JPS6016725B2 - Manufacturing method of voltage nonlinear resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a part of the oxide powder used as a non-linear resistor material and all of the various additives are heated and reacted in advance, and then pulverized, and then pulverized together with the remaining oxide powder. The present invention relates to a method for manufacturing a voltage nonlinear resistor in which, by sintering, an element body is free from cracks during late sintering and has excellent electrical properties.

Conventionally, oxide nonlinear resistors, such as nonlinear resistors whose main component is zinc oxide Zn○, have excellent nonlinear characteristics and are therefore ideal for use as nonlinear resistors such as earth protectors. However, because the manufacturing method was not appropriate, the element body cracked during sintering and its electrical properties were poor.

That is, non-linear resistors are generally made of high-purity metal oxides (e.g. ZNO), bismuth Bi, cobalt Co, manganese Mn.
, Antimony S is mixed, granulated, etc. with the addition of oxides such as
After molding and special treatment to form a high-resistance layer on the sides of the element body, it is obtained by firing at a high temperature of 1000 pm or more.
There is a large contraction between 0qo and at temperatures within that range, various complex reactions occur inside the element body and a small amount of liquid phase is formed, so the distribution of additives in the element body becomes uneven. In addition, cracks are more likely to occur in the element itself.

Furthermore, the crystal phases formed in the element bodies located near the surface of the Qin body and in the center of the Qin body are also shown in Figure 1a.
, b, the size and number of peaks are different. This is because the difference in reaction rate manifests as a difference in crystal phase. Furthermore, there are also disadvantages in that the grain growth rate of the oxide particles used as the nonlinear resistor material varies, and the nonlinear characteristics deteriorate more in the large current region than in the small current region. An object of the present invention is to provide a method for obtaining a nonlinear resistor with excellent nonlinearity without causing any cracks in the initial phase.

For this purpose, the present invention first heats and reacts a part of the oxide powder as a nonlinear resistor material with all of the additives, then crushes the mixture, and then phosphorsizes this and the remaining oxide powder. In this way, the objective is to obtain a nonlinear resistor.

Hereinafter, the present invention will be described in Figs. 2 to 4, assuming that the oxide is zinc oxide.
This will be explained using figures.

When obtaining a non-linear resistor according to the present invention, first, SQ03 and Bj20 as additives are added to a part of zinc oxide Zn0.
3, C0203, Mn02, Cr203, Si02, etc. are added and mixed.

The weight mixing ratio in this case is as shown in Table 1. table
1. Zn○ and additives are thoroughly mixed in an appropriate weight ratio and then slurried and dried.
The material is calcined at a temperature of 0.000 m and then pulverized.

The remaining Zn○ is then mixed with the pulverized Zn○ and additives, and then a binder is added and granulated.
A molded body is obtained by pressure molding after granulation, and a nonlinear resistor is obtained by firing this molded body at a temperature of 1000 to 1400 oo. Here, to briefly describe the reaction between Zn○ and additives, Sb203 of the additives becomes Sb204 at 57,000 degrees Celsius, and B
It reacts with i203, Zn○, etc. to form the intermediate product pyrochlore (Zn2S broad Bi30,4), and furthermore, at 800 to 900qo, spinel SP (Zn
23 Sbo. 6704).

Further, Bi203 reacts with Cr203 to form a Bi-Cr-○-based oxide from around 750q0, and when the temperature is further increased, it turns into a liquid phase and functions to promote grain growth of Zn○.
Sj02 also starts to react with Zn◯ from around 70,000 to form zinc silicate (Zn2Si04). By the way, while the Qin body rapidly contracts at 700 to 1000°C, the above-mentioned complicated reactions occur inside the Qin body. Accordingly, according to the conventional method, the entire body becomes unable to react uniformly. Figures 1a and b, which have already been explained, are for an element body with a low side and a thickness of 32 ribs at a temperature of 90 psi, and it can be seen from these that the reaction is non-uniform. Such rapid shrinkage and non-uniform reaction during molding cause distortion and cracks in the element body, and differences in the liquid phase state due to differences in the formation of reaction products cause differences in the growth rate of Zn0 grains. As a result, the particle size of the Zn◯ particles comes to vary. When large-sized Zn0 particles exist inside the element, the current avoids the high-resistance grain boundary layer with non-ohmic characteristics and concentrates on the coarse Znq crystal grains.
Nonlinear characteristics also deteriorate. SUMMARY OF THE INVENTION Therefore, the present invention aims to eliminate the drawbacks that have been observed in the past by manufacturing a non-linear resistor as described above.

In other words, by reacting the additive with a portion of Zn○ in advance, the amount of shrinkage during firing, and thus the shrinkage rate, can be suppressed to a small level, and the pre-reaction also suppresses the formation of spinel SP, pyrochlore, and zinc silicate. Necessary Zn○
By allowing these to react, it is possible to preliminarily include in the compact a substance similar to the crystalline phase that forms the grain boundary layer of the fired product, thereby making the reaction uniform. Hereinafter, to continue explaining the present invention, FIGS.
d indicates the difference in crystal structure for the weight mixing ratios A to D listed in Table 1, respectively.

Although the crystal structure differs depending on the weight mixing ratio, the characteristics of the nonlinear resistor also differ depending on the component composition of the additives, so a suitable mixing ratio and additives should be selected depending on the purpose. still,
Bi-Q-0 in FIGS. 2a to 2d collectively represents various compounds of bismuth oxide and chromium oxide. Also,
Figure 3 shows the heating temperature of the element body obtained by mixing the remaining Zn○ with the pulverized material after heating at 900°C for 2 hours under the condition of weight mixing ratio B, and the heating temperature of the element body according to the conventional method. This shows the amount of shrinkage in the thickness direction.

The weight of the element or molded body in this case is 35 kg, the folding plate has 38 ribs, and a pressing force of 250 k9 is applied. As shown in the figure, it is obvious that the initial thickness of the element body according to the present invention is smaller than that shown by the solid line, but it also shrinks slowly as the heating temperature increases, and the final thickness is also smaller than that of the element body according to the conventional method. .

Incidentally, the final shrinkage rate in this case was 19.3% in the case of the present invention and 21.2% in the case of the conventional method.
It was %. Finally, the microstructures of nonlinear resistors obtained by secondary electron images obtained by the present invention and the secondary method will be specifically explained with reference to FIGS. 4a and 4b.

FIGS. 4a and 4b show secondary electron images obtained by the conventional method and the method of the present invention, respectively. In the case of the method of the present invention, the Zn○ particle size is relatively uniform, whereas in the case of the conventional method, It can be seen that not only are Zn0 particles with relatively large diameters present in the center, but also there are relatively many pores. This difference manifests itself in the quality of electrical characteristics. Table 2 shows an example of the electrical characteristics of the nonlinear resistor according to the present invention and the nonlinear resistor according to the conventional method, and it can be seen that the resistor according to the present invention has good nonlinearity and a large discharge withstand capacity. . However, the characteristics are for a sample with a diameter of 64 bars and a thickness of 22 bars. Table 2 Song: V, mA: Peak value of applied voltage, V, when a resistance current of lmA flows.

KA: Applied voltage peak value when a resistance current of 10 KA flows) The present invention is as described above, but the amount of Zdo mixed with the additive is at least 3.5 times the molar amount of Sb2Q added, and the molar amount of Bi2Q added. 1.3 times the amount is required,
When adding Si02, it is further desirable to heat Zn0 with the additive in an amount twice the molar amount of Sj02 added.

As explained above, in the present invention, a part of the metal oxide that is the nonlinear resistor material and all of the additives are heat-treated in advance, so that the shrinkage rate during firing is small and no cracks occur. Not only that, but the reduction in pores makes the reaction more uniform and the particle size of the metal oxide is uniform, which has the effect of improving its electrical properties.

[Brief explanation of the drawing]

Figures 1a and b are explanatory diagrams showing that even in the same element, the crystal phase differs depending on the part, and Figures 2a to d are diagrams showing that part of the metal oxide and all of the additives are combined according to the present invention. A diagram to explain the crystal structure when mixed at various weight mixing ratios,
FIG. 3 is a diagram for explaining the amount of shrinkage in the thickness direction with respect to the heating temperature of the element body according to the present invention and the element body according to the conventional method, and FIGS. 4 a and b are diagrams for explaining the difference in microstructure. This is a diagram for Figure 1 Figure 2 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 A part of the metal oxide powder as a non-linear resistor material mixed in an appropriate weight ratio and all of the additives are heated and reacted in advance and then pulverized, and the remaining metal oxide is removed from the pulverized material. A voltage nonlinear resistor, which is characterized by adding a substance powder, mixing, granulating, and molding, processing to form a high resistance layer on the side surface of the element, and then firing at an appropriate high temperature. Production method.