Title of Invention

A METHOD FOR PREPARING A BARIUM TITANATE SERIES SEMICONDUCTOR PORCELAIN COMPOSITION

Abstract

The present invention discloses a method for preparing a barium titanate series semiconductor porcelain composition, said method comprising (a) mixing, a principal component of barium titanate or a solid solution thereof, such as herein described, having a part of Ba of BaTiO3 replaced with from 1 to 25 mol% Ca, from 1 to 30 mol% Sr and from 1 to 50 mol% Pb ; a semi conducting agent, such as herein described, added in an amount of from 0.2 to 1.0 mol% calculated as the element to 100 mol% of the principal component; and additives, being manganese oxide, added in an amount of from 0.01 to 0.10 mol% calculated as Mn; silica added in an amount of from 0.5 to 5 mol% calculated as SiO2; and magnesium oxide added in an amount of from 0.0028 to 0.093 mol% calculated as Mg; and (b) calcining the mixture, so obtained, at a desired calcining temperature after dehydrating and drying the same.

Full Text

FIELD OF THE INVENTION The present invention relates to a method for preparing a barium titanate series semiconductor porcelain composition. BACKGROUND OF THE INVENTION Hitherto, as barium titanate series semiconductor porcelain composition, following compositions are known. That is, Examined Published Japanese Patent Application No. 62-43522 discloses that a barium titanate series semiconductor porcelain made up of BaTiO3 as the principal component or a barium titanate series semiconductor porcelain made up of BaTiO3, wherein a part of Ba is replaced with Pb, contains from 0.00035 to 0.0072% by weight magnesium based on the above-described barium titanate series porcelain taken as 100 for increasing the break-down voltage. Also, Examined Published Japanese Patent Application No. 63-28324 discloses a barium titanate series porcelain semiconductor composition comprising from 30 to 95 mol% BaTi03, from 30 to 25 mol% CaTiO3 from 1 to 30 mol% SrTiO3 , and from 1 to 50 mol% PbTiO3 as the principal components and that by simultaneously replacing a part of Ba of BaTiO3 with Ca, Sr, and Pb as described above, the barium titanate series porcelain semiconductor composition is excellent in the withstand voltage 1A characteristics and the rush current resisting characteristics as compared with conventional ones. Also, Examined Published Japanese Patent Application No. 62-58642 discloses a semiconductor porcelain composition having a not high rush current and the positive resistant temperature characteristics showing less change with the passage of time, such as an intermittent test, etc. Furthermore, Unexamined Published Japanese Patent Application No. 2-48464 discloses that by a barium titanate series semiconductor porcelain wherein a part of Ba of BaTi03 is simultaneously replaced with from 0-001 to 0.1 atomic% Mg and from 0.01 to 2.0 atomic% Ca ; or a barium titanate series semiconductor porcelain wherein a part of BaTi03 is simultaneously replaced with from 0.01 to 5.0 atomic% Pb and from 0.01 to. 2.0 atomic% Ca; or a barium titanate series semiconductor porcelain wherein a part of BaTi03 is simultaneously replaced with from 0 .001 to 0.1 atomic% Mg, from 0.01 to 5.0 atomic% Pb, and from 0.01 to 2.0 atomic% Ca, the change of the resistance based on the temperature change in the temperature range of the environment for use can be restrained and also the specific resistance value at normal temperature can be retrained low. Still further, Unexamined published Japanese Patent Application No. 2-4 84 65 discloses that by a barium titanate series semiconductor porcelain wherein a part of Ba of BaTi03 2 is replaced with from 0.001 to 0.1 atomic % Mg, a barium titanate series semiconductor porcelain wherein a part of Ba of BaTiO3 is replaced with from 0.01 to 5.0 atomic% Pb, or a barium titanate series semiconductor porcelain wherein a part of Ba of BaTiO3 is simultaneously replaced with from 0.001 to 0.1 atomic% Mg and from 0.01 to 5.0 atomic% Pb, the change of resistance based on the temperature change in the temperature range of the environment for use can be restrained. Recently, with small-sizing and the increase of the density of electronic instruments, in a positive characteristic thermistor element composed of a barium titanate series semiconductor porcelain composition, which is used for the electronic instruments, small-sizing is also advanced. However, it is known that when the positive characteristic thermistor element is small-sized, the rush current resisting characteristics (the flash withstand voltage characteristics)are lowered and thus conventional positive characteristics thermistor elements cannot sufficiently cope with the needs of market requiring more small-sizing thereof. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preparing a barium titanate series semiconductor porcelain composition capable of small-sizing a positive characteristic thermistor by improving the rush current resisting characteristics. The present invention has been made for achieving the 3 above-described object. Accordingly, the present invention provides a method for preparing a barium titanate series semiconductor porcelain composition, said method comprising (a) mixing, a principal component of barium titanate or a solid solution thereof, such as herein described, having a part of Ba of BaTiO3 replaced with from 1 to 25 mol% Ca, from 1 to 30 mol% Sr and from 1 to 50 mol% Pb ; a semiconducting agent, such as herein described, added in an amount of from 0.2 to 1.0 mol% calculated as the element to 100 mol% of the principal component; and additives, being manganese oxide, added in an amount of from 0.01 to 0.10 mol% calculated as Mn; silica added in an amount of from 0.5 to 5 mol% calculated as SiO2; and magnesium oxide added in an amount of from 0.0028 to 0.093 mol% calculated as Mg; and (b) calcining the mixture, so obtained, at a desired calcining temperature after dehydrating and drying the same. Also, it is preferred that the semiconducting agent is at least one of the elements selected from Yttrium, Lanthanum, Cerium, Niobium, Bismuth, Antimony, Tungsten, Tantalum, Dysprosium, Gadolinium, Neodymium and Samarium. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING Fig. 1 is a graph showing the relation of the measured time and the electric current value in a positive characteristic thermistor element. 4 DETAILED DESCRIPTION OF THE INVENTION The present invention is described in detail below. The barium titanate series semiconductor composition of the present invention contains a principal component made up of barium titanate or a solid solution thereof, wherein a part of Ba of BaTiO3 is replaced with Ca, Sr, and rb in the compounding ratios (mol%) described above, contains a semiconducting agent, and also contains manganese oxide, silica, and magnesium oxide in the above-described compounding ratios (mol%). By having the above-described composition, the rush current resisting characteristics can be improved, whereby small-sizing of a positive characteristic thermistor element becomes possible. This is because by simultaneously replacing a part of Ba of BaTiO3 with Pb, Ca, and Sr and adding thereto Mg, the rush current resisting characteristics can be greatly improved as compared with the conventional case of replacing a part of Ba of BaTiO3 with each component singly or with two kinds of components and adding Mg. In addition, as to the compounding ratios, when the total amount of the composition is taken as 100 mol%, the compounding ratio of the principal component is the value obtained by subtracting the total mol% of the semiconducting agent and the additives from 100 mol%. Also, there is no particular restriction on the semiconducting agent used in the present invention and various 5 kinds of semiconducting agents can be used. Practical examples thereof include elements such as Y, La, Ce, Nb, Bi, Sb, w, Dy, Gd, Nd, and Sm. The present invention is more practically described below based on the following example but the present invention is not limited to the example only. Example As raw materials, BaCO3, CaCO3, Pb3O4, SrCO3, and TiO2 as the principal components; Y2O3, La2O3, Er2O3, and Nd2O3 as the semiconducting agents; and MnCO3, SiO2, and MgCO3 as the additives were prepared, these raw materials were compounded such that each of the semiconductor porcelain compositions having the compounding ratios shown in Table 1 to Table 4 was obtained, and the compounded mixture was further wet-blended. The mixture was dehydrated and dried, and then calcined for 2 hours at a temperature of from 1,100 to 1,200°C. Then, the calcined raw materials were ground, further wet-blended with the addition of a binder, followed by granulation, and molded into a disc form at a molding pressure of 1,000 kg/cm2. Then, by burning the molded disc at a temperature of from 1,300 to 1,400°C, a disc-form semiconductor porcelain of 11.5 mm in diameter and 2.2 mm in thickness was obtained. On both principal surfaces of the semiconductor porcelain obtained was formed an electrode of an Ni-Ag layer structure composed of a non-electrolytically nickel plate electrode (1st 6 layer) and a silver-baked electrode (2nd layer) to provide each sample. About each of these samples obtained, the resistance value at normal temperature (25°C), the withstand voltage characteristics, the Curie temperature, and the rush current resisting characteristics (the flash withstand voltage characteristics) were measured and the values were shown in Table 5 to Table 8 below. In the above-described various characteristics, the withstand voltage characteristics show the highest applied voltage value directly before occurring breaking of the sample when the voltage applied to the sample is gradually increased. Also, the rush current resisting characteristics show the maximum voltage value (the flash withstand voltage) at which the semiconductor porcelain is not broken when an alternating rush voltage is applied to the sample. In addition, in the tables, the sample numbers added with ( * ) are outside the ranges of the present invention. 7 8 Table 1I Table 2 9 Table 3 10 Table 4 Table 5 1) WITHSTAND VOLTAGE CHARACTERISTICS 2) RUSH CURRENT RESISTING CHARACTERISTICS 1 2 Table 6 1) WITHSTAND VOLTAGE CHARACTERISTICS 2) RUSH CURRENT RESISTING CHARACTERISTICS 13 Table 7 1) WITHSTAND VOLTAGE CHARACTERISTICS 2) RUSH CURRENT RESISTING CHARACTERISTICS 14 Table 8 1) WITHSTAND VOLTAGE CHARACTERISTICS 2) RUSH CURRENT RESISTING CHARACTERISTICS 15 Now, the reasons for limiting the numerals of the composition ranges of the present invention are explained. In the principal components made up of barium titanate or a solid solution thereof, the reason for limiting the ranges that a part of Ba of BaTiO3 is replaced with from 1 to 25 mol% Ca That is, when Ca is less than 1 mol%, the addition effect thereof is insufficient and the rush current resisting characteristics are lowered as compared with the withstand voltage characteristics as shown in Sample No. 1, Sample No. 2, and Sample No. 3. On the other hand, when Ca exceeds 25 mol%, the resistance value greatly increases and the rush current resisting characteristics are lowered as compared with the withstand voltage characteristics as shown in Sample No. 20 and Sample No. 21. Also, when Sr is less than 1 mol%-, the rush current resisting characteristics are lowered as compared with the withstand voltage characteristics as shown in Sample No. 22 and Sample No. 23. In addition, Sample No. 22 and Sample No. 23 are the examples of not adding Sr, but even where Sr is practically added in an amount of less than 1 mol%, it has been confirmed that the addition effect thereof is insufficient and the rush current resisting characteristics are lowered as compared with the withstand voltage characteristics. 16 On the other hand, when Sr exceeds 30 mol%, the resistance value greatly increases and the rush, current -resisting characteristics are lowered as compared with the withstand voltage characteristics as shown in Sample No. 38, Sample No. 39, and Sample No 40. Also, when Pb is less than 1 mol%, the rush current resisting characteristics are lowered as compared with the withstand voltage characteristics as shown in Sample No. 41 and Sample No. 42. In addition, Sample No. 41 and Sample No. 42 are the examples of not adding Pb, but even when Pb is practically added in an amount of less than 1 mol%, it has been confirmed that the addition effect thereof is insufficient and the rush current resisting characteristics are lowered as compared with the withstand voltage characteristics. On the other hand, when Pb exceeds 50 mol%, it becomes difficult to form a semiconductor as shown in Sample No. 58, Sample No. 59, and Sample No. 60. Then, the reason for limiting the compounding ratio of the semiconducting agent to the range of from 0.2 to 1.0 mol% to 100 mol% of the above-described principal components is as follows. That is, when the addition amount of the semiconducting agent is less than 0.2 mol%, the addition effect thereof is insufficient, a semiconductor is not formed, and the resistance value extremely increases as shown in Sample No. 61, Sample No. 17 62, Sample No. 78, Sample No. 96, and Sample No. 97. On the other hand, when the addition amount thereof exceeds 1.0 mol%, the resistance value extremely increases and the withstand voltage characteristics and the rush current resisting characteristics are deteriorated as shown in Sample No. 76, Sample No. 77, Sample No. 94, Sample No. 95, Sample No. 106, and Sample No. 107. Also, the reason for limiting the compounding amount of manganese oxide as the additive to the range of from 0.01 to 0.10 mol% calculated as Mn to 100 mol% of the above-described principal components is as follows. That is, when the addition amount of manganese oxide is less than 0.01 mol% , the addition effect thereof is insufficient, the resistance temperature changing ratio is small, and thus the barium titanate semiconductor porcelain composition obtained is lacking in practicability as shown in Sample No. 112, Sample No. 113, and Sample No. 114. On the other hand, when the addition amount thereof exceeds 0.10 mol%, the resistance value greatly increases and the product obtained is lacking in practicability as shown in Sample No. 124 to Sample No. 140. Furthermore, the reason for limiting the compounding amount of silica as the additive to the range of from 0.5 to 5 mol% calculated as SiO2 to 100 mol% of the above-described principal components is as follows. 18 That is, when the addition amount of silica is less than 0.5 mol%, the addition effect is insufficient and the deviation of the specific resistance to the slight deviation of the amount of the semiconducting agent cannot be sufficiently restrained as shown in Sample No. 126, Sample No. 127, and Sample No. 128. On the other hand, when the addition amount thereof exceeds 5 mol%, the resistance value greatly increases and the deviation of the specific resistance cannot be sufficiently restrained. Moreover, the reason for limiting the compounding amount of magnesium oxide to the range of from 0.0028 to 0.093 mol% calculated as Mg to 100 mol% of the above-described principal components is as follows. That is, when the addition amount of magnesium oxide is less than 0.0028 mol%, the effect of improving the characteristics is not obtained because the addition amount is a little, as shown in Sample Nos. 1, 4, 11, 12, 17, 22, 24, 29, 32, 34, 35, 38, 43, 43, 56, 58, 61, 63, 67, 70, 71, 76, 79, 82, 83, 90, 94, 96, 98, 102, 106, 108, 112, 115, 119, 120, 124, 126, 129, 133, 134, and 139. On the other hand, when the addition amount thereof exceeds 0.093 mol%, the resistance value increases owing to the excessive addition and the effect of improving the characteristics is not obtained as shown in Sample Nos. 7, 10, 15, 19, 31, 54, 66, 75, 81, 87, 88, 89, 93, 101, 105, 111, 118, 123, 132, and .138. 19 In addition, samples based on Examp c 3 of Examined Published Japanese Patent Application No. 6 2-43522. were prepared as reference examples as shown in Table 9 below and the flash withstand voltage characteristics of each sample were measured by the same method as described above. The results obtained were shown in Table 9. Also, the Curie points (Tc) and the specific resistance (f>) of the samples were shown in the same table. In addition, the addition amount of each component is shown as mo1%. [Table 9] According to these samples of the reference example, it can be seen that in the barium titanate series semiconductor porcelain compositions of the Ba-Pb series principal components, even when the addition amcuni of magnesium oxide is from 0.028 to 0.056 mol% calculated as Mg , the sufficient flash withstand voltage characteristics are not obtained. 2 0 Also, samples of the Ba-Pb-Sr-Ca series each having almost same p and TC as those shown in Table 9 above were prepared as shown in Table 10 below and the flash withstand voltage characteristics of each sample were measured by the same method described above. The results obtained were shown in the same table. [Table 10] According to these samples, it can be seen that by employing the Ba-Pb-Sr-C series, the flash withstand voltage characteristics are improved and that when Mg is added within the range of the present invention, the flash withstand voltage is further improved. Also, samples of a 3a series only as the principal components (Sample Nos. 216 and 217), samples of a Ba-Sr series (Sample Nos. 210 and 219), samples of a Ba-Ca series (Sample Nos- 220 and 221), samples of a Ba-Pb-Sr series (Sample Nos. 222 and 223), samples of a Ba-Pb-Ca series (Sample Nos. 224 and 21 225), samples of a Ba-Sr-Ca series (Sample Nos. 226 and 221), samples of a Ba-Pb series (Sample Nos. 228 and 229) and samples of a Ba-Pb-Sr-Ca series (Sample Nos. 230 and 231) were prepared as shown in Table 11 below and the flash withstand voltage characteristics of each sample were measured by the same method as described above. The results obtained were shown in the same table. According to these samples, it can be seen that in the barium titanate series semiconductor porcelain composition of the Ba-Pb-Sr-Ca series as the principal components, when the addition amount of magnesium oxide calculated as Mg is 0.028 mol%, the good flash withstand voltage characteristics are obtained. Then, disc-form thermostat elements each having the Ni-Ag electrode formed using the sample optionally selected from the samples shown in Table 1 to Table 4 described above were prepared 22 and the current decay characteristics (Pmax) and the stable current characteristics thereof were measured. The results were shown in Table 12 below. In addition, the current decay characteristics (Pmax) is the largest value of P when the changed amount (I1 - I2) of an optional peak value I1 to the adjacent peak value I2 is defined as p as shown in Fig. 1 and the stable current characteristics is the electric current value passing through the circuit 3 minutes after-initiation of the measurement. As shown in Table 12 above, it can be seen that the disc-form elements each having the Ni-Ag electrode formed the sample containing the principal components, the semiconducting agent, and the additives other than magnesium oxide within the above-described ranges of the present invention and added with magnesium oxide in the range of from 0.0028 to 0.093 mol% calculated an Mg show excellent characteristics in the current 23 decay characteristics (Pmax) and the stable current characteristics. As described above, by using the barium titanate series semiconductor porcelain composition of the present invention, the rush current resisting characteristics (flash withstand voltage characteristics) are improved, whereby a thermistor element can be more small-sized. Furthermore, because in the case of using the barium titanate series semiconductor porcelain composition of the present invention, the excellent characteristics are also obtained in the current decay characteristics and,the stable current characteristics, the electric reliability can be more improved. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 24 WE CLAIM: 1. A method for preparing a barium titanate series semiconductor porcelain composition, said method comprising (a) mixing, a principal component of barium titanate or a solid solution thereof, such as herein described, having a part of Ba of BaTiO3 replaced with from 1 to 25 mol% Ca, from 1 to 30 mol% Sr and from 1 to 50 mol% Pb ; a semiconducting agent, such as herein described, added in an amount of from 0.2 to 1.0 mol% calculated as the element to 100 mol% of the principal component; and additives, being manganese oxide, added in an amount of from 0.01 to 0.10 mol% calculated as Mn; silica added in an amount of from 0.5 to 5 mol% calculated as SiO2; and magnesium oxide added in an amount of from 0.0028 to 0.093 mol% calculated as Mg; and (b) calcining the mixture, so obtained, at a desired calcining temperature after dehydrating and drying the same. 2. The method as claimed in claim 1, wherein the semiconducting agent is atleast one of the elements selected from Yttrium, Lanthanum, Cerium, Niobium, Bismuth, Antimony, Tungsten, Tantalum, Dysprosium, Gadolinium, Neodymium and Samarium. 25 3. A thermistor element incorporating the barium titanate series semiconductor porcelain composition, prepared by any of the preceding claims. 4. A method for preparing a barium titanate series semiconductor porcelain composition, substantially as herein described, particularly with reference to the foregoing examples and tables. The present invention discloses a method for preparing a barium titanate series semiconductor porcelain composition, said method comprising (a) mixing, a principal component of barium titanate or a solid solution thereof, such as herein described, having a part of Ba of BaTiO3 replaced with from 1 to 25 mol% Ca, from 1 to 30 mol% Sr and from 1 to 50 mol% Pb ; a semi conducting agent, such as herein described, added in an amount of from 0.2 to 1.0 mol% calculated as the element to 100 mol% of the principal component; and additives, being manganese oxide, added in an amount of from 0.01 to 0.10 mol% calculated as Mn; silica added in an amount of from 0.5 to 5 mol% calculated as SiO2; and magnesium oxide added in an amount of from 0.0028 to 0.093 mol% calculated as Mg; and (b) calcining the mixture, so obtained, at a desired calcining temperature after dehydrating and drying the same.

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