JP2010010466A - Method of manufacturing antimony-added zinc oxide varistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ZnO varistor having a higher varistor voltage, a higher non-linear index, and an excellent anti-charging deterioration characteristic with least addition of antimony Sb. <P>SOLUTION: The antimony-added zinc oxide varistor is manufactured by wet-mixing of silicon dioxide of 100 to 1,500 ppm in the average grain size of 5 to 10 nm added to zinc oxide of 98.8 mol%, bismuth oxide of 0.5 mol%, manganese oxide of 0.5 mol%, Co3O4 of 0.2 mol%, and water-soluble salt of antimony of 200 to 2,400 ppm, tentatively baking a mixture obtained, then milling the mixture, pressure-molding the milled mixture, and finally baking the molded mixture obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a zinc oxide (ZnO) varistor, particularly an antimony (Sb) -added zinc oxide varistor.

  ZnO varistors have steep voltage-current characteristics due to electrical barriers formed in the vicinity of grain boundaries, and are widely used as lightning arresters and protective devices for electronic devices. However, when the ZnO varistor is continuously used, the characteristics are deteriorated due to electrical stress. This is called electrical degradation, and is considered to be caused by distortion of the electrical barrier caused by movement of oxygen ions, interstitial Zn ions, or both through ZnO grain boundaries.

By the way, in the ZnO varistor for high voltage currently on the market, antimony trioxide (Sb ₂ O ₃ ) is added for the purpose of controlling the varistor voltage, but Sb is toxic and has a large environmental load. A ZnO varistor in which the amount of Sb added is as small as possible and is excellent in the electric charge deterioration characteristics is desired. In addition, about 2.6 mol% and 3.6 mol% of Sb and silicon (Si) are used in ZnO varistors for high voltage currently on the market, respectively.

As a result of investigating the influence of Sb on the voltage degradation characteristics by previous studies, the twin crystal formed by the addition of Sb changes the orientation of the ZnO crystal, and accordingly, the voltage degradation is suppressed. It is known (see Non-Patent Document 1).
Also, by adding 1.6 mol% or more of Sb ₂ O ₃ and silicon dioxide (SiO ₂ ) to the ZnO varistor, a varistor voltage of about 220 V / mm can be obtained, and by adding SiO ₂ It is known that the nonlinear index becomes smaller (see Non-Patent Document 2).

  However, in these conventional manufacturing methods, it is necessary to add Sb in an amount of 3.2 mol% or more. With a smaller amount of Sb added, the varistor voltage is high and the nonlinear index is high, and the electric charging deterioration characteristics are excellent. It was difficult to manufacture a ZnO varistor.

Masayuki Takada, Hiroyuki Yoshino, Shinzo Yoshimon, "Relationship between grain boundaries of ZnO varistors and electrical degradation", Electron Theory, 2006, Vol. 126, p. 105-112 T. Takemura, M. Kobayashi, Y. Takada, K. Sato, “Effects of Antimony Oxide on the Characteristics of ZnO Varistors” J. Am. Ceram. Soc, 1987, Vol. 70, No. 4, p. 237-241

  Accordingly, an object of the present invention is to provide a ZnO varistor having as little Sb addition as possible, a high varistor voltage, a high non-linear index, and excellent electric charging deterioration characteristics.

  In order to solve the above problems, the present invention provides zinc oxide 98.8 mol%, bismuth oxide 0.5 mol%, manganese oxide 0.5 mol%, tetracobalt trioxide 0.2 mol%, and antimony water-soluble salt 200-2400 ppm. A mixture of 100 to 1500 ppm of silicon dioxide having an average particle size of 5 to 10 nm is wet-mixed, the resulting mixture is temporarily fired and then pulverized, the pulverized product is pressure-molded, and the resulting molded product is subjected to main firing. Thus, a method for producing an antimony-added zinc oxide varistor is constituted. Here, ppm means molppm. The same applies hereinafter.

In the above configuration, the water-soluble salt of antimony is preferably antimony chloride or antimony nitrate. The wet mixing is preferably performed using water or ethanol.
Moreover, it is preferable that the said temporary baking is performed at the temperature of 500-800 degreeC in the air, and the said main baking is performed at the temperature of 1100-1200 degreeC in the air.

  According to the present invention, it is possible to manufacture a ZnO varistor having as little Sb addition as possible, a high varistor voltage, a high non-linear exponent, and excellent electrical charging deterioration characteristics.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a flowchart of a method for manufacturing a ZnO varistor according to an embodiment of the present invention.
As shown in FIG. 1, according to the present invention, first, zinc oxide 98.8 mol%, bismuth oxide 0.5 mol%, manganese oxide 0.5 mol%, tetroxide 3 mol 0.2 mol%, and antimony water-soluble salt 200 A mixture obtained by adding 100 to 1500 ppm of silicon dioxide having a nanoparticle (for example, an average particle diameter of 5 to 10 nm) to ˜2400 ppm is wet-mixed (step S <b> 1 in FIG. 1).
Here, antimony chloride (SbCl ₃ ) or antimony nitrate is used as a water-soluble salt of antimony. Moreover, wet mixing is performed for a predetermined time with a ball mill using water or ethanol, for example.

Next, the mixture obtained in step S1 is temporarily fired (step S2 in FIG. 1).
Specifically, the preliminary baking is performed in air at a temperature of 500 to 800 ° C. for a predetermined time.

Thereafter, the temporarily fired product obtained in step S2 is pulverized (step S3 in FIG. 1).
The pulverization is performed using, for example, a cemented mortar.

Then, the pulverized material obtained in step S3 is pressure-molded (step S4 in FIG. 1).
In this case, for example, it is formed into a disk shape having a diameter of 20 mm by vacuum pressing.

Furthermore, a ZnO varistor is formed by subjecting the above molded product to main firing (step S5 in FIG. 1).
Specifically, the main baking is performed in air at a temperature of 1100 to 1200 ° C. for a predetermined time.

Next, a ZnO varistor was actually manufactured by the method of the present invention, and it was examined whether or not the desired effect could be obtained.
[Example 1]
Zinc oxide 98.8 mol%, bismuth oxide 0.5 mol%, manganese oxide 0.5 mol%, tetracobalt tetroxide 0.2 mol%, and antimony chloride 2400 ppm added with silicon dioxide 100 ppm with an average particle size of 7 nm are ethanol. The mixture obtained was wet-mixed for 24 hours using a ball mill, and the resulting mixture was calcined in air at 600 ° C. for 3 hours and then pulverized, and the pulverized product was formed into a disk shape having a diameter of 20 mm by vacuum pressing. The obtained molded product was finally fired in air at 1150 ° C. for 3 hours to produce a ZnO varistor.
[Example 2]
A ZnO varistor was produced by adding 300 ppm of silicon dioxide in the same manner as in Example 1 except for silicon dioxide.
[Example 3]
A ZnO varistor was manufactured by adding 700 ppm of silicon dioxide in the same manner as in Example 1 except for silicon dioxide.
[Example 4]
A ZnO varistor was manufactured by adding 1500 ppm of silicon dioxide in the same manner as in Example 1 except for silicon dioxide.
[Comparative Example 1]
A ZnO varistor was produced in the same manner as in Example 1 except that silicon dioxide was not added without adding silicon dioxide.

[Comparison study 1]
Various characteristics of the ZnO varistors in Examples 1 to 4 and Comparative Example 1 were examined. For each sample, the non-linear exponent α before the deterioration of electric charge, the non-linear exponent α after the deterioration of electric charge (α _{30 min} ), the area intensity of the (002) plane of the ZnO crystal, and the varistor voltage were measured.

FIG. 2 is a graph showing measurement results of the non-linear exponent α before degradation of the ZnO varistors in Examples 1 to 4 and Comparative Example 1.
FIG. 3 is a graph showing the measurement results of the non-linear exponent α of the ZnO varistor after the deterioration of voltage application in Examples 1 to 4 and Comparative Example 1, and the area strength of the (002) plane of the ZnO crystal.
FIG. 4 is a graph showing measurement results of varistor voltages of ZnO varistors in Examples 1 to 4 and Comparative Example 1.

[Example 5]
A mixture of 98.8 mol% of zinc oxide, 0.5 mol% of bismuth oxide, 0.5 mol% of manganese oxide, 0.2 mol% of 3 cobalt oxide and 200 ppm of antimony chloride and 100 ppm of silicon dioxide having an average particle diameter of 7 nm The mixture obtained was wet-mixed for 24 hours using a ball mill, and the resulting mixture was calcined in air at 600 ° C. for 3 hours and then pulverized, and the pulverized product was formed into a disk shape having a diameter of 20 mm by vacuum pressing. The obtained molded product was finally fired in air at 1150 ° C. for 3 hours to produce a ZnO varistor.
[Example 6]
A ZnO varistor was produced by adding 300 ppm of silicon dioxide in the same manner as in Example 5 except for silicon dioxide.
[Example 7]
A ZnO varistor was manufactured by adding 700 ppm of silicon dioxide in the same manner as in Example 5 except for silicon dioxide.
[Example 8]
A ZnO varistor was produced by adding 1500 ppm of silicon dioxide in the same manner as in Example 5 except for silicon dioxide.
[Comparative Example 2]
A ZnO varistor was manufactured in the same manner as in Example 5 except that silicon dioxide was not added without adding silicon dioxide.

[Comparison study 2]
Various characteristics of the ZnO varistors in Examples 5 to 8 and Comparative Example 2 were examined. For each sample, the non-linear exponent α before the deterioration of electric charge, the non-linear exponent α after the deterioration of electric charge (α _{30 min} ), the area intensity of the (002) plane of the ZnO crystal, and the varistor voltage were measured.

FIG. 5 is a graph showing measurement results of the non-linear exponent α before degradation of the ZnO varistors in Examples 5 to 8 and Comparative Example 2.
FIG. 6 is a graph showing the measurement results of the non-linear exponent α of ZnO varistors after degradation of voltage applied in Examples 5 to 8 and Comparative Example 2, and the area intensity of the (002) plane of the ZnO crystal.
FIG. 7 is a graph showing measurement results of varistor voltages of ZnO varistors in Examples 5 to 8 and Comparative Example 2.

なお、Ｉ_Ｎは定数であり、Ｖ_１ｍＡは電流を１ｍＡ流したときの電圧で降伏電圧を示す尺度でありバリスタ電圧と呼ばれる。
また、課電劣化前後の測定には同じ試料を用いた。試料は、空気中で直流電流１００ｍＡ／ｃｍ^２を、合計時間で３０分間流して課電劣化させた。 Here, the value of the nonlinear index α was calculated by using the following equation 1 by measuring the voltage-current characteristic by a constant current method in a current range of 10 ⁻⁸ to 10 ⁻⁴ A.

Note that I _N is a constant, and V _{1 mA} is a voltage indicating a breakdown voltage as a voltage when a current of 1 mA flows, and is called a varistor voltage.
In addition, the same sample was used for the measurement before and after the degradation of electric power. The sample was subjected to voltage degradation by applying a direct current of 100 mA / cm ² for 30 minutes in the air.

  As can be seen from FIG. 2, the values of the nonlinear index α of the ZnO varistors of Examples 1 to 4 are about 40 to 60, and samples having high nonlinearity comparable to that of the ZnO varistor of Comparative Example 1 were obtained.

  As can be seen from FIG. 3, the value of the nonlinear index α after 30 minutes of degradation of the voltage applied to each ZnO varistor is about 7 in the ZnO varistor of Comparative Example 1, whereas in the ZnO varistors of Examples 1 to 4. Increased as the amount of Si added was increased. In particular, the ZnO varistor of Example 3 was about 35, showing a maximum value. It can also be seen that the area strength of the (002) plane increases as the amount of Si added increases. This is considered to be a result of suppressing the deterioration of electric charging because the addition of Si causes a change in the surface free energy at the grain boundary and affects the orientation of the ZnO crystal.

  As can be seen from FIG. 4, the varistor voltage of the ZnO varistors of Examples 1 to 4 is about 220 V / mm or more, which is sufficiently higher than the varistor voltage of about 165 V / mm, which is the varistor voltage of the ZnO varistor of Comparative Example 1. A sample with was obtained. In particular, the varistor voltage of the ZnO varistor of Example 2 showed a maximum value of about 240 V / mm. This is considered to be due to the fact that a new barrier is formed at the twin interface even if there is no effect of suppressing the growth of ZnO particles due to the addition of silicon dioxide having a small average particle diameter.

  As can be seen from FIG. 5, the non-linear index α of the ZnO varistors of Examples 5 to 8 is about 40 to 50, and a sample having high non-linearity similar to that of the ZnO varistors of Examples 1 to 4 is obtained. It was.

  As can be seen from FIG. 6, the value of the nonlinear index α after 30 minutes of degradation of the voltage applied to each ZnO varistor is about 16 in the ZnO varistor of Comparative Example 2, whereas in the ZnO varistors of Examples 5-7. Increased as the amount of Si added increased, and in particular, the ZnO varistor of Example 5 was about 24, indicating a maximum value. It can also be seen that the area strength of the (002) plane becomes weaker as the amount of Si added is increased. This is considered to be a result of suppressing the deterioration of electric charging because the addition of Si causes a change in the surface free energy at the grain boundary and affects the orientation of the ZnO crystal.

  As can be seen from FIG. 7, the varistor voltages of the ZnO varistors of Examples 6 to 8 are about 160 V / mm or more, which is sufficiently higher than the varistor voltage of about 120 V / mm which is the varistor voltage of the ZnO varistor of Comparative Example 2. A sample with was obtained. As described above, a sample in which the varistor voltage was increased by the addition of silicon dioxide was obtained even in the ZnO varistor having the Sb addition amount of 200 ppm.

Furthermore, since Example 3 had the best electrical degradation characteristics, the following ZnO varistors were manufactured in order to examine how much the amount of Sb added can be reduced.
[Example 9]
A mixture of 98.8 mol% of zinc oxide, 0.5 mol% of bismuth oxide, 0.5 mol% of manganese oxide, 0.2 mol% of tetracobalt tetroxide, and 200 ppm of antimony chloride with 700 ppm of silicon dioxide having an average particle diameter of 7 nm is added to ethanol. The mixture obtained was wet-mixed for 24 hours using a ball mill, and the resulting mixture was calcined in air at 600 ° C. for 3 hours and then pulverized, and the pulverized product was formed into a disk shape having a diameter of 20 mm by vacuum pressing. The obtained molded product was finally fired in air at 1150 ° C. for 3 hours to produce a ZnO varistor.
[Example 10]
A ZnO varistor was produced in the same manner as in Example 9 except that antimony chloride was used as 800 ppm of antimony chloride.
[Example 11]
A ZnO varistor was produced in the same manner as in Example 9 except for antimony chloride, using 1600 ppm of antimony chloride.
[Example 12]
A ZnO varistor was produced in the same manner as in Example 9 except for antimony chloride, using 2400 ppm of antimony chloride.

[Comparison study 3]
Various characteristics of the ZnO varistors in Examples 9 to 12 were examined. For each sample, the non-linear exponent α after voltage degradation and the varistor voltage were measured.

FIG. 8 is a graph showing the measurement results of the varistor voltage of the ZnO varistors in Examples 9-12.
FIG. 9 is a graph showing the measurement results of the non-linear exponent α after the degradation of ZnO varistors in Examples 9-12.

  As can be seen from FIG. 8, by increasing the amount of Sb added, the varistor voltage of the ZnO varistor of Example 9 was increased to about 160 V / mm, and the varistor voltage of the ZnO varistors of Examples 10 to 12 was about 200. It became constant at ˜230 V / mm.

  As can be seen from FIG. 9, by increasing the amount of Sb added, the nonlinear index α of the ZnO varistor of Example 9 was about 19, and the nonlinear index α of the ZnO varistors of Examples 10 to 12 was about 34. .

  From the above, according to the present invention, in particular, in the ZnO varistors of Examples 10 and 11, the Sb addition amount was about 1/30 and the Si addition amount was about 1/50. ZnO varistors having a non-linear index α of about 45 V and a non-linear index α of about 45) and a non-linear index α of about 34).

It is a flowchart of the manufacturing method of the ZnO varistor by one Example of this invention. 6 is a graph showing measurement results of nonlinear exponent α before degradation of ZnO varistors in Examples 1 to 4 and Comparative Example 1. It is the graph which showed the measurement result of the area | region intensity | strength of the nonlinear index | exponent α after the electrical charging degradation of the ZnO varistor in Examples 1-4 and the comparative example 1, and the ZnO crystal | crystallization. 4 is a graph showing measurement results of varistor voltages of ZnO varistors in Examples 1 to 4 and Comparative Example 1. FIG. It is the graph which showed the measurement result of the nonlinear index | exponent (alpha) before the charging deterioration of the ZnO varistor in Examples 5-8 and the comparative example 2. FIG. It is the graph which showed the measurement result of the area | region intensity | strength of the nonlinear index | exponent α after the electrical charging degradation of the ZnO varistor in Examples 5-8 and the comparative example 2, and the Zn002 crystal | crystallization. 6 is a graph showing measurement results of varistor voltages of ZnO varistors in Examples 5 to 8 and Comparative Example 2. It is the graph which showed the measurement result of the varistor voltage of the ZnO varistor in Examples 9-12. It is the graph which showed the measurement result of the nonlinear index | exponent after the electrical charging degradation of the ZnO varistor in Examples 9-12.

Claims (4)

  100% of silicon dioxide having an average particle diameter of 5 to 10 nm was added to 98.8 mol% of zinc oxide, 0.5 mol% of bismuth oxide, 0.5 mol% of manganese oxide, 0.2 mol% of 3 cobalt oxide and 200 to 2400 ppm of an antimony water-soluble salt. A mixture with ˜1500 ppm added is wet-mixed, the resulting mixture is calcined and then pulverized, the pulverized product is pressure-molded, and the resulting molded product is calcined to produce an antimony-added zinc oxide varistor. Method.   The method of claim 1, wherein the water-soluble salt of antimony is antimony chloride or antimony nitrate.   The method according to claim 1 or 2, wherein the wet mixing is performed using water or ethanol.   The said temporary baking is performed in the temperature of 500-800 degreeC in the air, and the said main baking is performed in the temperature of 1100-1200 degreeC in any one of the Claims 1-3 characterized by the above-mentioned. the method of.

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