JPH0373123B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a metal oxide nonlinear resistor, particularly a metal oxide nonlinear resistor used in an overvoltage protection device in an electrical system.

[Technical background of the invention and its problems]

Overvoltage protection devices are used in electrical systems to protect the electrical system by removing overvoltages superimposed on normal voltages.

This overvoltage protection device uses a non-linear resistor that exhibits almost insulating properties at normal voltage and has a relatively low resistance value when overvoltage is applied.

Nonlinear resistors are made by mixing silicon carbide (SiC) or zinc oxide (ZnO) with a metal oxide, and firing the molded material.

For example, ZnO 80 mol%, magnesium oxide (MgO) 14 mol%, bismuth oxide (Bi ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ), cobalt oxide (CoO), manganese oxide (MnO), chromium oxide (Cr ₂ O) ₃ ) and 0.05 to 3.5 mol% of iron oxide (Fe ₂ O ₃ ) each in a total of 6
mole %, weigh and mix. For example, a ball mill is used as the mixing device.

Next, this mixture is made into spherical aggregates having a particle size of, for example, 100 to 300 microns using a granulating device, such as a spray dryer.

This powder mixture is filled into a cylindrical mold and pressure-molded using a uniaxial press machine, for example, with a diameter of 75 mm.
A disc-shaped molded body with a thickness of 25 mm and a thickness of 25 mm is obtained.

This molded body is fired at a temperature of, for example, 1200°C to 1300°C for 6 hours to produce a disc-shaped nonlinear resistor material with a diameter of 60 mm and a thickness of 20 mm, and electrodes are formed by metal spraying at room temperature. , a nonlinear resistor.

In the non-linear resistor manufactured in this way, the rate of change in resistance of the non-linear resistor is large when a large current pulse is applied. There has been a need for metal oxide nonlinear resistors with electrical properties that are unsuitable and stable over long periods of time in devices.

[Object of the Invention] The present invention has been made in view of the above-mentioned needs, and it is an object of the present invention to provide a method for manufacturing a metal oxide nonlinear resistor whose electrical characteristics are less likely to deteriorate even when overcurrent pulses are repeatedly applied over a long period of time. be.

[Summary of the invention]

In order to achieve this object, the present invention provides a method for manufacturing a metal oxide nonlinear resistor, which involves mixing zinc oxide with a metal oxide, molding it, sintering the molded body, and attaching electrodes to the sintered body. The electrode attachment is performed by heating the sintered body within a range of 50° C. or higher and sintering temperature or lower.

Note that the heating temperature of the sintered body is preferably 50° C. or higher.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings. For example, if ZnO is 80 mol%, the metal oxide analogy is
MgO 14 mol%, Bi ₂ O ₃ 2 mol%, Sb ₂ O ₃ 1.5 mol%,
Weigh out 1.1 mol% CoO, _0.5 mol% _Cr2O3 , 0.5 mol% MnO, and _0.4 mol% _Fe2O3 . The weighed oxide is then placed in, for example, a ball mill and mixed together with deionized water and an organic binder by running the ball mill for 24 hours.

The mixed oxide and organic binder are substantially homogeneously mixed.

Next, the oxide is made into spherical aggregates having a particle size of, for example, 100 to 300 microns using a granulating device, such as a spray dryer.

This powdery mixture is applied to a uniaxial press machine and formed into a disk shape of, for example, 75 mm in diameter and 25 mm in thickness.

Next, this molded body is placed in an electric furnace and fired and sintered. The firing temperature is, for example, 1250℃, and the time is, for example, 6
The time is appropriate.

The disc-shaped sintered body after firing shrinks more than before firing, but has a substantially homogeneous composition and density.

Next, both sides of the disc-shaped sintered body are lightly polished to expose the sintered body. After that, this sintered body is heated to approx.
A nonlinear resistor is manufactured by thermally spraying aluminum, for example, onto the exposed surface while maintaining the temperature at 150°C to attach electrodes.

The electrical characteristics of the metal oxide nonlinear resistor manufactured in this manner are shown in FIGS. 1 and 2.

Figure 1 shows the rate _of change [ _△ V ₁ m _A
= (V ₁ m _A ′−V ₁ m _A )/V ₁ m _A ×100]. In the figure, curve A shows the value of the non-linear resistor manufactured by the conventional manufacturing method, and curve B shows the value of the non-linear resistor of the present invention. As is clear from the figure, the electrical characteristics of the metal oxide nonlinear resistor produced by the manufacturing method of the present invention are significantly improved.

Figure 2 shows the pass rate when the applied shock wave current value was varied up to 100KA. Curve A is conventional, curve B
are the pass rates of metal oxide nonlinear resistors produced by the respective manufacturing methods of the present invention.

As is clear from the figure, when the applied current is small, the difference between both curves A and B is small, but when a large current pulse is applied, the pass rate of the conventional nonlinear resistor drops significantly.

In addition, Figure 3 shows the electrical characteristics of metal oxide nonlinear resistors manufactured by varying the heating temperature of the sintered body.
It is shown in Figure 4. Figure 3 shows that when a sintered body is heated to 50℃ or higher and electrodes are attached by metal spraying, a square wave current (800A-2mS) is applied 100 times.
It shows that V ₁ m _A hardly changes.
Figure 4 shows that when the sintered body is heated to 50°C or higher and the electrodes are attached, the pass rate is high even when a shock wave large current of 100 KA is applied.

When attaching electrodes by metal spraying, heating the sintered body as described above has better discharge resistance because the adhesion strength between the sintered body and the electrode (sprayed metal film) increases. This is thought to be due to the following. That is, since the thermal expansion coefficients of the sintered body and the metal sprayed film (electrode) are different, stress is generated between the sintered body and the metal sprayed film when the temperature changes from the temperature during spraying to a different temperature.
When thermal spraying is carried out at a high temperature, a tensile force acts on the thermal sprayed film at room temperature, but the thermal sprayed film has sufficient spreadability and can adapt to the sintered body and maintain strong adhesion.
On the other hand, when thermal spraying is performed at low temperatures, compressive force acts on the sprayed film at high temperatures. The sprayed film is quite weak against this compressive force, and peels off immediately. When a discharge current flows through a non-linear resistor, the temperature quickly rises to around 200℃ due to Joule heat. Under such usage conditions, it is found that it is better to carry out thermal spraying at a high temperature for the reasons mentioned above.

The upper limit of the heating temperature may be within a temperature range that does not deteriorate the characteristics of the nonlinear resistor and does not cause deterioration of the sprayed metal. That is, the temperature may be lower than the sintering temperature.

In the above examples, the content rate of zinc oxide and the composition and content rate of metal oxides are not limited to the above examples.

Furthermore, it goes without saying that the conditions of the process are not limited to those of the above embodiments.

〔Effect of the invention〕

As explained above, according to the present invention, the sintered body is
By forming electrodes by heating within a range of .degree. C. or above and below the sintering temperature, it is possible to provide a metal oxide nonlinear resistor whose electrical characteristics are less likely to deteriorate even when overcurrent pulses are repeatedly applied over a long period of time.

[Brief explanation of drawings]

1 to 4 are curve diagrams illustrating the electrical characteristics of a metal oxide nonlinear resistor manufactured using the manufacturing process of the present invention.

Claims (1)

[Claims] 1 After mixing metal oxide with zinc oxide, molding it,
In a method for manufacturing a metal oxide nonlinear resistor, the molded body is sintered, and an electrode is attached to the sintered body.
A method for manufacturing a metal oxide nonlinear resistor, characterized in that the electrode attachment is carried out by heating the sintered body within a range of 50° C. or more and a sintering temperature or less.