阅读说明：本技术 一种熔盐法制备max相金属陶瓷材料的方法 (Method for preparing MAX phase cermet material by molten salt growth method ) 是由 李升� 陈洪祥 戴品强 林智杰 洪春福 常发 于 2021-06-25 设计创作，主要内容包括：本发明公开了一种熔盐法制备MAX相金属陶瓷材料的方法。本发明首先将MAX相的M位金属元素、A位主族元素和X位C/N元素按元素比例配比,在真空条件下进行预反应烧结,再将预反应烧结后的产物与NaCl或KCl等单种盐或混合盐混合研磨,再经高温真空烧结得到目标产物。本发明中所使用的熔盐法对于MAX相金属陶瓷的制备具有以下优点：提高物相纯度,降低反应温度,增大反应物间的接触面积,加速反应进行,本发明为M-(n+)-1A-(n)X的高纯物相制备提供了新思路,为该系列化合物的本征物性研究提供了有力的保证。(The invention discloses a method for preparing MAX phase cermet materials by a molten salt growth method. The method comprises the steps of proportioning M-site metal elements, A-site main group elements and X-site C/N elements of MAX phase according to element proportion, carrying out pre-reaction sintering under vacuum condition, mixing and grinding the pre-reaction sintered product with single salt or mixed salt such as NaCl or KCl, and carrying out high-temperature vacuum sintering to obtain the target product. The molten salt method used in the invention has the following advantages for the preparation of MAX phase metal ceramics: improving phase purity, reducing reaction temperature, increasing contact area between reactants and accelerating reaction, and the invention is M n + 1 A n The preparation of the high-purity phase of X provides a new idea and provides a powerful guarantee for the intrinsic physical property research of the series of compounds.)

1. A method for preparing MAX phase cermet material by a molten salt growth method is characterized in that the molecular formula of the cermet material is expressed as M₃A₂X, wherein M is a transition group metal element, A is a main group element, and X is a C/N element, the method comprising the steps of:

1) mixing the M element powder, the A element powder and the X element powder according to the proportion of 3:2:1, and grinding in a mortar to uniformly mix the M element powder, the A element powder and the X element powder;

2) tabletting and molding the uniformly mixed powder, putting the powder into a vacuum quartz tube, carrying out pre-reaction sintering in a high-temperature furnace, keeping the sintering temperature not higher than 1000 ℃ for a period of time, and cooling to room temperature;

3) uniformly mixing the product after pre-reaction sintering and composite salt in a mortar, putting the mixture into an alumina crucible, putting the alumina crucible into a vacuum quartz tube, carrying out secondary calcination in high-temperature furnace equipment, heating to 700-800 ℃, keeping the temperature for a period of time, then heating to 1150-1550 ℃, keeping the temperature for a period of time, and cooling to room temperature to obtain a final-fired product;

4) and washing the salt of the final-fired product with water, filtering and drying to obtain the MAX-phase cermet material.

2. The method for preparing MAX phase cermet material through molten salt method as claimed in claim 1, wherein the cermet material has a molecular formula expressed as Nb₃P₂And C, step 1) is to mix Nb powder, P powder and graphite powder in proportion.

3. The method for preparing MAX phase cermet materials by molten salt method as claimed in claim 1, wherein sintering temperature in step 2) is 700-850 ℃ and holding time is 2-40 hours.

4. The method of claim 1, wherein the complex salt in step 3) is a mixture of NaCl and KCl in a molar ratio of 1: 1.

5. The method for preparing MAX phase cermet materials by molten salt method as claimed in claim 1, wherein in step 3), the mass ratio of the pre-reaction sintered product to the composite salt is 1: 3.

6. The method for preparing MAX phase cermet materials by the molten salt method according to claim 1, wherein in step 3), the temperature is raised to 700 ℃ -800 ℃ during the second calcination, the temperature is kept for more than 2 hours, then the temperature is rapidly raised to 1200 ℃ -1350 ℃ within 120min, the temperature is kept for 6-20 hours, and then the temperature is naturally cooled to room temperature.

7. The method for preparing MAX phase cermet materials by molten salt method as claimed in claim 1, wherein step 4) the final fired product is washed three or more times with deionized water.

8. The method for preparing MAX phase cermet materials by the molten salt method as claimed in claim 1, wherein said drying in step 4) is drying in an electrothermal blowing dry oven at 40-120 ℃ for more than 2 hours.

Technical Field

The invention relates to the fields of inorganic non-metallic materials, high-temperature conductive ceramics, structural functional ceramics and the like, in particular to a method for preparing MAX phase cermet materials by a molten salt growth method.

Background

The MAX phase is a series of conductive ceramic materials with a layered structure, and is called conductive ceramic because it combines the advantages of metal and ceramic materials. MAX generally has good electrical conductivity, thermal conductivity, low thermal expansion coefficient, high bulk modulus and elastic modulus, good oxidation resistance and corrosion resistance, and the like, and has good application prospects in many fields, especially in the fields of high-temperature structural components, high-temperature conductive components, and the like.

New MAX (M) s have been discovered this year_n+1A_nX) phase comprising Nb₃A₂C、Nb₃P₂C、Ta₃P₂C and V₃As₂C. Nb is found by high-pressure X-ray diffraction research₃As₂C still has not taken place the phase transition under the pressure up to 47GPa, have good stability, through studying the change with pressure of unit cell parameter, find Nb₃As₂The volume modulus of C is up to 225(3) GPa, which is the highest of all MAX phases. In addition, through the first principle calculation, the series of materials are further proved to have excellent elastic mechanical properties, wherein Nb is₃P₂C theoretical elastic modulus up to E_V371.8GPa, shear modulus G_V152.0GPa, its theoretical bulk modulus ratio Nb₃As₂C is still higher, and is one of the materials with the best elastic mechanical property in MAX phase. The material has low toxicity and low density, so the material has optimistic application prospect. But currently M_n+1A_nPreparation of the X-phase high-purity phase is difficult, except for Nb₃As₂C is a pure phase, the purity of other three phases is usually only 50-60%, and the product contains 211 phases, binary compounds and other mixed phases. The existence of the impure phase seriously interferes the characterization of the intrinsic mechanical, electrical, thermal, magnetic properties and the like of the series of materials, and the high-purity M_n+1A_nThe preparation of the X phase is a problem that is currently urgently to be solved.

At present, the preparation methods of MAX phase metal ceramic powder mainly comprise the following steps: self-propagating high-temperature synthesis, mechanical alloying, pressureless sintering, molten salt method and the like. Although the self-propagating high-temperature synthesis has simple process, the combustion process has larger thermal gradient and faster condensation speed, and complex phases are likely to be formed; the mechanical alloying can lead the crystal grains to be evenly refined, but the experimental period is long and the oxidation is easy; pressureless sintering is the simplest sintering method, but sometimes fails to meet the synthesis requirements of some compounds; the molten salt method has the advantages of improving the phase purity, reducing the reaction temperature, increasing the contact area between reactants, accelerating the reaction and the like due to low cost, has obvious effect on powder synthesis, and is widely applied all the time.

Disclosure of Invention

The invention aims to provide a method for preparing MAX phase cermet materials by a molten salt growth method.

In order to achieve the purpose, the invention adopts the following technical scheme:

MAX phase cermet material, wherein the molecular formula of the cermet material is expressed as M₃A₂X, wherein M is a transition group metal element, A is a main group element, and X is a C/N element; the metal ceramic material has a hexagonal crystal structure, and the unit cell is formed by alternately stacking a single-layer MX octahedron layer and double-layer MA triangular prism layers.

Further, the molecular formula of the cermet material is expressed as Nb₃P₂C。

A method for preparing MAX phase cermet material by a molten salt growth method comprises the following steps:

1) mixing the M element powder, the A element powder and the X element powder according to the proportion of 3:2:1, and grinding in a mortar to uniformly mix the M element powder, the A element powder and the X element powder;

2) tabletting and molding the uniformly mixed powder, putting the powder into a vacuum quartz tube, carrying out pre-reaction sintering in a high-temperature furnace, keeping the sintering temperature not higher than 1000 ℃, and naturally cooling to room temperature after keeping the temperature for a period of time;

3) uniformly mixing the product after pre-reaction sintering and composite salt in a mortar, putting the mixture into an alumina crucible, putting the alumina crucible into a vacuum quartz tube, carrying out secondary calcination in high-temperature furnace equipment, heating to 700-800 ℃, keeping the temperature for a period of time, then quickly heating to 1150-1550 ℃, keeping the temperature for a period of time, and naturally cooling to room temperature to obtain a final calcination product;

4) and washing the salt of the final-fired product with deionized water, filtering and drying to obtain MAX phase metal ceramic material powder.

In the step 2), the sintering temperature is 700-850 ℃, and the heat preservation time is 2-40 hours.

The compound salt in the step 3) is a mixture of NaCl and KCl with a molar ratio of 1: 1.

In the step 3), the mass ratio of the product after pre-reaction sintering to the composite salt is 1: 3.

In the step 3), the temperature is firstly raised to 700-800 ℃ during the secondary calcination, the temperature is kept for more than 2 hours, then the temperature is rapidly raised to 1200-1350 ℃ within 120min, the temperature is kept for 6-20 hours, and then the mixture is naturally cooled to the room temperature.

And 4) washing the final-burned product with deionized water for more than three times in the step 4).

And 4) drying for more than 2 hours in an electrothermal blowing drying oven at the temperature of 40-120 ℃.

The invention adopts a molten salt method to prepare high-purity M for the first time₃A₂X phase, the series of materials have excellent mechanical and thermal properties such as low thermal expansion coefficient, high volume modulus, high elastic modulus and the like, and the molten salt method used in the invention is used for MAX (M)_n+1A_nX) phase cermet preparation has the following advantages: (1) the phase purity is improved. (2) Reducing the reaction temperature, (3) increasing the contact area between reactants, and (4) accelerating the reaction.

The method is simple and easy, has short reaction period, and can obtain a high-purity product M_n+1A_nThe preparation of the high-purity phase of X provides a new idea and provides a powerful guarantee for the intrinsic physical property research of the series of compounds.

Drawings

FIG. 1 is Nb₃P₂A crystal structure diagram of phase C;

FIG. 2 is Nb₃P₂Scanning Electron Micrographs (SEM) of phase C;

FIG. 3 is Nb₃P₂Energy spectrum of phase C (EDS);

FIG. 4 is Nb₃P₂X-ray powder diffraction fine modification spectrogram of the C phase.

Detailed Description

Example 1

MAX phase cermet material (Nb) prepared by molten salt method₃P₂C) The method comprises the following steps:

weighing Nb powder with the purity of 99%, P powder with the purity of 99% and graphite powder with the purity of 99% according to the proportion of 3:2:1, and carefully grinding in a mortar; and then tabletting and molding the uniformly mixed sample by using a tablet machine, placing the sample in a quartz tube, vacuumizing and sealing, and carrying out pre-reaction sintering on the sample: the temperature is raised from room temperature to 650 ℃ for 6 hours, the temperature is preserved for 2120 minutes, then the temperature is raised to 800 ℃ within 2 hours, the temperature is preserved for 2 hours, and then the mixture is naturally cooled.

Taking out the pre-reaction sintered product and mixed salt, carefully grinding the pre-reaction sintered product and the mixed salt in a mortar according to the mass ratio of 1:3 to uniformly mix the pre-reaction sintered product and the mixed salt, putting the ground mixture into an alumina crucible, putting the alumina crucible into a quartz tube, vacuumizing and sealing the quartz tube, and then carrying out final sintering: heating to 700 deg.C from room temperature within 2 hr, holding for 3 hr, heating to 1250 deg.C within 2 hr, holding for 10 hr, naturally cooling to room temperature, washing the sintered mixture with deionized water for more than three times until the salt is completely removed, and drying in 70 deg.C electrothermal blowing dry box for 5 hr to obtain high-purity Nb₃P₂And C, sampling.

Nb₃P₂The phase C crystal structure is shown in FIG. 1 and is formed by alternately stacking double-layer NbP triangular prism layers and single-layer NbC octahedral layers; from the SEM photograph of fig. 2, it can be seen that it has typical MAX phase layered characteristics, and the grain size can reach more than 50 microns; EDS surface energy spectrum analysis (figure 3) is carried out on the alloy to find that the proportion of Nb element is 14.8 percent, the proportion of P element is 9.6 percent, the proportion of Nb and P element is approximate to 3:2, and the proportion of each element accords with the design; getNb prepared in example 1₃P₂C, observing the diffraction spectrum of the sample by using an X-ray diffractometer, identifying the object image by using the diffraction spectrum and performing single-phase refinement (figure 4), wherein the space group of the sample is P6₃A phase close to pure phase with a unit cell parameter of The obtained refinement parameter is R_p＝7.3％,R_wp9.28%, the reliability of the crystal structure was confirmed.

In summary, the present application provides Nb by the molten salt method₃P₂The purity of C is improved from 50-60% to nearly pure phase, the effect is obvious, and good precondition guarantee is provided for intrinsic physical property research of the material and future application exploration of the material.

Example 2

MAX phase cermet material (Nb) prepared by molten salt method₃P₂C) The method comprises the following steps:

1) weighing Nb powder with the purity of 99%, P powder with the purity of 99% and graphite powder with the purity of 99% according to the proportion of 3:2:1, and grinding in a mortar to uniformly mix the Nb powder, the P powder and the graphite powder;

2) tabletting and forming the uniformly mixed powder, putting the powder into a vacuum quartz tube, carrying out pre-reaction sintering in a high-temperature furnace, keeping the sintering temperature at 800 ℃, and naturally cooling to room temperature after 8 hours of heat preservation;

3) uniformly mixing a product subjected to pre-reaction sintering and mixed salt in a mortar, wherein the mixed salt is a compound of NaCl and KCl with a molar ratio of 1:1, then loading the mixture into an alumina crucible, then placing the alumina crucible into a vacuum quartz tube, carrying out secondary calcination in high-temperature furnace equipment, raising the temperature to 800 ℃, preserving heat for 2 hours, then rapidly raising the temperature to 1350 ℃, continuing to preserve heat for 15 hours, and then naturally cooling to room temperature to obtain a final-calcined product;

4) washing the final-burned product with deionized water three times, filtering, and drying in an electrothermal blowing drying oven at 100 deg.CMedium drying for 2 hours to obtain high-purity Nb₃P₂And C, sampling.

Example 3

MAX phase cermet material (Nb) prepared by molten salt method₃P₂C) The method comprises the following steps:

1) weighing Nb powder with the purity of 99%, P powder with the purity of 99% and graphite powder with the purity of 99% according to the proportion of 3:2:1, and grinding in a mortar to uniformly mix the Nb powder, the P powder and the graphite powder;

2) tabletting and molding the uniformly mixed powder, putting the powder into a vacuum quartz tube, carrying out pre-reaction sintering in a high-temperature furnace, keeping the sintering temperature at 750 ℃, and naturally cooling to room temperature after 8 hours of heat preservation;

3) uniformly mixing a product subjected to pre-reaction sintering and mixed salt in a mortar, wherein the mixed salt is a compound of NaCl and KCl with a molar ratio of 1:1, then loading the mixture into an alumina crucible, then placing the alumina crucible into a vacuum quartz tube, carrying out secondary calcination in high-temperature furnace equipment, raising the temperature to 750 ℃, preserving the heat for 2 hours, then rapidly raising the temperature to 1300 ℃, continuing to preserve the heat for 10 hours, and then naturally cooling to room temperature to obtain a final-calcined product;

4) washing the final-burned product with deionized water for three times, filtering, and drying in an electrothermal blowing dry box at 80 ℃ for more than 2 hours to obtain high-purity Nb₃P₂And C, sampling.

It should be noted that the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above examples. It is to be understood that other modifications and variations, which may be directly derived or suggested to one skilled in the art without departing from the basic concept of the invention, are to be considered as included within the scope of the invention.