Sintering furnace equipment and sintering method of potassium-sodium niobate-based lead-free piezoelectric ceramic piece

Abstract

The invention discloses sintering furnace equipment and a sintering method of a potassium-sodium niobate-based lead-free piezoelectric ceramic piece, and belongs to the technical field of lead-free piezoelectric ceramic preparation. A crucible with a downward opening is arranged in a hearth of the sintering furnace equipment, and a closed space is formed by the crucible and the bottom of the hearth. A sagger with an upward opening is arranged in the closed space, and a clamping device is arranged in the sagger and used for clamping sintering raw materials. According to the sintering furnace equipment, a stable temperature field in the sintering process is kept through the common design of the saggar and the crucible, excessive volatilization of potassium and sodium can be restrained when the potassium-sodium niobate-based leadless piezoelectric ceramic piece is prepared, and the prepared potassium-sodium niobate-based leadless piezoelectric ceramic piece is excellent in performance and good in appearance.

Description

Technical Field

[0001] This invention relates to the field of lead-free piezoelectric ceramic preparation technology, and in particular to a sintering furnace equipment and a sintering method for potassium sodium niobate-based lead-free piezoelectric ceramic sheets. Background Technology

[0002] Piezoelectric ceramics are widely used materials, which can be divided into lead-based piezoelectric ceramics and lead-free piezoelectric ceramics. Although lead-based piezoelectric ceramics, such as lead zirconate titanate piezoelectric ceramics, have excellent properties and good temperature characteristics and stability, lead has significant toxic side effects on humans and the environment. With the continuous development of cutting-edge technology, more and more lead-free piezoelectric materials are beginning to emerge. Among them, potassium sodium niobate-based lead-free piezoelectric ceramics are the most promising materials to replace lead-based piezoelectric ceramics because their piezoelectric properties can approach those of lead-based piezoelectric ceramics after doping modification.

[0003] However, the sintering stability of potassium sodium niobate-based lead-free piezoelectric ceramics is relatively poor. They are very sensitive to sintering temperature and require high stability of the temperature field. During high-temperature sintering, potassium and sodium volatilize. This excessive volatilization causes the ceramic composition to deviate significantly from the preset composition, which in turn affects the performance of the piezoelectric ceramic. Furthermore, when the green body is thin and the area is large, it is more prone to warping and deformation during sintering, affecting the appearance and application. Traditionally, direct sintering, debinding-sintering in a stepwise manner, or powder coating sintering are often used for preparation. However, these methods have technical drawbacks such as poor quality of sintered products, cumbersome process steps, and high preparation costs. Moreover, they cannot achieve effective sintering and forming of large-size thin sheet piezoelectric ceramics.

[0004] Therefore, it is particularly important to invent a simple and low-cost sintering method for preparing large-area thin-film potassium sodium niobate-based lead-free piezoelectric ceramics with excellent performance and good appearance. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a sintering furnace and a sintering method for potassium sodium niobate-based lead-free piezoelectric ceramic sheets. The potassium sodium niobate-based lead-free piezoelectric ceramic sheets prepared using the sintering furnace described in this invention have excellent performance and a good appearance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a sintering furnace device, wherein a crucible with an opening facing downward is arranged inside the furnace chamber, and the crucible and the bottom of the furnace chamber form a sealed space;

[0008] The sealed space is equipped with an upward-facing sagger, and the sagger is equipped with a clamping device for clamping the sintering raw materials.

[0009] The small space formed by the internal recessed structure of the sagger described in this invention can reduce airflow fluctuations during sintering, providing a stable temperature field for sintering. Furthermore, the enclosed space further stabilizes the temperature field during sintering.

[0010] Preferably, the clamping device of the present invention includes pads I and II;

[0011] Preferably, the gaskets I and II are parallel to each other.

[0012] In this invention, the gaskets I and II can be placed parallel to the bottom of the sagger or perpendicular to the bottom of the sagger.

[0013] If the gaskets I and II are placed perpendicular to the bottom of the crucible, the clamping device will require other components to secure the gaskets I and II.

[0014] Preferably, when the number of saggers is ≥2, the saggers are stacked vertically.

[0015] In the sintering furnace equipment, the crucible is larger than a single sagger or stacked saggers.

[0016] Preferably, the depth of the sagger is 5-100 mm; more preferably 15-50 mm; and even more preferably 25 mm.

[0017] Preferably, the thickness of the sagger is 2-30 mm; more preferably 8-20 mm; and even more preferably 10 mm.

[0018] The present invention does not impose any special limitation on the shape of the sagger; any shape known to those skilled in the art is acceptable, such as cylindrical, elliptical, or rectangular.

[0019] In some specific embodiments of the present invention, the shape of the sagger is preferably rectangular.

[0020] The present invention does not impose any particular limitation on the shape of the crucible; any shape known to those skilled in the art is acceptable.

[0021] In some specific embodiments of the present invention, the crucible is preferably rectangular in shape.

[0022] Preferably, the gaskets I and II are made of zirconium oxide.

[0023] Preferably, in this invention, the gaskets I and II are the same size;

[0024] Preferably, the thickness of the gaskets I and II is 1~5 mm;

[0025] The surfaces of gaskets I and II are flat and smooth.

[0026] The present invention uses gaskets I and II with a certain porosity to ensure smooth glue discharge.

[0027] Preferably, the porosity of the gaskets I and II is 5% to 45%; more preferably 15% to 35%; and even more preferably 20%.

[0028] Preferably, the density of gaskets I and II is 3.0~5.5 g / cm³. -3 More preferably, it is 4.0~5.0 g / cm³. -3 .

[0029] The present invention also provides a method for sintering potassium sodium niobate-based lead-free piezoelectric ceramic sheets using the above-mentioned sintering furnace equipment, comprising the following steps:

[0030] A thin sheet of potassium sodium niobate-based lead-free piezoelectric ceramic is placed between the clamping devices, and debinding and sintering are performed sequentially to prepare the potassium sodium niobate-based lead-free piezoelectric ceramic sheet.

[0031] The internal concave structure of the sagger and the sealed space of the crucible in the sintering furnace equipment of the present invention work together to further stabilize the sintering temperature field. Furthermore, the sealed space contains a certain saturated vapor pressure, which can effectively suppress the excessive volatilization of sodium and potassium, thereby improving the quality of the potassium sodium niobate-based lead-free piezoelectric ceramic sheet.

[0032] The present invention uses the clamping device to clamp the thin sheet green body of the potassium sodium niobate-based lead-free piezoelectric ceramic before sintering, thus avoiding warping and deformation of the thin sheet green body during the sintering process.

[0033] The sintering method of the present invention uses the sintering equipment to continuously debind and sinter to prepare the potassium sodium niobate-based lead-free piezoelectric ceramic sheet.

[0034] Preferably, the temperature for discharging the adhesive is 500℃~700℃; more preferably, it is 600℃.

[0035] Preferably, the glue removal time is 5~20 h; more preferably, it is 8~15 h.

[0036] Preferably, the heating rate of the adhesive removal process is 0.2~5℃ / min; more preferably 0.8~2℃ / min; and even more preferably 1℃ / min.

[0037] Preferably, the sintering temperature is 1020℃~1220℃; more preferably 1100℃~1200℃; and even more preferably 1160℃.

[0038] Preferably, the sintering holding time is 2 to 12 hours; more preferably 4 to 8 hours; and even more preferably 5 hours.

[0039] Preferably, before sintering, the heating rate from the debinding section to the sintering section is 1~10℃ / min; more preferably 2~5℃ / min; and even more preferably 3℃ / min.

[0040] The sintering method described in this invention is simple and efficient. The gaskets I and II, as well as the saggers and crucibles used, can be cleaned and reused multiple times, which significantly reduces costs.

[0041] In some specific embodiments of the present invention, the sintering method includes the following steps:

[0042] S1. Take gasket I, place the thin ceramic green body cut from the casting process flat on gasket I, and cover it with gasket II so that gasket I and II clamp the thin ceramic green body and fit together from top to bottom.

[0043] S2. Place the sagger inside the sintering furnace and place the bonded gasket and thin ceramic green body in the middle of the bottom of the sagger;

[0044] S3. An inverted crucible is placed over the outside of a sagger, and the saggers are stacked inside the crucible, with at least one stacked layer. The furnace is then closed.

[0045] S4. Run the debinding and sintering temperature profile program;

[0046] S5. After the operation ends, the sample is allowed to cool naturally before being removed from the furnace, yielding the potassium sodium niobate-based lead-free piezoelectric ceramic sheet.

[0047] The present invention also provides a potassium sodium niobate-based lead-free piezoelectric ceramic sheet, which is prepared by the above-described sintering method.

[0048] The potassium sodium niobate-based lead-free piezoelectric ceramic sheet of the present invention has dense grain growth and good overall appearance except for a small amount of cracks and roughness at the edges and corners.

[0049] Silver electrodes were sequentially coated and sintered on the surface of the potassium sodium niobate-based lead-free piezoelectric ceramic sheet to realize the input and detection of electrical signals. Its electric displacement performance was tested under a square wave voltage signal of 300 V and 1 Hz, and its displacement amplitude reached 600 μm, which is good performance.

[0050] Replacing the saggar with a non-recessed sintering plate of the same material in the sintering method described in this invention results in a more compact grain growth of the potassium sodium niobate-based lead-free piezoelectric ceramic sheet. However, due to the lack of a stable temperature field formed by the saggar, it exhibits uneven color and wavy edge warping. Under the same testing conditions, the displacement amplitude reaches 300 μm, indicating poor performance.

[0051] Removing the crucible from the sintering method described in this invention results in poor grain density of the potassium sodium niobate-based lead-free piezoelectric ceramic sheet due to excessive potassium and sodium volatilization. Under the same test conditions, the displacement amplitude reaches 20 μm, indicating even worse performance.

[0052] The present invention achieves excellent performance of potassium sodium niobate-based lead-free piezoelectric ceramic sheets prepared by the sintering method through the joint design of the sagger and crucible.

[0053] Compared with existing technologies, the sintering furnace equipment provided by this invention has a crucible with its opening facing downwards inside the furnace chamber, forming a sealed space with the bottom of the furnace chamber. An upward-opening sagger is placed within this sealed space, and a clamping device is installed inside the sagger to hold the sintering raw materials. The sintering furnace equipment, through the combined design of the sagger and crucible, maintains a stable temperature field during sintering. Furthermore, it suppresses excessive volatilization of potassium and sodium when preparing potassium sodium niobate-based lead-free piezoelectric ceramic sheets, resulting in potassium sodium niobate-based lead-free piezoelectric ceramic sheets with excellent performance and a good appearance. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the sintering furnace equipment described in this invention, wherein 1 is the bottom of the furnace chamber of the sintering furnace, 2 is the sagger, 3 is gasket I, 4 is the sintering raw material, 5 is gasket II, and 6 is the crucible;

[0055] Figure 2 Appearance diagrams of the piezoelectric ceramics prepared in Example 1(i), Comparative Example 1(ii), and Comparative Example 2(iii);

[0056] Figure 3 SEM images of the piezoelectric ceramics prepared in Example (i) and Comparative Example 1 (ii) and Comparative Example 2 (iii);

[0057] Figure 4 Figure (a) shows the appearance of the elongated ceramic sheet after the piezoelectric ceramic prepared in Example 1 was cut, and Figure (b) shows the appearance of the piezoelectric ceramic prepared in Example 1 after it was coated and sintered to form a silver electrode.

[0058] Figure 5 The electric displacement performance of the piezoelectric ceramics prepared in Example 1 (i), Comparative Example 1 (ii) and Comparative Example 2 (iii) was tested under a square wave voltage signal of 300V and 1HZ after silver electrodes were prepared on the surface of the ceramics. Detailed Implementation

[0059] To further illustrate the present invention, the sintering furnace equipment and the sintering method of potassium sodium niobate-based lead-free piezoelectric ceramic sheets provided by the present invention will be described in detail below with reference to embodiments.

[0060] Figure 1This is a schematic diagram of the sintering furnace equipment described in this invention, where 1 represents the bottom of the furnace chamber, and 2 represents a sagger (the sagger is stacked in at least one layer). Figure 1 The stacked layers are 2), 3 is gasket I, 4 is sintering raw material, 5 is gasket II, and 6 is crucible.

[0061] Example 1

[0062] A sintering method for potassium sodium niobate-based lead-free piezoelectric ceramic sheets based on tape casting, the method comprising the following steps:

[0063] S1. Take gasket I and place the thin sheet of potassium sodium niobate-based lead-free piezoelectric ceramic (sintering raw material) cut from the casting process flat on gasket I. Cover it with gasket II, and clamp the ceramic green body tightly with gaskets I and II. The dimensions of the ceramic green body are 100×70×0.5mm, the dimensions of the gaskets are 110×80×3mm, the material of gaskets I and II is zirconium oxide, the thickness of each is 3.5mm, the porosity of gaskets I and II is 20%, and the density of gaskets I and II is 4.5g / cm³. -3 .

[0064] S2. Place the fitted green blank and spacer in the middle of the bottom of the sagger. The sagger is 25mm deep and 10mm thick. Place the sagger in the furnace and stack it in 1 layer.

[0065] S3. Cover the placed sagger with an inverted crucible and close the furnace.

[0066] S4. Set the temperature curves for debinding and sintering, run the program, the heating rate of the debinding section is 1℃ / min, the debinding temperature is 600℃, the debinding time is 10h, the heating rate from debinding to sintering section is 3℃ / min, the sintering temperature is 1160℃, and the sintering holding time is 5h.

[0067] S5. After the program finishes running, allow it to cool naturally before removing it from the furnace to obtain the required potassium sodium niobate-based lead-free piezoelectric ceramic sheet.

[0068] The appearance of the sintered ceramic sheet is shown in the attached image. Figure 2 As shown in (i), apart from a few minor cracks and roughness at the edges and corners, the overall appearance is good. The dimensions are 80×56×0.4mm. Its SEM image is attached. Figure 3 As shown in (i), the potassium sodium niobate ceramic grains are densely grown. After removing the rough edges, the material is cut into multiple long strips of 50×10×0.4mm. Silver electrodes are then sequentially coated and sintered onto the surface of these ceramic strips to prepare electrical signal input and detection. Figure 4 Figure (a) shows a picture of the cut elongated ceramic sheet, and Figure (b) shows the appearance of the piezoelectric ceramic prepared in Example 1 after sequential coating and sintering to form a silver electrode. The electric displacement performance was tested under a 300V, 1Hz square wave voltage signal with the wire connected. The results are shown in the appendix. Figure 5 As shown in (i), its displacement amplitude reaches 600μm, which is good performance.

[0069] Comparative Example 1

[0070] The difference between Comparative Example 1 and Example 1 is that the sagger used in step S2 is replaced with a firing plate of the same material without a recessed structure; all other aspects are the same.

[0071] The appearance of the sintered ceramic sheet is shown in the attached image. Figure 2 As shown in (ii), the dimensions are 80×56×0.4mm. It exhibits uneven coloring and wavy, warped edges. This is because a stable temperature field was not formed by the sagger. Its SEM image is shown below. Figure 3 As shown in (ii), the potassium sodium niobate ceramic grains are relatively dense.

[0072] After removing the rough edges, the material was cut into multiple long strips of ceramic, each measuring 50×10×0.4mm. Silver electrodes were then coated and sintered onto the surface of each ceramic strip. The electrodisplacement performance was tested under a 300V, 1Hz square wave voltage signal with a connecting wire. The results are shown in the attached figure. Figure 5 As shown in (ii), its displacement amplitude reaches 300μm, and its performance is average.

[0073] Comparative Example 2

[0074] The difference between Comparative Example 2 and Example 1 is that the crucible was not inverted in step S3, but everything else is the same.

[0075] The appearance of the sintered ceramic sheet is shown in the attached image. Figure 2 As shown in (iii), apart from a few minor cracks and roughness at the edges and corners, the overall appearance is good. The dimensions are 80×56×0.4mm. Its SEM image is attached. Figure 3 As shown in (iii), the potassium sodium niobate ceramic grains have poor density, which is due to excessive volatilization of potassium and sodium caused by the lack of an external crucible seal.

[0076] After removing the rough edges, the material was cut into multiple long strips of ceramic, each measuring 50×10×0.4mm. Silver electrodes were then coated and sintered onto the surface of each ceramic strip. The electrodisplacement performance was tested under a 300V, 1Hz square wave voltage signal with a connecting wire. The results are shown in the attached figure. Figure 5 As shown in (iii), its displacement amplitude reaches 20μm, which is poor performance.

[0077] Based on the comparison of Example 1 and Comparative Examples 1 and 2 above, the results show that the sintering process described in this invention can produce potassium sodium niobate-based lead-free piezoelectric ceramic sheets with good appearance and excellent performance. The structure of the crucible will affect the appearance and performance of the product during the sintering process, while the sealing effect of the outer crucible inhibits the excessive volatilization of potassium and sodium, which has a great impact on performance.

[0078] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A sintering furnace device, characterized in that, The furnace chamber contains a crucible with its opening facing downwards, and the crucible and the bottom of the furnace chamber form a sealed space; The sealed space is equipped with an upward-facing sagger, and the sagger is equipped with a clamping device for clamping the sintering raw materials.

2. The sintering furnace equipment according to claim 1, characterized in that, The clamping device includes pads I and II; Gaskets I and II are parallel to each other.

3. The sintering furnace equipment according to claim 1, characterized in that, When the number of saggers is ≥2, the saggers are stacked vertically.

4. The sintering furnace equipment according to any one of claims 1-3, characterized in that, The depth of the sagger is 5~100mm; The thickness of the sagger is 2~30 mm.

5. The sintering furnace equipment according to claim 2, characterized in that, The gaskets I and II are made of zirconium oxide.

6. The sintering furnace equipment according to claim 5, characterized in that, Gaskets I and II are the same size; The thickness of gaskets I and II is 1~5 mm; The porosity of gaskets I and II is 5%~45%; The density of gaskets I and II is 3.0~5.5 g / cm³. -3 .

7. A method for sintering potassium sodium niobate-based lead-free piezoelectric ceramic sheets using the sintering furnace equipment described in any one of claims 1 to 6, characterized in that, Includes the following steps: A thin sheet of potassium sodium niobate-based lead-free piezoelectric ceramic is placed between the clamping devices, and debinding and sintering are performed sequentially to prepare the potassium sodium niobate-based lead-free piezoelectric ceramic sheet.

8. The method according to claim 7, characterized in that, The temperature for discharging the adhesive is 500℃~700℃; The glue removal time is 5~20 h; The heating rate for the glue removal process is 0.2~5℃ / min.

9. The method according to claim 7 or 8, characterized in that, The sintering temperature is 1020℃~1220℃; The holding time for sintering is 2 to 12 hours; Before sintering, the heating rate from the debinding section to the sintering section is 1~10℃ / min.

10. A potassium sodium niobate-based lead-free piezoelectric ceramic sheet, characterized in that, It is prepared by the method described in any one of claims 7 to 9.

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