JPH0142606B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic composition for obtaining a voltage nonlinear resistor (hereinafter referred to as a varistor) containing Sr _(1-x) Ca _x TiO ₃ as a main component. Various varistors are used to absorb or eliminate abnormal voltages, noise, etc. generated in electronic equipment, and Sr _(1-x) Ca _x TiO ₃ as shown in Japanese Patent Application No. 1987-71425. A varistor having as a main component not only has a varistor function but also a capacitor function, so it can satisfactorily absorb or bypass glow discharge, arc discharge, abnormal voltage, noise, etc. This varistor also has the advantage of superior temperature characteristics than conventional varistors whose main component is SrTiO ₃ . However, in recent years, there has been a demand for varistors whose characteristics are less likely to deteriorate due to the application of surge voltage and/or current. Additionally, a varistor with a small temperature change rate of varistor voltage is required. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a voltage nonlinear ceramic composition that exhibits less deterioration of varistor voltage, nonlinear coefficient, and temperature characteristics of varistor voltage due to the application of a surge, and a small rate of temperature change of varistor voltage. It is in. The first invention of the present application to achieve the above object is based on 100 mole parts of Sr _(1-x) Ca _x TiO ₃ (where x is a value in the range of 0.01 to 0.5) (hereinafter referred to as the first component). ,
_{Nb2O5 , Ta2O5} , _WO3 , _{La2O3 , CeO2 , Nd2O3 ,}
At least one metal oxide of Y ₂ O ₃ , Sm ₂ O ₃ , Pr ₆ O ₁₁ , and Dy ₂ O ₃ (hereinafter referred to as the second component)
0.01 to 3.00 mol parts, 0.02 to 2.50 mol parts of Na ₂ O (hereinafter referred to as the third component), and 0.01 to 1.50 mol parts of Al ₂ O ₃ (hereinafter referred to as the fourth component). It is related to things. According to the above invention, Na ₂ O ₃ is added as a third component to the first component (main component) that can reduce the temperature change rate of the varistor voltage and the second component that mainly contributes to making porcelain a semiconductor. By adding Al 2 O 3 in a range of 0.02 to 2.50 mol parts, and adding Al ₂ O ₃ in a range of 0.01 to 1.50 mol parts, it becomes possible to significantly reduce changes in the temperature characteristics of the varistor voltage due to the application of surges. Moreover, it becomes possible to reduce the rate of change of the varistor voltage with temperature. Furthermore, Al ₂ O ₃ contributes to an increase in the nonlinear coefficient α. The second invention of the present application further includes a component that contributes to improving the nonlinear coefficient in the first composition.
One or more oxides of Ag ₂ O, CuO, MnO ₂ and SiO ₂ (hereinafter referred to as the fifth component) from 0.01 to
This relates to compositions containing 3.00 mole parts. This makes it possible to provide a varistor that has a large nonlinear coefficient and is prevented from deteriorating due to surges. Examples related to the present invention will be described below. Example 1 Sr _(1-x) Ca _x TiO ₃ (first component) with a purity of 99.0% or more so that x is the value in the first component column of Table 1.
SrCO ₃ , CaCO ₃ and TiO ₂ were weighed and blended,
Stirred in a ball mill for 10 hours, it was dried and then ground. After that, the above pulverized material was heated to 1200℃.
The mixture was baked for 2 hours and ground again. This gives x
As shown in Table 1, various different first components are obtained. Next, to 100 mole parts (constant) of the first component obtained as described above, Nb ₂ O ₅ with a purity of 99.0%,
Ta ₂ O ₅ , WO ₃ , La ₂ O ₃ , CeO ₂ , Nd ₂ O ₃ , Pr ₆ O ₁₁ ,
A powder of one or more metal oxides (second component) selected from Dy ₂ O ₃ , Y ₂ O ₃ and Sm ₂ O ₃ and a purity of 97.0.
% of Na ₂ O and NaF.
The powder of Na compound (third component) and Al ₂ O ₃ (fourth component) were weighed so as to have the ratio shown in Table 1. Next, each raw material powder was put into a mortar and stirred (dry type) for 20 hours. Next, 10 to 15% by weight of polyvinyl alcohol is mixed as an organic binder into the varistor raw materials shown in Table 1 and granulated, and this granulated mixture is molded into a disk at a molding pressure of about 1500 kg/ ^cm2 . did. These disks were heated with N ₂ (95% by volume) + H ₂ (5% by volume)
Approximately 1350℃ in a reducing atmosphere (non-oxidizing atmosphere), 4
After firing for several hours, semiconductor porcelain with a diameter of 10 mm and a thickness of 0.8 mm was obtained. Next, heat treatment (reoxidation treatment) was performed in air (in an oxidizing atmosphere) at a temperature range of 1000 to 1200°C for 3 hours. As a result, Na ₂ O,
Porcelain with the same composition as the starting material was obtained, except that NaF was converted to Na ₂ O, respectively. Therefore, in Table 1, the description of the first component, second component, and fourth component after firing is omitted, and only Na ₂ O obtained after firing is listed corresponding to the Na compound. Next, in order to investigate the characteristics of the above-mentioned porcelain, a known silver paste was applied to both main surfaces of the porcelain 1 as shown in FIG.
3 was formed, and Barista 4 was completed. Next, in order to evaluate the characteristics of the varistor, the varistor voltage V ₁ , the nonlinear coefficient α, the temperature change rate of V ₁ ΔV ₁ ,
When measuring the capacitance C, the rate of change of V ₁ and α due to the application of the surge voltage ΔV ₁ p and Δαp, and the rate of temperature change of V ₁ after the application of the surge voltage ΔV _1T ,
The second result was obtained. To explain each measurement method in more detail, the varistor voltage _V1 was measured using the circuit shown in FIG.
That is, the varistor 4 is connected to the DC constant current source 6, and the ammeter 8 is connected between the DC constant current source 6 and the varistor 4.
Connect the voltmeter 9 in parallel to the varistor 4, place only the varistor 4 in a constant temperature oven 20 kept at a temperature of 20°C, apply a current of ₁ mA to the varistor 4, and measure the voltage at that time. Varistor voltage (V ₁ )
And so. In addition, the nonlinear coefficient α is determined by using the device shown in Fig. 2, and in addition to the varistor voltage V ₁ , the varistor 4 is set at 10 mA.
The applied voltage V ₁₀ was measured when a current I ₁₀ of was applied, and was determined by the following formula. α=log(I ₁₀ /I ₁ )/log(V ₁₀ /V ₁ )=1/log(V ₁₀
/V ₁ ) Also, the temperature change rate ΔV ₁ is determined by changing the constant temperature chamber 20 in the range of -40°C to +125°C in the apparatus shown in FIG.
The varistor voltage V _1T was measured when 1 mA was applied to the varistor 4 at each temperature T (° C.), and the amount of change from V ₁ at 20° C. was determined by calculating the following equation. Note that each table shows only the maximum value of ΔV ₁ within the above temperature range. ΔV ₁ = V _1T −V ₁ /V ₁ ×100/T(℃)−20(℃)(%/℃
) Next, in order to simulate how the characteristics of the varistor 4 change when a sharp pulse of overvoltage, that is, a surge voltage, is applied, a constant DC voltage of 2 kV was applied as shown in Figure 3. A voltmeter 11 is connected in parallel to the power source 10, and a voltmeter 11 is connected to the power source 10 through a 5Ω resistor 12 and a contact 13a of a single-pole double-throw switch 13.
A 2.5μF capacitor 14 is connected, and a varistor 4 is connected to the contact 13b of the switch 13, and the charging energy of the capacitor 14 is transferred to the varistor 4 at 5 second intervals.
5 times, then measure the varistor voltage V ₁ p and the nonlinear coefficient αp using the circuit shown in Figure 2, and calculate the rate of change ΔV ₁ p (%) of the varistor voltage and the rate of change Δαp of α using the following equations. (%) was calculated. ΔV ₁ p=V ₁ p−V ₁ /V ₁ ×100(%) Δαp=αp−α/α×100(%) Also, the varistor of varistor 4 after applying surge voltage and current in the circuit shown in Figure 3 The temperature change rate of voltage ΔV _1T was determined using the apparatus shown in FIG. 2 in the same manner as ΔV ₁ described above. Further, the capacitance C (nF) of each sample was measured at 1kHz. Also, for comparison, Na ₂ O and Al ₂ O _3
Among the conventional Sr (1 _{- x)} Ca _x TiO _3- based varistors _that do not contain
As a result of measuring the characteristics of a semiconductor ceramic varistor consisting of 0.50 molar parts of Nb ₂ O ₅ and 3.00 molar parts of Bi ₂ O ₃ based on the above-mentioned measurement methods, V ₁ is 28.5.
(V), α is 27.3, ΔV ₁ is -0.1 (%/℃), C is 140
(nF), ΔV ₁ p is −29.4%, Δαp is −36.3%, ΔV _1T
was -0.25 (%/°C). Furthermore, in order to investigate the effect of Al ₂ O ₃ , we made porcelain compositions of various compositions consisting of 100 mol parts of the first component, 0.01 to 3.00 mol parts of the second component, and 0.02 to 2.50 mol parts of the third component, and measured their characteristics. As a result, V ₁ is 10.0 to 47.2 (V), and α is
18.0~24.9, ΔV ₁ is 0.01~0.02 (%/℃), C is 90~
166 (nF), ΔV ₁ p is 0.2-1.0 (%), Δαp is 0.3-1.0
(%) and ΔV _1T were 0.01 to 0.02 (%/°C).

【table】

【table】

【table】

[Table] As is clear from Tables 1 and 2 above, 1st component 100 mol parts 2nd component 0.01 to 3.00 mol parts 3rd component (Na ₂ O) 0.02 to 2.50 mol parts 4th component (Al ₂ O3) By setting the amount to 0.01 to 1.50 mol parts, a varistor with good characteristics can be provided. That is, by adding the third component (Na ₂ O) and the fourth component (Al ₂ O ₃ ), compared to a varistor that does not contain these components, ΔV ₁ p is reduced from -29.4% of the conventional varistor. It can be improved to 0.4 to -0.8%. Furthermore, Δαp can be improved from -36.3% in the conventional case to -0.3 to -0.8%. Also,
The absolute value of ΔV _1T furnace has also been reduced from 0.25%/℃ to 0-0.01
can be improved. Also, if the fourth component (Al ₂ O ₃ ) is added, the first component without this addition can be
~Compared to the third component varistor, the absolute value of ΔV ₁ can be made smaller. Also, α can be increased. In addition, in the range where the third component (Na ₂ O) exceeds 2.50 mol parts, the absolute values of ΔV ₁ p and Δαp are 10%.
, and the absolute value of ΔV _1T exceeds 0.15%/℃. On the other hand, if the third component (Na ₂ O) is less than 0.02 mole part, there is no effect of improving the characteristics by applying a surge voltage. Therefore, the preferred range of Na ₂ O to provide a varistor that can withstand the current or voltage is 0.02
~2.50 mole parts, and a more preferable range is 0.5~2.50 mole parts
It is 1.50 mole parts. Also, Al ₂ O ₃ (fourth component)
If it exceeds 1.5 mole part, the absolute values of ΔV ₁ p, Δαp, and ΔV _1T will become large, and if it is less than 0.01 mole part, the effect of its addition will be small. Therefore, the preferred range of Al ₂ O ₃ is
It is 0.01 to 1.5 mole part. Furthermore, if the second component exceeds 3.00 mole parts, sintering may be incomplete (unsintered) or various properties may deteriorate. On the other hand, the second component
If the amount is less than 0.01 mole part, semiconductor formation is not performed well, so that α is small and the characteristics deteriorate significantly after application of a surge voltage. Therefore, the second
The preferred range of components is 0.01 to 3.00 mole parts. The first component is ΔV ₁ p and Δαp when x exceeds 0.50.
The absolute value of exceeds 12%. On the other hand, when x is smaller than 0.01, the absolute value of the temperature characteristic ΔV ₁ becomes 0.03%/°C or more. Therefore, the preferred range of x for the first component is 0.01
~0.50. Example 2 A varistor consisting of the first to fourth components shown in Example 1 was added with one or more oxides (fifth component) selected from Ag ₂ O, CuO, MnO, and SiO ₂ . It was produced in the same manner as in Example 1, and its characteristics were measured in the same manner. That is, as shown in Table 3, assuming that the weight of the first component is constant at 100, the first to fifth components are
When a varistor containing the ingredients was made and its characteristics were measured, the results shown in Table 4 were obtained.

【table】

【table】

【table】

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[Table] As is clear from Tables 3 and 4 above, the fifth
By adding 0.01 to 3.00 mole parts of the component, a varistor with extremely small characteristic deterioration after application of a surge voltage and with a high α can be obtained. Furthermore, the fifth component is
If it exceeds 3.00 mol parts, the characteristics deteriorate significantly after application of surge energy, and the absolute values of ΔV ₁ p and Δαp exceed 10%. Also, ΔV _1T is 0.10% in absolute value.
Exceed. On the other hand, if the fifth component is less than 0.01 part by mole, there is no improvement in α. Therefore, the preferred range of the fifth component is 0.01 to 3.00 parts by mole. Example 3 In order to confirm that there is no problem in adding the third component (Na ₂ O) after calcination without adding it to the starting material, 100 mol of Sr _0.70 Ca _0.30 TiO ₃ (first component) was added. Powders of 0.50 mol parts of Nb ₂ O ₅ (second component) and 0.1 mol parts of Al ₂ O ₃ (fourth component) were put into a mortar and 20
Stirring (dry type) was performed for hours. Next, 10 to 15% by weight of polyvinyl alcohol was mixed as an organic binder into this varistor raw material and granulated, and the granulated mixture was molded into a disk at a molding pressure of about 1500 kg/cm ² . Next, this disk was heated with N ₂ (95 volume%) + H ₂ (5 volume%)
Approximately 1350℃ in a reducing atmosphere (non-oxidizing atmosphere), 4
After firing for several hours, it was made into semiconductor porcelain with a diameter of 10 mm and a thickness of 0.8 mm. Next, NaF paste was applied to one main surface of this semiconductor porcelain at a rate of 0.90mg/ ^cm2 , and heat treatment was performed at 900℃ to 1100℃ for 2 hours in the air (oxidizing atmosphere). Na ₂ O
was thermally diffused into semiconductor porcelain, and then Example 1
When I made a varistor using the same method and measured its characteristics using the same method, V ₁ was 24.6V, α was 23.8, and ΔV ₁ was 0.
%/℃, C is 139nF, ΔV ₁ p is -0.5%, Δαp is -
0.5%, ΔV _1T was 0%/°C. Example 4 Instead of the porcelain of Example 3, Sr _0.8 Ca _0.2 TiO ₃ (first component) 100 mole parts, Ta ₂ O ₅ (second component) 0.5 mole parts Al ₂ O ₃ (fourth component) 1.0 mole A piece of porcelain was made, and instead of the NaF paste in Example 3, Na ₂ O paste was applied to the porcelain at a rate of 1.40 mg/cm ² and diffused in the same manner as in Example 3, and then the same as in Example 1 was applied. When I made a varistor using the method and measured its characteristics, V ₁ was 15.1V, α was 22.9, and ΔV ₁ was +
0.01%/℃, C is 142nF, ΔV ₁ p is -0.8%, Δαp
was −0.9%, and ΔV _1T was +0.01%/°C. Example 5 Instead of the porcelain of Example 3, Sr _0.99 Ca _0.01 TiO ₃ (first component) 100 mole parts La ₂ O ₅ (second component) 0.1 mole part Al ₂ O ₃ (fourth component) 0.01 mole part Make porcelain with 0.5 mol part of SiO ₂ (fifth component) and add 1.80 mol of NaF paste to this porcelain.
mg/cm ² and diffused in the air at 1000-1200°C. A varistor was made from this porcelain in the same manner as in Example 1, and its characteristics were measured _.
49.3V, α is 29.9, ΔV ₁ is -0.01%/℃, C is
72 nF, ΔV ₁ p was -0.5%, Δαp was -0.6%, and ΔV _1T was -0.01%/°C. Example 6 Instead of the porcelain of Example 3, Sr _0.60 Ca _0.40 TiO ₃ (first component) 100 mole parts, Nb ₂ O ₅ (second component) 1.00 mole parts, Al ₂ O ₃ (fourth component) 0.5 Make porcelain with 0.10 molar parts of MnO ₂ (fifth component), and add 1.50 molar parts of Na ₂ O paste to this porcelain.
mg/cm ² and diffused in the atmosphere at 1000-1200°C. A varistor was made from this porcelain in the same manner as in Example 1, and its characteristics were measured. V ₁ was 30.1 V, α was
36.9, ΔV ₁ was +0.01%/°C, C was 118 nF, ΔV ₁ p was −0.4%, Δαp was −0.4%, and ΔV _1T was +0.01%/°C. As is clear from this result, Na
By thermal diffusion into semiconductor porcelain without adding compounds
Even if it contains Na ₂ O, a surge-resistant varistor can be provided. Modifications The following has been confirmed by the above examples and other experiments. (a) The heating temperature in the reducing atmosphere is preferably
The temperature range is from 1300 to 1500°C, and more preferably from 1350 to 1450°C. Furthermore, this processing time is 2 to 8
time is preferable. (b) The oxidation treatment is preferably carried out at 850°C to 1350°C for 1 to 5 hours. (c) The starting materials for the second component and the fifth component correspond to the respective components of the fired porcelain in the examples, but if a metal oxide can be finally obtained, the purpose of the present invention is is achieved, the starting materials may be metal elements, carbonates, hydroxides, nitrates, and oxalates instead of metal oxides. (d) A property-improving substance may be further added to the varistor according to the present invention as long as the properties of the varistor are not impaired. (e) The preferable range of the organic binder is 5 to 20% by weight, based on the total weight of the first to fourth or first to fifth components, first and second, and the more preferable range is 10 to 20% by weight.
It is 15% by weight. (f) Firing may be performed in a neutral atmosphere instead of a reducing atmosphere. (g) Pressure molding may be carried out at any suitable value in the range of 500 Kg/cm ² to 2000 Kg/cm ² .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing a varistor according to a first embodiment. FIG. 2 is a circuit diagram of an apparatus for measuring V ₁ , α, and ΔV ₁ . FIG. 3 is a circuit diagram of the surge application device. 1...porcelain body, 2, 3...electrode, 4...varistor.

Claims (1)

[Claims] 1 100 mole parts of Sr _(1-x) Ca _x TiO ₃ (where x is a value in the range of 0.01 to 0.5), Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ , La ₂ O ₃ , _CeO2 ,
0.01 to 3.00 mol parts of at least one metal oxide of Nd ₂ O ₃ , Y ₂ O ₃ , Sm ₂ O ₃ , Pr ₆ O ₁₁ , and Dy ₂ O ₃ and 0.02 to 2.50 mol of Na _{2 O} and 0.01 to 1.50 mole parts of Al ₂ O ₃ . 2 100 mol parts of Sr _(1-x) Ca _x TiO ₃ (where x is a value in the range of 0.01 to 0.5), Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ , La ₂ O ₃ , CeO ₂ ,
0.01 to 3.00 mol parts of at least one metal oxide of Nd ₂ O ₃ , Y ₂ O ₃ , Sm ₂ O ₃ , Pr ₆ O ₁₁ , and Dy ₂ O ₃ and 0.02 to 2.50 mol of Na _{2 O} 0.01 to 3.00 mol parts of at least one oxide of Ag ₂ O, CuO, MnO ₂ and SiO ₂ , and 0.01 to 1.50 mol parts of Al ₂ O ₃ . .