A preparation method of ultrafine boron carbide spray granulation powder

Abstract

The present invention relates to the field of ceramic technology, and particularly relates to a preparation method of ultrafine boron carbide spray granulation powder. The preparation method includes: (1) preparation of vinylated ultrafine boron carbide; (2) preparation of nitrogen silane oligomer; (3) high-temperature crosslinking of the nitrogen silane oligomer on the surface of vinylated ultrafine boron carbide; (4) ball milling and granulation. Compared with the ceramic body prepared by directly sintering ultrafine boron carbide, the ceramic body prepared by using the spray granulation powder of the present invention has a higher relative density, the flexural strength reaches above 480 MPa, and the fracture toughness reaches above 6.5 MPa·m¹ / ².

Description

Technical Field

[0001] The present invention relates to the technical field of ceramics, and particularly relates to a method for preparing ultrafine boron carbide spray granulation powder. Background Art

[0002] Boron carbide is a ceramic material with high hardness, low density, high melting point and excellent wear resistance, and is widely used in fields such as bulletproof armor, wear-resistant components and nuclear radiation shielding. However, the inherent brittleness and low fracture toughness of boron carbide ceramics limit their further application in high-performance structural materials. In order to improve the comprehensive properties of boron carbide ceramics, researchers usually improve their flexural strength and fracture toughness by refining grains, introducing toughening phases or optimizing sintering processes.

[0003] Ultrafine boron carbide powder, due to its high specific surface area and high activity, has become an ideal raw material for preparing high-performance boron carbide ceramics. However, ultrafine boron carbide powder is prone to agglomeration in practical applications, resulting in poor contact between particles during the sintering process, and the relative density and mechanical properties of the sintered body are low. In addition, traditional toughening phases (such as silicon carbide, titanium carbide, etc.) are difficult to be uniformly distributed and fully contact with ultrafine boron carbide, further restricting the densification of the ceramic body and the toughening effect of the toughening agent. Therefore, how to effectively solve the agglomeration problem of ultrafine boron carbide and achieve the uniform distribution of the toughening phase is a key technical problem in the current field of boron carbide ceramic preparation. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to propose a method for preparing ultrafine boron carbide spray granulation powder to solve the problems that ultrafine boron carbide is easy to agglomerate, and traditional toughening agents are difficult to fully contact with ultrafine boron carbide, which restricts the densification of the ceramic body and the toughening effect of the toughening agent.

[0005] Based on the above purpose, the present invention provides a method for preparing ultrafine boron carbide spray granulation powder, including the following steps:

[0006] (1) Modify ultrafine boron carbide with vinyltriethoxysilane to obtain vinylated ultrafine boron carbide;

[0007] (2) Place the flask in an ice-water bath, then introduce nitrogen to isolate air. After 8 - 12 min, add n-hexane, start stirring, stir for 5 - 20 min, then add methyldichlorosilane and dimethyldichlorosilane, continue stirring for 20 - 40 min, introduce ammonia gas, continue stirring for 4 - 6 h, turn off the ammonia gas, then continue stirring for 20 - 40 min, turn off the nitrogen, filter by suction, distill to obtain a nitrogen-silane oligomer;

[0008] (3) Under a nitrogen atmosphere, add vinylated ultrafine boron carbide to the nitrogen-silane oligomer, stir for 20 - 40 min, then perform high-temperature crosslinking, grind and sieve to obtain a boron carbide composite powder;

[0009] (4) Add boron carbide composite powder and tetrabutyl titanate into deionized water, ball mill, sieve the slurry, spray granulate, and sieve the powder to obtain ultrafine boron carbide spray granulated powder.

[0010] Preferably, in the step (1), the weight ratio of vinyltriethoxysilane to ultrafine boron carbide is 0.05 - 0.2:10.

[0011] Preferably, in the step (1), the mesh number of the ultrafine boron carbide is 10000 - 14000 mesh.

[0012] Preferably, in the step (2), the addition amount of n - hexane is 8 - 12 times the total weight of methyl dichlorosilane and dimethyldichlorosilane.

[0013] Preferably, in the step (2), the content of methyl dichlorosilane in methyl dichlorosilane and dimethyldichlorosilane is 65wt - 75wt%.

[0014] Preferably, in the step (2), the flow rate of nitrogen is 0.1 - 1L / min, and the flow rate of ammonia is 0.3 - 0.5L / min.

[0015] Preferably, in the step (3), the weight ratio of vinylated ultrafine boron carbide to nitrogen - silicon oligomer is 10:0.8 - 1.2.

[0016] Preferably, in the step (3), the high - temperature cross - linking is to heat from room temperature to 370 - 380℃ at a rate of 5 - 20℃ / min and keep the temperature for 7 - 9h.

[0017] Preferably, in the step (4), the weight ratio of boron carbide composite powder, tetrabutyl titanate and deionized water is 10:0.1 - 0.3:8 - 12.

[0018] Preferably, in the step (4), the ball - to - material ratio of ball milling is 4:1, the ball - milling time is 20 - 28 h, the inlet air temperature of spray granulation is 180 - 200℃, the outlet air temperature is 80 - 100℃, the rotation speed of the feeding pump is 70 - 90rpm, and the vacuum degree is 0.25 - 0.35KPa.

[0019] The beneficial effects of the present invention:

[0020] The present invention significantly improves the comprehensive properties of boron carbide ceramics by preparing ultrafine boron carbide spray granulation powder. Compared with the ceramic body prepared by directly sintering ultrafine boron carbide, the ceramic body prepared by using the spray granulation powder of the present invention has a higher relative density, a flexural strength of more than 480 MPa, and a fracture toughness of more than 6.5 MPa·m¹ / ². This is mainly due to the in-situ generated titanium-based and silicon-based reinforcing phases during the sintering process, which play a pinning role at the grain boundaries, refine the grains and disperse the crack propagation paths, thereby improving the mechanical properties of the ceramics.

[0021] The vinyl modification of boron carbide in the present invention further improves the relative density and mechanical properties of the ceramic body. The vinyl modification reduces the surface energy of boron carbide, reduces the agglomeration phenomenon, and through cross-linking with the highly active Si-H groups in the nitrogen silane oligomer, the nitrogen silane oligomer is uniformly coated on the surface of boron carbide, and plays a full role in promoting sintering during the sintering process, thereby improving the flexural strength and fracture toughness.

[0022] The present invention uses tetrabutyl titanate as a binder, which significantly improves the relative density, Vickers hardness, flexural strength and fracture toughness of the ceramics prepared from the spray granulation powder. On the one hand, tetrabutyl titanate as a binder increases the green density, and on the other hand, it provides a titanium source and a carbon source, which helps to in-situ generate titanium-based and silicon-based reinforcing phases and further enhance the comprehensive properties of the ceramics. Specific Embodiments

[0023] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0024] In the specific embodiments of the present invention, the mesh number of the ultrafine boron carbide is 12,500 mesh.

[0025] Example 1:

[0026] (1) Add 0.05 g of vinyltriethoxysilane to a mixed solution of 90 g of absolute ethanol and 30 g of deionized water, stir for 20 min, then add 10 g of ultrafine boron carbide, ultrasonicate for 10 min, heat up to 60 °C, stir for 5 h, wash with water, wash with alcohol, and dry to obtain vinyl-modified ultrafine boron carbide;

[0027] (2) Place the flask in an ice-water bath at 0 °C, then introduce nitrogen to isolate the air, the ammonia gas flow rate is 0.1 L / min, after 12 min, add 8 g of n-hexane, stir for 5 min, then add 0.65 g of methyldichlorosilane and 0.35 g of dimethyldichlorosilane, continue to stir for 20 min, introduce ammonia gas, the ammonia gas flow rate is 0.3 L / min, continue to stir for 4 h, turn off the ammonia gas, then continue to stir for 20 min, turn off the nitrogen, filter by suction, distill to obtain the nitrogen silane oligomer;

[0028] (3) Under a nitrogen atmosphere, 10 g of vinyl-functionalized ultrafine boron carbide was added to 0.8 g of a nitrogen-silane oligomer, and the mixture was stirred for 20 min. Then, the temperature was raised from room temperature to 370 °C at a rate of 5 °C / min and held for 7 h. The mixture was ground and passed through a 100-mesh sieve to obtain a boron carbide composite powder;

[0029] (4) 10 g of the boron carbide composite powder and 0.1 g of tetrabutyl titanate were added to 8 g of deionized water, and the mixture was placed in a ball-milling barrel equipped with boron carbide balls for ball milling. The ball-to-material ratio was 4:1, and the ball-milling time was 20 h. Then, the ball-milled slurry was passed through an 80-mesh sieve and spray granulated in a centrifugal spray drying tower. The inlet air temperature was 180 °C, the outlet air temperature was 80 °C, the feed pump speed was 70 rpm, and the vacuum degree was 0.25 KPa. After spray granulation, the powder was passed through a 40-mesh sieve to obtain an ultrafine boron carbide spray granulated powder.

[0030] Example 2:

[0031] (1) 0.1 g of vinyltriethoxysilane was added to a mixed solution of 90 g of absolute ethanol and 30 g of deionized water, and the mixture was stirred for 30 min. Then, 10 g of ultrafine boron carbide was added, and the mixture was ultrasonicated for 20 min, heated to 60 °C, and stirred for 6 h. After washing with water, washing with alcohol, and drying, vinyl-functionalized ultrafine boron carbide was obtained;

[0032] (2) The flask was placed in an ice-water bath at 0 °C, and then nitrogen was introduced to isolate the air. The ammonia gas flow rate was 0.5 L / min. After 10 min, 10 g of n-hexane was added and stirred for 10 min. Then, 0.7 g of methyldichlorosilane and 0.3 g of dimethyldichlorosilane were added, and stirring was continued for 30 min. Ammonia gas was introduced, and the ammonia gas flow rate was 0.4 L / min. Stirring was continued for 5 h, the ammonia gas was turned off, and stirring was continued for 30 min. The nitrogen was turned off, and the mixture was filtered by suction and distilled to obtain a nitrogen-silane oligomer;

[0033] (3) Under a nitrogen atmosphere, 10 g of vinyl-functionalized ultrafine boron carbide was added to 1 g of the nitrogen-silane oligomer, and the mixture was stirred for 30 min. Then, the temperature was raised from room temperature to 380 °C at a rate of 10 °C / min and held for 8 h. The mixture was ground and passed through a 100-mesh sieve to obtain a boron carbide composite powder;

[0034] (4) 10 g of the boron carbide composite powder and 0.2 g of tetrabutyl titanate were added to 10 g of deionized water, and the mixture was placed in a ball-milling barrel equipped with boron carbide balls for ball milling. The ball-to-material ratio was 4:1, and the ball-milling time was 24 h. Then, the ball-milled slurry was passed through an 80-mesh sieve and spray granulated in a centrifugal spray drying tower. The inlet air temperature was 190 °C, the outlet air temperature was 90 °C, the feed pump speed was 80 rpm, and the vacuum degree was 0.3 KPa. After spray granulation, the powder was passed through a 40-mesh sieve to obtain an ultrafine boron carbide spray granulated powder.

[0035] Example 3:

[0036] (1) Add 0.2 g of vinyltriethoxysilane to a mixed solution of 90 g of absolute ethanol and 30 g of deionized water, stir for 40 min, then add 10 g of ultrafine boron carbide, sonicate for 30 min, heat up to 60 °C, stir for 7 h, wash with water, wash with alcohol, and dry to obtain vinyl-functionalized ultrafine boron carbide;

[0037] (2) Place the flask in an ice-water bath at 0 °C, then introduce nitrogen to isolate the air. The ammonia gas flow rate is 1 L / min. After 8 min, add 12 g of n-hexane, stir for 20 min, then add 0.75 g of methyldichlorosilane and 0.25 g of dimethyldichlorosilane, continue stirring for 40 min, introduce ammonia gas, the ammonia gas flow rate is 0.5 L / min, continue stirring for 6 h, turn off the ammonia gas, then continue stirring for 40 min, turn off the nitrogen, filter by suction, and distill to obtain a nitrogen-silane oligomer;

[0038] (3) Under a nitrogen atmosphere, add 10 g of vinyl-functionalized ultrafine boron carbide to 1.2 g of the nitrogen-silane oligomer, stir for 40 min, then heat from room temperature to 390 °C at a rate of 20 °C / min, hold for 9 h, grind through a 100-mesh sieve to obtain a boron carbide composite powder;

[0039] (4) Add 10 g of the boron carbide composite powder and 0.3 g of tetrabutyl titanate to 12 g of deionized water, put it into a ball-milling barrel equipped with boron carbide ball mills for ball milling. The ball-to-material ratio is 4:1, and the ball-milling time is 28 h. Then, sieve the ball-milled slurry through an 80-mesh sieve, and then perform spray granulation in a centrifugal spray drying tower. The inlet air temperature is 200 °C, the outlet air temperature is 100 °C, the feeding pump speed is 90 rpm, the vacuum degree is 0.35 KPa. After spray granulation, sieve the powder through a 40-mesh sieve to obtain an ultrafine boron carbide spray granulation powder.

[0040] Comparative Example 1:

[0041] The difference between Comparative Example 1 and Example 2 is that the ultrafine boron carbide was not subjected to vinyl-functionalization modification;

[0042] The specific steps are as follows:

[0043] (1) Place the flask in an ice-water bath at 0 °C, then introduce nitrogen to isolate the air. The ammonia gas flow rate is 0.5 L / min. After 10 min, add 10 g of n-hexane, stir for 10 min, then add 0.7 g of methyldichlorosilane and 0.3 g of dimethyldichlorosilane, continue stirring for 30 min, introduce ammonia gas, the ammonia gas flow rate is 0.4 L / min, continue stirring for 5 h, turn off the ammonia gas, then continue stirring for 30 min, turn off the nitrogen, filter by suction, and distill to obtain a nitrogen-silane oligomer;

[0044] (2) Under a nitrogen atmosphere, 10 g of ultrafine boron carbide was added to 1 g of a nitrogen-silane oligomer, stirred for 30 min, then heated from room temperature to 380 °C at a rate of 10 °C / min, held for 8 h, ground through a 100-mesh sieve to obtain a boron carbide composite powder;

[0045] (3) 10 g of the boron carbide composite powder and 0.2 g of tetrabutyl titanate were added to 10 g of deionized water, placed in a ball mill barrel equipped with boron carbide balls for ball milling, the ball-to-material ratio was 4:1, the ball milling time was 24 h, then the milled slurry was passed through an 80-mesh sieve, and then spray granulation was carried out in a centrifugal spray drying tower. The inlet air temperature was 190 °C, the outlet air temperature was 90 °C, the feed pump speed was 80 rpm, the vacuum was 0.3 KPa. After spray granulation, the powder was passed through a 40-mesh sieve to obtain an ultrafine boron carbide spray granulation powder.

[0046] Comparative Example 2:

[0047] The difference between Comparative Example 2 and Example 2 is that: in step (2), methyl dichlorosilane was replaced with dimethyldichlorosilane;

[0048] The specific steps are as follows:

[0049] (1) 0.1 g of vinyltriethoxysilane was added to a mixed solution of 90 g of absolute ethanol and 30 g of deionized water, stirred for 30 min, then 10 g of ultrafine boron carbide was added, ultrasonicated for 20 min, heated to 60 °C, stirred for 6 h, washed with water, washed with alcohol, and dried to obtain vinyl-functionalized ultrafine boron carbide;

[0050] (2) The flask was placed in an ice-water bath at 0 °C, then nitrogen was introduced to isolate air, the ammonia flow rate was 0.5 L / min, after 10 min, 10 g of n-hexane was added, stirred for 10 min, then 1 g of dimethyldichlorosilane was added, continued to stir for 30 min, ammonia was introduced, the ammonia flow rate was 0.4 L / min, continued to stir for 5 h, the ammonia was turned off, and then continued to stir for 30 min, the nitrogen was turned off, filtered by suction, and distilled to obtain a nitrogen-silane oligomer;

[0051] (3) Under a nitrogen atmosphere, 10 g of vinyl-functionalized ultrafine boron carbide was added to 1 g of the nitrogen-silane oligomer, stirred for 30 min, then heated from room temperature to 380 °C at a rate of 10 °C / min, held for 8 h, ground through a 100-mesh sieve to obtain a boron carbide composite powder;

[0052] (4) Add 10 g of boron carbide composite powder and 0.2 g of tetrabutyl titanate to 10 g of deionized water, put it into a ball mill barrel equipped with boron carbide balls for ball milling, the ball-to-material ratio is 4:1, the ball milling time is 24 h, then sieve the ball-milled slurry through an 80-mesh sieve, and then perform spray granulation in a centrifugal spray drying tower. The inlet air temperature is 190 °C, the outlet air temperature is 90 °C, the feeding pump speed is 80 rpm, the vacuum degree is 0.3 KPa. After spray granulation, sieve the powder through a 40-mesh sieve to obtain ultrafine boron carbide spray granulated powder.

[0053] Comparative Example 3:

[0054] The difference between Comparative Example 3 and Example 2 is that: in step (2), dimethyldichlorosilane is replaced by methyldichlorosilane;

[0055] The specific steps are as follows:

[0056] (1) Add 0.1 g of vinyltriethoxysilane to a mixed solution of 90 g of absolute ethanol and 30 g of deionized water, stir for 30 min, then add 10 g of ultrafine boron carbide, ultrasonicate for 20 min, heat up to 60 °C, stir for 6 h, wash with water, wash with alcohol, and dry to obtain vinylated ultrafine boron carbide;

[0057] (2) Place the flask in an ice-water bath at 0 °C, then introduce nitrogen to isolate air, the ammonia gas flow rate is 0.5 L / min. After 10 min, add 10 g of n-hexane, stir for 10 min, then add 1 g of methyldichlorosilane, continue to stir for 30 min, introduce ammonia gas, the ammonia gas flow rate is 0.4 L / min, continue to stir for 5 h, turn off the ammonia gas, then continue to stir for 30 min, turn off the nitrogen, filter by suction, and distill to obtain a nitrogen-silane oligomer;

[0058] (3) Under a nitrogen atmosphere, add 10 g of vinylated ultrafine boron carbide to 1 g of nitrogen-silane oligomer, stir for 30 min, then heat from room temperature to 380 °C at a rate of 10 °C / min, keep warm for 8 h, grind and sieve through a 100-mesh sieve to obtain boron carbide composite powder;

[0059] (4) Add 10 g of boron carbide composite powder and 0.2 g of tetrabutyl titanate to 10 g of deionized water, put it into a ball mill barrel equipped with boron carbide balls for ball milling, the ball-to-material ratio is 4:1, the ball milling time is 24 h, then sieve the ball-milled slurry through an 80-mesh sieve, and then perform spray granulation in a centrifugal spray drying tower. The inlet air temperature is 190 °C, the outlet air temperature is 90 °C, the feeding pump speed is 80 rpm, the vacuum degree is 0.3 KPa. After spray granulation, sieve the powder through a 40-mesh sieve to obtain ultrafine boron carbide spray granulated powder.

[0060] Comparative Example 4:

[0061] The difference between Comparative Example 4 and Example 2 is that in step (4), tetrabutyl titanate was not added;

[0062] The specific steps are as follows:

[0063] (1) Add 0.1 g of vinyltriethoxysilane to a mixed solution of 90 g of absolute ethanol and 30 g of deionized water, stir for 30 min, then add 10 g of ultrafine boron carbide, ultrasonicate for 20 min, heat up to 60 °C, stir for 6 h, wash with water, wash with alcohol, and dry to obtain vinylated ultrafine boron carbide;

[0064] (2) Place the flask in an ice-water bath at 0 °C, then introduce nitrogen to isolate air, the ammonia flow rate is 0.5 L / min. After 10 min, add 10 g of n-hexane, stir for 10 min, then add 0.7 g of methyldichlorosilane and 0.3 g of dimethyldichlorosilane, continue to stir for 30 min, introduce ammonia, the ammonia flow rate is 0.4 L / min, continue to stir for 5 h, turn off the ammonia, then continue to stir for 30 min, turn off the nitrogen, filter by suction, distill to obtain a nitrogen-silane oligomer;

[0065] (3) Under a nitrogen atmosphere, add 10 g of vinylated ultrafine boron carbide to 1 g of the nitrogen-silane oligomer, stir for 30 min, then heat from room temperature to 380 °C at a rate of 10 °C / min, hold for 8 h, grind through a 100-mesh sieve to obtain a boron carbide composite powder;

[0066] (4) Add 10 g of the boron carbide composite powder to 10 g of deionized water, place it in a ball mill barrel equipped with boron carbide ball mills for ball milling, the ball-to-material ratio is 4:1, the ball milling time is 24 h, then sieve the ball-milled slurry through an 80-mesh sieve, and then perform spray granulation in a centrifugal spray drying tower, the inlet air temperature is 190 °C, the outlet air temperature is 90 °C, the feed pump speed is 80 rpm, the vacuum degree is 0.3 KPa. After spray granulation, sieve the powder through a 40-mesh sieve to obtain an ultrafine boron carbide spray granulation powder.

[0067] Comparative Example 5:

[0068] The difference between Comparative Example 5 and Example 2 is that the boron carbide composite powder in step (4) is replaced with ultrafine boron carbide;

[0069] The specific steps are as follows:

[0070] Add 10 g of ultrafine boron carbide and 0.2 g of polyvinyl alcohol 1788 to 10 g of deionized water, put it into a ball milling barrel equipped with boron carbide ball mills for ball milling. The ball-to-material ratio is 4:1, and the ball milling time is 24 h. Then, sieve the ball-milled slurry through a 80-mesh sieve, and perform spray granulation in a centrifugal spray drying tower. The inlet air temperature is 190 °C, the outlet air temperature is 90 °C, the feeding pump speed is 80 rpm, the vacuum degree is 0.3 KPa. After spray granulation, sieve the powder through a 40-mesh sieve to obtain ultrafine boron carbide spray granulated powder.

[0071] Performance test:

[0072] Preparation of ceramic body: Pour the ultrafine boron carbide spray granulated powder prepared in the examples and comparative examples into a mold, and the forming pressure is 2 T / cm 2 to obtain a green body. Then, put the green body into a sintering furnace, heat it from room temperature to 600 °C at a rate of 5 °C / min, hold for 2 h, then heat it from 600 °C to 1500 °C at a rate of 10 °C / min, and then introduce argon for protection, heat it from 1500 °C to 2200 °C at a rate of 10 °C / min, and hold for 3 h to obtain a ceramic body.

[0073] Relative density: The relative density of the ceramic bodies corresponding to the examples and comparative examples was measured by the Archimedes drainage method, and the results are shown in Table 1.

[0074] Hardness: The Vickers hardness of the ceramic bodies corresponding to the examples and comparative examples was measured by a microhardness tester, and the results are shown in Table 1.

[0075] Flexural strength: The flexural strength of the ceramic bodies corresponding to the examples and comparative examples was measured by a double-column bench-top material testing machine, and the results are shown in Table 1.

[0076] Fracture toughness: The fracture toughness of the ceramic bodies corresponding to the examples and comparative examples was measured by the single-edge notched beam method, with a notch depth of 0.5 mm and a width of 0.2 m, and the results are shown in Table 1.

[0077] Table 1 Performance test results

[0078]

[0079] Data analysis:

[0080] From the data of Examples 1-3 and Comparative Example 5 in Table 1, it can be seen that compared with the ceramic body prepared by directly sintering ultrafine boron carbide, the ultrafine boron carbide spray granulated powder provided by the present invention has a significantly increased relative density. Although the Vickers hardness decreases slightly, its flexural strength reaches above 480 MPa, and the fracture toughness reaches 6.5 MPa·m 1 / 2The above is mainly because the in-situ generated titanium-based and silicon-based reinforcing phases during sintering can play a pinning role at the grain boundaries of boron carbide as the sintering temperature increases, hinder the movement of boron carbide grain boundaries, effectively refine the grains, disperse the crack propagation path at the same time, reduce the crack propagation energy, and thus improve the comprehensive performance of the product.

[0081] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that the vinyl modification of boron carbide helps to increase the relative density of the ceramic body, overcome the problem of a significant decrease in Vickers hardness, and further improve the flexural strength and fracture toughness. This is mainly because the vinyl-modified ultrafine boron carbide reduces the surface energy of the ultrafine boron carbide. On the one hand, it reduces the agglomeration of the ultrafine boron carbide, and on the other hand, it improves its dispersion in the silazane oligomer. Moreover, the vinyl group can crosslink with the highly active Si-H groups in the silazane oligomer, so that the silazane oligomer uniformly wraps the surface of the ultrafine boron carbide and fully plays a sintering aid role during the subsequent sintering process.

[0082] From the data of Example 2 and Comparative Example 2 in Table 1, it can be seen that when only dimethyldichlorosilane is used, the relative density of the ceramic body is low, and both the flexural strength and fracture toughness decrease. This is mainly because the silazane oligomer formed by only using dimethyldichlorosilane lacks highly active Si-H groups and is difficult to effectively wrap the surface of the ultrafine boron carbide through crosslinking. And during the subsequent sintering process, large-particle-size silicon-based reinforcing phases will be formed, resulting in a decrease in the contact area between the reinforcing phase and the ultrafine boron carbide, and it is difficult to fully play the role of sintering aid and strengthening.

[0083] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that when only methyldichlorosilane is used, the Vickers hardness of the ceramic body decreases significantly. This is mainly because the carbon content in methyldichlorosilane is low, and the contents of high-hardness silicon carbide and titanium carbide generated during the sintering process are low, thus reducing the Vickers hardness.

[0084] From the data of Example 2 and Comparative Example 4 in Table 1, it can be seen that the addition of tetrabutyl titanate effectively improves the relative density, Vickers hardness, flexural strength and fracture toughness of the ceramic. This is mainly because tetrabutyl titanate, on the one hand, acts as a binder to increase the green density of the green body, and on the other hand, provides a titanium source and a carbon source, which helps to in-situ generate titanium-based and silicon-based reinforcing phases.

[0085] Those of ordinary skill in the art should understand that the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing ultrafine boron carbide spray granulation powder, characterized in that: The following steps are involved: (1) Using vinyl triethoxysilane to modify ultrafine boron carbide to obtain olefinated ultrafine boron carbide; (2) Place the flask in an ice water bath, then introduce nitrogen to isolate the air, add n-hexane after 8-12 minutes, start stirring, stir for 5-20 minutes, then add methyldichlorosilane and dimethyldichlorosilane, continue stirring for 20-40 minutes, introduce ammonia, continue stirring for 4-6 hours, turn off the ammonia, continue stirring for 20-40 minutes, turn off the nitrogen, filter, and distill to obtain nitrogen silane oligomers; (3) Under a nitrogen atmosphere, add olefin-modified ultrafine boron carbide to nitrogen silane oligomer, stir for 20-40 minutes, cross-link at high temperature, grind and sieve to obtain boron carbide composite powder; (4) adding boron carbide composite powder and tetrabutyl titanate into deionized water, ball milling, sieving the slurry, spray granulating, and sieving the powder to obtain ultrafine boron carbide spray granulated powder; In step (2), the amount of n-hexane added is 8-12 times the total weight of methyldichlorosilane and dimethyldichlorosilane; In the step (2), the content of methyldichlorosilane in methyldichlorosilane and dimethyldichlorosilane is 65wt%-75wt%; In step (2), the flow rate of nitrogen is 0.1-1 L / min, and the flow rate of ammonia is 0.3-0.5 L / min; In the step (3), the weight ratio of olefinated ultrafine boron carbide to nitrogen silane oligomer is 10:0.8-1.

2.

2. The method for preparing ultrafine boron carbide spray granulation powder according to claim 1, characterized in that: In the step (1), the weight ratio of vinyltriethoxysilane to ultrafine boron carbide is 0.05-0.2:

10.

3. The method for preparing ultrafine boron carbide spray granulation powder according to claim 1, characterized in that: The mesh size of the ultrafine boron carbide in step (1) is 10000-14000 mesh.

4. The method for preparing ultrafine boron carbide spray granulation powder according to claim 1, characterized in that: In the step (3), the high temperature crosslinking is carried out by heating the temperature from room temperature to 370-380°C at a rate of 5-20°C / min and keeping the temperature for 7-9h.

5. The method for preparing ultrafine boron carbide spray granulation powder according to claim 1, characterized in that: In the step (4), the weight ratio of the boron carbide composite powder, tetrabutyl titanate and deionized water is 10:0.1-0.3:8-12.

6. The method for preparing ultrafine boron carbide spray granulation powder according to claim 1, characterized in that: In the step (4), the ball-to-material ratio of the ball milling is 4:1, the ball milling time is 20-28 h, the inlet air temperature of the spray granulation is 180-200°C, the outlet air temperature is 80-100°C, the feed pump speed is 70-90rpm, and the vacuum degree is 0.25-0.35KPa.

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