Preparation method of a high temperature coefficient thermosensitive material

Abstract

The present invention belongs to the technical field of the preparation of electronic ceramic components. More specifically, it relates to a preparation method of a high temperature coefficient thermosensitive material. Graphene is uniformly mixed with ceramic powder. After reduction sintering, graphene is uniformly dispersed at the grain boundaries of barium titanate ceramic grains. During the reoxidation process, graphene is oxidized and removed to form two-dimensional pores, which serve as oxygen transmission paths to promote the reoxidation of the ceramic grain boundaries to form barriers, thereby preparing a high-density, low reoxidation temperature, high temperature coefficient porous barium titanate-based thermosensitive ceramic. The present invention can be applied to the existing preparation process of barium titanate thermosensitive ceramics. By adding only a small amount of graphene, the reoxidation temperature of barium titanate thermosensitive ceramics can be reduced, and a barium titanate thermosensitive ceramic with high density, a relatively high rise-to-resistance ratio, and a high temperature coefficient can be prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of electronic ceramic components, and more specifically, relates to a method for preparing a high temperature coefficient thermosensitive material. Background Art

[0002] Microelectronic technology has been continuously driving the development of various electronic components towards the trend of integration and miniaturization. Room temperature resistivity and temperature coefficient are two important electrical parameters of BaTiO3-based thermosensitive ceramics. For multi-layer chip BaTiO3-based PTCR thermosensitive components aiming at miniaturization and low resistance, it is desired to reduce the room temperature resistivity as much as possible and increase the temperature coefficient. It is difficult to significantly reduce the inherent room temperature resistivity of BaTiO3-based PTCR thermosensitive ceramics. Generally, its room temperature resistivity is above 10 Ω·cm. At the same time, restricted by the device size, this results in a very high room temperature resistance of traditional bulk BaTiO3-based PTCR thermosensitive ceramics, thus hindering their application scope, such as overcurrent protection, etc. Based on this, researchers have developed multi-layer chip-structured BaTiO3-based PTCR thermosensitive ceramics, which are mainly composed of Ni internal electrodes and film-like BaTiO3-based PTCR thermosensitive ceramics. The multi-layer chip BaTiO3-based PTCR thermosensitive ceramics have the advantages of small size and low room temperature resistance, and are often used as overcurrent and overheat protection components in electronic products.

[0003] To achieve a low room temperature resistance of thermosensitive ceramics, it is necessary to add sintering aids or sinter at a higher temperature to prepare samples with a higher density. When the highly dense ceramic body is re-oxidized in air, it is difficult for oxygen to be transported through the grain boundaries, and it is difficult to obtain an appropriate temperature coefficient. To obtain the thermosensitive ceramic properties suitable for industrial production requirements, the re-oxidation temperature of thermosensitive ceramics is usually ≥800 °C. However, increasing the re-oxidation temperature or time will cause the oxidation of metal electrodes and deteriorate the product performance. Therefore, when using the reduction-reoxidation method to prepare BaTiO3-based thermosensitive ceramics, a certain porosity needs to be left. These pores can serve as the transmission path for re-oxidation oxygen and promote the oxidation of grain boundaries.

[0004] Currently, related research mainly prepares donor-doped nano-barium titanate powder through wet chemical methods such as the sol-gel method described in CN103626489A to achieve a higher density at a lower temperature, or forms a liquid phase by adding sintering aids such as SiO2, BN, Al2O3, etc. to promote the rearrangement and rapid densification of the powder. In addition, as described in CN102531574A, the solid content of the green body is adjusted by changing the binder content during the tape casting process. However, the above methods cannot achieve an appropriate balance between high density and porosity. Summary of the Invention

[0005] Aiming at the defects of the prior art, the purpose of the present invention is to provide a preparation method of a high temperature coefficient thermosensitive material, so as to solve the technical problems in the prior art that when preparing barium titanate thermosensitive ceramics, it is impossible to achieve an appropriate balance between high density and porosity, resulting in the inability to obtain barium titanate thermosensitive ceramics with low room temperature resistivity and high temperature coefficient, etc.

[0006] To achieve the above purpose, the present invention provides a preparation method of a high temperature coefficient barium titanate-based thermosensitive ceramic, including the following steps:

[0007] (1) Mix the donor-doped barium titanate-based powder with barium carbonate powder, silicon dioxide powder and graphene, and form a ceramic green body; heat-treat to remove the organic matter introduced during the forming process to obtain a debinded green body.

[0008] (2) Calcinate the debinded green body obtained in step (1) in an inert atmosphere or a reducing atmosphere to obtain a ceramic block.

[0009] (3) Re-oxidize the ceramic block obtained in step (2) in an oxygen-containing atmosphere. During the re-oxidation process, graphene is oxidized and removed to form two-dimensional pores, and the ceramic grain boundaries are re-oxidized to form barriers, obtaining a high temperature coefficient barium titanate-based thermosensitive ceramic material.

[0010] Preferably, in step (1), the barium carbonate powder accounts for 0.1%-2% of the mass of the donor-doped barium titanate-based powder; the silicon dioxide powder accounts for 0.5%-4% of the mass of the donor-doped barium titanate-based powder; the graphene accounts for 0.1%-10% of the mass of the donor-doped barium titanate-based powder.

[0011] Preferably, in step (1), the heat treatment temperature is 300°C - 500°C, and the time is 2h - 48h.

[0012] Preferably, for the donor-doped barium titanate-based powder in step (1), the donor element is one or more of trivalent metal elements and pentavalent metal elements; the donor doping is A-site doping, B-site doping or A, B-site co-doping.

[0013] Preferably, the graphene in step (1) is monolayer or multilayer, more preferably 1 - 10 layers, and the lateral dimension is 1 - 10μm.

[0014] Preferably, in step (2), the calcination is to raise the temperature to 950°C - 1400°C at a heating rate of 200°C / h - 500°C / h, then hold for 0.5h - 5h, and then cool to 800°C at a cooling rate of 100°C / h - 400°C / h, and then cool with the furnace to room temperature.

[0015] Preferably, the atmosphere used in the calcination in step (2) is nitrogen or a mixture of nitrogen and hydrogen, and more preferably a mixture of nitrogen and hydrogen.

[0016] Preferably, the re-oxidation in step (3) is specifically as follows: heating to 600°C - 900°C at a heating rate of 60°C / h - 300°C / h, then holding for 0.5 h - 4 h, and then cooling with the furnace, thus obtaining the thermosensitive ceramic material.

[0017] Generally speaking, the present invention proposes to use graphene as a sacrificial template and add it into the donor-doped barium titanate-based ceramic matrix to prepare barium titanate-based thermosensitive ceramics with high relative density, low re-oxidation temperature, and high temperature coefficient. Specifically, graphene is added to the barium titanate-based powder after pre-calcination, and the uniformly dispersed graphene is retained during the reduction sintering, while it is oxidized and forms two-dimensional voids during the re-oxidation process. These voids can serve as a pathway for oxygen transmission to promote the oxidation of ceramic grains, so as to achieve a high temperature coefficient of barium titanate thermosensitive ceramics at a lower re-oxidation temperature. Compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects are obtained:

[0018] (1) In the present invention, compared with the control group (the sample without graphene addition), a lower graphene doping amount can achieve a reduction in the re-oxidation temperature, an increase in the resistance increase ratio and the temperature coefficient on the premise of ensuring a lower room temperature resistance, and there is a relatively wide graphene doping regulation range according to specific requirements.

[0019] (2) In the present invention, as a carbon material, graphene will not affect the chemical composition of the matrix material during the sintering and re-oxidation processes, so it has good stability and repeatability.

[0020] (3) In the present invention, graphene can serve as a barrier layer to inhibit the diffusion of metal into the ceramic matrix at high temperatures and avoid the degradation of ceramic properties.

[0021] (4) In the present invention, graphene can limit the excessive growth of ceramic grains at high temperatures, which helps to prepare fine-grained ceramics and has the potential to further reduce the single-layer film thickness.

[0022] (5) In the present invention, on the premise of ensuring the temperature coefficient and the resistance increase ratio, the ceramic density can be increased and the grain size can be reduced, which helps to improve the mechanical properties of the ceramic.

[0023] (6) The high-density and low-re-oxidation-temperature porous barium titanate-based thermosensitive ceramic material prepared by the present invention can be applied to the dry pressing process to prepare chip PTCR ceramics, and can also be used in the forming processes of multilayer chip PTCR devices such as roll forming, injection molding, slip casting, and tape casting. It is not limited by the forming process, and the preparation method is simple and easy to operate. Description of the Drawings

[0024] Figure 1 The flow chart for preparing porous barium titanate thermosensitive ceramics using graphene as a sacrificial template.

[0025] Figure 2 SEM image of the cross-section of Specimen 2 after reduction sintering.

[0026] Figure 3 SEM image of the surface of Specimen 2 after re-oxidation. Detailed implementation manners

[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Graphene, as a two-dimensional material composed of carbon atoms tightly packed by sp 2 hybrid bonds, theoretically has a specific surface area of up to 2.630 m 2 / g, and at the same time has good mechanical properties, excellent electrical and thermal conductivity. Since its discovery in 2004, various preparation methods and extensive application fields have been developed. Its preparation process has become increasingly mature, the cost has been greatly reduced, and it has gradually achieved commercial applications in multiple industries.

[0029] A porous barium titanate-based thermosensitive ceramic prepared using graphene as a sacrificial template provided by the present invention includes a barium titanate-based thermosensitive ceramic matrix, and two-dimensional pores formed by the oxidation and removal of graphene two-dimensional nanomaterials uniformly distributed at the grain boundaries during the re-oxidation process. The two-dimensional pores generated by a lower graphene doping amount will not have an obvious impact on the relative density of the ceramic matrix, and its continuous layered pores near the grain boundaries will effectively promote the transmission of oxygen and significantly promote the re-oxidation of the ceramic grain boundaries.

[0030] The method for preparing a porous barium titanate-based thermosensitive ceramic with a low re-oxidation temperature, a high resistance ratio and a high temperature coefficient using graphene as a sacrificial template provided by the present invention, as Figure 1 shown, specifically includes the following steps:

[0031] (1) Mixing of graphene and forming of ceramic green body: Mix donor-doped barium titanate-based powder, barium carbonate powder, silicon dioxide powder and graphene, and form a ceramic green body; perform heat treatment to remove the organic matter introduced during the forming process to obtain a debinded green body;

[0032] (2) Reduction sintering: Calcinate the debinded green body described in step (1) in an inert atmosphere or a reducing atmosphere to obtain a ceramic block;

[0033] (3) Reoxidation of the thermosensitive ceramic: Reoxidize the ceramic body described in step (2) in an oxygen-containing atmosphere such as air. During the reoxidation process, graphene is oxidized and removed to form two-dimensional pores, and the ceramic grain boundaries are reoxidized to form barriers, obtaining a highly dense porous barium titanate thermosensitive ceramic material with a high temperature coefficient.

[0034] In some embodiments, the barium carbonate powder described in step (1) accounts for 0.1%-2% of the mass of the donor-doped barium titanate-based powder; the silica powder accounts for 0.5%-4% of the mass of the donor-doped barium titanate-based powder; the graphene accounts for 0.1%-10% of the mass of the donor-doped barium titanate-based powder, more preferably 0.5%-5%. The forming in step (1) can be dry pressing, tape casting, rolling, injection molding, slip casting and other methods in conventional forming methods, preferably tape casting. The heat treatment temperature in step (1) is 300°C-500°C, and the time is 2h-48h.

[0035] For the donor-doped barium titanate-based powder described in step (1), the donor element is one or more of trivalent metal elements and pentavalent metal elements; the donor doping is A-site doping, B-site doping or A and B-site co-doping. For example, the donor doping ions can be lanthanum, yttrium, samarium substituted at the A-site, or antimony, niobium substituted at the B-site, or co-substituted at the A and B-sites.

[0036] The preparation method of the donor-doped barium titanate-based powder of the present invention is not limited, and can be a solid-phase method, a sol-gel method, a co-precipitation method, a hydrothermal method, etc., preferably prepared by a solid-phase method. In some embodiments, the donor-doped barium titanate powder is prepared by a solid-phase method, specifically including the following steps: Weigh barium oxide or barium carbonate, titanium dioxide, donor ion compound and Curie temperature shifting agent and other powders according to the stoichiometric ratio of (Ba 1-x-y Re x M y )TiO3, and mix them to obtain a mixture; where Re is a rare earth ion, and its content is 1wt‰≤x≤10wt‰, M is a Curie temperature shifting metal ion; use deionized water as the medium to ball-mill and mix the weighed powders above, and dry and screen to obtain a mixed powder. Calcinate the mixed powder at 1000°C-1200°C for 0.5h-3h to obtain the donor-doped barium titanate powder. The rare earth metal compound is an oxide of lanthanum, yttrium, samarium, antimony, niobium, and the Curie temperature shifting agent includes Sr 2+ , Pb 2+ , etc.; the trivalent elements in the donor elements such as La, Y, Ce, Er, etc.; the pentavalent elements such as Nb, V, Ta, etc.

[0037] The donor-doped barium titanate-based powder described in step (1) of the present invention can be not only the donor-doped barium carbonate powder itself, but also other barium titanate-based powders for preparing PTCR ceramics obtained by introducing a small amount of PbTiO3, (Bi 0.5 Na 0.5 )TiO3 or (Bi 0.5 K 0.5 )TiO3, etc. into the barium titanate powder according to application requirements.

[0038] In some embodiments, the thickness of the graphene described in step (1) is single-layer or multi-layer. Preferably, the number of graphene layers is less than 20 layers, more preferably 1-10 layers. The theoretical thickness of single-layer graphene is 0.35 nm; the sheet diameter or lateral dimension of the graphene is 1-10 μm. The graphene used in the present invention can be the layered graphene prepared by any method in the prior art, and its thickness can be from single-layer to dozens of layers, and can be prepared by methods such as mechanical exfoliation method, reduction oxidation method, epitaxial method, etc.

[0039] In some embodiments, the calcination in step (2) is to raise the temperature to 950°C - 1400°C at a heating rate of 200°C / h - 500°C / h, then hold for 0.5 h - 5 h, and then cool to 800°C at a cooling rate of 100°C / h - 400°C, and then cool to room temperature with the furnace. The atmosphere used for the calcination in step (2) is nitrogen, or a mixture of nitrogen and hydrogen, preferably a mixture of nitrogen and hydrogen. For barium titanate-based powders obtained by different preparation methods, when preparing high-density and low re-oxidation temperature porous barium titanate-based thermosensitive ceramics by the method of the present invention, the calcination temperature in step (2) may be slightly different. For example, when preparing barium titanate-based powders by the solid-phase method and further preparing high-density and low re-oxidation temperature porous barium titanate-based thermosensitive ceramics, the calcination temperature is preferably 1200°C - 1400°C; when preparing barium titanate-based powders by the sol-gel method and further preparing high-density and low re-oxidation temperature porous barium titanate-based thermosensitive ceramics, the corresponding calcination temperature is slightly lower.

[0040] In some embodiments, the re-oxidation in step (3) is specifically: raise the temperature to 600°C - 900°C at a heating rate of 60°C / h - 300°C / h, then hold for 0.5 h - 4 h, and then cool with the furnace to obtain the thermosensitive ceramic material.

[0041] A method for preparing porous barium titanate thermistor ceramics with high density, low re-oxidation temperature, high lift-drag ratio and temperature coefficient using graphene as a sacrificial template. After uniformly mixing graphene with ceramic powder, graphene is uniformly dispersed at the grain boundaries of barium titanate ceramic grains after reduction sintering, and graphene is oxidized and excluded during the re-oxidation process to form two-dimensional pores as the oxygen transmission path, promoting the re-oxidation of the ceramic grain boundaries to form barriers. The present invention can be applied to the existing preparation process of barium titanate thermistor ceramics, and only a small amount of graphene needs to be added to reduce the re-oxidation temperature of barium titanate thermistor ceramics, and at the same time, prepare barium titanate thermistor ceramics with high density, high lift-drag ratio and temperature coefficient.

[0042] The following are examples:

[0043] Example 1

[0044] (1) Preparation of pre-sintered powder: Weigh 84.54 g of barium carbonate, 34.12 g of titanium dioxide, and 0.20 g of niobium pentoxide powder according to the stoichiometric ratio of BaTi 0.9965 Nb 0.0035 O3. Add 200 ml of deionized water as the medium and obtain a mixture through planetary ball milling. After drying and sieving, a mixed powder is obtained. The mixed powder is calcined at 1150 °C for 2 h to obtain a donor-doped barium titanate powder.

[0045] (2) Forming of ceramic green body: Weigh 100 g of the donor-doped barium titanate powder obtained in step (1), a total of 4 portions, and additionally add 1.32 g of barium carbonate and 2 g of silicon dioxide to each portion. The graphene (commercially available graphene, the lateral size of the graphene sheet is 5 - 10 microns, and the thickness is 3 - 10 nanometers) is 0 g, 1 g, 2 g, and 4 g for each portion, denoted as numbers 1 - 4. Add 36 g of polyvinyl butyral (PVB) as a binder for tape casting, 0.5 g of n-octanol as an antifoaming agent, and 0.5 g of tributyl phosphate as a dispersant to each portion. Using 30 g of toluene and 30 g of ethanol as solvents, ball mill at a rate of 30 r / min for 12 h in a roller ball mill to obtain a slurry. The obtained slurry is subjected to tape casting using a tape casting machine to obtain a ceramic green body film, and after cutting, laminating, and dividing, small pieces are obtained, and then debinded at 400 °C for 24 h to obtain a ceramic green body.

[0046] (3) Reduction sintering: Heat the above ceramic green body in a mixed atmosphere of N2-H2 to 1300 °C at a rate of 300 °C / h and hold for 2 h, then cool to 800 °C at a rate of 240 °C / h and then cool to room temperature with the furnace to obtain a reduction-sintered sample.

[0047] (4) Re-oxidation: Heat the reduction-sintered sample in air to 800 °C at a rate of 120 °C / h and re-oxidize for 1 h, then cool to room temperature with the furnace to obtain barium titanate thermistor ceramics of numbers 1 - 4. Test the performance of the barium titanate thermistor ceramic specimens of numbers 1 - 4, where the temperature coefficient α at the Curie point temperature T 10 / 25Defined as:

[0048]

[0049] Wherein R1 is the resistance at T + 10°C and R2 is the resistance at T + 25°C.

[0050] The results are shown in Table 1:

[0051] Table 1

[0052]

[0053] It can be seen from Table 1 that compared with the No. 1 sample without graphene, different contents of graphene are added to the No. 2-4 samples, the Curie temperature is all at 120 ± 5°C, and the lift-to-resistance ratio and temperature coefficient can be significantly improved. With the increase of the graphene content, the densification of the sample will be inhibited to a certain extent, and the pores between grains will increase after re-oxidation. As the degree of re-oxidation increases, the room temperature resistance will increase.

[0054] Figure 2 It is the SEM image of the sample cross-section after the reduction sintering in step (3) during the preparation process of sample 2. It can be seen that the graphene presents a two-dimensional sheet-like shape, without obvious agglomeration, passing through the grains. Among them, the sheet-like is graphene and the granular is barium titanate powder. It can be observed that in the sample without graphene, during the high-temperature sintering process, the metal electrode is easy to diffuse into the ceramic matrix. In this embodiment, the graphene can still maintain a stable two-dimensional structure at high temperature, and it is difficult for metal atoms to diffuse through the graphene. Therefore, graphene can be used as a barrier layer to inhibit the diffusion of metal into the ceramic matrix at high temperature and avoid the degradation of ceramic properties.

[0055] Figure 3 It is the SEM image of the surface after re-oxidation in step (4) during the preparation process of sample 2. It can be seen that the sheet-like graphene has been oxidized and removed, leaving sheet-like pores, and connecting the isolated dot-like pores, promoting the re-oxidation of the sample. The granular is the barium titanate ceramic matrix.

[0056] Compared with the ceramic material without graphene, the ceramic material prepared in this embodiment realizes a higher lift-to-resistance ratio and temperature coefficient at the same room temperature resistance, or a lower room temperature resistance at the same lift-to-resistance ratio and temperature coefficient. The grains of the prepared thermosensitive ceramic material are sub-micron-sized.

[0057] Example 2

[0058] The steps are the same as those in Example 1, except that 1 g of graphene is added in step (1), and the reduction sintering temperatures are 1250°C, 1350°C, and 1400°C to obtain samples No. 5-7. The test performance results are shown in Table 2.

[0059] Table 2

[0060]

[0061] As can be seen from Table 2, under the condition of the same graphene addition amount, in step (3), as the reduction sintering temperature increases, the density of the thermosensitive ceramic material increases and the degree of semiconductor conversion improves, and the room temperature resistivity is lower. However, at the same time, it may cause partial oxidation of graphene during the high-temperature process and a decrease in the actual content. Therefore, the resistance ratio and temperature coefficient will also decrease to a certain extent, but the improvement of its performance by graphene can still be observed.

[0062] Comparing Table 1 and Table 2, as the sintering temperature increases, the density of the thermosensitive ceramic material increases, the room temperature resistance decreases, and the resistance ratio and temperature coefficient are generally inversely correlated with the density of the sample. Although they also decrease, they are still better than the control group without graphene.

[0063] Example 3

[0064] The steps are the same as those in Example 1, except that in step (1), 70.64 g of barium carbonate, 13.21 g of strontium carbonate, 35.63 g of titanium dioxide, and 0.21 g of niobium pentoxide powder are weighed according to the stoichiometric ratio of Ba 0.8 Sr 0.2 Ti 0.9965 Nb 0.0035 O3. 200 ml of deionized water is added as the medium, and the mixture is obtained by planetary ball milling. After drying and sieving, the mixed powder is obtained. The mixed powder is calcined at 1150 °C for 2 h to obtain the donor-doped barium strontium titanate powder. Similarly, 8-11 thermosensitive ceramic specimens with different graphene contents are obtained, and the test results are shown in Table 3.

[0065] Table 3

[0066]

[0067]

[0068] As can be seen from Table 3, similar to the barium titanate thermosensitive ceramic system in Example 1 and Example 2, when strontium is added to move the Curie temperature of the specimen to about 50 °C, although its room temperature resistivity increases, comparing specimens 8-11, it can be seen that the addition of graphene is still applicable to this environment and has an obvious effect of improving the resistance ratio and temperature coefficient.

[0069] Comparative Example 1

[0070] Other steps are the same as those in Example 1. The difference is that graphene is replaced by carbon nanotubes, and the addition amounts of carbon nanotubes are 1 wt% and 2 wt% respectively. The obtained specimens are denoted as serial numbers 12 and 13, and the test performance results are shown in Table 4:

[0071] Table 4

[0072]

[0073] It can be seen that replacing graphene with carbon nanotubes does not significantly promote the re-oxidation of the reduced sintered sample. After adding carbon nanotubes, compared with the undoped sample, the room temperature resistance slightly increases, while the resistance increase ratio and temperature coefficient do not increase significantly. Thus, although carbon nanotubes, like graphene, are low-dimensional materials, due to the specific structural characteristics of carbon nanotubes, the contact area between the pores formed by them and the grain boundaries is limited, making it difficult to achieve the above purpose. Therefore, the performance of the doped sample is not significantly improved.

[0074] Example 4

[0075] The procedure is the same as that of Example 1, except that in step (2), 10 g of donor-doped barium titanate powder is weighed, and in addition, 0.132 g of barium carbonate, 0.2 g of silicon dioxide, and 0.1 g of graphene are added. 50 g of deionized water is added as a medium, and ball milling is carried out in a planetary ball mill at 300 revolutions per minute for 5 h, followed by drying, sieving, adding PVA for granulation, dry pressing into tablets, and then debinding at 450 °C for 5 h to obtain a ceramic green body.

[0076] Example 5

[0077] The procedure is the same as that of Example 1, except that in step (1), 84.35 g of barium carbonate, 34.26 g of titanium dioxide, and 0.21 g of lanthanum oxide powder are weighed according to Ba 0.997 La 0.003 TiO3.

[0078] Example 6

[0079] The procedure is the same as that of Example 1, except that in step (1), 84.35 g of barium carbonate, 34.26 g of titanium dioxide, 0.21 g of lanthanum oxide powder, and 0.20 g of niobium pentoxide powder are weighed according to Ba 0.997 La 0.003 Ti 0.9965 Nb 0.0035 O3.

[0080] Example 7

[0081] The procedure is the same as that of Example 1, except that in step (1), calcination is carried out at 1050 °C for 2 h, and in step (3), the holding temperature is 1250 °C.

[0082] Example 8

[0083] The procedure is the same as that of Example 1, except that in step (4), the temperature is raised to 650 °C, 700 °C, and 750 °C at 120 °C / h and then re-oxidized for 1 h.

[0084] Examples 4 to 8 were also found by testing that by adding different amounts of graphene, the prepared ceramic materials achieved a higher lift-to-drag ratio at the same room temperature resistance compared to the ceramic materials without graphene addition, or a lower room temperature resistance at the same lift-to-drag ratio.

[0085] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a barium titanate-based thermosensitive ceramic with a high temperature coefficient, characterized in that, It includes the following steps: (1) Mix the donor-doped barium titanate-based powder with barium carbonate powder, silicon dioxide powder, and graphene, and form it into a ceramic green body; heat-treat to remove the organic matter introduced during the forming process to obtain the debound green body; (2) Calcinate the debound green body described in step (1) in an inert atmosphere or a reducing atmosphere to obtain a ceramic block; (3) Re-oxidize the ceramic block described in step (2) in an oxygen-containing atmosphere. During the re-oxidation process, graphene is oxidized and removed to form two-dimensional pores, and the ceramic grain boundaries are re-oxidized to form barriers, thereby obtaining a barium titanate-based thermosensitive ceramic material with a high temperature coefficient.

2. The preparation method according to claim 1, characterized in that, The barium carbonate powder described in step (1) accounts for 0.1% - 2% of the mass of the donor-doped barium titanate-based powder; the silicon dioxide powder accounts for 0.5% - 4% of the mass of the donor-doped barium titanate-based powder; the graphene accounts for 0.1% - 10% of the mass of the donor-doped barium titanate-based powder.

3. The preparation method according to claim 1, characterized in that, The forming in step (1) is dry pressing, tape casting, rolling, injection molding, or slip casting.

4. The preparation method according to claim 1, wherein, The heat treatment temperature in step (1) is 300°C - 500°C, and the time is 2h - 48h.

5. The preparation method according to claim 1, characterized in that, For the donor-doped barium titanate-based powder in step (1), the donor element is one or more of trivalent metal elements and pentavalent metal elements; the donor doping is A-site doping, B-site doping, or A and B-site co-doping.

6. The preparation method according to claim 1, characterized in that, The graphene in step (1) is single-layer or multi-layer, and the lateral size is 1 - 10 μm.

7. The preparation method according to claim 6, characterized in that, The graphene in step (1) is 1 - 10 layers.

8. The preparation method according to claim 1, wherein, The calcination in step (2) is to raise the temperature to 950°C - 1400°C at a heating rate of 200°C / h - 500°C / h, then hold for 0.5h - 5h, and then cool to 800°C at a cooling rate of 100°C / h - 400°C / h, and then cool in the furnace to room temperature.

9. The preparation method according to claim 1, characterized in that, The atmosphere used for the calcination in step (2) is nitrogen, or a mixture of nitrogen and hydrogen.

10. The preparation method according to claim 1, characterized in that, The re-oxidation in step (3) is specifically: raise the temperature to 600°C - 900°C at a heating rate of 60°C / h - 300°C / h, then hold for 0.5h - 4h, and then cool in the furnace, and the thermosensitive ceramic material is obtained.

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