WO2010044534A1

WO2010044534A1 - Ceramic composition for lead-free ptc(positive temperature coefficient of resistance) thermistor and the ptc ceramic thermistor prepared using the same

Info

Publication number: WO2010044534A1
Application number: PCT/KR2009/003916
Authority: WO
Inventors: 백종후; 이영진; 정영훈; 김철민; 이우영; 최진수
Original assignee: 한국세라믹기술원; (주)하이엘
Priority date: 2008-10-16
Filing date: 2009-07-16
Publication date: 2010-04-22
Also published as: KR20100042567A; KR100991391B1; CN102177105A

Abstract

The present invention relates to a ceramic composition for a lead-free PTC thermistor which does not contain a lead (Pb) component and has a low specific resistance value at room temperature and a Curie temperature (Tc) of 130℃ or more. The ceramic composition for a lead free PTC thermistor according to the present invention comprises any one selected from formulas 1-4. [Formula 1] Ba_1-x(Bi_0.5 Na_0.5)xTiO₃ + y mol% M1O_w [Formula 2] Ba_1-x(Bi_0.5Na_0.5)xTiO₃ + y mol% M1₂O_w + z wt% M2O₂ [Formula 3] Ba_1-x(Bi_0.5K_0.5)xTiO₃ + y mol% M1O_w [Formula 4] Ba_1-x(Bi_0.5K_0.5)xTiO₃ + y mol% M1O_w + z wt% M2O₂ (In formulas 1-4, 0.01≤x≤0.05, 0.00＜y≤0.40, 0.00＜z≤0.40; M1 is one or more elements selected from the group consisting of Nb, Sb, La, Y; M2 is Mn; and w is 3 when M1 is a trivalent element and is 5 when M1 is a pentavalent element.) In addition, the invention comprises a ceramic composition for a PTC thermistor of the following formula 5 in which Na_0.5K_0.5NbO₃(NKN) is formed as a solid solution of BaTiO₃(BT). [Formula 5] (1-x)BT-xNKN (0<x≤0.05) The invention provides a PTC ceramic thermistor prepared using the compositions of the formulas.

Description

Ceramic Composition for Lead-Free Ptc Thermistors and Ptc Ceramic Thermistors Prepared Using the Same

The present invention relates to a ceramic composition, and more particularly, to a ceramic composition for PTC thermistor containing no lead component.

PTC (Positive Temperature Coefficient of resistance) thermistor shows the characteristic that the resistance increases with increasing temperature, and generally BaTiO ₃ is the basic composition.

BaTiO ₃ (BT) -based semiconducting ceramics are compounds of a typical perovskite crystal structure represented by ABO ₃ and are occupied by divalent Ba ions at A-site and tetravalent Ti ions at B-site. The crystal structure has various polymorphic properties that transition to a rhombohedral, orthorhombic, tetragonal and cubic depending on temperature.

In particular, resistance-temperature characteristics are obtained by measuring the electrical resistance of the PTC thermistor at ambient temperatures below 1.5V _DC . In this characteristic, the temperature at which the resistance value increases sharply is called resistance temperature (switching temperature) or Curie temperature, which is generally the temperature corresponding to twice the minimum resistance value or the reference temperature (25 ° C) resistance value. It is defined as, and is an important parameter of material properties.

In BaTiO ₃ ceramics, the Curie temperature (Tc) is a temperature of 130 ° C that transitions from the tetragonal phase of ferroelectric phase to the cubic phase of phase dielectric. To increase the operating temperature of PTC thermistor above 130 ° C, lead (Pb) ) Substituted PbTiO ₃ is used.

Since PbTiO ₃ has a Curie temperature (Tc) of 490 ° C., it is possible to sufficiently raise the operating temperature. However, the lead (Pb) component is harmful to the human body and may cause environmental pollution, and the lead component evaporated in the device may also deteriorate the uniformity of the device.

Recently, as interest in environmentally friendly materials for humans and the environment has increased, researchers have developed a lead-free PTC thermistor composition having a higher Curie temperature (Tc) than BaTiO ₃ in place of a PTC thermistor material containing lead (Pb). It is actively progressed recently.

Bi _1/2 Na _1/2 TiO ₃ (BiNT), Bi _1/2 K ₁ having a perovskite structure as representative candidate materials among the lead-free PTC thermistors having a Curie temperature (Tc) of 120 ° C. or higher. _{/ 2} TiO ₃ (BiKT), NaNbO ₃ , BiFeO ₃ and the like have been introduced.

However, the PTC properties of the materials have not been fully verified, and in particular, the development of ceramic compositions having high Curie temperatures (High Tc> 130 ° C.) used in automotive heaters is still insignificant.

The problem to be achieved by the present invention is a PTC thermistor which does not contain lead (Pb) and has a low resistivity value at room temperature, a PTCR effect of 10 ³ or more, a temperature coefficient of 10% or more, and a Curie temperature (Tc) of 130 ° C or more. It is to provide a ceramic composition for.

Moreover, an object of this invention is to provide the PTC ceramic thermistor manufactured using the said ceramic composition.

The ceramic composition for PTC thermistor according to the present invention for solving the above problems is characterized by consisting of any one selected from the following [Formula 1] to [Formula 5].

[Formula 1] Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% M1O _w

[Formula 2] Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% M1 ₂ O _w + z wt% M2O ₂

[Formula 3] Ba _1-x (Bi _0.5 K _0.5 ) _x TiO ₃ + y mol% M1O _w

[Formula 4] Ba _1-x (Bi _0.5 K _0.5 ) _x TiO ₃ + y mol% M1O _w + z wt% M2O ₂

(1-x) BT-xNKN

(In [Formula 1] to [Formula 4] is 0.01≤x≤0.05, 0.00 <y≤0.40, 0.00 <z≤0.40, M1 is at least one element selected from the group consisting of Nb, Sb, La, Y , M2 is Mn, w is 3 when M1 is a trivalent element, and 5 when it is a pentavalent element.

In Formula 5, 0 <x ≦ 0.03, and BT is BaTiO.₃NKN is Na_0.5K_0.5NbO₃ego,NKN is a solid solution of BT.)

In addition, the PTC ceramic thermistor according to the present invention is characterized by being manufactured from the ceramic composition described above.

Here, the ceramic composition is characterized in that it further comprises a dopant material consisting of Nb ₂ O ₅ powder, characterized in that the Nb ₂ O ₅ is added in the range of 0 to 0.2 mol%.

In addition, the Na _{_0.5} K _0.5 NbO ₃ to the manufacturing method PTC ceramic thermistors proceeds with the BaTiO ₃ (BT) to provide a 99.9% pure BaTiO ₃ (BT) (NKN), according to an embodiment of the invention in solid solution Forming (1-x) BT-xNKN (0 <x≤0.03) ceramic raw powder, and putting the ceramic raw powder into HDPE (High Density Polyethylene) jar for 24 hours using distilled water as a dispersion medium. During the first ball milling step, drying the first ball milled ceramic raw material powder at 120 ° C., and then putting it in a mortar and pulverizing; putting the pulverized ceramic raw material powder in an alumina crucible at 1000 ° C. Calcining for 2 hours, putting the calcined ceramic raw material powder into HDPE (High Density Polyethylene) jar, and performing a second ball milling for 24 hours using distilled water as a dispersion medium and the second ball milling treatment. Ceramic raw powder mold Insert is characterized in that it comprises a step of producing a sensor type by applying pressure of 1 ton / cm ^2.

According to the ceramic composition according to the present invention, a PTC thermistor which may have a low resistivity value, a PTCR effect of 10 ³ or more, a temperature coefficient of 10% or more, and a Curie temperature (Tc) of 130 ° C or higher without containing lead (Pb) at room temperature It will be possible to manufacture.

Accordingly, the present invention provides an effect that can be applied not only to automobile heaters but also to PTC heaters, PCT current limiters, PTC resistors, and the like which require high performance.

1 to 9 are graphs of measurement results of measuring PTC characteristics of Examples 1 to 33. FIG.

10 to 15 are graphs of measurement results of measuring PTC characteristics of Examples 34 to 53. FIG.

Figure 16 is a graph measuring the specific resistance of the (1-x) BT-xNKN ceramic according to the present invention.

Figure 17 is a graph measuring the room temperature specific resistance of the concentration of Nb ₂ O ₅ added to (1-x) BT-xNKN ceramics according to the present invention.

18 is a graph measuring the Curie temperature for each concentration of Nb ₂ O ₅ added to the (1-x) BT-xNKN ceramic according to the present invention.

19 is a graph measuring PTC jump characteristics for each concentration of Nb ₂ O ₅ added to (1-x) BT-xNKN ceramics according to the present invention.

20 is a graph measuring the resistance temperature coefficient characteristics of the concentration of Nb ₂ O ₅ added to the (1-x) BT-xNKN ceramic according to the present invention.

In the present invention, as a main component of the ceramic composition for PTC thermistor, barium bismuth sodium titanum oxide; Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ ) and barium bismuth potassium titanum oxide; Ba _1-x (Bi _0.5 K _0.5 ) _x TiO ₃ ) based ceramics were used. (0.01≤x≤0.05)

Here the M1O _w, and M2O ₂ was used as a substituent on.

At this time, M1 is a trivalent or pentavalent element, specifically, at least one selected from Nb, Sb, La, Y may be used, and M2 may specifically use Mn as a divalent element.

M1Ow ratio is a ratio which is substituted on the above main component is 0.00 or less than 0.40mol%, M2O ₂ is substituted for the main component is determined in a range of 0.00 or less than 0.40wt%.

In sum, the ceramic composition for PTC thermistor according to the present invention may be represented by any one selected from the following Chemical Formulas 1 to 4.

[Formula 1] Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% M1O _w

[Formula 3] Ba _1-x (Bi _0.5 K _0.5 ) _x TiO ₃ + y mol% M1O _w

(In [Formula 1] to [Formula 4] is 0.01≤x≤0.05, 0.00 <y≤0.40, 0.00 <z≤0.40, M1 is at least one element selected from the group consisting of Nb, Sb, La, Y , M2 is Mn, w is 3 if M1 is a trivalent element, and 5 if it is a pentavalent element.)

In the above [Formula 1] to [Formula 4] is defined as 0.01≤x≤0.05, the reason is that if x is less than 0.01 or exceeds 0.05 it is not possible to obtain a good sintered body PTC heater, PCT current limiter, PTC resistor, etc. Because the application is difficult.

In the above [Formula 1] to [Formula 4] is defined as 0.00 <y ≤ 0.40, the reason is that if y exceeds 0.40, the room temperature specific resistance is increased so that it is difficult to measure the PTC heater, PCT current limiter, PTC resistor, etc. This is because the application is difficult.

In the above [Formula 2] and [Formula 4] is defined as 0.00 <z ≤ 0.40, the reason is that if z exceeds 0.40, the room temperature specific resistance is increased to the extent that it is difficult to measure the PTC heater, PTC limiter, PTC resistor, etc. This is because the application is difficult.

Hereinafter, in the ceramic composition for PTC thermistors according to the present invention, specific examples and comparative examples will be described with respect to the reason why the x, y, and z values should have the above ranges.

<실시예 1 ~ 실시예 33><Example 1 to Example 33>

TiO ₂ , Bi ₂ O ₃ , Na ₂ CO ₃ , Nb ₂ O ₅ , MnO ₂ , BaTiO ₃ were prepared as starting materials, and the raw materials were weighed to form a composition in the range of the present invention.

In each sample, the starting elements were ball milled for 24 hours using a ball mill, and the mixed sample was dried at 100 to 120 ° C., and then the powder was placed in a mortar and pulverized and placed in an alumina crucible at 1000 ° C. 2 hours was calcined.

The calcined powder was put in a mortar again and pulverized, and then wet milled for 24 hours using zirconia balls. Thereafter, the mixed sample was sufficiently dried at 100 to 120 ° C., and then the prepared sample was uniaxially molded into a cylindrical mold (10 mm) at a pressure of 1 [ton / cm ² ] to form a disc-shaped specimen. .

The molded specimens were sintered at 1300 ~ 1350 ° C. for 4 hours, and the temperature increase rate was heated to 1300 ~ 1350 ° C. for 4 hours at 5.4 ~ 5.6 ° C. per minute.

The temperature reduction rate was 100 degreeC / hr, 200 degreeC / hr, and 600 degreeC / hr, and the PTC element was produced.

XRD analysis was performed to analyze the formation of conductive BaTiO ₃ containing TiO ₂ , Bi ₂ O ₃ , and Na ₂ CO ₃ . The PTC device thus produced measured PTC characteristics such as resistance after electrode treatment.

Table 1 below shows the details of chemical quantification of the samples prepared in Examples 1 to 33 and the PTC characteristic measurement results.

1 to 9 are graphs of these measurement results.

Table 1

<실시예 34 ~ 실시예 53><Example 34 to Example 53>

A PTC device was manufactured in the same manner as in Example 1, except that TiO ₂ , Bi ₂ O ₃ , K ₂ CO ₃ , Nb ₂ O ₅ , MnO ₂ , and BaTiO ₃ were prepared as starting materials. Details of chemical quantification and PTC characteristic measurement results of the samples prepared in Examples 34 to 53 are shown.

10 to 15 are graphs of these measurement results.

TABLE 2

Referring to Tables 1 and 2 and FIGS. 1 to 15, samples satisfying each condition of 0.01 ≦ x ≦ 0.05, 0 <y ≦ 0.40, and 0.00 <z ≦ 0.40 have a low room temperature resistivity and T _c. Curie temperature shows excellent characteristics of 130 ° C or higher.

In addition, although a high purity BaTiO ₃ (BT) is used as a main component of the ceramic composition for PTC thermistors according to an embodiment of the present invention, Na _0.5 K _0.5 NbO ₃ (NKN), which has been used as a lead-free piezoelectric material, is dissolved. By using it, it is possible to ensure a high Curie temperature (High Tc> 130 ℃).

In addition, Nb ₂ O ₅ may be used as an additive to the composition of the above example to ensure effective PTC properties.

First, the main component of the ceramic composition for PTC thermistor according to the embodiment of the present invention follows the formula [5].

[Formula 5]

(1-x) BT-xNKN (0 <x≤0.03)

In

Formula

5, 0 <x ≦ 0.03, which is defined as the reason that when x is less than 0 or more than 0.03, a good sintered body cannot be obtained, and the ceramic composition may be applied to a PTC heater, a PCT current limiter, a PTC resistor, or the like. This is because there is a problem that is difficult to apply.

That is, BaTiO ₃ (BT) exhibits insulator characteristics at room temperature as an insulator, and if Na _0.5 K _0.5 NbO ₃ (NKN) is dissolved in an appropriate amount, the resistance at room temperature is rapidly lowered to have conductivity. In addition, the Curie temperature of Na _0.5 K _0.5 NbO ₃ (NKN) is about 420 ° C, and the Curie temperature of about 120 ° C of pure BaTiO ₃ (BT) is improved by employing Na _0.5 K _0.5 NbO ₃ (NKN). . However, employing an excess of Na _0.5 K _0.5 NbO ₃ (NKN) (greater than 0.03 mol%) increases the grain boundary resistance due to the presence of some of the unsustained Na _0.5 K _0.5 NbO ₃ (NKN) particles at the grain boundary. This decreases the conductivity, which leads to a sharp increase in specific resistance at room temperature. Therefore, it is desirable to comply with the above employment range.

Next, an Nb ₂ O ₅ dopant material may be added to the ceramic composition for PTC thermistor according to the embodiment within a range of 0 to 0.05 mol%. The Nb ₂ O ₅ dopant material slightly reduced the PTC jump properties, but can still maintain effective PTC properties.

However, when added in excess of 0.05 mol%, since the room temperature specific resistance increases rapidly and changes into an insulator, a problem may occur that the PTC characteristics disappear.

Then, using the above-described ceramic composition for PTC thermistor according to an embodiment of the present invention, there is provided a method for producing a PTC ceramic thermistor by a solid phase synthesis method.

First, high purity BaTiO of more than 99.9%₃, Nb₂O₅,Powders can be used to minimize the effects of impurities.

(1-x) BT-xNKN (0 <x ≦ 0.03) Nb ₂ O ₅ (99.9%) may be added to the ceramic as a dopant material, but Nb ₂ O ₅ may be added to 0 to 0.05 mol%. At this time, the raw material powder is preferably weighed precisely to 10 ^-4 g using an electronic balance.

Next, the raw powder is placed in a high density polyethylene (HDPE) jar, and a first ball milling process is performed using zirconia balls for 24 hours using distilled water as a dispersion medium.

Then, the sample mixed in the first ball milling process is dried at 120 ° C., and then placed in a mortar and ground.

Then, the ground raw powder is placed in an alumina crucible and calcined at 1000 ° C. for 2 hours.

Then, the calcined powder is put back into a high density polyethylene (HDPE) jar and a second ball milling process is performed for 24 hours using distilled water as a dispersion medium.

Then, the dried and pulverized sample is placed in a cylindrical mold (Φ: 10 mm) and molded into a disc-shaped PTC ceramic thermistor by applying a pressure of 1 ton / cm ² .

Next, the molded PTC ceramic thermistor is used by sintering at 1300 ° C. for 4 hours.

The characteristics of the PTC ceramic thermistors manufactured as described above are as follows.

First, in order to analyze PTC characteristics, the prepared disk-type PTC ceramic thermistor is used as a specimen.

Next, Ag-Zn electrodes are formed on the upper and lower surfaces of the disk, respectively, and then the resistance of the specimen is measured while increasing the temperature from room temperature to 320 ° C. A digital multimeter (Agilent, 34410A) is used to measure the resistance, and the specific resistance ρ is calculated using Equation 1 below.

Equation 1

Where R is the resistance, d is the thickness of the specimen, and A is the area of the specimen.

Next, the resistance temperature coefficient α representing the slope of the resistance according to the temperature change is calculated from the following [Equation 2].

[Equation 2]

Here, T ₁ = Tc, T ₂ = T ₁ + 80 ° C., R ₁ is the resistance at T ₁ , and R ₂ is the resistance at T ₂ .

16 is a graph measuring the specific resistance of the (1-x) BT-xNKN ceramic according to the present invention.

Referring to FIG. 16, 0.99 BaTiO ₃ −0.01 (Na _0.5 K _0.5 ) NbO ₃ − x mol% Nb ₂ O ₅ compositions were used to prepare ceramics for PTC thermistors. Since these all showed uniform microstructure, favorable sintered compact was obtained.

Specimens were prepared by sintering at 1300 ° C. for 4 hours (Sintering temp .: 130 ° C., Sintering time: 4 h) and cooling to 600 ° C. per hour (Cooling rate: 600 ° C./hr), where Nb ₂ O ₅ was not added. (x = 0) was shown as Example 54, the case where 0.025 mol% was added (x = 0.025) was shown as Example 55, and the case where 0.05 mol% was added (x = 0.05) was shown as Example 56. In this case, x described is a coefficient different from x in the above [Formula 5], and is used to easily express a constant value described on the x-axis in analyzing the experimental data.

Here, in Example 54, the Curie temperature (Tc) was 138 ° C, and the specific resistance ρ ₁ was 19 kΩ · cm, which showed low specific resistance.

In Example 55, the Curie temperature (Tc) was 137 ° C., and the specific resistance ρ ₂ was 49 kΩ · cm, which showed low specific resistance.

In Example 56, the Curie temperature (Tc) was 138 ° C., and the specific resistance ρ ₃ was 136 Ω · cm, which showed low specific resistance.

Figure 17 is a graph measuring the room temperature specific resistance of the concentration of Nb ₂ O ₅ added to (1-x) BT-xNKN ceramic according to the present invention.

Referring to FIG. 17, it can be seen that the room temperature specific resistance gradually increases as Nb ₂ O ₅ is added to the 0.99BT-0.01NKN ceramic. On the other hand, referring to Figures 18 and 19, it can be seen that the Curie temperature (Tc) and PTC jump (Jump) characteristics are rather reduced.

18 is a graph measuring the Curie temperature for each concentration of Nb ₂ O ₅ added to the (1-x) BT-xNKN ceramic according to the present invention, and FIG. 19 is a (1-x) BT-xNKN ceramic according to the present invention. a it is a graph measuring the PTC jump characteristic by the concentration of Nb ₂ O ₅ to be added to.

18 and 19, when Nb ₂ O ₅ was doped up to 0.05 mol%, PTC characteristics appeared, but when Nb ₂ O ₅ or more added at 0.1 mol%, the room temperature resistivity increased rapidly and turned into an insulator. Not implemented Curie temperature (T _c ) of 0.99BT-0.01NKN ceramics doped with 0.05 mol% of Nb ₂ O ₅ was about 136 ° C, and the low specific temperature resistance of 136 Ω · ㎝ and the ratio of maximum specific resistance and minimum specific resistance The PTC jump characteristic (ρ _max / ρ _min ) was 3.2 × 10 ³ .

FIG. 20 is a graph illustrating resistance temperature coefficient characteristics of concentrations of Nb ₂ O ₅ added to (1-x) BT-xNKN ceramics according to the present invention.

Referring to FIG. 20, PTC ceramic thermistors according to Examples 54 to 56 of the present invention exhibit excellent PTCR characteristics having resistance temperature coefficients of 7.9, 7.0, and 5.3% / ° C., respectively. Able to know.

Claims

The ceramic composition for PTC thermistor, characterized in that made of any one selected from the following [Formula 1] to [Formula 5].

[Formula 1] Ba 1-x (Bi 0.5 Na 0.5 ) x TiO 3 + y mol% M1O w

[Formula 2] Ba 1-x (Bi 0.5 Na 0.5 ) x TiO 3 + y mol% M1 2 O w + z wt% M2O 2

[Formula 3] Ba 1-x (Bi 0.5 K 0.5 ) x TiO 3 + y mol% M1O w

[Formula 4] Ba 1-x (Bi 0.5 K 0.5 ) x TiO 3 + y mol% M1O w + z wt% M2O 2

(1-x) BT-xNKN

(In [Formula 1] to [Formula 4] is 0.01≤x≤0.05, 0.00 <y≤0.40, 0.00 <z≤0.40, M1 is at least one element selected from the group consisting of Nb, Sb, La, Y , M2 is Mn, w is 3 when M1 is a trivalent element, and 5 when it is a pentavalent element.

In Formula 5, 0 <x ≦ 0.03, and BT is BaTiO.3NKN is Na0.5K0.5NbO3ego, NKN is a solid solution of BT.)
The method of claim 1,

The ceramic composition further comprises a dopant material comprising a Nb 2 O 5 powder.
The method of claim 2,

The Nb 2 O 5 is a ceramic composition for PTC thermistor, characterized in that added within the range of 0.05 mol% or less.
A PTC ceramic thermistor made of the ceramic composition of claim 1.
Preparing at least 99.9% high purity BaTiO 3 (BT);

Preparing (1-x) BT-xNKN (0 <x ≦ 0.03) ceramic raw powder by forming Na 0.5 K 0.5 NbO 3 (NKN) as a solid solution in BaTiO 3 (BT);

Putting the ceramic raw material powder into a high density polyethylene (HDPE) jar and performing first ball milling for 24 hours using distilled water as a dispersion medium;

Drying the first ball milling-treated ceramic raw material powder at 120 ° C., and then pulverizing it in a mortar;

Pulverizing the ceramic raw powder in an alumina crucible and calcining at 1000 ° C. for 2 hours;

Putting the calcined ceramic raw material powder into a high density polyethylene (HDPE) jar and performing a second ball milling for 24 hours using distilled water as a dispersion medium; And

And inserting the second ball milled ceramic raw powder into a mold and applying a pressure of 1 ton / cm 2 to produce a ceramic ceramic thermistor.
The method of claim 5,

The method of manufacturing a PTC ceramic thermistor, characterized in that further adding a dopant material consisting of Nb 2 O 5 powder to the ceramic raw powder.
The method of claim 6,

The Nb 2 O 5 is a PTC ceramic thermistor manufacturing method characterized in that it is added within the range of 0.05 mol% or less.