JPH0640768A - Production of ptc ceramics having high characteristic - Google Patents

Abstract

PURPOSE:To provide PTC ceramics having low resistivity at room temp., high max. resistivity and high PTC characteristics. CONSTITUTION:Starting materials generating BaTiO3, BaSrTiO3 and BaPbTiO3 are mixed with starting materials for incorporating Fe and/or Co and this mixture is compacted and fired in a high-pressure oxidizing atmosphere under >=30atm partial pressure of O2 to produce the objective PTC ceramics based on BaTiO3, BaSrTiO3 and BaPbTiO3 and contg. 0.001-0.1 atomic % Fe and/or Co basing on the amt. of Ba.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-performance PTC ceramics, and more particularly to BaTiO ₃ , BaSrT.
A raw material for producing iO ₃ , BaPbTiO ₃ and an iron and / or cobalt-based raw material are mixed, shaped and fired to form B.
The aTiO _3, BaSrTiO _3, BaPbTiO ₃ mainly, iron and / or cobalt compound, with respect to Ba, in terms of Fe and / or Co 0.001 to 0.1
The present invention relates to an improvement in a method for producing a PTC ceramic containing atomic%.

[0002]

2. Description of the Related Art Generally, semiconductors show a tendency that electric resistance decreases as temperature rises.
The TiO ₃ sintered body has a low electric resistance on the low temperature side, and has a property of rapidly increasing the electric resistance at a certain temperature, that is, at the Curie temperature at which the crystal transition occurs. This is called PTC effect or PTC characteristic, and BaTiO ₃ sintered body is widely used in various fields as a demagnetizing element, a heater element, etc. by utilizing the PTC characteristic.

Such PTC characteristics in BaTiO ₃ ceramics are considered to be due to a small amount of doping element (dopant) dissolved in BaTiO ₃ .
That is, by dissolving the doping element in a solid solution, movable electrons are generated, and at a temperature lower than the Curie temperature, the electrons move around in the sintered body, so that the BaTiO ₃ ceramics exhibits low electric resistance, Even at a high temperature, it becomes difficult for the electrons to move beyond the crystal grain boundaries of the sintered body, so that the BaTiO ₃ ceramic exhibits a high electric resistance.

In particular, such PTC ceramics such as BaTiO ₃ system are often used as protective circuit parts by utilizing their PTC characteristics. In this case, PTC
When ceramics are connected in series to a circuit and an overcurrent flows through the circuit to generate heat in the PTC ceramics itself and the temperature rises, the electrical resistance increases and the current in the circuit is interrupted to protect the circuit.

Therefore, from the use as such a protection circuit component, PTC ceramics has an electric resistance as much as possible in the temperature region lower than the Curie temperature, such as room temperature. The room temperature resistivity is small), the current can flow easily, and the power consumption is low. On the contrary, in the temperature range higher than the Curie temperature such as when the temperature rises due to overcurrent, the electric resistance (hereinafter , The maximum value of the electric resistance in the high temperature region is called "maximum resistivity") is large, and the circuit can be protected by reliably cutting off the overcurrent, that is, the room temperature resistivity is low and the resistivity It is desired that the degree of rise is steep, the maximum resistivity is high, and the PTC characteristics are large.

Conventionally, increasing the content of the doping element has been considered as a method for improving the PTC characteristics of PTC ceramics.

[0007]

However, when the content of the doping element is increased, the sintering does not proceed well due to firing, resulting in a sintered body having a low bulk density, or conversely, PTC.
It is not preferable to increase the number of doping elements, because it causes problems such as deterioration of characteristics.

Conventionally, as the crystal structure for exhibiting the PTC effect, it is necessary to have a fine structure in which the crystal grains of the sintered body are a ferroelectric semiconductor and the crystal grain boundaries exhibit high electric resistance close to that of an insulator. Though it is considered, the reality is that it has not been clarified in detail.

The present invention has been made in view of the above conventional circumstances, and has a low room temperature resistivity and a high maximum resistivity.
High-performance BaTiO ₃ system BaSrTi with large PTC characteristics
It is an object of the present invention to provide a method for producing an O ₃ -based or BaPbTiO ₃ -based PTC ceramics.

[0010]

The method for producing high-performance PTC ceramics according to the present invention is based on BaTiO ₃ , BaSrTi.
A raw material that produces at least one selected from the group consisting of O ₃ and BaPbTiO _3, and an iron-based raw material and / or a cobalt-based raw material are mixed, molded, and fired to form BaTiO 3.
₃ , at least one selected from the group consisting of BaSrTiO ₃ and BaPbTiO ₃ is the main component, and an iron compound and / or a cobalt compound is converted into Fe and / or Co in an amount of 0.001 to 0.1 atomic% based on Ba P included in proportion
The method for producing TC ceramics is characterized in that the firing is performed in a high-pressure oxidizing atmosphere having an O ₂ partial pressure of 30 atm or more.

The present invention will be described in detail below.

In the present invention, first, BaTiO ₃ ,
A raw material (hereinafter referred to as “Ba”) which produces at least one selected from the group consisting of BaSrTiO ₃ and BaPbTiO _3.
It is referred to as "TiO ₃ -based raw material". ) And an iron-based raw material and / or a cobalt-based raw material are mixed at a predetermined ratio and molded according to a conventional method.

Next, the obtained molded body is fired. In the present invention, this firing is performed in a high-pressure oxidizing atmosphere with an O ₂ partial pressure of 30 atm or more. If the O ₂ partial pressure in this firing atmosphere is less than 30 atm, sufficient PTC according to the present invention will be obtained.
The effect of improving the characteristics cannot be obtained. Usually, the O ₂ partial pressure is preferably in the range of 30 to 2000 atm.

In terms of work safety, pure O ₂
It is preferable to use an atmosphere in which a rare gas such as Ar is mixed with O ₂ instead of the (100% O ₂ ) atmosphere. O in atmosphere gas
The ratio of ₂ is preferably about 3 to 20% by volume.

In the present invention, the firing in the high pressure oxidizing atmosphere is performed by hot isostatic pressing (H
It is preferable to carry out IP) treatment. This HIP process is
If the treatment is performed for an excessively long treatment time or treatment temperature, the crystal grains may be oxidized and grain growth may occur. Therefore, the HIP treatment is performed at a temperature of 900 to 1280 ° C and a total pressure of 500 to 1000.
It is preferable to carry out the treatment at 0 atm and a treatment time of about 0.5 to 20 hours.

In the present invention, as the BaTiO ₃ -based raw material, BaCO ₃ , TiO ₂ , BaO, SrCO _{3 are used.}
, Oxides of Ba, Ti, Sr, Pb such as PbCO ₃ ,
Alternatively, nitrates, carbonates and the like that produce oxides by firing may be used.

As the iron-based raw material and the cobalt-based raw material,
Iron, cobalt oxides, nitrates, carbonates, hydrochlorides, hydroxides and the like, specifically Fe ₂ O ₃ , Fe (NO ₃ ) ₂ ,
FeCl ₂ , FeO, Fe ₃ O ₄ , Fe (OH) ₃ , C
o (NO ₃ ) ₂ , CoCl ₂ , CoO, Co ₃ O ₄ , C
and o (OH) _{2 and the} like.

In the present invention, the iron-based raw material and the cobalt-based raw material have a Ba content in the BaTiO ₃ -based sintered body of which the content of the iron compound and / or the cobalt compound is Ba and Fe, respectively. For 0.001-0.1
It is used so that it becomes atomic%. If this proportion is less than 0.001 atomic%, a good PTC effect due to the addition of the doping element cannot be obtained, and conversely, if it exceeds 0.1 atomic%, the amount of the doping element is too large and the room temperature resistivity becomes unfavorably high.

In the present invention, as the doping element, elements other than Fe and Co, such as V, Cr and M, are used.
n, Ni, Cu, Zn, Ru, Ga, Rh, In, T
You may add l, Ag, etc. in the range which does not impair the characteristic. In this case, the content of the compound of these other doping elements is preferably 0.5 atomic% or less based on Ba in terms of the element conversion amount.

[0020]

Since Fe and Co are elements that can have a high valence by oxidation, if Fe and Co are added as doping elements and firing is performed in a high pressure oxidizing atmosphere with an O ₂ partial pressure of 30 atm or more. The Fe and Co elements in the obtained sintered body are
The valence is higher than that of divalent or trivalent. As a result, at high temperature, an acceptor level relatively far from the conduction band is formed. Therefore, the movement of electrons in the high temperature region is blocked, and the high temperature resistivity increases.

On the other hand, since the maximum resistivity is increased by the oxidation during firing in this way, the doping element can be reduced to 0.1 atomic% or less in the ratio of Fe and / or Co with respect to Ba. The room temperature resistivity can be kept low.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Examples 1 to 6 Using the following BaTiO ₃ raw materials and iron-based raw materials and / or cobalt-based raw materials, HIP treatment was performed at an O ₂ partial pressure shown in Table 1 to obtain iron oxides and / or iron oxides shown in Table 1. Alternatively, BaTiO ₃ -based PTC ceramics containing cobalt oxide were manufactured.

BaTiO ₃ raw material: BaTiO ₃ iron-based raw material: Fe (NO ₃ ) ₃ cobalt-based raw material: Co (NO ₃ ) ₂ The conditions other than the O ₂ partial pressure in the HIP treatment are as follows.

Total pressure: 100 atm (gas other than O ₂ is Ar) Temperature: 1200 ° C. Time: 2 hours About the obtained BaTiO ₃ -based PTC ceramics,
The room temperature resistivity (25 ° C.) and the maximum resistivity were measured, and the results are shown in Table 1.

Comparative Example 1 A BaTiO ₃ PTC ceramic was produced in the same manner as in Example 2 except that the O ₂ partial pressure was 10 atm, and its resistivity was examined. The results are shown in Table 1.

Comparative Examples 2 to 5 In the same manner as in Example 1, except that the addition amount of the iron-based raw material was changed or the cobalt-based raw material was replaced, B
The aTiO ₃ -based PTC ceramics were manufactured and their resistivity was investigated. The results are shown in Table 1.

[0028]

[Table 1]

From Table 1, according to the method of the present invention, Ba having a low room temperature resistivity, a high maximum resistivity and a large PTC characteristic.
It is clear that TiO ₃ -based PTC ceramics can be obtained.

On the other hand, in Comparative Example 1 in which the partial pressure of O ₂ in the firing atmosphere is low, the maximum resistivity is low, and in Comparative Examples 2 and 4 in which the iron and / or cobalt content is low, the maximum resistivity is low. On the contrary, in Comparative Examples 3 and 5 in which the content is large, the room temperature resistivity is high, and in either case, good PTC characteristics cannot be obtained.

In Examples 1 to 6, BaTiO 3 was used.
₃ in the same manner except that was replaced by BaSrTiO ₃ to produce a PTC ceramic was measured for its properties were exactly the same as Examples 1-6. In addition, PTC ceramics were manufactured in the same manner as in Examples 1 to 6 except that BaTiO ₃ was replaced with BaPbTiO ₃ , and the characteristics were measured. The results were exactly the same as Examples 1 to 6.

[0032]

As described in detail above, the high-performance PT of the present invention
According to the method for producing C ceramics, the high-temperature characteristic Ba having a low room temperature resistivity, a high maximum resistivity, and a large PTC property is obtained.
A TiO ₃ -based PTC ceramic is obtained.

Since the PTC ceramics produced by the present invention have remarkably good PTC characteristics, they show excellent performance as a member for a protection circuit and are industrially very useful.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ishi ▲ Saki ▼ Kozo 1769 Fukasawa-cho, Nagaoka-shi, Niigata 1 (72) Inventor Herb Lehitz Ben 1-38-67 Midori-cho, Nagaoka-shi, Niigata (72) Inventor Kiuchi Yoshiaki 4-13-4 Miyaseki, Nagaoka City, Niigata Prefecture

Claims (1)

[Claims] 1. BaTiO ₃ , BaSrTiO ₃ and B
A raw material that produces at least one selected from the group consisting of aPbTiO ₃ and an iron-based raw material and / or a cobalt-based raw material are mixed, shaped, and fired to form BaTiO ₃ , BaSr.
Mainly at least one selected from the group consisting of TiO ₃ and BaPbTiO _3, iron compound and / or cobalt compound Fe and / or proportion of 0.001 to 0.1 atomic% with respect to Ba in terms of Co The method for producing high-performance PTC ceramics is characterized in that the firing is performed in a high-pressure oxidizing atmosphere having an O ₂ partial pressure of 30 atm or more.