JPH01309302A - Manufacture of nonlinear resistor - Google Patents

Abstract

PURPOSE:To obtain a homogeneous sintered body having no defect in structure by using tricobalt tetroxide containing not more than 10mol% cobalt oxide as a cobalt raw material and a substance including not more than 1000ppm iron as an impurity. CONSTITUTION:Water and an organic binder are added to a raw material containing zinc oxide as a principal ingredient, cobalt as a by-component and bismuth oxide, antimony oxide, etc., as additives, and mixed. The mixture is granulated, molded, heated and pre-baked, thus manufacturing a base material. A sintered body is acquired from the base material, and electrodes are formed onto both surfaces of the sintered body. Tricobalt tetroxide including not more than 10mol% cobalt oxide and a substance containing not more than 1000ppm iron as an impurity are employed as cobalt raw materials at that time. Consequently, oxygen is also fed from the inside of the base material in a sintering process, and a normal reaction progresses both on the inside and outside of the base material. Accordingly, the homogeneous sintered body having no defect in structure is obtained.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a non-linear resistor, particularly in the form of a raw material in which cobalt is added as a subcomponent to zinc oxide as a main component. This invention relates to a method of manufacturing a non-linear resistor used in lightning arresters and the like.

(Prior Art) Lightning arresters are used to protect the power system by suppressing abnormal voltages generated in the power system. Lightning arresters use non-linear resistors that exhibit insulating properties at normal voltages, but exhibit low resistance when abnormal voltages are applied; a typical example of this is one whose main component is zinc oxide. ing.

In general, non-linear resistors made of metal oxides used in lightning arresters etc. have zinc oxide (ZnO) as a main component, as described in, for example, Japanese Patent Application Laid-open No. 59-65405.
Bismuth (Bi), antimony (Sb), cobalt (C
o), manganese (Mn), chromium (Cr), nickel (
Ni).

Containing components such as silicon (Sin) and aluminum (Aj2'), these materials are manufactured by mixing raw materials, granulating, molding, sintering, and attaching electrodes to both end faces.

To be more specific, zinc oxide and oxides, or subcomponent raw materials that can be converted into oxides through sintering, are thoroughly mixed with water and an organic binder, and then granulated using a spray dryer, etc., and the resulting granulated powder is sieved. A manufacturing method that removes coarse particles and secondary agglomerated particles, places them in a mold, molds, and sinters them to eliminate voids and pinholes that occur inside the resistor and prevent a decline in surge resistance and energized life characteristics. Are known.

(Problem to be solved by the invention) In recent years, electric power systems have become larger in capacity and higher in voltage in order to reduce power transmission costs.As a result, 500KV lightning arresters have been put into practical use, and 1000KV (UHV) lightning arresters are also planned in the near future. has been done. The non-linear resistors used in these lightning arresters must handle extremely large surge energy, and therefore measures such as increasing the capacity of the non-linear resistors and increasing the number of non-linear resistors connected in parallel are used. However, an increase in the number of parallel-connected resistors is limited due to characteristic problems such as an imbalance in current sharing, which inevitably leads to an increase in the capacity of the nonlinear resistor. However, since the thickness is limited by the limiting voltage of the lightning arrester, etc., the diameter must be increased. In this way 500KV, 100
Non-linear resistor for OKV - each shape has a diameter φ of 100# to 1
20#, thickness t is 20~ due to deformation during sintering and economic efficiency.
It can be as much as 45M. Such non-linear resistors are difficult to sinter and often result in variations in discharge withstand characteristics, and a stable manufacturing method has been desired.

The present invention has been made in consideration of the above points, and provides a method for manufacturing a nonlinear resistor that is stabilized during sintering, improves discharge withstand characteristics, reduces variation, and improves nonlinear characteristics. It is about providing.

[Structure of the Invention] (Means for Solving the Problems) The present invention uses zinc oxide as a main component, cobalt as a subcomponent, bismuth oxide, antimony oxide, manganese dioxide, chromium oxide, etc. as additives. ! Water and an organic binder are added to and mixed with a raw material containing at least one of nickel i-oxide, silicon oxide, and aluminum oxide, and this mixture is granulated and then molded into a predetermined shape, and this molded body is heated to release the water and A non-linear resistor in which the organic binder is removed, pre-fired to form an element body, a high-resistance substance is coated on the sides of this element body, and the element is fired to form a sintered body, and electrodes are formed on both sides of this sintered body. In the manufacturing method, the cobalt as the subcomponent is cobalt tetraoxide (Co 304 ) with a cobalt oxide (Co, O) content of 10 mol% or less and iron (Fe) as an impurity of 1000 ppm or less. It is characterized by being maintained.

(Function) In the present invention, cobalt tetraoxide (Co304), which is uniformly dispersed in zinc oxide (ZnO) when raw materials, water, and an organic binder are mixed, is mixed with CoO and O during the sintering process.
As the non-linear resistor is decomposed, sufficient oxygen is supplied to the inside of the sintered element, creating an oxidizing atmosphere, creating conditions desirable for sintering the non-linear resistor, and allowing normal reactions to proceed. As a result, a non-linear resistor with improved discharge withstand characteristics with less variation can be obtained.

(Example) Hereinafter, an example of the method for manufacturing a non-linear resistor of the present invention will be described with reference to FIGS. 1 and 2.

Bismuth oxide (Bi 203 ), manganese dioxide (
Mn 02 ), 0.5 mol% each of chromium oxide (CizO3) and silicon dioxide (Si ○2), cobalt tetraoxide (CO304), and antimony e-oxide (Sbz 03
>, nickel oxide (Ni 2 O) is each 1 mol %, aluminum oxide (Af!, z 03 ) is 0.003 mol %, and the remainder is zinc oxide, and they are weighed accurately. Weigh to add a trace amount of boron oxide (8203) to the colander.

These raw materials are mixed together with water and an organic binder such as a dispersant in a mixing device. Next, the mixture is spray granulated using a spray dryer. These granulated powders are placed in a mold and molded, heated in air at 500°C to remove added water and organic binders, and then pre-fired at 1050°C to form a high-resistance layer on the sides. After that, a high resistance material is applied and fired in air at 1200'C, color coating is performed, and color firing is performed. Further, both halves were polished, and electrodes sprayed with aluminum were attached to both halves to obtain a nonlinear resistor having a diameter of 100mm and a thickness of 22#.

The discharge withstand capacity of the nonlinear resistor obtained as described above was measured. The measurement method was to apply a 2.5 ms square wave current five times. In Figure 1, the vertical axis shows the energy at which the resistor did not break when 10 resistors were tested, and the horizontal axis shows the energy of cobalt oxide (Co) in cobalt tetraoxide (Co304).
The content of o) is shown.

It was found that when the content of cobalt oxide (Coo) exceeds 10 mol %, the variation becomes large and the durability characteristics deteriorate rapidly.

In Figure 2, the horizontal axis shows the Fe content (PPM) in the cobalt raw material.
) Wow, the vertical axis shows the non-linear characteristics (V10KV/VtmA)
FIG. As is clear from FIG. 2, it is recognized that if the amount of iron exceeds 11,000 pp, it will have an adverse effect. From these results, it is recommended to use cobalt tetraoxide (Co 304 ) with a cobalt oxide (Coo) content of 10 mol% or less and iron (Fe) as an impurity of 11,000 pp or less as a cobalt raw material. Accordingly, a non-linear resistor with improved discharge withstand characteristics and non-linear characteristics can be obtained. Although the reason for this is not clear, it is thought to be as follows. That is, Co 304 changes to Co 304-3Co O+0 during the sintering process. It is thought that the oxygen released during this reaction has a favorable effect on the reaction for producing the nonlinear resistor.

Regardless of the non-linear resistor, sintering of oxide-based ceramics in air or in an oxidizing atmosphere of air and oxygen provides good characteristics. Therefore, if sufficient oxygen does not reach inside the element during sintering, the normal production reaction may be inhibited and the properties may be adversely affected.

In this way, it is desirable that oxygen be supplied from the nonlinear resistor itself. Even if oxygen is not sufficiently distributed to the inside of the element by only supplying oxygen from outside the sintered body, an oxygen atmosphere is formed by supplying oxygen from the inside.
It is thought that a homogeneous nonlinear resistor with no structural defects was obtained by the normal production reaction progressing to the inside, and the discharge withstand characteristics were improved.

On the other hand, CoO is used in the low temperature region 1 (~450'C) of the sintering process.
), the opening reaction of 3Co O+O−+Co 304 occurs. Therefore, contrary to Co 304, it deprives oxygen from the surroundings. Therefore, in this temperature range, an oxygen-deficient state occurs and normal production reactions are inhibited. However, if the content of Co 2 O is within 10 mol %, it will not adversely affect the discharge durability characteristics.

Roughly speaking, when iron (Fe) enters a nonlinear resistor, it accumulates in grain boundary layers, etc., and obstructs the flow of current, resulting in nonlinear characteristics (VI
OKA/V1mA) worsens. However, the amount of iron is 1
At 1000 pp or less, there is no adverse effect.

Note that in this example, the size of the nonlinear resistor is 100 mm in diameter.
However, it has been confirmed that the same effect can be achieved even with the smallest material shown in the example with a thickness of 22mm. The effect of increasing the capacity of the nonlinear resistor is obvious and necessary for the reasons described above.

[Effects of the Invention] According to the present invention, cobalt oxide (Co
By using cobalt tetraoxide with a content of o) of 10 mol% or less and iron ([e) as an impurity of 1000 ppm or less, it is possible to remove oxygen from the inside of the element during the sintering process. A homogeneous sintered body with no structural defects inside can be obtained by allowing a normal reaction to proceed inside and outside the element body. As a result, the discharge withstand characteristics are extremely high, and by keeping the impurity iron (Fe) below 11,000pp, the properties of the grain boundary layer are not impaired and the nonlinear characteristics (VI OKA/V1mA >
It is possible to provide an excellent method for manufacturing a non-linear resistor.

[Brief explanation of the drawing]

Figures 1 and 2 are for detailed explanation of the present invention, and Figure 1 shows cobalt oxide (Cod) in the cobalt raw material.
) Characteristic diagram showing the relationship between the content rate and the discharge withstand characteristics, 2nd
The figure shows the amount of iron (Fe) in the cobalt raw material and the nonlinear characteristics (
It is a characteristic diagram showing the relationship between VIOKA/Vl mA). (8733) Agent: Yoshiaki Inomata, patent attorney (and others)
1 person) 01020 30t, 0 50ko) Gurugami, i
Figure i Figure 2

Claims (1)

[Claims] Water and an organic binder are added to a raw material containing zinc oxide as a main component, cobalt as a subcomponent, and at least one of bismuth oxide, antimony oxide, manganese dioxide, chromium oxide, nickel oxide, silicon oxide, and aluminum oxide as additives. This mixture is granulated and then molded into a predetermined shape. This molded body is heated to remove the water and organic binder, and then pre-fired to form an element body. Anti-resistance materials are coated on both sides of this element body. In the method for manufacturing a non-linear resistor in which a sintered body is formed by coating and firing, and electrodes are formed on both sides of the sintered body, the cobalt as the subcomponent has a cobalt oxide (CoO) content of 10 mol. % or less
A method for manufacturing a nonlinear resistor, characterized in that it is made of cobalt trioxide (Co_3O_4) and iron (Fe) as an impurity is maintained at 1000 ppm or less.