A method for modifying boride ceramic powder with Mo

Abstract

A method for modifying boride ceramic powder with Mo, which uses boride ceramic powder (HfB2, ZrB2, NbB2, TaB2, TiB2) and Mo-containing compounds (MoO2, MoO3, Na2MoO4, H2MoO4, (NH4)6·Mo7O 24 , (NH4)2·Mo4O 13 , (NH4)2·Mo2O7) as raw materials, mixes them uniformly, and completes heat treatment in a protective atmosphere and a reducing atmosphere to achieve coating of Mo particles on the surface of ceramic powder particles and avoid oxidation of the ceramic powder and generation of impurity phases. The method can achieve modification of Mo on the surface of boride powder, mix refractory metal Mo with ceramic powder uniformly, and avoid powder agglomeration.

Description

Technical Field

[0001] The technical solution of this invention is used to prepare Mo-modified boride ceramic powder, belonging to the field of powder preparation. Background Technology

[0002] Ultra-high temperature ceramics (UHTCs) possess excellent resistance to oxidation and ablation, extremely high melting points, high thermal conductivity, and low coefficients of thermal expansion, making them candidate materials for thermal protection components of hypersonic vehicles and propulsion system components of reusable launch vehicles. Ultra-high temperature boride ceramics mainly refer to a class of ceramic materials represented by transition metal borides such as zirconium boride (ZrB2), hafnium boride (HfB2), tantalum boride (TaB2), and niobium boride (NbB2). They exhibit high melting points, high hardness, low density, good mechanical properties, and high-temperature stability. However, boride ceramics suffer from difficulties in sintering and poor fracture toughness, limiting their practical applications.

[0003] Many researchers choose to introduce additives into boride ceramics to improve their fracture toughness. Common additives are categorized into ceramic phases and metallic phases. Ceramic phase additives, such as SiC, Si3N4, AlN, WC, and B4C, can effectively improve the mechanical properties, oxidation resistance, and ablation resistance of boride ceramics. However, ceramic phase additives are unlikely to significantly improve the fracture toughness of boride ceramics. Metallic phase additives, such as refractory metals like Ni, Nb, Hf, Mo, and Ta, possess high melting points and good ductility, which theoretically should help enhance the fracture toughness of boride ceramics. However, numerous studies have shown that refractory metal additives do not have a significant toughening effect on boride ceramics. This is mainly because traditional mixing methods cannot effectively and uniformly disperse the metallic phase in the boride ceramic phase, leading to agglomeration of the metallic phase and affecting the improvement of boride ceramic properties. Among metallic phase additives, Mo has low density, a high melting point, and a thermal expansion coefficient similar to that of borides, making it a potential additive that can significantly improve the properties of boride ceramics.

[0004] Boride ceramics are brittle and have poor fracture toughness, making them unsuitable for the harsh environments requiring high-temperature thermal protection in aerospace applications. Therefore, improving the performance of boride ceramics through a novel technical solution is crucial and has significant implications for expanding their future applications. This invention achieves uniform Mo coating on the surface of boride powder through in-situ modification, potentially leading to a significant improvement in the performance of boride ceramic materials. Summary of the Invention

[0005] The purpose of this invention is to provide a new method for introducing refractory metal Mo into boride ceramic powder, so as to solve the problems of uneven dispersion of metal Mo and easy agglomeration of Mo powder particles in existing methods for introducing refractory metal Mo, and to achieve uniform dispersion of Mo in ceramic powder, thereby providing a raw material basis for the preparation of high-performance boride-Mo composite materials.

[0006] This invention modifies the surface of boride ceramic powder particles with metallic Mo through a chemical reaction. A Mo compound is mixed with the boride ceramic powder, and then reduced with hydrogen to obtain refractory metallic Mo. The resulting Mo powder is uniformly distributed within the boride ceramic powder, and the fine Mo powder particles coat the boride ceramic powder particles, thus completing the surface modification of the boride ceramic powder with refractory metallic Mo.

[0007] Compared to existing methods for introducing refractory metal Mo, the advantages of this invention lie in the chemical reaction that incorporates refractory metal Mo additives into boride ceramic powder, thus solving the problems of powder particle agglomeration and uneven metal phase dispersion. Simultaneously, precise control of heat treatment process conditions avoids the oxidation of borides caused by reactions between borides and oxides. Furthermore, the preparation method of this invention is low-cost, simple, and has a short time cycle. This invention provides new ideas and methods for the surface modification of boride powders and the performance improvement of ultra-high temperature ceramics.

[0008] This invention relates to a method for producing Mo-modified boride ceramic powder, the method comprising the following steps: (1) Mix the Mo-containing compound and boride ceramic powder evenly, wherein the Mo-containing compound is MoO2, MoO3, Na2MoO4, H2MoO4, (NH4)6·Mo7O 24 (NH4)2·Mo4O 13 One or more of (NH4)2·Mo2O7; the boride ceramic powder is one or more of HfB2, ZrB2, NbB2, TaB2, and TiB2; (2) Transfer the mixed powder obtained in step (1) to a tube furnace and perform powder pretreatment in a protective atmosphere. The protective atmosphere is Ar or N2, the gas flow rate is 0.1-1000 mL / min, the heating rate is 0-100 ℃ / min, the pretreatment temperature is 200-600 ℃, and the holding time is 1-300 min. (3) The product obtained in step (2) is placed in a reducing atmosphere for heat treatment. The reducing atmosphere is H2 gas or H2 / Ar mixture, wherein the volume fraction of H2 in the H2 / Ar mixture is 0.1-50%, the gas flow rate is 0.1-1000 mL / min, the heating rate is 0.1-100 ℃ / min, the heat treatment temperature is 300-800 ℃, and the holding time is 1-360 min, and finally Mo modified boride ceramic powder is obtained.

[0009] The method for producing Mo-modified boride ceramic powder is characterized in that, in step (1), the mass ratio of boride ceramic powder to Mo-containing compound is 1:1-100:1, the powder is mixed by dry mechanical ball milling, wet mechanical ball milling or mortar grinding, and the mixing time is 1-600 min. Attached Figure Description

[0010] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the Mo-modified ZrB2 powder prepared in Example 1. Figure 2 The images shown are scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) spectra of the Mo-modified ZrB2 powder prepared in Example 1. Figure 3 The image shows the X-ray diffraction (XRD) pattern of the Mo-modified ZrB2 powder prepared in Comparative Example 1. Figure 4 The images show scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) spectra of the Mo-modified ZrB2 powder prepared in Comparative Example 1. Figure 5 The figures show the bending fracture curves of ceramic samples obtained by sintering Mo-modified ZrB2 powders prepared in Example 1 and Comparative Example 1, respectively. Figure 6 The bending fracture curves are shown for the ceramic samples obtained by sintering the Mo-modified ZrB2 powder prepared in Examples 2-7.

[0011] The present invention will be further described below with reference to embodiments. The scope of the present invention is not limited to the following embodiments. Those skilled in the art will understand that various changes and modifications can be made to the present invention without departing from its spirit and scope.

[0012] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0013] Example: Example 1: A method for Mo-modified boride ceramic powder, comprising the following steps: (1) ZrB2 and (NH4)2·Mo4O 13 Weigh the materials at a mass ratio of 1:1 and grind and mix them in a mortar and pestle for 30 minutes. (2) The mixed powder was placed in a tube furnace and heated with Ar gas as the protective gas at a flow rate of 200 mL / min. The heat treatment process was as follows: the temperature was increased to 500 ℃ at a heating rate of 10 ℃ / min and held for 30 min. (3) The sample was heated from 500 °C to 620 °C at a heating rate of 10 °C / min to convert Ar gas into H2 (5 vol.%) / Ar. The H2 (5 vol.%) / Ar gas flow rate was 300 mL / min. The sample was kept at 620 °C for 240 min, and then cooled to 600 °C at a rate of 10 °C / min. The H2 / Ar gas was kept flowing through the sample. The sample was taken out after cooling to room temperature. In this embodiment, the Mo-modified ZrB2 powder has a Mo purity of 98.32% and is uniformly dispersed within the ZrB2 powder. The XRD pattern of this powder is shown in [Figure number missing]. Figure 1 See SEM and EDS. Figure 2 The Mo-modified ZrB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample withstood a maximum load of 607.18 N and a fracture toughness of 4.72 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 5 .

[0014] Example 2, a method for Mo-modified boride ceramic powder, comprising the following steps: (1) Weigh ZrB2 and MoO3 at a mass ratio of 15:1 and grind and mix them in a mortar for 45 min; (2) The mixed raw materials are placed in a tube furnace for heating, with Ar gas as the protective gas, the Ar gas flow rate is 300 mL / min, the temperature is increased to 500 ℃ at a heating rate of 10 ℃ / min, and held for 30 min; (3) Heat to 630 ℃ at a heating rate of 10 ℃ / min and hold at 630 ℃ for 180 min; when the temperature of the tube furnace is 630 ℃, convert Ar gas to H2 (10 vol.%) / Ar and the H2 (10 vol.%) / Ar gas flow rate is 100 mL / min; then, cool to 500 ℃ at a rate of 10 ℃ / min and cool with the furnace while keeping the gas in. Take it out after cooling to room temperature. In this embodiment, the Mo-modified ZrB2 powder has a Mo purity of 98.73% and is uniformly dispersed within the ZrB2 powder. The Mo-modified ZrB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample exhibited a maximum load of 574.16 N and a fracture toughness of 3.89 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 6 .

[0015] Example 3, a method for Mo-modified boride ceramic powder, comprising the following steps: (1) Weigh HfB2 and H2MoO4 at a mass ratio of 24:1 and mix them by wet mechanical ball milling for 60 min; (2) The mixed powder sample was placed in a tube furnace for heating, with N2 gas as the protective gas, the N2 gas flow rate was 300 mL / min, the temperature was increased to 600 ℃ at a heating rate of 8 ℃ / min, and held for 40 min. (3) Heat to 800 ℃ at a heating rate of 8 ℃ / min, and hold at 800 ℃ for 360 min; when the temperature of the tube furnace is 800 ℃, convert N2 gas to H2, and the H2 gas flow rate is 50 mL / min; then, cool to 400 ℃ at a rate of 8 ℃ / min and cool with the furnace, keeping the gas in, and take it out after cooling to room temperature; In this embodiment, the Mo-modified HfB2 powder has a Mo purity of 97.83% and is uniformly dispersed within the HfB2 powder. The Mo-modified HfB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample exhibited a maximum load of 568.31 N and a fracture toughness of 4.05 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 6 .

[0016] Example 4, a method for Mo-modified boride ceramic powder, comprising the following steps: (1) Weigh HfB2 and MoO2 at a mass ratio of 76:1 and mix them by dry mechanical ball milling for 15 min; (2) The mixed powder sample was placed in a tube furnace for heating, with Ar gas as the protective gas, the Ar gas flow rate was 150 mL / min, and the temperature was increased to 250 ℃ at a heating rate of 5 ℃ / min, and held for 60 min. (3) Heat to 750 ℃ ​​at a heating rate of 5 ℃ / min, and hold at 750 ℃ ​​for 300 min; when the temperature of the tube furnace is 750 ℃, convert Ar gas to H2 (20 vol.%) / Ar, and the H2 (20 vol.%) / Ar gas flow rate is 350 mL / min; then, cool to 200 ℃ at a rate of 5 ℃ / min and cool with the furnace, keeping the gas in, and take it out after cooling to room temperature; In this embodiment, the Mo-modified HfB2 powder has a Mo purity of 98.53% and is uniformly dispersed within the HfB2 powder. The Mo-modified HfB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample exhibited a maximum load of 498.21 N and a fracture toughness of 3.76 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 6 .

[0017] Example 5, a method for Mo-modified boride ceramic powder, comprising the following steps: (1) Weigh NbB2 and Na2MoO4 at a mass ratio of 37:1 and grind and mix them in a mortar for 30 min; (2) The mixed powder sample was placed in a tube furnace for heating, with N2 gas as the protective gas, the N2 gas flow rate was 200 mL / min, the temperature was increased to 450 ℃ at a heating rate of 10 ℃ / min, and held for 30 min. (3) Heat to 650 ℃ at a heating rate of 10 ℃ / min and hold at 650 ℃ for 360 min; when the temperature of the tube furnace is 650 ℃, convert N2 gas to H2 at a flow rate of 70 mL / min; then, cool to 400 ℃ at a rate of 10 ℃ / min and cool with the furnace while keeping the gas flowing in, and take it out after cooling to room temperature; In this embodiment, the Mo-modified NbB2 powder has a Mo purity of 96.94% and is uniformly dispersed within the NbB2 powder. The Mo-modified NbB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample exhibited a maximum load of 501.37 N and a fracture toughness of 4.69 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 6 .

[0018] Example 6, a method for Mo-modified boride ceramic powder, comprising the following steps: (1) Mix TaB2 and (NH4)6·Mo7O 24Weigh the materials at a mass ratio of 19:1 and mix them by wet mechanical ball milling for 50 min; (2) The mixed powder sample was placed in a tube furnace for heating, with N2 gas as the protective gas, the N2 gas flow rate was 100 mL / min, the temperature was increased to 600 ℃ at a heating rate of 5 ℃ / min, and held for 45 min. (3) Heat to 800 ℃ at a heating rate of 5 ℃ / min, and hold at 800 ℃ for 240 min; when the temperature of the tube furnace is 800 ℃, convert N2 gas to H2 (7 vol.%) / Ar, and the H2 (7 vol.%) / Ar gas flow rate is 200 mL / min; then, cool to 600 ℃ at a rate of 5 ℃ / min and cool with the furnace, keeping the gas in, and take it out after cooling to room temperature; In this embodiment, the Mo-modified TaB2 powder has a Mo purity of 97.91% and is uniformly dispersed within the TaB2 powder. The Mo-modified TaB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample exhibited a maximum load of 541.88 N and a fracture toughness of 4.10 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 6 .

[0019] Example 7, a method for Mo-modified boride ceramic powder, comprising the following steps: (1) Weigh TaB2 and (NH4)2·Mo2O7 at a mass ratio of 100:1 and grind and mix them in a mortar for 25 minutes; (2) The mixed powder sample was placed in a tube furnace for heating, with Ar gas as the protective gas, the Ar gas flow rate was 250 mL / min, and the temperature was increased to 580 ℃ at a heating rate of 10 ℃ / min, and held for 60 min. (3) Heat to 750 ℃ ​​at a heating rate of 10 ℃ / min, and hold at 750 ℃ ​​for 240 min; when the temperature of the tube furnace is 750 ℃, convert Ar gas to H2 (15 vol.%) / Ar, and the H2 (15 vol.%) / Ar gas flow rate is 100 mL / min; then, cool to 500 ℃ at a rate of 10 ℃ / min and cool with the furnace, keeping the gas in, and take it out after cooling to room temperature; In this embodiment, the Mo-modified TaB2 powder has a Mo purity of 96.98% and is uniformly dispersed within the TaB2 powder. The Mo-modified TaB2 powder prepared in this embodiment was hot-pressed and sintered at 1800 °C for 30 min at 30 MPa. The resulting ceramic sample exhibited a maximum load of 522.61 N and a fracture toughness of 3.68 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 6 .

[0020] Comparative Example 1: Unlike Example 1, in steps (2) and (3), the temperature was increased to 150 °C at 15 °C / min in an Ar atmosphere, held for 10 min, and then increased to 280 °C at 15 °C / min to convert Ar gas to H2 (1 vol.%) / Ar, and held for 50 min. The remaining experimental conditions were the same. In the Mo-modified ZrB2 powder prepared in this comparative example, the purity of Mo was 95.43%. The XRD pattern of this powder is shown in [Figure number missing]. Figure 3 See SEM and EDS. Figure 4 Combined with appendix Figure 2 It is evident that the uniformity of Mo dispersion in the Mo-modified ZrB2 powder obtained in Comparative Example 1 is lower than that in Example 1. The ceramic sample obtained from the Mo-modified ZrB2 powder prepared in this comparative example, sintered using the same process as in Example 1, exhibited a maximum load of 455.23 N and a fracture toughness of 2.39 MPa·m. 1 / 2 The bending fracture curve of the specimen is shown in the figure. Figure 5 It is precisely the high dispersion uniformity of Mo in ZrB2 powder in Example 1 that ensures the uniformity of the composite ceramic structure obtained after sintering, thereby improving the mechanical properties of the material.

[0021] Comparative Example 2: Unlike Example 1, the grinding time was set to 5 min instead of 30 min, while the other experimental conditions remained the same. In this comparative example, the purity of Mo in the Mo-modified ZrB2 powder was 84.72%, and the uniformity of Mo dispersion in the ZrB2 powder was lower than that in Example 1. (The remaining text appears to be unrelated and possibly a fragment from another source.) Figure 1 It can be seen that the XRD diffraction peaks of the Mo-modified ZrB2 powder obtained in Example 1 are completely consistent with the standard PDF cards of ZrB2 and Mo, with no extra impurity peaks; as shown in the attached... Figure 2 It can be seen that the distribution of Mo in the Mo-modified ZrB2 powder obtained in Example 1 is very uniform and there is no obvious agglomeration phenomenon.

[0022] In publicly available reports, most scholars have chosen to introduce Mo into boride ceramic powders through ball milling and mixing. However, this method is difficult to achieve uniform Mo distribution and easily leads to Mo agglomeration. In contrast, introducing Mo into ceramic powders by reducing Mo-containing compounds with H2 can achieve uniform Mo distribution within the ceramic powder, and with appropriate heat treatment control, oxidation of the boride powder can be avoided. Therefore, this method provides a novel and feasible solution for Mo-modified boride ceramic powders.

Claims

1. A method for modifying Mo-boride ceramic powder, characterized in that: Its preparation process includes the following steps: (1) Mix the Mo-containing compound and boride ceramic powder evenly, wherein the Mo-containing compound is MoO2, MoO3, Na2MoO4, H2MoO4, (NH4)6·Mo7O 24 (NH4)2·Mo4O 13 One or more of (NH4)2·Mo2O7; the boride ceramic powder is one or more of HfB2, ZrB2, NbB2, TaB2, and TiB2; (2) Transfer the mixed powder obtained in step (1) to a tube furnace and perform powder pretreatment in a protective atmosphere. The protective atmosphere is Ar or N2, the gas flow rate is 0.1-1000 mL / min, the heating rate is 0-100 ℃ / min, the pretreatment temperature is 200-600 ℃, and the holding time is 1-300 min. (3) The product obtained in step (2) is placed in a reducing atmosphere for heat treatment. The reducing atmosphere is H2 gas or H2 / Ar mixture, wherein the volume fraction of H2 in the H2 / Ar mixture is 0.1-50%, the gas flow rate is 0.1-1000 mL / min, the heating rate is 0.1-100 ℃ / min, the heat treatment temperature is 300-800 ℃, and the holding time is 1-360 min, and finally Mo modified boride ceramic powder is obtained.

2. The method for producing Mo-modified boride ceramic powder according to claim 1, characterized in that, In step (1), the mass ratio of boride ceramic powder to Mo-containing compound is 1:1-100:

1. The powder is mixed by dry mechanical ball milling, wet mechanical ball milling or mortar grinding, and the mixing time is 1-600 min.

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