阅读说明：本技术 硅热还原氧化法制备氮化铪陶瓷粉体的方法 (Method for preparing hafnium nitride ceramic powder by silicon thermal reduction oxidation method ) 是由 陆有军 刘乡 徐倩 杨璐同 刘洋 孙文周 张明君 于 2021-11-16 设计创作，主要内容包括：本发明提供了一种硅热还原氧化法制备氮化铪陶瓷粉体的方法,以成本低的氮化硅和氧化铪作为原料,通过研磨混合-压制成型-无压烧结-破碎筛分等步骤加工而成。在该氮化铪陶瓷粉体体系中,一方面过渡金属元素Hf的价电子浓度和配位数较高,而N的原子半径较小,易形成键长较短、键强较强的共价键,从而具有很高的熔点和硬度,另一方面其化学键中同时具有金属键、离子键和共价键,从而易调控形成多种不同的化学计量比和晶体结构。过渡金属原子向主族原子的电荷转移,使本来空间分布比较局域的d电子受到的电子屏蔽更少,增强了d电子的局域性和相互关联,从而提高了氮化铪陶瓷粉体的韧性。利用本发明可降低氮化铪陶瓷粉体生产成本、改善陶瓷韧性。(The invention provides a method for preparing hafnium nitride ceramic powder by a silicon thermal reduction oxidation method, which takes low-cost silicon nitride and hafnium oxide as raw materials and is processed by the steps of grinding, mixing, press forming, pressureless sintering, crushing, screening and the like. In the hafnium nitride ceramic powder system, on one hand, the valence electron concentration and coordination number of the transition metal element Hf are high, the atomic radius of N is small, covalent bonds with short bond length and strong bond strength are easy to form, so that the hafnium nitride ceramic powder system has high melting point and hardness, and on the other hand, the chemical bonds of the hafnium nitride ceramic powder system simultaneously have metal bonds, ionic bonds and covalent bonds, so that various different stoichiometric ratios and crystal structures are easy to regulate and control. The charge transfer from the transition metal atoms to the main group atoms ensures that the electron shielding of the d electrons which are originally distributed in space and are local is less, and enhances the locality and the correlation of the d electrons, thereby improving the toughness of the hafnium nitride ceramic powder. The invention can reduce the production cost of the hafnium nitride ceramic powder and improve the toughness of the ceramic.)

1. A method for preparing hafnium nitride ceramic powder by a silicon thermal reduction oxidation method is characterized by comprising the following steps:

(1) grinding and mixing: weighing hafnium oxide powder and silicon nitride powder according to a certain ratio, placing the hafnium oxide powder and the silicon nitride powder into a grinding body, adding a proper amount of alcohol as a grinding medium, and grinding for 0.5-2 hours to obtain a mixed material;

(2) and (3) pressing and forming: drying the mixed material in a drying oven, adding the dried mixed material into a forming die, maintaining the pressure for 5-60 s under the pressure of 10-100 MPa, and pressing to form loose blocky materials;

(3) pressureless sintering: putting the pressed and formed block-shaped material into a crucible filled with graphite fibrofelt and graphite paper, then laying a layer of graphite fibrofelt above the block-shaped material, finally placing the block-shaped material into a sintering furnace, carrying out pressureless sintering at 1500-2000 ℃, carrying out heat preservation sintering for 0.5-2 h, and then naturally cooling to room temperature;

(4) crushing and screening: and crushing and sieving the sintered material to obtain the hafnium nitride ceramic powder.

2. The method for preparing hafnium nitride ceramic powder according to claim 1, wherein the mass ratio of the hafnium oxide powder to the silicon nitride powder in the step (1) is 1: (1-2).

3. The method for preparing hafnium nitride ceramic powder according to claim 1, wherein the amount of the alcohol added in step (1) is 4 times the total amount of the hafnium oxide powder and the silicon nitride powder.

4. The method for preparing hafnium nitride ceramic powder according to claim 1, wherein the grinding body in step (1) is agate mortar.

5. The method for preparing hafnium nitride ceramic powder by using the silicothermic reduction oxidation method according to claim 1, wherein the oven temperature in the step (2) is 80 ℃ and the drying time is 5-15 h.

6. The method for preparing hafnium nitride ceramic powder according to claim 1, wherein in the step (3), the sintering furnace is evacuated, protective gas is filled, the temperature is raised to 1800-1950 ℃ at a rate of 6-10 ℃/min, and the hafnium nitride ceramic powder is naturally cooled to room temperature after being sintered for 1-1.5 min.

7. The method for preparing hafnium nitride ceramic powder according to claim 1, wherein the hafnium nitride ceramic powder is sieved with 200 mesh sieve in step (4).

Technical Field

The invention relates to the technical field of ceramic powder preparation, in particular to a method for preparing hafnium nitride ceramic powder by a silicon thermal reduction oxidation method.

Background

The ultra-high temperature ceramic generally refers to transition metal carbide, boride, nitride and complex phase ceramic thereof with the melting point of more than 3000 ℃, has the advantages of high melting point, low density, high strength, excellent chemical stability and the like, and has wide application in the fields of aerospace, energy and the like. Among them, the transition metal carbon/nitride ultra high temperature ceramics are receiving attention from researchers due to their excellent physical connotation and excellent material properties.

At present, one of the common methods for preparing hafnium nitride ceramic powder is to directly nitride hafnium particles in a nitrogen atmosphere by using a planetary ball mill, and then synthesize the hafnium nitride ceramic powder by mechanochemistry. The hafnium nitride is generated by directly nitriding the metal hafnium, and the biggest defect is that the metal hafnium raw material is expensive and the preparation cost of the hafnium nitride ceramic powder is too high; the other preparation method is to use hafnium oxide, sodium azide and magnesium metal as raw materials to react under high pressure to generate hafnium nitride, and the hafnium nitride cannot be synthesized in large batch due to the limitation of reaction conditions. In addition, the hafnium nitride ceramic material prepared by the two methods has low purity, so that the ceramic material has the defect of low toughness, the requirement of engineering reliability cannot be met, and the application of the hafnium nitride ceramic material is seriously influenced.

Therefore, research on a new process for preparing hafnium nitride ceramic powder to reduce the production cost of the hafnium nitride ceramic powder and improve the toughness of the ceramic becomes an important problem to be solved in the field of high temperature ceramic materials.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for preparing hafnium nitride ceramic powder by a silicon thermal reduction oxidation method, wherein silicon nitride and hafnium oxide with low raw material cost can be used for producing high-purity superfine nano-grade hafnium nitride powder in a large scale at normal pressure and low temperature, so that the production cost of the hafnium nitride ceramic powder is reduced, and the toughness of the ceramic is improved.

The invention provides a method for preparing hafnium nitride ceramic powder by a silicon thermal reduction oxidation method, which comprises the following steps:

(1) grinding and mixing: weighing hafnium oxide powder and silicon nitride powder according to a certain ratio, placing the hafnium oxide powder and the silicon nitride powder into a grinding body, adding a proper amount of alcohol as a grinding medium, and grinding for 0.5-2 hours to obtain a mixed material;

(2) and (3) pressing and forming: drying the mixed material in a drying oven, adding the dried mixed material into a forming die, maintaining the pressure for 5-60 s under the pressure of 10-100 MPa, and pressing to form loose blocky materials;

(3) pressureless sintering: putting the pressed and formed block-shaped material into a crucible filled with graphite fibrofelt and graphite paper, then laying a layer of graphite fibrofelt above the block-shaped material, finally placing the block-shaped material into a sintering furnace, carrying out pressureless sintering at 1500-2000 ℃, carrying out heat preservation sintering for 0.5-2 h, and then naturally cooling to room temperature;

(4) crushing and screening: and crushing and sieving the sintered material to obtain the hafnium nitride ceramic powder.

Preferably, the mass ratio of the hafnium oxide powder to the silicon nitride powder in the step (1) is 1: (1-2).

Preferably, the mass of the alcohol added in the step (1) is 4 times of the total mass of the hafnium oxide powder and the silicon nitride powder.

Preferably, the grinding body in the step (1) is an agate mortar.

Preferably, the temperature of the oven in the step (2) is 80 ℃, and the drying time is 5-15 h.

Preferably, in the step (3), the sintering furnace is vacuumized, protective gas is filled into the sintering furnace, the temperature is raised to 1800-1950 ℃ at the speed of 6-10 ℃/min, and the sintering furnace is naturally cooled to the room temperature after heat preservation and sintering are carried out for 1-1.5 min.

Preferably, in the step (4), 200-mesh sieve is used for sieving.

The working principle of the invention is as follows: silicon heat of the inventionThe method for preparing the hafnium nitride ceramic powder by the reduction oxidation method comprises the following steps of taking silicon nitride and hafnium oxide as raw materials, sintering at a high temperature to form the hafnium nitride ceramic powder, wherein the reaction formula is as follows: 4Si₃N₄+6HfO₂→6HfN+12SiO+5N₂. In the formed hafnium nitride ceramic powder system, on one hand, the valence electron concentration and coordination number of the transition metal element Hf are high, the atomic radius of N is small, covalent bonds with short bond length and strong bond strength are easy to form, so that the hafnium nitride ceramic powder system has high melting point and hardness, and on the other hand, the chemical bonds of the hafnium nitride ceramic powder system simultaneously have metal bonds, ionic bonds and covalent bonds, so that various different stoichiometric ratios and crystal structures are easy to regulate and control. The charge transfer from the transition metal atoms to the main group atoms ensures that the electron shielding of the d electrons which are originally distributed in space and are local is less, and enhances the locality and the correlation of the d electrons, thereby improving the toughness of the hafnium nitride ceramic powder.

The invention has the beneficial effects that: according to the method for preparing the hafnium nitride ceramic powder by the silicon thermal reduction oxidation method, silicon nitride and hafnium oxide with low raw material cost can be used for producing high-purity superfine nano-grade hafnium nitride powder in a large scale at normal pressure and low temperature, so that the production cost of the hafnium nitride ceramic powder is reduced, and the toughness of the ceramic is improved.

Drawings

FIG. 1 is an XRD pattern of a starting hafnium oxide;

FIG. 2 is an XRD pattern of the starting silicon nitride;

FIG. 3 is an XRD pattern of the hafnium nitride ceramic powder prepared according to the present invention;

FIG. 4 is an SEM and EDS view of the hafnium oxide feedstock;

FIG. 5 is an SEM and EDS view of a mixed material of hafnium oxide and silicon nitride as raw materials;

FIG. 6 is SEM and EDS diagrams of the hafnium nitride ceramic powder prepared by the present invention;

FIG. 7 shows the results of laser particle size analysis of hafnium oxide as a raw material;

FIG. 8 shows the laser particle size analysis results of the hafnium nitride ceramic powder prepared by the present invention.

Detailed Description

In order to make the technical scheme of the invention easier to understand, the technical scheme of the invention is clearly and completely described by adopting a mode of a specific embodiment in combination with the attached drawings.

Detailed description of the preferred embodiments

Example 1:

the method for preparing the hafnium nitride ceramic powder by the silicon thermal reduction oxidation method in the embodiment comprises the following steps:

(1) grinding and mixing: the mass ratio of the components is 1: 1, weighing hafnium oxide powder and silicon nitride powder, placing the hafnium oxide powder and the silicon nitride powder into an agate mortar, adding alcohol with the mass 4 times of the total mass of the hafnium oxide powder and the silicon nitride powder as a grinding medium, and grinding for 1 hour to obtain a mixed material;

(2) and (3) pressing and forming: putting the mixed material into a drying oven, drying for 5-8 h at 80 ℃, adding into a forming die, maintaining the pressure for 40-60 s under the pressure of 10-50 MPa, and pressing to form a loose blocky material;

(3) pressureless sintering: putting the pressed and formed block-shaped material into a crucible filled with graphite fiber felt and graphite paper, then laying a layer of graphite fiber felt above the block-shaped material, finally placing the block-shaped material into a sintering furnace, vacuumizing the sintering furnace, filling protective gas, heating to 1500 ℃ at the speed of 6 ℃/min, preserving heat, sintering for 2 hours, and naturally cooling to room temperature;

(4) crushing and screening: and crushing the sintered material and sieving the crushed material with a 200-mesh sieve to obtain the hafnium nitride ceramic powder.

Example 2:

the method for preparing the hafnium nitride ceramic powder by the silicon thermal reduction oxidation method in the embodiment comprises the following steps:

(1) grinding and mixing: the mass ratio of the components is 1: 1.5 weighing hafnium oxide powder and silicon nitride powder, placing the hafnium oxide powder and the silicon nitride powder in an agate mortar, adding alcohol with the mass 4 times of the total mass of the hafnium oxide powder and the silicon nitride powder as a grinding medium, and grinding for 1.5 hours to obtain a mixed material;

(2) and (3) pressing and forming: putting the mixed material into a drying oven, drying for 7-10 h at 80 ℃, adding into a forming die, maintaining the pressure for 20-30 s at 30-70 MPa, and pressing to form loose blocky materials;

(3) pressureless sintering: putting the pressed and formed block-shaped material into a crucible filled with graphite fiber felt and graphite paper, then laying a layer of graphite fiber felt above the block-shaped material, finally placing the block-shaped material into a sintering furnace, vacuumizing the sintering furnace, filling protective gas, heating to 1800 ℃ at the rate of 8 ℃/min, preserving heat, sintering for 1.5h, and naturally cooling to room temperature;

(4) crushing and screening: and crushing the sintered material and sieving the crushed material with a 200-mesh sieve to obtain the hafnium nitride ceramic powder.

Example 3:

the method for preparing the hafnium nitride ceramic powder by the silicon thermal reduction oxidation method in the embodiment comprises the following steps:

(1) grinding and mixing: the mass ratio of the components is 1: 2, weighing hafnium oxide powder and silicon nitride powder, placing the hafnium oxide powder and the silicon nitride powder into an agate mortar, adding alcohol with the mass 4 times of the total mass of the hafnium oxide powder and the silicon nitride powder as a grinding medium, and grinding for 2 hours to obtain a mixed material;

(2) and (3) pressing and forming: putting the mixed material into a drying oven, drying for 12-15 h at 80 ℃, adding into a forming die, maintaining the pressure for 5-10 s under the pressure of 90-100 MPa, and pressing to form loose blocky materials;

(3) pressureless sintering: putting the pressed and formed block-shaped material into a crucible filled with graphite fiber felt and graphite paper, then laying a layer of graphite fiber felt above the block-shaped material, finally placing the block-shaped material into a sintering furnace, vacuumizing the sintering furnace, filling protective gas, heating to 2000 ℃ at the speed of 10 ℃/min, preserving heat, sintering for 1h, and naturally cooling to room temperature;

(4) crushing and screening: and crushing the sintered material and sieving the crushed material with a 200-mesh sieve to obtain the hafnium nitride ceramic powder.

Second, material characterization analysis

1. XRD result analysis of the raw material and the hafnium nitride powder:

FIG. 1 is an XRD pattern of a starting hafnium oxide; FIG. 2 is an XRD pattern of the starting silicon nitride; FIG. 3 is an XRD pattern of the hafnium nitride ceramic powder prepared by the present invention. Comparing fig. 1 to fig. 3, it can be seen that the reaction between the hafnium oxide and silicon nitride as the raw materials is complete, and there are no diffraction peaks of other impurities except the characteristic peaks of the cubic phase hafnium nitride.

2. SEM electron microscope appearance and EDS energy spectrum analysis of raw materials and hafnium nitride powder:

FIG. 4 is an SEM and EDS view of the hafnium oxide feedstock; FIG. 5 is an SEM and EDS view of a mixed material of hafnium oxide and silicon nitride as raw materials; FIG. 6 is SEM and EDS diagrams of the hafnium nitride ceramic powder prepared by the present invention. Comparing fig. 4 to 6, it can be seen that the particle size of the resultant hafnium nitride is in the submicron level, similar to the particle size and morphology of the starting hafnium oxide. Besides the residual carbon element on the conductive adhesive, no other impurity elements exist, which indicates that the purity is very high.

3. Laser particle size analysis and BET results of the raw materials and the hafnium nitride powder:

FIG. 7 shows the results of laser particle size analysis of hafnium oxide as a raw material; FIG. 8 shows the laser particle size analysis results of the hafnium nitride ceramic powder prepared by the present invention. Comparing fig. 7 and fig. 8, it can be seen that the measured particle size of hafnium nitride is equivalent to that of hafnium oxide, so that there are serious soft agglomerates inside the hafnium nitride, and the hafnium nitride can be dispersed and opened by simple mechanical force, so as to obtain submicron or even nanometer-level hafnium nitride powder. The grain diameter of the obtained hafnium nitride powder is obviously normally distributed, and the distribution effect is better than that of the raw material hafnium oxide.

According to the BET multipoint method (P/P0 is 0.0400-0.3200), the specific surface area of the hafnium nitride ceramic powder prepared by the invention is 5.1287m²/g。

4. Analysis result of oxygen and nitrogen content:

when the testing temperature of the oxygen-nitrogen analyzer reaches 2000 ℃, the oxygen content is as follows: 0.045%; nitrogen content: 0.0641 percent. When the testing temperature of the oxygen-nitrogen analyzer reaches 3000 ℃, the oxygen content is as follows: 0.216 percent.

5. Purity analysis results:

from the results of XPS tests, it is known that the sample contains HfN, HfO2, SiO, and SiC as the substances composed of Hf, O, N, and Si elements, and the content of the product hafnium nitride in the sample is more than 98.5% (excluding a small amount of SiC) by combining the physical properties of these substances (the decomposition temperature of hafnium nitride is more than 3000 ℃, the decomposition temperature of hafnium oxide is less than 3000 ℃, and silicon monoxide is completely decomposed at 1900 ℃), wherein the sample contains a small amount of hafnium oxide (< 1.2%), and a trace amount of silicon monoxide and silicon nitride (< 0.2%).

In conclusion, the analysis shows that the hafnium nitride ceramic powder prepared by the invention has high purity (more than or equal to 98.5 percent), an ultrafine nano structure and a grain diameter of about hundreds of nanometers, and only has serious soft agglomeration, which is the same as the agglomeration condition of the hafnium oxide serving as the raw material.

It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all implementations of the present invention, and the embodiments are only examples, which are only used to provide a more intuitive and clear understanding of the present invention, and are not intended to limit the technical solutions of the present invention. All other embodiments, as well as other simple substitutions and various changes to the technical solutions of the present invention, which can be made by those skilled in the art without inventive work, are within the scope of the present invention without departing from the spirit of the present invention.