JPH1072254A - Production of barium titanate-base semiconductor porcelain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain semiconductor porcelain having superior electrical characteristics by using TiO2 having a specified BET specific surface area as one of starting materials and imparting a compsn. represented by a prescribed formula. SOLUTION: Starting materials such as BaCO3 , SrCO3 , Pb3 O4 , Y(NO3 )3 .6H2 O, Mn(NO3 )3 .6H2 O, SiO2 and TiO2 having 4-50m<2> /g BET specific surface area are blended to prepare a slurry of the compds. contg. elements in a ratio represented by the formula (where Z is Y or La as a semiconductor forming agent, 0.05<=x<=0.40, 0.05<=y<=0.40, 0.25<=x+y<=0.48, 0.990<=A/B<=1.000, 0.001<=p<0.002, 0.05<=q/p<=0.15 and 0.003<=r$0.03). The slurry is mixed with an ammonia buffer, dehydrated, dried and calcined at about 1,100 deg.C. The resultant calcined powder is dispersed in water to prepare a slurry again, a binder is added and they are granulated, press-compacted and fired at about 1,320 deg.C to obtain the objective BaTiO3 -base semiconductor porcelain having low specific resistance at room temp. and positive resistance-temp. characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a barium titanate-based semiconductor porcelain having a low room temperature specific resistance and a positive resistance-temperature characteristic.

[0002]

2. Description of the Related Art By adding a trace amount of rare earth elements or elements such as Nb and Sb to barium titanate,
It is known that a semiconductor porcelain having a positive resistance temperature characteristic can be obtained. Furthermore, it is also known that the addition of a small amount of Mn and Si can increase the temperature coefficient of resistance in the resistance temperature characteristics.

Semiconductor porcelains having such a positive resistance-temperature characteristic are used for current limiting, temperature detection, constant temperature heating elements, etc., but barium titanate-based semiconductor porcelains generally used for current limiting are used. The characteristics are that the resistivity [ρ] at room temperature is small, the withstand voltage [V] is high,
For example, the resistance temperature coefficient [α] is large. In other words, in order to obtain a small, light, and low-resistance element, the current-limiting semiconductor porcelain is required to have a low room-temperature specific resistance and a high withstand voltage.

For this reason, the ratio of each constituent element in a semiconductor porcelain composition has been studied for the purpose of improving the specific resistance-withstand voltage characteristics (JP-A-55-134901;
3-28324). Further, in order to improve the above characteristics, a titanium oxide powder having a particle size of 0.1 to 0.6 μm may be used as a starting material (JP-A-5-294625), or a titanate powder prepared by a wet coprecipitation method may be used. Various studies have been made, such as the use (JP-B-5-59068).

[0005]

However, in the conventional method, when the specific resistance at room temperature is reduced, the withstand voltage and the temperature coefficient of resistance tend to decrease with the decrease of the room temperature specific resistance. No satisfactory one has been obtained. For example, even the one with the lowest specific resistance is 4
Ωcm, 85 V / mm, 9% / ° C., which is insufficient for current limiting applications for batteries and vehicles that require particularly low resistance.

[0006]

SUMMARY OF THE INVENTION The present invention provides a barium titanate-based semiconductor porcelain which has a sufficiently low specific resistance at room temperature, a good specific resistance-withstand voltage characteristic, and a large temperature coefficient of resistance. Is what you do.

Namely first aspect of the present invention, porcelain _{composition, (Ba 1-xy Sr x} Pb y) A Ti B O 3 + pZ + qM
n + rSiO ₂ (where Z is a rare earth element such as Y or La and Nb,
Sb represents a semiconducting agent consisting of at least one of the group consisting of Sb), and x, y, and
A, B, p, q, r, the ratios of the respective constituent elements are respectively 0.05 ≦ x ≦ 0.40 0.05 ≦ y ≦ 0.40 0.25 ≦ x + y ≦ 0.48 0. 990 ≦ A / B ≦ 1.000 0.001 ≦ p <0.002 0.05 ≦ q / p ≦ 0.15 0.003 ≦ r ≦ 0.03 A titanium oxide is used as one of the raw materials, and the specific surface area of the titanium oxide is 4 m ² / g or more and 50 m or more as a BET specific surface area.
² / g or less, a method for producing a barium titanate-based semiconductor ceramic.

In the above composition formula, x, y,
The ratio of each of the constituent elements represented by A, B, p, q, and r is further calculated as follows: 0.05 ≦ x ≦ 0.40 0.05 ≦ y ≦ 0.40 0.25 ≦ x + y ≦ 0.45 0.992 ≦ A / B ≦ 1.000 0.001 ≦ p ≦ 0.0018 0.05 ≦ q / p ≦ 0.10 0.005 ≦ r ≦ 0.03 A porcelain having excellent electrical properties is obtained.

A second gist of the present invention is that, in the production of a semiconductor porcelain having the above composition, when mixing the starting materials, each of the porcelain components other than the semiconducting agent and Mn is used as an oxide or oxide thereof as a starting material. Using a carbonate, an aqueous solution of a water-soluble salt thereof as a starting material for the semiconducting agent and Mn, adjusting the pH of the mixed slurry to 8 or more and 11 or less with a weak base, and then performing a mixing treatment. This is a method for producing a barium titanate-based semiconductor porcelain.

By applying the present invention, the room temperature resistivity is 5 Ωcm or less, the ratio between the withstand voltage and the room temperature resistivity is 25 or more, and the ratio between the temperature coefficient of resistance and the logarithmic value of the room temperature resistivity is 15 or more. Is obtained.

Hereinafter, the present invention will be specifically described.
First, the composition of the semiconductor porcelain will be described. When Sr or Pb is contained in the barium titanate-based semiconductor porcelain, it replaces the Ba site of barium titanate, and the withstand voltage characteristics and the temperature coefficient of resistance are improved. The appropriate ranges are Sr (element ratio in composition formula: x) and Pb (element ratio in composition formula:
y) Both are 5 atomic% or more, and their sum is 25 atomic% or more. When the substitution amount of either Sr or Pb is less than 5 atomic%, respectively, or when the sum of the substitution amounts of Sr and Pb is less than 25 atomic%, the particle size of the obtained sintered body is less likely to be small, As a result, the ratio between the withstand voltage and the room temperature specific resistance decreases to 25 or less, and the ratio of the logarithmic value of the resistance temperature coefficient and the room temperature resistance value decreases to 15 or less,
Not preferred. If the substitution amount of either Sr or Pb exceeds 40 atomic% or the sum of the substitution amounts of Sr and Pb exceeds 48 atomic%, the room temperature resistivity becomes 5 Ωcm.
Is not preferred. When the sum of the substitution amounts of Sr and Pb is in the range of 25 atomic% or more and 45 atomic% or less, it is possible to obtain a porcelain having a lower specific resistance at room temperature in addition to the above excellent electric characteristics.

[0012] Barium titanate portion of the semiconductor ceramic composition, i.e. _{(Ba 1-xy Sr x Pb} y) A Ti B
A site component in O ₃ (Ba _1-xy Sr _x Pb
_y ) and the atomic ratio (A / B) of the B site constituent (Ti)
Value) is preferably 0.990 or more and 1.000 or less. A
When the / B value is less than 0.990, the room temperature resistivity is 5Ω.
If the A / B value exceeds 1.000, the ratio between the withstand voltage and the room temperature specific resistance decreases to 25 or less, and the ratio of the logarithmic value between the resistance temperature coefficient and the room temperature resistance becomes 1
It is not preferable because it is reduced to 5 or less. When the A / B value is in the range of 0.992 or more and 1.000 or less,
In addition to the above excellent electrical characteristics, it is possible to obtain a porcelain having a lower specific resistance at room temperature.

As a semiconducting agent for the barium titanate-based porcelain (element represented by Z in the composition formula), Y, L
At least one or more elements may be selected from rare earth elements such as a and Nb and Sb. The addition amount (element ratio in the composition formula: p) is preferably 0.1 atomic% or more and less than 0.20 atomic% with respect to Ti atoms of barium titanate. When the amount of the semiconducting agent is less than 0.1 atomic%, the specific resistance exceeds 5 Ωcm, the ratio between the withstand voltage and the room temperature specific resistance decreases to 25 or less, and the temperature coefficient of resistance and the room temperature resistance value increase. Is reduced to 15 or less. At 0.20 atomic% or more, the room temperature specific resistance is 5Ω.
cm. When the addition amount of the semiconducting agent is in the range of 0.1 atomic% or more and 0.18 atomic% or less, a porcelain having a lower room temperature specific resistance can be obtained in addition to the above excellent electric characteristics.

Addition amount of Mn (element ratio in composition formula:
Regarding q), the content is preferably 5 atomic% or more and 15 atomic% or less with respect to the addition amount of the above-described semiconductor agent. Semiconducting agent and Mn
Means that the electric properties of the sintered body are mutually affected, and when the ratio (q / p) of the amount of the semiconducting agent to the amount of Mn is less than 0.05, the withstand voltage and the room temperature resistivity are reduced. The ratio is 2
As the temperature decreases to 5 or less, the ratio of the logarithmic value of the temperature coefficient of resistance to the room temperature resistance decreases to 15 or less. If the ratio exceeds 0.15, the room temperature specific resistance exceeds 5 Ωcm, which is not preferable. When the ratio is in the range of 0.05 or more and 0.10 or less, it is possible to obtain a porcelain having a lower specific resistance at room temperature in addition to the above excellent electric characteristics.

The amount of SiO ₂ added (element ratio in the composition formula: r) is set to be 0.1 to 0.1 with respect to the Ti atom of barium titanate.
It is preferably from 3 atomic% to 3.0 atomic%. When the amount of SiO ₂ is less than 0.3 atomic%, the specific resistance exceeds 5 Ωcm, and the ratio between the withstand voltage and the room temperature specific resistance is reduced to 25 or less. On the other hand, if it exceeds 3.0 atomic%, the ratio of the logarithmic value of the temperature coefficient of resistance to the resistivity at room temperature drops to 15 or less, which is not preferable. _{2. The} amount of SiO ₂ is 0.5 atomic% or more.
When the content is within the range of 0 atomic% or less, it is possible to obtain a porcelain having low specific resistance at room temperature in addition to the above excellent electric characteristics.

In the production of the barium titanate-based semiconductor porcelain having the porcelain composition of the present invention, titanium oxide is used as a starting material for the titanium component, and its specific surface area (BET specific surface area) is 4 m ² / g or more and 50 m ² / g. In the following, preferably, a porcelain having excellent electrical characteristics can be obtained by using a porcelain of 5 to 30 m ² / g.

Titanium oxide is generally used as a pigment in many cases, and one having a purity of 95% or more and a specific surface area of 5 to 10 m ² / g is commercially available. However, these pigment-grade titanium oxides contain elements that greatly change electrical characteristics when used as semiconductor porcelain, such as niobium and iron remaining from raw minerals, and cannot be used as they are. Therefore, the purity is 99.5%
Although it is necessary to use the above-mentioned high-purity titanium oxide, the particle size becomes large due to the treatment at the time of production, and only products having a specific surface area of at most 2-3 m ² / g could be used.

[0018] The present inventors, the specific surface area of the high-purity titanium oxide used 4m ² / g or more 50 m ² / g or less, preferably, by setting the 5 to 30 m ² / g, titanium in a specific ceramic composition The inventors have found that the electrical characteristics of barium oxide-based semiconductor porcelain are improved, and arrived at the present invention. When the specific surface area value of the titanium oxide used is less than 4 m ² / g, the particle size of the obtained sintered body becomes large, and as a result, the specific resistance-withstand voltage characteristics decrease. On the other hand, when it exceeds 50 m ² / g, the particle size distribution of the obtained sintered body is deteriorated,
Since the ratio between the withstand voltage and the room temperature specific resistance is reduced to 25 or less, it is not preferable.

The present inventors have also selected and specified starting materials (compounds used for the starting materials) of each component element in the barium titanate-based semiconductor porcelain, and further adjusted the pH in the system during the mixing treatment of these starting materials. It has also been found that the electric properties of the obtained semiconductor porcelain can be improved by adjusting to a weak basicity. For example, although the amount of addition to the above-mentioned semiconductor porcelain is very small, as for the semiconducting agent and Mn which have a great influence on the PTC characteristics and various electric characteristics, the water solubility of corresponding elements such as nitrates and acetates as starting materials, for example, It is preferable to select a salt, add an aqueous solution thereof, and mix uniformly. Thereby, the resistance of the semiconductor porcelain can be further reduced. It is preferable to use an oxide or a carbonate as a starting material for each component element other than the above.

The starting materials are sufficiently wet-mixed by a technique such as a ball mill. When a water-soluble salt is used as a starting material for the semiconducting agent or Mn, a hydrolysis reaction occurs in the mixing process. By adjusting the pH at this time to 8 or more and 11 or less by using a weak base such as ammonia, the specific resistance-withstand voltage characteristics and the specific resistance-resistance temperature coefficient characteristics are improved. When the pH is less than 8, the ratio between the withstand voltage and the room temperature resistivity decreases to 25 or less. Further, it is uneconomical to adjust the pH so as to exceed 11, since the amount of the weak base to be added becomes extremely large.

The wet-mixed slurry is dehydrated and dried, and then calcined at about 1000 to 1150 ° C. to obtain a barium titanate-based solid solution powder. When the calcination temperature is 1000 ° C. or lower, the solid solution of each component does not sufficiently advance, and when it is 1150 ° C. or higher, fusion occurs and it becomes difficult to grind the powder after calcination. The barium titanate-based solid solution powder thus obtained is wet-milled to form a slurry, a binder is added, granulated, molded, and fired to form a semiconductor porcelain.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention, these production examples,
It is not limited only to the embodiment.

Production Example of High Purity Titanium Oxide Titanium tetrachloride aqueous solution (containing 16.4% as Ti content)
Was diluted with distilled water to a concentration of 3.0% as a Ti content, and heated to 70 ° C. After maintaining at this temperature for one hour, the above-mentioned aqueous solution of titanium tetrachloride was additionally charged to give a Ti content of 7.2%. Thereafter, the temperature was raised and the mixture was refluxed for 5 hours. After the reflux, the obtained slurry was repeatedly filtered and washed with water to remove impurities, and then dried at 110 ° C. When the chlorine content of the obtained titanium oxide was measured, it was 100 ppm or less. This was heat-treated at 800 ° C. to obtain a titanium oxide having a specific surface area of 5.7 m ² / g.

Example 1 TiO ₂ having a specific surface area of 5.7 m ² / g, commercially available BaCO ₃ ,
SrCO ₃ , CaCO ₃ , Pb ₃ O ₄ , Y (NO ₃ ) _{3
· 6H 2 O, La (CH} 3 COO) 3 · 3 / 2H 2 O,
_{NbCl 5, SbCl 3, Mn (} NO 3) 2 · 6H
₂ O, selected from SiO _2, the ceramic composition after _{firing, (Ba 1-xy Sr x} Pb y) A Ti B O 3 + pZ + qM
Each compound was blended so that the element ratio was as shown in Table 1 in a composition formula of n + rSiO ₂ (where Z represents a semiconducting agent composed of Y, La, Nb, and Sb) to form a slurry.

[0025]

[Table 1]

An ammonia buffer having a pH of 9.0 was added to the slurry so that the concentration became 0.02 mol / l, and the mixture was subjected to wet ball mill mixing for 15 hours. The powder obtained by dehydration and drying was calcined at 1100 ° C. for 2 hours. The obtained calcined powder was pulverized by a pin mill, and pure water and 0.5% by weight of a dispersant were added to prepare a 70% by weight slurry, which was pulverized by a wet ball mill for 3 hours. A zirconia ball having a diameter of 10 mm was used as a grinding media. A binder is added to the slurry after pulverization, and granulation is performed, and the mixture is pressed at a molding pressure of 1000 kg / cm ² .
A disk-shaped molded body having a diameter of 20 mm and a thickness of 1.0 mm was obtained. The molded body was formed into a semiconductor porcelain through a firing step of raising the temperature at 300 ° C./hour, maintaining the temperature at 1320 ° C. for 1 hour, and then decreasing the temperature at 300 ° C./hour. An In-Ga alloy was applied to both main surfaces of the obtained semiconductor ceramic, and the room temperature specific resistance [ρ], the withstand voltage [V], and the temperature coefficient of resistance [α] were measured. As the withstand voltage, the AC voltage applied to the sample was gradually increased, and the voltage value immediately before the sample was destroyed was determined. As the temperature coefficient of resistance, T ₁ was a temperature showing 10 times the resistance value at room temperature. the T ₂ as a temperature showing a 100 times the resistance of the resistance at room temperature, α = {2.303 / (T 2 / T 1)} × 100
(% / ° C.). Table 2 shows the obtained results.

[0027]

[Table 2]

Sample numbers 1, 2, 5, 7, 8, 9, 10, 13, 14, 1 marked with * in Tables 1 and 2
The porcelain compositions of 5, 16, and 19 are not within the scope of the present invention. As shown in the results of Table 2, the porcelain obtained by the production method of the present invention has a room temperature specific resistance of 5 Ωcm.
In the following, the ratio between the withstand voltage and the room temperature resistivity is 25 or more, and the ratio between the temperature coefficient of resistance and the logarithmic value of the room temperature resistivity is 1
It turns out that it is 5 or more. In addition, sample numbers 21 and 22
Uses a chlorine compound as a starting material for the semiconducting agent. Generally, if chlorine remains, it does not have a very good effect on the electrical characteristics of the semiconductor porcelain, but the porcelain obtained by the manufacturing method of the present invention hardly shows such an effect. I understand.

Example 2 Titanium oxides having various specific surface values were prepared by changing the temperature of the heat treatment in the final step to each temperature shown in Table 3 in the above-mentioned "Production example of high-purity titanium oxide". Using each of these titanium oxides as a starting material, each compound was blended so as to have the composition of Sample No. 4 in Example 1, and a porcelain was prepared in the same manner as in Example 1. The surface of the obtained porcelain was observed with a scanning electron microscope, and the particle size range was measured. Table 4 shows the results of measuring the electrical characteristics of the obtained porcelain in the same manner as in Example 1.

[0030]

[Table 3]

[0031]

[Table 4]

In Tables 3 and 4, 2 marked with *
In the porcelains of sample numbers 3 and 28, the specific surface area of titanium oxide used as a starting material is out of the range of the present invention. It can be seen that the porcelain prepared using these titanium oxides has a relatively large sintered body particle size or a wide particle size range. Table 4 also shows that the specific resistance-withstand voltage characteristics and the specific resistance-resistance temperature coefficient characteristics are inferior.

Example 3 The procedure of Example 1 was repeated except that the pH of the slurry was adjusted to the value shown in Table 5 by adjusting the ammonia buffer added to the slurry when performing the wet ball mill mixing, and then the mixing treatment was performed. The same operation was performed to prepare a porcelain having the composition of Sample No. 4. Table 5 shows the results of evaluating the electrical characteristics of the obtained porcelain.

[0034]

[Table 5]

When a water-soluble salt is used as the semiconducting agent (Y) and the Mn element component used as a starting material, when the pH of the slurry at the time of wet ball mill mixing is not in the range of 8 to 11, the specific resistance-resistance is used. It can be seen that the voltage characteristics and the specific resistance-resistance temperature coefficient characteristics decrease (Sample No. 29).

Example 4 In Example 3, Y and Mn used as starting materials
, Instead of using nitrates, Y ₂ O ₃ , MnC
The same operation was performed except that O ₃ was used to prepare a porcelain having the composition of Sample No. 4. Table 6 shows the results of evaluating the electrical characteristics of the obtained porcelain.

[0037]

[Table 6]

When oxides and carbonates are used as the materials of the semiconducting agent and Mn, respectively, the specific resistance at room temperature slightly increases, but the specific resistance-withstand voltage characteristic and the specific resistance-resistance temperature coefficient characteristic are improved. It can be seen that

[0039]

According to the present invention, in a method for producing a barium titanate-based semiconductor porcelain, titanium oxide is used as one of the starting materials, and the specific surface area of the titanium oxide is 4 m ^2.
By setting the content to not less than / g and not more than 50 m ² / g, it is possible to obtain a semiconductor porcelain having excellent electrical characteristics in a specific composition.

Claims (3)

[Claims] 1. A ceramic _{composition, (Ba 1-xy Sr x} Pb y) A Ti B O 3 + pZ + qM
n + rSiO ₂ (where Z is a rare earth element such as Y or La and Nb,
Sb represents a semiconducting agent consisting of at least one of the group consisting of Sb), and x, y, and
A, B, p, q, r, the ratios of the respective constituent elements are respectively 0.05 ≦ x ≦ 0.40 0.05 ≦ y ≦ 0.40 0.25 ≦ x + y ≦ 0.48 0. 990 ≦ A / B ≦ 1.000 0.001 ≦ p <0.002 0.05 ≦ q / p ≦ 0.15 0.003 ≦ r ≦ 0.03 A titanium oxide is used as one of the raw materials, and the specific surface area of the titanium oxide is 4 m ² / g or more and 50 m or more as a BET specific surface area.
^A method for producing a barium titanate-based semiconductor porcelain, which is not more than ² / g. 2. The method for producing a barium titanate-based semiconductor porcelain according to claim 1, wherein the ratios of the constituent elements indicated by x, y, A, B, p, q, and r are respectively within the following ranges. 0.05≤x≤0.40 0.05≤y≤0.40 0.25≤x + y≤0.45 0.992≤A / B≤1.000 0.001≤p≤0.0018 0.05 ≤ q / p ≤ 0.10 0.005 ≤ r ≤ 0.03 3. When mixing the starting materials, their oxides or carbonates are used as starting materials for each of the porcelain components other than the semiconducting agent and Mn, and their water-soluble components are used as starting materials for the semiconducting agent and Mn. 3. The method for producing barium titanate-based semiconductor porcelain according to claim 1 or 2, wherein the pH of the mixed slurry is adjusted to 8 or more and 11 or less with a weak base using a neutral salt.