JPH05251207A - Manufacturing method of ptc ceramics - Google Patents

Abstract

PURPOSE:To decrease the electric resistivity in low temperature region by a method wherein PTC ceramics material powder containing exceeding specific amount of dopant containing penta doping element is baked in reducing atmosphere. CONSTITUTION:Exceeding 0.5% of penta doping element such as Nb, etc., as a dopant is contained in PTC ceramics material powder mainly composed of barium titanate, etc. Next, said material powder containing this dopant is baked in reducing atmosphere. At this time, the sintering step can be satisfactorily advanced resultantly decreasing the electric resistivity. Through these procedures, the electric resistivity in the low temperature region as well as the power consumption of the PTC ceramics can be decreased as little as possible.

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 PTC ceramics.

[0002]

BACKGROUND OF THE INVENTION Generally, semiconductors tend to decrease in electric resistance as temperature rises.
The io ₃ sintered body exhibits 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. And this P
It is widely used in various fields as a demagnetizing element, a heater element, etc. due to the TC effect.

Such PTC characteristics in BaTiO ₃ ceramics are due to the fact that easily moving electrons generated when a small amount of doping element such as La (trivalent) is dissolved in barium titanate at low temperature (temperature lower than the phase transition temperature). However, it is thought that it is difficult to move beyond the grain boundaries in the sintered body at a temperature higher than the phase transition temperature.

By the way, P represented by BaTiO ₃
TC ceramics are also used as protective circuit components based on their PTC characteristics.

When the PTC ceramics are connected in series to the circuit, when an overcurrent flows in the circuit, the resistance of the PTC ceramics is increased due to heat generation and temperature rise, so that the circuit current is cut off and the circuit is protected. Of.

When using PTC ceramics as such a protective circuit component, it is desirable that the electrical resistivity is smaller at room temperature, strictly speaking, at a temperature lower than the phase transition temperature. This is because the higher the electrical resistivity at room temperature, the more power is consumed.

As a method for reducing the electrical resistivity of PTC ceramics in the low temperature region, it is conceivable to add a large amount of a doping agent to the raw material, but the amount that can be contained as a conventional doping agent is 0.5 mol% at most.
However, if the content exceeds this range, the sintering will not be performed well, and the obtained fired product will have a low bulk density and become porous, and will not have PTC characteristics.

[0008]

The present invention has been made in view of such circumstances, and the gist thereof is that a PTC ceramic raw material powder contains a doping agent containing a pentavalent doping element in a molar amount of 0.5. % Or more, and the raw material powder containing the doping agent is fired in a reducing atmosphere.

[0009]

In view of the above circumstances, the present inventor conducted a firing test of PTC ceramics under various conditions so as to contain a larger amount of the doping agent than before, and in the process, the pentavalent doping element was added. If this is 0.5 mol%
It has been found that, even when the above content is included, if the firing is performed in a reducing atmosphere, the sintering proceeds well and the electrical resistivity also decreases accordingly. The present invention was made based on such knowledge.

The PTC sintered product thus reduced and fired is then subjected to oxidative firing to obtain a desired PTC.
Properties can be imparted.

Since the PTC ceramics obtained by the present invention have a low electric resistance in a low temperature region, power consumption can be reduced as much as possible when used as the protection circuit component.

[0012]

EXAMPLES In order to further clarify the characteristics of the present invention, examples thereof will be described in detail below. BaC on a molar basis (%)
_{o 3: 100, TiO 2:} 100.5, SiO 2: 0.3
In barium titanate ceramic raw material powder consisting of,
Nb ₂ O ₃ as a doping agent is 0.2, 0.5, 2.5,
Those contained in each amount of 5.0 and La for comparison
_A mixture containing 0.2, 2.5 and 5.0 of ₂ O ₃ in a reducing atmosphere of H ₂ : 8% and N ₂ : 92% at 1400 ° C.
It was baked for 4 hours. In addition, 1350 to 138 in the air
A firing experiment was performed under the condition of 0 ° C. × 1 hour.

The bulk density and the electrical resistivity of the obtained fired product were measured and found to be as shown in FIGS. .

As can be seen from these results, when trivalent La is used as the doping element, the bulk density is extremely low in both the oxidation firing and the reduction firing when the amount of the doping agent is more than 0.2%, which is good. Did not sinter.

On the other hand, in the case where pentavalent Nb is used as the doping element, sintering proceeds even if the amount of the doping agent exceeds 0.2%.

However, as can be seen from the results shown in FIG. 2, when the doping agent exceeds 0.2%, the electrical resistivity becomes remarkably high as it becomes closer to an insulator when it is oxidized and fired.

On the other hand, in the case of reduction firing, the electrical resistivity does not increase even if the amount of the dopant exceeds 0.2%, but rather decreases depending on the amount of the dopant added.

Thus, the product obtained by reducing and firing the Nb dopant in this way does not show the PTC characteristic as it is, but when it is oxidatively fired, it shows a good PTC characteristic as shown in FIG. Indicated.

In FIG. 3, Nb ₂ O ₃ as a doping agent is added at 5 mo.
The results are obtained by adding 1%.

The embodiment of the present invention has been described in detail above, but this is merely an example, and the present invention can be applied to PTC ceramics other than barium titanate, for example, within the scope of the invention. It can be implemented with various modifications based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of a doping agent and the bulk density obtained in an example of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of the dopant and the electrical resistivity obtained in the same example.

FIG. 3 is a diagram showing a relationship between temperature and electric resistivity obtained in the same example.

Continuation of the front page (72) Inventor Ishi ▲ Saki ▼ Kozo 1769-1 Fukasawa-cho, Nagaoka-shi, Niigata

Claims (1)

[Claims] 1. A PTC ceramic raw material powder containing 0.5% or more of a doping agent containing a pentavalent doping element on a molar basis, and firing the raw material powder containing the doping agent in a reducing atmosphere. And a method for manufacturing PTC ceramics.