JPS6390807A - Voltage nonlinear resistor - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to a zinc oxide-based voltage nonlinear resistor (hereinafter referred to as a varistor) containing bismuth, which has excellent stability against thermal history. related to).

(Prior art) In recent years, there has been a remarkable development of various varistors, and among them, zinc oxide-based varistors containing bismuth have been recognized for their excellent stability in nonlinearity, surge absorption, and constant voltage performance. Widely used as a protective varistor or constant voltage varistor against lightning surges and abnormal voltages. However, this type of varistor uses zinc oxide as the main component and bismuth and cobalt as additives.

Several to ten or more types of manganese, nickel, chromium, etc. are added and mixed, and the sintered body is granulated and sintered. Silver paste is coated on both sides of the sintered body and then baked, or the electrode metal is metallized. After that, electrodes were formed and put into practical use.

Therefore, the varistor used in this way has a small idling current (leakage current) under normal (normal) voltage conditions, and has a large absorption capacity when absorbing abnormal voltages and lightning surges, and the subsequent electrical It is required that the change in characteristics be extremely small. Conventionally, as a technique to meet such demands, Japanese Patent Publication No. 53-21509,
Alternatively, there is one disclosed in Japanese Patent Publication No. 60-38841.

The technology disclosed in Japanese Patent Publication No. 53-21509 (hereinafter referred to as the former) is stable against DC loads by containing 10% or more of the Bi2O3 contained in the sintered body as γ-Bi2O3. Furthermore, it is designed to exhibit stable and excellent varistor characteristics even with pulsed current.

Also, Special Publication No. 60-38841 (hereinafter referred to as the latter)
The technology disclosed in 2003-2020 is characterized by the addition of silver-containing bismuth borosilicate glass and by making more than 90% by weight of the Bi2O3 in the sintered body into body-centered cubic bismuth oxide (γ-81203). The present invention relates to a varistor having characteristics such that leakage current changes over time even after a long period of time under electrical conditions, and furthermore, decreases over time.

In other words, the former has an α-Bi203 phase in the sintered body depending on the type of additives, calcination conditions, firing conditions, etc.

β-B i 203 phase, 7-B i 203 phase (7
) In addition, δ-Bi203 phase is generated, and electrode baking occurs even in the sintered body that does not contain γ-Bi2O3 phase at the time of firing.
Or after a thermal history such as reheating during use, α-Bi
203 phase, β-Bi203 phase, δ-Bi203 phase is γ-
The γ-Bt203 phase when transformed to the Bi2O3 phase is 10
% or more, a stable varistor can be obtained. The latter is obtained by adding silver-containing bismuth borosilicate glass. Bismuth oxide, which constitutes a sintered body containing bismuth oxide, usually starts to react at 800 to 900°C, once forming a birochlore crystal phase, and then β-3 decomposes to produce a spinel crystal phase and a liquid phase of bismuth oxide (1), and is formed during the progress of sintering of zinc oxide.
A sintered body containing i2Q3 phase and δ-8i203 phase was published in Journal of Absorbed Physics (Japan), 1
According to the method described in Volume 5 (1976) page 1847,
By re-firing at 700°C in the atmosphere, more than 90% of the bismuth (III) oxide in the sintered body is converted to γ-Bi.
It was discovered that a stable varistor can be obtained by changing the phase to the 2O3 phase.

As a result of extensive studies based on the above-mentioned technology, the present inventors found that α contained in the sintered body in both the former and the latter disclosed as the above-mentioned prior art.

The thermal history of bismuth oxide exhibiting the Bi2O3 phase of β and δ during the manufacturing process, that is, the cumulative thermal history of electrical energy during practical use even for plated and metallicon products that do not have a thermal history during electrode baking or electrode formation. It was found that the γ-B i 203 phase transforms (phase change) and the voltage-current (V-1) characteristic decreases in the low current region.

However, the present inventors have discovered that B, which constitutes the grain boundary segregation region, is produced by producing a thermally stable bismuth compound in the grain boundary segregation region of the crystal grains mainly composed of zinc oxide that constitute the sintered body.
Focusing on the fact that the phase change due to heat in the i2O3 phase can be reduced, various developments were carried out, leading to the present invention.

(Problems to be Solved by the Invention) As described above, in order to obtain a stable varistor, varistors are formed at grain boundary segregation areas of crystal grains in a sintered body depending on the type of additives, calcination conditions, firing conditions, etc. Desired suspension γ in Bt203 phase
- Even if the Bi2O3 phase is obtained, the remaining α, β, and δ Bi2O3 phases undergo a phase change due to subsequent thermal history, that is, electrode baking and electrical energy during use, resulting in V-1 characteristics in the low current region. It is not possible to prevent the decline in

The object of the present invention is to provide an extremely stable varistor with excellent nonlinearity and no change over time by reducing the Bi2O3 phase present in the grain boundary segregated areas in a sintered body.

[Structure of the Invention] (Means for Solving the Problems) The varistor of the present invention contains zinc oxide as a main component, and at least calcium and bismuth as additives.

Contains tin and antimony, and the relationship between calcium and bismuth, and between tin and bismuth in the additive is Ca/B i =0.
05~0.5゜Sn/B1-0.2~2.0, convert bismuth to B1□03: 0.05~
1.0 mol%, 0.0% when antimony is converted to Sb2O3.
In a sintered body containing 05 to 3.0 mol%, at least 50% of the total bismuth in the sintered body is contained in a birochlore-type compound in the grain boundary segregation of crystal grains containing zinc oxide as a main component. It is composed of:

(Function) According to the varistor configured as described above, by converting 50% or more of the total bismuth into a birochlore type compound as a segregated substance intervening in the grain boundary segregation area of crystal grains in the sintered body, the varistor can be heated to about 1000°C. It can be formed as a thermally stable material that does not undergo any transformation up to
-■ There is very little deterioration in characteristics, and excellent nonlinear characteristics that cannot be obtained conventionally can be obtained.

(Example) Hereinafter, embodiments of the present invention will be described in detail.

Zinc oxide (ZnO) as the main component, bismuth oxide (B ; 2o3>, calcium chloride (Cab) as additives)
, FA tin<5n02), antimony oxide (Sb20
3>, Cobalt M (COO>, ROM (Cr2)
o3), nickel Mide (Nip), manganese oxide (Mn
It contains at least calcium oxide, bismuth oxide, tin oxide, and antimony oxide from among the oxides of O), and the relationship between calcium and bismuth and tin and bismuth in the additive is Ca/B i =0.05 to 0.5.゜Sn/Bi=0.2 to 2.0, Bi OO,
05-1.0 mol%.

Ceramic powder containing 0.05 to 3.0 mol% of Sb203 is granulated and fired at a temperature of 1000 to 1300°C, and both sides of the obtained plate-shaped sintered body are coated with silver baking, plating, or metallized to form electrodes. It is formed by forming.

The table shows the difference between ZnO crystal grains determined from the main peak intensity ratio by X-ray diffraction of a sintered body heat-treated at 700°C under the same conditions as for forming a silver baked electrode, depending on the type of additive and m (mol%) added. Vloo μA-VI was measured by forming an aluminum metallicon electrode without thermal history in order to understand the birochlore-type compound contained in the birochlore-type compound as a component of the grain boundary segregation component that constitutes the sintered body, and the electrical characteristics of the sintered body itself. α of IrLA, viooμ△-V measured by silver-baked electrode formation with thermal history
It shows α of l77LA and also Vl mA/s.

The size of the sintered body used as a sample was 14 m in diameter.
The lR1 thickness is 1M and the electrode diameter is 13.4#.

Next, in order to make the results shown in the table above easier to understand, the results will be explained with reference to FIGS. 1 to 9.

Figures 1 and 3 show the relationship between Ca/Bi or Sn/3i and nonlinearity α (V 100μA-V177LA), and Figures 2 and 4 show the relationship between Ca/Bi or Sn/3i and nonlinearity α (V 100μA-V177LA).
Sn/Bi in Figures 1 and 2 does not indicate the amount of bismuth contained in n/Bi and birochlore type compounds.
is 1.0, and Ca/B i in FIGS. 3 and 4 is 0.25. Furthermore, Figure 5 shows the relationship between bismuth contained in a virochlore type compound and LC fluctuation due to annealing at 700°C, and Figure 6 shows the relationship between the amount of bismuth contained in a virochlore type compound and high temperature electrification (105°C,
DC2yrLA.

It shows the relationship with LC fluctuation after 1000h). Note that this sample uses an aluminum metallicon electrode. Furthermore, FIG. 7 shows the voltage-current characteristics of v100μA-VlmA of Example 9 and Conventional Example 73 shown in the table above, and FIGS. 8 and 9 show the voltage-current characteristics of the same sample used in FIG. This shows an X-ray diffraction graph, and the 8th
The figure shows the sintered body before heat treatment, and FIG. 9 shows the sintered body after heat treatment (700° C.).

As is clear from the above table and FIGS. 1 to 4, Ca
The proportion of birochlore contained in birochlore type compounds tends to increase as /B i and Sn/8i increase, and the range of Ca/B i and Sn/Bi where nonlinearity α becomes maximum is Ca/B It can be seen that i=0.05-0.5°Sn/B i =0.2-2.0.

In other words, Bi2O3 decreases due to the increase in birochlore-type compound bismuth matrix contained in the grain boundary segregation area of the sintered body, resulting in excellent nonlinearity, but Ca/B + , Sn/B
It is presumed that if i becomes too large beyond the upper limit, the reaction stage of birochlorization becomes too rapid, impairing sinterability. Furthermore, as is clear from the above table as well as from Figures 5 and 6, pi[''chlore type compounds containing bismuth damage of 50% or more have very little change in the nonlinear α characteristic due to thermal history and are excellent. This shows the characteristics of the varistor. Furthermore, as is clear from FIG. 7, the voltage drop in the conventional example without the presence of a virochlore type compound is significant in the low current range, whereas the voltage drop in the current example is only slight even in the low current range of 1 μA. The results showed that the leakage current was extremely small. However, the reason why the product according to the present invention exhibits the above-mentioned excellent effects is as clear from FIGS. 8 and 9, as it is clear from FIGS. This is because the birochlore-type compound contains 50% or more of the total bismuth contained in the sintered body, and the B12o3 phase, which changes in phase due to heat and purulent history, can be suppressed to a small extent.

It is assumed that a part of bismuth exists as vitrified bismuth that does not undergo phase change.

[Effects of the Invention] As described above, according to the present invention, it has excellent nonlinearity,
Moreover, it is possible to obtain an extremely stable varistor with high practical value without characteristic deterioration due to thermal history.

[Brief explanation of the drawing]

Figure 1 is a Ca/B i-α characteristic curve diagram, Figure 2 is a ca/B i-α characteristic curve diagram.
A correlation diagram of bismuth m contained in at-virochloa type compounds, Figure 3 is a Sn/Bi-α characteristic curve diagram, and Figure 4 is a diagram of S
Bismuth m contained in n/Bi-Birochlore type compound
Figure 5 is a ΔLC/LC characteristic curve diagram due to annealing between bismuth contained in a virochlore type compound, and Figure 6 is a diagram showing a ΔLC/LC characteristic curve between bismuth contained in a virochlore type compound and due to high temperature charging. , Figure 7 shows the current -
A voltage ratio characteristic curve diagram, FIG. 8 is an X-ray diffraction graph of the sintered body before heat treatment, and FIG. 9 is an X-ray diffraction graph of the sintered body after heat treatment. Patent application Marcon Electronics Co., Ltd. Ca/B Contained bismuth a (%) Fig. 1 tl 10u 100μm'aA 1
0W/ci'II (1) Fig. 7 Conventional example (W3). Implementation example (9) 2θ (den) D”/:CIVrOCillOr13 Conventional example (73) Tora Implementation example (9) sp:5pinel Dy:0/rOc+110re

Claims (1)

[Scope of Claims] The main component is zinc oxide, and contains at least additives of calcium, bismuth, tin, and antimony, and the relationships between calcium and bismuth, and between tin and bismuth in the additives are Ca/Bi=0.05 to 0.5, in the range of Sn/Bi=0.2 to 2.0, bismuth is converted to Bi_2O_3 and is 0.0.
In a sintered body containing 5 to 1.0 mol% of antimony and 0.05 to 3.0 mol% of antimony calculated as Sb_2O_3, the total amount of bismuth in the sintered body is A voltage nonlinear resistor characterized in that it contains 50% or more of a virochlore type compound.