CN114477185B - beta-SiC with lamellar structure and preparation method thereof - Google Patents

Abstract

According to the invention, graphene is used as a carbon source, and is combusted and synthesized with silicon powder in a nitrogen atmosphere by igniting a chemical furnace to prepare beta-SiC, so that the beta-SiC has a regular lamellar structure, does not contain free silicon, and has high phase purity; beta-SiC nanowhiskers are present at the edges of the lamellar structure, which internally comprises mutually staggered, fine and short SiC nanowhiskers, and interconnected SiC nanoparticles. The thermal conductivity of the material and the toughness of the ceramic material are greatly improved, and the ceramic material can be applied to occasions with high thermal performance requirements such as electronic device packaging substrates, heat exchangers and the like; and the preparation process is simple, the cost is low, the reaction time is short, and the industrial production is facilitated.

Description

A kind of β-SiC with lamellar structure and its preparation method

technical field

The invention relates to the field of silicon carbide ceramic materials, in particular to a β-SiC powder with a lamellar structure and a preparation method thereof.

Background technique

Silicon carbide ceramics have the characteristics of high hardness, high temperature resistance, oxidation resistance, good chemical stability and good thermal shock resistance, and can be widely used in machinery, aviation, chemical industry, metallurgy and other fields, especially suitable for fields with high thermal performance requirements. The current typical preparation methods of β-SiC include the following:

(1) The reaction sintering method, as mentioned in CN107602131A, adopts silicon carbide coarse powder i, silicon carbide fine powder ii, graphene nanosheets, charcoal black, silicon powder, dispersant, adhesive, and is prepared by reaction sintering β-SiC, in which graphene nanosheets provide a carbon source for the silicon-carbon reaction, and the silicon carbide formed after reacting with silicon has a typical layered structure, which can improve the mechanical properties of β-SiC. As mentioned in CN104926313A, dense silicon carbide can be prepared by using silicon carbide, graphene, carbon powder, surfactant, dispersant, etc., by reaction sintering at high temperature through mixed molding. However, the reaction sintering method has complex raw materials, high energy consumption, and a long time. Usually, free silicon is easily contained, and the industrialization cost is high.

(2) Microwave reaction method, Zhang Hao mentioned in "Microwave Preparation of Silicon Carbide and Its Electromagnetic Shielding", using microwave reaction method to prepare β-SiC products by reacting different carbon sources with silicon powder and silicon oxide powder. Most of the nanowires, nanorods and micro-nano grains prepared by using artificial graphite powder as the carbon source are nanowires, nanorods and micro-nano grains, and the content of nanowires is relatively small; Most of the olefin microsheets prepared as carbon sources are micro-nano crystals. Although pure phase β-SiC can be produced, it cannot obtain a graphene-like sheet structure, so its mechanical properties are limited.

Contents of the invention

In order to overcome the above disadvantages, the present invention provides a method for preparing β-SiC powder with a lamellar structure by high-temperature combustion synthesis, which can achieve the advantages of energy saving, high efficiency and low cost, and the shape of the powder can be controlled, which is conducive to the improvement of mechanical properties .

Specifically provide the following technical solutions:

A β-SiC ceramic material with a lamellar structure, characterized in that the lamellar structure is a flaky structure with a completely open surface, the diameter of the lamellar layer is between 4-30 μm, and the thickness of the lamellar layer is 200-500 nm; There are β-SiC nanowhiskers on the edge of the sheet structure, and the aspect ratio of the β-SiC nanowhiskers is 10-30; the inside of the sheet structure includes interlaced, small and short SiC nanowhiskers, and interconnected SiC nanoparticles.

Preferably, the aspect ratio of the SiC nano whiskers inside the lamellar structure is 5-12;

Preferably, the size of SiC nanoparticles inside the lamellar structure is 100-300nm;

The present invention also provides a method for preparing a β-SiC ceramic material with a lamellar structure, which is characterized in that graphene is used as a carbon source, silicon powder is used as a silicon source, silicon powder and graphene are mixed evenly, and dried and sieved , Put the carbon-silicon mixed powder into the reaction boat, the carbon-silicon mixed powder is surrounded by thermite as a chemical furnace, and placed in the combustion synthesis reaction kettle, and 1-3MPa nitrogen is introduced, and the carbon is made by igniting the chemical furnace. The silicon mixed powder undergoes a combustion synthesis reaction to prepare a β-SiC powder with a lamellar structure.

Preferably, the chemical furnace uses Ti, C mixed powder and Al, Fe ₂ O ₃ mixed powder as the thermite, and a tungsten wire coil is placed at one end of the powder.

The ignition chemical furnace is ignited by passing an alternating current in a tungsten wire coil.

Preferably, the Ti, C mixed powder accounts for 60%-90% of the weight of the carbon-silicon mixed powder _; the Al, _Fe2O3 mixed powder accounts for 10% of the weight of the carbon-silicon mixed powder -40%.

Preferably, the ratio of the silicon source to the carbon source is a molar ratio of 1:1-1:1.2;

Preferably, the silicon powder and graphene are mixed by a wet method, adding anhydrous ethanol with a weight of 1:1 with the carbon silicon mixed powder, stirring and wet mixing, continuous ultrasonication in the ultrasonic instrument for 3 hours, adding ethanol every 45min, each time The amount of ethanol added is 25% of the weight of the carbon-silicon mixed powder.

Preferably, the drying and sieving is carried out by putting the wet mixed powder into an oven at 80° C. for drying, and after drying, the mixed powder is ground through a 45-60 mesh sieve.

The present invention adopts a chemical furnace combined with a combustion synthesis method, and the prepared β-SiC can effectively retain the sheet structure of graphene. The reaction principle is shown in Figure 1. The edge of the sheet has a relatively high chemically active C atom due to the dangling C bond (as shown in Figure 1(a)). At the same time, in the process of product preparation, the high temperature environment of ultrasonic mixing treatment and combustion synthesis It will cause more defect sites, surface steps and partially broken C-C bonds in the graphene network lattice, which makes the graphene sheets also have local active C atoms (as shown in Figure 1(a)). During the reaction process, when the gaseous silicon source (Si, SiO) diffuses to the surface of graphene, it reacts with the active C atoms in graphene to form SiC crystal nuclei (as shown in Figure 1(b)), because graphene has a high crystallinity Therefore, with the continuous deposition of the gas-phase silicon source, the SiC crystal nucleus grows along the one-dimensional direction according to the VS mechanism to form SiC nano whiskers, and under the limitation of the graphene sheet carbon source , SiC whiskers are intertwined to maintain a micron-scale sheet structure (as shown in Figure 1(c)). Because the activity of C atoms at the edge of the graphene sheet is higher than that of C atoms inside the sheet surface, SiC whiskers are first formed at the edge, and the aspect ratio of SiC whiskers at the edge is generally the same as that of SiC whiskers inside the sheet. Due to the limitation of the activity of C atoms inside the sheet, some SiC whiskers formed will be very short, which can be directly regarded as SiC particles. Generally, the length of SiC whiskers and the thickness of the sheet structure formed by intertwining whiskers are related to gas-phase silicon source and graphene activity, and both are related to reaction temperature and reaction pressure. The pressure determines to a certain extent the length of SiC whiskers and the thickness of the formed lamellar structure.

Because this synthesis experiment was completed under the condition of a thermite as a chemical furnace and a nitrogen atmosphere, when the nitrogen pressure was used as a variable, as the nitrogen pressure increased (1-3MPa), the gas-phase silicon source decreased, and the length of the formed whiskers was shortened. Correspondingly, the thickness of the sheet decreases to a certain extent; the thermite is composed of Ti, C, Al and Fe ₂ O ₃ , in which the reaction between Ti and C is mild and the heat release is high, and the reaction between Al and Fe ₂ O ₃ is violent and the heat release is high. Less heat release, when the ratio of Ti and C is high, the chemical furnace heats up slowly but the attainable temperature is high, and the holding time is long; when the ratio of Al and Fe ₂ O ₃ is high, the chemical furnace heats up quickly but the reachable temperature is low, and the holding time short. Therefore, the SiC whiskers obtained by using a higher proportion of Ti and C as a chemical furnace are longer, and correspondingly, the thickness of the sheet is larger.

At the same time, since Si/C is a weakly exothermic reaction system, the adiabatic temperature is only 1600-1700K, and it is difficult to synthesize SiC by direct ignition of elements. At the same time, because the amount of reactants is relatively small, it is necessary to use Si nitriding under nitrogen. Coupled with a chemical furnace, the exothermic auxiliary Si/C system is used for combustion synthesis, so there is no need to add SiC diluent.

The beneficial effects of the present invention are as follows:

1. The β-SiC prepared by the combustion synthesis method of the present invention presents a regular lamellar structure, does not contain free silicon, has high phase purity, greatly improves the thermal conductivity of the material and the toughness of the ceramic material, and can be applied to electronic device packaging substrates , heat exchangers and other occasions with high thermal performance requirements; and the preparation process is simple, the cost is low, and the reaction time is short, which is beneficial to industrial production.

2. The present invention uses graphene as a carbon source, on the one hand to provide a carbon source, and on the other hand graphene provides a template for the formation of flake-like β-SiC, because cracks will develop along the flake-like structure when the ceramic breaks, requiring more consumption The fracture energy of ceramics is not easy to increase in fracture toughness, and there are a large number of nano whiskers on the edge of the sheet, which also plays the role of strengthening and toughening.

Description of drawings

Hereinafter, the present invention will be described in more detail based on the embodiments with reference to the accompanying drawings. in:

Figure 1. Schematic diagram of the formation of SiC sheet structure;

Figure 2. XRD pattern of β-SiC with lamellar structure;

Figure 3. SEM spectra of reactant graphene and β-SiC with sheet structure, (a) SEM images of carbon source graphene; (b), (c) Ti, C mixed powder accounted for 80% thermite (d) SEM image of the product synthesized under the condition of 90% Ti and C mixed powder and thermite and 1MPa nitrogen pressure; (e) Ti and C mixed The SEM image of the product synthesized under the condition of 70% thermite powder and 2MPa nitrogen pressure; (f) the SEM image of the product synthesized under the condition of 60% Ti and C mixed powder thermite and 3MPa nitrogen pressure .

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some representative embodiments of the present invention, rather than all embodiments. All other embodiments obtained by persons of ordinary skill without making creative efforts belong to the protection scope of the present invention.

Example 1

Select 12g of graphene, select 28g of silicon powder, mix silicon powder and graphene to obtain 40g of carbon-silicon mixed powder, add dehydrated alcohol with a weight ratio of 1:1 to carbon-silicon mixed powder, stir and wet mix, and continuously Ultrasound for 3 hours, because ethanol will volatilize during the ultrasonic process, so ethanol is added once every 45 minutes, and the amount of ethanol added each time is 25% of the weight of the carbon-silicon mixed powder. Then put the ultrasonically prepared wet-mixed powder into an oven at 80°C for drying, and grind the dried mixed powder through a 45-mesh sieve for later use. Put the ground and sieved carbon-silicon mixed powder into a stainless steel reaction boat lined with carbon felt. The mixed powder of Ti and C with a molar ratio of 1:1 accounts for 80% of the weight, and the mixed powder of Al and Fe with a molar ratio of 1: ₁ O ₃ mixed powder accounting for 20% of thermite is placed around the Si and C mixed powder to make a chemical furnace, and a tungsten wire coil for ignition is placed at one end of the powder, and then placed together in a closed combustion synthesis reaction Inside the cauldron. After the reactor was evacuated, it was filled with high-purity nitrogen gas at 1MPa. Then, an alternating current is passed into the tungsten wire coil, the chemical furnace is ignited, and then the combustion synthesis reaction of the Si and C mixed powder is initiated, and the β-SiC powder with a lamellar structure is obtained. Through XRD characterization, it is found that the product is a pure-phase β-SiC powder, does not contain free silicon, and Sf is caused by silicon carbide stacking layers; through SEM characterization, most of the products maintain a scale and shape similar to graphene in appearance The lamellar structure has an average diameter of 15 μm and an average thickness of 400 nm, but on a smaller scale, SiC nanowhiskers with large aspect ratios at the edge of the lamellar structure are intertwined with each other, and the aspect ratio is about 20, while in The interior of the lamellar structure is composed of interlaced, small and short SiC nano whiskers and interconnected and agglomerated SiC nanoparticles. The average aspect ratio of the short whiskers is about 10, and the average diameter of the nanoparticles is 150nm.

Example 2

Adopt the experimental condition as in embodiment 1, wherein choose graphene 12g, choose silicon powder 33.6g, silicon powder and graphene batching obtain carbon-silicon mixed powder 45.6g, thermite adopts Ti, C mixed powder to account for 90 %, Al, Fe ₂ O ₃ mixed powder accounted for 10%; the dried mixed powder was ground through a 60-mesh sieve for later use. Other conditions are consistent with Example 1. Through XRD characterization, it is found that the product is a pure-phase β-SiC powder without free silicon; through SEM characterization, it has a lamellar structure with an average diameter of 4 μm and an average thickness of 500 nm. The edge of the lamellar structure has a relatively large length and diameter. SiC nanowhiskers are intertwined with each other, and the aspect ratio is about 25, while inside the sheet structure, it is composed of interlaced, small and short SiC nanowhiskers and interconnected and agglomerated SiC nanoparticles, and the short whiskers have an average aspect ratio. is about 12, and the average diameter of nanoparticles is 200nm.

Example 3

Adopt the experimental conditions as in Example 1, wherein the thermite uses Ti, C mixed powder to account for 70% _, Al, _Fe2O3 mixed powder accounts for 30%; after vacuumizing the reactor, fill it with high-purity nitrogen 2MPa. Other conditions are consistent with Example 1. Through XRD characterization, it is found that the product is a pure-phase β-SiC powder without free silicon; through SEM characterization, it has a lamellar structure with an average diameter of 20 μm and an average thickness of 200 nm. The edge of the lamellar structure has a relatively large length and diameter. SiC nanowhiskers are intertwined with each other, and the aspect ratio is about 17, while inside the lamellar structure, it is composed of interlaced, small and short SiC nanowhiskers and interconnected and agglomerated SiC nanoparticles, and the short whisker aspect ratio The average is about 8, and the average diameter of nanoparticles is 180nm.

Example 4

Adopt the experimental conditions as in Example 1, wherein _the thermite is made of Ti, C mixed powder accounting for 60%, and Al, _Fe2O3 mixed powder accounting for 40%; after the reactor is evacuated, it is filled with high-purity nitrogen 1MPa. Other conditions are consistent with Example 1. Through XRD characterization, it is found that the product is a pure-phase β-SiC powder without free silicon; through SEM characterization, it has a lamellar structure with an average diameter of 30 μm and an average thickness of 200 nm. The edge of the lamellar structure has a relatively large length and diameter. SiC nanowhiskers are intertwined with each other, and the aspect ratio is about 15, while inside the sheet structure, it is composed of interlaced, small and short SiC nanowhiskers and interconnected and agglomerated SiC nanoparticles, and the short whisker aspect ratio The average is about 7, and the average diameter of nanoparticles is 280nm.

Example 5

Adopt the experimental conditions as in Example 1, wherein the thermite is made of Ti, C mixed powder accounting for 60%, and Al, _Fe2O3 mixed powder accounting for 40%; after the reactor is evacuated, it is filled with high-purity _nitrogen 3 MPa. Other conditions are consistent with Example 1. Through XRD characterization, it is found that the product is a pure-phase β-SiC powder without free silicon; through SEM characterization, it has a lamellar structure with an average diameter of 25 μm and an average thickness of 150 nm. The edge of the lamellar structure has a relatively large length and diameter. SiC nanowhiskers are intertwined with each other, and the aspect ratio is about 10, while inside the sheet structure, it is composed of interlaced, small and short SiC nanowhiskers and interconnected and agglomerated SiC nanoparticles, and the short whiskers have an average aspect ratio. is about 5, and the average diameter of nanoparticles is 300nm.

As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still understand the foregoing The technical solutions recorded in each embodiment are modified, or some of the technical features are replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (10)

1. The beta-SiC ceramic material with the lamellar structure is characterized in that the lamellar structure is a lamellar structure with a completely open surface, the lamellar diameter is between 4 and 30 mu m, and the lamellar thickness is 200 to 500nm; beta-SiC nanowhiskers are arranged at the edge of the lamellar structure, and the length-diameter ratio of the beta-SiC nanowhiskers is 10-30; the interior of the lamellar structure comprises mutually staggered, fine and short SiC nanowhiskers and mutually connected SiC nanoparticles.

2. The beta-SiC ceramic material having a lamellar structure in accordance with claim 1, characterized in that the SiC nanowhisker inside the lamellar structure has an aspect ratio of 5 to 12.

3. The beta-SiC ceramic material having a lamellar structure according to claim 1, characterized in that the SiC nanoparticle size inside the lamellar structure is 100 to 300nm.

4. The method for preparing the beta-SiC ceramic material with the lamellar structure according to claim 1, wherein graphene is used as a carbon source, silicon powder is used as a silicon source, the silicon powder and the graphene are uniformly mixed, the silicon powder is dried and sieved, carbon-silicon mixed powder is filled into a reaction boat, a thermite is used as a chemical furnace around the carbon-silicon mixed powder, the carbon-silicon mixed powder is placed into a combustion synthesis reaction kettle, 1-3MPa of nitrogen is introduced, and the carbon-silicon mixed powder is subjected to combustion synthesis reaction by igniting the chemical furnace to prepare the beta-SiC powder with the lamellar structure.

5. The method for preparing beta-SiC ceramic material with lamellar structure according to claim 4, wherein the chemical furnace adopts Ti and C mixed powder and Al and Fe ₂ O ₃ The mixed powder is used as thermite, and a tungsten filament coil is placed at one end of the powder.

6. The method for preparing a beta-SiC ceramic material with a lamellar structure according to claim 5, wherein the weight of the Ti and C mixed powder is 60% -90% of that of the thermite powder; the Al, fe ₂ O ₃ The mixed powder accounts for 10-40% of the weight of the thermite powder; the molar ratio of Ti to C in the Ti and C mixed powder is 1:1, al, fe ₂ O ₃ Al, fe in the mixed powder ₂ O ₃ The molar ratio is 1:1.

7. the method for producing a β -SiC ceramic material having a layered structure according to any one of claims 4 to 6, wherein the ignition chemical burner is ignited by passing an alternating current through a tungsten wire coil.

8. The method for preparing a beta-SiC ceramic material having a lamellar structure according to claim 4, wherein the ratio of the silicon source to the carbon source is 1:1 to 1:1.2.

9. The method for preparing the beta-SiC ceramic material with the lamellar structure according to claim 4, wherein silicon powder and graphene are mixed by a wet method, and the mixed powder with carbon and silicon is added in an amount of 1:1, continuously carrying out ultrasonic treatment in an ultrasonic instrument for 3 hours, adding ethanol every 45min, wherein the addition amount of each ethanol is 25% of the weight of the carbon-silicon mixed powder.

10. The method for preparing a beta-SiC ceramic material having a layered structure according to claim 9, wherein the drying and sieving is performed by putting the wet mixed powder into a drying oven at 80 ℃ for drying, and grinding the dried mixed powder and sieving with a 45-60 mesh sieve.

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