Silicon nitride ceramic with low sintering aid content and preparation method thereof
By using low-content Al2O3, MgO, and AlN as sintering aids and combining them with hot pressing sintering technology, the problems of high cost and performance degradation of rare earth oxide aids were solved, and low-cost, high-performance Si3N4 ceramics were prepared.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-25
- Publication Date
- 2026-03-27
AI Technical Summary
In the existing technology, silicon nitride ceramics produced by using rare earth oxides as sintering aids have high production costs, and the high content of aids weakens the high-temperature mechanical properties and oxidation resistance of the ceramics, making it difficult to meet the requirements of harsh working conditions.
Low-content Al2O3, MgO and AlN are used as sintering aids to form a liquid phase with SiO2 on the surface of Si3N4 powder. The densification of Si3N4 ceramics is achieved by hot pressing sintering, which reduces production costs and improves the purity and mechanical properties of the ceramics.
The densification of Si3N4 ceramics under extremely low content conditions significantly reduces production costs, improves the ceramics' tribological and wear resistance and corrosion resistance, and enhances their high-temperature mechanical properties.
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Figure CN121735655A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of silicon nitride ceramic preparation, and relates to a silicon nitride ceramic with low content of sintering aid and its preparation method. Background Technology
[0002] Si3N4, as an important structural ceramic, possesses excellent comprehensive properties such as high strength, thermal stability, high thermal conductivity, thermal shock resistance, and corrosion resistance. Dense silicon nitride ceramics have broad application prospects in the semiconductor industry, aerospace, and biomedicine.
[0003] Silicon nitride (SiN) is difficult to sinter due to its strong covalent bonds. In sintering methods such as reaction sintering, hot pressing, gas pressure sintering, or atmospheric pressure sintering, sintering aids are required to promote densification. These aids react with SiO2 on the Si3N4 surface to generate a liquid phase, promoting particle rearrangement and liquid phase diffusion, thereby achieving densification. Currently, the most commonly used sintering aid systems both domestically and internationally are rare earth metal oxides (Y2O3, CeO2, Yb2O3, Lu2O3, CeO2, La2O3, Eu2O3, etc.). However, the following problems exist: rare earth oxide raw materials are expensive and fluctuate greatly, increasing the production cost of Si3N4 ceramics; to achieve sufficient densification, existing technologies typically require the addition of relatively high amounts (5-10 wt%) of sintering aids, which weakens the excellent properties of Si3N4 ceramics if the aid content is too high; and the intergranular glassy phase formed after liquid phase cooling leads to a significant decrease in high-temperature mechanical strength and oxidation resistance, making it unsuitable for use in high-temperature environments. Therefore, in order to expand the application fields of Si3N4 ceramics and meet more demanding working conditions, it is urgent to develop a new low-content sintering aid system to improve the high-temperature mechanical properties and oxidation resistance of Si3N4 ceramics. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention aims to provide a silicon nitride ceramic with low sintering aid content and its preparation method.
[0005] On one hand, the present invention provides a silicon nitride ceramic with low content of sintering aid, wherein the silicon nitride ceramic is prepared by sintering using Si3N4 and sintering aid as starting materials; in the starting materials, the mass percentage of Si3N4 is 97-99.6 wt%, and the mass percentage of the sintering aid is 0.4-3 wt%; the sintering aid is selected from two of Al2O3, MgO, and AlN.
[0006] This invention abandons the traditional rare earth oxide sintering aid system and instead uses a small amount of two of Al2O3, MgO, and AlN as sintering aids to form a liquid phase with SiO2 on the surface of Si3N4 powder to promote the densification sintering process. This not only reduces production costs but also reduces the proportion of grain boundary phase, improves the purity of Si3N4 ceramics, and reduces the introduction of other elements.
[0007] Preferably, the sintering aid is 0.5 to 1 wt% by mass, and more preferably 0.6 wt%.
[0008] Preferably, the sintering agent is Al2O3 and MgO, wherein the mass ratio of Al2O3 to MgO is 1:(1-5).
[0009] Preferably, the sintering agent is MgO and AlN, wherein the mass ratio of MgO to AlN is (1-5):(1-5).
[0010] Preferably, the silicon nitride ceramic has a flexural strength of 464.1–1048.6 MPa and a fracture toughness of 6.0–9.8 MPa·m. 1 / 2 Its Vickers hardness is 13.4–18.1 GPa, and its relative density is 92.8%–99.4%.
[0011] On the other hand, the present invention also provides a method for preparing the above-mentioned low-content silicon nitride ceramic with sintering aid, comprising: using two of Al2O3 powder, MgO powder and AlN powder as sintering aid, mixing with Si3N4 powder, and then molding and sintering to obtain the low-content silicon nitride ceramic with sintering aid.
[0012] Preferably, the median particle size of the Si3N4 powder is 0.4–0.6 mm; and the oxygen content of the Si3N4 powder is 0.8–1.5%. The median particle size of the Al2O3 powder is 0.1–0.3 μm; the median particle size of the MgO is 0.2–0.4 μm; and the median particle size of the AlN powder is 0.4–0.6 μm.
[0013] Preferably, the mixing method is ball milling; the parameters of the ball milling include: a ball-to-material ratio of 1:(1-3), a ball milling speed of 100-300 rpm, and a ball milling time of 4-6 hours.
[0014] Preferably, the raw material powder is mixed and then dried and sieved; preferably, the drying temperature is 80-100℃ and the time is 8-12 hours; preferably, the sieve mesh size is 100-200 mesh.
[0015] Preferably, the sintering method is hot pressing sintering; the sintering parameters include: sintering temperature of 1600-1800℃, holding time of 2-4 hours, and sintering pressure of 20-40 MPa; preferably, the heating rate is 5-10℃ / min; and the ambient atmosphere is a nitrogen atmosphere of 1-2 atm. Beneficial effects
[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention abandons traditional rare earth oxide sintering aids, instead using a small amount of two of Al2O3, MgO, and AlN as sintering aids, combined with silicon nitride powder with a specific oxygen content and hot pressing sintering. This allows for the densification of Si3N4 ceramics with an extremely low addition content of only 0.6 wt%. This approach not only significantly reduces production costs but also effectively reduces the proportion of grain boundary phases in Si3N4 ceramics, improving material purity and enhancing the tribological properties and corrosion resistance of Si3N4 ceramics. Attached Figure Description
[0017] Figure 1 These are phase analysis diagrams of the silicon nitride ceramics prepared in Examples 1-5 and Comparative Example 1 of the present invention; Figure 2 The images show the cross-sectional morphology of the silicon nitride ceramics prepared in Examples 1-8 of this invention. Figure 3 This is a cross-sectional morphology diagram of the silicon nitride ceramic prepared in Comparative Example 1 of the present invention. Detailed Implementation
[0018] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention's content, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention.
[0019] First, this invention provides a silicon nitride ceramic with a low content of sintering aid, wherein the silicon nitride ceramic is prepared by sintering Si3N4 and a sintering aid as starting materials; in the starting materials, the mass percentage of Si3N4 is 97-99.6 wt%, and the mass percentage of the sintering aid is 0.4-3 wt%; the sintering aid is selected from two of Al2O3, MgO, and AlN. The sintering aid is Al2O3 and MgO, wherein the mass ratio of Al2O3 to MgO is 1:(1-5); the sintering aid is MgO and AlN, wherein the mass ratio of MgO to AlN is (1-5):(1-5). This invention utilizes SiO2 on the surface of Si3N4 powder as the basis for in-situ liquid phase formation without introducing conventional rare earth sintering aids. It introduces a small amount of two of Al2O3, MgO, and AlN to form a composite aid system, thereby obtaining high-density and high-performance Si3N4 ceramics through hot pressing sintering process while significantly reducing the total amount of sintering aids added.
[0020] In this invention, SiO2 on the surface of Si3N4 powder serves as the in-situ liquid phase base. MgO, as a sintering aid, significantly lowers the melting point of silicates and forms the main component of the low-temperature liquid phase with SiO2 on the Si3N4 powder surface. A small amount of Al2O3 or AlN forms a solid solution with Si3N4 grains, promoting sintering while pinning grain boundaries. Simultaneously, hot-pressing sintering is used to promote the sintering shrinkage process through external pressure, achieving densification of Si3N4 ceramics. MgO, as the main component for liquid phase formation, must be present in sufficient quantity to avoid insufficient liquid phase content, which severely affects the sintering process. Al2O3 or AlN dissolves into the interior of Si3N4 grains. Due to the higher solubility of AlN, it more effectively regulates the N / O content of the liquid phase, inhibiting excessive growth of Si3N4 grains in the later stages of sintering. The sintering temperature of hot pressing plays a crucial role in the development and phase transformation of Si3N4 grains. Excessively high temperatures lead to abnormal grain growth, while excessively low temperatures prevent complete phase transformation into the β-Si3N4 phase. Too low an oxygen content in the initial Si3N4 powder results in a low SiO2 content, leading to insufficient liquid phase formation and affecting the sintering process; conversely, too high an oxygen content causes an imbalance in the liquid phase ratio, allowing oxygen to enter the Si3N4 lattice and form defects.
[0021] The following exemplifies the preparation method of silicon nitride ceramics with low content sintering aid provided by the present invention.
[0022] Using Si3N4 powder as the raw material, and two of Al2O3 powder, MgO powder, and AlN powder as sintering aids, the raw material powder and sintering aids are ball-milled to obtain a ceramic slurry with a solid content of 33-67 wt%. The ball-to-material ratio is 1:(1-3), the ball milling speed is 100-300 rpm, and the ball milling time is 4-6 hours. The mixed slurry is dried at 80-100℃ for 8-12 hours and passed through a 100-200 mesh sieve. Then it is pressed into shape to obtain a silicon nitride ceramic green body.
[0023] In an optional embodiment, the median particle size of the Si3N4 powder is 0.4–0.6 mm; the oxygen content of the Si3N4 powder is 0.8–1.5%. The oxygen content of the Si3N4 powder regulates the amount and chemical composition of the liquid phase formed during sintering, thereby affecting the phase transformation and grain growth process of Si3N4. If the oxygen content is too low, there is insufficient SiO2 on the surface of the Si3N4 powder, resulting in a small amount of liquid phase; if the oxygen content is too high, an "oxygen-rich" liquid phase is formed, and oxygen easily enters the Si3N4 lattice, forming defects. The median particle size of the Al2O3 powder is 0.1–0.3 μm; the median particle size of the MgO is 0.2–0.4 μm; and the median particle size of the AlN powder is 0.4–0.6 μm.
[0024] A silicon nitride ceramic blank is placed in a graphite hot press mold and sintered in a hot press furnace under a nitrogen atmosphere to obtain the silicon nitride ceramic with low sintering aid content.
[0025] In an optional embodiment, the sintering parameters include: a sintering temperature of 1600–1800°C, a holding time of 2–4 hours, and a sintering pressure of 20–40 MPa; preferably, the heating rate is 5–10°C / min; and the ambient atmosphere is a nitrogen atmosphere of 1–2 atm. If the sintering temperature is too low, the β-Si3N4 phase transformation is incomplete, resulting in lower flexural strength and reduced fracture toughness; if the sintering temperature is too high, abnormal grain growth occurs, significantly reducing flexural strength. Compared to gas pressure sintering and atmospheric pressure sintering, the hot-pressing sintering method of this invention can apply uniaxial pressure to the sample, providing additional sintering driving force, promoting the densification process of Si3N4 ceramics, and improving the density of the sample.
[0026] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values in the examples below. Examples 1-3
[0027] 99.4 g of Si3N4 powder (oxygen content 1.3%) was weighed, and two of Al2O3, MgO, and AlN were added as sintering aids (total amount 0.6 g). Anhydrous ethanol was added to prepare a slurry with a solid content of 50 wt%. The slurry was ball-milled at 300 rpm for 4 h, then dried and passed through a 100-mesh sieve. After dry pressing, the slurry was placed in a graphite mold and hot-pressed under a nitrogen atmosphere of 1 atm. The sintering temperature was 1800℃, the sintering time was 2 h, the sintering pressure was 30 MPa, and the heating rate was 10℃ / min. The difference between Examples 1-3 lies in the different proportions of sintering aids, as shown in Table 1. Wherein, "SiO2" refers to the SiO2 on the surface of the initial Si3N4 raw material powder (99.4g), and its mass is calculated by converting the oxygen content of the initial Si3N4 raw material powder; the mass of the Si3N4 powder is the difference between the mass of the initial Si3N4 raw material powder and the mass of SiO2. Example 4
[0028] The preparation process of the low-content silicon nitride ceramic in Example 4 is the same as in Example 3, except that the hot pressing sintering temperature is 1750℃. Example 5
[0029] The preparation process of the low-content silicon nitride ceramic in Example 5 is the same as in Example 3, except that the hot pressing sintering temperature is 1700℃. Examples 6-8
[0030] The preparation process of silicon nitride ceramics in Examples 6-8 is the same as in Example 3, except that: different oxygen contents of initial Si3N4 powder are used (the mass of Si3N4 in the powder is fixed at 97g), the mass ratio of MgO to AlN is fixed at 5:1, and different masses of Si3N4 powder and sintering aids are weighed as raw materials. The specific formula is shown in Table 1. Comparative Example 1
[0031] The preparation process of the low-content silicon nitride ceramic in Comparative Example 1 is the same as that in Example 3, except that the mass ratio of Al2O3 to MgO is 5:1. Comparative Example 2
[0032] The preparation process of the silicon nitride ceramic with low content of sintering aid in Comparative Example 2 is the same as that in Example 3, except that the content of sintering aid is 0.3%.
[0033] Table 1: .
[0034] Table 2 lists the performance parameters of the silicon nitride ceramics prepared in Examples 1-8 and Comparative Examples 1-2.
[0035] Table 2: .
[0036] As shown in Tables 1 and 2, a high MgO ratio is fundamental for dense sintering. AlN exhibits better sintering performance, and Si3N4 ceramics with AlN incorporation show superior mechanical properties compared to those with Al2O3. However, an excessively high Al2O3 to MgO mass ratio (Comparative Example 1), meaning a low MgO content, means that Al2O3 alone cannot provide sufficient liquid phase to promote the sintering process, resulting in lower density and poorer overall mechanical properties in the prepared Si3N4 ceramics. Lowering the sintering temperature refines the grains and slightly improves the flexural strength of Si3N4 ceramics, but simultaneously reduces fracture toughness. In Examples 6-8, the initial Si3N4 powder had a lower oxygen content; to ensure a consistent Si3N4 proportion in the final samples, a higher content of sintering aid was required. The reduced oxygen content alters the liquid phase ratio and content, resulting in a slight decrease in strength, but still maintaining a relatively high strength. The sintering aid content was too low (Comparative Example 2). Despite using a better MgO and AlN ratio, the overall liquid phase content was too low, which limited the phase transformation and grain growth of Si3N4. As a result, the Si3N4 ceramic obtained had low density and poor performance.
[0037] Figure 1 The figures show the phase analysis of silicon nitride ceramics prepared in Examples 1-5 and Comparative Example 1 of this invention. As can be seen from the figures, in Comparative Example 1, due to the low MgO content, Al2O3 alone could not provide sufficient liquid phase to promote the sintering process, resulting in a large amount of α-Si3N4 failing to complete the phase transformation. Similarly, in Example 5, due to the lower sintering temperature, a small amount of α-Si3N4 also failed to complete the phase transformation. The low content of sintering aids provided sufficient liquid phase to completely transform the α-Si3N4 in Examples 1, 2, 3, and 4 into β-Si3N4, and no other crystalline phases were observed, indicating high purity.
[0038] Figure 2 The figures show the cross-sectional morphology of the silicon nitride ceramics prepared in Examples 1-8 of this invention. As can be seen from the figures, the silicon nitride ceramic prepared in Example 3 has a smaller grain size, with many grain pull-out marks observed, and no obvious porosity. Therefore, Example 3 exhibits both high flexural strength (997.9 MPa) and high fracture toughness (9.5 MPa·m). 1 / 2Due to the low content of grain boundary phase, the majority of the silicon nitride ceramics prepared in Examples 1 and 2 consist of high-hardness Si3N4 grains, exhibiting high Vickers hardness that increases with decreasing sintering temperature (Examples 3, 4, and 5). Due to significant differences in liquid phase composition, the silicon nitride ceramics prepared in Examples 1 and 2 contain a small amount of porosity, resulting in lower mechanical strength compared to Example 3. For Examples 6-8, the grain morphology of silicon nitride ceramics prepared from Si3N4 powders with different oxygen contents varies. While the grain size of the silicon nitride varies slightly due to slight differences in the particle size of the raw material powder, the overall density is high, and no significant large pores are present.
[0039] Figure 3 This is a cross-sectional morphology diagram of the silicon nitride ceramic prepared in Comparative Example 1 of the present invention. As can be seen from the figure, the silicon nitride ceramic prepared in Comparative Example 1 has a large number of pores and many spherical α-Si3N4 particles that have not undergone phase transformation are observed, resulting in a mechanical strength that is significantly lower than that of Example 3.
[0040] In summary, this invention achieves densification sintering of Si3N4 ceramics under low-additive-content conditions by controlling the sintering aid ratio. Specifically, hot pressing sintering is employed, using two of Al2O3, MgO, and AlN at 0.6 wt% as a composite sintering aid to form a liquid phase with SiO2 on the surface of the Si3N4 raw material powder, promoting the sintering of Si3N4 ceramics. This low-content liquid phase helps refine grains and control the content of grain boundary phases, ensuring high mechanical strength while maintaining high Vickers hardness, thus improving the tribological properties of Si3N4 ceramics. Furthermore, the introduction of fewer foreign phases significantly improves the purity of Si3N4 ceramics, correspondingly enhancing corrosion resistance. While Si3N4 powder with lower oxygen content can also achieve densification sintering, variations in the sintering aid content and differences in powder properties lead to a decrease in the overall mechanical properties of Si3N4 ceramics.
[0041] The above description represents only some preferred embodiments of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content and spirit of the present invention, shall still fall within the protection scope of the present invention.
Claims
1. A silicon nitride ceramic with low sintering aid content, characterized in that, The silicon nitride ceramic is prepared by sintering using Si3N4 and sintering aid as starting materials; in the starting materials, the mass percentage of Si3N4 is 97-99.6 wt%, and the mass percentage of the sintering aid is 0.4-3 wt%; the sintering aid is selected from two of Al2O3, MgO, and AlN.
2. The low-content silicon nitride ceramic according to claim 1, characterized in that, The sintering aid has a mass percentage of 0.5 to 1 wt%, preferably 0.6 wt%.
3. The low-content silicon nitride ceramic according to claim 1, characterized in that, The sintering agent is Al2O3 and MgO, wherein the mass ratio of Al2O3 to MgO is 1:(1-5).
4. The low-content silicon nitride ceramic according to claim 1, characterized in that, The sintering agent is MgO and AlN, wherein the mass ratio of MgO to AlN is (1-5):(1-5).
5. The low-content silicon nitride ceramic according to claim 1, characterized in that, The silicon nitride ceramic exhibits a flexural strength of 464.1–1048.6 MPa and a fracture toughness of 6.0–9.8 MPa·m. 1 / 2 Its Vickers hardness is 13.4–18.1 GPa, and its relative density is 92.8%–99.4%.
6. A method for preparing silicon nitride ceramics with low sintering aid content according to any one of claims 1-5, characterized in that, include: Two of Al2O3 powder, MgO powder and AlN powder are used as sintering aids and mixed with Si3N4 powder. After molding and sintering, the silicon nitride ceramic with low content of sintering aid is obtained.
7. The preparation method according to claim 6, characterized in that, The median particle size of the Si3N4 powder is 0.4–0.6 mm; the oxygen content of the Si3N4 powder is 0.8–1.5%. The median particle size of the Al2O3 powder is 0.1–0.3 μm; the median particle size of the MgO is 0.2–0.4 μm; and the median particle size of the AlN powder is 0.4–0.6 μm.
8. The preparation method according to claim 6 or 7, characterized in that, The mixing method is ball milling; the parameters of the ball milling include: a ball-to-material ratio of 1:(1-3), a ball milling speed of 100-300 rpm, and a ball milling time of 4-6 hours.
9. The preparation method according to any one of claims 6-8, characterized in that, The raw material powder is mixed and then dried and sieved; preferably, the drying temperature is 80-100℃ and the time is 8-12 hours; preferably, the sieve mesh size is 100-200 mesh.
10. The preparation method according to any one of claims 6-9, characterized in that, The sintering method is hot pressing sintering; the sintering parameters include: sintering temperature of 1600-1800℃, holding time of 2-4 hours, and sintering pressure of 20-40 MPa; preferably, the heating rate is 5-10℃ / min; and the ambient atmosphere is a nitrogen atmosphere of 1-2 atm.