JP4443187B2 - Alumina porcelain and manufacturing method thereof - Google Patents

Description

  The present invention relates to an alumina porcelain and a method for producing the same, and more particularly to a ceramic porcelain that has high strength and is suitably used in the field of sliding members such as bearings and mechanical seals, and a method for producing the same.

  Ceramics have been shown to be superior to metal materials in wear resistance and corrosion resistance, and have been used as wear-resistant materials in place of conventional metals. As this type of ceramics, alumina, zirconia, silicon nitride, silicon carbide, etc. are usually known, but among them, alumina ceramics mainly composed of alumina, which is high in hardness, excellent in corrosion resistance and inexpensive, are widely used. Has been.

  In general, alumina has high wear resistance and corrosion resistance, so its performance can be fully demonstrated when used alone. However, since sinterability itself is poor, sintering aid is necessary to obtain a dense sintered body. Baking is performed by adding a minimum amount of the agent.

  For example, 0.01 to 0.2% by mass of magnesia powder and 0.01 to 0.2% by mass of yttria powder are added to the alumina powder, mixed with polyvinyl alcohol, and mixed with magnesia in the alumina powder. It is proposed to produce a translucent alumina porcelain by firing at a high temperature of 1600 to 2000 ° C. using a raw material powder in which yttria is uniformly dispersed (see, for example, Patent Document 1).

Further, a molded body containing 0.7 to 3% by mass of chromium oxide powder and 0.05% by mass or less of magnesia powder with respect to the alumina powder was fired at 1280 ° C., and then this sintered body was 1300 to 1310 ° C., A method has been proposed in which HIP treatment is performed under the condition of 1000 to 2000 atm to dissolve chromium oxide and magnesia in a solid solution, thereby producing a light-transmitting ruby free of coarse particles of 4 μm or more.
Japanese Patent Laying-Open No. 5-43308 Japanese Patent Publication No. 5-83511, claims 1 and 2

  However, although the alumina porcelain produced by the method of Patent Document 1 has an advantage that it has translucency, the magnesium compound easily aggregates, and therefore, there is a problem that Mg is difficult to uniformly disperse in the alumina porcelain.

  Moreover, although the alumina porcelain described in Patent Document 2 has the advantage that there is no coarse particle of 4 μm or more and translucency is obtained, the magnesium compound is not uniformly dispersed, and the HIP treatment is performed after firing. However, the defects remained and the strength was low.

  Accordingly, an object of the present invention is to provide an alumina porcelain having improved Mg dispersibility and a method for producing the same.

The alumina porcelain of the present invention is an alumina porcelain containing 0.01 to 0.5% by mass of Mg in terms of oxide , and includes an alumina-containing first slurry (hereinafter sometimes referred to as a first slurry). Using a second slurry in which alumina powder is added and mixed (hereinafter sometimes referred to as a second slurry), a molded body is produced, and the molded body is fired. When a surface analysis is performed with a probe microanalyzer, a high concentration region of Mg and a low concentration region adjacent to the high concentration region are observed. The Mg concentration in the high concentration region is C ₁ , and the Mg concentration in the low concentration region is C ₂ , where R is the diameter when the area of the high concentration region is converted into a circle, the high concentration region satisfying C ₁ / C ₂ ≧ 2 and R ≧ 5 μm is within the measurement region of 0.05 mm ² 1 in It is characterized in that 5 a.

The manufacturing method of alumina ceramic according to the present invention, high-purity alumina powder 60-99% by volume, after the first Ichisu slurry was prepared by mixing Mg compound powder in a proportion of 1 to 40% by volume, said Ichisu against Larry, the Mg content, a high purity alumina powder as a concentration lower than the concentration in the first Ichisu Larry added, the first varnish slurry was prepared by mixing this said thereafter the compact was produced using the first varnish slurry, and firing the shaped body, and a high concentration region of Mg to the surface of the alumina porcelain upon surface analysis by electron probe microanalyzer obtained, the high concentration region The Mg concentration in the high concentration region is C ₁ , the Mg concentration in the low concentration region is C ₂ , and the diameter when the area of the high concentration region is converted into a circle is R. _{when, C 1 / C 2 ≧ 2} , and, R High concentration region satisfying 5μm is characterized in Rukoto obtain alumina porcelain is 1-5 in the measurement area of 0.05 mm ^2.

The Mg compound is preferably Mg (OH) ₂ .

  It is preferable that the average particle diameter of the alumina powder is 0.3 to 0.7 μm.

The Mg compound powder preferably has an average particle size of 0.5 to 10 μm and a BET specific surface area of 10 to 50 m ² / g.

  It is preferable to perform a high-temperature and high-pressure treatment after the firing.

  In the present invention, when the amount of Mg compound is small with respect to alumina, for example, when it is 0.5% by mass or less, particularly 0.2% by mass or less, the amount of Mg compound is small, so Mg is uniformly dispersed in the slurry. It is difficult to obtain a slurry in which Mg compounds are aggregated. Alumina porcelain produced using this slurry forms a high concentration region and a low concentration region of Mg, and the high concentration region becomes a source of destruction. It is based on the new knowledge that it is easy.

  The present invention also provides a magnesium compound as a sintering aid by mixing a mixed powder having a higher ratio of Mg compound powder to alumina powder and then adding alumina powder to prepare a slurry of the original composition. It becomes easy to uniformly disperse the powder in the alumina powder, and as a result, there are few high concentration areas of Mg, and high strength alumina porcelain can be manufactured, especially when a small amount of sintering aid is used. It shows a remarkable effect.

The alumina porcelain of the present invention is an alumina porcelain containing 0.01 to 0.5% by mass of Mg in terms of oxide , and a high concentration of Mg when the surface of the alumina porcelain is analyzed by an electron beam probe microanalyzer. A region and a low concentration region adjacent to the high concentration region are observed, the Mg concentration in the high concentration region is C ₁ , the Mg concentration in the low concentration region is C ₂ , and the area of the high concentration region is converted into a circle when the diameter of the case and the _{R, C 1 / C 2 ≧} 2, and, for high-concentration region satisfying R ≧ 5 [mu] m is a five 1 in the 0.05 mm ² measurement region, coagulation of the magnesium compound As a result of the reduction in the number of voids generated by the aggregated coarse particles, there is an effect that the mechanical properties (bending strength, wear resistance) of the sintered body are improved. Since the content of the sintering aid is small, the characteristics of alumina itself can be exhibited.

The manufacturing method of alumina ceramic according to the present invention, the high purity alumina powder powder, after the preparation of the first slurry containing the Mg compound Powder at the rate of 1 to 40% by weight, the said first slurry in contrast, the content of Mg is, the high-purity alumina powder powder added to a concentration lower than the concentration of the first in the slurry to prepare a second slurry by mixing it, said thereafter the molded body produced using the second slurry, for firing the molded body, there is an effect that can be further uniformly dispersed without once dispersed Mg compound powder is re-aggregation.

Since the Mg compound is Mg (OH) ₂ , there is an effect that no harmful gas is generated during the sintering process as in the case of chlorides, nitrates, sulfates and the like.

  Since the average particle diameter of the alumina powder is 0.3 to 0.7 μm, a dense sintered body having a uniform crystal particle diameter can be formed, and there is an effect that a smooth surface is obtained without removing particles by polishing. .

Since the Mg compound powder has an average particle size of 0.5 to 10 μm and a BET specific surface area of 10 to 50 m ² / g, it has a high specific surface area and eliminates coarse particles by crushing for about 100 hours. There is an effect that uniform dispersion is possible.

  Since high-temperature and high-pressure treatment is performed after the firing, large voids can be reduced, the wear surface can be easily maintained, and the wear amount can be reduced.

  The present invention will be described with reference to the drawings. FIG. 1 shows the results of surface analysis of the surface of an alumina porcelain using an electron beam probe microanalyzer, (a) is a schematic diagram showing the distribution state of Mg in the measurement region, and (b) is the shape of the high concentration region. Is a schematic diagram showing a high-concentration region in which the diameter is calculated by converting the area into a circle and redisplayed.

  First, an electron beam probe microanalyzer (EPMA) used in the present invention will be described.

  When an electronic material (sample) is irradiated with an electron beam, various signals such as various X-rays and reflected electrons are generated. The characteristic X-ray generated here is an X-ray having a wavelength unique to the element constituting the substance. By measuring this characteristic X-ray, the constituent elements can be determined, and the existence ratio can be determined from the intensity. EMPA is an application of this principle.

  Specifically, the sample is irradiated with an electron beam, and various signals are excited from the irradiated part. The type and concentration of the element are calculated by selecting X-rays having an arbitrary set wavelength from the excited signal with a spectroscopic crystal and measuring it with a detector.

  For example, a two-dimensional enlarged scanning image, that is, an X-ray image is displayed on the CRT based on the X-ray pulse detected by the wavelength dispersion X-ray spectrometer, and the state of the sample surface is recorded. Further, the electron probe is scanned in the X direction on the sample (corresponding to the horizontal direction on the CRT), and the intensity change of the X-rays generated at that time is regarded as a change in amplitude (amplitude modulation) in the vertical direction of the CRT. The waveform, that is, the X-ray line profile is displayed, and the element concentration distribution (on the analysis line) in the line scanned portion is recorded.

In this way, the distribution state of a specific element, that is, the element concentration can be expressed in a map form by representing all analysis regions with an X-ray intensity distribution of a specific wavelength. The probe current (sensitivity) was 1.0 × 10 ⁻⁷ A, the acceleration voltage was 15 kV, and the analysis region was 200 μm × 200 μm.

In the present invention, a JXA-8600 type device manufactured by JEOL Ltd. is used, a 200 μm × 200 μm region of the sample is observed at a measurement magnification of 500 times, and a sintered body is molded at a current value of 3 × 10 ⁻⁷ A. The body was observed at a current value of 1 × 10 ⁻⁷ A.

  When the alumina porcelain containing Mg is subjected to surface analysis by EPMA analysis, the Mg concentration distribution as shown in FIG. 1A is displayed.

According to the present invention, from such a surface analysis result of Mg, the high concentration region 2 in which the Mg concentration in the measurement region 1 is twice or more higher than the surroundings is specified, and the area of the high concentration region 2 is converted into a circle. The diameter of the case is R, the Mg concentration in the high concentration region 2 is C ₁ , the Mg concentration in the low concentration region 3 adjacent to the high concentration region 2 is C ₂ , C ₁ / C ₂ ≧ 2, and R ≧ 5 μm. When the number of high concentration regions 2 to be filled is measured , it is important that the number is 1 to 5 in a measurement region having a measurement area of 0.05 mm ² .

As described above, FIG. 1A showing the Mg distribution on the surface of the alumina porcelain of the present invention shows four high-concentration regions 2 satisfying the above conditions in the measurement region 1 of 0.05 mm ² . According to the present invention, this number is 1 to 5 , and is not limited to 4 in FIG.

  The maximum value of the diameter R of the high-concentration region 2 converted into a circle is 5 μm or less, particularly 4 μm or less, more preferably 3 μm or less, and more preferably 2 μm or less so as not to cause a large void when used as a sliding member. It is preferable. Even when the high concentration region 2 appears in this way, a smoother surface can be maintained when used as a sliding member if its size is small.

  Since there are often coarse voids in the high-concentration region 2 of Mg, reducing the number of high-concentration regions 2 can reduce voids that cause destruction, and as a result, prevent a decrease in strength. It becomes.

According to the present invention, the content of Mg is, in order to sufficiently exhibit the characteristics of the alumina porcelain is 0.5 mass% or less in terms of oxide, in particular 0.2 wt% or less, even 0.1 % Or less, more preferably 0.05% by mass. When the content of Mg, that is, the content of the sintering aid is small, good properties such as mechanical properties, electrical properties, thermal properties, and the like that alumina itself has can be sufficiently expressed. Moreover, since Mg compound plays the role as a sintering auxiliary agent, it is 0.01 mass% or more. When Mg is contained at such a ratio, the sinterability can be improved.

  In addition to Mg, elements such as Ca, Si, Fe, Na, or K and compounds thereof can be included. In particular, the total amount of these elements may be 0.1% by mass or less, particularly 0.05% by mass or less. It is preferable in that abnormal particle growth can be suppressed and void generation can be suppressed.

  Part of Mg may be in solid solution, or may exist in the crystal grain boundary of alumina as a compound such as spinel, but there is no such compound because it may be a source of destruction Is most preferred.

  The average crystal grain size of the alumina porcelain is preferably 0.3 to 2 μm, particularly preferably 0.3 to 1.5 μm, and more preferably 0.3 to 1 μm. Alumina crystals are composed of small crystals, and a homogeneous and dense sintered body is formed. Large crystals are crushed by polishing, and the alumina porcelain is damaged by the sized large particles, suppressing abnormal wear resulting in large wear, and a smooth surface. Can be maintained.

  The alumina porcelain of the present invention is a high-purity alumina, has a feature that a uniform and fine particle size is used, and a dense sintered body can be obtained. Therefore, the alumina porcelain is suitably used in the field of sliding parts, bearings or mechanical seals. Can be used.

  In order to reduce the high concentration region, the production method of the alumina porcelain of the present invention mixes the magnesium compound powder with the alumina powder at a high concentration to prepare the first slurry in advance, and then, into the first slurry, Alumina powder is added so as to be smaller than the Mg concentration in the first slurry, and the magnesium compound powder is uniformly dispersed in the slurry.

  Next, the method for producing an alumina porcelain of the present invention will be described by taking as an example one embodiment in which magnesium hydroxide is used as the Mg compound that does not generate harmful gas during the sintering process.

First, a high-purity alumina powder having a purity of 99.99%, an average particle size of 0.3 to 0.7 μm, and a BET specific surface area of about 5 to 6 m ² / g is prepared. Using alumina powder with an average particle size in this range, a homogeneous and dense sintered body can be obtained, and a coarse surface can be removed by polishing, resulting in damage to the sintered body and development of abnormal wear. Can be maintained.

Further, magnesium hydroxide powder having a purity of 60% or more and an average particle diameter of 0.5 to 10 μm, particularly 1 to 8 μm, and further 2 to 5 μm is prepared. The specific surface area of Mg _{(OH) 2} is, 10~50m ² / g, especially 15~40m ² / g, more preferably a 20 to 30 m ² / g. By using a powder having such an average particle size and specific surface area, finer and more uniform dispersion can be achieved, and generation of harmful gas can be avoided.

Mg compounds can be used safely because they do not generate harmful gases during the sintering process, as in the case of chlorides, nitrates, sulfates, etc., and damage to the firing furnace is reduced, It is preferable to use Mg (OH) ₂ that can contribute to low cost.

The above raw material powder is prepared in a proportion of 60 to 99% by volume of alumina powder and 1 to 40% by volume of Mg (OH) ₂ , pure water is added, and balls are added and mixed. In order to disperse Mg (OH) ₂ more uniformly, it is particularly preferable that Mg (OH) ₂ is mixed in a proportion of 5 to 35% by volume, more preferably 10 to 30% by volume. By using a high-purity alumina ball of 99% or more, especially 99.9% or more as a ball, mixing of impurities can be suppressed and mixing efficiency can be further increased.

  The mixing method can be performed by a known method such as a rotary mill. Thus, the Mg compound can be effectively mixed by preparing a slurry containing the Mg compound at a high concentration in advance.

  Magnesium compounds easily aggregate, so even if a low concentration magnesium compound of 0.5% by mass or less, particularly 0.2% by mass or less is directly mixed with alumina, for example, for 24 hours, aggregated particles remain, There are coarse aggregated grains. The magnesium compound reacts with alumina during firing to form spinel, causing volume reduction. This volume reduction leads to void formation, which in turn causes the mechanical properties (bending strength, wear resistance) to deteriorate.

Next, a high-purity alumina powder is additionally added to the obtained first slurry so as to have a predetermined composition and mixed again to prepare a second slurry. Thus, by mixing in two steps, Mg (OH) ₂ powder, which is a sintering aid, can be uniformly dispersed even with an addition amount of 0.5% by mass or less.

  A molded object is produced using the obtained second slurry. As the molding method, a known method such as a die pressing method, a cold isostatic pressing (CIP) method, a tape molding method such as a doctor blade method, an extrusion method, or an injection molding method can be used.

  Next, the molded body is processed into a predetermined shape as desired, and the molded body is fired. As for the firing conditions, the firing temperature is preferably 1200 to 1700 ° C, particularly preferably 1300 to 1600 ° C.

  Moreover, it is preferable to process the sintered compact obtained by baking at high temperature and high pressure. That is, if high-temperature and high-pressure treatment is performed after firing, densification can be further promoted, large voids can be reduced, and when used as a wear-resistant material, the wear surface can be kept smooth and the wear amount can be further increased. It can be reduced.

  First, a first slurry was prepared. In other words, 99.99% of the high-purity alumina powder having the average particle size shown in Table 1 and 60% of the magnesium hydroxide powder having the average particle size and specific surface area S shown in Table 1 were prepared so as to have the primary mixed composition of Table 1. Then, 150% by volume of water was added to the mixed powder, 400% by volume of 99.9% high-purity alumina balls were added, and the mixture was pulverized for 92 hours with a rotary mill to prepare a first slurry.

  Next, the same alumina powder as described above was added so as to have the secondary mixed composition shown in Table 2, and further mixed for 24 hours to prepare a second slurry.

After the obtained second slurry was dried, it was subjected to a mesh pass using a mesh having a mesh size opening diameter of 74 μm, uniaxially molded at 98 MPa, and fired under the firing conditions shown in Table 1. Then, if desired, HIP treatment was performed for 1 hour in argon gas under the conditions of a pressure of 196 MPa (2000 kg / cm ² ) and a temperature of 1350 ° C.

In addition, Mg dot map analysis was performed on this measurement region with EPMA. At this time, the probe current (sensitivity) of EPMA is 3.0 × 10 ⁻⁷ A.

本発明の試料Ｎｏ．２〜８、１０〜１４、１６〜２９は、高濃度領域の数が０．０５ｍｍ^２の測定領域において、１〜５個であった。
From the obtained concentration map, the area of each high concentration region is converted into a circle to calculate its diameter R, and C ₁ and C ₂ are measured in each high concentration region and the low concentration region adjacent thereto, and C ₁ / C ₂ was calculated, and the number of high concentration regions satisfying C ₁ / C ₂ ≧ 2 and R ≧ 5 μm was measured. The measurement range was 0.05 mm ² . The results are shown in Table 1. Sample No. Reference numeral 15 is a reference sample.

Sample No. of the present invention. 2～8,10～ 14,16～29 the number of high-concentration region is in the measurement region of 0.05 mm ^2, it was 5 1.

On the other hand, the amount of Mg compound in the primary mixture composition is as small as 0.5% by volume, and the sample No. No. 1 is in a poorly dispersed state of the Mg compound, and in the measurement region where the number of high concentration regions is 0.05 mm ² , the dispersion state is poor at 27, and the content of the Mg compound is too small and the sinterability is poor. There were 55 coarse voids exceeding 5 μm.

Sample No. 1 of the present invention in which the amount of Mg compound in the primary mixed composition is as large as 50% by volume. No. 9 has a dispersion state as bad as 10 in the measurement area where the number of high concentration areas is 0.05 mm ² , and the content of Mg compound is too high and the sinterability is poor, so the number of coarse voids exceeding 5 μm There were 22 pieces.

The surface analysis result of the surface of the alumina porcelain with an electron beam probe microanalyzer is shown, (a) is a schematic diagram showing the distribution state of Mg in the measurement region, (b) is the shape of the high concentration region, its area It is a schematic diagram which shows the high concentration area | region which calculated the diameter by converting into circle and redisplayed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Measurement area | region 2 ... High concentration area | region 3 ... Low concentration area | region C ₁ ... Mg density | concentration C in a high concentration area | region ₂ ... Mg density | concentration R in a low concentration area | region ... High concentration area | region Half of the area converted to yen

Claims (6)

Alumina porcelain containing 0.01 to 0.5% by mass of Mg in terms of oxide , and forming a molded body using a second slurry obtained by adding and mixing alumina powder to an alumina-containing first slurry containing an Mg compound Then, the compact is fired, and when the surface of the alumina porcelain is subjected to surface analysis by an electron beam probe microanalyzer, a high concentration region of Mg and a low concentration region adjacent to the high concentration region are observed, When the Mg concentration in the high concentration region is C ₁ , the Mg concentration in the low concentration region is C ₂ , and the diameter when the area of the high concentration region is converted into a circle is R, C ₁ / C ₂ ≧ 2, and The alumina porcelain is characterized in that the number of high concentration regions satisfying R ≧ 5 μm is 1 to 5 in a measurement region of 0.05 mm ² . High purity alumina powder 60-99% by volume, after the preparation of the first Ichisu slurry by mixing a Mg compound powder in a proportion of 1 to 40% by volume, relative to said Ichisu rally, the content of Mg, the high purity alumina powder as a concentration lower than the concentration in the Ichisu rally added, which the first varnish slurry was prepared by mixing, to prepare a molded body with said varnish slurry and thereafter When the surface of the resulting alumina porcelain is fired with an electron probe microanalyzer, a high concentration region of Mg and a low concentration region adjacent to the high concentration region are observed, When the Mg concentration in the high concentration region is C ₁ , the Mg concentration in the low concentration region is C ₂ , and the diameter when the area of the high concentration region is converted into a circle is R, C ₁ / C ₂ ≧ 2, and High concentration region satisfying R ≧ 5 μm is 0.05 mm Method for producing an alumina ceramic, wherein Rukoto obtain alumina porcelain is 1-5 in ² measurement area. The method for producing an alumina porcelain according to claim ₂ , wherein the Mg compound is Mg (OH) ₂ .   The method for producing an alumina porcelain according to claim 2 or 3, wherein the alumina powder has an average particle size of 0.3 to 0.7 µm. The method for producing an alumina porcelain according to any one of claims 2 to 4, wherein the Mg compound powder has an average particle size of 0.5 to 10 µm and a BET specific surface area of 10 to 50 m ² / g.   The method for producing an alumina porcelain according to any one of claims 2 to 5, wherein a high-temperature and high-pressure treatment is performed after the firing.

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