Silicon nitride-aluminum nitride / polymer composite and method for producing the same

Abstract

The application belongs to the technical field of nitride ceramics and its heat-conducting material, and discloses a silicon nitride-aluminum nitride / polymer composite material and a preparation method thereof. The preparation method comprises the following steps: mixing a silicon source and an aluminum source, and then directly carrying out a nitriding reaction under a nitrogen atmosphere to obtain a silicon nitride-aluminum nitride composite powder; then, the aluminum powder, the adhesive, the sintering aid and the dispersing agent are added into an organic solvent to be uniformly mixed to obtain a suspension; after the suspension is subjected to directional freezing forming, a vacuum freeze-drying is carried out to obtain an aluminum-containing raw material powder skeleton, then in-situ nitriding reaction sintering is carried out in a nitrogen-containing atmosphere to obtain a silicon nitride-aluminum nitride skeleton containing one-dimensional rod-shaped aluminum nitride whiskers; finally, a polymer impregnation liquid is used to carry out vacuum impregnation and solidification treatment on the silicon nitride-aluminum nitride skeleton to obtain the silicon nitride-aluminum nitride / polymer composite material. The silicon nitride-aluminum nitride / polymer composite material obtained by the application has the characteristics of high surface heat-conducting coefficient and good mechanical properties.

Description

Technical Field

[0001] This invention belongs to the technical field of nitride ceramics and their thermally conductive materials, specifically relating to a silicon nitride-aluminum nitride / polymer composite material and its preparation method. Background Technology

[0002] Since the beginning of this century, with the rapid development of the electronic information industry, especially 5G, the trend of high power, high density and high operating speed of electronic components has become increasingly obvious, which makes efficient heat dissipation an urgent problem to be solved.

[0003] Polymer-based composites with high thermal conductivity play a crucial role in heat dissipation in electronic devices, such as electronic packaging. There are many fillers for thermally conductive polymer composites, including ceramics, carbon, and metals. Among them, ceramics have received widespread attention due to their high insulation and good thermal conductivity, especially nitride ceramics, which have become increasingly popular in recent years.

[0004] Among all nitride ceramics, silicon nitride and aluminum nitride are among the most representative thermally conductive fillers. For silicon nitride ceramics, especially β-silicon nitride, the thermal conductivity along the a-axis and c-axis is 57 W / mK and 169 W / mK, respectively. For aluminum nitride ceramics, its thermal conductivity is second only to beryllium oxide among ceramic materials, making it an ideal material for power microelectronics applications. However, aluminum nitride also suffers from problems such as high raw material cost and susceptibility to hydrolysis.

[0005] In summary, if the advantages of silicon nitride and aluminum nitride can be combined to prepare polymer composite materials with excellent thermal conductivity using them as composite thermally conductive fillers, it will be of great significance for promoting the solution of heat dissipation problems in the operation of electronic devices or products. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the existing technology, the primary objective of this invention is to provide a method for preparing silicon nitride-aluminum nitride / polymer composite materials.

[0007] Another object of the present invention is to provide a silicon nitride-aluminum nitride / polymer composite material prepared by the above method.

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

[0009] A method for preparing a silicon nitride-aluminum nitride / polymer composite material includes the following preparation steps:

[0010] (1) Mix silicon source and aluminum source, and then carry out direct nitriding reaction in nitrogen atmosphere to obtain silicon nitride-aluminum nitride composite powder;

[0011] (2) The silicon nitride-aluminum nitride composite powder obtained in step (1) is mixed with aluminum powder, binder, sintering aid and dispersant in an organic solvent to obtain a suspension;

[0012] (3) After the suspension obtained in step (2) is subjected to directional freeze-drying, an aluminum-containing raw material powder skeleton is obtained by vacuum freeze-drying;

[0013] (4) The aluminum-containing raw material powder skeleton obtained in step (3) is sintered in situ in a nitrogen atmosphere to obtain a silicon nitride-aluminum nitride skeleton containing one-dimensional rod-shaped aluminum nitride whiskers.

[0014] (5) The silicon nitride-aluminum nitride skeleton obtained in step (4) is subjected to vacuum impregnation and curing treatment using polymer impregnation liquid to obtain silicon nitride-aluminum nitride / polymer composite material.

[0015] Further, in step (1), the silicon source is at least one of purified photovoltaic crystalline silicon waste and silicon powder; the aluminum source is aluminum powder with a size of 1 to 3 μm; and the mass ratio of the silicon source to the aluminum source is 2 to 3: 1 to 2.

[0016] Furthermore, the direct nitriding reaction temperature of the silicon source and aluminum source in step (1) is 1300-1600℃, and the time is 120-180min.

[0017] Further, in step (2), the mass ratio of silicon nitride-aluminum nitride composite powder to aluminum powder is 5-6:5-4; the total amount of silicon nitride-aluminum nitride composite powder and aluminum powder added is 30-60% of the total mass of the suspension.

[0018] Further, the adhesive in step (2) includes at least one of polyvinyl butyral and polyvinyl alcohol; the amount of adhesive added is 1 to 8% of the total mass of the suspension.

[0019] Further, the dispersant in step (2) includes at least one of glycerol and citric acid, and the amount of dispersant added is 0.5 to 5% of the total mass of the suspension.

[0020] Furthermore, the organic solvent mentioned in step (2) is tert-butanol.

[0021] Further, the sintering aid in step (2) includes a primary sintering aid and a secondary sintering aid; the primary sintering aid is YF3, and the secondary sintering aid includes at least one of La2O3, Y2O3, and CaF2; the mass ratio of the primary sintering aid to the secondary sintering aid is greater than 1; the sintering aid accounts for 1 to 6% of the total mass of the suspension.

[0022] Further, in step (3), the temperature for directional freeze-drying is -100 to -50°C and the time is 3 to 10 minutes; the temperature for vacuum freeze-drying is -70 to -60°C and the time is 12 to 36 hours.

[0023] Further, the nitrogen-containing atmosphere in step (4) is an atmosphere containing at least one gas selected from nitrogen and ammonia.

[0024] Furthermore, the in-situ nitriding reaction sintering temperature in step (4) is 1350–1550 °C, and the time is 120–180 min.

[0025] Further, the polymer impregnation liquid in step (5) includes at least one of epoxy resin impregnation liquid, polyimide resin impregnation liquid, polytetrafluoroethylene resin impregnation liquid and silicone rubber impregnation liquid.

[0026] Further, in step (5), the mass ratio of silicon nitride-aluminum nitride to polymer impregnation liquid is 1-5:9-5.

[0027] Furthermore, the vacuum impregnation temperature in step (5) is 55–65°C, and the vacuum degree of the vacuum impregnation is less than 10. -1 Pa, the vacuum impregnation time is 1 to 2 hours.

[0028] Furthermore, the curing treatment mentioned in step (5) refers to curing at 80-90℃ for 2-3 hours first, and then curing at 120-130℃ for 2-3 hours.

[0029] A silicon nitride-aluminum nitride / polymer composite material is prepared by the above method.

[0030] The principle of this invention is as follows: using silicon nitride-aluminum nitride composite powder and aluminum powder prepared in advance by direct nitriding as the main raw materials, a uniform suspension of the raw material powder is first prepared, and then it is directionally frozen and freeze-dried to obtain an aluminum-containing raw material powder skeleton. Next, after nitriding reaction and sintering, the aluminum-containing raw material powder skeleton is transformed in situ into a silicon nitride-aluminum nitride ceramic skeleton containing one-dimensional rod-shaped aluminum nitride whiskers. Finally, a silicon nitride-aluminum nitride / polymer composite material is obtained by vacuum infiltration.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) The silicon nitride in the composite nitride ceramic powder prepared in this invention can be obtained from purified photovoltaic silicon waste containing only silicon as the silicon source. The raw material source is wide and the cost is quite low, making it more economical when prepared on a large scale.

[0033] (2) The silicon nitride in the composite nitride ceramic powder prepared in this invention is a β crystal form that is difficult to obtain. Its intrinsic thermal conductivity is higher than that of the common α crystal form silicon nitride. It is beneficial to use it as a filler to improve the thermal conductivity of polymer composite materials.

[0034] (3) In the process of preparing composite nitride ceramic powder in this invention, since aluminum powder is added as a raw material, the nitriding reaction to generate aluminum nitride will release a lot of heat, which is conducive to the crystal transformation of α-silicon nitride to β-silicon nitride. Therefore, β-silicon nitride powder can be obtained at a lower reaction temperature.

[0035] (4) In this invention, the aluminum powder added to the silicon nitride-aluminum nitride composite powder before directional freeze-forming can be transformed into one-dimensional rod-shaped aluminum nitride whiskers through in-situ nitriding reaction during subsequent sintering. These whiskers act as "bridges" connecting adjacent silicon nitride (or aluminum nitride) grains, providing more continuous heat transfer channels for phonons. Simultaneously, the increased width of the filler due to the growth of numerous whiskers also provides a wider "highway" for phonon heat transfer. These factors all contribute to improving the thermal conductivity of the polymer composite material. Conversely, without the formation of rod-shaped aluminum nitride whiskers during reactive sintering, phonons can only transfer heat along the particles of the silicon nitride-aluminum nitride composite ceramic powder, which only achieves the effect of preparing thermally conductive composite materials using the general directional freeze-forming method. Attached Figure Description

[0036] Figure 1 This is a characterization diagram of the silicon nitride-aluminum nitride composite powder synthesized in step (1) of Example 1 of the present invention;

[0037] Figure 2 This is a fracture morphology diagram of the aluminum-containing raw material powder skeleton obtained in step (3) of Example 1 of the present invention;

[0038] Figure 3 The image shows the characterization of the silicon nitride-aluminum nitride framework obtained in step (4) of Example 1 of the present invention.

[0039] Figure 4 This is a characterization diagram of the silicon nitride-aluminum nitride / polymer composite material obtained in step (5) of Example 1 of the present invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0041] Example 1

[0042] (1) The purified photovoltaic crystalline silicon waste containing only silicon and spherical aluminum powder were mixed in a mass ratio of 2:1, and then a direct nitriding reaction was carried out at 1500℃ for 3 hours in a nitrogen atmosphere to prepare silicon nitride-aluminum nitride composite powder.

[0043] (2) Silicon nitride-aluminum nitride composite powder, spherical aluminum powder, sintering aid (including YF3 and La2O3 in a mass ratio of 3:2), and additives (including binder polyvinyl butyral and dispersant glycerol) are added to tert-butanol solvent. After magnetic stirring for 4 hours, a uniform suspension is obtained. The mass ratio of silicon nitride-aluminum nitride composite powder to aluminum powder is 5:4, the mass ratio of the sum of the masses of silicon nitride-aluminum nitride composite powder and aluminum powder to tert-butanol is 45:46, the sintering aid accounts for 5% of the total mass of the suspension, the binder accounts for 3% of the total mass of the suspension, and the dispersant accounts for 1% of the total mass of the suspension.

[0044] (3) After the suspension is oriented frozen at -70℃ for 3 minutes to form a solid, it is then vacuum freeze-dried at -60℃ for 36 hours to remove ice crystals and obtain an aluminum-containing raw material powder skeleton.

[0045] (4) The aluminum-containing raw material powder skeleton obtained in step (3) is placed in a sintering furnace and sintered at 1400℃ for 3 hours under a flowing nitrogen atmosphere of 100 sccm to obtain a silicon nitride-aluminum nitride skeleton containing one-dimensional rod-shaped aluminum nitride whiskers.

[0046] (5) Epoxy resin, 4-methylhexahydrophthalic anhydride, and 1-p-methylbenzenesulfonylimidazole were magnetically stirred at 60°C (500 r / min) for 1 h at a mass ratio of 100:86:1 to obtain an impregnation solution. The silicon nitride-aluminum nitride skeleton obtained in step (4) was immersed in the impregnation solution at a mass ratio of 2:3. Vacuum impregnation was performed at 60°C for 2 h, followed by curing at 90°C and 120°C for 3 h respectively to obtain a silicon nitride-aluminum nitride / polymer composite material.

[0047] 1. The silicon nitride-aluminum nitride composite powder of step (1) in this embodiment was characterized using X-ray diffraction (XRD; Smart Lab, Rigaku, Japan), field emission scanning electron microscopy (SEM, GeminiSEM 360, ZEISS, Germany), and transmission electron microscopy (TEM; Talos F200S, Thermoscientific, USA), combined with energy dispersive spectroscopy (EDS, X-max50, Oxford, UK). The results are as follows: Figure 1 As shown. From Figure 1 The XRD patterns of the raw materials before and after the reaction show that the silicon and aluminum sources are completely transformed into silicon nitride and aluminum nitride after the nitriding reaction. Figure 1 As can be seen from b, the nitriding reaction products mainly consist of fine-grained aggregates and a few inserted crystal rods. From Figure 1 HRTEM images of the crystal rod in region 1 and the grain in region 2 ( Figure 1In sections b-1 and b-2), the spacing between adjacent parallel lattice fringes was measured to be... and This corresponds to the interplanar spacing of the silicon nitride (011) crystal plane (JCPDS CARD No. 35569) and aluminum nitride (100) crystal planes (JCPDS CARD No. 163950), respectively. Therefore, the crystal rods in the product powder and the grains in region 2 are silicon nitride and aluminum nitride, respectively, which can also be seen from the selected area electron diffraction (SAED) patterns corresponding to regions 1 and 2. Figure 1 b-1 and Figure 1 This was confirmed by the EDS surface scan of the product powder (see the lower left corner image of b-2). Figure 1 The results (e.g.) further confirm that the crystal rod in region 1 is silicon nitride and the grain in region 2 is aluminum nitride. Moreover, the fact that the distribution areas of Si, Al and N elements largely overlap indicates that the silicon nitride and aluminum nitride powders in the product are mixed relatively uniformly.

[0048] 2. The cross-section of the aluminum-containing raw material powder skeleton obtained in step (3) was analyzed using a field emission scanning electron microscope (GeminiSEM 360; ZEISS, Germany). The results are as follows: Figure 2 As shown. From Figure 2 It can be seen that after low-temperature directional freezing and vacuum freeze-drying, the ice crystals generated during the freezing process are completely sublimated, so the cross-section of the raw material powder skeleton shows a directional vertical channel structure, in which spherical aluminum powder is clearly visible.

[0049] 3. The cross-sections of the silicon nitride-aluminum nitride framework obtained in step (4) were analyzed using a field emission scanning electron microscope (GeminiSEM 360; ZEISS, Germany) and a transmission electron microscope (TEM; Talos F200S, Thermo Scientific, USA), combined with an energy dispersive spectroscopy (EDS, X-max50, Oxford, UK). The results are as follows: Figure 3 As shown. From Figure 3 It can be seen that after the aluminum-containing raw material powder skeleton is sintered by nitriding reaction, although the silicon nitride-aluminum nitride composite powder still basically retains traces of vertical arrangement, the fillers in each row are no longer strictly separated, but show signs of merging. This is mainly because after nitriding reaction sintering, many crystal rods appear in the silicon nitride-aluminum nitride composite ceramic skeleton. The aspect ratio of the crystal rods leads to a significant increase in the wall thickness of the ceramic skeleton, thus making the vertical channels between each row of ceramic fillers narrower or even disappear, and therefore less easy to distinguish. A crystal rod was selected and characterized by TEM and EDS. Figure 3 (in ce). Among them, in the HRTEM diagram ( Figure 3 The lattice fringe spacing of the crystal rod measured in region c and region 1) is approximately The spacing between the planes is consistent with that of the AlN(102) crystal plane, indicating that it is an AlN crystal rod. Figure 3 The EDS mapping results from the Chinese database further confirmed that the crystal rod is composed of Al and N elements.

[0050] 4. The cross-section of the silicon nitride-aluminum nitride / polymer composite material obtained in step (5) was analyzed using a scanning electron microscope (GeminiSEM 360; ZEISS, Germany) and an energy dispersive spectroscopy (EDS, Oxford, the UK). The results are as follows: Figure 4 As shown. From Figure 4 As shown in section ab, there are no obvious pores at the interface between the filler and the epoxy matrix, indicating that the viscous flow of the epoxy resin solution under vacuum conditions can effectively impregnate the composite ceramic filler skeleton. From Figure 4 The EDS mapping of the CE matrix shows that Al, Si, and N atoms are distributed quite uniformly in the composite material, indicating that the vacuum impregnation process of the resin solution did not significantly damage the silicon nitride-aluminum nitride framework. The distribution of N atoms reveals that the composite ceramic filler no longer shows obvious vertical alignment marks. This is because a large number of randomly arranged aluminum nitride crystals were generated during the nitriding reaction sintering process, and these crystals largely filled the narrow pore channels between the composite ceramic filler walls left after ice sublimation.

[0051] 5. The surface thermal conductivity of the obtained silicon nitride-aluminum nitride / polymer composite material was tested using a laser thermal conductivity meter (model LFA467HT); the flexural strength was obtained using a universal testing machine (AGS-X, Shimadzu, Japan). Experimental results show that the surface thermal conductivity of the silicon nitride-aluminum nitride / polymer composite material obtained in this embodiment is 7.04 W·m. -1 ·k -1 The flexural strength is 117.70 MPa.

[0052] Example 2

[0053] (1) The purified photovoltaic crystalline silicon waste containing only silicon and spherical aluminum powder were mixed in a mass ratio of 2:1, and then a direct nitriding reaction was carried out at 1500℃ for 3 hours in a nitrogen atmosphere to prepare silicon nitride-aluminum nitride composite powder.

[0054] (2) Silicon nitride-aluminum nitride composite powder, spherical aluminum powder, sintering aid (including YF3 and Y2O3 in a mass ratio of 3:2), and additives (including binder polyvinyl butyral and dispersant glycerol) are added to tert-butanol solvent. After magnetic stirring for 4 hours, a suspension is obtained. The mass ratio of silicon nitride-aluminum nitride composite powder to aluminum powder is 5:4, the mass ratio of the sum of the masses of silicon nitride-aluminum nitride composite powder and aluminum powder to tert-butanol is 45:46, the sintering aid accounts for 5% of the total mass of the suspension, the binder accounts for 3% of the total mass of the suspension, and the dispersant accounts for 1% of the total mass of the suspension.

[0055] (3) After the suspension is oriented frozen at -70℃ for 3 minutes to form a solid, it is then vacuum freeze-dried at -60℃ for 36 hours to remove ice crystals and obtain an aluminum-containing raw material powder skeleton.

[0056] (4) The aluminum-containing raw material powder skeleton obtained in step (3) is placed in a sintering furnace and sintered at 1400℃ for 3 hours under a flowing nitrogen atmosphere of 100 sccm to obtain a silicon nitride-aluminum nitride skeleton containing one-dimensional rod-shaped aluminum nitride whiskers.

[0057] (5) Epoxy resin, 4-methylhexahydrophthalic anhydride, and 1-p-methylbenzenesulfonylimidazole were magnetically stirred at 60°C (500 r / min) for 1 h at a mass ratio of 100:86:1 to obtain an impregnation solution. The silicon nitride-aluminum nitride skeleton obtained in step (4) was immersed in the impregnation solution at a mass ratio of 2:3. Vacuum impregnation was performed at 60°C for 2 h, followed by curing at 90°C and 120°C for 3 h respectively to obtain a silicon nitride-aluminum nitride / polymer composite material.

[0058] The surface thermal conductivity of the silicon nitride-aluminum nitride / polymer composite material obtained in this embodiment is 4.41 W·m. -1 ·k -1 The bending strength is 112.50 MPa.

[0059] Example 3

[0060] (1) The purified photovoltaic crystalline silicon waste containing only silicon and spherical aluminum powder were mixed in a mass ratio of 2:1, and then a direct nitriding reaction was carried out at 1500℃ for 3 hours in a nitrogen atmosphere to prepare silicon nitride-aluminum nitride composite powder.

[0061] (2) Silicon nitride-aluminum nitride composite powder, spherical aluminum powder, sintering aid (including YF3 and CaF2 in a mass ratio of 3:2), and additives (including binder polyvinyl butyral and dispersant glycerol) are added to tert-butanol solvent. After magnetic stirring for 4 hours, a suspension is obtained. The mass ratio of silicon nitride-aluminum nitride composite powder to aluminum powder is 5:4, the mass ratio of the sum of the masses of silicon nitride-aluminum nitride composite powder and aluminum powder to tert-butanol is 45:46, the sintering aid accounts for 5% of the total mass of the suspension, the binder accounts for 3% of the total mass of the suspension, and the dispersant accounts for 1% of the total mass of the suspension.

[0062] (3) After the suspension is oriented frozen at -70℃ for 3 minutes to form a solid, it is then vacuum freeze-dried at -60℃ for 36 hours to remove ice crystals and obtain an aluminum-containing raw material powder skeleton.

[0063] (4) The aluminum-containing raw material powder skeleton obtained in step (3) is placed in a sintering furnace and sintered at 1400℃ for 3 hours under a flowing nitrogen atmosphere of 100 sccm to obtain a silicon nitride-aluminum nitride skeleton containing one-dimensional rod-shaped aluminum nitride whiskers.

[0064] (5) Epoxy resin, 4-methylhexahydrophthalic anhydride, and 1-p-methylbenzenesulfonylimidazole were magnetically stirred at 60°C (500 r / min) for 1 h at a mass ratio of 100:86:1 to obtain an impregnation solution. The silicon nitride-aluminum nitride skeleton obtained in step (4) was immersed in the impregnation solution at a mass ratio of 2:3. Vacuum impregnation was performed at 60°C for 2 h, followed by curing at 90°C and 120°C for 3 h respectively to obtain a silicon nitride-aluminum nitride / polymer composite material.

[0065] The surface thermal conductivity of the silicon nitride-aluminum nitride / polymer composite material obtained in this embodiment is 3.47 W·m. -1 ·k -1 The bending strength is 80.10 MPa.

[0066] Comparative Example 1

[0067] Compared with Example 1, the raw material powder skeleton in this comparative example does not contain aluminum powder. The specific steps are as follows:

[0068] (1) The purified photovoltaic silicon waste containing only silicon and the spherical aluminum powder were mixed in a mass ratio of 2:1, and then a direct nitriding reaction was carried out at 1500℃ for 3 hours in a nitrogen atmosphere to prepare silicon nitride-aluminum nitride composite powder.

[0069] (2) Silicon nitride-aluminum nitride composite powder, sintering aid (including YF3 and La2O3 in a mass ratio of 3:2), and additives (including binder polyvinyl butyral and dispersant glycerol) are added to tert-butanol solvent. After magnetic stirring for 4 hours, a suspension is obtained. The mass ratio of silicon nitride-aluminum nitride composite powder to tert-butanol is 45:46. The sintering aid accounts for 5% of the total mass of the suspension, the binder accounts for 3% of the total mass of the suspension, and the dispersant accounts for 1% of the total mass of the suspension.

[0070] (3) After the suspension is oriented frozen at -70℃ for 3 minutes to form a solid, it is then vacuum freeze-dried at -60℃ for 36 hours to remove ice crystals and obtain an aluminum-free raw material powder skeleton.

[0071] (4) The aluminum-free raw material powder skeleton obtained in step (3) is placed in a sintering furnace and sintered at 1400℃ for 3 hours under a nitrogen atmosphere of 100 sccm to obtain a silicon nitride-aluminum nitride ceramic skeleton without one-dimensional rod-shaped aluminum nitride whiskers.

[0072] (5) Epoxy resin, 4-methylhexahydrophthalic anhydride, and 1-p-methylbenzenesulfonylimidazole were magnetically stirred at 60°C (500 r / min) for 1 h at a mass ratio of 100:86:1 to obtain an impregnation solution. The obtained silicon nitride-aluminum nitride skeleton was immersed in the impregnation solution at a mass ratio of 2:3 to silicon nitride-aluminum nitride and the impregnation solution. Vacuum impregnation was carried out at 60°C for 2 h, and then cured at 90°C and 120°C for 3 h respectively to obtain a silicon nitride-aluminum nitride / polymer composite material.

[0073] The surface thermal conductivity of the silicon nitride-aluminum nitride / polymer composite material obtained in this comparative example is 2.05 W·m. -1 ·k -1 The bending strength is 85.30 MPa.

[0074] The comparison results between this comparative example and Example 1 show that if the raw material powder skeleton does not contain aluminum powder, even if other raw materials and preparation methods are completely the same, after high-temperature sintering in the same manner, the obtained composite ceramic filler skeleton is an aluminum nitride-silicon nitride skeleton without one-dimensional rod-shaped aluminum nitride whiskers. There is a lack of "bridges" connecting the aluminum nitride and silicon nitride powders, and the width of the oriented silicon nitride-aluminum nitride skeleton is not increased. Therefore, the thermal conductivity of the finally obtained silicon nitride-aluminum nitride / polymer composite material is relatively low.

[0075] Comparative Example 2

[0076] Compared with Example 1, this comparative example uses CeO2 instead of La2O3 as a secondary sintering aid. The specific steps are as follows:

[0077] (1) The purified photovoltaic crystalline silicon waste containing only silicon and spherical aluminum powder were mixed in a mass ratio of 2:1, and then a direct nitriding reaction was carried out at 1500℃ for 3 hours in a nitrogen atmosphere to prepare silicon nitride-aluminum nitride composite powder.

[0078] (2) Silicon nitride-aluminum nitride composite powder, spherical aluminum powder, sintering aid (including YF3 and CeO2 in a mass ratio of 3:2), and additives (including binder polyvinyl butyral and dispersant glycerol) are added to tert-butanol solvent. After magnetic stirring for 4 hours, a suspension is obtained. The mass ratio of silicon nitride-aluminum nitride composite powder to aluminum powder is 5:4, the mass ratio of the sum of the masses of silicon nitride-aluminum nitride composite powder and aluminum powder to tert-butanol is 45:46, the sintering aid accounts for 5% of the total mass of the suspension, the binder accounts for 3% of the total mass of the suspension, and the dispersant accounts for 1% of the total mass of the suspension.

[0079] (3) After the suspension is oriented frozen at -70℃ for 3 minutes to form a solid, it is then vacuum freeze-dried at -60℃ for 36 hours to remove ice crystals and obtain an aluminum-containing raw material powder skeleton.

[0080] (4) The aluminum-containing raw material powder skeleton obtained in step (3) is placed in a sintering furnace and sintered at 1400℃ for 3 hours under a flowing nitrogen atmosphere of 100 sccm to obtain a silicon nitride-aluminum nitride skeleton without one-dimensional rod-shaped aluminum nitride whiskers.

[0081] (5) Epoxy resin, 4-methylhexahydrophthalic anhydride, and 1-p-methylbenzenesulfonylimidazole were magnetically stirred at 60°C (500 r / min) for 1 h at a mass ratio of 100:86:1 to obtain an impregnation solution. The silicon nitride-aluminum nitride skeleton obtained in step (4) was immersed in the impregnation solution at a mass ratio of 2:3. Vacuum impregnation was performed at 60°C for 2 h, followed by curing at 90°C and 120°C for 3 h respectively to obtain a silicon nitride-aluminum nitride / polymer composite material.

[0082] The surface thermal conductivity of the silicon nitride-aluminum nitride / polymer composite material obtained in this embodiment is 2.60 W·m. -1 ·k -1 The flexural strength is 128.30 MPa.

[0083] The comparison results between this comparative example and Example 1 show that although the raw material powder skeleton contains aluminum powder, if the specific sintering aid of the present invention is not used, the aluminum powder can only be converted into zero-dimensional aluminum nitride grains after nitriding reaction sintering. The resulting composite ceramic filler skeleton is an aluminum nitride-silicon nitride skeleton without one-dimensional rod-shaped aluminum nitride whiskers. Therefore, there is a lack of "bridges" between aluminum nitride and silicon nitride powders, and the width of the oriented silicon nitride-aluminum nitride raw material is also limited. As a result, the thermal conductivity of the final silicon nitride-aluminum nitride / polymer composite material is relatively low.

[0084] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon nitride-aluminum nitride / polymer composite material, characterized in that, The preparation steps include the following: (1) Mix silicon source and aluminum source, and then carry out direct nitriding reaction in nitrogen atmosphere to obtain silicon nitride-aluminum nitride composite powder; (2) The silicon nitride-aluminum nitride composite powder obtained in step (1) is mixed with aluminum powder, binder, sintering aid and dispersant in an organic solvent to obtain a suspension; (3) After the suspension obtained in step (2) is subjected to directional freeze-drying, an aluminum-containing raw material powder skeleton is obtained by vacuum freeze-drying; (4) The aluminum-containing raw material powder skeleton obtained in step (3) is sintered in situ in a nitrogen atmosphere to obtain a silicon nitride-aluminum nitride skeleton containing one-dimensional rod-shaped aluminum nitride whiskers. (5) The silicon nitride-aluminum nitride skeleton obtained in step (4) is subjected to vacuum impregnation and curing treatment using polymer impregnation liquid to obtain silicon nitride-aluminum nitride / polymer composite material; The silicon source mentioned in step (1) is purified photovoltaic crystalline silicon waste; The mass ratio of silicon nitride-aluminum nitride composite powder to aluminum powder in step (2) is 5~6:5~4; The sintering aids mentioned in step (2) include a primary sintering aid and a secondary sintering aid; the primary sintering aid is YF3, and the secondary sintering aid includes at least one of La2O3, Y2O3 and CaF2.

2. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The aluminum source in step (1) is aluminum powder with a size of 1~3 µm; the mass ratio of the silicon source to the aluminum source is 2~3:1~2; the direct nitriding reaction temperature of the silicon source and the aluminum source is 1300~1600 ℃, and the time is 120~180 min.

3. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The total amount of silicon nitride-aluminum nitride composite powder and aluminum powder added in step (2) is 30-60% of the total mass of the suspension.

4. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The adhesive in step (2) includes at least one of polyvinyl butyral and polyvinyl alcohol; the amount of adhesive added is 1 to 8% of the total mass of the suspension; the dispersant includes at least one of glycerol and citric acid, and the amount of dispersant added is 0.5 to 5% of the total mass of the suspension; the organic solvent is tert-butanol.

5. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The mass ratio of the primary sintering aid to the secondary sintering aid is greater than 1; the sintering aid accounts for 1 to 6% of the total mass of the suspension.

6. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The temperature for directional freezing in step (3) is -100 to -50 ℃ and the time is 3 to 10 min; the temperature for vacuum freeze drying is -70 to -60 ℃ and the time is 12 to 36 h.

7. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The nitrogen-containing atmosphere mentioned in step (4) is an atmosphere containing at least one gas, namely nitrogen and ammonia; the in-situ nitriding reaction sintering temperature is 1350~1550 ℃ and the time is 120~180 min.

8. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The polymer impregnation liquid in step (5) includes at least one of epoxy resin impregnation liquid, polyimide resin impregnation liquid, polytetrafluoroethylene resin impregnation liquid and silicone rubber impregnation liquid; the mass ratio of silicon nitride-aluminum nitride to polymer impregnation liquid is 1~5:9~5.

9. The method for preparing a silicon nitride-aluminum nitride / polymer composite material according to claim 1, characterized in that, The vacuum impregnation temperature in step (5) is 55~65 ℃, and the vacuum degree of vacuum impregnation is less than 10. -1 Pa, the vacuum impregnation time is 1~2 h; the curing treatment refers to first curing at 80~90 ℃ for 2~3 h, and then curing at 120~130 ℃ for 2~3 h.

10. A silicon nitride-aluminum nitride / polymer composite material, characterized in that, It is prepared by the method described in any one of claims 1 to 9.

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