Method for in-situ preparation of TiB2-B4C composite ceramic from sapphire fine grinding waste

Abstract

The application belongs to the field of ceramic powder preparation, and discloses a method for in-situ preparation of high-performance TiB2-B4C composite ceramic from sapphire fine grinding waste. The method uses the waste produced in the sapphire grinding process as raw material (B4C, Al2O3 and Fe), adds TiO2 and C after alkali washing and purification, and combines with the discharge plasma sintering to in-situ prepare TiB2-B4C composite ceramic. The method not only realizes the comprehensive recovery of B4C in the sapphire fine grinding waste slurry, reduces environmental pollution, but also provides a method for in-situ preparation of TiB2-B4C composite ceramic from waste, changes waste into treasure, and realizes the secondary use of resources. In addition, the raw material cost is low, and the method has obvious economic value and environmental protection significance. The method has the advantages of short process, small pollution, simplicity and the like, and can be used for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of TiB2-based composite ceramics, and specifically relates to a method for in-situ preparation of TiB2-B4C composite ceramics using sapphire fine grinding waste. Background Technology

[0002] In the fine grinding process of sapphire (mainly composed of Al2O3), B4C micro-powders such as W5 (basic particle size 3.5–5 μm) and W7 (basic particle size 5–7 μm) are often used as grinding media. During the grinding process, the B4C particles gradually become finer and the particle size gradually decreases, while the impurities (Al2O3 and Fe) increase significantly. Ultimately, the B4C abrasive becomes sapphire grinding waste and cannot be used anymore. This not only wastes resources but also easily pollutes the environment. However, sapphire fine grinding waste contains more than 80% high-quality B4C, and after grinding, the B4C particle size is relatively fine (D50 < 3 μm), with a large specific surface area and high reactivity. It can be used as a reaction raw material for the boronothermal / carbothermal preparation of TiB2 powder (2TiO2 + B4C + 3C = 2TiB2 + 4CO).

[0003] Titanium boride (TiB2) ceramic is a novel engineering ceramic material. Due to its superior properties such as high strength, high hardness, high temperature resistance, excellent corrosion resistance, and high thermal shock resistance, it can be widely used in cutting tools, molds, crucibles for smelting metals, wear-resistant and corrosion-resistant materials, and wettable cathodes in aluminum electrolysis cells. In particular, TiB2 ceramic exhibits significant advantages in performance due to its high blast resistance and low armor spalling, making it a novel bulletproof ceramic material.

[0004] TiB2's high covalent bond content and low atomic diffusion coefficient make it a difficult material to sinter using traditional sintering methods, resulting in a dense ceramic material. Currently, the preparation of TiB2-B4C composite ceramics generally involves mechanically mixing TiB2 and B4C powders, followed by hot pressing or pressureless sintering. However, using pressureless sintering at 2400℃ for 1 hour yields a density of only 91%; while hot pressing at 1800℃ for 2 hours results in a density of only 97%. This demonstrates that even with long reaction times and high temperatures, the resulting ceramic material still exhibits less than ideal density and other properties. To improve the density and properties of TiB2 ceramics, existing technologies involve mechanically mixing TiB2 and B4C powders and then using a novel sintering technique—spark plasma sintering (SPS)—combined with methods such as refining TiB2 grains or adding sintering aids like SiC. While these methods can improve the density and properties of TiB2 ceramics to some extent, they also introduce other phases or increase the complexity of the process, leading to uncontrollable performance of the TiB2-B4C composite ceramics. Optimizing the mixing method and improving the sintering process remain the key challenges and difficulties in enhancing the density and mechanical properties of TiB2-B4C composite ceramics. Summary of the Invention

[0005] To address the shortcomings of current methods for recycling B4C from sapphire grinding waste, and the difficulties in achieving density and poor performance of TiB2-based composite ceramics prepared by traditional sintering methods, this invention proposes a method for in-situ preparation of high-performance TiB2-B4C composite ceramics from sapphire grinding waste using SPS sintering. After simple purification, sapphire grinding waste, combined with TiO2 and C, can be used to prepare high-performance TiB2-B4C composite ceramics in situ. Using sapphire grinding waste as a raw material not only achieves waste recycling but also reduces environmental pollution, streamlines processes, significantly lowers production costs, and yields higher purity and better performance TiB2-based composite ceramic materials, resulting in significant socio-economic benefits.

[0006] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0007] A method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste includes the following steps:

[0008] Step 1: Add the sapphire fine grinding waste to an alkaline solution for enhanced alkaline washing to obtain a purified raw material with an Al2O3 content ≤0.30wt%. The mass fractions of each component in the sapphire fine grinding waste are: B4C 86-92.5wt%, Al2O3 7-12wt%, and Fe 0.5-2wt%. The particle size range of the sapphire fine grinding waste is 0.5-10μm, and the average particle size D50 is 2-3μm. Then, dry the waste to obtain the dried purified material.

[0009] Step 2: Weigh and mix the purified material prepared in Step 1 with TiO2 and C in a weight ratio of 4.45:(2.38~3.23):1, then sieve and granulate to obtain granulated material;

[0010] Step 3: The granulated material obtained in Step 2 is placed in a spark plasma sintering furnace and a vacuum is applied. In the first stage, the temperature is held at 1350–1550℃ and 5–20 MPa for 5–20 min. Then, in the second stage, the temperature is rapidly increased to 1700–1850℃, and spark plasma sintering is performed at 20–40 MPa for 3–10 min. After cooling, TiB2-B4C composite ceramic is obtained. The in-situ reactions occurring in this step are as follows:

[0011] 2TiO2+(1+2x)B4C+4C=2(TiB2-xB4C)+4CO, x=0.2~0.4

[0012] Further, in step 1, the enhanced alkaline washing temperature is 205-250℃, the alkaline washing time is 0.5-3h, the alkaline solution concentration is 25-45wt%, and the mass ratio of alkaline solution to solid material is (3-8):1.

[0013] Further, in step 1, the added alkaline solution is a sodium hydroxide solution.

[0014] Further, in step 1, the strengthening process of the enhanced alkaline washing is enhanced by microwave or autoclave.

[0015] Further, in step 1, the drying is vacuum drying, with a vacuum degree of 350-600 Pa, a drying temperature of 100-150℃, and a drying time of 2-6 hours.

[0016] Further, in step 2, the average particle size of the TiO2 used is <1μm, and the purity is ≥99%; the average particle size of C is 1-3μm, and its purity is ≥98%; the C is one of petroleum coke, activated carbon, carbon black or graphite.

[0017] Further, in step 2, the mixing is carried out by wet ball milling, the medium used is anhydrous ethanol, the ratio of material:ball:medium is 1:2:(1~5), the ball milling speed is 300~600 rpm, and the mixing time is 4~10h.

[0018] Further, in step (2), the mixing is wet ball milling, the medium used is anhydrous ethanol, the ratio of material:ball:medium is 1:2:(1~5), the ball milling speed is 300~600 rpm, and the mixing time is 4~10h.

[0019] Furthermore, in step 2, the sieving and granulation is performed by sieving and granulating the mixed powder using a 60 or 100 mesh sieve.

[0020] Further, in step 3, the first stage is 1350℃ and the second stage is 1700℃.

[0021] Further, in step 3, the heating rate of the second stage rapid heating is 100-200℃ / min.

[0022] The TiB2-B4C composite ceramic obtained in step 3 above has a density ≥98.5%, a hardness of 28–35 GPa, and a fracture toughness of 3–6 MPa / m. 1 / 2 Its bending strength is 610–750 MPa.

[0023] The benefits of this invention are as follows:

[0024] (1) This invention employs a boronothermal / carbothermal reduction method, using purified sapphire grinding waste as raw material. The main component of the purified sapphire grinding waste is B4C, which has a high purity of 98%–99.5%, making it a high-purity raw material for the preparation of TiB2 using the boronothermal / carbothermal reduction method. Furthermore, during the grinding process, the particle size of B4C continuously decreases, with a D50 of 2–3 μm. The fine particle size results in a large specific surface area and high reactivity. The high-purity, fine-particle-size B4C raw material is beneficial for improving the kinetics of the in-situ reaction and promoting its occurrence. In addition, it also achieves the recycling and regeneration of sapphire grinding waste, turning waste into treasure. The low price of sapphire grinding waste significantly reduces costs.

[0025] (2) This invention uses fine-grained B4C as raw material. The TiB2 obtained by in-situ reaction at a relatively low temperature (1350-1550℃) for 5-20 minutes has a fine particle size, with an average particle size ≤1μm, a large specific surface area, and a low O impurity content (<0.2%), resulting in high sintering activity, which is beneficial for ceramic sintering densification. In contrast, the industrial preparation temperature of TiB2 is too high (1800-2000℃) and the holding time is too long (>20h), resulting in coarse TiB2 grains with an average particle size of 3-5μm, which greatly reduces its sintering activity; and the O impurity content is too high (0.8-1.5%), and O is the main factor that prevents TiB2 from sintering densification, making it difficult to densify.

[0026] (3) In this invention, the main component of the purified sapphire fine grinding waste is B4C-(0.5-2wt%)Fe. The Fe contained in the waste itself does not need to be introduced additionally. Fe can act as a catalyst to promote the reaction; at the same time, Fe can generate a liquid phase during sintering, which improves the density of TiB2-based composite ceramics through liquid phase sintering; in addition, Fe will also react with B4C to improve the ceramic properties.

[0027] 4Fe + B₄C = 4FeB + C

[0028] (4) This invention uses B4C from purified sapphire fine grinding waste as raw material, adds TiO2 and C, and TiB2 undergoes heterogeneous nucleation on the surface of B4C. B4C and TiB2 achieve molecular-level uniform mixing, improve the interface bonding between TiB2 and B4C, and thus facilitate ceramic densification. This avoids the drawbacks of uneven mixing and poor micro-interface bonding caused by traditional mechanical mixing, which lead to a decline in ceramic performance.

[0029] (5) This invention employs a two-stage SPS sintering method. The first stage rapidly forms TiB2-B4C composite powder at low temperatures. The second stage further reduces the diffusion activation energy and promotes sintering by purifying and activating the powder surface through discharge plasma, thus possessing advantages that traditional hot pressing and pressureless sintering technologies cannot replace. In addition, the rapid heating rate (100-150℃ / min), low sintering temperature (1700-1850℃), and short sintering time (3-10min) can effectively suppress grain coarsening behavior at high temperatures and significantly improve its mechanical properties. Attached Figure Description

[0030] Figure 1 This is a particle size distribution diagram of the sapphire fine grinding waste described in Embodiment 1 of the present invention.

[0031] Figure 2 This is a comparison of XRD patterns of sapphire grinding waste before and after purification, as described in Example 2 of this invention.

[0032] Figure 3 This is an SEM image of the purified sapphire fine grinding waste described in Example 2 of the present invention.

[0033] Figure 4 This is a surface SEM image of the TiB2-B4C composite ceramic obtained in Example 3 of the present invention.

[0034] Figure 5 The image shown is the XRD pattern of the product obtained by holding at 1350°C for 20 min as described in Example 4 of this invention.

[0035] Figure 6 This is a SEM image of the product obtained by holding at 1350℃ for 20 min as described in Example 4 of the present invention.

[0036] Figure 7 The images show a comparison of surface SEM images of TiB2-B4C composite ceramics prepared in Example 4(a) and Comparative Example 1(b) of this invention. Detailed Implementation

[0037] Example 1: A method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to the present invention, comprising the following steps:

[0038] Step 1: Sapphire fine grinding waste (86wt% B4C, 12wt% Al2O3, 2wt% Fe; average particle size D50 is 2.2μm) was added to an alkaline solution and subjected to microwave-enhanced alkaline washing at a temperature of 205℃ for 3 hours. The NaOH concentration was 25wt%, and the mass ratio of alkaline solution to solid material was 3:1, resulting in a purified raw material with an Al2O3 content of 0.24wt%. This was then dried at 100℃ under a vacuum of 350Pa for 6 hours to obtain the dried purified material.

[0039] Step 2: Weigh the purified material prepared in Step 1, TiO2 (D50 = 0.8 μm), and carbon black (D50 = 1.0 μm) at a weight ratio of 4.45:2.38:1 and ball mill them together. The material:ball:ethanol ratio is 1:2:2. The ball mill speed is 300 rpm and the mixing time is 10 h. The mixed powder is then sieved and granulated using a 60-mesh sieve.

[0040] Step 3: The granulated material obtained in Step 2 is placed in a spark plasma sintering furnace and evacuated. It is held at 1350℃ and 5MPa for 20 minutes, then heated to 1700℃ at a rate of 150℃ / min and sintered at 40MPa for 10 minutes using spark plasma sintering. After cooling, TiB2-B4C composite ceramic is obtained. The TiB2-B4C composite ceramic has a density of 98.5%, a hardness of 28 GPa, and a fracture toughness of 6 MPa / m. 1 / 2 Its bending strength is 610 MPa.

[0041] Figure 1 The particle size distribution diagram of the sapphire grinding waste described in this invention shows that the particle size distribution ranges from 0.5 to 10 μm, the average particle size D50 is 2.2 μm, the particle size is relatively fine, and the reactivity is relatively high.

[0042] Example 2: A method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to the present invention, comprising the following steps:

[0043] Step 1: Sapphire fine grinding waste (92.5wt% B4C, 7.0wt% Al2O3, 0.5wt% Fe; average particle size D50 is 3μm) was added to an alkaline solution and subjected to microwave-enhanced alkaline washing at a temperature of 250℃ for 0.5h. The NaOH concentration was 45wt%, and the alkaline solution to solid material mass ratio was 8:1 to obtain a purified raw material with an Al2O3 content of 0.10wt%. Then, it was dried at 150℃ under a vacuum of 600Pa for 2h to obtain the dried purified material.

[0044] Step 2: Weigh the purified material prepared in Step 1, TiO2 (D50 = 0.5 μm), and carbon black (D50 = 3.0 μm) in a weight ratio of 4.45:3.23:1 and ball mill them together. The material:ball:ethanol ratio is 1:2:5. The ball milling speed is 600 rpm and the mixing time is 4 hours. The mixed powder is then sieved and granulated using a 100-mesh sieve.

[0045] Step 3: The granulated material obtained in Step 2 is placed in a spark plasma sintering furnace and a vacuum is drawn. It is held at 1550℃ and 20MPa for 5 minutes, then heated at a rate of 200℃ / min to 1850℃, and spark plasma sintered at 20MPa for 3 minutes. After cooling, TiB2-B4C composite ceramic is obtained. The density of the TiB2-B4C composite ceramic is 99.2%, the hardness is 35 GPa, and the fracture toughness is 3 MPa / m. 1 / 2 Its bending strength is 750 MPa.

[0046] Figure 2 The images show a comparison of XRD patterns of sapphire grinding waste before and after purification. As can be seen from the images, the sapphire grinding waste consists of B4C and Al2O3. The Fe impurity content may be below the detection limit of XRD and therefore not shown. However, alkaline washing cannot remove Fe from the raw material, so the Fe impurity content in the purified material remains unchanged. The waste purified by alkaline washing consists of pure phase B4C without other impurity phases, indicating that the Al2O3 impurity has been largely removed through alkaline washing purification.

[0047] Figure 3This is a SEM image of the purified sapphire fine grinding waste. XRD analysis shows that it is pure phase B4C with relatively uniform and fine particle size (<5μm). There are also many submicron (<1μm) B4C ultrafine powders attached to the surface of the large B4C particles, which may be due to the breakage of the large B4C particles after long-term grinding.

[0048] Example 3: A method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to the present invention, comprising the following steps:

[0049] Step 1: Sapphire fine grinding waste (90.0 wt% B4C, 9.0 wt% Al2O3, 1.0 wt% Fe; average particle size D50 is 2.2 μm) was added to an alkaline solution and subjected to microwave-enhanced alkaline washing at a temperature of 220℃ for 1.5 h. The NaOH concentration was 30 wt%, and the mass ratio of alkaline solution to solid material was 4:1, resulting in a purified raw material with an Al2O3 content of 0.10 wt%. This was then dried at a vacuum of 450 Pa and 120℃ for 4 h to obtain the dried purified material.

[0050] Step 2: Weigh the purified material prepared in Step 1, TiO2 (D50 = 0.8 μm), and petroleum coke (D50 = 3.0 μm) in a weight ratio of 4.45:2.77:1 and ball mill them together. The material:ball:ethanol ratio is 1:2:4. The ball mill speed is 450 rpm and the mixing time is 8 hours. The mixed powder is then sieved and granulated using a 60-mesh sieve.

[0051] Step 3: The granulated material obtained in Step 2 is placed in a spark plasma sintering furnace and evacuated. It is held at 1500℃ and 10MPa for 10 minutes, then heated to 1750℃ at a rate of 100℃ / min and sintered at 30MPa for 8 minutes using spark plasma sintering. After cooling, TiB2-B4C composite ceramic is obtained. The TiB2-B4C composite ceramic has a density of 99.0%, a hardness of 34 GPa, and a fracture toughness of 5.0 MPa / m. 1 / 2 The bending strength is 700 MPa.

[0052] Figure 4 SEM images of the TiB2-B4C composite ceramics were obtained. The images show that the gray matrix represents the TiB2 phase, and the black matrix represents the B4C phase. The B4C second phase is uniformly dispersed within the TiB2 matrix. Combined with the liquid-phase sintering effect of Fe, this effectively improves the density of the composite ceramic. The intrinsic hardness of B4C is higher than that of TiB2, which effectively increases the hardness of the TiB2-B4C composite ceramic. Furthermore, the difference in thermal expansion coefficients between TiB2 and B4C induces microcracks during cooling, thereby consuming the energy for crack propagation and improving the toughness of the ceramic.

[0053] Example 4: A method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to the present invention, comprising the following steps:

[0054] Step 1: Sapphire fine grinding waste (88.0 wt% B4C, 10.5 wt% Al2O3, 1.5 wt% Fe; average particle size D50 of 2.5 μm) was added to an alkaline solution and subjected to high-pressure autoclave intensive alkaline washing at a temperature of 210℃ for 2.5 h. The NaOH concentration was 35 wt%, and the mass ratio of alkaline solution to solid material was 6:1, resulting in a purified raw material with an Al2O3 content of 0.15 wt%. This was then dried at a vacuum of 500 Pa and 110℃ for 4.5 h to obtain the dried purified material.

[0055] Step 2: Weigh the purified material prepared in Step 1, TiO2 (D50 = 0.6 μm), and activated carbon (D50 = 3.0 μm) in a weight ratio of 4.45:2.57:1 and ball mill them together. The material:ball:ethanol ratio is 1:2:3. The ball milling speed is 500 rpm and the mixing time is 6 hours. The mixed powder is then sieved and granulated using a 100-mesh sieve.

[0056] Step 3: The granulated material obtained in Step 2 is placed in a spark plasma sintering furnace and evacuated. It is held at 1350℃ and 10MPa for 15 minutes, then heated to 1820℃ at a rate of 150℃ / min and sintered at 35MPa for 8 minutes using spark plasma sintering. After cooling, TiB2-B4C composite ceramic is obtained. The TiB2-B4C composite ceramic has a density of 98.9%, a hardness of 30 GPa, and a fracture toughness of 5.5 MPa / m. 1 / 2 Its bending strength is 680 MPa.

[0057] Figure 5 The XRD pattern of the product obtained by holding at 1350℃ for 20 min is shown in the figure. As can be seen from the figure, its phase composition is mainly TiB2 and B4C, without diffraction peaks of other impurity phases (TiO2, C). This indicates that the particle size of B4C in the purified waste is relatively fine and has high reactivity. In addition, the Fe impurity in the waste can act as a "catalyst". Combined with the unique heating characteristics of SPS, pure phase TiB2 can be rapidly prepared in situ at a relatively low temperature of 1350℃.

[0058] Figure 6The image shows the SEM image of the product obtained by holding at 1350℃ for 20 min. The TiB2 prepared in situ by the boronothermic / carbothermic reduction reaction has a fine particle size with an average particle size of ≤1μm, which is a submicron-sized powder with an irregular morphology. This may be due to the low temperature and short holding time, which prevents the grains from growing. At the same time, there are also B4C crystals with a particle size of 2μm. The B4C crystals have an irregular polyhedral morphology, and the fine-grained TiB2 is mostly attached to the surface of the B4C crystals. This confirms that the TiB2-B4C is uniformly mixed at the molecular level and has strong micro-interfacial bonding, which is beneficial to improving its sintering performance.

[0059] Comparative Example 1: The present invention discloses a method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste, which is carried out through the following steps:

[0060] Step 1: Sapphire fine grinding waste (88.0 wt% B4C, 10.5 wt% Al2O3, 1.5 wt% Fe; average particle size D50 of 2.5 μm) was added to an alkaline solution and subjected to high-pressure autoclave intensive alkaline washing at a temperature of 210℃ for 2.5 h. The NaOH concentration was 35 wt%, and the mass ratio of alkaline solution to solid material was 6:1, resulting in a purified raw material with an Al2O3 content of 0.15 wt%. This was then dried at a vacuum of 500 Pa and 110℃ for 4.5 h to obtain the dried purified material.

[0061] Step 2: Weigh the purified material prepared in Step 1, TiO2 (D50 = 0.6 μm), and activated carbon (D50 = 3.0 μm) in a weight ratio of 4.45:2.57:1 and ball mill them together. The material:ball:ethanol ratio is 1:2:3. The ball milling speed is 500 rpm and the mixing time is 6 hours. The mixed powder is then sieved and granulated using a 100-mesh sieve.

[0062] Step 3: The granulated material obtained in Step 2 is placed in a hot-pressing sintering furnace and vacuumed. It is held at 1350℃ and 10MPa for 15 minutes, then heated to 1820℃ at a rate of 10℃ / min and hot-pressed at 35MPa for 60 minutes. After cooling, TiB2-B4C composite ceramic is obtained. The density of the TiB2-B4C composite ceramic is 90.4%, the hardness is 18GPa, and the fracture toughness is 3.20MPa / m. 1 / 2 The bending strength is 400 MPa.

[0063] Figure 7 The images show a surface SEM comparison of the TiB2-B4C composite ceramics prepared in Example 4 and Comparative Example 1. The difference between Example 4 and Comparative Example 1 is that Comparative Example 1 used hot pressing sintering, while Example 4 used SPS sintering. The comparison shows that… Figure 7 (a) It has fewer surface pores and a higher degree of densification, while Figure 7 (b) Numerous pores and poor density indicate... Figure 7 (a) has a significantly higher density than Figure 7 (b) Increased density leads to improved mechanical properties. A comparative analysis shows that SPS sintering utilizes plasma purification and powder surface activation to promote ceramic densification and improve its mechanical properties.

[0064] Comparative Example 2: The present invention discloses a method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste, which is carried out through the following steps:

[0065] Step 1: Sapphire fine grinding waste (90.0 wt% B4C, 8.5 wt% Al2O3, 1.5 wt% Fe; average particle size D50 is 2.5 μm) was added to an alkaline solution and subjected to high-pressure autoclave intensive alkaline washing at a temperature of 225℃ for 2.0 h. The NaOH concentration was 30 wt%, and the mass ratio of alkaline solution to solid material was 5:1, resulting in a primary purified raw material with an Al2O3 content of 0.20 wt%. The primary purified material was then reacted in 30% H2SO4 at a temperature of 60℃ for 2 h to ensure complete removal of Fe. Finally, it was dried under a vacuum of 500 Pa and at 110℃ for 4.5 h to obtain the dried secondary purified material (B4C).

[0066] Step 2: The purified material prepared in Step 1 and commercially available TiB2 micro powder (D50 < 1 μm, O content 1.0%) are mixed in a mass ratio of 10:3 and ball-milled. The material:ball:ethanol = 1:2:3, the ball mill speed is 500 rpm, and the mixing time is 6 h. The mixed powder is then sieved and granulated using a 100-mesh sieve.

[0067] Step 3: The granulated material obtained in Step 2 is placed in a hot-press sintering furnace or plasma sintering furnace and a vacuum is drawn. The temperature is increased to 1750℃ at a rate of 150℃ / min, and spark plasma sintering is performed at 30MPa for 8 minutes. After cooling, TiB2-B4C composite ceramic is obtained. The density of TiB2-B4C composite ceramic is 93.0%, the hardness is 20 GPa, and the fracture toughness is 3.50 MPa / m. 1 / 2 Its bending strength is 480 MPa.

[0068] Table 1 compares the raw material composition, preparation method, and ceramic properties of Example 3 and Comparative Example 2. As shown in the table, the TiB2-B4C composite ceramic prepared in Example 3 exhibits significantly higher density, hardness, fracture toughness, and flexural strength than the ceramic prepared in Comparative Example 2.

[0069] Table 1. Comparison of raw material composition, preparation method, and ceramic properties between Example 3 and Comparative Example 2 of the present invention.

[0070]

[0071] There are four reasons: (1) The role of Fe impurities: Fe impurities can form liquid phase sintering during sintering, which promotes ceramic densification; (2) The preparation method and O content of TiB2 are different. Example 3 uses B4C in-situ reaction preparation with extremely low O content (<0.2%), while Comparative Example 2 uses commercially available TiB2 with an O content of about 1.0%. A higher O content will reduce the surface diffusion rate and thus prevent ceramic densification; (3) The mixing methods of B4C and TiB2 are different. In Example 3, TiB2 nucleates on the surface of B4C, and TiB2-B4C is mixed uniformly at the molecular level, with strong micro-interface bonding, which is beneficial to improving its sintering performance; while Comparative Example 2 uses mechanical mixing, which is not uniform and has poor micro-interface bonding; (4) The difference in sintering process: Example 3 uses a two-stage SPS sintering process, while Comparative Example 2 uses a one-stage sintering process.

[0072] The embodiments described above are preferred embodiments of the present invention and do not impose any other limitations on the present invention. Any person skilled in the art may make changes or imitations based on the above content. However, any changes made to the above embodiments based on the essence of the method of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste, characterized in that, Includes the following steps: Step 1: Add the sapphire fine grinding waste to an alkaline solution for enhanced alkaline washing to obtain a purified raw material with an Al2O3 content ≤0.30wt%. The mass fractions of each component in the sapphire fine grinding waste are: B4C 86-92.5wt%, Al2O3 7-12wt%, and Fe 0.5-2wt%. The particle size range of the sapphire fine grinding waste is 0.5-10μm, and the average particle size D50 is 2-3μm. Then, dry the waste to obtain the dried purified material. Step 2: Weigh and mix the purified material prepared in Step 1 with TiO2 and C in a weight ratio of 4.45:(2.38~3.23):1, then sieve and granulate to obtain granulated material; Step 3: Place the granulated material obtained in Step 2 into a spark plasma sintering furnace and evacuate it. In the first stage, hold the material at 1350-1550℃ and 5-20MPa for 5-20 minutes. Then, in the second stage, rapidly raise the temperature to 1700-1850℃ and perform spark plasma sintering at 20-40MPa for 3-10 minutes. After cooling, TiB2-B4C composite ceramic is obtained.

2. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 1, the enhanced alkaline washing temperature is 205-250℃, the alkaline washing time is 0.5-3h, the alkaline solution concentration is 25-45wt%, and the mass ratio of alkaline solution to solid material is (3-8):

1.

3. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 1, the added alkaline solution is a sodium hydroxide solution.

4. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 1, the enhanced alkaline washing process is enhanced by microwave or autoclave.

5. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 1, the drying is vacuum drying, with a vacuum degree of 350-600 Pa, a drying temperature of 100-150℃, and a drying time of 2-6 hours.

6. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 2: The average particle size of TiO2 used is <1μm, and its purity is ≥99%; the average particle size of C is 1-3μm, and its purity is ≥98%; the C is one of petroleum coke, activated carbon, carbon black or graphite.

7. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 2, the mixing is wet ball milling, the medium used is anhydrous ethanol, the ratio of material:ball:medium is 1:2:(1~5), the ball milling speed is 300~600 rpm, and the mixing time is 4~10h.

8. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 2, the sieving and granulation is performed by sieving and granulating the mixed powder using a 60 or 100 mesh sieve.

9. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 3: the first stage is 1350℃, and the second stage is 1700℃.

10. The method for in-situ preparation of TiB2-B4C composite ceramics from sapphire fine grinding waste according to claim 1, characterized in that, Step 3, the heating rate of the second stage rapid heating is 100-200℃ / min.

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