JP2001002466A - High-voltage-withstanding aluminous sintered compact and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminous sintered compact appropriate as the material for a ceramic product needing high insulating and voltage withstanding properties at a high temp. and its production method. SOLUTION: A mullite crystal phase is formed in the aluminous sintered compact consisting essentially of alumina and contg. an assitant component consisting of a silicon component, calcium component and/or magnesium component. Further, the relative density of the sintered compact is increased to >=95%, the major axis of the pore present in the compact is controlled to <=10 μm, and a high-voltage-withstanding aluminous sintered compact is obtained. The withstand voltage of the compact is kept at >=60 kV/mm at 700 deg.C, and the compact is appropriately used as an insultor used in a spark plug, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina-based sintered body having high insulation properties and high withstand voltage, which is suitable as a material for ceramic products, and a method for producing the same. In particular, it is suitable as a high withstand voltage alumina-based sintered body used for an insulator used for a spark plug or the like.

[0002]

2. Description of the Related Art Alumina ceramics are excellent in withstand voltage, heat resistance, mechanical properties and the like and are inexpensive. Therefore, ceramics such as insulators for spark plugs and multilayer wiring boards for IC packages are used. It is practically used as a material. In particular, insulators for spark plugs are required to have high insulation properties from room temperature to a high temperature of around 700 ° C., and various approaches have conventionally been made. Conventionally, an alumina-based sintered body using a ternary system composed of SiO ₂ —CaO—MgO as a sintering aid has been used as an insulator material such as a spark plug.

However, since the ternary sintering aid exists as a low-melting glass at the grain boundary of alumina after sintering, the material has a high withstand voltage by optimizing the compounding ratio of SiO ₂ —CaO—MgO. Naturalization had its own limits.

[0004] On the other hand, when the amount of these sintering aids is reduced, a large number of pores are generated at the alumina grain boundaries, which causes a decrease in withstand voltage. Basically, it is thought that dielectric breakdown of the alumina material occurs at the residual pores or low-melting grain boundary glass existing at the grain boundaries. Improving the properties is a guideline for improving the withstand voltage of the material.

For example, in Japanese Patent Publication No. 63-1262, it is generally used as a sintering aid for alumina.
SiO ₂ —CaO— existing as grain boundary glass after sintering
High withstand voltage is obtained by limiting the mixing ratio of MgO. Japanese Patent Application Laid-Open No. 62-100474 discloses a method of controlling the particle size of granulated particles.
No. 66 discloses a technique of using two types of alumina raw materials having different particle diameters to reduce residual pores in a sintered body and improve voltage resistance. Tokuhei 7-1
No. 7436 discloses Y ₂ O ₃ , La ₂ O ₃ , and ZrO.
By using a new sintering aid such as No. _2, the melting point of the grain boundary glass is improved. In Japanese Patent No. 2,564,842, the sintering aid is uniformly dispersed using an organometallic compound as a raw material, and a Y ₄ Al ₂ O ₉ crystal phase is generated at a grain boundary to improve the heat resistance of the grain boundary. , High withstand voltage of the material is achieved.

However, with the recent downsizing of engines and enlargement of valves, spark plugs have been reduced in diameter.
Insulators also need to be thinner. For this reason, the voltage resistance of the insulating material has not reached a sufficient level even when the above-described conventional technology is used.

[0007]

The problems to be solved in the prior art are that the pore diameter remaining at the grain boundary of the alumina-based sintered body is large, the relative density is low, and the melting point is low at the grain boundary. The point is that a low glass is generated, so that the withstand voltage becomes low.

[0008]

A first aspect of the present invention is an alumina-based sintered material containing alumina (Al ₂ O ₃ ) as a main component and a silicon component and a calcium and / or magnesium component as subcomponents. Mullite (Al ₆ Si) in the body
₂ O ₁₃ ) A crystal phase is generated, and the relative density of the alumina-based sintered body is set to 95% or more, whereby 700 ° C.
It achieves excellent withstand voltage even at high temperatures.

The location of the mullite crystal phase is not particularly limited. However, in order to more effectively improve the withstand voltage at a high temperature of 700 ° C., two grain boundaries and / or three alumina grains are required. It is preferably present at the point of emphasis. The mullite crystal that enhances the voltage resistance of the alumina-based sintered body is effectively generated by a reaction during sintering, but may be added in advance as a raw material powder. In this case, the average particle size of the mullite raw material powder is preferably 1 μm or less, particularly preferably 0.5 μm or less. In addition, a submicron class ultrafine powder can be used.

According to a second aspect of the present invention, there is provided a silicon component of the auxiliary component (a silicon component and a calcium component and / or a magnesium component) contained in the alumina-based sintered body according to the first aspect.
Oxide-converted composition ratios (SiO ₂ , CaO,
MgO) is specified. In such a composition range, mullite in the alumina-based sintered body _{(Al 6 Si 2 O 1 3} ) crystalline phase is effectively generated,
Excellent withstand voltage can be realized even at a high temperature of 700 ° C.

When the amount of SiO ₂ conversion is less than the above range, almost no mullite crystal phase is formed, and the withstand voltage at a high temperature of 700 ° C. is not improved. On the other hand, if the content is too large, the sinterability decreases, and it is difficult to obtain a dense body.

[0012] CaO and / or MgO equivalent amount is larger than this range, respectively, without mullite crystal phase was generated to SiO ₂ equivalent amount is reduced, it is not improved voltage resistance at a high temperature of 700 ° C.. On the other hand, if the CaO equivalent amount is smaller than this, the withstand voltage at high temperatures will be low as a result.

[0013] The invention of claim 3 is claim 1 or claim 2.
In the ternary composition diagram of the silicon component-calcium component-magnesium component of the auxiliary component (silicon component and calcium component and / or magnesium component) contained in the alumina-based sintered body described in (1), the oxide-converted composition ratio (SiO
₂ , CaO, MgO). In this composition range, mullite crystals are more effectively generated in the alumina-based sintered body, and as a result, the voltage resistance of the alumina-based sintered body at a high temperature of 700 ° C. is further improved.

The invention according to claim 4 is the invention according to claims 1 to 3.
Preferred structure of the alumina-based sintered body according to any of
This is an example. Coarse pores in alumina sintered body
If present, it is easy to apply high voltage locally to these pores.
Causes dielectric breakdown and low withstand voltage even at room temperature
It becomes. As in the present invention, at least mullite (Al ₆
Si₂O₁₃) Having a crystalline phase and the relative density of the sintered body
Present in alumina sintered body having a degree of 95% or more
Control so that the major axis is 10 μm or less.
Effectively improves withstand voltage at high temperatures of 700 ° C
it can. In this case, the density of the alumina
However, it is higher when the pores are more finely dispersed in the sintered body.
High withstand voltage.

[0015] The invention of claim 5 is the invention of claims 1 to 4.
The method for producing an alumina-based sintered body according to any one of the above. By using the firing conditions of the present invention, a mullite crystal phase can be effectively precipitated in the alumina-based sintered body, so that an alumina-based sintered body having excellent withstand voltage at a high temperature of 700 ° C. Can be easily manufactured. It is preferable to use a raw material powder having an average particle size of 1 μm or less. This is because mullite crystals can be generated more effectively in the alumina-based sintered body. Especially 0.
5 μm or less is preferred. It is also effective to use a submicron-class ultrafine powder.

The invention of claim 6 exemplifies a method of manufacturing an alumina-based sintered body according to any one of claims 1 to 4, as in the case of claim 5. By using the firing conditions of the present invention, mullite crystals are more effectively generated in the alumina-based sintered body, and as a result, the withstand voltage of the alumina-based sintered body at a high temperature of 700 ° C. is further improved. It is preferable to use a raw material powder having an average particle size of 1 μm or less. This is because mullite crystals can be generated more effectively in the alumina-based sintered body. Especially 0.5μ
m or less is preferable. It is also effective to use a submicron-class ultrafine powder.

According to a seventh aspect of the present invention, there is provided the first to fourth aspects.
The content of the sodium component contained in the alumina-based sintered body according to any of the above items is specified. By controlling the content of sodium component to a predetermined range,
Sinterability can be improved while maintaining high withstand voltage at a high temperature of 700 ° C. of the alumina-based sintered body. It is presumed that the reason for this is that the presence of such a small amount of the sodium component increases the generation rate of mullite crystals in the alumina-based sintered body, thereby enabling more effective generation. By selecting and using an alumina raw material powder containing a trace amount of sodium component as an unavoidable component within the scope of the present invention, the production cost can be reduced.

An eighth aspect of the present invention exemplifies a method for producing an alumina-based sintered body according to the seventh aspect. To uniformly disperse a trace amount of sodium component in the alumina-based sintered body, rather than adding a sodium compound powder,
The method in which the sodium component is previously contained in the alumina raw material powder as in the present invention is more effective in improving the withstand voltage of the alumina-based sintered body at a high temperature of 700 ° C. By selecting and using an alumina raw material powder containing a trace amount of sodium component as an unavoidable component within the scope of the present invention, the production cost can be reduced.

[0019]

(Example 1) Al ₂ O having an average particle size of 0.5 μm
₍₃ ) Si having an average particle size of 0.6 μm as a sintering aid
Powders obtained by weighing and mixing O ₂ powder, CaCO ₃ powder having an average particle diameter of 0.8 μm, and MgO powder having an average particle diameter of 0.3 μm (Sample Nos. 1 to No. .
10) was manufactured. Each of these compounded powders was mixed in ethanol using a 20 mmφ alumina ball in a ball mill for 16 hr, and then dried in hot water to obtain a mixed powder.

Each of these mixed powders was 150 MPa
Molded into a molded body of 50 × 50 × 20 mm by a hydrostatic pressure press, and then fired at a firing temperature (1
(450 ° C to 1650 ° C).

Here, the Ca compound means not only CaO but also C
oxidized at high temperatures in the atmosphere, such as carbonates and nitrates
Is not particularly limited as long as it changes to. In addition, Mg
The same applies to compounds.

If the firing temperature is lower than 1450 ° C., a sufficiently dense body cannot be obtained. If the firing temperature is higher than 1650 ° C., abnormal grain growth of alumina particles occurs during firing. Not only the characteristics are reduced, but also large pores are generated at the triple point of the grain boundary, and the withstand voltage is reduced.

If the firing time is shorter than 1 hour, a sufficiently dense body cannot be obtained and, at the same time, no mullite crystals are formed. On the other hand, if the firing time is longer than 8 hours,
Excessive grain growth is caused, and the withstand voltage decreases as in the case where the firing temperature is too high.

For the above reasons, a preferable firing condition is that the firing temperature is maintained at 1450 to 1650 ° C. for 1 to 8 hours. More preferably, 1500 to 160
It is to keep at a firing temperature of 0 ° C. for 2 to 6 hours.

The relative density, oxide equivalent value, maximum pore size, presence or absence of a mullite crystal phase and 70%
Table 2 summarizes the withstand voltage values at 0 ° C.

Here, the relative density was measured by the Archimedes method and expressed as a ratio to the theoretical density according to the mixing rule. The larger the numerical value of the relative density, the denser the sintered body and the higher the withstand voltage.

The oxide conversion value is a value obtained by analyzing the sintered body by X-ray fluorescence and converting the detected amounts of Al, Si, Ca and Mg into Al ₂ O ₃ , SiO ₂ , CaO and MgO, respectively. showed that.

The maximum pore diameter was measured by subjecting a sample to mirror polishing and then using a scanning electron microscope to measure the SEM
Photographs were taken and those with the largest pore diameter were measured. FIG. 4 shows an SEM image of Sample No. 3 which is an example, and FIG. 5 shows an SEM image of Sample No. 12 which is a comparative example.

The presence or absence of the mullite crystal phase was analyzed by X-ray diffraction analysis of the sintered body, and JCPDS card No. 15-
Judgment was made based on whether or not a spectrum corresponding to 776 was present. An X-ray diffraction chart is shown in FIG.

The withstand voltage at 700 ° C. was 1
It processed into 6x16x0.65mm, and measured by the apparatus shown in FIG.

Example 2 The amount of sodium described in Table 3
Component (Na_Two5 types of Al containing O ₂O₃
Raw material powder was used. Each Al₂O₃Raw material powder 95
SiO by weight₂4.0 parts by weight of powder, CaCO₃
0.5 parts by weight of powder in terms of CaO and 0.5 parts of MgO powder
A powder was prepared by weighing and blending parts by weight. The firing temperature is shown in the table.
The four conditions shown in 3 were set. Others were performed according to Example 1.
The results are shown in Table 3.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

According to Table 2, a mullite crystal phase exists in the alumina-based sintered body, and Si, Ca,
The composition ratio when Mg is converted to oxide is SiO ₂ —CaO
-In the MgO ternary composition diagram, A (9
5, 5, 0), B (75, 25, 0), C (75, 5, 2)
0) is within the range (including the line segment) surrounded by the line segment connecting the three points (see FIGS. 1 and 2), and particularly, the relative density is 95% or more, and the sintered body It can be seen that when the long diameter of the pores remaining in the alumina is 10 μm or less, the withstand voltage value of the alumina-based sintered body at a high temperature of 700 ° C. shows a high value of 60 kV / mm or more.

The mullite crystal phase is present in the alumina-based sintered body, and the residual pores are reduced to increase the relative density of the alumina-based sintered body to 95% or more.
It is considered that the effect of improving the withstand voltage of the alumina-based sintered body at a high temperature of 00 ° C. is obtained.

[0037] More preferably, Si present in the alumina-based sintered body, Ca, the composition ratio when converted oxide _Mg, D (92 weight standard% in SiO 2 -CaO-MgO ternary composition diagram , 8,0), E (78,22,
0) and F (78, 8, 14) within a range (including a line segment) (FIGS. 1 and 2).
reference). In the composition ratio in this range, the mullite crystal phase is more effectively generated, and as a result, the withstand voltage of the alumina-based sintered body at a high temperature of 700 ° C. is further improved.

On the other hand, in Table 2, sample No. 12 of the comparative example
Did not produce a mullite crystal phase and had a low withstand voltage value of 34 kV / mm because the density was low and the major axis of the pores was large. In addition, since the mullite crystal phase was not generated in Sample Nos. 13 to 18, the withstand voltage value was low.

In sample No. 19, the mullite crystal phase was not formed, and the sintering temperature was 1450 ° C. or less (1425 ° C.), so the relative density was 95% or less (89.3%), and the withstand voltage value was Decreased to 30 kV / mm. Sample No. 20 was oversintered since the firing temperature was 1650 ° C. or higher (1675 ° C.), and the relative density was 9%.
This is as low as 4.8%, and the withstand voltage value is as low as 45 kV / mm.

In Table 2, the sintered bodies of Sample No. 1 to Sample No. 11 according to the technology of the present invention correspond to Sample No. 12 of Comparative Example.
It can be seen that the withstand voltage at a high temperature of 700 ° C. can be higher than that of the sintered body of Sample No. 20. As described above, according to the present invention, it is possible to obtain an alumina-based sintered body having a high withstand voltage suitable as a material of a ceramic product requiring excellent withstand voltage at a high temperature of 700 ° C., such as a plug. it can.

From the results shown in Table 3, the sample No. 2 which is an example
In samples 1 to 24, Al₂O ₃Raw material powder 100 weight
Content of sodium component (Na_TwoO exchange
Is calculated to be 0.07 parts by weight or less, the resulting alumina
Content of sodium component contained in the base sintered body (Na_TwoO
(Converted) to 0.05 parts by weight or less and 60 kV /
It can be seen that a high withstand voltage value of not less than mm can be obtained. In particular
Is the content of sodium component (Na_TwoO conversion) is 0.0
Sample No. 22 and Sample No. 23, which were 26 parts by weight or less,
Are as high as 72 kV / mm and 65 kV / mm, respectively.
It can be seen that a withstand voltage value is obtained.

On the other hand, in Sample No. 25 which is a comparative example, the content of the sodium component (in terms of Na ₂ O) contained in the obtained alumina-based sintered body was 0.05 parts by weight or more (0.07 parts by weight).
8 parts by weight) and is 60 kV / mm or less (58 kV / mm).
V / mm) can be obtained.

[0043]

According to the present invention, there is provided an alumina-based sintered body having high insulating properties and high voltage resistance, and a method for producing the same, which is suitable as a material for a ceramic product requiring excellent voltage resistance at high temperatures. can do. In particular, it is suitable as an alumina-based sintered body used for an insulator used for a spark plug or the like.

[Brief description of the drawings]

FIG. 1 is a ternary composition diagram of SiO ₂ —CaO—MgO used in an alumina-based fired body and a method for producing the same according to the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an X-ray diffraction chart of an alumina-based sintered body having an alumina-based mullite crystal phase.

FIG. 4 is a SEM photograph of a 1000-fold structure taken with a scanning electron microscope in order to measure the long diameter of pores in an alumina-based sintered body after mirror-polishing the sample of the example of the present invention. .

FIG. 5 is a SEM photograph of a 1000-fold structure taken by a scanning electron microscope in order to measure the long diameter of pores in an alumina-based sintered body after mirror polishing the sample of the comparative example.

FIG. 6 is a schematic diagram of an evaluation method used in the present invention.

[Explanation of symbols]

 Reference Signs List 1 Test piece made of alumina-based sintered body 2a Alumina insulator 2b Alumina insulator 3 Sealing glass 4a Electrode 4b electrode 5 Heating heater 6 High voltage generator 7 Glass joined body 8 Heating box

Continued on the front page (72) Inventor: Atsushi Shimamori 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Japan Special Ceramics Co., Ltd. (72) Inventor Masaya Ito 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture F-term (reference) in Japan Special Ceramics Co., Ltd. 4G030 AA07 AA08 AA36 AA37 BA12 CA01 CA05 GA27 5G303 AA10 AB02 BA09 CA01 CB01 CB06 CB17 CB30 DA05 5G331 AA01 AA02 AA03 AA04 AA05 AA06 BA01 BC18 CA02

Claims (8)

[Claims] 1. An alumina-based sintered body containing alumina (Al ₂ O ₃ ) as a main component and a silicon component and a calcium component and / or a magnesium component as sub-components. At least mullite (Al ₆ S
i 2 _{O 13)} has a crystal phase, and a high voltage resistance alumina-based sintered body, wherein the relative density of the sintered body is 95% or more. 2. The alumina-based sintered body according to claim 1, wherein the content of the sub-component contained in the sintered body is 100% by weight in terms of oxide, and the content is silicon component-calcium component-magnesium. Of the three components (SiO
₍₂ , CaO, MgO) within a range surrounded by a line connecting the three points A, B, and C in the following percentage by weight standard: body. Where A
(95, 5, 0), B (75, 25, 0), C (75,
5, 20). 3. The alumina-based sintered body according to claim 1, wherein, when the sub-component contained in the sintered body is 100% by weight in terms of oxide, a silicon component is used. The composition ratio (SiO ₂ , CaO, MgO) of the three components in terms of oxide in the ternary composition diagram of the calcium component-magnesium component is expressed by a line segment connecting the following three points D, E, and F in weight standard%. A high withstand voltage alumina-based sintered body characterized by being within an enclosed range. Where D
(92,8,0), E (78,22,0), F (78,
8, 14). 4. The long diameter of pores existing in a sintered body is 10 μm.
The high withstand voltage alumina-based sintered body according to any one of claims 1 to 3, wherein m is equal to or less than m. 5. The method for producing an alumina-based sintered body according to claim 1, wherein the average particle diameter is 1 μm or less with respect to the alumina powder having an average particle diameter of 1 μm or less. Mixing a silicon dioxide powder, a calcium compound powder having an average particle diameter of 1 μm or less and / or a magnesium compound powder having an average particle diameter of 1 μm or less to obtain a raw material mixed powder, and a molded article using the raw material mixed powder And firing the compact at a firing temperature of 1450 to 1650 ° C. for 1 to 8 hours to obtain a mullite (Al ₆ Si ₂ O ₁₃ ) crystal phase in the obtained alumina sintered body. And a method for producing a high withstand voltage alumina-based sintered body. 6. The method for producing an alumina-based sintered body according to claim 1, wherein the average particle diameter is 1 μm or less with respect to the alumina powder having an average particle diameter of 1 μm or less. Mixing a silicon dioxide powder, a calcium compound powder having an average particle diameter of 1 μm or less and / or a magnesium compound powder having an average particle diameter of 1 μm or less to obtain a raw material mixed powder, and a molded article using the raw material mixed powder And firing the molded body at a firing temperature of 1500 to 1600 ° C. for 2 to 6 hours to obtain a mullite (Al ₆ Si ₂ O ₁₃ ) crystal phase in the obtained alumina sintered body. And a method for producing a high withstand voltage alumina-based sintered body. 7. The alumina-based sintered body according to claim 1, wherein the content of the sodium component in 100 parts by weight of the alumina-based sintered body is calculated in terms of oxide. A high withstand voltage alumina-based sintered body characterized in that the content is 0.05 part by weight or less. 8. The method for producing an alumina-based sintered body according to claim 7, wherein the content of the sodium component in 100 parts by weight of the alumina powder used as the raw material powder is 0.07 in terms of oxide.
A method for producing a high withstand voltage alumina-based sintered body, which is not more than part by weight.