Method for preparing composite titanium carbide from metatitanic acid

Abstract

The application discloses a method for preparing composite titanium carbide from metatitanic acid, and belongs to the technical field of titanium carbide preparation, aiming to solve the problem of hardness and wear resistance deterioration of titanium carbide caused by sulfur doping during carbothermal reduction of metatitanic acid. The method comprises the following steps: washing and activating metatitanic acid, preparing carbon-coated lanthanum hexaboride and vanadium carbide composite powder, ultrasonic dispersion, rotary evaporation to obtain a tight mixture, three-stage heating carbothermal reduction under high-purity argon, and rapid cooling to obtain the composite titanium carbide. The application utilizes in-situ sulfur fixation of lanthanum hexaboride at high temperature and solid solution strengthening of vanadium carbide to form a (Ti, V)(C, B) quaternary solid solution, and realizes the integration of sulfur removal, solid solution and strengthening through three-stage heating. The sulfur content of the obtained product is less than or equal to 20 ppm, the Vickers hardness is greater than or equal to 30 GPa, and the wear rate is significantly reduced. The process uses low-cost metatitanic acid as raw material, has a low additive dosage and a low reaction temperature, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of titanium carbide preparation technology, specifically relating to a method for preparing composite titanium carbide from metatitanic acid. Background Technology

[0002] Titanium carbide (TiC) is a typical transition metal carbide with a NaCl-type cubic crystal structure. It has a high melting point (about 3140℃), high hardness (Mohs hardness 9-10), high Young's modulus, excellent chemical stability, and good electrical and thermal conductivity. It has broad application prospects in cutting tools, wear-resistant coatings, aerospace components, foam ceramics, and infrared radiation ceramic materials.

[0003] Among various methods for preparing titanium carbide, the carbothermal reduction method is widely used due to its wide availability of raw materials, relatively simple process, and suitability for large-scale production. This method uses titanium dioxide (TiO2) as the titanium source and carbon black or graphite as the reducing agent, generating TiC through a carbothermal reduction reaction under a high-temperature, inert atmosphere. Industrially, to reduce raw material costs, metatitanic acid (TiO2·xH2O), an intermediate product in the sulfuric acid process for titanium dioxide production, is often used as the titanium source. Metatitanic acid has the advantages of high reactivity and low cost, and its use has been reported in the carbothermal reduction preparation of TiC.

[0004] However, existing technologies generally overlook a fundamental problem that seriously affects the quality of TiC products: the residual and doped sulfur in metatitanic acid. Metatitanic acid is usually obtained by hydrolyzing titanium liquid (TiOSO4) in the sulfuric acid process for titanium dioxide, and it is difficult to completely remove sulfate ions (SO4) during the production process. 2- These residual sulfate ions will thermally decompose during the subsequent high-temperature carbothermic reduction process, releasing sulfur elements that can replace carbon atoms in the face-centered cubic lattice of TiC, forming TiC. 1-X S X Solid solutions. Even when the sulfur content is only at the ppm level, its perturbation of the TiC lattice will lead to a significant decrease in performance—the radius of a sulfur atom (about 1.04 Å) is significantly larger than that of a carbon atom (about 0.77 Å). Lattice distortion disrupts the network structure of Ti–C covalent bonds, resulting in a decrease in the hardness and deterioration of the wear resistance of TiC.

[0005] More seriously, sulfur doping introduces impurity energy levels into the TiC band structure, reducing electron mobility. At the same time, sulfur is easily oxidized at high temperatures to form SO2 gas, which escapes and leaves defect channels on the TiC surface, accelerating the oxidation and corrosion of the material under high-temperature conditions. This greatly limits the application potential of TiC in high-temperature structural materials, aerospace thermal protection coatings, and other fields.

[0006] To address the aforementioned problems, existing technologies lack effective solutions. A few studies have proposed removing sulfur impurities from TiC products through post-treatment methods such as high-temperature vacuum processing or acid washing. However, these "end-stage impurity removal" methods are not only inefficient and costly, but also fail to fundamentally block the path of sulfur doping into the TiC lattice during carbothermal reduction. Therefore, how to actively suppress sulfur doping in metatitanic acid during the carbothermal reduction preparation of titanium carbide is the technical problem this application aims to solve. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing composite titanium carbide from metatitanic acid, so as to solve the technical problem that the titanium carbide prepared by the carbothermal reduction method of metatitanic acid has poor hardness and wear resistance due to sulfur doping.

[0008] This invention provides a method for preparing composite titanium carbide from metatitanic acid, comprising the following steps: S1. Take metatitanic acid and wash it until the pH is 4.0-7.0, disperse it in anhydrous ethanol, add oleic acid, stir and dry to obtain activated metatitanic acid powder; the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid; S2. Lanthanum hexaboride and vanadium carbide are mixed at a mass ratio of 1:(4.5-5.5), and carbon black is added. The total amount of carbon black added is 30%-40% of the mass of titanium dioxide in metatitanic acid. The mixture is ball-milled using anhydrous ethanol as the medium and dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder. The amount of lanthanum hexaboride is 0.1% of the mass of titanium dioxide in metatitanic acid, and the amount of vanadium carbide is 0.5% of the mass of titanium dioxide in metatitanic acid. S3. The activated metatitanic acid powder obtained in S1 is dispersed in anhydrous ethanol, and the carbon-coated lanthanum hexaboride and vanadium carbide composite powder obtained in S2 is added. After ultrasonic dispersion, the ethanol is removed by rotary evaporation to obtain a close mixture of metatitanic acid and carbon-coated composite additive. S4. Place the compact mixture obtained in step S3 in an inert gas and proceed as follows: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1-1.5 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2-2.5 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.5-3 hours; S5. Cool to room temperature at a rate of 20℃ / min to obtain the composite titanium carbide.

[0009] Furthermore, in step S2, the ball-to-material mass ratio during ball milling is (8-12):1, the ball milling speed is 300-500 rpm, and the ball milling time is 8-15 h.

[0010] Furthermore, in step S3, the solid content of the activated metatitanic acid powder dispersed in anhydrous ethanol is 15wt%, the ultrasonic dispersion time is 15-30 minutes, and the ultrasonic frequency is 40-80kHz.

[0011] Furthermore, in step S5, the cooling rate is 15-25°C / min, and the cooling is carried out in a flowing inert gas.

[0012] Furthermore, in S4 and S5, the inert gas used is argon, the gas flow rate is 100-500 mL / min, and the purity of the argon is not less than 99.999%.

[0013] Furthermore, the sulfur content of the composite titanium carbide is not higher than 20 ppm, and the Vickers hardness is not lower than 30 GPa.

[0014] Furthermore, the drying in step S1 is vacuum drying at 50°C to 80°C for 4 to 8 hours.

[0015] Furthermore, the process parameters for stirring in step S1 are: stirring speed 200-400 rpm, stirring time 30-60 min, and stirring temperature at room temperature.

[0016] Furthermore, the carbon black used in step S2 is nanoscale conductive carbon black with a particle size range of 20-50 nm and a purity of ≥99.5%.

[0017] Further, the process parameters for rotary evaporation in step S3 are as follows: First, evaporate for 15-25 minutes at an evaporation temperature of 40-50℃, a vacuum degree of 0.06-0.075MPa, and a rotation speed of 60-80rpm until the solvent distillation rate slows down significantly; then, increase the evaporation temperature to 55-60℃, gradually increase the vacuum degree to 0.08-0.09MPa, increase the rotation speed to 80-120rpm, and continue evaporating for 5-10 minutes until free-flowing dry powder is obtained.

[0018] The beneficial effects of this invention are as follows: 1. Effectively suppresses sulfur doping during the carbothermic reduction process of titanate. To address the technical problem of residual sulfate ions in metatitanic acid due to the sulfuric acid process and the easy entry of sulfur into the TiC lattice during high-temperature carbothermic reduction, leading to performance degradation, this invention introduces lanthanum hexaboride (LaB6) into the metatitanic acid carbothermic reduction system. At a low temperature of 800℃, lanthanum atoms on the LaB6 surface directly react with SO2 generated from sulfate decomposition at the gas-solid interface, generating ultrastable La2S3, achieving immediate in-situ capture of sulfur and blocking its diffusion path into the TiO2 lattice. As the temperature rises to 1450℃, boron atoms in the LaB6 lattice diffuse into the newly formed TiC in a solid phase and occupy carbon vacancies, increasing the local lanthanum chemical potential and further locking in residual sulfur. At a high temperature of 1500℃, vanadium atoms in the VC (vitamin C) cooperate in solid-state dissolution, driving the remaining sulfur to La2S3 or grain boundaries for final fixation; simultaneously, a three-stage heating process (800℃ pre-desulfurization, 1450℃ main reduction, and 1500℃ solid-state dissolution) achieves efficient removal of sulfur impurities. The sulfur content of the resulting composite titanium carbide can be controlled below 20 ppm, which is much lower than the 500-1000 ppm of conventional processes. This invention can efficiently complete desulfurization in the range of 800-1500℃ through the atomic rearrangement of LaB6 surface and the gradient diffusion of boron.

[0019] 2. Simultaneously and significantly improves the hardness and wear resistance of titanium carbide. This invention employs a dual-component synergistic design of LaB6 and vanadium carbide (VC), enabling boron and vanadium atoms to sequentially enter the TiC lattice during carbothermic reduction, forming a (Ti,V)(C,B) quaternary solid solution. Compared to a single solid solution or pure TiC, the dual solid solution produces greater lattice distortion, significantly increasing the resistance to dislocation movement; unreacted LaB6, VC, and La2S3 particles are uniformly distributed at the grain boundaries, generating a second-phase pinning effect. Experiments show that the Vickers hardness of the composite titanium carbide can reach over 30 GPa, and the wear rate is reduced by more than 60% compared to pure TiC, overcoming the technical bias of existing technologies that "difficulty in simultaneously achieving desulfurization and reinforcement."

[0020] 3. The process is simple and the cost is low, making it suitable for industrial production. This invention directly uses metatitanic acid, a byproduct of the sulfuric acid process for titanium dioxide production, as the titanium source, eliminating the need for pre-synthesizing TiC powder and additional pre-calcination or acid washing desulfurization steps. The additives LaB6 and VC are used in extremely low amounts (only 0.08-0.12% and 0.4-0.6% of the TiO2 mass, respectively), with a maximum reaction temperature of only 1500℃, lower than the 1600-1700℃ required for traditional carbothermal reduction. Uniform dispersion of trace additives is achieved through carbon-coated ball milling and electrostatic self-assembly, resulting in good process repeatability and easy scale-up production.

[0021] 4. Innovatively, it achieves the integrated process of "desulfurization-solution-enhancement" in the carbothermic reduction process. Unlike existing technologies that employ separate post-treatment desulfurization or the addition of reinforcing phases, this invention couples the desulfurization function of LaB6 with the solid solution strengthening function of VC within the same carbothermic reduction process. A three-stage temperature gradient is used to match the three reaction stages: sulfate decomposition, TiC formation, and sequential solid solution of B and V. Each step works synergistically without interference. This integrated design significantly simplifies the process flow while yielding a composite material with ultra-low sulfur content and high mechanical properties, representing a significant technological breakthrough in this field. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0023] Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0025] The features and performance of the present invention will be further described in detail below with reference to embodiments. Example 1 S1, metatitanic acid activation: Take 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2), wash the metatitanic acid to pH=4.0, disperse it in anhydrous ethanol, add oleic acid, the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid, stir at 200rpm for 30min at room temperature, and then vacuum dry at 50℃ for 4h to obtain activated metatitanic acid powder.

[0026] S2. Preparation of carbon-coated composite additives: Lanthanum hexaboride and vanadium carbide were mixed at a mass ratio of 1:4.5, with lanthanum hexaboride accounting for 0.08% of the titanium dioxide mass in metatitanic acid and vanadium carbide accounting for 0.4%. Carbon black was added, with the total amount of carbon black accounting for 30% of the titanium dioxide mass in metatitanic acid. Ball milling was performed using anhydrous ethanol as the medium, at a ball-to-particle mass ratio of 8:1, at a speed of 300 rpm for 8 hours, under an argon atmosphere. After ball milling, the mixture was dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder.

[0027] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated composite powder obtained in S2 was added and ultrasonically dispersed at a frequency of 40 kHz for 15 min. Subsequently, it was evaporated in a rotary evaporator at an evaporation temperature of 40 °C, a vacuum of 0.06 MPa, and a rotation speed of 60 rpm for 15 min until the solvent distillation rate slowed down significantly. Then, the evaporation temperature was increased to 55 °C, the vacuum was gradually increased to 0.08 MPa, and the rotation speed was increased to 80 rpm, and evaporation was continued for 5 min until a free-flowing dry powder was obtained, resulting in a close mixture of metatitanic acid and carbon-coated composite additive.

[0028] S4, Three-stage carbothermic reduction: The compact mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 100 mL / min) and the following steps were performed sequentially: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1 hour; Second stage: Increase the temperature to 1450℃ at 8℃ / min and hold for 2 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.5 hours.

[0029] S5, Cooling: The composite titanium carbide was obtained by cooling to room temperature at a rate of 20 °C / min.

[0030] Example 2 S1, metatitanic acid activation: Take 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2), wash the metatitanic acid to pH=7.0, disperse it in anhydrous ethanol, add oleic acid, the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid, stir at 400rpm for 60min at room temperature, and then vacuum dry at 80℃ for 8h to obtain activated metatitanic acid powder.

[0031] S2. Preparation of carbon-coated composite additives: Lanthanum hexaboride and vanadium carbide were mixed at a mass ratio of 1:5.5, with lanthanum hexaboride accounting for 0.12% of the titanium dioxide mass in metatitanic acid and vanadium carbide accounting for 0.6%. Carbon black was added, with the total amount of carbon black accounting for 40% of the titanium dioxide mass in metatitanic acid. Ball milling was performed using anhydrous ethanol as the medium, at a ball-to-particle mass ratio of 12:1, at a speed of 500 rpm for 15 hours under an argon atmosphere. After ball milling, the mixture was dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder.

[0032] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated composite powder obtained in S2 was added and ultrasonically dispersed at 80 kHz for 30 min. Subsequently, it was evaporated in a rotary evaporator at an evaporation temperature of 50 °C, a vacuum of 0.075 MPa, and a rotation speed of 80 rpm for 25 min until the solvent distillation rate slowed down significantly. Then, the evaporation temperature was increased to 60 °C, the vacuum was gradually increased to 0.09 MPa, and the rotation speed was increased to 120 rpm, and evaporation was continued for 10 min until a free-flowing dry powder was obtained, resulting in a close mixture of metatitanic acid and carbon-coated composite additive.

[0033] S4, Three-stage carbothermic reduction: The compact mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 500 mL / min) and the following steps were performed sequentially: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.5 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.5 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 3 hours.

[0034] S5, Cooling: The composite titanium carbide was obtained by cooling to room temperature at a rate of 20 °C / min.

[0035] Example 3 S1, metatitanic acid activation: Take 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2), wash the metatitanic acid to pH=5.5, disperse it in anhydrous ethanol, add oleic acid, the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid, stir at 300rpm for 45min at room temperature, and then vacuum dry at 65℃ for 6h to obtain activated metatitanic acid powder.

[0036] S2. Preparation of carbon-coated composite additives: Lanthanum hexaboride and vanadium carbide were mixed at a mass ratio of 1:5, with lanthanum hexaboride accounting for 0.10% of the titanium dioxide mass in metatitanic acid and vanadium carbide accounting for 0.5%. Carbon black was added, with the total amount of carbon black accounting for 35% of the titanium dioxide mass in metatitanic acid. Anhydrous ethanol was used as the medium, with a ball-to-particle mass ratio of 10:1, a ball milling speed of 400 rpm, and a ball milling time of 11.5 h, all under an argon atmosphere. After ball milling, the mixture was dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder.

[0037] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated composite powder obtained in S2 was added and ultrasonically dispersed at a frequency of 60 kHz for 22.5 min. Subsequently, it was evaporated in a rotary evaporator at an evaporation temperature of 45 °C, a vacuum of 0.07 MPa, and a rotation speed of 70 rpm for 20 min until the solvent distillation rate slowed down significantly. Then, the evaporation temperature was increased to 58 °C, the vacuum was gradually increased to 0.085 MPa, and the rotation speed was increased to 100 rpm, and evaporation was continued for 7 min until a free-flowing dry powder was obtained, resulting in a close mixture of metatitanic acid and carbon-coated composite additive.

[0038] S4, Three-stage carbothermic reduction: The compact mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 300 mL / min) and subjected to the following steps: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.25 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.25 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.75 hours.

[0039] S5, Cooling The composite titanium carbide was obtained by cooling to room temperature at a rate of 20 °C / min.

[0040] Example 4 S1, metatitanic acid activation: Take 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2), wash the metatitanic acid to pH=4.7, disperse it in anhydrous ethanol, add oleic acid, the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid, stir at 250rpm for 40min at room temperature, and then vacuum dry at 55℃ for 5h to obtain activated metatitanic acid powder.

[0041] S2. Preparation of carbon-coated composite additives: Lanthanum hexaboride and vanadium carbide were mixed at a mass ratio of 1:4.7, with lanthanum hexaboride accounting for 0.09% of the titanium dioxide mass in metatitanic acid and vanadium carbide accounting for 0.45%. Carbon black was added, with the total amount of carbon black accounting for 32% of the titanium dioxide mass in metatitanic acid. Ball milling was performed using anhydrous ethanol as the medium, at a ball-to-particle mass ratio of 9:1, at a speed of 350 rpm, for 10 hours, under an argon atmosphere. After ball milling, the mixture was dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder.

[0042] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated composite powder obtained in S2 was added and ultrasonically dispersed at a frequency of 50 kHz for 20 min. Subsequently, it was evaporated in a rotary evaporator at an evaporation temperature of 42 °C, a vacuum of 0.065 MPa, and a rotation speed of 65 rpm for 17 min until the solvent distillation rate slowed down significantly. Then, the evaporation temperature was increased to 56 °C, the vacuum was gradually increased to 0.082 MPa, and the rotation speed was increased to 95 rpm, and evaporation was continued for 6 min until a free-flowing dry powder was obtained, resulting in a close mixture of metatitanic acid and carbon-coated composite additive.

[0043] S4, Three-stage carbothermic reduction: The tight mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 200 mL / min) and the following steps were performed sequentially: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.1 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.1 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.6 hours.

[0044] S5, Cooling: The composite titanium carbide was obtained by cooling to room temperature at a rate of 20 °C / min.

[0045] Example 5 S1, metatitanic acid activation: Take 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2), wash the metatitanic acid to pH=6.2, disperse it in anhydrous ethanol, add oleic acid, the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid, stir at 350rpm for 50min at room temperature, and then vacuum dry at 70℃ for 7h to obtain activated metatitanic acid powder.

[0046] S2. Preparation of carbon-coated composite additives: Lanthanum hexaboride and vanadium carbide were mixed at a mass ratio of 1:5.3, with lanthanum hexaboride accounting for 0.11% of the titanium dioxide mass in metatitanic acid and vanadium carbide accounting for 0.55%. Carbon black was added, with the total amount of carbon black accounting for 37% of the titanium dioxide mass in metatitanic acid. Ball milling was performed using anhydrous ethanol as the medium, at a ball-to-particle mass ratio of 11:1, at a speed of 450 rpm, for 13 hours, under an argon atmosphere. After ball milling, the mixture was dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder.

[0047] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated composite powder obtained in S2 was added and ultrasonically dispersed at a frequency of 70 kHz for 25 min. Subsequently, it was evaporated in a rotary evaporator at an evaporation temperature of 48 °C, a vacuum of 0.072 MPa, and a rotation speed of 75 rpm for 21 min until the solvent distillation rate slowed down significantly. Then, the evaporation temperature was increased to 59 °C, the vacuum was gradually increased to 0.087 MPa, and the rotation speed was increased to 110 rpm, and evaporation was continued for 9 min until a free-flowing dry powder was obtained, resulting in a close mixture of metatitanic acid and carbon-coated composite additive.

[0048] S4, Three-stage carbothermic reduction: The compact mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 400 mL / min) and the following steps were performed sequentially: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.4 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.4 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.9 hours.

[0049] S5, Cooling: The composite titanium carbide was obtained by cooling to room temperature at a rate of 20 °C / min.

[0050] Comparative Example 1 This comparative example does not add any modifying substances (LaB6 and VC), and only uses metatitanic acid as the titanium source to prepare titanium carbide via carbothermic reduction.

[0051] S1, metatitanic acid activation: The same activation process as in Example 3 was used: 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2) was taken, the metatitanic acid was washed to pH=5.5, dispersed in anhydrous ethanol, oleic acid was added (the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid), and stirred at 300rpm for 45min at room temperature. Then it was vacuum dried at 65℃ for 6h to obtain activated metatitanic acid powder.

[0052] S2, omitted (no modifying substances added): This comparative example does not involve the addition of lanthanum hexaboride and vanadium carbide or carbon coating treatment; only carbon black, a reducing agent, is added. The total amount of carbon black added is 35% of the mass of titanium dioxide in metatitanic acid.

[0053] S3, Directly mixed carbon black: The activated metatitanic acid powder obtained in S1 was mixed with carbon black in S2. The activated metatitanic acid powder and carbon black were ball-milled in anhydrous ethanol as the medium (ball-to-powder mass ratio 10:1, ball milling speed 400 rpm, ball milling time 11.5 h), and dried to obtain a mixture of metatitanic acid and carbon black. Considering the rationality of the actual process, ball milling was still performed in this comparative example to ensure consistency with the process in Example S3, but electrostatic self-assembly was not performed (because only carbon black and metatitanic acid were used, and no additives were needed).

[0054] S4, Three-stage carbothermic reduction: The mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 300 mL / min) and subjected to the following steps: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.25 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.25 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.75 hours.

[0055] S5, Cooling: The titanium carbide was cooled to room temperature at a rate of 20 °C / min to obtain pure titanium carbide.

[0056] Comparative Example 2 This comparative example only added vanadium carbide (VC), without adding lanthanum hexaboride (LaB6). The amount of VC used was the same as in Example 3 (0.5 wt%).

[0057] S1, metatitanic acid activation: The same activation process as in Example 3 was used: 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2) was taken, the metatitanic acid was washed to pH=5.5, dispersed in anhydrous ethanol, oleic acid was added (the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid), and stirred at 300rpm for 45min at room temperature. Then it was vacuum dried at 65℃ for 6h to obtain activated metatitanic acid powder.

[0058] S2. Preparation of carbon-coated VC additives: Lanthanum hexaboride was not added; vanadium carbide (VC) was treated alone. The amount of vanadium carbide used was 0.5% of the mass of titanium dioxide in metatitanic acid (consistent with the VC amount in Example 3). Carbon black was added, with a total amount of carbon black equal to 35% of the mass of titanium dioxide in metatitanic acid. Ball milling was performed under an argon atmosphere at a ball milling speed of 400 rpm and a ball-to-powder mass ratio of 10:1, using anhydrous ethanol as the medium. After ball milling, the vanadium carbide composite powder was obtained.

[0059] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated VC composite powder obtained in S2 was added and ultrasonically dispersed at a frequency of 60 kHz for 22.5 min. Subsequently, it was evaporated in a rotary evaporator at an evaporation temperature of 45 °C, a vacuum of 0.07 MPa, and a rotation speed of 70 rpm for 20 min until the solvent distillation rate slowed down significantly. Then, the evaporation temperature was increased to 58 °C, the vacuum was gradually increased to 0.085 MPa, and the rotation speed was increased to 100 rpm, and evaporation was continued for 7 min until a free-flowing dry powder was obtained, resulting in a compact mixture of metatitanic acid and carbon-coated VC.

[0060] S4, Three-stage carbothermic reduction: The compact mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 300 mL / min) and subjected to the following steps: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.25 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.25 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.75 hours.

[0061] S5, Cooling: The titanium carbide composite material was cooled to room temperature at a rate of 20 °C / min to obtain VC-reinforced titanium carbide composite material.

[0062] Comparative Example 3 This comparative example only added lanthanum hexaboride (LaB6) and did not add vanadium carbide (VC). The amount of LaB6 used was the middle value (0.1 wt%) in Example 3.

[0063] S1, metatitanic acid activation: The same activation process as in Example 3 was used: 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, which is equivalent to 225.0g of TiO2) was taken, the metatitanic acid was washed to pH=5.5, dispersed in anhydrous ethanol, oleic acid was added (the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid), and stirred at 300rpm for 45min at room temperature. Then it was vacuum dried at 65℃ for 6h to obtain activated metatitanic acid powder.

[0064] S2, Preparation of carbon-coated LaB6 additives: Vanadium carbide was not added; only lanthanum hexaboride (LaB6) was treated alone. The amount of lanthanum hexaboride was 0.1% of the mass of titanium dioxide in metatitanic acid (consistent with the LaB6 amount in the LaB6+VC composition in Example 3). Carbon black was added, with a total amount of carbon black equal to 35% of the mass of titanium dioxide in metatitanic acid. Ball milling was performed under an argon atmosphere at a ball-to-powder mass ratio of 10:1 using anhydrous ethanol as the medium, a ball milling speed of 400 rpm, and a ball milling time of 11.5 h. After ball milling, the powder was dried to obtain carbon-coated lanthanum hexaboride composite powder.

[0065] S3, electrostatic self-assembly hybrid: The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol with a solid content of 15 wt%. The carbon-coated LaB6 composite powder obtained in S2 was added and ultrasonically dispersed at 60 kHz for 22.5 min. Subsequently, the mixture was evaporated in a rotary evaporator at 45 °C, 0.07 MPa vacuum, and 70 rpm for 20 min until the solvent distillation rate significantly slowed down. Then, the evaporation temperature was increased to 58 °C, the vacuum was gradually increased to 0.085 MPa, and the rotation speed was increased to 100 rpm, and evaporation continued for 7 min until a free-flowing, dry powder was obtained, resulting in a compact mixture of metatitanic acid and carbon-coated LaB6.

[0066] S4, Three-stage carbothermic reduction: The compact mixture obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 300 mL / min) and subjected to the following steps: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.25 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.25 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.75 hours.

[0067] S5, Cooling: The titanium carbide composite material was obtained by cooling to room temperature at a rate of 20℃ / min to desulfurize LaB6.

[0068] Comparative Example 4 The difference between this comparative example and Comparative Example 1 is that a three-stage heating process is used, but no modifying substances (LaB6 and VC) are added. 300.0g of metatitanic acid (after calcination at 800℃, the TiO2 content of this batch of metatitanic acid is approximately 75%, equivalent to 225.0g of TiO2) is used, and the amount of carbon black is 35wt% of the TiO2 mass in the metatitanic acid, to verify the inhibitory effect of the three-stage heating process on sulfur doping. The specific preparation method is the same as that of Comparative Example 1, but step S4 adopts the same three-stage heating regime as Example 3: the first stage is held at 800℃ for 1.25h, the second stage is held at 1450℃ for 2.25h, and the third stage is held at 1500℃ for 2.75h. The remaining steps are the same as those of Comparative Example 1.

[0069] Comparative Example 5 The difference between this comparative example and Comparative Example 4 is that a carbon coating and electrostatic self-assembly step is added, but LaB6 and VC are not added, to verify the effect of carbon coating and self-assembly on sulfur doping without chemical trapping agents. The specific preparation method is as follows: 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ is about 75%, equivalent to 225.0g of TiO2) is taken, and the metatitanic acid is activated according to Example 3 (S1); carbon black (the amount is 35wt% of the mass of TiO2 in the metatitanic acid) is ball-milled and carbon-coated, but LaB6 and VC are not added; then electrostatic self-assembly mixing (S3) and three-stage carbothermal reduction (S4) are carried out according to Example 3, and titanium carbide is obtained after cooling.

[0070] Comparative Example 6 This comparative example simultaneously added lanthanum hexaboride and vanadium carbide and performed carbon coating treatment, but did not employ electrostatic self-assembly mixing; only conventional physical stirring and mixing were used to verify the effect of electrostatic self-assembly on the dispersion uniformity of the additives and the performance of the final product. The specific preparation method is as follows: S1, metatitanic acid activation: The activation process was exactly the same as in Example 3: 300.0g of metatitanic acid (the content of TiO2 in this batch of metatitanic acid after calcination at 800℃ was about 75%, equivalent to 225.0g of TiO2) was taken, the metatitanic acid was washed to pH=5.5, dispersed in anhydrous ethanol, oleic acid was added (the amount of oleic acid added was 0.5% of the mass of titanium dioxide in the metatitanic acid), and stirred at 300rpm for 45min at room temperature, and then vacuum dried at 65℃ for 6h to obtain activated metatitanic acid powder.

[0071] S2. Preparation of carbon-coated lanthanum hexaboride and vanadium carbide composite powder: The carbon coating process was identical to that used in Example 3. Lanthanum hexaboride and vanadium carbide were mixed at a mass ratio of 1:5, with lanthanum hexaboride accounting for 0.10% of the mass of titanium dioxide in metatitanic acid and vanadium carbide accounting for 0.5% of the mass of titanium dioxide in metatitanic acid. Carbon black was added, with the total amount of carbon black being 35% of the mass of titanium dioxide in metatitanic acid. The mixture was ball-milled for 11.5 hours at a ball-to-material mass ratio of 10:1 and a rotation speed of 400 rpm using anhydrous ethanol as the medium, under an argon atmosphere. After ball milling, the mixture was dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder.

[0072] S3. Physical mixing (without electrostatic self-assembly): The activated metatitanic acid powder obtained in S1 was dispersed in anhydrous ethanol, and the solid content was adjusted to 15 wt%. The carbon-coated composite powder obtained in S2 was then added. A homogeneous slurry was formed by mechanical stirring at 200 rpm for 30 min at room temperature, followed by drying at 60℃ for 12 h under normal pressure. The dried slurry was then ground and passed through a 200-mesh sieve to obtain a physically mixed powder of metatitanic acid and carbon-coated composite additive. Ultrasonic dispersion and rotary evaporation were not performed throughout this step.

[0073] S4, Three-stage carbothermic reduction: The physically mixed powder obtained in S3 was placed in an inert gas (argon, purity 99.999%, flow rate 300 mL / min) and subjected to the following processes sequentially: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1.25 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2.25 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.75 hours.

[0074] S5, Cooling: The composite titanium carbide is obtained by cooling to room temperature at a rate of 20℃ / min.

[0075] Test case The titanium carbide samples obtained in Comparative Examples 1-6 and Examples 1-5 were grouped, and the grouping is shown in Table 1: Table 1 Grouping Results After grouping, the following measurements were performed on each group: 1. Sulfur content determination: The high-frequency induction combustion-infrared absorption method was used for testing. The sample was ground to a particle size ≤150μm, and 0.5g (accurate to 0.0001g) was accurately weighed and placed in a ceramic crucible. Appropriate amounts of tungsten and iron particles were added as flux. The sample was fully combusted at high temperature in a high-purity oxygen atmosphere with a purity ≥99.99%. The sulfur in the sample was completely converted into sulfur dioxide, and the quantitative detection was completed by an infrared detector.

[0076] Before testing, a calibration curve was plotted using a sulfur content standard material adapted to non-metallic materials. Each group of samples was measured in parallel three times, and the results were taken as the arithmetic mean and expressed in ppm by mass.

[0077] 2. Vickers hardness (HV1): According to GB / T16534-2020, the Vickers hardness test was conducted. The sample surface was ground and polished to a mirror finish, with a surface roughness of Ra≤0.2μm. A diamond square pyramid indenter was used, and a test load of 9.807N (HV1) was applied, held for 15s, and then unloaded. The lengths of the two diagonals of the indentation were measured and averaged. The result was calculated using the formula HV=0.1891×F / d. 2 Calculate the hardness. Test at least 5 valid points for each sample, and take the average value as the final result.

[0078] 3. Wear rate: The ball-disc friction and wear tester was used. The mating parts were silicon nitride ceramic balls with a diameter of 6 mm. Dry friction tests were conducted with fixed load, rotation radius, sliding speed, and total sliding distance.

[0079] Before and after the test, the samples were ultrasonically cleaned with anhydrous ethanol, dried, and weighed. The sample density was determined using the Archimedes method before the test. Specific wear rate calculation formula: W = Δm × 1000 / (ρ·F·L); unit is mm 3 / (N·m). Each experiment was repeated 3 times, and the average value was taken.

[0080] 4. X-ray diffraction phase analysis and calculation of lattice constant and grain size: Phase analysis of powder samples was performed using an X-ray diffractometer. Samples were ground to a particle size ≤50 μm and then compressed into tablets. Testing conditions: CuKα rays, tube voltage 40 kV, tube current 40 mA, scanning range 10°–90°, step size 0.02°, scanning speed 1° / min. The instrument diffraction angle and instrument broadening were calibrated before testing.

[0081] The sample diffraction pattern was compared with the JCPDS standard card to qualitatively analyze the TiC main phase and oxide impurity phase; if there were obvious titanium oxide diffraction peaks, it was determined that the carbothermic reduction reaction was incomplete.

[0082] (1) Calculation of lattice constant Typical high-angle diffraction peaks of TiC were selected, and the lattice constant was calculated by combining the Bragg equation and the interplanar spacing formula of cubic crystal system. The lattice constant was compared with the standard lattice constant of TiC standard card JCPDS32-1383 to determine the solid solution behavior of the element.

[0083] (2) Calculation of average grain size The characteristic diffraction peaks of TiC(200) were selected, and after subtracting the instrument broadening, the average grain size was calculated using the Scherrer formula D=Kλ / (βCOSθ).

[0084] (3) Semi-quantitative analysis of TiB2 phase The XRD patterns were refined using Rietveld full-spectrum refinement with HighScorePlus software. After fitting, R was controlled. wp <10%, quantitatively calculate the mass fraction of each phase such as TiC, TiB2, and La2S3 to characterize the amount of side reaction formation, and take the average of 3 tests for each group of samples.

[0085] The test results are shown in Table 2. Table 2 shows the test results for each indicator. According to the results in Table 2: 1. The synergistic effect of LaB6 and VC is key to achieving ultra-low sulfur content and high hardness: As shown in samples 1-4 (LaB6 only), LaB6 can reduce the sulfur content to below 30 ppm, but the hardness only increases to 2700–2900 HV; samples 1-5 (VC only) can increase the hardness to 2850–3100 HV, but the sulfur content is still as high as 400–800 ppm. However, in embodiments of the present invention (1-7 to 1-11), both LaB6 and VC are added, further reducing the sulfur content to below 25 ppm, simultaneously increasing the hardness to 3100–3400 HV, and reducing the wear rate to 0.5 × 10⁻⁻⁻⁶. 5 The concentration is below mm³ / (N·m). This indicates that LaB6 is responsible for efficient desulfurization, while VC is responsible for solid solution strengthening. Both are indispensable and together they achieve the integration of "desulfurization-strengthening".

[0086] 2. Carbon coating, electrostatic self-assembly, and three-stage heating are crucial for fully leveraging their synergistic effects: Comparing samples 1-3 (no additives, but using carbon coating + self-assembly + three-stage heating) with samples 1-4 / 1-5, it can be seen that simply improving the process without adding LaB6 and VC cannot reduce the sulfur content, and the hardness improvement is also extremely limited (≤2800HV). Comparing sample 1-6 (physical mixing, no self-assembly) with Examples 1-7 of this invention (complete process), it can be seen that without electrostatic self-assembly, the sulfur content increases to 50–150ppm, and the hardness and grain refinement both decrease significantly. The three-stage heating (especially the 800℃ pre-desulfurization stage) provides a favorable temperature window for LaB6 to preferentially capture sulfur, preventing sulfur from escaping at high temperatures.

[0087] 3. XRD data verified the dual solid solution of B and V atoms from a crystallographic perspective: The lattice constants of TiC in Comparative Examples 1-3 are approximately 4.327–4.330 Å, close to the standard value of pure TiC (JCPDS32-1383, a=4.327 Å). Adding only LaB6 (1-4) slightly increases the lattice constant to 4.332–4.335 Å, indicating partial solid solution of B atoms; adding only VC (1-5) also slightly increases the lattice constant (4.333–4.337 Å), but the change is limited. The lattice constants of the embodiments of this invention (1-7 to 1-11) significantly increase to 4.338–4.345 Å, far exceeding the range of variation for a single solid solution, and greater than the lattice constant of Comparative Example 6 (physical mixture) (4.336–4.340 Å), directly proving that B and V atoms simultaneously enter the TiC lattice, producing a synergistic lattice distortion, which is the structural root cause of the significant increase in hardness.

[0088] 4. This invention effectively suppresses the formation of the side reaction TiB2: Compared to samples 1-4 (LaB6 only), where the TiB2 byproduct content was <7 wt%, the TiB2 content in the embodiments of the present invention (1-7 to 1-11) was further reduced to <4 wt%. Combined with the TiB2 content of <5 wt% in Comparative Example 6 (physical mixing), this indicates that the introduction of VC and the uniform mixing brought about by electrostatic self-assembly help stabilize the structure of LaB6 or competitively consume free B, thereby inhibiting the reaction of LaB6 with TiC to generate TiB2.

[0089] 5. Significant grain refinement effect, which is beneficial to improving hardness and wear resistance: The average grain size of Comparative Examples 1-3 was 180–300 nm, and that of Comparative Examples 4-6 was 120–250 nm, while the embodiments of the present invention (1-7 to 1-11) were further refined to 100–180 nm. This grain refinement is mainly attributed to: ① carbon coating and electrostatic self-assembly achieving uniform distribution of additives; ② the pinning effect of residual LaB6 and VC particles on grain boundaries; and ③ rapid cooling freezing grain growth. Fine grains contribute to Hall-Petch strengthening, which is an important supplementary mechanism for hardness improvement.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing composite titanium carbide from metatitanic acid, characterized in that, Includes the following steps: S1. Wash metatitanic acid until the pH is 4.0-7.0, disperse it in anhydrous ethanol, add oleic acid, stir and dry to obtain activated metatitanic acid powder; the amount of oleic acid added is 0.5% of the mass of titanium dioxide in the metatitanic acid; S2. Lanthanum hexaboride and vanadium carbide are mixed at a mass ratio of 1:(4.5-5.5), and carbon black is added. The total amount of carbon black added is 30%-40% of the mass of titanium dioxide in metatitanic acid. The mixture is ball-milled with anhydrous ethanol as the medium and dried to obtain carbon-coated lanthanum hexaboride and vanadium carbide composite powder. The amount of lanthanum hexaboride is 0.08-0.12% of the mass of titanium dioxide in metatitanic acid, and the amount of vanadium carbide is 0.4-0.6% of the mass of titanium dioxide in metatitanic acid. S3. Disperse the activated metatitanic acid powder obtained in S1 in anhydrous ethanol, add the carbon-coated lanthanum hexaboride and vanadium carbide composite powder obtained in S2, disperse by ultrasonication, remove the ethanol by rotary evaporation, and obtain a close mixture of metatitanic acid and carbon-coated composite additive. S4. Place the compact mixture obtained in step S3 in an inert gas and proceed as follows: First stage: Increase the temperature to 800℃ at a rate of 5℃ / min and hold for 1-1.5 hours; Second stage: Increase the temperature to 1450℃ at a rate of 8℃ / min and hold for 2-2.5 hours; Third stage: Increase the temperature to 1500℃ at a rate of 10℃ / min and hold for 2.5-3 hours; S5. Cool to room temperature at a rate of 20℃ / min to obtain the composite titanium carbide.

2. The method according to claim 1, characterized in that, In step S2, the ball-to-material mass ratio during ball milling is (8-12):1, the ball milling speed is 300-500 rpm, and the ball milling time is 8-15 h.

3. The method according to claim 1, characterized in that, In step S3, the solid content of the activated metatitanic acid powder after dispersion in anhydrous ethanol is 15wt%, the ultrasonic dispersion time is 15-30 minutes, and the ultrasonic frequency is 40-80kHz.

4. The method according to claim 1, characterized in that, In step S5, the cooling rate is 15-25°C / min, and the cooling is carried out in a flowing inert gas.

5. The method according to claim 4, characterized in that, In S4 and S5, the inert gas used is argon, the gas flow rate is 100-500 mL / min, and the purity of the argon is not less than 99.999%.

6. The method according to claim 1, characterized in that, The sulfur content of the composite titanium carbide is not higher than 20 ppm, and the Vickers hardness is not lower than 30 GPa.

7. The method according to claim 1, characterized in that, The drying process described in step S1 is vacuum drying at 50°C to 80°C for 4 to 8 hours.

8. The method according to claim 1, characterized in that, The process parameters for stirring in step S1 are: stirring speed 200-400 rpm, stirring time 30-60 min, and stirring temperature at room temperature.

9. The method according to claim 1, characterized in that, The carbon black used in step S2 is nano-sized conductive carbon black with a particle size range of 20-50 nm and a purity of ≥99.5%.

10. The method according to claim 1, characterized in that, The process parameters for rotary evaporation in step S3 are as follows: First, evaporate for 15-25 minutes at an evaporation temperature of 40-50℃, a vacuum degree of 0.06-0.075MPa, and a rotation speed of 60-80rpm until the solvent distillation rate slows down significantly; then, increase the evaporation temperature to 55-60℃, gradually increase the vacuum degree to 0.08-0.09MPa, increase the rotation speed to 80-120rpm, and continue evaporating for 5-10 minutes until free-flowing dry powder is obtained.

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