Low thermal expansion high thermal shock barium zirconate composite ceramic and method of making same

Abstract

This invention relates to a low thermal expansion and high thermal shock barium zirconate composite ceramic and its preparation method. The technical solution is as follows: Barium zirconate powder and ethanol are ground and dried to obtain barium zirconate powder; the barium zirconate powder is mixed with a lanthanum compound, ball-milled, and the ball-milled mixture is dried and granulated, machine-pressed, and then isostatically pressed to obtain a ceramic green body; the isostatic pressing process involves five pressure increases: the pressures of the five pressure increases are 25–35 MPa, 40–70 MPa, 80–100 MPa, 110–130 MPa, 140–200 MPa, and 140–200 MPa, respectively, and the pressure is maintained at 140–200 MPa; the ceramic green body is heated at different rates to 980–1020℃, 1290–1310℃, 1490–1510℃, and 1550–1650℃, respectively, and held at 1550–1650℃ for 1–6 hours to obtain a low-expansion, high-thermal-shock barium zirconate composite ceramic. The present invention features low sintering temperature and low carbon emissions, and the resulting products have low bulk density, high apparent porosity, low coefficient of thermal expansion, and good thermal shock resistance.

Description

Technical Field

[0001] This invention belongs to the technical field of barium zirconate composite ceramics. In particular, it relates to a barium zirconate composite ceramic with low thermal expansion and high thermal shock, and its preparation method. Background Technology

[0002] Zirconium dioxide has a high melting point (2680℃), stable chemical properties, strong resistance to slag erosion, and is not wetted by liquid metal. In the iron and steel metallurgical process, zirconium components are mainly used as zirconium plates in converter slide gates and zirconium cores in tundish sizing nozzles. During converter tapping, the slide gate is subjected to strong erosion from high-temperature molten steel and slag, and also needs to withstand the large surface pressure of the hydraulic mechanism. Frequent opening and closing processes can cause surface erosion, scratching, and steel clamping. Moreover, drastic changes in ambient temperature make the zirconium plates susceptible to thermal shock damage. Due to the low thermal conductivity of zirconium dioxide, the temperature gradient generated during continuous casting in the tundish sizing nozzle can cause the interconversion of m-ZrO2 and c-ZrO2 in the zirconium core, resulting in microcracks. The synergistic effect of the temperature gradient on the structure and slag erosion accelerates the damage of the zirconium core, thereby reducing its performance and service life.

[0003] Barium zirconate has a cubic perovskite structure, a melting point of 2700℃, and a theoretical density of 6.23 g / cm³. 3 Barium zirconate ceramics do not undergo phase transformation and possess excellent high-temperature mechanical and thermal properties, making them suitable for refractory industry production. They hold promise for applications such as replacing zirconium plates in converters and replacing zirconium core materials in tundishes. However, the thermal shock cracking problem caused by the evaporation of barium oxide and the subsequent monoclinic zirconium oxide phase transformation remains a key limitation to their application. According to the theories of thermal stress fracture and Hasselma, reducing the coefficient of thermal expansion of barium zirconate ceramics is beneficial to improving their thermal shock resistance and extending their lifespan, thus attracting the attention of those skilled in the art.

[0004] The patented technology, "A Dense Barium Zirconate-Based Composite Ceramics and Its Preparation Method" (CN 113336545 A), involves mixing barium carbonate, calcium carbonate, zirconium dioxide, and titanium dioxide; holding the mixture at 1100℃~1300℃ for 1~3h, crushing, and grinding to obtain barium zirconate-based composite ceramic powder; pressing the barium zirconate-based composite ceramic powder under 50~100MPa to obtain a barium zirconate-based composite ceramic green body; and heating to 1500~1650℃ and holding for 3~5h to obtain a dense barium zirconate-based composite ceramic. However, this technology involves pre-firing and crushing, as well as the decomposition of barium carbonate and calcium carbonate, which increases carbon emissions. The prepared barium zirconate ceramic has a dense structure, high bulk density, and low apparent porosity.

[0005] A patented method for preparing high-density barium zirconate ceramics (CN 103864419A) describes a process using commercially available barium zirconate powder as raw material. The powder is ground, dry-pressed, and isostatically pressed to obtain a green body. This green body is then heated to 1600℃-1800℃ in a vacuum or air atmosphere at a rate of 1-20℃ / min and held for 2-12 hours to obtain the barium zirconate ceramic material. However, this invention requires a high sintering temperature and a long holding time. The prepared barium zirconate ceramic has a density close to the theoretical density, high bulk density, low apparent porosity, and high elastic modulus.

[0006] Reference I (Han D, Hatada N, Uda T. Chemical expansion of yttrium-dopedbariumzirconate and correlation with proton concentration and conductivity[J]. Journal of the American Ceramic Society, 2016, 99:3745–3753) reports that the coefficient of thermal expansion of barium zirconate was 8.02 × 10⁻⁶ at 30–1000 °C using HT-XRD in dry atmosphere. -6 K -1 It has a relatively large coefficient of thermal expansion.

[0007] Reference II (Jianing Wang Shujing Li, Yuanbing Li. Fabrication and thermal shock behavior of BaZrO3–MgO composites[J]. Ceramics International, 2022, 48: 33801–33808) reports the preparation of BaZrO3–MgO composite ceramics, but the coefficient of thermal expansion of BaZrO3 is 8.7 × 10⁻⁶ at 298–1352 °C. -6 K -1 The coefficient of thermal expansion of MgO is 14.3 × 10⁻⁶ °C between 20 and 1000 °C. -6 K -1 The coefficients of thermal expansion are large and vary considerably, resulting in technical defects such as thermal shock cracking and poor thermal shock performance. Summary of the Invention

[0008] The present invention aims to overcome the defects of the prior art and provides a method for preparing barium zirconate composite ceramics with low thermal expansion and high thermal shock, which has low sintering temperature, short holding time and low carbon emissions. The barium zirconate composite ceramics prepared by this method have low bulk density, high apparent porosity, low elastic modulus, low coefficient of thermal expansion, good thermal shock stability and crack resistance.

[0009] To achieve the above objectives, the preparation method of the technical solution adopted in this invention is as follows:

[0010] Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1-0.99 μm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder.

[0011] Step 2: Mix 85-99 wt% of the barium zirconate powder and 1-15 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture.

[0012] Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body.

[0013] The isostatic pressing process consists of five stages of pressure increase: the first stage pressure is 25–35 MPa, the second stage pressure is 40–70 MPa, the third stage pressure is 80–100 MPa, the fourth stage pressure is 110–130 MPa, and the fifth stage pressure is 140–200 MPa, with the pressure held at 140–200 MPa for 2–8 minutes.

[0014] Step 4: The ceramic green body is fired according to the heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic.

[0015] The heating regime is as follows:

[0016] First, raise the temperature from room temperature to 980–1020℃ at a rate of 1–10℃ / min;

[0017] Then raise the temperature to 1290–1310℃ at a rate of 1–6℃ / min;

[0018] Then, the temperature is increased to 1490–1510 °C at a rate of 1–3 °C / min;

[0019] Finally, the temperature is increased to 1550–1650℃ at a rate of 1–2℃ / min, and held at 1550–1650℃ for 1–6 hours.

[0020] The purity of the barium zirconate powder is 95-99.99%; the particle size of the barium zirconate powder is 0.05-0.1 mm.

[0021] The lanthanum compound is one of lanthanum chloride, lanthanum hydroxide, lanthanum nitrate, and organolanthanum; the purity of the lanthanum compound is 99-99.99%, and the particle size of the lanthanum compound is 0.1-0.99 μm.

[0022] The tank of the high-energy ball mill is made of zirconium oxide, the ball-to-material ratio of the high-energy ball mill is 1:0.4 to 0.6, and the rotation speed of the high-energy ball mill is 300 to 800 r / min.

[0023] The drying process is carried out at a temperature of 90–130°C for 22–28 hours.

[0024] The drying and granulation speed is 20,000 to 30,000 r / min, and the drying and granulation temperature is 200 to 300℃.

[0025] The pressure of the machine pressing is 80-120 MPa.

[0026] By adopting the above technical solution, the present invention has the following positive effects compared with the prior art.

[0027] 1. Because this invention employs high-energy ball milling technology to grind barium zirconate powder to the nanoscale, the nanoparticles possess numerous defects and extremely high surface energy, resulting in high sintering driving force and promoting sintering. Furthermore, because this invention utilizes spray drying technology, the spray-dried barium zirconate composite granules exhibit good flowability, facilitating the molding and demolding of ceramic green bodies. This reduces large porosity and crack defects. The spray-dried barium zirconate composite granules have a large specific surface area, good dispersibility, and more uniform distribution of different components and particle size, which is beneficial for sintering. The low thermal expansion and high thermal shock barium zirconate composite ceramic sintering temperature is lowered. Compared to pre-sintering and crushing, this invention features a simpler process, lower sintering temperature, shorter holding time, and lower carbon emissions.

[0028] 2. The lanthanum compound used in this invention decomposes into lanthanum oxide and gas during heat treatment at 25-1000℃. During the gas volatilization process, uniform micropores are formed in the material. An appropriate amount of micropores will increase the apparent porosity of barium zirconate composite ceramics with low thermal expansion and high thermal shock, and reduce its bulk density, elastic modulus and coefficient of thermal expansion.

[0029] 3. Based on existing technology, the radius of zirconium ions is 0.072 nm; the radius of barium ions is 0.135 nm; the radius of oxygen ions is 0.14 nm; and the radius of lanthanum ions is 0.103 nm. Furthermore, according to solid solution theory, lanthanum ions can dissolve into the barium zirconate lattice, replacing barium ions to form a substitution solid solution. This significantly improves the thermodynamic stability of barium zirconate, inhibits barium oxide evaporation cracking, and enhances the bonding strength of low-thermal-expansion, high-thermal-shock barium zirconate ceramics. The nanostructure increases the elastic strain effect in low-thermal-expansion, high-thermal-shock barium zirconate composite ceramics, reducing the material's elastic modulus. The decomposition of lanthanum compounds facilitates the formation of uniform micropores in low-thermal-expansion, high-thermal-shock barium zirconate composite ceramics. When the material is subjected to thermal stress, cracks are pinned by these micropores, hindering crack propagation. Lanthanum oxide reacts with some zirconium oxide to form lamellar lanthanum zirconate, which pins between barium zirconate grains, refining the grains and inhibiting crack propagation. Therefore, the thermal shock resistance of low-thermal-expansion, high-thermal-shock barium zirconate composite ceramics is improved.

[0030] The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared by this invention was tested and found to have a bulk density of 5.63–5.73 g / cm³. 3 Apparent porosity 5.33–6.21%; elastic modulus 110.3–121.3 GPa; coefficient of thermal expansion at 25–1400℃ 5.34–5.82 × 10⁻⁶ -6 K -1 The flexural strength retention rate after three flexural cycles at 1100℃ is 77.7%–157.5%.

[0031] Therefore, the present invention has the characteristics of low sintering temperature, short holding time and low carbon emissions. The prepared low thermal expansion and high thermal shock barium zirconate composite ceramic has low bulk density, high apparent porosity, low elastic modulus, low coefficient of thermal expansion, good thermal shock performance and crack resistance, providing a good application basis for converter zirconium plates and tundish zirconium core replacement materials. Attached Figure Description

[0032] Figure 1 SEM image of a low thermal expansion and high thermal shock barium zirconate composite ceramic prepared according to the present invention;

[0033] Figure 2 for Figure 1 The XRD pattern of barium zirconate powder used in the preparation of barium zirconate composite ceramics with low thermal expansion and high thermal shock is shown.

[0034] Figure 3 for Figure 1 The XRD pattern of the low thermal expansion and high thermal shock barium zirconate composite ceramic is shown. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of protection thereof.

[0036] A low thermal expansion, high thermal shock barium zirconate composite ceramic and its preparation method are described in this specific embodiment.

[0037] Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1-0.99 μm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder.

[0038] Step 2: Mix 85-99 wt% of the barium zirconate powder and 1-15 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture.

[0039] Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body.

[0040] The isostatic pressing process consists of five stages of pressure increase: the first stage pressure is 25–35 MPa, the second stage pressure is 40–70 MPa, the third stage pressure is 80–100 MPa, the fourth stage pressure is 110–130 MPa, and the fifth stage pressure is 140–200 MPa, with the pressure held at 140–200 MPa for 2–8 minutes.

[0041] Step 4: The ceramic green body is fired according to the heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic.

[0042] The heating regime is as follows:

[0043] First, raise the temperature from room temperature to 980–1020℃ at a rate of 1–10℃ / min;

[0044] Then raise the temperature to 1290–1310℃ at a rate of 1–6℃ / min;

[0045] Then, the temperature is increased to 1490–1510 °C at a rate of 1–3 °C / min;

[0046] Finally, the temperature is increased to 1550–1650℃ at a rate of 1–2℃ / min, and held at 1550–1650℃ for 1–6 hours.

[0047] The purity of the barium zirconate powder is 95-99.99%.

[0048] The lanthanum compound is one of lanthanum chloride, lanthanum hydroxide, lanthanum nitrate, and organolanthanum compounds; the purity of the lanthanum compound is 99–99.99%.

[0049] The ball-to-material ratio of the high-energy ball mill is 1:0.4 to 0.6; the rotational speed of the high-energy ball mill is 300 to 800 r / min.

[0050] The drying process is carried out at a temperature of 90–130°C for 22–28 hours.

[0051] The drying and granulation speed is 20,000 to 30,000 r / min, and the drying and granulation temperature is 200 to 300℃.

[0052] The pressure of the machine pressing is 80-120 MPa.

[0053] In this specific implementation:

[0054] The barium zirconate powder has a particle size of 0.05–0.1 mm;

[0055] The particle size of the lanthanum compound is 0.1–0.99 μm;

[0056] The tank of the high-energy ball mill is made of zirconium oxide.

[0057] The details will not be repeated in the examples.

[0058] Example 1

[0059] A low thermal expansion, high thermal shock barium zirconate composite ceramic and its preparation method. The preparation method described in this embodiment is as follows:

[0060] Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1-0.99 μm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder.

[0061] Step 2: Mix 99 wt% of the barium zirconate powder and 1 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture.

[0062] Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body.

[0063] The isostatic pressing process consists of five pressure increases: the first pressure increase is 25 MPa, the second pressure increase is 40 MPa, the third pressure increase is 80 MPa, the fourth pressure increase is 110 MPa, and the fifth pressure increase is 140 MPa. The pressure is held at 140 MPa for 2 minutes.

[0064] Step 4: The ceramic green body is fired according to the heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic.

[0065] The heating regime is as follows:

[0066] First, the temperature is increased from room temperature to 980℃ at a rate of 1℃ / min;

[0067] Then raise the temperature to 1290℃ at a rate of 1℃ / min;

[0068] Then the temperature is increased to 1490℃ at a rate of 1℃ / min;

[0069] Finally, the temperature was increased to 1550℃ at a rate of 1℃ / min and held at 1550℃ for 1 hour.

[0070] The purity of the barium zirconate powder is 95%.

[0071] The lanthanum compound is lanthanum chloride; the purity of the lanthanum compound is 99%.

[0072] The ball-to-material ratio of the high-energy ball mill is 1:0.6; the rotational speed of the high-energy ball mill is 300 r / min.

[0073] The drying process is carried out at a temperature of 90°C for 22 hours.

[0074] The drying and granulation speed is 20,000 r / min, and the drying and granulation temperature is 200℃.

[0075] The pressure of the machine pressing is 80 MPa.

[0076] The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in this embodiment was measured to have the following bulk density (g / cm³): 3 The apparent porosity (%) was 5.73; the elastic modulus (GPa) was 5.33; the coefficient of thermal expansion (K) at 25–1400℃ was 121.3; and the coefficient of thermal expansion (K) at 25–1400℃ was 5.73. -1 The value is 5.82 × 10 -6 The flexural strength retention rate (%) after three flexural cooling at 1100℃ was 77.7%.

[0077] Compared with pure barium zirconate ceramics, the barium zirconate composite ceramics have lower bulk density, significantly higher apparent porosity, lower elastic modulus, lower coefficient of thermal expansion, and significantly improved thermal shock resistance.

[0078] Example 2

[0079] A low thermal expansion, high thermal shock barium zirconate composite ceramic and its preparation method. The preparation method described in this embodiment is as follows:

[0080] Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1-0.99 μm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder.

[0081] Step 2: Mix 95 wt% of the barium zirconate powder and 5 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture.

[0082] Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body.

[0083] The isostatic pressing process consists of five pressure increases: the pressure of the first pressure increase is 28 MPa, the pressure of the second pressure increase is 60 MPa, the pressure of the third pressure increase is 90 MPa, the pressure of the fourth pressure increase is 113 MPa, and the pressure of the fifth pressure increase is 170 MPa. The pressure is held at 170 MPa for 4 minutes.

[0084] Step 4: The ceramic green body is fired according to the heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic.

[0085] The heating regime is as follows:

[0086] First, the temperature is increased from room temperature to 1005℃ at a rate of 8℃ / min;

[0087] Then raise the temperature to 1295℃ at a rate of 3℃ / min;

[0088] Then the temperature is increased to 1500℃ at a rate of 2℃ / min;

[0089] Finally, the temperature was increased to 1600℃ at a rate of 1.5℃ / min and held at 1600℃ for 2 hours.

[0090] The purity of the barium zirconate powder is 97%.

[0091] The lanthanum compound is lanthanum hydroxide; the purity of the lanthanum compound is 99.1%.

[0092] The ball-to-material ratio of the high-energy ball mill is 1:0.43; the rotational speed of the high-energy ball mill is 500 r / min.

[0093] The drying process is carried out at a temperature of 115°C for 24 hours.

[0094] The drying and granulation speed is 23000 r / min, and the drying and granulation temperature is 270℃.

[0095] The pressure of the machine pressing is 110 MPa.

[0096] The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in this embodiment was measured to have the following bulk density (g / cm³): 3 The apparent porosity (%) was 5.70; the apparent porosity (%) was 5.46; the elastic modulus (GPa) was 115.1; and the coefficient of thermal expansion (K) at 25–1400℃ was [missing value]. -1 The strength was 5.76×10-6; the retention rate of the flexural strength after three flexural cycles at 1100℃ was 83.9%.

[0097] Compared with pure barium zirconate ceramics, the barium zirconate composite ceramics have lower bulk density, significantly higher apparent porosity, lower elastic modulus, lower coefficient of thermal expansion, and significantly improved thermal shock resistance.

[0098] Example 3

[0099] A low thermal expansion, high thermal shock barium zirconate composite ceramic and its preparation method. The preparation method described in this embodiment is as follows:

[0100] Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1-0.99 μm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder.

[0101] Step 2: Mix 92 wt% of the barium zirconate powder and 8 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture.

[0102] Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body.

[0103] The isostatic pressing process consists of five pressure increases: the first pressure increase is 30 MPa, the second pressure increase is 50 MPa, the third pressure increase is 95 MPa, the fourth pressure increase is 115 MPa, and the fifth pressure increase is 150 MPa, with the pressure held at 150 MPa for 5 minutes.

[0104] Step 4: The ceramic green body is fired according to the heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic.

[0105] The heating regime is as follows:

[0106] First, the temperature is increased from room temperature to 990℃ at a rate of 7℃ / min;

[0107] Then raise the temperature to 1305℃ at a rate of 4℃ / min;

[0108] Then the temperature is increased to 1495℃ at a rate of 3℃ / min;

[0109] Finally, the temperature was increased to 1600℃ at a rate of 2℃ / min and held at 1600℃ for 3 hours.

[0110] The purity of the barium zirconate powder is 96%.

[0111] The lanthanum compound is lanthanum nitrate; the purity of the lanthanum compound is 99.3%.

[0112] The ball-to-material ratio of the high-energy ball mill is 1:0.47; the rotational speed of the high-energy ball mill is 600 r / min.

[0113] The drying process is carried out at a temperature of 110°C for 25 hours.

[0114] The drying and granulation speed is 24000 r / min, and the drying and granulation temperature is 260℃.

[0115] The pressure of the machine pressing is 100 MPa.

[0116] The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in this embodiment was measured to have the following bulk density (g / cm³): 3 The apparent porosity (%) was 5.68; the apparent porosity (%) was 5.75; the elastic modulus (GPa) was 112.5; and the coefficient of thermal expansion (K) at 25–1400℃ was [missing value]. -1 The value is 5.61 × 10 -6 The flexural strength retention rate (%) after three flexural cooling at 1100℃ was 102.2%.

[0117] Compared with pure barium zirconate ceramics, the barium zirconate composite ceramics have lower bulk density, significantly higher apparent porosity, lower elastic modulus, lower coefficient of thermal expansion, and significantly improved thermal shock resistance.

[0118] Example 4

[0119] A low thermal expansion, high thermal shock barium zirconate composite ceramic and its preparation method. The preparation method described in this embodiment is as follows:

[0120] Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1-0.99 μm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder.

[0121] Step 2: Mix 85 wt% of the barium zirconate powder and 15 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture.

[0122] Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body.

[0123] The isostatic pressing process consists of five pressure increases: the first pressure increase is 35 MPa, the second pressure increase is 70 MPa, the third pressure increase is 100 MPa, the fourth pressure increase is 130 MPa, and the fifth pressure increase is 200 MPa. The pressure is held at 200 MPa for 8 minutes.

[0124] Step 4: The ceramic green body is fired according to the heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic.

[0125] The heating regime is as follows:

[0126] First, the temperature is increased from room temperature to 1020℃ at a rate of 10℃ / min;

[0127] Then increase the temperature to 1310℃ at a rate of 6℃ / min;

[0128] Then the temperature is increased to 1510℃ at a rate of 3℃ / min;

[0129] Finally, the temperature was increased to 1650℃ at a rate of 1℃ / min and held at 1650℃ for 6 hours.

[0130] The purity of the barium zirconate powder is 99.99%.

[0131] The lanthanum compound is an organolanthanum compound; the purity of the lanthanum compound is 99.99%.

[0132] The ball-to-material ratio of the high-energy ball mill is 1:0.4; the rotational speed of the high-energy ball mill is 800 r / min.

[0133] The drying process is carried out at a temperature of 130°C for 28 hours.

[0134] The drying and granulation speed is 30,000 r / min, and the drying and granulation temperature is 300℃.

[0135] The pressure of the machine pressing is 120 MPa.

[0136] The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in this embodiment was measured to have the following bulk density (g / cm³): 3 The apparent porosity (%) was 5.63; the apparent porosity (%) was 6.21; the elastic modulus (GPa) was 110.3; and the coefficient of thermal expansion (K) at 25–1400℃ was [missing value]. -1 The value is 5.34 × 10 -6 The flexural strength retention rate (%) after three flexural cooling at 1100℃ was 157.5%.

[0137] Compared with pure barium zirconate ceramics, the barium zirconate composite ceramics have lower bulk density, significantly higher apparent porosity, lower elastic modulus, lower coefficient of thermal expansion, and significantly improved thermal shock resistance.

[0138] This specific implementation method has the following positive effects compared with the prior art.

[0139] 1. Because this specific embodiment employs high-energy ball milling technology to grind barium zirconate powder to the nanoscale, the nanoparticles possess numerous defects and extremely high surface energy, resulting in high sintering driving force and promoting sintering. Furthermore, because this specific embodiment utilizes spray drying technology, the spray-dried barium zirconate composite granules exhibit good fluidity, facilitating the molding and demolding of ceramic green bodies. This reduces large porosity and crack defects. The spray-dried barium zirconate composite granules have a large specific surface area, good dispersibility, and more uniform distribution of different components and particle size, which is beneficial for sintering. The low thermal expansion and high thermal shock barium zirconate composite ceramic sintering temperature is lowered. Compared to pre-sintering and crushing, this specific embodiment features a simpler process, lower sintering temperature, shorter holding time, and lower carbon emissions.

[0140] 2. The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in this specific embodiment is shown in the attached figure. Figure 1 SEM image of a low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in Example 2; Figure 2 for Figure 1 The XRD pattern of barium zirconate powder used in the preparation of barium zirconate composite ceramics with low thermal expansion and high thermal shock is shown. Figure 3 for Figure 1 The image shows the XRD pattern of a barium zirconate composite ceramic with low thermal expansion and high thermal shock. From... Figure 1 It can be seen that the manufactured product has a large number of pores, with pore sizes ranging from approximately 5 to 40 μm; from Figure 2 It can be seen that the barium zirconate powder contains a barium zirconate phase and a small amount of monoclinic zirconium oxide impurity phase, because monoclinic zirconium oxide is generated by the evaporation of barium oxide during the electrofusion production process of barium zirconate raw materials. Figure 3 It can be seen that the low thermal expansion and high thermal shock barium zirconate composite ceramic prepared in Example 2 contains the formation of a lanthanum zirconate phase. Specifically, the lanthanum compound used in this embodiment decomposes into lanthanum oxide and gas during heat treatment at 25–1000°C. The lanthanum oxide reacts with some monoclinic zirconium oxide to form plate-like lanthanum zirconate, and the gas volatilizes to form uniform micropores within the material. An appropriate amount of micropores increases the apparent porosity of the low thermal expansion and high thermal shock barium zirconate composite ceramic, while reducing its bulk density, elastic modulus, and coefficient of thermal expansion.

[0141] 3. Based on existing technology, the radius of zirconium ions is 0.072 nm; the radius of barium ions is 0.135 nm; the radius of oxygen ions is 0.14 nm; and the radius of lanthanum ions is 0.103 nm. Furthermore, according to solid solution theory, lanthanum ions can dissolve into the barium zirconate lattice, replacing barium ions to form a substitution solid solution. This significantly improves the thermodynamic stability of barium zirconate, inhibits barium oxide evaporation cracking, and enhances the bonding strength of low-thermal-expansion, high-thermal-shock barium zirconate ceramics. The nanostructure increases the elastic strain effect in low-thermal-expansion, high-thermal-shock barium zirconate composite ceramics, reducing the material's elastic modulus. The decomposition of lanthanum compounds facilitates the formation of uniform micropores in low-thermal-expansion, high-thermal-shock barium zirconate composite ceramics. When the material is subjected to thermal stress, cracks are pinned by these micropores, hindering crack propagation. The lamellar lanthanum zirconate pins between barium zirconate grains, refining the grains and inhibiting crack propagation. Therefore, the thermal shock resistance of low-thermal-expansion, high-thermal-shock barium zirconate composite ceramics is improved.

[0142] The low thermal expansion and high thermal shock barium zirconate composite ceramic prepared according to this specific embodiment has a bulk density of 5.63–5.73 g / cm³. 3 Apparent porosity 5.33–6.21%; elastic modulus 110.3–121.3 GPa; coefficient of thermal expansion at 25–1400℃ 5.34–5.82 × 10⁻⁶ -6 K -1 The flexural strength retention rate after three flexural cycles at 1100℃ is 77.7%–157.5%.

[0143] Performance testing standards for this specific implementation method:

[0144] GB / T 25995-2010 uses the Archimedes method to test the bulk density and apparent porosity of heat-treated ceramics.

[0145] GB / T 6569-2006 specifies the use of the three-point bending method on a WanCe testing machine to test the bending strength of heat-treated ceramics, with a span of 20 mm and a displacement speed of 0.15 mm / min.

[0146] JC / T 2172-2013 uses the pulse excitation method to test the elastic modulus of heat-treated ceramics;

[0147] GB / T16535-2008 uses the push rod method to test the average linear thermal expansion coefficient of heat-treated ceramics.

[0148] GB / T 37246-2018 Test the retention rate of ceramic thermal shock after three air-cooling cycles following heat treatment by holding at 1100℃ for 15 min.

[0149] Therefore, this specific embodiment features low sintering temperature, short holding time, and low carbon emissions. The prepared low thermal expansion and high thermal shock barium zirconate composite ceramic has low bulk density, high apparent porosity, low elastic modulus, low coefficient of thermal expansion, good thermal shock performance, and crack resistance, providing a good application basis for converter zirconium plates and tundish zirconium core replacement materials.

Claims

1. A method for preparing a barium zirconate composite ceramic with low thermal expansion and high thermal shock, characterized in that: The preparation method is as follows: Step 1: Place barium zirconate powder and ethanol into the tank of a high-energy ball mill, add grinding balls, and grind the barium zirconate powder to a particle size of 0.1~0.99µm to obtain a barium zirconate suspension; dry the barium zirconate suspension to obtain barium zirconate powder. Step 2: Mix 85-99 wt% of the barium zirconate powder and 1-15 wt% of the lanthanum compound, place the mixture in a ball mill jar, add pure water, and ball mill to obtain a mixture. Step 3: Place the mixture into a spray dryer for drying and granulation to obtain granulated material; first press the granulated material into shape by machine, and then press it into shape by isostatic pressing to obtain ceramic green body; The isostatic pressing process consists of five stages of pressure increase: the first stage pressure increase is 25~35MPa, the second stage pressure increase is 40~70MPa, the third stage pressure increase is 80~100MPa, the fourth stage pressure increase is 110~130MPa, and the fifth stage pressure increase is 140~200MPa, with the pressure held at 140~200MPa for 2~8 minutes. Step 4: The ceramic green body is fired according to the following heating regime to obtain low-expansion, high-thermal-shock barium zirconate composite ceramic. First, raise the temperature from room temperature to 980-1020℃ at a rate of 1-10℃ / min. Then increase the temperature to 1290~1310℃ at a rate of 1~6℃ / min. Then, the temperature is increased to 1490-1510℃ at a rate of 1-3℃ / min. Finally, the temperature is increased to 1550-1650℃ at a rate of 1-2℃ / min, and held at 1550-1650℃ for 1-6 hours. The barium zirconate powder has a purity of 95-99.99% and a particle size of 0.05-0.1 mm. The lanthanum compound is one of lanthanum chloride, lanthanum hydroxide, lanthanum nitrate, and organolanthanum, and the purity of the lanthanum compound is 99~99.99%, and the particle size of the lanthanum compound is 0.1~0.99μm; The tank of the high-energy ball mill is made of zirconium oxide, the ball-to-material ratio of the high-energy ball mill is 1:0.4~0.6, and the rotation speed of the high-energy ball mill is 300~800 r / min; The drying and granulation speed is 20,000~30,000 r / min, and the drying and granulation temperature is 200~300℃.

2. The preparation method of the low thermal expansion and high thermal shock barium zirconate composite ceramic as described in claim 1, characterized in that: The drying process is carried out at a temperature of 90~130℃ for 22~28 hours.

3. The preparation method of the low thermal expansion and high thermal shock barium zirconate composite ceramic as described in claim 1, characterized in that: The pressure of the machine pressing is 80~120MPa.

4. A low thermal expansion, high thermal shock barium zirconate composite ceramic, characterized in that: The low thermal expansion and high thermal shock barium zirconate composite ceramic is prepared by the preparation method of the low thermal expansion and high thermal shock barium zirconate composite ceramic according to any one of claims 1 to 3.

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