JPS6236614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage nonlinear resistor containing ZnO as a main component.

Characteristic elements of surge absorbers and lightning arresters include:
Nonlinear resistors containing ZnO as a main component and Bi ₂ O ₃ as an additive are becoming popular. This is ZnO
By taking advantage of the element's excellent nonlinearity (nonlinearity index α > 20) and high energy absorption ability, we have realized a so-called semiconductor lightning arrester that eliminates the need for gap elements. This ZnO element has high purity
A small amount of oxides such as bismuth (Bi), cobalt (Co), manganese (Mn), and antimony (Sb) are added to ZnO and mixed, granulated, and molded to form a high-resistance layer on the side of the element body. After special processing,
It is created by firing at a high temperature of over 1000°C while carefully suppressing the volatilization of Bi ₂ O ₃ , and its nonlinear induction mechanism is directly related to the microstructure. For example, ZnO elements for lightning arresters are made by surrounding ZnO particles of 8 to 30 μm in which Co, Mn, Ni, etc. are dissolved.
It forms a basic structure surrounded by a bismuth oxide (Bi ₂ O ₃ ) layer of less than 1 μm in which Mn, Zn, Sb, etc. are dissolved, and nonlinearity is induced at the interface between the ZnO element and the Bi ₂ O ₃ layer. Ru.

However, the stability of the nonlinearity of _the ZnO element is determined by assuming that _{the ZnO particles and the Bi 2 O 3} layer do not change after firing.
It has a _three- phase Bi ₂ O type and exhibits a high nonlinearity of α > 50, but it is extremely unstable and easily undergoes thermal runaway when normal electrical current is applied. 500 for this thermal runaway
The properties can be stabilized by reheating at a high temperature of ℃ or higher to change the Bi ₂ O ₃ phase from the δ and β types to the γ type. However, the nonlinearity becomes worse (α20).

This decrease in nonlinearity is caused by the high voltage that is constantly applied to the element, that is, the large leakage current due to the use of a high charging rate, when the lightning arrester is configured without a series gap and applied to high voltage or ultra-high voltage power transmission systems. As a side effect of the high charging rate due to overvoltage that frequently occurs in the grid, overcurrent flows to the ZnO element,
There is a risk of burning out the ZnO element.

In this way, conventional non-linear resistors mainly composed of ZnO become non-linear when subjected to heat treatment to convert them into γ-Bi ₂ O ₃ in order to improve the instability of the Bi ₂ O ₃ layer surrounding ZnO particles. There was a problem that led to a decline in sexuality. In addition, careful firing was required to suppress the volatilization of Bi ₂ O ₃ , which led to problems with mass production.

The purpose of the present invention is to provide a voltage nonlinear resistor that is thermally stable and has excellent nonlinearity by having a structure in which ZnO particles are surrounded by a molybdenum (Mo) compound layer instead of the _three Bi ₂ O layers. shall be.

The Mo compound layer type non-voltage linear resistor according to the present invention is formed by the same general ceramic manufacturing method as the conventional ZnO element manufacturing method, but there are differences in firing temperature and firing time. That is, the conventional ZnO element is Bi ₂ O ₃
However, in _{the ZnO} element of the present invention, for example, oxides are difficult to volatilize even when fired at temperatures above 1400°C. Therefore, by firing at a preferable high temperature for a long time, an excellent sintered body can be obtained with improved firing strength, that is, good energy resistance.

The Mo compound type ZnO element according to the present invention is manufactured as follows. 70-99.9 mole percent as ZnO, 0.1-20 as Mo compound e.g. _MoO3
Molpanto's ZnO and Mo compounds are the basic composition, and a Co compound such as Co ₂ O ₃ is added to this basic composition.
0.05-5 mole percent Mn compounds e.g. MnO ₂
0.05 to 5 mol percent, 0 to 5 as Sb ₂ O ₃
Weigh out various proportions in a range of mole percentages and wet mix in a ball mill. After adding a binder such as polyvinyl alcohol (PVA) to this mixture and ^granulating it, for example, 40 mm diameter, 20 mm
It is pressure-molded to a thickness, calcined once at 900°C to 1000°C, and undergoes gradual removal of the binder, reaction in the mixing system, and preliminary sintering. After this, for the main firing, a mixed vapor atmosphere of Sb ₂ O ₃ , MoO ₃ , PbO, etc. is created in the yarn made of alumina, etc., and side insulation is applied by a gas phase-solid phase reaction, and sintering is performed at a high temperature of 1100℃ or more Bake for several hours or more. The resulting sintered body has a diameter of, for example, 32 mm and a thickness of 16 mm, and both end faces are polished, and after cleaning, aluminum metallicon electrodes are attached to complete the device. In addition,
The above pre-firing is not necessarily necessary, and in order to observe the thermal stability of the element, the sintered body is coated with an Ag base and baked at 500 to 800°C.
In addition, regarding the mixed vapor atmosphere during the above-mentioned firing, there is a case where side materials are attached after firing, and when ZnO−Sb ₂ O ₃ −MoO ₃
It is not necessary when applying a special inorganic side surface material as a paste with an organic binder added.

The microstructure of the ZnO element created in this way is shown in Figure 1 a to f, as shown in the secondary electron image (Figure 1 a) and the distribution image of each element (Figure 1 b to f) by the X microanalyzer. Become. As seen in FIG. 1, the ZnO element according to the present invention has ZnO particles (first
It has a basic structure in which Mo oxide (Fig. 1 c) surrounds the box shown in Fig. b), and other additives such as Co ₂ O ₃
(Fig. 1 f), Sb ₂ O ₃ (Fig. 1 d), and MnO ₂ (Fig. 1 e), Sb forms a spinel structure with Zn and Zn ₂ . ₃₃ Sb ₀ . ₆₇ O ₄ , but Co and Mn are ZnO particles, Mo oxide layer,
It is dispersed in the spinel layer, etc.

The voltage-current characteristics of the ZnO element of the present invention having the above structure in a small current range (10 ^-6 to 10 ^-3 A) were measured. In order to judge whether the nonlinearity is good or bad from this measurement result, the relational expression between the current, voltage V, and nonlinearity index α is I=(V/C)〓 where C is a constant, and from the approximate expression, the nonlinearity index α and its nonlinearity are Threshold voltage (starting voltage for operation) that produces the desired characteristics V ₁ mA/mm
was calculated. Note that the non-linear index is calculated from the following equation in which both sides of the above equation are taken as logarithms.

The results of the above measurements and α calculations for ZnO elements in which the amount of Sb ₂ O ₃ added, the amount of MoO ₃ added, and the amount of MnO ₂ added were varied are shown in FIGS. 2 to 5. FIG. 2 shows the α value with MnO ₂ as a parameter, with Sb ₂ O ₃ constant at 1 mol percent and Co ₂ O ₃ constant at 0.5 mol percent, with the horizontal axis representing the amount of MoO ₃ added. FIG. 3 shows the α value when MnO ₂ in FIG. 2 is constant at 0.6 mol percent and Co ₂ O ₃ is used as a parameter. Figure 4 shows MoO ₃ with the amount of Co ₂ O ₃ on the horizontal axis.
The α value is shown with 0.5 mol percent constant, Sb ₂ O ₃ constant at 1 mol percent, and MnO ₂ as a parameter. FIG _. 5 shows the α value with Co 2 O 3 as a parameter, with the amount of MnO ₂ on the horizontal axis, MoO ₃ constant at 5 mol percent, Sb _{2 O 3} constant at 1 mol percent.
In addition, the threshold voltage V ₁ mA is 100V ~ for all elements.
I entered 300V.

As is clear from these measured values, the element according to the present invention has a basic structure in which ZnO particles are surrounded by Mo compounds, and the basic composition is ZnO and Mo compounds, with Co compounds, Mn compounds, and Sb compounds as appropriate. It was found that a ZnO element with high nonlinearity could be realized by blending, granulating, molding, and firing at high temperature for a long time. In particular, as for ZnO and Mo compounds, as is clear from Fig. 2 and Fig. 3, ZnO is determined in the range of 70 to 99.8 mol%, and Mo compound is determined in the range of 0.1 to 20 mol%, taking into account other additives. The Co compound ranges from 0.05 to 5 mol percent as shown in Figure 4, and the Mn compound ranges from 0.05 to 5 mole percent as shown in Figure 5.
A ZnO element with excellent nonlinear characteristics can be realized by adding 5 mol percent of the Sb compound and the remaining Sb compound in the range of 0 to 5 mol percent. The lower limit of the amount of Mo compound added is set at 0.1 mol percent because if it is less than that, a liquid phase is difficult to form during firing, so it is necessary to raise the firing temperature. Further, the reason why the upper limit of the Mo compound is set to 20 mol percent is that the nonlinearity deteriorates when the amount exceeds this value. Similarly,
This is because significant nonlinearity does not occur when Co, Sb, and Mn compounds are added in amounts outside the range.

Next, regarding the stability of the nonlinear characteristics of the ZnO element according to the present invention, there is no change in the α value and the threshold voltage V ₁ mA/mm even after baking the Ag electrode.
0.7×V ₁ mA as a charging condition in an atmosphere of 140℃
The increase in leakage current with respect to time was measured by applying a DC voltage of 10 -3 mA/h, and the increase rate was as low as 10 ^-3 mA/h, confirming excellent stability.

As described above, in the present invention, since the basic composition is a molybdenum compound as an interface forming element with ZnO particles instead of bismuth oxide Bi ₂ O ₃ , the problem of volatilization during firing is solved, and the Since volatilization can be suppressed even during firing for several tens of hours, it is possible to select the optimal firing temperature for the fired body, and the sintered body is not thermally unstable and does not require reheating, and its composition does not suffer from thermal damage due to constant electrical application. Become a stable element without fear. In addition, the basic composition of ZnO particles surrounded by Mo compounds has a nonlinearity-inducing factor.
Nonlinearity is obtained by forming an electrical barrier at the interface between the ZnO particles and the Mo compound layer by dissolving transition metals such as Co and Mn and Sb, etc., but the stability of the nonlinearity is This is due to the ZnO particles and Mo compound layer, and since the Mo compound layer is very stable, nonlinearity is also stable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a secondary electron image a and distribution images b, c, d, e, f of each element taken by an X-ray microanalyzer of a voltage nonlinear resistor according to the present invention; FIG.
3, 4, and 5 are nonlinear exponential characteristic diagrams of the voltage nonlinear resistor according to the present invention.

Claims (1)

[Claims] 1 Mix zinc oxide (ZnO), molybdenum (Mo) compound, cobalt (Co) compound, manganese (Mn) compound, and antimony (Sb) compound, granulate,
By molding and firing at high temperatures, a basic structure is created in which zinc oxide particles are surrounded by a molybdenum compound, antimony (Sb) forms a spinel structure with zinc, and cobalt (Co) and manganese (Mn) are dispersed throughout. A voltage nonlinear resistor characterized by being a sintered body comprising: