r / min, and the ball milling time is 12-24 h.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) In this invention, boric acid is used to modify yttrium oxide to prevent its hydrolysis. Moreover, this process also adapts the zeta potential value to calcium carbonate, which increases the stability of the powder and reduces the viscosity of the slurry.

[0021] (2) In this invention, calcium carbonate is added, and after drying, sieving, and calcination, calcium oxide-doped modified yttrium oxide powder is obtained, which is beneficial to the densification of yttrium oxide, accelerates the diffusion of yttrium oxide grain boundaries, and improves the bending strength of yttrium oxide.

[0022] (3) The green injection molding technology used in this invention is simple in process, can obtain slurry with good dispersibility, and can form yttrium oxide ceramics with complex shapes, resulting in high strength ceramic green bodies. Most importantly, the drying shrinkage and sintering shrinkage of the samples prepared by this gel system are uniform and calculable, with small processing allowance, which greatly reduces the need for subsequent processing and lowers costs. Attached Figure Description

[0023] Figure 1 This is the SEM image of the yttrium oxide ceramic prepared in Example 1.

[0024] Figure 2 This is a photograph of the yttrium oxide ceramic prepared in Example 1. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] Step 1: First, take 100g of yttrium oxide powder (d 5050 g, 30 g, and 20 g of 50 μm, 3 μm, and 550 nm powders were added respectively and ultrasonically dispersed in 250 g of 5% boric acid solution under heating at 45 °C. After heating and ultrasonication for 0.5 h, the powders were dried at 80 °C for 18 h and passed through a 120-mesh sieve to obtain modified yttrium oxide powder.

[0028] Step 2: Add 250g of deionized water, 100g of modified yttrium oxide powder, and 5g of calcium carbonate to a ball mill jar and mix and disperse. Zirconia balls are used for milling, with a ball-to-material ratio of 1:1. The milling speed is 500 r / min, and the milling time is 24 h. Dry at 80℃ for 24 h, pass through a 120-mesh sieve, and calcine at 800℃ for 10 h to obtain calcium oxide-doped modified yttrium oxide powder.

[0029] Step 3: Add 10g Isobam104 gelling agent to 100g deionized water to prepare a 10wt% solution. Adjust the pH to 8 with lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add 60g calcium oxide-doped modified yttrium oxide powder and 0.3g zirconium oxide to the premixed solution. Add 180g zirconium oxide balls and ball mill at 500r / min for 24h to obtain calcium oxide-doped modified yttrium oxide slurry.

[0030] Step 4: After vacuum degassing, the calcium oxide-doped modified yttrium oxide slurry is injected into the mold at a pressure of -0.5 MPa for 60 minutes. It is then cured for 5 minutes under microwave heating at 30°C. After demolding, it is dried in a constant temperature and humidity chamber at 70% humidity and 35°C for 15 hours to obtain a calcium oxide-doped modified yttrium oxide preform. Finally, the ceramic preform is sintered in a sintering furnace. The specific sintering process is as follows: the temperature is increased to 800°C at a rate of 1°C / min and held for 1 hour; then increased to 1650°C at a rate of 1°C / min and held for 2 hours; finally, the obtained ceramic is annealed in air at 1000°C in a muffle furnace for 3 hours to obtain calcium oxide-doped modified yttrium oxide ceramic.

[0031] The SEM image of the ceramic is as follows: Figure 1 As shown, the ceramic grains are uniform with no obvious pores, exhibiting high density; the ceramic fractures are mostly transgranular fractures, which reflects the large energy consumed during ceramic fracture and the high strength of the ceramic.

[0032] The actual image of the ceramic is as follows: Figure 2 As shown, the prepared ceramic has a diameter of 80 mm and a smooth, defect-free surface.

[0033] Example 2

[0034] Step 1: First, take 125g of yttrium oxide powder (d 5075g, 30g, and 20g of 50μm, 3μm, and 550nm powders were added respectively and ultrasonically dispersed in 250g of 7.5% boric acid solution under heating at 50℃. The mixture was heated and ultrasonicated for 45min, dried at 90℃ for 20h, and passed through a 120-mesh sieve to obtain modified yttrium oxide powder.

[0035] Step 2: Add 250g of deionized water, 125g of modified yttrium oxide powder, and 9.375g of calcium carbonate to a ball mill jar and mix and disperse. Zirconia balls are used for milling, with a ball-to-material ratio of 1:2. The milling speed is 400 r / min, and the milling time is 18 h. Dry at 85℃ for 22 h, pass through a 120-mesh sieve, and calcine at 850℃ for 9 h to obtain calcium oxide-doped modified yttrium oxide powder.

[0036] Step 3: Add 15g Isobam104 gelling agent to 100g deionized water to prepare a 15wt% solution. Adjust the pH to 9 with lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add 70g calcium oxide-doped modified yttrium oxide powder and 0.456g zirconium oxide to the premixed solution; add 166g zirconium oxide balls, ball mill at 400r / min for 20h to obtain calcium oxide-doped modified yttrium oxide slurry.

[0037] Step 4: The calcium oxide-doped modified yttrium zirconium oxide slurry is injected into the mold after vacuum degassing. The vacuum degassing pressure is -0.7 MPa and the vacuum degassing time is 50 min. It is then cured for 7 min under microwave heating at 35℃. After demolding, it is dried in a constant temperature and humidity chamber at 75% humidity and 40℃ for 18 h to obtain the calcium oxide-doped modified yttrium oxide ceramic green body. Finally, the ceramic green body is sintered in a sintering furnace. The specific sintering process is as follows: the temperature is increased to 800℃ at a rate of 3℃ / min and held for 1 h, then increased to 1680℃ at a rate of 2℃ / min and held for 4 h. The obtained ceramic is then annealed in air at 1050℃ in a muffle furnace for 2.5 h to obtain calcium oxide-doped modified yttrium oxide ceramic.

[0038] Example 3

[0039] Step 1: First, take 150g of yttrium oxide powder (d 50 50 g, 50 g, and 50 g of 50 μm, 3 μm, and 550 nm powders were added respectively and ultrasonically dispersed in 250 g of 9% boric acid solution under heating at 55 °C. After heating and ultrasonication for 1 h, the powder was dried at 90 °C for 20 h and passed through a 120-mesh sieve to obtain modified yttrium oxide powder.

[0040] Step 2: Add 250g of deionized water, 150g of modified yttrium oxide powder, and 10.5g of calcium carbonate to a ball mill jar and mix and disperse. Zirconia balls are used for milling, with a ball-to-powder ratio of 1:2. The milling speed is 350 r / min, and the milling time is 20 h. Dry at 90℃ for 22 h, pass through a 120-mesh sieve, and calcine at 875℃ for 8.5 h to obtain calcium oxide-doped modified yttrium oxide powder.

[0041] Step 3: Add 20g Isobam104 gelling agent to 100g deionized water to prepare a 20wt% solution. Adjust the pH to 10 with lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add 75g calcium oxide-doped modified yttrium oxide powder and 0.75g zirconium oxide to the premixed solution. Add 510g zirconium oxide balls and ball mill at 300r / min for 18h to obtain calcium oxide-doped modified yttrium oxide slurry.

[0042] Step 4: After vacuum degassing, the calcium oxide-doped modified yttrium oxide slurry is injected into the mold at a pressure of -1 MPa for 60 minutes. It is then cured for 10 minutes under microwave heating at 40°C. After demolding, it is dried in a constant temperature and humidity chamber at 85% humidity and 50°C for 15 hours to obtain a calcium oxide-doped modified yttrium oxide ceramic green body. Finally, the ceramic green body is sintered in a sintering furnace. The specific sintering process is as follows: the temperature is increased to 800°C at a rate of 5°C / min and held for 2 hours; then increased to 1700°C at a rate of 3°C / min and held for 5 hours; finally, the obtained ceramic is annealed in air at 1000°C in a muffle furnace for 2 hours to obtain calcium oxide-doped modified yttrium oxide ceramic.

[0043] Example 4

[0044] Step 1: First, add 137.5g of yttrium oxide powder (d 50 77.5g, 30g, and 30g of 50μm, 3μm, and 550nm powders were added respectively and ultrasonically dispersed in 250g of 10% boric acid solution under heating at 60℃. After heating and ultrasonication for 50min, the powders were dried at 100℃ for 18h and passed through a 120-mesh sieve to obtain modified yttrium oxide powder.

[0045] Step 2: Add 250g of deionized water, 137.5g of modified yttrium oxide powder, and 11g of calcium carbonate to a ball mill jar and mix and disperse. Zirconia balls are used for milling, with a ball-to-material ratio of 1:3. The milling speed is 300 r / min, and the milling time is 24 h. Dry at 100℃ for 18 h, pass through a 120-mesh sieve, and calcine at 900℃ for 8 h to obtain calcium oxide-doped modified yttrium oxide powder.

[0046] Step 3: Prepare a 20wt% solution by mixing 20g Isobam104 gelling agent with deionized water. Adjust the pH to 8 using lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add 70g of calcium oxide-doped modified yttrium oxide and 0.63g of zirconium oxide to the premixed solution. Add 340g of zirconium oxide balls and ball mill at 450r / min for 24h to obtain a calcium oxide-doped modified yttrium oxide slurry.

[0047] Step 4: The calcium oxide-doped modified yttrium oxide slurry is injected into the mold after vacuum degassing. The vacuum degassing pressure is -1 MPa and the vacuum degassing time is 60 min. It is then cured for 6 min under microwave heating at 30℃. After demolding, it is dried in a constant temperature and humidity chamber at 80% humidity and 40℃ for 18 h to obtain the calcium oxide-doped modified yttrium oxide ceramic green body. Finally, the ceramic green body is sintered in a sintering furnace. The specific sintering process is as follows: the temperature is increased to 800℃ at a rate of 2℃ / min and held for 2 h, then increased to 1720℃ at a rate of 3℃ / min and held for 3.5 h. The obtained ceramic is then annealed in air at 1100℃ in a muffle furnace for 2 hours to obtain calcium oxide-doped modified yttrium oxide ceramic.

[0048] Comparative Example

[0049] Step 1: First, take 120g of yttrium oxide powder (d 50 70g, 30g, and 20g of 50μm, 3μm, and 550nm powders were added respectively, and ultrasonically dispersed in 250g of 10% boric acid solution under heating at 60℃. After heating and ultrasonication for 50min, the powder was dried at 100℃ for 18h and passed through a 120-mesh sieve to obtain modified yttrium oxide powder.

[0050] Step 2: Add 250g of deionized water and 137.5g of modified yttrium oxide powder to a ball mill jar and mix and disperse. Zirconia balls are used for milling, with a ball-to-powder ratio of 1:3. The milling speed is 300 r / min, and the milling time is 24 h. Dry at 100℃ for 18 h, pass through a 120-mesh sieve, and calcine at 900℃ for 8 h to obtain modified yttrium oxide powder.

[0051] Step 3: Prepare a 20wt% solution by mixing 20g Isobam104 gelling agent with deionized water. Adjust the pH to 8 using lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add 70g modified yttrium oxide and 0.63g zirconium oxide to the premixed solution. Add 340g zirconium oxide balls and ball mill at 450r / min for 24h to obtain a modified yttrium oxide slurry.

[0052] Step 4: After vacuum degassing, the modified yttrium oxide slurry is injected into the mold. The vacuum degassing pressure is -1 MPa and the vacuum degassing time is 60 min. It is then cured for 6 min under microwave heating at 30℃. After demolding, it is dried in a constant temperature and humidity chamber at 80% humidity and 40℃ for 18 h to obtain the modified yttrium oxide ceramic green body. Finally, the ceramic green body is sintered in a sintering furnace. The specific sintering process is as follows: the temperature is increased to 866℃ at a rate of 2℃ for 5 min and held for 2 h, then increased to 1726℃ at a rate of 3℃ for 5 min and held for 3.5 h. The obtained ceramic is then annealed in air at 1666℃ in a muffle furnace for 2 h to obtain the modified yttrium oxide ceramic.

[0053] The ceramic properties obtained in Examples 1-4 and the comparative examples are detailed in Table 1.

[0054] Table 1. Test results of ceramic properties obtained in Examples 1-4 and comparative examples.

[0055] Example Strength (MPa) Thermal shock resistance (number of thermal shock cycles from 25℃ to 1166℃) Example 1 76 25 Example 2 74 26 Example 3 81 28 Example 4 76 25 Comparative Example 55 12

[0056] Strength testing: A universal electronic testing machine was used. The test followed GB5T 3661-2617.

[0057] Thermal shock resistance test: The test was conducted using a ceramic thermal stability tester, following the GB5T36873-2614 standard. The comparative example was yttrium oxide ceramic without calcium oxide doping modification.

[0058] As shown in Table 1, the calcium oxide-doped modified yttrium oxide ceramics prepared by this invention all have a strength exceeding 76 MPa and exhibit no cracks after more than 25 thermal shock cycles at 25℃-1166℃, indicating that they possess excellent mechanical properties and higher thermal shock resistance.

[0059] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing yttrium oxide ceramics by gel casting, characterized in that, Includes the following steps: Step 1: First, heat the yttrium oxide powder at 45-60℃ and sonicate it for 0.5-1h. Then, disperse it in a boric acid solution with a mass concentration of 5-10%. After drying and sieving, the modified yttrium oxide powder is obtained. Step 2: Add deionized water, modified yttrium oxide powder, and calcium carbonate to a ball mill jar and mix and disperse them. The calcium carbonate accounts for 5%-10% of the modified yttrium oxide powder by mass. After drying, sieving, and calcining at 800-850℃ for 8-10 hours, calcium oxide-doped modified yttrium oxide powder is obtained. Step 3: Mix Isobam gelling agent with ultrapure water, then adjust the pH value to 8-10 with lactic acid and tetramethylammonium hydroxide to obtain a premixed solution. Finally, add calcium oxide-doped modified yttrium oxide powder and sintering aid to the premixed solution, and mix by ball milling to obtain a slurry. Step 4: After vacuum degassing, the slurry is injected into a mold and cured under microwave heating. After demolding, it is dried to obtain a yttrium oxide ceramic green body. Finally, the ceramic green body is sintered in a vacuum sintering furnace and then annealed in a muffle furnace to obtain yttrium oxide ceramic.

2. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step one, the yttrium oxide powder has three different particle sizes, d 50 The particle sizes are 50μm, 3μm, and 550nm, respectively, with a ratio of 5:3:2; the amount of yttrium oxide added is 40-60wt%; the drying temperature is 80-100℃, the drying time is 18-24h, and it is passed through a 120-mesh sieve.

3. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step two, the modified yttrium oxide powder accounts for 40%-60% of the mass of the mixture; the drying temperature is 80-100℃, the drying time is 18-24h, and it is passed through a 120-mesh sieve.

4. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step three, the Isobam gelling agent is Isobam104, which is fully dissolved in ultrapure water to prepare a solution with a concentration of 10-20 wt%.

5. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step three, the solid content of calcium oxide-doped modified yttrium oxide powder in the slurry is 60-75% by mass; the sintering aid is zirconium oxide, and the amount added is 0.5-1 wt% of the calcium oxide-doped modified yttrium oxide powder.

6. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step four, the vacuum degassing pressure is -0.5 to -1 MPa, and the vacuum degassing time is 40-60 min; the microwave heating temperature is 30-40℃, and the curing time is 5-10 min; the specific drying process is as follows: dry in a constant temperature and humidity chamber with a humidity of 70-85% and a temperature of 35-50℃ for 15-20 h.

7. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step four, the sintering process is as follows: heat up to 800℃ at a rate of 1-5℃ / min, hold for 1-2 hours, then heat up to 1650-1720℃ at a rate of 1-3℃ / min, and hold for 2-4 hours.

8. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In step four, the sintered ceramic is placed in a muffle furnace and annealed in air at 1000-1100℃ for 2-3 hours.

9. The method for preparing yttrium oxide ceramic by gel casting according to claim 1, characterized in that, In steps two and three, the grinding balls used in the ball mill are zirconia balls, the ball-to-material ratio is 1:1~3, the ball milling speed is 300-500 r / min, and the ball milling time is 12-24 h.

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