JPH078744B2 - Positive characteristic semiconductor porcelain with reduction resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a positive temperature coefficient semiconductor porcelain having PTC characteristics in which the electric resistance value remarkably increases when the Curie temperature is exceeded, and is mainly used in a reducing atmosphere. The present invention relates to a reduction-resistant positive-characteristic semiconductor porcelain used for a self-temperature control type heater, a temperature sensor, and the like.

[Prior Art] Conventionally, barium titanate was added with a rare earth element such as Y, La, Sm, Ce, or Ga or a transition element such as Nb or Ta.
It is known that porcelain fired at 00 to 1400 ° C exhibits a so-called positive characteristic (PTC characteristic) in which the electric resistance value suddenly increases at the Curie point. Utilizing this characteristic, it is used for heaters, temperature sensors and the like.

A conventional semiconductor device using a positive-characteristic semiconductor porcelain mainly composed of barium titanate semiconductor has a characteristic PTC characteristic when used in a reducing atmosphere such as hydrogen gas or gasoline. There was a problem of deterioration.
For example, when used as a self-temperature control type heater, due to deterioration of PTC characteristics (hereinafter referred to as RT deterioration),
There was a problem that the resistance value did not rise even at the temperature to be controlled, and in the worst case, the PTC element was melted and damaged due to energization. It is also known that RT deterioration does not occur only in a reducing atmosphere, but RT deterioration also occurs to some extent in a neutral atmosphere such as nitrogen or argon gas.

From the above, the use environment of the semiconductor element using the positive-characteristic semiconductor porcelain containing the barium titanate semiconductor as the main component had to be limited. When used in an environment of the above reducing atmosphere, as shown in FIG. 4, the element 11 must be enclosed in a case 4 made of resin or metal and shielded from the environment. There wasn't. As a result, there have been problems such as a decrease in performance due to deterioration of heat dissipation, and an increase in cost due to an increase in the number of parts and assembling steps.

[Problems to be Solved by the Invention] The present invention overcomes the above-mentioned problems and provides a positive-characteristic semiconductor porcelain having good reduction resistance and not requiring encapsulation of an element in a predetermined case. The purpose is to

The present invention also relates to an improvement of a reduction-resistant positive-characteristic semiconductor porcelain (patent application No. 59-281418) according to an unknown prior application filed by the same applicant as the present application in order to overcome the above-mentioned conventional technique. In the positive temperature coefficient semiconductor porcelain according to the previously unknown prior application, the flux component is 0.14 to 2.88 parts by weight of TiO ₂
And 0.1 to 1.6 parts by weight of Al ₂ O ₃ and 0.1 to 1.6 parts by weight of SiO ₂
It consists of and. In the present invention, a zinc compound is further added to the flux component consisting of these three components to achieve the desired purpose.

[Means for Solving the Problems] The positive-characteristic semiconductor porcelain having reduction resistance of the present invention comprises a barium titanate-based composition and 0.2 parts by weight or more to 1.6 parts by weight or more per 100 parts by weight of the barium titanate-based composition. parts than alumina (Al ₂ O _3), 0.14~2.88
Parts by weight of titanium dioxide (TiO ₂ ), 0.1 to 1.6 parts by weight of silicon dioxide (SiO ₂ ), and the above barium titanate-based composition 100
The zinc content is 0.05 when converted to zinc contained per mol.
And a flux component composed of a zinc compound in an amount of up to 0.5 mol.

Barium carbonate (BaCO ₃ ) as the main component of barium titanate used in the positive-characteristic semiconductor porcelain having reduction resistance of the present invention
And titanium oxide (TiO ₂ ) are usually mixed in equimolar amounts. However, it is not necessary to be equimolar depending on the purpose of use, and a barium titanate-based composition represented by the general formula (1) or (2) can be used.

Ba ₁ xM ³ _x TiO ₃ (1) BaTi ₁ yM ⁵ _y O ₃ (2) where M ³ and M ⁵ are semiconducting agents selected from commonly used rare earth elements and transition elements, M ³ , Y, La,
It may be any rare earth element such as Sm, Ce or Ga, and M ⁵ may be any transition element such as Nb or Ta. Also x and y
It is desirable that the values of 0.001 to 0.005 and 0.0005 to 0.005, respectively.

The flux component, which is the greatest feature of the present invention, is alumina.
(Al ₂ O ₃ ), titanium dioxide (TiO ₂ ), silicon dioxide (SiO ₂ ), and a zinc compound, and the addition ratio of each flux component is 100 parts by weight of the barium titanate-based composition.
0.2 to 1.6 parts by weight of l ₂ O ₃ , 0.14 to 2.88 parts by weight of TiO ₂ , SiO ₂
Is 0.1 to 1.6 parts by weight and the zinc compound is 100 mol of the barium titanate-based composition, the zinc content is 0.05 to 0.5 mol in terms of zinc contained. It is necessary that each of the flux components be added within the above range, and it is not preferable if the added amount is less than the above range or too much. Furthermore, as the amount of the flux component added increases, the specific resistance of the PTC semiconductor ceramic tends to increase. To solve this inconvenience, the flux component is A based on 100 parts by weight of the barium titanate-based composition.
l ₂ O ₃ is 0.2 to 0.4 parts by weight, TiO ₂ is 0.14 to 1.15 parts by weight, and
When 0.2 to 0.8 parts by weight of SiO ₂ and 100 mol of the barium titanate-based composition are used, it is desirable that the zinc content is 0.05 to 0.2 mol in terms of zinc contained. If the content of each component is within this content range, most of the positive resistance semiconductor porcelain obtained has a specific resistance of 100 Ω · cm or less, which is suitable for application to automobile parts.

The zinc compound, which is one of the above-mentioned flux components, is usually zinc oxide (ZnO), but is not limited to this, and is contained in the positive temperature coefficient semiconductor porcelain of the present invention as a zinc compound under predetermined sintering conditions. It may be included. The raw material of the zinc compound may be ZnO, zinc carbonate (ZnCO ₃ ), zinc nitrate (Zn (NO ₃ ) ₂ ), zinc chloride (ZnC 3
l ₂ ), zinc oxalate (Zn (C ₂ O ₄ )), zinc fluoride (ZnF ₂ ), or the like, or a mixture thereof.
Most of the raw material is zinc oxide in the manufacturing process such as calcination or firing, but it may be one that does not become ZnO (for example, ZnF ₂ etc.) depending on the type of raw material, firing conditions, etc.
It does not have to be O.

ZnO or ZnCO ₃ is usually used as the raw material.

Also in the above flux components Al ₂ O ₃ , TiO ₂ or SiO ₂ , the components contained in the positive temperature coefficient semiconductor porcelain after firing may be Al ₂ O ₃ , TiO ₂ or SiO ₂ , respectively, as a raw material thereof. Is not limited to oxides. Therefore, the raw material may be a hydroxide of each metal such as Al.

The above flux component is Ba, which is the main agent of barium titanate.
It is mixed with CO ₃ and TiO _2, etc. and fired. By adding the above-mentioned four components within the above range, it is possible to obtain a positive temperature coefficient semiconductor ceramic having extremely good reduction resistance. Further, by changing the ratio of each component within the above range or the addition amount as the whole flux, it becomes possible to adjust the growth degree of the crystal particles of the positive characteristic semiconductor porcelain and the positive characteristic semiconductor having various performances. It becomes possible to obtain porcelain.

In addition to the above components, the positive temperature coefficient semiconductor porcelain of the present invention may contain titanates such as strontium titanate or lead titanate, zirconates such as barium zirconate, stannates such as barium stannate, and the like. Good. Regarding the lead component,
Rather than adding after calcination and making a solid solution with BaTiO ₃ during firing,
It is more effective for reduction resistance to add before calcination and to form a solid solution during calcination.

It is also preferable to add elements such as Pb, Sr, Zr and Sn as Curie point control agents, and it is also preferable to add a trace amount of elements such as Mn, Fe and Co as additives for improving PTC characteristics.

The positive temperature coefficient semiconductor porcelain of the present invention is mixed in the same manner as in the conventional method,
It is obtained by molding and firing. The process of making the semiconductor is as follows.

First, barium titanate is produced at a temperature of 800 to 1100 ° C, but the crystal lattice is still disordered in this state. 1200 ~
At 1280 ° C, part of the flux component begins to melt, and barium titanate rapidly grows into a semiconductor. Then, the flux component is completely melted, and the barium titanate particles are converted into a semiconductor in the liquid phase of the flux component. In the cooling process after firing in this way, the liquid phase of the flux component is solidified while covering the barium titanate semiconductor particles, and is integrated.

Although the mechanism by which the positive-characteristic semiconductor porcelain of the present invention has resistance to reduction is not clear, it is presumed that the flux component covers the barium titanate semiconductor grain boundary and protects it from the reducing atmosphere. Further, the water absorption rate of the conventional positive temperature coefficient semiconductor porcelain was about 0.5% by weight, whereas the water absorption rate of the positive temperature coefficient semiconductor porcelain of the present invention was about 0.01% by weight or less, which was almost 0%, and the water absorption rate was remarkable. It is falling. For this reason, it is considered that the reduction substance invasion is reduced, which is one of the reasons for the reduction resistance.

[Advantages of the Invention] The positive temperature coefficient semiconductor porcelain of the present invention has excellent PTC characteristics with little RT deterioration even when used in a reducing atmosphere. Therefore, not only in a neutral atmosphere such as nitrogen and carbon dioxide, but also in a reducing atmosphere such as hydrogen gas or gasoline, it is not necessary to seal with resin or metal, and it is possible to use it in an exposed structure, so the performance is In addition to improvement, the degree of freedom in product design is expanded, and it is particularly effective in reducing costs.

Further, since the positive temperature coefficient semiconductor porcelain of the present invention is not easily affected by impurities, firing conditions, and the amount of addition of the semiconducting agent,
It is much easier to manufacture than in the past, because cheap industrial raw materials can be used.

As described above, the reduction-resistant positive-characteristic semiconductor porcelain of the present invention can be applied to various products such as intake air heaters, fuel heaters, and temperature sensors as automobile parts.

[Test Example] The performance of the positive temperature coefficient semiconductor porcelain of the present invention will be described below with reference to test examples.

(Test Example 1) - BaCO ₃ in the discussion this test example of reduction resistance in the hydrogen _{gas, TiO 2, Al 2 O 3} , SiO 2, yttrium oxide (Y ₂ O _3), ZnO or ZnCO ₃ and PbO or PbTiO ₃ was used as the raw material. All of these were industrial raw materials. Each of these raw materials was blended into 55 types of compositions shown in Tables 1 to 3, and each was wet-processed with an agate boulder in a ball mill.
Grinding and mixing was performed for 20 hours. Then, these mixtures were dried and then calcined at a temperature of about 1100 ° C. for 4 hours. A small amount of manganese dioxide (MnO ₂ ) was added to the thus obtained calcined product in order to improve the withstand voltage (R, T, characteristics), and the mixture was again pulverized and mixed with agate boulders for 20 hours in a wet manner using a ball mill.
After drying, add 1% by weight of 10% polyvinyl alcohol aqueous solution as a binder to each mixed powder, and mix, 800 kg / cm
^It was press molded at a pressure of ² . These molded products were fired in air at about 1320 ° C. for about 1 hour to produce a disk-shaped positive-characteristic semiconductor porcelain having a diameter of 25 mm and a thickness of 2.5 mm.

The specific resistance of the positive temperature coefficient semiconductor porcelain related to Test Example No. 24 is 4
2Ω · cm, Curie point is 200 ℃, withstand voltage is 150V,
In addition, the water absorption rate is 0.01 wt%, which is almost zero and the conventional element (0.
5wt%) It was extremely low compared to.

In order to investigate the characteristics of the obtained 55 types of positive-characteristic semiconductor porcelain, Ni-Ag electrodes (Ni electroless plating, Ag paste) were applied to both sides of each positive-characteristic semiconductor porcelain, and the electrical resistance value ( The specific resistance Ro) was measured, and the results are shown in Table 1 and Table 2.
The results are shown in Tables and Table 3. Also, put each PTC semiconductor porcelain in a hydrogen gas atmosphere, and at 300 ° C, the electrical resistance value (R ₁ ) immediately after putting each PTC semiconductor porcelain and the electrical resistance value (R ₂ ) after 30 minutes.
Was measured, and the resistance change rate (ΔR) was measured by the following equation (3).

ΔR = 100 × (R ₂ −R ₁ ) / R ₁ (3) Here, the closer R ₂ is to R ₁ , that is, the closer ΔR is to 0, the better the reduction resistance.

The evaluation of each positive-characteristic semiconductor porcelain was as follows: Table 1, Table 2 and Table 3 show that ΔR is 0 to -10% (○), -10 to -50% is (△), and -50% is (x). Shown in the table.

In Table 1, Al ₂ O ₃ is 0.2 to 1.6 parts by weight as a flux component to the barium titanate-based 100 parts by weight of the composition (hereinafter wt% referred.) TiO ₂ is from 0.14 to 2.88 wt%, SiO ₂
0.1 to 1.6% by weight, and barium titanate-based composition 10
Positive-characteristic semiconductor porcelain (No. 19-22, No. 24-2) containing 0.05-0.3 mol (hereinafter referred to as mol%) of zinc compound per 0 mol.
7, 29, 30, 34 to 55) are the other positive characteristic semiconductor porcelains (No. 12, 17, 18, 28, 31 to 3) whose main components are the same composition.
3 (corresponding No. among the above is No. 19-22, 29, 30, 34-5
5) and No. 16 (No. 26, 27), ΔR is -0.3 to -9.
It is as small as 5 (-11 to -31 in Comparative Example), and is clearly excellent in reduction resistance. In addition, particularly preferable range is Al ₂ O ₃
0.2 to 0.4% by weight, TiO ₂ 0.14 to 1.15% by weight, SiO ₂ 0.
Positive characteristic semiconductor porcelain containing 2 to 0.8% by weight and 0.05 to 0.2 mol% of Zn compound (No. 19 to 21, 24 to 27, 29, 35, 3
6, 39, 40, 43 to 45, 49 to 51) has a specific resistance (Ro) of 100 Ω
・ It is less than cm and ΔR is smaller (-0.3 to-)
8.8, most of which have an absolute value of 6 or less.) It is even more excellent in reduction resistance, making it ideal for application to automotive parts.

(Test Example 2) -Study of reduction resistance in sour gasoline Next, using a raw material having the same composition as that used in Test Example 1, mixing, molding and firing were performed in the same manner as in Test Example 1 to obtain a diameter. A disc-shaped positive-characteristic semiconductor porcelain having a thickness of 25 mm and a thickness of 2.5 mm was manufactured. The obtained positive-characteristic semiconductor porcelain was provided with a Ni-Ag electrode on the surface in the same manner as in Test Example 1, and the electric resistance value of each positive-characteristic semiconductor porcelain was measured almost continuously in the air from room temperature to 300 ° C. Then, the PT of the solid line (a) shown in the conceptual diagram of FIG.
A curve representing the C characteristic was obtained. Next, each positive-characteristic semiconductor porcelain was immersed in sour gasoline, and an immersion current durability test was performed in which a voltage of 30 V was applied for 200 hours or more. Here, sour gasoline is gasoline that has been oxidized to generate peroxides and acids, and is used for accelerated tests. After the immersion current durability test, the positive resistance semiconductor porcelain was measured for electrical resistance in the atmosphere from room temperature to 300 ° C almost continuously, and the curve showing the PTC characteristic of the broken line (b) in Fig. 2 was obtained. . The RT deterioration (A) shown in FIG. 2 was obtained from the difference between the two obtained curves, and the results are shown in Tables 1-3.
The RT deterioration (A) is obtained by the following equation.

log (R'max / R'min) -log (Rmax / Rmin) = RT deterioration (A) (R ... resistance value before endurance test, R '... resistance value after endurance test, max ... maximum value, min… Minimum value) In Tables 1 to 3, there is a part where the measurement result is not described, but this is because the positive resistance semiconductor porcelain with a specific resistance of 100 Ω · cm or more shows sufficient heat generation in the immersion current durability test. It was not measured because it was not possible to obtain reliable data. In addition, in the determination of the result, the degree of (A) is within 1 (o), 1-2 is (Δ), and 2 or more is (x).

In Tables 1 to 3, the positive-characteristic semiconductor porcelain of the present invention (No. 1
9-21, 24-27, 29, 35-37, 39, 40, 49-51) are other positive characteristic semiconductor porcelains (eg No. 12, 16, 32, 33)
The RT deterioration is small as +0.2 to -0.7 in the logarithmic value (-0.9 to -3.2 in Comparative Example), and the reduction resistance is obviously excellent. In addition, the positive temperature coefficient semiconductor ceramics containing 0.2 to 0.4% by weight of Al ₂ O _3, 0.14 to 1.15% by weight of TiO ₂ , 0.2 to 0.8% by weight of SiO ₂ and 0.05 to 0.2 mol% of Zn compound, which are particularly desirable ranges ( No. 19-21, 24-27, 29, 35, 36, 39, 40, 49-5
In 1), RT deterioration is +0.2 to -0.6, except for No.49, especially +
It is 0.2 to −0.4, which shows that the reduction resistance is particularly excellent.

(Study of results of Test Examples 1 and 2) (1) Examination of raw material zinc compound The raw material zinc compound showed almost the same performance in both ZnO and ZnCO ₃ (No. 24 and 25, No. 26 and 27).

(2) Examination of composition ratio of each flux component The zinc compound (ZnO) is 100 barium titanate-based composition.
When the amount is 0.05, 0.1, 0.2, 0.3, 0.5 mol% (No. 19 to 23, respectively), the reduction resistance is excellent. However, if it is 0.01, 0.02 mol% (No. 17, 18 respectively),
The performance evaluation for both hydrogen and sour gasoline is Δ, and the reduction resistance for both is insufficient.

When the composition ratio of Al ₂ O ₃ is 0.1% by weight (No. 31 to 33),
The reduction resistance to hydrogen is Δ, the reduction resistance to sour gasoline is Δ or ×, and the reduction resistance is not good.

In the test examples of Tables 1 to 3, the flux component is Al ₂ O ₃ ,
In the case of TiO ₂ , SiO ₂ and zinc compounds, the proportion of each flux component in the PTC semiconductor porcelain of the present invention is Al ₂ O ₃
0.2-1.6 wt%, TiO ₂ 0.14-2.88 wt% SiO ₂ 0.1-
When 1.6 wt% and ZnO etc. are 0.05 to 0.5 mol%, the reduction resistance to hydrogen and sour gasoline is excellent.

(3) Lead addition method For positive-characteristic semiconductor porcelain with a high Curie point, rather than adding PbTiO ₃ after calcination (No. 10 to 12, 24, 25), P
It is effective for reduction resistance that bO is added before calcination and made solid solution with BaTiO ₃ during calcination (No. 13 to 15, 26, 27) because Pb is less scattered and the water absorption rate is lower. .

(Test Example 3) Of the positive temperature coefficient semiconductor porcelain used in Test Example 1, No. 12 was selected as the conventional composition and No. 24 was selected as the composition of the present invention, and mixing, molding and firing were performed in the same manner as in Test Example 1. 25 mm in diameter,
A disk-shaped positive-characteristic semiconductor porcelain with a thickness of 2.5 mm was manufactured. Ni-Ag electrodes were applied to both sides of the obtained two types of positive-characteristic semiconductor porcelain, and the temperature was 300 ° C in hydrogen gas, which is a reducing atmosphere.
Left for 30 minutes. The electric resistance value of each positive-characteristic semiconductor porcelain during the 30 minutes was measured almost continuously, and the resistance change rate was calculated based on the electric resistance value immediately after being put into the reducing atmosphere. The results are shown in Fig. 1. Show. As is clear from Fig. 1, the positive-characteristic semiconductor porcelain No. 12 with the conventional composition is 68% in hydrogen gas.
%, The resistance change rate (ΔR) of the positive temperature coefficient semiconductor porcelain No. 24 of the present invention is only 4.4% decrease in hydrogen gas, which is almost the same. There was no. That is, the positive-characteristic semiconductor porcelain of the present invention is excellent in reduction resistance because the electric resistance value hardly changes even in a reducing atmosphere of hydrogen gas.

Although the mechanism of improvement in reduction resistance is not clear, addition of flux of Al ₂ O ₃ , TiO ₂ , SiO ₂ and Zn compound significantly reduced water absorption rate and reduced penetration of reducing substances. It is considered to be a cause.

(Test Example 4) The present invention makes it possible to use a positive-characteristic semiconductor porcelain in an exposed structure in gasoline. Therefore, an intake air heater having a conventional sealed structure (Fig. 4) (heating a gas mixture of gasoline) is used. FIG. 5 shows the results of comparison of engine torque performance between the heater) and the heater having an exposed structure (FIG. 3). The engine conditions in this case are 1600 rpm (1500 cc), 4.5 kg
m, W / choke, A / F: 11 to 12, and the positive-characteristic semiconductor porcelain had the composition of No. 24.

According to this result, when the positive-characteristic semiconductor porcelain according to the present invention is used, the exposed structure becomes possible, and the engine torque performance becomes better than that of the conventional sealed structure.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in electric resistance value in hydrogen gas, and FIG. 2 is a diagram showing RT deterioration in sour gasoline. FIG. 3 is an explanatory diagram in which the positive-characteristic semiconductor porcelain having reduction resistance of the present invention is applied to an intake air heater with an exposed structure. FIG. 4 is an explanatory diagram in which the positive-characteristic semiconductor porcelain having reduction resistance of the present invention is applied to an intake air heater with a sealed structure. FIG. 5 is a diagram showing the engine torque performance when the intake air heaters shown in FIGS. 3 and 4 are used. 1, 11 …… Positive characteristic semiconductor porcelain 2, 21 …… Gas engine heat insulator 3, 31 …… Spring 4 …… Case (A) …… RT deterioration (a) …… Initial state (b) …… After durability test

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Junji Aiba, 1-1, Showa-machi, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Naoto Miwa, 1-1, Showa-machi, Kariya city, Aichi prefecture, Nippon Denso Within the corporation (56) References JP-A-55-95673 (JP, A) JP-A-54-105113 (JP, A) JP-B-52-12919 (JP, B2) US Patent 4593670 (US, A) US Patent 3586642 (US, A)

Claims (4)

[Claims] 1. A barium titanate-based composition, and 0.2 to 0.6 parts by weight of alumina (Al ₂ O ₃ ) and 0.14 to 2.88 parts by weight of dioxide based on 100 parts by weight of the barium titanate-based composition. Titanium (TiO ₂ ), 0.1 to 1.6 parts by weight of silicon dioxide (SiO ₂ ), and 100 mol of the barium titanate-based composition, the zinc content in terms of zinc contained is 0.05 to.
A positive-characteristic semiconductor porcelain having reduction resistance, comprising: a flux component composed of 0.5 mol of a zinc compound; 2. The flux component is 0.2 to 0.4 parts by weight of alumina (Al ₂ O) per 100 parts by weight of the barium titanate-based composition.
_3), 0.14 to 1.15 parts by weight of titanium dioxide (TiO _2), 0.2 to 0.8
Claims consisting of parts by weight of silicon dioxide (SiO ₂ ) and a zinc compound having a zinc content of 0.05 to 0.2 mol in terms of zinc contained with respect to 100 mol of the barium titanate-based composition. A positive-characteristic semiconductor porcelain having reduction resistance according to claim 1. 3. The positive-characteristic semiconductor porcelain having reduction resistance according to claim 1, wherein the zinc compound is zinc oxide (ZnO). 4. A barium titanate-based composition has the general formula Ba _1-x M
³ _x TiO ₃ or BaTi _1-y M ⁵ _y O ₃ (M ³ is Y, La, Sm,
Rare earth elements such as Ce and Ga, M ⁵ is a transition element such as Nb and Ta, x is
The positive-characteristic semiconductor porcelain having reduction resistance according to claim 1, which has a composition of 0.001 to 0.005 and y is 0.0005 to 0.005, respectively.