JPH05294625A - Production of barium titanate based semiconductor ceramic having positive characteristic - Google Patents

Abstract

PURPOSE:To provide a method for producing a semiconductor ceramic of barium titanate having positive characteristics, capable of lowering a specific resistance at ordinary temperature, increasing coefficient of resistance/temperature and further increasing flash dielectric strength larger. CONSTITUTION:The objective semiconductor ceramic of barium titanate with positive characteristics having good characteristics is obtained by forming an average particle diameter of titanium oxide powder which is a raw material into the range of 0.1-0.6mum expressed in terms of an accumulated weight distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a barium titanate-based positive-characteristic semiconductor ceramic.

[0002]

2. Description of the Related Art Generally, barium titanate has a Curie point near 120 ° C., and below that, it is a ferroelectric substance and exhibits insulating properties. However, it is known that when at least one of bismuth, yttrium, niobium, antimony, tantalum, and rare earth elements is added to barium titanate in a trace amount, it becomes a semiconductor, and the resistivity at room temperature is lowered to about 10 to 10 ³ Ωcm. There is. Such a barium titanate made into a semiconductor usually has a characteristic that it exhibits an abnormal resistance increase when it exceeds the Curie point. It is also known that the Curie point of barium titanate can be changed by adding elements such as strontium, zirconium and lead. Furthermore, by adding manganese, silicon, aluminum, etc., or by adding titanium in a larger amount than the stoichiometry,
It is also known to have effects such as increasing the degree of resistance increase and stabilizing the characteristics.

The main characteristics of the positive-characteristic semiconductor porcelain are the specific resistance value at room temperature, the rate of change of resistance near the Curie point (temperature coefficient of resistance α), and the like. The temperature coefficient of resistance α is expressed by α = {ln (R ₂ / R ₁ ) / (T ₂ / T ₁ )} × 100 [% / ° C.], and R ₁ is 10 of the resistance value (R ₂₅ ) at 25 ° C. ^twice the resistance value, T ₁ is the temperature when the R _1, R ₂ is 10 ³ times the resistance value of R _25, T ₂ is the temperature at the R _2. Positive-characteristic semiconductor porcelain is used as a switching element for driving a degaussing circuit in a television receiver, a motor starting element, a constant temperature heating element, a current limiting element, a temperature controlling element, and the like. Among these, for degaussing circuits, motor starting, current limiting, etc., there is a demand for smaller elements, so there is a need for a positive-characteristic semiconductor porcelain with low room temperature specific resistance and large flash withstand voltage while maintaining a large temperature coefficient of resistance. Has been. However, it is known that the conventional temperature coefficient decreases as the specific resistance decreases. For example, when the specific resistance is about 70 Ωcm, α is about 20, and the flash withstand voltage characteristic is 140 V / mm. (Nishii, Electronic Ceramics, '88, May issue (198
8), 22)

In general, barium titanate-based positive temperature coefficient semiconductor porcelain is prepared by mixing raw materials in a predetermined ratio, calcining and crushing.
It is manufactured in the steps of granulating, molding and firing. As an attempt to obtain a positive temperature coefficient semiconductor ceramic having a low room temperature specific resistance and a large flash withstand voltage while maintaining a large temperature coefficient of resistance by finely pulverizing the powder in each step, Japanese Patent Laid-Open Publication No.
4-2001, JP-A-2-289426, JP-A-3-
There is 88770. Japanese Unexamined Patent Publication No. 64-22001 discloses that when 90% by weight or more is crushed and classified to 1.0 to 3.0 .mu.m, the flash withstand voltage is improved.
In 89426 and JP-A-3-88770, primary particles and secondary particles of BaTiO ₃ , SrTiO _{3 and the} like prepared by a wet coprecipitation method are used to define the respective primary particles and secondary particles. For example, Ba
It is disclosed that when TiO ₃ is 0.2 μm or less in primary particles and the secondary particles having open pores have an average particle size of 150 to 250 μm, a low resistance PTC can be obtained.

[0005]

The conventional barium titanate-based positive-characteristic semiconductor porcelain is not yet sufficient as the excellent withstand voltage characteristic (flash withstand voltage characteristic) capable of sufficiently withstanding a large applied voltage. Further, there is a growing demand for lowering the room temperature specific resistance and increasing the resistance temperature coefficient α.

[0006]

The present inventor has made earnest studies in order to solve the above problems in view of the current situation, and as a result, the following invention has been achieved. That is, in the method for manufacturing a barium titanate-based positive-characteristic semiconductor porcelain, a powder having a mean particle size of titanium oxide powder of the raw material mixed powder of 0.1 to 0.6 to μm in terms of cumulative weight distribution is used. The manufacturing method was found.

The present invention will be described in detail below. The main raw material component of barium titanate-based positive temperature coefficient semiconductor porcelain is B as an element.
a and Ti, Sr as an element that changes the Curie point,
Pb, Ca, Zr or the like is used. Besides these, Bi,
In some cases, Y, Nb, Sb, Ta, rare earth elements, and the like are used as a trace amount addition element for converting to semiconductor. Furthermore, Mn,
Si, Al, V, Cr, Fe, Co, etc. may be added as a trace additive element.

In the barium titanate positive-characteristic semiconductor porcelain, generally, the molar ratio is 0.4 to 0.9 mol of Ba; 1.0 to 1.1 mol of Ti; Sr, Pb, Ca and Z.
r is 0.1 to 0.4 mol in total, and the above Bi,
Y, Nb, etc. are 0.01-0.05 mol in total, Mn,
Si, Al and the like are contained in a total amount of 0.01 to 0.1 mol. In the present invention, the raw material can be any compound in the form of a solid, and the Ti element is added as TiO ₂ , and Ba, Sr, P
In the case of b and Ca elements, carbonates, sulfates, nitrates, phosphates, oxides and hydroxides can be used, and in the case of Zr, oxides and hydroxides can be used. Since the characteristics change depending on the trace impurities in the raw materials, the content of impurities in each raw material is preferably 0.1% or less.

The smaller the average particle size in the cumulative weight distribution display of the titanium oxide TiO ₂ powder in the raw material mixed powder, the more it is 20%.
Although the resistivity at room temperature is small and the flash withstand voltage is large while maintaining the temperature coefficient of resistance above / ° C, the reactivity of the powder is high when it is less than 0.1 μm, and abnormal grains are easily formed during sintering. As a result, the flash withstand voltage is less than 10 kW, which is inferior. If it exceeds 0.6 μm, the resistivity at room temperature is 70 Ωc
m is higher than that of the conventional product, which is not preferable. Therefore, the range of 0.1 to 0.6 μm is preferable as the average particle size of TiO _{2 in} the mixed raw material powder, and the range of 0.2 to 0.4 μm is more preferable. TiO ₂
20% / when the average particle size of the powder is 0.1-0.6 μm
The resistivity at room temperature is 70 while maintaining the temperature coefficient of resistance above ℃
It was found that a barium titanate-based semiconductor ceramic having a flash withstand voltage (= (withstand voltage) ² / (room temperature resistance)) of 10 kW or more and lower than Ωcm can be obtained.

As a method for mixing the raw materials, mortar mixing, ball mill mixing, medium stirring type mixing, air flow crushing mixing and the like are used, but it is necessary to give sufficient consideration to impurities during mixing. In the case of ball-mill mixing, the pots or mills and balls used should be those lined or coated with nylon resin or urethane rubber or balls made of zirconia to minimize contamination with impurities. Raw material TiO of the present invention
_{In order to make the two} powders have a predetermined particle size, the powder may have a predetermined particle size at the same time as mixing with other raw material powders, or may be made into TiO ₂ powder having a predetermined particle size before mixing. But it's okay. The method of adjusting the particle size as described above may be carried out by a generally used pulverizing method. For example, in the case of a ball mill pulverizing and mixing method, the specific gravity and diameter of the balls are changed or the number of revolutions is adjusted to adjust the particle size to a predetermined value according to the present invention. Adjust to the range. When the particle size of the TiO ₂ powder is adjusted by grinding after mixing, T
Since iO ₂ is insoluble in hydrochloric acid, nitric acid, and hydrofluoric acid other than H ₂ SO ₄ , powders other than TiO ₂ are dissolved in these mineral acids, and the particle size of TiO ₂ powder is measured as a sample. However, the particle size of the TiO ₂ powder may be adjusted.

The raw material mixed to a predetermined particle size is powdered or molded, and then calcined at 800 to 1300 ° C. in the atmosphere. The lower the calcination temperature, the smaller the temperature coefficient of resistance,
When the specific resistance at room temperature becomes high and the calcination temperature becomes high, the specific resistance at room temperature also becomes high, which is not preferable. 1150-125
A calcination temperature in the range of 0 ° C is more preferred. If it is molded and calcined, it is calcinated and then crushed or crushed. If it is calcinated as a powder, it is crushed, and a binder such as PVA or PVB is added, and it is adjusted to 1 to 50 μm φ with a spray dryer or the like. Granulate and shape it at about 500-8000 kg / cm ² . Then, the molded product is 1250 to 1 in normal air.
Sinter at 400 ° C. If the holding time at the maximum sintering temperature is long, the specific resistance at room temperature increases, so the holding time is preferably short. Moreover, the characteristics strongly depend on the cooling rate, and the cooling rate from the maximum temperature to about 1000 ° C. is 30 to 100.
It is preferable that the temperature is in the range of ° C / hour. Since the calcination temperature and the sintering temperature strongly influence each other, it is necessary to determine the optimum combination.

[0012]

[Examples] Examples and comparative examples will be described below.
In the following examples and comparative examples, Ba, T
However, the present invention is not limited to this system, and similar results were obtained with a system containing Pb, Ca or Zr instead of Sr. Example 1 Barium carbonate (Nippon Kagaku Kogyo's high-purity product F03, average particle size d ₅₀ = 2.2 μm), strontium carbonate (Nippon Tokushu Kasei's high-purity product, d ₅₀ = 6.2 μm), yttrium oxide (Wako Pure) Pharmaceutical grade), titanium oxide (Showa Denko super titania G2, d ₅₀ = 0.52 μm), manganese carbonate (Hanai Chemical grade), silicon oxide (Showa Denko high-purity spherical monodisperse silica, d ₅₀ = 0) 0.5 μm), aluminum oxide (CR6 made by Baikovsky, d ₅₀ = 0.3 μm)
) Is mixed with Ti atom of 1.0000 in the following ratio. Ba 0.7706 Sr 0.2192 Y 0.0065 Si 0.0432 Mn 0.0010 Al 0.0024

130 g of this blend was taken and pure water 2
Put it in a 0.7 liter urethane lining pot mill together with 00 g and 10 mmφ nylon coated ball 50
The number of revolutions was 20 rpm and the mixing was performed for 20 hours. After wet mixing and pulverization, the balls were separated and collected in a slurry state. A part of this slurry was dissolved with 1N hydrochloric acid, and an insoluble precipitate of TiO ₂ powder was washed with water, and a wet sample was used as it was for Granulometer 850 manufactured by CILAS.
The particle size was measured at. The average particle size d ₅₀ of the cumulative distribution of the TiO ₂ powder was 0.52 μm. 100 for the rest of the slurry
Dry at 0 ° C, put the dried powder in an alumina bowl, and raise the temperature to 1180 ° C in the air at 150 ° C / hour,
The temperature was maintained at 2 ° C for 2 hours, and the temperature was lowered at 150 ° C / hour to perform calcination.

The calcined powder obtained is crushed in a mortar to give 2.5
Add a weight% PVA aqueous solution to a slurry concentration of 20% by weight and use a spray dryer to obtain an average particle size of 20 μm.
Granulated into The granules were uniaxially pressure-molded at 4 ton / cm ² to obtain pellet-shaped molded bodies having a diameter of 16 mmφ and a thickness of 1.7 mm. This molded product is heated to 300 ° C in the atmosphere for 10
0 ° C./hour, then increase to 1300 ° C. at 200 ° C./hour, and immediately lower the temperature at 1300 ° C. without holding,
The temperature was decreased to 50 ° C./hour, and then to 200 ° C./hour, and the temperature was lowered to room temperature, followed by sintering.

The obtained pellet-shaped sintered body (13.4 mm
φ × 1.6 mmt) was attached with a Ni electrode having a thickness of 7 to 8 μm by nickel-boron-based electroless plating, and was further baked with a silver paste to attach a silver electrode. This sample was set in a constant temperature bath, the resistance value at 25 to 200 ° C. was measured by the two-terminal method (at n = 10), and the room temperature specific resistance at 25 ° C. and the temperature coefficient of resistance α were obtained. The average value of each is shown in Table 1. In addition, the flash withstand voltage was measured under the following conditions. That is, the pellet-shaped sample with electrodes at room temperature
The voltage of V is applied for 1 minute. After applying a voltage for raising the sample temperature, the sample is allowed to cool for 15 minutes. Next, a voltage of 30 V is applied to the sample for 1 minute and left to cool for 15 minutes. In this way voltage application,
The cooling operation is sequentially performed by increasing the voltage by 15 V and continues until the pellet-shaped sample is broken. The highest voltage E among the unbroken voltages is calculated, and the flash withstand voltage (kW) is calculated by the following formula. The minimum value is shown in Table 1 as 10 values. Flash withstand voltage (kW) = E ² / (room temperature resistance) The room temperature resistance was 25 ° C.

Examples 2 to 5 In the sample manufacturing method and the characteristic measurement conditions of Example 1,
The sample characteristic results in Table 1 were obtained in the same manner as in Example 1 except that the calcination and sintering temperatures were changed as shown in Table 1.

[0017]

[Table 1]

Examples 6 to 12 Showa Denko Super Titania G1 as titanium oxide
The procedure of Example 1 was repeated except that (d ₅₀ = 0.30 μm) was used. However, the calcination and sintering temperatures are the conditions shown in Table 2. The d ₅₀ of the TiO ₂ powder after mixing the raw materials was measured after the treatment in the same manner as in Example 1, and the value was 0.2.
It was 9 μm. The results of the properties of these samples are shown in Table 2.

[0019]

[Table 2]

Comparative Examples 1 to 3 As titanium oxide, titania made by Toho Titanium (d ₅₀ =
Samples of Comparative Examples 1 to 3 were prepared under the same conditions as in Example 1 except that 0.69 μm) was used. However, the calcination and sintering temperatures are the conditions shown in Table 3. In addition, T after mixing the raw materials
The d _{50 of the} iO ₂ powder was measured by the same treatment as in Example 1,
It was 0.68 μm. Table 3 shows the characteristics of Comparative Examples 1 to 3.

[0021]

[Table 3]

Comparative Examples 4 to 6 Titanium IT-PC (d ₅₀ manufactured by Idemitsu Kosan Co., Ltd. as titanium oxide
= 0.06 µm), the samples of Comparative Examples 4 to 6 were prepared under the same conditions as in Example 1. However, the calcination temperature is 1
200 ° C. and sintering temperature are the conditions shown in Table 3. The d ₅₀ of the TiO ₂ powder after mixing the raw materials was 0.06 μm, which was unchanged. Table 3 shows the characteristics of Comparative Examples 4 to 6.

Examples 13 to 18 The same conditions as in Example 1 except that the 10 mmφ nylon-coated balls of Example 1 were mixed and ground with 50 20 mmφ zirconia balls for 40 hours at a rotation speed of 100 rpm. Samples of Examples 13 to 18 were prepared in. However, the calcination and sintering temperatures are the conditions shown in Table 4. The d ₅₀ of the TiO ₂ powder after mixed and pulverized was treated in the same manner as in Example 1 and the particle size was measured. As a result, 0.4
It was 5 μm. Table 4 shows the characteristics of the sintered samples of Examples 13 to 18.

The zirconium content in the powder obtained by mixing and grinding the raw materials was 320 ppm as a result of chemical analysis.

[0025]

[Table 4]

Examples 19 to 27 In Example 13, titanium oxide was used as super titania G2.
However, the samples of Examples 19 to 27 were prepared under the conditions of calcination and sintering temperatures shown in Table 5 in the same manner as in Example 13 except that Super Titania G1 was used instead. The particle size of the TiO ₂ powder after mixed pulverization was treated and measured in the same manner, and the d ₅₀ was 0.24 μm. The zirconium content in the powder after mixing and grinding is 300 pp.
It was m. Table 5 shows the characteristics of the samples of Examples 19 to 27.

[0027]

[Table 5]

Examples 28 to 30 Super Titania G2 was heat-treated at 820 ° C. for 2 hours to give a TiO ₂ powder having a d ₅₀ of 0.64 μm. The samples of Examples 28 to 30 were prepared under the conditions shown in Table 6 for the calcination and sintering temperatures, except that the TiO ₂ powder after this heat treatment was used. TiO ₂ after mixed grinding
The particle size of the powder was treated and measured in the same manner, but the d ₅₀ was 0.56.
It was μm. The zirconium content in the powder after mixed and pulverized was 320 ppm. Table 6 shows the characteristics of the sintered samples of Examples 28 to 30.

[0029]

[Table 6]

Comparative Examples 7 to 10 As titanium oxide, titania (d ₅₀ =, manufactured by Toho Titanium) was used.
Samples of Comparative Examples 7 to 10 were prepared under the same conditions as in Example 13 except that 0.69 μm) was used. The calcination and sintering temperature conditions are shown in Table 7. The particle size of the TiO ₂ powder after mixed and pulverized was d ₅₀ = 0.61 μm, and the zirconium content in the powder after mixed and pulverized was 300 ppm. Table 7 shows the characteristics of the sintered samples of Comparative Examples 7 to 10.

Comparative Examples 11 to 17 Titanium IT-PC (d ₅₀ manufactured by Idemitsu Kosan Co., Ltd. as titanium oxide
Was prepared under the same conditions as in Example 13 except that 0.06 μm) was used. Comparative Examples 11 to 17 were produced under the conditions of calcination and sintering temperature shown in Table 7. Also, Ti after mixed and pulverized
The particle size of the O ₂ powder was d ₅₀ = 0.06 μm, which was unchanged, and the zirconium content in the powder after mixing and pulverization was 280 ppm. Table 7 shows the characteristics of the sintered samples of Comparative Examples 11 to 17.

[0032]

[Table 7]

[0033]

EFFECTS OF THE INVENTION If the raw material of titanium oxide powder has an average particle size of 0.1 to 0.6 μm in terms of cumulative weight distribution, it is mixed and blended with other raw materials as it is. By setting the particle size within the range, it is possible to further lower the room temperature specific resistance, increase the resistance temperature coefficient, and increase the flash withstand voltage as compared with the related art.

Claims (1)

[Claims] 1. A method for manufacturing a barium titanate-based positive-characteristic semiconductor porcelain, wherein the average particle size of titanium oxide powder in the raw material mixed powder is 0.1 to 0.6 μm in terms of cumulative weight distribution.
A method comprising using a powder that is