KR20150122418A - Pb-FREE PIEZOELECTRICITY FOR AN AUTOMOBILE KNOCKING SENSOR, METHOD OF MANUFACTURING THE SAME AND AUTOMOBILE KNOCKING SENSOR INCLUDING THE SAME - Google Patents

Abstract

A lead-free piezoelectric material for a vehicle knock sensor comprises: (Na_(1-x)K_x)NbO_3; and an additive CuO of z mol%, and has the sintering temperature of 940 to 980°C, wherein x is 0.5 or 1, and 0.5 <= z <= 2.0.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-connected piezoelectric member for a vehicle knocking sensor, a manufacturing method thereof, and an automobile knocking sensor including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002]

TECHNICAL FIELD The present invention relates to a non-linked piezoelectric member for a vehicle knocking sensor, a method of manufacturing the same, and an automobile knocking sensor including the same. More particularly, the present invention relates to a non-connected piezoelectric member that does not include lead (Pb) A manufacturing method of the non-linked piezoelectric body, and an automobile knocking sensor.

Piezoelectric bodies are widely used as materials for ultrasonic vibrators, electromechanical transducers, and actuator parts used in a wide range of fields such as ultrasonic devices, video devices, acoustic devices, communication devices, and sensors.

Up to now, piezoelectric materials of Pb (Zr, Ti) O ₃ (hereinafter referred to as PZT) have high properties and are utilized as most piezoelectric material. However, lead (Pb) is a toxic substance, volatilizes during the sintering process and causes serious environmental pollution. Therefore, research and development of nonconjugated piezoelectric materials for replacing PZT have been actively conducted.

On the other hand, in the case of a non-leaded piezoelectric body, it has excellent characteristics that can be applied to a vibration sensor for an automobile knocking sensor. Therefore, it is considered that PZT can be substituted if only the proper composition for the non-piezoelectric ceramics is developed. In addition, through the development of the composition of the non-lead piezoelectric material, it is possible to sufficiently utilize not only a vibration sensor such as a car knocking sensor but also a piezoelectric acoustic device and an actuator.

BaTiO ₃ , (Bi _1/2 Na _1/2 ) TiO ₃ and Alkali-Niobate series ceramics are used as the material of the non-connected piezoelectric substance. The alkali-based ceramics have excellent piezoelectric characteristics and a high phase transition temperature (T _c ) of 400 ° C or higher.

Recently, much research has been conducted on (Na, K) NbO ₃ (hereinafter referred to as NKN) and KNbO ₃ (hereinafter referred to as KN) ceramics, which are one kind of alkali-based ceramics. In particular, NKN-LNTS has piezoelectric properties similar to PZT, and many researches have been conducted on non-connected piezoelectric materials that can replace PZT at present. However, NKN ceramics are sintered due to the volatilization of sodium (Na) at temperatures higher than 1,000 ^° C. Such sodium volatilization makes it difficult to complete the sintering of NKN ceramics and the insulation resistance of the ceramic itself falls. The decrease of the insulation resistance affects the polarization process of the piezoelectric ceramics and may cause deterioration of the piezoelectric characteristics.

Therefore, it is necessary to study the improvement of piezoelectric characteristics while suppressing the volatilization of sodium by sintering the NKN ceramics at a low temperature. If the above problem is solved, it is considered that the non-piezoelectric piezoelectric composition to replace PZT can be secured in various fields.

On the other hand, S. Wada et al. (2001) reported that KN monocrystals have excellent piezoelectric properties and relatively high phase transition temperatures of 430 ^° C. However, in KN production, K ₂ O is volatilized at a high sintering temperature of 1,000 ^° C or higher, and a secondary phase is formed, which has been a serious problem of deteriorating piezoelectric characteristics.

As such, the KN piezoelectric body has a higher phase transition temperature (T _c ) than that of the conventional non-piezoelectric piezoelectric material, and has been recognized as a non-connected piezoelectric body capable of replacing PZT. However, the manufacturing process is complicated, the piezoelectric characteristics are low, and the sintering temperature is similar to the melting point of KN ceramics.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a non-connected piezoelectric body for an automobile knock sensor having improved piezoelectric characteristics.

Another object of the present invention is to provide a method of manufacturing a non-connected piezoelectric material for automobile knock sensors having excellent piezoelectric properties that can be manufactured at a reduced sintering temperature through a relatively simple manufacturing process.

In order to achieve one object of the present invention, the non-associated piezoelectric knocking sensor for automobiles in accordance with an embodiment of the invention _{(Na 1-x K x)} NbO 3; And z mol% of additive CuO, and has a sintering temperature of 940 to 980 [deg.] C. Here, x is 0.5 or 1, and 0.5? Z? 2.0.

According to another aspect of the present invention, there is provided a method of manufacturing a non-connected piezoelectric member for a vehicle knock sensor, comprising: (Na ₂ CO ₃ or K ₂ CO ₃ ) and Nb ₂ O ₅ are mixed as a raw material to form a first mixture, and the first mixture is used to form a first powder through a first milling process and a second drying process. Calcining the first powder to form a (Na _1-x K _x ) NbO ₃ powder (where x is 0.5 or 1), adding to the (Na _1-x K _x ) NbO ₃ powder z mol% CuO where 0.5? Z? 2.0 is added to form a second mixture. Thereafter, a second powder is formed through a second milling process and a second drying process using the second mixture, and the second powder is sintered at a temperature of 940 to 980 DEG C to form a sintered body.

 In one embodiment of the present invention, the first milling step may include milling the first mixture in a nylon jar together with an anhydrous alcohol solvent and using a zirconia ball for 2 to 24 hours.

 In one embodiment of the present invention, the second milling step may include pulverizing the second mixture in a nylon jar together with an anhydrous alcohol solvent using a zirconia ball for 48 hours to 72 hours.

 In one embodiment of the present invention, the step of sintering the second powder to form the sintered body may be performed for 2 to 20 hours.

According to the non-connected piezoelectric member for automobile knock sensor and the method of manufacturing the same according to the embodiments of the present invention described above, CuO is added and lead (Pb) is not added, so that environmental problems can be suppressed. Further, a non-connected piezoelectric substance can be produced through a relatively simple process. Particularly, since the low-temperature sintering process is possible at a temperature lower than 1,000 ° C, the volatilization of Na ₂ O and K ₂ O is suppressed, so that a non-connected piezoelectric material having a uniform composition can be manufactured. Further, the non-connected piezoelectric material to which CuO is added can realize excellent piezoelectric characteristics and dielectric properties. In particular, the non-connected piezoelectric member according to the above-described embodiments of the present invention has a relatively high piezoelectric constant (g ₃₃ ) value, a quality coefficient (Q _m ) value, and a high phase transition temperature (T _c ), it can be applied to non-linked piezoelectric sensors.

1 is a flowchart illustrating a method of manufacturing a non-connected piezoelectric member for a vehicle knock sensor according to an embodiment of the present invention.
FIG. 2 is a graph showing changes in relative density, dielectric characteristics, and piezoelectric characteristics of CuO-added NKN piezoelectric materials with changes in sintering temperature.
FIG. 3 is an electron micrograph showing microstructure of CuO-added KN piezoelectric ceramics sintered at 960.degree. C. for 2.0 hours according to the change of CuO addition amount.
FIG. 4 is a graph showing the relative density, dielectric characteristics, and piezoelectric characteristics of CuO-doped KN piezoelectric ceramics sintered at 960 ° C for 2.0 hours.
5 is a graph showing the sensor sensitivity of a knocking sensor using a knocking sensor manufactured using an NKN piezoelectric body (Example 1) with CuO added at 960 ° C for 2.0 hours and a car knocking sensor using PZT FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In the accompanying drawings, the sizes and the quantities of objects are shown enlarged or reduced from the actual size for the sake of clarity of the present invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprise", "comprising", and the like are intended to specify that there is a feature, step, function, element, or combination of features disclosed in the specification, Quot; or &quot; an &quot; or &lt; / RTI &gt; combinations thereof.

On the other hand, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Non-connected piezoelectric body

Decoupled piezoelectric knocking sensor for automobiles in accordance with embodiments of the present invention comprises _{(Na 1-x K x)} NbO 3 and z mol% of CuO additives. Here, x is 0.5 or 1 and has a range of 0.5? Z? 2.0. That is, when x is 0.5, the non-connected piezoelectric material includes (Na _0.5 K _0.5 ) NbO ₃ and corresponds to an NKN series piezoelectric substance. When x is 1, KNbO ₃ is included. do.

The additive comprises CuO. The additive reacts with (Na _1-x K _x ) NbO _{3 in} the sintering process for producing the non-interconnected piezoelectric body to form an intermediate, and the intermediate has a relatively low melting point, So that it can proceed. That is, the sintering process can be performed at a sintering temperature of 940 to 980 ° C. Accordingly, as the sintering process proceeds at the reduced sintering temperature, volatilization of Na ₂ O and K ₂ O is suppressed, so that a non-connected piezoelectric material having a uniform composition can be manufactured. Further, the non-connected piezoelectric material to which CuO is added can realize excellent piezoelectric characteristics and dielectric properties

Method of manufacturing non-connected piezoelectric body

1 is a flowchart illustrating a method of manufacturing a non-connected piezoelectric member for a vehicle knock sensor according to an embodiment of the present invention.

Referring to Figure 1, (Na ₂ CO _3, or K ₂ CO ₃ ) and Nb ₂ O ₅ are mixed as a raw material to form a first mixture (S110)

Depending on the composition of the first mixture, a purity of 99% or more (Na ₂ CO ₃ or K ₂ CO ₃ ) and Nb ₂ O ₅ are subjected to a batch process for calculating mass ratios, and a weighing process is performed for weighing each weight according to the batch result. Thereafter, depending on the amount and the weighting process (Na ₂ CO ₃ or K ₂ CO ₃ ) and Nb ₂ O ₅ are mixed to form a first mixture. That is, when the first mixture is formed by mixing Na ₂ CO _3, K ₂ CO ₃ and Nb ₂ O ₅ , an NKN series piezoelectric material is formed, while K ₂ CO ₃ and Nb ₂ O ₅ are mixed When a mixture is formed, a KN series piezoelectric substance can be formed.

Thereafter, the first powder is formed through the first milling process and the second drying process using the first mixture (S120)

In the first milling step, a first ball-milling process is performed in which a wet nylon jar is wet-mixed with a zirconia ball using an anhydrous alcohol solvent for 2 to 24 hours and pulverized by a powder Can be performed. Then, in the first ball-milling step, a drying process for removing the mixed anhydrous alcohol is performed, thereby forming a first powder in powder form.

Thereafter, the first powder is calcined to form (Na _1-x K _x ) NbO ₃ powder (where x is 0.5 or 1) (S 130)

Here, when x is 0.5, the non-connected piezoelectric material includes (Na _0.5 K _0.5 ) NbO ₃ and corresponds to a piezoelectric material of NKN series. When x is 1, KNbO ₃ is included. do. Here, the calcination process can be performed at 800 to 1000 ° C for 2 to 10 hours.

Z mol% of additive CuO is added to the (Na _1-x K _x ) NbO ₃ powder to form a second mixture (S140), where 0.5? Z? 2.0.

The additive reacts with (Na _1-x K _x ) NbO ₃ in a subsequent sintering process to form an intermediate and the intermediate has a relatively low melting point so that the liquid phase sintering process can proceed at a reduced sintering temperature . That is, the sintering process can be performed at a sintering temperature of 940 to 980 ° C. Accordingly, as the sintering process proceeds at the reduced sintering temperature, volatilization of Na ₂ O and K ₂ O is suppressed, so that a non-connected piezoelectric material having a uniform composition can be manufactured. Further, the non-connected piezoelectric material to which CuO is added can realize excellent piezoelectric characteristics and dielectric properties.

Next, a second powder is formed through the second milling process and the second drying process using the second mixture (S150)

According to the second milling process, a second powder composed of (Na _1-x K _x ) NbO ₃ and CuO is wet-mixed with an anhydrous alcohol solvent for 48 to 72 hours, and the second powder is pulverized using zirconia balls A second ball-milling process can be performed. Thereafter, a drying process for removing the anhydrous alcohol solvent used in the second ball-milling process may be performed. This forms a second powder of NKN and KN series to which CuO is added as an additive.

Subsequently, a sintering process is performed to sinter the second powder at 940 to 980 ° C. (S 160)

The sintered body may have various shapes and sizes as a piezoelectric body used for a sonic device, an image device, an acoustic device, a communication device, a sensor, an ultrasonic vibrator, an electromechanical transducer or an actuator.

In one embodiment of the present invention, a sieving process for sieving the second powder at a uniform size is performed prior to the sintering process and a pressing process for forming a specific shape of the sieved powder is performed in advance . As an example, the sintered body may be pressure-molded so as to have a cylindrical shape or a ring shape.

In one embodiment of the present invention, a post-treatment process may be additionally performed on the sintered body. According to the post-treatment process, the electrode material is coated on the surface of the sintered body after the sintered body is polished, immersed in the silicone oil, and a 3 to 5 kV / mm DC bias is applied for 1 hour at a temperature of 120 to 150 ° C.

Evaluation of non-connected piezoelectric body

Na ₂ CO ₃ , K ₂ CO ₃ and Nb ₂ O ₅ having an initial raw material purity of 99.9% were mixed and wet mixed with a zirconia ball in a nylon jar for 24 hours using an anhydrous alcohol solvent to obtain a first mixture .

Then, the first mixture was dried and calcined at 950 ° C for 3 hours to prepare a first powder by synthesizing NbO ₃ (first embodiment) and KNbO ₃ (second embodiment) powder (Na _0.5 K _0.5 ) . 0.5 to 5.0 mol% of CuO was added to the first powder, wet mixed and pulverized using an anhydrous alcohol solvent for 72 hours, and then dried to form a second mixture. Subsequently, the dried powder was press-molded into a cylindrical shaped article having a diameter of 18 mm and a height of about 1.3 to 1.5 mm, and then sintered at 960 ° C for 2 hours to form a sintered body.

After the sintered body was polished and the electrode material was applied, the characteristics were measured after applying the 3-5 kV / mm DC bias for 1 hour at 120-150 ° C in the silicone oil.

2 is a graph showing changes in relative density, dielectric characteristics, and piezoelectric characteristics of an NKN piezoelectric body (Example 1) to which CuO is added according to a change in sintering temperature.

Referring to FIG. 2, it can be seen that it has a high sintered density even at a low temperature of 1,000 ° C or more. However, when the sintering temperature is close to 1,000 ° C, the relative density gradually decreases due to excessive liquid phase formation. Since the volatilization of sodium (Na) was suppressed, the liquid phase sintering behavior by Cu-Nb reaction occurred in the NKN piezoelectric body to which CuO was added. Also, as relative densities decrease, other piezoelectric and dielectric properties also decrease slowly. That is, according to the above-described manufacturing method, the KN piezoelectric body, which is sintered at a low temperature of 960 ^° C and in which 1.5 mol% of CuO is added, has g ₃₃ = 55 Vm / N, kp = 0.4, ₃ ^T / ?? ₀ = 195 and Q _m = 880, respectively.

3 is an electron micrograph showing the microstructure of CuO-added KN piezoelectric ceramics (Example 2) sintered at 960 ° C for 2.0 hours according to the change of CuO addition amount.

Referring to FIG. 3, when CuO is not added, the degree of sintering is too low to take a micrograph. (a) shows that when a very small amount (0.5 mol%) of CuO is added, the densification occurs but the amount of the liquid phase is not sufficient and the grain growth does not occur. However, as shown in (b), when 1.0 mol% of CuO is added, a dense microstructure having almost no pores is formed.

In addition, (c) and (d) show that when the amount of CuO is increased to 2.0 mol% or more, a dense microstructure is formed, and most of the grain size is greatly grown.

4 is a graph showing the relative density, dielectric characteristics, and piezoelectric characteristics of a KN piezoelectric body (Example 2) to which CuO was sintered at 960 ° C for 2.0 hours.

Referring to FIG. 4, the sample not containing CuO at 960 ^° C. is sintered and has a relatively low relative density. However, even when only a small amount of CuO of 0.5 mol% is added, liquid phase sintering of the KN piezoelectric material occurs, Of the total. The piezoelectric constant (d ₃₃ ), the piezoelectric constant (g ₃₃ ), the dielectric constant and the electromechanical coupling coefficient (K _p ) of the KN piezoelectric body tend to decrease gradually with the amount of CuO added.

On the other hand, the mechanical quality factor (Q _m ) increases rapidly with the addition of CuO. This can be explained by the Hardening Effect caused by the employment of a part of Cu by KN. Especially, the specimen with 1.5 mol% of CuO showed a high Q _m of 2,300. In addition, due to the low permittivity, the piezoelectric constant (g ₃₃₎ has a high value of 44 Vm / N. It can be seen that the piezoelectric constant is the highest value among the non-ceramic piezoelectric materials known so far and is sufficiently applicable to a knock sensor for automobile, which is one type of vibration sensor.

As a result, when the piezoelectric voltage constant, the mechanical quality factor and the electromechanical coupling coefficient necessary for a piezoelectric vibration sensor such as an automobile knocking sensor are comprehensively judged, when 1.0 mol% of CuO is added, high piezoelectric characteristics can be obtained . That is, according to the above-described manufacturing method, a KN piezoelectric body to which 1.0 mol% of CuO sintered at a low temperature of 960 ^° C is g ₃₃ = 48 Vm / N, kp = 0.27, ₃ ^T / ?? ₀ = 208 and Q _m = 1787, respectively.

5 shows the sensitivity of a knocking sensor using a knocking sensor manufactured using an NKN piezoelectric body (Example 1) to which CuO was sintered at 960 ° C for 2.0 hours and a knocking sensor using a PZT (conventional product, comparative example) FIG.

Referring to FIG. 5, it can be seen that the NKN piezoelectric body (Example 1) to which CuO is sintered for 2.0 hours at a frequency of 1 to 20 kHz, which is a frequency used for a knocking sensor, has a sensor sensitivity 1.5 times higher than that of the conventional product. It can be seen that such a high sensor sensitivity is due to the excellent piezoelectric constant (g33) of the non-piezoelectric ceramic. Therefore, it can be seen that CuO added NKN and KN ceramics can be fully utilized as a non-piezoelectric piezoelectric automobile knocking sensor and other vibration sensors.

Further, the embodiment _{1 (Na 0.5 K 0.5) NbO} 3 [NKN] + 1.5 mol% CuO), Example _{2 (KNbO 3 [KN] +} 1.0 mol% CuO) and Comparative Examples (P-6C ^TM, Murata社) Are summarized in the following table. &Lt; tb &gt;&lt; TABLE &gt;

g _{33 (} Vm / N) d _{33 (} pC / N) ₎ Relative dielectric constant Qm Kp Sintering temperature
(˚C) Phase transition temperature
(˚C) Example 1 55 95 195 880 0.4 960 406 Example 2 48 88 208 1,787 0.27 960 430 Comparative Example 19 135 800 680 0.39 - 320

It can be seen that Examples 1 and 2 have excellent piezoelectric properties suitable for a vibration sensor than Comparative Examples. In particular, it can be seen that the piezoelectric constant constant which directly affects the sensitivity of the vibration sensor is high.

The non-linked piezoelectric material according to the embodiments of the present invention can be directly applied to the production of a vibration sensor, particularly, a knock sensor for automobile by adjusting the amount of additive (CuO).

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

Claims (7)

_{(Na 1 - x K x)} NbO 3; And
z mol% of additive CuO, and having a sintering temperature of 940 to 980 [deg.] C. (Where x is 0.5 or 1 and 0.5? Z? 2.0) (Na ₂ CO ₃ or K ₂ CO ₃ ) and Nb ₂ O ₅ as raw materials to form a first mixture;
Forming a first powder through the first milling process and the second drying process using the first mixture;
Forming (Na _1-x K _x) NbO ₃ powder (where, x is 0.5 or 1) by calcining the first powder;
Adding z mol% of an additive CuO (wherein 0.5? Z? 2.0) to the (Na _1-x K _x ) NbO ₃ powder to form a second mixture;
Forming a second powder through the second milling process and the second drying process using the second mixture; And
And sintering the second powder at a temperature of 940 to 980 ° C to form a sintered body. 3. The knocking sensor according to claim 2, wherein the first milling step comprises grinding the first mixture in a nylon jar together with an anhydrous alcohol solvent using a zirconia ball for 2 to 24 hours, And a method of manufacturing the non-connected piezoelectric body. [3] The automobile knocking sensor according to claim 2, wherein the second milling step comprises grinding the second mixture in a nylon jar together with an anhydrous alcohol solvent using a zirconia ball for 48 to 72 hours, And a method of manufacturing the non-connected piezoelectric body. 3. The method of claim 2, wherein the step of sintering the second powder to form a sintered body is performed for 2 to 20 hours. A vehicle knocking sensor comprising the non-connected piezoelectric body of claim 1. A manufacturing method of a vehicle knocking sensor manufactured by using the manufacturing method according to any one of claims 2 to 5.

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