In-situ hot pressing sintering method for preparing high-density Magnéli phase conductive ceramics

Abstract

The present invention relates to an in-situ hot pressing and sintering preparation method of a high-density Magnéli phase conductive ceramic, comprising: (1) mixing titanium dioxide coarse powder, titanium dioxide fine powder and a reducing agent to obtain a raw material powder; the reducing agent is titanium powder or carbon powder; (2) placing the obtained raw material powder into a hot pressing mold, and then placing it in a hot pressing and sintering furnace for in-situ hot pressing and sintering to obtain the Magnéli phase conductive ceramic.

Description

Technical Field

[0001] The invention relates to an in-situ hot pressing and sintering preparation method of high-density Magnéli phase conductive ceramics, belonging to the technical field of ceramic preparation. Background Art

[0002] Titanium oxide ceramics have the excellent characteristics of acid and alkali resistance, corrosion resistance, wide source, low cost, non-toxic and odorless, and environmental optimization. 2 4s 2 , so the main valence states of the formed compounds are +2, +3 and +4. Magnéli phase is a non-stoichiometric titanium oxide phase, a series of homologous triclinic phases with a unified chemical formula Ti n O 2n-1 , including Ti4O7, Ti5O9, T6O 11 、Ti7O 13 、Ti8O 15 、Ti9O 17 、Ti 10 O 19 . The Magnéli phase has a stable structure in an air atmosphere at 500°C, with a boundary of monoclinic Ti3O5 on one side and reduced rutile TiO2 on the other side, extending infinitely in two directions. In the Magnéli phase, every n-1 layer of TiO2 is adjacent to a TiO layer, and the TiO layer is connected to the adjacent TiO2 layer by sharing O on the surface, rather than sharing the edge like rutile TiO2. The conductivity of the material is contributed by the TiO layer, while the chemical resistance and corrosion resistance are shared by the TiO2 layer. The TiO layer is protected by being sandwiched between the TiO2 layers. The Magnéli phase has high conductivity, strong visible light response, and excellent electrochemical properties (including high chemical stability, wide potential window, etc.). Taking Ti4O7 in this material system as an example, the theoretical conductivity can reach 1.52×10 5 S / m, twice that of graphite. Due to these advantages, Magnéli phases are often used in fields such as electrode materials and LED black matrix materials. Magnéli phase ceramics are excellent conductors of electricity and heat, while also possessing the high strength and stability of traditional ceramic materials. They are a very important class of transition metal oxide ceramics.

[0003] Most of the existing Magnéli phase ceramic preparation processes are divided into two steps: powder synthesis and molding and sintering. Magnéli phase powder itself is not easy to obtain, and requires precise control of the synthesis path. Commonly used Magnéli phase powder synthesis methods include hydrogen reduction of titanium dioxide, metal thermal reduction, carbon thermal reduction, etc. After the powder is synthesized, the powder is sintered into porcelain by methods such as spark plasma sintering, microwave sintering, normal pressure / hot pressing sintering, etc. Under the traditional process flow, two or more high-temperature treatment processes are often required, which is extremely time-consuming and energy-consuming. In addition, during the powder synthesis process, due to the high temperature, the product obtained often has a slight sintering phenomenon, which increases the powder particle size, which also worsens the molding and sintering properties of the powder. Therefore, obtaining highly conductive, dense, and strong Magnéli phase ceramics is costly and complex. Summary of the Invention

[0004] To this end, the present invention provides an in-situ hot pressing and sintering method for preparing a high-density Magnéli phase conductive ceramic, comprising:

[0005] (1) mixing titanium dioxide coarse powder, titanium dioxide fine powder and a reducing agent to obtain a raw material powder; the reducing agent is titanium powder or carbon powder;

[0006] (2) placing the obtained raw material powder into a hot pressing mold, and then placing it in a hot pressing sintering furnace for in-situ hot pressing sintering to obtain the Magnéli phase conductive ceramic.

[0007] To address the time-consuming and energy-consuming problems and powder quality degradation caused by multiple high-temperature treatments in the current preparation of a large number of Magnéli phase ceramics, as well as the difficulty in controlling the Magnéli phase composition, the present invention directly mixes a reducing agent with titanium dioxide powder and then hot-presses and sinters it. During the sintering process, the Magnéli phase is directly formed in situ due to the characteristic of oxygen vacancies in titanium dioxide shifting from high concentration to low concentration. At the same time, the movement of a large number of oxygen vacancies also promotes material exchange between powders, thereby optimizing the sintering activity of the material. Specifically, the present invention combines the reaction of generating new phases with the ceramic sintering process, that is, using reactive hot pressing to prepare dense ceramics that require multiple synthetic sintering steps. The in-situ hot pressing sintering proposed by the present invention has the following advantages: first, it simplifies the process flow by reducing the heat treatment process, reducing preparation costs and energy consumption; second, it effectively avoids the reduction in sintering activity caused by the inevitable increase in powder particle size during the high-temperature powder preparation process. It is precisely because the pre-sintering heat treatment is avoided that the present invention can use titanium dioxide fine powder to enhance sintering. The present invention uses in-situ sintering to solve the problem, combining the powder preparation reaction process with the sintering process. During the sintering process, the pre-embedded reducing agent directly reacts with the titanium dioxide to complete the phase change.

[0008] Preferably, the particle size of the coarse titanium dioxide powder is 1 μm to 10 μm, and the particle size of the fine titanium dioxide powder is 20 nm to 500 nm. The mass ratio of the fine titanium dioxide powder to the coarse titanium dioxide powder is (0 to 1):1, preferably (0.1 to 0.5):1. The combination of coarse and fine powders in the present invention is to grade the powders so that the ceramic body achieves a higher bulk density without heating. In addition, the submicron and nanometer-scale fine powders increase sintering activity, which helps significantly reduce the sintering temperature and improve sintering efficiency.

[0009] Preferably, when titanium powder is the reducing agent, the amount of titanium powder added is 1-11% of the total mass of the titanium dioxide powder. Carbon reacts during the hot pressing process to produce carbon dioxide and carbon monoxide, which accumulate in the relatively closed mold and easily form pores, adversely affecting the density of the ceramic. Using titanium as a sintering reducing agent is easier to produce dense ceramics than carbon.

[0010] Preferably, when the reducing agent is carbon powder, the amount of the carbon powder added is 3-10% of the total mass of the titanium dioxide powder.

[0011] Preferably, the mixing method is planetary ball milling; the parameters of the planetary ball milling include: anhydrous ethanol as a dispersant, metal oxide grinding balls as ball milling media, a rotation speed of 240 to 400 r / min, and a ball milling time of 3 to 12 hours; preferably, drying and sieving are performed after the planetary ball milling is completed; more preferably, the drying is drying at 60 to 100° C. for 6 to 12 hours; the mesh size of the sieving is 60 to 200 meshes.

[0012] Preferably, the sintering atmosphere of the in-situ hot pressing sintering is vacuum, reducing atmosphere or inert atmosphere; the sintering pressure of the in-situ hot pressing sintering is 5-50 MPa, the sintering temperature of the in-situ hot pressing sintering is 900° C.-1300° C., and the time of the in-situ hot pressing sintering is 0.5-3 h.

[0013] Furthermore, preferably, the pressurization rate of the in-situ hot pressing sintering is 0.05 to 0.5 MPa / min, and the pressure release rate of the in-situ hot pressing sintering is 0.05 to 0.5 MPa / min.

[0014] Furthermore, preferably, the heating rate of the in-situ hot pressing sintering is 5 to 15° C. / min, and the cooling rate of the in-situ hot pressing sintering is 5 to 15° C. / min.

[0015] Preferably, after the in-situ hot pressing sintering is completed, the mold is taken out and demoulded, and then processed to remove surface impurities.

[0016] On the other hand, the present invention also provides a high-density Magnéli phase conductive ceramic prepared according to the above-mentioned in-situ hot pressing sintering preparation method, wherein the composition of the high-density Magnéli phase conductive ceramic includes Ti4O7, Ti5O9, T6O 11 、Ti7O 13 、Ti8O 15 、Ti9O 17 、Ti 10 O 19 At least one of; and, the high-density Magnéli phase conductive ceramic does not contain impurities other than titanium oxide.

[0017] Preferably, the electrical conductivity of the high-density Magnéli phase conductive ceramic is 10 to 1300 S / cm.

[0018] Preferably, the absolute density of the high-density Magnéli phase conductive ceramic is 3.68 to 4.31 g / cm 3 .

[0019] Preferably, the density of the high-density Magnéli phase conductive ceramic is 85-99.5%.

[0020] Preferably, the compressive strength of the high-density Magnéli phase conductive ceramic is above 300 MPa.

[0021] Preferably, the three-point bending strength of the high-density Magnéli phase conductive ceramic is 30 to 300 MPa.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention adopts in-situ sintering to form Magnéli phase conductive ceramics in one step, combining the two separate steps of powder preparation and ceramic sintering in the preparation process of Magnéli phase ceramics, thereby optimizing the process and reducing the time cost and energy consumption required for multiple high-temperature treatments. In addition, the occurrence of powder sintering growth during the high-temperature synthesis of powders and the deterioration of ceramic sintering performance caused by powder growth are avoided.

[0024] (2) The preparation of traditional Magnéli phase conductive ceramic powders requires extremely precise control of the sintering temperature and sintering atmosphere, especially since the Magnéli phase is extremely sensitive to oxygen partial pressure at high temperatures. The present invention uses hot pressing sintering in a relatively closed environment with a solid reducing agent for reduction, which can limit the reaction to the hot pressing mold to the greatest extent, and largely avoid the influence of the external atmosphere and even the sintering temperature on the internal reaction (the sintering temperature no longer significantly affects the phase composition but only affects the sintering degree). This makes it possible to more accurately control the product phase when sintering in a non-reducing atmosphere by calculating the reaction formula to control the amount of solid reducing agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation method of the Magnéli phase conductive ceramic according to the present invention;

[0026] Figure 2 This is an SEM image of a cross-section of the Magnéli phase conductive ceramic prepared in Example 3. Impurities on the grains were introduced by bending strength tests and Archimedean drainage measurements.

[0027] Figure 3 The electrical conductivity test results of the Magnéli phase conductive ceramics of Examples 1-5 (tested using the four-terminal method);

[0028] Figure 4 XRD patterns of the Magnéli phase conductive ceramics of Examples 1-5;

[0029] Figure 5 XRD patterns of the Magnéli phase conductive ceramics obtained in Example 3 and Examples 6-8;

[0030] Figure 6 This is an optical photograph of Example 6 after machining and cutting, and the surface is not polished;

[0031] Figure 7 : This is the SEM image of the Magnéli phase conductive ceramic obtained in Example 7. DETAILED DESCRIPTION

[0032] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0033] In the present invention, titanium dioxide powders of different particle sizes are graded and then common materials such as titanium or carbon are added thereto as solid reducing agents. The powders are evenly dispersed by stirring or ball milling, and then placed in a vacuum reactor for reaction. Magnéli phase conductive ceramics are obtained by hot pressing and sintering, and finally the final product is obtained through post-processing. It is difficult to complete a complete phase change during the sintering process by sintering at normal pressure, so hot pressing is used to give a stronger driving force to the reaction, i.e., in-situ hot pressing and sintering. During the in-situ hot pressing and sintering process, we found that too low temperature or pressure will also cause incomplete reaction and produce microscopic defects in the microstructure of the ceramic product. Therefore, the present invention has also optimized the sintering process based on a large number of experiments, and extended the reaction time to overcome this problem. In addition, the present invention also prepares pure phase Magneli phase ceramics by regulating the ratio of reactants and adopting a relatively closed sintering process.

[0034] The Magnéli phase conductive ceramic and its preparation method provided by the present invention are exemplarily described below.

[0035] Coarse titanium dioxide powder and fine titanium dioxide powder are mixed by planetary ball milling. After a certain period of planetary ball milling, a reducing agent is added and ball milling is continued until the mixture is uniform and a uniform ceramic slurry is obtained. The resulting slurry is dried in a drying oven to a powder, which is then sieved to obtain the raw material powder.

[0036] In an optional embodiment, the particle size of the titanium dioxide coarse powder is 1 to 10 μm. The particle size of the titanium dioxide fine powder is 20 nm to 500 nm. The ratio of the titanium dioxide fine powder to the coarse powder is 0 to 1. The purpose of the titanium dioxide coarse powder gradation is to increase the powder compaction density and improve the sintering activity.

[0037] In an optional embodiment, the reducing agent is a material, such as titanium or carbon, that can deprive titanium dioxide of lattice oxygen and produce a gas or the target product itself without introducing solid impurities into the ceramic body. For example, titanium can be added in an amount of 1 to 10% of the total mass of the titanium dioxide powder.

[0038] In an optional embodiment, the coarse and fine titanium dioxide powders are mixed using planetary ball milling with anhydrous ethanol as the dispersant and metal oxide grinding balls as the milling medium. The milling time is 0 to 3 hours at a speed of 240 to 400 r / min. This step is intended to better mix the coarse and fine titanium dioxide powders to achieve inter-filling of the graded powders, thereby increasing the compacted density of the powders. Another purpose is to moderately reduce the milling time of the reducing agent, thereby slightly reducing the oxidation of the reducing agent powder caused by localized heat during milling. After adding the reducing agent, the milling is continued at a speed of 240 to 400 r / min for 3 to 12 hours.

[0039] In an optional embodiment, the slurry drying step is to dry the slurry at 60-100° C. for 6-12 hours. This step needs to ensure the removal of ethanol and physically adsorbed water in the powder, but at the same time the temperature must be controlled to ensure that the reducing agent is not oxidized in large quantities.

[0040] In an optional embodiment, the powder is screened through a sieve with a mesh size of 60 to 200 to obtain ceramic powder with good fluidity and no agglomeration.

[0041] The raw powder is placed in a hot pressing mold and then placed in a hot pressing furnace for hot pressing and sintering. The powder can be poured directly into the mold. Preferably, the mold interior can be covered with graphite paper or boron nitride coating to prevent the powder from reacting with the mold. The ceramic powder can be pre-formed and then placed into the mold.

[0042] In an optional embodiment, hot pressing sintering is to place the mold into a hot pressing furnace; the sintering atmosphere is a vacuum or inert or reducing atmosphere, and the reducing atmosphere must be selected with caution, which will greatly affect the final phase composition and micromorphology of the ceramic; the sintering heating rate is 5 to 15°C / min; the sintering temperature is 900°C to 1300°C; the sintering pressure is 5 to 50MPa; the sintering pressurization and decompression rate is 0.05 to 0.5MPa / min; and the sintering heat preservation and pressure holding time is 0.5 to 3h.

[0043] After sintering, the mold is removed and then post-processed to remove surface impurities to obtain the Magnéli-phase conductive ceramic. During the demolding process, care must be taken to prevent any reactions between the reactants and the mold, and to prevent damage to both the sample and the mold. Ideally, the process can utilize specialized machining methods such as electrical discharge machining (EDM) to fully utilize the ceramic's electrical conductivity.

[0044] In the present invention, a certain proportion of a solid reducing agent that can reduce titanium dioxide without introducing impurities is mixed with titanium dioxide graded powder and placed in a hot pressing mold for hot pressing and sintering, thereby preparing a pure and high-quality Magnéli phase conductive ceramic with excellent conductivity and high mechanical properties.

[0045] The conductivity of the Magnéli phase conductive ceramic obtained by the present invention is 10 to 1300 S / cm when tested by a four-terminal resistance test system. The absolute density of the Magnéli phase conductive ceramic obtained by the Archimedean buoyancy method is 3.68 to 4.31 g / cm 3 Calculations between absolute and theoretical density indicate that the density of the Magnéli phase conductive ceramic is 85-99.5%. Testing using a universal testing machine revealed that the compressive strength of the Magnéli phase conductive ceramic is above 300 MPa. Testing using a universal testing machine also revealed that the three-point flexural strength of the Magnéli phase conductive ceramic is between 30 and 300 MPa.

[0046] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below.

[0047] Examples 1-6:

[0048] The distribution ratio (mass ratio) of each component of the Magnéli phase conductive ceramics of Examples 1-6 is shown in Table 1.

[0049] Table 1:

[0050] Components Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 <![CDATA[TiO2 / 1μm]]> 70 70 70 70 70 70 <![CDATA[TiO2 / 25nm]]> 30 30 30 30 30 30 Ti (wt%) 7 8 9 10 11 12 .

[0051] The preparation methods of Examples 1-6 are the same, and the specific steps are as follows:

[0052] 1. Preparation of ceramic powder: According to the ratio described in Table 1, micron titanium dioxide powder, nano titanium dioxide powder and reducing agent titanium powder were weighed respectively. The two titanium dioxide powders with different particle sizes were first placed in a polyurethane ball mill, and anhydrous ethanol was added as a dispersant. Zirconia grinding balls were added as the ball milling medium. The mass ratio of powder, dispersant and grinding balls was 1:1:2. After being loaded into a planetary ball mill and ball milled at a speed of 300 r / min for 3 h, the ball mill was taken out, the lid was opened, and the weighed titanium powder was added. The ball milling was continued for 9 h. The ball-milled slurry was placed in an 80°C oven and dried for 12 h. After confirming that the powder was completely dry, it was passed through a 100-mesh sieve to obtain a hot-pressed powder with excellent fluidity and no obvious agglomeration.

[0053] 2. In-situ hot pressing reaction sintering: Take 40g of ceramic powder and place it in a 40mm×40mm mold. Dry press it on the press at a pressure of 10MPa for 2 minutes to obtain a green body of 40×40×(11-15)mm. Select a 40mm×40mm graphite mold, select the upper and lower pressure heads of appropriate sizes, spray high-temperature lubricant in the mold and lay a suitable size of graphite paper to prevent the raw material from reacting with the graphite mold. Place the simply pressed green body in the mold and assemble it. After that, place it in a vacuum hot pressing furnace. Extract the gas in the furnace and keep the pressure in the furnace <100Pa. Set the heating and pressurization program as follows: heat up to 600℃ at 10℃ / min, then increase the temperature from 600℃ to 1000℃ in 80min, and increase the pressure from 0MPa to 30MPa in the same time. After maintaining the maximum temperature and pressure for 120min (2h), it also takes 80min to release the pressure to 0, cool to 600℃, and then cool in the furnace. After cooling to room temperature, remove the mold;

[0054] 3. Post-sintering processing: Place the mold on the press, demould according to the relevant process, use a scraper to remove the graphite paper and other impurities on the ceramic surface as much as possible, and then perform machining to obtain Magnéli phase conductive ceramics.

[0055] Table 2 shows the performance parameters of the Magnéli phase conductive ceramics prepared in Examples 1-6:

[0056]

[0057]

[0058] From Table 2, Figure 2 、 Figure 3 、 Figure 4 as well as Figure 6 It can be seen that the Magnéli phase conductive ceramics prepared by the method of the present invention can meet the actual use conditions, and the ceramic properties and ceramic phase composition will change regularly to a certain extent with the change of the amount of solid reducing agent added, which indirectly proves the possibility of consciously designing the properties of Magnéli phase conductive ceramics by changing the amount of solid reducing agent.

[0059] Examples 7-10

[0060] The distribution ratio of each component of the Magnéli phase conductive ceramic in Examples 7-10 is consistent with that in Example 3, that is, TiO2-1μm:TiO2-25nm:Ti (mass ratio) = 70:30:9, but the sintering temperature is adjusted. The sintering temperature changes are detailed in Table 3.

[0061] Table 3:

[0062] Example 7 Example 8 Example 3 Example 9 Example 10 Sintering temperature of in-situ hot pressing sintering / ℃ 800 900 1000 1100 1200 .

[0063] The preparation methods of Examples 7-9 are basically the same as those of Examples 1-5, and the specific steps are as follows:

[0064] 1. Preparation of ceramic powder: Weigh micron titanium dioxide powder, nano titanium dioxide powder and reducing agent titanium powder in a ratio of 70:30:9 respectively. Place the two titanium dioxide powders of different particle sizes into a polyurethane ball mill first, add anhydrous ethanol as a dispersant, add zirconium oxide grinding balls as the ball milling medium, and the mass ratio of powder, dispersant and grinding balls is 1:1:2. Place the powder into a planetary ball mill and ball mill at a speed of 300 r / min for 3 hours. Then, take out the ball mill, open the lid and add the weighed titanium powder. Continue ball milling for 9 hours. Place the ball-milled slurry in an 80°C oven and dry it for 12 hours. After confirming that the powder is completely dry, pass it through a 100-mesh sieve to obtain a hot-pressed powder with good fluidity and no obvious agglomeration.

[0065] 2. In-situ hot pressing reaction sintering: Take 40g of ceramic powder and place it in a 40mm×40mm mold. Dry press it on the press at a pressure of 10MPa for 2 minutes to obtain a green body of 40×40×(11-15)mm. Select a 40mm×40mm graphite mold, select the upper and lower pressure heads of appropriate sizes, spray high-temperature lubricant in the mold and lay a suitable size of graphite paper to prevent the raw material from reacting with the graphite mold. Place the simply pressed green body in the mold and assemble it. After that, place it in a vacuum hot pressing furnace. Extract the gas in the furnace and keep the pressure in the furnace <100Pa. Set the heating and pressurization program as follows: heat up to 400℃ / 500℃ / 700℃ / 800℃ at 10℃ / min, then increase the temperature from 400℃ / 500℃ / 700℃ / 800℃ to 800℃ / 900℃ / 1100℃ / 1200℃ in 80min, and increase the pressure from 0MPa to 30MPa in the same time. After maintaining the maximum temperature and pressure for 120min (2h), use 80min to release the pressure to 0, cool to 400℃ / 500℃ / 700℃ / 800℃, then cool with the furnace, and remove the mold after it cools to room temperature.

[0066] 3. Post-sintering processing: Place the mold on the press, demould according to the relevant process, use a scraper to remove the graphite paper and other impurities on the ceramic surface as much as possible, and then perform machining to obtain Magnéli phase conductive ceramics.

[0067] Table 4 shows the performance parameters of the Magnéli phase conductive ceramics prepared in Examples 7-9:

[0068] <![CDATA[Density / (g*cm -3 )]]> Conductivity / (S*cm) Bending strength / MPa Compressive strength / Mpa Example 7 3.70 89.3 95.7 730 Example 8 3.87 725.81 146.0 1120 Example 3 4.28 1129.0 125.6 1180 Example 9 4.26 819.67 66.4 670 Example 10 4.21 37.66 8.2 310 .

[0069] From Table 4 and Figure 5 It can be seen that the Magnéli phase conductive ceramics prepared by the method of the present invention will not undergo significant changes in phase composition even if the sintering temperature is greatly changed under vacuum conditions ( Figure 5 The changes shown in the figure are mainly due to the change in the size of the ceramic grains and the incomplete solid-phase reduction reaction at low temperatures). The sintering temperature will also have a great impact on the performance of the ceramic sintering. By simultaneously controlling the sintering temperature and the amount of reducing agent added, the performance of the ceramic can be designed within a certain range. However, it should be noted that if the temperature is too low, the sample uniformity will be greatly reduced. Figure 7 shown.

[0070] Examples 11-14

[0071] The preparation methods of Examples 11-14 are basically the same as those of Example 3, except for the mass ratio of the fine titanium dioxide powder to the coarse titanium dioxide powder, as shown in Table 5.

[0072] Table 5:

[0073]

[0074] Table 6 shows the performance parameters of the Magnéli phase conductive ceramics prepared in Examples 11-14:

[0075] <![CDATA[Density / (g*cm -3 )]]> Conductivity / (S*cm) Bending strength / MPa Compressive strength / Mpa Example 11 4.25 736.2 107.2 940 Example 12 4.28 1083.3 128.2 1150 Example 3 4.28 1129.0 125.6 1180 Example 13 4.30 1032.8 152.7 1175 Example 14 4.31 992.6 173.5 1133 .

[0076] It can be seen from Table 6 that due to the use of in-situ hot pressing sintering, titanium dioxide fine powder can play a role in appropriately improving the density and strength during the ceramic sintering process because it does not undergo heat treatment before sintering. However, too much titanium dioxide fine powder will excessively increase the sintering activity of the sample, resulting in abnormal grain growth under the same sintering conditions, which will in turn deteriorate the performance of the sample.

Claims

1. A method for preparing a high-density Magnéli phase conductive ceramic by in-situ hot pressing sintering, characterized in that: include: (1) Mixing titanium dioxide coarse powder, titanium dioxide fine powder and a reducing agent to obtain a raw material powder; the reducing agent is titanium powder; wherein the particle size of the titanium dioxide coarse powder is 1 μm to 10 μm, and the particle size of the titanium dioxide fine powder is 20 nm to 500 nm; the mass ratio of the titanium dioxide fine powder to the titanium dioxide coarse powder is (0.1 to 0.5):1; the amount of the titanium powder added is 1 to 11% of the total mass of the titanium dioxide powder; (2) placing the obtained raw material powder into a hot pressing mold, and then placing it in a hot pressing sintering furnace for in-situ hot pressing sintering to obtain the Magnéli phase conductive ceramic; wherein the sintering atmosphere of the in-situ hot pressing sintering is a vacuum, a reducing atmosphere or an inert atmosphere; the sintering pressure of the in-situ hot pressing sintering is 5 to 50 MPa, the sintering temperature of the in-situ hot pressing sintering is 900°C to 1300°C, and the time of the in-situ hot pressing sintering is 0.5 to 3 hours.

2. The in-situ hot pressing sintering preparation method according to claim 1, characterized in that: The mixing method is planetary ball milling; the parameters of the planetary ball milling include: using anhydrous ethanol as a dispersant, metal oxide grinding balls as a ball milling medium, a rotation speed of 240 to 400 r / min, and a ball milling time of 3 to 12 hours.

3. The in-situ hot pressing sintering preparation method according to claim 2, characterized in that: After the planetary ball milling, it is dried and screened.

4. The in-situ hot pressing sintering preparation method according to claim 3, characterized in that: The drying is performed at 60-100° C. for 6-12 hours; the sieving screen has a mesh size of 60-200 meshes.

5. The in-situ hot pressing sintering preparation method according to claim 1, characterized in that: The pressurization rate of the in-situ hot pressing sintering is 0.05-0.5 MPa / min, and the pressure release rate of the in-situ hot pressing sintering is 0.05-0.5 MPa / min; the heating rate of the in-situ hot pressing sintering is 5-15°C / min, and the cooling rate of the in-situ hot pressing sintering is 5-15°C / min.

6. The in-situ hot pressing sintering preparation method according to claim 1, characterized in that: After the in-situ hot pressing sintering is completed, the mold is removed and demoulded, and then processed to remove impurities remaining on the surface.

7. A high-density Magnéli phase conductive ceramic prepared by the in-situ hot pressing sintering preparation method according to any one of claims 1 to 6, characterized in that: The high-density Magnéli phase conductive ceramic comprises Ti4O7, Ti5O9, T6O 11 、Ti7O 13 、Ti8O 15 、Ti9O 17 、Ti 10 O 19 At least one of; and, the high-density Magnéli phase conductive ceramic does not contain impurities other than titanium oxide.

8. The high-density Magnéli phase conductive ceramic according to claim 7, characterized in that: The high-density Magnéli phase conductive ceramic has an electrical conductivity of 10 to 1300 S / cm and an absolute density of 3.68 to 4.31 g / cm 3 The density is 85-99.5%, the compressive strength is above 300MPa, and the three-point bending strength is 30-300MPa.

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