JP2014144897A - Alumina-based sintered compact, and voltage-resistant member obtained by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alumina-based sintered compact hardly causing creeping dielectric breakdown due to the voltage to be applied thereto, and to provide a voltage-resistant member obtained by using the alumina-based sintered compact.SOLUTION: The alumina-based sintered compact contains alumina being a main crystal and spinel being another crystal of a compound oxide of an alkaline-earth metal and aluminum and can be made to hardly cause the creeping dielectric breakdown due to the voltage to be applied thereto by forming solid solutions from the alumina and a transition metal and the spinel and the transition metal. Since the voltage-resistant member, which is obtained by using the alumina-based sintered compact, hardly causes an instantaneous voltage drop, omission of data due to the instantaneous voltage drop can be minimized. Since the allowable voltage is large until the instantaneous voltage drop is caused, a creeping distance can be made shorter and consequently, the instrument or device to be mounted thereon can be miniaturized.

Description

  The present invention relates to an alumina sintered body that hardly causes creeping dielectric breakdown due to application of a voltage, and a withstand voltage member using the same.

  Conventionally, such as a housing of an X-ray tube to which a high voltage is applied between a cathode and an anode used in medical devices such as CT scans and analyzers such as a transmission electron microscope, a wall member of a large accelerator, a high voltage introduction terminal, etc. Various ceramics are applied to parts where high insulation is required.

  For example, Patent Document 1 proposes using alumina ceramics as an insulating member in a high voltage bushing (soot tube) of an X-ray tube.

JP-A-8-106828

  Ceramics used between the cathode and anode of medical devices such as CT scans and analyzers such as transmission electron microscopes emit electrons from the cathode side to the anode side when a voltage is applied. Secondary electrons are emitted by colliding with the surface. Then, creepage breakdown occurs when the amount of secondary electrons reaching the anode side exceeds the allowable range. It is considered that this creeping breakdown is caused by the fact that electrons easily move when there are many oxygen defects on the surface of the ceramic, and many secondary electrons are emitted accordingly.

  When such creepage breakdown occurs, in a medical device such as a CT scan or an analyzer such as a transmission electron microscope, the voltage applied between the cathode and the anode drops instantaneously (hereinafter referred to as an instantaneous voltage drop). ) And loss of important medical and analytical data occurs. Therefore, ceramics used for such applications need to reduce the emission of secondary electrons and reduce the occurrence of creepage breakdown.

  In addition, from the viewpoint of accuracy improvement and weight reduction, miniaturization is desired in medical equipment and analyzers, but creeping insulation breakdown will occur if the creepage distance between the cathode and anode is simply shortened. In order to meet the demand for miniaturization, it is necessary to increase the allowable voltage until creeping breakdown occurs.

  The present invention has been devised to satisfy the above requirements, and an object thereof is to provide an alumina sintered body that is less likely to cause creeping breakdown due to application of a voltage, and a withstand voltage member using the same. To do.

  The alumina-based sintered body of the present invention includes alumina as a main crystal and spinel as an oxide crystal composed of an alkaline earth metal and aluminum, and a transition metal is dissolved in the alumina and the spinel. It is characterized by this.

  In addition, the withstand voltage member of the present invention is characterized in that the alumina sintered body having the above-described configuration is used at a site where discharge occurs.

  According to the alumina-based sintered body of the present invention, the main crystal is obtained by dissolving the transition metal in the form of alumina, which is the main crystal, and spinel, which is an oxide crystal composed of an alkaline earth metal and aluminum. Further, since oxygen defects in the spinel crystal are reduced, emission of secondary electrons can be suppressed, so that creeping breakdown due to application of voltage can be made difficult to occur.

  In addition, according to the voltage-resistant member of the present invention, the use of the alumina sintered body of the present invention at the site where discharge is generated makes it difficult for creeping breakdown to occur, thereby reducing data loss due to an instantaneous voltage drop. be able to. In addition, since the allowable voltage to creepage breakdown can be increased, the creepage distance can be shortened, and the equipment and apparatus to be mounted can be reduced in size.

  Hereinafter, an example of the alumina sintered body of this embodiment and a withstand voltage member using the same will be described.

The alumina sintered body of the present embodiment includes alumina (Al ₂ O ₃ ) that is a main crystal, and spinel (MAl ₂ O ₄ ) that is an oxide crystal made of alkaline earth metal (M) and aluminum (Al). ) And transition metals are dissolved in alumina and spinel.

  By satisfying such a configuration, the alumina sintered body of the present embodiment has fewer oxygen defects present in alumina and spinel due to the solid solution of the transition metal, thereby suppressing the emission of secondary electrons. Therefore, it is possible to make creepage breakdown less likely to occur due to the application of voltage.

  The fact that creepage breakdown due to application of voltage is less likely to be said that the allowable voltage to creepage breakdown is large, so that medical equipment such as CT scan and transmission type If the alumina sintered body of the present embodiment is used between the cathode and anode of an analyzer such as an electron microscope, data loss due to an instantaneous voltage drop can be reduced. At the same time, the creepage distance can be shortened, and the equipment and devices to be mounted can be reduced in size, so that the accuracy and weight can be reduced.

  Moreover, since the grain growth of alumina whose main crystal is spinel can be suppressed and densified, an alumina sintered body having excellent mechanical strength and less likely to cause creeping dielectric breakdown can be obtained.

  In addition, the main crystal in the alumina sintered body of the present embodiment appears on the chart as the highest main peak in the measurement by an X-ray diffractometer using Cu Kα rays. What is necessary is just to collate with the JCPDS card data about identification of the obtained peak.

  The alkaline earth metal (M) is composed of any one of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), etc. Consisting of either.

The confirmation of the presence of spinel (MAl ₂ O ₄ ), which is an oxide crystal composed of alkaline earth metal (M) and aluminum (Al), was measured with an X-ray diffractometer using Cu Kα rays. Then, it may be identified by collating with JCPDS card data.

  Whether the transition metal is dissolved in alumina and spinel or not is determined by observing the polished surface of the alumina sintered body with a transmission electron microscope (TEM) and attaching the attached energy dispersion. Whether or not a transition metal is detected when a spot (φ1 nm) is applied to each crystal grain using a type X-ray spectrometer (EDS) can be confirmed.

Specifically, when the spinel is, for example, MgAl ₂ O ₄ , if a transition metal is detected in addition to Mg, Al, and O when a spot is applied in the crystal grain, the detected transition metal is It can be said that it is dissolved in spinel. In this analysis, it is possible to know the mass ratio of each element when the mass at the spot of φ1 nm is 100 mass%.

  The allowable voltage until creeping breakdown can be confirmed by the creeping breakdown voltage. The creeping breakdown voltage is obtained by dividing the voltage that has caused a voltage drop due to creeping breakdown between the cathode and the anode by the creeping distance (distance between the cathode and the anode). According to the bonded body, the creeping breakdown voltage reaches 6 kV / mm or more.

The alumina sintered body of the present embodiment has α, β, and γ when the molar percentages are α for alumina, β for transition metal oxide, and γ for alkaline earth metal oxide, respectively. However, it is preferable that 80 ≦ α ≦ 99.8, 0.1 ≦ β ≦ 10, 0.1 ≦ γ ≦ 10 and α + β + γ = 100 are satisfied.

  In the alumina sintered body having a spinel whose main crystal is alumina and an oxide crystal composed of an alkaline earth metal and aluminum, and satisfying the above composition formula, The abundance (content) is optimized and the spinel suppresses the grain growth of alumina and can be densified. Therefore, creeping dielectric breakdown hardly occurs, and alumina-based sintering with excellent mechanical strength It can be a body.

  The mol% ratio of the alumina sintered body of the present embodiment is determined by first crushing a part of the alumina sintered body, dissolving the obtained powder in a solution such as hydrochloric acid, and then ICP (Inductively Coupled). Plasma) Measured using an emission spectroscopic analyzer (manufactured by Shimadzu Corporation: ICPS-8100), and converted into oxides from the obtained contents of Al, transition metal and alkaline earth metal. Then, a molar ratio may be obtained by calculating a molar ratio from each molecular weight, calculating the total molar ratio as a denominator, and calculating each molar ratio as a numerator.

Specifically, when the transition metal is titanium and the alkaline earth metal is magnesium, Al, Ti. By converting the Mg content into Al ₂ O ₃ , TiO ₂ , and MgO, respectively, calculating the molar ratio from each molecular weight, calculating the total molar ratio as the denominator, and calculating each molar ratio as the numerator, What is necessary is just to obtain a% ratio.

In addition, when the spinel is, for example, MgAl ₂ O ₄ , the amount of alumina and spinel is regarded as the amount of spinel converted from Mg content to MgAl ₂ O ₄ . The content of Al necessary for the conversion of spinel is subtracted from the content and converted to Al ₂ O ₃ may be regarded as the abundance of alumina.

In the alumina sintered body of the present embodiment, it is preferable that the transition metal is titanium and the alkaline earth metal is magnesium. When the transition metal is titanium and the alkaline earth metal is magnesium, the emission of secondary electrons is further suppressed. The reason for this is not clear, but it is thought that the presence of magnesium makes it easier for titanium to enter oxygen defects in alumina and spinel. In the alumina sintered body of this embodiment, when the transition metal is titanium and the alkaline earth metal is magnesium, the creeping dielectric breakdown voltage is 9 kV / mm or more.

  Next, an example of the manufacturing method of the alumina sintered body of this embodiment is demonstrated.

First, alumina (aluminum oxide) powder, transition metal oxide powder, and alkaline earth metal oxide powder are prepared, and a predetermined amount is weighed to obtain a primary material. Needless to say, not only oxide powder but also hydroxide powder may be used. Next, for example, 5% by mass or less of a sintering aid, and 1% of the primary raw material powder after weighing, and 100% by mass of the weighed primary raw material powder,
A binder such as PVA of ~ 1.5% by mass, a solvent of 100% by mass, and a dispersant of 0.1 to 0.5% by mass is mixed and stirred in a stirrer to form a slurry, which is then spray granulated (sprayed) Granulate with a dryer to obtain granules.

  Thereafter, the obtained granules are formed into a predetermined shape by various molding methods such as a die press molding method and an isostatic pressing method (rubber press), and after being subjected to cutting as necessary, this is fired. Bake in a furnace at a maximum temperature of 1400-1700 ° C in an air atmosphere. After firing, the alumina sintered body of the present embodiment can be obtained by final finishing by grinding.

Here, in order to obtain the alumina-based sintered body of the present embodiment, the transition metal must be dissolved in alumina or spinel, so that the average is higher than the alumina powder or the powder serving as the alkaline earth metal source. A powder serving as a transition metal source having a small particle size is used. Specifically, a powder serving as a transition metal source having an average particle size of 0.7 μm or less is used. The average particle size of the powder serving as the transition metal source can be determined by a laser diffraction scattering method using a microtrack device (MT3300EXII manufactured by Nikkiso).

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

Each sample having a different solid solution state in the crystal was prepared, and the creeping breakdown voltage was measured to confirm the difficulty of creeping breakdown.
1) Preparation of granules of a sample according to the present invention First, an aluminum oxide powder having an average particle diameter of 1.0 μm, a titanium oxide powder having an average particle diameter of 0.5 μm, and a magnesium hydroxide powder having an average particle diameter of 1.0 μm. Got ready. Thereafter, the primary raw material was weighed so that the molar ratio of alumina (aluminum oxide): titanium oxide: magnesium oxide was 80:10:10. Then, the primary raw material after weighing, and 100% by mass of the primary raw material, 1% by mass of PVA (polyvinyl alcohol), 100% by mass of solvent, and 0.2% by mass of the dispersing agent are stirred. The mixture was mixed and stirred to make a slurry. Then, this slurry was granulated with a spray granulator (spray dryer) to obtain granules.
2) Preparation of sample granule of Comparative Example 1 Except for using titanium oxide powder having an average particle size of 1.0 μm, the sample of Comparative Example 1 was prepared by the same method as that for preparation of the sample granule of the present invention. Granules were made.
3) Preparation of sample granules as Comparative Example 2 Predetermined amounts of aluminum oxide powder, magnesium hydroxide powder, and titanium oxide powder are mixed and heated to 1200 ° C. in the atmosphere in a firing furnace to produce titanium as a transition metal. Spinel (MgAl ₂ O ₄ ) in solid solution was calcined and synthesized. Then, it took out from the furnace and grind | pulverized until it became an average particle diameter of 1.0 micrometer, and the synthetic spinel powder was obtained. Comparative Example 2 and Comparative Example 2 were prepared in the same manner as in the preparation of the granule of the sample according to the present invention, except that synthetic spinel powder having an average particle diameter of 1.0 μm and aluminum oxide powder having an average particle diameter of 1.0 μm were used as starting materials. A sample granule was prepared.
4) Preparation of Sample Granule of Comparative Example 3 A sample granule of Comparative Example 3 was prepared in the same manner as in the preparation of the sample granule of the present invention except that no titanium oxide powder was added.

  Next, using each of the obtained granules, the mold was filled and pressed, and then subjected to cutting to obtain a molded body having a predetermined shape. Next, the obtained molded body was put in a firing furnace and fired at a maximum temperature of 1600 ° C. in an air atmosphere. Then, grinding was performed after firing, and a plurality of disk-shaped samples each having an outer diameter of φ20 mm and a thickness of 5 mm were obtained.

Further, using a X-ray diffractometer (manufactured by PANalytical: X'Pert PRO), a plurality of sample surfaces were measured under the conditions of 2θ = 8 ° to 80 ° and CuKα ₁ measurement, and JCPDS was obtained from the obtained X-ray diffraction chart. The main peak was identified based on the card, and it was confirmed that alumina was the main crystal and spinel was present.

  In addition, after cutting one of the samples and polishing the cut surface, it was observed with a transmission electron microscope, and using an attached energy dispersive X-ray spectrometer, φ1 nm was observed at a plurality of locations in the crystal grains. The spot analysis was performed. In alumina and spinel, “◯” is shown for samples in which titanium as a transition metal was detected, and “-” is shown for Tables in which titanium was not detected.

  Next, the creepage breakdown voltage was measured for each sample, and the results are shown in Table 1.

  From Table 1, the sample of the present invention in which titanium is detected (solid solution) in alumina and spinel is an alumina sintered body having a high creeping breakdown voltage and hardly causing creeping breakdown due to the applied voltage. I understood it.

  Next, transition metal and alkaline earth metal were variously changed as shown in Table 2. 1 to 8 were fabricated, creeping breakdown voltage was measured, and the obtained values were ranked. In addition, it was set as the method similar to Example 1 except having changed the powder used as a transition metal source or an alkaline-earth metal source. The results are shown in Table 2.

  From Table 2, when the transition metal was Ti (titanium) and the alkaline earth metal was Mg (magnesium), the highest creeping breakdown voltage value was obtained.

Next, sample Nos. With various changes in composition as shown in Table 3 were used. 9 to 38 were prepared, and creeping breakdown voltage was measured. As a production method, an aluminum oxide powder having an average particle diameter of 1.0 μm, a titanium oxide powder having an average particle diameter of 0.5 μm, and a magnesium hydroxide powder having an average particle diameter of 1.0 μm are used. Aluminum oxide: titanium oxide: A primary raw material was weighed so that the mol% ratio of magnesium oxide was the value shown in Table 3. The subsequent manufacturing method was the same as in Example 1. The results are shown in Table 3.

From Table 3, the sample Nos. Whose molar percentages satisfy 80 ≦ α ≦ 99.8, 0.1 ≦ β ≦ 10, 0.1 ≦ γ ≦ 10 and α + β + γ = 100 are satisfied. For 10-15, 18-22, 26-36, the creeping dielectric breakdown voltage is as high as 11 kV / mm or more, and it is a good alumina sintered body that is less susceptible to creeping breakdown due to the applied voltage. I found out.

  Sample No. From the results of 9 to 16, it was found that the molar ratio of the transition metal oxide and the alkaline earth metal oxide is preferably equimolar.

Sample No. When a test piece based on JIS R 1601-1995 was cut out from 10 to 15 and the three-point bending strength was measured, a value exceeding 300 MPa was obtained, and it was confirmed that the mechanical strength was excellent.

  As is clear from these examples, the alumina sintered body of the present invention is less prone to creepage breakdown, and therefore, when used in a site where discharge occurs, data loss due to instantaneous voltage drop is reduced. Therefore, it was found that it is suitable as a withstand voltage member. In addition, since the allowable voltage to creepage breakdown can be increased, the creepage distance can be shortened by using the alumina sintered body withstand voltage member of the present invention. It was found that the device can be downsized.

Claims (4)

Alumina sintered body comprising alumina as a main crystal and spinel as a crystal of an oxide composed of an alkaline earth metal and aluminum, wherein the transition metal is dissolved in the alumina and the spinel. . The respective mole percentages are characterized in that α, β and γ satisfy the following conditions, where α is the alumina, β is the oxide of the transition metal, and γ is the oxide of the alkaline earth metal. The alumina sintered body according to claim 1.
80 ≦ α ≦ 99.8
0.1 ≦ β ≦ 10
0.1 ≦ γ ≦ 10
α + β + γ = 100 The alumina-based sintered body according to claim 1 or 2, wherein the transition metal is titanium and the alkaline earth metal is magnesium. A withstand voltage member using the alumina sintered body according to any one of claims 1 to 3 at a site where electric discharge occurs.