JPH0831615A - Voltage non-linear resistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a dense and homogeneous voltage non-linear resistor having less holes, excellent energy resistance, small evenness rate in current-voltage characteristics, and less deterioration by moisture absorption in electric characteristics. CONSTITUTION:This is a voltage non-linear resistor mainly composed of zinc oxide, and the hole rate of diameter of 1mum or smaller measured by a mercury porosimeter is 5mul/g or smaller. This voltage non-linear resistor is manufactured by a two-staged calcination system in which an in-the-air firing operation is conducted after raw material is mixed and molded into the prescribed shape, and then a firing operation is conducted again in an oxidizing atmosphere. As a result, the voltage non-linear resistor, having excellent energy resistance and a small evenness rate, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage non-linear resistor and a method for manufacturing the same, and more specifically, to a voltage suitable for use in a lightning arrester, a surge absorber, etc. The present invention relates to a non-linear resistor and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, it is well known that a sintered body obtained by adding bismuth oxide, cobalt oxide or another oxide to zinc oxide exhibits remarkable voltage non-linearity and absorbs a steep (surge) current. Surge to protect the circuit elements by
It is widely used as an arrester and a lightning arrester to protect power equipment from abnormal voltage such as lightning strike.

A typical conventional sintered body has a structure as shown in the schematic diagram of the fine structure shown in FIG.
That is, the spinel particles 1 made of an antimony compound having a particle size of about 1 μm to several μm are mainly composed of those existing in the zinc oxide particles 2 and bismuth oxide 3 existing near the triple point (multipoint) of zinc oxide. There are two states, that is, the inside of the grain boundary layer and the one existing adjacent thereto. It can be seen that part of the bismuth oxide 3 penetrates not only to the multiple points but also to the deep part between the zinc oxide particles 2. 4 in the figure
It is a twin boundary in zinc oxide.

It is clear from the experiment using the point electrode that the particles containing zinc oxide as a main component themselves merely act as a resistor and exhibit voltage non-linearity at the boundary between the zinc oxide particles 2 and the zinc oxide particles 2. (GD Mahan, LM Levin
son and HR Phillip, “Theo-ry of conduction in ZnO
varistors ", J.Appl.Phys.50 (4) 2799 (1979)). It has been confirmed by experiments that the number of boundaries (grain boundaries) between the zinc oxide particles 2 and the zinc oxide particles 2 determines the varistor voltage. .

A sintered body containing zinc oxide as a main component having such a fine structure usually has a voltage-current (VI) characteristic as shown in FIG. This VI curve is divided into three regions due to the physical mechanism. (1) A region where the current is limited by the Schottky barrier at the grain boundary and the leakage current is small with respect to the applied voltage. (In a region including L in FIG. 9, a typical value is about φ (diameter) 100
For devices with a size of mm, 10 μA is generally chosen. (2) A region where the applied voltage increases, the tunnel current passing through the grain boundaries increases, and the resistance sharply decreases with respect to the applied voltage. (In the region including S in FIG. 9, 1 to 3 mA is generally selected for a device having a size of about φ100 mm as a typical value.) (3) VI region determined by the resistance of ZnO itself . (In the region including H in FIG. 9, a typical value is about φ100 mm.
10 kA is generally chosen for devices of size. )

In the zinc oxide particles in the sintered body, which is an n-type semiconductor, an electron trap level is formed at the interface when excess oxygen is adsorbed at the crystal grain boundary, and the electron is trapped there, so that the grain interface is formed. A depletion layer in which no electrons exist is generated along with this, and eventually an electronic barrier (Schottky barrier) is formed at the grain boundary portion. Therefore, the larger the barrier height of the Schottky barrier is, the smaller the leakage current is, and the resistance is more excellent in flatness in the small current region. The electrical characteristics at the grain boundaries greatly affect the flatness of the small current region, while the resistance of zinc oxide itself greatly affects the flatness of the large current region. If the resistance of zinc oxide itself increases, the flatness deteriorates, so the resistance of zinc oxide itself should be small.

In recent years, in the field of electric power, as the transmission voltage has become higher, there has been a strong demand for higher performance of the arrester in order to protect various transmission equipment. In order to meet this requirement, a voltage non-linear resistor having more excellent characteristics, for example, a flatness factor (representing the non-linearity of the resistor, which is an important element of lightning arrester characteristics, as shown in FIG. is the ratio V _H / V _L of the voltage V _L of the voltage V _H and the small-current region L in H,
In particular, the ratio V _S / V _L with the varistor voltage V _S is smaller than the flatness ratio in the small current region, and V _H / V _S is the flatness ratio in the large current region. The market demand for devices with excellent withstand capability is ever increasing.

In order to reduce the flatness, the voltage non-linearity of the resistor is improved, that is, the barrier height of the Schottky barrier existing at the grain boundaries between the zinc oxide particles is increased, and the energy is increased. In order to improve the durability, it is necessary to establish a manufacturing technique that enables the entire resistor to be dense and uniform. For this reason, experiments of additive effects have been repeated. However, in the conventional technique, the effect of improving the flatness ratio of the large current region deteriorates the flatness ratio of the small current region at the same time, and the effect of improving the flatness ratio of the small current region decreases the flatness ratio of the large current region at the same time. Made it worse. Therefore,
As a method of reducing the flatness rate in both the large current region and the small current region, we tried firing in an oxidizing atmosphere.

In order to supply sufficient oxygen to the grain boundaries between the zinc oxide crystal grains, the diffusion rate of the liquid is generally higher than that of the solid, so that the grain boundary layer containing bismuth oxide as the main component is melted. Baking for a long time in the temperature range is desirable. However, it has been found that firing in an oxidizing atmosphere can reduce the flatness ratio in the small current region by 20 to 40%, but the number of pores in the sintered body increases, causing a problem in moisture resistance.

Since it is a sintered body, it is inevitable that some holes are present in the resistor. However, the diameter is 1 μm
If the following small holes are too numerous, they will absorb moisture when used in a high humidity environment, and will affect the voltage-current characteristics. In particular, lightning arresters are required to have stable characteristics and high reliability even when used in all environments because of their role of protecting electric power equipment. Therefore, the change in electrical characteristics due to humidity becomes a problem.

In addition, several zinc oxide crystal grains (φ100 μ
If there are many relatively large pores (about m), the resistor loses its denseness and its density becomes small. Since the current distribution is not uniform in such a resistor, when a high-energy surge is applied, the heat generation temperature rises locally, the voltage-current characteristics deteriorate, and the current flows even more locally. Fall into a vicious circle. Then, element breakdown is likely to occur, and the energy withstand capability decreases.

[0012]

In the voltage non-linear resistor as described above, if the firing is carried out in an oxidizing atmosphere, the flatness of the small current region, which was difficult in the firing in air, can be greatly improved. However, there is a problem that the porosity is increased, the energy resistance is lowered, and the electric characteristics are newly deteriorated due to moisture absorption. The present invention has been made to solve such a problem, and has a small number of holes in the sintered body, is dense, is uniform throughout the resistor, is excellent in energy resistance, and has a small flatness ratio. It is an object of the present invention to obtain a voltage non-linear resistor containing zinc oxide as a main component and a method for manufacturing the same.

[0013]

The invention according to claim 1 of the present invention comprises zinc oxide as a main component, bismuth oxide,
A voltage non-linear resistor containing antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide,
The porosity at a diameter of 6 nm to 1 μm at any portion is 5 μl (microliter) / g or less.

The invention according to claim 2 of the present invention comprises zinc oxide as a main component, bismuth oxide, antimony oxide,
A voltage non-linear resistor containing chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide, wherein the bulk density of the whole sintered body is calculated from the simple mole fraction of the raw material. The theoretical density is 94 to 97%.

The invention according to claim 3 of the present invention comprises zinc oxide as a main component, bismuth oxide, antimony oxide,
A voltage non-linear resistor containing chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide, wherein the difference between the maximum and minimum of the bulk density distribution of the entire sintered body is 3 of the average value. % Or less.

The invention according to claim 4 of the present invention comprises zinc oxide as a main component, bismuth oxide, antimony oxide,
Raw materials containing chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide are weighed, mixed and molded into a predetermined shape,
A method of manufacturing a voltage non-linear resistor according to a two-step firing method in which first-step firing is performed in air and second-step firing is performed again in an oxidizing atmosphere. Then, the temperature raising rate in at least a part of the temperature range from 500 ° C. to the maximum firing temperature is 30 ° C./hour or less, and in the temperature raising process in the second stage firing, the temperature raising rate is 50 to 500 ° C./hour. In addition, in the temperature lowering process in the second stage firing, the maximum firing temperature is 950 ° C. or higher and does not exceed the maximum firing temperature in the first stage, and the temperature lowering rate change point is 900 to 650 ° C. The temperature decrease rate from the temperature to this temperature decrease rate change point is 15 to 2
The temperature decreasing rate from the temperature change rate changing point to the room temperature is 50 ° C./hour or less.

[0017]

According to the first aspect of the present invention, when the porosity in the voltage non-linear resistor is 5 μl / g or less, the number of voids in the resistor is small and the electrical characteristics are not deteriorated by moisture absorption.

According to the second aspect of the present invention, the bulk density is 94 to 97% of the theoretical density, and the sintering becomes extremely dense.

In the third aspect of the present invention, the variation of the bulk density is 3% or less, the inside of the sintered body is made uniform and dense, and the energy resistance is good.

According to the fourth aspect of the present invention, the sintering reaction is allowed to proceed slowly during the first-stage firing in air, so that the sintered body has few pores, is dense, and is homogeneous throughout. To get Then, during the second-step firing in an oxidizing atmosphere, which is performed next, sufficient oxygen is supplied to the grain boundaries between the zinc oxide crystal grains to increase the barrier height of the Schottky barrier at the grain boundary portions. By these actions, a voltage non-linear resistor having excellent energy resistance and a small flatness is obtained.

[0021]

EXAMPLE As described above, the voltage non-linear resistor of the present invention contains zinc oxide as a main component and contains bismuth oxide, antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and It is produced by a production method characterized by a two-step firing method in which boron oxide is mixed and mixed, shaped into a predetermined shape, fired in air, and fired again in an oxidizing atmosphere.

Bismuth oxide usually has an average particle size of 1 to 5 μm.
m is used. The blending amount of this bismuth oxide is
When it is more than 5 mol (mol)%, it has an adverse effect on the zinc oxide particle growth inhibitory effect, and 0.1 mol
If it is less than%, the leakage current increases. Therefore,
It is desirable that the raw material of the voltage non-linear resistor (hereinafter, simply referred to as raw material) is contained in an amount of 0.1 to 5 mol%, particularly preferably 0.2 to ₂ mol% in terms of Bi ₂ O _3. .

Antimony oxide has the property of increasing the varistor voltage. As such antimony oxide, one having an average particle diameter of 0.5 to 5 μm is usually used. When the compounding amount of this antimony oxide is more than 5 mol%, a large amount of spinel particles (insulators) that are a reaction product with zinc oxide exist, and the current-carrying path is greatly limited, so that the energy resistance is small. When the amount is less than 0.5 mol%, the effect of suppressing the growth of zinc oxide particles cannot be sufficiently exerted. Therefore, 0.5 to 5 m in terms of Sb ₂ O ₃ in the raw material
It is desirable to prepare it so as to contain ol%, particularly preferably 0.7 to 2 mol%.

Further, in the voltage non-linear resistor of the present invention, chromium oxide, nickel oxide, cobalt oxide, manganese oxide and silicon oxide are blended in order to improve the voltage non-linearity. As these components, it is usually preferable to use those having an average particle size of 5 μm or less. In order to provide sufficient voltage non-linearity, the ingredients are mixed in the respective raw materials such as NiO, Co ₃ O ₄ , and Mn.
It is desirable that the content is adjusted to be 0.1 mol% or more, particularly preferably 0.2 mol% or more in terms of ₃ O ₄ and SiO ₂ . However, if the blending amount is more than 5 mol%, the amount of the spinel phase, the pyrochlore phase (intermediate reaction substance of spinel forming reaction) and the zinc silicate, which are insulators, increases, and the current-carrying path bends. In addition, the energy withstand capability tends to decrease and the voltage non-linearity tends to deteriorate. Therefore, NiO, Co ₃ O ₄ , M
It is desirable that the content is adjusted to 3 mol% or less, particularly preferably 2 mol% or less in terms of n ₃ O ₄ and SiO ₂ .

Further, in the present invention, in order to reduce the resistance of the zinc oxide particles and improve the voltage non-linearity, the bismuth oxide is further made to have a lower melting point, its fluidity is improved, and voids existing between the particles are improved. In order to effectively reduce the pores, for example, aluminum oxide is converted into Al ₂ O ₃ in an amount of 0.0001 to 0.01 mol%, and boron oxide is converted into B ₂ O _3.
The amount may be 0.001 to 0.1 mol% in the raw material.

The balance of the raw material of the voltage non-linear resistor is zinc oxide, but from the comprehensive viewpoint of improving the voltage non-linearity, improving the energy resistance and extending the life, the content of zinc oxide is ZnO in the raw material. It is desirable to prepare such that the content is 90 to 97 mol%, particularly preferably 92 to 96 mol%.

Next, a method of manufacturing the voltage nonlinear resistor of the present invention made of the above-mentioned raw materials will be described. First, the average particle diameter of the raw material is appropriately adjusted using a ball mill or the like, and then a slurry is formed using, for example, a polyvinyl alcohol aqueous solution, and dried using a spray dryer or the like to granulate. The obtained granulated powder is, for example, 200 to
Uniaxial pressure is applied with a pressure of about 500 kgf / cm ² to produce a powder compact having a predetermined shape. In order to remove the binder (for example, polyvinyl alcohol) from the powder compact, the powder compact is preheated at a temperature of about 600 ° C. and then fired.

The firing in the first stage has a maximum temperature of 1000 to 1300 ° C., preferably 11 at least in air.
0 to 1270 ° C for 1 to 20 hours, preferably 3 to
Hold for 10 hours. The temperature rising process by this firing is
In order to improve the fluidity of bismuth oxide, which is the main component of the grain boundary existing between zinc oxide particles, and effectively reduce the pores remaining between particles, in the melting temperature range of bismuth oxide of 500 ° C or higher, 30 ° C / less than hr (hour), preferably 25 ° C / h
r or less.

The firing in the second stage is preferably adjusted so that the oxygen partial pressure is at least 80% by volume or more in an oxidizing atmosphere. Since the first-stage firing resulted in a dense, dense, and homogeneous sintered body with few pores, oxygen deficiency of the zinc oxide particles was reduced by this firing, and excess oxygen was removed between the zinc oxide particles. The purpose is to supply the world. Therefore, the fluidity of bismuth oxide, which is the main component of the grain boundaries existing between the zinc oxide particles, is improved, and oxygen is supplied through bismuth oxide, which is a good conductor of oxygen ions, to increase the barrier height of the Schottky barrier. It has a higher effect. Therefore, in the temperature rising process, 50 to 500 ° C
/ Hr, preferably 100 to 200 ° C./hr, and in the temperature decreasing process, around the crystallization temperature region of bismuth oxide and its vicinity, that is, the temperature decreasing rate change point (650 to 900).
(C) as a boundary, the rate of temperature decrease is preferably 15 to 200 ° C / hr in the first half, preferably 30 to 150 ° C / hr, and 50 ° C / hr or less in the latter half, preferably 30 ° C / hr or less.

Under the above conditions, the solid phase reaction sufficiently occurs,
Sintering reaction proceeds sufficiently, it is a condition for obtaining a sintered body having more excellent characteristics, in particular, because the crystallization temperature range of bismuth oxide that changes the cooling rate is slightly different depending on the composition, For example, it can be set by using TMA (thermal analysis device) or the like. The voltage non-linear resistor of the present invention is excellent in energy resistance and has a small flatness ratio by the method of first firing in air and then second firing in an oxidizing atmosphere. It is possible to meet the demand for higher performance of the element, which has excellent moisture resistance.

Next, the voltage non-linear resistor of the present invention and the method for manufacturing the same will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1. Samples 1-9 and comparative samples 1-11. Zinc oxide, bismuth oxide, antimony oxide, chromium oxide, nickel oxide,
Cobalt oxide, manganese oxide, silicon oxide, aluminum oxide, and boron oxide were each converted into the form shown in Table 1 to adjust the content.

[0033]

[Table 1]

The zinc oxide is synthesized by a dry method (sublimation method) and has an average particle diameter of 1 μm, antimony oxide has an average particle diameter of 5 μm, and other raw materials have an average particle diameter of about 5 μm or less. Was prepared as follows. In addition, the purity of the raw material was set to industrial grade (99.0 to 99.9%).

Next, the above raw materials and a polyvinyl alcohol aqueous solution as a binder were mixed using a disper mill to form a slurry, which was then dried using a spray dryer and granulated. 200-500 the obtained granulated powder
Uniaxial pressure was applied with a pressure of kgf / cm ² to obtain a powder compact. In each of Samples 1 to 9 and Comparative Samples 1 to 7, the nominal diameter was 125 mm and the thickness was 30 mm. These powder compacts were preheated at 600 ° C. for 5 hours to remove the binder.

Subsequently, firing was performed under the conditions shown in Table 2 for firing atmosphere and maximum temperature. However, the firing temperature pattern is as shown in FIGS. 1 (a) and 1 (b), where Va is the heating rate from 500 ° C. to the maximum firing temperature in the first-stage firing, and Vb is the maximum firing temperature in the first-stage firing. , Vc is the temperature increase rate up to the maximum firing temperature in the second-stage firing, Ta is the maximum firing temperature in the second-stage firing, and Vd is the temperature reduction from the maximum firing temperature in the second-stage firing to the temperature-falling rate change point. Velocity, Tb represents a temperature decrease rate change point in the second stage firing, and Ve represents a temperature decrease rate after the temperature decrease rate change point in the second stage firing.

[0037]

[Table 2]

The voltage non-linear resistance element thus obtained was polished,
After washing, an aluminum electrode was formed and various electrical characteristics were measured. In the _{measurement, V L = V 10 μ A} , V S = V
_3mA , _VH = _V10KA . Table 3, the second step firing relative to the measured value of the flatness ratio (V _H / V _S) after the first stage baking of the respective flat rate (V _S / V _L) and a large current region of the small-current region The rate of change after is shown.

[0039]

[Table 3]

After measuring the electrical characteristics, these devices were cut and the porosity and bulk density were measured. 5 from the element center
After cutting out a square mm sample, polishing paper # 320 to # 8
The porosity (μl / g) of a sample whose surface was sequentially polished using up to 00 was measured by a mercury porosimeter (commercially available product: Shimadzu Poisizer 9310, pressure measurement range 0 to 30).
000 psi, pore diameter of 6 nm or more can be measured). An example of the measurement result is shown in FIG.

Here, the diameter of zinc oxide crystal grains (up to several μ)
m) The following pores are considered to actually affect moisture absorption deterioration. Therefore, the cumulative porosity due to pores of φ6 nm to 1 μm excluding polishing scratches of more than 1 μm remaining on the sample surface is shown in Table 3.
It was shown to. Similarly, a 5 mm square sample was cut out from the central portion and the peripheral portion of the element as shown in FIG.
The surface was sequentially polished using up to 800. 2 at 150 ° C
The dry weight W ₁ after drying for an hour was measured, boiling was performed for 2 hours, and the saturated water weight W ₂ and the water weight W ₃ were measured. From these, the bulk density D was determined by the following equation (1). However, ρ represents the density of water at the measured temperature.

[0042]

[Equation 1]

Table 3 shows the average values of the obtained bulk densities. From the results shown in Tables 2 and 3, the following can be seen. In the first stage, the heating rate during firing in air was 100.
When the temperature was faster than ° C / hr, the sintering reaction inside the resistor was delayed as compared with the vicinity of the surface and cracks occurred in most of the elements when the diameter was large as in this sample and the comparative sample. Sample 1,
Comparing No. 2 and Comparative Sample 1, the slower the heating rate, the more uniform the sintering reaction in the device, the smaller the porosity, the larger the bulk density, and the resistor having the desired characteristics was obtained. Next, comparing Samples 1, 3 and 4, although the flatness ratio in the large current region was slightly improved as the temperature lowering rate in the first-stage firing in air was higher, the factors that greatly affect the characteristics were Absent. Therefore, the temperature lowering rate here may be increased within the range allowed by the manufacturing conditions in consideration of the second-stage firing.

Further, comparing Samples 1, 5 and 6,
Oxidizing atmosphere in the second stage (oxygen partial pressure 10 in the sample
(0% by volume) The temperature rising rate in medium firing is 50 to 200 ° C./h
There is no significant change in flatness between r. However, when the temperature is raised at 500 ° C./hr or more, cracks occur in the resistor, and since the first-stage sintering is completed, considering the production efficiency and economic efficiency, 500 ° C./hr or less, preferably 50 to It is desirable to set it to 200 ° C./hr.

Further, comparing Sample 1 and Comparative Samples 2 to 7, when the maximum firing temperature in the second stage is higher than that in the first stage, as in Comparative Samples 6 and 7, a small current region is obtained. Although the flatness of the element is greatly improved, the porosity is increased at the same time, which causes the element to deteriorate due to moisture absorption. On the other hand, when the maximum firing temperature is lower than 950 ° C., the flatness ratio in the small current region deteriorates as in Comparative Sample 2, and 2
The effect of stepwise firing cannot be exhibited. This is shown in FIG. Therefore, it is desirable that the maximum firing temperature in the second stage is 950 ° C. or higher at which the effect of the two-stage firing can be exhibited, and that it does not exceed the maximum firing temperature in the first stage so as not to be affected by moisture absorption deterioration.

Further, comparing Samples 1 and 7 and Comparative Sample 8, the higher the temperature-falling rate from the maximum temperature in the firing in the second stage to the temperature-falling rate change point, the smaller the flatness ratio in the large current region. , 200 ° C./hr, the flatness of the small current region is deteriorated at the same time.
C./hr, preferably 30 to 150.degree. C./hr.

The temperature lowering rate change point in the second stage firing is a very important factor in the main firing. That is, in order to reduce the oxygen deficiency of the zinc oxide particles and to supply excess oxygen to the grain boundaries between the zinc oxide particles in this temperature lowering process, the crystallization temperature of bismuth oxide which is a good conductor of oxygen ions. The cooling rate is changed in the region and the temperature region in the vicinity thereof. When Samples 1 and 8 and Comparative Samples 9 and 10 are compared and the change point is lowered, the flatness ratio in the small current region deteriorates and the effect of the two-step firing does not appear. Further, if this change point is raised, no large change in characteristics is observed.
Since the flatness in the small current region cannot be improved unless the cooling rate after the rate of change of cooling rate is slower than that before that, considering the production efficiency, the point of changing the rate of cooling should be set to a low temperature within the range where the effect appears. Is. Therefore, it is desirable to set the temperature in the range of 550 to 950 ° C., particularly preferably 650 to 900 ° C., depending on the composition of the raw material and various conditions during firing.

Further, comparing Samples 1 and 9 and Comparative Sample 11, the slower the rate of temperature decrease after the temperature decreasing rate change point in the second-stage firing, the smaller the flatness ratio in the small current region becomes, and the temperature is 100 ° C./hr. At 50 ℃ / h
It is desirable that the temperature is r or less, and particularly preferably 30 ° C./hr or less. Next, the calculation method of theoretical density is shown. The molecular weight of the raw material i is Ai, the density is ρi (g / cm ³ ), and the mole fraction is Mi.
(%), The weight W of the raw material is expressed by the following equation (2).

[0049]

[Equation 2]

The volume V of the raw material is expressed by the following equation (3).

[0051]

(Equation 3)

From this, the logical density ρt is obtained by the following equation (4).

[0053]

[Equation 4]

However, when the starting material is nitrate or carbonate, it is converted to a stable oxide at 500 to 600 ° C.
For example, when MnCO ₃ is used as the starting material for manganese oxide, it is converted to Mn ₃ O ₄ and aluminum oxide is converted to Al (N
In the case of O ₃ ) ₃ , it is calculated by converting to Al ₂ O ₃ . Table 1
The theoretical density calculated from the mole fraction shown in 5. is 5.64.
g / cm ³ , and from Table 3, the bulk density of the whole sintered body according to the sample of the present invention is 94 to 97% of this theoretical density (5.30 to
It is in the range of 5.47 g / cm ³ ) and it can be seen that the sintering is extremely dense.

Example 2. Samples 10-12 and Comparative Samples 12-16. Samples 1-9
The raw materials were prepared and molded under the same conditions as in Comparative Samples 1 to 11, and then preheated at 600 ° C. for 5 hours. continue,
Firing was performed according to the firing atmosphere and the maximum temperature shown in Table 4.

[0056]

[Table 4]

After the obtained element was polished and washed, an aluminum electrode was formed and various electric characteristics were measured. Further, after measuring the electrical characteristics, these devices were cut, and the porosity was measured in the same manner as in Samples 1 to 9 and Comparative Samples 1 to 11. The results are shown in Table 5.

[0058]

[Table 5]

From these results, the flatness in the small current region is improved in the firing in the oxidizing atmosphere as compared with the firing in the air, but the porosity is increased and the withstand capability is lowered. It is not easy to improve the element once sintered in such a state by the second firing. That is, the elements related to the morphology inside the element such as the denseness and the porosity are determined here by the first firing. In this sense, Comparative Samples 13 to 16 are not particularly subjected to the two-step firing, but it is considered that there is no difference in the bulk density and the porosity described below.

In particular, samples 10, 11 and comparative sample 12
Comparing with each other, the porosity increases as the heating rate Va increases. This tendency was observed in Comparative Samples 13, 14 and 1
Comparing Nos. 5 and 16 is more remarkable in the oxidizing atmosphere than that in air. FIG. 5 shows the results of measuring the bulk densities of the parts shown in FIG. 3 and examining the distributions of these resistors.
Shown in Further, Table 5 shows the variation (%) of the bulk density, which indicates how much the average value has the difference (variation) between the maximum value and the minimum value of each part.

As shown in FIG. 5, the bulk density is smaller in the central portion than in the peripheral portion of the surface, and the whole cannot be sintered uniformly. This is also the same as the porosity. When comparing Samples 10 and 11 and Comparative Sample 12, the difference becomes larger as the heating rate Va is higher,
Comparative Samples 13, 14, 15 and 16 are more prominent in an oxidizing atmosphere than in air. That is, if the heating rate is high, a temperature difference occurs between the surface of the resistor and the inside,
The whole cannot be sintered uniformly, which shows that firing in an oxidizing atmosphere is more remarkable than sintering in air.

Further, the increase in the porosity and the variation in the bulk density distribution cause deterioration of electric characteristics due to moisture absorption of the resistor as shown in FIG. Here, the electrical characteristic deterioration rate (%) in the figure is the normal V _L measured in a well-dried state and 25
C, R.C. H. After maintaining 40 hours at 80% 'difference △ V _L with (= V _L -V _L' the V _L measured) ratio, which is △ V _L / V _L. That is, it is indicated that the larger the deterioration rate of the electrical characteristics, the worse the V _L. From FIG. 6, the porosity of the resistor is 5 μl
/ G or less, the electrical property deterioration rate is within 10%,
Can be used stably. In this case, the difference between the maximum and the minimum of the bulk density at each site is within 3% of the average value.

That is, the deterioration of the electrical characteristics due to moisture absorption, which was not a particular problem in the case of firing in air, was too fast in the first stage firing, exceeding 30 ° C./hr, or under an oxidizing atmosphere. When fired in, the number of voids in the resistor increases, and the electrical characteristics deteriorate and the surface is exposed. This increase in porosity also affects the bulk density distribution of the entire resistor, and consequently also lowers the energy resistance. As described above, when the porosity is 5 μl / g or less, the number of pores in the resistor is small, and the distribution of bulk density is close to uniform. As shown in Table 5, if the variation in bulk density is within 3%, the energy resistance is good, and the inside of the sintered body is uniform and dense, so that it can be used stably.

Although the flatness, the porosity and the bulk density in the large current region are good by one firing in air, it is difficult to further improve the flatness ratio in the small current region. On the other hand, when firing is performed in an oxidizing atmosphere, the flatness ratio in the small current region is significantly improved, but the flatness ratio in the large current region is deteriorated and the porosity is also greatly increased. In the two-step firing method according to the present invention, the firing pattern is such that the excellent effects of both firings can be utilized to the maximum in device manufacturing.

In the above-mentioned samples, the oxygen partial pressure in the oxidizing atmosphere in the second stage firing was 100% by volume.
However, the flatness ratio V _H / V _L with the oxygen partial pressure as a parameter
The change in the value of is as shown in FIG. 7, and the smaller the oxygen partial pressure is, the smaller the value is.

Regarding the heating furnace used in the first-stage firing in the present invention, any one such as a tunnel furnace, a pusher furnace, a batch furnace, etc., can be used as long as it can be fired in the atmosphere and can be fired in the temperature pattern. It may be of the form. Also, regarding the heating furnace used in the second-stage firing in the present invention, the type of furnace is not particularly limited as long as the oxygen partial pressure can be maintained at 80% by volume or more and the firing can be performed in the temperature pattern. .

Further, the firing in the present invention is carried out by the method of firing two tunnel furnaces in series, air in the same batch furnace,
A method of controlling the firing temperature pattern of the oxidizing atmosphere and firing twice may be considered. Needless to say, the type and method of the furnace such as the combination of the tunnel furnace and the batch furnace are not particularly limited, and the present invention can be applied and the same effects can be obtained similarly to the above-mentioned sample.

[0068]

As described above, according to the first aspect of the present invention, the main component is zinc oxide, and bismuth oxide, antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide are used. And a non-linear voltage resistor containing boron oxide, having a porosity of 5 nm in diameter of 6 nm to 1 μm at any portion thereof.
Since it is not more than μl / g, there is an effect that there are few holes in the resistor and a resistor which is not deteriorated in electric characteristics due to moisture absorption can be obtained.

The second aspect of the present invention is a voltage containing zinc oxide as a main component and containing bismuth oxide, antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide. Since it is a non-linear resistor and the bulk density of the whole sintered body is 94 to 97% of the theoretical density calculated by the simple mole fraction of the raw material, a very densely sintered resistor is obtained. The effect of being able to be played.

According to a third aspect of the present invention, a voltage containing zinc oxide as a main component and containing bismuth oxide, antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide. Since it is a non-linear resistor and the difference between the maximum and minimum of the bulk density distribution of the whole sintered body is 3% or less of the average value, the inside of the sintered body is uniform and dense, so the energy resistance is excellent and stable. The effect that a resistor that can be used as a product is obtained.

The fourth aspect of the present invention is a raw material containing zinc oxide as a main component and containing bismuth oxide, antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide. A method for manufacturing a voltage non-linear resistor by a two-step firing method in which the first step is fired in air after being weighed and mixed to form a predetermined shape, and then the second step is fired again in an oxidizing atmosphere. In the temperature raising process in the first stage firing, the temperature raising rate in at least a part of the temperature range from 500 ° C. to the maximum firing temperature is 30 ° C./hour or less, and the temperature raising process in the second stage firing is performed. Then, the heating rate is 50 ~
500 ° C./hour, and in the temperature lowering process in the second stage firing, the maximum firing temperature is 950 ° C. or higher and
The temperature does not exceed the maximum firing temperature of the stage, the temperature decrease rate change point is 900 to 650 ° C., and the temperature decrease rate from the maximum firing temperature to this temperature decrease rate change point is 15 to 200 ° C./hour. Since the temperature decrease rate from room temperature to room temperature is 50 ° C / hour or less, there are few pores in the internal structure, it is dense and homogeneous throughout, it has an excellent energy resistance, a small flatness factor, and there is no deterioration in electrical characteristics due to moisture absorption. An effect that a voltage non-linear resistor is obtained is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a two-step firing temperature pattern according to an embodiment of the present invention.

FIG. 2 is a diagram showing typical measurement results of a mercury porosimeter in samples of the present invention and comparative samples.

FIG. 3 is a schematic view showing the positions of the samples of the present invention and comparative samples whose bulk density was measured.

FIG. 4 is a graph showing the relationship between the second stage firing temperature, the electrical property deterioration rate (%), and the small current region flatness change rate (%) in Sample 1 and Comparative Samples 2 to 7 of the present invention.

FIG. 5: Samples 10 to 12 of the present invention and comparative sample 1
It is a diagram which shows the relationship between the bulk density measured in 2-16 and a measurement position.

FIG. 6 Samples 10 to 12 of the present invention and Comparative Sample 1
It is a diagram which shows the relationship between the porosity measured in 2-16 and the electrical characteristic deterioration rate (%) by moisture absorption.

FIG. 7 is a diagram showing the relationship between oxygen concentration and V _H / V _L in the firing atmosphere.

FIG. 8 is a schematic diagram showing a general fine structure of a conventional voltage nonlinear resistor.

FIG. 9 is a diagram showing current / voltage characteristics of a conventional voltage nonlinear resistor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshio Takada 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Material Devices Research Laboratory (72) Inventor Hiroshi Nakajo 8-1-1 Tsukaguchihonmachi, Amagasaki Mitsubishi Electric Devices Co., Ltd. Material Devices Research Center (72) Inventor Keiichiro Kobayashi 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Corporation Materials Devices Research Center (72) Inventor Hideki Nakamura 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi (72) Inventor Yukio Fujiwara 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Itami Works

Claims (4)

[Claims] 1. A bismuth oxide containing zinc oxide as a main component,
A voltage non-linear resistor containing antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide,
A voltage nonlinear resistor having a porosity of 5 μl / g or less with a diameter of 6 nm to 1 μm at any portion thereof. 2. Zinc oxide as a main component, bismuth oxide,
A voltage non-linear resistor containing antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide,
A voltage non-linear resistor characterized in that the bulk density of the entire sintered body is 94 to 97% of the theoretical density obtained by calculation from the simple mole fraction of the raw material. 3. Zinc oxide as a main component, bismuth oxide,
A voltage non-linear resistor containing antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide,
The maximum and minimum difference in the bulk density distribution of the entire sintered body is 3% of the average value.
A voltage non-linear resistor characterized in that: 4. Zinc oxide as a main component, bismuth oxide,
Raw materials containing antimony oxide, chromium oxide, nickel oxide, cobalt oxide, manganese oxide, silicon oxide, aluminum oxide and boron oxide are weighed and mixed to be molded into a predetermined shape, and then the first stage firing is performed in air. A method of manufacturing a voltage non-linear resistor according to a two-step firing method in which the second-step firing is performed again in an oxidizing atmosphere, wherein the temperature raising process in the first-step firing is performed from 500 ° C. to the maximum firing temperature. The temperature rising rate in at least a part of the temperature region is set to 30 ° C./hour or less, and in the temperature rising process in the second stage baking, the temperature rising rate is set to 50 to 500 ° C./hour and the temperature decrease in the second step baking is performed. In the process, the maximum firing temperature is 950 ° C. or higher and does not exceed the maximum firing temperature of the first stage, and the temperature decreasing rate change point is 900 to 650.
C., the temperature decrease rate from the maximum firing temperature to this temperature decrease rate change point is 15 to 200 ° C./hour, and the temperature decrease rate from this temperature decrease rate change point to room temperature is 50 ° C./hour or less. Manufacturing method of non-linear resistor.