Silicon nitride ceramic and preparation method thereof

Abstract

The invention relates to the technical field of ceramic preparation, in particular to silicon nitride ceramic and a preparation method thereof. Through collaborative design of Er2O3 and MgSiN2, synchronous achievement of'low oxygen content ', 'high compactness' and'optimized microstructure 'is achieved, and under the technical scheme limited by the application, the relative density of the prepared silicon nitride ceramic can reach 96% or above, and meanwhile, the silicon nitride ceramic has high thermal conductivity (63.04 W m <-1 > k <-1 >) and excellent mechanical property (the strength is 1012.98 MPa).

Description

Technical Field

[0001] This invention relates to the field of ceramic preparation technology, and particularly to a silicon nitride ceramic and its preparation method. Background Technology

[0002] As electronic power devices evolve towards higher voltage, higher current, and higher power density, they generate more heat and experience greater thermal stress during operation. This places higher demands on the heat dissipation performance and reliability of the ceramic substrates used in these devices. Compared to other ceramic materials, Si3N4 ceramics have significant advantages, especially in terms of high-temperature resistance, high thermal conductivity, chemical inertness to metals, and ultra-high hardness. The flexural strength of Si3N4 ceramics can reach more than twice that of AlN. Particularly in terms of material reliability, Si3N4 ceramic substrates have unparalleled advantages over other materials. Numerous studies have demonstrated that silicon nitride has a very high theoretical thermal conductivity, comparable to that of AlN ceramics. Furthermore, silicon nitride ceramics possess excellent mechanical properties, good insulation properties, and are non-toxic, making them an ideal ceramic substrate material that combines high thermal conductivity and high strength. However, there is still a significant gap between the actual and theoretical thermal conductivity of silicon nitride ceramics. Therefore, improving thermal conductivity while maintaining excellent mechanical properties is a key research direction in this field.

[0003] Therefore, existing technologies improve the properties of silicon nitride ceramics by adding sintering aids. This is because silicon nitride is a strongly covalent compound with a very low self-diffusion coefficient, resulting in insufficient sintering driving force and making it difficult to achieve densification through simple solid-state sintering. However, sintering aids can facilitate the densification process through liquid-phase sintering. The principle of liquid-phase sintering of silicon nitride ceramics involves the reaction of sintering aids with SiO2 on the surface of silicon nitride powder to form a liquid phase. Under the action of the liquid phase, densification is achieved through particle rearrangement, dissolution-precipitation, and grain growth.

[0004] Existing technology 1 provides a silicon nitride ceramic sintering aid, a high thermal conductivity silicon nitride ceramic, and a preparation method thereof (application number 202311234046.5). It uses a composite of silicon nitride magnesium, rare earth oxygen-free additives, and β-phase silicon nitride as a sintering aid, and performs two-stage heating sintering and two-stage heat preservation treatments to prepare silicon nitride ceramics with low lattice oxygen content, few lattice defects, and a high β-phase ratio. These ceramics exhibit high thermal conductivity, high flexural strength, and excellent fracture toughness, possessing both mechanical and thermal properties. However, it requires α-phase silicon nitride powder, sintering aid slurry, dispersant, binder, water-reducing agent, plasticizer, molding agent, release agent, deionized water, etc., resulting in a complex composition and cumbersome preparation process.

[0005] Prior art 2 discloses a sintering aid for preparing silicon nitride ceramics and its application, as well as a method for preparing silicon nitride ceramics (application number: 202110423754.8). The sintering aid comprises component A, component B, and component C; the particle size of the sintering aid is ≤100 nm; the mass ratio of component A, component B, and component C is (1-5):(1-10):(1-10); component A includes titanium dioxide; component B includes boron oxide, magnesium oxide, or calcium oxide; and component C includes rare earth metal oxides. The titanium dioxide can promote the growth of silicon nitride grains, reduce porosity, and increase the hardness of the silicon nitride ceramic material; the substance of component B can cause silicon nitride to form a liquid phase at a lower temperature, promoting the dissolution of α-silicon nitride and the precipitation of β-silicon nitride; the component C can form a second phase (specifically, oxides formed by the segregation of rare earth ions at the grain boundaries) at the silicon nitride grain boundaries, increasing the high-temperature mechanical properties of the silicon nitride ceramic. However, while the addition of rare earth metal oxides improved the mechanical properties in this scheme, its effect on thermal conductivity was not mentioned, and the densification of the prepared sample was low.

[0006] Therefore, a ceramic preparation method that is simple to prepare and can simultaneously guarantee the mechanical properties and thermal conductivity of silicon nitride ceramics is needed in this field. Summary of the Invention

[0007] Based on the above analysis, this application provides a silicon nitride ceramic and its preparation method. By introducing erbium oxide and magnesium nitrogen silicon (Er2O3-MgSiN2) as composite sintering aids, and controlling the composition of the aids, this application explores a feasible path for synergistic improvement of the mechanical properties and thermal conductivity of Si3N4 ceramic samples and the mechanism of action of the composite aids, thereby realizing the preparation of high-performance Si3N4 ceramic materials.

[0008] To achieve the above objectives, the first technical solution of this application discloses a method for preparing silicon nitride ceramics, which includes mixing powders α-Si3N4, Er2O3, and MgSiN2 and then sintering them in a vacuum environment to obtain silicon nitride ceramics.

[0009] Furthermore, the mass ratio of the powder α-Si3N4:(2~20):(0~20).

[0010] Furthermore, the vacuum level of the vacuum environment is 8.9e~10 Pa.

[0011] Furthermore, the sintering process also includes pressurization, wherein the axial pressure of the pressurization is 10~60MPa.

[0012] Furthermore, the sintering temperature is 1700~1850℃, and the holding time is 3-10min.

[0013] Preferably, the sintering method is spark plasma sintering.

[0014] And silicon nitride ceramics prepared according to any of the above-described preparation methods.

[0015] Beneficial effects: This application achieves simultaneous attainment of "low oxygen content," "high density," and "optimized microstructure" through the synergistic design of Er2O3 and MgSiN2. Furthermore, under the technical solution defined in this application, the prepared silicon nitride ceramic can achieve a relative density of over 96%, while also possessing high thermal conductivity (63.04 W / m²). -1 k -1 It has excellent mechanical properties (strength 1012.98MPa). Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the preparation process of silicon nitride ceramics according to this application;

[0018] Figure 2 The image shows a SEM image of the silicon nitride ceramic prepared in Example 1. Detailed Implementation

[0019] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] like Figure 1 As shown, the first embodiment of this application discloses a method for preparing silicon nitride ceramics, comprising mixing powders α-Si3N4, Er2O3, and MgSiN2 and then sintering them under vacuum to obtain silicon nitride ceramics. The mass ratio of the powders α-Si3N4, Er2O3, and MgSiN2 is (80~98):(2~20):(0~20). The vacuum degree of the vacuum environment is 8.9e~10 Pa, and the axial pressure is 10~60 MPa. The sintering temperature is 1700~1850℃, and the holding time is 3-10 min. The sintering method can be any sintering method disclosed in the art, such as hot pressing sintering, hot isostatic pressing sintering, gas pressure sintering, pressureless sintering, spark plasma sintering, or reaction sintering. This application preferably uses spark plasma sintering.

[0021] Preferably, the sintering method is spark plasma sintering.

[0022] In this embodiment, the Er2O3 (rare earth oxide) and MgSiN2 (non-oxide) composite additive system overcomes the limitations of traditional single oxide or oxide-oxide composite additives, achieving a three-in-one control of "deoxidation-densification-grain optimization" through the synergistic effect of the two. MgSiN2 provides a low-oxygen liquid phase, inhibiting the generation of oxygen in the β-Si3N4 lattice; Er2O3 reacts with SiO2 impurities in the raw material to eliminate surface oxygen obstacles, while simultaneously regulating the liquid phase viscosity to promote particle rearrangement, thus solving the technical problem of traditional additives that "deoxidation and densification are difficult to achieve simultaneously".

[0023] It should be noted that the steps of mixing the raw materials and then ball milling, vibrating and compacting the raw materials, sintering and cooling them in the furnace are common knowledge in the field and are not limited by this application.

[0024] The technical effects of the technical solution of this application will be described in detail below through specific embodiments.

[0025] Example 1: Preparation of silicon nitride ceramics

[0026] 1. Mix 93g of α-Si3N4 powder, 4g of Er2O3 powder, and 3g of MgSiN2 powder by ball milling, and then place the mixture in a graphite mold and vibrate to compact it.

[0027] 2. The compacted raw material powder is fed into a spark plasma sintering furnace for sintering, maintaining a vacuum of 6 Pa, a sintering temperature of 1850℃, a holding time of 5 min, and a sintering pressure of 50 MPa. After sintering, the temperature is first lowered to 650℃, and then cooled to room temperature in the furnace. The graphite mold is then removed, and the graphite mold and surface graphite paper are removed to obtain a silicon nitride ceramic sample. The silicon nitride ceramic prepared by the above process can achieve a relative density of over 96% and a thermal conductivity of 63.04 W / m². -1 k -1 It also possesses excellent mechanical properties, with a bending strength of 1012.98 MPa.

[0028] Example 2 Preparation of silicon nitride ceramics

[0029] 1. Mix 80g of α-Si3N4 powder, 18g of Er2O3 powder, and 2g of MgSiN2 powder by ball milling, and then place the mixture in a graphite mold and vibrate to compact it.

[0030] 2. The compacted raw material powder is fed into a spark plasma sintering furnace for sintering, maintaining a vacuum of 6 Pa, a sintering temperature of 1750℃, a holding time of 5 min, and a sintering pressure of 10 MPa. After sintering, the temperature is first lowered to 650℃, and then cooled to room temperature in the furnace. The graphite mold is then removed, and the graphite mold and surface graphite paper are removed to obtain the silicon nitride ceramic sample. The silicon nitride ceramic prepared by the above process can achieve a relative density of over 96%, and a thermal conductivity of 52.83 W / m². -1 k -1 It also possesses excellent mechanical properties, with a bending strength of 908.99 MPa.

[0031] Example 3 Preparation of silicon nitride ceramics

[0032] 1. Mix 98g of α-Si3N4 powder, 1g of Er2O3 powder, and 1g of MgSiN2 powder by ball milling, and then place the mixture in a graphite mold and vibrate to compact it.

[0033] 2. The compacted raw material powder is fed into a spark plasma sintering furnace for sintering, maintaining a vacuum of 6 Pa, a sintering temperature of 1700℃, a holding time of 5 min, and a sintering pressure of 60 MPa. After sintering, the temperature is first lowered to 650℃, and then cooled to room temperature in the furnace. The graphite mold is then removed, and the graphite mold and surface graphite paper are removed to obtain the silicon nitride ceramic sample. The silicon nitride ceramic prepared by the above process can achieve a relative density of over 96%, and a thermal conductivity of 45.80 W / m². -1 k -1 It also possesses excellent mechanical properties, with a bending strength of 815.03 MPa.

[0034] Comparative Example 1

[0035] The difference between Comparative Example 1 and Example 1 above is that Er₂O₃ is replaced with Y₂O₃ in this comparative example; otherwise, they are the same as in Example 1. The resulting silicon nitride ceramic has a relative density of 99.16% and a thermal conductivity of 56.86 W / m². -1 k -1 Its mechanical property, bending strength, is 765.07 MPa.

[0036] Comparative Example 2

[0037] The difference between Comparative Example 2 and Example 1 is that Er₂O₃ and MgSiN₂ are both replaced with Y₂O₃ in this comparative example; otherwise, they are the same as in Example 1. The resulting silicon nitride ceramic has a relative density of 99.95% and a thermal conductivity of 33.29 W / m². -1 k -1 Its mechanical property, bending strength, is 866.22 MPa.

[0038] Of the above indicators, the flexural strength (mechanical property) was measured according to the standard GB / T 6569-2006 "Test Method for Bending Strength of Fine Ceramics"; the thermal conductivity was measured according to the standard GB / T 39862-2021 "Detection of Thermal Conductivity of High Thermal Conductivity Ceramics". It can be seen that the thermal conductivity of Example 1 reached 63.04 W / m². -1 k -1 The high-level vacuum sintering atmosphere effectively reduced the formation of oxide impurity phases, and the high densification reduced phonon scattering losses during transmission, laying the foundation for high thermal conductivity. The uniformly distributed β-Si3N4 grains formed continuous thermally conductive channels, reducing obstacles in the phonon transmission path and facilitating efficient phonon conduction, thus improving thermal conductivity. Comparative Example 1, which replaced Er2O3 in Example 1 with Y2O3 while maintaining the same preparation processes and parameters, showed a thermal conductivity of 56.86 W / m². -1 k -1 All performance characteristics are lower than those of Example 1, because Y 3 + It tends to accumulate at grain boundaries, resulting in a higher degree of disorder in the grain boundary phase structure, which increases the scattering probability during phonon transport and thus reduces thermal conductivity. In Comparative Example 2, replacing Er2O3 and MgSiN2 in Example 1 with Y2O3 reduced the thermal conductivity to 33.29 W / m. -1 k -1 The thermal conductivity of the sample is significantly different from that of Example 1. The single Y2O3 system tends to increase the thickness of the grain boundary phase and increase the proportion of disordered structure in the grain boundary region, which further aggravates phonon scattering and causes a significant decrease in thermal conductivity.

[0039] Among them, the SEM of Example 1 Figure 2 As shown, the long columnar β-Si3N4 grains in silicon nitride ceramics are intertwined and not easily pulled out. The glassy phase (Er2Si2O7, MgSiO3) at the grain boundaries can improve the bonding state between Si3N4 grains, increase the interfacial bonding strength, and reduce interfacial defects, thereby improving the overall mechanical properties of the sample, making its bending strength reach 1012.98 MPa.

[0040] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for preparing silicon nitride ceramics, characterized in that, It consists of mixed powders α-Si3N4, Er2O3, and MgSiN2, which are then sintered in a vacuum environment to obtain silicon nitride ceramics.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the powder α-Si3N4:(2~20):(0~20).

3. The preparation method according to claim 1, characterized in that, The vacuum level of the vacuum environment is 8.9e~10Pa.

4. The preparation method according to claim 1, characterized in that, The sintering process also includes pressurization, with an axial pressure of 10~60MPa.

5. The preparation method according to claim 1, characterized in that, The sintering temperature is 1700~1850℃, and the holding time is 3-10min.

6. The preparation method according to claim 5, characterized in that, The sintering method is spark plasma sintering.

7. A silicon nitride ceramic prepared by any one of the preparation methods according to claims 1-6.

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