JPH0253932B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a zinc oxide-based voltage nonlinear resistor (hereinafter referred to as a varistor) containing bismuth that has excellent stability against thermal history. (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 is made by mixing zinc oxide as the main component with several to ten additives such as bismuth, cobalt, manganese, nickel, and chromium.
Electrodes are formed and put into practical use by coating and baking silver paste on both sides of the sintered body formed by granulating and sintering, or by metallizing the electrode metal. 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, there is a technique disclosed in Japanese Patent Publication No. 53-21509 or Japanese Patent Publication No. 60-38841 as a technique to meet such demands. The technology disclosed in Japanese Patent Publication No. 53-21509 (hereinafter referred to as the former) is to contain 10% or more of the Bi ₂ O ₃ contained in the sintered body as γ-Bi ₂ O ₃ , thereby reducing the DC load. The varistor is stable against pulsed currents and exhibits excellent varistor characteristics. Also, Special Publication No. 60-38841 (hereinafter referred to as the latter)
In the technology disclosed in 2003, bismuth borosilicate glass containing silver is added, and more than 90% by weight of Bi ₂ O ₃ in the sintered body is converted into body-centered cubic bismuth oxide (γ-
This invention relates to a varistor that has characteristics such that, by using Bi ₂ O ₃ ), the change in leakage current over a long period of time is extremely small even under extremely severe energizing conditions, and furthermore, it decreases over time. . In other words, in the former case, α-Bi ₂ O ₃ phase, β-
In addition to the Bi ₂ O ₃ phase and the γ-Bi ₂ O ₃ phase, the δ-Bi ₂ O ₃ phase is generated, and even if the sintered body does not contain the γ-Bi ₂ O ₃ phase at the time of firing, electrode baking or After thermal history such as reheating during use, α-Bi ₂ O ₃ phase, β-
We found that a stable varistor can be obtained when the γ-Bi ₂ O ₃ phase is 10% or more when the Bi 2 O 3 phase and _{the δ} -Bi ₂ O ₃ phase transform into the γ-Bi ₂ O ₃ phase. It is something. 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.
The sinter forms a pyrochlore crystal phase, which then decomposes to produce a spinel crystal phase and a liquid phase of bismuth oxide (), followed by the β-Bi ₂ O ₃ phase, δ, which is formed during the evolution of sintering of zinc oxide. - Re-sintering the sintered body containing the Bi ₂ O ₃ phase at 700°C in the atmosphere according to the method described in Journal of Applied Physics (Japan), Vol. 15 (1976), p. 1847. of bismuth oxide () in the sintered body by
It was discovered that a stable varistor can be obtained by changing over 90% of the phase to the γ-Bi ₂ O ₃ phase. As a result of various studies based on the above-mentioned technology, the present inventors found that both α, β, and
Bismuth oxide, which exhibits the Bi ₂ O ₃ phase of each δ, has a thermal history 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. Therefore, it transforms into γ-Bi ₂ O ₃ phase (phase change)
It was found that the voltage-current (-) characteristics deteriorate in the low current region. However, the inventors of the present invention have developed a bismuth compound that is stable to heat at the grain boundary segregation of crystal grains mainly composed of zinc oxide, which constitutes the sintered _body . Focusing on the fact that the phase change due to heat in the O ₃ phase can be reduced, various developments were carried out and the present invention was achieved. (Problems to be Solved by the Invention) As described above, in order to obtain a stable varistor, the formation of varistors at grain boundaries of crystal grains in a sintered body depends on the type of additives, calcination conditions, firing conditions, etc. Bi ₂ O ₃
Even if the desired amount of γ-Bi ₂ O ₃ phase is obtained in the phase, the remaining α, β, and δ Bi ₂ O ₃ phases will be affected by subsequent thermal history, that is, electrode baking and electrical energy during use. As a result, a phase change occurs, making it impossible to prevent the characteristics from deteriorating in the low current region. The present invention exists in grain boundary segregation areas in a sintered body.
The purpose of this invention is to provide an extremely stable varistor with excellent nonlinearity and no change over time by reducing the amount of the Bi ₂ O ₃ phase. [Structure of the Invention] (Means for Solving the Problems) The varistor of the present invention has zinc oxide as a main component, and contains at least lead, bismuth, tin, and antimony as additives, and the lead, bismuth, and If the relationship between tin and bismuth is Pb/Bi=0.05~0.5, Sn/Bi=0.2~2.0, bismuth is converted to Bi ₂ O ₃ and is 0.05~1.0.
Mol%, antimony converted to Sb ₂ O ₃ 0.05 to 3.0
50% or more of the total bismuth in the sintered body is composed of a pyrochlore type compound in the grain boundary segregation area of crystal grains containing zinc oxide as a main component in the sintered body containing mol%. It is something. (Function) According to the varistor having the above structure, 1000 It can be formed as a thermally stable substance that does not undergo transformation up to temperatures around ℃, and the amount of Bi ₂ O ₃ phase that changes to γ-Bi ₂ O ₃ phase during the thermal history process is minimized, and the deterioration of characteristics in the low current region is minimized. It is possible to obtain excellent nonlinear characteristics that cannot be obtained conventionally. (Example) Hereinafter, examples of the present invention will be described in detail.
Zinc oxide (ZnO) is the main component, and additives include bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO), tin oxide (SnO ₂ ), antimony oxide (Sb ₂ O ₃ ), cobalt oxide (CoO), Contains at least lead oxide, bismuth oxide, tin oxide, and antimony oxide from among the oxides of chromium oxide (Cr ₂ O ₃ ), nickel oxide (NiO), and manganese oxide (MnO), and contains lead and bismuth in the additives. Ceramic powder containing 0.05 to 1.0 mol% of Bi ₂ O _{3 and} 0.05 to 3.0 mol% of Sb ₂ O ₃ with a relationship between tin and bismuth in the range of Pb/Bi = 0.05 to 0.5 and Sn/Bi = 0.2 to 2.0. Granule molded and fired at a temperature of 1000 to 1300℃,
Electrodes are formed by applying silver baking, plating, or metallic coating to both sides of the obtained plate-shaped sintered body. The table shows the same conditions as for forming silver baked electrodes depending on the type and amount (mol%) of additives.
The amount of bismuth contained in the pyrochlore-type compound as a component of the grain boundary segregation between ZnO crystal grains, which was determined from the main peak intensity ratio of the X-ray diffraction of the sintered body subjected to °C heat treatment, and the electricity of the sintered body itself. In order to understand the physical characteristics, measurements were made by forming aluminum metallicon electrodes without thermal history.
α of V100μA-V1mA, V100μA-V1mA measured by forming a silver baked electrode with thermal history
, and also V1mA/mm. The sintered body used as a sample had a diameter of 14 mm, a thickness of 1 mm, and an electrode diameter of 13.4 mm. Next, let us make the results shown in the table above easier to understand.

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[Table] The following description will be made with reference to FIGS. 1 to 9. Figures 1 and 3 show the relationship between Pb/Bi or Sn/Bi and nonlinearity α (V100μA - V1mA), and Figures 2 and 4 show the relationship between Pb/Bi or Sn/Bi.
This shows the amount of bismuth contained in pyrochlore type compounds, and the Sn/
Bi is 1.0, Pb/Bi in Figures 3 and 4 is
When it is 0.25. In addition, Figure 5 shows the relationship between the amount of bismuth contained in the pyrochlore type compound and the LC fluctuation due to annealing at 700°C. ,1000h) after LC
This shows the relationship with fluctuations. Note that this sample uses an aluminum metallicon electrode. Furthermore, Fig. 7 shows the voltage-current characteristics of V100μA - V1mA 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. 7. The X-ray diffraction graphs are shown in FIG. 8 before heat treatment and FIG. 9 after heat treatment (700° C.) of the sintered body. As is clear from the above table and Figures 1 to 4, the ratio of bismuth contained in the pyrochlore type compound tends to increase as Pb/Bi and Sn/Bi increase, and the nonlinearity α is at its maximum. becomes
The range of Pb/Bi and Sn/Bi is Pb/Bi=0.05~
0.5, Sn/Bi=0.2 to 2.0. In other words, as the amount of bismuth contained in the pyrochlore type compound increases in the grain boundary segregation area of the sintered body, Bi ₂ O ₃ decreases and exhibits excellent nonlinearity, but Pb/Bi,
It is presumed that if Sn/Bi becomes too large beyond the upper limit, the reaction stage of pyrochlorization becomes too rapid, impairing sinterability. Furthermore, as is clear from the above table as well as Figures 5 and 6, pyrochlore compounds containing 50% or more of bismuth are excellent varistors with very little change in nonlinear α characteristics due to thermal history. It shows the characteristics. Furthermore, as is clear from Fig. 7, the voltage drop of the conventional example without the presence of a pyrochlore type compound is significant in the low current range, whereas the voltage drop of the present invention is 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 present invention exhibits the above-mentioned excellent effects is that pyrochlore is present in the grain boundary segregation between the crystal grains of the sintered body, as is clear from FIGS. 8 and 9. This is because the pyrochlore type compound contains 50% or more of the total bismuth contained in the sintered body, thereby suppressing the Bi ₂ O ₃ phase that changes in phase due to thermal history. 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 is possible to obtain an extremely stable varistor with excellent nonlinearity and no characteristic deterioration due to thermal history, and a high practical value.

[Brief explanation of the drawing]

Figure 1 is a Pb/Bi-α characteristic curve diagram, Figure 2 is
Figure 3 is a correlation diagram of the amount of bismuth contained in Pb/Bi-pyrochlore type compounds. Figure 4 is a diagram of the Sn/Bi-α characteristic curve. Figure 4 is a correlation diagram of the amount of bismuth contained in Sn/Bi-pyrochlore type compounds. Figure 5 is a graph showing the amount of bismuth contained in a pyrochlore type compound - △LC/LC characteristic curve due to annealing, Figure 6 is a graph showing the amount of bismuth contained in a pyrochlore type compound - △LC/LC characteristic curve due to high temperature charging, Figure 7 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.

Claims (1)

[Scope of Claims] 1 The main component is zinc oxide and contains at least additives of lead, bismuth, tin, and antimony, and the relationship between lead and bismuth and tin and bismuth in the additives is Pb/Bi=0.05 to 0.5. , Sn/Bi = 0.2 to 2.0, bismuth converted to Bi ₂ O ₃ is 0.05 to 1.0
Mol%, antimony converted to Sb ₂ O ₃ 0.05 to 3.0
A voltage nonlinear resistor characterized in that a pyrochlore type compound containing 50% or more of the total bismuth in the sintered body is contained in the grain boundary segregation part of crystal grains in the sintered body containing mol%. .