CN103265031B - A kind of method of carbothermic method low-temperature growth ZrC-WC or ZrC-TaC mixed powder - Google Patents

Abstract

The invention relates to a method for preparing ZrC-WC or ZrC-TaC mixed powder at low temperature by carbothermal reduction method, which belongs to the technical field of structural ceramics. The method uses sucrose, phenolic resin, epoxy resin or pitch as a carbon source, and mixed oxides as a metal source, and the mixed oxide is a mixture of zirconia and tungsten oxide or a mixture of zirconia and tantalum pentoxide. In the present invention, sucrose, phenolic resin, epoxy resin or asphalt and mixed oxides are used as raw materials, and the cost of raw materials is low, and the mixing of sucrose, phenolic resin, epoxy resin or asphalt and oxides is wet mixing, which is evenly mixed and difficult to agglomerate , The synthesis process is carried out in a high-purity argon environment or in a vacuum, and the reduction reaction can occur at a lower temperature to synthesize ZrC-WC (ZrC-TaC) powder.

Description

A method for preparing ZrC-WC or ZrC-TaC mixed powder at low temperature by carbothermal reduction method

technical field

The invention relates to a method for preparing ZrC-WC or ZrC-TaC mixed powder at low temperature by carbothermal reduction method, which belongs to the technical field of structural ceramics.

Background technique

Ultra-high temperature ceramics (UHTCs) refer to carbides of transition metals with excellent high-temperature oxidation resistance, ablation resistance and thermal shock resistance above 1800 °C and in a reactive atmosphere (such as oxygen atoms). and boride materials, mainly including TaC, HfC, ZrC, HfB ₂ , ZrB ₂ , etc., whose excellent high-temperature performance enables them to adapt to extreme environments such as hypersonic flight, atmospheric reentry, transatmospheric flight, and rocket propulsion systems. It is used in various key parts or components such as the nose cone of the aircraft, the leading edge of the wing, and the hot end of the engine. Refractory metal carbides TaC, HfC, and ZrC are the only material systems other than carbon that can withstand high temperatures above 3500°C. Among them, the high specific strength, high specific modulus and low preparation cost of ZrC make it one of the most potential ultra-high temperature materials.

However, difficult sintering and weak oxidizability are the main problems limiting its application. Since ZrC is covalently bonded, its diffusion rate is low, and high temperature and high pressure are required to sinter densely. Aiming at the difficult sintering of ZrC materials, especially at low temperature, the key is to prepare high-purity ultra-fine ZrC powder, which can significantly improve its sintering properties. On the other hand, ZrC is easy to oxidize to form a loose zirconia layer in a high-temperature oxidizing environment, and it is difficult to effectively hinder the diffusion of oxygen into the material. In order to improve its oxidation resistance, researchers added compounds containing high-valent cations (such as W ⁵⁺ , Ta ⁵⁺ and Nb ⁵⁺ , etc.) to Zr-containing compounds, such as WC, TaC and NbC. During the oxidation process of this kind of material, a protective layer with passive oxidation is formed, which can hinder the diffusion of oxygen into the material and effectively improve its oxidation resistance. Moreover, adding high-valent cationic compounds such as WC to the material can increase its high-temperature flexural strength by about 1 time. Therefore, ZrC-WC composite ceramics can not only improve its oxidation resistance but also increase its high-temperature flexural strength. The application range of the ZrC material is improved. Therefore, there is an urgent demand for the synthesis of high-purity ultrafine ZrC-WC composite powders.

At present, the preparation methods of synthesizing ZrC powder mainly include: direct synthesis method, carbothermal reduction method, sol-gel method, mechanical alloying method, self-propagating combustion synthesis method, etc. Among them, the process that can realize industrial production is the carbothermal reduction method, and the method for synthesizing ZrC powder is to use carbon black to reduce zirconia. The chemical reaction equation is as follows:

ZrO ₂ +3C=ZrC+2CO(g) (1)

Similarly, the method of synthesizing WC and TaC powders can use carbon black to reduce the corresponding oxides, and the chemical reaction equation is as follows:

2WO ₃ +7C=W ₂ C+6CO(g) (2)

WO ₃ +4C=WC+3CO(g) (3)

Ta ₂ O ₅ +6C=Ta ₂ C+5CO(g) (4)

Ta ₂ O ₅ +7C=2TaC+5CO(g) (5)

According to thermodynamic calculations (as shown in Figure 1 and Figure 2), it can be seen that the condition of high-purity argon is a necessary condition for low-temperature synthesis of high-purity ultrafine powder. The use of sucrose as a carbon source can solve the problem of uneven solid-solid mixing, and realize the method of liquid-solid-wet mixing, so that the surface of the oxide powder is evenly coated with a layer of sucrose (a layer of C film is formed after cracking), which is beneficial to carbon heat Reduction reaction, the synthesized powder has the characteristics of high purity and small particle size.

Contents of the invention

The object of the present invention is a method for preparing ZrC-WC or ZrC-TaC mixed powder at low temperature by carbothermal reduction method, which has simple process, low temperature and short time consumption, and can obtain high-purity ultrafine ZrC-WC (TaC) powder body.

The purpose of the present invention is achieved through the following technical solutions.

A method for preparing ZrC-WC or ZrC-TaC mixed powder at low temperature by carbothermal reduction method of the present invention, the method uses sucrose, phenolic resin, epoxy resin or pitch as carbon source, and mixed oxide as metal source, mixing The oxide is a mixture of zirconia and tungsten oxide or a mixture of zirconia and tantalum pentoxide, the molar ratio of zirconia and tungsten oxide is 1:10 to 1:5, and the molar ratio of zirconia and tantalum pentoxide is 1:10～1:5, the ratio of the molar weight of carbon in the carbon source to the total molar weight of the mixed oxide is 3～20:1, and the steps of the method are:

1) Put the mixed oxide into the ball milling tank, add solvent A, the mass of the added solvent A is 1% to 5% of the total mass of the mixed oxide, then add zirconia ball milling medium, ball mill and mix for 10-48h, put The mixed oxides were transferred to a vessel containing solvent A, and ultrasonically dispersed to obtain a mixed solution;

2) Dissolving the carbon source in solvent B to obtain a carbon source solution, and then pouring the obtained carbon source solution into the mixed solution obtained in step 1); then heating and stirring to obtain a uniformly mixed reactant;

3) Put the reactant obtained in step 2) into a graphite crucible, put the graphite crucible into a flowing argon protection or vacuum heat treatment furnace for heating, then cool to room temperature with the furnace, and then grind to obtain ZrC-WC (or ZrC -TaC) powder, the particle size of the obtained powder is 50-200nm.

The total concentration of the mixed solution obtained in the above step 1) is 1-5mol/L, and the ultrasonic dispersion time is 0.5-2h; the purity of zirconia is ≥99.9wt.%, and the particle size is 50-120nm; the purity of tungsten oxide is ≥99.9 wt.%, the particle size is 50-120nm; the purity of tantalum pentoxide is ≥99.9wt.%, and the particle size is 50-120nm.

The concentration of the carbon source solution in the above step 2) is 3-15mol/L. When the carbon source is sucrose, the solvent B is water; when the carbon source is phenolic resin, epoxy resin or pitch, the solvent B is ethanol, n-hexane or cyclohexane; the carbon source is analytically pure; the heating temperature is 100-250°C, and the heating time is 0.5-2h; the stirring method is magnetic stirring;

The heating program in the heat treatment furnace in the above-mentioned step 3) is heating to 1200-1600°C at a heating rate of 10°C/min and keeping the temperature for 0.5-2h.

In the present invention, the mixed oxide powder and sucrose (or phenolic resin, epoxy resin, asphalt, etc.) solution are used for wet mixing in the ball milling process, and the mixing is uniform, which solves the uneven mixing of the two solid phase powders, and the purity is not high and easy The problem of agglomeration; high-purity argon or vacuum is used in the preparation process, and the reduction reaction can occur at a lower temperature to prepare ultrafine ZrC-WC (ZrC-TaC) powder.

Beneficial effect

In the present invention, sucrose, phenolic resin, epoxy resin or asphalt and mixed oxides are used as raw materials, the cost of raw materials is low, and the mixing of sucrose, phenolic resin, epoxy resin or asphalt and oxides is wet mixing, which is evenly mixed and difficult to agglomerate , the synthesis process is carried out in a high-purity argon environment or in a vacuum, and the reduction reaction can occur at a lower temperature to synthesize ZrC-WC (ZrC-TaC) powder, that is, the method has simple process, low temperature and short time consumption. In the invention, organic matter is evenly coated around mixed oxide particles to achieve the purpose of uniform mixing, and high-purity ZrC-WC (ZrC-TaC) mixed powder is prepared.

Description of drawings

Fig. 1 is the relationship between Gibbs free energy and temperature under standard atmospheric pressure;

Figure 2 is the relationship between Gibbs free energy and temperature under high-purity Ar;

Fig. 3 is the X-ray diffraction spectrum of the prepared ZrC-WC powder and ZrC-TaC powder; Wherein, the unit of ordinate intensity is cps, and the unit of abscissa diffraction angle is °;

Fig. 4 is the scanning electron micrograph of the ZrC-WC powder that embodiment prepares;

Fig. 5 is a scanning electron micrograph of the ZrC-TaC powder prepared in the embodiment.

Detailed ways

The present invention will be further described below in conjunction with embodiment.

Example 1

Using sucrose as carbon source, zirconia and tungsten oxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 23.2g of WO ₃ powder with a purity of 99.9wt.% and a particle size of 80nm, and put them together into a ball mill jar, add 100ml of absolute ethanol, and mix them with zirconia balls for 24 hours. The homogenized oxides were transferred to a vessel containing 100ml of absolute ethanol, and ultrasonically dispersed for 0.5h;

2) Weigh 365.1g of sucrose and add it to 100ml of water, stir to make it evenly mixed, then add it to the solution obtained in step 1), heat while magnetically stirring, the heating temperature is 120°C, and the heating time is 2h, and a well-mixed reaction is obtained thing;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1600°C at a heating rate of 10°C/min 1h, then cooled to room temperature with the furnace, and then ground to obtain a mixed powder material; the X-ray diffraction pattern of the obtained powder material is shown in Figure 3, and its scanning electron microscope photo is shown in Figure 4, and the scanning voltage is 15kv. It can be seen from Figure 3 that the obtained powder material is ZrC-5mol%WC mixed powder; it can be seen from Figure 4 that the average particle size of ZrC-5mol%WC powder is 100nm.

Example 2

Using sucrose as carbon source, zirconia and tungsten oxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 46.4g of WO ₃ powder with a purity of 99.9wt.% and a particle size of 70nm, and put them together into a ball mill jar, add 100ml of absolute ethanol, and mix them with zirconia balls for 24 hours. The homogenized oxides were transferred to a vessel containing 100ml of absolute ethanol, and ultrasonically dispersed for 1h;

2) Weigh 388g of sucrose and add it to 100ml of water, stir to make it evenly mixed, then add it to the solution obtained in step 1), heat while magnetically stirring, the heating temperature is 140°C, and the heating time is 2h, to obtain a uniformly mixed reactant ;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1600°C at a heating rate of 10°C/min 1h, then cool to room temperature with the furnace, and then grind to obtain a mixed powder material; the X-ray diffraction pattern of the obtained powder material is as shown in Figure 3, as can be seen from Figure 3, the obtained powder material is ZrC-10mol%WC Mix powder.

Example 3

Using sucrose as carbon source, zirconia and tantalum pentoxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 44.2g of Ta ₂ O ₅ powder with a purity of 99.9wt.% and a particle size of 60nm, put them together into a ball mill jar, add 120ml of absolute ethanol, and mix them with zirconia balls for 12 hours. Move the mixed oxide into a vessel containing 100ml of absolute ethanol, and disperse it ultrasonically for 2 hours;

2) Weigh 382.2g of sucrose and add it to 110ml of water, stir to make it evenly mixed, then add it to the solution obtained in step 1), and heat while magnetically stirring, the heating temperature is 160°C, and the heating time is 1h, and a well-mixed reaction is obtained thing;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1500°C at a heating rate of 10°C/min 2h, then cooled to room temperature with the furnace, and then ground to obtain a mixed powder material; the X-ray diffraction pattern of the obtained powder material is shown in Figure 3, and its scanning electron microscope photo is shown in Figure 5, and the scanning voltage is 15kv. It can be seen from Figure 3 that the obtained powder material is ZrC-10mol%TaC mixed powder; it can be seen from Figure 5 that the average particle size of ZrC-10mol%TaC powder is 100nm.

Example 4

Using sucrose as carbon source, zirconia and tantalum pentoxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 88.4g of Ta ₂ O ₅ powder with a purity of 99.9wt.% and a particle size of 90nm, put them together into a ball mill jar, add 120ml of absolute ethanol, and mix them with zirconia balls for 24 hours. Transfer the mixed oxides to a vessel containing 150ml of absolute ethanol, and ultrasonically disperse for 1.5h;

2) Weigh 422.2g of sucrose and add it to 120ml of water, stir to make it evenly mixed, then add it to the solution obtained in step 1), heat while magnetically stirring, the heating temperature is 130°C, and the heating time is 2h, and a well-mixed reaction is obtained thing;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1600°C at a heating rate of 10°C/min 1h, then cool to room temperature with the furnace, and then grind to obtain a mixed powder material; the X-ray diffraction pattern of the obtained powder material is as shown in Figure 3, as can be seen from Figure 3, the obtained powder material is ZrC-20mol%TaC Mix powder.

Example 5

Use phenolic resin as the carbon source, and zirconia and tungsten oxide as the refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 23.2g of WO ₃ powder with a purity of 99.9wt.% and a particle size of 60nm, put them together into a ball mill jar, add 110ml of absolute ethanol, and mix them with zirconia balls for 24 hours. The homogenized oxide was transferred to a vessel containing 110ml of absolute ethanol, and ultrasonically dispersed for 1h;

2) Weigh 342g of phenolic resin and add it to 150ml of absolute ethanol, stir to make it evenly mixed, then add it to the solution obtained in step 1), and heat it with magnetic stirring at the same time. The heating temperature is 150°C and the heating time is 1.5h. uniformly mixed reactants;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1400°C at a heating rate of 10°C/min 2h, then cooled to room temperature with the furnace, and then ground to obtain ZrC-5mol%WC mixed powder.

Example 6

Use phenolic resin as carbon source, zirconia and tantalum pentoxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 88.4g of Ta ₂ O ₅ powder with a purity of 99.9wt.% and a particle size of 80nm, put them together into a ball mill jar, add 130ml of absolute ethanol, and mix them with zirconia balls for 48 hours. Transfer the mixed oxides to a vessel containing 150ml of absolute ethanol, and ultrasonically disperse for 1.5h;

2) Weigh 395.4g of phenolic resin and add it to 130ml of n-hexane, stir to make it evenly mixed, and then add it to the solution obtained in step 1), and heat it with magnetic stirring at the same time. The heating temperature is 120°C and the heating time is 2.5h, and the obtained uniformly mixed reactants;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1300°C at a heating rate of 10°C/min 2h, then cooled to room temperature with the furnace, and then ground to obtain ZrC-20mol%TaC mixed powder.

Example 7

Use epoxy resin as carbon source, zirconia and tungsten oxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 46.4g of WO ₃ powder with a purity of 99.9wt.% and a particle size of 90nm, put them together into a ball mill jar, add 130ml of absolute ethanol, and mix them with zirconia balls for 24 hours. The homogenized oxide was transferred to a vessel containing 150ml of absolute ethanol, and ultrasonically dispersed for 1h;

2) Weigh 396.9g of epoxy resin and add it to 130ml of cyclohexane, stir to make it evenly mixed, then add it to the solution obtained in step 1), and heat while magnetically stirring. The heating temperature is 140°C and the heating time is 2h. Obtain a uniformly mixed reactant;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1700°C at a heating rate of 10°C/min 1h, then cooled to room temperature with the furnace, and then ground to obtain ZrC-10mol%WC mixed powder.

Example 8

Use pitch as carbon source, zirconia and tantalum pentoxide as refractory metal source;

1) Weigh 246.4g of ZrO ₂ powder and 44.2g of Ta ₂ O ₅ powder with a purity of 99.9wt.% and a particle size of 70nm, put them together into a ball mill jar, add 140ml of absolute ethanol, and mix them with zirconia balls for 12 hours. Move the mixed oxide into a vessel containing 100ml of absolute ethanol, and disperse it ultrasonically for 2 hours;

2) Weigh 380g of asphalt and add it to 210ml of absolute ethanol, stir to make it evenly mixed, then add it to the solution obtained in step 1), and heat it with magnetic stirring at the same time. The heating temperature is 150°C and the heating time is 0.5h, and the mixture uniform reactants;

3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1400°C at a heating rate of 10°C/min 2h, then cooled to room temperature with the furnace, and then ground to obtain ZrC-10mol%TaC mixed powder.

Claims (2)

1. a method for preparing ZrC-WC mixed powder by carbothermal reduction method at low temperature, is characterized in that the steps of the method are: Using sucrose as carbon source, zirconia and tungsten trioxide as refractory metal source; 1) Weigh 246.4g ZrO ₂ powder, 23.2g WO ₃ powder, its purity is 99.9wt.%, particle diameter is 80nm, put into ball mill tank together, add 100ml dehydrated alcohol, zirconia ball mill mixes 24h, will The mixed oxides were transferred to a vessel containing 100ml of absolute ethanol, and ultrasonically dispersed for 0.5h; 2) Weigh 365.1g of sucrose and add it to 100ml of water, stir to make it evenly mixed, then add it to the solution obtained in step 1), and heat while stirring magnetically, the heating temperature is 120°C, and the heating time is 2h, and a well-mixed reaction is obtained thing; 3) Put the reactant obtained in step 2) into a graphite crucible, and then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating. The heating program is to heat up to 1600°C at a heating rate of 10°C/min and keep warm 1h, then cool down to room temperature with the furnace, and then grind to obtain the mixed powder material. 2. A method for preparing ZrC-TaC mixed powder at low temperature by carbothermal reduction, characterized in that the steps are: Using sucrose as carbon source, zirconia and tantalum pentoxide as refractory metal source; 1) Weigh 246.4g of ZrO ₂ powder and 44.2g of Ta ₂ O ₅ powder with a purity of 99.9wt.% and a particle size of 60nm, put them together into a ball mill jar, add 120ml of absolute ethanol, and mix them with zirconia balls for 12 hours , move the mixed oxide to a vessel containing 100ml of absolute ethanol, and ultrasonically disperse for 2h; 2) Weigh 382.2g of sucrose and add it to 110ml of water, stir to make it evenly mixed, then add it to the solution obtained in step 1), and heat while magnetic stirring, the heating temperature is 160°C, and the heating time is 1h, and a well-mixed reaction is obtained thing; 3) Put the reactant obtained in step 2) into a graphite crucible, then put the graphite crucible into a high-purity argon-protected heat treatment furnace for heating, and the heating program is to heat up to 1500°C at a heating rate of 10°C/min 2h, then cool down to room temperature with the furnace, and then grind to obtain the mixed powder material.