Barium titanate ceramic sintering method

Abstract

The invention discloses a barium titanate ceramic sintering method, and relates to the field of ceramic material preparation, a room temperature rapid sintering device is built, a novel carbon electrode structure is used, direct current voltage is applied to a large-diameter and large-thickness barium titanate wafer green body, and barium titanate is rapidly sintered under the heat effect of current at room temperature. The shape and the size of the barium titanate ceramic sample adapt to actual application scenes. Compared with a traditional barium titanate ceramic sintering method, the room-temperature rapid sintering method has the advantages that the device structure is simple, the requirements on a power supply and the environment are low, and the performance of the sample can be optimized. According to the invention, the room-temperature rapid sintering of the barium titanate ceramic is realized, the sintering time is shortened, the energy efficiency is improved, the application field of the room-temperature rapid sintering method is further expanded, and the feasibility of the room-temperature rapid sintering method in industrial production application is proved.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation, and specifically to a method for sintering barium titanate ceramics. Background Technology

[0002] Barium titanate is an important electronic ceramic material with characteristics such as stable ferroelectric domain structure, polarization direction that can be conditioned by an external electric field, high dielectric constant, significant piezoelectric and pyroelectric effects, and good chemical stability. It is widely used in ferroelectric memories, electro-optic modulators, miniature high-density capacitors, high-performance sensors, piezoelectric sensors, pyroelectric infrared detectors, and other fields.

[0003] The traditional sintering method for barium titanate ceramics is conventional solid-state sintering, which promotes particle growth and bonding at high temperatures to form a dense ceramic material. However, traditional sintering methods for barium titanate ceramics have problems such as long sintering time, high sintering temperature, and easy overgrowth of grains. New sintering technologies such as flash sintering have also been applied to the sintering of barium titanate ceramics.

[0004] Flash sintering is a novel ceramic sintering technology. By applying various forms of electric fields during the sintering process, the sintering temperature can be significantly reduced and the sintering time shortened. It also allows for the formation of microstructures different from traditionally sintered samples, resulting in superior electrothermal and mechanical properties. However, current flash sintering techniques for barium titanate ceramics mostly utilize dog-bone shaped green bodies. While this shape facilitates successful flash sintering experiments, it lacks practical applications and requires very high sintering temperatures, limiting industrial application. Therefore, it is necessary to propose a method that requires less stringent equipment and environmental conditions, enabling rapid room-temperature sintering of disc-shaped barium titanate ceramics more suitable for industrial production. Summary of the Invention

[0005] The purpose of this invention is to at least solve one of the technical problems existing in the prior art and to provide a method for sintering barium titanate ceramics.

[0006] The technical solution of the present invention is as follows:

[0007] Includes the following steps:

[0008] S1: Prepare barium titanate ceramic green body; S2: Use a composite stacked carbon electrode structure, consisting of copper electrode, graphite felt, graphite paper, and green body from the outside to the inside, symmetrically arranged and fixed with a support. Connect DC power supply to both ends of the electrode to form a room temperature rapid sintering device, and fix the barium titanate ceramic green body between the two electrodes; S3: Apply DC voltage and current to the barium titanate ceramic to generate a thermal effect, and obtain barium titanate ceramic after holding for a period of time.

[0009] Preferably, the ceramic green body is prepared from barium titanate powder through granulation, pressing, debinding, and pre-firing, and the green body is in the shape of a disc.

[0010] Preferably, the binder used in step S1 to prepare the ceramic green body is polyvinyl alcohol.

[0011] Preferably, in step S2, the graphite paper has a thickness of 0.03-0.2 mm, the graphite felt has a thickness of 2.0-20.0 mm, and the porosity is 50%-95%.

[0012] Preferably, the barium titanate flash sintering device directly uses air as the atmosphere, and the sintering temperature is room temperature.

[0013] Preferably, step S3 specifically includes the following steps: initially, the output is in voltage control mode, outputting a constant voltage; when the current through the circuit increases to the set limit current value, it immediately switches to current control mode, outputting a constant current, the value of which is the limit current value. After maintaining this for a period of time, the power is cut off, resulting in room temperature rapid sintering of barium titanate ceramic.

[0014] Preferably, when increasing the current, the limited current value is increased stepwise at a rate of 0.5A / s-3A / s, and after maintaining it for a certain period of time, the limited current is reduced to 0A at the same rate of 0.5A / s-3A / s, and the flash burn ends.

[0015] The beneficial effects of this invention are: the sintering method of this invention can rapidly sinter large-diameter, thick-diameter circular barium titanate ceramics at room temperature without the need for a heating furnace, which simplifies the sintering equipment, optimizes the sintering environment, and reduces the sintering cost. The circular barium titanate ceramics broaden the shape limitations of the original flash sintering technology, which helps to realize the industrialization and large-scale production of barium titanate ceramics at room temperature flash sintering. Attached Figure Description

[0016] Figure 1 This is a structural diagram of a barium titanate ceramic flash firing device. In the diagram, 1-high voltage power supply, 2-upper copper electrode, 3-upper graphite felt, 4-upper graphite paper, 5-barium titanate green sample, 6-lower graphite paper, 7-lower graphite felt, 8-lower copper electrode, and 9-power supply grounding terminal.

[0017] Figure 2 This is a scanning electron microscope (SEM) image of a barium titanate ceramic disc obtained by flash calcination at room temperature.

[0018] Figure 3 This is the traditional solid-state sintering temperature profile for barium titanate ceramics.

[0019] Figure 4 SEM images of barium titanate ceramic discs obtained by traditional solid-state sintering methods Detailed Implementation

[0020] To better understand the technical solution of the present invention, the present invention will be described in detail below through specific embodiments and comparative examples, in conjunction with the accompanying drawings:

[0021] Example

[0022] This invention provides a method for rapid room temperature sintering of barium titanate ceramics. The experimental apparatus includes a support, a composite stacked carbon electrode, a DC power supply, and barium titanate ceramic green bodies, etc. See below for details of the apparatus. Figure 1 .

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0025] like Figure 1 As shown in the preferred embodiment of the present invention, a method for rapid room temperature sintering of barium titanate ceramics is provided, comprising the following steps:

[0026] S1: Preparation of barium titanate ceramic green body;

[0027] S2: A composite stacked carbon electrode structure is used, consisting of copper electrode, graphite felt, graphite paper, and green body from the outside to the inside. The structure is symmetrical and fixed with a bracket. The two ends of the electrode are connected to a DC power supply to form a room temperature rapid sintering device, which fixes the barium titanate ceramic green body between the two electrodes.

[0028] S3: Apply DC voltage and current to barium titanate ceramic to generate a thermal effect. After maintaining this effect for a period of time, barium titanate ceramic is obtained.

[0029] In step S1: the binder used to prepare the ceramic green body is polyvinyl alcohol.

[0030] In step S2: the graphite paper is 0.1 mm thick, the graphite felt is 8.0 mm thick, and the porosity is about 90%.

[0031] Step S3 specifically includes the following steps: Initially, the output is in voltage control mode, outputting a constant voltage; when the current through the circuit increases to the set limit current value, it immediately switches to current control mode, outputting a constant current, the value of which is the limit current value. After maintaining this for a period of time, the power is cut off, resulting in room temperature rapid sintering of barium titanate ceramic.

[0032] The following are specific examples.

[0033] Example 1: The specific steps are as follows:

[0034] (1) Barium titanate powder with an average particle size of 50 nm was selected for the experiment. The powder was mixed with 0.5 wt% polyvinyl alcohol aqueous solution at a mass ratio of 10:1, ground, and sieved. A cylindrical mold with a diameter of 20 mm was used for uniaxial pressing at 400 MPa for 2 min to obtain barium titanate ceramic green bodies with a diameter of 20 mm, a thickness of 1.73 mm, and a weight of 2.2 g. The green bodies were then heated to 400 °C at a rate of 5 °C / min and held for 2 h to remove the binder. The circular green bodies were then subjected to cold isostatic pressing at 300 MPa for 5 min to improve the mechanical strength of the green bodies.

[0035] (2) Use a support to fix the composite stacked carbon electrode, which consists of a copper electrode, a graphite felt, a graphite paper, and a green blank from the outside to the inside, and is symmetrical from top to bottom. Place the barium titanate sample from (1) between the electrodes.

[0036] (3) Connect the upper and lower electrodes to the positive and negative terminals of a high-power DC power supply, respectively. The power supply operates as follows: after starting to output or adjusting the limited current, it enters voltage control mode, outputting a constant voltage; when the current through the circuit increases to the set limited current value, it immediately switches to current control mode, outputting a constant current, the value of which is the limited current value. In the flash burn experiment of this embodiment, whenever the power supply is turned on or the limited current is adjusted, the power supply reaches the limited value within 0.1s and switches to current control mode. Before the flash burn begins, the output voltage is set to 100V and the limited current is set to 0A. At the start of the flash burn, the power supply is turned on, and the limited current is gradually increased from 0A to 5A at a rate of 1A / s. After maintaining this for a certain period of time (approximately 180s), the limited current is also reduced to 0A at a rate of 1A / s, and the flash burn ends.

[0037] (4) During the experiment, voltage and current data during the flash firing process were recorded using the voltage and current measurement module built into the power supply. Temperature data at various locations within the device during the flash firing process were recorded using an infrared thermal imager. Phenomena at different times during the flash firing process were recorded using a camera. For the obtained barium titanate ceramic discs, the density was measured using the water displacement method and the relative density was calculated. The microstructure of the samples was observed using a cold / hot field scanning electron microscope (SEM) to detect the elemental distribution in the samples. The relative permittivity of the samples was tested using a broadband dielectric spectrometer. The experimental results showed that the relative density of the room temperature flash-fired samples was between 91.53% and 93.11%. The SEM images of the samples are shown below. Figure 2 As shown, the peak dielectric constant of the sample is around 5℃, and barium titanate undergoes a transformation from tetragonal to orthorhombic phase around 5℃.

[0038] Comparative Example 1

[0039] To verify the superiority of the room temperature rapid sintering method for barium titanate ceramics provided by this invention, a comparative example of conventional solid-state sintered barium titanate ceramics was set up.

[0040] Comparative Example 1 of the present invention utilizes a conventional solid-state sintering method to flash-fire barium titanate ceramic discs, comprising the following steps:

[0041] S1: Preparation of barium titanate ceramic green body;

[0042] S2: The barium titanate ceramic green body is placed in a muffle furnace for pressureless sintering to obtain the finished barium titanate ceramic disc.

[0043] In step S1: the binder used to prepare the ceramic green body is polyvinyl alcohol.

[0044] In step S2: according to... Figure 3 The traditional sintering temperature curve of the barium titanate ceramic shown is used to heat the ceramic to obtain traditional solid-state sintered barium titanate ceramic.

[0045] The following are specific comparative examples.

[0046] Comparative Example: The specific steps are as follows:

[0047] (1) Barium titanate powder with an average particle size of 50 nm was selected for the experiment. The powder was mixed with 0.5 wt% polyvinyl alcohol aqueous solution at a mass ratio of 10:1, ground, and sieved. A cylindrical mold with a diameter of 20 mm was used for uniaxial pressing at 400 MPa for 2 min to obtain barium titanate ceramic green bodies with a diameter of 20 mm, a thickness of 1.73 mm, and a weight of 2.2 g. The green bodies were then heated to 400 °C at a rate of 5 °C / min and held for 2 h to remove the binder. The circular green bodies were then subjected to cold isostatic pressing at 300 MPa for 5 min to improve the mechanical strength of the green bodies.

[0048] (2) Place the green blanks in a muffle furnace and, according to Figure 3 The sintering curves of the traditional sintering method for barium titanate ceramics are shown. Barium titanate ceramics were subjected to pressureless sintering. First, the temperature was raised from room temperature to 400℃ in 175 min and held for 120 min. Then, the temperature was raised from 400℃ to 1250℃ in 170 min and held for 120 min. Finally, the temperature was lowered to obtain traditional solid-state sintered barium titanate ceramic disc samples as a control group.

[0049] (3) For the obtained barium titanate ceramic discs, the density was measured using the water displacement method and the relative density was calculated. The microstructure of the samples was observed using cold / hot field scanning electron microscopy (SEM) and the elemental distribution was detected. The relative permittivity of the samples was tested using a broadband dielectric spectrometer. The relative density of the obtained conventionally sintered samples was 96.71%. The SEM images of the samples are shown below. Figure 4 As shown.

[0050] The above examples and comparative test results show that the relative density of the flash-sintered samples is higher than 91.5%, with the highest relative density reaching 93.11%. Although this is lower than the 96.71% of the traditionally sintered samples, it still meets the basic requirements for industrial applications. Comparing the SEM images of barium titanate ceramic discs obtained using room-temperature flash sintering and traditional solid-state sintering methods reveals that, compared to the traditionally sintered samples, the flash-sintered samples have smaller grain sizes and a more uniform grain size distribution, which is beneficial for achieving good electrical and mechanical properties. Furthermore, the relative permittivity of the barium titanate samples obtained by room-temperature flash sintering is significantly better than that of the traditionally sintered samples. This is because room-temperature flash sintering results in tighter grain bonding, fewer pores, stronger polarization ability, lower polarization loss, and a higher permittivity.

[0051] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of the present invention.

Claims

1. A method for sintering barium titanate ceramics, characterized in that, Includes the following steps: S1: Preparation of barium titanate ceramic green body; S2: A composite stacked carbon electrode structure is used, consisting of copper electrode, graphite felt, graphite paper, and green body from the outside to the inside. The structure is symmetrical and fixed with a bracket. The two ends of the electrode are connected to a DC power supply to form a room temperature rapid sintering device, which fixes the barium titanate ceramic green body between the two electrodes. S3: Apply DC voltage and current to barium titanate ceramic to generate a thermal effect. After maintaining this effect for a period of time, barium titanate ceramic is obtained.

2. The sintering method for barium titanate ceramics according to claim 1, characterized in that, The ceramic green body is prepared from barium titanate powder through granulation, pressing, debinding, and pre-firing, and the green body is in the shape of a round sheet.

3. The sintering method for barium titanate ceramics according to claim 1, characterized in that, In step S1, the binder used to prepare the ceramic green body is polyvinyl alcohol.

4. The sintering method for barium titanate ceramics according to claim 1, characterized in that, In step (2), the thickness of the graphite paper is 0.03-0.2 mm, the thickness of the graphite felt is 2.0-20.0 mm, and the porosity is 50%-95%.

5. The sintering method for barium titanate ceramics according to claim 1, characterized in that, The barium titanate flash sintering device directly uses air as the atmosphere, and the sintering temperature is room temperature.

6. The sintering method for barium titanate ceramics according to claim 1, characterized in that, Step S3 specifically includes the following steps: initially, the output is in voltage control mode, outputting a constant voltage; when the current through the circuit increases to the set limit current value, it immediately switches to current control mode, outputting a constant current, the value of which is the limit current value; after maintaining this for a period of time, the power is cut off to obtain room temperature rapid sintering barium titanate ceramic.

7. The sintering method for barium titanate ceramics according to claim 1, characterized in that, When increasing the current, the limit current value is increased step by step at a rate of 0.5A / s-3A / s. After maintaining this rate for a certain period of time, the limit current is reduced to 0A at a rate of 0.5A / s-3A / s, and the flashover ends.

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