KR102670819B1 - Lead free piezoelectric ceramic having core shell structure with excellent piezoelectric and dielectric properties and method of manufacturing thereof - Google Patents

Abstract

The present invention discloses a lead-free piezoelectric ceramic with a core-shell structure having excellent piezoelectric and dielectric properties.
To this end, the lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to the present invention is arranged to surround a core layer made of LNKN doped with Bi ₂ O ₃ and the surface of the core layer, and Bi, Na and A lead-free piezoelectric ceramic body including a BNK coating layer made of K component; and a skin current connection electrode disposed on at least one surface of the lead-free piezoelectric ceramic body, wherein the skin current connection electrode includes an internal hollow connection electrode disposed in an inner central portion, and an outer surface spaced apart from the internal hollow connection electrode. It has an external hollow connection electrode arranged to have a cone shape surrounding the internal hollow connection electrode, and a plurality of air outlets formed to penetrate a lower side of the external hollow connection electrode, wherein the internal hollow connection electrode has a bottom surface of the lead-free piezoelectric ceramic body. is connected to, a hollow cooling hole is disposed in the center, and the inner wall of the hollow cooling hole is provided with a heat dissipation groove, and the LNKN is (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is It is characterized by having a composition ratio of 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8.

Description

Lead-free piezoelectric ceramic with core-shell structure with excellent piezoelectric and dielectric properties and method of manufacturing the same {LEAD FREE PIEZOELECTRIC CERAMIC HAVING CORE SHELL STRUCTURE WITH EXCELLENT PIEZOELECTRIC AND DIELECTRIC PROPERTIES AND METHOD OF MANUFACTURING THEREOF}

The present invention relates to a lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties and a method of manufacturing the same. More specifically, after synthesizing Bi ₂ O ₃ doped LNKN powder, the surface of the Bi ₂ O ₃ doped LNKN powder By coating the surface of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) with Bi, Na, and K components to form a lead-free piezoelectric ceramic with a core-shell structure, low-temperature firing is possible and low sintering is possible. It relates to a lead-free piezoelectric ceramic with a core-shell structure that can secure excellent density, piezoelectric and dielectric properties even at high temperatures and a method of manufacturing the same.

Piezoelectric ceramics are used to output electrical signals with a wavelength in response to physical pressure to cause vibration by input power.

For this purpose, Pb(Zr,Ti)O ₃ series ceramics with excellent piezoelectric properties are used as piezoelectric ceramics.

However, because PZT series piezoelectric ceramics contain lead (Pb), they are not only harmful to the human body and cause environmental pollution, but also have restrictions on their use due to strengthening regulations.

In addition, the PZT series piezoelectric ceramics suffer from loss of electrical signals supplied to the piezoelectric ceramic body, and since the power cable is designed to be simply connected to the piezoelectric ceramic body by soldering, the binding of the power cable is not perfect. There was this.

Related prior literature includes Korean Patent Publication No. 10-2004-0054965 (published on June 26, 2004), which describes lead-free piezoelectric ceramics and their manufacturing method.

The purpose of the present invention is to synthesize BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K) having Bi, Na and K components on the surface of Bi ₂ O ₃ doped LNKN powder after synthesizing LNKN powder doped with Bi ₂ O _{3 2} O) is surface coated to form a lead-free piezoelectric ceramic with a core-shell structure, enabling low-temperature sintering and a core-shell structure with excellent piezoelectric and dielectric properties that can secure excellent density, piezoelectric and dielectric properties even at low sintering temperatures. To provide lead-free piezoelectric ceramics and a manufacturing method thereof.

To achieve the above object, a method for manufacturing lead-free piezoelectric ceramics with a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention is (a) (Li _1-x Na _1-y K _1-z )NbO ₃ (where , x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8.) Bi ₂ O ₃ is added to LNKN piezoelectric material having a composition ratio to synthesize LNKN powder doped with Bi ₂ O ₃ step; (b) Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ were weighed to have the composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), then an acidic solution was added and stirred to form a BNK coating solution. forming a; (c) mixing the Bi ₂ O ₃ doped LNKN powder with a BNK coating solution and a binder, performing ball milling, followed by drying and pulverizing to form a lead-free piezoelectric ceramic powder with a core-shell structure; (d) calcining the core-shell structure lead-free piezoelectric ceramic powder, adding a binder and press molding to form a core-shell structure lead-free piezoelectric ceramic molded body; and (e) two-stage sintering of the lead-free piezoelectric ceramic molded body of the core-shell structure, wherein in step (e), the two-stage sintering is performed at a temperature of 650 to 800° C., followed by a primary sintering treatment at 950 to 950° C. It is characterized by secondary sintering at 1,150°C.

In step (a), Bi ₂ O ₃ is added in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material.

In step (c), the BNK coating solution is added in an amount of 15 to 30 parts by weight based on 100 parts by weight of the Bi ₂ O ₃ doped LNKN powder.

In step (d), the pressure molding is performed at 100 to 180°C and a pressure of 1 to 3 ton/cm2 for 1 to 60 minutes.

In step (e), the two-stage sintering includes a first sintering treatment at 650 to 800 ° C. for 10 to 60 minutes and a secondary sintering treatment at 950 to 1,150 ° C. for 30 to 240 minutes. do.

In order to achieve the above object, a lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention is arranged to surround a core layer made of LNKN doped with Bi ₂ O ₃ and the surface of the core layer. A lead-free piezoelectric ceramic body including a BNK coating layer composed of Bi, Na, and K components; and a skin current connection electrode disposed on at least one surface of the lead-free piezoelectric ceramic body, wherein the skin current connection electrode includes an internal hollow connection electrode disposed in an inner central portion, and an outer surface spaced apart from the internal hollow connection electrode. It has an external hollow connection electrode arranged to have a cone shape surrounding the internal hollow connection electrode, and a plurality of air outlets formed to penetrate a lower side of the external hollow connection electrode, wherein the internal hollow connection electrode has a bottom surface of the lead-free piezoelectric ceramic body. It is connected to, a hollow cooling hole is disposed in the center, and the inner wall of the hollow cooling hole is provided with a heat dissipation groove, and the LNKN is (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 It is characterized by having a composition ratio of ~ 0.99, y is 0.3 ~ 0.7, and z is 0.5 ~ 0.8.

The external hollow connection electrode is provided with a cable insertion hole for inserting a power cable into the space between the internal hollow connection electrode, and its bottom is connected to the lead-free piezoelectric ceramic body.

The external hollow connection electrode is formed to penetrate the lower part of the external hollow connection electrode and has a plurality of air outlets for discharging the internal air to the outside so that the solder filled into the cable insertion hole flows.

The plurality of air outlets are formed to penetrate a lower portion of the external hollow connection electrode, and are formed to penetrate a lower portion of the external hollow connection electrode, including a first air outlet disposed at a first position, and the plurality of air outlets are formed to penetrate a lower portion of the external hollow connection electrode. It has a second air outlet spaced apart from the first air outlet in a zigzag shape at a higher second position.

The skin current connection electrode is disposed to be spaced apart from the bottom surface of the external hollow connection electrode in contact with the lead-free piezoelectric ceramic body, and further includes a vibration attenuation cutout disposed at a second position corresponding to the second air outlet.

The lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to the present invention and the manufacturing method thereof include synthesizing LNKN powder doped with Bi ₂ O ₃ and then depositing Bi, Na and K on the surface of the LNKN powder doped with Bi ₂ O ₃ By coating the surface of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) with a core-shell structure to form lead-free piezoelectric ceramics, low-temperature sintering is possible and excellent density and piezoelectric properties are achieved even at low sintering temperatures. and genetic characteristics can be secured.

In addition, the lead-free piezoelectric ceramic with a core-shell structure with excellent piezoelectric and dielectric properties according to the present invention and the method for manufacturing the same are lead-free with a core-shell structure consisting of a core layer composed of LNKN-based doped with Bi ₂ O ₃ and a coating layer composed of BNK-based. By consisting of a piezoelectric ceramic body and a skin current connection electrode provided on at least one side of the lead-free piezoelectric ceramic body, environmental pollution is minimized because lead is not added, and electricity is transmitted to the lead-free piezoelectric ceramic body through the skin current connection electrode. Not only can the signal supply be stably transmitted without loss, but the reliability of the power cable binding can be secured.

In addition, in the lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to the present invention and the manufacturing method thereof, the external hollow connection electrode of the skin current connection electrode is formed in a cone shape, and the extension of the cone is bound to the lead-free piezoelectric ceramic body. As the area expands toward the lead-free piezoelectric ceramic body, internal resistance can be minimized.

In addition, the lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to the present invention and the manufacturing method thereof include a first air outlet disposed at a first position and a second air outlet disposed at a second position higher than the first position. By arranging them spaced apart from each other in a zigzag shape, it is possible to further increase the passage through which solder can be discharged without interference between the first and second air outlets.

Accordingly, the lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to the present invention and the manufacturing method thereof include soldering a power cable to the lead-free piezoelectric ceramic body for connection of the internal hollow connection electrode and the external hollow connection electrode. During the process, the incoming solder flows more smoothly, the internal air is discharged to the outside, and the air outlets are spaced apart in a zigzag pattern so that the solder is stably bound, so the power cable can be connected stably and signal loss is minimized. It has structural advantages.

Figure 1 is a process flow chart showing a method for manufacturing lead-free piezoelectric ceramics with a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention.
Figure 2 is a perspective view showing a lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention.
Figure 3 is a cross-sectional view showing a lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention.
Figure 4 is an enlarged perspective view of the skin current connection electrode of Figure 2.
Figure 5 is an enlarged perspective view of the skin current connection electrode according to a modified example of the present invention.
Figure 6 is a cross-sectional view taken along line Ⅵ-VI' in Figure 5.
Figure 7 is an enlarged cross-sectional view of portion A of Figure 6.

The advantages and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. The present embodiments only serve to ensure that the disclosure of the present invention is complete and that common knowledge in the technical field to which the present invention pertains is not limited. It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties and a manufacturing method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

Figure 1 is a process flow chart showing a method for manufacturing lead-free piezoelectric ceramics with a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention.

As shown in FIG. 1, the method for manufacturing lead-free piezoelectric ceramics with a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention includes the step of synthesizing LNKN powder doped with Bi ₂ O ₃ (S110), forming a BNK coating solution. It includes a step (S120), a step of forming a lead-free piezoelectric ceramic powder with a core-shell structure (S130), a step of forming a lead-free piezoelectric ceramic molded body with a core-shell structure (S140), and a sintering step (S150).

Bi ₂ O ₃ Synthesis of false-doped LNKN powder

In the Bi ₂ O ₃ doped LNKN powder synthesis step (S110), (Li _1-x Na _1-y K _1-z )NbO ₃ (hereinafter abbreviated as LNKN) (where x is 0.8 to 0.99, Bi ₂ O ₃ is added to the LNKN piezoelectric material having a composition ratio (y is 0.3 to 0.7 and z is 0.5 to 0.8) to synthesize LNKN powder doped with Bi ₂ O ₃ .

Here, Bi ₂ O ₃ is doped to improve density properties, piezoelectric properties, and dielectric properties. For this purpose, Bi ₂ O ₃ is preferably added in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material. When Bi ₂ O ₃ is added in an amount of less than 0.1 parts by weight based on 100 parts by weight of the LNKN piezoelectric material, the amount added is so small that it is difficult to properly exert the effect of improving density, piezoelectricity, and dielectric properties. On the contrary, if Bi ₂ O ₃ is added in a large amount exceeding 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material, it is not economical because only a large amount of Bi ₂ O ₃ is needed without further increasing the effect.

BNK coating solution formation

In the BNK coating solution forming step (S120), Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ are weighed to have the composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), and then an acidic solution is added. and stirred to form a BNK coating solution.

At this time, it is preferable to add each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ sequentially after confirming that they are completely dissolved at 10-minute intervals. The acidic solution may be one or more selected from nitric acid, hydrochloric acid, and sulfuric acid.

In this step, stirring is preferably performed for 1 to 12 hours at a speed of 300 to 700 rpm.

If the stirring speed is less than 300 rpm or the stirring time is less than 1 hour, there is a risk that uniform mixing between each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ and the acidic solution may not be achieved. On the other hand, if the stirring speed exceeds 700 rpm or the stirring time exceeds 12 hours, it may act as a factor that increases manufacturing costs without any further effect, making it uneconomical.

During such stirring, it is more preferable to perform ultrasonic treatment together with output power conditions of 30 to 50 kHz and 150 to 250 W. In this way, after weighing Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ to have the composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), in the process of adding and stirring the acidic solution, When ultrasonic treatment is performed together, when the bubble collapses after a certain period of time, local temperature of 5000K, pressure of about 1000bar, and heating and cooling rates of 10 ¹⁰ K/s are extreme conditions. (extreme condition), dispersion efficiency can be maximized.

At this time, if the ultrasonic output power is less than 150W, it is not desirable because there is a risk that uniform mixing between each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ and the acidic solution may not be achieved despite ultrasonic treatment. . Conversely, if the ultrasonic output power exceeds 250W, it is undesirable because excessive ultrasonic treatment may damage the raw materials Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ .

Formation of lead-free piezoelectric ceramic powder with core-shell structure

In the core-shell structure lead-free piezoelectric ceramic powder forming step (S130), Bi ₂ O ₃ doped LNKN powder is mixed with a BNK coating solution and a binder, ball milled, dried and pulverized to produce core-shell structure lead-free piezoelectric ceramic powder. form

Here, the binder may be one or more selected from polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and polyethylene glycol (PEG), of which polyvinyl alcohol is used. It is more preferable to use When using polyvinyl alcohol as a binder, when the negative charge of (-OH) in PVA is set to 1, the charges of Bi ³⁺ , Na ⁺ and K ⁺ are calculated and added in a ratio of 1:1. It is desirable.

Here, the ball milling method is preferably performed for 10 to 30 hours after adding Bi ₂ O ₃ doped LNKN powder, BNK coating solution, and binder to a zirconia ball.

At this time, drying may be performed at 100 to 150°C for 5 to 20 hours.

In this step, it is preferable to add 15 to 30 parts by weight of the BNK coating solution, based on 100 parts by weight of Bi ₂ O ₃ doped LNKN powder, and a more preferable range is 20 to 25 parts by weight. If the BNK coating solution is added in less than 15 parts by weight based on 100 parts by weight of Bi ₂ O ₃ doped LNKN powder, the amount added is so small that there is a risk that BNK may not completely coat the Bi ₂ O ₃ doped LNKN powder. There is. Conversely, if a large amount of the BNK coating solution is added in excess of 30 parts by weight based on 100 parts by weight of Bi ₂ O ₃ doped LNKN powder, it is undesirable because there is a risk of deteriorating piezoelectric performance.

Formation of lead-free piezoelectric ceramic molded body with core-shell structure

In the step of forming a lead-free piezoelectric ceramic molded body with a core-shell structure (S140), the lead-free piezoelectric ceramic powder with a core-shell structure is calcined, a binder is added, and pressure molded to form a lead-free piezoelectric ceramic molded body with a core-shell structure.

At this time, pressure molding is preferably performed at 100 to 180°C and under pressure conditions of 1 to 3 ton/cm2 for 1 to 60 minutes.

If the pressure molding temperature is less than 100°C or the pressure molding time is less than 1 minute, there is a high risk that sufficient curing will not occur. Conversely, if the pressure molding temperature exceeds 180°C or the pressure molding time exceeds 60 minutes, it may act as a factor in increasing manufacturing costs without significant changes in physical properties, making it uneconomical.

Additionally, if the press molding pressure is less than 1 ton/cm2, there may be difficulties in securing strength. Conversely, if the pressurized molding pressure exceeds 3 ton/cm2, there is a risk that the shape of the core-shell structured lead-free piezoelectric ceramic molded body may be deformed due to excessive pressure.

sintering

In the sintering step (S150), the core-shell structure lead-free piezoelectric ceramic molded body is sintered in two stages.

In this step, two-stage sintering includes a primary sintering process at 650 to 800°C for 10 to 60 minutes and a secondary sintering process at 950 to 1,150°C for 30 to 240 minutes. In this way, by performing two-stage sintering, which involves first sintering at a low temperature of 650 to 800 ℃ and then secondary sintering at a high temperature of 950 to 1,150 ℃, it is possible to carry out sintering while gradually increasing the temperature. , it is possible to prevent cracks from occurring in the lead-free piezoelectric ceramic molded body due to rapid temperature changes. As a result, it is possible to manufacture lead-free piezoelectric ceramics with excellent piezoelectric and dielectric properties and high strength.

At this time, if the secondary sintering temperature is less than 950°C or the secondary sintering time is less than 30 minutes, there may be difficulties in securing the target strength, density, piezoelectric and dielectric properties. Conversely, if the secondary sintering temperature exceeds 1,150°C or the secondary sintering time exceeds 240 minutes, the strength may increase, but there is a problem of poor piezoelectric and dielectric properties.

With this, the method for manufacturing lead-free piezoelectric ceramics with a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention can be completed.

The method for manufacturing lead-free piezoelectric ceramics with a core-shell structure according to the above-described embodiment of the present invention is to synthesize LNKN powder doped with Bi ₂ O ₃ and then synthesize the LNKN powder doped with Bi ₂ O ₃ with Bi, Na and K components on the surface of the LNKN powder doped with Bi 2 O 3 . By coating the surface of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) to form lead-free piezoelectric ceramics with a core-shell structure, low-temperature firing is possible and excellent density, piezoelectric and dielectric properties are achieved even at low sintering temperatures. can be secured.

In addition, the method for manufacturing lead-free piezoelectric ceramics with a core-shell structure according to an embodiment of the present invention includes a lead-free piezoelectric ceramic body with a core-shell structure consisting of a core layer composed of LNKN-based doped with Bi ₂ O ₃ and a coating layer composed of BNK-based; By consisting of a skin current connection electrode provided on at least one side of the lead-free piezoelectric ceramic body, no lead is added, thereby minimizing environmental pollution, and the supply of electric signals to the lead-free piezoelectric ceramic body through the skin current connection electrode without loss. Not only can it be delivered stably, but also the reliability of the power cable binding can be secured.

Hereinafter, a lead-free piezoelectric ceramic with a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention will be described in more detail with reference to the attached drawings.

Figure 2 is a perspective view showing a lead-free piezoelectric ceramic with a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention, and Figure 3 is a lead-free piezoelectric ceramic with a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention. It is a cross-sectional view showing a ceramic, and Figure 4 is an enlarged perspective view of the skin current connection electrode of Figure 2.

2 to 4, the lead-free piezoelectric ceramic 200 having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention includes a lead-free piezoelectric ceramic body 220 and a skin current connection electrode 240. do.

The lead-free piezoelectric ceramic body 220 includes a core layer made of LNKN doped with Bi ₂ O ₃ and a BNK coating layer composed of Bi, Na, and K components, which is arranged to surround the surface of the core layer. Here, LNKN has a composition ratio of (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8).

The skin current connection electrode 240 is disposed on at least one surface of the lead-free piezoelectric ceramic body 220.

This skin current connection electrode 240 has an internal hollow connection electrode 241, an external hollow connection electrode 242, and an air outlet 244.

The internal hollow connection electrode 241 is disposed in the inner central part and may have the shape of a hollow pipe with an empty central part. The bottom of this internal hollow connection electrode 241 is connected to the lead-free piezoelectric ceramic body 220, and a hollow cooling hole 245 is disposed in the center.

Here, the hollow cooling hole 245 is disposed in an empty hollow structure at the inner center of the internal hollow connection electrode 241. With this natural cooling method through the hollow cooling hole 245, heat dissipation can be smoothly achieved by smooth air flow inside the internal hollow connection electrode 241.

The external hollow connection electrode 242 is disposed to have a cone shape surrounding the internal hollow connection electrode 241 on the outside, spaced apart from the internal hollow connection electrode 241. This external hollow connection electrode 242 is provided with a cable insertion hole 243 for inserting a power cable into the space between the internal hollow connection electrode 241, and its bottom is connected to the lead-free piezoelectric ceramic body 220.

Here, the external hollow connection electrode 242 is formed to penetrate the lower part of the external hollow connection electrode 242, and has a plurality of air outlets ( 244).

These plurality of air outlets 244 are formed to penetrate the lower part of the external hollow connection electrode 242, and include the first air outlet 244a disposed at the first position and the lower part of the external hollow connection electrode 242. It is more preferable to have a second air outlet (244b) that is formed to penetrate through and is spaced apart from the first air outlet (244a) in a zigzag shape at a second position that is higher than the first position.

In this way, the plurality of air outlets 244 are spaced apart from each other in a zigzag shape, with the first air outlet 244a disposed at the first position and the second air outlet 244b disposed at the second position higher than the first position. By doing so, it is possible to have a structural advantage in that the passage through which solder can be discharged without mutual interference can be further increased compared to arranging them at the same location. As a result, the air inside the external hollow connection electrode 242 can be smoothly discharged to the outside through the air outlet 244 having a zigzag arrangement structure, making it possible to flow the solder filled into the cable insertion hole more smoothly. It becomes possible.

As such, the lead-free piezoelectric ceramic 200 having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention is a core shell composed of a core layer composed of LNKN-based doped with Bi ₂ O ₃ and a coating layer composed of BNK-based. By being composed of a lead-free piezoelectric ceramic body 220 and a skin current connection electrode 240 provided on at least one surface of the lead-free piezoelectric ceramic body 220, no lead is added, minimizing environmental pollution, and the skin current connection electrode 240 is provided on at least one surface of the lead-free piezoelectric ceramic body 220. Not only can the electric signal supply to the lead-free piezoelectric ceramic body 220 be stably transmitted without loss through the current connection electrode 240, but also the reliability of the power cable binding can be secured.

In addition, in the lead-free piezoelectric ceramic 200 having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention, the outer hollow connection electrode 242 of the skin current connection electrode 240 is formed in a cone shape, and the cone The extension part is bound to the lead-free piezoelectric ceramic body 220, and its area increases in the direction of the lead-free piezoelectric ceramic body 220, thereby minimizing internal resistance.

In addition, the lead-free piezoelectric ceramic 200 having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention has a first air outlet 244a disposed at a first location and a second location higher than the first location. By arranging the second air outlets 244b spaced apart from each other in a zigzag shape, it is possible to further increase the passage through which solder can be discharged without interference between the first and second air outlets 244a and 244b. .

Accordingly, the lead-free piezoelectric ceramic 200 having a core-shell structure with excellent piezoelectric and dielectric properties according to an embodiment of the present invention is used for connection of the internal hollow connection electrode 241 and the external hollow connection electrode 242. During the process of soldering the power cable to the main body 220, the air outlet 244 is spaced apart in a zigzag manner so that the incoming solder can flow more smoothly, the air inside is discharged to the outside, and the solder is stably bound. It has the structural advantage of ensuring stable connection of the power cable and minimizing signal loss.

Meanwhile, Figure 5 is an enlarged perspective view showing the skin current connection electrode according to a modified example of the present invention, Figure 6 is a cross-sectional view taken along the line Ⅵ-VI' of Figure 5, and Figure 7 is Figure 6 This is an enlarged cross-sectional view of part A.

First, as shown in FIG. 5, the skin current connection electrode 200 according to a modified example of the present invention is according to the embodiment described with reference to FIG. 4, except that it further has a vibration damping cutout 246. Since it is substantially the same as the skin current connection electrode, redundant explanation will be omitted and the explanation will focus on the differences.

That is, the skin current connection electrode 240 according to a modified example of the present invention has a vibration damping cutout 246 disposed on the bottom surface of the external hollow connection electrode 242 in contact with the lead-free piezoelectric ceramic body (220 in FIG. 2). Includes more.

At this time, if the vibration damping cutout 246 is formed in a portion corresponding to the first position where the first air outlet 244a is disposed, the space may be narrowed due to the position being closer to the lead-free piezoelectric ceramic body compared to the second position. There is a risk of damage to the first and second air outlets 244a and 244b. Therefore, it is preferable that the vibration damping cutout 246 is spaced apart at regular intervals at a second position corresponding to the second air outlet 244b. This vibration damping cutout 246 may have a triangular shape when viewed in cross section, but this is an example and its shape may be changed in various ways.

In this way, in the skin current connection electrode 240 according to the modified example of the present invention, the vibration damping cutout 246 is disposed at regular intervals at the second position corresponding to the second air outlet 244b, so the lead-free piezoelectric Attenuation due to the internal and external hollow connection electrodes 241 and 242 can be minimized when vibration occurs due to the supply of an electric signal to the ceramic body 220.

In addition, as shown in FIGS. 6 and 7, the skin current connection electrode 240 according to the modified example of the present invention differs only in the detailed configuration of the internal hollow connection electrode 241, as described with reference to FIG. 4. Since it is substantially the same as the skin current connection electrode according to the embodiment, redundant description will be omitted and the description will focus on the differences.

The internal hollow connection electrode 241 according to a modification of the present invention has a bottom surface connected to a lead-free piezoelectric ceramic body (200 in FIG. 2), a hollow cooling hole 245 is disposed in the center, and a hollow cooling hole 245 The inner wall is provided with a heat dissipation groove (T).

In addition, the internal hollow connection electrode 241 according to a modified example of the present invention further includes a heat dissipation protrusion 247 disposed in the heat dissipation groove T.

These heat dissipation protrusions 247 are preferably formed as an integrated structure with the internal hollow connection electrode 241 to ensure durability. At this time, a plurality of heat dissipation protrusions 247 protrude in a hemispherical shape within the heat dissipation groove T, and are preferably arranged to be spaced apart from each other at regular intervals. In this way, the internal hollow connection electrode 241 according to the modified example of the present invention can increase the surface area by arranging a plurality of heat dissipation protrusions 247 protruding in a hemispherical shape in the heat dissipation groove T, thereby allowing hollow cooling. By increasing the contact area with the air flowing in through the sphere 245, the heat dissipation effect can be further maximized.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and should not be construed as limiting the present invention in any way.

Any information not described here can be technically inferred by anyone skilled in the art, so description thereof will be omitted.

1. Lead-free piezoelectric ceramic manufacturing

Example 1

(Li _0.05 Na _0.57 K _0.38 ) LNKN powder doped with Bi ₂ O ₃ was synthesized by adding 0.3 parts by weight of Bi ₂ O ₃ to 100 parts by weight of LNKN piezoelectric material having a composition ratio of NbO ₃ .

Next, Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ were weighed to have the composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) and then added to 1M HNO ₃ at a speed of 500 rpm. A BNK coating solution was prepared by stirring for 6 hours.

Next, the Bi ₂ O ₃ doped LNKN powder was mixed with the BNK coating solution and binder, ball milled for 20 hours, dried at 110°C for 24 hours, and then ground to produce lead-free piezoelectric ceramic powder with a core-shell structure. did. At this time, the BNK coating solution was added in an amount of 20 parts by weight based on 100 parts by weight of LNKN powder doped with Bi ₂ O ₃ .

Next, the core-shell structured lead-free piezoelectric ceramic powder was calcined at 650°C for 3 hours, then an aqueous PVA solution (5 wt%) as a binder was added and press-molded at 150°C at a pressure of 2 ton/cm2 for 30 minutes. A lead-free piezoelectric ceramic molded body with a core-shell structure was manufactured.

Next, the core-shell structure lead-free piezoelectric ceramic molded body was first sintered at 700°C for 30 minutes, and then secondarily sintered at 1,100°C for 120 minutes to produce lead-free piezoelectric ceramic.

Example 2

When preparing the BNK coating solution, lead-free piezoelectric ceramic was manufactured in the same manner as in Example 1, except that ultrasonic treatment was also performed under output power conditions of 40 kHz and 200 W.

Example 3

Lead-free piezoelectric ceramic was manufactured in the same manner as in Example 1, except that primary sintering was performed at 650°C for 50 minutes, followed by secondary sintering at 1,000°C for 200 minutes.

Example 4

Lead-free piezoelectric ceramic was manufactured in the same manner as in Example 1, except that primary sintering was performed at 750°C for 20 minutes, followed by secondary sintering at 1,050°C for 180 minutes.

Comparative Example 1

(Li _0.05 Na _0.57 K _0.38 ) LNKN powder doped with Bi ₂ O ₃ was synthesized by adding 0.3 parts by weight of Bi ₂ O ₃ to 100 parts by weight of LNKN piezoelectric material having a composition ratio of NbO ₃ .

Next, the LNKN powder doped with Bi ₂ O ₃ was calcined at 600°C for 2 hours, then an aqueous PVA solution (5 wt%) as a binder was added and press molded at 150°C for 30 minutes at a pressure of 2 ton/cm2. A lead-free piezoelectric ceramic molded body was manufactured.

Next, lead-free piezoelectric ceramic was manufactured by sintering the lead-free piezoelectric ceramic molded body at 1,100°C for 3 hours.

2. Physical property evaluation

Table 1 shows the physical property evaluation results for the lead-free piezoelectric ceramics manufactured according to Examples 1 to 4 and Comparative Example 1. At this time, in order to measure the electrical properties, the lead-free piezoelectric ceramics manufactured according to Examples 1 to 4 and Comparative Example 1 were polished to a thickness of 1 mm, Ag electrodes were applied, and after heat treatment, they were heated at 30 kV/cm in insulating oil at 120°C. Polarization treatment was performed by applying a direct current electric field for 30 minutes, and the electrical properties were measured 24 hours later. In addition, dielectric properties were measured using an LCR meter (AN DO AG-4304).

[Table 1]

As shown in Table 1, the lead-free piezoelectric ceramics manufactured according to Examples 1 to 4 not only had higher sintered densities than the lead-free piezoelectric ceramics manufactured according to Comparative Example 1, but also had higher piezoelectric and dielectric properties. It can be seen that the physical properties have clearly improved.

As can be seen based on the above experimental results, the lead-free piezoelectric ceramics according to Examples 1 to 4 subjected to two-stage sintering exhibit superior piezoelectric and dielectric properties compared to the lead-free piezoelectric ceramics according to Comparative Example 1 using one-stage sintering. Confirmed.

The present invention is part of the 2021 material and component technology development project hosted by the Korea Institute of Industrial Technology Evaluation and Planning under the Ministry of Trade, Industry and Energy, “Development of bismuth-based coe-shell lead-free piezoelectric material for biomedical piezoelectric sensors (Project identification number: 1415175377, Research and development project number: This study was conducted with support from 20016729).

Although the above description focuses on the embodiments of the present invention, various changes or modifications can be made by a person skilled in the art in the technical field to which the present invention pertains. These changes and modifications can be said to belong to the present invention as long as they do not depart from the scope of the technical idea provided by the present invention. Therefore, the scope of rights of the present invention should be determined by the claims described below.

S110: Bi ₂ O ₃ doped LNKN powder synthesis step
S120: BNK coating solution formation step
S130: Step of forming lead-free piezoelectric ceramic powder with core-shell structure
S140: Forming step of lead-free piezoelectric ceramic molded body with core-shell structure
S150: Sintering step
200: Lead-free piezoelectric ceramic with core-shell structure 220: Lead-free piezoelectric ceramic body
240: Skin current connection electrode 241: Internal hollow connection electrode
242: External hollow connection electrode 243: Cable insertion hole
244: air outlet 244a: first air outlet
244b: second air outlet 245: hollow cooling port
246: vibration damping cutout 247: heat dissipation protrusion
T: Heat dissipation groove

Claims (10)

(a) LNKN piezoelectric having a composition ratio of (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8) Synthesizing LNKN powder doped with Bi ₂ O ₃ by adding Bi ₂ O ₃ to the material;
(b) Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ were weighed to have the composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), then an acidic solution was added and stirred to form a BNK coating solution. forming a;
(c) mixing the Bi ₂ O ₃ doped LNKN powder with a BNK coating solution and a binder, performing ball milling, followed by drying and pulverizing to form a lead-free piezoelectric ceramic powder with a core-shell structure;
(d) calcining the core-shell structure lead-free piezoelectric ceramic powder, adding a binder and press molding to form a core-shell structure lead-free piezoelectric ceramic molded body; and
(e) sintering the core-shell structured lead-free piezoelectric ceramic molded body in two stages to form a core-shell structured lead-free piezoelectric ceramic,
In step (e), the two-stage sintering involves first sintering at 650 to 800°C, followed by secondary sintering at 950 to 1,150°C,
After step (e), the lead-free piezoelectric ceramic of the core-shell structure is arranged to surround the surface of the core layer, a core layer made of LNKN doped with Bi ₂ O ₃ , and BNK composed of Bi, Na, and K components. A lead-free piezoelectric ceramic body including a coating layer; and a skin current connection electrode disposed on at least one surface of the lead-free piezoelectric ceramic body,
The skin current connection electrode includes an internal hollow connection electrode disposed in an inner central portion, an external hollow connection electrode disposed to have a cone shape surrounding the internal hollow connection electrode on an outside spaced apart from the internal hollow connection electrode, and the external hollow connection electrode. It has a plurality of air outlets formed to penetrate the lower side of the connection electrode,
The internal hollow connection electrode has a bottom surface connected to the lead-free piezoelectric ceramic body, a hollow cooling hole is disposed in the center, and an inner wall of the hollow cooling hole is provided with a heat dissipation groove. A core shell with excellent piezoelectric and dielectric properties. Method for manufacturing lead-free piezoelectric ceramics in structure.
According to paragraph 1,
In step (a) above,
The Bi ₂ O ₃ is
A method of manufacturing a lead-free piezoelectric ceramic with a core-shell structure having excellent piezoelectric and dielectric properties, characterized in that 0.1 to 0.5 parts by weight is added based on 100 parts by weight of the LNKN piezoelectric material.
According to paragraph 1,
In step (c) above,
The BNK coating solution is
A method for manufacturing lead-free piezoelectric ceramics with a core-shell structure with excellent piezoelectric and dielectric properties, characterized in that 15 to 30 parts by weight are added to 100 parts by weight of the Bi ₂ O ₃ doped LNKN powder.
According to paragraph 1,
In step (d) above,
The pressure molding is
A method of manufacturing lead-free piezoelectric ceramics with a core-shell structure with excellent piezoelectric and dielectric properties, characterized in that it is carried out at 100 ~ 180 ℃ and under a pressure of 1 ~ 3 ton / ㎠ for 1 ~ 60 minutes.
According to paragraph 1,
In step (e) above,
The two-stage sintering is
Primary sintering at 650 to 800°C for 10 to 60 minutes,
A method of manufacturing a lead-free piezoelectric ceramic with a core-shell structure having excellent piezoelectric and dielectric properties, comprising the step of secondary sintering at 950 to 1,150°C for 30 to 240 minutes.
A lead-free piezoelectric ceramic body including a core layer made of LNKN doped with Bi ₂ O ₃ and a BNK coating layer arranged to surround the surface of the core layer and made of Bi, Na, and K components; and
It includes a skin current connection electrode disposed on at least one surface of the lead-free piezoelectric ceramic body,
The skin current connection electrode includes an internal hollow connection electrode disposed in an inner central portion, an external hollow connection electrode disposed to have a cone shape surrounding the internal hollow connection electrode on an outside spaced apart from the internal hollow connection electrode, and the external hollow connection electrode. It has a plurality of air outlets formed to penetrate the lower side of the connection electrode,
The internal hollow connection electrode has a bottom connected to the lead-free piezoelectric ceramic body, a hollow cooling hole is disposed at the center, and an inner wall of the hollow cooling hole is provided with a heat dissipation groove,
The LNKN is characterized by having a composition ratio of (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8.) A lead-free piezoelectric ceramic with a core-shell structure that has excellent piezoelectric and dielectric properties.
According to clause 6,
The external hollow connection electrode is
A lead-free piezoelectric ceramic with a core-shell structure having excellent piezoelectric and dielectric properties is provided with a cable insertion hole for inserting a power cable in the space between the internal hollow connection electrodes, and the bottom surface is connected to the lead-free piezoelectric ceramic body. .
In clause 7,
The external hollow connection electrode is
A core having excellent piezoelectric and dielectric properties, which is formed to penetrate the lower part of the external hollow connection electrode and has a plurality of air outlets for discharging the internal air to the outside so that the solder filled into the cable insertion hole flows. Lead-free piezoelectric ceramic with shell structure.
According to clause 8,
The plurality of air outlets are
a first air outlet formed to penetrate a lower portion of the external hollow connection electrode and disposed at a first position;
Piezoelectric and dielectric properties are formed to penetrate the lower part of the external hollow connection electrode, and have a second air outlet spaced apart from the first air outlet in a zigzag shape at a second position higher than the first position. Lead-free piezoelectric ceramic with excellent core-shell structure.
According to clause 9,
The skin current connection electrode is
a vibration-attenuating cutout disposed to be spaced apart from a bottom surface of the external hollow connection electrode in contact with the lead-free piezoelectric ceramic body and disposed at a second position corresponding to the second air outlet;
A lead-free piezoelectric ceramic with a core-shell structure having excellent piezoelectric and dielectric properties, further comprising:

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