JPH0648642B2 - Voltage nonlinear porcelain composition and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage non-linear porcelain composition {having non-linear voltage-current characteristics and forming an element of a voltage non-linear resistor (varistor). Porcelain composition}, and particularly to a voltage nonlinear porcelain composition containing zinc oxide as a main component.

[Prior Art] As a voltage non-linear porcelain composition containing zinc oxide as a main component, various metal oxide powders such as Bi and Sb are added to ZnO powder and mixed, and these are formed into a disk shape, for example. After that, it is known to be sintered at a temperature of about 1200 ° C. in an oxidizing atmosphere.

In the voltage nonlinear ceramic composition of this example, by sintering, semiconductor particles made of ZnO in the voltage nonlinear ceramic composition,
A grain boundary phase of a metal oxide such as Bi ₂ O ₃ formed at the grain boundary of the semiconductor particles and a spinel phase formed of Zn ₂ Sb ₃ O ₄ are formed.

The non-linear voltage-current characteristics of the voltage non-linear porcelain composition are
It is generated by the interface between the semiconductor particles made of ZnO and the grain boundary phase of the metal oxide such as Bi ₂ O ₃ .

By the way, the non-linear voltage-current characteristic of the voltage non-linear porcelain composition is evaluated by the varistor voltage V and the non-linear coefficient α.

Here, the varistor voltage V is the voltage at which the electrical resistance suddenly decreases, and the nonlinear coefficient α is obtained by approximating the change of the current I flowing through the voltage nonlinear ceramic composition with respect to the voltage V by the following equation. It is a numerical value obtained in.

I = KV ^α (where I is the current flowing in the voltage nonlinear ceramic composition, V
Is a voltage applied, and K is a constant. And, since the voltage nonlinear porcelain composition containing zinc oxide as a main component has a large nonlinear coefficient α of about 50, it is particularly excellent in response to an abnormal high voltage (surge). ing.

Further, this voltage nonlinear porcelain composition containing zinc oxide as a main component can be manufactured at a low cost because the raw material ZnO is cheap.

[Problems to be Solved by the Invention] However, since the conventional voltage nonlinear porcelain composition containing zinc oxide as a main component has a high varistor voltage V of about 200 V, a low voltage such as various small motors is used. It could not be used for removing noise generated from electrical equipment.

An object of the present invention is to obtain a voltage nonlinear porcelain composition having a low varistor voltage by using a ZnO-based material that is inexpensive.

[Means for Solving the Problems] The voltage nonlinear porcelain composition according to the present invention is fired by firing a composition containing zinc oxide as a main component and at least one metal oxide as a sub-component. A sintered body, the sintered body is a semiconductor portion that has been reduced to a semiconductor state,
An oxide layer is formed on the semiconductor portion in a layered manner with a predetermined thickness.

Here, as an accessory component, Bi, Sb, Mn, Co, N
Mention may be made of oxides of one or more metals selected from i, Cr, Mg, Al and Si.

This voltage non-linear porcelain composition is mainly composed of zinc oxide,
After molding the above composition containing at least one metal oxide as an accessory component into a predetermined shape, it is heated in a reducing atmosphere to become a semiconductor, and then heated in an oxidizing atmosphere to oxidize the surface. It can be manufactured by

Here, the heating temperature in the reducing atmosphere is 1
The range of 100-1300 degreeC is preferable. Heating temperature is 11
If the temperature is lower than 00 ° C, the sintering becomes insufficient, and if the temperature exceeds 1300 ° C, the low-melting point component such as Bi ₂ O ₃ is released, which adversely affects the characteristics. Because there is no.

The heating temperature in the oxidizing atmosphere is 600.
The range of ~ 750 ° C is preferred. If the heating temperature is less than 600 ° C, the varistor voltage V becomes too low, and the nonlinear coefficient α
Is too small, and the varistor voltage V becomes too high when the temperature exceeds 750 ° C., but the varistor voltage V and the nonlinear coefficient α become appropriate values in the range of 600 to 750 ° C.

In addition, this voltage nonlinear porcelain composition is formed by molding the above composition containing zinc oxide as a main component and at least one metal oxide as an accessory component into a predetermined shape, and then heating the composition in an oxidizing atmosphere. It is also possible to oxidize the surface, then heat in a reducing atmosphere to reduce it, and then heat in an oxidizing atmosphere to re-oxidize the surface.

Here, the heating temperature in the oxidizing atmosphere is preferably in the range of 1100 to 1300 ° C. If the heating temperature is less than 1100 ° C, sintering will be insufficient and the temperature will be 1300 ° C.
If it exceeds, the low-melting-point subcomponents such as Bi ₂ O ₃ will escape,
This is because the characteristics are adversely affected, but such a phenomenon does not occur in the range of 1100 to 1300 ° C.

The heating temperature in the reducing atmosphere is 700
The range of ˜1100 ° C. is preferred. If the heating temperature is lower than 700 ° C, the reduction is insufficient and the varistor characteristics cannot be completely removed. If the heating temperature exceeds 1100 ° C, particle growth proceeds and the initial characteristics deteriorate, but in the range of 700 to 1100 ° C, Because there is no such thing.

Further, the heating temperature in the later oxidizing atmosphere is 6
The range of 00 to 750 ° C is preferable. Heating temperature is 600 ℃
If the temperature is less than 1, the varistor voltage V becomes too low, or the nonlinear coefficient α becomes too small, and if it exceeds 750 ° C, the varistor voltage V becomes too high, but in the range of 600 to 750 ° C, the varistor voltage V and the nonlinear coefficient α become too small. Is an appropriate value.

[Examples] Experiment 1 Bi, Sb, Mn, Co, Ni, Cr, M was added to ZnO powder.
Oxides of elements selected from g, Al or Si were added in the proportions shown in Sample Nos. 3, 15 and 27 in Table 1, mixed well, and then calcined at 720 ° C. for 2 hours.

Next, the product obtained by the calcination is sufficiently crushed, and the crushed product is molded with a mold to obtain an outer diameter of 12.25 mm,
A plurality of ring-shaped compacts having an inner diameter of 7.75 mm were manufactured.

Next, this ring-shaped molded body was subjected to H ₂ 2.0% + N ₂ 98
% Reducing atmosphere at 1150 ° C. for 2 hours followed by oxidative baking at 650 ° C. in air.

Next, a silver electrode is baked on each of the oxide-fired products to form a varistor, and the varistor voltage at 25 ° C. is V _{10 mA.}
Then, the nonlinear coefficient α was obtained.

The results are shown in Table 1.

Experiment 2 Next, except that the additive components were set as shown in Sample Nos. 37, 38 and 39 of Table 1 and that the molded body was heated and oxidized once at a heating temperature of 1150 ° C. in an oxidizing atmosphere. A varistor as a conventional example was formed in the same manner as in Experiment 1, and the varistor voltage V _{10 mA at} 25 ° C. and the nonlinear coefficient α were obtained.

The results are shown in Table 1.

According to Experiment 1, the varistor voltage V _10mA was 5 to 35V. It can be seen that this is much lower than the result of Experiment 2, that is, the conventional example.

The varistor voltage V _{10mA in} Experiment 1 was significantly lower than the varistor voltage V _10mA in Experiment 2, while the voltage nonlinear ceramic composition obtained in Experiment 2 had a BL structure. It is considered that this is because the voltage nonlinear ceramic composition obtained in Experiment 1 has a surface reoxidation type structure.

Experiment 3 Next, sample Nos. 1 to 6, 13 to 18, 25 to 30 in Table 2
The molded product having the composition shown in 550 to 800 ° C. in air
The same as Experiment 1 except that the calcination was performed in the range of 25.
The varistor voltage V at ₁₀ ° C. and the nonlinear coefficient α were determined.

The results are shown in Table 2.

From the results of Experiment 3, in oxidation firing in air,
When the heating temperature is 550 ° C, the varistor voltage V _10mA is 0.1
.About.0.5 V and the non-linear coefficient .alpha. Were also about 1, and satisfactory electrical characteristics could not be obtained.

In addition, the heating temperature is 8 during oxidation firing in air.
At 00 ° C., the varistor voltage V _{10 mA} became too high around 300 V, and satisfactory electrical characteristics could not be obtained.

Therefore, in the oxidation firing in air, the heating temperature is preferably in the range of 600 to 750 ° C.

Experiment 4 The molded bodies having the compositions shown in Sample Nos. 7 to 12, 19 to 24, and 31 to 36 in Table 3 were first subjected to 1150 in an oxidizing atmosphere.
A voltage nonlinear porcelain composition was formed in the same manner as in Experiment 1 except that the voltage nonlinear porcelain composition was heated and oxidatively baked at 25 ° C., and the varistor voltage at 25 ° C. and the nonlinear coefficient α of this voltage nonlinear porcelain composition were determined.

The results are shown in Table 3.

The above results are almost the same as those in Experiment 1 and Experiment 3, and it can be seen that similar results can be obtained even if the molded body is previously oxidized before being reduced and baked.

[Advantages of the Invention] According to the present invention, it is possible to obtain a voltage nonlinear porcelain composition having a low varistor voltage by using a low-cost zinc oxide-based material.

Claims (3)

[Claims] 1. A sintered body obtained by firing a composition containing zinc oxide as a main component and at least one metal oxide as an accessory component, the sintered body being reduced to give a semiconductor. 1. A voltage non-linear porcelain composition comprising a semiconductor portion in the above state and an oxide layer coated on the semiconductor portion to a predetermined thickness. 2. A composition containing zinc oxide as a main component and at least one metal oxide as a subcomponent, is heated in a reducing atmosphere to be a semiconductor, and is then heated in an oxidizing atmosphere. A method for producing a voltage non-linear porcelain composition, characterized by oxidizing the surface of the composition. 3. A composition containing zinc oxide as a main component and at least one metal oxide as a secondary component is heated in an oxidizing atmosphere to be oxidized, and then heated in a reducing atmosphere. To semiconductor, and then heating in an oxidizing atmosphere to reoxidize the surface, a method for producing a voltage nonlinear porcelain composition.