JPH0439761B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a voltage nonlinear resistor made of a sintered body containing zinc oxide as a main component, which can be used for arresters, surge absorbers, etc., and a method for manufacturing the same. BACKGROUND OF THE INVENTION Zinc oxide-based voltage nonlinear resistors are manufactured using generally well-known ceramic sintering techniques.
The main component is zinc oxide (ZnO) powder, and it also contains bismuth oxide (Bi ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ), cobalt oxide (Co ₂ O ₃ ), manganese oxide (MnO ₂ ), and oxide. Chromium (Cr ₂ O ₃ ), silicon oxide (SiO ₂ ), boron oxide (B ₂ O ₃ ), aluminum oxide (Al ₂ O ₃ ), etc. are added and mixed thoroughly, followed by water and a suitable binder such as polyvinyl alcohol. is added, granulated and molded. This molded body has SiO ₂ −Sb ₂ O ₃ − on the side surface of the resistor for the purpose of preventing creepage.
Bi ₂ O ₃ ternary component is applied and the temperature is increased using an electric furnace.
Fire at 1000-1300℃. Finally, both the upper and lower end surfaces of the fired body are polished and adjusted to a predetermined thickness, and electrodes are formed by thermal spraying or baking to form a voltage nonlinear resistor. Recently, Bi ₂ O ₃ −B ₂ O ₃ −Ag ₂ O glass or
Non-linear resistors to which a small amount of ZnO-B ₂ O ₃ -SiO ₂ glass is added have significantly improved lifespan when applied with electricity, and are therefore put into practical use along with the above-mentioned voltage non-linear resistors without glass. Zinc oxide-based voltage nonlinear resistors have extremely superior voltage-current characteristics compared to conventionally known SiC and other materials. However, in practical terms, (1) improvement of low current region characteristics, especially reduction of leakage current (2) improvement of nonlinearity in wide current region (3) improvement of square wave withstand capability by square wave and impulse current (4) AC Alternatively, it is desired to improve DC charging life characteristics. FIG. 1 illustrates the internal structure of a conventionally known zinc oxide-based voltage nonlinear resistor. That is, the first
The figure is a schematic diagram of the internal microstructure of a conventional zinc oxide-based voltage nonlinear resistor, where 1 is a ZnO crystal grain;
2 means a spinel phase crystal grain, and 3 means a Bi ₂ O ₃ grain boundary phase. Each ZnO crystal grain has a diameter of about 10 μm,
It occupies most of the total volume of the sintered body. On the other hand, spinel phase crystal grains have a diameter of 1 to 2 μm, which is smaller than ZnO crystal grains, and are dispersed between ZnO crystal grains, particularly at triple points (where three crystal grains are in contact with each other). The composition is Zn ₇ Sb ₂ O ₁₂ , and Co, Mn, Cr, Ni, etc. are dissolved in solid solution. Bi ₂ O ₃ phase is ZnO in contact with it
This is effective for forming a potential barrier near the grain boundaries of crystal grains. Although the Bi ₂ O ₃ phase tends to condense at the triple points of particles, it has been confirmed that a layer with a high Bi atom concentration exists over a thickness of 20 to 200 Å even at boundaries where no boundary layer is observed. Figure 2 shows ZnO− in the composition shown in Figure 1 above.
This is a schematic diagram of the internal microstructure of a conventional zinc oxide-based resistor to which 1% by weight of B ₂ O ₃ -SiO ₂ -based glass is added. Synonymously, 4 means a glass phase. ZnO grain 1′,
The spinel phase crystal grains 2' and the Bi ₂ O ₃ phase 3' are arranged in the same way as in Figure 1, but precipitates of the glass phase 4 are scattered inside the Bi ₂ O ₃ phase 3' or in the boundary layer. I can see that it is. However, none of these conventional devices can be said to fully satisfy the above-mentioned practical needs. [Objective of the Invention] The object of the present invention is to reduce the intragranular resistance of ZnO, improve the flatness rate, and improve the charging life, while at the same time reducing the leakage current that increases due to the reduction in the intragranular resistance of ZnO. An object of the present invention is to provide a voltage nonlinear resistor with improved low current characteristics and a method for manufacturing the same. [Summary of the Invention] To summarize the present invention, the first invention of the present invention relates to a voltage nonlinear resistor, which includes a high resistance layer on the side surface of a sintered body mainly composed of zinc oxide (ZnO). In a voltage nonlinear resistor in which electrodes are formed on both the upper and lower end surfaces of the sintered body, the sintered body has 0.0003 to 0.03% by weight of aluminum diffused into the ZnO-based crystal grains, and It is characterized in that copper is diffused near the surface of the ZnO-based crystal grains. Further, the second invention of the present invention relates to a method for manufacturing a voltage nonlinear resistor, which contains zinc oxide as a main component and bismuth oxide as an additive component in an amount of 0.2 to 2 mol % in terms of Bi ₂ O ₃ . , silicon oxide ₁ to 4 mol% in terms of SiO2, cobalt oxide 0.8 to ₃ mol% in terms of _Co2O3 , antimony oxide 0.1 _{to 3} mol% in terms of _Sb2O3 , oxidation A composition containing 0.1 to 3 mol% of manganese in terms of _MnO2 , 0.1 to 2 mol% of chromium oxide _in terms of _Cr2O3 , and 0.0005 to _0.05 mol% of aluminum in terms of _Al2O3 . copper to
Mix raw material powder containing 0.1 to 2% by weight of copper-zinc borosilicate glass containing 0.001 to 20% by weight in terms of Cu ₂ O and 40 to 70% by weight in terms of zinc as ZnO.
Granulation, molding, attaching a high-resistance layer to the side surface and firing resulted in diffusion of 0.0003 to 0.03% by weight of aluminum into the ZnO-based crystal grains, and further diffusion of copper near the surface of the ZnO-based crystal grains. The method is characterized in that a sintered body is obtained and electrodes are formed on both upper and lower end surfaces of the sintered body. FIG. 3 is a schematic diagram of the internal microstructure of the voltage nonlinear resistor of the present invention, where the symbols 1'' to 3'' and 4' have the same meanings as in FIG. 2, and 5 means a copper diffusion layer. ZnO grain 1″, spinel phase grain 2″, Bi ₂ O ₃
Phase 3'' and glass phase 4' have the same structure as shown in Fig. 2, but Cu diffusion layer 5 is formed on the surfaces of ZnO crystal grain 1'' and spinel phase crystal grain 2''. Formed by the production method of the present invention.In particular, at a temperature of 1150 to 1300°C,
During calcination for hours, ZnO grains are formed and the glass powder is trapped in the bismuth oxide liquid phase while grain growth occurs. At the same time, Cu atoms are diffused to the surfaces of ZnO crystal grains and spinel phase crystal grains, and finally a diffusion layer is formed. The thickness of the diffusion layer is adjusted depending on the amount of copper oxide and firing conditions, but it is preferably 0.01 to 1 μm and about 1/10 to 1/10,000 of the crystal grain radius. The resistivity of this diffusion layer is measured to be between 10 and 100 Ωcm.
It is approximately 10 to 100 times higher than the ZnO crystal grain resistance of 1 to 2 Ω·cm. If this diffusion layer is formed near the Bi ₂ O ₃ boundary layer, the Schottky barrier is deformed, the barrier voltage increases, the leakage current decreases, and the flatness improves at the same time. FIG. 4 is a graph showing the relationship between current A (horizontal axis) and voltage (V/mm) of the present invention and the conventional voltage nonlinear resistor. In FIG. 4, 7 is the characteristic curve of the resistor of the present invention, and 8 is the conventional resistor containing neither copper borosilicate zinc glass nor Al (conventional product A).
characteristic curve, and 9 is the conventional aluminum nitrate
This is a characteristic curve of a resistor (conventional product B) containing both 0.02% by weight and 1% by weight of zinc borosilicate glass.
Compared to curve 8, in curve 9, the leakage current in the low current range increases due to the addition of Al, but the flatness rate improves. On the other hand, in curve 7 of the present invention, despite the addition of 0.02% by weight of aluminum nitrate, the presence of the Cu diffusion layer increases the barrier and reduces the leakage current in the low current range. The flatness rate also improves. Figure 5 shows the energizing time [(energizing time) 1/2] in the AC energizing life test of the present invention and the conventional resistor.
(horizontal axis) and leakage current increase rate (leakage current/initial current)
(horizontal axis) is a graph showing the relationship between curve 7' and
9' corresponds to curves 7 to 9 in FIG. The power application test was conducted at a power application rate of 85% and a temperature of 130°C. As is clear from FIG. 5, the charging characteristics of curve 7' are significantly improved compared to curve 8', and are even better than curve 9'. During firing, Cu atoms migrate from the glass phase to the ZnO crystal grains. ZnO belongs to an n-type semiconductor oxide, and conduction electrons are responsible for electrical conduction, but they are captured by Cu ions in the Cu diffusion layer and increase resistivity. The results of cutting out a part of the sintered body of the present invention and observing a thin section with an electron microscope show that the Bi ₂ O ₃ boundary layer tends to condense at the triple points of particles, but the boundary layer is very thin with a thickness of about 20 to 200 Å. Exist over a wide range of areas. A Cu diffusion layer is formed in such a portion, which significantly increases the barrier and improves voltage nonlinearity. The amounts of zinc oxide, boron oxide, and silicon oxide in copper-zinc borosilicate glass are selected in order to synthesize a transparent glass and to minimize the rate of increase in leakage current against constantly applied voltage, while at the same time making ZnO with a large nonlinear coefficient α.
In order to obtain a system voltage non-linear resistor, the above 0.1~
A range of 2% by weight is suitable. In addition, the amount of copper oxide in this glass ranges from 1/100th to 1/100th of the depth from the surface of the ZnO crystal grains.
In order to make a high resistance layer of several μm, the above-mentioned 0.001 to 20
A range of weight percent is suitable. On the other hand, the amount of aluminum oxide or aluminum nitrate is 0.0005 to 0.05 in terms of aluminum oxide.
Mol% is appropriate. At more than 0.05 mol%,
The leakage current increases and the nonlinear coefficient α decreases,
On the other hand, if it is less than 0.0005 mol %, the leakage current decreases, but the nonlinear coefficient α decreases over a wide current range, which is not preferable. The firing temperature is preferably in the range of 1150° to 1300°C.
If the temperature is lower than 1150°C, bubbles will occur, and if it exceeds 1300°C, bismuth oxide and antimony oxide will evaporate, resulting in a porous structure and a decrease in density, which is undesirable. In this temperature range, a healthy sintered body can be obtained, and in particular, a Cu diffusion layer with an appropriate thickness can be obtained. The glass phase has the effect of controlling the diffusion of Zn ions within the crystal grains, especially interstitial Zn ions, into the boundary layer when a voltage is applied, thereby preventing deterioration caused by the voltage application. [Examples of the Invention] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. In addition, FIG. 6 shows a resistor of one embodiment of the present invention,
Furthermore, Figure 7 shows a schematic diagram of the microstructure observed under a transmission electron microscope of thin sections obtained by cutting and polishing the resistor of conventional product A, and the inside of the ZnO crystal grains and the vicinity of the Bi ₂ O ₃ boundary layer. The energy dispersive X-ray spectrum of
It is a spectrum diagram shown in relation to line intensity. Furthermore, FIG. 8 shows the firing temperature (°C) (horizontal axis) and varistor voltage (V _1nA ) of the resistor of one embodiment of the present invention.
Nonlinear coefficient ( ₁₀ 〓 _A α _1nA ) and flatness rate (V _10KA /
V _1nA ) (each vertical axis). Example 1 To 7630 g of zinc oxide as the main component, 325 g of bismuth oxide (Bi ₂ O ₃ ), 166 g of cobalt oxide (Co ₂ O ₃ ), and 57 g of manganese oxide (MnO) were added as additives.
Accurately weigh 292 g of antimony oxide (Sb ₂ O ₃ ), 76 g of chromium oxide (Cr ₂ O ₃ ), 90 g of silicon oxide (SiO ₂ ), and 1.5 g of aluminum nitrate [Al(NO ₃ ) ₂・9H ₂ O]. In addition, 65% by weight of ZnO, 20% by weight of B ₂ O ₃ ,
86 g of copper-zinc borosilicate glass consisting of 10% by weight of SiO ₂ and 5% by weight of Cu ₂ O was weighed and wet mixed in a ball mill for 12 hours. After drying, the mixed powder is granulated into 20mm particles.
It was molded to φ×10mmt. SiO ₂ −Sb ₂ O ₃ in the molded body
−After applying the Bi ₂ O ₃ based high resistance layer, heat it to 1200℃.
It was baked for 2 hours. The upper and lower surfaces of this sintered body were polished and cleaned approximately 0.5 mm each using a Lapmaster to form Al sprayed electrodes. The results of comparing the electrical properties of the product of the present invention, conventional product A (does not contain aluminum nitrate or copper-zinc borosilicate glass), and conventional product B (contains 0.02% by weight of aluminum nitrate and 1% by weight of zinc borosilicate glass). Shown in Table 1. V _1nA is
The varistor voltage when 1mA is applied, ₁₀ 〓 _A α _1nA is the nonlinear coefficient, V _10KA /V _1nA is the limiting voltage ratio, and the deterioration caused by charging is due to temperature.
It shows the value obtained by dividing the leakage current corresponding to 85% V _1nA after 4 hours of electricity at 130°C and 95% electricity application rate by the leakage current before electricity application.

[Table] From Table 1, it can be seen that the electrical properties of the product of the present invention are improved in all characteristics compared to conventional values. Furthermore, as is clear from the comparison between Figures 6 and 7, the components of ZnO crystal grains include Zn, which is the main component, and
Some amounts of Si and Co are recognized. On the other hand, near the Bi ₂ O ₃ boundary layer, in addition to the main components Bi and Zn, a small amount of Si and
Although Co and the like are dissolved in solid solution, Cu is particularly detected in the sintered body of the present invention. Example 2 The same raw material powders as in Example 1 were mixed, granulated, and molded, then a high resistance layer was applied, and the sintered bodies were fired at various temperatures between 1000 and 1350°C, and electrodes were applied. The current characteristics were measured. Figure 8 shows firing temperature, varistor voltage V _1nA , nonlinear coefficient ₁₀ 〓 _A α _1nA , and flatness rate.
The relationship between V _10KA /V _1nA is shown graphically. V _1nA gradually decreases with firing temperature. The main reason for this is that crystal grain growth occurs and the barrier number decreases. _10〓
A α _1nA gradually increases with the firing temperature, but 1250
It shows maximum value at ℃ and decreases above 1300℃. The limiting voltage ratio V _10KA /V _1nA increases as the firing temperature increases. If the firing temperature is too low, ₁₀ 〓 _A α _1nA decreases, and at the same time bubbles are generated inside the sintered body, especially near the boundary layer, which is not preferable. On the other hand, if the firing temperature is too high, ₁₀ 〓 _A α _1nA will decrease significantly, V _10KA /V _1nA will increase, and at the same time, components will evaporate, which is not preferable. Example 3 SiO ₂ 1.5 mol%, Bi ₂ O ₃ 0.7 mol%, Co ₂ O ₃ 1 mol%, MnCO ₃ 0.5 mol%, Cr ₂ O ₃ so that the mixed powder containing zinc oxide as the main component weighs 8 kg. _0.5 mol%, _Sb2O31
Mol% _, 65 wt% ZnO - 10 wt% SiO ₂ - 20 wt% B ₂ O 3 for 0.005 mol% of Al( _{NO3 ) 3.9H2O}
-5 wt% Cu ₂ O glass was added in a range of 0 to 3 wt%, and the diameter was 50 mm in the same manner as in Example 1.
A voltage nonlinear resistor with a thickness of 23 mm and a thickness of 23 mm was fabricated. Table 2 shows the characteristic values of the sintered bodies for each amount of copper-zinc borosilicate glass. The power application time indicates the time until thermal runaway occurs when electricity is applied at a temperature of 100°C and an AC power application rate of 95%.

【table】

[Table] As is clear from Table 2 above, excellent properties are exhibited when the amount of copper zinc borosilicate glass is around 1% by weight. V _1nA is maximum, ₁₀ 〓 _A α _1nA = 50 maximum,
The minimum value of V _10KA /V _1nA is 1.76, and the maximum thermal runaway time determined by the voltage application test is over 3000 hours. The amount of copper borosilicate zinc glass added is 0.1 to 2
It can be seen that weight % is desirable. Example 4 The component amount of the copper-zinc borosilicate glass was changed in four ways from A to D as shown in Table 3, and the amount of the glass was further changed.
The characteristic values of the voltage non-linear resistors were measured in the same manner as in Example 3, with the amount of aluminum nitrate varied in the range of 0.05 to 3% by weight and the amount of aluminum nitrate varied in the range of 0.005 to 0.05% by weight.

[Table] For comparison of characteristic values, the case without copper-zinc borosilicate glass, the case with copper-zinc borosilicate glass,
The case without aluminum nitrate is also shown. These results are shown in Table 4.

【table】

〔Effect of the invention〕

As explained in detail above, according to the present invention,
By adding a small amount of copper-zinc borosilicate glass to the zinc oxide mixed powder, mixing it, and sintering it, the glass is dispersed near the Bi ₂ O ₃ boundary layer and at the same time the copper is diffused, increasing the barrier and widening the area. It is possible to achieve a remarkable effect of improving nonlinear characteristics over the current range.

[Brief explanation of drawings]

1 and 2 are schematic diagrams of the internal microstructure of a conventional zinc oxide-based nonlinear resistor, FIG. 3 is a schematic diagram of the internal microstructure of the voltage nonlinear resistor of the present invention, and FIG.
The figure is a graph showing the relationship between current and voltage of the voltage non-linear resistors of the present invention 7 and conventional 8 and 9, and Fig. 5 is a graph showing the energizing time and voltage in the AC energizing life test of the present invention and the conventional resistors. A graph showing the relationship with the leakage current increase rate, FIG. 6 is a schematic diagram of the fine structure of a resistor according to an embodiment of the present invention, and FIG. 7 is an example of a conventional resistor, observed using a transmission electron microscope. Energy-dispersive X-ray spectra of A within the ZnO crystal grains and B near the Bi ₂ O ₃ boundary layer, Figure 8 is a diagram of resistor 1 of the present invention.
It is a graph showing the relationship between firing temperature, varistor voltage, nonlinear coefficient, and flatness ratio in Examples. 1: ZnO crystal grains, 2: Spinel phase crystal grains, 3:
Bi ₂ O ₃ grain boundary phase, 4: glass phase, 5: copper diffusion phase.

Claims (1)

[Claims] 1. A voltage nonlinear resistor in which a high resistance layer is formed on the side surface of a sintered body mainly composed of zinc oxide (ZnO), and electrodes are formed on both upper and lower end surfaces of the sintered body. , the sintered body contains 0.0003~
0.03% by weight of aluminum diffuses and further the ZnO
A voltage nonlinear resistor characterized by copper diffused near the surface of system crystal grains. 2 Zinc oxide is the main component, and as additional components, bismuth oxide is 0.2 to 2 mol% in terms of Bi ₂ O ₃ , silicon oxide is 1 to 4 mol % in terms of SiO ₂ , and cobalt oxide is Co ₂ O ₃ 0.8 to 3 mol% converted to Sb 2 O 3, antimony oxide 0.1 to 3 mol% converted to Sb ₂ O ₃ , manganese oxide 0.1 to 3 mol % converted to MnO ₂ , chromium oxide to Cr ₂ O ₃ 0.1 to 2 mol% in terms of aluminum, 0.0005 to 0.05 mol% in terms of aluminum as Al ₂ O ₃
The composition containing copper is 0.001 to Cu ₂ O.
Raw material powder containing 0.1 to 2% by weight of copper borosilicate zinc glass containing 20% by weight and 40 to 70% by weight of zinc converted to ZnO is mixed, granulated, and formed, and a high-resistance layer is attached to the side surface. The inside of the ZnO crystal grains is
A sintered body in which 0.0003 to 0.03% by weight of aluminum is diffused and further copper is diffused near the surface of the ZnO-based crystal grains is obtained, and electrodes are formed on both upper and lower end surfaces of the sintered body. Manufacturing method of voltage nonlinear resistor. 3. The copper-zinc borosilicate glass contains copper oxide.
0.001-20% by weight, boron oxide 10-30% by weight,
5 to 20% by weight of silicon oxide and 40 to 40% of zinc oxide
Claim 2 which contains 70% by weight
2. Method for manufacturing a voltage nonlinear resistor described in Section 1. 4. The method for manufacturing a voltage nonlinear resistor according to claim 2, wherein the firing is performed in a temperature range of 1150 to 1300°C.