JPS626324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage nonlinear resistor containing zinc oxide as a main component, and particularly to a voltage nonlinear resistor that has excellent life characteristics and a small flatness rate in current-voltage characteristics.

In recent years, as voltage non-linear resistors with very good non-linear characteristics, those obtained by adding bismuth oxide, cobalt oxide, manganese oxide, antimony oxide, chromium oxide, silicon oxide, etc. to zinc oxide have been known. Although this zinc oxide-based voltage nonlinear resistor has extremely superior current-voltage characteristics compared to conventionally known SiC, etc., its characteristics deteriorate due to surge absorption or long-term energization. There is a problem of an increase in leakage current, and when used as a surge absorber or arrester, there is a risk of thermal runaway during power application or surge processing. This property deterioration due to surge absorption or electrification is caused by the fact that some or all of the Bi ₂ O ₃ contained in the zinc oxide sintered body is γ.
-Bi ₂ O ₃ phase (hereinafter abbreviated as γ phase) is known to be extremely small. Therefore, although the life characteristics of zinc oxide nonlinear resistors containing such a γ phase are very good, other characteristics other than life may not be as good as those that do not contain a γ phase. In particular, the flatness ratio (the ratio of the voltage at a normal current of 10 kA to the voltage at 1 mA, V10 kA/
V1mA) is present when the γ phase is present.
The drawback was that it was not necessarily small.

It is an object of the present invention to provide a zinc oxide type lightning arrester that has good life characteristics without increasing leakage current even when charged over a long period of time under actual usage conditions, and has a small flatness rate in current-voltage characteristics. To provide a voltage non-linear resistor. That is, in the voltage nonlinear resistor of the present invention, the bismuth oxide concentration in the surface layer of the electrode-formed end face of the sintered body is the same as or lower than that in the center of the element, and most (preferably all) of the bismuth oxide is present. ) is present in the form of γ phase.

The present inventors conducted a detailed experimental study on the relationship between the amount added, life span, and flatness of various oxides added to zinc oxide sintered bodies, and found that zinc oxide sintered bodies containing γ phase In the case of , the life is particularly long when most of the bismuth oxide contained is in the γ phase, and the flatness rate varies greatly depending on the amount of total bismuth oxide contained in the sintered body. It has been found that the flatness ratio takes a small value when bismuth exists mostly in the γ phase and the amount is in the range of 0.6 to 2.0 mol≠% in terms of Bi ₂ O ₃ . The present invention is based on these experimental findings. When Bi ₂ O ₃ exists in the γ phase and when it exists in a phase other than the γ phase, the crystal structure of the Bi ₂ O ₃ phase,
Because the crystallinity and the type and amount of elements solidly dissolved in the phase differ, the trap level and electrical resistance in the Bi ₂ O ₃ phase existing at the grain boundaries of ZnO differ. The flatness rate is mainly determined by the height of the barrier that forms the Bi ₂ O ₃ phase (depending on trap density, etc.) and the resistivity of the ZnO particles, so if the Bi ₂ O ₃ phase is mostly the γ phase, ,
It is thought that the range of the amount of Bi ₂ O ₃ at which the flatness rate is minimum differs from that in other cases (when the Bi ₂ O ₃ phase consists mostly of α phase, β phase, and/or δ phase).

Note that the γ phase generally has high crystallinity, has few internal defects, contains Bi ⁵⁺ , and has a large volume, which has the effect of preventing oxygen diffusion through grain boundaries. It is thought that the movement of oxide ions present on the surface of the ZnO particles is prevented, resulting in a long device life. In this way, in order to stabilize the device, the higher the proportion of γ phase in the bismuth oxide phase contained, the better; practically speaking, approximately
It is desirable that 80% or more be in the γ phase.

Further, it is desirable that the Bi ₂ O ₃ content is within the range of 0.6 to 2 mol%. When the amount of Bi ₂ O _{3 is} less than 0.6 mol%, the Bi ₂ O ₃ phase does not work effectively as a barrier for grain boundaries, resulting in an increase in leakage current and a relative _decrease in V1mA. If it is more than 2.0 mol %, V10 kA becomes relatively high due to the influence of the resistance of the Bi ₂ O ₃ phase, and the flatness rate also increases, which is not desirable.

In addition to zinc oxide and bismuth oxide, the voltage nonlinear resistor of the present invention also contains 0.01 to 10 mol% of each of manganese oxide, cobalt oxide, chromium oxide, ammothine oxide, nickel oxide, silicon oxide, and boron oxide.
It can contain 0.001 to 0.05 mol% of aluminum oxide, gallium oxide, etc.

Further, the amount of boron oxide is particularly preferably in the range of 0.02 to 0.2 mol %, and at this time, the γ-type Bi ₂ O ₃ phase, which is a metastable phase, is stably maintained for a long period of time at room temperature.

Bismuth oxide in the sintered body is normally in the α, β, and δ crystal systems, but in order to make it into the γ type,
After cooling the sintered body to a temperature lower than 500℃,
℃ heat treatment method and method of diffusing Bi ₂ O ₃ from the surface of the sintered body (diffusion temperature range: 850-
1100℃). In the latter method, when bismuth oxide is diffused from the surface of the sintered body, the bismuth oxide becomes γ
As the phase changes in the mold, it also diffuses through the grain boundaries of the ZnO particles, so the ZnO particles are uniformly surrounded by the γ phase, and the open pores in the sintered body are filled with the γ phase. . As a result, there is an advantage that desorption of oxygen from the ZnO particle surface is prevented and the properties become particularly stable. Note that diffusion is normally performed from the electrode formation surface.

When diffusing bismuth oxide into the sintered body, it is desirable that the sintered body contains 0.05 mol % or more of bismuth oxide in advance. If the amount of bismuth oxide in the sintered body is less than 0.05 mol%,
The sinterability of the sintered body deteriorates, and voltage nonlinearity is impaired. In addition, the amount of bismuth oxide that diffuses should be sufficient to close the open pores of the sintered body.
Generally, it is desirable that the content be 0.01 mol% or more.

Note that when bismuth oxide is diffused, depending on the diffusion conditions (for example, when the amount of diffused bismuth oxide is large), the distribution of the amount of γ-type bismuth oxide in the sintered body will be large at the diffusion surface and small at the center. There are cases. In such cases, the diffusion surface (electrode formation surface)
As the V1mA decreases and current flows more easily on the surface, a problem arises in that the device characteristics tend to change due to contamination of the side surfaces of the device (surfaces on which no electrodes are formed). Therefore, the distribution of the γ-type bismuth oxide phase should be such that the electrode formation surface has the same or lower concentration as the element center, and by preventing a decrease in resistance on the electrode formation surface, characteristic changes due to side surface contamination or moisture aggregation can be avoided. It is particularly desirable to prevent this in order to ensure a long lifespan under actual conditions of use as a lightning arrester.

Hereinafter, the present invention will be explained according to examples.

Example 1 ZnO with 0.3 to _3.0 mol% of _Bi2O3 , 0.5 mol% of _MnCO3 , _1.0 mol% of _Co2O3 , _0.5 mol% of _Cr2O3 ,
Add 1.0 mol% of Sb ₂ O ₃ , 1.0 mol% of NiO, 1.5 mol% of SiO ₂ and 0.1 mol% of B ₂ O ₃ and use a ball mill.
Wet mixed for 10 hours. After drying this, 10% by weight of a 3% polyvinyl alcohol aqueous solution was added to granulate it into a disk shape. This was fired in the air at 1250°C for 1 hour to produce a sintered body with a diameter of 60 mm and a thickness of 20 mm.
Next, a paste consisting of 83% by weight of bismuth oxide, 2% by weight of ethyl cellulose, 14% by weight of butyl carbitol, and 1% by weight of n-butyl acetate was uniformly applied to both main surfaces of this sintered body. Application amount is 0.025g/cm ²
It was hot. After heat-treating this in the air at 950°C for 3 hours, Al was sprayed on both main surfaces to form electrodes. The distribution of Bi ₂ O ₃ in the obtained element (hereinafter abbreviated as element A) was almost uniform as shown in FIG. this is
Since Bi ₂ O ₃ becomes a liquid phase and diffuses in the sintered body,
It is thought that the diffusion is sufficiently rapid and the distribution is almost uniform. In addition, as a result of investigating by X-ray diffraction, it was found that
All Bi ₂ O ₃ was in the γ phase. On the contrary,
In the element (hereinafter abbreviated as B element) in which electrodes were attached as-fired without the paste application and heat treatment processes as described above, the distribution of Bi ₂ O ₃ is the lowest concentration on the surface as shown in Figure 1. The concentration of Bi 2 O 3 increased as it went deeper into the structure, but the Bi ₂ O ₃ was not in the γ phase but in the β, δ, etc. phases. In order to investigate the life characteristics of these A and B elements, we investigated the resistance leakage when continuously energized at 90°C with a 100% charge rate (applying an AC voltage peak value equal to the voltage when a DC 1mA current flows at 20°C). FIG. 2 shows the change in current over time.
As shown in the figure, the change in resistance leakage current of the A element, in which Bi ₂ O ₃ is in the γ phase, is very small compared to the B element, which is in the β and δ phases other than the γ phase, and the energized life is significantly longer. It took a long time. Furthermore, even when a rectangular wave surge of 1000 Aδ x 10 μs was applied 50 times, the leakage current hardly increased. In addition, even if the amount of Bi ₂ O ₃ was changed in both the A element and the B element, almost no change was observed in the respective life characteristics.

Figure 3 shows the total Bi ₂ O ₃ contained in element A.
Amount and flatness rate (voltage V ₁ when current flows at 3×10 ² A/cm ² and voltage V ₂ when current flows at 3×10 ^-5 A/cm ²
It is expressed as V ₁ /V ₂ . ) shows the relationship. As seen in the figure, the flatness ratio became particularly small when the amount of Bi ₂ O ₃ was in the range of 0.6 to 2.0 mol %. In addition, the flatness ratio is 1.6 or less for lightning arresters for 1100kV systems;
For lightning arresters for 420kV systems, it must be 1.7 or less. In addition, the analysis result of the amount of Bi ₂ O ₃ contained in the sintered body was 0.06 to 0.08 higher in element A than in element B.
The mole percentage was higher. Therefore, the paste coating and subsequent heat treatment process reduce the
It is clear that Bi ₂ O ₃ diffused into the device and increased the amount of Bi ₂ O ₃ .

Example 2 A sintered body was prepared in the same manner as in Example 1, and 0.055 g/cm ² of paste was applied thereto. Next, heat this at 1050℃
After heat treatment in the atmosphere for 4 hours, Al
I attached the electrodes. The distribution of Bi ₂ O ₃ in the obtained element (hereinafter abbreviated as element C) was as shown in FIG. 1, with a low concentration at the surface and increasing concentration as it went into the interior of the sintered body. This is considered to be because some Bi ₂ O ₃ was volatilized during diffusion. The life characteristics of this element were almost the same as those of element A in FIG. or,
The relationship between the total amount of Bi ₂ O ₃ contained and the flatness ratio became small when the amount of Bi ₂ O ₃ was 0.6 to 2.0 mol %, as in the case of element A in FIG. In addition, in this C element, the analysis result of the total amount of Bi ₂ O ₃ contained is B
It was only about 0.1 mol% more than the element. This is due to the Bi ₂ O ₂₃ paste inside the sintered body during the heat treatment process.
It is thought that the increased amount was smaller than the applied amount (0.15 mol%) because some of it was volatilized as it was diffused.

Example 3 In Example 1, the amount of MnCO ₃ added was changed from 0.5 to
Elements were produced which were subjected to diffusion heat treatment in the same manner as in Examples 1 and 2, with the concentration being changed within a range of 1.5 mol %.
As a result of X-ray diffraction, all Bi ₂ O ₃ in this device was in the γ phase. The life characteristics are as good as the A element of Example 1, and the flatness rate varies slightly depending on the amount of MnCO ₃ added, but in any case,
Similarly, when the total amount of Bi ₂ O ₃ in the device was in the range of 0.6 to 2.0 mol %, the value became small as in FIG. 3.

Example 4 Among the additives in Example 1, additives other than Bi ₂ O ₃ and MnCO ₃ were treated in the same manner as in Example 3, respectively.
By creating devices with different amounts of addition, the life characteristics,
The flatness rate was investigated. The results were similar to those in Example 3.

Example 5 An as-fired sintered body (without diffusion heat treatment) produced in the same manner as in Example 1 was heat treated in the air at 800°C for 15 minutes without applying paste, and then electrodes were attached and the device was assembled. was created. The distribution of Bi ₂ O ₃ in the sintered body was similar to that of the C element, with a low concentration at the surface and increasing concentration toward the inside. As a result of investigating by X-ray diffraction, 80% of Bi ₂ O ₃ contained in the element is γ.
It was a phase. The measurement results of the charged life characteristics of these elements were slightly worse than those of element A of Example 1, and the rate of increase in resistance leakage current was about twice that of element A.
It showed much better characteristics than the conventional device. Figure 4 shows the flatness rate of the device according to this example and the total Bi ₂ O ₃ in the device.
It shows the relationship between quantities. As in Examples 1-4
When part of Bi ₂ O ₃ is diffused from the surface (Figure 2)
Compared to , the value of flatness is slightly larger overall, but as shown in the figure, the total amount of Bi ₂ O ₃ is 0.6 to 2.0 mol%.
It was the same as in the case of FIG. 3 that the flatness rate was small in the range of .

As described above, according to the present invention,
It is possible to obtain a voltage nonlinear resistor with excellent charging life characteristics and a small flatness ratio.

[Brief explanation of the drawing]

Figure 1 shows the distribution of Bi ₂ O ₃ in the device, Figure 2 shows the change in resistance leakage current over time, and Figure 3 shows the distribution of Bi 2 O 3 in the device.
4 are diagrams showing the relationship between the amount of Bi ₂ O ₃ and the flatness rate. A, B, C... elements.

Claims (1)

[Scope of Claims] 1. A voltage nonlinear resistor comprising electrodes provided on the upper and lower end faces of a sintered body containing zinc oxide as a main component and at least bismuth oxide as an additive, wherein the electrode-forming end face of the sintered body is 1. A voltage nonlinear resistor characterized in that the bismuth oxide concentration in the surface layer is the same as or lower than that in the center of the element, and most of the bismuth oxide exists in the form of γ phase. 2. Claim 1, wherein the amount of bismuth oxide in the sintered body is 0.6 to 2.0 mol%.
Voltage nonlinear resistor described in section. 3. Claim 1, characterized in that all bismuth oxide in the sintered body exists in the form of γ phase.
Voltage nonlinear resistor according to item 1 or 2.