JPH04132203A - Manufacture of voltage-dependent nonlinear resistance element - Google Patents

Abstract

PURPOSE:To obtain a giant particle directly from a varistor powder, to be a low cost and to be provided with an excellent characteristic by a method wherein zinc oxide is used as a main component, an auxiliary component in very small quantities is added to and mixed with it and this mixture is molded and baked in an active oxygen atmosphere. CONSTITUTION:For example, a raw material in which an auxiliary component such as praseodymium oxide (Pr6O11), lanthanum oxide (La2O3), boron oxide (B2O3) or the like in proper quantities has been added to zinc oxide (ZnO) powder is mixed sufficiently by using a wet ball mill; a granulated powder (a varistor raw-material powder) is obtained by using a spray drier; and it is baked for several hours. As a baking atmosphere, the concentration of air and nitrous oxide (N2O) is changed; and the powder is baked under their atmospheric pressure. When the varistor powder is baked in an active oxygen atmosphere, it is not required to manufacture nucleus particles. Atoms are diffused easily in the active oxygen atmosphere because particles are grown; and giant particles can be obtained at a low temperature and in a short time. The auxiliary component is evaporated little.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a voltage nonlinear resistance element, and more particularly to a method for firing the element.

[Conventional technology]

Ceramics are made by mixing zinc oxide (ZnO) with trace amounts of additives and then sintering it.
It is known to exhibit excellent voltage nonlinearity, and is widely used as a varistor to suppress abnormal voltage (surge) in electrical circuits.

Z! The voltage nonlinearity of the 1G varistor is due to the 1-socket barrier formed at the grain boundaries of ZnO particles. In a practical varistor, the varistor voltage per layer of grain boundaries formed by bonding ZnO particles is approximately constant regardless of the size of the crystal grains, and its value is about 2V. Varistor voltage is the voltage between the terminals when a current of 1 mA is passed through the varistor, and is usually V81. It is expressed as Therefore, the varistor voltage of the voltage nonlinear resistance element is
It is determined by the number of grain boundary layers existing between the electrodes provided on the Zoo sintered body. Therefore, for elements used in low voltage circuits, it is necessary to reduce the thickness of the element or to sufficiently increase the ZnO particle diameter.

For example, when applying a Zoo varistor to a DC 12V circuit, a varistor voltage of 22V is used in consideration of circuit voltage fluctuations, but as mentioned above, the varistor voltage for one layer of grain boundaries is approximately 2V, the number of grain boundaries that can exist between the terminal electrodes of this element is 11 layers at most.

On the other hand, since the grain size of ZnO varistor sintered bodies produced by the usual method is 10 to 20μ, the thickness of the element must be 0.1 to 0.2μ in order to obtain a varistor voltage of about 22V. However, sintered bodies such as 'lsO varistors have low mechanical strength at a thickness of 0.1 to 0.2 mm.
It is not practical to make the device this thin because of problems such as cracks occurring during manufacturing.

To solve this problem, when creating Zoo Barista,
Zn with a much larger particle size than this is added to the nO raw material powder.
Japanese Patent Publication No. Sho 56-11203 discloses a method in which a small amount of O single crystal is added and grain growth is promoted using the ZnO single crystal (hereinafter referred to as a core particle) as a core. Figure 6 shows the flowchart of this method, and Figure 7 shows the state of crystal growth when core particles are added and fired at a temperature of 1350°C in the atmosphere. 1 grows on the core particle 3 and becomes a grain! 100-200- Z+>
Giant particles 4 of O are obtained.

Figure 8 shows the state of crystal growth when varistor powder, which is made by granulating a mixture of ZnO raw material powder 1 and a small amount of additives (not shown) without adding core particles 3, is fired in the atmosphere. It shows. In this case, the sintering temperature is set to 1500
Even if the temperature is raised to ℃ or the sintering time is lengthened, only crystal grains with a grain size of 50 m can be obtained.Furthermore, when devices are manufactured using this method, additives evaporate due to the long sintering at high temperatures. As a result, the voltage nonlinear coefficient α of the element decreases significantly,
It becomes impossible to put it into practical use.

[1lII that the invention tries to solve! ] As mentioned above, the method of adding core particles and firing in the atmosphere can easily produce giant particles, but this method requires a separate process to manufacture the core particles, which increases the manufacturing cost ( There is a problem.

This invention has been made with the above points in mind, and its purpose is to provide a method for manufacturing a voltage nonlinear resistance element with excellent characteristics at low cost by directly obtaining giant particles from varistor powder. It is in.

(Means for solving III) According to the present invention, the above-mentioned object is achieved by forming a molded product using zinc oxide as a main component, adding and mixing a small amount of auxiliary components thereto.

In a method for manufacturing a voltage nonlinear resistance element by firing,
This is achieved by firing in an active oxygen atmosphere.

[Effect]

Sintering the varistor powder in an active oxygen atmosphere eliminates the need to produce core particles. In an active oxygen atmosphere, atomic diffusion for grain growth becomes easy, and giant particles can be obtained at low temperatures and in a short time. Therefore, evaporation of subcomponents is also reduced.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

1↓ Zinc oxide (ZaO) raw material powder, praseodymium oxide (
PraO++), fII-formed Lafrantane ag's)
The raw materials to which appropriate amounts of subcomponents such as boron oxide (R, O,
It was baked at ℃ for several hours. Here, the firing atmosphere was 0,000,000 by varying the concentration ratio of air and nitrous oxide (NtO), and firing at large pressures.The size of the obtained sintered body was 14cm in diameter and 1cm in thickness. there were. A rod having an ohmic contact with a diameter of 11.5 mm was provided on the opposing surface of this sintered body, and the varistor characteristics were measured. The results are shown in the diagrams in Figures 1 to 3.
The horizontal scales in Figures 1 to 3 are all nitrous oxide concentrations, and the vertical axes are grain size in Figure 1 and VV in Figure 2.
1116/'+Figure 3 represents the nonlinear coefficient.

In Figure 1, when the nitrous oxide concentration is 5% or more, the crystal grain size is as large as 100- or more, and therefore, v tea / t is 20 as shown in Figure 11A2.
V/fi or less, which indicates that it is suitable as a voltage nonlinear resistance element for low voltage circuits. Nitrous oxide concentration is 4%
If the value is lower, grain growth will not proceed much, and if V+am/l is 20
V/m or more, which is not practical for use as a voltage nonlinear resistance element for low voltage circuits.As shown in FIG. 3, the nonlinear coefficient α is also excellent at 30 or more.

As described above, it can be seen that the device according to this example has characteristics that are equal to or better than the devices manufactured using the core particles shown in FIGS. 1 to 3 (・). .

A varistor element was produced using the same procedure as in Example 1, but here the firing atmosphere was changed to a different mixing ratio of nitrogen dioxide (N(h) and air) instead of nitrous oxide. . Figure 4 is a diagram showing the relationship between nitrogen dioxide concentration and crystal grain size. From Figure 4, it is clear that the present invention is effective when the nitrogen dioxide concentration is 4% or more. ■l□/ l, α
Although the relationship with ``1'' is not shown in the figure, almost the same results as in ``Example 1'' were obtained.

A direct 1fL varistor element was produced by the same procedure as in Main Example 1, but this time the firing atmosphere was changed to ozone (O2) instead of nitrous oxide.
s) and air were used with different mixing ratios. FIG. 5 is a diagram showing the relationship between ozone concentration and crystal grain size. It is clear from FIG. 5 that the present invention is effective when the ozone concentration is 4% or more. Same as IEJlil < V +waa /
The relationship between t and α is not shown in the figure, but in this case as well, almost the same results are obtained as in the case of the application limit.

〔Effect of the invention〕

According to the present invention, in the method for manufacturing a voltage nonlinear resistance element made of zinc oxide as a main component, mixed with a small amount of subcomponents, molded and fired, the firing is performed in an active oxygen atmosphere. Grain growth is faster and takes the same amount of time as when using core particles.

Since a giant crystal can be obtained at a certain temperature, the varistor voltage V tam /t per unit thickness can be reduced to 20 V/volt or less, and an element suitable for low voltage circuits can be obtained. Furthermore, since the crystal grows at the same time and temperature as in the case of using core particles, there is little evaporation of trace additives, and an element with an excellent nonlinear coefficient α can be obtained.

Furthermore, according to the present invention, since no core particles are used, the manufacturing process is simplified and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between crystal grain size and nitrous oxide concentration of an element according to an embodiment of the present invention in comparison with a conventional one, and FIG. A diagram showing the relationship between the varistor voltage per unit thickness and the nitrous oxide concentration in comparison with the conventional one, and FIG. 3 shows the nonlinear coefficient α and the nitrous oxide concentration of the element according to the embodiment of the present invention. Figure 4 is a line showing the relationship between the crystal grain size and nitrogen dioxide concentration of the element according to the embodiment of the present invention in comparison with the conventional one. Fig. 5 is a diagram showing the relationship between the crystal grain size and ozone concentration of the element according to the embodiment of the present invention in comparison with the conventional one, and Fig. 6 is a manufacturing process diagram of the conventional element, fJT The figure is a schematic diagram showing crystal growth in a conventional manufacturing method using core particles, and FIG. 8 is a schematic diagram showing crystal growth in a conventional manufacturing method not using core particles. 1m zinc raw material powder, 2: crystal grains, 3: core particles, 4:
giant particles.

Claims (1)

[Scope of Claims] 1) A method for manufacturing a voltage non-linear resistance element made of zinc oxide as a main component, mixed with a small amount of subcomponents, molded and fired, in which the firing is performed in an active oxygen atmosphere. A method for manufacturing a voltage nonlinear resistance element characterized by: 2) The method of manufacturing a voltage nonlinear resistance element according to claim 1, wherein the active oxygen atmosphere contains air containing 4% or more of nitrous oxide. 3) The method of manufacturing a voltage nonlinear resistance element according to claim 1, wherein the active oxygen atmosphere contains air containing 4% or more of nitrogen dioxide. 4) The method of manufacturing a voltage nonlinear resistance element according to claim 1, wherein the active oxygen atmosphere contains air containing 4% or more of ozone.