A high thermal conductivity AlSiC encapsulation material based on in-situ synthesis of porous SiC framework from photovoltaic silica mud and its preparation method.

Abstract

This invention discloses an AlSiC high thermal conductivity encapsulation material based on in-situ synthesis of a porous SiC framework using photovoltaic silicon sludge and its preparation method, belonging to the field of high-value utilization of industrial solid waste. The method involves mixing a metal / alumina binder precursor with silicon sludge powder, carbon source powder, binder, and pore-forming agent, followed by granulation and molding. The resulting 6H-SiC porous framework, coated with metal or alumina nanoparticles, is then treated with a variable atmosphere gradient high-temperature sintering process. The presence of the metal or alumina nanoparticles improves the wettability of the aluminum melt on the surface of the silicon carbide particles. Vacuum pressure aluminizing further enhances the density and thermal conductivity of the prepared AlSiC composite material, while also exhibiting good structural controllability. By adjusting parameters such as the proportion of raw materials, molding process, and sintering process, this invention precisely controls the silicon carbide crystal structure and the porosity, pore size, and distribution of the porous preform, meeting the quality requirements of aluminum silicon carbide materials for porous silicon carbide preforms.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization of industrial solid waste, specifically relating to an AlSiC high thermal conductivity encapsulation material based on in-situ synthesis of a porous SiC framework from photovoltaic silicon mud and its preparation method. Background Technology

[0002] With the rapid development of electronic information technology, the integration level of electronic devices is constantly increasing, and the power density is continuously rising. If the large amount of heat generated cannot be dissipated in a timely and effective manner, it will affect the performance and lifespan of electronic devices. Aluminum silicon carbide (AlSiC) composite materials have become one of the high-performance thermal management materials in the field of electronic packaging due to their excellent properties such as high thermal conductivity, good matching with the thermal expansion coefficient of silicon chips, low density, and high strength.

[0003] The poor wettability of molten aluminum on the SiC surface weakens the bonding force between the molten aluminum and the SiC surface, thus reducing the mechanical and thermophysical properties of AlSiC composites. Currently, AlSiC composites are mainly prepared using powder metallurgy, spray deposition, and liquid phase infiltration. Powder metallurgy requires multiple processes such as mixing silicon carbide powder and aluminum powder, pressing, and sintering, which not only demands high-end equipment and consumes a lot of energy, but also easily leads to silicon carbide particle agglomeration during high-temperature sintering, resulting in uneven thermal conductivity distribution within the material. Spray deposition, which involves atomizing molten aluminum and co-depositing it with silicon carbide particles, suffers from problems such as difficulty in precisely controlling the porosity of the silicon carbide framework and the easy formation of pore defects within the material. Liquid phase infiltration, which involves first preparing a porous SiC preform and then solidifying it through high-temperature aluminizing, yields AlSiC composites with high density. While AlSiC has advantages such as good thermophysical properties, existing liquid-phase aluminizing methods use α-silicon carbide powder prepared by the Atchison method and then ultra-finely ground as raw material. This powder is then mixed with binders / pore-forming agents, granulated, shaped, dried, and sintered to obtain porous silicon carbide preforms. This process results in high raw material costs, long process flow, and high production costs. On the other hand, the poor wettability of aluminum melt on the surface of silicon carbide particles leads to high aluminizing temperature, high aluminizing pressure, and easy formation of harmful Al4C3 interface phases, resulting in low thermal conductivity and high coefficient of thermal expansion of AlSiC composite materials.

[0004] Meanwhile, silicon-based solid waste from the photovoltaic industry mainly consists of cutting waste slurry and grinding waste, rich in silicon (over 90%) and small amounts of impurities such as carbon, iron, nickel, nitrogen, and sulfur. Notably, silicon and carbon in photovoltaic silicon sludge are key raw materials for SiC preparation. If their material utilization in fields such as electronics and information technology can be realized, a green closed loop of "solid waste reduction - resource regeneration - high-value application" will be formed. Patent application CN103266234A discloses a method for preparing silicon carbide particle-reinforced aluminum-based composite materials using silicon carbide micropowder obtained from crystalline silicon cutting waste and aluminum-based powder. The crystalline silicon cutting waste is acid-washed and alkali-washed to remove iron oxide, metallic impurities, silicon dioxide, silicon, and other substances. After filtration and drying, pure silicon carbide micropowder with a particle size range of 1-12 μm is obtained. The silicon carbide micropowder is then pressed into a blank with aluminum-based powder at a total component ratio of 10-80%, followed by heat treatment to obtain the aluminum-silicon carbide composite material. However, the above process obtains silicon carbide components through pretreatment and uses powder metallurgy to prepare AlSiC composite materials. SiC exists in the composite material in powder form. Due to the poor wetting properties between the SiC surface and the aluminum melt surface, the mechanical properties, thermal expansion coefficient and thermal conductivity, etc., deteriorate.

[0005] Therefore, developing a new in-situ synthesis-in-situ surface conditioning-vacuum pressure aluminizing process for porous silicon carbide preforms using photovoltaic silicon mud as raw material can overcome the technical bottleneck of poor wettability of Al melt on SiC surface during the preparation of traditional AlSiC composite materials. This process can not only effectively solve the problem of industrial solid waste disposal, but also provide low-cost, high-performance thermal management materials for the electronic packaging field. It has dual strategic significance for promoting the green transformation of the photovoltaic industry and the technological upgrading of the electronic information industry. Summary of the Invention

[0006] The purpose of this invention is to provide an AlSiC high thermal conductivity encapsulation material based on in-situ synthesis of a porous modified SiC framework from photovoltaic silicon mud and its preparation method, in order to solve the problems of poor surface wetting performance and difficulty in disposing of high-value photovoltaic silicon mud in existing AlSiC composite material preparation methods, realize the high-value utilization of photovoltaic silicon mud, and prepare AlSiC encapsulation materials with high thermal conductivity and controllable structure; and meet the requirements of aluminum silicon carbide high thermal conductivity encapsulation materials for porous silicon carbide preforms.

[0007] A method for preparing AlSiC high thermal conductivity encapsulation material based on in-situ synthesis of porous SiC framework from photovoltaic silicon mud includes the following steps:

[0008] (1) Raw material pretreatment: Photovoltaic silicon mud is washed and then separated into solid and liquid to obtain silicon mud filter cake;

[0009] (2) Ingredient mixing and granulation: Dissolve and disperse the binder in water to obtain a binder solution, then add the metal / alumina binder precursor, pore-forming agent, carbon source powder and silica mud filter cake and mix thoroughly to obtain a mixed slurry. The mixed slurry is then made into secondary granules.

[0010] (3) Molding and drying: The secondary granulated material is shaped into a green body under certain pressure and temperature and then dried to obtain a green body;

[0011] (4) Preparation of 6H-SiC porous preform by in-situ reaction of variable atmosphere gradient sintering: The shaped and dried green blank is placed in a sintering furnace and heated to 250~450 ℃ in air atmosphere and held for 1~4 h. Then the temperature is raised to 600~700 ℃ and held for 0.5~2 h to form a porous structure. After the holding is completed, the vacuum is drawn and argon gas is introduced. The vacuum is drawn again and the temperature is raised to 1450~1600 ℃ and held for 1~8 h. Finally, the temperature is raised to 2100~2500 ℃ and held for 4~12 h to obtain 6H-SiC porous preform.

[0012] (5) Vacuum pressure aluminizing: The prepared 6H-SiC porous preform is placed in a vacuum pressure aluminizing device, aluminum ingots are added, and the mixture is heated to above the melting point of aluminum in a vacuum environment to completely melt the aluminum liquid. Then a certain pressure is applied to allow the aluminum liquid to penetrate into the pores of the silicon carbide porous preform. After cooling, aluminum silicon carbide composite material is obtained.

[0013] Furthermore,

[0014] In step (1), the selected photovoltaic silicon mud raw material contains Si ≥ 92 wt.%, O ≤ 7 wt.%, and the balance is impurity elements including at least one of Fe, Ni, Al, Cl, P, N, and S. The photovoltaic silicon mud is washed to make the pH value 6.5~8, and then the silicon mud filter cake is obtained by solid-liquid separation. The carbon source powder includes one or two of petroleum coke powder and graphite powder, with a carbon content ≥ 99.0 wt.%.

[0015] In step (1), the silica mud raw material is wet ball milled and the powder passes through a 400-mesh sieve; the average particle size of the carbon source powder is 5~45 μm.

[0016] Furthermore,

[0017] In step (2), the metal / alumina binder precursor includes one or more of the following: copper acetate, nickel acetate, aluminum isopropoxide, aluminum dihydrogen phosphate, alumina, and aluminum sulfate; the binder includes one or more of the following: polyvinyl alcohol, carboxymethyl cellulose, ethyl cellulose, sodium carboxymethyl cellulose, and dextrin; and the pore-forming agent includes one or more of the following: starch and ammonium bicarbonate.

[0018] In step (2), the amount of carbon source is determined according to the silicon content in the silica mud filter cake, and the carbon / silicon molar ratio is controlled to be 0.9~1.3, preferably 1~1.08; the amount of metal / alumina binder precursor is 3~10 wt.% of the total dry weight of the mixture; the amount of binder added is 3~8 wt.% of the total dry weight of the mixture, and the amount of pore-forming agent added is 5~20 wt.% of the total dry weight of the mixture; the mixture is silica mud filter cake and carbon source.

[0019] In step (2), a mixed slurry with a moisture content of 50-80 wt.% is made into secondary granules by spray granulation or wet granulation after pressure filtration. During spray granulation, the moisture content of the mixed slurry is 50-65 wt.%; during wet granulation, the mixed slurry is pressure filtered to obtain a filter cake with a moisture content of 25-35 wt.% for granulation. The particle size of the granules is controlled between 0.1-2 mm, preferably 0.3-1 mm, and dried to a moisture content ≤5.0 wt.%; preferably a moisture content of 1-2.0 wt.% for easy molding.

[0020] In step (3), molding or isostatic pressing is used; the molding pressure is 10~100 MPa, and the holding time is 2~10 min. Preferably, it is 40~60 MPa, and the holding time is 3~6 min. After molding, it is dried until the moisture content is ≤1wt.%, so that the blank has a certain strength and shape stability.

[0021] Furthermore,

[0022] In step (4), the formed blank is placed in a sintering furnace, and the heating rate is controlled at 1~10 ℃ / min in an air atmosphere. The temperature is raised to 250~350 ℃ and held for 1~4 h. Then, the heating rate is controlled at 1~10 ℃ / min, and the temperature is raised to 600~700 ℃ and held for 0.5~2 h. After the holding period, the vacuum is evacuated to below 0.1 MPa, and argon gas is introduced to control the oxygen content in the furnace to not exceed 0.05 vol.‰. Then, the vacuum is evacuated to 10 ℃. -2 The temperature is kept below 10 kPa and then increased to 1450–1600 °C at a rate of 8–15 °C / min, and held for 1–8 h. Finally, the temperature is increased to 2100–2500 °C at a rate of 10–20 °C / min and held for 4–12 h to obtain a porous 6H-SiC preform. The SiC content in the obtained preform is ≥98 wt.%, and the porosity is controlled between 30 and 40%.

[0023] Furthermore,

[0024] Air atmosphere sintering is employed, with a preferred heating rate of 2-6℃ / min. The temperature is raised to 250-350℃ and held for 1-4 hours. Then, the heating rate is maintained at 2-6℃ / min, raising the temperature to 600-700℃ and holding for 0.5-2 hours. This allows for the complete decomposition of the metal / alumina binder precursor, organic binder, pore-forming agent, and trace organic matter remaining in the silica sludge, forming a porous structure. After the holding period, a vacuum is applied to below 0.1 MPa, and argon gas is introduced to thoroughly purge air and carbon dioxide from the furnace (oxygen content not exceeding 0.05 vol.‰). Finally, a vacuum is applied to 10 MPa under an argon atmosphere. -2 Below KPa, the temperature is preferably raised to 1450-1600 ℃ at a heating rate of 10-12 ℃ / min and held for 4-6 h. At this temperature, the silica mud is completely melted and reacts fully with carbon powder to form 3C-SiC. Finally, the temperature is preferably held at 2300-2400 ℃ for 6-8 h to complete the 6H-SiC silicon carbide phase transformation.

[0025] Furthermore,

[0026] In step (5), the aluminizing process maintains a system vacuum of (0.5~1)×10⁻⁶. -3 The pressure is 0.5-5 MPa, the temperature is 650-800 ℃, the pressure is 0.5-5 MPa, and the holding time is 0.5-2 h.

[0027] The present invention also provides an AlSiC high thermal conductivity encapsulation material with a porous SiC framework prepared by the above-described preparation method.

[0028] The obtained AlSiC high thermal conductivity encapsulation material has a density of (2.97~3.05) g / cm³, a thermal conductivity of (180~210) W / (m·K), and a coefficient of thermal expansion of (7~8)×10⁻⁶. -6 / K.

[0029] Beneficial effects of the invention

[0030] (1) This invention uses photovoltaic silicon mud as raw material. It utilizes the in-situ reaction of elemental silicon and carbon in photovoltaic silicon mud to generate porous silicon carbide preforms to replace commercially available silicon carbide powder to prepare porous silicon carbide preforms. This realizes the resource utilization of photovoltaic silicon mud, which is currently mainly composed of elemental silicon, reduces the emission of solid waste, reduces environmental pollution, and also reduces the preparation cost.

[0031] (2) By adding a metal / alumina binder precursor, mixing it with silica mud powder, carbon source powder, binder, and pore-forming agent, granulating and forming it, and then treating it with a variable atmosphere gradient high temperature sintering process, a 6H-SiC porous framework coated with metal or alumina nanoparticles is synthesized in situ. The presence of metal or alumina nanoparticles improves the wettability of aluminum melt on the surface of silicon carbide particles, making the prepared AlSiC composite material denser, better thermal conductivity, and with good structural controllability.

[0032] (3) By adjusting parameters such as the proportion of raw materials, molding process, and sintering process, the silicon carbide crystal form was precisely controlled to be 6H-SiC and the pore structure of the porous silicon carbide preform was controlled to make its porosity adjustable from 30% to 40%, and its pore size 2 to 3 μm and uniformly distributed. The resulting AlSiC high thermal conductivity encapsulation material had a density of (2.97~3.05) g / cm³, a thermal conductivity of (180~210) W / (m·K), and a coefficient of thermal expansion of (7~8)×10⁻⁶. -6 / K. The performance of AlSiC high thermal conductivity packaging materials prepared by traditional methods is superior, meeting the quality requirements of aluminum silicon carbide materials for porous silicon carbide preforms. Attached Figure Description

[0033] Figure 1 : Schematic diagram of the porous 6H-silicon carbide porous preform of Embodiment 1 of the present invention;

[0034] Figure 2 The pore size distribution of the porous 6H-silicon carbide porous preform in Example 1 of this invention;

[0035] Figure 3 XRD phase composition of the porous 6H-silicon carbide porous preform of Example 1 of the present invention;

[0036] Figure 4 Metallographic structure of AlSiC composite material in Example 1 of this invention. Detailed Implementation

[0037] The following examples are intended to further illustrate the present invention, but not to limit it.

[0038] In this invention, the porosity of 6H-SiC was tested using the boiling method in GB / T 1966-2024, "Determination of Apparent Porosity and Bulk Density of Porous Ceramics"; the pore size and distribution were tested using the mercury intrusion porosimetry method.

[0039] In this invention, the SiC volume fraction of aluminum silicon carbide is tested using the dissolution method according to GB / T 41737-2022 Test Method for Volume Fraction of Silicon Carbide in Aluminum-based Composite Materials.

[0040] Example 1

[0041] A certain photovoltaic silica sludge contains 92.4 wt.% Si, 7.3 wt.% O, 0.016 wt.% Fe, 0.02 wt.% Ni, and 0.026 wt.% S. The silica sludge was washed with water until the pH of the washing solution reached 7.0 ± 0.1, then wet-milled until all particles passed through a 400-mesh sieve. The washed silica sludge filter cake was obtained and its solid content was determined to be 51 wt.%. Next, the required graphite powder (particle size 38 μm) was weighed according to a carbon / silicon molar ratio of 1.05. Polyvinyl alcohol, starch and copper acetate were weighed according to 5 wt.%, 10 wt.% and 5 wt.% of the total mass (dry basis) of (silica mud + graphite powder) as binder, pore-forming agent and metal / alumina binder precursor, respectively. Polyvinyl alcohol was first fully dissolved in water to prepare a polyvinyl alcohol solution with a concentration of 5 wt.%. Then, starch, copper acetate and graphite powder were added and stirred evenly to obtain a mixture. Then, washed silica mud filter cake was added and mixed evenly to obtain a mixed slurry with a water content of 50 wt.%. Next, the mixed slurry was processed into spherical secondary agglomerates with a particle size of approximately 0.3 mm using a spray granulation method. The moisture content of the agglomerates was controlled at 3 wt.%, and then compression molding was performed. The granular material was placed in a mold and held at 50 MPa pressure at room temperature for 5 min to prepare a 140 mm × 190 mm × 5.5 mm silicon carbide preform. This preform was then dried in an oven at 120 ℃ to obtain a silicon carbide preform with a moisture content ≤1 wt.%. The preform was then placed in a sintering furnace and heated to 280 ℃ at a rate of 4 ℃ / min, held for 4 h, and then heated to 600 ℃ at a rate of 4 ℃ / min, held for 1 h. A vacuum was then applied to 0.1 MPa, and argon gas was introduced until the oxygen content in the furnace was 0.05 vol.‰. Finally, a vacuum was applied to 10 vol.‰. -2 The temperature was increased to 1500 °C at a heating rate of 10 °C / min and held for 6 h. Then, the temperature was further increased to 2100 °C at a heating rate of 10 °C / min and held for 8 h, followed by cooling to obtain a porous 6H-silicon carbide preform. Testing showed that its silicon carbide content was 99.2 wt.% and its porosity was 40%. Figure 2 It can be seen that the pore size of the prepared porous preform is between 30-4000 nm, with the main pore size concentrated between 1200-3000 nm, which meets the requirements for subsequent aluminizing. The preform is then placed in a vacuum pressure impregnation apparatus at a vacuum degree of 1×10⁻⁶. -3 Molten aluminum was infiltrated into a porous silicon carbide preform under a pressure of 5 MPa and a holding time of 700 ℃ for 30 min at a pressure of 1 kPa. After cooling, an aluminum-silicon carbide composite material was obtained. Testing showed that the silicon carbide volume fraction of this composite material was 60%, the thermal conductivity reached 184 W / (m·K), the density was 3.00 g / cm³, and the coefficient of thermal expansion was 7.5 × 10⁻⁶. -6 / K meets the performance requirements of high thermal conductivity packaging materials for electronic devices.

[0042] Example 2

[0043] A certain photovoltaic silica sludge contains 96.4 wt.% Si, 3.1 wt.% O, 0.018 wt.% Fe, 0.014 wt.% Al, 0.02 wt.% Ni, and 0.026 wt.% S. The silica sludge was washed with water until the pH of the washing solution reached 7.6 ± 0.1, then wet-milled until all particles passed through a 400-mesh sieve. The washed silica sludge filter cake was obtained and its solid content was determined to be 50.6 wt.%. Next, the required graphite powder (particle size 38 μm) was weighed according to a carbon / silicon molar ratio of 1.08. Polyvinyl alcohol, starch, and copper acetate were weighed at 5 wt.%, 10 wt.%, and 5 wt.% of the total mass (dry basis) of (silica mud + graphite powder) as binder, pore-forming agent, and metal / alumina binder precursor, respectively. Polyvinyl alcohol was first fully dissolved in water to prepare a polyvinyl alcohol solution with a concentration of 5 wt.%, and then starch, copper acetate, and graphite powder were added and stirred evenly to obtain a mixture. Then, washed silica mud filter cake was added and thoroughly mixed to obtain a mixed slurry with a water content of 50 wt.%. Next, the mixed slurry was processed into spherical secondary agglomerates with a particle size of approximately 0.2 mm using a spray granulation method. The moisture content of the agglomerates was controlled at 3 wt.%, and then compression molding was performed. The granular material was placed in a mold and held at 80 MPa pressure at room temperature for 3 min to prepare a 140 mm × 190 mm × 5.5 mm silicon carbide preform. This preform was then dried in an oven at 120 ℃ to obtain a silicon carbide preform with a moisture content ≤1 wt.%. The preform was then placed in a sintering furnace and heated to 340 ℃ at a rate of 3 ℃ / min, held for 3 h, and then heated to 650 ℃ at a rate of 3 ℃ / min, held for 0.5 h. After evacuation to 0.1 MPa, argon gas was introduced until the oxygen content in the furnace was 0.05 vol.‰, and then evacuation was performed to 10 vol.‰. -2 The temperature was increased to 1600 °C at a heating rate of 15 °C / min and held for 4 h. Then, the temperature was further increased to 2300 °C at a heating rate of 15 °C / min and held for 5 h before cooling to obtain a porous 6H-silicon carbide preform. Testing showed that its silicon carbide content was 99.3 wt.% and its porosity was 38%. The preform was then placed in a vacuum pressure impregnation apparatus at a vacuum degree of 0.8 × 10⁻⁶ kPa. -3 Molten aluminum was infiltrated into a porous silicon carbide preform under a pressure of 5 MPa and a holding time of 700 ℃ for 30 min at a pressure of 1 kPa. After cooling, an aluminum-silicon carbide composite material was obtained. Testing showed that the silicon carbide volume fraction of this composite material was 60%, the thermal conductivity reached 189 W / (m·K), the density was 3.01 g / cm³, and the coefficient of thermal expansion was 7.3 × 10⁻⁶. -6 / K meets the performance requirements of high thermal conductivity packaging materials for electronic devices.

[0044] Example 3

[0045] A certain photovoltaic silica sludge contained 98.3 wt.% Si, 0.8 wt.% O, 0.016 wt.% Fe, 0.02 wt.% Ni, and 0.026 wt.% S. The silica sludge was washed with water until the pH of the washing solution reached 7.2 ± 0.1, then wet-milled until all particles passed through a 400-mesh sieve. The resulting filter cake was determined to have a solid content of 51.7 wt.%. Next, the required coke powder (particle size 25 μm) was weighed according to a carbon / silicon molar ratio of 1.05. Carboxymethyl cellulose, ammonium bicarbonate and nickel acetate were weighed at 3 wt.%, 15 wt.% and 4 wt.% of the total mass (dry basis) of (silica mud + coke powder) as binder, pore-forming agent and metal / alumina binder precursor, respectively. Carboxymethyl cellulose was first fully dissolved in water to prepare a solution with a concentration of 4 wt.%, and then ammonium bicarbonate, nickel acetate and coke powder were added and stirred evenly to obtain a mixture. Then, washed silica mud filter cake was added and mixed evenly to obtain a mixed slurry with a water content of 60 wt.%. Next, a filter cake with a moisture content of 35 wt.% was obtained by pressure filtration and processed into secondary granules with a particle size of approximately 1.5~2 mm using a wet granulation process. The moisture content of the granules was controlled at 3 wt.%, and then the granules were molded. The granular material was placed in a mold and held at 50 MPa pressure at room temperature for 5 min to prepare a 140 mm × 190 mm × 5.5 mm silicon carbide preform. The preform was then dried in an oven at 120 ℃ to obtain a silicon carbide preform with a moisture content ≤1 wt.%. Then, the silicon carbide preform was placed in a sintering furnace and heated to 300 ℃ at a heating rate of 5 ℃ / min and held for 4 h. Then, the heating rate was continued at 5 ℃ / min to 700 ℃ and held for 0.5 h. After evacuating to 0.1 MPa, argon gas was introduced until the oxygen content in the furnace was 0.04 vol.‰. Then, the furnace was evacuated to 10 vol.‰. -2 The temperature was increased to 1550 °C at a heating rate of 12 °C / min and held for 5 h, then increased to 2400 °C at a heating rate of 15 °C / min and held for 3 h to complete high-temperature sintering. After cooling, a porous 6H-silicon carbide preform was obtained. Testing showed that the preform had a porosity of 35% and a silicon carbide content of 99.3 wt.%. The preform was then placed in a vacuum pressure impregnation apparatus at a vacuum degree of 0.5 × 10⁻⁶ kPa. -3 Molten aluminum was infiltrated into a porous 6H-silicon carbide preform under a pressure of 5 MPa and a holding time of 700 ℃ for 30 min. After cooling, an aluminum-silicon carbide composite material was obtained. Testing showed that the silicon carbide volume fraction of this composite material was 65%, the thermal conductivity reached 182 W / (m·K), the density was 3.02 g / cm³, and the coefficient of thermal expansion was 7.0 × 10⁻⁶. -6 / K meets the performance requirements of high thermal conductivity packaging materials for electronic devices.

[0046] Example 4

[0047] A certain photovoltaic silica mud contains 98.3 wt.% Si, 0.8 wt.% O, 0.016 wt.% Fe, 0.02 wt.% Ni, and 0.026 wt.% S. The silica mud was washed with water until the pH of the washing solution reached 7.2 ± 0.1 and then filtered to obtain a filter cake, the solid content of which was determined to be 51.7 wt.%. Next, coke powder (particle size 25 μm) was weighed according to a carbon / silicon molar ratio of 1.05. Carboxymethyl cellulose, ammonium bicarbonate, and nickel acetate were weighed at 3 wt.%, 15 wt.%, and 4 wt.% of the total mass (dry basis) of (silicon mud + coke powder) as binder, pore-forming agent, and metal / alumina binder precursor, respectively. Carboxymethyl cellulose was first fully dissolved in water to prepare a 4 wt.% solution, then ammonium bicarbonate, nickel acetate, and coke powder were added and stirred evenly to obtain a mixture. The washed silica mud filter cake was then added and thoroughly mixed to obtain a mixed slurry with a moisture content of 60 wt.%. Next, a filter cake with a moisture content of 30 wt.% was obtained by pressure filtration and processed into secondary granules with a particle size of approximately 1.5~2 mm using a wet granulation process. The moisture content of the granules was controlled at 3 wt.%, and then the granules were molded. The granular material was placed in a mold and held at 70 MPa at room temperature for 4 min to prepare a 140 mm × 190 mm × 5.5 mm silicon carbide preform. The preform was then dried in an oven at 120 ℃ to obtain a silicon carbide preform with a moisture content ≤1 wt.%. The preform was then placed in a sintering furnace and heated to 260 ℃ at a heating rate of 3 ℃ / min, held for 6 h, and then heated to 600 ℃ at a controlled heating rate of 3 ℃ / min, held for 2 h. After evacuation to 0.1 MPa, argon gas was introduced until the oxygen content in the furnace was 0.05 vol.‰, and then evacuation was continued to 10 vol.‰. -2 The temperature was increased to 1450 °C at a heating rate of 10 °C / min and held for 6 h, then increased to 2200 °C at a heating rate of 18 °C / min and held for 7 h to complete high-temperature sintering. After cooling, a porous 6H-silicon carbide preform was obtained. Testing showed that the preform had a porosity of 34% and a silicon carbide content of 99.1 wt.%. The preform was then placed in a vacuum pressure impregnation apparatus at a vacuum degree of 1 × 10⁻⁶ kPa. -3 Molten aluminum was infiltrated into a porous silicon carbide preform under a pressure of 5 MPa and a holding time of 700 ℃ for 30 min at a pressure of 1 kPa. After cooling, an aluminum-silicon carbide composite material was obtained. Testing showed that the silicon carbide volume fraction of this composite material was 66%, the thermal conductivity reached 181 W / (m·K), the density was 3.03 g / cm³, and the coefficient of thermal expansion was 7.0 × 10⁻⁶. -6 / K meets the performance requirements of high thermal conductivity packaging materials for electronic devices.

[0048] Example 5

[0049] A certain photovoltaic silica mud contains 98.3 wt.% Si, 0.8 wt.% O, 0.016 wt.% Fe, 0.02 wt.% Ni, and 0.026 wt.% S. The silica mud was washed with water until the pH of the washing solution reached 7.2 ± 0.1 and then filtered to obtain a filter cake, the solid content of which was determined to be 51.7 wt.%. Next, coke powder (particle size 25 μm) was weighed according to a carbon / silicon molar ratio of 1.05. Dextrin, ammonium bicarbonate, and aluminum dihydrogen phosphate were weighed at 3 wt.%, 15 wt.%, and 5 wt.% of the total mass (dry basis) of (silicon mud + coke powder) as binders, pore-forming agents, and metal / alumina binder precursors, respectively. Dextrin was first fully dissolved in water to prepare a 5 wt.% solution, then ammonium bicarbonate, aluminum dihydrogen phosphate, and coke powder were added and stirred evenly to obtain a mixture. Finally, the washed silica mud filter cake was added and thoroughly mixed to obtain a mixed slurry with a moisture content of 60 wt.%. Next, a filter cake with a moisture content of 30 wt.% was obtained by pressure filtration. This cake was then processed into secondary granules with a particle size of approximately 1.5–2 mm using a wet granulation process, controlling the moisture content of the granules to 3 wt.%. These granules were then molded, with the granular material placed in a mold and held at 30 MPa for 6 min at room temperature to prepare a 140 mm × 190 mm × 5.5 mm silicon carbide preform. This preform was then dried in a 120 ℃ oven to obtain a silicon carbide preform with a moisture content ≤1 wt.%. The preform was then placed in a sintering furnace and heated to 240 ℃ at a rate of 3 ℃ / min, held for 6 h, and then further heated to 700 ℃ at a rate of 3 ℃ / min, held for 0.5 h. After evacuation to 0.1 MPa, argon gas was introduced until the oxygen content in the furnace reached 0.04 vol.‰, and then evacuation was continued to 10 vol.‰. -2 The temperature was increased to 1450 °C at a heating rate of 10 °C / min and held for 6 h, then increased to 2200 °C at a heating rate of 18 °C / min and held for 7 h to complete high-temperature sintering. After cooling, a porous 6H-silicon carbide preform was obtained. Testing showed that the preform had a porosity of 35% and a silicon carbide content of 98.9 wt.%. The preform was then placed in a vacuum pressure impregnation apparatus at a vacuum degree of 1 × 10⁻⁶ kPa. -3 Molten aluminum was infiltrated into a porous silicon carbide preform under a pressure of 5 MPa and a holding time of 700 ℃ for 30 min at a pressure of 1 kPa. After cooling, an aluminum-silicon carbide composite material was obtained. Testing showed that the silicon carbide volume fraction of this composite material was 65%, the thermal conductivity reached 189 W / (m·K), the density was 3.02 g / cm³, and the coefficient of thermal expansion was 7.6 × 10⁻⁶. -6 / K meets the performance requirements of high thermal conductivity packaging materials for electronic devices.

[0050] Comparative Example 1

[0051] Using the same silica mud and graphite powder as in Example 1, and with the same types and amounts of binder and pore-forming agent, the batching, mixing, granulation, molding, sintering, and aluminizing process control requirements were all the same as in Example 1. However, copper acetate was not added as a precursor for the metal / alumina binder layer, resulting in poor wettability of the Al melt on the SiC surface. The prepared AlSiC composite material had a silicon carbide volume fraction of 62%, a thermal conductivity of 164 W / (m·K), a density of 2.95 g / cm³, and a coefficient of thermal expansion of 8.5 × 10⁻⁶. -6 GB / T 41736 requires that the thermal conductivity of AlSiC used in electronic components be ≥180 W / (m·K), and the coefficient of thermal expansion be 7~8×10⁻⁶. -6 / K.

[0052] Comparative Example 2

[0053] Using the same silica mud and graphite powder as in Example 1, the types and amounts of binder, pore-forming agent, and metal / alumina binder were identical. The batching, mixing, granulation, molding, and aluminizing process control requirements were also the same as in Example 1. However, the variable atmosphere gradient sintering process was not used to prepare the porous silicon carbide preform. The shaped and dried preform was placed in a high-temperature sintering furnace and heated to 2300℃ at a heating rate of 10℃ / min under an argon atmosphere, holding for 6 hours to obtain a porous silicon carbide preform (a mixture of 6H-SiC, 4H-SiC, and 3C-SiC, with 6H-SiC accounting for approximately 85 wt.%). After aluminizing, the resulting AlSiC composite material had a silicon carbide volume fraction of 59.6%, a thermal conductivity of 170 W / (m·K), a density of 2.96 g / cm³, and a coefficient of thermal expansion of 8.3 × 10⁻⁶. -6 / K.

Claims

1. A method for preparing AlSiC high thermal conductivity encapsulation material based on in-situ synthesis of porous SiC framework from photovoltaic silica mud, characterized in that, Includes the following steps: (1) Raw material pretreatment: Photovoltaic silicon mud is washed and then separated into solid and liquid to obtain silicon mud filter cake; (2) Ingredient mixing and granulation: Dissolve and disperse the binder in water to obtain a binder solution, then add the metal / alumina binder precursor, pore-forming agent, carbon source powder and silica mud filter cake and mix thoroughly to obtain a mixed slurry. The mixed slurry is then granulated into secondary granules. The metal / alumina binder precursor includes one or more of the following: copper acetate, nickel acetate, aluminum isopropoxide, aluminum dihydrogen phosphate, alumina, and aluminum sulfate. (3) Molding and drying: The secondary granulated material is shaped into a green body under certain pressure and temperature and then dried to obtain a green body; (4) Preparation of 6H-SiC porous preform by in-situ reaction of variable atmosphere gradient sintering: The shaped and dried green blank is placed in a sintering furnace and heated to 250~450 ℃ in air atmosphere and held for 1~4 h. Then the temperature is raised to 600~700 ℃ and held for 0.5~2 h to form a porous structure. After the holding is completed, the vacuum is drawn and argon gas is introduced. The vacuum is drawn again and the temperature is raised to 1450~1600 ℃ and held for 1~8 h. Finally, the temperature is raised to 2100~2500 ℃ and held for 4~12 h to obtain 6H-SiC porous preform. (5) Vacuum pressure aluminizing: The prepared 6H-SiC porous preform is placed in a vacuum pressure aluminizing device, aluminum ingots are added, and the mixture is heated to above the melting point of aluminum in a vacuum environment to completely melt the aluminum liquid. Then pressure is applied to allow the aluminum liquid to penetrate into the pores of the silicon carbide porous preform. After cooling, aluminum silicon carbide composite material is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the selected photovoltaic silicon mud raw material contains Si ≥ 92 wt.%, O ≤ 7 wt.%, and the balance is impurity elements including at least one of Fe, Ni, Al, Cl, P, N, and S. The photovoltaic silicon mud is washed to make the pH value 6.5~8, and then the silicon mud filter cake is obtained by solid-liquid separation. The carbon source powder mentioned in step (2) includes one or two of petroleum coke powder and graphite powder, with a carbon content ≥ 99.0 wt.%.

3. The preparation method according to claim 1, characterized in that, In step (1), the silica mud raw material is wet ball milled and the powder passes through a 400-mesh sieve; the carbon source powder in step (2) has an average particle size of 5~45 μm.

4. The preparation method according to claim 1, characterized in that, In step (2), the binder includes one or more of polyvinyl alcohol, carboxymethyl cellulose, ethyl cellulose, sodium carboxymethyl cellulose, and dextrin; the pore-forming agent includes one or more of starch and ammonium bicarbonate.

5. The preparation method according to claim 1, characterized in that, In step (2), the amount of carbon source is determined according to the silicon content in the silica mud filter cake, and the carbon / silicon molar ratio is controlled to be 0.9~1.3; the amount of metal / alumina binder precursor is 3~10 wt.% of the total dry weight of the mixture; the amount of binder added is 3~8 wt.% of the total dry weight of the mixture, and the amount of pore-forming agent added is 5~20 wt.% of the total dry weight of the mixture; the mixture is silica mud filter cake and carbon source.

6. The preparation method according to claim 1, characterized in that, In step (2), the mixed slurry with a moisture content of 50~80wt.% is made into secondary granules by spray granulation or wet granulation after pressure filtration. During spray granulation, the moisture content of the mixed slurry is 50~65wt.% and during wet granulation, the mixed slurry is pressure filtered to obtain a filter cake with a moisture content of 25~35wt.% for granulation. The particle size of the granules is controlled between 0.1~2 mm and dried to a moisture content ≤5.0wt.%.

7. The preparation method according to claim 1, characterized in that, In step (3), molding or isostatic pressing is used; the molding pressure is 10~100 MPa, and the holding time is 2~10 min; the blank is dried to a moisture content of ≤1wt.%.

8. The preparation method according to claim 1, characterized in that, In step (4), the formed blank is placed in a sintering furnace, and the heating rate is controlled at 1~10℃ / min in an air atmosphere. The temperature is raised to 250~350℃ and held for 1~4 h. Then, the heating rate is controlled at 1~10℃ / min, and the temperature is raised to 600~700℃ and held for 0.5~2 h. After the holding period, the furnace is evacuated to below 0.1MPa and argon gas is introduced. The oxygen content in the furnace is controlled to not exceed 0.05 vol.‰. Then, the furnace is evacuated to 10... -2 The temperature is below kPa, and the temperature is increased to 1450-1600℃ at a heating rate of 8-15℃ / min and held for 1-8 hours. Finally, the temperature is increased to 2100-2500℃ at a heating rate of 10-20℃ / min and held for 4-12 hours to obtain a 6H-SiC porous preform with a porosity of 30-40%.

9. The preparation method according to claim 1, characterized in that, In step (5), the aluminizing process maintains a system vacuum of (0.5~1)×10⁻⁶. -3 The pressure is 0.5-5 MPa, the temperature is 650-800℃, the pressure is 0.5-5 MPa, and the holding time is 0.5-2 h.

10. The porous SiC framework AlSiC high thermal conductivity encapsulation material prepared by the preparation method according to any one of claims 1-9.

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