A dense high-strength high-modulus near-zero-expansion cordierite ceramic and a preparation method and application thereof

Abstract

The application discloses a kind of dense high-strength high-modulus cordierite ceramics and its preparation method and application;The cordierite ceramic is mixed after high-purity cordierite powder, mullite whisker, alumina whisker, thermal expansion coefficient regulator and boron oxide are granulated, the powder obtained after granulation is pressed into shape and then cold isostatic pressing treatment is carried out, glue is discharged, high-temperature normal-pressure sintering is carried out, and cordierite ceramic is obtained, and then hot isostatic pressing sintering is carried out;Control the hot isostatic pressing sintering temperature to be 1200~1300 ℃, the holding time is 0.5~4h, and the pressure applied is 100~300MPa;The high-purity cordierite powder with cordierite crystal phase content ≥99.5% and hot isostatic pressing and other measures are used in the application, and the cordierite ceramic is realized with mechanical properties and thermal properties, and the specific stiffness is ≥59.0N / tex, the room temperature expansion coefficient is ≤3×10 ‑8 ℃ ‑1 .

Description

Technical Field

[0001] This invention relates to cordierite ceramics, specifically to a dense, high-strength, high-modulus, near-zero expansion cordierite ceramic, its preparation method, and its applications; belonging to the field of structural ceramics technology. Background Technology

[0002] With social development and technological progress, cordierite ceramic materials are constantly being discovered to have new functions and applications. Cordierite ceramics are silicate materials with excellent properties. Their low dielectric constant makes them suitable for use as electronic packaging materials and in printed circuit boards. In addition, cordierite has a low coefficient of thermal expansion and high mechanical strength, making it suitable for use in refractory materials. For example, the actual service temperature of heat transmission pipes used in solar power generation is approximately 1100℃, and the pipe material must withstand thermal shocks with temperature differences exceeding 800℃ for extended periods. Under such harsh operating conditions, ordinary alloy and ceramic materials generally suffer from short service life, poor resistance to high-temperature oxidation, and inadequate high-temperature strength.

[0003] Cordierite crystals exist in three allotropes: α-, β-, and μ-. α-Cordierite, also known as Indian stone, belongs to the hexagonal crystal system. The coefficient of thermal expansion of α-cordierite exhibits anisotropy, showing positive values ​​along the a and b axes and negative values ​​along the c axis, resulting in a low coefficient of thermal expansion. Chinese invention patent application CN1090262A describes the preparation of dense cordierite ceramics by sintering at 1320–1400℃. While this technique produces cordierite ceramics with high density, the excessively high sintering temperature and prolonged holding time significantly increase the content of the glassy phase. Compared to α-cordierite, the glassy phase has a higher coefficient of thermal expansion. This mismatch in coefficients of thermal expansion makes the ceramics highly susceptible to microcracks, which is detrimental to the mechanical properties of cordierite ceramics. As reported in "The Influence of Additives on the Synthesis Temperature and Coefficient of Thermal Expansion of Cordierite," adding co-solvents such as lithium oxide can promote the densification of cordierite ceramics and reduce their coefficient of thermal expansion. However, the resulting cordierite has low purity, with the cordierite crystalline phase content in the ceramics being only 90 wt%, which keeps the coefficient of thermal expansion of the prepared cordierite ceramics at a relatively high level. Furthermore, while co-solvents can lower the liquid phase formation temperature and reduce the liquid phase viscosity, they can also lead to a decrease in the mechanical properties of the material. According to the report "Densification and Characterization of β-Spodumene-Cordierite Compositions" (Naga, SM, AMERICAN CERAMIC SOCIETY BULLETIN, Volume 85, Issue 11, Pages: 9101-9110), the introduction of spodumene into the cordierite ceramic matrix can help reduce the coefficient of thermal expansion of the prepared samples. However, with the increase of spodumene content, the mechanical properties of the material also decrease without the introduction of a reinforcing phase. The highest flexural strength of the prepared cordierite ceramic is only 101.75 MPa, which will limit the application of the prepared cordierite ceramic.

[0004] Therefore, while introducing thermal expansion coefficient regulators and sintering aids into cordierite ceramics can improve the thermal properties of the material, it will also reduce its mechanical properties. Thus, it is necessary to introduce reinforcing phases, such as alumina whiskers and mullite whiskers, into cordierite ceramics for reinforcement. However, these second phases hinder the sintering of the ceramics. The mullite whisker-reinforced cordierite ceramics prepared in "Preparation of In-situ Reinforced Cordierite-Mullite Porous Ceramics with Mullite Whiskers" (Lian Xiaoqing, Refractory Materials, 57(01), 65-69) had a sintering temperature as high as 1350℃. Furthermore, its microstructure shows that the mullite whiskers intertwine to form a network, making it difficult to eliminate pores and form porous ceramics. Hot isostatic pressing (HIP) can solve the problem of mullite whiskers hindering sintering because HIP applies uniform high pressure to the material at high temperatures, which can eliminate pores in the sample and promote the densification of the ceramic.

[0005] In the field of ceramics, although there have been reports mentioning near-zero expansion, currently it is basically only possible to test the coefficient of thermal expansion of 10 at room temperature. -6 At the °C-1 level, for example, the team of Professors Zhou Chang and Wu Gaohui from Harbin Institute of Technology first introduced reinforcement configuration design into negative thermal expansion (NTE) particle-reinforced Al-based composites, successfully preparing near-zero expansion bipolar zirconium tungstate aluminum-based composites via pressure infiltration. The relevant research results were published in *Composites Part B: Engineering* (Near-zero thermal expansion of ZrW2O8 / Al–Si composites with three-dimensional interpenetrating network structure). They believe that the configuration design of zirconium tungstate enables the formation of a bipolar structure in the composite material. Under the dual coupling effect of the negative thermal expansion effect of the reinforcement and the inhibition of thermal expansion by the bipolar configuration, the continuous ceramic network suppresses the expansion of the aluminum matrix, achieving near-zero expansion for the first time over a wide temperature range. The test results showed that, at a volume fraction of 64%, compared to particle-reinforced ZrW₂O₈ / Al composites, the γ-phase (high-pressure phase) content of the double-connected ZrW₂O₈ / Al composite decreased from 68.1% to 18.7%, and the coefficient of thermal expansion decreased from 3.21 × 10⁻⁶ in the range of −50 to 120 °C (ΔT = 170 °C). −6 ℃ -1 It decreased to 1.09×10 −6 ℃ -1Chinese invention patent application CN103803957A discloses a cordierite ceramic material with an ultra-low coefficient of thermal expansion and its preparation method. The main measure is the improvement of the formula. It claims that the obtained cordierite ceramic material has a density of 99.9%, a flexural strength of 220.5-332.7 MPa, a dielectric constant of 4.81-6.75, and a coefficient of thermal expansion of 0.5 × 10⁻⁶. -6 ~1.8×10 -6 ℃ -1 Furthermore, since there is generally a contradiction between reducing the coefficient of thermal expansion and improving mechanical properties, it is difficult for existing technologies to achieve both a reduction in the coefficient of thermal expansion and an improvement in mechanical properties. Summary of the Invention

[0006] This invention aims to solve one of the problems existing in the production process of cordierite ceramics, and provides a dense, high-strength, high-modulus, near-zero expansion cordierite ceramic that takes into account both mechanical and thermal properties, as well as its preparation method. The room temperature thermal expansion coefficient of the cordierite ceramic reaches 10. -8 ℃ -1 Under the premise of grade, the elastic modulus is ≥140GPa, the flexural strength is ≥220MPa, and the microhardness is ≥8.5GPa.

[0007] Another objective of this invention is to provide the application of the dense, high-strength, high-modulus, near-zero expansion cordierite ceramic in the preparation of mirrors for three-dimensional measuring instruments, mirror surface materials for reflectors, and high-performance processing platforms.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic is produced by mixing high-purity cordierite powder, mullite whiskers, alumina whiskers, a thermal expansion coefficient regulator, and boron oxide, followed by granulation. The granulated powder is then pressed into shape and subjected to cold isostatic pressing treatment, followed by debinding and high-temperature atmospheric pressure sintering to obtain cordierite ceramic. This ceramic is then subjected to hot isostatic pressing sintering. The hot isostatic pressing sintering temperature is controlled at 1200~1300℃, the holding time is 0.5~4h, and the applied pressure is 100~300MPa.

[0010] The high-purity cordierite powder is obtained by mixing magnesium oxide, aluminum oxide and silicon dioxide raw materials, granulating them, pressing the granulated powder into shape, debinding it, and refining it after high-temperature reaction; the pressing pressure of the granulated powder is controlled at 4~10MPa.

[0011] The ceramic contains 95.0~98.0 wt% high-purity cordierite powder, 0.1~1.0 wt% mullite whiskers, 0.1~1.0 wt% alumina whiskers, 0.3~3.0 wt% thermal expansion coefficient regulator, and 0.1~2.5 wt% boron oxide; the cordierite crystalline phase content in the high-purity cordierite powder is ≥99.5%.

[0012] To further achieve the purpose of this invention, preferably, the raw material of the high-purity cordierite powder contains 12.9~14.0 wt% magnesium oxide, 34.5~35.5 wt% aluminum oxide, and 51.0~52.0 wt% silicon dioxide.

[0013] Preferably, the high-temperature reaction temperature is 1125~1275℃, and the holding time is 0.5~2h.

[0014] Preferably, the coefficient of thermal expansion regulator is lithium oxide, spodumene, and aluminum oxide, with the lithium oxide content being 0.1-1%, the spodumene content being 0.1-1 wt%, and the aluminum oxide content being 0.1-1 wt%, based on a dosage of 0.3-3.0 wt% of the coefficient of thermal expansion regulator.

[0015] Preferably, the pressure of the cold isostatic pressing is 100MPa~300MPa, and the holding time is 30s~200s.

[0016] Preferably, the sintering temperature of the high-temperature atmospheric pressure sintering is 1220~1350℃, and the holding time is 1~8h.

[0017] Preferably, the pressure for pressing the granulated powder is 20~40MPa, and the holding time is 5~15s.

[0018] Preferably, the granulation after mixing is carried out by spray granulation.

[0019] Preferably, the holding time for pressing the granulated powder is 5-15 seconds.

[0020] The preparation method of the dense, high-strength, high-modulus, near-zero expansion cordierite ceramic includes the following steps:

[0021] 1) Magnesium oxide, aluminum oxide and silicon dioxide raw materials are mixed and granulated. The granulated powder is pressed into shape and then debinded. High-purity cordierite powder is obtained by high-temperature reaction synthesis. The pressing pressure of the granulated powder is controlled to be 4~10MPa.

[0022] 2) The high-purity cordierite powder obtained by reaction synthesis was refined using deionized water as a medium;

[0023] 3) Mix high-purity cordierite powder, mullite whiskers, alumina whiskers, boron oxide, and thermal expansion coefficient regulator, and then spray granulate.

[0024] 4) The granulated powder is pressed into shape using a mold, and a dense blank is obtained using a cold isostatic pressing device;

[0025] 5) Perform glue removal treatment on the blank obtained in step 4);

[0026] 6) The blanks after the debinding treatment in step 5) are sintered at high temperature and normal pressure, and after cooling, preliminary densified ceramics are obtained.

[0027] 7) Perform hot isostatic pressing sintering on the pre-densified ceramic from step 6), controlling the hot isostatic pressing sintering temperature to be 1200~1300℃, the holding time to be 0.5~4h, and the applied pressure to be 100~300MPa.

[0028] Preferably, the magnesium oxide, aluminum oxide, and silicon dioxide described in step 1) are mixed evenly with water as a medium and then spray granulation is performed.

[0029] The glue removal temperature in steps 1) and 5) is 700~800℃, and the time is 0.5~3h;

[0030] Step 2) The refining process involves refining the cordierite obtained from the reaction synthesis using a sand mill to obtain high-purity cordierite powder with an average particle size of 1~2μm.

[0031] Application of the dense, high-strength, high-modulus, near-zero expansion cordierite ceramic in the preparation of mirrors for three-dimensional measuring instruments, mirror surface materials for reflectors, and high-performance processing platforms.

[0032] The cordierite ceramics prepared by this invention exhibit high specific strength, specific stiffness, and a near-zero coefficient of thermal expansion of 10 at room temperature. -8 ℃ -1 This level of sophistication allows it to be applied to the manufacture of mirrors for 3D measuring instruments, mirror surface materials, and high-performance processing platforms.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] 1) The cordierite ceramic of this invention is a dense, high-strength, high-modulus, near-zero expansion material. It uses high-purity cordierite powder with a cordierite crystal phase content of ≥99.5%, which can make the prepared cordierite ceramic have lower thermal stress at high temperature. The high-purity cordierite powder also makes the prepared cordierite ceramic have a lower coefficient of thermal expansion, and the operating temperature is wider than that of existing products.

[0035] 2) This invention employs hot isostatic pressing (HIP) sintering. Compared to traditional atmospheric pressure sintering for preparing cordierite ceramics, HIP sintering applies a pressure exceeding 150 MPa uniformly to the sample during the sintering process, promoting the expulsion of closed pores and facilitating further densification of the sample. Higher density is a prerequisite for obtaining excellent mechanical properties. Furthermore, HIP sintering can overcome the side effects of mullite whiskers and alumina whiskers in the formulation. While alumina and mullite whiskers improve the mechanical properties of cordierite, they hinder the sintering of cordierite ceramics. HIP, however, promotes the expulsion of closed pores, resulting in cordierite with higher density.

[0036] 3) The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic formulation of this invention includes, in addition to high-purity cordierite powder, mullite whiskers, alumina whiskers, a coefficient of thermal expansion regulator, and boron oxide. These components have a synergistic effect. For example, the adverse effect of alumina whiskers and mullite whiskers on the sintering of cordierite ceramics can be mitigated by adding boron oxide as a sintering aid, which promotes the generation of liquid phase and densification of cordierite ceramics. Although coefficient of thermal expansion regulators have been previously discussed, the combination of the coefficient of thermal expansion regulator of this invention with mullite whiskers and alumina whiskers helps to keep the absolute value of the coefficient of thermal expansion of cordierite ceramics at a low level.

[0037] 4) The cordierite ceramics prepared by this invention have a relative density ≥99% and a bulk density ≥2.52 g·cm³. -3 Flexural strength ≥ 220 MPa, elastic modulus ≥ 140 GPa, specific strength ≥ 8.65 × 10⁻⁶ -2 N / tex, specific stiffness ≥ 59.0 N / tex, microhardness ≥ 8.5 GPa, coefficient of thermal expansion at room temperature ≤ 3 × 10⁻⁶ -8 ℃ -1 It possesses both excellent mechanical properties and maintains an extremely low coefficient of thermal expansion, enabling new applications based on the improved performance of cordierite ceramics. It is very suitable for use as a mirror for three-dimensional measuring instruments, a mirror surface for reflecting mirrors, and a material for high-performance processing platforms.

[0038] 5) The preferred thermal expansion coefficient regulators of this invention are lithium oxide, spodumene, and alumina. Lithium ions can enter the six-membered ring structure of cordierite crystals, causing lattice distortion, generating anisotropy, and reducing the thermal expansion coefficient of cordierite. Alumina powder, alumina whiskers, and mullite whiskers have positive thermal expansion coefficients. The synergistic effect of the two makes the absolute value of the thermal expansion coefficient of cordierite ceramics keep at a low level.

[0039] 6) The mullite whiskers and alumina whiskers of the present invention can be used to improve the elastic modulus of materials and enhance the mechanical properties of cordierite ceramics, thereby giving cordierite ceramic products both high density and high strength and high elastic modulus. Attached Figure Description

[0040] Figure 1 The image shows a scanning electron microscope (SEM) image of the cordierite ceramic powder prepared in Example 1.

[0041] Figure 2 The image shows the surface microstructure of the cordierite ceramics prepared in Example 2.

[0042] Figure 3 The image shows the surface microstructure of the cordierite ceramics prepared in Comparative Example 5. Detailed Implementation

[0043] The advantages of the technical solution and product of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the specific embodiments of the present invention, and not all of the embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0044] Ceramic material testing methods

[0045] The bulk density of cordierite ceramics was tested according to GB / T 25995-2010.

[0046] The flexural strength of cordierite ceramics was tested using the three-point bending method according to GB / T 6569-2006.

[0047] The elastic modulus of cordierite ceramics was tested according to GB / T 10700-2006.

[0048] The microhardness of cordierite ceramics was tested according to GB / T 16534-2009.

[0049] Specific strength is the flexural strength divided by the bulk density.

[0050] Specific stiffness is the elastic modulus divided by the bulk density.

[0051] Relative density is the ratio of bulk density to theoretical density.

[0052] The coefficient of thermal expansion of cordierite ceramics was tested according to GB / T 16535-2008.

[0053] Addressing the shortcomings of existing technologies: 1. Cordierite ceramics prepared by traditional sintering methods have low density, which severely degrades their mechanical properties and greatly limits their application in fields such as telescopes, laser communication, and fiber optic communication systems. 2. The narrow sintering temperature range of cordierite ceramics makes densification difficult. Some oxides, such as boron oxide and lithium oxide, can broaden the sintering temperature range and lower the sintering temperature, but their impact on the material's thermal properties has not been reported. 3. Currently prepared cordierite ceramics have low mechanical strength, making them difficult to withstand harsh operating environments. Some ceramic whiskers, such as mullite whiskers and alumina whiskers, can improve the mechanical properties of cordierite ceramics. 4. The α-cordierite content in currently prepared cordierite ceramics is relatively low, and there is a lack of control over the thermal expansion coefficient of cordierite. These factors contribute to a high thermal expansion coefficient in currently prepared cordierite ceramics; even those claiming near-zero expansion have a thermal expansion coefficient of 10. -6 ℃-1 level; a high coefficient of thermal expansion will cause the reflector to produce large strain under temperature fluctuations, resulting in insufficient clarity of the captured target image. 5. Existing technologies are difficult to balance the mechanical properties of ceramics and the control of the coefficient of thermal expansion. This invention, based on the existing cordierite ceramic production process, introduces high-purity cordierite powder and hot isostatic pressing (HIP) sintering process, and improves the formula, especially by fully utilizing the synergistic effect of mullite whiskers, alumina whiskers, and a coefficient of thermal expansion regulator, to provide a dense, high-strength, high-modulus, near-zero expansion cordierite ceramic. High-purity cordierite powder, mullite whiskers, alumina whiskers, a coefficient of thermal expansion regulator, and boron oxide are mixed and granulated. The granulated powder is pressed into shape and then subjected to cold isostatic pressing, debinding, and high-temperature atmospheric pressure sintering to obtain cordierite ceramic, which is then subjected to HIP sintering. The HIP sintering temperature is controlled at 1200~1300℃ to maintain The heating time is 0.5~4h, and the applied pressure is 100~300MPa; the high-purity cordierite powder is obtained by mixing magnesium oxide, aluminum oxide, and silicon dioxide raw materials, granulating them, pressing the granulated powder into shape, debinding, and refining after high-temperature reaction; the pressing pressure of the granulated powder is controlled at 4~10MPa; the ceramic contains 95.0~98.0wt% high-purity cordierite powder, 0.1~1.0wt% mullite whiskers, 0.1~1.0wt% alumina whiskers, 0.3~3.0wt% thermal expansion coefficient regulator, and 0.1~2.5wt% boron oxide; the cordierite crystal phase content in the high-purity cordierite powder is ≥99.5%.

[0054] This invention, based on existing technology, utilizes high-purity cordierite powder and introduces alumina whiskers and mullite whiskers into the high-purity cordierite matrix. This addresses the issue of low cordierite strength. The introduction of a thermal expansion coefficient regulator balances the thermal expansion coefficient of the cordierite ceramic. While alumina and mullite whiskers improve the mechanical properties of cordierite, they can hinder the sintering of the cordierite ceramic. Hot isostatic pressing (HIP) promotes the removal of closed pores, resulting in a higher density of the prepared cordierite. This invention's process, while enhancing the performance of cordierite ceramics, leads to new applications and expands the application range of cordierite ceramics.

[0055] The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic obtained by this invention has a relative density ≥99% and a bulk density ≥2.52 g·cm³. -3 Flexural strength ≥ 220 MPa, elastic modulus ≥ 140 GPa, specific strength ≥ 8.65 × 10⁻⁶ -2 N / tex, specific stiffness ≥ 59.0 N / tex, microhardness ≥ 8.5 GPa; coefficient of thermal expansion at room temperature ≤ 3 × 10⁻⁶ -8 ℃ -1 It can be used as a material for mirrors in 3D measuring instruments, reflective mirrors, and high-performance machining platforms, and has 10 -8 ℃ -1 A near-zero coefficient of thermal expansion and a specific stiffness ≥59.0 N / tex are required to meet the demands of high-precision dimensional measurement and imaging.

[0056] Example 1

[0057] A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic comprises the following steps:

[0058] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 4 MPa for 5 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The sample was then reacted at 1250℃ for 1 h to synthesize cordierite blocks.

[0059] 2) The cordierite blocks obtained from the reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 6 hours using deionized water as the medium to obtain high-purity cordierite powder. The scanning electron microscope image of the powder is attached. Figure 1 As shown in the figure, the fined high-purity cordierite powder has a uniform particle size distribution with a particle diameter of approximately 0.5-1 μm.

[0060] 3) Based on the percentage by weight of raw materials, a mixture consisting of 97wt% high-purity cordierite powder, 0.75wt% mullite whiskers, 0.75wt% alumina whiskers, 0.4wt% lithium oxide, 0.4wt% spodumene, 0.4wt% alumina, and 0.3wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0061] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 250MPa / 180s.

[0062] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0063] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample with a density of ≥97% was obtained under a sintering regime of 1280℃ / 2h.

[0064] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1200℃ for 1.5h, with an atmosphere pressure of 200MPa.

[0065] The cordierite ceramic obtained in Example 1 was tested and found to have a relative density of 99.2% and a bulk density of 2.53 g·cm³. -3 The flexural strength is 232 MPa, the elastic modulus is 160 GPa, and the specific strength is 9.17 × 10⁻⁶. -2 It has a specific stiffness of 63.2 N / tex, a microhardness of 9.6 GPa, and a coefficient of thermal expansion at room temperature of 1.7 × 10⁻⁶. -8 ℃ -1In this embodiment, high-purity cordierite powder with a cordierite crystal phase content ≥99.5% is used. This results in cordierite ceramics with lower internal stress and a lower coefficient of thermal expansion. Furthermore, mullite whiskers and alumina whiskers are added to the cordierite matrix as reinforcing components, improving the flexural strength and elastic modulus of cordierite. The addition of lithium oxide, spodumene, and alumina as coefficient of thermal expansion modifiers, along with the small radius of lithium ions, facilitates their entry into the α-... The channels between two adjacent six-membered rings in cordierite cause lattice distortion and anisotropy, which is beneficial for reducing the coefficient of thermal expansion. Alumina whiskers and mullite whiskers are suggested to improve the mechanical properties of cordierite, but they will hinder the sintering of cordierite ceramics. Adding boron oxide as a sintering aid and using hot isostatic pressing can promote the discharge of closed pores, thereby making the prepared cordierite have a higher density. This results in cordierite ceramics with high density, high strength, and near-zero modulus expansion.

[0066] Example 2

[0067] A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic comprises the following steps:

[0068] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at 10 MPa for 15 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 3 h. Cordierite was synthesized by holding at 1275℃ for 1.5 h.

[0069] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 6 hours using deionized water as the medium to obtain high-purity cordierite powder.

[0070] 3) A mixture consisting of 98wt% high-purity cordierite powder, 0.1wt% mullite whiskers, 0.1wt% alumina whiskers, 0.4wt% lithium oxide, 0.4wt% spodumene, 0.2wt% alumina, and 0.8wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain a powder with good flowability.

[0071] 4) The granulated powder is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) under a holding pressure of 40MPa for 10s. Then, the shaped sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 300MPa / 200s.

[0072] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 3 hours.

[0073] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample with a density of ≥97% was obtained under a sintering regime of 1350℃ / 8h.

[0074] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1230℃ for 1.5h, with an atmosphere pressure of 200MPa.

[0075] The cordierite ceramic obtained in Example 2 was tested and found to have a relative density of 99.5% and a bulk density of 2.54 g·cm³. -3 The flexural strength is 220 MPa, the elastic modulus is 151 GPa, and the specific strength is 8.66 × 10⁻⁶. -2 It has a specific stiffness of 59.4 N / tex, a microhardness of 8.8 GPa, and a coefficient of thermal expansion at room temperature of 2.4 × 10⁻⁶. -8 In this embodiment, by increasing the hot isostatic pressing sintering temperature and the content of the flux, the content of the glass phase is increased, thereby improving the density. The prepared cordierite ceramics were characterized by SEM, as shown in the attached figure. Figure 2 As shown, the prepared cordierite ceramic has a dense structure with almost no pores, and the high density is beneficial to improving the mechanical properties of cordierite.

[0076] Example 3

[0077] A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic comprises the following steps:

[0078] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at 4 MPa for 5 s. The sample was then placed in a muffle furnace and debinded at 700℃ for 0.5 h. Cordierite was synthesized by holding at 1125℃ for 0.5 h.

[0079] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 1 h using deionized water as the medium to obtain high-purity cordierite powder.

[0080] 3) A mixture consisting of 96wt% high-purity cordierite powder, 1.0wt% mullite whiskers, 1.0wt% alumina whiskers, 0.5wt% lithium oxide, 0.5wt% spodumene, 0.5wt% alumina, and 0.5wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h with water as the medium to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0081] 4) The granulated powder is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at a holding pressure of 20MPa for 10s. Then, the shaped sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 100MPa / 30s.

[0082] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 700℃ for 0.5h.

[0083] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample with a density of ≥97% was obtained under a sintering regime of 1220℃ / 8h.

[0084] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1300℃ / 4h under an atmosphere pressure of 300MPa.

[0085] The cordierite ceramic obtained in Example 3, as tested, had a relative density of 99.6% and a bulk density of 2.54 g·cm³. -3 The flexural strength is 258 MPa, the elastic modulus is 152 GPa, and the specific strength is 10.16 × 10⁻⁶. -2 It has a specific stiffness of 59.8 N / tex, a microhardness of 9.6 GPa, and a coefficient of thermal expansion at room temperature of 2.9 × 10⁻⁶. -8 ℃-1.

[0086] Example 4

[0087] A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic comprises the following steps:

[0088] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 4 MPa for 5 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The sample was then reacted at 1250℃ for 3 h to synthesize cordierite blocks.

[0089] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 1 h using deionized water as the medium to obtain high-purity cordierite powder.

[0090] 3) A mixture consisting of 96wt% high-purity cordierite powder, 0.25wt% mullite whiskers, 0.25wt% alumina whiskers, 1.0wt% lithium oxide, 1.0wt% spodumene, 0.2wt% alumina, and 1.3wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0091] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 100MPa / 30s.

[0092] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0093] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample with a density of ≥97% was obtained under a sintering regime of 1220℃ / 1h.

[0094] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1200℃ / 4h under an atmosphere pressure of 150MPa.

[0095] The cordierite ceramic obtained in Example 4 was tested and found to have a relative density of 99.2% and a bulk density of 2.53 g·cm³. -3 The flexural strength is 221 MPa, the elastic modulus is 152 GPa, and the specific strength is 8.74 × 10⁻⁶. -2 It has a specific stiffness of 60.1 N / tex, a microhardness of 9.1 GPa, and a coefficient of thermal expansion at room temperature of 1.9 × 10⁻⁶. -8 ℃ -1 .

[0096] Example 5

[0097] A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic comprises the following steps:

[0098] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was then pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at 4 MPa for 5 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. Cordierite blocks were then synthesized by holding the sample at 1270℃ for 1.5 h.

[0099] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 6 hours using deionized water as the medium to obtain high-purity cordierite powder.

[0100] 3) A mixture consisting of 95wt% high-purity cordierite powder, 0.5wt% mullite whiskers, 0.5wt% alumina whiskers, 0.25wt% lithium oxide, 0.25wt% spodumene, 1.0wt% alumina, and 2.5wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain a powder with good flowability.

[0101] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 20MPa for 5s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 300MPa / 200s.

[0102] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0103] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample with a density of ≥97% was obtained under a sintering regime of 1300℃ / 2h.

[0104] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1300℃ / 3h under an atmosphere pressure of 300MPa.

[0105] The cordierite ceramic obtained in Example 5 was tested and found to have a relative density of 99.6% and a bulk density of 2.54 g·cm³. -3 Its flexural strength is 225 MPa, its elastic modulus is 153 GPa, and its specific strength is 8.86 × 10⁻⁶. -2 It has a specific stiffness of 60.2 N / tex, a microhardness of 9.0 GPa, and a coefficient of thermal expansion at room temperature of 1.9 × 10⁻⁶. -8 ℃ -1 .

[0106] Comparative Example 1

[0107] 1) Al2O3, MgO and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. The mixed sample was then placed in a muffle furnace and held at 1300℃ for 1 h to synthesize cordierite.

[0108] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain cordierite powder.

[0109] 3) A mixture consisting of 97.5 wt% cordierite powder, 0.5 wt% alumina whiskers, 0.5 wt% mullite crystals, 0.4 wt% lithium oxide, 0.4 wt% spodumene, 0.4% alumina, and 0.3 wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0110] 4) The granulated powder is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the shaped sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 250MPa / 180s.

[0111] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0112] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample was obtained under a sintering regime of 1280℃ / 2h.

[0113] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1225℃ for 1.5h, with an atmosphere pressure of 200MPa.

[0114] The cordierite ceramic obtained in Comparative Example 1 had a relative density of 98.4% and a bulk density of 2.51 g·cm³. -3 Because the high-purity cordierite powder was not synthesized according to the method of this invention, and the granulated powder was not compressed into shape, the reaction between the raw materials was insufficient, resulting in a lower purity of the synthesized cordierite powder. This leads to an increase in the coefficient of thermal expansion of the material, increasing the internal stress of the cordierite ceramic. Consequently, the flexural strength of the prepared cordierite ceramic is 164 MPa, the elastic modulus is 119 GPa, and the specific strength is 6.53 × 10⁻⁶. -2It has a specific stiffness of 47.4 N / tex, a microhardness of 8.1 GPa, and a coefficient of thermal expansion at room temperature of 10.2 × 10⁻⁶. -8 ℃ -1 .

[0115] Comparative Example 2

[0116] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 4 MPa for 5 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The sample was then reacted at 1250℃ for 1 h to synthesize cordierite blocks.

[0117] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain high-purity cordierite powder.

[0118] 3) A mixture consisting of 93wt% high-purity cordierite powder, 0.35wt% mullite whiskers, 0.35wt% alumina whiskers, 1.1wt% lithium oxide, 1.1wt% spodumene, 1.1wt% alumina, and 3.0wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0119] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 200MPa / 180s.

[0120] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0121] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample was obtained under a sintering regime of 1280℃ / 2h.

[0122] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1200℃ for 1.5h, with an atmosphere pressure of 200MPa.

[0123] The cordierite ceramic obtained in Comparative Example 2 was tested and found to have a relative density of 99.2% and a bulk density of 2.53 g·cm³. -3Its flexural strength is 174 MPa, its elastic modulus is 121 GPa, and its specific strength is 6.88 × 10⁻⁶. -2 It has a specific stiffness of 47.8 N / tex, a microhardness of 7.7 GPa, and a coefficient of thermal expansion at room temperature of 8.9 × 10⁻⁶. -8 ℃ -1 In this comparative example, since the cordierite content was not controlled according to the formula of the present invention, the amount used was low, and a large amount of sintering aids were also included, which increased the glass phase in the prepared material, thereby increasing the coefficient of thermal expansion and reducing the mechanical properties.

[0124] Comparative Example 3

[0125] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 2 MPa for 3 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. Cordierite blocks were then synthesized by holding at 1300℃ for 1 h.

[0126] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain cordierite powder.

[0127] 3) Based on the percentage by weight of raw materials, a mixture consisting of 97wt% high-purity cordierite powder, 0.75wt% mullite whiskers, 0.75wt% alumina whiskers, 0.4wt% lithium oxide, 0.4wt% spodumene, 0.4wt% alumina, and 0.3wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0128] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 80MPa / 25s.

[0129] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0130] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample was obtained under a sintering regime of 1250℃ / 2h.

[0131] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1200℃ for 1.5h, with an atmosphere pressure of 200MPa.

[0132] The cordierite ceramic obtained in Comparative Example 3 was tested and found to have a relative density of 98.2% and a bulk density of 2.51 g·cm³. -3 The flexural strength is 184 MPa, the elastic modulus is 136 GPa, and the specific strength is 7.33 × 10⁻⁶. -2 It has a specific stiffness of 54.2 N / tex, a microhardness of 8.3 GPa, and a coefficient of thermal expansion at room temperature of 4.9 × 10⁻⁶. -8 ℃ -1 Because the pressure of granulation powder pressing was not controlled to be 4~10MPa during the preparation of cordierite powder, but instead 2MPa was used for pressing and molding, the pressure applied between the raw materials was too small, resulting in insufficient reaction of synthesized cordierite. At the same time, the cold isostatic pressing was too small, resulting in low green body density. As a result, the mechanical properties of the prepared cordierite ceramics could not meet the requirements, and the coefficient of thermal expansion of the material would also increase.

[0133] Comparative Example 4

[0134] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was then pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at 4 MPa for 10 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The mixture was then held at 1350℃ for 1 h to react and synthesize cordierite blocks.

[0135] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain cordierite powder.

[0136] 3) A mixture consisting of 97.5 wt% cordierite powder, 0.5 wt% mullite whiskers, 0.5 wt% alumina whiskers, 0.4 wt% lithium oxide, 0.4 wt% spodumene, 0.4 wt% alumina, and 0.3 wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain a powder with good flowability.

[0137] 4) Press the granulated powder into shape in a steel rectangular mold (inner mold size is 50mm×5mm×10mm) under a pressure of 30MPa for 10s.

[0138] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0139] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. Cordierite ceramics were obtained under a sintering regime of 1250℃ / 2h.

[0140] Testing revealed that the cordierite ceramic obtained in Comparative Example 4, which had not undergone hot isostatic pressing (HIP) sintering, exhibited alumina and mullite whiskers that hindered grain boundary movement. This impeded densification of the cordierite ceramic, resulting in a lower density (relative density 94.7%) and a bulk density of 2.41 g·cm³. -3 This results in poor mechanical properties; its flexural strength is 112 MPa, its elastic modulus is 84 GPa, and its specific strength is 4.65 × 10⁻⁶. -2 It has a specific stiffness of 34.9 N / tex, a microhardness of 6.9 GPa, and a coefficient of thermal expansion at room temperature of 9.4 × 10⁻⁶. -8 ℃ -1 .

[0141] Comparative Example 5

[0142] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 8 MPa for 10 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The sample was then reacted at 1275℃ for 1 h to synthesize cordierite blocks.

[0143] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain high-purity cordierite powder.

[0144] 3) A mixture consisting of 97wt% high-purity cordierite powder, 0.5wt% mullite whiskers, 0.5wt% alumina whiskers, 0.5wt% lithium oxide, 0.5wt% spodumene, 0.5wt% alumina, and 0.5wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0145] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 15s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 250MPa / 180s.

[0146] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0147] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample was obtained under a sintering regime of 1270℃ / 2h.

[0148] 7) The sample after atmospheric pressure sintering was placed in a hot isostatic pressing furnace and sintered at 1320℃ / 5h under an atmosphere pressure of 320MPa.

[0149] The cordierite ceramic obtained in Comparative Example 5 was tested and found to have a relative density of 98.2% and a bulk density of 2.50 g·cm³. -3 Its flexural strength is 194 MPa, its elastic modulus is 141 GPa, and its specific strength is 7.76 × 10⁻⁶. -2 It has a specific stiffness of 56.4 N / tex, a microhardness of 8.8 GPa, and a coefficient of thermal expansion at room temperature of 5.5 × 10⁻⁶. -8 ℃ -1 This is due to excessively high hot isostatic pressing temperature and excessively long holding time, as shown in the attached image. Figure 3 As shown, the glass phase content on the surface of cordierite ceramics increases, and the grains of cordierite ceramics grow abnormally. The pores inside the material may not be expelled, but instead enter into these large grains, thereby reducing the density and mechanical properties of the sample.

[0150] Comparative Example 6

[0151] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 8 MPa for 10 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The sample was then reacted at 1275℃ for 1 h to synthesize cordierite blocks.

[0152] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain high-purity cordierite powder.

[0153] 3) A mixture consisting of 97wt% high-purity cordierite powder, 0.5wt% mullite whiskers, 0.5wt% alumina whiskers, 0.5wt% lithium oxide, 0.5wt% spodumene, 0.5wt% alumina, and 0.5wt% B2O3 was placed in a ball mill jar and ball-milled at 500 r / min for 4 h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0154] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 15s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 250MPa / 180s.

[0155] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0156] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample was obtained under a sintering regime of 1270℃ / 2h.

[0157] 7) The sample after atmospheric pressure sintering was placed in a hot isostatic pressing furnace and sintered at 1175℃ for 0.3h, with an atmosphere pressure of 130MPa.

[0158] The cordierite ceramic obtained in Comparative Example 6 was tested and found to have a relative density of 97.3% and a bulk density of 2.48 g·cm³. -3 Its flexural strength is 153 MPa, its elastic modulus is 112 GPa, and its specific strength is 61.7 × 10⁻⁶. -2 It has a specific stiffness of 45.2 N / tex, a microhardness of 7.4 GPa, and a coefficient of thermal expansion at room temperature of 4.9 × 10⁻⁶. -8 ℃ -1 This is because if the hot isostatic pressing temperature, holding time, and applied pressure are too low, it is difficult to eliminate the pores in the cordierite ceramic, resulting in a lower density and poorer mechanical properties in the prepared cordierite ceramic.

[0159] Comparative Example 7

[0160] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at a speed of 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at a pressure of 4 MPa for 10 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The sample was then reacted at 1250℃ for 1 h to synthesize cordierite blocks.

[0161] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain cordierite powder.

[0162] 3) The mixture consisting of 97wt% high-purity cordierite powder, 1.5wt% mullite whiskers and 1.5wt% alumina whiskers was placed in a ball mill jar and ball milled at 500r / min for 4h to ensure that the raw materials were fully mixed; the mixed raw materials were spray granulated to obtain granulated powder with good flowability.

[0163] 4) The granulated powder is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the shaped sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 250MPa / 180s.

[0164] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0165] 6) After debinding, the sample was placed in a muffle furnace and sintered at atmospheric pressure. The sample was obtained under a sintering regime of 1375℃ / 9h.

[0166] 7) The sample after atmospheric pressure sintering was placed in a hot isostatic pressing furnace and sintered at 1150℃ for 0.4h, with an atmosphere pressure of 200MPa.

[0167] The cordierite ceramic obtained in Comparative Example 7 was tested and found to have a relative density of 97.3% and a bulk density of 2.48 g·cm³. -3 Its flexural strength is 184 MPa, its elastic modulus is 132 GPa, and its specific strength is 7.42 × 10⁻⁶. -2 It has a specific stiffness of 53.2 N / tex, a microhardness of 8.2 GPa, and a coefficient of thermal expansion at room temperature of 7.2 × 10⁻⁶. -8 ℃ -1 Adding more alumina and mullite whiskers to the raw materials can improve the mechanical properties of cordierite ceramics. However, due to the lack of a coefficient of thermal expansion regulator to control the coefficient of thermal expansion of the material, the coefficient of thermal expansion of cordierite increases. This will cause greater internal stress to be generated inside the cordierite ceramic at higher operating temperatures. When the internal stress reaches a critical value, microcracks will appear inside the cordierite ceramic, thus affecting the service life of the product.

[0168] Comparative Example 8

[0169] 1) Al2O3, MgO, and SiO2 were mixed according to stoichiometry (MgO:Al2O3:SiO2=2:2:5) and mixed in a ball mill at 500 r / min for 3 h. After mixing, the powder with good flowability was obtained by spray granulation. The powder was then pressed into shape using a steel cylindrical mold (inner mold diameter of 70 mm) at 4 MPa for 5 s. The sample was then placed in a muffle furnace and debinded at 800℃ for 2 h. The mixture was then reacted at 1275℃ for 1.5 h to synthesize cordierite blocks.

[0170] 2) The cordierite blocks obtained by reaction synthesis were placed in a sand mill and refined at a speed of 1500 r / min for 2 hours using deionized water as the medium to obtain high-purity cordierite powder.

[0171] 3) A mixture consisting of 98wt% high-purity cordierite powder, 0.5wt% lithium oxide, 0.5wt% spodumene, 0.5wt% alumina and 0.5wt% B2O3 was placed in a ball mill jar and ball-milled at 500r / min for 4h to ensure thorough mixing of the raw materials; after mixing, spray granulation was used to obtain powder with good flowability.

[0172] 4) The obtained powder with good flowability is pressed into shape in a steel cuboid mold (inner mold size is 50mm×5mm×10mm) at 30MPa for 10s. Then, the molded sample is subjected to cold isostatic pressing to obtain a further densified blank. The cold isostatic pressing process is 250MPa / 180s.

[0173] 5) Place the sample obtained after cold isostatic pressing in a muffle furnace and perform debinding treatment at 800℃ for 2 hours.

[0174] 6) After debinding, the sample was placed in a muffle furnace for sintering at atmospheric pressure at 1250℃ for 0.5h.

[0175] 7) The sample after atmospheric pressure sintering is placed in a hot isostatic pressing furnace and sintered at 1200℃ for 1.5h, with an atmosphere pressure of 200MPa.

[0176] The cordierite ceramic obtained in Comparative Example 8 was tested and found to have a relative density of 99.2% and a bulk density of 2.53 g·cm³. -3 Its flexural strength is 187 MPa, its elastic modulus is 121 GPa, and its specific strength is 7.4 × 10⁻⁶. -2 It has a specific stiffness of 47.8 N / tex, a microhardness of 8.2 GPa, and a coefficient of thermal expansion at room temperature of 4.2 × 10⁻⁶. -8 ℃ -1In this comparative example, the cordierite ceramics prepared did not contain any reinforcing phases such as mullite whiskers and alumina whiskers, which resulted in a high density but reduced strength.

[0177] The high-purity cordierite ceramic powder successfully prepared by this invention can significantly reduce the internal stress and thermal expansion coefficient of cordierite ceramics; the prepared cordierite ceramics have a relative density ≥99% and a bulk density ≥2.52 g·cm³. -3 Flexural strength ≥ 220 MPa, elastic modulus ≥ 140 GPa, specific strength ≥ 8.65 × 10⁻⁶ -2 N / tex, specific stiffness ≥ 59.0 N / tex, microhardness ≥ 8.5 GPa, coefficient of thermal expansion at room temperature ≤ 3 × 10⁻⁶ -8 At ℃-1, its overall performance is currently the best. This invention results in cordierite ceramics with high density, high strength, and a thermal expansion coefficient reaching 10. -8 ℃ -1 This level of sophistication allows it to be used as a mirror material for 3D measuring instruments and reflectors, as well as for the fabrication of high-performance machining platforms.

[0178] As can be seen from the examples 1-3 above, if the high-purity cordierite powder preparation method of the present invention is not adopted, if the granulated powder is not pressed into shape, or if the pressing pressure is too low, or if the high-purity cordierite powder in the formula is less than 95.0~98.0 wt%, the performance of the obtained cordierite ceramics is significantly lower than that of all embodiments of the present invention.

[0179] As can be seen from the examples 4-6 above, cordierite ceramics with the performance characteristics of the present invention cannot be prepared without adopting the hot isostatic pressing measures of the present invention, or with excessively high hot isostatic pressing temperature, excessively long holding time, or excessively low hot isostatic pressing temperature, holding time, and applied pressure.

[0180] As can be seen from Comparative Examples 7 and 8, the cordierite ceramics prepared by not following the raw material formulation requirements of this invention, not using alumina whiskers and mullite whiskers, or using too much or too little alumina whiskers, had significantly lower performance than those prepared in this invention. Lithium oxide, spodumene, and alumina can be used as thermal expansion coefficient regulators to control the thermal expansion coefficient of cordierite, making it have near-zero expansion. Alumina whiskers and mullite whiskers, as reinforcing phases of the matrix, significantly enhance the mechanical properties of the matrix, but they can hinder sintering. Therefore, boron oxide was used as a sintering aid to promote the generation of the liquid phase. Hot isostatic pressing (HIP) was used to apply high pressure to eliminate the pores inside the material, solving the problem of difficult sintering. Thus, cordierite ceramics with high density, high strength, and near-zero modulus expansion were successfully prepared.

Claims

1. A dense, high-strength, high-modulus, near-zero expansion cordierite ceramic, characterized in that, The process involves mixing high-purity cordierite powder, mullite whiskers, alumina whiskers, a thermal expansion coefficient regulator, and boron oxide, granulating the mixture, pressing the granulated powder into shape, cold isostatic pressing, debinding, and high-temperature atmospheric pressure sintering to obtain cordierite ceramics. These ceramics are then subjected to hot isostatic pressing (HIP) sintering. The HIP sintering temperature is controlled at 1200~1300℃, the holding time is 0.5~4h, and the applied pressure is 100~300MPa. The high-purity cordierite powder is obtained by mixing magnesium oxide, aluminum oxide and silicon dioxide raw materials, granulating them, pressing the granulated powder into shape, debinding it, and refining it after high-temperature reaction; the pressing pressure of the granulated powder is controlled at 4~10MPa. The ceramic contains 95.0~98.0 wt% high-purity cordierite powder, 0.1~1.0 wt% mullite whiskers, 0.1~1.0 wt% alumina whiskers, 0.3~3.0 wt% thermal expansion coefficient regulator, and 0.1~2.5 wt% boron oxide; the cordierite crystalline phase content in the high-purity cordierite powder is ≥99.5%.

2. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that, The raw material of the high-purity cordierite powder contains 12.9-14.0 wt% magnesium oxide, 34.5-35.5 wt% aluminum oxide, and 51.0-52.0 wt% silicon dioxide.

3. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that, The high-temperature reaction is carried out at a temperature of 1125~1275℃ and the holding time is 0.5~2h.

4. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that, The coefficient of thermal expansion regulator is lithium oxide, spodumene, and aluminum oxide. Based on a dosage of 0.3 to 3.0 wt% of the coefficient of thermal expansion regulator, the lithium oxide content is 0.1 to 1%, the spodumene content is 0.1 to 1 wt%, and the aluminum oxide content is 0.1 to 1 wt%.

5. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that: The pressure of the cold isostatic pressing is 100MPa~300MPa, and the holding time is 30s~200s.

6. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that: The sintering temperature of the high-temperature atmospheric pressure sintering is 1220~1350℃, and the holding time is 1~8h.

7. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that, The pressure for pressing the granulated powder is 20~40MPa, and the holding time is 5~15s.

8. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 7, characterized in that, All the granulation after mixing is carried out by spray granulation.

9. The dense, high-strength, high-modulus, near-zero expansion cordierite ceramic according to claim 1, characterized in that: The holding time for the granulated powder compression molding is 5~15s.

10. The method for preparing dense, high-strength, high-modulus, near-zero expansion cordierite ceramics according to any one of claims 1-9, characterized in that... Includes the following steps: 1) Magnesium oxide, aluminum oxide and silicon dioxide raw materials are mixed and granulated. The granulated powder is pressed into shape and then debinded. High-purity cordierite powder is synthesized by high-temperature reaction. The pressing pressure of the granulated powder is controlled to be 4~10MPa. 2) The high-purity cordierite powder obtained by reaction synthesis was refined using deionized water as a medium; 3) Mix high-purity cordierite powder, mullite whiskers, alumina whiskers, boron oxide, and thermal expansion coefficient regulator, and then spray granulate. 4) The granulated powder is pressed into shape using a mold, and a dense blank is obtained using a cold isostatic pressing device; 5) Perform glue removal treatment on the blank obtained in step 4); 6) The blanks after the debinding treatment in step 5) are sintered at high temperature and normal pressure, and after cooling, preliminary densified ceramics are obtained. 7) Perform hot isostatic pressing sintering on the pre-densified ceramic from step 6), controlling the hot isostatic pressing sintering temperature to be 1200~1300℃, the holding time to be 0.5~4h, and the applied pressure to be 100~300MPa.

11. The method for preparing dense, high-strength, high-modulus, near-zero expansion cordierite ceramics according to claim 10, characterized in that, Step 1) involves mixing magnesium oxide, aluminum oxide, and silicon dioxide evenly with water as the medium, followed by spray granulation. The glue removal temperature in steps 1) and 5) is 700~800℃, and the time is 0.5~3h; Step 2) The refining process involves refining the cordierite obtained from the reaction synthesis using a sand mill to obtain high-purity cordierite powder with an average particle size of 1~2μm.

12. The application of the dense, high-strength, high-modulus, near-zero expansion cordierite ceramic as described in any one of claims 1-9 in the preparation of mirrors for three-dimensional measuring instruments, mirror surface materials for reflectors, and high-performance processing platforms.

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